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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 appropriately.

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

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)

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | LINUX-SPECIFIC REMARKS | SEE ALSO

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