F21 systemd log flood - how to stop

[Andy Hairston]

After even more Google searching, I found the command
systemd-analyze set-log-level warn

Running this as root, I got:
Failed to issue method call: Access denied

Strangely, I can run it with 'notice' instead of 'warn', and it silently 
completes - probably meaning it's already set to notice.

Why does this produce an 'access denied' message even when run as root?