getgrent(3) - Manual pages

NAME

getgrent, getgrent_r, getgrnam, getgrnam_r, getgrgid, getgrgid_r, setgroupent, setgrent, endgrent — group database operations

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);

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 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 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 functionality is unnecessary 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 programs must explicitly set errno to zero before calling any of these functions 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 setgroupent() function returns the value 1 if successful, otherwise the value 0 is returned. The endgrent() function has 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 available.

STANDARDS

The getgrent(), getgrnam(), getgrnam_r(), getgrgid(), getgrgid_r() and endgrent() functions conform to ISO/IEC 9945-1:1996 (“POSIX.1”).

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 and DragonFly 2.1.

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 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() functions make no attempt to suppress duplicate information if multiple sources are specified in nsswitch.conf(5).

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