# Bash 的 chmod 命令

chmod [OPTION]... MODE[,MODE]... FILE...

$ chmod u=rwx file  # 对所有者设为可读、可写、可执行
$ chmod g+rx file   # 对所属组添加读取、执行权限
$ chmod o= file     # 对其他人设为没有任何权限

$ chmod u+s file    # 添加 setuid
$ chmod g+s file    # 添加 setgid
$ chmod u-s file    # 取消 setuid
$ chmod g-s file    # 取消 setgid

$ chmod +t dir      # 添加粘滞位
$ chmod -t dir      # 取消粘滞位

$ chmod 750 file    # 所有者=7 所属组=5 其他=0
$ chmod 7750 dir    # 特殊=7 所有者=7 所属组=5 其他=0

CHMOD(1)                         User Commands                        CHMOD(1)

NAME
       chmod - change file mode bits

SYNOPSIS
       chmod [OPTION]... MODE[,MODE]... FILE...
       chmod [OPTION]... OCTAL-MODE FILE...
       chmod [OPTION]... --reference=RFILE FILE...

DESCRIPTION
       This manual page documents the GNU version of chmod.  chmod changes the
       file  mode  bits of each given file according to mode, which can be ei‐
       ther a symbolic representation of changes to make, or an  octal  number
       representing the bit pattern for the new mode bits.

       The  format  of a symbolic mode is [ugoa...][[-+=][perms...]...], where
       perms is either zero or more letters from the set rwxXst, or  a  single
       letter  from  the set ugo.  Multiple symbolic modes can be given, sepa‐
       rated by commas.

       A combination of the letters ugoa controls which users' access  to  the
       file  will  be  changed:  the  user who owns it (u), other users in the
       file's group (g), other users not in the file's group (o), or all users
       (a).  If none of these are given, the effect is as if (a)  were  given,
       but bits that are set in the umask are not affected.

       The  operator  +  causes the selected file mode bits to be added to the
       existing file mode bits of each file; - causes them to be removed;  and
       = causes them to be added and causes unmentioned bits to be removed ex‐
       cept  that a directory's unmentioned set user and group ID bits are not
       affected.

       The letters rwxXst select file mode bits for the affected  users:  read
       (r), write (w), execute (or search for directories) (x), execute/search
       only  if  the file is a directory or already has execute permission for
       some user (X), set user or group ID on execution (s), restricted  dele‐
       tion  flag or sticky bit (t).  Instead of one or more of these letters,
       you can specify exactly one of the letters ugo: the permissions granted
       to the user who owns the file (u), the  permissions  granted  to  other
       users  who  are  members  of  the file's group (g), and the permissions
       granted to users that are in neither of the  two  preceding  categories
       (o).

       A  numeric  mode  is  from  one  to four octal digits (0-7), derived by
       adding up the bits with values 4, 2, and 1.  Omitted digits are assumed
       to be leading zeros.  The first digit selects the set user ID  (4)  and
       set group ID (2) and restricted deletion or sticky (1) attributes.  The
       second  digit  selects permissions for the user who owns the file: read
       (4), write (2), and execute (1);  the  third  selects  permissions  for
       other  users  in the file's group, with the same values; and the fourth
       for other users not in the file's group, with the same values.

       chmod never changes the permissions of symbolic links; the chmod system
       call cannot change their permissions.  This is not a problem since  the
       permissions  of  symbolic links are never used.  However, for each sym‐
       bolic link listed on the command line, chmod changes the permissions of
       the pointed-to file.  In contrast, chmod ignores symbolic links encoun‐
       tered during recursive directory traversals.

SETUID AND SETGID BITS
       chmod clears the set-group-ID bit of a regular file if the file's group
       ID does not match the user's effective group ID or one  of  the  user's
       supplementary  group  IDs,  unless the user has appropriate privileges.
       Additional restrictions may cause the set-user-ID and set-group-ID bits
       of MODE or RFILE to be ignored.  This behavior depends  on  the  policy
       and  functionality of the underlying chmod system call.  When in doubt,
       check the underlying system behavior.

       For directories chmod preserves set-user-ID and set-group-ID  bits  un‐
       less  you  explicitly specify otherwise.  You can set or clear the bits
       with symbolic modes like u+s and g-s.  To clear these bits for directo‐
       ries with a numeric mode  requires  an  additional  leading  zero  like
       00755, leading minus like -6000, or leading equals like =755.

RESTRICTED DELETION FLAG OR STICKY BIT
       The  restricted  deletion flag or sticky bit is a single bit, whose in‐
       terpretation depends on the file type.  For  directories,  it  prevents
       unprivileged  users  from  removing or renaming a file in the directory
       unless they own the file or the  directory;  this  is  called  the  re‐
       stricted  deletion  flag  for  the  directory, and is commonly found on
       world-writable directories like /tmp.  For regular files on some  older
       systems,  the  bit saves the program's text image on the swap device so
       it will load more quickly when run; this is called the sticky bit.

OPTIONS
       Change the mode of each FILE to MODE.   With  --reference,  change  the
       mode of each FILE to that of RFILE.

       -c, --changes
              like verbose but report only when a change is made

       -f, --silent, --quiet
              suppress most error messages

       -v, --verbose
              output a diagnostic for every file processed

       --no-preserve-root
              do not treat '/' specially (the default)

       --preserve-root
              fail to operate recursively on '/'

       --reference=RFILE
              use  RFILE's  mode  instead of specifying MODE values.  RFILE is
              always dereferenced if a symbolic link.

       -R, --recursive
              change files and directories recursively

       --help display this help and exit

       --version
              output version information and exit

       Each          MODE          is          of           the           form
       '[ugoa]*([-+=]([rwxXst]*|[ugo]))+|[-+=][0-7]+'.

AUTHOR
       Written by David MacKenzie and Jim Meyering.

REPORTING BUGS
       GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
       Report any translation bugs to <https://translationproject.org/team/>

COPYRIGHT
       Copyright  ©  2023  Free Software Foundation, Inc.  License GPLv3+: GNU
       GPL version 3 or later <https://gnu.org/licenses/gpl.html>.
       This is free software: you are free  to  change  and  redistribute  it.
       There is NO WARRANTY, to the extent permitted by law.

SEE ALSO
       chmod(2)

       Full documentation <https://www.gnu.org/software/coreutils/chmod>
       or available locally via: info '(coreutils) chmod invocation'

GNU coreutils 9.4                 April 2024                          CHMOD(1)