svcadm(8)을 검색하려면 섹션에서 8 을 선택하고, 맨 페이지 이름에 svcadm을 입력하고 검색을 누른다.
sudoers(4)
SUDOERS(4) File Formats Manual SUDOERS(4)
NAME
sudoers - default sudo security policy plugin
DESCRIPTION
The sudoers policy plugin determines a user's sudo privileges. It is
the default sudo policy plugin. The policy is driven by the
/etc/sudoers file or, optionally in LDAP. The policy format is
described in detail in the SUDOERS FILE FORMAT section. For
information on storing sudoers policy information in LDAP, please see
sudoers.ldap(4).
Configuring sudo.conf for sudoers
sudo consults the sudo.conf(4) file to determine which policy and I/O
logging plugins to load. If no sudo.conf(4) file is present, or if it
contains no Plugin lines, sudoers will be used for policy decisions and
I/O logging. To explicitly configure sudo.conf(4) to use the sudoers
plugin, the following configuration can be used.
Plugin sudoers_audit sudoers.so
Plugin sudoers_policy sudoers.so
Plugin sudoers_io sudoers.so
Starting with sudo 1.8.5, it is possible to specify optional arguments
to the sudoers plugin in the sudo.conf(4) file. Plugin arguments, if
any, should be listed after the path to the plugin (i.e., after
sudoers.so). The arguments are only effective for the plugin that
opens (and parses) the sudoers file.
For sudo version 1.9.1 and higher, this is the sudoers_audit plugin.
For older versions, it is the sudoers_policy plugin. Multiple
arguments may be specified, separated by white space. For example:
Plugin sudoers_audit sudoers.so sudoers_mode=0400 error_recovery=false
The following plugin arguments are supported:
error_recovery=bool
The error_recovery argument can be used to control whether
sudoers should attempt to recover from syntax errors in the
sudoers file. If set to true (the default), sudoers will try
to recover from a syntax error by discarding the portion of
the line that contains the error until the end of the line.
A value of false will disable error recovery. Prior to
version 1.9.3, no error recovery was performed.
ldap_conf=pathname
The ldap_conf argument can be used to override the default
path to the ldap.conf file.
ldap_secret=pathname
The ldap_secret argument can be used to override the default
path to the ldap.secret file.
sudoers_file=pathname
The sudoers_file argument can be used to override the default
path to the sudoers file.
sudoers_uid=uid
The sudoers_uid argument can be used to override the default
owner of the sudoers file. It should be specified as a
numeric user-ID.
sudoers_gid=gid
The sudoers_gid argument can be used to override the default
group of the sudoers file. It must be specified as a numeric
group-ID (not a group name).
sudoers_mode=mode
The sudoers_mode argument can be used to override the default
file mode for the sudoers file. It should be specified as an
octal value.
For more information on configuring sudo.conf(4), please refer to its
manual.
User Authentication
The sudoers security policy requires that most users authenticate
themselves before they can use sudo. A password is not required if the
invoking user is root, if the target user is the same as the invoking
user, or if the policy has disabled authentication for the user or
command. Unlike su(1), when sudoers requires authentication, it
validates the invoking user's credentials, not the target user's (or
root's) credentials. This can be changed via the rootpw, targetpw and
runaspw flags, described later.
If a user who is not listed in the policy tries to run a command via
sudo, mail is sent to the proper authorities. The address used for
such mail is configurable via the mailto Defaults entry (described
later) and defaults to root.
Note that no mail will be sent if an unauthorized user tries to run
sudo with the -l or -v option unless there is an authentication error
and either the mail_always or mail_badpass flags are enabled. This
allows users to determine for themselves whether or not they are
allowed to use sudo. By default, all attempts to run sudo (successful
or not) are logged, regardless of whether or not mail is sent.
If sudo is run by root and the SUDO_USER environment variable is set,
the sudoers policy will use this value to determine who the actual user
is. This can be used by a user to log commands through sudo even when
a root shell has been invoked. It also allows the -e option to remain
useful even when invoked via a sudo-run script or program. Note,
however, that the sudoers file lookup is still done for root, not the
user specified by SUDO_USER.
sudoers uses per-user time stamp files for credential caching. Once a
user has been authenticated, a record is written containing the user-ID
that was used to authenticate, the terminal session ID, the start time
of the session leader (or parent process) and a time stamp (using a
monotonic clock if one is available). The user may then use sudo
without a password for a short period of time (5 minutes unless
overridden by the timestamp_timeout option) . By default, sudoers uses
a separate record for each terminal, which means that a user's login
sessions are authenticated separately. The timestamp_type option can
be used to select the type of time stamp record sudoers will use.
Logging
By default, sudoers logs both successful and unsuccessful attempts (as
well as errors). The log_allowed and log_denied flags can be used to
control this behavior. Messages can be logged to syslog(3), a log
file, or both. The default is to log to syslog(3) but this is
configurable via the syslog and logfile settings. See LOG FORMAT for a
description of the log file format.
sudoers is also capable of running a command in a pseudo-terminal and
logging all input and/or output. The standard input, standard output
and standard error can be logged even when not associated with a
terminal. I/O logging is not on by default but can be enabled using
the log_input and log_output options as well as the LOG_INPUT and
LOG_OUTPUT command tags. See I/O LOG FILES for details on how I/O log
files are stored.
Starting with version 1.9, the log_servers setting may be used to send
event and I/O log data to a remote server running sudo_logsrvd or
another service that implements the protocol described by
sudo_logsrv.proto(4).
Command environment
Since environment variables can influence program behavior, sudoers
provides a means to restrict which variables from the user's
environment are inherited by the command to be run. There are two
distinct ways sudoers can deal with environment variables.
By default, the env_reset flag is enabled. This causes commands to be
executed with a new, minimal environment. On AIX (and Linux systems
without PAM), the environment is initialized with the contents of the
/etc/environment file. The HOME, MAIL, SHELL, LOGNAME and USER
environment variables are initialized based on the target user and the
SUDO_* variables are set based on the invoking user. Additional
variables, such as DISPLAY, PATH and TERM, are preserved from the
invoking user's environment if permitted by the env_check or env_keep
options. A few environment variables are treated specially. If the
PATH and TERM variables are not preserved from the user's environment,
they will be set to default values. The LOGNAME and USER are handled
as a single entity. If one of them is preserved (or removed) from the
user's environment, the other will be as well. If LOGNAME and USER are
to be preserved but only one of them is present in the user's
environment, the other will be set to the same value. This avoids an
inconsistent environment where one of the variables describing the user
name is set to the invoking user and one is set to the target user.
Environment variables with a value beginning with () are removed unless
both the name and value parts are matched by env_keep or env_check, as
they may be interpreted as functions by the bash shell. Prior to
version 1.8.11, such variables were always removed.
If, however, the env_reset flag is disabled, any variables not
explicitly denied by the env_check and env_delete options are allowed
and their values are inherited from the invoking process. Prior to
version 1.8.21, environment variables with a value beginning with ()
were always removed. Beginning with version 1.8.21, a pattern in
env_delete is used to match bash shell functions instead. Since it is
not possible to block all potentially dangerous environment variables,
use of the default env_reset behavior is encouraged.
Environment variables specified by env_check, env_delete, or env_keep
may include one or more ‘*’ characters which will match zero or more
characters. No other wildcard characters are supported.
By default, environment variables are matched by name. However, if the
pattern includes an equal sign (‘=’), both the variables name and value
must match. For example, a bash shell function could be matched as
follows:
env_keep += "BASH_FUNC_my_func%%=()*"
Without the “=()*” suffix, this would not match, as bash shell
functions are not preserved by default.
The complete list of environment variables that are preserved or
removed, as modified by global Defaults parameters in sudoers, is
displayed when sudo is run by root with the -V option. Please note
that the list of environment variables to remove varies based on the
operating system sudo is running on.
Other sudoers options may influence the command environment, such as
always_set_home, secure_path, set_logname, and set_home.
On systems that support PAM where the pam_env module is enabled for
sudo, variables in the PAM environment may be merged in to the
environment. If a variable in the PAM environment is already present
in the user's environment, the value will only be overridden if the
variable was not preserved by sudoers. When env_reset is enabled,
variables preserved from the invoking user's environment by the
env_keep list take precedence over those in the PAM environment. When
env_reset is disabled, variables present the invoking user's
environment take precedence over those in the PAM environment unless
they match a pattern in the env_delete list.
Note that the dynamic linker on most operating systems will remove
variables that can control dynamic linking from the environment of set-
user-ID executables, including sudo. Depending on the operating system
this may include _RLD*, DYLD_*, LD_*, LDR_*, LIBPATH, SHLIB_PATH, and
others. These type of variables are removed from the environment
before sudo even begins execution and, as such, it is not possible for
sudo to preserve them.
As a special case, if the -i option (initial login) is specified,
sudoers will initialize the environment regardless of the value of
env_reset. The DISPLAY, PATH and TERM variables remain unchanged;
HOME, MAIL, SHELL, USER, and LOGNAME are set based on the target user.
On AIX (and Linux systems without PAM), the contents of
/etc/environment are also included. All other environment variables
are removed unless permitted by env_keep or env_check, described above.
Finally, the restricted_env_file and env_file files are applied, if
present. The variables in restricted_env_file are applied first and
are subject to the same restrictions as the invoking user's
environment, as detailed above. The variables in env_file are applied
last and are not subject to these restrictions. In both cases,
variables present in the files will only be set to their specified
values if they would not conflict with an existing environment
variable.
SUDOERS FILE FORMAT
The sudoers file is composed of two types of entries: aliases
(basically variables) and user specifications (which specify who may
run what).
When multiple entries match for a user, they are applied in order.
Where there are multiple matches, the last match is used (which is not
necessarily the most specific match).
The sudoers file grammar will be described below in Extended Backus-
Naur Form (EBNF). Don't despair if you are unfamiliar with EBNF; it is
fairly simple, and the definitions below are annotated.
Quick guide to EBNF
EBNF is a concise and exact way of describing the grammar of a
language. Each EBNF definition is made up of production rules. E.g.,
symbol ::= definition | alternate1 | alternate2 ...
Each production rule references others and thus makes up a grammar for
the language. EBNF also contains the following operators, which many
readers will recognize from regular expressions. Do not, however,
confuse them with “wildcard” characters, which have different meanings.
? Means that the preceding symbol (or group of symbols) is
optional. That is, it may appear once or not at all.
* Means that the preceding symbol (or group of symbols) may appear
zero or more times.
+ Means that the preceding symbol (or group of symbols) may appear
one or more times.
Parentheses may be used to group symbols together. For clarity, we
will use single quotes ('') to designate what is a verbatim character
string (as opposed to a symbol name).
Aliases
There are four kinds of aliases: User_Alias, Runas_Alias, Host_Alias
and Cmnd_Alias. Beginning with sudo 1.9.0, Cmd_Alias may be used in
place of Cmnd_Alias if desired.
Alias ::= 'User_Alias' User_Alias_Spec (':' User_Alias_Spec)* |
'Runas_Alias' Runas_Alias_Spec (':' Runas_Alias_Spec)* |
'Host_Alias' Host_Alias_Spec (':' Host_Alias_Spec)* |
'Cmnd_Alias' Cmnd_Alias_Spec (':' Cmnd_Alias_Spec)* |
'Cmd_Alias' Cmnd_Alias_Spec (':' Cmnd_Alias_Spec)*
User_Alias ::= NAME
User_Alias_Spec ::= User_Alias '=' User_List
Runas_Alias ::= NAME
Runas_Alias_Spec ::= Runas_Alias '=' Runas_List
Host_Alias ::= NAME
Host_Alias_Spec ::= Host_Alias '=' Host_List
Cmnd_Alias ::= NAME
Cmnd_Alias_Spec ::= Cmnd_Alias '=' Cmnd_List
NAME ::= [A-Z]([A-Z][0-9]_)*
Each alias definition is of the form
Alias_Type NAME = item1, item2, ...
where Alias_Type is one of User_Alias, Runas_Alias, Host_Alias, or
Cmnd_Alias. A NAME is a string of uppercase letters, numbers, and
underscore characters (‘_’). A NAME must start with an uppercase
letter. It is possible to put several alias definitions of the same
type on a single line, joined by a colon (‘:’). E.g.,
Alias_Type NAME = item1, item2, item3 : NAME = item4, item5
It is a syntax error to redefine an existing alias. It is possible to
use the same name for aliases of different types, but this is not
recommended.
The definitions of what constitutes a valid alias member follow.
User_List ::= User |
User ',' User_List
User ::= '!'* user name |
'!'* #uid |
'!'* %group |
'!'* %#gid |
'!'* +netgroup |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
'!'* User_Alias
A User_List is made up of one or more user names, user-IDs (prefixed
with ‘#’), system group names and IDs (prefixed with ‘%’ and ‘%#’
respectively), netgroups (prefixed with ‘+’), non-Unix group names and
IDs (prefixed with ‘%:’ and ‘%:#’ respectively) and User_Aliases. Each
list item may be prefixed with zero or more ‘!’ operators. An odd
number of ‘!’ operators negate the value of the item; an even number
just cancel each other out. User netgroups are matched using the user
and domain members only; the host member is not used when matching.
A user name, uid, group, gid, netgroup, nonunix_group or nonunix_gid
may be enclosed in double quotes to avoid the need for escaping special
characters. Alternately, special characters may be specified in
escaped hex mode, e.g., \x20 for space. When using double quotes, any
prefix characters must be included inside the quotes.
