DESCRIPTION

     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 user ID, or the current value of fsuid.

RETURN VALUE

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

CONFORMING TO

     setfsuid is Linux specific and should not be  used  in  pro-
     grams intended to be portable.

BUGS

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

SEE ALSO

     setfsgid(2)