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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 ef-
       fective 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)  pro-
       gram  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	privi-
       leges,  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 ef-
       fective 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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