Suspecting bad sectors, how can I tell?
 

A few days ago a user reported strange ticking noises coming from the hard disk while the whole system was idle but unresponsive. It was resetted and upon reboot the usual fsck check after an unclean unmount failed and gave me a minimal console with / mounted as read-only. I prompted me to run fsck manually because it had found errors.

All I did was type

fsck /dev/sda5

and answer yes to everything.

After that few small files ended up linked to /lost+found. (Is there a log fsck leaves behind in those cases?)

The ticking noises are gone, all data seems to be intact, a few following fsck checks have been succesful, BUT if I try to cat any of the files that appear in the /lost+found directory, the disk starts the ticking noises again and everything seems a bit unresponsive.

I managed to reboot (shutdown -r now) in that moment to stop the ticking.

The last time I had bad sectors was in a 42 MB disk running DOS 5 and Windows 3.1 so I'm not familiar with this topic on Linux.

This an ext4 partition and it is the only partition (no separate /boot or /home).

I heard about smartctl (which is not installed on this system yet), but I fear it will try to read those files in /lost+found and die or increase the damage.

Is there a way to check for bad sectors? Or to mark them so they don't get used anymore? Should I forget about the files in /lost+found and continue using the disk as if nothing had happened?

fedetxf,

smartctrl/smartmontools does not read the storage area of the drive at all. It reads the drives internal error log.

Get the vendors drive test software. It will test the disk in a way the manufacturer approves of (it may need to destroy all the data in he process). The manufacturer will take the result as proof of a warranty claim, if the drive is still in warranty.

If the drive has bad sectors that the operating system can detect, its because its run out of spares.
Drives are made with spare sectors, which are swapped in throughout the useful life of the drive as original sectors show signs of failing. When all spares are used, the drive is end of life.