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

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. Identi

cal 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 threadsafe versions of getgrent(), getgrnam(), and getgrgid(), re

spectively.
The caller must provide storage for the results of the

search in the grp,
buffer, bufsize, and result arguments. When these functions

are successful, 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, significantly speeding functions subsequent calls. This function

ality is unnecessary for getgrent() as it does not close its file descrip

tors 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 programs must explicitly set errno to zero before calling any

of these functions if they need to distinguish between a non-existent en

try and an
error. The functions getgrent_r(), getgrnam_r(), and

getgrgid_r() return
0 if no error occurred, or an error number to indicate fail

ure. 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 ex

ists.)

The functions setgroupent() and setgrent() return the value

1 if successful, 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 speci

fication of
alternate password databases, has been deprecated and is no

longer available.

SEE ALSO

getpwent(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 func

tion will modify 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() func

tions make no
attempt to suppress duplicate information if multiple

sources are specified in nsswitch.conf(5).

BSD April 16, 2003

BSD