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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
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SETGID(2) Linux Programmer's Manual SETGID(2)
setgid - set group identity
#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.
POSIX.1-2001, POSIX.1-2008, 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.
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).
getgid(2), setegid(2), setregid(2), capabilities(7),
credentials(7), user_namespaces(7)
This page is part of release 5.13 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 2021-03-22 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(5), systemd.exec(5), credentials(7), nptl(7), signal-safety(7), user_namespaces(7)
Copyright and license for this manual page
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