07-Job-management.md

title	author	date	lang
Job management	CSC Training	2020-04	en

Contents of this session

UNIX/Linux are multi-tasking operating systems. Consequently, the users need to know something about managing their jobs (=running applications). This session deals with ...

• displaying jobs on your system
• fore- and background jobs in shell
• suspending and terminating of jobs

Jobs on system

• Linux/UNIX are multi-tasking systems
• One can display the currently running jobs using the top command

  $ top

  • press P to order jobs by their processor load
  • press M to order jobs by their memory consumption
  • press u to prompt for displaying jobs of certain user (enter cscuser)
  • press q to exit

Fore- and background

• By default commands (jobs) in the shell are run in foreground, e.g.,

  $ emacs newfile

• Now, try to enter something in your shell
  • It does not respond. Why?
  • as long as you do not quit emacs (the currently running program), it blocks the shell
  • we say: the job (emacs in this case) is running in the foreground of the shell
• Terminating (=killing) a running foreground job: in shell press ctrl + C
  • That is usually not recommended, except for non responding jobs

Managing jobs

• Launch again into foreground
  • Type something into emacs
• Suspending a job: in shell press ctrl + z
  • Shell reports on stopped job
• Type a command into the shell:

  $ ls -ltr

  • Try to type something into emacs. What happens?
    • The process of emacs is suspended, hence does not accept any input
      • In fact, the input buffer keeps the typed stuff and will fill it into emacs, once it is active again

Managing jobs

• Sending the suspended job to background:

  $ bg

  • type a command into the shell:

  $ ls -ltr

  • type something into emacs
  • It works now for both! Because emacs is running in background and your shell accepts commands

Managing jobs

• Fetching back to foreground:

  $ fg

  • Shell is blocked again
  • emacs accepts input
  • quit emacs either by menu or ctrl+x, ctrl+c
• Can I directly launch into background ?
  • Yes. Type command followed by &

  $ emacs newfile &

Managing jobs

• Lets launch two jobs into background

  $ xterm -T "first" &
  $ xterm -T "second" &

  • if program xterm is not installed, install it
• To list all jobs of the shell:

  $ jobs

  should report something like (numbers in brackets might differ)

  [1] - Running      xterm -T "first" &
  [2] + Running      xterm -T "second" &

  • the + after job [2] means that job [2] listens to commands, like fg

Managing jobs

• Bringing job [1] to foreground needs a way to address the job:

  $ fg %1
  -> xterm -T "first"

  • address a certain job with % followed by its number
  • to send it back ctrl + z, followed by

  $ bg

Managing jobs

• To kill (= terminate) a certain job

  $ kill -9 %1
  $ jobs
  -> [1]-  Killed                  xterm -T "first"
  [2]+  Running                 xterm -T "second" &

• Playing terminator (killing all jobs of a kind):

  $ for i in {1..5}; do xterm & done
  $ pkill xterm

  • this first launches 5 xterms and then kills all xterm processes under your user-id