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命令用途

chmod（change mode）是 Linux/Unix 系统中用来更改文件或目录权限的命令。它可以设置文件或目录的读、写、执行权限，并且可以指定权限的设置方式，通常用于控制文件的访问权限。

常用用法示例

  1. 给文件添加执行权限

    1
    chmod +x script.sh

    这条命令给 script.sh 文件添加了执行权限。执行后，script.sh 文件将变为可执行文件。

  2. 去除文件的写权限

    1
    chmod -w file.txt

    去除了 file.txt 文件的写权限，执行后文件内容将无法编辑。

  3. 设置文件权限为 755

    1
    chmod 755 program

    将 program 文件的权限设置为 rwxr-xr-x，即所有者可以读、写、执行，组用户和其他用户可以读取和执行。

  4. 设置文件权限为 644

    1
    chmod 644 document.txt

    将 document.txt 文件的权限设置为 rw-r–r–，即所有者可以读、写，组用户和其他用户只能读取。

  5. 递归更改目录及其子文件权限

    1
    chmod -R 755 /path/to/directory

    使用 -R 选项递归地将 /path/to/directory 目录及其下所有文件的权限设置为 rwxr-xr-x。

  6. 给所有者和组用户添加写权限

    1
    chmod ug+w file.txt

    给 file.txt 文件的所有者和组用户添加写权限。此命令执行后，所有者和组用户都能修改文件内容。

  7. 给文件去除执行权限

    1
    chmod -x script.sh

    去除 script.sh 文件的执行权限，执行后文件将不再可以作为可执行文件运行。

  8. 通过符号模式设置权限

    1
    chmod u=rwx,g=rx,o=r myfile

    通过符号模式设置 myfile 文件的权限为所有者可读、写、执行，组用户可读、执行，其他用户只能读取。

常用参数选项

  • -R, –recursive
    递归地更改目录及其所有子目录和文件的权限。例如，chmod -R 755 /path/to/directory。

  • -v, –verbose
    显示权限更改的详细信息。使用该选项后，每次权限更改都会在终端中输出提示信息。

  • -c, –changes
    仅在权限更改时输出信息。与 -v 类似，但只会在更改发生时打印出变更内容。

  • -f, –silent, –quiet
    忽略所有错误消息。如果操作失败，系统不会显示错误信息。

  • –no-dereference
    不改变符号链接的权限，仅影响文件本身。

  • –reference=file
    将 file 文件的权限复制到目标文件。例如，chmod –reference=example.txt myfile 会将 example.txt 的权限应用到 myfile 上。

  • u, g, o
    用于指定文件的所有者（user）、组（group）和其他用户（other）。例如，chmod u+x file 表示给所有者添加执行权限。

  • +/-/
    用于增加、去除或设置权限。例如，chmod +x file 表示添加执行权限，chmod -x file 表示去除执行权限，chmod =r file 表示只保留读取权限。

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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 either 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, separated 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 except 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 deletion 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 doesn't change the permissions of symbolic links; the chmod
       system call cannot change their permissions on most systems, and
       most systems ignore permissions of symbolic links.  However, for
       each symbolic link listed on the command line, chmod changes the
       permissions of the pointed-to file.  In contrast, chmod ignores
       symbolic links encountered during recursive directory traversals.
       Options that modify this behavior are described in the OPTIONS
       section.

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
       unless 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 directories 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
       interpretation 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 restricted 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

       --dereference
              affect the referent of each symbolic link, rather than the
              symbolic link itself

       -h, --no-dereference
              affect each symbolic link, rather than the referent

       --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

       The following options modify how a hierarchy is traversed when the
       -R option is also specified.  If more than one is specified, only
       the final one takes effect. -H is the default.

       -H     if a command line argument is a symbolic link to a
              directory, traverse it

       -L     traverse every symbolic link to a directory encountered

       -P     do not traverse any symbolic links

       --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 © 2025 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'

COLOPHON 

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       manipulation utilities) project.  Information about the project
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       have a bug report for this manual page, see
       ⟨http://www.gnu.org/software/coreutils/⟩.  This page was obtained
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       ⟨http://ftp.gnu.org/gnu/coreutils/⟩ on 2024-02-02.  If you
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