名称

       chmod - 改变文件模式比特位

概述

       chmod [选项]... 模式[,模式]... 文件列表...
       chmod [选项]... 八进制模式字符串 文件列表...
       chmod [选项]... --reference=参考文件 文件列表...

描述

       本手册页记录了 GNU 版本的 chmod。chmod 根据给定 模式改变每个给出文件的模式比特位，其模式字
       符串既可以是修改目标的符号表示，也可以是用一个八进制数字来代表新的模式比特位形式。

       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 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 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.

SETUID 和 SETGID 比特位

       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, or leading = like 00755 , or =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.

选项

       将每个文件的权限模式变更至指定模式。使用  --reference 选项时，把指定文件的模式设置为与参考
       文件相同。

       -c, --changes
              类似 verbose 选项，但只在做出修改时进行报告

       -f, --silent, --quiet
              隐藏大多数错误信息

       -v, --verbose
              对每一个处理的文件输出诊断信息

       --no-preserve-root
              不要对“/”特别对待（默认）

       --preserve-root
              不要在“/”下进行递归操作

       --reference=参考文件
              使用参考文件的模式作为具体模式值

       -R, --recursive
              递归修改文件和目录

       --help 显示此帮助信息并退出

       --version
              显示版本信息并退出

       每个模式字符串都应该匹配如下格式："[ugoa]*([-+=]([rwxXst]*|[ugo]))+|[-+=][0-7]+"。

作者

       由 David MacKenzie 和 Jim Meyering 编写。

报告错误

       GNU coreutils 的在线帮助： <https://www.gnu.org/software/coreutils/>
       请向 <https://translationproject.org/team/zh_CN.html> 报告翻译错误。

版权

       Copyright © 2020 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.

参见

       chmod(2)

       完整文档请见： <https://www.gnu.org/software/coreutils/chmod>
       或者在本地使用： info '(coreutils) chmod invocation'

跋

       本页面中文版由中文 man 手册页计划提供。
       中文 man 手册页计划：https://github.com/man-pages-zh/manpages-zh