06 Process Management

View processes

• ps - Shows the list of running processes for the current user.
• ps aux - Shows processes from other users as well.
• top - Shows real time statistics about the processes.

Note: PID means process id.

Managing processes

• kill - Terminates a process.
• Signals associated with the kill command determines how cleanly the process should be terminated.
  • SIGTERM - Kills the process but allows cleanup to be done before that.
  • SIGKILL - Kills the process and does not allow cleanup.
  • SIGSTOP - Stops or suspends the process.

Process hierarchy

• Namespaces is a way of isolating one process from another. This is great for security.
• systemd is the process with id 0 and it starts when the operating system boots up.
• Any program or service that the user starts will be a child process of systemd. All these processes will run as a separate process but it is controlled by systemd.

Start on boot

• Some critical process needs to be started on boot.
• systemctl command helps us to do the below actions on processes.
  • Start
  • Stop
  • Enable
  • Disable
• For example: sudo systemctl start apache2 starts apache2 server on boot.

Background process

• To run a process in background add & at the end of the command.
• For example: echo hello &.
• Background processes are great for long running processes such as copy files, downloading, etc.
• We could also use Ctrl+Z instead of appending & at the end of the command.

Foregrounding a process

• Use ps aux to view the list of running processes.
• fg command brings the background process to foreground.