setuid — set user identity
#include <sys/types.h> #include <unistd.h>
int
setuid( |
uid_t | uid) ; |
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, 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 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 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
setuid
(). You can accomplish
this with the (non-POSIX, BSD) call seteuid(2).
On success, zero is returned. On error, −1 is
returned, and errno
is set
appropriately.
The uid
does
not match the current uid and uid
brings process over
its NPROC rlimit.
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.
SVr4, POSIX.1-2001. Not quite compatible with the 4.4BSD call, which sets all of the real, saved, and effective user IDs.
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.
getuid(2), seteuid(2), setfsuid(2), setreuid(2), capabilities(7)
|