There are two types of people in the world; those who have lost data and those who are about to. Given that entropy will bite eventually, the objective should be to minimise data loss. Some key rules for this backup, backup often, and backup with redundancy. Whilst an article on that subject will be produced, at this stage discussion is directed to the very specific task of recovering data from old machines which may not be accessible anymore using Linux. There number of times I've done this in past years is somewhat more than the number of fingers I have - however, like all good things it deserves to be documented in the hope that other people might find it useful.

To do this one will need a Linux live distribution of some sort as an ISO, as a bootable USB drive. A typical choice would be a Ubuntu Live or Fedora Live. If one is dealing with damaged hardware the old Slackware-derived minimalist distribution Recovery is Possible (RIP) is certainly worth using; it's certainly saved me in the past. If you need help in creating a bootable USB, the good people at HowToGeek provide some simple instructions.

With a Linux bootable disk of some description inserted in one's system, the recovery process can begin. Firstly, boot the machine and change the book order (in BIOS/UEFI) that the drive in question becomes the first in the boot order. Once the live distribution boots up, usually in a GUI environment, one needs to open the terminal application (e.g., GNOME in Fedora uses Applications, System Tools, Terminal) and change to the root user with the su command for Fedora or sudo -i for Ubuntu (there's no password on a live CD to be root!).

At this point one needs to create a mount point directory, where the data is going to be stored; mkdir /mnt/recovery. After this one needs to identify the disk which one is trying to access. The fdisk -l command will provide a list of all disks in the partition table. Some educated guesswork from the results is required here, which will provide the device filesystem Type; it almost certainly isn't an EFI System, or Linux swap for example. Typically one is trying to access something like: /dev/sdaX

Then one must mount the device to the directory that was just created, for example: mount /dev/sda2 /mnt/recovery. Sometimes a recalcitrant device will need to have the filesystem explicitly stated; the most common being ext3, ext4, fat, xfs, vfat, and ntfs-3g. To give a recent example I needed to run mount -t ext3 /dev/sda3 /mnt/recovery. From there one can copy the data from the mount point to a new source; a USB drive is probably the quickest, although one may take the opportunity to copy it to an external system (e.g., google drive) - and that's it! You've recovered your data!