In Linux, effective process control and termination are crucial for managing system resources and ensuring smooth operation. Users and administrators often need to pause, resume, or terminate processes based on system demands or troubleshooting needs. Linux provides a rich set of commands and signals to control running processes, facilitating graceful shutdowns or immediate termination when necessary.
Process Control Basics
Efficient multitasking in Linux depends on understanding process control. Below is a list of essential job control concepts and commands.
1. Foreground and Background Processes:
- Foreground processes run interactively with terminal input/output.
- Background processes run independently, freeing the terminal for other tasks.
2. Job Control Commands:
- bg: Resume a suspended process in the background.
- fg: Bring a background or suspended job to the foreground.
- jobs: List current jobs started by the terminal session with their states (running, stopped).
Example:
$ sleep 500
^Z
[1]+ Stopped sleep 500
$ bg 1
[1]+ sleep 500 &Signals for Process Management
Linux processes respond to signals—notifications sent to trigger actions like termination or suspension.
Sending Signals to Processes
Sending signals helps suspend, resume, or terminate running processes. Following are the Linux commands used for process signaling.
1. kill Command: Sends signals to specific processes by PID.
Usage:
kill PID # sends SIGTERM by default
kill -9 PID # sends SIGKILL to force termination
kill -s SIGSTOP PID # suspends process2. killall Command: Sends a signal to all processes by name.
Usage:
killall processname
killall -9 processname3. pkill Command: Similar to killall but with more pattern matching options.
Suspending and Resuming Processes
Suspending a process frees the terminal without stopping execution permanently. The following commands explain how to pause and continue processes.
- Suspend current foreground process: Press Ctrl+Z.
- List suspended and background jobs:
jobs- Resume job in background:
bg %job_number- Resume job in foreground:
fg %job_numberPractical Example Workflow
1. Start a long-running command:
tar -czvf backup.tar.gz /home/user2. Suspend it: press Ctrl+Z.
3. View jobs:
jobs4. Resume it in background:
bg %15. If needed, terminate forcefully:
kill -9 PID