|SETREUID(2)||System Calls Manual||SETREUID(2)|
setreuid — set
real and effective user IDs
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 new value of the effective user ID differs from 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.
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
When setting the real and effective user IDs to the same value, the setuid(2) function is preferred.
Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.
setreuid() function conforms to the
IEEE Std 1003.1-2008 (“POSIX.1”)
specification, except that the conditions for changing the saved user ID
differ and that, if it is changed, the saved user ID is set to the real user
ID instead of the effective user ID.
setreuid() system call first appeared
in 4.1cBSD, predating POSIX. A semantically
different version appeared in 4.4BSD. The current
version, with the original semantics restored, appeared in
|February 5, 2015||OpenBSD-6.5|