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I have two Linux servers:

fileserver
Debian 5.0.3 (2.6.26-2-686)
Samba version 3.4.2

apache
Ubuntu 10.04 LTS (2.6.32-23-generic)
Apache 2.2.14

I have a number of Samba shares on fileserver so that I can access files from Windows PCs. I am also exporting /data/www-data to the apache server, where I have it mounted as /var/www.

The setup is okay, except for when I come to create files on the NFS mount. I end up with files that cannot be read by Apache, or which cannot be modified by other users on my system.

With Samba, I can specify force user, force group, create mask and directory mask, and this ensures that all files are created with suitable permissions for my Apache web server. I can't find a way to do this with NFS. Is there a way to force permissions and ownership with NFS - am I missing something obvious?

Although I've spent quite a bit of time with Linux, and am weaning myself off Windows, I still haven't quite got to grip with Linux permissions... If this is not the right way to do things, I am open to alternative suggestions.

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2 Answers 2

up vote 6 down vote accepted

Given you're coming from Windows, you'll find that NFS is....different.

The issue you're running into is fairly common. NFS is passing the UID and GID of the files/directories back and forth between the machines with the assumption that the user and group IDs are mapped identically on both. This means that you can get a situation where the UID/GID on the server is passed back to a NFS client, but it can't matched in the client's /etc/passwd or /etc/group, which means no access.

In the (distant) past this was co-oridnated with NIS and NIS+, although there are other schemes that have been wedged into this framework (Samba's Winbind being one of them). However, this requires a central ID server, followed by a lot of hand-fixing permissions.

There are different ways to fix this, but the cheapest/quickest is to create a group with the same group ID number on both machines - say, group ID 50000 - and set the group bits on the file server while adding the appropriate user to the group on the client; then use the group permissions on the files to control access. Not a great solution but it will work. Note that you could have problems with services that explicitly change their group at runtime (aka privledge drop) and you might need to change the setting that controls what group is assumed at runtime to ensure it is the one you have created.

For those files that come inbound via a Windows share (aka Samba) simply force the group to be the same as the one you create. That way all files automatically get the "right" GID.

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Thanks for the considered response. I'll look into the group bits method, and let you know how I get on. –  Mike Jul 15 '10 at 5:28
    
I created a www-data group on the File server, assigned the necessary users, then set the same www-data group ID on both servers. I also set the group bits on the /data/www-data folder with chmod -R g+s /var/www-data. It's now working perfectly. Thanks for your help. –  Mike Jul 15 '10 at 7:52
    
Glad to hear it! –  Avery Payne Jul 15 '10 at 17:14
    
It would be nice if NFS could do this for Mac clients. –  d-_-b Jul 8 '11 at 13:11

You could also use the all_squash option which makes anonymous (user & group) all the exported files & folder, and attach them to a specific GID & UID.

/data/www-data apache(rw,all_squash,anonuid=<your UID>,anongid=<your GID>,sync)

The problem with that is that all users on the apache server will see your mount point with nobody nobody as user & group, and could write in the mount (but anyway, on the Samba server, the files will be created as <your UID>/<your GID>).

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