Is there any way to boot from iso while running system from live disk?

Tested on VM. Was able to boot from Trisquel Live ISO (residing on hard disk) using this method.

Required steps would look like this:

1. After booting to your Ubuntu Live disk, start it's installation process. You would need to do at least minimal installation of the system on /dev/sda4 to get a working and bootable GRUB. But it's easier to just do full installation (it's rather quick).

   1.a. Be sure to restrict the installation to change only the contents of /dev/sda4. To do so you would need to select "Something else" when asked about hard disk settings.

2. Test that your fresh GRUB is working by booting to the installed system.

   2.a. Note: Under Ubuntu to show GRUB menu press and hold Shift on system start. This question contains instructions on how to enable showing of GRUB menu on every boot.

3. Now you need to add the required menuentry as explained in this method that you mentioned. Providing adaptation:

   3.a. I assume, that the Trisquel ISO is located at root of /dev/sda3/.

   The menuentry for the ISO image needs to be added to /etc/grub.d/40_custom file. Edit the file by:

   sudo apt-get install gksu gksudo gedit /etc/grub.d/40_custom 

   And replace the text in that file with this one:

   #!/bin/sh exec tail -n +3 $0 # This file provides an easy way to add custom menu entries. Simply type the # menu entries you want to add after this comment. Be careful not to change # the 'exec tail' line above. menuentry "Trisquel ISO" { set isofile="/trisquel_7.0_amd64.iso" loopback loop (hd0,3)$isofile linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=$isofile noprompt noeject initrd (loop)/casper/initrd } 

   Where is:

   • Trisquel ISO = The name you want to display in the Grub menu.
   • /trisquel_7.0_amd64.iso = The path to the ISO image on target partition.
   • (hd0,3) = The partition which contains the ISO image (for GRUB it's equal to /dev/sda3 from linux: "sda1" == "(hd0,1)"; "sdb2" == "(hd1,2)"; ...).
   • note: the tail -n +3 means simply "which line grub starts to read the configuration from as is". the 3th line in this example is the first comment line, which is fine.
     
     

   3.b. Save and close this file and now run this command (to apply changes):

   sudo update-grub 

4. Now you should be able to boot from ISO on hard disk.
   Note: if you require using /dev/sda3 in installation process, then use this command from the Live CD environment:

   sudo umount -l /isodevice 

Futher reading: reference and examples of Ubuntu menuentries.

I was able to achieve this on a kickstart-base distro, but it should work as well for others. mount the iso, pull out files: cat .....isolinux/initrd.img | unxz | cpio -idm modify the kickstart file and store in new file

Now the tricky part... take the iso and shove it into a new initrd tree (copied from the original initrd.img), then use dracut to put a script in that will create a device file for it with 'losetup' in the early boot. Then use boot param inst.repo=hd:/dev/loop9 (your loop) and use inst.ks=file://// (the kickstart file.. potentially pulled from the iso if there was one).

Then use kexec -l to load the new initramfs and kernel and rebooting will cause the iso to be loaded/started.

I'm mainly placing this answer here to confirm that a) it can be done, and b) my experience has been that it's pretty complex.