Por que não consigo remover informações de log com 'journalctl --vacuum-size = 0M'?

Question

journalctl --vacuum-size=0M
Vacuuming done, freed 0B of archived journals on disk.

Talvez todos os registros tenham sido removidos; Eu verifiquei com journalctl -u sshd .

journalctl -u sshd
-- Logs begin at Thu 2018-01-18 22:38:54 EST, end at Sat 2018-01-27 08:10:12 EST
Jan 18 22:38:54 localhost sshd[1016]: Bad protocol version identification 'GET /
Jan 18 22:38:54 localhost sshd[1017]: Did not receive identification string from
Jan 18 23:38:55 localhost sshd[1019]: Did not receive identification string from
Jan 19 00:38:53 localhost sshd[1020]: Bad protocol version identification 'GET /

Por que não consigo remover as informações de log com journalctl --vacuum-size=0M ?