Ubuntu :: User File System Check When Mounted?

A non techie friend has helped an even less techie friend by contacting me by email to discuss an ailing laptop. A few emails were exchanged, with more details, and it was not looking good because it seemed that suddenly the CD drive was not responding, nor any USB devices, the wireless icon was gone, but Ubuntu still seemed to work (for now), with wired ethernet also working. I was struggling to think of what could be done, with the favourite routes of Live CD and Live USB apparently gone.

After a few more hours - another email: 'It's now working! After so many reboots it checked disc for errors and repaired itself! Is there some way of doing that when needed anyway?'I see there is 'Disk Utility', and this would presumably fit the bill, but how does it do checks and repair when the damaged file system is being run, and is currently *mounted*? I thought utilities like fsck(?) could only be run on unmounted file systems? Have I misunderstood the disk utility fs check repair function? And anyway, what might be a good answer to my (nontechie) friend's question 'After so many reboots it checked disc for errors and repaired itself! Is there some way of doing that when needed anyway?'

For the record: (quote) It is a toshiba EA60-155 Model number PSA67E-00300C8J. He put in extra ram to install ubuntu. He thinks he may have deleted something! There is a 'trash' file on his USB drive with loads of stuff in it and he doesn't know how or why but because it won't now read the drive on her laptop we cant replace it! (end quote)