Service and Process Management

Service and Process Management in Linux#

Overview#

Linux provides robust tools for managing system services and processes. This section explains how to handle background services (daemons) and running processes, with particular focus on modern systems using systemd.

Service Management#

Types of Services#

System Services: Critical services required for system operation (e.g., systemd, sshd)
User-Installed Services: Optional services providing additional functionality (e.g., web servers, databases)

Service Management with systemctl#

The systemctl command is the primary interface for service management in systemd-based systems:

Command	Description
`systemctl start <service_name>`	Starts a specified service
`systemctl status <service_name>`	Displays current status of a service
`systemctl enable <service_name>`	Configures service to start at boot
`systemctl list-units --type=service`	Lists all available services
`journalctl -u <service_name> --no-pager`	Shows service logs

Process Management#

Process States#

Processes may exist in various states:

Running: Actively executing
Waiting: Paused for resources
Stopped: Suspended execution
Zombie: Completed but not yet removed

Process Control Commands#

Process Termination#

Command	Description
`kill <PID>`	Sends termination signal to process
`kill -9 <PID>`	Forces immediate termination (SIGKILL)
`kill -15 <PID>`	Requests graceful termination (SIGTERM)
`kill -19 <PID>`	Stops/pauses a process (SIGSTOP)

Background Process Management#

Command	Description
`[Ctrl + Z]`	Suspends current foreground process
`bg`	Resumes suspended process in background
`command &`	Runs command directly in background
`jobs`	Lists background jobs
`fg`	Brings background job to foreground

Process Monitoring#

Command	Description
`ps -aux`	Lists all running processes
`kill -l`	Displays all available signals
`top`	Interactive process viewer

Practical Examples#

Starting and enabling a service:

systemctl start nginx
systemctl enable nginx

Checking service status:

systemctl status sshd

Terminating a process:

ps -aux | grep chrome
kill -15 1234

Managing background processes:

long_running_command &
jobs
fg %1