Linux Processes and Jobs: A Beginner's Guide

A process is a running program. Linux assigns each process a process ID (PID), and records details such as its owner, parent process, state, and resource use. The shell can also run a job in the background while you continue working.

This guide uses a harmless sleep command as a practice process. Keep the same terminal open while following the steps so the shell can track the job.

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Step 1: List Running Processes

01

View a Process Snapshot

Process Basics

Use ps for a one-time snapshot and top for a live, refreshing view. Press q to leave top. The PID identifies a process; PPID identifies its parent. The example sorts your user’s processes by CPU use. CPU time is accumulated since the process started, not a live percentage.

ps -u "$USER" -o pid,ppid,stat,%cpu,%mem,etime,comm --sort=-%cpu | head -n 15
top

❯ View Expected Console Output

PID   PPID STAT %CPU %MEM ELAPSED COMMAND
2184  2101 S     1.2  0.8    02:31 firefox
2417  2101 S     0.1  0.2    01:09 bash

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Step 2: Find a Process by Name and Inspect Its PID

02

Search for a Process and Read Its Details

Identify

pgrep -a searches process names and prints matching command lines. Use the PID from the result to inspect one process with ps. Process names and available details vary by distribution and permissions.

pgrep -a -u "$USER" bash

# Replace 2417 with a PID returned by pgrep.
ps -p 2417 -o pid,ppid,user,stat,etime,args

❯ View Expected Console Output

2417 bash
  PID  PPID USER  STAT ELAPSED COMMAND
 2417  2101 sam   S       01:09 bash

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Step 3: Start and Track a Background Job

03

Run a Practice Command in the Background

Shell Jobs

Add & to start a command in the background. The shell prints a job number and PID. jobs -l shows jobs started by this shell; it is not a system-wide process list. Save the PID in a variable so you can identify this exact practice process later.

sleep 300 &
LAB_PID=$!
jobs -l
ps -p "$LAB_PID" -o pid,ppid,stat,etime,args

❯ View Expected Console Output

[1] 3150
[1]+ 3150 Running                 sleep 300 &
  PID  PPID STAT ELAPSED COMMAND
 3150  2417 S       00:00 sleep 300

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Step 4: Stop the Practice Process Cleanly

04

Send SIGTERM to the PID You Started

Safe Control

With no signal specified, kill sends SIGTERM, which lets a program handle a clean shutdown. Confirm the PID belongs to the practice command before signaling it. Then wait for the job and check that it has exited.

ps -p "$LAB_PID" -o pid,comm
kill -TERM "$LAB_PID"
wait "$LAB_PID" 2>/dev/null || true
ps -p "$LAB_PID" -o pid,comm

❯ View Expected Console Output

  PID COMMAND
 3150 sleep
  PID COMMAND

Use SIGKILL only as a last resort

kill -9 sends SIGKILL, which a process cannot catch to clean up temporary state or close files. First confirm the PID, try the normal SIGTERM, and investigate why it did not exit. Do not signal a PID copied from an old note; PIDs can be reused.

Foreground jobs and Ctrl+C

A foreground command occupies the shell until it exits. Pressing Ctrl+C sends an interrupt to the foreground job. In a shell, Ctrl+Z suspends a foreground job; bg resumes it in the background and fg brings it back. These job-control commands apply to jobs in the current shell.

References

• Linux ps manual
• Linux pgrep and pkill manual
• Linux kill manual