It is reproducible on a clean VM and LXD container.

I guess we have a small data-race during services startup.

I added echo $(date) to maas-rack-controller.postinst just before the line where we call chown
```
+ echo Wed Mar 13 08:55:50 UTC 2024
Wed Mar 13 08:55:50 UTC 2024
```

After inspecting `journalctl -u maas-rackd` it is clear that the first attempt to start rackd happens before the maas-rack-controller.postinst script finishes execution.

Mar 13 08:55:46 maas-deb systemd[1]: Starting MAAS Rack Controller...
Mar 13 08:55:46 maas-deb systemd[1]: Started MAAS Rack Controller.
Mar 13 08:55:47 maas-deb rackd[72993]: Traceback (most recent call last):
Mar 13 08:55:47 maas-deb rackd[72993]:   File "/usr/sbin/rackd", line 33, in <module>
Mar 13 08:55:47 maas-deb rackd[72993]:     sys.exit(load_entry_point('maas==3.5.0rc1', 'console_scripts', 'rackd')())
Mar 13 08:55:47 maas-deb rackd[72993]:   File "/usr/lib/python3/dist-packages/provisioningserver/server.py", line 95, in run
Mar 13 08:55:47 maas-deb rackd[72993]:     runService("maas-rackd")
Mar 13 08:55:47 maas-deb rackd[72993]:   File "/usr/lib/python3/dist-packages/provisioningserver/server.py", line 90, in runService
Mar 13 08:55:47 maas-deb rackd[72993]:     UnixApplicationRunner(config).run()
Mar 13 08:55:47 maas-deb rackd[72993]:   File "/usr/lib/python3/dist-packages/twisted/application/app.py", line 370, in run
Mar 13 08:55:47 maas-deb rackd[72993]:     self.application = self.createOrGetApplication()
Mar 13 08:55:47 maas-deb rackd[72993]:   File "/usr/lib/python3/dist-packages/twisted/application/app.py", line 432, in createOrGetApplication
Mar 13 08:55:47 maas-deb rackd[72993]:     ser = plg.makeService(self.config.subOptions)
Mar 13 08:55:47 maas-deb rackd[72993]:   File "/usr/lib/python3/dist-packages/provisioningserver/plugin.py", line 241, in makeService
Mar 13 08:55:47 maas-deb rackd[72993]:     install_boot_method_templates(tftp_root)
Mar 13 08:55:47 maas-deb rackd[72993]:   File "/usr/lib/python3/dist-packages/provisioningserver/boot/__init__.py", line 367, in install_boot_method_templates
Mar 13 08:55:47 maas-deb rackd[72993]:     m.install_templates(tftp_root)
Mar 13 08:55:47 maas-deb rackd[72993]:   File "/usr/lib/python3/dist-packages/provisioningserver/boot/ipxe.py", line 118, in install_templates
Mar 13 08:55:47 maas-deb rackd[72993]:     with open(config_dst, "wb") as stream:
Mar 13 08:55:47 maas-deb rackd[72993]: PermissionError: [Errno 13] Permission denied: '/var/lib/maas/tftp_root/ipxe.cfg'
Mar 13 08:55:47 maas-deb systemd[1]: maas-rackd.service: Main process exited, code=exited, status=1/FAILURE
Mar 13 08:55:47 maas-deb systemd[1]: maas-rackd.service: Failed with result 'exit-code'.
Mar 13 08:55:57 maas-deb systemd[1]: maas-rackd.service: Scheduled restart job, restart counter is at 1.
Mar 13 08:55:57 maas-deb systemd[1]: Stopped MAAS Rack Controller.
Mar 13 08:55:57 maas-deb systemd[1]: Starting MAAS Rack Controller...
Mar 13 08:55:57 maas-deb systemd[1]: Started MAAS Rack Controller.
Mar 13 08:56:50 maas-deb systemd[1]: Stopping MAAS Rack Controller...
Mar 13 08:56:50 maas-deb systemd[1]: maas-rackd.service: Deactivated successfully.
Mar 13 08:56:50 maas-deb systemd[1]: Stopped MAAS Rack Controller.
Mar 13 08:56:50 maas-deb systemd[1]: Starting MAAS Rack Controller...
Mar 13 08:56:50 maas-deb systemd[1]: Started MAAS Rack Controller.


This might happen because of maas-region-controller.postinst trying to start rackd (when both are installed on the same machine)