| SETUID(2) | System Calls Manual | SETUID(2) | 
setuid, seteuid,
  setgid, setegid —
#include <unistd.h>
int
  
  setuid(uid_t
    uid);
int
  
  seteuid(uid_t
    euid);
int
  
  setgid(gid_t
    gid);
int
  
  setegid(gid_t
    egid);
setuid() function sets the real and effective user
  IDs and the saved set-user-ID of the current process to the specified value.
  The setuid() function is permitted if the specified ID
  is equal to the real user ID of the process, or if the effective user ID is
  that of the super user.
The setgid() function sets the real and
    effective group IDs and the saved set-group-ID of the current process to the
    specified value. The setgid() function is permitted
    if the specified ID is equal to the real group ID of the process, or if the
    effective user ID is that of the super user. Supplementary group IDs remain
    unchanged.
The seteuid() function
    (setegid()) sets the effective user ID (group ID) of
    the current process. The effective user ID may be set to the value of the
    real user ID or the saved set-user-ID (see
    intro(2) and
    execve(2)); in this way, the
    effective user ID of a set-user-ID executable may be toggled by switching to
    the real user ID, then re-enabled by reverting to the set-user-ID value.
    Similarly, the effective group ID may be set to the value of the real group
    ID or the saved set-group-ID.
If the user is not the super user, or the uid specified is not the real, effective ID, or saved ID, these functions return -1.
setuid() and setgid()
  functions are compliant with the IEEE Std 1003.1-1990
  (“POSIX.1”) specification with
  _POSIX_SAVED_IDS not defined. We do not implement the
  _POSIX_SAVED_IDS option as specified in the standard
  because this would make it impossible for a set-user-ID executable owned by a
  user other than the super-user to permanently revoke its privileges.
The seteuid() and
    setegid() functions are compliant with
    IEEE Std 1003.1-2001 (“POSIX.1”).
setuid() and setgid()
  functions appeared in Version 1 AT&T UNIX
  and Version 4 AT&T UNIX, respectively.
| September 2, 2019 | NetBSD 9.4 |