Rocky Linux Core Commands: Page 8

This page covers commands for managing processes, sending signals, and handling background/foreground jobs.

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36. kill - Send Signals to Processes

Purpose: The kill command is used to send signals to processes. The most common use is to terminate processes (kill them).

Syntax: kill [SIGNAL] PID...

Common Signals:

• -9 or SIGKILL: Forceful termination. Cannot be caught or ignored by the process. Use as a last resort.
• -15 or SIGTERM: Graceful termination. Asks the process to shut down. The process can perform cleanup before exiting. This is the default signal if none is specified.

You can find the PID (Process ID) using commands like ps aux or top.

Examples:

kill 12345             # Send SIGTERM (15) to PID 12345
kill -9 54321          # Forcefully kill PID 54321

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37. killall - Kill Processes by Name

Purpose: The killall command terminates processes by their name, rather than by their process ID (PID). This is useful for stopping all instances of a specific application.

Syntax: killall [OPTIONS] PROCESS_NAME...

Key Options:

• -SIGNAL: Specify the signal to send (e.g., -9 for SIGKILL).

Examples:

killall firefox
killall -9 nginx

Caution: Ensure you know what processes you are killing, as this affects all instances with that name.

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38. bg - Send a Job to the Background

Purpose: The bg command resumes a suspended (stopped) job in the background. It allows the job to continue executing without tying up your terminal.

To suspend a running foreground job, press Ctrl+Z.

Syntax: bg [JOB_SPEC]

Examples:

# Run a long command, then press Ctrl+Z
# You'll see: [1]+  Stopped        long_running_script.sh
bg

This will resume the job in the background.

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39. fg - Bring a Job to the Foreground

Purpose: The fg command brings a job that is running in the background (or suspended) back to the foreground, allowing you to interact with it directly in your terminal.

Syntax: fg [JOB_SPEC]

Examples:

# After running `bg` on a job, bring it back:
fg
# If you have multiple background jobs, use 'jobs' to see their numbers
# then 'fg %JOB_NUMBER' (e.g., fg %2)

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40. jobs - List Active Jobs

Purpose: The jobs command displays a list of currently active jobs (processes started from the current shell) that are either running in the background or suspended.

Syntax: jobs [OPTIONS]

Examples:

jobs

Output typically shows the job number, status (Running/Stopped), and the command that was executed.