Pxe files - kernel, initrd

nbelavic · September 10, 2019, 11:42am

Problem:

How to find out which files in /srv/tftp/boot directory belongs to which OS?

lzap · September 11, 2019, 1:50pm

Depending on the Foreman version, those files will be named after the OS type name. E.g. Redhat-x86_64-7.7-initram.img for OS of the type “Redhat” architecture “x86_64” and version 7.7.

However if you have another OS of this same kind named differently “e.g. My RHEL 7.7”, then the file will be overwritten on every provisioning. Newer versions of Foreman add first 12 characters SHA1 hash of the installation media URL encoded in base64 so it will be two different names.

I think it would be easy to include Operating System database ID to the name, so it would read something like Redhat-12-x86_86-7.7-vmlinuz, or the whole operating system name instead like My_RHEL_7.7-vmlinuz. I slightly prefer the former one because people tend to create weird names to things.

When using Katello, this is completely overriden. Then the naming convention is Product name and Content View ID. We would like to change that however because on deployments with many promotions this create unnecessary amount of boot files as the CV ID increases.

nbelavic · September 12, 2019, 11:49am

My names contain only mirror name and SHA1 hash.
It would be much easier to have something like “debian_9.9” in file name.

root@foreman-2-proxy-1:/srv/tftp/boot# ls -w1 *linu*
centos-mirror-qVbSBrznIWMc-vmlinuz
centos-mirror-Y9DBxqXs2LJ9-vmlinuz
debian-mirror-dgxKgBg5J79O-linux
debian-mirror-gbCq4bcqf6Lp-linux
debian-mirror-wXTzvPQ8AfC3-linux
ubuntu-mirror-MlgxQLc5gvg6-linux
ubuntu-mirror-WKCIULkETfqj-linux

My current workaround is to do file command and google default kernel version for different distributions

root@foreman-2-proxy-1:/srv/tftp/boot# file debian-mirror-*-linux | cut -d',' -f2
 version 4.9.0-11-amd64 (debian-kernel@lists.debian.org) #1 SMP Debian 4.9.189-3 (2019-09-02)
 version 3.16.0-6-amd64 (debian-kernel@lists.debian.org) #1 SMP Debian 3.16.56-1+deb8u1 (2018-05-08)
 version 4.19.0-6-amd64 (debian-kernel@lists.debian.org) #1 SMP Debian 4.19.67-2 (2019-08-28)

BTW; foreman doesn’t allow me to create same OS with identical major/minor numbers.

lzap · September 12, 2019, 2:04pm

Oh you are right, what I described in my previous post was the previous behavior. Now the name is made of installation media name and SHA1 hash of the URL. Out of curiosity, why you need that? Foreman should manage PXE files for you.

I agree this is probably more confusing than it was (we occasionally saw incorrect OS entries but that was misconfiguration). We can put it back with planned refactoring Feature #26709: Rethink TFTP naming conventions for PXE files - Foreman

nbelavic · September 12, 2019, 2:17pm

There was an error on debian mirror or somewhere in my squid, and i finished with wrong version of kernel and initrd and netinstall from that point failed.

Nevertheless, please confirm what I found:
It is always safe to delete this files, foreman will re-download latest version from mirror (installation media) if these files are missing (on next provisioning action)… In other words, if someone encounters a problem with debian netinstall kernel and initrd, it is safe to do: rm -rf /srv/tftp/boot/debian-mirror-* )

lzap · September 12, 2019, 2:26pm

Ehm, ehm. Yes, plus it will download with wget -c which means continue. If a file is refreshed on the server and bigger, it will actually append the rest and this will cause random issues (depending on the initramdisk data - weird stuff). Be aware, I always recommend to wipe out the TFTP directory. Exit and enter build mode to redownload TFTP files.

The issue I have linked actually aim to fix this problem.

nbelavic · September 23, 2019, 12:22pm

I am having problems with this again. Now it is CentOS new minor release (7.7). I have deleted centos files from /srv/tftp/boot and let foreman to re-download. I have following problem:

Foreman initiated download of pxe files, but build started BEFORE download of this files finished, which led to host trying to boot partially downloaded kernel and crashed … how can i avoid this situation?

lzap · September 24, 2019, 6:47am

You can’t avoid it, it’s a known issue and the solution is more complex and that’s the reason why we delay to fix so long. It’s just matter of resources to refactor everything. In the meantime, pick a faster mirror or add a delay to the PXELinux or Grub2 (timeout).

nbelavic · November 2, 2020, 12:21pm

@lzap, anything changed here in 2.0 and later releases?
I am still on 1.23 … Is it a good time to upgrade?

lzap · November 2, 2020, 2:11pm

Nothing changes here, just make your timeout in your PXE template long enough so files gets downloaded.

nbelavic · November 2, 2020, 2:45pm

Newer versions of Foreman add first 12 characters SHA1 hash of the installation media URL encoded in base64 so it will be two different names.

Can you please explain this in detail or point me to exact script which generates initrd and kernel file names like “debian-mirror-dgxKgBg5J79O-linux”.

I have tried to do something like:

echo "media_url" | sha1sum | base64 | cut -c1-12

but without success. I need a way to recreate names with my custom script.

lzap · November 2, 2020, 4:16pm

If you dont use Katello then it is:

github.com

theforeman/foreman/blob/develop/app/services/medium_providers/default.rb#L27-L33


def unique_id
  @unique_id ||= begin
    digest = Base64.urlsafe_encode64(Digest::SHA1.digest(medium_uri(entity.operatingsystem.pxedir(self)).to_s + entity.operatingsystem.major + entity.operatingsystem.minor), padding: false)
    # return first 12 characters of encoded digest stripped down of non-alphanums for better readability
    "#{entity.medium.name.parameterize}-#{digest.gsub(/[-_]/, '')[1..12]}"
  end
end

While if you use Katello there is a different provider (search the codebase for the same file/method).

nbelavic · November 2, 2020, 4:46pm

tnx!