This is an exercise from the Extras part of the Tutorial SURF Research Boot Camp 2018-11-02.
This exercise lets you experience the difference between local and remote computation: you can organize your work so that it continues after you close your laptop.
You will run a simple program that outputs a line each few seconds and experience what happens when you detach from the program in various ways.
templatesthat you have created so far; but you can always import a new appliance from the AppMarket).
example.sh. You can use your favourite editor. In our example we use nano, like this:
cd nano example.sh
#!/bin/bash while sleep 2 do date done
Save the file and exit the editor. For example, in nano, you press
control-x and then you press
Y to confirm that you want to save your changes. Then you are back in the terminal.
Make the script executable:
chmod u+x example.sh
pstreethat your script runs,
pstree # look for a line like this: # ... -example.sh---sleep
Food for brain:
pstreecommand installed? If not, are you able to figure out how to install it? After all, you are the sysadmin!
Suggestion just in case:
- Find the Linux distribution (aka distro) name and version you are running.
- Find the package for the distro you are running that provides
- Install the package using the package manager for your linux distro. Tip, try the
pstreeagain to verify the the execution has stopped.
nohupto run the example script in the background:
nohup ./example.sh &
The output will be:
nohup: ignoring input and appending output to ‘nohup.out’
pstreeand have a look at the progress:
tail -f nohup.out
pstreeto verify that your script is still running
tail -f nohup.out
For more information read the manual, it is small and simple but effective.
You will use a program called
screen. Similar programs are:
pstreeto see that you are actually in a screen session: look for a line similar to
screenand line says something similar to:
[detached from 14691.pts-0.145]
find the script still running
[screen is terminating]
screen command has a lot of options. Reading the manual page will provide you with a wealth of information.
screen, type a command, so that you can recognize the session
c, as before)
Play with these switching commands between the three sessions using
control-a and a digit or the
TAB) and between sessions in that pane