How To List Services In Linux

How to List Services in Linux

Misconfigured or malfunctioning services cripple infrastructure fast. Knowing which daemons are up, which are enabled at boot, and which have failed is fundamental—regardless of whether the system runs Ubuntu 22.04 (systemd), Debian 7 (SysVinit), or some Frankenstein hybrid in production.

Understand: What "Services" Means in Practice

In Linux, "services" are long-running background processes—database engines, SSH daemons, monitoring agents. Most are started via the system init daemon; some are socket-activated, others started manually.

Modern Systems: systemd (systemctl)

List All Service Unit Files

See everything present, regardless of whether it's enabled/running:

systemctl list-unit-files --type=service

This lists service units like:

nginx.service        enabled
fail2ban.service     enabled
app-migrator.service disabled
cups-browsed.service disabled

Note: masked means the service is explicitly blocked from starting, often to avoid accidental activation.

View Only Running Services

For ongoing troubleshooting or resource usage checks:

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

Provides:

postgresql.service   loaded active running   PostgreSQL RDBMS
sshd.service         loaded active running   OpenSSH server daemon

Expect transient *.service units for short-lived ones (e.g., systemd-update-utmp-runlevel.service).

Inspect a Specific Service

systemctl status nginx.service

Returns state, cgroup, logs, and exit code. Look for lines like:

Active: failed (Result: exit-code) since ...
Main PID: 1023 (code=exited, status=1/FAILURE)

Gotcha

If troubleshooting why something isn't enabled at boot, use:

systemctl is-enabled yourservice.service

This avoids misreading a deactivated service as simply "inactive".

SysVinit / Legacy Systems

Enumerate All Services

service --status-all

Outputs:

 [ + ]  ssh
 [ - ]  rsync
 [ ? ]  httpd

[ + ] = running, [ - ] = stopped, [ ? ] = unknown/unclear status.

Status of a Single Service

service ssh status

Older Debian/Ubuntu systems might output very limited information if the LSB (Linux Standard Base) script lacks status support.

Non-obvious tip

On certain distributions, /etc/init.d/yourservice status gives more detail. However, some init scripts don’t implement the status action—returns code 3.

RHEL/CentOS Extras: chkconfig

For static runlevel configuration (esp. RHEL 6.x and CentOS 6.x):

chkconfig --list

Gives a matrix of runlevels vs. enabled state (on/off). Useful for verifying startup order after legacy migrations.

Ad Hoc: Process Lists

Sometimes you just want to check if a rogue daemon is alive, regardless of the init system:

ps aux | grep [n]ginx

This filters out the grep process itself and shows matching processes. Pair with pgrep for a cleaner approach:

pgrep -fl nginx

Common Scenarios—What Fails and Why

• Service appears enabled but isn't running: Check systemctl status for ExecStartPre or ExecStart failures—commonly permissions or missing directory.
• Old init scripts after systemd migration: Check /lib/systemd/system-generators/ for compatibility issues.
• Masked services: They won’t start—even if you issue a start command.
  Unmask with:

  systemctl unmask bad.service
  

• Note: systemctl --failed quickly lists units that have failed startup—essential for post-reboot analysis.

Quick Reference Table

Summary

Service visibility isn’t perfect—especially with mish-mashed environments or half-migrated init setups. Confirm the init system before running commands. Whenever possible, combine systemctl list-unit-files with real process listings (ps, pgrep) and journal logs (journalctl -u servicename) for the clearest operational picture. Don't trust default service statuses in containers—PID 1 could be the service itself with no init system at all. If you care about runtime state automation, wire these queries into your monitoring.

Side note:
There are third-party tools like htop, monit, and GUIs for service management. Not covered here—they add complexity, not always clarity. Stick with the shell for critical triage.