setgid(2) - Linux manual page (original) (raw)

setgid(2) System Calls Manual setgid(2)

NAME top

   setgid - set group identity

LIBRARY top

   Standard C library (_libc_, _-lc_)

SYNOPSIS top

   **#include <unistd.h>**

   **int setgid(gid_t** _gid_**);**

DESCRIPTION top

   **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.

RETURN VALUE top

   On success, zero is returned.  On error, -1 is returned, and _[errno](../man3/errno.3.html)_
   is set to indicate the error.

ERRORS top

   **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.

VERSIONS top

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).

STANDARDS top

   POSIX.1-2008.

HISTORY top

   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.

SEE ALSO top

   [getgid(2)](../man2/getgid.2.html), [setegid(2)](../man2/setegid.2.html), [setregid(2)](../man2/setregid.2.html), [capabilities(7)](../man7/capabilities.7.html),
   [credentials(7)](../man7/credentials.7.html), [user_namespaces(7)](../man7/user%5Fnamespaces.7.html)

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Linux man-pages 6.10 2024-07-23 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)