Is there any tools or some way in linux which can be used to view internals of filesystems ? How to view the inode related structures and journal  ? and cached pages of files (pagecache).
Filesystem and journal layout
linux;filesystems;inode
This will of course depend on what filesystem you are using, e2fsprogs contains debugfs which will work with ext2, ext3 and ext4, and is used to manually view or modify internal structures of the file systemman page for debugfs is here