svcadm(1M)을 검색하려면 섹션에서 1M 을 선택하고, 맨 페이지 이름에 svcadm을 입력하고 검색을 누른다.
nc(1)
nc(1) User Commands nc(1)
NAME
nc, netcat - arbitrary TCP and UDP connections and listens
SYNOPSIS
nc -h
nc [-46Cdnrtuvz] [-i interval] [-P proxy_username] [-p port]
[-s source_ip_address] [-T dspc] [-w timeout]
[-X proxy_protocol] [-x proxy_address[:port]][-L timeout]
[-e program] [-b bufsize] [-q timeout] [-m bytes]
[-I bufsize][-O bufsize] [-M sla-prop] hostname port_list
nc -l [-46CDdEFnrtuvzZ] [-i interval] [-T dspc] [-e program]
[-b bufsize] [-q timeout] [-R address/port[/proto]] [-m bytes]
[-L timeout] [-I bufsize] [-O bufsize] [-M sla-prop] [hostname] port
nc -l [-46CDEFdnrtuvzZ] [-i interval] [-T dspc] [-e program]
[-b bufsize] [-q timeout] [-R address/port[/proto]] [-m bytes]
[-L timeout] [-I bufsize] [-O bufsize]
[-M sla-prop] -p port [hostname]
nc -U [-Ddtvz] [-i interval] [-w timeout] [-e program]
[-b bufsize] [-q timeout] [-m bytes] path
nc -Ul [-46DdktvZ] [-i interval] [-e program] [-b bufsize]
[-q timeout] [-R address/port[/proto]] [-m bytes] path
DESCRIPTION
The nc (or netcat) utility is used for a variety of tasks associated
with TCP or UDP. nc can open TCP connections, send UDP packets, listen
on arbitrary TCP and UDP ports, perform port scanning, and deal with
both IPv4 and IPv6. Unlike telnet(1), nc scripts nicely, and separates
error messages onto standard error instead of sending them to standard
output.
The nc command is often used for the following tasks:
o simple TCP proxies
o shell-script based HTTP clients and servers
o network daemon testing
o a SOCKS or HTTP ProxyCommand for ssh(1)
The nc command can also be run as netcat, using the identical options.
OPTIONS
The following options are supported:
-4
Forces nc to use IPv4 addresses only
-6
Forces nc to use IPv6 addresses only
-b bufsize
Specifies buffer size for read operations
The default value is 1024 bytes
-C
Does not send out any data, unless a full TCP segment can be sent
It is an error to use this option with protocol other than TCP
-D
Enables debugging on the socket
-d
Does not attempt to read from stdin
-E
Uses exclusive bind for listening TCP or UDP socket.
It is an error to use this option without the -l option
This option does not have any effect when used in conjunction with
the -U option
-e program
Executes external program after accepting a connection or making
connection. Before the execution stdin,stdout,stderr is redirected
to the network descriptor. Only one port can be used with this
option
It is an error to use this option in conjunction with the -R, -k,
or -i options
-F
Does not close network socket for writing after seeing EOF on stdin
-h
Prints nc help
-I bufsize
Sets receive (input) socket buffer size
This option does not have any effect when used in conjunction with
the -U option
-i interval
Specifies a delay time of interval between lines of text sent and
received.
The interval is specified in seconds, with possible fractions
This option also causes a delay time between connections to multi‐
ple ports, and therefore also affects port scan mode
-k
Forces nc to listen for another connection after its current con‐
nection is closed
It is an error to use this option without the -l option
It is an error to use this option in conjunction with the -e option
-L timeout
Linger on close - wait for messages to be sent after network
descriptor is closed up to specified timeout in seconds
-l
Listens for an incoming connection rather than initiate a connec‐
tion to a remote host
It is an error to use this option in conjunction with the -s or -z
options
If the -l option is used with a wildcard socket (no IP address or
hostname specified) and without the -4 /-6 options, it accepts both
IPv4 and IPv6 connections
-m byte_count
Quits after receiving at least byte_count bytes. When used with -l
option byte_count is compared to number of bytes received from the
client
byte_count must be greater than 0 and less than INT_MAX.
