setfsuid - set user identity used for file system checks
int setfsuid(uid_t fsuid))
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
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.
On success, the previous value of fsuid is returned. On
error, the current value of fsuid is returned.
setfsuid is Linux specific and should not be used in pro-
grams intended to be portable.
No error messages of any kind are returned to the caller. At
the very least, EPERM should be returned when the call