How to Manage Processes in Unix

Processes are the running programs on your Unix system, and managing them is key to understanding how your system operates. Unix provides various commands to monitor, control, and optimize processes.

In this blog, we’ll explore how to view processes, terminate them, and manage their priority using clear examples.

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What Is a Process?

A process is an instance of a running program. Unix assigns each process a unique Process ID (PID) to identify it. Processes can be:

• Foreground: Interacting directly with the user.
• Background: Running silently in the background.

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1. Viewing Processes

Use the ps Command

The ps command lists processes running on the system.

Example:

$ ps

This shows processes running in your current terminal session.

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See All Processes

Use the -e option to display all processes on the system:

$ ps -e

Add the -f option for detailed output (full format):

$ ps -ef

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Use the top Command

The top command provides a real-time view of running processes, showing their CPU and memory usage.

Example:

$ top

Press q to exit the top view.

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Use the htop Command

The htop command (if installed) offers an interactive, colorful view of processes, making it easier to manage them.

Example:

$ htop

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2. Killing Processes

If a process is unresponsive or consuming too many resources, you can terminate it.

Kill a Process by PID

Use the kill command followed by the process’s PID:

$ kill 1234

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Forcefully Kill a Process

If a process doesn’t terminate with kill, use the -9 option:

$ kill -9 1234

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Kill by Name with pkill

The pkill command lets you kill processes by name:

$ pkill firefox

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Kill Multiple Processes

You can combine commands like ps and grep with xargs to kill multiple processes.

Example:

$ ps -ef | grep "python" | awk '{print $2}' | xargs kill

This kills all Python processes.

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3. Background and Foreground Processes

Run a Process in the Background

Add & at the end of a command to run it in the background:

$ sleep 100 &

View Background Jobs

Use the jobs command to list background processes:

$ jobs

Bring a Process to the Foreground

Use the fg command followed by the job number:

$ fg %1

Pause a Process

Press Ctrl + Z to pause a running process and move it to the background.

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4. Managing Process Priority

View Process Priority

The top command shows process priorities in the PR and NI columns:

• PR: Process priority.
• NI: Niceness value (ranges from -20 to +19, with lower values being higher priority).

Change Process Priority: renice

The renice command adjusts the priority of a running process.

Example:

• Increase priority:

  $ sudo renice -5 -p 1234

• Decrease priority:

  $ sudo renice 10 -p 1234

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Practice Time!

1. List all processes on your system:

   $ ps -ef

2. Kill a process named “chrome”:

   $ pkill chrome

3. Run a process in the background and then bring it to the foreground:

   $ sleep 100 &
   $ jobs
   $ fg %1

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Summary

• Use ps, top, or htop to monitor processes.
• Use kill and pkill to terminate processes by PID or name.
• Manage process priority with renice.
• Use jobs and fg to control background and foreground processes.