-N file
Specifies file with pattern for UDP port scanning. The contents of
this file are used as payload for each emitted UDP packet
It is an error to use this option without the -u and -z options
-n
Do not do any naming or service lookups on any addresses, host‐
names, or ports.
Use of this option means that hostname and port arguments are
restricted to numeric values.
If used with -v option all addresses and ports are printed in
numeric form, in addition to the restriction imposed on the argu‐
ments. This option does not have any effect when used in conjunc‐
tion with the -U option.
-O bufsize
Set send (output) socket buffer size.
This option does not have any effect when used in conjunction with
the -U option.
-P proxy_username
Specify a username (proxy_username) to present to a proxy server
that requires authentication. If proxy_username is not specified,
authentication is not attempted. Proxy authentication is only sup‐
ported for HTTP CONNECT proxies at present.
It is an error to use this option in conjunction with the -l
option.
-p port
When used without -l option, specify the source port nc should use,
subject to privilege restrictions and availability. When used with
the -l option, set the listen port.
This option can be used with -l option only provided global port
argument is not specified.
-q timeout
After receiving EOF on stdin, wait for specified number of seconds
and quit.
-R addr/port[/proto]
Perform port redirection to given host and port.
After the connection has been accepted, nc connects to the remote
host/port and passes all data between the client and the remote
host. The proto (protocol) part of the redirect specification can
be either tcp or udp. If the proto is not specified, redirector
uses the same protocol as the server.
It is an error to use this option in conjunction with the -z
option.
-r
Choose destination ports randomly instead of sequentially within
all ports specified by the port_list argument.
It is an error to use this option in conjunction with the -l
option.
-s source_ip_address
Specify the IP of the interface which is used to send the packets.
It is an error to use this option in conjunction with the -l
option.
-M sla-prop
Specify the MAC flow for the socket to join and/or specify proper‐
ties of the MAC flow for the socket. sla-prop is supplied as a
comma-separated list of 'name=value' of properties.
Currently supported property names are maxbw, priority, flow, and
inherit.
maxbw and priority come from the properties defined in flowadm(8)
and denote maximum bandwidth and priority of the flow. Allowed val‐
ues for maxbw are integer plus optional suffix, which defaults to
Mega. priority can take values from 'high', 'medium' and 'low'.
flow takes a flow name as argument. The flow is created if it does
not already exist.
At least one of flow or maxbw and priority need to be specified for
flow creation.
inherit can take values from 'on' and 'off' with default value of
'off'. By default, an accepted/new socket (returned from
accept(3C)) does not inherit the properties of the listener socket.
When it is set to 'on', the new socket will inherit the properties
of the listener socket. This is useful with -l option when the
properties need to be enforced on the new socket.
This option requires SYS_FLOW_CONFIG privilege. This option also
requires the IP address or the hostname to be specified.
-T dscp
Specify Differentiated Services Code Point for the connection.
For IPv4 this specifies the IP Type of Service (ToS) IP header
field and the valid values for the argument are the string tokens:
lowdelay, throughput, reliability, or an 8-bit hexadecimal value
preceded by 0x.
For IPv6 (Traffic Class) only hexadecimal value can be used.
-t
Cause nc to send RFC 854 DON'T and WON'T responses to RFC 854 DO
and WILL requests. This makes it possible to use nc to script tel‐
net sessions.
-U
Specify the use of UNIX Domain Sockets. If you specify this option
without -l, nc, it becomes AF_UNIX client. If you specify this
option with the -l option, a AF_UNIX server is created.
Use of this option requires that a single argument of a valid UNIX
domain path has to be provided to nc, not a host name or port.
-u
Use UDP instead of the default option of TCP.
-v
Specify verbose output.
-w timeout
Silently close the connection if a connection and stdin are idle
for more than timeout seconds.
The default is no timeout.
This option has no effect on the connection establishment phase in
client mode or waiting for a connection in server mode.
-X proxy_protocol
Use the specified protocol when talking to the proxy server. Sup‐
ported protocols are 4 (SOCKS v.4), 5 (SOCKS v.5) and connect (HTTP
proxy). If the protocol is not specified, SOCKS v. 5 is used.
It is an error to use this option in conjunction with the -l
option.
-x proxy_address[:port]
Request connection to hostname using a proxy at proxy_address and
port. If port is not specified, the well-known port for the proxy
protocol is used (1080 for SOCKS, 3128 for HTTP).