The actual nonunix_group and nonunix_gid syntax depends on the
underlying group provider plugin. For instance, the QAS AD plugin
supports the following formats:
• Group in the same domain: "%:Group Name"
• Group in any domain: "%:Group Name@FULLY.QUALIFIED.DOMAIN"
• Group SID: "%:S-1-2-34-5678901234-5678901234-5678901234-567"
See GROUP PROVIDER PLUGINS for more information.
Note that quotes around group names are optional. Unquoted strings
must use a backslash (‘\’) to escape spaces and special characters.
See Other special characters and reserved words for a list of
characters that need to be escaped.
Runas_List ::= Runas_Member |
Runas_Member ',' Runas_List
Runas_Member ::= '!'* user name |
'!'* #uid |
'!'* %group |
'!'* %#gid |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
'!'* +netgroup |
'!'* Runas_Alias
A Runas_List is similar to a User_List except that instead of
User_Aliases it can contain Runas_Aliases. Note that user names and
groups are matched as strings. In other words, two users (groups) with
the same user (group) ID are considered to be distinct. If you wish to
match all user names with the same user-ID (e.g., root and toor), you
can use a user-ID instead of a name (#0 in the example given). Note
that the user-ID or group-ID specified in a Runas_Member need not be
listed in the password or group database.
Host_List ::= Host |
Host ',' Host_List
Host ::= '!'* host name |
'!'* ip_addr |
'!'* network(/netmask)? |
'!'* +netgroup |
'!'* Host_Alias
A Host_List is made up of one or more host names, IP addresses, network
numbers, netgroups (prefixed with ‘+’) and other aliases. Again, the
value of an item may be negated with the ‘!’ operator. Host netgroups
are matched using the host (both qualified and unqualified) and domain
members only; the user member is not used when matching. If you
specify a network number without a netmask, sudo will query each of the
local host's network interfaces and, if the network number corresponds
to one of the hosts's network interfaces, will use the netmask of that
interface. The netmask may be specified either in standard IP address
notation (e.g., 255.255.255.0 or ffff:ffff:ffff:ffff::), or CIDR
notation (number of bits, e.g., 24 or 64). A host name may include
shell-style wildcards (see the Wildcards section below), but unless the
host name command on your machine returns the fully qualified host
name, you'll need to use the fqdn flag for wildcards to be useful.
Note that sudo only inspects actual network interfaces; this means that
IP address 127.0.0.1 (localhost) will never match. Also, the host name
“localhost” will only match if that is the actual host name, which is
usually only the case for non-networked systems.
digest ::= [A-Fa-f0-9]+ |
[A-Za-z0-9\+/=]+
Digest_Spec ::= "sha224" ':' digest |
"sha256" ':' digest |
"sha384" ':' digest |
"sha512" ':' digest
Digest_List ::= Digest_Spec |
Digest_Spec ',' Digest_List
Cmnd_List ::= Cmnd |
Cmnd ',' Cmnd_List
command name ::= file name |
file name args |
file name '""'
Edit_Spec ::= "sudoedit" file name+
Cmnd ::= Digest_List? '!'* command name |
'!'* directory |
'!'* Edit_Spec |
'!'* Cmnd_Alias
A Cmnd_List is a list of one or more command names, directories, and
other aliases. A command name is a fully qualified file name which may
include shell-style wildcards (see the Wildcards section below). A
simple file name allows the user to run the command with any arguments
they wish. However, you may also specify command line arguments
(including wildcards). Alternately, you can specify "" to indicate
that the command may only be run without command line arguments. A
directory is a fully qualified path name ending in a ‘/’. When you
specify a directory in a Cmnd_List, the user will be able to run any
file within that directory (but not in any sub-directories therein).
If a Cmnd has associated command line arguments, then the arguments in
the Cmnd must match exactly those given by the user on the command line
(or match the wildcards if there are any). Note that the following
characters must be escaped with a ‘\’ if they are used in command
arguments: ‘,’, ‘:’, ‘=’, ‘\’. The built-in command “sudoedit” is used
to permit a user to run sudo with the -e option (or as sudoedit). It
may take command line arguments just as a normal command does. Note
that “sudoedit” is a command built into sudo itself and must be
specified in the sudoers file without a leading path. If a leading
path is present, for example /usr/bin/sudoedit, the path name will be
silently converted to “sudoedit”. A fully-qualified path for sudoedit
is treated as an error by visudo.
A command name may be preceded by a Digest_List, a comma-separated list
of one or more Digest_Spec entries. If a Digest_List is present, the
command will only match successfully if it can be verified using one of
the SHA-2 digests in the list. Starting with version 1.9.0, the ALL
reserved word can be used in conjunction with a Digest_List. The
following digest formats are supported: sha224, sha256, sha384 and
sha512. The string may be specified in either hex or base64 format
(base64 is more compact). There are several utilities capable of
generating SHA-2 digests in hex format such as openssl, shasum,
sha224sum, sha256sum, sha384sum, sha512sum.
For example, using openssl:
$ openssl dgst -sha224 /bin/ls
SHA224(/bin/ls)= 118187da8364d490b4a7debbf483004e8f3e053ec954309de2c41a25
It is also possible to use openssl to generate base64 output:
$ openssl dgst -binary -sha224 /bin/ls | openssl base64
EYGH2oNk1JC0p9679IMATo8+BT7JVDCd4sQaJQ==
Warning, if the user has write access to the command itself (directly
or via a sudo command), it may be possible for the user to replace the
command after the digest check has been performed but before the
command is executed. A similar race condition exists on systems that
lack the fexecve(2) system call when the directory in which the command
is located is writable by the user. See the description of the fdexec
setting for more information on how sudo executes commands that have an
associated digest.
Command digests are only supported by version 1.8.7 or higher.
Defaults
Certain configuration options may be changed from their default values
at run-time via one or more Default_Entry lines. These may affect all
users on any host, all users on a specific host, a specific user, a
specific command, or commands being run as a specific user. Note that
per-command entries may not include command line arguments. If you
need to specify arguments, define a Cmnd_Alias and reference that
instead.
Default_Type ::= 'Defaults' |
'Defaults' '@' Host_List |
'Defaults' ':' User_List |
'Defaults' '!' Cmnd_List |
'Defaults' '>' Runas_List
Default_Entry ::= Default_Type Parameter_List
Parameter_List ::= Parameter |
Parameter ',' Parameter_List
Parameter ::= Parameter '=' Value |
Parameter '+=' Value |
Parameter '-=' Value |
'!'* Parameter
Parameters may be flags, integer values, strings, or lists. Flags are
implicitly boolean and can be turned off via the ‘!’ operator. Some
integer, string and list parameters may also be used in a boolean
context to disable them. Values may be enclosed in double quotes ("")
when they contain multiple words. Special characters may be escaped
with a backslash (‘\’).
Lists have two additional assignment operators, += and -=. These
operators are used to add to and delete from a list respectively. It
is not an error to use the -= operator to remove an element that does
not exist in a list.
Defaults entries are parsed in the following order: generic, host, user
and runas Defaults first, then command defaults. If there are multiple
Defaults settings of the same type, the last matching setting is used.
The following Defaults settings are parsed before all others since they
may affect subsequent entries: fqdn, group_plugin, runas_default,
sudoers_locale.
See SUDOERS OPTIONS for a list of supported Defaults parameters.
User specification
User_Spec ::= User_List Host_List '=' Cmnd_Spec_List \
(':' Host_List '=' Cmnd_Spec_List)*
Cmnd_Spec_List ::= Cmnd_Spec |
Cmnd_Spec ',' Cmnd_Spec_List
Cmnd_Spec ::= Runas_Spec? Option_Spec* Tag_Spec* Cmnd
Runas_Spec ::= '(' Runas_List? (':' Runas_List)? ')'
Option_Spec ::= (Solaris_Priv_Spec | Date_Spec | Timeout_Spec)
Solaris_Priv_Spec ::= ('PRIVS=privset' | 'LIMITPRIVS=privset')
Date_Spec ::= ('NOTBEFORE=timestamp' | 'NOTAFTER=timestamp')
Timeout_Spec ::= 'TIMEOUT=timeout'
Chdir_Spec ::= 'CWD=directory'
Chroot_Spec ::= 'CHROOT=directory'
Tag_Spec ::= ('EXEC:' | 'NOEXEC:' | 'FOLLOW:' | 'NOFOLLOW' |
'LOG_INPUT:' | 'NOLOG_INPUT:' | 'LOG_OUTPUT:' |
'NOLOG_OUTPUT:' | 'MAIL:' | 'NOMAIL:' | 'PASSWD:' |
'NOPASSWD:' | 'SETENV:' | 'NOSETENV:')
A user specification determines which commands a user may run (and as
what user) on specified hosts. By default, commands are run as root,
but this can be changed on a per-command basis.
The basic structure of a user specification is “who where = (as_whom)
what”. Let's break that down into its constituent parts:
Runas_Spec
A Runas_Spec determines the user and/or the group that a command may be
run as. A fully-specified Runas_Spec consists of two Runas_Lists (as
defined above) separated by a colon (‘:’) and enclosed in a set of
parentheses. The first Runas_List indicates which users the command
may be run as via the -u option. The second defines a list of groups
that can be specified via the -g option in addition to any of the
target user's groups. If both Runas_Lists are specified, the command
may be run with any combination of users and groups listed in their
respective Runas_Lists. If only the first is specified, the command
may be run as any user in the list but no -g option may be specified.
If the first Runas_List is empty but the second is specified, the
command may be run as the invoking user with the group set to any
listed in the Runas_List. If both Runas_Lists are empty, the command
may only be run as the invoking user. If no Runas_Spec is specified
the command may be run as root and no group may be specified.
A Runas_Spec sets the default for the commands that follow it. What
this means is that for the entry:
dgb boulder = (operator) /bin/ls, /bin/kill, /usr/bin/lprm
The user dgb may run /bin/ls, /bin/kill, and /usr/bin/lprm on the host
boulder—but only as operator. E.g.,
$ sudo -u operator /bin/ls
It is also possible to override a Runas_Spec later on in an entry. If
we modify the entry like so:
dgb boulder = (operator) /bin/ls, (root) /bin/kill, /usr/bin/lprm
Then user dgb is now allowed to run /bin/ls as operator, but /bin/kill
and /usr/bin/lprm as root.
We can extend this to allow dgb to run /bin/ls with either the user or
group set to operator:
dgb boulder = (operator : operator) /bin/ls, (root) /bin/kill,\
/usr/bin/lprm
Note that while the group portion of the Runas_Spec permits the user to
run as command with that group, it does not force the user to do so.
If no group is specified on the command line, the command will run with
the group listed in the target user's password database entry. The
following would all be permitted by the sudoers entry above:
$ sudo -u operator /bin/ls
$ sudo -u operator -g operator /bin/ls
$ sudo -g operator /bin/ls
In the following example, user tcm may run commands that access a modem
device file with the dialer group.
tcm boulder = (:dialer) /usr/bin/tip, /usr/bin/cu,\
/usr/local/bin/minicom
Note that in this example only the group will be set, the command still
runs as user tcm. E.g.
$ sudo -g dialer /usr/bin/cu
Multiple users and groups may be present in a Runas_Spec, in which case
the user may select any combination of users and groups via the -u and
-g options. In this example:
alan ALL = (root, bin : operator, system) ALL
user alan may run any command as either user root or bin, optionally
setting the group to operator or system.
Option_Spec
A Cmnd may have zero or more options associated with it. Options may
consist of Solaris privileges sets, start and/or end dates and command
timeouts. Once an option is set for a Cmnd, subsequent Cmnds in the
Cmnd_Spec_List, inherit that option unless it is overridden by another
option. Note that the option names are reserved words in sudoers.
This means that none of the valid option names (see below) can be used
when declaring an alias.
Solaris_Priv_Spec
On Solaris systems, sudoers file entries may optionally specify Solaris
privilege set and/or limit privilege set associated with a command. If
privileges or limit privileges are specified with the command it will
override any default values specified in sudoers.
A privilege set is a comma-separated list of privilege names. The
ppriv(1) command can be used to list all privileges known to the
system. For example:
$ ppriv -l
In addition, there are several “special” privilege strings:
none the empty set
all the set of all privileges
zone the set of all privileges available in the current zone
basic the default set of privileges normal users are granted at
login time
Privileges can be excluded from a set by prefixing the privilege name
with either an ‘!’ or ‘-’ character.
Date_Spec
sudoers rules can be specified with a start and end date via the
NOTBEFORE and NOTAFTER settings. The time stamp must be specified in
Generalized Time as defined by RFC 4517. The format is effectively
yyyymmddHHMMSSZ where the minutes and seconds are optional. The ‘Z’
suffix indicates that the time stamp is in Coordinated Universal Time
(UTC). It is also possible to specify a timezone offset from UTC in
hours and minutes instead of a ‘Z’. For example, ‘-0500’ would
correspond to Eastern Standard time in the US. As an extension, if no
‘Z’ or timezone offset is specified, local time will be used.
The following are all valid time stamps:
20170214083000Z
2017021408Z
20160315220000-0500
20151201235900
Timeout_Spec
A command may have a timeout associated with it. If the timeout
expires before the command has exited, the command will be terminated.
