Terminating Processes

Managing tasks from the command line

Every so often, a program misbehaves. Sometimes, it’s due to something we configured incorrectly. Other times, it’s because the program has a bug. We’ve probably experienced a stuck program before and figured out how to kill the task using a graphical task manager. We can manage tasks from the command-line interface as well. All we need is the process ID.

Let’s start a long-running task in the background. In our terminal, we execute the following command:

sleep 9999999 &

This process is now running. We use the jobs -l command to list the running background jobs and show the process ID in addition to the job ID:

jobs -l

The kill command

The kill command terminates processes by sending the process a signal. A well-behaved program listens for these signals and responds appropriately. We specify the kill command to terminate a process, followed by the signal we want to send, followed by the process ID.

The SIGHUP signal, which means “hang up,” is the disconnection signal. It’s the signal that gets sent when we press “Ctrl+d” or when we close a terminal session. Programs have to be designed to respond to this signal and can choose to ignore it. Let’s use kill -SIGHUP followed by the process ID to send the signal to the program:

kill -SIGHUP {process ID}
jobs -l

Execute the last two commands in the terminal below:

The nohup utility program

Sometimes, the program doesn’t respond to the hangup signal, so we have to be a little more aggressive. Let’s use the nohup program to start this job. The ...