[Swan-dev] f22 vms and corrupt prompt: -bash-4.3#

[Neal P. Murphy]

On Mon, 4 Jul 2016 15:12:19 -0400
Andrew Cagney <andrew.cagney at gmail.com> wrote:

> If you notice kvm testsuite crashes that have something to do with a
> failed login then check for the text:
> 
>    -bash-4.3#
> 
> somewhere in the output.  What's happened is the VM has somehow become
> corrupt and needs a rebuild.
> 
> The sequence below is one trigger; however I've also seen this when a
> normal reboot was in play:
> 
> -- start the domain
> 
> $ sudo virsh start f22.east
> Domain f22.east started
> 
> -- connect to the console and let it boot/login:
> 
> $ sudo virsh console f22.east
> Connected to domain f22.east
> Escape character is ^]
> [...]
> east login: root
> Password:
> [root at east ~]#
> 
> -- now lets pull the virtual power cord
> 
> $ sudo virsh destroy f22.east
> Domain f22.east destroyed
> $ sudo virsh start f22.east
> Domain f22.east started
> 
> -- again let the machine boot and log in
> 
> $ sudo virsh console f22.east
> [...]
> east login: root
> Password:
> Last login: Mon Jul  4 14:56:08 on ttyS0
> -bash-4.3#
> 
> -- notice how the prompt isn't the usual "[root at east ~]# "!
> 
> It might take a few tries :-) and once the damage is done it stays
> damaged - the VM needs rebuilding.
> 
> I tend to suspect f22 more than KVM - it has a log file system (I
> assume), and at the time the cord was pulled was relatively "idle", so
> really should survive these reboots.
> 
> Hints on what to look for also welcome.

Is the VM's disk cache set to write-through (write() doesn't return until the host says data are on disk; this can cause huge amounts of data writes to be queued in the VM and, thus, lost in a virtual power failure) or write-back (writes cache in hosts' disk cache, to be written to disk 'later')? If you trust your host OS and hardware, write-back is preferred. And generally much faster.