List all socket units

All socket-activated units and their state

systemctl list-units --type=socket --all

More systemd commands

Mask a service

systemctl mask snapd.service

Prevent a service from being started by anything
Show environment of service

systemctl show myapp.service -p Environment

Print environment variables injected into the service
Boot critical chain

systemd-analyze critical-chain <unit>

Show the serialized dependency chain that actually delays boot; more honest than blame
Boot timeline SVG

systemd-analyze plot > boot.svg

Render full parallel boot timeline as an SVG to spot serialized stalls visually
Drop-in override

systemctl edit <unit> # writes /etc/systemd/system/<unit>.d/override.conf

Patch a unit via drop-in without touching the vendor file; use --full to fork the whole unit