Update Alpine, Arch, Fedora and RHEL root on ZFS guides
Signed-off-by: Maurice Zhou <jasper@apvc.uk>
This commit is contained in:
Maurice Zhou
committed by
George Melikov
George Melikov
parent
a0c149af5b
commit
a69befb2ce
@@ -0,0 +1,172 @@
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.. highlight:: sh
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Create a Boot Environment
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==========================
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This page is tested for Alpine, Arch Linux, Fedora and
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RHEL guides. Not useful for NixOS since system rollback
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is already managed by Nix.
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With Root on ZFS, it is possible to take snapshots of
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existing root file systems, which is a read-only copy of
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that file system. A new, full-fledged file system --
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clones -- can be then created from this snapshot. This
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bootable clone of the current system is then called a
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"Boot Environment".
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This could be useful if you are performing a major
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system upgrade and wish to have the option to go back to
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a previous state if the upgrade fails.
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#. Identify which dataset is currently mounted as root
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``/`` and boot ``/boot``::
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findmnt /
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# output
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TARGET SOURCE FSTYPE OPTIONS
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/ rpool/archlinux/root zfs rw,relatime,xattr,posixacl
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findmnt /boot
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# output
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TARGET SOURCE FSTYPE OPTIONS
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/boot bpool/archlinux/root zfs rw,relatime,xattr,posixacl
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#. Identify your distribution in the dataset (file system) path::
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DISTRO=archlinux # or `fedora', `alma', `alpinelinux'
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#. Choose a name for the new boot environment::
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BE_NAME=backup
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#. Take snapshots of the ``/`` and ``/boot`` datasets::
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zfs snapshot rpool/$DISTRO/root@$BE_NAME
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zfs snapshot bpool/$DISTRO/root@$BE_NAME
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#. Create clones from read-only snapshots::
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zfs clone -o canmount=noauto \
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-o mountpoint=/ \
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rpool/$DISTRO/root@$BE_NAME \
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rpool/$DISTRO/$BE_NAME
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zfs clone -o canmount=noauto \
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-o mountpoint=legacy \
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bpool/$DISTRO/root@$BE_NAME \
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bpool/$DISTRO/$BE_NAME
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#. Mount clone and update file system table (fstab) ::
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mount -t zfs -o zfsutil rpool/$DISTRO/$BE_NAME /mnt
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mount -t zfs bpool/$DISTRO/$BE_NAME /mnt/boot
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sed -i "s|rpool/$DISTRO/root|rpool/$DISTRO/$BE_NAME|g" /mnt/etc/fstab
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sed -i "s|bpool/$DISTRO/root|bpool/$DISTRO/$BE_NAME|g" /mnt/etc/fstab
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If legacy mountpoint is used, omit ``-o zfsutil``
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from mount command.
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#. Create GRUB menu for new clone::
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m='/dev /proc /sys'
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for i in $m; do mount --rbind $i /mnt/$i; done
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chroot /mnt /usr/bin/env sh <<EOF
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if which grub-mkconfig; then
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grub-mkconfig -o /boot/grub.cfg
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else
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grub2-mkconfig -o /boot/grub.cfg
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fi
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EOF
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GRUB menu contains information on kernel version and initramfs.
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#. Unmount clone::
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umount -Rl /mnt
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#. Add new boot environment as GRUB menu entry::
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tee -a new_entry <<EOF
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menuentry 'ZFS Clone of ${DISTRO}: ${BE_NAME}' { configfile (hd0,gpt2)/${DISTRO}/${BE_NAME}@/grub.cfg }
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EOF
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find /boot/efis/ -name "grub.cfg" \
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| while read i; do
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if grep -q "${DISTRO}" $i; then
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cat $i new_entry > grub.cfg
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cp grub.cfg $i
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fi
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done
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rm new_entry
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#. After reboot, select boot environment entry from GRUB
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menu to boot from the clone. Press ESC inside
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submenu to return to the previous menu.
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#. Steps above can also be used to create a new clone
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from an existing snapshot.
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#. To set a boot environment as default, replace
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existing ``grub.cfg`` inside EFI system partition
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with the one from the boot environment::
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mount -t zfs bpool/$DISTRO/$BE_NAME /mnt
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# backup existing grub.cfg inside EFI
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# then replace it with menu from clone
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mkdir -p /mnt/grub_menu_backup
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menu_counter=1
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find /boot/efis/ -name "grub.cfg" \
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| while read i; do
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if grep -q "${DISTRO}" $i; then
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cp $i /mnt/grub_menu_backup/grub_${menu_counter}.cfg
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echo $i > /mnt/grub_menu_backup/grub_${menu_counter}_path.txt
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cp /mnt/grub.cfg $i
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menu_counter=$(($menu_counter + 1))
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fi
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done
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umount -Rl /mnt
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#. To delete the boot environment, check with
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``findmnt`` that the boot environment is not
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currently used::
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findmnt /
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findmnt /boot
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Set variables::
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DISTRO=archlinux
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Then check the origin snapshot::
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zfs get origin rpool/archlinux/backup
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# rpool/archlinux/root@backup
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zfs get origin bpool/archlinux/backup
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# bpool/archlinux/root@backup
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RM_BE=backup
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RM_SNAPSHOT=root@backup
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Finally, destroy clone (boot environment) and its
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origin snapshot::
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zfs destroy rpool/${DISTRO}/${RM_BE}
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zfs destroy rpool/${DISTRO}/${RM_SNAPSHOT}
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zfs destroy bpool/${DISTRO}/${RM_BE}
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zfs destroy bpool/${DISTRO}/${RM_SNAPSHOT}
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Remove GRUB entry::
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find /boot/efis/ -name "grub.cfg" \
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if grep -q "${DISTRO}/${RM_BE}@/grub.cfg" $i; then
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head -n -1 $i > grub.cfg
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cp grub.cfg $i
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fi
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done
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