I intend to use fsck for checking my Linux partition of the main disk, because its file system is suspicious of being

not unmounted cleanly

by shutting down the system. I have searched in my environment variables: none of them except of PATH should control the fsck program. But the program apparently needs to be used during a boot:

:~$ fsck -V

fsck from util-linux 2.20.1

Checking all file systems.

[/sbin/fsck.ext4 (1) -- /] fsck.ext4 /dev/sda6 

e2fsck 1.42 (29-Nov-2011)

/dev/sda6 is mounted.


WARNING!!!  The filesystem is mounted.   If you continue you WILL

cause SEVERE filesystem damage.

Do you really want to continue? no

check aborted.

(There is no /forcefsck file in my root according to How do I find out if there will be a fsck during the next boot? . My etc/fstab file contains

 

# /etc/fstab: static file system information.

#

# Use 'blkid' to print the universally unique identifier for a

# device; this may be used with UUID= as a more robust way to name devices

# that works even if disks are added and removed. See fstab(5).

#

#                

proc            /proc           proc    nodev,noexec,nosuid 0       0

# / was on /dev/sda6 during installation

UUID=1ac55d8d-c112-4bc7-9e79-921d196f9f79 /               ext4    errors=remount-ro 0       1

# swap was on /dev/sda7 during installation

UUID=54f7e314-50e2-419b-a45d-47c3058ecc00 none            swap    sw              0       0

/dev/fd0        /media/floppy0  auto    rw,user,noauto,exec,utf8 0       0

).

According to an answer to Slow reboot - understanding fsck and tune2fs I have tried tune2fs hoping that I'll get the present value of the

max_mounts_count

parameter to be able to set it to 1 for checking the partition during the next boot. But after

sudo rm /var/lib/update-notifier/fsck-at-reboot

and a restart I have only got a response

:~$ tune2fs -l /dev/sda6

tune2fs 1.42 (29-Nov-2011)

tune2fs: Permission denied while trying to open /dev/sda6

Couldn't find valid filesystem superblock

.
Can I use

sudo tune2fs -l /dev/sda6

safely? Thanks.