Linux – How to Disable All Services Except SSH

linuxmaintenanceservicesystemd

How can I disable all services except ssh on modern (systemd based) linux distributions?

I need to implement a maintenance mode.

All these services need to be down:

  • postgres
  • postfix
  • apache
  • cups
  • cron
  • dovecot

But ssh must not be shut down, since this gets used to do tasks during the maintenance mode.

Of course I could write a shell script which loops over a list of services which I would like to disable. But this feels like I reinventing something which already exists, but which I don't know up to now.

Best Answer

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

and back

# systemctl isolate multi-user.target
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