So... I discovered that my wtmp file was really big today, like 2.1GB.
I deleted it and recreated it, but...
Is there any way I can tell logrotate to well, rotate the log?
Check man logrotate
Logrotate figures out which files need to be rotated based on the settings in /etc/logrotate.conf.
I think the default for wmtp is
/var/log/wtmp {
monthly
create 0664 root utmp
minsize 1M
rotate 1
}
If that's not in there, you can add it. If it's not sufficient, you can change it, or add a "size = whatever" directive to tell it to rotate whenever the size exceeds the set value.
Logrotate should be in the /etc/cron.daily. If it's not running often enough, you can call logrotate -f to force it.