libc/gen/getgrent.3

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.\"     @(#)getgrent.3	8.2 (Berkeley) 4/19/94
.\"
.Dd April 30, 2008
.Dt GETGRENT 3
.Os
.Sh NAME
.Nm getgrent ,
.Nm getgrent_r ,
.Nm getgrgid ,
.Nm getgrgid_r ,
.Nm getgrnam ,
.Nm getgrnam_r ,
.Nm setgroupent ,
.\" .Nm setgrfile ,
.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
.Fo getgrent_r
.Fa "struct group *grp"
.Fa "char *buffer"
.Fa "size_t buflen"
.Fa "struct group **result"
.Fc
.Ft struct group *
.Fn getgrgid "gid_t gid"
.Ft int
.Fo getgrgid_r
.Fa "gid_t gid"
.Fa "struct group *grp"
.Fa "char *buffer"
.Fa "size_t buflen"
.Fa "struct group **result"
.Fc
.Ft struct group *
.Fn getgrnam "const char *name"
.Ft int
.Fo getgrnam_r
.Fa "const char *name"
.Fa "struct group *grp"
.Fa "char *buffer"
.Fa "size_t buflen"
.Fa "struct group **result"
.Fc
.Ft int
.Fn setgroupent "int stayopen"
.\" .Ft void
.\" .Fn setgrfile "const char *name"
.Ft void
.Fn setgrent void
.Ft void
.Fn endgrent void
.Sh DESCRIPTION
These functions operate on the group database which is described in
.Xr group 5 .
Each line of the database is defined by the structure
.Ar 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
.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
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 functions will open the group file for reading, if necessary.
.Pp
The functions
.Fn getgrnam_r ,
.Fn getgrgid_r ,
and
.Fn getgrent_r
act like their non re-entrant counterparts
respectively, updating the contents of
.Ar grp
and storing a pointer to that in
.Ar result ,
and returning
.Dv 0 .
Storage used by
.Ar grp
is allocated from
.Ar buffer ,
which is
.Ar buflen
bytes in size.
If the requested entry cannot be found,
.Ar result
will point to
.Dv NULL
and
.Dv 0
will be returned.
If an error occurs,
a non-zero error number will be returned and
.Ar result
will point to
.Dv NULL .
Calling
.Fn getgrent_r
from multiple threads will result in each thread reading a disjoint portion
of the group database.
.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 equivalent to
.Fn setgroupent
with an argument of zero.
.Pp
The
.Fn endgrent
function closes any open files.
.Sh RETURN VALUES
The functions
.Fn getgrgid ,
.Fn getgrnam ,
and
.Fn getgrent
return a valid pointer to a group structure on success
and a
.Dv NULL
pointer if the entry was not found or an error occured.
If an error occured, the global variable
.Dv errno
is set to indicate the nature of the failure.
.Pp
The functions
.Fn getgrgid_r ,
.Fn getgrnam_r ,
and
.Fn getgrent_r
return
.Dv 0
on success or entry not found, and non-zero on failure, setting the global
variable
.Dv errno
to indicate the nature of the failure.
.Pp
The
.Fn setgroupent
function returns the value 1 if successful, otherwise the value
0 is returned, setting the global variable
.Dv errno
to indicate the nature of the failure.
.Pp
The
.Fn endgrent
and
.Fn setgrent
functions have no return value.
.Sh ERRORS
The following error codes may be set in
.Va errno
for
.Nm getgrent ,
.Nm getgrent_r ,
.Nm getgrnam ,
.Nm getgrnam_r ,
.Nm getgrgid ,
.Nm getgrgid_r ,
and
.Nm setgroupent :
.Bl -tag -width Er
.It Bq Er EIO
An I/O error has occurred.
.It Bq Er EINTR
A signal was caught during the database search.
.It Bq Er EMFILE
The limit on open files for this process has been reached.
.It Bq Er ENFILE
The system limit on open files has been reached.
.El
.Pp
The following error code may be set in
.Va errno
for
.Nm getgrent_r ,
.Nm getgrnam_r ,
and
.Nm getgrgid_r :
.Bl -tag -width Er
.It Bq Er ERANGE
The resulting
.Ft struct group
does not fit in the space defined by
.Dv buffer
and
.Dv buflen
.El
.Pp
Other
.Dv errno
values may be set depending on the specific database backends.
.Sh FILES
.Bl -tag -width /etc/group -compact
.It Pa /etc/group
group database file
.El
.Sh SEE ALSO
.Xr getpwent 3 ,
.Xr group 5 ,
.Xr nsswitch.conf 5
.Sh STANDARDS
The
.Fn getgrgid
and
.Fn getgrnam
functions conform to
.St -p1003.1-90 .
The
.Fn getgrgid_r
and
.Fn getgrnam_r
functions conform to
.St -p1003.1c-95 .
The
.Fn endgrent ,
.Fn getgrent ,
and
.Fn setgrent
functions conform to
.St -xpg4.2
and
.St -p1003.1-2004
(XSI extension).
.Sh HISTORY
The functions
.Fn endgrent ,
.Fn getgrent ,
.Fn getgrgid ,
.Fn getgrnam ,
and
.Fn setgrent
appeared in
.At v7 .
The functions
.Fn setgrfile
and
.Fn setgroupent
appeared in
.Bx 4.3 Reno .
The functions
.Fn getgrgid_r
and
.Fn getgrnam_r
appeared in
.Nx 3.0 .
.Sh COMPATIBILITY
The historic function
.Fn setgrfile ,
which allowed the specification of alternative group databases, has
been deprecated and is no longer available.
.Sh BUGS
The functions
.Fn getgrent ,
.Fn getgrgid ,
.Fn getgrnam ,
.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 endgrent ,
.Fn setgroupent ,
and
.Fn setgrent
are fairly useless in a networked environment and should be
avoided, if possible.
.Fn getgrent
makes no attempt to suppress duplicate information if multiple
sources are specified in
.Xr nsswitch.conf 5