I traced it back to the following:
Before and after the upgrade to 15.04 I was running kernel 4.0 (same as reporter). Apparently with this kernel something doesn't want to trace (whatever that means in this context). As a result no 'pack' file is generated in /var/lib/ureadahead. The missing pack file causes ureadahead again to try to trace on the next boot, which again fails.
Solution: boot one time as 15.04 default kernel (3.19.0) with systemd, not upstart. This will let ureadahead create the 'pack'. Lot's of uninteresting stuff fills syslog (about ignoring relative path blabla). On the next boot with kernel 4.0 ureadahead failure disappeared.
Yes, I had the same.
I traced it back to the following: ureadahead. The missing pack file causes ureadahead again to try to trace on the next boot, which again fails.
Before and after the upgrade to 15.04 I was running kernel 4.0 (same as reporter). Apparently with this kernel something doesn't want to trace (whatever that means in this context). As a result no 'pack' file is generated in /var/lib/
Solution: boot one time as 15.04 default kernel (3.19.0) with systemd, not upstart. This will let ureadahead create the 'pack'. Lot's of uninteresting stuff fills syslog (about ignoring relative path blabla). On the next boot with kernel 4.0 ureadahead failure disappeared.