It is an error to use this option in conjunction with the -l
option.
This option does not work with numeric representation of IPv6
addresses.
-Z
In listening mode bind to address/port in all zones using the
SO_ALLZONES socket option.
This option requires SYS_NET_CONFIG privilege.
-z
Perform port scan. For TCP ports (default), connect scan (full
3-way handshake) is tried with no data sent. For UDP (-u) empty UDP
packets are sent by default. To specify UDP payload the -N option
can be used.
The UDP scan mode is estimative, it considers a port to be open if
it does not receive negative response (ICMP Destination Port
Unreachable message). For this mode the timeout set with the -w
option is used to wait for the ICMP messages or data from remote
node. With -v any received data is dumped as hexadecimal bytes to
stderr.
As most of the operating systems employ rate limiting for sending
ICMP messages in reaction to input packets, it is necessary to use
-i when performing UDP scan otherwise the results is not reliable.
It is an error to use this option in conjunction with the -l
option.
OPERANDS
The following operands are supported:
hostname Specify host name.
hostname can be a numerical IP address or a symbolic host‐
name (unless the -n option is specified).
In general, hostname must be specified, unless the -l
option is given or -U is used (in which case the argument
is a path). If hostname argument is specified with -l
option then port argument must be given as well and nc
tries to bind to that address and port. If hostname argu‐
ment is not specified with -l option then nc tries to lis‐
ten on a wildcard socket for given port.
path Specify pathname.
port Specify port.
port_list
port_list can be specified as single integers, ranges or
combinations of both. Specify ranges in the form of nn-mm.
The port_list must have at least one member, but can have
multiple ports/ranges separated by commas.
In general, a destination port must be specified, unless
the -U option is given, in which case a UNIX Domain Socket
path must be specified instead of hostname.
It is an error to use list of ports containing more than
one port in conjunction with the -e option.
USAGE
Client/Server Model
It is quite simple to build a very basic client/server model using nc.
On one console, start nc listening on a specific port for a connection.
For example, the command:
$ nc -l 1234
listens on port 1234 for a connection. On a second console (or a second
machine), connect to the machine and port to which nc is listening:
$ nc 127.0.0.1 1234
There should now be a connection between the ports. Anything typed at
the second console is concatenated to the first, and vice-versa. After
the connection has been set up, nc does not really care which side is
being used as a server and which side is being used as a client. The
connection can be terminated using an EOF (Ctrl/d).
Data Transfer
The example in the previous section can be expanded to build a basic
data transfer model. Any information input into one end of the connec‐
tion is output to the other end, and input and output can be easily
captured in order to emulate file transfer.
Start by using nc to listen on a specific port, with output captured
into a file:
$ nc -l 1234 > filename.out
Using a second machine, connect to the listening nc process, feeding it
the file which is to be transferred:
$ nc host.example.com 1234 < filename.in
After the file has been transferred, the connection closes automati‐
cally.
Talking to Servers
It is sometimes useful to talk to servers by hand rather than through a
user interface. It can aid in troubleshooting, when it might be neces‐
sary to verify what data a server is sending in response to commands
issued by the client.
For example, to retrieve the home page of a website:
$ echo -n "GET / HTTP/1.0\r\n\r\n" | nc host.example.com 80
This also displays the headers sent by the web server. They can be fil‐
tered, if necessary, by using a tool such as sed(1).
More complicated examples can be built up when the user knows the for‐
mat of requests required by the server. As another example, an email
can be submitted to an SMTP server using:
$ nc localhost 25 << EOF
HELO host.example.com
MAIL FROM: <user@host.example.com
RCTP TO: <user2@host.example.com
DATA
Body of email.
.
QUIT
EOF
Port Scanning
It can be useful to know which ports are open and running services on a
target machine. The -z flag can be used to tell nc to report open
ports, rather than to initiate a connection.
In this example:
$ nc -z host.example.com 20-30
Connection to host.example.com 22 port [tcp/ssh] succeeded!
Connection to host.example.com 25 port [tcp/smtp] succeeded!
The port range was specified to limit the search to ports 20 - 30.
