10.8.5. Q: When I restore after booting from the media, I sometimes get errors like, "Running out of memory" or "Segmentation fault". What is going on?
From their FAQ:

A: It sounds as if you are running out of disk space, probably ram disk space. Type 'df -m' to see which partitions are running low on space. Please send as much information as you can to the mondorescue mailing list. This problem is believed to have been fixed in 1.63 and 1.71.

MondoRescue HOWTO

If you have the ability to do so, you can take a "poor man's" backup of the machine to clone it by putting the other disk into an enclosure (USB or Firewire) and then attaching it to the original machine.

If you can take downtime, drop to single user mode and copy the physical device to the other physical device such as:

dd if=/dev/sda of=/dev/sdb

where "if" is the input file (the disk you are copying) and "of" is the output file, the place you are copying it to.

This will copy EVERYTHING from the first disk to the second disk, barring failures or hardware issues. However, it will copy blank space and will take a long time. Figure on about 6hrs easily.

Also, if you accidentally screw up the if and of parts, you will have destroyed your machine (No joke, all data will be lost)