The timeout may be specified in combinations of days, hours, minutes
and seconds with a single-letter case-insensitive suffix that indicates
the unit of time. For example, a timeout of 7 days, 8 hours, 30
minutes and 10 seconds would be written as 7d8h30m10s. If a number is
specified without a unit, seconds are assumed. Any of the days,
minutes, hours or seconds may be omitted. The order must be from
largest to smallest unit and a unit may not be specified more than
once.
The following are all valid timeout values: 7d8h30m10s, 14d, 8h30m,
600s, 3600. The following are invalid timeout values: 12m2w1d,
30s10m4h, 1d2d3h.
This setting is only supported by version 1.8.20 or higher.
Chdir_Spec
The working directory that the command will be run in can be specified
using the CWD setting. The directory must be a fully-qualified path
name beginning with a ‘/’ or ‘~’ character, or the special value “*”.
A value of “*” indicates that the user may specify the working
directory by running sudo with the -D option. By default, commands are
run from the invoking user's current working directory, unless the -i
option is given. Path names of the form ~user/path/name are
interpreted as being relative to the named user's home directory. If
the user name is omitted, the path will be relative to the runas user's
home directory.
This setting is only supported by version 1.9.3 or higher.
Chroot_Spec
The root directory that the command will be run in can be specified
using the CHROOT setting. The directory must be a fully-qualified path
name beginning with a ‘/’ or ‘~’ character, or the special value “*”.
A value of “*” indicates that the user may specify the root directory
by running sudo with the -R option. This setting can be used to run
the command in a chroot(2) “sandbox” similar to the chroot(1m) utility.
Path names of the form ~user/path/name are interpreted as being
relative to the named user's home directory. If the user name is
omitted, the path will be relative to the runas user's home directory.
This setting is only supported by version 1.9.3 or higher.
Tag_Spec
A command may have zero or more tags associated with it. The following
tag values are supported: EXEC, NOEXEC, FOLLOW, NOFOLLOW, LOG_INPUT,
NOLOG_INPUT, LOG_OUTPUT, NOLOG_OUTPUT, MAIL, NOMAIL, PASSWD, NOPASSWD,
SETENV, and NOSETENV. Once a tag is set on a Cmnd, subsequent Cmnds in
the Cmnd_Spec_List, inherit the tag unless it is overridden by the
opposite tag (in other words, PASSWD overrides NOPASSWD and NOEXEC
overrides EXEC).
EXEC and NOEXEC
If sudo has been compiled with noexec support and the underlying
operating system supports it, the NOEXEC tag can be used to prevent a
dynamically-linked executable from running further commands itself.
In the following example, user aaron may run /usr/bin/more and
/usr/bin/vi but shell escapes will be disabled.
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
See the Preventing shell escapes section below for more details on
how NOEXEC works and whether or not it will work on your system.
FOLLOW and NOFOLLOW
Starting with version 1.8.15, sudoedit will not open a file that is a
symbolic link unless the sudoedit_follow flag is enabled. The FOLLOW
and NOFOLLOW tags override the value of sudoedit_follow and can be
used to permit (or deny) the editing of symbolic links on a per-
command basis. These tags are only effective for the sudoedit
command and are ignored for all other commands.
LOG_INPUT and NOLOG_INPUT
These tags override the value of the log_input flag on a per-command
basis. For more information, see the description of log_input in the
SUDOERS OPTIONS section below.
LOG_OUTPUT and NOLOG_OUTPUT
These tags override the value of the log_output flag on a per-command
basis. For more information, see the description of log_output in
the SUDOERS OPTIONS section below.
MAIL and NOMAIL
These tags provide fine-grained control over whether mail will be
sent when a user runs a command by overriding the value of the
mail_all_cmnds flag on a per-command basis. They have no effect when
sudo is run with the -l or -v options. A NOMAIL tag will also
override the mail_always and mail_no_perms options. For more
information, see the descriptions of mail_all_cmnds, mail_always, and
mail_no_perms in the SUDOERS OPTIONS section below.
PASSWD and NOPASSWD
By default, sudo requires that a user authenticate him or herself
before running a command. This behavior can be modified via the
NOPASSWD tag. Like a Runas_Spec, the NOPASSWD tag sets a default for
the commands that follow it in the Cmnd_Spec_List. Conversely, the
PASSWD tag can be used to reverse things. For example:
ray rushmore = NOPASSWD: /bin/kill, /bin/ls, /usr/bin/lprm
would allow the user ray to run /bin/kill, /bin/ls, and /usr/bin/lprm
as root on the machine rushmore without authenticating himself. If
we only want ray to be able to run /bin/kill without a password the
entry would be:
ray rushmore = NOPASSWD: /bin/kill, PASSWD: /bin/ls, /usr/bin/lprm
Note, however, that the PASSWD tag has no effect on users who are in
the group specified by the exempt_group setting.
By default, if the NOPASSWD tag is applied to any of a user's entries
for the current host, the user will be able to run “sudo -l” without
a password. Additionally, a user may only run “sudo -v” without a
password if all of the user's entries for the current host have the
NOPASSWD tag. This behavior may be overridden via the verifypw and
listpw options.
SETENV and NOSETENV
These tags override the value of the setenv flag on a per-command
basis. Note that if SETENV has been set for a command, the user may
disable the env_reset flag from the command line via the -E option.
Additionally, environment variables set on the command line are not
subject to the restrictions imposed by env_check, env_delete, or
env_keep. As such, only trusted users should be allowed to set
variables in this manner. If the command matched is ALL, the SETENV
tag is implied for that command; this default may be overridden by
use of the NOSETENV tag.
Wildcards
sudo allows shell-style wildcards (aka meta or glob characters) to be
used in host names, path names and command line arguments in the
sudoers file. Wildcard matching is done via the glob(3) and fnmatch(3)
functions as specified by IEEE Std 1003.1 (“POSIX.1”).
* Matches any set of zero or more characters (including white
space).
? Matches any single character (including white space).
[...] Matches any character in the specified range.
[!...] Matches any character not in the specified range.
\x For any character ‘x’, evaluates to ‘x’. This is used to
escape special characters such as: ‘*’, ‘?’, ‘[’, and ‘]’.
Note that these are not regular expressions. Unlike a regular
expression there is no way to match one or more characters within a
range.
Character classes may be used if your system's glob(3) and fnmatch(3)
functions support them. However, because the ‘:’ character has special
meaning in sudoers, it must be escaped. For example:
/bin/ls [[\:alpha\:]]*
Would match any file name beginning with a letter.
Note that a forward slash (‘/’) will not be matched by wildcards used
in the file name portion of the command. This is to make a path like:
/usr/bin/*
match /usr/bin/who but not /usr/bin/X11/xterm.
When matching the command line arguments, however, a slash does get
matched by wildcards since command line arguments may contain arbitrary
strings and not just path names.
Wildcards in command line arguments should be used with care.
Command line arguments are matched as a single, concatenated string.
This mean a wildcard character such as ‘?’ or ‘*’ will match across
word boundaries, which may be unexpected. For example, while a sudoers
entry like:
%operator ALL = /bin/cat /var/log/messages*
will allow command like:
$ sudo cat /var/log/messages.1
It will also allow:
$ sudo cat /var/log/messages /etc/shadow
which is probably not what was intended. In most cases it is better to
do command line processing outside of the sudoers file in a scripting
language.
Exceptions to wildcard rules
The following exceptions apply to the above rules:
"" If the empty string "" is the only command line argument in
the sudoers file entry it means that command is not allowed
to be run with any arguments.
sudoedit Command line arguments to the sudoedit built-in command
should always be path names, so a forward slash (‘/’) will
not be matched by a wildcard.
Including other files from within sudoers
It is possible to include other sudoers files from within the sudoers
file currently being parsed using the @include and @includedir
directives. For compatibility with sudo versions prior to 1.9.1,
#include and #includedir are also accepted.
An include file can be used, for example, to keep a site-wide sudoers
file in addition to a local, per-machine file. For the sake of this
example the site-wide sudoers file will be /etc/sudoers and the per-
machine one will be /etc/sudoers.local. To include /etc/sudoers.local
from within /etc/sudoers one would use the following line in
/etc/sudoers:
@include /etc/sudoers.local
When sudo reaches this line it will suspend processing of the current
file (/etc/sudoers) and switch to /etc/sudoers.local. Upon reaching
the end of /etc/sudoers.local, the rest of /etc/sudoers will be
processed. Files that are included may themselves include other files.
A hard limit of 128 nested include files is enforced to prevent include
file loops.
The path to the include file may contain white space if it is escaped
with a backslash (‘\’). Alternately, the entire path may be enclosed
in double quotes (""), in which case no escaping is necessary. To
include a literal backslash in the path, ‘\\’ should be used.
If the path to the include file is not fully-qualified (does not begin
with a ‘/’), it must be located in the same directory as the sudoers
file it was included from. For example, if /etc/sudoers contains the
line:
@include sudoers.local
the file that will be included is /etc/sudoers.local.
The file name may also include the %h escape, signifying the short form
of the host name. In other words, if the machine's host name is
“xerxes”, then
@include /etc/sudoers.%h
will cause sudo to include the file /etc/sudoers.xerxes.
The @includedir directive can be used to create a sudoers.d directory
that the system package manager can drop sudoers file rules into as
part of package installation. For example, given:
@includedir /etc/sudoers.d
sudo will suspend processing of the current file and read each file in
/etc/sudoers.d, skipping file names that end in ‘~’ or contain a ‘.’
character to avoid causing problems with package manager or editor
temporary/backup files. Files are parsed in sorted lexical order.
That is, /etc/sudoers.d/01_first will be parsed before
/etc/sudoers.d/10_second. Be aware that because the sorting is
lexical, not numeric, /etc/sudoers.d/1_whoops would be loaded after
/etc/sudoers.d/10_second. Using a consistent number of leading zeroes
in the file names can be used to avoid such problems. After parsing
the files in the directory, control returns to the file that contained
the @includedir directive.
Note that unlike files included via @include, visudo will not edit the
files in a @includedir directory unless one of them contains a syntax
error. It is still possible to run visudo with the -f flag to edit the
files directly, but this will not catch the redefinition of an alias
that is also present in a different file.
Other special characters and reserved words
The pound sign (‘#’) is used to indicate a comment (unless it is part
of a #include directive or unless it occurs in the context of a user
name and is followed by one or more digits, in which case it is treated
as a user-ID). Both the comment character and any text after it, up to
the end of the line, are ignored.
The reserved word ALL is a built-in alias that always causes a match to
succeed. It can be used wherever one might otherwise use a Cmnd_Alias,
User_Alias, Runas_Alias, or Host_Alias. Attempting to define an alias
named ALL will result in a syntax error. Please note that using ALL
can be dangerous since in a command context, it allows the user to run
any command on the system.
The following option names permitted in an Option_Spec are also
considered reserved words: CHROOT, PRIVS, LIMITPRIVS, TIMEOUT, CWD,
NOTBEFORE and NOTAFTER. Attempting to define an alias with the same
name as one of the options will result in a syntax error.
An exclamation point (‘!’) can be used as a logical not operator in a
list or alias as well as in front of a Cmnd. This allows one to
exclude certain values. For the ‘!’ operator to be effective, there
must be something for it to exclude. For example, to match all users
except for root one would use:
ALL,!root
If the ALL, is omitted, as in:
!root
it would explicitly deny root but not match any other users. This is
different from a true “negation” operator.
Note, however, that using a ‘!’ in conjunction with the built-in ALL
alias to allow a user to run “all but a few” commands rarely works as
intended (see SECURITY NOTES below).
Long lines can be continued with a backslash (‘\’) as the last
character on the line.
White space between elements in a list as well as special syntactic
characters in a User Specification (‘=’, ‘:’, ‘(’, ‘)’) is optional.
The following characters must be escaped with a backslash (‘\’) when
used as part of a word (e.g., a user name or host name): ‘!’, ‘=’, ‘:’,
‘,’, ‘(’, ‘)’, ‘\’.
SUDOERS OPTIONS
sudo's behavior can be modified by Default_Entry lines, as explained
earlier. A list of all supported Defaults parameters, grouped by type,
are listed below.
Boolean Flags:
always_query_group_plugin
If a group_plugin is configured, use it to resolve
groups of the form %group as long as there is not
also a system group of the same name. Normally, only
groups of the form %:group are passed to the
group_plugin. This flag is off by default.
always_set_home If enabled, sudo will set the HOME environment
variable to the home directory of the target user
(which is the root user unless the -u option is
used). This flag is largely obsolete and has no
effect unless the env_reset flag has been disabled or
HOME is present in the env_keep list, both of which
are strongly discouraged. This flag is off by
default.
authenticate If set, users must authenticate themselves via a
password (or other means of authentication) before
they may run commands. This default may be
overridden via the PASSWD and NOPASSWD tags. This
flag is on by default.
case_insensitive_group
If enabled, group names in sudoers will be matched in
a case insensitive manner. This may be necessary
when users are stored in LDAP or AD. This flag is on
by default.
case_insensitive_user
If enabled, user names in sudoers will be matched in
a case insensitive manner. This may be necessary
when groups are stored in LDAP or AD. This flag is
on by default.
closefrom_override
If set, the user may use the -C option which
overrides the default starting point at which sudo
begins closing open file descriptors. This flag is
off by default.
compress_io If set, and sudo is configured to log a command's
input or output, the I/O logs will be compressed
using zlib. This flag is on by default when sudo is
compiled with zlib support.
exec_background By default, sudo runs a command as the foreground
process as long as sudo itself is running in the
foreground. When the exec_background flag is enabled
and the command is being run in a pseudo-terminal
(due to I/O logging or the use_pty flag), the command
will be run as a background process. Attempts to
read from the controlling terminal (or to change
terminal settings) will result in the command being
suspended with the SIGTTIN signal (or SIGTTOU in the
case of terminal settings). If this happens when
sudo is a foreground process, the command will be
granted the controlling terminal and resumed in the
foreground with no user intervention required. The
advantage of initially running the command in the
background is that sudo need not read from the
terminal unless the command explicitly requests it.
