How to use chmod to change a file's permission?

Question

I used ls -l to find file permissions in a shell and found this:

File 1: -rw-r--r-- 1 root root 451 Mar 9 15:25 file.class.php

File 2: -rw-rw-r-- 1 andy dev 872 Mar 9 15:43 file.class.php

I want file 1's permissions to be changed to file 2's permissions. I have root access and am cd'd to the proper directories. I have never used chmod before and am having some trouble. When I try to do this:

chmod 872 file.clas.php

I get the error: chmod: invalid mode: '872'

Answer 1

That 5th column is the filesize, not the permissions. The permissions are listed on the left in expanded form. The permissions on the first file are 644 in octal (add up the contributions from each bit: r-- = 4, -w- = 2, --x = 1, so rw- = 6), and the permissions on the second file are 664. Therefore, you want

chmod 664 file.class.php

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Alternately, remember that the three permission groups are user, group and other, so rw-rw-r-- is "user rw, group rw, other r". Then, to change rw-r--r-- into rw-rw-r--, you need to add group-write permissions, i.e.

chmod g+w file.class.php

This lets you update the permissions individually.