[arch-general] /var/log/btmp empty

[gt]

Hello folks

My failed login attempts aren't being recorded, and lastb shows no
output.

The permissions are correct:

-rw------- 1 root root 0 Nov 15 06:39 /var/log/btmp

Reading a previous message on the mailing list, i tried setting 

FTMP_FILE	/var/log/btmp

in /etc/login.defs. But this gives the following error (right after typing
the username on a tty):

configuration error - unknown item 'FTMP_FILE' (notify administrator)

So two questions:

1. Why isn't the option being recognised, even though it is present in
the man page for login.defs?

2. How do i enable logging to /var/log/btmp?

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