Comment 57 for bug 525154

In another limitation of upstart, or at least upstart is most likely responsible, the "recovery mode" boot hangs when in the /etc/fstab shown in #55 either /dev/sda6 is corrupt or there are network problems and the NFS mounts are not available. I guess using Mandriva spoiled me, because there booting "failsafe" resulted in the init being bright enough to start only the barest minimum of the operating system. Mandriva (and presumably RedHat and CentOS) come up when networks are broken and partitions (other than /boot and /) are screwed up. Not so Ubuntu - it tries to mount everything in /etc/fstab even when "single" is passed as a kernel option. Moreover, due to upstart's parallel nature, it isn't entirely clear at what point it is locking - it might not even be directly after the failed mount warnings, that might indirectly break something else. Perhaps there is some other Ubuntu/upstart specific kernel option to invoke a more low level boot, but if there is, that raises the question why it was not employed by the "recovery mode" boot option Ubuntu created at installation.