50 lines
1.6 KiB
Markdown
50 lines
1.6 KiB
Markdown
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---
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title: "NixOS: Stuck Boot (bad systemd unit)"
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date: 2024-01-07
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layout: Post
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---
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One of my systems at home runs NixOS and receives some (encrypted) backups via
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`zfs send`/`zfs recv` shenanigans. I don't want to actually decrypt these at
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boot, but I forgot to set `boot.zfs.requestEncryptionCredentials` appropriate,
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so I got dropped into a systemd recovery prompt.
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---
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To fix this enough that the system would boot, I manually made sure that I had
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imported and loaded the necessary keys for the ZFS pool in question (named
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"tank") manually:
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```
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zpool import tank
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zfs load-key tank/enc
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```
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Because zfs-import-tank is configured as `Type=oneshot` and
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`RemainAfterExit=true`, the unit only needs to be marked as successful once,
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then we can reload back to the "broken" config, but the fact that the unit ran
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will be remembered.
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As such, to make the system finish booting enough that I could reliably switch
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to a new system with a fixed config, I copied the systemd unit to /tmp, and
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sneakily edited it to replace the `ExecStart` with
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`/nix/var/nix/profiles/system/sw/bin/true`, then bind-mounted the unit over the
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one in /etc:
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```
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cat /etc/systemd/system/zfs-import-tank.service > /tmp/zfs-import-tank.service
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vim /tmp/zfs-import-tank.service
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mount --bind /tmp/zfs-import-tank.service /etc/systemd/system/zfs-import-tank.service
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# Start our hacked-up zfs-import-tank service
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systemctl daemon-reload
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systemctl start zfs-import-tank
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# Revert the system to its prior state for cleanliness
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umount /etc/systemd/system/zfs-import-tank.service
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systemctl daemon-reload
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# Finish booting
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systemctl default
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```
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