Otherwise, any terminal input must be passed to the
command, whether it has required it or not (the
kernel buffers terminals so it is not possible to
tell whether the command really wants the input).
This is different from historic sudo behavior or when
the command is not being run in a pseudo-terminal.
For this to work seamlessly, the operating system
must support the automatic restarting of system
calls. Unfortunately, not all operating systems do
this by default, and even those that do may have
bugs. For example, macOS fails to restart the
tcgetattr() and tcsetattr() system calls (this is a
bug in macOS). Furthermore, because this behavior
depends on the command stopping with the SIGTTIN or
SIGTTOU signals, programs that catch these signals
and suspend themselves with a different signal
(usually SIGTOP) will not be automatically
foregrounded. Some versions of the linux su(1)
command behave this way. This flag is off by
default.
This setting is only supported by version 1.8.7 or
higher. It has no effect unless I/O logging is
enabled or the use_pty flag is enabled.
env_editor If set, visudo will use the value of the SUDO_EDITOR,
VISUAL or EDITOR environment variables before falling
back on the default editor list. Note that visudo is
typically run as root so this flag may allow a user
with visudo privileges to run arbitrary commands as
root without logging. An alternative is to place a
colon-separated list of “safe” editors int the editor
variable. visudo will then only use SUDO_EDITOR,
VISUAL or EDITOR if they match a value specified in
editor. If the env_reset flag is enabled, the
SUDO_EDITOR, VISUAL and/or EDITOR environment
variables must be present in the env_keep list for
the env_editor flag to function when visudo is
invoked via sudo. This flag is on by default.
env_reset If set, sudo will run the command in a minimal
environment containing the TERM, PATH, HOME, MAIL,
SHELL, LOGNAME, USER and SUDO_* variables. Any
variables in the caller's environment or in the file
specified by the restricted_env_file setting that
match the env_keep and env_check lists are then
added, followed by any variables present in the file
specified by the env_file setting (if any). The
contents of the env_keep and env_check lists, as
modified by global Defaults parameters in sudoers,
are displayed when sudo is run by root with the -V
option. If the secure_path setting is enabled, its
value will be used for the PATH environment variable.
This flag is on by default.
fast_glob Normally, sudo uses the glob(3) function to do shell-
style globbing when matching path names. However,
since it accesses the file system, glob(3) can take a
long time to complete for some patterns, especially
when the pattern references a network file system
that is mounted on demand (auto mounted). The
fast_glob flag causes sudo to use the fnmatch(3)
function, which does not access the file system to do
its matching. The disadvantage of fast_glob is that
it is unable to match relative path names such as
./ls or ../bin/ls. This has security implications
when path names that include globbing characters are
used with the negation operator, ‘!’, as such rules
can be trivially bypassed. As such, this flag should
not be used when the sudoers file contains rules that
contain negated path names which include globbing
characters. This flag is off by default.
fqdn Set this flag if you want to put fully qualified host
names in the sudoers file when the local host name
(as returned by the hostname command) does not
contain the domain name. In other words, instead of
myhost you would use myhost.mydomain.edu. You may
still use the short form if you wish (and even mix
the two). This flag is only effective when the
“canonical” host name, as returned by the
getaddrinfo() or gethostbyname() function, is a
fully-qualified domain name. This is usually the
case when the system is configured to use DNS for
host name resolution.
If the system is configured to use the /etc/hosts
file in preference to DNS, the “canonical” host name
may not be fully-qualified. The order that sources
are queried for host name resolution is usually
specified in the /etc/nsswitch.conf,
/etc/netsvc.conf, /etc/host.conf, or, in some cases,
/etc/resolv.conf file. In the /etc/hosts file, the
first host name of the entry is considered to be the
“canonical” name; subsequent names are aliases that
are not used by sudoers. For example, the following
hosts file line for the machine “xyzzy” has the
fully-qualified domain name as the “canonical” host
name, and the short version as an alias.
192.168.1.1 xyzzy.sudo.ws xyzzy
If the machine's hosts file entry is not formatted
properly, the fqdn flag will not be effective if it
is queried before DNS.
Beware that when using DNS for host name resolution,
turning on fqdn requires sudoers to make DNS lookups
which renders sudo unusable if DNS stops working (for
example if the machine is disconnected from the
network). Also note that just like with the hosts
file, you must use the “canonical” name as DNS knows
it. That is, you may not use a host alias (CNAME
entry) due to performance issues and the fact that
there is no way to get all aliases from DNS.
This flag is off by default.
ignore_audit_errors
Allow commands to be run even if sudoers cannot write
to the audit log. If enabled, an audit log write
failure is not treated as a fatal error. If
disabled, a command may only be run after the audit
event is successfully written. This flag is only
effective on systems for which sudoers supports audit
logging, including FreeBSD, Linux, macOS and Solaris.
This flag is on by default.
ignore_dot If set, sudo will ignore "." or "" (both denoting
current directory) in the PATH environment variable;
the PATH itself is not modified. This flag is off by
default.
ignore_iolog_errors
Allow commands to be run even if sudoers cannot write
to the I/O log (local or remote). If enabled, an I/O
log write failure is not treated as a fatal error.
If disabled, the command will be terminated if the
I/O log cannot be written to. This flag is off by
default.
ignore_logfile_errors
Allow commands to be run even if sudoers cannot write
to the log file. If enabled, a log file write
failure is not treated as a fatal error. If
disabled, a command may only be run after the log
file entry is successfully written. This flag only
has an effect when sudoers is configured to use file-
based logging via the logfile setting. This flag is
on by default.
ignore_local_sudoers
If set via LDAP, parsing of /etc/sudoers will be
skipped. This is intended for Enterprises that wish
to prevent the usage of local sudoers files so that
only LDAP is used. This thwarts the efforts of rogue
operators who would attempt to add roles to
/etc/sudoers. When this flag is enabled,
/etc/sudoers does not even need to exist. Since this
flag tells sudo how to behave when no specific LDAP
entries have been matched, this sudoOption is only
meaningful for the cn=defaults section. This flag is
off by default.
ignore_unknown_defaults
If set, sudo will not produce a warning if it
encounters an unknown Defaults entry in the sudoers
file or an unknown sudoOption in LDAP. This flag is
off by default.
insults If set, sudo will insult users when they enter an
incorrect password. This flag is off by default.
log_allowed If set, sudoers will log commands allowed by the
policy to the system audit log (where supported) as
well as to syslog and/or a log file. This flag is on
by default.
This setting is only supported by version 1.8.29 or
higher.
log_denied If set, sudoers will log commands denied by the
policy to the system audit log (where supported) as
well as to syslog and/or a log file. This flag is on
by default.
This setting is only supported by version 1.8.29 or
higher.
log_host If set, the host name will be included in log entries
written to the file configured by the logfile
setting. This flag is off by default.
log_input If set, sudo will run the command in a pseudo-
terminal and log all user input. If the standard
input is not connected to the user's tty, due to I/O
redirection or because the command is part of a
pipeline, that input is also captured and stored in a
separate log file. Anything sent to the standard
input will be consumed, regardless of whether or not
the command run via sudo is actually reading the
standard input. This may have unexpected results
when using sudo in a shell script that expects to
process the standard input. For more information
about I/O logging, see the I/O LOG FILES section.
This flag is off by default.
log_output If set, sudo will run the command in a pseudo-
terminal and log all output that is sent to the
screen, similar to the script(1) command. For more
information about I/O logging, see the I/O LOG FILES
section. This flag is off by default.
log_server_keepalive
If set, sudo will enable the TCP keepalive socket
option on the connection to the log server. This
enables the periodic transmission of keepalive
messages to the server. If the server does not
respond to a message, the connection will be closed
and the running command will be terminated unless the
ignore_iolog_errors flag (I/O logging enabled) or the
ignore_log_errors flag (I/O logging disabled) is set.
This flag is on by default.
This setting is only supported by version 1.9.0 or
higher.
log_server_verify
If set, the server certificate received during the
TLS handshake must be valid and it must contain
either the server name (from log_servers) or its IP
address. If either of these conditions is not met,
the TLS handshake will fail. This flag is on by
default.
This setting is only supported by version 1.9.0 or
higher.
log_year If set, the four-digit year will be logged in the
(non-syslog) sudo log file. This flag is off by
default.
long_otp_prompt When validating with a One Time Password (OTP) scheme
such as S/Key or OPIE, a two-line prompt is used to
make it easier to cut and paste the challenge to a
local window. It's not as pretty as the default but
some people find it more convenient. This flag is
off by default.
mail_all_cmnds Send mail to the mailto user every time a user
attempts to run a command via sudo (this includes
sudoedit). No mail will be sent if the user runs
sudo with the -l or -v option unless there is an
authentication error and the mail_badpass flag is
also set. This flag is off by default.
mail_always Send mail to the mailto user every time a user runs
sudo. This flag is off by default.
mail_badpass Send mail to the mailto user if the user running sudo
does not enter the correct password. If the command
the user is attempting to run is not permitted by
sudoers and one of the mail_all_cmnds, mail_always,
mail_no_host, mail_no_perms or mail_no_user flags are
set, this flag will have no effect. This flag is off
by default.
mail_no_host If set, mail will be sent to the mailto user if the
invoking user exists in the sudoers file, but is not
allowed to run commands on the current host. This
flag is off by default.
mail_no_perms If set, mail will be sent to the mailto user if the
invoking user is allowed to use sudo but the command
they are trying is not listed in their sudoers file
entry or is explicitly denied. This flag is off by
default.
mail_no_user If set, mail will be sent to the mailto user if the
invoking user is not in the sudoers file. This flag
is on by default.
match_group_by_gid
By default, sudoers will look up each group the user
is a member of by group-ID to determine the group
name (this is only done once). The resulting list of
the user's group names is used when matching groups
listed in the sudoers file. This works well on
systems where the number of groups listed in the
sudoers file is larger than the number of groups a
typical user belongs to. On systems where group
lookups are slow, where users may belong to a large
number of groups, and where the number of groups
listed in the sudoers file is relatively small, it
may be prohibitively expensive and running commands
via sudo may take longer than normal. On such
systems it may be faster to use the
match_group_by_gid flag to avoid resolving the user's
group-IDs to group names. In this case, sudoers must
look up any group name listed in the sudoers file and
use the group-ID instead of the group name when
determining whether the user is a member of the
group.
Note that if match_group_by_gid is enabled, group
database lookups performed by sudoers will be keyed
by group name as opposed to group-ID. On systems
where there are multiple sources for the group
database, it is possible to have conflicting group
names or group-IDs in the local /etc/group file and
the remote group database. On such systems, enabling
or disabling match_group_by_gid can be used to choose
whether group database queries are performed by name
(enabled) or ID (disabled), which may aid in working
around group entry conflicts.
The match_group_by_gid flag has no effect when
sudoers data is stored in LDAP. This flag is off by
default.
This setting is only supported by version 1.8.18 or
higher.
netgroup_tuple If set, netgroup lookups will be performed using the
full netgroup tuple: host name, user name and domain
(if one is set). Historically, sudo only matched the
user name and domain for netgroups used in a
User_List and only matched the host name and domain
for netgroups used in a Host_List. This flag is off
by default.
noexec If set, all commands run via sudo will behave as if
the NOEXEC tag has been set, unless overridden by an
EXEC tag. See the description of EXEC and NOEXEC
above as well as the Preventing shell escapes section
at the end of this manual. This flag is off by
default.
pam_acct_mgmt On systems that use PAM for authentication, sudo will
perform PAM account validation for the invoking user
by default. The actual checks performed depend on
which PAM modules are configured. If enabled,
account validation will be performed regardless of
whether or not a password is required. This flag is
on by default.
This setting is only supported by version 1.8.28 or
higher.
pam_rhost On systems that use PAM for authentication, sudo will
set the PAM remote host value to the name of the
local host when the pam_rhost flag is enabled. On
Linux systems, enabling pam_rhost may result in DNS
lookups of the local host name when PAM is
initialized. On Solaris versions prior to Solaris 8,
pam_rhost must be enabled if pam_ruser is also
enabled to avoid a crash in the Solaris PAM
implementation.
This flag is off by default on systems other than
Solaris.
This setting is only supported by version 1.9.0 or
higher.
pam_ruser On systems that use PAM for authentication, sudo will
set the PAM remote user value to the name of the user
that invoked sudo when the pam_ruser flag is enabled.
This flag is on by default.
This setting is only supported by version 1.9.0 or
higher.
pam_session On systems that use PAM for authentication, sudo will
create a new PAM session for the command to be run
in. Unless sudo is given the -i or -s options, PAM
session modules are run with the “silent” flag
enabled. This prevents last login information from
being displayed for every command on some systems.
