Mount a folder inside another folder (Binding)

I'll show you how to mount a folder residing somewhere in a filesystem to another folder.

Its a line command,
sudo mount -o bind /sourcefolderurl /destinationfolderurl

Done! Now where is it useful?
I ran into this problem during my ftp server setup,
ftp://myserver mapped to file system /media/sda7/ftpshared, ie ftp://myserver/a.mp3 mapped to /media/sda7/ftpshared/a.mp3.

But i also had to share /opt/cache/apt/archives (all the .deb files) within the ftp server, creating symbolic links wasn't working since proftpd worked in a chrooted environment, thus this was a good solution.

sudo mount -o bind /opt/cache/apt/archives/ /media/sda7/ftpshared/archives

To automatically mount the folder, make an entry in /etc/fstab file at the very end,
/var/cache/apt/archives /media/sda7/ftpshared/archives auto bind,gid=46,defaults 0 0

And on every boot, the folder is automatically mounted.

Cheers!!