1 .\" Copyright (C) 1995, Thomas K. Dyas <tdyas@eden.rutgers.edu>
3 .\" Permission is granted to make and distribute verbatim copies of this
4 .\" manual provided the copyright notice and this permission notice are
5 .\" preserved on all copies.
7 .\" Permission is granted to copy and distribute modified versions of this
8 .\" manual under the conditions for verbatim copying, provided that the
9 .\" entire resulting derived work is distributed under the terms of a
10 .\" permission notice identical to this one.
12 .\" Since the Linux kernel and libraries are constantly changing, this
13 .\" manual page may be incorrect or out-of-date. The author(s) assume no
14 .\" responsibility for errors or omissions, or for damages resulting from
15 .\" the use of the information contained herein. The author(s) may not
16 .\" have taken the same level of care in the production of this manual,
17 .\" which is licensed free of charge, as they might when working
20 .\" Formatted or processed versions of this manual, if unaccompanied by
21 .\" the source, must acknowledge the copyright and authors of this work.
23 .\" Created 1995-08-06 Thomas K. Dyas <tdyas@eden.rutgers.edu>
24 .\" Modified 2000-07-01 aeb
25 .\" Modified 2002-07-23 aeb
26 .\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com>
27 .\" Added notes on capability requirements
29 .TH SETFSUID 2 2008-12-05 "Linux" "Linux Programmer's Manual"
31 setfsuid \- set user identity used for file system checks
33 .B #include <unistd.h>
34 /* glibc uses <sys/fsuid.h> */
36 .BI "int setfsuid(uid_t " fsuid );
40 sets the user ID that the Linux kernel uses to check for all accesses
42 Normally, the value of
44 will shadow the value of the effective user ID.
46 effective user ID is changed,
48 will also be changed to the new value of the effective user ID.
54 are usually only used by programs such as the Linux NFS server that
55 need to change what user and group ID is used for file access without a
56 corresponding change in the real and effective user and group IDs.
57 A change in the normal user IDs for a program such as the NFS server
58 is a security hole that can expose it to unwanted signals.
62 will only succeed if the caller is the superuser or if
64 matches either the real user ID, effective user ID, saved set-user-ID, or
68 On success, the previous value of
71 On error, the current value of
75 This system call is present in Linux since version 1.2.
76 .\" This system call is present since Linux 1.1.44
77 .\" and in libc since libc 4.7.6.
80 is Linux-specific and should not be used in programs intended
83 When glibc determines that the argument is not a valid user ID,
84 it will return \-1 and set \fIerrno\fP to
89 Note that at the time this system call was introduced, a process
90 could send a signal to a process with the same effective user ID.
91 Today signal permission handling is slightly different.
93 No error messages of any kind are returned to the caller.
97 should be returned when the call fails (because the caller lacks the
103 .BR capabilities (7),