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.\" From: @(#)getgrent.3 8.2 (Berkeley) 4/19/94
.\" $FreeBSD: src/lib/libc/gen/getgrent.3,v 1.16 2001/10/01 16:08:51 ru Exp $
.\"
.Dd September 29, 1994
.Dt GETGRENT 3
.Os
.Sh NAME
.Nm endgrent ,
.Nm getgrent ,
.Nm getgrgid ,
.Nm getgrgid_r ,
.Nm getgrnam ,
.Nm getgrnam_r ,
.Nm setgrent ,
.\" .Nm setgrfile ,
.Nm setgroupent
.Nd group database operations
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In grp.h
.Ft void
.Fo endgrent
.Fa void
.Fc
.Ft struct group *
.Fo getgrent
.Fa void
.Fc
.Ft struct group *
.Fo getgrgid
.Fa "gid_t gid"
.Fc
.Ft int
.Fo getgrgid_r
.Fa "gid_t gid"
.Fa "struct group *grp"
.Fa "char *buffer"
.Fa "size_t bufsize"
.Fa "struct group **result"
.Fc
.Ft struct group *
.Fo getgrnam
.Fa "const char *name"
.Fc
.Ft int
.Fo getgrnam_r
.Fa "const char *name"
.Fa "struct group *grp"
.Fa "char *buffer"
.Fa "size_t bufsize"
.Fa "struct group **result"
.Fc
.Ft void
.Fo setgrent
.Fa void
.Fc
.\" .Ft void
.\" .Fn setgrfile "const char *name"
.Ft int
.Fo setgroupent
.Fa "int stayopen"
.Fc
.Sh DESCRIPTION
These functions operate on the group database file
.Pa /etc/group ,
which is described
in
.Xr group 5 .
Each line of the database is defined by the structure
.Ar group ,
found in the include
file
.Aq Pa grp.h :
.Bd -literal -offset indent
struct group {
char *gr_name; /* group name */
char *gr_passwd; /* group password */
int gr_gid; /* group id */
char **gr_mem; /* group members */
};
.Ed
.Pp
The functions
.Fn getgrnam
and
.Fn getgrgid
search the group database for the given group name (pointed to by
.Ar name )
or the group id (pointed to by
.Ar gid ) ,
respectively, returning the first one encountered. Identical group
names or group ids may result in undefined behavior.
.Pp
All of these routines are thread-safe.
The
.Fn getgrent ,
.Fn getgrgid ,
and
.Fn getgrnam
routines return a pointer to a result managed by the system library in a
thread-specific data structure.
Every thread has space for a pointer to a struct group and allocates its own storage for the result.
Neither previously returned values in memory nor a previously returned pointer value should be used
by a thread after calling any one of these three routines.
Memory allocated by a thread is automatically released on subsequent calls by the same thread to any of these
three routines, and when the thread exits.
.Pp
The functions
.Fn getgrgid_r
and
.Fn getgrnam_r
take additional arguments which supply storage space for the returned result.
The
.Fa grp
parameter is a pointer to a struct group, which must be allocated by the caller.
The
.Fa buffer
parameter is a pointer to a block of memory with a size specified by
.Pa bufsize .
This buffer is used to hold the values which are pointed to by values filled in
the
.Fa grp
structure.
Zero is returned on success.
If insufficient memory is supplied, these routines return ERANGE.
.Pp
The
.Fn getgrent
function
sequentially reads the group database and is intended for programs
that wish to step through the complete list of groups.
.Pp
All three routines will open the group file for reading, if necessary.
.Pp
The
.Fn setgroupent
function
opens the file, or rewinds it if it is already open. If
.Fa stayopen
is non-zero, file descriptors are left open, significantly speeding
functions' subsequent calls. This functionality is unnecessary for
.Fn 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.
.Pp
The
.Fn setgrent
function
is identical to
.Fn setgroupent
with an argument of zero.
.Pp
The
.Fn endgrent
function
closes any open files.
.Sh RETURN VALUES
The functions
.Fn getgrent ,
.Fn getgrgid ,
and
.Fn getgrnam
each 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 function
.Fn setgroupent
returns the value 1 if successful;
otherwise, the value 0 is returned.
The functions
.Fn endgrent ,
.Fn setgrent ,
and
.Fn setgrfile
have no return value.
.Sh FILES
.Bl -tag -width /etc/group -compact
.It Pa /etc/group
group database file
.El
.Sh LEGACY SYNOPSIS
.Fd #include <grp.h>
.Pp
.Ft int
.br
.Fo setgrent
.Fa void
.Fc ;
.Pp
The function
.Fn setgrent
returns the value 1 if successful;
otherwise, the value 0 is returned.
.Sh SEE ALSO
.Xr getpwent 3 ,
.Xr yp 8 ,
.Xr group 5
.Sh HISTORY
The functions
.Fn endgrent ,
.Fn getgrent ,
.Fn getgrnam ,
.Fn getgrgid ,
and
.Fn setgrent
appeared in
.At v7 .
The functions
.Fn setgrfile
and
.Fn setgroupent
appeared in
.Bx 4.3 Reno .
.Sh COMPATIBILITY
The historic function
.Fn setgrfile ,
which allowed the specification of alternate password databases, has
been deprecated and is no longer available.
.Sh BUGS
The functions
.Fn getgrent ,
.Fn getgrnam ,
and
.Fn getgrgid ,
leave their results in internal thread-specific memory and return
a pointer to that object.
Subsequent calls to any of these three routines by the same thread will
release the object and return a new pointer value.