If you want to boot Trisquel from *DD you need to add to the
/etc/grub.d/40_custom :
menuentry 'Trisquel 7 amd64'{
set isofile="/trisquel_7.0_amd64.iso"
loopback loop (hd0,2)$isofile
linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile noprompt
noeject
initrd (loop)/casper/initrd
}
For security reasons you can remove one or more characters from the isofile
path or filename so that it will only boot if you edit the grub entry at boot
as a superuser.
And then run sudo update-grub.
If you actually want to install the OS from *DD you need to know that the iso
needs to be on a separate partition from the ones used in the installation
process.
