Mastering systemd: List, filter, and manage Linux services with simple commands

Overview of Linux services and systemd

Linux provides a variety of system and network services that run as background daemons. Modern distributions use systemd as the unified service manager, and the systemctl command is the primary interface for controlling these services.

Listing all loaded services

Running systemctl without arguments displays every loaded unit, including services, and shows each unit’s current state. # systemctl To list only service units, use the --type=service option.

# systemctl list-units --type=service

Filtering by service state

To see only active (loaded) services, add --state=active. For services that are currently running, use --state=running.

# systemctl list-units --type=service --state=active

# systemctl list-units --type=service --state=running

Creating a convenient alias

For frequent use, add an alias to ~/.bashrc: # vim ~/.bashrc Append the following line:

alias running_services='systemctl list-units --type=service --state=running'

After saving the file, the new command running_services instantly lists all loaded, running services.

Checking which ports services listen on

Use netstat or ss to display listening sockets. The -l flag shows listening sockets, -t for TCP, -u for UDP, -n for numeric ports, and -p to reveal the owning process.

# netstat -ltup | grep mysqld.service

# ss -ltup | grep zabbix_agentd

The output’s fifth column contains the local address and port; for example, zabbix_agentd listens on port 10050.

Viewing firewall‑allowed services and ports

Depending on the distribution, use firewall-cmd (Firewalld) or ufw to list services and ports permitted through the firewall.

# firewall-cmd --list-services   [FirewallD]
# firewall-cmd --list-ports
$ sudo ufw status                [UFW Firewall]

Summary

We demonstrated how to list and filter systemd services, create a shortcut alias for quickly viewing running services, inspect the ports those services use, and query firewall rules that affect them. These techniques help Linux administrators monitor and manage server workloads efficiently.