====== Bootloader ======

**linux boot process tricks**

==== howto clone harddisc and boot new system ====

**To transfer all system files,** it's best to get a live USB-stick or CD and boot into it \\
(all live-distros from ubuntu to systemrescuecd are ok). \\
In a livesystem, you can mount the partitions and transfer the data anyway you like (as root user):


1. **rsync** needs params and data must be excluded, (but works f&f in a running system), eg., :

  rsync -a -v -z -h --perms -E -o -g  --times --compress --update --delete \
        --exclude="/proc/*" --exclude="/sys/*" --exclude="/mnt/*" --exclude="/media/*" / /mnt/newsys/

-> may cause strange bugs, like permissions in /var/run/, maybe /dev probs

2. simple **copy** with "**cp**" (untested):
  cp -afv /from/sourcesystem/* /mnt/newsys/
  [ or ]
  cp -ax /from/sourcesystem/* /mnt/newsys/
  

3. **dd** - clones each sector - can only be used, if both partitions have exactly the same size!


4. **parted** - no ext4, only from livesystems

etc...

----
\\
**Fix partition-identifier UUIDs in fstab** of the new system.  \\
The UUIDs need to be replaced by the new UUIDs in **/mnt/newsys/etc/fstab**
This shows 'em all: :)
  ls -l /dev/disk/by-uuid/ 

----
\\

**Install grub2 bootloader** to the new disc - \\
unfortunately a complete change-root environment is required to fool grub-install:

**mount dev, proc, sys** via "bind"-option **into the new root / chroot**:
  mount -o bind /dev /mnt/newsys/dev
  mount -t proc none  /mnt/newsys/proc
  mount -t sysfs none /mnt/newsys/sys


**Enter** the new (virtual) root system:
  chroot /mnt/newsys/


Now inside this future system, grub2 installer scripts will work - \\
**generate a new (/mnt/newsys) /boot/grub/grub.cfg**: 
  update-grub

In case of error "no such disc" run
  grub-mkdevicemap


**Install to the MBR (no partition number) of the new disc, finally:**
  grub-install /dev/sdX

reboot & good luck!


----
\\

** initramfs **
the step after the bootloader needs all (fs, rais,..) modules to mount root, check: /etc/initramfs-tools/modules

update existing initramfs:
  update-initramfs -u -k all 

** RAID **
if you changed your raid setup, you need to update initramfs:
  dpkg-reconfigure mdadm 

make sure these modules are in /etc/initramfs-tools/modules
  raid0
  raid1
  md

\\
References: http://unix.stackexchange.com/questions/5297/debian-grub2-moving-root-partition-to-new-drive


\\
==== howto boot from grub2 rescue console ====

If you drop to the grub rescue after cloning a system disc or something, it's possible to boot an existing system.

Enter this, to start a system on sda3 for example:  sda = hd0 + partition 3 = (hd0,3)

  set prefix=(hd0,3)/boot/grub
  insmod (hd0,3)/boot/grub/linux.mod

if this works, the console gets upgraded to standard grub console.

if it doesn't work, try another partition. grub counts partitions from 1 (not 0), btw.

This boots arch linux:

  set root=(hd0,3)
  linux /boot/vmlinuz26 root=/dev/sda5
  initrd /boot/kernel26.img
  boot

This is required to boot debian - unfortunately the filenames contain versionnumbers :( 
  set root=(hd0,3)
  linux /boot/vmlinuz-3.1.0-1-amd64 root=/dev/sda3
  initrd /boot/initrd.img-3.1.0-1-amd64
  boot
  

This should boot your system. Just re-install grub:

  update-grub
  grub-install /dev/sdX


===== Bugs =====

Inside a chroot, grub complains 
  # update-grub                                                                                                                                                                                                                   
  Generating grub configuration file ...
  WARNING: Device /dev/ram0 not initialized in udev database even after waiting 10000000 microseconds.
  ...

Fix:

Outside chroot /debian/:

  mkdir /debian/run/udev
  mount --bind /run/udev /debian/run/udev
  mount --bind /run/udev /mnt/run/udev


===== Crypto Bugs =====


Grub complains root device couldn't be found 

Fix: 
- set 
  GRUB_ENABLE_CRYPTODISK=y

  apt install cryptsetup-initramfs lvm2
  

- if it is a brtfs, set in /etc/initramfs/modules
  btrfs 


Commands to execute in chroot to reinstall grub:

  update-initramfs -c -k all
  grub-install /dev/sdX
  update-grub


If update-grub echos: "cannot find device for / in fstab" and you have a btrfs rootsys:

  mount -o "subvol=@" /dev/mapper/vgubuntu-root 

is required to mount the @ subvol!