Repairing an Unbootable System

ZFS is designed to be robust and stable despite errors. Even so, software bugs or certain unexpected pathologies might cause the system to panic when a pool is accessed. As part of the boot process, each pool must be opened, which means that such failures will cause a system to enter into a panic-reboot loop. In order to recover from this situation, ZFS must be informed not to look for any pools on startup.

ZFS maintains an internal cache of available pools and their configurations in /etc/zfs/zpool.cache. The location and contents of this file are private and are subject to change. If the system becomes unbootable, boot to the none milestone by using the m milestone=none boot option. Once the system is up, remount your root file system as writable and then remove /etc/zfs/zpool.cache. These actions cause ZFS to forget that any pools exist on the system, preventing it from trying to access the bad pool causing the problem. You can then proceed to a normal system state by issuing the svcadm milestone all command. You can use a similar process when booting from an alternate root to perform repairs.

Once the system is up, you can attempt to import the pool by using the zpool import command. However, doing so will likely cause the same error that occurred during boot, because the command uses the same mechanism to access pools. If more than one pool is on the system and you want to import a specific pool without accessing any other pools, you must re-initialize the devices in the damaged pool, at which point you can safely import the good pool.