If you see this error when running proftpd in debug mode:
USERÂ username (Login failed): Invalid shell: '/bin/false'
it would likely mean that /bin/false is not listed in your /etc/shells file.For proftpd, it shouldn't even be checking this. Â Ensure you've got:
RequireValidShell    no
set in your /etc/proftpd.conf file.Else, manually add /bin/false to /etc/shells, but this isn't the best option.