Disabling pam_session may be needed on older PAM
implementations or on operating systems where opening
a PAM session changes the utmp or wtmp files. If PAM
session support is disabled, resource limits may not
be updated for the command being run. If
pam_session, pam_setcred, and use_pty are disabled,
log_servers has not been set and I/O logging has not
been configured, sudo will execute the command
directly instead of running it as a child process.
This flag is on by default.
This setting is only supported by version 1.8.7 or
higher.
pam_setcred On systems that use PAM for authentication, sudo will
attempt to establish credentials for the target user
by default, if supported by the underlying
authentication system. One example of a credential
is a Kerberos ticket. If pam_session, pam_setcred,
and use_pty are disabled, log_servers has not been
set and I/O logging has not been configured, sudo
will execute the command directly instead of running
it as a child process. This flag is on by default.
This setting is only supported by version 1.8.8 or
higher.
passprompt_override
If set, the prompt specified by passprompt or the
SUDO_PROMPT environment variable will always be used
and will replace the prompt provided by a PAM module
or other authentication method. This flag is off by
default.
path_info Normally, sudo will tell the user when a command
could not be found in their PATH environment
variable. Some sites may wish to disable this as it
could be used to gather information on the location
of executables that the normal user does not have
access to. The disadvantage is that if the
executable is simply not in the user's PATH, sudo
will tell the user that they are not allowed to run
it, which can be confusing. This flag is on by
default.
preserve_groups By default, sudo will initialize the group vector to
the list of groups the target user is in. When
preserve_groups is set, the user's existing group
vector is left unaltered. The real and effective
group-IDs, however, are still set to match the target
user. This flag is off by default.
pwfeedback By default, sudo reads the password like most other
Unix programs, by turning off echo until the user
hits the return (or enter) key. Some users become
confused by this as it appears to them that sudo has
hung at this point. When pwfeedback is set, sudo
will provide visual feedback when the user presses a
key. Note that this does have a security impact as
an onlooker may be able to determine the length of
the password being entered. This flag is off by
default.
requiretty If set, sudo will only run when the user is logged in
to a real tty. When this flag is set, sudo can only
be run from a login session and not via other means
such as cron(1m) or cgi-bin scripts. This flag is
off by default.
root_sudo If set, root is allowed to run sudo too. Disabling
this prevents users from “chaining” sudo commands to
get a root shell by doing something like “sudo sudo
/bin/sh”. Note, however, that turning off root_sudo
will also prevent root from running sudoedit.
Disabling root_sudo provides no real additional
security; it exists purely for historical reasons.
This flag is on by default.
rootpw If set, sudo will prompt for the root password
instead of the password of the invoking user when
running a command or editing a file. This flag is
off by default.
runas_allow_unknown_id
If enabled, allow matching of runas user and group
IDs that are not present in the password or group
databases. In addition to explicitly matching
unknown user or group IDs in a Runas_List, this
option also allows the ALL alias to match unknown
IDs. This flag is off by default.
This setting is only supported by version 1.8.30 or
higher. Older versions of sudo always allowed
matching of unknown user and group IDs.
runas_check_shell
If enabled, sudo will only run commands as a user
whose shell appears in the /etc/shells file, even if
the invoking user's Runas_List would otherwise permit
it. If no /etc/shells file is present, a system-
dependent list of built-in default shells is used.
On many operating systems, system users such as
“bin”, do not have a valid shell and this flag can be
used to prevent commands from being run as those
users. This flag is off by default.
This setting is only supported by version 1.8.30 or
higher.
runaspw If set, sudo will prompt for the password of the user
defined by the runas_default option (defaults to
root) instead of the password of the invoking user
when running a command or editing a file. This flag
is off by default.
set_home If enabled and sudo is invoked with the -s option,
the HOME environment variable will be set to the home
directory of the target user (which is the root user
unless the -u option is used). This flag is largely
obsolete and has no effect unless the env_reset flag
has been disabled or HOME is present in the env_keep
list, both of which are strongly discouraged. This
flag is off by default.
set_logname Normally, sudo will set the LOGNAME and USER
environment variables to the name of the target user
(usually root unless the -u option is given).
However, since some programs (including the RCS
revision control system) use LOGNAME to determine the
real identity of the user, it may be desirable to
change this behavior. This can be done by negating
the set_logname option. Note that set_logname will
have no effect if the env_reset option has not been
disabled and the env_keep list contains LOGNAME or
USER. This flag is on by default.
set_utmp When enabled, sudo will create an entry in the utmp
(or utmpx) file when a pseudo-terminal is allocated.
A pseudo-terminal is allocated by sudo when it is
running in a terminal and one or more of the
log_input, log_output or use_pty flags is enabled.
By default, the new entry will be a copy of the
user's existing utmp entry (if any), with the tty,
time, type and pid fields updated. This flag is on
by default.
setenv Allow the user to disable the env_reset option from
the command line via the -E option. Additionally,
environment variables set via the command line are
not subject to the restrictions imposed by env_check,
env_delete, or env_keep. As such, only trusted users
should be allowed to set variables in this manner.
This flag is off by default.
shell_noargs If set and sudo is invoked with no arguments it acts
as if the -s option had been given. That is, it runs
a shell as root (the shell is determined by the SHELL
environment variable if it is set, falling back on
the shell listed in the invoking user's /etc/passwd
entry if not). This flag is off by default.
stay_setuid Normally, when sudo executes a command the real and
effective UIDs are set to the target user (root by
default). This option changes that behavior such
that the real UID is left as the invoking user's UID.
In other words, this makes sudo act as a set-user-ID
wrapper. This can be useful on systems that disable
some potentially dangerous functionality when a
program is run set-user-ID. This option is only
effective on systems that support either the
setreuid(2) or setresuid(2) system call. This flag
is off by default.
sudoedit_checkdir
If set, sudoedit will check all directory components
of the path to be edited for writability by the
invoking user. Symbolic links will not be followed
in writable directories and sudoedit will refuse to
edit a file located in a writable directory. These
restrictions are not enforced when sudoedit is run by
root. On some systems, if all directory components
of the path to be edited are not readable by the
target user, sudoedit will be unable to edit the
file. This flag is on by default.
This setting was first introduced in version 1.8.15
but initially suffered from a race condition. The
check for symbolic links in writable intermediate
directories was added in version 1.8.16.
sudoedit_follow By default, sudoedit will not follow symbolic links
when opening files. The sudoedit_follow option can
be enabled to allow sudoedit to open symbolic links.
It may be overridden on a per-command basis by the
FOLLOW and NOFOLLOW tags. This flag is off by
default.
This setting is only supported by version 1.8.15 or
higher.
syslog_pid When logging via syslog(3), include the process ID in
the log entry. This flag is off by default.
This setting is only supported by version 1.8.21 or
higher.
targetpw If set, sudo will prompt for the password of the user
specified by the -u option (defaults to root) instead
of the password of the invoking user when running a
command or editing a file. Note that this flag
precludes the use of a user-ID not listed in the
passwd database as an argument to the -u option.
This flag is off by default.
tty_tickets If set, users must authenticate on a per-tty basis.
With this flag enabled, sudo will use a separate
record in the time stamp file for each terminal. If
disabled, a single record is used for all login
sessions.
This option has been superseded by the timestamp_type
option.
umask_override If set, sudo will set the umask as specified in the
sudoers file without modification. This makes it
possible to specify a umask in the sudoers file that
is more permissive than the user's own umask and
matches historical behavior. If umask_override is
not set, sudo will set the umask to be the union of
the user's umask and what is specified in sudoers.
This flag is off by default.
use_netgroups If set, netgroups (prefixed with ‘+’), may be used in
place of a user or host. For LDAP-based sudoers,
netgroup support requires an expensive sub-string
match on the server unless the NETGROUP_BASE
directive is present in the /etc/ldap.conf file. If
netgroups are not needed, this option can be disabled
to reduce the load on the LDAP server. This flag is
on by default.
use_pty If set, and sudo is running in a terminal, the
command will be run in a pseudo-terminal (even if no
I/O logging is being done). If the sudo process is
not attached to a terminal, use_pty has no effect.
A malicious program run under sudo may be capable of
injecting commands into the user's terminal or
running a background process that retains access to
the user's terminal device even after the main
program has finished executing. By running the
command in a separate pseudo-terminal, this attack is
no longer possible. This flag is off by default.
user_command_timeouts
If set, the user may specify a timeout on the command
line. If the timeout expires before the command has
exited, the command will be terminated. If a timeout
is specified both in the sudoers file and on the
command line, the smaller of the two timeouts will be
used. See the Timeout_Spec section for a description
of the timeout syntax. This flag is off by default.
This setting is only supported by version 1.8.20 or
higher.
utmp_runas If set, sudo will store the name of the runas user
when updating the utmp (or utmpx) file. By default,
sudo stores the name of the invoking user. This flag
is off by default.
visiblepw By default, sudo will refuse to run if the user must
enter a password but it is not possible to disable
echo on the terminal. If the visiblepw flag is set,
sudo will prompt for a password even when it would be
visible on the screen. This makes it possible to run
things like “ssh somehost sudo ls” since by default,
ssh(1) does not allocate a tty when running a
command. This flag is off by default.
Integers:
closefrom Before it executes a command, sudo will close all
open file descriptors other than standard input,
standard output and standard error (ie: file
descriptors 0-2). The closefrom option can be used
to specify a different file descriptor at which to
start closing. The default is 3.
command_timeout The maximum amount of time a command is allowed to
run before it is terminated. See the Timeout_Spec
section for a description of the timeout syntax.
This setting is only supported by version 1.8.20 or
higher.
log_server_timeout
The maximum amount of time to wait when connecting to
a log server or waiting for a server response. See
the Timeout_Spec section for a description of the
timeout syntax. The default value is 30 seconds.
This setting is only supported by version 1.9.0 or
higher.
maxseq The maximum sequence number that will be substituted
for the “%{seq}” escape in the I/O log file (see the
iolog_dir description below for more information).
While the value substituted for “%{seq}” is in base
36, maxseq itself should be expressed in decimal.
Values larger than 2176782336 (which corresponds to
the base 36 sequence number “ZZZZZZ”) will be
silently truncated to 2176782336. The default value
is 2176782336.
Once the local sequence number reaches the value of
maxseq, it will “roll over” to zero, after which
sudoers will truncate and re-use any existing I/O log
path names.
This setting is only supported by version 1.8.7 or
higher.
passwd_tries The number of tries a user gets to enter his/her
password before sudo logs the failure and exits. The
default is 3.
syslog_maxlen On many systems, syslog(3) has a relatively small log
buffer. IETF RFC 5424 states that syslog servers
must support messages of at least 480 bytes and
should support messages up to 2048 bytes. By
default, sudoers creates log messages up to 980 bytes
which corresponds to the historic BSD syslog
implementation which used a 1024 byte buffer to store
the message, date, hostname and program name. To
prevent syslog messages from being truncated, sudoers
will split up log messages that are larger than
syslog_maxlen bytes. When a message is split,
additional parts will include the string “(command
continued)” after the user name and before the
continued command line arguments.
This setting is only supported by version 1.8.19 or
higher.
Integers that can be used in a boolean context:
loglinelen Number of characters per line for the file log. This
value is used to decide when to wrap lines for nicer
log files. This has no effect on the syslog log
file, only the file log. The default is 80 (use 0 or
negate the option to disable word wrap).
passwd_timeout Number of minutes before the sudo password prompt
times out, or 0 for no timeout. The timeout may
include a fractional component if minute granularity
is insufficient, for example 2.5. The default is 5.
timestamp_timeout
Number of minutes that can elapse before sudo will
ask for a passwd again. The timeout may include a
fractional component if minute granularity is
insufficient, for example 2.5. The default is 5.
Set this to 0 to always prompt for a password. If
set to a value less than 0 the user's time stamp will
not expire until the system is rebooted. This can be
used to allow users to create or delete their own
time stamps via “sudo -v” and “sudo -k” respectively.
umask File mode creation mask to use when running the
command. Negate this option or set it to 0777 to
prevent sudoers from changing the umask. Unless the
umask_override flag is set, the actual umask will be
the union of the user's umask and the value of the
umask setting, which defaults to 0022. This
guarantees that sudo never lowers the umask when
running a command.
If umask is explicitly set in sudoers, it will
override any umask setting in PAM or login.conf. If
umask is not set in sudoers, the umask specified by
PAM or login.conf will take precedence. The umask
setting in PAM is not used for sudoedit, which does
not create a new PAM session.
Strings:
authfail_message Message that is displayed after a user fails to
authenticate. The message may include the ‘%d’
escape which will expand to the number of failed
password attempts. If set, it overrides the default
message, %d incorrect password attempt(s).
badpass_message Message that is displayed if a user enters an
incorrect password. The default is Sorry, try again.
unless insults are enabled.
editor A colon (‘:’) separated list of editors path names
used by sudoedit and visudo. For sudoedit, this list
is used to find an editor when none of the
SUDO_EDITOR, VISUAL or EDITOR environment variables
are set to an editor that exists and is executable.
For visudo, it is used as a white list of allowed
editors; visudo will choose the editor that matches
the user's SUDO_EDITOR, VISUAL or EDITOR environment
variable if possible, or the first editor in the list
that exists and is executable if not. Unless invoked
as sudoedit, sudo does not preserve the SUDO_EDITOR,
VISUAL or EDITOR environment variables unless they
are present in the env_keep list or the env_reset
option is disabled. The default is vi.
iolog_dir The top-level directory to use when constructing the
path name for the input/output log directory. Only
used if the log_input or log_output options are
enabled or when the LOG_INPUT or LOG_OUTPUT tags are
present for a command. The session sequence number,
if any, is stored in the directory. The default is
/var/log/sudo-io.
