SETUID(2) System Calls SETUID(2)

NAME

setuid, setegid, seteuid, setgid - set user and group IDs

SYNOPSIS

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

int setuid(uid_t uid);


int setgid(gid_t gid);


int seteuid(uid_t euid);


int setegid(gid_t egid);

DESCRIPTION

The setuid() function sets the real user ID, effective user ID, and saved
user ID of the calling process. The setgid() function sets the real group
ID, effective group ID, and saved group ID of the calling process. The
setegid() and seteuid() functions set the effective group and user IDs
respectively for the calling process. See Intro(2) for more information
on real, effective, and saved user and group IDs.


At login time, the real user ID, effective user ID, and saved user ID of
the login process are set to the login ID of the user responsible for the
creation of the process. The same is true for the real, effective, and
saved group IDs; they are set to the group ID of the user responsible for
the creation of the process.


When a process calls one of the exec(2) family of functions to execute a
file (program), the user and/or group identifiers associated with the
process can change. If the file executed is a set-user-ID file, the
effective and saved user IDs of the process are set to the owner of the
file executed. If the file executed is a set-group-ID file, the effective
and saved group IDs of the process are set to the group of the file
executed. If the file executed is not a set-user-ID or set-group-ID file,
the effective user ID, saved user ID, effective group ID, and saved group
ID are not changed.


If the {PRIV_PROC_SETID} privilege is asserted in the effective set of
the process calling setuid(), the real, effective, and saved user IDs are
set to the uid argument. If the uid argument is 0 and none of the saved,
effective or real UID is 0, additional restrictions apply. See
privileges(7).


If the {PRIV_PROC_SETID} privilege is not asserted in the effective set,
but uid is either the real user ID or the saved user ID of the calling
process, the effective user ID is set to uid.


If the {PRIV_PROC_SETID} privilege is asserted in the effective set of
the process calling setgid(), the real, effective, and saved group IDs
are set to the gid argument.


If the {PRIV_PROC_SETID} privilege is not asserted in the effective set,
but gid is either the real group ID or the saved group ID of the calling
process, the effective group ID is set to gid.

RETURN VALUES

Upon successful completion, 0 is returned. Otherwise, -1 is returned and
errno is set to indicate the error.

ERRORS

The setuid() and setgid() functions will fail if:

EINVAL
The value of uid or gid is out of range.


EPERM
For setuid() and seteuid(), the {PRIV_PROC_SETID} privilege is
not asserted in the effective set of the calling process and
the uid argument does not match either the real or saved user
IDs, or an attempt is made to change to UID 0 and none of the
existing UIDs is 0, in which case additional privileges are
required.

For setgid() and setegid(), the {PRIV_PROC_SETID} privilege is
not asserted in the effective set and the gid argument does not
match either the real or saved group IDs.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+--------------------+-------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-------------------+
|Interface Stability | Standard |
+--------------------+-------------------+
|MT-Level | Async-Signal-Safe |
+--------------------+-------------------+

SEE ALSO

Intro(2), exec(2), getgroups(2), getuid(2), stat.h(3HEAD), attributes(7),
privileges(7), standards(7)

January 20, 2003 SETUID(2)