'\" et
.TH SETREGID "3P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.

.SH NAME
setregid
\(em set real and effective group IDs
.SH SYNOPSIS
.LP
.nf
#include <unistd.h>
.P
int setregid(gid_t \fIrgid\fP, gid_t \fIegid\fP);
.fi
.SH DESCRIPTION
The
\fIsetregid\fR()
function shall set the real and effective group IDs of the calling
process.
.P
If
.IR rgid
is \(mi1, the real group ID shall not be changed; if
.IR egid
is \(mi1, the effective group ID shall not be changed.
.P
The real and effective group IDs may be set to different values in the
same call.
.P
Only a process with appropriate privileges can set the real group ID
and the effective group ID to any valid value.
.P
A non-privileged process can set either the real group ID to the saved
set-group-ID from one of the
.IR exec
family of functions, or the effective group ID to the saved
set-group-ID or the real group ID.
.P
If the real group ID is being set (\c
.IR rgid
is not \(mi1), or the effective group ID is being set to a value not
equal to the real group ID, then the saved set-group-ID of the current
process shall be set equal to the new effective group ID.
.P
Any supplementary group IDs of the calling process remain unchanged.
.SH "RETURN VALUE"
Upon successful completion, 0 shall be returned. Otherwise, \(mi1
shall be returned and
.IR errno
set to indicate the error, and neither of the group IDs are changed.
.SH ERRORS
The
\fIsetregid\fR()
function shall fail if:
.TP
.BR EINVAL
The value of the
.IR rgid
or
.IR egid
argument is invalid or out-of-range.
.TP
.BR EPERM
The process does not have appropriate privileges and a change other
than changing the real group ID to the saved set-group-ID, or changing
the effective group ID to the real group ID or the saved set-group-ID,
was requested.
.LP
.IR "The following sections are informative."
.SH EXAMPLES
None.
.SH "APPLICATION USAGE"
If a non-privileged set-group-ID process sets its effective group ID to
its real group ID, it can only set its effective group ID back to the
previous value if
.IR rgid
was \(mi1 in the
\fIsetregid\fR()
call, since the saved-group-ID is not changed in that case. If
.IR rgid
was equal to the real group ID in the
\fIsetregid\fR()
call, then the saved set-group-ID will also have been changed to the
real user ID.
.SH RATIONALE
Earlier versions of this standard did not specify whether the saved
set-group-ID was affected by
\fIsetregid\fR()
calls. This version specifies common existing practice that constitutes an
important security feature. The ability to set both the effective group
ID and saved set-group-ID to be the same as the real group ID means that
any security weakness in code that is executed after that point cannot
result in malicious code being executed with the previous effective
group ID. Privileged applications could already do this using just
\fIsetgid\fR(),
but for non-privileged applications the only standard method available
is to use this feature of
\fIsetregid\fR().
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIexec\fR\^",
.IR "\fIgetegid\fR\^(\|)",
.IR "\fIgeteuid\fR\^(\|)",
.IR "\fIgetgid\fR\^(\|)",
.IR "\fIgetuid\fR\^(\|)",
.IR "\fIsetegid\fR\^(\|)",
.IR "\fIseteuid\fR\^(\|)",
.IR "\fIsetgid\fR\^(\|)",
.IR "\fIsetreuid\fR\^(\|)",
.IR "\fIsetuid\fR\^(\|)"
.P
The Base Definitions volume of POSIX.1\(hy2008,
.IR "\fB<unistd.h>\fP"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
(This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.unix.org/online.html .

Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .