The problem has been resolved now, but we noticed that the df command shows
the following output in which /etc/filesystem was mounted with a temporary file in /tmp which causing the /etc/filesystems to be inaccessible, we unmount the /etc/filesystems and the problem got resolved.
df output:
/tmp/fs1.286834 3145728 1693376 47% 9619 /etc/filesystems
We didn't understand where the "/tmp/fs1.286834" comes from & why
we checked the "fs1.286834" in /tmp filesystem but didn't found it.
If you have any idea about please let us know.