Process Management & System Services Flashcards

Which command provides a dynamic, real-time, auto-refreshing view of system processes sorted by resource usage?

Answer: top

top displays an interactive and continuously updated view of processes, memory, and CPU usage, refreshing every few seconds by default.

How does 'systemctl mask nginx' differ from 'systemctl disable nginx'?

Answer: It prevents the service from being started by any means, including manually or as a dependency

Masking creates a symlink from the unit file to /dev/null, completely blocking all start attempts whether manual, automatic, or as a dependency.

What happens when you append an ampersand (&) to a shell command such as 'long-script.sh &'?

Answer: The command runs in the background, freeing the terminal for other commands

Appending & runs the command as a background job, returning control to the shell immediately while the process continues running.

What is the primary purpose of the 'at' command in Linux?

Answer: To schedule a one-time command to execute at a specified future time

The at command schedules a command or script to run exactly once at a specified future time, which distinguishes it from cron's recurring scheduling.

Which signal cannot be caught, blocked, or ignored by any process, including processes running as root?

Answer: SIGKILL (9)

SIGKILL is handled entirely by the kernel and bypasses any signal handlers registered by the process, guaranteeing termination.

What does the 'fuser' command identify when run against a specific file or device?

Answer: The PIDs of processes that currently have the file or device open

fuser reports the PIDs of processes using a specified file, directory, or socket, which is useful for diagnosing 'device is busy' errors.

Which command lists all cron jobs configured for a specific user named 'webadmin'?

Answer: crontab -u webadmin -l

crontab -u -l lists the crontab entries for the specified user; this requires root or sudo privileges to view another user's crontab.