SETUID(2)           Linux Programmer's Manual           SETUID(2)


NAME
       setuid - set user identity

SYNOPSIS
       #include <unistd.h>

       int setuid(uid_t uid)

DESCRIPTION
       setuid  sets the effective user ID of the current process.
       If the caller is the superuser, the real  and  saved  user
       ID's are also set.

       Under   Linux,   setuid  is  implemented  like  SYSV  with
       SAVED_IDS.  This allows a setuid (other than root) program
       to drop all of it's user privileges, do some un-privileged
       work, and then re-engage the original effective user ID in
       a secure manner.

       If the user is root or the program is setuid root, special
       care must be taken. The setuid function checks the  effec-
       tive  uid  of  the  caller and if it is the superuser, all
       process related user ID's are set to uid.  After this  has
       occurred,  it is impossible for the program to regain root
       privileges.

RETURN VALUE
       On success, zero is returned.  On error, -1  is  returned,
       and errno is set appropriately.

ERRORS
       EPERM   The  user  is not the super-user, and uid does not
               match the effective or saved user ID of the  call-
               ing process.

CONFORMING TO
       System V

SEE ALSO

getuid, setreuid, seteuid,

Linux 1.1.36               29 July 1994                         1