[redundant](https://www.freedesktop.org/software/systemd/man/systemctl.html]:
```
Unit commands listed above take either a single unit name (designated as UNIT), or multiple unit specifications (designated as PATTERN…). In the first case, the unit name with or without a suffix must be given. If the suffix is not specified (unit name is "abbreviated"), systemctl will append a suitable suffix, ".service" by default, and a type-specific suffix in case of commands which operate only on specific unit types. For example,
# systemctl start sshd
and
# systemctl start sshd.service
are equivalent
```
Anton Kutepov