GETGRENT(3) BSD Library Functions Manual GETGRENT(3)NAME
getgrent, getgrent_r, getgrnam, getgrnam_r, getgrgid, getgrgid_r,
setgroupent, setgrent, endgrent — group database operations
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <grp.h>
struct group *
getgrent(void);
int
getgrent_r(struct group *grp, char *buffer, size_t bufsize,
struct group **result);
struct group *
getgrnam(const char *name);
int
getgrnam_r(const char *name, struct group *grp, char *buffer,
size_t bufsize, struct group **result);
struct group *
getgrgid(gid_t gid);
int
getgrgid_r(gid_t gid, struct group *grp, char *buffer, size_t bufsize,
struct group **result);
int
setgroupent(int stayopen);
int
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 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.
The getgrent() function sequentially reads the group database and is
intended for programs that wish to step through the complete list of
groups.
The functions getgrent_r(), getgrnam_r(), and getgrgid_r() are thread-
safe versions of getgrent(), getgrnam(), and getgrgid(), respectively.
The caller must provide storage for the results of the search in the grp,
buffer, bufsize, and result arguments. When these functions are success‐
ful, the grp argument will be filled-in, and a pointer to that argument
will be stored in result. If an entry is not found or an error occurs,
result will be set to NULL.
These functions will open the group file for reading, if necessary.
The setgroupent() function opens the file, or rewinds it if it is already
open. If stayopen is non-zero, file descriptors are left open, signifi‐
cantly speeding functions subsequent calls. This functionality is unnec‐
essary for getgrent() as it does not 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.
The setgrent() function is identical to setgroupent() with an argument of
zero.
The endgrent() function closes any open files.
RETURN VALUES
The functions getgrent(), getgrnam(), and getgrgid(), return a pointer to
a group structure on success or NULL if the entry is not found or if an
error occurs. If an error does occur, errno will be set. Note that pro‐
grams must explicitly set errno to zero before calling any of these func‐
tions if they need to distinguish between a non-existent entry and an
error. The functions getgrent_r(), getgrnam_r(), and getgrgid_r() return
0 if no error occurred, or an error number to indicate failure. It is
not an error if a matching entry is not found. (Thus, if result is set
to NULL and the return value is 0, no matching entry exists.)
The functions setgroupent() and setgrent() return the value 1 if success‐
ful, otherwise the value 0 is returned. The functions endgrent() and
setgrfile() have no return value.
FILES
/etc/group group database file
COMPATIBILITY
The historic function setgrfile(), which allowed the specification of
alternate password databases, has been deprecated and is no longer avail‐
able.
SEE ALSOgetpwent(3), group(5), nsswitch.conf(5), yp(8)STANDARDS
The getgrent(), getgrnam(), getgrnam_r(), getgrgid(), getgrgid_r() and
endgrent() functions conform to ISO/IEC 9945-1:1996 (“POSIX.1”). The
setgrent() function differs from that standard in that its return type is
int rather than void.
HISTORY
The functions endgrent(), getgrent(), getgrnam(), getgrgid(), and
setgrent() appeared in Version 7 AT&T UNIX. The functions setgrfile()
and setgroupent() appeared in 4.3BSD-Reno. The functions getgrent_r(),
getgrnam_r(), and getgrgid_r() appeared in FreeBSD 5.1.
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 mod‐
ify the same object.
The functions getgrent(), getgrent_r(), endgrent(), setgroupent(), and
setgrent() are fairly useless in a networked environment and should be
avoided, if possible. The getgrent() and getgrent_r() functions make no
attempt to suppress duplicate information if multiple sources are speci‐
fied in nsswitch.conf(5).
BSD April 16, 2003 BSD
