xref: /freebsd/lib/libc/gen/getgrent.3 (revision dc36d6f9bb1753f3808552f3afd30eda9a7b206a)

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.Dd July 31, 2016
.Dt GETGRENT 3
.Os
.Sh NAME
.Nm getgrent ,
.Nm getgrent_r ,
.Nm getgrnam ,
.Nm getgrnam_r ,
.Nm getgrgid ,
.Nm getgrgid_r ,
.Nm setgroupent ,
.Nm setgrent ,
.Nm endgrent
.Nd group database operations
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In grp.h
.Ft struct group *
.Fn getgrent void
.Ft int
.Fn getgrent_r "struct group *grp" "char *buffer" "size_t bufsize" "struct group **result"
.Ft struct group *
.Fn getgrnam "const char *name"
.Ft int
.Fn getgrnam_r "const char *name" "struct group *grp" "char *buffer" "size_t bufsize" "struct group **result"
.Ft struct group *
.Fn getgrgid "gid_t gid"
.Ft int
.Fn getgrgid_r "gid_t gid" "struct group *grp" "char *buffer" "size_t bufsize" "struct group **result"
.Ft int
.Fn setgroupent "int stayopen"
.Ft void
.Fn setgrent void
.Ft void
.Fn endgrent void
.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
.Vt group
found in the include
file
.In grp.h :
.Bd -literal -offset indent
struct group {
	char	*gr_name;	/* group name */
	char	*gr_passwd;	/* group password */
	gid_t	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
.Fa name
or the group id pointed to by
.Fa gid ,
respectively, returning the first one encountered.
Identical group
names or group gids may result in undefined behavior.
.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
The functions
.Fn getgrent_r ,
.Fn getgrnam_r ,
and
.Fn getgrgid_r
are thread-safe versions of
.Fn getgrent ,
.Fn getgrnam ,
and
.Fn getgrgid ,
respectively.
The caller must provide storage for the results of the search in
the
.Fa grp ,
.Fa buffer ,
.Fa bufsize ,
and
.Fa result
arguments.
When these functions are successful, the
.Fa grp
argument will be filled-in, and a pointer to that argument will be
stored in
.Fa result .
If an entry is not found or an error occurs,
.Fa result
will be set to
.Dv NULL .
.Pp
These functions 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 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.
.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 getgrnam ,
and
.Fn getgrgid ,
return a pointer to a group structure on success or
.Dv NULL
if the entry is not found or if an error occurs.
If an error does occur,
.Va errno
will be set.
Note that programs must explicitly set
.Va errno
to zero before calling any of these functions if they need to
distinguish between a non-existent entry and an error.
The functions
.Fn getgrent_r ,
.Fn getgrnam_r ,
and
.Fn 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
.Fa result
is set to
.Dv NULL
and the return value is 0, no matching entry exists.)
.Pp
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 COMPATIBILITY
The historic function
.Fn setgrfile ,
which allowed the specification of alternate password databases, has
been deprecated and is no longer available.
.Sh SEE ALSO
.Xr getpwent 3 ,
.Xr group 5 ,
.Xr nsswitch.conf 5 ,
.Xr yp 8
.Sh STANDARDS
The
.Fn getgrent ,
.Fn getgrnam ,
.Fn getgrnam_r ,
.Fn getgrgid ,
.Fn getgrgid_r
and
.Fn endgrent
functions conform to
.St -p1003.1-96 .
The
.Fn setgrent
function differs from that standard in that its return type is
.Vt int
rather than
.Vt void .
.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 .
The functions
.Fn getgrent_r ,
.Fn getgrnam_r ,
and
.Fn getgrgid_r
appeared in
.Fx 5.1 .
.Sh BUGS
The functions
.Fn getgrent ,
.Fn getgrnam ,
.Fn getgrgid ,
.Fn setgroupent
and
.Fn 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.
.Pp
The functions
.Fn getgrent ,
.Fn getgrent_r ,
.Fn endgrent ,
.Fn setgroupent ,
and
.Fn setgrent
are fairly useless in a networked environment and should be
avoided, if possible.
The
.Fn getgrent
and
.Fn getgrent_r
functions
make no attempt to suppress duplicate information if multiple
sources are specified in
.Xr nsswitch.conf 5 .