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############
# xfscrash # crash testing setup for XFS
############
*** disclaimers ***
work-in-progress, buyer-beware, your-mileage-may-vary, this-is-a-hack
*** what xfscrash does ***
xfscrash allows realistic testing of XFS log recovery and XFS check/repair
by generating log activity on an XFS partition, then rebooting the machine
at a random point. When the machine comes back up, xfscrash is restarted
and then tests either the log recovery or xfs_repair on the dirtied
filesystem. All going well the process continues.
*** getting ready for crash testing ***
Most filesystems (ext2 included) can't withstand having the machine
they're running on rebooted while they're active. So the crash test
machine needs to have all filesystems other than the test FS mounted
read-only so they won't get trashed when the machine reboots.
*** mouting FSes read-only ***
Following is a recipe for making a redhat linux (6.2) machine with a single
ext2 FS mounted on root able to be booted read-only. Your Mileage May
Vary - don't try this on an important machine.
The idea is to move anything that needs to be r/w into the /initrd_init
directory, replacing the moved directories with links to the moved ones.
That way the /initrd_init directory may be copied to a ramdisk, and
mounted over /initrd on the root FS which never gets remounted r/w.
# go to single user
init 1
# make a mount point for the ramdisk
mkdir /initrd
# link across to the /initrd_init directory for when
# the ramdisk isn't mounted
ln -s /initrd_init/dev .
ln -s /initrd_init/etc .
ln -s /initrd_init/proc .
ln -s /initrd_init/sbin .
ln -s /initrd_init/tmp .
ln -s /initrd_init/var .
# make the /initrd_init directory
mkdir /initrd_init
cd /initrd_init
# move /dev
mv /dev .
ln -s /dev /initrd/dev
# move /etc
mv /etc .
ln -s /etc /initrd/etc
# make proc mount
mkdir proc
# move /tmp
mkdir tmp
rm -rf /tmp
ln -s /tmp /initrd/tmp
# link /sbin
ln -s /sbin .
# setup a tree for parts of /var
mkdir var var/cache var/lock var/lock/console var/lock/subsys
mkdir var/log var/preserve var/run
touch /var/run/utmp /var/log/utmp /var/log/wtmp
# move parts of /var
rm -rf /var/cache /var/lock /var/log /var/preserve /var/run
ln -s /initrd/var/cache /var/cache
ln -s /initrd/var/lock /var/lock
ln -s /initrd/var/log /var/log
ln -s /initrd/var/preserve /var/preserve
ln -s /initrd/var/run /var/run
# make a mount for /var/shm
mkdir var/shm
ln -s /var/shm /initrd/var/shm
# move /var/spool
mkdir var/spool
mkdir var/spool/mail var/spool/anacron var/spool/at var/spool/lpd
mkdir var/spool/rwho var/spool/mqueue var/spool/cron
rm -rf /var/spool
ln -s /var/spool /initrd/var/spool
# move /var/tmp
mkdir var/tmp
rm -rf /var/tmp
ln -s /var/tmp /initrd/var/tmp
# trim /dev - too many inodes here - remove anything you don't need
# (small ramdisk has a small number of inodes)
rm -rf /initrd/dev/<....>
All going well, all the directories you've made should link through
/initrd and into /initrd_init, and the machine should come back up
if you restart it.
You want to keep the contents of /initrd_init to a minimum because
this stuff has to fit into the ramdisk.
*** getting the ramdisk going ***
See the rc.sysinit file for some details of what to do to get the
ro-root/ramdisk up and running.
Once everything is going, the root FS should never be remounted to
r/w on boot and should be in r/o mode when the machine comes up.
All going well, any open files have been redirected through the
symlinks onto the ramdisk, so you should be able to remount the
root FS to r/w and then remount it back to r/o.
Since there's no r/w filesystems mounted, it should be ok to
reboot the machine with 'reboot -fn' and everything should come
back without dirty filesystems and without having to fsck.
*** starting xfscrash ***
The simplest way to restart xfscrash on reboot is to start it
in the background from rc.local. The script logs to /dev/tty1,
/dev/console & a logfile by default, so the output should be
easy to find.
Link the xfscrash directory off an NFS mounted FS so you can make
changes while the machine is rebooting and so you can touch the
'stop' and 'start' control files.
To configure the system, change the parameters in the configuration
section of the 'xfscrash' script.
To start the system, touch the 'start' control file and then either
reboot or manually run the 'xfscrash' script.
To stop the system, touch the 'stop' control file and wait for the
next cycle to start when the control file will be checked and
the test terminated.
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