SETEUID(2) Linux Programmer's Manual SETEUID(2)
seteuid, setegid - set effective user or group ID
int seteuid(uid_t euid);
int setegid(gid_t egid);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
_BSD_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600
seteuid() sets the effective user ID of the calling process. Unprivileged user processes
may only set the effective user ID to the real user ID, the effective user ID or the saved
Precisely the same holds for setegid() with "group" instead of "user".
On success, zero is returned. On error, -1 is returned, and errno is set appropriately.
EPERM The calling process is not privileged (Linux: does not have the CAP_SETUID capabil-
ity in the case of seteuid(), or the CAP_SETGID capability in the case of sete-
gid()) and euid (respectively, egid) is not the real user (group) ID, the effective
user (group) ID, or the saved set-user-ID (saved set-group-ID).
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
Under libc4, libc5 and 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 (dependeing 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
geteuid(2), setresuid(2), setreuid(2), setuid(2), capabilities(7), credentials(7)
This page is part of release 3.55 of the Linux man-pages project. A description of the
project, and information about reporting bugs, can be found at
Linux 2012-07-02 SETEUID(2)