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  effec-
     tive  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 effective user ID of the calling  process  is  super-
     user,  the real user ID and the effective user ID can be set
     to any legal value.

     If the effective user ID  of  the  calling  process  is  not
     super-user, either the real user ID can be set to the effec-
     tive user ID, or the effective user ID can either be set  to
     the saved set-user ID from execve() (seeexec(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.

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 calling process's effective user  ID  is  not  the
           super-user  and  a change 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, was specified.

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.

SEE ALSO

     exec(2), getuid(2), setregid(2), setuid(2)