mirror of
https://github.com/coreutils/coreutils.git
synced 2024-11-24 10:23:31 +08:00
112 lines
4.5 KiB
Plaintext
112 lines
4.5 KiB
Plaintext
'\" Copyright (C) 1998, 1999, 2001, 2006, 2007, 2009 Free Software Foundation, Inc.
|
|
'\"
|
|
'\" This is free software. You may redistribute copies of it under the terms
|
|
'\" of the GNU General Public License <http://www.gnu.org/licenses/gpl.html>.
|
|
'\" There is NO WARRANTY, to the extent permitted by law.
|
|
[NAME]
|
|
chmod \- change file mode bits
|
|
[DESCRIPTION]
|
|
This manual page
|
|
documents the GNU version of
|
|
.BR chmod .
|
|
.B chmod
|
|
changes the file mode bits of each given file according to
|
|
.IR 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.
|
|
.PP
|
|
The format of a symbolic mode is [\c
|
|
\fBugoa\fP.\|.\|.][[\fB+-=\fP][\fIperms\fP.\|.\|.].\|.\|.],
|
|
where
|
|
.I "perms"
|
|
is either zero or more letters from the set
|
|
\fBrwxXst\fP, or a single letter from the set \fBugo\fP.
|
|
Multiple symbolic
|
|
modes can be given, separated by commas.
|
|
.PP
|
|
A combination of the letters \fBugoa\fP controls which users' access
|
|
to the file will be changed: the user who owns it (\fBu\fP), other
|
|
users in the file's group (\fBg\fP), other users not in the file's
|
|
group (\fBo\fP), or all users (\fBa\fP). If none of these are given,
|
|
the effect is as if \fBa\fP were
|
|
given, but bits that are set in the umask are not affected.
|
|
.PP
|
|
The operator \fB+\fP causes the selected file mode bits to be added to
|
|
the existing file mode bits of each file; \fB-\fP causes them to be
|
|
removed; and \fB=\fP 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.
|
|
.PP
|
|
The letters \fBrwxXst\fP select file mode bits for the affected users:
|
|
read (\fBr\fP), write (\fBw\fP), execute (or search for directories)
|
|
(\fBx\fP), execute/search only if the file is a directory or already
|
|
has execute permission for some user (\fBX\fP), set user or group ID
|
|
on execution (\fBs\fP), restricted deletion flag or sticky bit
|
|
(\fBt\fP). Instead of one or more of these letters, you can specify
|
|
exactly one of the letters \fBugo\fP: the permissions granted to the
|
|
user who owns the file (\fBu\fP), the permissions granted to other
|
|
users who are members of the file's group (\fBg\fP),
|
|
and the permissions granted to users that are in neither of the two preceding
|
|
categories (\fBo\fP).
|
|
.PP
|
|
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.
|
|
.PP
|
|
.B chmod
|
|
never changes the permissions of symbolic links; the
|
|
.B 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,
|
|
.B chmod
|
|
changes the permissions of the pointed-to file.
|
|
In contrast,
|
|
.B chmod
|
|
ignores symbolic links encountered during recursive directory
|
|
traversals.
|
|
.SH "SETUID AND SETGID BITS"
|
|
.B 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
|
|
.I MODE
|
|
or
|
|
.I RFILE
|
|
to be ignored. This behavior depends on the policy and
|
|
functionality of the underlying
|
|
.B chmod
|
|
system call. When in
|
|
doubt, check the underlying system behavior.
|
|
.PP
|
|
.B chmod
|
|
preserves a directory's set-user-ID and set-group-ID bits unless you
|
|
explicitly specify otherwise. You can set or clear the bits with
|
|
symbolic modes like
|
|
.B u+s
|
|
and
|
|
.BR g\-s ,
|
|
and you can set (but not clear) the bits with a numeric mode.
|
|
.SH "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
|
|
.I "restricted deletion flag"
|
|
for the directory, and is commonly found on world-writable directories
|
|
like \fB/tmp\fP. 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
|
|
.IR "sticky bit" .
|
|
.SH OPTIONS
|
|
[SEE ALSO]
|
|
chmod(2)
|