Tribblix: manual page: setreuid.2

SETREUID(2) System Calls SETREUID(2)

NAME

setreuid - set real and effective user IDs

SYNOPSIS

#include <unistd.h>

int setreuid(uid_t ruid, uid_t euid);

DESCRIPTION

The setreuid() function is used to set the real and effective user
IDs of the calling process. If ruid is -1, the real user ID is not
changed; if euid is -1, the effective user ID is not changed. The
real and effective user IDs may be set to different values in the
same call.

If the {PRIV_PROC_SETID} privilege is asserted in the effective set
of the calling process, the real user ID and the effective user ID
can be set to any legal value.

If the {PRIV_PROC_SETID} privilege is not asserted in the effective
set of the calling process, either the real user ID can be set to the
effective user ID, or the effective user ID can either be set to the
saved set-user ID from execve() (see exec(2)) or the real user ID.

In either case, if the real user ID is being changed (that is, if
ruid is not -1), or the effective user ID is being changed to a
value not equal to the real user ID, the saved set-user ID is set
equal to the new effective user ID.

All privileges are required to change to uid 0.

RETURN VALUES

Upon successful completion, 0 is returned. Otherwise, -1 is returned,
errno is set to indicate the error, and neither of the user IDs will
be changed.

ERRORS

The setreuid() function will fail if:

EINVAL
The value of ruid or euid is less than 0 or greater than
UID_MAX (defined in <limits.h>).

EPERM
The {PRIV_PROC_SETID} privilege is not asserted in the
effective set of the calling processes and a change was
specified other than changing the real user ID to the
effective user ID, or changing the effective user ID to the
real user ID or the saved set-user ID. See privileges(7)
for additional restrictions which apply when changing to
UID 0.

USAGE

If a set-user-ID process sets its effective user ID to its real user
ID, it can still set its effective user ID back to the saved set-user
ID.

ATTRIBUTES