1 .\" Copyright (C) 1995, Thomas K. Dyas <tdyas@eden.rutgers.edu>
3 .\" %%%LICENSE_START(VERBATIM)
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13 .\" Since the Linux kernel and libraries are constantly changing, this
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25 .\" Created 1995-08-06 Thomas K. Dyas <tdyas@eden.rutgers.edu>
26 .\" Modified 2000-07-01 aeb
27 .\" Modified 2002-07-23 aeb
28 .\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com>
29 .\" Added notes on capability requirements
31 .TH SETFSGID 2 2010-11-22 "Linux" "Linux Programmer's Manual"
33 setfsgid \- set group identity used for file system checks
35 .B #include <unistd.h>
36 /* glibc uses <sys/fsuid.h> */
38 .BI "int setfsgid(uid_t " fsgid );
42 sets the group ID that the Linux kernel uses to check for all accesses
44 Normally, the value of
46 will shadow the value of the effective group ID.
48 effective group ID is changed,
50 will also be changed to the new value of the effective group ID.
56 are usually used only by programs such as the Linux NFS server that
57 need to change what user and group ID is used for file access without a
58 corresponding change in the real and effective user and group IDs.
59 A change in the normal user IDs for a program such as the NFS server
60 is a security hole that can expose it to unwanted signals.
64 will succeed only if the caller is the superuser or if
66 matches either the real group ID, effective group ID,
67 saved set-group-ID, or the current value of
70 On success, the previous value of
73 On error, the current value of
77 This system call is present in Linux since version 1.2.
78 .\" This system call is present since Linux 1.1.44
79 .\" and in libc since libc 4.7.6.
82 is Linux-specific and should not be used in programs intended
85 When glibc determines that the argument is not a valid group ID,
86 it will return \-1 and set \fIerrno\fP to
91 Note that at the time this system call was introduced, a process
92 could send a signal to a process with the same effective user ID.
93 Today signal permission handling is slightly different.
97 system call supported only 16-bit group IDs.
98 Subsequently, Linux 2.4 added
100 supporting 32-bit IDs.
103 wrapper function transparently deals with the variation across kernel versions.
105 No error messages of any kind are returned to the caller.
109 should be returned when the call fails (because the caller lacks the
115 .BR capabilities (7),