anon@jolly:~$ e2fsck -f /dev/sdb2
e2fsck 1.42.12 (29-Aug-2014)
/dev/sdb2 is mounted.



WARNING!!!  The filesystem is mounted.   If you continue you ***WILL***
cause ***SEVERE*** filesystem damage.


Do you really want to continue<n>? no
check aborted.
anon@jolly:~$ sudo umount /dev/sdb?
anon@jolly:~$ e2fsck -f /dev/sdb2
e2fsck 1.42.12 (29-Aug-2014)
e2fsck: Permission denied while trying to open /dev/sdb2
You must have r/w access to the filesystem or be root
anon@jolly:~$ sudo e2fsck -f /dev/sdb2
e2fsck 1.42.12 (29-Aug-2014)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/sdb2: 134523/221184 files (0.8% non-contiguous), 804491/871167 blocks
anon@jolly:~$