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There are two ways to change a file's permissions. The first way is to set the permissions with a text string. Say we wish to make a file owner=read, group=read, and other=read. To do this we would do
chmod ugo=r foo
where u=owner, g=group, and o=other, and foo is the filename. Now doing an ls -l, will produce the following output:
-r--r--r-- 1 tot 2437 Sep 8 15:59 foo
Alternatively, (from `foo''s current state), we could do:
chmod u+wx foo
where the `+' means add to the current permissions, produces:
-rwxr--r-- 1 tot 2437 Sep 8 15:59 foo
This method should be obvious by now. The second method uses three sets of binary numbers, converted to decimal. So, if you wish to give owner read, write, group permission and all others read permission, enter:
chmod 644 foo
where the first digit is for the owner, second is for the group, and third is for all other, would produce:
-rw-r--r-- 1 tot 2437 Sep 8 15:59 foo
Notice the 644 is easily extracted from `-rw-r--r--'.
6 4 4
| | |
4 + 2 | |
\ | | |
\ | | |
421 421 421
rw- r-- r--
All you have to do is look and see which bits are turned on, add them up and, poof, you have your number to call chmod with. Say you wish read, write, and execute (rwx) on owner, read and execute on group and all others (r-x), enter:
chmod 755 foo
-rwxr-xr-x 1 tot 2437 Sep 8 15:59 foo
Figure shows how you can obtain 755 from `-rwxr-xr-x'.
7 5 5
| | |
4 + 2 + 1 4+1 4+1
\ | / | | | |
\ |/ | | | |
421 421 421
rwx r-x r-x
You may take your pick of whichever method you prefer. Directory permissions work the same way, except what it means to execute a directory is basically permissions to list the contents of it. Hence, a directory of:
drwxr-xr-x 2 tot 512 Sep 8 17:46 foo
(notice the `d' on the far left, that means it's a directory)
this means the owner tot, may read, write & execute it (cd into it and list it's contents). It is uncommon to only give a user read privilege to a directory and not execute, although you may. This would allow one to read from your directory but not list it's contents.
One more thing, if you wish all files to be created with some certain permissions, use umask. For example, if you issue umask 022 you will mask all your upcoming created files with 022, thus producing a newly created file with permissions (644):
-rw-r--r-- 1 tot 2437 Sep 8 18:12 foo
If you do a man on umask (man umask) it will explain in more
detail about file masking.
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