The following percent (‘%’) escape sequences are
supported:
%{seq}
expanded to a monotonically increasing base-36
sequence number, such as 0100A5, where every
two digits are used to form a new directory,
e.g., 01/00/A5
%{user}
expanded to the invoking user's login name
%{group}
expanded to the name of the invoking user's
real group-ID
%{runas_user}
expanded to the login name of the user the
command will be run as (e.g., root)
%{runas_group}
expanded to the group name of the user the
command will be run as (e.g., wheel)
%{hostname}
expanded to the local host name without the
domain name
%{command}
expanded to the base name of the command being
run
In addition, any escape sequences supported by the
system's strftime(3) function will be expanded.
To include a literal ‘%’ character, the string ‘%%’
should be used.
iolog_file The path name, relative to iolog_dir, in which to
store input/output logs when the log_input or
log_output options are enabled or when the LOG_INPUT
or LOG_OUTPUT tags are present for a command. Note
that iolog_file may contain directory components.
The default is “%{seq}”.
See the iolog_dir option above for a list of
supported percent (‘%’) escape sequences.
In addition to the escape sequences, path names that
end in six or more Xs will have the Xs replaced with
a unique combination of digits and letters, similar
to the mktemp(3) function.
If the path created by concatenating iolog_dir and
iolog_file already exists, the existing I/O log file
will be truncated and overwritten unless iolog_file
ends in six or more Xs.
iolog_flush If set, sudo will flush I/O log data to disk after
each write instead of buffering it. This makes it
possible to view the logs in real-time as the program
is executing but may significantly reduce the
effectiveness of I/O log compression. This flag is
off by default.
This setting is only supported by version 1.8.20 or
higher.
iolog_group The group name to look up when setting the group-ID
on new I/O log files and directories. If iolog_group
is not set, the primary group-ID of the user
specified by iolog_user is used. If neither
iolog_group nor iolog_user are set, I/O log files and
directories are created with group-ID 0.
This setting is only supported by version 1.8.19 or
higher.
iolog_mode The file mode to use when creating I/O log files.
Mode bits for read and write permissions for owner,
group or other are honored, everything else is
ignored. The file permissions will always include
the owner read and write bits, even if they are not
present in the specified mode. When creating I/O log
directories, search (execute) bits are added to match
the read and write bits specified by iolog_mode.
Defaults to 0600 (read and write by user only).
This setting is only supported by version 1.8.19 or
higher.
iolog_user The user name to look up when setting the user and
group-IDs on new I/O log files and directories. If
iolog_group is set, it will be used instead of the
user's primary group-ID. By default, I/O log files
and directories are created with user and group-ID 0.
This setting can be useful when the I/O logs are
stored on a Network File System (NFS) share. Having
a dedicated user own the I/O log files means that
sudoers does not write to the log files as user-ID 0,
which is usually not permitted by NFS.
This setting is only supported by version 1.8.19 or
higher.
lecture_status_dir
The directory in which sudo stores per-user lecture
status files. Once a user has received the lecture,
a zero-length file is created in this directory so
that sudo will not lecture the user again. This
directory should not be cleared when the system
reboots. The default is /var/db/sudo/lectured.
limitprivs The default Solaris limit privileges to use when
constructing a new privilege set for a command. This
bounds all privileges of the executing process. The
default limit privileges may be overridden on a per-
command basis in sudoers. This option is only
available if sudoers is built on Solaris 10 or
higher.
log_server_cabundle
The path to a certificate authority bundle file, in
PEM format, to use instead of the system's default
certificate authority database when authenticating
the log server. The default is to use the system's
default certificate authority database. This setting
has no effect unless log_servers is set and the
remote log server is secured with TLS.
This setting is only supported by version 1.9.0 or
higher.
log_server_peer_cert
The path to the client's certificate file, in PEM
format. This setting is required when log_servers is
set and the remote log server is secured with TLS.
This setting is only supported by version 1.9.0 or
higher.
log_server_peer_key
The path to the client's private key file, in PEM
format. This setting is required when log_servers is
set and the remote log server is secured with TLS.
This setting is only supported by version 1.9.0 or
higher.
mailsub Subject of the mail sent to the mailto user. The
escape %h will expand to the host name of the
machine. Default is “*** SECURITY information for %h
***”.
noexec_file As of sudo version 1.8.1 this option is no longer
supported. The path to the noexec file should now be
set in the sudo.conf(4) file.
pam_login_service
On systems that use PAM for authentication, this is
the service name used when the -i option is
specified. The default value is “sudo”. See the
description of pam_service for more information.
This setting is only supported by version 1.8.8 or
higher.
pam_service On systems that use PAM for authentication, the
service name specifies the PAM policy to apply. This
usually corresponds to an entry in the pam.conf file
or a file in the /etc/pam.d directory. The default
value is “sudo”.
This setting is only supported by version 1.8.8 or
higher.
passprompt The default prompt to use when asking for a password;
can be overridden via the -p option or the
SUDO_PROMPT environment variable. The following
percent (‘%’) escape sequences are supported:
%H expanded to the local host name including the
domain name (only if the machine's host name is
fully qualified or the fqdn option is set)
%h expanded to the local host name without the
domain name
%p expanded to the user whose password is being
asked for (respects the rootpw, targetpw and
runaspw flags in sudoers)
%U expanded to the login name of the user the
command will be run as (defaults to root)
%u expanded to the invoking user's login name
%% two consecutive % characters are collapsed into
a single % character
On systems that use PAM for authentication,
passprompt will only be used if the prompt provided
by the PAM module matches the string “Password: ” or
“username's Password: ”. This ensures that the
passprompt setting does not interfere with challenge-
response style authentication. The
passprompt_override flag can be used to change this
behavior.
The default value is “Password: ”.
privs The default Solaris privileges to use when
constructing a new privilege set for a command. This
is passed to the executing process via the inherited
privilege set, but is bounded by the limit
privileges. If the privs option is specified but the
limitprivs option is not, the limit privileges of the
executing process is set to privs. The default
privileges may be overridden on a per-command basis
in sudoers. This option is only available if sudoers
is built on Solaris 10 or higher.
runas_default The default user to run commands as if the -u option
is not specified on the command line. This defaults
to root.
sudoers_locale Locale to use when parsing the sudoers file, logging
commands, and sending email. Note that changing the
locale may affect how sudoers is interpreted.
Defaults to “C”.
timestamp_type sudoers uses per-user time stamp files for credential
caching. The timestamp_type option can be used to
specify the type of time stamp record used. It has
the following possible values:
global A single time stamp record is used for all of
a user's login sessions, regardless of the
terminal or parent process ID. An additional
record is used to serialize password prompts
when sudo is used multiple times in a
pipeline, but this does not affect
authentication.
ppid A single time stamp record is used for all
processes with the same parent process ID
(usually the shell). Commands run from the
same shell (or other common parent process)
will not require a password for
timestamp_timeout minutes (5 by default) .
Commands run via sudo with a different parent
process ID, for example from a shell script,
will be authenticated separately.
tty One time stamp record is used for each
terminal, which means that a user's login
sessions are authenticated separately. If no
terminal is present, the behavior is the same
as ppid. Commands run from the same terminal
will not require a password for
timestamp_timeout minutes (5 by default) .
kernel The time stamp is stored in the kernel as an
attribute of the terminal device. If no
terminal is present, the behavior is the same
as ppid. Negative timestamp_timeout values
are not supported and positive values are
limited to a maximum of 60 minutes. This is
currently only supported on OpenBSD.
The default value is tty.
This setting is only supported by version 1.8.21 or
higher.
timestampdir The directory in which sudo stores its time stamp
files. This directory should be cleared when the
system reboots. The default is /var/run/sudo/ts.
timestampowner The owner of the lecture status directory, time stamp
directory and all files stored therein. The default
is root.
env_check Environment variables to be removed from the user's
environment unless they are considered “safe”. For
all variables except TZ, “safe” means that the
variable's value does not contain any ‘%’ or ‘/’
characters. This can be used to guard against
printf-style format vulnerabilities in poorly-written
programs. The TZ variable is considered unsafe if
any of the following are true:
• It consists of a fully-qualified path name,
optionally prefixed with a colon (‘:’), that does
not match the location of the zoneinfo directory.
• It contains a .. path element.
• It contains white space or non-printable
characters.
• It is longer than the value of PATH_MAX.
The argument may be a double-quoted, space-separated
list or a single value without double-quotes. The
list can be replaced, added to, deleted from, or
disabled by using the =, +=, -=, and ! operators
respectively. Regardless of whether the env_reset
option is enabled or disabled, variables specified by
env_check will be preserved in the environment if
they pass the aforementioned check. The global list
of environment variables to check is displayed when
sudo is run by root with the -V option.
env_delete Environment variables to be removed from the user's
environment when the env_reset option is not in
effect. The argument may be a double-quoted, space-
separated list or a single value without double-
quotes. The list can be replaced, added to, deleted
from, or disabled by using the =, +=, -=, and !
operators respectively. The global list of
environment variables to remove is displayed when
sudo is run by root with the -V option. Note that
many operating systems will remove potentially
dangerous variables from the environment of any set-
user-ID process (such as sudo).
env_keep Environment variables to be preserved in the user's
environment when the env_reset option is in effect.
This allows fine-grained control over the environment
sudo-spawned processes will receive. The argument
may be a double-quoted, space-separated list or a
single value without double-quotes. The list can be
replaced, added to, deleted from, or disabled by
using the =, +=, -=, and ! operators respectively.
The global list of variables to keep is displayed
when sudo is run by root with the -V option.
Preserving the HOME environment variable has security
implications since many programs use it when
searching for configuration or data files. Adding
HOME to env_keep may enable a user to run
unrestricted commands via sudo and is strongly
discouraged. Users wishing to edit files with sudo
should run sudoedit (or sudo -e) to get their
accustomed editor configuration instead of invoking
the editor directly.
log_servers A list of one or more servers to use for remote event
and I/O log storage, separated by white space. Log
servers must be running sudo_logsrvd or another
service that implements the protocol described by
sudo_logsrv.proto(4).
Server addresses should be of the form
“host[:port][(tls)]”. The host portion may be a host
name, an IPv4 address, or an IPv6 address in square
brackets.
If the optional tls flag is present, the connection
will be secured with Transport Layer Security (TLS)
version 1.2 or 1.3. Versions of TLS prior to 1.2 are
not supported.
If a port is specified, it may either be a port
number or a well-known service name as defined by the
system service name database. If no port is
specified, port 30343 will be used for plaintext
connections and port 30344 will be used for TLS
connections.
When log_servers is set, event log data will be
logged both locally (see the syslog and log_file
settings) as well as remotely, but I/O log data will
only be logged remotely. If multiple hosts are
specified, they will be attempted in reverse order.
If no log servers are available, the user will not be
able to run a command unless either the
ignore_iolog_errors flag (I/O logging enabled) or the
ignore_log_errors flag (I/O logging disabled) is set.
Likewise, if the connection to the log server is
interrupted while sudo is running, the command will
be terminated unless the ignore_iolog_errors flag
(I/O logging enabled) or the ignore_log_errors flag
(I/O logging disabled) is set.
This setting is only supported by version 1.9.0 or
higher.
GROUP PROVIDER PLUGINS
The sudoers plugin supports its own plugin interface to allow non-Unix
group lookups which can query a group source other than the standard
Unix group database. This can be used to implement support for the
nonunix_group syntax described earlier.
Group provider plugins are specified via the group_plugin setting. The
argument to group_plugin should consist of the plugin path, either
fully-qualified or relative to the /usr/local/libexec/sudo directory,
followed by any configuration options the plugin requires. These
options (if specified) will be passed to the plugin's initialization
function. If options are present, the string must be enclosed in
double quotes ("").
The following group provider plugins are installed by default:
group_file
The group_file plugin supports an alternate group file that
uses the same syntax as the /etc/group file. The path to the
group file should be specified as an option to the plugin.
For example, if the group file to be used is /etc/sudo-group:
Defaults group_plugin="group_file.so /etc/sudo-group"
system_group
The system_group plugin supports group lookups via the
standard C library functions getgrnam() and getgrid(). This
plugin can be used in instances where the user belongs to
groups not present in the user's supplemental group vector.
This plugin takes no options:
Defaults group_plugin=system_group.so
The group provider plugin API is described in detail in sudo_plugin(4).
LOG FORMAT
sudoers can log events in either JSON or sudo format, this section
describes the sudo log format. Depending on sudoers configuration,
sudoers can log events via syslog(3), to a local log file, or both.
The log format is almost identical in both cases.
Accepted command log entries
Commands that sudo runs are logged using the following format (split
into multiple lines for readability):
date hostname progname: username : TTY=ttyname ; PWD=cwd ; \
USER=runasuser ; GROUP=runasgroup ; TSID=logid ; \
ENV=env_vars COMMAND=command
Where the fields are as follows:
date The date the command was run. Typically, this is in the
format “MMM, DD, HH:MM:SS”. If logging via syslog(3),
the actual date format is controlled by the syslog
daemon. If logging to a file and the log_year option is
enabled, the date will also include the year.
hostname The name of the host sudo was run on. This field is only
present when logging via syslog(3).
progname The name of the program, usually sudo or sudoedit. This
field is only present when logging via syslog(3).
username The login name of the user who ran sudo.
ttyname The short name of the terminal (e.g., “console”, “tty01”,
or “pts/0”) sudo was run on, or “unknown” if there was no
terminal present.
cwd The current working directory that sudo was run in.
runasuser The user the command was run as.
runasgroup The group the command was run as if one was specified on
the command line.
logid An I/O log identifier that can be used to replay the
command's output. This is only present when the
log_input or log_output option is enabled.
env_vars A list of environment variables specified on the command
line, if specified.
command The actual command that was executed.
