# Prevent reboot on kernel panic?



## `Orum (Oct 9, 2016)

I've got a system that I'm booting via the FreeBSD 11 memstick, as I'm trying to copy data from a backup (connected locally) to a fresh root zfs raid-z1 pool.  The dataset in question is about 2.2 TiB that I'm transferring via `zfs send` piped to `zfs recv`, and part of the way through the transfer, the system presumably kernel panics and reboots.

I say "presumably" because I'm not sure if that's what is happening, but if memory serves, FreeBSD waits kern.panic_reboot_wait_time (default 15 seconds), and then reboots, normally leaving a kernel dump.  The problem is, this is a memstick, and the mounted filesystems are mounted on md(), so any dump is lost on a reboot.

In theory, as I already have the base system copied on to the new pool, I could just boot to that to avoid this issue, but then my worry is, if the system is locking due to failed disk writes (which is what I suspect) then it may not be able to write a kernel dump to those disks anyway.  I'd mainly like to just see the panic screen so I can get some idea of what's causing it to reboot.

So what's the canonical way to disable rebooting on a panic?  Would simply running `sysctl kern.panic_reboot_wait_time=0` do it?  Or would that instantly reboot the system ?

Edit: grepping through FreeBSD's source, it looks like, according to line 504 of /sys/kern/kern_shutdown.c, that kern.panic_reboot_wait_time should be set to -1 to prevent rebooting (setting it to 0 is an immediate reboot), assuming I'm reading the source correctly.  I'll give that a try and report back assuming it crashes again.


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