Both
Before installing module-init-tools.tcz:
modprobe is /sbin/modprobe
After installing module-init-tools.tcz:
modprobe is a tracked alias for /sbin/modprobe
After editing the .ashrc:
modprobe is a tracked alias for /sbin/modprobe
After typing "alias /sbin/modprobe='/usr/local/sbin/modprobe'":
modprobe is /usr/local/sbin/modprobe