Detailed explanation of the usage and difference between nohup and & in Linux

Example:

We use the Python code loop_hello.py as an example. The code outputs the number of loops and hello world! in a loop, and sleeps for 1 second after each output.

The sample code is as follows:

import time
 
def main():
 i = 0 
 while True:
  i += 1
  print('%d: hello world!' %(i))
  time.sleep(1)
 
if '__main__' == __name__:
 main()

Run loop_hello.py and the output is as follows:

The program will output a string to the terminal every second. If you type Ctrl+C at this time, the program will receive a SIGINT signal. If no special processing is done, the default behavior of the program is to terminate (as shown above).

&

Using python loop_hello.py &, the effect is as follows:

First, the process number will be displayed in the terminal as 2367

Type Ctrl + C to send a SIGINT signal and the program will continue to run.

When the session is closed, the program will receive a SIGHUP signal. You can see through ps aux | grep loop_hello.py that process 2367 is also closed.

nohup

Use nohup python loop_hello.py, the effect is as follows:

1. No process number appears in the foreground
2. There is a prompt "Ignore input and append output to "nohup.out""
3. The output of hello does not appear in the foreground

If I close the session, will the program close?

1. Use ps aux | grep loop_hello to view the process ID
2. When you close the session, the program will receive a SIGHUP signal.
3. Use ps aux | grep loop_hello again and find that the process still exists
4. Kill the process

Test Ctrl + C

Use nohup to start loop_hello.py. If you type Ctrl+C, the program will be closed directly after receiving the SIGINT signal.

& and nohup are used together

Use nohup python loop_hello.py & to run the program. The effect is as follows:

Type Ctrl + C to send a SIGINT signal. Use ps aux to check that the process still exists.

Close the session, send a SIGHUP signal and use ps aux to check that the process still exists

If you want to terminate the process, you can only use kill

Summarize:

Use & to run the program in the background:

1. The results will be output to the terminal
2. Use Ctrl+C to send SIGINT signal, program immunity
3. Close the session and send a SIGHUP signal, the program will close

Run the program using nohup:

1. The results will be output to nohup.out by default
2. Use Ctrl+C to send a SIGINT signal and the program will close
3. Close the session and send SIGHUP signal, the program is immune

On weekdays, nohup and & are often used together to start programs online:

1. Immune to both SIGINT and SIGHUP signals

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