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In general, AFS can be used in the same manner as a regular UNIX file
system, but the way in which permissions work does effect where all
users should do their work. Users who run long jobs or disk intensive jobs may
also need to adjust the ways in which they work. People who compile and run
their own programs should note that a program compiled on one computer will not
run on another computer.
For All Users
After logging in, all users should move to their private
directory to work (each user's private directory is directly below their home
directory). The reason for moving to the private directory is to ensure that a
user's work is protected and is only viewable by the owner of the file. Other
users can see the names of files that are created in any users
home directory, but they cannot see the contents unless the
user changes the AFS permissions on their home directory. Changing the AFS
permissions on a home directory is strongly discouraged. Experienced users can
create additional directories and make these public or private using the
share and protect commands.
The "AFS Home Account Structure" diagram shows in more detail the
directories that are created as part of your AFS account. Note that files you
want to share with other users can be copied to the public directory to make
them available.
For Users With Disk Intensive Jobs
Writing/reading large amounts of data to a disk can cause performance
problems for some programs if the disk being written/read to is not local to
the computer running the program. AFS is a remote file system that is accessed
via the network, and often times writing/reading large amounts of data to AFS
disks will cause jobs to run slower then if the data was on a local disk.
Most programs use scratch or temporary space that is local to the computer
running the program, but if you explicitly write/read large amounts of data to
your home directory, it is quite possible that your jobs are not running as
quickly as they might if they were writing/reading to local disks.
There are some simple ways to address the performance problems for disk
intensive jobs. If you need to read/write large amounts of data in your home
directory, contact research.computing.
For Users With Long Running Jobs
AFS disconnects users from the file system after a pre-set period of time.
This "time-out" period (token lifetime) can be extended for users who have jobs
that run for more than a day, but even users with extended "time-outs" need to
be aware of how to "refresh" their login session to get the maximum time-out
period.
Hints for Running Long Jobs
- If your jobs might run for more then 24 hours, contact research.computing and
request a longer "token lifetime."
- You get a new AFS "token" every time you log in, but if you have been
logged in for a while, you can use the klog command to
"refresh" your token before running a long job.
- Users who stayed logged in for multiple days should klog
every morning to make sure that jobs will be authorized to read/write
their data files for the entire day.
Users who log in each day do not need to use the klog command,
as they will receive a new token at each login.
AFS Quick Reference and Commands
AFS commands are not intuitive, so some Dartmouth-specific programs have
been written to hide some of the command details. These programs are denoted
with a "**".
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Function/Action
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Command
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When you first log in, move to your protected/private directory to prevent
other users from seeing the names of your files.
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cd private
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To see a short list of AFS or UNIX commands.**
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help
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Check your disk space (quota) for your home directory.**
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quota
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Check how much time remains on your "token." A "token" is what gives you
permission to access your files. In general, only users who need to run long
jobs or users who stay logged in for multiple days will need to pay attention
to token lifetimes.
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tokens
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To get a new token (increase the lifetime of a token).
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klog
(you will be asked to enter your password) l
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Look at the access permissions on a directory.**
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permission [directory_name]
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Allow all users to see/read a file. This sequence of commands first moves
you to your home directory, then copies the file to be shared from a protected
directory "private" to a world readable directory "public."
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cd
cp public/[file_name] private/[file_name]
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Share a directory with another user. Please note that AFS permissions are
very different then standard UNIX permissions.**
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share [directory_name]
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Protect a directory from all users. Do not protect your home directory.
Permissions on your home directory have been set up to allow some system
programs access to your home directory. Other users can see the names of files
in your home directory, but cannot see the contents of the files.**
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protect [directory_name]
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