Ubuntu – Using a bootable live cd disk image mounted on the hard drive

Setting Up Your USB Stick

Setting up a device for use as Live CD persistent storage device is fairly simple. We just partition it and format it while giving it a special name that the Live CD recognizes. Although you can use any device visible to the CD for persistent storage, in this example we will discuss using a USB stick since they are pretty common now and are relatively inexpensive. There are no minimum size requirements for your storage device, but naturally, the more storage space you have the more applications you can install and settings you can save.

Plug your USB Stick into your computer and let's get it ready for Live CD persistence.

Note: If you previously followed the instructions on this page for "casper-cow" and it didn't work, that's because it should have read "casper-rw".

Note 2: In the instructions below the ext3 file-system is used. For a memory stick however where space is tight, the ext2 file-system will use up considerably less overhead and is probably good enough for this purpose.

Note 3: The instructions use all terminal commands, many of them looking quite serious. However it can all be done using the graphical Gnome Partition Editor tool you find in the System -> Administration menu. The exception is giving the partition a label, for this you'd still need to go to a terminal and issue the command

sudo e2label /dev/<yourpartition> casper-rw

Determine Which Device Your USB Stick Is

Note: if you prefer, you can use GPartEd to identify and format the usb thumb drive to ext3 (or a different compatible format) and then skip directly to the "Creating the "casper-rw" File System" section.

In order to partition and format your USB Stick, we first need to determine which device your computer recognizes it as and what its mount point is. To find this information run the following command:

df -h

The output of df -h should look something like this:

Filesystem Size Used Avail Use% Mounted on

/dev/hda1 187G 4.0G 183G 3% /

varlock 9.3G 507M 8.8G 6% /var/lock

udev 506M 156K 506M 1% /dev

devshm 506M 0 506M 0% /dev/shm /dev/hdb3 7.5G 1.4M 7.5G 1% /tmp

/dev/hdb2 9.3G 507M 8.8G 6% /var

/dev/sda1 124M 31M 94M 25% /media/USB DISK

As you can see, on my computer, my USB Stick is the last entry in the list and is seen as /dev/sda1 and is mounted and accessible at /media/USB DISK. Now that we know where our USB Stick is, let's go ahead and partition it properly.

Partitioning Your USB Stick

Partitioning your USB Stick is a fairly simple task and only requires a few short steps. To partition your USB Stick we will use the command fdisk so run the following command to start the process (replacing /dev/sda with your device path):

sudo fdisk /dev/sda

Without getting in depth about how to use fdisk (which is outside the scope of this document) here is how you can partition your USB by deleting any existing partitions and creating one new partition.

First type “p” at the command prompt and hit to print the current partition table. The output of this command should look something like this:

 Command (m for help): p

 Disk /dev/sda: 130 MB, 130023424 bytes
 16 heads, 32 sectors/track, 496 cylinders
 Units = cylinders of 512 * 512 = 262144 bytes

 Device Boot      Start         End      Blocks   Id  System
 /dev/sda1   *           1         496      126960    6  FAT16

Again, for this example, we will just delete all of the existing partitions so now type “d” at the command prompt. Then enter the number of the partition you wish to delete. Repeat this process for each partition on your USB Stick until they are all deleted. The following is a example of what your session might look like:

 Command (m for help): d
 Partition number (1-4): 1

 Command (m for help): d
 Partition number (1-4): 2

 Command (m for help): d
 Partition number (1-4): 3

 Command (m for help): d
 Selected partition 4

 Command (m for help): p

 Disk /dev/sda1: 130 MB, 130007040 bytes
 16 heads, 32 sectors/track, 495 cylinders
 Units = cylinders of 512 * 512 = 262144 bytes

Device Boot      Start         End      Blocks   Id  System

Command (m for help):

As you can see we have now deleted all of the partitions on our USB Stick. Now we can create one new partition by typing “n” at the command prompt followed by your desired partition number. Once that is done type “w” and hit to write the partition table changes to your USB Stick. Here is the output from my session:

 Command (m for help): n
 Command action
   e   extended
   p   primary partition (1-4)
 p
 Partition number (1-4): 1
 First cylinder (1-495, default 1):
 Using default value 1
 Last cylinder or +size or +sizeM or +sizeK (1-495, default 495):
 Using default value 495

 Command (m for help): w
 The partition table has been altered!

 Calling ioctl() to re-read partition table.

 WARNING: Re-reading the partition table failed with error 22: Invalid argument.
 The kernel still uses the old table.
 The new table will be used at the next reboot.
 Syncing disks.

Now that we have our partition table all set let's format it.

Creating the "casper-rw" File System

Formatting your USB Stick is also a very simple task. First we will unmount the device so we can format it, then just format it.

First unmount your USB Stick by running the following command:

sudo umount /dev/sda1

Now that your USB Stick is unmounted we can format it. The only special consideration is that we must give the formatted partition the label “casper-rw”. This is the name the Live CD looks for to store persistent information. You can properly format your USB Stick by issuing the following command:

sudo mkfs.ext3 -b 4096 -L casper-rw /dev/sda1

The output of this command should look something like this:

 mke2fs 1.38 (30-Jun-2005)
 Filesystem label=casper-rw
 OS type: Linux
 Block size=4096 (log=2)
 Fragment size=4096 (log=2)
 31744 inodes, 31740 blocks
 1587 blocks (5.00%) reserved for the super user
 First data block=0
 1 block group
 32768 blocks per group, 32768 fragments per group
 31744 inodes per group

 Writing inode tables: done
 Creating journal (1024 blocks): done
 Writing superblocks and filesystem accounting information: done

 This filesystem will be automatically checked every 20 mounts or
 180 days, whichever comes first.  Use tune2fs -c or -i to override.

