Linux

• The "operating system" of the UPPMAX and most of the other clusters is Linux.

Questions

• What is Linux?
• How to use the command line?

Objectives

• We'll briefly get an overview of Linux
• How the command line works
• Some text editors
• Things to be aware of

Want a video?

Here is video that gives an introduction to Linux

What is Linux?

• Daily speaking: The Linux Operating system is a UNIX like and UNIX compatible Operating system.
• Linux is a "Kernel" on which many different programs can run.
• The shell (bash, sh, ksh, csh, tcsh and many more) is one such program.

• Actually, for it to be an OS, it is supplied with GNU software and other additions giving us the name GNU/Linux.
  • Linux naming controversy

• Linux has a multiuser platform at its base which means permissions and security comes easy.

Linux comes in different distributions, dialects or, say, flavours

• UPPMAX runs CentOS and RedHat

Using the command line

Below usage of the command line is discussed in text. If you prefer video, here is how to use the command-line on the UPPMAX Bianca cluster.

Command line with bash (Bourne Again Shell)

• A Unix shell and command language.
• Often default shell

• The command-line interface: the bash prompt $
• bash can be seen as a program that finds and runs other programs
• bash is scripting language that is referred to as a shell
  • (because it sits around the kernel making it easy to interact with)

The prompt

[info]$ word1 word2 word3 [...]

• [info] is configurable, and usually tells you who you are, on what system, and where in the file system.

  • Example:

  [bjornc@rackham3 linux_tutorial]$
  

  • For changing info (only for advanced users!) Does not matter for this course!:
    • https://www.cyberciti.biz/tips/howto-linux-unix-bash-shell-setup-prompt.html
  • The program to run is the first word
  • All words are separated by spaces

Example bash command

• Terminal screen shows

Tab Completion

• Whenever you’re writing a path or filename on the bash prompt, you can strike the ‘tab’ key to ask Bash to complete what you’re writing.

• Get in the habit of this — it will save you many hours!

Editing files

To edit files, you will use a text editor. The UPPMAX HPC clusters have multiple text editors installed, which are described at the UPPMAX 'Text editors' page here.

Example

Start nano and save a file called first.txt

$ nano first.txt

• Type test text
• End and save with <ctrl>-X followed by Y and <enter>.

Typical sources of error

Warning

• Capitalization matters in file names and program names
• Spaces matter.
• Always have a space after the program name.
• Don’t add spaces within file names.
• Check that you are in the right place in the file system.
• File permissions. Check that the right read, write and execute permission are set. See next session.

Caution

Warning

• There is no undo for:
• copy (cp),
• move (mv), and
• remove (rm).
• Beware of overwriting files and deleting the wrong ones.

Tip

• Tip: make "rm" ask if you really want to erase:

• Within a session: Type in the command prompt

  alias rm='rm -i'
  

• Override asking with

  rm –f <>
  

• Edit file .bashrc in home directory by adding the alias line for this to start everytime.

• This will also work for mv and cp!

Note

• If you do destroy your data, email UPPMAX support, we may be able to help.

Keypoints

• Linux Operating system is a UNIX-like and UNIX compatible Operating system.
• Typical command: $ program word1 word2 word3 […]
• Use text editors to edit files
• Tips
  • use Tab completion
  • capitalization and spaces matters
  • no undo:s for copying, moving and removing
  • Solution: alias rm='rm -i'

Links

• A free online book about Linux: 'The Linux Command Line'.