diff --git a/knowledge base/systemd.md b/knowledge base/systemd.md
index d4908ba..f8e1f9a 100644
--- a/knowledge base/systemd.md	
+++ b/knowledge base/systemd.md	
@@ -7,29 +7,32 @@
 systemctl list-unit-files
 
 # List failed units only.
-systemctl list-units --state=failed
+systemctl list-units --state='failed'
 
 # Start services.
-sudo systemctl start adb.service
-systemctl --user start keybase.service
+sudo systemctl start 'adb.service'
+systemctl --user start 'keybase.service'
 
 # Restart services.
-sudo systemctl restart bluetooth.service
-systemctl --user restart davmail.service
+sudo systemctl restart 'bluetooth.service'
+systemctl --user restart 'davmail.service'
 
 # Stop services.
-sudo systemctl stop cups.service
-systemctl --user stop davmail.service
+sudo systemctl stop 'cups.service'
+systemctl --user stop 'davmail.service'
 
 # Enable services on boot.
-sudo systemctl enable sshd.service
-sudo systemctl enable --now docker.service
-systemctl --user enable --now davmail.service
+sudo systemctl enable 'sshd.service'
+sudo systemctl enable --now 'docker.service'
+systemctl --user enable --now 'davmail.service'
 
 # Disable services from boot.
-sudo systemctl disable clamav-freshclam.service
-sudo systemctl disable --now gdm.service
-systemctl --user disable --now davmail.service
+sudo systemctl disable 'clamav-freshclam.service'
+sudo systemctl disable --now 'gdm.service'
+systemctl --user disable --now 'davmail.service'
+
+# Check a service is currently active.
+systemctl is-active 'wpa_supplicant.service'
 
 # Suspend the system.
 # Saves the state to RAM only.
@@ -52,8 +55,8 @@ systemctl suspend-then-hibernate
 # Show log entries.
 journalctl
 journalctl -f
-journalctl -n 20
-journalctl -o json-pretty
+journalctl -n '20'
+journalctl -o 'json-pretty'
 journalctl --no-pager
 journalctl --utc
 
@@ -66,22 +69,22 @@ journalctl -b
 journalctl -b -3
 
 # Display logs in a specific time window
-journalctl --since yesterday
+journalctl --since 'yesterday'
 journalctl --since "2015-01-10 17:15:00"
-journalctl --since 09:00 --until "1 hour ago"
+journalctl --since '09:00' --until "1 hour ago"
 journalctl --since "2015-01-10" --until "2015-01-11 03:00"
 
 # Filter logs by unit.
-journalctl -u nginx.service
-journalctl -u nginx.service -u php-fpm.service --since today
+journalctl -u 'nginx.service'
+journalctl -u 'nginx.service' -u 'php-fpm.service' --since 'today'
 
 # Filter logs by process, user id or group id.
-journalctl _PID=8088
-journalctl _UID=33 --since today
-journalctl -F _GID
+journalctl _PID='8088'
+journalctl _UID='33' --since 'today'
+journalctl -F '_GID'
 
 # Filter logs by path.
-journalctl /usr/bin/bash
+journalctl '/usr/bin/bash'
 
 # Display kernel logs only.
 # Works like `dmesg`.
@@ -101,18 +104,18 @@ journalctl -a
 journalctl --disk-usage
 
 # Delete old logs.
-sudo journalctl --vacuum-size=1G
-sudo journalctl --vacuum-time=1years
+sudo journalctl --vacuum-size='1G'
+sudo journalctl --vacuum-time='1years'
 
 # List available timezones.
 timedatectl list-timezones
 
 # Set timezones.
-sudo timedatectl set-timezone UTC
-sudo timedatectl set-timezone Europe/Dublin
+sudo timedatectl set-timezone 'UTC'
+sudo timedatectl set-timezone 'Europe/Dublin'
 
 # Set the time.
-sudo timedatectl set-time 15:58:30
+sudo timedatectl set-time '15:58:30'
 sudo timedatectl set-time '2015-11-20 16:14:50'
 
 # Set the hardware clock to UTC.
@@ -134,8 +137,8 @@ hostnamectl --pretty status
 hostnamectl --static status
 
 # Set hostnames.
-hostnamectl set-hostname staticky --static
-hostnamectl set-hostname prettiky --pretty
+hostnamectl set-hostname 'static_hostname' --static
+hostnamectl set-hostname 'pretty_hostname' --pretty
 ```
 
 ## User services
@@ -158,8 +161,8 @@ EOF
 and can be acted upon as normal using `systemctl`'s `--user` switch
 
 ```sh
-systemctl --user enable --now davmail.service
-systemctl --user status davmail.service
+systemctl --user enable --now 'davmail.service'
+systemctl --user status 'davmail.service'
 ```
 
 ## Keep past boots record (persistent logging)
@@ -179,7 +182,7 @@ Storage=persistent
 1. disable and stop the systemd-resolved service:
 
    ```sh
-   sudo systemctl disable --now systemd-resolved.service
+   sudo systemctl disable --now 'systemd-resolved.service'
    ```
 
 1. set NetworkManager to use the default DNS resolution.
@@ -193,13 +196,13 @@ Storage=persistent
 1. delete `/etc/resolv.conf`:
 
    ```sh
-   sudo unlink /etc/resolv.conf
+   sudo unlink '/etc/resolv.conf'
    ```
 
 1. restart NetworkManager
 
    ```sh
-   sudo service network-manager restart
+   sudo service 'network-manager' restart
    ```
 
 ## Sources