setgid32(2) — Linux manual page


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

NAME         top

       setgid - set group identity

SYNOPSIS         top

       #include <sys/types.h>
       #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 is
       set appropriately.

ERRORS         top

       EINVAL The group ID specified in gid is not valid in this user

       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

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008, SVr4.

NOTES         top

       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         top

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

COLOPHON         top

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Linux                            2019-03-06                        SETGID(2)

Pages that refer to this page: syscalls(2)