Originální popis anglicky:
chmod - change access permissions of files
Návod, kniha: General Commands Manual
chmod [options] mode file...
POSIX options:
[-R] [--]
GNU mode denotation:
[--reference=rfile]
GNU options (shortest form):
[-cfvR] [--help] [--version] [--]
chmod changes the permissions 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 permissions.
The format of a symbolic mode change argument is
`[ugoa...][[+-=][rwxXstugo...]...][,...]'.
Such an argument is a list of symbolic mode change commands, separated by
commas. Each symbolic mode change command starts with zero or more of the
letters `ugoa'; these control 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). Thus, `a' is here equivalent to
`ugo'. 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 permissions selected to be added to the existing
permissions of each file; `-' causes them to be removed; and `=' causes them
to be the only permissions that the file has.
The letters `rwxXstugo' select the new permissions for the affected users: read
(r), write (w), execute (or access for directories) (x), execute only if the
file is a directory or already has execute permission for some user (X), set
user or group ID on execution (s), sticky bit (t), the permissions that the
user who owns the file currently has for it (u), the permissions that other
users in the file's group have for it (g), and the permissions that other
users not in the file's group have for it (o). (Thus, `chmod g-s file' removes
the set-group-ID (sgid) bit, `chmod ug+s file' sets both the suid and sgid
bits, while `chmod o+s file' does nothing.)
The name of the `sticky bit' derives from the original meaning: keep program
text on swap device. These days, when set for a directory, it means that only
the owner of the file and the owner of that directory may remove the file from
that directory. (This is commonly used on directories like /tmp that have
general write permission.)
A numeric mode is from one to four octal digits (0-7), derived by adding up the
bits with values 4, 2, and 1. Any omitted digits are assumed to be leading
zeros. The first digit selects the set user ID (4) and set group ID (2) and
save text image [`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, since 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.
- -R
- Recursively change permissions of directories and their
contents.
- --
- Terminate option list.
A GNU extension (new in fileutils 4.0) allows one to use
--reference=rfile as a mode description: the same mode as that
of
rfile.
- -c, --changes
- Verbosely describe the action for each file whose
permissions actually changes.
- -f, --silent, --quiet
- Do not print error messages about files whose permissions
cannot be changed.
- -v, --verbose
- Verbosely describe the action or non-action taken for every
file.
- -R, --recursive
- Recursively change permissions of directories and their
contents.
- --help
- Print a usage message on standard output and exit
successfully.
- --version
- Print version information on standard output, then exit
successfully.
- --
- Terminate option list.
The variables LANG, LC_ALL, LC_CTYPE and LC_MESSAGES have the usual meaning. For
an XSI-conforming system: NLSPATH has the usual meaning.
POSIX 1003.2 only requires the -R option. Use of other options may not be
portable. This standard does not describe the 't' permission bit. This
standard does not specify whether
chmod must preserve consistency by
clearing or refusing to set the suid and sgid bits, e.g., when all execute
bits are cleared, or whether
chmod honors the `s' bit at all.
Above we described the use of the `t' bit on directories. Various systems attach
special meanings to otherwise meaningless combinations of mode bits. In
particular, Linux, following System V (see System V Interface Definition
(SVID) Version 3), lets the sgid bit for files without group execute
permission mark the file for mandatory locking. For more details, see the file
/usr/src/linux/Documentation/mandatory.txt.
This page describes
chmod as found in the fileutils-4.0 package; other
versions may differ slightly.
chattr(1),
chown(1),
install(1),
chmod(2),
stat(2),
umask(2)
