I guess I wrote that badly. busybox isn't actually required by cryptsetup, just recommended, but it should be required by something. The example shows it's possible to make packages uninstallable, if they pull the initramfs trigger, by removing busybox, which you can do cleanly as far as apt is concerned:
# dpkg -l initramfs* Desired=Unknown/Install/Remove/Purge/Hold | Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend |/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad) ||/ Name Version Architecture Description +++-==============-============-============-================================= ii initramfs-tool 0.130 all generic modular initramfs generat ii initramfs-tool 0.130 all generic modular initramfs generat # dpkg -l busybox* Desired=Unknown/Install/Remove/Purge/Hold | Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend |/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad) ||/ Name Version Architecture Description +++-==============-============-============-================================= un busybox <none> <none> (no description available) un busybox-static <none> <none> (no description available) # apt-get check Reading package lists... Done Building dependency tree Reading state information... Done #
