preinst is in telnetd 0.17-36build2.
This file is a maintainer script. It is executed when installing (*inst) or removing (*rm) the package.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 | #!/bin/sh -e
case "$1" in
upgrade)
## change the HOME dir of telnetd to something not /
if [ -n "$2" ] && dpkg --compare-versions "$2" lt 0.17-27; then
usermod -d /nonexistent telnetd
fi
;;
esac
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