While running Ubuntu 18.04.1 on a laptop, the following errors were observed.
mce: hardware error cpu 0 machine check 0 bank 6 ae0000000040110a mce: hardware error tsc 0 addr ffb07540 misc 238a0000086 mce: hardware error processor 0:40651 time 1540082330 socket 0 Apic 0 microcode 24 ipmi dmi invalid offset 0
The system would stop in the single user mode.
2.1 Running fsck
There were some problems with a hard disk partition and it was rectified by running the fsck command for that disk partition, accepting all the corrections suggested by fsck.
$ fsck /dev/sda6
2.2 Re-install of Ubuntu 18.04.1
Ubuntu 18.04.01 was reinstalled. The disk was partitioned such that the OS was on a separate (root) partition and the user home directories were on another partition. The OS was reinstalled on the disk partition mounted as / and care was taken such that the disk partition containing the user directories was not formatted during the re-install process. To do this, one has to choose
Something else as the installation type and NOT check the format box for the partitions containing the user home directories.
2.3 Post re-install
After, the re-installation, there were no errors.