PECF

Cornell University
Physics Educational Computing Facility (PECF)

Tips

Here's a few bits of information that don't fit in elsewhere. If you think something else belongs here, you should suggest it.

Backups

Our new computer cluster introduces vastly improved backups. The entire filesystem is snapshotted every day to keep as backup.

If you've accidentally deleted a file or want to access a previous version of your home directory for some other reason, go to the hidden .zfs/snapshot directory in your home directory. Each day will be in its own directory.

GNU Screen/Running Jobs

You can use GNU Screen to start a terminal session, disconnect from it, and then reconnect to it again later. This lets you for example run jobs on the machines in the background (but see the policies page for some things to keep in mind).

There are a number of tutorials online explaining how to use it, like this one from Debian Administration. If that one doesn't appeal to you, a Google search has many others to try.

Finding a Free Machine

If you're trying to run a job on a machine which already has high usage, your process will not have as much computing capacity available to it. To find a machine which is less in use, run
ruptime -rl
which outputs the uptime of machines in the cluster, sorted by system load. Higher usage is towards the bottom, and the load values you can interpret as being approximately out of a maximum of eight. Pick a machine or machines towards the top (and starting with "nws") and you should be fine.

Changing Your Password Online

If you forget your password to the cluster, you can reset it on our website. Go to the account management page and after logging in with your NetID you can change your password on the cluster. Later we may add other useful abilities to that page as well, but for now it's only for password changes.

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