SETUID(2)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, effec‐
tive, 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 effec‐
tive 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(5).
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 privi‐
leges 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(5) for descriptions of the following attributes:
┌────────────────────┬───────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├────────────────────┼───────────────────┤
│Interface Stability │ Standard │
├────────────────────┼───────────────────┤
│MT-Level │ Async-Signal-Safe │
└────────────────────┴───────────────────┘
SEE ALSOIntro(2), exec(2), getgroups(2), getuid(2), stat.h(3HEAD),
attributes(5), privileges(5), standards(5)
Jan 20, 2003 SETUID(2)
