Manual browser: getgrent(3)

GETGRENT(3) Library Functions Manual GETGRENT(3)


getgrent, getgrent_r, getgrgid, getgrgid_r, getgrnam, getgrnam_r, setgroupent, setgrent, endgrentgroup database operations


Standard C Library (libc, -lc)


#include <grp.h>

struct group *

getgrent_r(struct group *grp, char *buffer, size_t buflen, struct group **result);

struct group *
getgrgid(gid_t gid);

getgrgid_r(gid_t gid, struct group *grp, char *buffer, size_t buflen, struct group **result);

struct group *
getgrnam(const char *name);

getgrnam_r(const char *name, struct group *grp, char *buffer, size_t buflen, struct group **result);

setgroupent(int stayopen);




These functions operate on the group database 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 ids 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 functions will open the group file for reading, if necessary.

The functions getgrnam_r(), getgrgid_r(), and getgrent_r() act like their non re-entrant counterparts respectively, updating the contents of grp and storing a pointer to that in result, and returning 0. Storage used by grp is allocated from buffer, which is buflen bytes in size. If the requested entry cannot be found, result will point to NULL and 0 will be returned. If an error occurs, a non-zero error number will be returned and result will point to NULL. Calling getgrent_r() from multiple threads will result in each thread reading a disjoint portion of the group database.

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 equivalent to setgroupent() with an argument of zero.

The endgrent() function closes any open files.


The functions getgrgid(), getgrnam(), and getgrent() return a valid pointer to a group structure on success and a NULL pointer if the entry was not found or an error occured. If an error occured, the global variable errno is set to indicate the nature of the failure.

The functions getgrgid_r(), getgrnam_r(), and getgrent_r() return 0 on success or entry not found, and non-zero on failure, setting the global variable errno to indicate the nature of the failure.

The setgroupent() function returns the value 1 if successful, otherwise the value 0 is returned, setting the global variable errno to indicate the nature of the failure.

The endgrent() and setgrent() functions have no return value.


group database file


The historic function setgrfile(), which allowed the specification of alternative group databases, has been deprecated and is no longer available.


The following error codes may be set in errno for getgrent, getgrent_r, getgrnam, getgrnam_r, getgrgid, getgrgid_r, and setgroupent:
A signal was caught during the database search.
An I/O error has occurred.
The limit on open files for this process has been reached.
The system limit on open files has been reached.

The following error code may be set in errno for getgrent_r, getgrnam_r, and getgrgid_r:

The resulting struct group does not fit in the space defined by buffer and buflen

Other errno values may be set depending on the specific database backends.


The getgrgid() and getgrnam() functions conform to IEEE Std 1003.1-1990 (“POSIX.1”). The getgrgid_r() and getgrnam_r() functions conform to IEEE Std 1003.1c-1995 (“POSIX.1c”). The endgrent(), getgrent(), and setgrent() functions conform to X/Open Portability Guide Issue 4, Version 2 (“XPG4.2”) and IEEE Std 1003.1-2004 (“POSIX.1”) (XSI extension).


The functions endgrent(), getgrent(), getgrgid(), getgrnam(), and setgrent() appeared in Version 7 AT&T UNIX. The functions setgrfile() and setgroupent() appeared in 4.3BSD-Reno. The functions getgrgid_r() and getgrnam_r() appeared in NetBSD 3.0.


The functions getgrent(), getgrgid(), getgrnam(), 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. getgrent() makes no attempt to suppress duplicate information if multiple sources are specified in nsswitch.conf(5)

April 30, 2008 NetBSD 7.0