NAME
getgrent,
getgrnam, getgrnam_r,
getgrgid, getgrgid_r,
setgroupent, setgrent,
endgrent —
group database operations
SYNOPSIS
#include
<grp.h>
struct group *
getgrent(void);
struct group *
getgrnam(const
char *name);
int
getgrnam_r(const
char *name, struct group
*grp, char *buf,
size_t bufsize,
struct group
**result);
struct group *
getgrgid(gid_t
gid);
int
getgrgid_r(gid_t
gid, struct group
*grp, char *buf,
size_t bufsize,
struct group
**result);
int
setgroupent(int
stayopen);
void
setgrent(void);
void
endgrent(void);
DESCRIPTION
These functions operate on the group database file
/etc/group which is described in
group(5). Each line of the database is defined by the structure
struct group found in the include file
<grp.h>:
struct group {
char *gr_name; /* group name */
char *gr_passwd; /* group password */
gid_t gr_gid; /* group id */
char **gr_mem; /* group members */
};
The functions
getgrnam()
and
getgrgid()
search the group database for the given group name pointed to by
name or the group ID pointed to by
gid, respectively, returning the first one
encountered. Identical group names or group GIDs may result in undefined
behavior.
getgrent()
sequentially reads the group database and is intended for programs that wish
to step through the complete list of groups.
All three routines will open the group file for reading, if necessary.
setgroupent()
opens the file, or rewinds it if it is already open. If
stayopen is non-zero, file descriptors are left open,
significantly speeding subsequent function calls. This functionality is
unnecessary for getgrent() as it doesn't close its
file descriptors by default. It should also be noted that it is dangerous
for long-running programs to use this functionality as the group file may be
updated.
setgrent()
is equivalent to setgroupent() with an argument of
zero.
The
endgrent()
function closes any open files.
The
getgrgid_r()
and
getgrnam_r()
functions both update the group structure pointed to by
grp and store a pointer to that structure at the
location pointed to by result. The structure is filled
with an entry from the group database with a matching
gid or name. Storage referenced
by the group structure will be allocated from the memory provided with the
buf parameter, which is bufsiz
characters in size. The maximum size needed for this buffer can be
determined with
sysconf(_SC_GETGR_R_SIZE_MAX).
YP support
If YP is active, the functions getgrent()
and getgrnam() also use the
group.byname YP map and the function
getgrgid() also uses the
group.bygid YP map in addition to the group file,
respecting the order of normal and YP entries in the group file.
RETURN VALUES
The functions getgrent(),
getgrnam(), and getgrgid()
return a pointer to the group entry if successful; if end-of-file is reached
or an error occurs a NULL pointer is returned.
The setgroupent() function returns the
value 1 if successful, otherwise 0.
The endgrent() and
setgrent() functions have no return value.
The functions getgrgid_r() and
getgrnam_r() update result to
point to grp if a match is found or set it to
NULL if no match is found or an error occurs. They
return 0 on success, even if no match is found, or an error number if an
error occurs; see ERRORS.
FILES
- /etc/group
- group database file
ERRORS
The getgrgid_r() and
getgrnam_r() functions may fail if:
- [
ERANGE] - The storage supplied via buf and bufsize is too small and cannot contain all the strings to be returned in grp.
The getgrent(),
getgrgid(), getgrgid_r(),
getgrnam(), and getgrnam_r()
functions may also fail for any of the errors specified for
fgets(3), getc(3), and
strtoul(3). If YP is active, they may also fail due to errors caused
by the YP subsystem.
The setgroupent() function may fail for
any of the errors specified for
fopen(3).
The endgrent(),
getgrgid_r(), getgrnam_r(),
and setgrent() functions do not set errno.
SEE ALSO
STANDARDS
The functions getgrgid(),
getgrgid_r(), getgrnam(),
and getgrnam_r() are compliant with the
IEEE Std 1003.1-2008 (“POSIX.1”)
specification.
The functions endgrent(),
getgrent(), and setgrent()
are compliant with the X/Open System Interfaces option of the
IEEE Std 1003.1-2008 (“POSIX.1”)
specification.
YP support and the
setgroupent() function are extensions to that
specification.
HISTORY
The functions endgrent(),
getgrent(), getgrnam(),
getgrgid(), and setgrent()
appeared in Version 7 AT&T UNIX. The
setgroupent() function appeared in
4.3BSD-Reno.
The historic function setgrfile(), which
allowed the specification of alternate group databases, has been deprecated
and is no longer available.
BUGS
The functions getgrent(),
getgrnam(), getgrgid(),
setgroupent(), and
setgrent() leave their results in an internal static
object and return a pointer to that object. Subsequent calls to the same
function will modify the same object.
The functions getgrent(),
endgrent(), setgroupent(),
and setgrent() are fairly useless in a networked
environment and should be avoided, if possible.