hang-up

Finally, let's discuss the SIGUP signal, or the hang-up signal. In CentOS 7, if you run a program in the background, like the sleep command, and log out of the system, then log in again, you'll see the command or process still running. So, in CentOS 7, we can easily run background processes and log out of the SSH session, which is useful to run programs that need to run all the time or to do some heavy calculations that take hours, days, or even months. In other Linux distributions, if you log out of the system, the kernel will send the hang-up signal, or in short SIGUP, to all running background processes and terminate them. In such systems, to disable the hang-up signal that is sent to your processes, use nohup; prefix your command with the nohup command, such as nohup sleep 1000 &. This way you can safely log out of the system and your job will not stop running. But, as mentioned before, on a CentOS 7 system, you don't have to do this.