Unix writing permissions for two users?

Question

I have a development machine where I have subvserions projects checked out, so my user account has ownership permissions for those files. However, they are websites, and sometimes the apache user (www-data) needs to write to the directory (temporary files, uploads, etc.).

I'm not so familiar with Unix permissions, but when I give ownership to one, the other can't write. How can I get it so that both can write to the directories? (I've changed permissions to 755 for all the dirs.)

Answer 1

Add them both to a group, and give that group writing permissions for the directory you want them both to write to.

Create a new group:
    $ sudo groupadd groupname

Add users to the group:
    $ sudo usermod -a -G groupname username1
    $ sudo usermod -a -G groupname username2

Set the permissions as you want them to be for everyone else. 
(755 as it is now is probably unwise...)

Set the directory ownership to the group:
    $ sudo chgrp -R groupname /directory

Give the group write permission:
    $ sudo chmod -R g+w /directory

If you want more users to have write access, just add them to that group using:

$ sudo usermod -a -G groupname username