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README.md

Process Management in Linux

Introduction to Process Management

A process is an instance of a running program. Linux provides multiple utilities to monitor, manage, and control processes effectively. Each process has a unique Process ID (PID) and belongs to a parent process.

Index of Commands Covered

Viewing Processes

  • ps aux – View all running processes
  • ps -u username – View processes for a specific user
  • ps -C processname – Show a process by name
  • pgrep processname – Find a process by name and return its PID
  • pidof processname – Find the PID of a running program

Managing Processes

  • kill PID – Terminate a process by PID
  • pkill processname – Terminate a process by name
  • kill -9 PID – Force kill a process
  • pkill -9 processname – Kill all instances of a process
  • kill -STOP PID – Stop a running process
  • kill -CONT PID – Resume a stopped process
  • renice -n 10 -p PID – Lower priority of a process
  • renice -n -5 -p PID – Increase priority of a process (requires root)

Background & Foreground Processes

  • command & – Run a command in the background
  • jobs – List background jobs
  • fg %jobnumber – Bring a job to the foreground
  • Ctrl + Z – Suspend a running process
  • bg %jobnumber – Resume a suspended process in the background

Monitoring System Processes

  • top – Interactive process viewer
  • htop – User-friendly process viewer (requires installation)
  • nice -n 10 command – Run a command with a specific priority
  • renice -n -5 -p PID – Change priority of an existing process

Daemon Process Management

  • systemctl list-units --type=service – List all system daemons
  • systemctl start service-name – Start a daemon/service
  • systemctl stop service-name – Stop a daemon/service
  • systemctl enable service-name – Enable a service at startup

Viewing Process Details

Using ps

Show processes for a specific user:

ps -u username

Show a process by name:

ps -C processname

Using pgrep

Find a process by name and return its PID:

pgrep processname

Using pidof

Find the PID of a running program:

pidof processname

Managing Processes

Killing Processes

To terminate a process by PID:

kill PID

To terminate using process name:

pkill processname

Force kill a process:

kill -9 PID

Kill all instances of a process:

pkill -9 processname

Stopping & Resuming Processes

Stop a running process:

kill -STOP PID

Resume a stopped process:

kill -CONT PID

Changing Process Priority

View process priorities:

top  # Look at the NI column

Change priority of a running process:

renice -n 10 -p PID  # Lower priority (positive values)
renice -n -5 -p PID  # Higher priority (negative values, root required)

Running Processes in the Background

Run a command in the background:

command &

List background jobs:

jobs

Bring a job to the foreground:

fg %jobnumber

Send a running process to the background:

Ctrl + Z  # Suspend process
bg %jobnumber  # Resume in background

Monitoring System Processes

Using top

Interactive process viewer:

  • Press k and enter a PID to kill a process.
  • Press r to renice a process.
  • Press q to quit.

Using htop

A user-friendly alternative to top:

htop

Allows mouse-based interaction for process management.

Using nice & renice

Run a command with a specific priority:

nice -n 10 command

Change the priority of an existing process:

renice -n -5 -p PID

Daemon Processes

Daemon processes run in the background without user intervention. List all system daemons:

systemctl list-units --type=service

Start a daemon:

systemctl start service-name

Stop a daemon:

systemctl stop service-name

Enable a service at startup:

systemctl enable service-name

Conclusion

Process management is crucial for system performance and stability. By using tools like ps, top, htop, kill, and nice, you can efficiently control and monitor Linux processes.