On an Ubuntu 18.04 (Bionic), the following problem showed up when I was trying to remove a package (ksh) using apt:
root@bionic:~# apt-get remove ksh
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be REMOVED:
ksh
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
After this operation, 3,384 kB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 52797 files and directories currently installed.)
Removing ksh (93u+20120801-3.1ubuntu1) ...
/var/lib/dpkg/info/ksh.prerm: 11: /var/lib/dpkg/info/ksh.prerm: update-binfmts: not found
dpkg: error processing package ksh (--remove):
installed ksh package pre-removal script subprocess returned error exit status 127
Errors were encountered while processing:
ksh
E: Sub-process /usr/bin/dpkg returned an error code (1)
The failure comes from the so-called Debian package pre-remove (prerm) definition. This is a shell script launched before the package's files are deleted from the system:
root@bionic:~# cat /var/lib/dpkg/info/ksh.prerm
#!/bin/sh
set -e
case "$1" in
remove|deconfigure)
update-alternatives --remove ksh /bin/ksh93
# remove compatibility symlink if broken
test '!' -h /usr/bin/ksh || test -e /usr/bin/ksh || rm -f /usr/bin/ksh
update-binfmts --package ksh --remove ksh /bin/ksh93
;;
upgrade|failed-upgrade)
;;
*)
echo "prerm called with unknown argument \`$1'" >&2
exit 0
;;
esac
exit 0
The pre-removal script of the ksh package wants to run the update-binfmts command. But update-binfmts can cause problems in LXC containers, hence this package was removed a while ago:
root@bionic:~# dpkg -l|grep binfmt
rc binfmt-support 2.1.8-2 amd64 Support for extra binary formats
This missing command now leads to an error inside the pre-removal script of the ksh package. Because it uses set -e, it fails and exits immediately. apt receives the error exit code and stops the package removal. apt now runs into a situation which cannot be fixed by itself.
In this situation, the pre-removal script of the affected package needs to be adjusted. By commenting (disabling) the update-binfmts command, the pre-removal script should run through just fine and allow the removal of the package:
root@bionic:~# sed -i "s/update-binfmts/#update-binfmts/" /var/lib/dpkg/info/ksh.prerm
root@bionic:~# cat /var/lib/dpkg/info/ksh.prerm | grep binfmt
#update-binfmts --package ksh --remove ksh /bin/ksh93
root@bionic:~# apt-get remove ksh
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages will be REMOVED:
ksh
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
After this operation, 3,384 kB disk space will be freed.
Do you want to continue? [Y/n] y
(Reading database ... 52797 files and directories currently installed.)
Removing ksh (93u+20120801-3.1ubuntu1) ...
Processing triggers for man-db (2.8.3-2ubuntu0.1) ...
root@bionic:~# dpkg -l|grep ksh
rc ksh 93u+20120801-3.1ubuntu1 amd64 Real, AT&T version of the Korn shell
Voilà, ksh package now successfully removed.
This method (fixing/adjusting the pre-removal script) should also apply to other packages which require certain (non-existant) commands.
The problem described above happend with the ksh package in Ubuntu 18.04 (Bionic). Taking a look at the ksh package in Ubuntu 20.04 (Focal), this problem should not occur in Ubuntu 20.04 anymore. The pre-removal script now contains a check, that the update-binfmts command actually exists:
if command -v update-binfmts >/dev/null; then
test -e /var/lib/binfmts/ksh && \
update-binfmts --package ksh --remove ksh \
/bin/ksh || true
fi
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