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getservbyname(3c)
Standard C Library Functions getservbyname(3C)
NAME
getservbyname, getservbyname_r, getservbyport, getservbyport_r, getser‐
vent, getservent_r, setservent, endservent - get service entry
SYNOPSIS
#include <netdb.h>
struct servent *getservbyname(const char *name, const char *proto);
struct servent *getservbyname_r(const char *name, const char *proto,
struct servent *result, char *buffer, int buflen);
struct servent *getservbyport(int port, const char *proto);
struct servent *getservbyport_r(int port, const char *proto,
struct servent *result, char *buffer, int buflen);
struct servent *getservent(void);
struct servent *getservent_r(struct servent *result, char *buffer,
int buflen);
int setservent(int stayopen);
int endservent(void);
DESCRIPTION
These functions are used to obtain entries for Internet services. An
entry may come from any of the sources for services specified in the
nsswitch.conf(5) configuration.
The getservbyname() and getservbyport() functions sequentially search
from the beginning of the file until a matching service name or port
number is found, or until end-of-file is encountered. If a protocol
name is also supplied (non-null), searches must also match the proto‐
col.
The getservbyname() function searches for an entry with the Internet
service name specified by the name parameter.
The getservbyport() function searches for an entry with the Internet
port number port.
All addresses are returned in network order. In order to interpret the
addresses, ntohs(3C) must be used for byte order conversion. The string
proto is used by both getservbyname() and getservbyport() to restrict
the search to entries with the specified protocol. If proto is NULL,
entries with any protocol can be returned.
The functions setservent(), getservent(), and endservent() are used to
enumerate entries from the services database.
The setservent() function sets (or resets) the enumeration to the
beginning of the set of service entries. This function should be called
before the first call to getservent(). Calls to the functions get‐
servbyname() and getservbyport() leave the enumeration position in an
indeterminate state. If the stayopen flag is non-zero, the system may
keep allocated resources such as open file descriptors until a subse‐
quent call to endservent().
The getservent() function reads the next line of the file, opening the
file if necessary. getservent() opens and rewinds the file. If the
stayopen flag is non-zero, the net database will not be closed after
each call to getservent() (either directly, or indirectly through one
of the other "getserv"calls).
Successive calls to getservent() return either successive entries or
NULL, indicating the end of the enumeration.
The endservent() function closes the file. The endservent() function
can be called to indicate that the caller expects to do no further ser‐
vice entry retrieval operations; the system can then deallocate
resources it was using. It is still allowed, but possibly less effi‐
cient, for the process to call more service entry retrieval functions
after calling endservent().
Reentrant Interfaces
The functions getservbyname(), getservbyport(), and getservent() use
static storage that is re-used in each call, making these functions
unsafe for use in multithreaded applications.
The functions getservbyname_r(), getservbyport_r(), and getservent_r()
provide reentrant interfaces for these operations.
Each reentrant interface performs the same operation as its non-reen‐
trant counterpart, named by removing the "_r" suffix. The reentrant
interfaces, however, use buffers supplied by the caller to store
returned results, and are safe for use in both single-threaded and mul‐
tithreaded applications.
Each reentrant interface takes the same parameters as its non-reentrant
counterpart, as well as the following additional parameters. The param‐
eter result must be a pointer to a struct servent structure allocated
by the caller. On successful completion, the function returns the ser‐
vice entry in this structure. The parameter buffer must be a pointer to
a buffer supplied by the caller. This buffer is used as storage space
for the service entry data. All of the pointers within the returned
struct servent result point to data stored within this buffer. See the
RETURN VALUES section of this manual page. The buffer must be large
enough to hold all of the data associated with the service entry. The
parameter buflen should give the size in bytes of the buffer indicated
by buffer.
For enumeration in multithreaded applications, the position within the
enumeration is a process-wide property shared by all threads. The set‐
servent() function can be used in a multithreaded application but
resets the enumeration position for all threads. If multiple threads
interleave calls to getservent_r(), the threads will enumerate disjoint
subsets of the service database.
