Re: file permissions

Ray Canzius wrote:

G'day all,

I am new to Ubuntu and I  am having problems finding out how to change
file permissions.
Anybody give me any clues.


Regards
Ray



Ray,

If you're using a console, it's quite simple:

chmod [ugo][+-][rwx] FILEs

Let me explain: in the `ugo' bit, it stands for `user', `group' and `others'. `rwx' stands for `read', `write' and `eXecute'.

Let's say you want to deny `others' (that is, everyone not in your group, and who is not you) permission to write to your file; rightly so. The command would be this:

chmod o-w my_file

How about, you want to give yourself access to read, write and execute?

chmod u+rwx my_file

Note that `execute' permissions are only useful on a) directories, and b) programs or scripts. You can also string these little bits together, like so:

chmod +r,go-w,u+w,-x my_file

By omitting the `ugo' parts, you imply it's all. This command above gives *everyone* read access, takes away `group' and `others' permissions to write, gives *yourself* write access, and gives no one execute access (presumably it is not needed).

To look at permissions on a file, type `ls -l my_file'. For example:

celtic@xyrias:~$ chmod +r,go-w,u+w,-x my_file
celtic@xyrias:~$ ls -l my_file
-rw-r--r--  1 celtic celtic 17 2006-01-27 12:00 my_file
celtic@xyrias:~$

Here, we can see that: a) `celtic' is the owner of the file, b) `celtic' is the group of the file, and the permissions. The permissions are written in this way:

`Suuugggooo'

S can be a hyphen, meaning a normal file (like here), a `c', indicating a character device file (like your keyboard), a `b', meaning a block device file (like your harddrive), or a `d', meaning a directory.

Then follows is the same `permission' set for user, group and others: --- means no permissions, rwx means read, write and execute permissions, or there might be some missing, eg. rw-, meaning only read/write.

You can control these same permissions from Nautilus, by right clicking the file, choosing `Properties' and selecting the `Permissions' tab. There are also `user ID', `group ID' and `sticky' bits, but those are more advanced concepts. (to do with execute permissions and if you can delete files)

Hope this helps,
- Yuki.

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