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chmod - 改變檔案模式位元位
chmod [選項]... 模式[,模式]... 檔案列表... chmod [選項]... 八進位制模式字串 檔案列表... chmod [選項]... --reference=參考檔案 檔案列表...
本手冊頁記錄了 GNU 版本的 chmod。chmod 根據給定 模式改變每個給出檔案的模式位元位，其模式字 串既可以是修改目標的符號表示，也可以是用一個八進位制數字來代表新的模式位元位形式。 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 位元位
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.
將每個檔案的許可權模式變更至指定模式。使用 --reference 選項時，把指定檔案的模式設定為與參 考檔案相同。 -c, --changes 類似 verbose 選項，但只在做出修改時進行報告 -f, --silent, --quiet 隱藏大多數錯誤資訊 -v, --verbose 對每一個處理的檔案輸出診斷資訊 --no-preserve-root 不要對“/”特別對待（預設） --preserve-root 不要在“/”下進行遞迴操作 --reference=參考檔案 使用參考檔案的模式作為具體模式值 -R, --recursive 遞迴修改檔案和目錄 --help 顯示此幫助資訊並退出 --version 顯示版本資訊並退出 每個模式字串都應該匹配如下格式："[ugoa]*([-+=]([rwxXst]*|[ugo]))+|[-+=][0-7]+"。
由 David MacKenzie 和 Jim Meyering 編寫。
GNU coreutils 的線上幫助： <https://www.gnu.org/software/coreutils/> 請向 <https://translationproject.org/team/zh_CN.html> 報告翻譯錯誤。
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.
chmod(2) 完整文件請見： <https://www.gnu.org/software/coreutils/chmod> 或者在本地使用： info '(coreutils) chmod invocation'
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