Rescue media(2)

TOC

This is updated memo of Rescue media(1) (in Japanese).

Rescue media

There are many iso images which are useful for system administration and rescue tasks available on the web. Here are some of the notable ones:

• GParted live
  • GOOD: active
  • GOOD: Debian based system rescue media.
  • GOOD: GUI partition manager
  • BAD: Currently, Debian Lacks GUI LVM manager like blivet-gui
    • TODO: Follow Create GParted live from scratch to install blivet-gui deb pakage
• debian-installer (netinst)
  • GOOD: active and stable
  • GOOD: This facilitates official Debian system install.
  • BAD: “rescue mode” needs to mount a functioning root filesystem and it can’t be unmounted for filesystem operation (fsck…).
• Debian live
  • GOOD: active
  • GOOD: Debian based system rescue media.
• Kali Linux Live image
  • GOOD: active
  • GOOD: Debian based system rescue media.
• SYSTEM RESCUE HOMEPAGE
  • GOOD: active
  • FAIR: ARCHlinux based system rescue media
• Super Grub2 Disk/Rescatux
  • GOOD: last release 2024 for Super Grub2 Disk (the multi disk/iso boot loader, now support btrfs)
  • BAD: last released in 2021 for Rescatux (outdated linux iso image)
• Ventoy
  • GOOD: active (the multi disk/iso boot loader w/o iso image)

Ventoy + Gparted for rescue USB-key

Since modern USB-keys have huge storage space, I decided to use ventoy and put all interesting iso images in it. This way, I only need to maintain one USB key.

For the moment, I will mostly use GParted live iso image.

Booting system with USB-key

• Sony Vaio SVT1313: power up system with a USB key inserted with “ASSIST” button.
• Thinkpad T14 Gen 1 (AMD): power up and press ENTER or F12

Use case: Migrating from ext4 to Btrfs for home

Let’s think about a system installed with d-i using its full disk install option with LUKS encryption on MBR SSD.

• hostname=casper
• /dev/sda1: /boot (1GB)
• /dev/sda2: extended partition holding /dev/sda5
• /dev/sda5: holds LUKS (479GB)
• LUKS: holds LVM2 PV /dev/mapper/sda5_crypt
• PV /dev/mapper/sda5_crypt: used as a only member of VG casper-vg
• VG casper-vg found in /dev/casper-vg holds 3 LVs
  • /dev/casper-vg/root = /dev/mapper/casper--vg-root (ext4, 32GB)
  • /dev/casper-vg/home = /dev/mapper/casper--vg-home (ext4, 438GB)
  • /dev/casper-vg/swap_1 = /dev/mapper/casper--vg-swap_1 (swap, 8.5GB)

Please note - in VG name is repeated in name used under /dev/mapper.

Let’s convert /dev/casper-vg/home to use btrfs instead of ext4.

• Boot from USB to use rescue boot shell
  • Decrypt LUKS partion (/dev/sda5)
    • sudo cryptosetup luksOpen /dev/sda5 sda5_crypt
    • Now you see /dev/mapper/casper--vg-home, /dev/mapper/casper--vg-root etc.
    • Mount /dev/mapper/casper--vg-home to mnt/home
    • Mount /dev/mapper/casper--vg-root to /mnt/root
  • Copy all data from /mnt/home/username to /mnt/root/home/.
  • Remove mounting of casper--vg-home iin /etc/fstab by adding # at the head of line..
• Boot normal SSD system
  • Install required program
    • sudo apt install btrfs-progs
  • Format forcebly the old home LV as btrfs
    • sudo mkfs.btrfs -f /dev/mapper/casper--vg-home
  • Check LV and VG names with lvs and vgs
  • Rename the old home LV to btrfs LV
    • sudo lvrename casper-vg home btrfs
  • Mount /dev/mapper/casper--vg-btrfs at /mnt
    • sudo mount /dev/mapper/casper--vg-btrfs /mnt
  • Create subvolume @home at /mnt
    • sudo btrfs subvolume create @home /mnt
  • Copy back data under /home to /mnt/@home.
  • Change mounting of home in /etc/fstab to use @home-subvolume for home.
    • Add /dev/mapper/casper--vg-btrfs btrfs default,subvol=@home 0 2 in /etc/fstab
  • Reboot

NOTE: Use pvs, vgs, lvs,and lvmdiskscan commands to assess LVM situation. These are lvm subcommands but can be invoked as normal commands without lvm prefix.

NOTE: lvresize can be invoked with -r option to perform FS resize along with LV resizing.