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diff --git a/content/devops/resizing_root_partition.rst b/content/devops/resizing_root_partition.rst new file mode 100644 index 0000000..e07f706 --- /dev/null +++ b/content/devops/resizing_root_partition.rst @@ -0,0 +1,210 @@ +Note to Self: Growing the Root File System on First Boot +######################################################## + +:date: 2019-02-16 22:13 +0530 +:slug: grow_rootfs +:tags: resize2fs, notetoself +:author: copyninja +:summary: Post discusses about expanding root file system of a system to full + extent of available space in device. + +These 2 are the use cases I came across for expanding root file system. + +1. RaspberryPi images which comes in smaller image size like 1GB which you write + bigger size SD cards like 32GB but you want to use full 32GB of space when + system comes up. + +2. You have a VM image which is contains basic server operating system and you want + to provision the same as a VM with much larger size root file system. + +My current use case was second but I learnt the trick from 1, that is the +`RaspberryPi3 image spec <https://github.com/Debian/raspi3-image-spec>`_ by +Debian project. + +Idea behind the expanding root file system is first expanding the root file +system to full available size and then run resize2fs on the expanded partition +to grow file system. *resize2fs* is a tool specific for ext2/3/4 file system. +But this needs to be done before the file system is mounted. + +Here is my modified script from `raspi3-image-spec repo +<https://github.com/Debian/raspi3-image-spec/blob/master/rpi3-resizerootfs>`_. +Only difference is I've changed the logic of extracting root partition device to +my need, and of course added comments based on my understanding. + +.. code:: shell + + #!/bin/sh + + # Just extracts root partition and removes partition number to get the device + # name eg. /dev/sda1 becomes /dev/sda + roottmp=$(lsblk -l -o NAME,MOUNTPOINT | grep '/$') + rootpart=/dev/${roottmp%% */} + rootdev=${rootpart%1} + + # Use sfdisk to extend partition to all available free space on device. + flock $rootdev sfdisk -f $rootdev -N 2 <<EOF + ,+ + EOF + + sleep 5 + + # Wait for all pending udev events to be handled + udevadm settle + + sleep 5 + + # detect the changes to partition (we extended it). + flock $rootdev partprobe $rootdev + + # remount the root partition in read write mode + mount -o remount,rw $rootpart + + # Finally grow the file system on root partition + resize2fs $rootpart + + exit 0fs + + +raspi3-image-spec uses `sytemd service +<https://github.com/Debian/raspi3-image-spec/blob/master/rpi3-resizerootfs.service>`_ +file to execute this script just before any file system is mounted. This is done +by a making service execute before *local-fs.pre* target. From the man page for +*systemd.special* + + local-fs.target + systemd-fstab-generator(3) automatically adds dependencies of type + Before= to all mount units that refer to local mount points for this + target unit. In addition, it adds dependencies of type Wants= to this + target unit for those mounts listed in /etc/fstab that have the auto + mount option set. + +Testing with VM +=============== + +*raspi3-image-spec* is well tested, but I wanted to make sure this works with my +use case for VM. Since I didn't have any spare physical disks to experiment with +I used kpartx with raw file images. Here is what I did + +1. Created a stretch image using vmdb2 with grub installed. Image size is 1.5G +2. I created another raw disk using fallocate of 4G size. +3. I created a partition on 4G disk. +4. Loop mounted the disk and wrote 1G image on it using dd +5. Finally created a VM using virt-install with this loop mounted device as + root disk. + +Below is my vmdb configuration yml again derived from `raspi3-image-spec +<https://github.com/Debian/raspi3-image-spec/blob/master/raspi3.yaml>`_ one with +some modifications to my needs. + +.. code:: yaml + + # See https://wiki.debian.org/RaspberryPi3 for known issues and more details. + steps: + - mkimg: "{{ output }}" + size: 1.5G + + - mklabel: msdos + device: "{{ output }}" + + - mkpart: primary + device: "{{ output }}" + start: 0% + end: 100% + tag: / + + - kpartx: "{{ output }}" + + - mkfs: ext4 + partition: / + label: RASPIROOT + + - mount: / + + - unpack-rootfs: / + + - debootstrap: stretch + mirror: http://localhost:3142/deb.debian.org/debian + target: / + variant: minbase + components: + - main + - contrib + - non-free + unless: rootfs_unpacked + + # TODO(https://bugs.debian.org/877855): remove this workaround once + # debootstrap is fixed + - chroot: / + shell: | + echo 'deb http://deb.debian.org/debian buster main contrib non-free' > /etc/apt/sources.list + apt-get update + unless: rootfs_unpacked + + - apt: install + packages: + - ssh + - parted + - dosfstools + - linux-image-amd64 + tag: / + unless: rootfs_unpacked + + - grub: bios + tag: / + + - cache-rootfs: / + unless: rootfs_unpacked + + - shell: | + echo "experimental" > "${ROOT?}/etc/hostname" + + # '..VyaTFxP8kT6' is crypt.crypt('raspberry', '..') + sed -i 's,root:[^:]*,root:..VyaTFxP8kT6,' "${ROOT?}/etc/shadow" + + sed -i 's,#PermitRootLogin prohibit-password,PermitRootLogin yes,g' "${ROOT?}/etc/ssh/sshd_config" + + install -m 644 -o root -g root fstab "${ROOT?}/etc/fstab" + + install -m 644 -o root -g root eth0 "${ROOT?}/etc/network/interfaces.d/eth0" + + install -m 755 -o root -g root rpi3-resizerootfs "${ROOT?}/usr/sbin/rpi3-resizerootfs" + install -m 644 -o root -g root rpi3-resizerootfs.service "${ROOT?}/etc/systemd/system" + mkdir -p "${ROOT?}/etc/systemd/system/systemd-remount-fs.service.requires/" + ln -s /etc/systemd/system/rpi3-resizerootfs.service "${ROOT?}/etc/systemd/system/systemd-remount-fs.service.requires/rpi3-resizerootfs.service" + + install -m 644 -o root -g root rpi3-generate-ssh-host-keys.service "${ROOT?}/etc/systemd/system" + mkdir -p "${ROOT?}/etc/systemd/system/multi-user.target.requires/" + ln -s /etc/systemd/system/rpi3-generate-ssh-host-keys.service "${ROOT?}/etc/systemd/system/multi-user.target.requires/rpi3-generate-ssh-host-keys.service" + rm -f ${ROOT?}/etc/ssh/ssh_host_*_key* + + root-fs: / + + # Clean up archive cache (likely not useful) and lists (likely outdated) to + # reduce image size by several hundred megabytes. + - chroot: / + shell: | + apt-get clean + rm -rf /var/lib/apt/lists + + # TODO(https://github.com/larswirzenius/vmdb2/issues/24): remove once vmdb + # clears /etc/resolv.conf on its own. + - shell: | + rm "${ROOT?}/etc/resolv.conf" + root-fs: / + +I could not run with vmdb2 installed from Debian archive, so I cloned +raspi3-image-spec and used vmdb2 submodule from it. + +.. code:: shell + + fallocate -l 4G rootdisk.img + # Create one partition with full disk + sfdisk -f rootdisk.img <<EOF + ,+ + EOF + kpartx -av rootdisk.img # mounts on /dev/loop0 for me + dd if=vmdb.img of=/dev/loop0 + sudo virt-install --name experimental --memory 1024 --disk path=/dev/loop0 --controller type=scsi,model=virtio-scsi --boot hd --network bridge=lxcbr0 + +Once VM booted I could see the root file system is 4G of size instead of 1.5G it +was after using dd to write image on to it. So success!. |