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chmod指令帮助手册

chmod指令用于设置权限，帮助手册如下。

CHMOD(1)                                                 User Commands                                                 CHMOD(1)
N***ME
       chmod - change file mode bits
SYNOPSIS
       chmod [OPTION]... MODE[,MODE]... FILE...
       chmod [OPTION]... OCT***L-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.
       *** 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 unmen‐
       tioned 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  directo‐
       ries)  (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).
       ***  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 encoun‐
       tered during recursive directory traversals.
SETUID ***ND 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.  ***dditional 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  re‐
       quires an additional leading zero, or leading = like 00755 , or =755
RESTRICTED DELETION FL***G OR STICKY BIT
       The restricted deletion flag or sticky bit is a single bit, whose interpretation depends on the file type.  For directo‐
       ries, 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 direc‐
       tories 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 MODE values
       -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]+'.
***UTHOR
       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  ?  2020  Free  Software  Foundation,  Inc.   License  GPLv3+: GNU GPL version 3 or later <https://gnu.org/li‐
       censes/gpl.html>.
       This is free software: you are free to change and redistribute it.  There is NO W***RR***NTY, to  the  extent  permitted  by
       law.
SEE ***LSO
       chmod(2)
       Full documentation <https://www.gnu.org/software/coreutils/chmod>
       or available locally via: info '(coreutils) chmod invocation'
GNU coreutils 8.32                                       February 2022                                                 CHMOD(1)

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