Service and Process Management

Services and processes are background workloads controlled with systemd, signals, and job control.

Overview

• Services can be started, stopped, restarted, enabled, and inspected
• Processes are identified by PIDs and may have parent processes
• Job control and command chaining are common shell workflows

Reference

systemctl

• start, stop, restart, and status control service state
• enable makes a service start at boot
• systemctl list-units --type=service shows active services

systemctl list-units --type=service

Process control

• Common states: running, waiting, stopped, zombie
• kill, pkill, pgrep, and killall send signals or locate processes
• kill -l lists available signals

Job control

• Ctrl+Z suspends the current job
• jobs lists suspended or background jobs
• bg resumes a job in the background
• fg <id> returns a job to the foreground
• & runs a command in the background immediately

Command chaining

• ; runs commands sequentially
• && runs the next command only on success
• | sends stdout from one command to the next

Mental Model

• systemd manages service lifecycle on most modern distributions
• PIDs identify running processes and /proc exposes process details
• Signals request state changes; jobs manage interactive shell work
• Simple commands become more powerful when chained together