setgid

SETGID(2)                  Linux Programmer's Manual                 SETGID(2)



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

CONFORMING TO
       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 5.03 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/.



Linux                             2019-03-06                         SETGID(2)