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.\" Copyright (C) 1995, Thomas K. Dyas <tdyas@eden.rutgers.edu>
.\"
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Permission is granted to copy and distribute modified versions of this
.\" manual under the conditions for verbatim copying, provided that the
.\" entire resulting derived work is distributed under the terms of a
.\" permission notice identical to this one
.\"
.\" Since the Linux kernel and libraries are constantly changing, this
.\" manual page may be incorrect or out-of-date. The author(s) assume no
.\" responsibility for errors or omissions, or for damages resulting from
.\" the use of the information contained herein. The author(s) may not
.\" have taken the same level of care in the production of this manual,
.\" which is licensed free of charge, as they might when working
.\" professionally.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
.\"
.\" Created Sun Aug 6 1995 Thomas K. Dyas <tdyas@eden.rutgers.edu>
.\"
.TH SETFSUID 2 "6 August 1995" "Linux 1.3.15" "Linux Programmer's Manual"
.SH NAME
setfsuid \- set user identity used for file system checks
.SH SYNOPSIS
.BI "int setfsuid(uid_t " fsuid )
.SH DESCRIPTION
.B setfsuid
sets the user ID that the Linux kernel uses to check for all accesses
to the file system. Normally, the value of
.I fsuid
will shadow the value of the effective user ID. In fact, whenever the
effective user ID is changed,
.I fsuid
will also be changed to new value of effective user ID.
An explict call to
.B 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.
.B setfsuid
will only succeed if the caller is the superuser or if
.I fsuid
matches either the real user ID, effective user ID, saved set-user-ID, or
the current value of
.IR fsuid .
.SH "RETURN VALUE"
On success, the previous value of
.I fsuid
is returned. On error, the current value of
.I fsuid
is returned.
.SH "CONFORMING TO"
.B setfsuid
is Linux specific and should not be used in programs intended to be portable.
.SH BUGS
No error messages of any kind are returned to the caller. At the very
least,
.B EPERM
should be returned when the call fails.
.SH "SEE ALSO"
.BR setfsgid (2)
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