Comment 3 for bug 1507796

It looks as if I downloaded a Ubuntu MATE 5.10 beta just shortly before the non-beta became available. The non-beta, just as the beta, has a panic in init when booted with an argument of "persistent". What follows are details about the panic in the beta. I have not investigated whether the details are the same in the non-beta, but I suspect they are.

A "No init found" panic occurs in init because an executable sbin/init file is not in the file system built by the mountroot function of /scripts/casper.

A sbin/init file is not there because the mountroot function did not properly do a union mount in the function setup_unionfs of /scripts/casper.

It did not because it did not find any ro filesystems to use in the union mount. It should have found at least /cdrom/casper/filesystem.squashfs. The live boot drive is expected to be mounted at /cdrom at that time.

It did not because earlier in the setup_unionfs function of /scripts/capser, /cdrom was unmounted within the find_cow_device function of /scripts/casper-helpers when that function was used to find a rw persistent filesystem.

The panic does not occur with Ubuntu MATE 15.04, because its setup_unionfs function is not the same as the one in Ubuntu MATE 15.10. In 15.04 the ro filesystems to be used in the union mount are mounted before the find_cow_device function is used. I suspect, but have not tried to confirm, that in 15.04 the unmount of /cdrom done in find_cow_device fails because the device is busy: /cdrom/casper/filesystem.squashfsis is currently mounted.