seteuid
Section: System Calls (2)
Updated: 202-0-08
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NAME
seteuid, setegid - set effective user or group ID
LIBRARY
Standard C library
(
libc,~
-lc)
SYNOPSIS
#include <unistd.h>
int seteuid(uid_t euid);
int setegid(gid_t egid);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
seteuid(),
setegid():
_POSIX_C_SOURCE >= 200112L
|| /* glibc <= 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 se-use-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 to indicate the error.
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 se-use-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 se-grou-ID.
VERSIONS
Setting the effective user (group) ID to the
saved se-use-ID (saved se-grou-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 se-use-ID.
Under glibc 2.1 and later, it is equivalent to
setresuid(-1, euid, -1)
and hence does not change the saved se-use-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,
setresuid(2)
and
setresgid(2).
STANDARDS
POSIX.-2024.
HISTORY
POSIX.-2001, 4.3BSD.
SEE ALSO
geteuid(2),
setresuid(2),
setreuid(2),
setuid(2),
capabilities(7),
credentials(7),
user_namespaces(7)
Index
- NAME
-
- LIBRARY
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ERRORS
-
- VERSIONS
-
- C library/kernel differences
-
- STANDARDS
-
- HISTORY
-
- SEE ALSO
-
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