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SETREUID(2) FreeBSD System Calls Manual 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 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. 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, the value 0 is returned; otherwise the value -1 is returned and the global variable 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 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. HISTORY The 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 OpenBSD 3.3. FreeBSD 14.1-RELEASE-p8 February 5, 2015 FreeBSD 14.1-RELEASE-p8