In case you are constructing a robotic, sensor platform, climate station you then don’t need the code to cease working whenever you disconnect from the terminal, and nohup is simply the factor for you.On this how-to, we’ll learn to use nohup by way of a collection of examples
There are occasions whenever you need to run a command, and depart it working even after you shut a terminal window / SSH session. The best method is utilizing nohup (no hangups) which is able to run any command or executable script lengthy after we shut the terminal.
Primary Nohup Use in Linux
At its most elementary, nohup can be utilized with solely a single argument, the title of the script / command that we need to run. For instance if we had a Bash script referred to as take a look at.sh we may run it as so.
nohup ./take a look at.shIf the script / command produces commonplace output, then that output is written to nohup.out and never the terminal. To test the output we will use tail to comply with the updates made to the file.
tail -f nohup.outAn Instance of Nohup Use
We created a easy Bash script that each second prints a message to the display, and updates the worth saved within the variable n. Right here is the code for that file, referred to as take a look at.sh.
#!/bin/bash
n=0
whereas true
do
echo "I preserve counting"
echo $n
n=$((n+1))
sleep 1
finished
1. Open a textual content editor and paste the instance code.
2. Save the file to your property listing as take a look at.sh.
3. Open a terminal and set take a look at.sh to be executable.
chmod +x take a look at.sh4. Take a look at that take a look at.sh is executable by working the command. If profitable press CTRL + C to cease.
5. Use nohup and use the take a look at.sh as an argument. Notice that we have to use ./take a look at.sh to inform the system the place to seek out the script. The one output within the Terminal is “ nohup: ignoring enter and appending output to ‘nohup.out’ “
nohup ./take a look at.sh6. Open one other terminal and use the tail command to comply with the updates made to the nohup.out file. You need to see “I preserve counting” and a quantity counting upwards scroll throughout the display.
tail -f nohup.out7. Shut the terminal working nohup. If requested to verify closure, choose Sure. The terminal working tail -f will preserve working, displaying that nohup continues to be working the script. We confirmed this by working htop and looking for take a look at.sh.
Redirecting the Nohup Output
Nohup has a limitation. By default it writes to nohup.out, so if we had two situations of nohup getting used, they might each write to the identical file.
To get round this we will use redirection to ship the output to a different file. So let’s use nohup together with the ping command to ping one among Google’s DNS servers, and save the output to GooglePing.txt.
1. Open a terminal window.
2. Utilizing the nohup command, use ping 8.8.8.8 as an argument. This may ping one among Google’s DNS servers each second, a helpful connectivity take a look at.
nohup ping 8.8.8.8 > GooglePing.txt3. Open one other terminal and use tail to comply with the output of GooglePing.txt. Press CTRL+C if you find yourself able to cease the tailing the output.
nohup ping 8.8.8.8 > GooglePing.txt4. Within the nohup terminal, press CTRL+C to cease the ping command.
Working a Nohup command within the background
When nohup runs it grabs management of the terminal, successfully disabling it. However with a bit extra Linux magic we will put the command into the background. By inserting the command into the background we will keep it up utilizing the terminal.
We’ll reuse the ping instance as an instance.
1. Open a terminal window.
2. Utilizing the nohup command, use ping 8.8.8.8 as an argument then add & to ship the command to the background. Notice that the output of working this command shall be a course of ID (PID). We are going to want this later.
nohup ping 8.8.8.8 > GooglePing.txt &
3. Open one other terminal and use tail to comply with the output of GooglePing.txt.
4. Within the nohup terminal press Enter to return to the immediate. The nohup command returns management to us, however the immediate just isn’t current. By urgent Enter we will see the right terminal immediate.
5. Use the kill command together with the method ID to terminate the background course of. If the method is now not required it’s best apply to kill it with a purpose to protect assets. If we left this instance to run it could regularly ping Google’s DNS server till the pc was switched off.
kill 28365
