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13.1 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=ref_file} file...

If used, new-owner specifies the new owner and/or group as follows (with no embedded white space):

 
[owner] [ [:] [group] ]

Specifically:

owner
If only an owner (a user name or numeric user id) is given, that user is made the owner of each given file, and the files' group is not changed.

owner`:'group
If the owner is followed by a colon and a group (a group name or numeric group id), with no spaces between them, the group ownership of the files is changed as well (to group).

owner`:'
If a colon but no group name follows owner, that user is made the owner of the files and the group of the files is changed to owner's login group.

`:'group
If the colon and following group are given, but the owner is omitted, only the group of the files is changed; in this case, chown performs the same function as chgrp.

You may use `.' in place of the `:' separator. This is a GNU extension for compatibility with older scripts. New scripts should avoid the use of `.' because GNU chown may fail if owner contains `.' characters.

The program accepts the following options. Also see 2. Common options.

`-c'
`--changes'
Verbosely describe the action for each file whose ownership actually changes.

`-f'
`--silent'
`--quiet'
Do not print error messages about files whose ownership cannot be changed.

`--from=old-owner'
Change a file's ownership only if it has current attributes specified by old-owner. old-owner has the same form as new-owner described above. This option is useful primarily from a security standpoint in that it narrows considerably the window of potential abuse. For example, to reflect a UID numbering change for one user's files without an option like this, root might run

 
find / -owner OLDUSER -print0 | xargs -0 chown NEWUSER

But that is dangerous because the interval between when the find tests the existing file's owner and when the chown is actually run may be quite large. One way to narrow the gap would be to invoke chown for each file as it is found:

 
find / -owner OLDUSER -exec chown NEWUSER {} \;

But that is very slow if there are many affected files. With this option, it is safer (the gap is narrower still) though still not perfect:

 
chown -R --from=OLDUSER NEWUSER /

`--dereference'
Do not act on symbolic links themselves but rather on what they point to.

`-h'
`--no-dereference'
Act on symbolic links themselves instead of what they point to. This is the default. This mode relies on the 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'.

`--reference=ref_file'
Change the user and group of each file to be the same as those of ref_file. If ref_file is a symbolic link, do not use the user and group of the symbolic link, but rather those of the file it refers to.

`-v'
`--verbose'
Output a diagnostic for every file processed. If a symbolic link is encountered during a recursive traversal on a system without the lchown system call, and `--no-dereference' is in effect, then issue a diagnostic saying neither the symbolic link nor its referent is being changed.

`-R'
`--recursive'
Recursively change ownership of directories and their contents.


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