linux equivalents for defrag and chkdsk

[Eric B]

>
>
>FWIW Ubuntu depaults to checking the root file system every 30 boots.
>
>If you want to Make it check and reboot presently
>
>sudo shutdown -r -F now
>
>Bryann

I'm curious....  where would I go to change the default of every 30 
boots down to a lower number, say 5.
I rarely reboot, so 30 reboots may be several months if not 
longer.  What man page refers to this?

Eric