Messages are logged using the locale specified by sudoers_locale, which
defaults to the “C” locale.
Denied command log entries
If the user is not allowed to run the command, the reason for the
denial will follow the user name. Possible reasons include:
user NOT in sudoers
The user is not listed in the sudoers file.
user NOT authorized on host
The user is listed in the sudoers file but is not allowed to run
commands on the host.
command not allowed
The user is listed in the sudoers file for the host but they are not
allowed to run the specified command.
3 incorrect password attempts
The user failed to enter their password after 3 tries. The actual
number of tries will vary based on the number of failed attempts and
the value of the passwd_tries option.
a password is required
The -n option was specified but a password was required.
sorry, you are not allowed to set the following environment variables
The user specified environment variables on the command line that
were not allowed by sudoers.
Error log entries
If an error occurs, sudoers will log a message and, in most cases, send
a message to the administrator via email. Possible errors include:
parse error in /etc/sudoers near line N
sudoers encountered an error when parsing the specified file. In
some cases, the actual error may be one line above or below the line
number listed, depending on the type of error.
problem with defaults entries
The sudoers file contains one or more unknown Defaults settings.
This does not prevent sudo from running, but the sudoers file should
be checked using visudo.
timestamp owner (username): No such user
The time stamp directory owner, as specified by the timestampowner
setting, could not be found in the password database.
unable to open/read /etc/sudoers
The sudoers file could not be opened for reading. This can happen
when the sudoers file is located on a remote file system that maps
user-ID 0 to a different value. Normally, sudoers tries to open the
sudoers file using group permissions to avoid this problem.
Consider either changing the ownership of /etc/sudoers or adding an
argument like “sudoers_uid=N” (where ‘N’ is the user-ID that owns
the sudoers file) to the end of the sudoers Plugin line in the
sudo.conf(4) file.
unable to stat /etc/sudoers
The /etc/sudoers file is missing.
/etc/sudoers is not a regular file
The /etc/sudoers file exists but is not a regular file or symbolic
link.
/etc/sudoers is owned by uid N, should be 0
The sudoers file has the wrong owner. If you wish to change the
sudoers file owner, please add “sudoers_uid=N” (where ‘N’ is the
user-ID that owns the sudoers file) to the sudoers Plugin line in
the sudo.conf(4) file.
/etc/sudoers is world writable
The permissions on the sudoers file allow all users to write to it.
The sudoers file must not be world-writable, the default file mode
is 0440 (readable by owner and group, writable by none). The
default mode may be changed via the “sudoers_mode” option to the
sudoers Plugin line in the sudo.conf(4) file.
/etc/sudoers is owned by gid N, should be 1
The sudoers file has the wrong group ownership. If you wish to
change the sudoers file group ownership, please add “sudoers_gid=N”
(where ‘N’ is the group-ID that owns the sudoers file) to the
sudoers Plugin line in the sudo.conf(4) file.
unable to open /var/run/sudo/ts/username
sudoers was unable to read or create the user's time stamp file.
This can happen when timestampowner is set to a user other than root
and the mode on /var/run/sudo is not searchable by group or other.
The default mode for /var/run/sudo is 0711.
unable to write to /var/run/sudo/ts/username
sudoers was unable to write to the user's time stamp file.
/var/run/sudo/ts is owned by uid X, should be Y
The time stamp directory is owned by a user other than
timestampowner. This can occur when the value of timestampowner has
been changed. sudoers will ignore the time stamp directory until
the owner is corrected.
/var/run/sudo/ts is group writable
The time stamp directory is group-writable; it should be writable
only by timestampowner. The default mode for the time stamp
directory is 0700. sudoers will ignore the time stamp directory
until the mode is corrected.
Notes on logging via syslog
By default, sudoers logs messages via syslog(3). The date, hostname,
and progname fields are added by the system's syslog() function, not
sudoers itself. As such, they may vary in format on different systems.
The maximum size of syslog messages varies from system to system. The
syslog_maxlen setting can be used to change the maximum syslog message
size from the default value of 980 bytes. For more information, see
the description of syslog_maxlen.
Notes on logging to a file
If the logfile option is set, sudoers will log to a local file, such as
/var/log/sudo. When logging to a file, sudoers uses a format similar
to syslog(3), with a few important differences:
1. The progname and hostname fields are not present.
2. If the log_year option is enabled, the date will also include the
year.
3. Lines that are longer than loglinelen characters (80 by default)
are word-wrapped and continued on the next line with a four
character indent. This makes entries easier to read for a human
being, but makes it more difficult to use grep(1) on the log
files. If the loglinelen option is set to 0 (or negated with a
‘!’), word wrap will be disabled.
I/O LOG FILES
When I/O logging is enabled, sudo will run the command in a pseudo-
terminal and log all user input and/or output, depending on which
options are enabled. I/O can be logged either to the local machine or
to a remote log server. For local logs, I/O is logged to the directory
specified by the iolog_dir option (/var/log/sudo-io by default) using a
unique session ID that is included in the sudo log line, prefixed with
“TSID=”. The iolog_file option may be used to control the format of
the session ID. For remote logs, the log_servers setting is used to
specify one or more log servers running sudo_logsrvd or another server
that implements the protocol described by sudo_logsrv.proto(4).
For both local and remote I/O logs, each log is stored in a separate
directory that contains the following files:
log A text file containing information about the command. The
first line consists of the following colon-delimited fields:
the time the command was run, the name of the user who ran
sudo, the name of the target user, the name of the target
group (optional), the terminal that sudo was run from, and
the number of lines and columns of the terminal. The second
and third lines contain the working directory the command was
run from and the path name of the command itself (with
arguments if present).
log.json A JSON-formatted file containing information about the
command. This is similar to the log file but contains
additional information and is easily extensible. The
log.json file will be used by sudoreplay(1m) in preference to
the log file if it exists. The file may contain the
following elements:
timestamp
A JSON object containing time the command was run.
It consists of two values, seconds and nanoseconds.
columns The number of columns of the terminal the command
ran on, or zero if no terminal was present.
command The fully-qualified path of the command that was
run.
lines The number of lines of the terminal the command ran
on, or zero if no terminal was present.
runargv A JSON array representing the command's argument
vector as passed to the execve(2) system call.
runenv A JSON array representing the command's environment
as passed to the execve(2) system call.
rungid The group ID the command ran as. This element is
only present when the user specifies a group on the
command line.
rungroup The name of the group the command ran as. This
element is only present when the user specifies a
group on the command line.
runuid The user ID the command ran as.
runuser The name of the user the command ran as.
submitcwd
The current working directory at the time sudo was
run.
submithost
The name of the host the command was run on.
submituser
The name of the user who ran the command via sudo.
ttyname The path name of the terminal the user invoked sudo
from. If the command was run in a pseudo-terminal,
ttyname will be different from the terminal the
command actually ran in.
timing Timing information used to replay the session. Each line
consists of the I/O log entry type and amount of time since
the last entry, followed by type-specific data. The I/O log
entry types and their corresponding type-specific data are:
0 standard input, number of bytes in the entry
1 standard output, number of bytes in the entry
2 standard error, number of bytes in the entry
3 terminal input, number of bytes in the entry
4 terminal output, number of bytes in the entry
5 window change, new number lines and columns
6 bug compatibility for sudo 1.8.7 terminal output
7 command suspend or resume, signal received
ttyin Raw input from the user's terminal, exactly as it was
received. No post-processing is performed. For manual
viewing, you may wish to convert carriage return characters
in the log to line feeds. For example: ‘gunzip -c ttyin | tr
"\r" "\n"’
stdin The standard input when no terminal is present, or input
redirected from a pipe or file.
ttyout Output from the pseudo-terminal (what the command writes to
the screen). Note that terminal-specific post-processing is
performed before the data is logged. This means that, for
example, line feeds are usually converted to line
feed/carriage return pairs and tabs may be expanded to
spaces.
stdout The standard output when no terminal is present, or output
redirected to a pipe or file.
stderr The standard error redirected to a pipe or file.
All files other than log are compressed in gzip format unless the
compress_io flag has been disabled. Due to buffering, it is not
normally possible to display the I/O logs in real-time as the program
is executing. The I/O log data will not be complete until the program
run by sudo has exited or has been terminated by a signal. The
iolog_flush flag can be used to disable buffering, in which case I/O
log data is written to disk as soon as it is available. The output
portion of an I/O log file can be viewed with the sudoreplay(1m)
utility, which can also be used to list or search the available logs.
Note that user input may contain sensitive information such as
passwords (even if they are not echoed to the screen), which will be
stored in the log file unencrypted. In most cases, logging the command
output via log_output or LOG_OUTPUT is all that is required.
Since each session's I/O logs are stored in a separate directory,
traditional log rotation utilities cannot be used to limit the number
of I/O logs. The simplest way to limit the number of I/O is by setting
the maxseq option to the maximum number of logs you wish to store.
Once the I/O log sequence number reaches maxseq, it will be reset to
zero and sudoers will truncate and re-use any existing I/O logs.
FILES
/etc/sudo.conf Sudo front end configuration
/etc/sudoers List of who can run what
/etc/group Local groups file
/etc/netgroup List of network groups
/var/log/sudo-io I/O log files
/var/run/sudo/ts Directory containing time stamps for the
sudoers security policy
/var/db/sudo/lectured Directory containing lecture status files for
the sudoers security policy
/etc/environment Initial environment for -i mode on AIX and
Linux systems
EXAMPLES
Below are example sudoers file entries. Admittedly, some of these are
a bit contrived. First, we allow a few environment variables to pass
and then define our aliases:
# Run X applications through sudo; HOME is used to find the
# .Xauthority file. Note that other programs use HOME to find
# configuration files and this may lead to privilege escalation!
Defaults env_keep += "DISPLAY HOME"
# User alias specification
User_Alias FULLTIMERS = millert, mikef, dowdy
User_Alias PARTTIMERS = bostley, jwfox, crawl
User_Alias WEBADMIN = will, wendy, wim
# Runas alias specification
Runas_Alias OP = root, operator
Runas_Alias DB = oracle, sybase
Runas_Alias ADMINGRP = adm, oper
# Host alias specification
Host_Alias SPARC = bigtime, eclipse, moet, anchor :\
SGI = grolsch, dandelion, black :\
ALPHA = widget, thalamus, foobar :\
HPPA = boa, nag, python
Host_Alias CUNETS = 128.138.0.0/255.255.0.0
Host_Alias CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0
Host_Alias SERVERS = primary, mail, www, ns
Host_Alias CDROM = orion, perseus, hercules
# Cmnd alias specification
Cmnd_Alias DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\
/usr/sbin/restore, /usr/sbin/rrestore,\
sha224:0GomF8mNN3wlDt1HD9XldjJ3SNgpFdbjO1+NsQ== \
/home/operator/bin/start_backups
Cmnd_Alias KILL = /usr/bin/kill
Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm
Cmnd_Alias SHUTDOWN = /usr/sbin/shutdown
Cmnd_Alias HALT = /usr/sbin/halt
Cmnd_Alias REBOOT = /usr/sbin/reboot
Cmnd_Alias SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh,\
/usr/local/bin/tcsh, /usr/bin/rsh,\
/usr/local/bin/zsh
Cmnd_Alias SU = /usr/bin/su
Cmnd_Alias PAGERS = /usr/bin/more, /usr/bin/pg, /usr/bin/less
Here we override some of the compiled in default values. We want sudo
to log via syslog(3) using the auth facility in all cases and for
commands to be run with the target user's home directory as the working
directory. We don't want to subject the full time staff to the sudo
lecture and we want to allow them to run commands in a chroot(2)
“sandbox” via the -R option. User millert need not provide a password
and we don't want to reset the LOGNAME or USER environment variables
when running commands as root. Additionally, on the machines in the
SERVERS Host_Alias, we keep an additional local log file and make sure
we log the year in each log line since the log entries will be kept
around for several years. Lastly, we disable shell escapes for the
commands in the PAGERS Cmnd_Alias (/usr/bin/more, /usr/bin/pg and
/usr/bin/less) . Note that this will not effectively constrain users
with sudo ALL privileges.
# Override built-in defaults
Defaults syslog=auth,runcwd=~
Defaults>root !set_logname
Defaults:FULLTIMERS !lecture,runchroot=*
Defaults:millert !authenticate
Defaults@SERVERS log_year, logfile=/var/log/sudo.log
Defaults!PAGERS noexec
The User specification is the part that actually determines who may run
what.
root ALL = (ALL) ALL
%wheel ALL = (ALL) ALL
We let root and any user in group wheel run any command on any host as
any user.
FULLTIMERS ALL = NOPASSWD: ALL
Full time sysadmins (millert, mikef, and dowdy) may run any command on
any host without authenticating themselves.
