A file is not merely its contents, a name, and a file type (see section 7. Special file types). A file also has an owner (a userid), a group (a group id), permissions (what the owner can do with the file, what people in the group can do, and what everyone else can do), various timestamps, and other information. Collectively, we call these a file's attributes.
These commands change file attributes.
chown
: Change file owner and group
chown
changes the user and/or group ownership of each given file
to new-owner or to the user and group of an existing reference file.
Synopsis:
chown [option]... {new-owner | --reference=file} file...
If used, new-owner specifies the new owner and/or group as follows (with no embedded white space):
[owner] [ [:.] [group] ]
Specifically:
chown
performs the same function as chgrp
.
The program accepts the following options. Also see section 2. Common options.
lchown
system call.
On systems that do not provide the lchown
system call,
chown
fails when a file specified on the command line
is a symbolic link.
By default, no diagnostic is issued for symbolic links encountered
during a recursive traversal, but see `--verbose'.
lchown
system call, and `--no-dereference'
is in effect, then issue a diagnostic saying neither the symbolic link nor
its referent is being changed.
chgrp
: Change group ownership
chgrp
changes the group ownership of each given file
to group (which can be either a group name or a numeric group id)
or to the group of an existing reference file. Synopsis:
chgrp [option]... {group | --reference=file} file...
The program accepts the following options. Also see section 2. Common options.
lchown
system call is provided.
chmod
: Change access permissions
chmod
changes the access permissions of the named files. Synopsis:
chmod [option]... {mode | --reference=file} file...
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.
If used, mode specifies the new permissions. For details, see the section on section 3. File permissions.
The program accepts the following options. Also see section 2. Common options.
touch
: Change file timestamps
touch
changes the access and/or modification times of the
specified files. Synopsis:
touch [option]... file...
If the first file would be a valid argument to the `-t' option and no timestamp is given with any of the `-d', `-r', or `-t' options and the `--' argument is not given, that argument is interpreted as the time for the other files instead of as a file name.
Any file that does not exist is created empty.
If changing both the access and modification times to the current
time, touch
can change the timestamps for files that the user
running it does not own but has write permission for. Otherwise, the
user must own the files.
The program accepts the following options. Also see section 2. Common options.
touch
.
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