setreuid - set real and effective user IDs
setreuid(uid_t ruid, uid_t euid);
The real and effective user IDs of the current process are
to the arguments. If the real user ID is changed, or the
ID is changed to a value other than the real user ID, then
the saved user
ID will be set to the effective user ID.
Unprivileged users may change either user ID to the current
value of the
real, effective, or saved user ID. Only the superuser may
Supplying a value of -1 for either the real or effective user ID forces
the system to substitute the current ID in place of the -1
The setreuid() function was intended to allow swapping the
real and effective
user IDs in set-user-ID programs to temporarily relinquish the
set-user-ID value. This purpose is now better served by the
use of the
seteuid() function (see setuid(2)).
When setting the real and effective user IDs to the same
setuid() function is preferred.
Upon successful completion, a value of 0 is returned. Otherwise, a value
of -1 is returned and errno is set to indicate the error.
[EPERM] The current process is not the superuser and a
than changing the effective user ID to the real user ID was
getuid(2), seteuid(2), setresuid(2), setuid(2)
The setreuid() function conforms to the IEEE Std 1003.1-2001
and X/Open Portability Guide Issue 4.3 (``XPG4.3''). specifications.
Note, however, that prior to IEEE Std 1003.1-2001
setreuid() function was not a part of the IEEE Std 1003.1
specification. As a result, it may not be implemented on
The setreuid() function call appeared in 4.2BSD. A semantically different
version appeared in 4.4BSD. The current version, with
semantics restored, appeared in OpenBSD 3.3.
The setreuid() function predates POSIX saved user IDs. This
changes the saved user ID to the new value of the effective user ID
if the real user ID is changed. Other implementations may
OpenBSD 3.6 January 29, 2003
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