es:Full system backup with SquashFS ja:SquashFS によるフルシステムバックアップ

Compressed backup archives of whole filesystems can be made in the SquashFS format. Backup and retrieval takes relatively less time with its random access capability, but any kind of modification other than appending is not yet possible.

Pros and cons

Pros:

• No partitioning, no guessing how much size is required

• Should be supported by most rescue disks running at least Linux 2.6.29 (released in 2009)

• Random access[citation needed], with a plain mount

• Duplicate files are removed by default (unless -no-duplicates flag is on)

Cons:

• Access Control Lists are not yet supported, and therefore not backed up

• Not accessible from Windows1

• Appendable but impossible to remove things from it

• To use the disk for some other purposes, you have to destroy the backup2

Prepare the backup drive

1. Wipe out all partitions /dev/sdBN, then the partition table /dev/sdB, with wipefs.

2. Synchronize all write caches # sync

3. Inform the OS of partition table changes # partprobe

Check for bad blocks:

• If the backup drive is an SSD, use S.M.A.R.T..

• If the backup drive is an HDD, use badblocks.

Prepare a live medium

Installation guide#Prepare an installation medium or archiso to /dev/sdL

Back up

Installation guide#Boot the live environment

Mount filesystems you would like to backup. (e.g. /dev/sdSRC to /mnt)

# fsck /dev/sdSRC
# mount -o ro /dev/sdSRC /mnt

Back up (example script)

# mksquashfs /mnt /dev/sdB \
  -not-reproducible \
  -xattrs \
  -wildcards \
  -noappend \
  -progress \
  -mem 5G \
  -e \
    var/cache/pacman/pkg \
    var/lib/pacman/sync \
    var/log/journal \
    efi \
    boot/grub \
    boot/initramfs-linux"*".img \
    boot/vmlinuz-linux

1. -not-reproducible: Slightly increase backup speed

2. -noappend: Overwrite

3. -mem: RAM granted to mksquashfs

4. -e: List of exclude dirs/files

(Optional) Test backup in QEMU

Grant permission

$ sudo chown $USER:$USER /dev/sdB

Launch QEMU

$ qemu-system-x86_64 \
  -kernel /boot/vmlinuz-linux \
  -append "root=/dev/sdB ro loglevel=3 init=/usr/lib/systemd/systemd" \
  -initrd /boot/initramfs-linux-fallback.img \
  -drive file=/dev/sdB,index=0,media=disk,format=raw \
  -m virtual_machine_ram_in_MiB \
  --enable-kvm \
  -cpu host

(Optional) Inspect backup

Get backup date

# date --date=@"$(unsquashfs -mkfs-time /dev/sdB)"

More superblock information

# unsquashfs -stat /dev/sdB

Checksum

# COUNT="$(unsquashfs -stat /dev/sdB  grep -F 'Filesystem size'  cut -d' ' -f3)"
# echo "$COUNT Byte"
# numfmt --to=iec-i "$COUNT"
# head -c "$COUNT" /dev/sdB  sha1sum  tee -a sha1sum.txt

Retrieve file from backup

# mount /dev/sdB /mnt
# cp /mnt/path/to/file /path/to/destination

Restore backup