Alternatively, it might be useful to know which server software is run‐
ning, and which versions. This information is often contained within
the greeting banners. In order to retrieve these, it is necessary to
first make a connection, and then break the connection when the banner
has been retrieved. This can be accomplished by specifying a small
timeout with the -w flag, or perhaps by issuing a QUIT command to the
server:
$ echo "QUIT" | nc host.example.com 20-30
SSH-2.0-Sun_SSH_1.1
Protocol mismatch.
220 host.example.com IMS SMTP Receiver Version 0.84 Ready
inetd Capabilities
One of the possible uses is to create simple services by using
inetd(8).
The following example creates a redirect from TCP port 8080 to port 80
on host realwww:
# cat << EOF >> /etc/services
wwwredir 8080/tcp # WWW redirect
EOF
# cat << EOF > /tmp/wwwredir.conf
wwwredir stream tcp nowait nobody /usr/bin/nc /usr/bin/nc -w 3 realwww 80
EOF
# inetconv -i /tmp/wwwredir.conf
wwwredir -> /var/svc/manifest/network/wwwredir-tcp.xml
Importing wwwredir-tcp.xml ...Done
# inetadm -l wwwredir/tcp
SCOPE NAME=VALUE
name="wwwredir"
endpoint_type="stream"
proto="tcp"
isrpc=FALSE
wait=FALSE
exec="/usr/bin/nc -w 3 realwww 80"
arg0="/usr/bin/nc"
user="nobody"
default bind_addr=""
default bind_fail_max=-1
default bind_fail_interval=-1
default max_con_rate=-1
default max_copies=-1
default con_rate_offline=-1
default failrate_cnt=40
default failrate_interval=60
default inherit_env=TRUE
default tcp_trace=TRUE
default tcp_wrappers=FALSE
Privileges
To bind to a privileged port number nc needs to be granted the net_pri‐
vaddr privilege. If Solaris Trusted Extensions are configured and the
port nc should listen on is configured as a multi-level port nc also
needs the net_bindmlp privilege.
Privileges can be assigned to the user or role directly, by specifying
them in the account's default privilege set in user_attr(5). However,
this means that any application that this user or role starts have
these additional privileges. To only grant the privileges(7) when nc is
invoked, the recommended approach is to create and assign an rbac(7)
rights profile. See EXAMPLES for additional information.
EXAMPLES
Example 1 Using nc
Open a TCP connection to port 42 of host.example.com, using port 3141
as the source port, with a timeout of 5 seconds:
$ nc -p 3141 -w 5 host.example.com 42
Open a TCP connection to port 7777 of host.example.com, setting a maxi‐
mum bandwidth of 50Mbps on the socket:
$ nc -M maxbw=50M host.example.com 7777
Open a UDP connection to port 53 of host.example.com:
$ nc -u host.example.com 53
Open a TCP connection to port 42 of host.example.com using 10.1.2.3 as
the IP for the local end of the connection:
$ nc -s 10.1.2.3 host.example.com 42
Use a list of ports and port ranges for a port scan on various ports:
$ nc -z host.example.com 21-25,53,80,110-120,443
Create and listen on a UNIX Domain Socket:
$ nc -lU /var/tmp/dsocket
Create and listen on a UDP socket with associated port 8888:
$ nc -u -l -p 8888
which is the same as:
$ nc -u -l 8888
Create and listen on a TCP socket with associated port 2222 and bind to
address 127.0.0.1 only:
$ nc -l 127.0.0.1 2222
Create and listen on a TCP socket with associated port 2222 and create
a high priority MAC flow on the listener and the connected sockets:
$ nc -l -M priority=high,inherit=on host.example.com 2222
Connect to TCP port, send some data and terminate the connection with
TCP RST segment (instead of classic TCP closing handshake) by setting
the linger option and timeout to 0:
$ echo "foo" | nc -L 0 host.example.com 22
Perform port redirection to port 22 on host host.example.com from local
port 4545:
$ nc -R host.example.com/22 -l 4545
After that, it should be possible to run ssh(1) client and connect to
host.example.com using host redir.example.com running the above com‐
mand:
$ ssh -oStrictHostKeyChecking=no -p 4545 redir.example.com
It is also possible to let nc listen on TCP port and convert the TCP
data stream to UDP (or vice versa):
$ nc -R host.example.com/53/udp -l 4666
Connect to port 42 of host.example.com using an HTTP proxy at 10.2.3.4,
port 8080. This example could also be used by ssh(1).
