Disable all services, except ssh
This sounds a lot like runlevels, replaced with targets in Systemd. So, instead of writing a script that starts and stop a list of services, you could create a new
maintenance.target containing only the services necessary, like SSH. Of course, SSH is not quite useful without networking, so in this example a simple
emergency-net.target is modified to include SSH.
[Unit] Description=Maintenance Mode with Networking and SSH Requires=maintenance.target systemd-networkd.service sshd.service After=maintenance.target systemd-networkd.service sshd.service AllowIsolate=yes
Then, you could enter your maintenance mode using
# systemctl isolate maintenance.target
# systemctl isolate multi-user.target
First list your services and search for their corresponding systemd-names.
Then build a list and stop each list member to enter maintenance, start each member after maintenance.