1 .\" Copyright (c) 1992 Drew Eckhardt (drew@cs.colorado.edu), March 28, 1992
2 .\" and Copyright (C) 2006, 2014 Michael Kerrisk
4 .\" %%%LICENSE_START(VERBATIM)
5 .\" Permission is granted to make and distribute verbatim copies of this
6 .\" manual provided the copyright notice and this permission notice are
7 .\" preserved on all copies.
9 .\" Permission is granted to copy and distribute modified versions of this
10 .\" manual under the conditions for verbatim copying, provided that the
11 .\" entire resulting derived work is distributed under the terms of a
12 .\" permission notice identical to this one.
14 .\" Since the Linux kernel and libraries are constantly changing, this
15 .\" manual page may be incorrect or out-of-date. The author(s) assume no
16 .\" responsibility for errors or omissions, or for damages resulting from
17 .\" the use of the information contained herein. The author(s) may not
18 .\" have taken the same level of care in the production of this manual,
19 .\" which is licensed free of charge, as they might when working
22 .\" Formatted or processed versions of this manual, if unaccompanied by
23 .\" the source, must acknowledge the copyright and authors of this work.
26 .\" Modified by Michael Haardt <michael@moria.de>
27 .\" Modified 1993-07-21 by Rik Faith <faith@cs.unc.edu>
28 .\" Modified 1997-01-12 by Michael Haardt
29 .\" <michael@cantor.informatik.rwth-aachen.de>: NFS details
30 .\" Modified 2004-06-23 by Michael Kerrisk <mtk.manpages@gmail.com>
32 .TH CHMOD 2 2017-09-15 "Linux" "Linux Programmer's Manual"
34 chmod, fchmod, fchmodat \- change permissions of a file
37 .B #include <sys/stat.h>
39 .BI "int chmod(const char *" pathname ", mode_t " mode );
40 .BI "int fchmod(int " fd ", mode_t " mode );
42 .BR "#include <fcntl.h>" " /* Definition of AT_* constants */"
43 .B #include <sys/stat.h>
45 .BI "int fchmodat(int " dirfd ", const char *" pathname ", mode_t " \
46 mode ", int " flags );
50 Feature Test Macro Requirements for glibc (see
51 .BR feature_test_macros (7)):
57 _POSIX_C_SOURCE >= 199309L
58 .\" || (_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED)
62 _BSD_SOURCE || _POSIX_C_SOURCE
64 _BSD_SOURCE || _XOPEN_SOURCE >= 500
65 || _POSIX_C_SOURCE >= 200809L
66 Glibc 2.11 and earlier:
67 _BSD_SOURCE || _XOPEN_SOURCE >= 500
68 .\" || (_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED)
74 _POSIX_C_SOURCE >= 200809L
83 system calls change a files mode bits.
84 (The file mode consists of the file permission bits plus the set-user-ID,
85 set-group-ID, and sticky bits.)
86 These system calls differ only in how the file is specified:
89 changes the mode of the file specified whose pathname is given in
91 which is dereferenced if it is a symbolic link.
94 changes the mode of the file referred to by the open file descriptor
97 The new file mode is specified in
99 which is a bit mask created by ORing together zero or
100 more of the following:
102 .BR S_ISUID " (04000)"
103 set-user-ID (set process effective user ID on
106 .BR S_ISGID " (02000)"
107 set-group-ID (set process effective group ID on
109 mandatory locking, as described in
111 take a new file's group from parent directory, as described in
116 .BR S_ISVTX " (01000)"
117 sticky bit (restricted deletion flag, as described in
120 .BR S_IRUSR " (00400)"
123 .BR S_IWUSR " (00200)"
126 .BR S_IXUSR " (00100)"
127 execute/search by owner ("search" applies for directories,
128 and means that entries within the directory can be accessed)
130 .BR S_IRGRP " (00040)"
133 .BR S_IWGRP " (00020)"
136 .BR S_IXGRP " (00010)"
137 execute/search by group
139 .BR S_IROTH " (00004)"
142 .BR S_IWOTH " (00002)"
145 .BR S_IXOTH " (00001)"
146 execute/search by others
148 The effective UID of the calling process must match the owner of the file,
149 or the process must be privileged (Linux: it must have the
153 If the calling process is not privileged (Linux: does not have the
155 capability), and the group of the file does not match
156 the effective group ID of the process or one of its
157 supplementary group IDs, the
159 bit will be turned off,
160 but this will not cause an error to be returned.
162 As a security measure, depending on the filesystem,
163 the set-user-ID and set-group-ID execution bits
164 may be turned off if a file is written.
165 (On Linux, this occurs if the writing process does not have the
168 On some filesystems, only the superuser can set the sticky bit,
169 which may have a special meaning.
170 For the sticky bit, and for set-user-ID and set-group-ID bits on
174 On NFS filesystems, restricting the permissions will immediately influence
175 already open files, because the access control is done on the server, but
176 open files are maintained by the client.
177 Widening the permissions may be
178 delayed for other clients if attribute caching is enabled on them.
184 system call operates in exactly the same way as
186 except for the differences described here.
188 If the pathname given in
190 is relative, then it is interpreted relative to the directory
191 referred to by the file descriptor
193 (rather than relative to the current working directory of
194 the calling process, as is done by
196 for a relative pathname).
206 is interpreted relative to the current working
207 directory of the calling process (like
217 can either be 0, or include the following flag:
219 .B AT_SYMLINK_NOFOLLOW
222 is a symbolic link, do not dereference it:
223 instead operate on the link itself.
224 This flag is not currently implemented.
228 for an explanation of the need for
231 On success, zero is returned.
232 On error, \-1 is returned, and
234 is set to indicate the error.
236 Depending on the filesystem,
237 errors other than those listed below can be returned.
239 The more general errors for
244 Search permission is denied on a component of the path prefix.
246 .BR path_resolution (7).)
250 points outside your accessible address space.
253 An I/O error occurred.
256 Too many symbolic links were encountered in resolving
264 The file does not exist.
267 Insufficient kernel memory was available.
270 A component of the path prefix is not a directory.
273 The effective UID does not match the owner of the file,
274 and the process is not privileged (Linux: it does not have the
279 The file is marked immutable or append-only.
281 .BR ioctl_iflags (2).)
284 The named file resides on a read-only filesystem.
286 The general errors for
304 The same errors that occur for
308 The following additional errors can occur for
313 is not a valid file descriptor.
316 Invalid flag specified in
323 is a file descriptor referring to a file other than a directory.
328 .BR AT_SYMLINK_NOFOLLOW ,
329 which is not supported.
332 was added to Linux in kernel 2.6.16;
333 library support was added to glibc in version 2.4.
337 4.4BSD, SVr4, POSIX.1-2001i, POSIX.1-2008.
342 .SS C library/kernel differences
345 wrapper function implements the POSIX-specified
346 interface described in this page.
347 This interface differs from the underlying Linux system call, which does
353 On older kernels where
355 is unavailable, the glibc wrapper function falls back to the use of
359 is a relative pathname,
360 glibc constructs a pathname based on the symbolic link in
362 that corresponds to the
372 .BR path_resolution (7),