NAME
setuid - set user identity
SYNOPSIS
#include <sys/types.h>
#include <unistd.h>
I int setuid(uid_t uid );
DESCRIPTION
R setuid ()
sets the effective user ID of the current process.
If the effective UID of the caller is root,
the real UID and saved set-user-ID are also set.
Under Linux,
R setuid ()
is implemented like the POSIX version with the _POSIX_SAVED_IDS feature.
This allows a set-user-ID (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 set-user-ID-root, special care must be
taken.
The
R setuid ()
function checks the effective user ID of the caller and if it is
the superuser, all process-related user ID's are set to
R uid .
After this has occurred, it is impossible for the program to regain root
privileges.
Thus, a set-user-ID-root program wishing to temporarily drop root
privileges, assume the identity of a non-root user, and then regain
root privileges afterwards cannot use
R setuid ().
You can accomplish this with the (non-POSIX, BSD) call
seteuid(2).
RETURN VALUE
On success, zero is returned.
On error, -1 is returned, and
errno
is set appropriately.
ERRORS
EAGAIN
The
uid
does not match the current uid and
uid
brings process over its
R RLIMIT_NPROC
resource limit.
EPERM
The user is not privileged (Linux: does not have the
CAP_SETUID
capability) and
uid
does not match the real UID or saved set-user-ID of the calling process.
CONFORMING TO
SVr4, POSIX.1-2001.
Not quite compatible with the 4.4BSD call, which
sets all of the real, saved, and effective user IDs.
NOTES
Linux Notes
Linux has the concept of filesystem user ID, normally equal to the
effective user ID.
The
R 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
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