PARTTIMERS ALL = ALL
Part time sysadmins bostley, jwfox, and crawl) may run any command on
any host but they must authenticate themselves first (since the entry
lacks the NOPASSWD tag).
jack CSNETS = ALL
The user jack may run any command on the machines in the CSNETS alias
(the networks 128.138.243.0, 128.138.204.0, and 128.138.242.0). Of
those networks, only 128.138.204.0 has an explicit netmask (in CIDR
notation) indicating it is a class C network. For the other networks
in CSNETS, the local machine's netmask will be used during matching.
lisa CUNETS = ALL
The user lisa may run any command on any host in the CUNETS alias (the
class B network 128.138.0.0).
operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\
sudoedit /etc/printcap, /usr/oper/bin/
The operator user may run commands limited to simple maintenance.
Here, those are commands related to backups, killing processes, the
printing system, shutting down the system, and any commands in the
directory /usr/oper/bin/. Note that one command in the DUMPS
Cmnd_Alias includes a sha224 digest, /home/operator/bin/start_backups.
This is because the directory containing the script is writable by the
operator user. If the script is modified (resulting in a digest
mismatch) it will no longer be possible to run it via sudo.
joe ALL = /usr/bin/su operator
The user joe may only su(1) to operator.
pete HPPA = /usr/bin/passwd [A-Za-z]*, !/usr/bin/passwd *root*
%opers ALL = (: ADMINGRP) /usr/sbin/
Users in the opers group may run commands in /usr/sbin/ as themselves
with any group in the ADMINGRP Runas_Alias (the adm and oper groups).
The user pete is allowed to change anyone's password except for root on
the HPPA machines. Because command line arguments are matched as a
single, concatenated string, the ‘*’ wildcard will match multiple
words. This example assumes that passwd(1) does not take multiple user
names on the command line. Note that on GNU systems, options to
passwd(1) may be specified after the user argument. As a result, this
rule will also allow:
passwd username --expire
which may not be desirable.
bob SPARC = (OP) ALL : SGI = (OP) ALL
The user bob may run anything on the SPARC and SGI machines as any user
listed in the OP Runas_Alias (root and operator.)
jim +biglab = ALL
The user jim may run any command on machines in the biglab netgroup.
sudo knows that “biglab” is a netgroup due to the ‘+’ prefix.
+secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser
Users in the secretaries netgroup need to help manage the printers as
well as add and remove users, so they are allowed to run those commands
on all machines.
fred ALL = (DB) NOPASSWD: ALL
The user fred can run commands as any user in the DB Runas_Alias
(oracle or sybase) without giving a password.
john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*
On the ALPHA machines, user john may su to anyone except root but he is
not allowed to specify any options to the su(1) command.
jen ALL, !SERVERS = ALL
The user jen may run any command on any machine except for those in the
SERVERS Host_Alias (primary, mail, www and ns).
jill SERVERS = /usr/bin/, !SU, !SHELLS
For any machine in the SERVERS Host_Alias, jill may run any commands in
the directory /usr/bin/ except for those commands belonging to the SU
and SHELLS Cmnd_Aliases. While not specifically mentioned in the rule,
the commands in the PAGERS Cmnd_Alias all reside in /usr/bin and have
the noexec option set.
steve CSNETS = (operator) /usr/local/op_commands/
The user steve may run any command in the directory
/usr/local/op_commands/ but only as user operator.
matt valkyrie = KILL
On his personal workstation, valkyrie, matt needs to be able to kill
hung processes.
WEBADMIN www = (www) ALL, (root) /usr/bin/su www
On the host www, any user in the WEBADMIN User_Alias (will, wendy, and
wim), may run any command as user www (which owns the web pages) or
simply su(1) to www.
ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\
/sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM
Any user may mount or unmount a CD-ROM on the machines in the CDROM
Host_Alias (orion, perseus, hercules) without entering a password.
This is a bit tedious for users to type, so it is a prime candidate for
encapsulating in a shell script.
SECURITY NOTES
Limitations of the ‘!’ operator
It is generally not effective to “subtract” commands from ALL using the
‘!’ operator. A user can trivially circumvent this by copying the
desired command to a different name and then executing that. For
example:
bill ALL = ALL, !SU, !SHELLS
Doesn't really prevent bill from running the commands listed in SU or
SHELLS since he can simply copy those commands to a different name, or
use a shell escape from an editor or other program. Therefore, these
kind of restrictions should be considered advisory at best (and
reinforced by policy).
In general, if a user has sudo ALL there is nothing to prevent them
from creating their own program that gives them a root shell (or making
their own copy of a shell) regardless of any ‘!’ elements in the user
specification.
Security implications of fast_glob
If the fast_glob option is in use, it is not possible to reliably
negate commands where the path name includes globbing (aka wildcard)
characters. This is because the C library's fnmatch(3) function cannot
resolve relative paths. While this is typically only an inconvenience
for rules that grant privileges, it can result in a security issue for
rules that subtract or revoke privileges.
For example, given the following sudoers file entry:
john ALL = /usr/bin/passwd [a-zA-Z0-9]*, /usr/bin/chsh [a-zA-Z0-9]*,\
/usr/bin/chfn [a-zA-Z0-9]*, !/usr/bin/* root
User john can still run /usr/bin/passwd root if fast_glob is enabled by
changing to /usr/bin and running ./passwd root instead.
Preventing shell escapes
Once sudo executes a program, that program is free to do whatever it
pleases, including run other programs. This can be a security issue
since it is not uncommon for a program to allow shell escapes, which
lets a user bypass sudo's access control and logging. Common programs
that permit shell escapes include shells (obviously), editors,
paginators, mail and terminal programs.
There are two basic approaches to this problem:
restrict Avoid giving users access to commands that allow the user to
run arbitrary commands. Many editors have a restricted mode
where shell escapes are disabled, though sudoedit is a better
solution to running editors via sudo. Due to the large
number of programs that offer shell escapes, restricting
users to the set of programs that do not is often unworkable.
noexec Many systems that support shared libraries have the ability
to override default library functions by pointing an
environment variable (usually LD_PRELOAD) to an alternate
shared library. On such systems, sudo's noexec functionality
can be used to prevent a program run by sudo from executing
any other programs. Note, however, that this applies only to
dynamically-linked executables. Statically-linked
executables and executables running under binary emulation
are not affected.
The noexec feature is known to work on SunOS, Solaris, *BSD,
Linux, IRIX, Tru64 UNIX, macOS, HP-UX 11.x and AIX 5.3 and
above. It should be supported on most operating systems that
support the LD_PRELOAD environment variable. Check your
operating system's manual pages for the dynamic linker
(usually ld.so, ld.so.1, dyld, dld.sl, rld, or loader) to see
if LD_PRELOAD is supported.
On Solaris 10 and higher, noexec uses Solaris privileges
instead of the LD_PRELOAD environment variable.
To enable noexec for a command, use the NOEXEC tag as
documented in the User Specification section above. Here is
that example again:
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
This allows user aaron to run /usr/bin/more and /usr/bin/vi
with noexec enabled. This will prevent those two commands
from executing other commands (such as a shell). If you are
unsure whether or not your system is capable of supporting
noexec you can always just try it out and check whether shell
escapes work when noexec is enabled.
Note that restricting shell escapes is not a panacea. Programs running
as root are still capable of many potentially hazardous operations
(such as changing or overwriting files) that could lead to unintended
privilege escalation. In the specific case of an editor, a safer
approach is to give the user permission to run sudoedit (see below).
Secure editing
The sudoers plugin includes sudoedit support which allows users to
securely edit files with the editor of their choice. As sudoedit is a
built-in command, it must be specified in the sudoers file without a
leading path. However, it may take command line arguments just as a
normal command does. Wildcards used in sudoedit command line arguments
are expected to be path names, so a forward slash (‘/’) will not be
matched by a wildcard.
Unlike other sudo commands, the editor is run with the permissions of
the invoking user and with the environment unmodified. More
information may be found in the description of the -e option in
sudo(1m).
For example, to allow user operator to edit the “message of the day”
file:
operator sudoedit /etc/motd
The operator user then runs sudoedit as follows:
$ sudoedit /etc/motd
The editor will run as the operator user, not root, on a temporary copy
of /etc/motd. After the file has been edited, /etc/motd will be
updated with the contents of the temporary copy.
Users should never be granted sudoedit permission to edit a file that
resides in a directory the user has write access to, either directly or
via a wildcard. If the user has write access to the directory it is
possible to replace the legitimate file with a link to another file,
allowing the editing of arbitrary files. To prevent this, starting
with version 1.8.16, symbolic links will not be followed in writable
directories and sudoedit will refuse to edit a file located in a
writable directory unless the sudoedit_checkdir option has been
disabled or the invoking user is root. Additionally, in version 1.8.15
and higher, sudoedit will refuse to open a symbolic link unless either
the sudoedit_follow option is enabled or the sudoedit command is
prefixed with the FOLLOW tag in the sudoers file.
Time stamp file checks
sudoers will check the ownership of its time stamp directory
(/var/run/sudo/ts by default) and ignore the directory's contents if it
is not owned by root or if it is writable by a user other than root.
Older versions of sudo stored time stamp files in /tmp; this is no
longer recommended as it may be possible for a user to create the time
stamp themselves on systems that allow unprivileged users to change the
ownership of files they create.
While the time stamp directory should be cleared at reboot time, not
all systems contain a /run or /var/run directory. To avoid potential
problems, sudoers will ignore time stamp files that date from before
the machine booted on systems where the boot time is available.
Some systems with graphical desktop environments allow unprivileged
users to change the system clock. Since sudoers relies on the system
clock for time stamp validation, it may be possible on such systems for
a user to run sudo for longer than timestamp_timeout by setting the
clock back. To combat this, sudoers uses a monotonic clock (which
never moves backwards) for its time stamps if the system supports it.
sudoers will not honor time stamps set far in the future. Time stamps
with a date greater than current_time + 2 * TIMEOUT will be ignored and
sudoers will log and complain.
If the timestamp_type option is set to “tty”, the time stamp record
includes the device number of the terminal the user authenticated with.
This provides per-terminal granularity but time stamp records may still
outlive the user's session.
Unless the timestamp_type option is set to “global”, the time stamp
record also includes the session ID of the process that last
authenticated. This prevents processes in different terminal sessions
from using the same time stamp record. On systems where a process's
start time can be queried, the start time of the session leader is
recorded in the time stamp record. If no terminal is present or the
timestamp_type option is set to “ppid”, the start time of the parent
process is used instead. In most cases this will prevent a time stamp
record from being re-used without the user entering a password when
logging out and back in again.
DEBUGGING
Versions 1.8.4 and higher of the sudoers plugin support a flexible
debugging framework that can help track down what the plugin is doing
internally if there is a problem. This can be configured in the
sudo.conf(4) file.
The sudoers plugin uses the same debug flag format as the sudo front-
end: subsystem@priority.
The priorities used by sudoers, in order of decreasing severity, are:
crit, err, warn, notice, diag, info, trace and debug. Each priority,
when specified, also includes all priorities higher than it. For
example, a priority of notice would include debug messages logged at
notice and higher.
The following subsystems are used by the sudoers plugin:
alias User_Alias, Runas_Alias, Host_Alias and Cmnd_Alias processing
all matches every subsystem
audit BSM and Linux audit code
auth user authentication
defaults sudoers file Defaults settings
env environment handling
ldap LDAP-based sudoers
logging logging support
match matching of users, groups, hosts and netgroups in the sudoers
file
netif network interface handling
nss network service switch handling in sudoers
parser sudoers file parsing
perms permission setting
plugin The equivalent of main for the plugin.
pty pseudo-terminal related code
rbtree redblack tree internals
sssd SSSD-based sudoers
util utility functions
For example:
Debug sudo /var/log/sudo_debug match@info,nss@info
For more information, see the sudo.conf(4) manual.
SEE ALSO
ssh(1), su(1), fnmatch(3), glob(3), mktemp(3), strftime(3),
sudo.conf(4), sudo_plugin(4), sudoers.ldap(4), sudoers_timestamp(4),
sudo(1m), visudo(1m)
AUTHORS
Many people have worked on sudo over the years; this version consists
of code written primarily by:
Todd C. Miller
See the CONTRIBUTORS file in the sudo distribution
(https://www.sudo.ws/contributors.html) for an exhaustive list of
people who have contributed to sudo.
CAVEATS
The sudoers file should always be edited by the visudo utility which
locks the file and checks for syntax errors. If sudoers contains
syntax errors, sudo may refuse to run, which is a serious problem if
sudo is your only method of obtaining superuser privileges. Recent
versions of sudoers will attempt to recover after a syntax error by
ignoring the rest of the line after encountering an error. Older
versions of sudo will not run if sudoers contains a syntax error.
When using netgroups of machines (as opposed to users), if you store
fully qualified host name in the netgroup (as is usually the case), you
either need to have the machine's host name be fully qualified as
returned by the hostname command or use the fqdn option in sudoers.
BUGS
If you feel you have found a bug in sudo, please submit a bug report at
https://bugzilla.sudo.ws/
SUPPORT
Limited free support is available via the sudo-users mailing list, see
https://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search
the archives.
DISCLAIMER
sudo is provided “AS IS” and any express or implied warranties,
including, but not limited to, the implied warranties of
merchantability and fitness for a particular purpose are disclaimed.
See the LICENSE file distributed with sudo or
https://www.sudo.ws/license.html for complete details.
Sudo 1.9.5p2 January 8, 2020 SUDOERS(4)