NAME    [Toc]    [Back]

       setfsuid - set user identity used for file system checks

SYNOPSIS    [Toc]    [Back]

       #include <unistd.h> /* glibc uses <sys/fsuid.h> */

       int setfsuid(uid_t fsuid);

DESCRIPTION    [Toc]    [Back]

       setfsuid  sets  the user ID that the Linux kernel uses to check for all
       accesses to the file system. Normally, the value of fsuid  will	shadow
       the  value  of  the  effective user ID. In fact, whenever the effective
       user ID is changed, fsuid will also be changed to new value  of	effective
 user ID.

       An  explict  call  to setfsuid is usually only used by programs such as
       the Linux NFS server that need to change what user ID is used for  file
       access  without	a  corresponding change in the real and effective user
       IDs. A change in the normal user IDs for a  program  such  as  the  NFS
       server  is  a security hole that can expose it to unwanted signals from
       other user IDs.

       setfsuid will only succeed if the caller is the superuser or  if  fsuid
       matches	either the real user ID, effective user ID, saved set-user-ID,
       or the current value of fsuid.

RETURN VALUE    [Toc]    [Back]

       On success, the previous value of fsuid is  returned.   On  error,  the
       current value of fsuid is returned.

CONFORMING TO    [Toc]    [Back]

       setfsuid  is Linux specific and should not be used in programs intended
       to be portable.

BUGS    [Toc]    [Back]

       No error messages of any kind are returned to the caller. At  the  very
       least, EPERM should be returned when the call fails.

NOTE    [Toc]    [Back]

       When  glibc  determines	that  the argument is not a valid uid, it will
       return -1 and set errno to EINVAL without attempting the system call.

SEE ALSO    [Toc]    [Back]

       setfsgid(2)



Linux 1.3.15			  1995-08-06			   SETFSUID(2)