System rescue#

System Rescue means recovering a system after it has become unbootable or unstable due to some sort of software complication (e.g. you've locked out yourself from sudo... ) or hardware failure. Mostly you want to access the system to recover data or to fix the problem. These two goals need different approaches.

In case of a hardware failure, you can remove the drive (provided not your hard-drive is the faulty one ) and connect it to another computer to recover data. If you just need to resolve a software issue, you can boot from a live USB and repair the system from there.

Now let's see how to do these.

Recover data#

1. Remove hard-drive and insert to another machine
2. Boot system

3. (If encrypted) Open LUKS container

   cryptsetup open DEVICE LUKS_CONTAINER
   
   where:
   DEVICE              Hard-drive device file (e.g. /dev/sdb)
   LUKS_CONTAINER      Name of the LUKS device (e.g. CRYPT_sdb)
   

4. Mount drive

   mount DRIVE MOUNT_POINT
   
   where:
   DRIVE               Hard-drive device file (e.g. /dev/sdb or /dev/mapper/CRYPT_sdb)
   MOUNT_POINT         Mount point (e.g. /mnt/backup)
   

5. Copy files

   cp -av MOUNT_POINT/* DESTINATION
   
   where:
   MOUNT_POINT         Mount point (e.g. /mnt/backup)
   DESTINATION         Destination directory (e.g. /home/user/backup)
   

Access system#

This method works if the machine is still bootable without faulty hardware. Basically you boot from a live USB and chroot to the installed system.

1. Boot from live USB

2. Mount root partition. You can mount anywhere, but I'll use /target in this example.

   1. (If encrypted) Open LUKS container

      cryptsetup open DEVICE LUKS_CONTAINER
      
      where:
      DEVICE              Hard-drive device file (e.g. /dev/sdb)
      LUKS_CONTAINER      Name of the LUKS device (e.g. CRYPT_sdb)
      

   2. Create mount point

      mkdir /target
      

   3. Mount drive

      mount DRIVE /target
      
      where:
      DRIVE               Hard-drive device file (e.g. /dev/sdb or /dev/mapper/CRYPT_sdb)
      

3. Mount device filesystems, so your installed system can access them

   ROOT=/target
   for n in proc sys dev etc/resolv.conf; do mount --rbind --make-rslave /$n "$ROOT/$n"; done
   

4. Access the installed system

   chroot /target
   

5. (Optional) Mount other partitions from /etc/fstab

   mount -a