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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.)

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up vote 8 down vote accepted

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
share|improve this answer
    
@user13743 Try it now, forgot the -a flag! Updated my answer. – BloodPhilia Aug 10 '10 at 18:50
    
Awesome! But group_name username seems to be backwards on my system; I had to user 'sudo adduser -a www-data web-directory-writers' – user13743 Aug 10 '10 at 18:52
    
@user13743 No! Then you added a user web-directory-writers to the group www-data! use like this: sudo useradd -a -G groupname username1 Don't forget the -G flag! What error do you get if you do it like that? – BloodPhilia Aug 10 '10 at 18:54
    
>sudo adduser -a web-directory-writers www-data adduser: The user 'web-directory-writers' does not exist. >sudo adduser -a www-data web-directory-writers The user 'www-data' is already a member of 'web-directory-writers'.` – user13743 Aug 10 '10 at 19:08
    
@user13743 You're forgetting the -G flag! sudo adduser -a **-G** web-directory-writers www-data – BloodPhilia Aug 10 '10 at 19:11

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