$ nc -x10.2.3.4:8080 -Xconnect host.example.com 42
The same example again, this time enabling proxy authentication with
username ruser if the proxy requires it:
$ nc -x10.2.3.4:8080 -Xconnect -Pruser host.example.com 42
Basic UDP port scan can be efficiently done like this:
$ nc -z -w 3 -u -i 0.5 host.example.com 11-100
Between each 2 ports it pauses for 0.5 second (thus evading ICMP mes‐
sage rate limiting) and waits up to 3 seconds for reply. If no reply
comes then the port might be open.
To run nc with the smallest possible set of privileges as a user or
role that has additional privileges (such as the default root account)
it can be invoked using ppriv(1) as well. For example, limiting it to
only run with the privilege to bind to a privileged port:
$ ppriv -e -sA=basic,!file_link_any,!proc_exec,!proc_fork,\
!proc_info,!proc_session,net_privaddr nc -l 42
To allow a user or role to use only nc with the net_privaddr privilege,
a rights profile needs to be created:
/etc/security/exec_attr
Netcat privileged:solaris:cmd:::/usr/bin/nc:privs=net_privaddr
/etc/security/prof_attr
Netcat privileged:::Allow nc to bind to privileged ports:help=None.html
Assigning this rights profile using user_attr(5) permits the user or
role to run nc allowing it to listen on any port. To permit a user or
role to use nc only to listen on specific ports a wrapper script should
be specified in the rights profiles:
/etc/security/exec_attr
Netcat restricted:solaris:cmd:::/usr/bin/nc-restricted:privs=net_privaddr
/etc/security/prof_attr
Netcat restricted:::Allow nc to bind to privileged ports:help=None.html
and write a shell script that restricts the permissible options, for
example, one that permits one to bind only on ports between 42 and 64
(non-inclusive):
/usr/bin/nc-restricted:
#!/bin/sh
[ $# -eq 1 ] && [ $1 -gt 42 -a $1 -lt 64 ] && /usr/bin/nc -l -p "$1"
This grants the extra privileges when the user or role invokes nc using
the wrapper script from a profile shell. See pfsh(1), pfksh(1),
pfcsh(1), and pfexec(1).
Invoking nc directly does not run it with the additional privileges,
and neither does invoking the script without using pfexec or a profile
shell.
ATTRIBUTES
See attributes(7) for descriptions of the following attributes:
tab() box; cw(2.75i) |cw(2.75i) lw(2.75i) |lw(2.75i) ATTRIBUTE TYPEAT‐
TRIBUTE VALUE _ Availabilitynetwork/netcat _ Interface StabilitySee
below.
The package name is Committed. The command line syntax is Committed for
the -4, -6, -l, -n, -p, -u, and -w options and their arguments (if
any). The name and port list arguments are Committed. The port range
syntax is Uncommitted. The interface stability level for all other com‐
mand line options and their arguments is Uncommitted.
SEE ALSO
cat(1), pfcsh(1), pfexec(1), pfksh(1), pfsh(1), ppriv(1), sed(1),
ssh(1), telnet(1), user_attr(5), attributes(7), privileges(7), rbac(7),
inetadm(8), inetconv(8), inetd(8)
AUTHORS
The original implementation of nc was written by Hobbit, hob‐
bit@avian.org.
nc was rewritten with IPv6 support by Eric Jackson, ericj@monkey.org.
NOTES
If an instance of nc is listening on a wildcard socket (regardless of
address family specification) it is still possible to bind another nc
process to concrete IP address and accept connections to this address.
For example, with the following process running:
$ nc -4 -l 5656
it is possible to run another nc process listening on specific IP
address and the same port:
$ nc -4 -l 10.20.30.40 5656
TCP connection to address 10.20.30.40 and port 5656 is accepted by the
latter process, all TCP connections to port 5656 and different
addresses is accepted by the former process.
Also, it is possible to steal IPv4 connections from a process which
listens on a wildcard socket (without address family specification) by
binding to IPv4 wildcard socket. To suppress this and the behavior
described above the -E option could be used.
Oracle Solaris 11.4 11 May 2021 nc(1)