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

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]((https://en.wikipedia.org/wiki/GNU/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

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]$ program 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 with file/text editors

gedit

• graphical user interface — GUI, needs X-server

• Also graphical editor within MobaXterm

nano

• keyboard shortcuts shown on-screen)

• Cheatsheet: http://staffwww.fullcoll.edu/sedwards/nano/UsefulNanoKeyCommands.html

  • ^ = Ctrl, M = meta key)

    • Windows M = Alt

    • On Mac: in the Terminal.app go to Preferences -> Settings -> Keyboard and turn on “Use option as meta key”: then M = Alt

Not to try today if you haven’t used before!!!

• If you start one of these editors you may have difficulties to exit!

vim

• fast and powerful, once you learn it

• on UPPMAX started with command vi

  • 1. Insert mode (type like normal text editor. Press i for insert mode)

  • 2. Command mode (give commands to the editor to get things done . Press <ESC> for command mode)

  • Cheat sheet: https://coderwall.com/p/adv71w/basic-vim-commands-for-getting-started

gvim

• vim with a GUI, lots of features very Fast

emacs

• fast and powerful, once you learn it

  • Cheat sheet: https://www.gnu.org/software/emacs/refcards/pdf/refcard.pdf

    • (C = <Ctrl>)

• also With GUI

  • emacs –nw

    • keeps you in terminal window.

The graphical editors

• When starting the graphical versions of an editor, add & to be able to use the command line while program is open.

  • Ex: gedit &

  • If not, you can <Ctrl>+z and type bg to send program to background.

Try out later!

Try them out and pick one favorite editor!

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.

Note

• 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 […]

• Example of file editors

  • terminal

    • nano

    • vim

    • emacs

  • graphical:

    • gedit

• Tips

  • use Tab completion

  • capitalization and spaces matters

  • no undo:s for copying, moving and removing

    • Solution: alias rm='rm -i'