> linux-purge --auto-only --keep=2 --simulate --debug[linux-purge] ERROR: There are no meta-kernels so can not decide which kernels 
to keep.
[linux-purge] NOTE: The debug information is saved in
/dev/shm/linux-purge.debug_b3n

> cat /dev/shm/linux-purge.debug_b3n
## start time: Mon Sep  7 12:47:59 BST 2020
## linux-purge version: 1.0.113-c15c34a
## options:  --auto-only --keep '2' --simulate --debug '' --
## OS: Linux Mint 18.3 Sylvia
## awk executable: /usr/bin/gawk
## awk version:
GNU Awk 4.1.3, API: 1.1 (GNU MPFR 3.1.4, GNU MP 6.1.0)
Copyright (C) 1989, 1991-2015 Free Software Foundation.

This program is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 3 of the License, or
(at your option) any later version.

This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with this program. If not, see http://www.gnu.org/licenses/.
## linux packages:
ii  linux-base
ii  linux-firmware
un  linux-firmware-snapdragon
un  linux-headers
un  linux-headers-2.6-686
un  linux-headers-2.6-amd64
un  linux-headers-3.0
ii  linux-headers-4.15.0-112
ii  linux-headers-4.15.0-112-generic
ii  linux-headers-4.15.0-115
ii  linux-headers-4.15.0-115-generic
ii  linux-headers-4.15.0-55
ii  linux-headers-4.15.0-55-generic
un  linux-headers-686-pae
un  linux-headers-amd64
un  linux-headers-generic
un  linux-headers-generic-pae
un  linux-hwe-tools
un  linux-image
ii  linux-image-4.15.0-112-generic
ii  linux-image-4.15.0-115-generic
un  linux-image-4.15.0-55-generic
un  linux-image-unsigned-4.15.0-112-generic
un  linux-image-unsigned-4.15.0-115-generic
ii  linux-image-unsigned-4.15.0-55-generic
un  linux-initramfs-tool
un  linux-kernel-headers
un  linux-kernel-log-daemon
ii  linux-libc-dev
ii  linux-modules-4.15.0-112-generic
ii  linux-modules-4.15.0-115-generic
ii  linux-modules-4.15.0-55-generic
ii  linux-modules-extra-4.15.0-112-generic
ii  linux-modules-extra-4.15.0-115-generic
un  linux-restricted-common
ii  linux-sound-base

## trace and output:
+ debug() 147: operate
++ debug() 147: tee -ia -- /dev/shm/linux-purge.debug_b3n
+ operate() 909: [[ -n '' ]]
+ operate() 912: purge_normally
++ debug() 147: tee -ia -- /dev/shm/linux-purge.debug_b3n
++ purge_normally() 748: dpkg-query -W '-f=${Package} ${db:Status-Abbrev}\n'
+++ purge_normally() 748: literalize 4.15.0-115-generic
+++ literalize() 247: printf %s 4.15.0-115-generic
+++ literalize() 247: sed -e 's/[^^]/[&]/g' -e 's/\^/\\^/g'
++ purge_normally() 748: grep -qE '^linux-image-(unsigned-)?[4][.][1][5][.][0][-][1][1][5][-][g][e][n][e][r][i][c] [ih]i $'
++ purge_normally() 758: dpkg-query -W '-f=${Package} ${Status}\n' 'linux-*'
++ purge_normally() 760: awk '$3!="ok" || ($4!="installed" && $4!="not-installed" && $4!="config-files")
	 '
+ purge_normally() 758: Pkgs=
+ purge_normally() 759: [[ -n '' ]]
++ purge_normally() 773: dpkg-query -W '-f=${db:Status-Abbrev} ${Package}\n'
++ purge_normally() 774: sed -nr 's/^[ih]i  linux-image-(unsigned-)?([0-9]+\..+)/\2/p'
++ purge_normally() 774: linux-version sort
+ purge_normally() 773: Releases='4.15.0-55-generic
4.15.0-112-generic
4.15.0-115-generic'
+ purge_normally() 775: [[ -n '' ]]
+ purge_normally() 777: [[ -z 1 ]]
+ purge_normally() 789: ReleasesToKeep=
++ purge_normally() 790: get_latest_releases
+++ get_latest_releases() 273: get_meta_kernels
+++ get_meta_kernels() 264: dpkg-query -W -f '${db:Status-Abbrev} ${Package}\n'
+++ get_meta_kernels() 265: awk '/^[ih].. linux-(.+-)?image-/{print $2}'
+++ get_meta_kernels() 266: grep -Ev '[[:digit:]]+\.[[:digit:]]+\.[[:digit:]]+'
++ get_latest_releases() 273: local meta_kernels=
++ get_latest_releases() 274: [[ -z '' ]]
+ purge_normally() 790: LatestReleases=
+ purge_normally() 791: [[ -n '' ]]
+ purge_normally() 792: error 'There are no meta-kernels so can not decide which kernels to keep.'
+ error() 76: printf '[%s] ERROR: %s\n' linux-purge 'There are no meta-kernels so can not decide which kernels to keep.'
+ error() 76: fold -s
[linux-purge] ERROR: There are no meta-kernels so can not decide which kernels 
to keep.
+ error() 77: [[ -n '' ]]
+ error() 77: echo 1
+ error() 78: exit 1
+ error() 1: finish
+ finish() 98: err=1
+ finish() 99: trap - EXIT
+ finish() 100: [[ -n 1 ]]
+ finish() 100: err=0
+ finish() 101: rm -- /dev/shm/linux-purge.error_GPG
+ finish() 102: restore_update_grub
+ restore_update_grub() 90: [[ -n '' ]]
+ finish() 103: [[ -n /dev/shm/linux-purge.debug_b3n ]]
+ finish() 104: [[ -f /dev/shm/linux-purge.debug_b3n ]]
+ finish() 104: [[ ! -s /dev/shm/linux-purge.debug_b3n ]]
+ finish() 108: [[ -n '' ]]
+ finish() 110: [[ -n 1 ]]
+ finish() 112: note 'The debug information is saved in
/dev/shm/linux-purge.debug_b3n'
+ note() 86: printf '[%s] NOTE: %s\n' linux-purge 'The debug information is saved in
/dev/shm/linux-purge.debug_b3n'
+ note() 86: fold -s
[linux-purge] NOTE: The debug information is saved in
/dev/shm/linux-purge.debug_b3n
+ finish() 116: [[ null == INT ]]
+ finish() 117: ((  err != 0 && err != 141  ))
+ finish() 121: return 0