getgrent(3) - Linux manual page

getgrent(3) - Linux manual page
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getgrent(3) — Linux manual page
NAME
LIBRARY
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
FILES
ATTRIBUTES
STANDARDS
HISTORY
SEE ALSO
COLOPHON
getgrent
(3) Library Functions Manual
getgrent
(3)
NAME
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getgrent, setgrent, endgrent - get group file entry
LIBRARY
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Standard C library (
libc
-lc
SYNOPSIS
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#include
#include
struct group *getgrent(void);
void setgrent(void);
void endgrent(void);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)
):
setgrent
():
_XOPEN_SOURCE >= 500
|| /* glibc >= 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
getgrent
(),
endgrent
():
Since glibc 2.22:
_XOPEN_SOURCE >= 500 || _DEFAULT_SOURCE
glibc 2.21 and earlier
_XOPEN_SOURCE >= 500
|| /* Since glibc 2.12: */ _POSIX_C_SOURCE >= 200809L
|| /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE
DESCRIPTION
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The
getgrent
() function returns a pointer to a structure
containing the broken-out fields of a record in the group database
(e.g., the local group file
/etc/group
, NIS, and LDAP). The first
time
getgrent
() is called, it returns the first entry; thereafter,
it returns successive entries.

The
setgrent
() function rewinds to the beginning of the group
database, to allow repeated scans.

The
endgrent
() function is used to close the group database after
all processing has been performed.

The
group
structure is defined in

as follows:

struct group {
char *gr_name; /* group name */
char *gr_passwd; /* group password */
gid_t gr_gid; /* group ID */
char **gr_mem; /* NULL-terminated array of pointers
to names of group members */
};

For more information about the fields of this structure, see
group(5)
RETURN VALUE
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The
getgrent
() function returns a pointer to a
group
structure, or
NULL if there are no more entries or an error occurs.

Upon error,
errno
may be set. If one wants to check
errno
after
the call, it should be set to zero before the call.

The return value may point to a static area, and may be
overwritten by subsequent calls to
getgrent
(),
getgrgid(3)
, or
getgrnam(3)
. (Do not pass the returned pointer to
free(3)
.)
ERRORS
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EAGAIN
The service was temporarily unavailable; try again later.
For NSS backends in glibc this indicates a temporary error
talking to the backend. The error may correct itself;
retrying later is suggested.
EINTR
A signal was caught; see
signal(7)
EIO
I/O error.
EMFILE
The per-process limit on the number of open file
descriptors has been reached.
ENFILE
The system-wide limit on the total number of open files has
been reached.
ENOENT
A necessary input file cannot be found. For NSS backends
in glibc this indicates the backend is not correctly
configured.
ENOMEM
Insufficient memory to allocate
group
structure.
ERANGE
Insufficient buffer space supplied.
FILES
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/etc/group
local group database file
ATTRIBUTES
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For an explanation of the terms used in this section, see
attributes(7)
┌─────────────┬───────────────┬──────────────────────────────────┐
Interface
Attribute
Value
├─────────────┼───────────────┼──────────────────────────────────┤
getgrent
() │ Thread safety │ MT-Unsafe race:grent │
│ │ │ race:grentbuf locale │
├─────────────┼───────────────┼──────────────────────────────────┤
setgrent
(), │ Thread safety │ MT-Unsafe race:grent locale │
endgrent
() │ │ │
└─────────────┴───────────────┴──────────────────────────────────┘

In the above table,
grent
in
race:grent
signifies that if any of
the functions
setgrent
(),
getgrent
(), or
endgrent
() are used in
parallel in different threads of a program, then data races could
occur.
STANDARDS
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POSIX.1-2008.
HISTORY
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POSIX.1-2001, SVr4, 4.3BSD.
SEE ALSO
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fgetgrent(3)
getgrent_r(3)
getgrgid(3)
getgrnam(3)
getgrouplist(3)
putgrent(3)
group(5)
COLOPHON
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Linux man-pages 6.16 2025-09-21
getgrent
(3)
Pages that refer to this page:
getent(1)
pmcd(1)
pmdapipe(1)
fgetgrent(3)
getgrent_r(3)
getgrnam(3)
getgrouplist(3)
putgrent(3)
setaliasent(3)
group(5)
nss(5)
nsswitch.conf(5)
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