Maintenance and Troubleshooting

The administrator’s daily routine: keeping the fleet clean, intervening on a host, rolling back after a bad configuration, reading logs.

Acting on a host

All these commands target a host (or a pattern / list) via colmena:

Command	Effect
`just enter <host>`	Open an SSH shell (alias `e`)
`just reboot <host>`	Reboot
`just halt <host>`	Shutdown
`just gc <host>`	Purge generations + clean the store
`just fix-boot <host>`	Reinstall the boot loader

Clean and format code

Before committing or deploying, normalize the repository:

just clean      # fix + check + generate + format

just check-all : unit tests + flake checking (before deployment).
just gc <host> : reclaim disk space (deletes old generations).

Rollback

Each deployment creates a NixOS generation. In case of issues:

At boot : choose a previous generation from the boot menu.
Live rollback : revert to the previous generation then make it active:
Fenêtre de terminal
```
just enter <host>
sudo nixos-rebuild switch --rollback
```
Through code : git revert the faulty configuration, then redeploy:
Fenêtre de terminal
```
just apply <host>
```

Reading logs

just enter <host>
journalctl -u <service> -n 100 --no-pager     # logs d'un service
journalctl -p err -b                          # erreurs depuis le démarrage
systemctl status <service>                    # état d'une unité