I'm a relatively new linux\ubuntu user and have run into a serious problem. My Ubuntu 15.4 installation won't boot. I'm not sure why, but when I try to access the grub loader by holding down the shift key, nothing happens. There I some files on the machine I need, so my thought was to boot from a USB drive, then recover the files. I was able to boot the machine from the one bootable USB I had on-hand (which is V 13.10, I think), but now I can't access my files because I don't have ownership privilege. I tried to use sudo from a terminal, but I still can't find my home directory with the files in it. Is there any way to get enough privilege to recover my files? Once I do that, I can either rebuild the operating system or replace the disk if it's bad.
Case 1: I think what went wrong with your bootable USB effort is you forgot to mount your old home folder if you created a separate partition for it.
Case 2: If you didn't create a separate partition for home you need to mount the old root folder.
Once you have done that and you can see the folder but just not access the contents inside it, then you need to
For Case 1:
sudo chown -R "$USER" /<MountPoint>/<OLDUSER>
For Case 2:
sudo chown -R "$USER" /<MountPoint>/home/<OLDUSER>
Replace and appropriately. Then you should be able to contents of folder
When booted with the Live OS, go to your hard drive with a file explorer. Ubuntu will automatically mount the disk. If the disk is not named, you may be able to recognize it by its capacity.
If you do not have permission to access the files on that disk, then you can open the file explorer as root.
The Live OS is probably using the GNOME desktop, which uses Nautilus.
For XFCE the default file explorer is Thunar.