To check whether a service is running, use the is-active subcommand. The output would either be active) or inactive, as shown in the following examples:

sudo systemctl is-active httpd

active

systemctl is-active sshd

inactive

The status subcommand provides a detailed summary of the status of a service, including a tree that displays the tasks in the control group (CGroup) that the service implements:

sudo systemctl status httpd

httpd.service - The Apache HTTP Server
   Loaded: loaded (/usr/lib/systemd/system/httpd.service; enabled; vendor preset: disabled)
   Active: active (running) since ...
     Docs: man:httpd.service(8)
 Main PID: 11832 (httpd)
   Status: "Started, listening on: port 80"
    Tasks: 213 (limit: 26213)
   Memory: 32.5M
   CGroup: /system.slice/httpd.service
           ├─11832 /usr/sbin/httpd -DFOREGROUND
           ├─11833 /usr/sbin/httpd -DFOREGROUND
           ├─11834 /usr/sbin/httpd -DFOREGROUND
           ├─11835 /usr/sbin/httpd -DFOREGROUND
           └─11836 /usr/sbin/httpd -DFOREGROUND

Jul 17 00:14:32 Unknown systemd[1]: Starting The Apache HTTP Server...
Jul 17 00:14:32 Unknown httpd[11832]: Server configured, listening on: port 80
Jul 17 00:14:32 Unknown systemd[1]: Started The Apache HTTP Server.

A cgroup is a collection of processes that are bound together so that you can control their access to system resources. In the example, the cgroup for the httpd service is httpd.service, which is in the system slice.

Slices divide the cgroups on a system into different categories. To display the slice and cgroup hierarchy, use the systemd-cgls command:

sudo systemd-cgls

Control group /:
-.slice
├─user.slice
│ └─user-1000.slice
│   ├─user@1000.service
│   │ └─init.scope
│   │   ├─6488 /usr/lib/systemd/systemd --user
│   │   └─6492 (sd-pam)
│   └─session-7.scope
│     ├─6484 sshd: root [priv]
│     ├─6498 sshd: root@pts/0
│     ├─6499 -bash
│     ├─6524 sudo systemd-cgls
│     ├─6526 systemd-cgls
│     └─6527 less
├─init.scope
│ └─1 /usr/lib/systemd/systemd --switched-root --system --deserialize 16
└─system.slice
  ├─rngd.service
  │ └─1266 /sbin/rngd -f --fill-watermark=0
  ├─irqbalance.service
  │ └─1247 /usr/sbin/irqbalance --foreground
  ├─libstoragemgmt.service
  │ └─1201 /usr/bin/lsmd -d
  ├─systemd-udevd.service
  │ └─1060 /usr/lib/systemd/systemd-udevd
  ├─polkit.service
  │ └─1241 /usr/lib/polkit-1/polkitd --no-debug
  ├─chronyd.service
  │ └─1249 /usr/sbin/chronyd
  ├─auditd.service
  │ ├─1152 /sbin/auditd
  │ └─1154 /usr/sbin/sedispatch
  ├─tuned.service
  │ └─1382 /usr/libexec/platform-python -Es /usr/sbin/tuned -l -P
  ├─systemd-journald.service
  │ └─1027 /usr/lib/systemd/systemd-journald
  ├─atd.service
  │ └─1812 /usr/sbin/atd -f
  ├─sshd.service
  │ └─1781 /usr/sbin/sshd

The system.slice contains services and other system processes. user.slice contains user processes, which run within transient cgroups called scopes. In the example, the processes for the user with ID 1000 are running in the scope session-7.scope under the slice /user.slice/user-1000.slice.

You can use the systemctl command to limit the CPU, I/O, memory, and other resources that are available to the processes in service and scope cgroups. See Controlling Access to System Resources.

For more information, see the systemctl(1) and systemd-cgls(1) manual pages.