How to List Running Services on Linux

In Linux systems, managing services is a critical task for system administrators. Services, also known as daemons, are background processes that perform various functions, from managing network connections to running scheduled tasks. Knowing how to list running services is essential for monitoring system health, troubleshooting issues, and ensuring that essential services are operational. This article will guide you through different methods to list running services on Linux, using various tools and commands, with detailed examples.

Understanding the status of running services helps in maintaining a Linux system efficiently. Services can be managed through different init systems, such as SysVinit, Upstart, or systemd. Each system has its own set of tools and commands for managing services. In this article, we will focus primarily on systemd, the most widely used init system in modern Linux distributions, but will also cover other methods where applicable.

Using Systemd to List Running Services

Systemd is the default init system for many Linux distributions, including Ubuntu, CentOS, Fedora, and Debian. It provides a unified method for managing system services and offers a range of commands to list and manage running services.

Listing All Active Services

To list all active services using systemd, you can use the systemctl command. This command interacts with the systemd system and service manager.

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

• list-units: Lists all active units.
• --type=service: Filters the output to show only services.
• --state=running: Shows only services that are currently running.

Example

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

Output:

UNIT                      LOAD   ACTIVE SUB     DESCRIPTION
acpid.service             loaded active running ACPI event daemon
apache2.service           loaded active running The Apache HTTP Server
dbus.service              loaded active running D-Bus System Message Bus
...

Listing All Services, Including Inactive and Failed

If you need to see all services, including those that are inactive or failed, you can omit the --state option.

systemctl list-units --type=service

Example

$ systemctl list-units --type=service

Output:

UNIT                      LOAD   ACTIVE SUB     DESCRIPTION
acpid.service             loaded active running ACPI event daemon
apache2.service           loaded active running The Apache HTTP Server
dbus.service              loaded active running D-Bus System Message Bus
example.service           loaded inactive dead Example service
...

Checking the Status of a Specific Service

To check the status of a specific service, use the systemctl status command followed by the service name.

systemctl status [service-name]

Example

$ systemctl status apache2

Output:

● apache2.service - The Apache HTTP Server
     Loaded: loaded (/lib/systemd/system/apache2.service; enabled; vendor preset: enabled)
     Active: active (running) since Fri 2024-07-19 12:34:56 UTC; 2h 15min ago
   Main PID: 1234 (apache2)
      Tasks: 6 (limit: 4915)
     Memory: 15.3M
     CGroup: /system.slice/apache2.service
             ├─1234 /usr/sbin/apache2 -k start
             ├─1235 /usr/sbin/apache2 -k start
...

Using the service Command

For systems that use SysVinit or Upstart, the service command is a traditional method for managing services. This command provides a simpler interface for checking the status of services.

Listing All Services

service --status-all

This command lists the status of all services, showing + for running services and - for stopped services.

Example

$ service --status-all

Output:

 [ + ]  acpid
 [ - ]  apache2
 [ + ]  dbus
 [ - ]  example
...

Checking the Status of a Specific Service

To check the status of a specific service:

service [service-name] status

Example

$ service apache2 status

Output:

apache2 is running

Using the ps Command

The ps command can be used to list processes, which includes services running in the background. While not specifically designed for service management, it can be useful for a general overview.

Listing Processes

ps aux

• a: Show processes for all users.
• u: Display the user/owner column.
• x: Show processes not attached to a terminal.

Example

$ ps aux

Output:

USER       PID %CPU %MEM    VSZ   RSS TTY      STAT START   TIME COMMAND
root         1  0.0  0.1  22560  1824 ?        Ss   Jul19   0:01 /sbin/init
www-data   1234  0.0  0.3  23456  3456 ?        S    Jul19   0:02 /usr/sbin/apache2 -k start
...

Using the top Command

The top command provides a real-time view of running processes and their resource usage. It’s useful for monitoring system performance and identifying resource-intensive services.

Running top

top

In the top output, you can see processes, their status, and resource usage.

Example

$ top

Output:

top - 12:50:20 up  2:15,  2 users,  load average: 0.10, 0.15, 0.10
Tasks: 152 total,   2 running, 150 sleeping,   0 stopped,   0 zombie
%Cpu(s):  2.5 us,  1.0 sy,  0.0 ni, 96.0 id,  0.5 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem :  2048348 total,   556972 free,   856828 used,   635548 buff/cache
KiB Swap:        0 total,        0 free,        0 used.  1084884 avail Mem 

  PID USER      PR  NI    VIRT    RES    SHR S  %CPU %MEM     TIME+ COMMAND
 1234 www-data  20   0  23456  3456  1234 S   0.1  0.2   0:01.23 apache2
...

Using htop for Enhanced Visualization

htop is an interactive process viewer that provides a more user-friendly and colorful display compared to top.

Installing htop

On Debian-based systems:

sudo apt install htop

On Red Hat-based systems:

sudo yum install htop

On Fedora:

sudo dnf install htop

Running htop

htop

Example

$ htop

Output:

A color-coded, interactive process list with CPU, memory, and swap usage graphs.

Additional Tips

• Understanding Service States: Knowing the different states of services (active, inactive, failed) can help in diagnosing system issues. Use systemctl list-units --type=service to see these states.
• Checking Logs: If a service is not running as expected, check its logs using journalctl -u [service-name] for systemd services or /var/log/ for traditional services.
• Service Management: Besides listing, you may need to start, stop, or restart services. Commands like systemctl start [service-name], systemctl stop [service-name], and systemctl restart [service-name] are useful in such scenarios.

Wrap up

Listing running services is an essential skill for Linux system administrators. Whether using systemd, SysVinit, or Upstart, understanding how to view and manage services ensures that your system runs smoothly and reliably.

From using systemctl to explore service statuses to employing ps, top, and htop for process insights, each tool provides unique advantages for monitoring and managing your Linux environment.

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