GETGRENT(3)

NAME
getgrent, getgrnam, getgrgid, setgroupent, setgrent, endgrent - group database operations

LIBRARY
libc

SYNOPSIS
#include <sys/types.h>
#include <grp.h>
struct group *
getgrent(void);
struct group *
getgrnam(const char *name);
struct group *
getgrgid(gid_t gid);
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 */
    	int	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.

All three routines 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 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.

The setgrent() function is identical to setgroupent() with an argument of zero.

The endgrent() function closes any open files.

YP/NIS INTERACTION
When the yp(4) group database is enabled, the getgrnam() and getgrgid() functions use the YP maps “group.byname” and “group.bygid”, respectively, if the requested group is not found in the local /etc/group file. The getgrent() function will step through the YP map “group.byname” if the entire map is enabled as described in group(5).

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 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

SEE ALSO
getpwent(3), yp(4), group(5)

HISTORY
The functions endgrent(), getgrent(), getgrnam(), getgrgid(), and setgrent() appeared in AT&T UNIX. The functions setgrfile() and setgroupent() appeared in 4.3BSD Reno.

COMPATIBILITY
The historic function setgrfile(), which allowed the specification of alternate password 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.