Forcing fsck at next reboot

Check /etc/fstab; the last column for the FSes you want to check must not be 0 (requirement not confirmed but does no harm).

Ensure that /etc/default/rcS has FSCKFIX set to yes (requirement not confirmed but does no harm).

Create a signal file (it will be removed after fscking has finished):

echo y > /forcefsck


or reboot with the shutdown command's -F option, for example:

shutdown -rF now