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For installing packages for the custom Ubuntu image, we need to setup DNS inside the chroot. Signed-off-by: Archana Shinde <archana.m.shinde@intel.com>
161 lines
4.5 KiB
Markdown
161 lines
4.5 KiB
Markdown
# How to create a custom Ubuntu image
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In the context of adding more utilities to the Ubuntu cloud image being used
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for integration testing, this quick guide details how to achieve the proper
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modification of an official Ubuntu cloud image.
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## Create the image
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Let's go through the steps on how to extend an official Ubuntu image. These
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steps can be applied to other distributions (with a few changes regarding
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package management).
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### Get latest Ubuntu cloud image
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```bash
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wget https://cloud-images.ubuntu.com/focal/current/focal-server-cloudimg-amd64.img
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```
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### Check the file format is QCOW2
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```bash
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file focal-server-cloudimg-amd64.img
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focal-server-cloudimg-amd64.img: QEMU QCOW2 Image (v2), 2361393152 bytes
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```
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### Convert QCOW2 into RAW
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```bash
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qemu-img convert -p -f qcow2 -O raw focal-server-cloudimg-amd64.img focal-server-cloudimg-amd64.raw
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```
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### Identify the Linux partition
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The goal is to mount the image rootfs so that it can be modified as needed.
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That's why we need to identify where the Linux filesystem partition is located
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in the image.
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```bash
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sudo fdisk -l focal-server-cloudimg-amd64.raw
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Disk focal-server-cloudimg-amd64.raw: 2.2 GiB, 2361393152 bytes, 4612096 sectors
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Units: sectors of 1 * 512 = 512 bytes
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Sector size (logical/physical): 512 bytes / 512 bytes
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I/O size (minimum/optimal): 512 bytes / 512 bytes
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Disklabel type: gpt
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Disk identifier: A1171ABA-2BEA-4218-A467-1B2B607E5953
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Device Start End Sectors Size Type
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focal-server-cloudimg-amd64.raw1 227328 4612062 4384735 2.1G Linux filesystem
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focal-server-cloudimg-amd64.raw14 2048 10239 8192 4M BIOS boot
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focal-server-cloudimg-amd64.raw15 10240 227327 217088 106M EFI System
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Partition table entries are not in disk order.
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```
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### Mount the Linux partition
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```bash
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mkdir -p /mnt
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sudo mount -o loop,offset=$((227328 * 512)) focal-server-cloudimg-amd64.raw /mnt
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```
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### Set up DNS
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The next step describes changing the root directory to the rootfs contained by
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the cloud image. For DNS to work in the root directory, you will need to first bind-mount
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the host `/etc/resolv.conf` onto the mounted linux partition of the cloud image.
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```bash
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sudo mount -o bind /etc/resolv.conf /mnt/etc/resolv.conf
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```
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### Change root directory
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Changing the root directory will allow us to install new packages to the rootfs
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contained by the cloud image.
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```bash
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sudo chroot /mnt
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mount -t proc proc /proc
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mount -t devpts devpts /dev/pts
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```
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### Install needed packages
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In the context Cloud Hypervisor's integration tests, we need several utilities.
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Here is the way to install them for a Ubuntu image. This step is specific to
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Ubuntu distributions.
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```bash
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apt update
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apt install fio iperf iperf3 socat stress
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```
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### Remove counterproductive packages
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* snapd:
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This prevents snapd from trying to mount squashfs filesystem when the kernel
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might not support it. This might be the case when the image is used with direct
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kernel boot. This step is specific to Ubuntu distributions.
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* pollinate:
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Remove this package which can fail and lead to the SSH daemon failing to start.
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See #2113 for details.
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```bash
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apt remove --purge snapd pollinate
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```
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### Cleanup the image
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Leave no trace in the image before unmounting its content.
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```bash
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umount /dev/pts
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umount /proc
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history -c
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exit
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umount /mnt/etc/resolv.conf
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umount /mnt
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```
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### Rename the image
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Renaming is important to identify this is a modified image.
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```bash
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mv focal-server-cloudimg-amd64.raw focal-server-cloudimg-amd64-custom-$(date "+%Y%m%d")-0.raw
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```
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The `-0` is the revision and is only necessary to change if multiple images are
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updated on the same day.
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### Create QCOW2 from RAW
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Last step is to create the QCOW2 image back from the modified image.
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```bash
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qemu-img convert -p -f raw -O qcow2 focal-server-cloudimg-amd64-custom-$(date "+%Y%m%d")-0.raw focal-server-cloudimg-amd64-custom-$(date "+%Y%m%d")-0.qcow2
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```
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## Switch CI to use the new image
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### Upload to Azure storage
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The next step is to update both images (QCOW2 and RAW) stored as part of the
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Azure storage account, replacing them with the newly created ones. This will
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make these new images available from the integration tests. This is usually
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achieved through the web interface.
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### Update integration tests
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Last step is about updating the integration tests to work with this new image.
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The key point is to identify where the Linux filesystem partition is located,
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as we might need to update the direct kernel boot command line, replacing
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`/dev/vda1` with the appropriate partition number.
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Update all references to the previous image name to the new one.
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