.\" Copyright 1997, Andries E. Brouwer <aeb@cwi.nl>
.\" Copyright 2007, Michael Kerrisk <mtk.manpages@gmail.com>
.\" Copyright, the authors of the Linux man-pages project
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.TH getresuid 2 2026-02-08 "Linux man-pages 6.19"
.SH NAME
getresuid, getresgid \- get real, effective, and saved user/group IDs
.SH LIBRARY
Standard C library
.RI ( libc ,\~ \-lc )
.SH SYNOPSIS
.nf
.BR "#define _GNU_SOURCE" "         /* See feature_test_macros(7) */"
.B #include <unistd.h>
.P
.BI "int getresuid(uid_t *" ruid ", uid_t *" euid ", uid_t *" suid );
.BI "int getresgid(gid_t *" rgid ", gid_t *" egid ", gid_t *" sgid );
.fi
.SH DESCRIPTION
.BR getresuid ()
returns the real UID, the effective UID, and the saved set-user-ID
of the calling process, in the arguments
.IR ruid ,
.IR euid ,
and
.IR suid ,
respectively.
.BR getresgid ()
performs the analogous task for the process's group IDs.
.SH RETURN VALUE
On success, zero is returned.
On error, \-1 is returned, and
.I errno
is set to indicate the error.
.SH ERRORS
.TP
.B EFAULT
One of the arguments specified an address outside the calling program's
address space.
.SH STANDARDS
POSIX.1-2024 XSI.
.SH HISTORY
Linux 2.1.44,
glibc 2.3.2,
POSIX.1-2024 XSI.
.P
The original Linux
.BR getresuid ()
and
.BR getresgid ()
system calls supported only 16-bit user and group IDs.
Subsequently, Linux 2.4 added
.BR getresuid32 ()
and
.BR getresgid32 (),
supporting 32-bit IDs.
The glibc
.BR getresuid ()
and
.BR getresgid ()
wrapper functions transparently deal with the variations across kernel versions.
.SH SEE ALSO
.BR getuid (2),
.BR setresuid (2),
.BR setreuid (2),
.BR setuid (2),
.BR credentials (7)