NOTE: This example uses the ext3 file system, but almost any file system should work. Among the file systems which won't work are VFAT and NTFS

Now that we have our partition created and formatted all that is left to do is use it. So let's go use it!

__Using a Loopback File__

Instead of using a USB stick, you can use a file on your hard disk to store persistent information. The file must be named casper-rw and must be on the root of a partition. This partition can be any type that can be mounted automatically (e.g. vfat or ext3). (The persistent mode still works, if the file is created on the root partition of an USB stick.)

The following commands assume that a partition is mounted at /media/hda1. You can use any partition; even / will do fine. A file 128 MB in size will be created on this partition. To change the size, modify the count parameter of the "dd" command.

dd if=/dev/zero of=/media/hda1/casper-rw bs=1M count=128

 128+0 records in
 128+0 records out
 134217728 bytes transferred in 0.947819 seconds (141606919 bytes/sec)

mkfs.ext3 /media/hda1/casper-rw

 mke2fs 1.38 (30-Jun-2005)
 /media/hda1/casper-rw is not a block special device.
 Proceed anyway? (y,n) y
 Filesystem label=
 OS type: Linux
 Block size=1024 (log=0)
 Fragment size=1024 (log=0)
 32768 inodes, 131072 blocks
 6553 blocks (5.00%) reserved for the super user
 First data block=1
 16 block groups
 8192 blocks per group, 8192 fragments per group
 2048 inodes per group
 Superblock backups stored on blocks:
    8193, 24577, 40961, 57345, 73729

 Writing inode tables: done
 Creating journal (4096 blocks): done
 Writing superblocks and filesystem accounting information: done

 This filesystem will be automatically checked every 23 mounts or
 180 days, whichever comes first.  Use tune2fs -c or -i to override.

That's it! You can now boot the Live CD as described below.

Booting the Live CD in Persistent Mode

Now we get to enjoy the fruits of our labor. Make sure your USB Stick is plugged into your computer and take the Live CD that you downloaded and burned earlier and put it in your CD drive (if it is not already there). Reboot your computer and boot up using this Live CD.

Before you reboot there are only two things that you need to remember. When the Live CD menu gets displayed hit the key to enter “Other Options”. This will display the arguments that the Live CD passes to the kernel. At the end of this argument list just add a space and add the word “persistent”. This will instruct the Live CD to maintain and use persistence. That is all. Go for it!

Note: It appears that with Flight 5, you need to create a new user in the Live CD session (go System -> Administration -> Users + Groups, then press the "Add User" button) for it to save your settings; it does not appear to save most changes to the default user, "ubuntu". When you create the new user, be sure to check the box in the "user privileges" tab that says "executing system administration tasks" or you'll be pretty limited in what you can do Smile :)

When you get back, or better yet, when you boot into your live environment come back to this page and see how you perform a few basic tests to make sure everything is working correctly.

Verifying That Everything Worked

Here are a few simple things you can do to verify that everything is working as expected.

Reboot the Live CD/USB

The first simple thing you can do to verify that persistence is working is install a few applications and change some environment settings (some thing highly visible and easily recognizable) like your theme or add some GNOME panel icons. Then just reboot... Hit , enter in “persistent” on the kernel arguments list and boot into your new custom Live CD environment. Your newly installed applications and your custom settings should all still be there.

If you want to dig a little deeper you could always inspect the contents of your USB Stick. This will also give you deeper insight into how this great system works.

(you can do this from the Live CD by going System -> Administration -> Disks, selecting the appropriate drive, setting the access path to /mnt and pressing the Enable button followed by the Browse button)

Investigating What Is Now On Your "casper-rw"

Another relatively simple thing you can do to verify that everything is working and to learn more about how everything works is to just inspect what is now on your USB Stick in isolation. Reboot back into your regularly installed system, plug in your USB Stick and just have a look around. The contents of your USB Stick is what makes your custom environment your own.

Automatic Persistence

By using reconstructor a CD can be remastered and an additional menu item (Persistent Mode) added on boot. The persistent mode was added as the default. No changes were made to the CD except for adding the persistent menu item. This may be best described in another how-to. If there is a place where a persistent ISO can be uploaded I'd be glad to share

Conclusion

The new Ubuntu Live CD persistence is an excellent capability and in addition to current Live CD uses, this will certainly make Live CDs very much more viable, useful and important. Now you can carry around your own custom Ubuntu environment on a CD and USB Stick that all just fits in your pocket. Now go gloat to your friends and co-workers about how much Ubuntu ROCKS!

Source: https://help.ubuntu.com/community/LiveCD/Persistence

If you encounter the problem of booting without persistence on on UEFI pc. See what Ubfan (ubfan1) wrote on 2013-04-29 here: https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1159016

Note the comments about using a more current version of the ISO, but your problem may be that you have a separate /home partition. Assuming your "newinstall" is a user home directory, the partition starts with /newinstall,,, not /home in the line

set isofile="/newinstall/kubuntu-14.10-desktop-amd64.iso"
loopback loop (hd1,6)$isofile

The other potential issue is the enumeration of disks may differ at the grub prompt and in the final running system. You would expect your sdb to be the hd1 at the grub prompt, but sometimes, hd0 and hd1 seem to be reversed. I did try the fix mentioned above, since I have an iso on a mounted partition, and the boot succeeded, but with an external (non-bootable) USB hard disk plugged in, the hd0 (in my case for sda) had to be manually changed to hd1 for the boot to work. Without the USB disk, the hs0 worked.