Linux man pages

Section (2) seteuid

Linux manual pages	Section 2

Name

seteuid, setegid — set effective user or group ID

Synopsis

#include <sys/types.h>

#include <unistd.h>

int seteuid( uid_t euid);

int setegid( gid_t egid);

Note

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
`seteuid`(), `setegid`():
`_POSIX_C_SOURCE` >= 200112L \|\| /* Glibc versions <= 2.19:
*/ `_BSD_SOURCE`

DESCRIPTION

seteuid() sets the effective user ID of the calling process. Unprivileged processes may only set the effective user ID to the real user ID, the effective user ID or the saved set-user-ID.

Precisely the same holds for setegid() with group instead of user.

RETURN VALUE

On success, zero is returned. On error, −1 is returned, and errno is set appropriately.

	Note
	there are cases where `seteuid`() can fail even when the caller is UID 0; it is a grave security error to omit checking for a failure return from `seteuid`().

ERRORS

EINVAL

The target user or group ID is not valid in this user namespace.

EPERM

In the case of seteuid(): the calling process is not privileged (does not have the CAP_SETUID capability in its user namespace) and euid does not match the current real user ID, current effective user ID, or current saved set-user-ID.

In the case of setegid(): the calling process is not privileged (does not have the CAP_SETGID capability in its user namespace) and egid does not match the current real group ID, current effective group ID, or current saved set-group-ID.

CONFORMING TO

POSIX.1-2001, POSIX.1-2008, 4.3BSD.

NOTES

Setting the effective user (group) ID to the saved set-user-ID (saved set-group-ID) is possible since Linux 1.1.37 (1.1.38). On an arbitrary system one should check _POSIX_SAVED_IDS.

Under glibc 2.0, seteuid(euid) is equivalent to setreuid(−1, euid) and hence may change the saved set-user-ID. Under glibc 2.1 and later, it is equivalent to setresuid(−1, euid, −1) and hence does not change the saved set-user-ID. Analogous remarks hold for setegid(), with the difference that the change in implementation from setregid(−1, egid) to setresgid(−1, egid, −1) occurred in glibc 2.2 or 2.3 (depending on the hardware architecture).

According to POSIX.1, seteuid() (setegid()) need not permit euid (egid) to be the same value as the current effective user (group) ID, and some implementations do not permit this.

C library/kernel differences

On Linux, seteuid() and setegid() are implemented as library functions that call, respectively, setreuid(2) and setregid(2).

COLOPHON

This page is part of release 4.16 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/.

  Copyright (C) 2001 Andries Brouwer (aebcwi.nl)

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[should really be seteuid.3]
Modified, 27 May 2004, Michael Kerrisk <mtk.manpagesgmail.com>
    Added notes on capability requirements