AFS Introduction

Introduction to the AFS file system in the Computer Science Department.

Reviewed by John Sopko 6/17/2014

The Computer Science Department uses the AFS file system for UNIX home directories, research space, and most of our web space.  Our default Linux and Windows installations include AFS client software.  Below is some general information on using AFS in this department.  You can also go to our help pages and search for AFS; there are several more specific pages.

There are several important reasons why we use AFS as a file system instead of the native file systems on Linux and Windows.  The Linux file system security model allows anyone that has a a root account or sudo access to change their login id to that of another user and gain access to that user’s files.  AFS does not allow root users to gain access to other files.  Microsoft Windows’ native NTFS file systems has a much better security model then Linux.  The advantage of running the Open AFS client on Windows is to allow you to access the same AFS file space from both Linux and Windows.  Currently there is not a good alternative for AFS.

AFS is a distributed file system.  It uses the client/server model, where all the files are stored on file server machines.  Files are transferred to client machines as necessary and cached on local disk.  The server part of AFS is called the AFS File Server, and the client part of AFS is called the AFS Cache Manager.  AFS provides Access Control Lists (ACLs) which provide for more control and flexibility than standard Linux file permissions.

AFS provides transparent access to local and remote files by using a consistent name space.  All files in AFS are found under the Linux directory /afs.  Under the /afs directory are the various sites which run AFS and make their file-system available to the Internet community.  These sites are called AFS Cells.  The Computer Science cell name is the same as our Internet name, cs.unc.edu.  Thus all files and directories under /afs/cs.unc.edu are in the Computer Science AFS file space.  The UNC campus AFS cell name is located at /afs/isis.unc.edu.

Any file located under /afs is located on an AFS file server.  If a remote cell that you wish to access is not listed, please email help@cs.unc.edu and tell us the cell you wish to access, and we will configure the cell into AFS.

The campus help site has some information on accessing AFS on the campus isis.unc.edu cell and other general AFS information.

Changing your AFS password

Use the  https://www.cs.unc.edu/webpass URL to change your Computer Science AFS password.  This will change your AFS, Linux, and Windows passwords at the same time.  This password is NOT the same as your Onyen password, though of course you can use the same password in both places.

Using AFS

The OpenAFS User Guide is the best resource on how to use AFS.  If you need assistance or have questions please emailhelp@cs.unc.edu.  In general, if you are using a Computer Science provided Windows or Linux machine, you will have the AFS client installed for you.  When you login you will automatically be authenticated to AFS as described in chapter 2 of the OpenAFS User Guide.  See also the Computer Science AFS Aklog information for specifics on authenticating to our cs.unc.edu AFS cell.

Accessing AFS on a Linux system

For Linux users, files in AFS are accessed much the same as files in the native linux file system.  The big difference is that AFS directory permissions take precedence over Linux file permissions.  The same is true of using AFS on Windows machines.

Accessing AFS on a Windows system

The recommended way to access AFS from a Windows machine is to use the Windows UNC (Uniform Naming Convention) path.  For example, to access your home directory you can make a Windows shortcut to the following location or enter the UNC path in the Windows Run… command box:

\\afs\cs.unc.edu\home\login

Where “login” is your Computer Science login name.  AFS file permissions take precedence over Windows file permissions.  You can create a shortcut with the UNC path name pointing to the AFS folder you wish to access.  You could also use the Windows Explorer to enter in the \\afs\cs.unc.edu\some_path_name to access AFS file space from your Windows machine.

You can access the Windows Users guide on your Windows 7 machine under this menu:

Start->All Programs->OpenAFS->Documentation->User Guide.

Your AFS home directory space

Most users with a Computer Science account receive a home directory located at:

/afs/cs.unc.edu/home/login

Where “login” is your Computer Science login name.  Quotas are described here.

Important file restoration tip

We take a nightly online snapshot of AFS space starting at 2am.  If you accidentally delete a file that existed during the last snapshot, you can restore your file without going through Computer Services.  To see the nightly snapshot of your home directory, go to the following location:

/afs/cs.unc.edu/home/last_backup/login

This is a read only copy of your home directory as it was when the last backup snapshot was taken.

Further information

The department is running OpenAFS, whose main page is:  http://www.openafs.org/.  Documentation on OperAFS is athttp://docs.openafs.org/index.html.  In particular, see the AFS Users’s Guide, which is an excellent manual for beginners.

Note that AFS is strictly open source and we have no support for the product other then the www.openafs.org web site.