Like their non-reentrant counterparts, getservbyname_r() and getservby‐
port_r() leave the enumeration position in an indeterminate state.
RETURN VALUES
Service entries are represented by the struct servent structure defined
in <netdb.h>:
struct servent {
char * s_name; /* official name of service */
char ** s_aliases; /* alias list */
int s_port; /* port service resides at */
char * s_proto; /* protocol to use */
};
The members of this structure are:
s_name The official name of the service.
s_aliases A zero terminated list of alternate names for the service.
s_port The port number at which the service resides. Port numbers
are returned in network byte order.
s_proto The name of the protocol to use when contacting the ser‐
vice.
The functions getservbyname(), getservbyname_r(), getservbyport(), and
getservbyport_r() each return a pointer to a struct servent if they
successfully locate the requested entry; otherwise they return NULL.
The functions getservent() and getservent_r() each return a pointer to
a struct servent if they successfully enumerate an entry; otherwise
they return NULL, indicating the end of the enumeration.
The functions getservbyname(), getservbyport(), and getservent() use
static storage, so returned data must be copied before a subsequent
call to any of these functions if the data is to be saved.
When the pointer returned by the reentrant functions getservbyname_r(),
getservbyport_r(), and getservent_r() is non-null, it is always equal
to the result pointer that was supplied by the caller.
ERRORS
The reentrant functions getservbyname_r(), getservbyport_r(), and get‐
servent_r() return NULL and set errno to ERANGE if the length of the
buffer supplied by caller is not large enough to store the result. See
Intro(2) for the proper usage and interpretation of errno in multi‐
threaded applications.
FILES
/etc/services Internet network services
/etc/netconfig network configuration file
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 _ Interface StabilityCommitted _ MT-LevelT{ See "Reen‐
trant Interfaces" in DESCRIPTION. T}
SEE ALSO
Intro(2), getaddrinfo(3C), netdir(3C), ntohs(3C), netdb.h(3HEAD), nss‐
witch.conf(5), netconfig(5), services(5), attributes(7)
WARNINGS
The reentrant interfaces getservbyname_r(), getservbyport_r(), and get‐
servent_r() are included in this release on an uncommitted basis only,
and are subject to change or removal in future minor releases.
NOTES
The functions that return struct servent return the least significant
16-bits of the s_port field in network byte order. getservbyport() and
getservbyport_r() also expect the input parameter port in the network
byte order. See htons(3C) for more details on converting between host
and network byte orders.
To ensure that they all return consistent results, getservbyname(),
getservbyname_r(), and netdir_getbyname() are implemented in terms of
the same internal library function. This function obtains the system-
wide source lookup policy based on the inet family entries in netcon‐
fig(5) and the services: entry in nsswitch.conf(5). Similarly, get‐
servbyport(), getservbyport_r(), and netdir_getbyaddr() are implemented
in terms of the same internal library function. If the inet family
entries in netconfig(5) have a '-' in the last column for nametoaddr
libraries, then the entry for services in nsswitch.conf will be used;
otherwise the nametoaddr libraries in that column will be used, and
nsswitch.conf will not be consulted.
There is no analogue of getservent() and getservent_r() in the netdir
functions, so these enumeration functions go straight to the services
entry in nsswitch.conf. Thus enumeration may return results from a dif‐
ferent source than that used by getservbyname(), getservbyname_r(),
getservbyport(), and getservbyport_r().
Use of the enumeration interfaces getservent() and getservent_r() is
discouraged; enumeration may not be supported for all database sources.
The semantics of enumeration are discussed further in nsswitch.conf(5).
HISTORY
The reentrant interfaces getservtbyname_r(), getservbyport_r(), and
getservent_r() were added to Oracle Solaris in the Solaris 2.3 release.
The getservbyname(), getservbyport(), getservent(), setservent(), and
endservent() functions have been present since the initial release of
Solaris.
Oracle Solaris 11.4 11 May 2021 getservbyname(3C)