[Bug 1877088] Re: [UBUNTU 20.04] installkernel script does not symlink /boot/initrd.img which is required with the default zipl.conf

[Sultan Alsawaf]

The script responsible for updating the /boot/initrd.img symlink is
called `linux-update-symlinks`. If a kernel is installed without that
script being run, the symlink will not be updated.

The only place where `linux-update-symlinks` is run is inside each of
our kernels, in `debian/templates/image.postinst.in`. This means that
when our kernels are built as .deb packages, the appropriate machinery
will be placed inside the .deb to thus update the /boot/initrd.img
symlink.

I checked the change history to `installkernel` and could not find any
point in time in which it ran `linux-update-symlinks`. Furthermore, the
help info inside `linux-update-symlinks` contains the following note:
"This command is intended to be called from the postinst and postrm
maintainer scripts of Linux kernel packages." It looks like `linux-
update-symlinks` was only ever intended to be used in postinst/postrm
hooks for .deb packages (and not called by `installkernel`).

There are a few remedies to this problem I can see, but I'm not sure which is the correct solution:
1. Add a call to `linux-update-symlinks` into `installkernel`
or
2. Add a script into /etc/kernel/postinst.d to run `linux-update-symlinks`
or
3. Run `linux-update-symlinks` manually after installing a kernel directly via `installkernel`

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Title:
  [UBUNTU 20.04] installkernel script does not symlink /boot/initrd.img
  which is required with the default zipl.conf

Status in Ubuntu on IBM z Systems:
  Triaged
Status in debianutils package in Ubuntu:
  New
Status in linux-base package in Ubuntu:
  New

Bug description:
  When testing development kernels I usually rely on the installkernel
  script either through the "make install" target of the Kernel source
  or manually. This used to work great on Ubuntu on Z.

  On Ubuntu 20.04 (freshly installed up to date) this fails however because
  /boot/initrd.img is not updated (/boot/vmlinuz is) and thus zipl installs the
  wrong kernel/initrd combination rendering the system unbootable.

  (with the correct modules already copied to /usr/lib/modules/5.7.0-rc4-06500-gb67ea026badd/)
  # sudo installkernel 5.7.0-rc4-06500-gb67ea026badd bzImage System.map /boot
  run-parts: executing /etc/kernel/postinst.d/apt-auto-removal 5.7.0-rc4-06500-gb67ea026badd /boot/vmlinuz-5.7.0-rc4-06500-gb67ea026badd
  run-parts: executing /etc/kernel/postinst.d/initramfs-tools 5.7.0-rc4-06500-gb67ea026badd /boot/vmlinuz-5.7.0-rc4-06500-gb67ea026badd
  update-initramfs: Generating /boot/initrd.img-5.7.0-rc4-06500-gb67ea026badd
  Using config file '/etc/zipl.conf'
  Building bootmap in '/boot'
  Building menu 'menu'
  Adding #1: IPL section 'ubuntu' (default)
  Adding #2: IPL section 'old'
  Preparing boot device: dasda (3844).
  Done.
  run-parts: executing /etc/kernel/postinst.d/zz-zipl 5.7.0-rc4-06500-gb67ea026badd /boot/vmlinuz-5.7.0-rc4-06500-gb67ea026badd
  Using config file '/etc/zipl.conf'
  Building bootmap in '/boot'
  Building menu 'menu'
  Adding #1: IPL section 'ubuntu' (default)
  Adding #2: IPL section 'old'
  Preparing boot device: dasda (3844).
  Done.
  # ls -l /boot
  total 178364
  -rw------- 1 root root    135168 May  6 11:52 bootmap
  -rw-r--r-- 1 root root     90471 Apr 29 15:34 config-5.4.0-29-generic
  lrwxrwxrwx 1 root root        27 May  6 11:40 initrd.img -> initrd.img-5.4.0-29-generic   <====== should point to new version
  -rw-r--r-- 1 root root  19663996 May  6 11:42 initrd.img-5.4.0-29-generic
  -rw-r--r-- 1 root root 125339494 May  6 11:52 initrd.img-5.7.0-rc4-06500-gb67ea026badd
  lrwxrwxrwx 1 root root        27 May  6 11:40 initrd.img.old -> initrd.img-5.4.0-29-generic
  -rw------- 1 root root   3087920 Apr 29 15:34 System.map-5.4.0-29-generic
  -rw-r--r-- 1 root root   4031691 May  6 11:52 System.map-5.7.0-rc4-06500-gb67ea026badd
  -rw-r--r-- 1 root root   4031691 May  6 11:49 System.map-5.7.0-rc4-06500-gb67ea026badd.old
  lrwxrwxrwx 1 root root        37 May  6 11:52 vmlinuz -> vmlinuz-5.7.0-rc4-06500-gb67ea026badd
  -rw------- 1 root root   8086072 Apr 29 15:54 vmlinuz-5.4.0-29-generic
  -rw-r--r-- 1 root root   9080832 May  6 11:52 vmlinuz-5.7.0-rc4-06500-gb67ea026badd
  -rw-r--r-- 1 root root   9080832 May  6 11:49 vmlinuz-5.7.0-rc4-06500-gb67ea026badd.old
  lrwxrwxrwx 1 root root        41 May  6 11:52 vmlinuz.old -> vmlinuz-5.7.0-rc4-06500-gb67ea026badd.old

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