1CHMOD(1) User Commands CHMOD(1)
2
6 chmod - change file mode bits
7
9 chmod [OPTION]... MODE[,MODE]... FILE...
10 chmod [OPTION]... OCTAL-MODE FILE...
11 chmod [OPTION]... --reference=RFILE FILE...
12
14 This manual page documents the GNU version of chmod. chmod changes the
15 file mode bits of each given file according to mode, which can be ei‐
16 ther a symbolic representation of changes to make, or an octal number
17 representing the bit pattern for the new mode bits.
18 The format of a symbolic mode is [ugoa...][[-+=][perms...]...], where
20 perms is either zero or more letters from the set rwxXst, or a single
21 letter from the set ugo. Multiple symbolic modes can be given, sepa‐
22 rated by commas.
23 A combination of the letters ugoa controls which users' access to the
25 file will be changed: the user who owns it (u), other users in the
26 file's group (g), other users not in the file's group (o), or all users
27 (a). If none of these are given, the effect is as if (a) were given,
28 but bits that are set in the umask are not affected.
29 The operator + causes the selected file mode bits to be added to the
31 existing file mode bits of each file; - causes them to be removed; and
32 = causes them to be added and causes unmentioned bits to be removed ex‐
33 cept that a directory's unmentioned set user and group ID bits are not
34 affected.
35 The letters rwxXst select file mode bits for the affected users: read
37 (r), write (w), execute (or search for directories) (x), execute/search
38 only if the file is a directory or already has execute permission for
39 some user (X), set user or group ID on execution (s), restricted dele‐
40 tion flag or sticky bit (t). Instead of one or more of these letters,
41 you can specify exactly one of the letters ugo: the permissions granted
42 to the user who owns the file (u), the permissions granted to other
43 users who are members of the file's group (g), and the permissions
44 granted to users that are in neither of the two preceding categories
45 (o).
46 A numeric mode is from one to four octal digits (0-7), derived by
48 adding up the bits with values 4, 2, and 1. Omitted digits are assumed
49 to be leading zeros. The first digit selects the set user ID (4) and
50 set group ID (2) and restricted deletion or sticky (1) attributes. The
51 second digit selects permissions for the user who owns the file: read
52 (4), write (2), and execute (1); the third selects permissions for
53 other users in the file's group, with the same values; and the fourth
54 for other users not in the file's group, with the same values.
55 chmod never changes the permissions of symbolic links; the chmod system
57 call cannot change their permissions. This is not a problem since the
58 permissions of symbolic links are never used. However, for each sym‐
59 bolic link listed on the command line, chmod changes the permissions of
60 the pointed-to file. In contrast, chmod ignores symbolic links encoun‐
61 tered during recursive directory traversals.
62
64 chmod clears the set-group-ID bit of a regular file if the file's group
65 ID does not match the user's effective group ID or one of the user's
66 supplementary group IDs, unless the user has appropriate privileges.
67 Additional restrictions may cause the set-user-ID and set-group-ID bits
68 of MODE or RFILE to be ignored. This behavior depends on the policy
69 and functionality of the underlying chmod system call. When in doubt,
70 check the underlying system behavior.
71 For directories chmod preserves set-user-ID and set-group-ID bits un‐
73 less you explicitly specify otherwise. You can set or clear the bits
74 with symbolic modes like u+s and g-s. To clear these bits for directo‐
75 ries with a numeric mode requires an additional leading zero like
76 00755, leading minus like -6000, or leading equals like =755.
77
79 The restricted deletion flag or sticky bit is a single bit, whose in‐
80 terpretation depends on the file type. For directories, it prevents
81 unprivileged users from removing or renaming a file in the directory
82 unless they own the file or the directory; this is called the re‐
83 stricted deletion flag for the directory, and is commonly found on
84 world-writable directories like /tmp. For regular files on some older
85 systems, the bit saves the program's text image on the swap device so
86 it will load more quickly when run; this is called the sticky bit.
87
89 Change the mode of each FILE to MODE. With --reference, change the
90 mode of each FILE to that of RFILE.
91 -c, --changes
93 like verbose but report only when a change is made
94 -f, --silent, --quiet
96 suppress most error messages
97 -v, --verbose
99 output a diagnostic for every file processed
100 --no-preserve-root
102 do not treat '/' specially (the default)
103 --preserve-root
105 fail to operate recursively on '/'
106 --reference=RFILE
108 use RFILE's mode instead of specifying MODE values. RFILE is
109 always dereferenced if a symbolic link.
110 -R, --recursive
112 change files and directories recursively
113 --help display this help and exit
115 --version
117 output version information and exit
118 Each MODE is of the form
120 '[ugoa]*([-+=]([rwxXst]*|[ugo]))+|[-+=][0-7]+'.
121
123 Written by David MacKenzie and Jim Meyering.
124
126 GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
127 Report any translation bugs to <https://translationproject.org/team/>
128
130 Copyright © 2023 Free Software Foundation, Inc. License GPLv3+: GNU
131 GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
132 This is free software: you are free to change and redistribute it.
133 There is NO WARRANTY, to the extent permitted by law.
134
136 chmod(2)
137 Full documentation <https://www.gnu.org/software/coreutils/chmod>
139 or available locally via: info '(coreutils) chmod invocation'
140GNU coreutils 9.3 September 2023 CHMOD(1)