chmod(1)

1CHMOD(1)                         User Commands                        CHMOD(1)
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NAME

6       chmod - change file mode bits
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SYNOPSIS

9       chmod [OPTION]... MODE[,MODE]... FILE...
10       chmod [OPTION]... OCTAL-MODE FILE...
11       chmod [OPTION]... --reference=RFILE FILE...
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DESCRIPTION

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
16       either a symbolic representation of changes to make, or an octal number
17       representing the bit pattern for the new mode bits.
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19       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.
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24       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, but
28       bits that are set in the umask are not affected.
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30       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
33       except that a directory's unmentioned set user and group  ID  bits  are
34       not affected.
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36       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).
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47       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, except that if  the  first  digit  is  omitted,  a
50       directory's  set  user  and  group ID bits are not affected.  The first
51       digit selects the set user ID (4) and set group ID (2)  and  restricted
52       deletion  or  sticky  (1) attributes.  The second digit selects permis‐
53       sions for the user who owns the file: read (4), write (2), and  execute
54       (1); the third selects permissions for other users in the file's group,
55       with the same values; and the fourth for other users not in the  file's
56       group, with the same values.
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58       chmod never changes the permissions of symbolic links; the chmod system
59       call cannot change their permissions.  This is not a problem since  the
60       permissions  of  symbolic links are never used.  However, for each sym‐
61       bolic link listed on the command line, chmod changes the permissions of
62       the pointed-to file.  In contrast, chmod ignores symbolic links encoun‐
63       tered during recursive directory traversals.
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RESTRICTED DELETION FLAG OR STICKY BIT

66       The restricted deletion flag or sticky  bit  is  a  single  bit,  whose
67       interpretation  depends on the file type.  For directories, it prevents
68       unprivileged users from removing or renaming a file  in  the  directory
69       unless  they  own  the  file  or  the  directory;  this  is  called the
70       restricted deletion flag for the directory, and is  commonly  found  on
71       world-writable  directories like /tmp.  For regular files on some older
72       systems, the bit saves the program's text image on the swap  device  so
73       it will load more quickly when run; this is called the sticky bit.
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OPTIONS

76       Change the mode of each FILE to MODE.
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78       -c, --changes
79              like verbose but report only when a change is made
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81       --no-preserve-root
82              do not treat `/' specially (the default)
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84       --preserve-root
85              fail to operate recursively on `/'
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87       -f, --silent, --quiet
88              suppress most error messages
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90       -v, --verbose
91              output a diagnostic for every file processed
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93       --reference=RFILE
94              use RFILE's mode instead of MODE values
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96       -R, --recursive
97              change files and directories recursively
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99       --help display this help and exit
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101       --version
102              output version information and exit
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104       Each MODE is of the form `[ugoa]*([-+=]([rwxXst]*|[ugo]))+'.
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AUTHOR

107       Written by David MacKenzie and Jim Meyering.
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REPORTING BUGS

110       Report bugs to <bug-coreutils@gnu.org>.
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COPYRIGHT

113       Copyright © 2007 Free Software Foundation, Inc.
114       This  is  free  software.   You may redistribute copies of it under the
115       terms      of      the      GNU      General       Public       License
116       <http://www.gnu.org/licenses/gpl.html>.   There  is NO WARRANTY, to the
117       extent permitted by law.
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