jobs control tools in linux

jobs_control.md

Commands:

• ./tst.py &: run in background
• nohup ./tst.py &: don't print output in stdout, and set the parent process as #0 process.nohup means No hangup signal.
• setsid ./tst.py &: print output in stdout, set the parent process as #1 process.
• disown %1: change the parent process of a background process
• hot key ctrl+z: suspend foreground process
• bg %1: trun foreground job #1 to background, equal to kill -CONT -pid_value
• bg: trun all foreground job to background
• fg %1: trun background job to foreground
• fg: trun all background job to foreground
• kill -9 %1: kill job #1
• ps -ef: this command will show the ppid

For example, we have a python script named tst.py like following:

#!/usr/bin/env python
  
import time

for i in range(1000):
    with open('info.log', 'a') as f:
        f.write(str(i))
        print(i)
        time.sleep(1.5)

Note: All the following experiments are tested with ssh remote connection:

Normal running

The process tree of this script: python ./tst.py -> -zsh -> sshd: linux_fhb@pts/1 -> sshd: linux_fhb[priv] -> /usr/sbin/sshd -D -> /sbin/init splash -> 0

Questions & Answers

Q1: How to run a background program?

A1: Just add an ampersand at the end of command. e.g. ./tst.py &.

Q2: How to turn the foreground process into a background process?

A2: You shoud take two steps.

1. Suspend foreground process with hot key ctrl + z, and the terminal will print like [1] + 13158 suspended ./tst.py, the first number 1 means the job number, and the second number 13158 is the process pid.
2. Run bg command : bg %1, the 1 is the job number you want run at background, if you want run all the jobs, run bg.

Q3: How to turn the background process into a foreground process?

A3: Run fg command : fg %1, if you want turn all jobs to foreground, run command fg.

Set process to the son of #0 process

• with nohup command: nohup ./tst.py &

• with setsid command: setsid ./tst.py &

• set system process as parent process of a background process: disown %1

Note: change the parent process with disown won't change the workspace directory.