cron is in /usr/sbin (and is a daemon, not a command you'd ever run manually); shutdown is in /sbin; and ulimit is a shell builtin, not a standalone executable

cron is in /usr/sbin (and is a daemon, not a command you'd ever run manually); shutdown is in /sbin; and ulimit is a shell builtin, not a standalone executable at all. If I had to guess, I'd say that /sbin and /usr/sbin aren't on your $PATH for some reason. systemd is unlikely to be the culprit.