purge-old-kernels may purge meta kernel(s) and consequently stop kernels updates from being offered.

[Jarno Suni]

Steps to reproduce:
You have just installed latest kernel update and immediately run "sudo purge-old-kernels --keep 0 -y"
or
you have just installed n custom kernels and run "sudo purge-old-kernels --keep k -y" where k is an integer in range 0..n".

Furthermore, if you have installed LTS Enablement Stack(s), the script may purge the original meta kernel (e.g linux-image-generic) and some newer meta kernels (e.g. linux-generic-lts-*); that may be expected, though.

Version: ~kirkland/byobu/trunk : /usr/bin/purge-old-kernels (revision 2487) or older

[Jarno Suni (jarnos)]

Also affects bikeshed, because purge-old-kernels is included in it in Trusty and Wily.

[Dustin Kirkland  (kirkland)]

Good catch. So I think I've maybe fixed this by changing the way we count old kernels, to being "version" based. It'll need some testing.

[Jarno Suni (jarnos)]

The new way counting old kernels does not fix it. Some manually installed kernels may be e.g. mainline kernels [1] that have greater version than any kernel found in the usual Ubuntu repositories.

Secondly, --human-numeric-sort you use is not version sort. sort has -V option for version sort, but even that does not sort linux versions correctly in some special cases:
$ echo -e "4.1\n4.1-rc6" | sort -V
4.1
4.1-rc6
It guess it is better to use linux-version - which is a perl script BTW - from linux-base:
$ echo -e "4.1\n4.1-rc6" | linux-version sort
4.1-rc6
4.1

apt-auto-removal script in Xenial sorts debian versions by "sort -V", which may work also.
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=787827

Older apt-auto-removal by Steve Langasek uses this kind of compare function:
version_test_gt ()
{
        local version_test_gt_sedexp="s/[._-]\(pre\|rc\|test\|git\|old\|trunk\)/~\1/g"
        local version_a="`echo "$1" | sed -e "$version_test_gt_sedexp"`"
        local version_b="`echo "$2" | sed -e "$version_test_gt_sedexp"`"
        $DPKG --compare-versions "$version_a" gt "$version_b"
        return "$?"
}
where $DPKG is dpkg executable name.

[1] https://wiki.ubuntu.com/Kernel/MainlineBuilds?action=show&redirect=KernelMainlineBuilds

[Jarno Suni (jarnos)]

Oh, the Ubuntu's mainline kernels seem to have "rc" after a six-digit number string starting by "0". "rc" does not exist in all mainline kernels. Still they should be considered to have smaller version than usual two-digit releases, right? For that, even "linux-version sort" does not work, neither does "sort -V".

"sort -n" works, if all numbers have the same number of digits in version elements compared to other versions.

[Jarno Suni (jarnos)]

Anyway, comparing mainline kernel version numbers and Ubuntu kernel version numbers may be too complicated, as Ubuntu kernels are based on mainline kernels that may have greater version number: http://people.canonical.com/~kernel/info/kernel-version-map.html

[Brian Murray (brian-murray)]

Running purge-old-kernels today I can confirm that it wants to remove the meta kernels:

 $ sudo purge-old-kernels
[sudo] password for bdmurray:
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
  libbluray1 libubuntu-app-launch3 linux-headers-4.10.0-11 linux-tools-4.9.0-15 linux-tools-4.9.0-15-generic snap-confine thermald
Use 'sudo apt autoremove' to remove them.
The following packages will be REMOVED:
  linux-generic* linux-headers-4.10.0-11-generic* linux-headers-generic* linux-image-4.10.0-11-generic* linux-image-extra-4.10.0-11-generic* linux-image-generic* linux-signed-generic* linux-signed-image-4.10.0-11-generic*
  linux-signed-image-generic*
0 upgraded, 0 newly installed, 9 to remove and 0 not upgraded.
After this operation, 233 MB disk space will be freed.
Do you want to continue? [Y/n] n

 $ apt-cache policy byobu
byobu:
  Installed: 5.115-0ubuntu1
  Candidate: 5.115-0ubuntu1
  Version table:
 *** 5.115-0ubuntu1 500
        500 http://192.168.10.7/ubuntu zesty/main amd64 Packages
        500 http://192.168.10.7/ubuntu zesty/main i386 Packages
        100 /var/lib/dpkg/status

[Dustin Kirkland  (kirkland)]

purge-old-kernels has been deprecated, in favor of "apt autoremove". If you have problems, please file bugs against apt.