setgid(2) — Linux manual page

setgid(2)                  System Calls Manual                 setgid(2)

NAME

       setgid - set group identity

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #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 (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

       On success, zero is returned.  On error, -1 is returned, and
       errno is set to indicate the error.

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 in its user namespace), and gid does
              not match the real group ID or saved set-group-ID of the
              calling process.

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).

STANDARDS

       POSIX.1-2008.

HISTORY

       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

       getgid(2), setegid(2), setregid(2), capabilities(7),
       credentials(7), user_namespaces(7)

COLOPHON

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Linux man-pages 6.9.1          2024-05-02                      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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