SETREUID(2)

NAME
setreuid - set real and effective user IDs

SYNOPSIS
#include <unistd.h>
int
setreuid(uid_t ruid, uid_t euid);

DESCRIPTION
The real and effective user IDs of the current process are set according to the arguments. The saved user ID will be set to the new value of the real user ID if a real user ID is specified and either the new real user ID value is different from the current value or the effective user ID is changed to a value other than the current saved 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 make other changes.

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 parameter.

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(2) function.

When setting the real and effective user IDs to the same value, the setuid(2) function is preferred.

RETURN VALUES
Upon successful completion, a value of 0 is returned. Otherwise, a value of -1 is returned and errno is set to indicate the error.

ERRORS

[EPERM]
    The current process is not the superuser and a change other than changing the effective user ID to the real user ID was specified.

SEE ALSO
getuid(2), seteuid(2), setregid(2), setresuid(2), setuid(2)

STANDARDS
The setreuid() function conforms to the p1003.1-2001 and xpg4.3. specifications.

Note, however, that prior to p1003.1-2001, the setreuid() function was not a part of the p1003.1 specification. As a result, it may not be implemented on all systems.

HISTORY
The setreuid() function call appeared in 4.2BSD. A semantically different version appeared in 4.4BSD. The current version, with the original semantics restored, appeared in OpenBSD 3.3.

CAVEATS
The setreuid() function predates POSIX saved user IDs. This implementation changes the saved user ID to the new value of the real user ID only if the real user ID is specified and either changed or the effective user ID is changed to a value other than the current saved user ID. Other implementations may behave differently.