text: setreuid(2) [freebsd man page]
  SETREUID(2) BSD System Calls Manual SETREUID(2) indi- cate. BSD
  February 8, 2001 BSD
  setreuid(2) System Calls setreuid(2) NAME
  setreuid - set real and effective user IDs SYNOPSIS
  #include <unistd.h> int setreuid(uid_t ruid, uid_t euid); DESCRIPTION. RETURN VALUES
  Upon successful completion, 0 is returned. Otherwise, -1 is returned, errno is set to indicate the error, and neither of the user IDs will be changed. ERRORS
  The setreuid() function will fail if: EINVAL The value of ruid or euid is less than 0 or greater than UID_MAX (defined in <limits.h>). EPERM. USAGE
  If a set-user-ID process sets its effective user ID to its real user ID, it can still set its effective user ID back to the saved set-user ID. ATTRIBUTES
  See attributes(5) for descriptions of the following attributes: +-----------------------------+-----------------------------+ | ATTRIBUTE TYPE | ATTRIBUTE VALUE | +-----------------------------+-----------------------------+ |Interface Stability |Standard | +-----------------------------+-----------------------------+ SEE ALSO
  exec(2), getuid(2), setregid(2), setuid(2), attributes(5), privileges(5), standards(5) SunOS 5.10 22 Mar 2004 setreuid(2)