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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
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setgid(2) System Calls Manual setgid(2)
setgid - set group identity
Standard C library (libc, -lc)
#include <unistd.h>
int setgid(gid_t gid);
setgid() sets the effective group ID of the calling process. If
the calling process is privileged (more precisely: 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.
On success, zero is returned. On error, -1 is returned, and errno
is set to indicate the error.
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 in its user namespace), and gid does
not match the real group ID or saved set-group-ID of the
calling process.
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).
POSIX.1-2008.
POSIX.1-2001, SVr4.
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.
getgid(2), setegid(2), setregid(2), capabilities(7),
credentials(7), user_namespaces(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.15.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-08-11. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.15 2025-05-17 setgid(2)
Pages that refer to this page: capsh(1), pmdammv(1), access(2), getgid(2), getgroups(2), setreuid(2), syscalls(2), cap_get_proc(3), euidaccess(3), proc_sys_fs(5), systemd.exec(5), credentials(7), nptl(7), signal-safety(7), user_namespaces(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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