Readline 8.1 is required for bash-5.1 to work properly. From bash-5.1 release message[1]: > Bash can be linked against an already-installed Readline library > rather than the private version in lib/readline if desired. Only > readline-8.1 and later versions are able to provide all of the symbols > that bash-5.1 requires; earlier versions of the Readline library will > not work correctly. [1] https://lists.gnu.org/archive/html/info-gnu/2020-12/msg00003.html