comment #1:

>This is a user requirement, maybe a system requirement (though I can't really see how), not a shell requirement.

Probably true. I just wondered if bash itself could maybe have this disk space reserved, not the GNU/Linux/Debian system.

Rarely my bash_history gets cleared or at least loses most entries. I still don't know for certain what caused it but I think I had to do a shutdown due to a freeze in at least one case and think this / the loss of bash_history entries was caused by a lack of disk space. I asked about it here: https://unix.stackexchange.com/questions/669880/how-to-find-out-what-caused-a-deletion-of-bash-history-entries-during-a-specifi

Please somehow implement a reserve of disk space in bash or Debian that can only be used by bash_history file growth, and is always considered "taken up" disk space for anything else in Debian. For example 512 kB that are displayed as "used" disk space. This also requires proper appending of entries to this file - so that the file is not emptied, then other files take up the disk space and the rewritten after the needed disk space isn't available anymore. If the file somehow gets spammed and quickly maliciously grows in size this reserved disk space could also serve as a maximum file-size barrier that once reached does things like not writing new entries to the file and/or removes duplicate entries to free up space. It would be very useful to always have some reserved disk space for bash-history in general, not just due to bugs and alike.