SETFSUID(2)         Linux Programmer's Manual         SETFSUID(2)

NAME
       setfsuid - set user identity used for file system checks

SYNOPSIS
       int setfsuid(uid_t fsuid)

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  pro-
       grams  such  as  the  Linux NFS server that need to change
       what user ID is used for file access without a correspond-
       ing 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)

Linux 1.3.15              6 August 1995                         1