I am getting crashes when trying to run innobackupex --apply-log. How can I find out what files it's processing at the time? I don't see a relevant option mentioned in the documentation.
Check the version you used to backup the data is the same as the one you are trying to use to restore. This can bite.
One easy way to do this would be by using strace, for example:
$ strace -e trace=open xtrabackup --prepare --target-dir=2014-11-27_06-06-49
Change 2014-11-27_06-06-49 for the path to your unprepared backup location. I'm using here xtrabackup as it is the lower level tool that innobackupex uses internally.
A poor man's replacement would be to do a polling, with something like this on a different session:
$ while true; do lsof +D ./2014-11-27_06-06-49 ; sleep 0.1; done
Again, change ./2014-11-27_06-06-49 for your backup location and adjust the sleep time if convenient.