SETUID - phpMan

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



NAME
       setuid - set user identity

SYNOPSIS
       #include <sys/types.h>
       #include <unistd.h>

       int setuid(uid_t uid);

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

       Under Linux, setuid is implemented like the POSIX version with the _POSIX_SAVED_IDS
       feature.   This  allows  a setuid (other than root) program to drop all of its 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 effective 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.

       Thus, a setuid-root program wishing to temporarily drop root privileges, assume the
       identity  of a non-root user, and then regain root privileges afterwards cannot use
       setuid.  You can accomplish this with the (non-POSIX, BSD) call seteuid.

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

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

       EAGAIN The uid does not match the current uid and  uid  brings  process  over  it’s
              NPROC rlimit.

CONFORMING TO
       SVr4,  SVID, POSIX.1.  Not quite compatible with the 4.4BSD call, which sets all of
       the real, saved, and effective user IDs.  SVr4 documents an additional EINVAL error
       condition.

LINUX-SPECIFIC REMARKS
       Linux  has  the concept of filesystem user ID, normally equal to the effective user
       ID.  The setuid call also sets the filesystem user ID of the current process.   See
       setfsuid(2).

       If  uid is different from the old effective uid, the process will be forbidden from
       leaving core dumps.

SEE ALSO
       getuid(2), setreuid(2), seteuid(2), setfsuid(2)



Linux 1.1.36                      1994-07-29                         SETUID(2)

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