NAME¶
setgid - set group identity
SYNOPSIS¶
#include <sys/types.h>
#include <unistd.h>
int setgid(gid_t gid);
DESCRIPTION¶
setgid() sets the effective group ID of the calling process. If the
calling process is privileged (has the
CAP_SETGID capability in its
user namespace), the real GID and saved set-group-ID are also set.
Under Linux,
setgid() is implemented like the POSIX version with the
_POSIX_SAVED_IDS feature. This allows a set-group-ID program that is
not set-user-ID-root to drop all of its group privileges, do some
un-privileged work, and then reengage the original effective group ID in a
secure manner.
RETURN VALUE¶
On success, zero is returned. On error, -1 is returned, and
errno is set
appropriately.
ERRORS¶
- EINVAL
- The group ID specified in gid is not valid in this user
namespace.
- EPERM
- The calling process is not privileged (does not have the CAP_SETGID
capability), and gid does not match the real group ID or saved
set-group-ID of the calling process.
POSIX.1-2001, POSIX.1-2008, SVr4.
NOTES¶
The original Linux
setgid() system call supported only 16-bit group IDs.
Subsequently, Linux 2.4 added
setgid32() supporting 32-bit IDs. The
glibc
setgid() wrapper function transparently deals with the variation
across kernel versions.
C library/kernel differences¶
At the kernel level, user IDs and group IDs are a per-thread attribute. However,
POSIX requires that all threads in a process share the same credentials. The
NPTL threading implementation handles the POSIX requirements by providing
wrapper functions for the various system calls that change process UIDs and
GIDs. These wrapper functions (including the one for
setgid()) employ a
signal-based technique to ensure that when one thread changes credentials, all
of the other threads in the process also change their credentials. For
details, see
nptl(7).
SEE ALSO¶
getgid(2),
setegid(2),
setregid(2),
capabilities(7),
credentials(7),
user_namespaces(7)
COLOPHON¶
This page is part of release 4.10 of the Linux
man-pages project. A
description of the project, information about reporting bugs, and the latest
version of this page, can be found at
https://www.kernel.org/doc/man-pages/.