Glossary

Key Points

Why Use a Cluster?	High Performance Computing (HPC) typically involves connecting to very large computing systems elsewhere in the world. These HPC systems can be used to do work that would either be impossible or much slower or smaller systems. The standard method of interacting with such systems is via a command line interface such as Bash.
Connecting to the remote HPC system	To connect to a remote HPC system using SSH and a password, run `ssh yourUsername@remote.computer.address`. To connect to a remote HPC system using SSH and an SSH key, run `ssh -i ~/.ssh/key_for_remote_computer yourUsername@remote.computer.address`. Protect your SSH keys by managing them carefully! 2-factor authentication is a way to help ensure a user’s identity by requiring two forms of identity evidence.
Moving around and looking at things	Your current directory is referred to as the working directory. To change directories, use `cd`. To view files, use `ls`. You can view help for a command with `man command` or `command --help`. Hit `tab` to autocomplete whatever you’re currently typing.
Writing and reading files	There are many different text editors available on DiRAC. Use `nano` to create or edit text files from a terminal. Use `cat file1 [file2 ...]` to print the contents of one or more files to the terminal. Use `mv old dir` to move a file or directory `old` to another directory `dir`. Use `mv old new` to rename a file or directory `old` to a `new` name. Use `cp old new` to copy a file under a new name or location. Use `cp old dir` copies a file `old` into a directory `dir`. Use `rm old` to delete (remove) a file. File extensions are entirely arbitrary on UNIX systems. Use `scp` to transfer files from and to a remote DiRAC resource. Use `tar` to de-archive and archive sets of numerous and/or large files.
Wildcards and pipes	The `*` wildcard is used as a placeholder to match any text that follows a pattern. Redirect a command’s output to a file with `>`. Commands can be chained with `\|`
Scripts, variables, and loops	A shell script is just a list of bash commands in a text file. To make a shell script file executable, run `chmod +x script.sh`.
Using Bash Scripts in Pipes	You can include your own Bash scripts in pipes. A common and useful pattern in Bash shell is to run a program or script that generates potentially a lot of output, then use pipes to filter out what you’re really after.

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Bash Shell: Using the Command Line: Glossary

Key Points

Glossary