Here I introduce two ways to keep your command running in the background. You need this when:
Run a command (e.g., downloading a large file) that takes a long time to finish.
Run a command in the background for a long time, for example, a .
SIGHUP
When you execute a command in the terminal, it will block other commands until it finishes. If you close the terminal during the execution, the command will terminate also. Because a will be sent to that process (the executing program), and terminate it. Below prevent this from happening even you close the terminal.
Run with nohup and &
nohup is a simple way to keep your command running, it means "no SIGHUP", so if you use nohup in front of a command, closing terminal will not terminate the command.
"&" means put the process will be put in the background, so it will not block terminal, and you can execute other commands in this same terminal.
Check out fg, bg , and jobs command again .
# Use the sleep command to mimic a long execution time.
$ sleep 100
# This will block terminal for 100s.
# Close terminal also terminates this.
$ nohup sleep 100
# This will still block terminal for 100s.
# But close terminal will not terminate this.
$ nohup sleep 100 &
# This will not block terminal.
# Close terminal will not terminate this.
$ jobs
[1] + running nohup sleep 100
# Use jobs command, you can see this job right now run in the background
$ fg
[1] + 5741 running nohup sleep 100
# Use fg, we move the command back to the foreground
# It blocks the terminal again
# If I press Ctrl+Z in here:
^Z
[2] + 5741 suspended nohup sleep 100
# it says this job is suspended
# use bg now can put it back to the background and start running
$ bg
[2] - 5741 continued nohup sleep 100
Screen
screen is an even better way. It can create named terminal screens, which will keep running independently to your terminal. Here are a few examples
# Create a screen called jupyter
$ screen -R jupyter
# when executed above command, the terminal seems refreshed,
# this is because you entered a new screen
# now I start a jupyter notebook server (explained in another page)
$ jupyter notebook --ip=localhost --port=8888
(skip output)
# this will keep running to provide me the jupyter notebook service
# now let's exit screen
# press ctrl+A first, then press d
# ctrl+A enters screen control, d means detach
^Z
d
# now terminal change back, and I saw this:
$ screen -R jupyter
[detached]
# Jupyter is still running!
# we can check all running screens
# we can open many screens
$ screen -ls
There is a screen on:
5892.jupyter (Detached)
# we can go back to screen by name or id at any time
$ screen -r jupyter
# now terminal change to the jupyter one
I will leave other usages of screen as homework, you can quickly learn this from google and youtube since you now know what to search 😏.
How to terminate a screen?
What's other options to control a screen when you press Ctrl+A in a screen?