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1 | .\" Copyright (C) 1995, Thomas K. Dyas <tdyas@eden.rutgers.edu> |
2 | .\" | |
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. | |
6 | .\" | |
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. | |
c13182ef | 11 | .\" |
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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13 | .\" manual page may be incorrect or out-of-date.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 | |
18 | .\" professionally. | |
c13182ef | 19 | .\" |
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20 | .\" Formatted or processed versions of this manual, if unaccompanied by |
21 | .\" the source, must acknowledge the copyright and authors of this work. | |
22 | .\" | |
23 | .\" Created 1995-08-06 Thomas K. Dyas <tdyas@eden.rutgers.edu> | |
24 | .\" Modified 2000-07-01 aeb | |
25 | .\" Modified 2002-07-23 aeb | |
c11b1abf | 26 | .\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com> |
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27 | .\" Added notes on capability requirements |
28 | .\" | |
d9343c5c | 29 | .TH SETFSGID 2 2004-05-27 "Linux" "Linux Programmer's Manual" |
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30 | .SH NAME |
31 | setfsgid \- set group identity used for file system checks | |
32 | .SH SYNOPSIS | |
33 | .B #include <unistd.h> | |
34 | /* glibc uses <sys/fsuid.h> */ | |
35 | .sp | |
36 | .BI "int setfsgid(uid_t " fsgid ); | |
37 | .SH DESCRIPTION | |
38 | The system call | |
e511ffb6 | 39 | .BR setfsgid () |
fea681da | 40 | sets the group ID that the Linux kernel uses to check for all accesses |
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41 | to the file system. |
42 | Normally, the value of | |
fea681da | 43 | .I fsgid |
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44 | will shadow the value of the effective group ID. |
45 | In fact, whenever the | |
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46 | effective group ID is changed, |
47 | .I fsgid | |
48 | will also be changed to the new value of the effective group ID. | |
49 | ||
50 | Explicit calls to | |
0bfa087b | 51 | .BR setfsuid (2) |
fea681da | 52 | and |
e511ffb6 | 53 | .BR setfsgid () |
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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. (But see below.) | |
59 | ||
e511ffb6 | 60 | .BR setfsgid () |
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61 | will only succeed if the caller is the superuser or if |
62 | .I fsgid | |
63 | matches either the real group ID, effective group ID, | |
64 | saved set-group-ID, or the current value of | |
65 | .IR fsgid . | |
66 | .SH "RETURN VALUE" | |
67 | On success, the previous value of | |
68 | .I fsgid | |
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69 | is returned. |
70 | On error, the current value of | |
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71 | .I fsgid |
72 | is returned. | |
73 | .SH "CONFORMING TO" | |
e511ffb6 | 74 | .BR setfsgid () |
8382f16d | 75 | is Linux-specific and should not be used in programs intended |
97c1eac8 | 76 | to be portable. |
fea681da | 77 | It is present since Linux 1.1.44 and in libc since libc 4.7.6. |
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78 | .SH NOTES |
79 | When glibc determines that the argument is not a valid group ID, | |
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80 | it will return \-1 and set \fIerrno\fP to |
81 | .B EINVAL | |
82 | without attempting | |
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83 | the system call. |
84 | .LP | |
85 | Note that at the time this system call was introduced, a process | |
86 | could send a signal to a process with the same effective user ID. | |
87 | Today signal permission handling is slightly different. | |
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88 | .SH BUGS |
89 | No error messages of any kind are returned to the caller. | |
90 | At the very | |
91 | least, | |
92 | .B EPERM | |
93 | should be returned when the call fails (because the caller lacks the | |
94 | .B CAP_SETGID | |
95 | capability). | |
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96 | .SH "SEE ALSO" |
97 | .BR kill (2), | |
98 | .BR setfsuid (2), | |
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99 | .BR capabilities (7), |
100 | .BR credentials (7) |