View source for Install Linux on a USB disk by cloning your computer

This describes how to [[install Linux on a USB disk]] by [[cloning]] your computer. We will clone your harddisk to a USB harddisk and then write a bootsector using [[grub]].

== Boot your favorite Linux ==
This has been tested with SUSE Linux 10.0 and Ubuntu 7.04.

== Connect the USB disk ==
Attach the USB disk and type <tt>[[dmesg]]</tt>. At the end of the messages, you will find something like "Attached SCSI device to /dev/sda". Then you know your USB disk's device name is /dev/sda. In this tutorial, we assume the device name is /dev/sda.

== Partition the USB disk ==
 [https://www.howtogeek.com/106873/how-to-use-fdisk-to-manage-partitions-on-linux/ fdisk] /dev/sda
In this tutorial, we will assume you create a partition /dev/sda1 for your root ( / ) directory.

== Format the USB disk ==
 mkfs -t ext3 /dev/sda1

== Clone your system ==
Copy over all files from / to your USB disk. See also [[Cloning]].
 [[mkdir]] -p /mnt/sda1
 mount /dev/sda1 /mnt/sda1
 [[cd]] /
 [[tar]] -c [[Bash_operators#.24.28.29|$(]][[ls]] -1 [[piping||]] [[grep]] -Ev "[[regex|proc|sys|tmp|media|mnt]]"[[Bash_operators#.24.28.29|)]] [[piping||]] (cd /mnt/sda1; tar -xv)

'''You should know''' that you will need the /dev folder to create the ramdisk later. You can also use tar -cl ('''l'''ocal filesystems only), but that might exclude your /boot partition.

== Make your USB disk bootable ==
Here are two possibilities for making the disk bootable, it is not unusual that one fails. Try the uppermost first. We assume your USB disk is drive ''/dev/sdx'' mounted to ''/mnt/sdx''.

=== Possibility (1) ===
 $ [[cp -pr]] ''/dev/sdx*'' ''/mnt/sdx1''/dev
 $ [[cd]] ''/mnt/sdx1''
 $ [[chroot]] .
Now make sure you can access all devices from /boot/grub/device.map.
 $ mount /proc
 $ grub-install ''/dev/sdx''
 $ exit

=== Possibility (2) ===
 $ grub-install --recheck --root-directory=''/mnt/sdx1'' ''/dev/sdx''
 Probing devices to guess BIOS drives. This may take a long time.
 Installation finished. No error reported.
 This is the contents of the device map /mnt/sda1/boot/grub/device.map.
 Check if this is correct or not. If any of the lines is incorrect,
 fix it and re-run the script `grub-install'.
 
 (fd0)   /dev/fd0
 (hd0)   /dev/hda
 (hd1)   /dev/hdb
 (hd2)   ''/dev/sdx''

=== TroubleShooting ===
==== The file /boot/grub/stage1 not read correctly ====
* '''Symptome''' is that grub-install fails with the message 
 The file /boot/grub/stage1 not read correctly

* '''Reason''' can be that your partition type is incorrect, e.g. like this:
 $ fdisk -l
 
 Disk ''/dev/sdx'': 160.0 GB, 160041885696 bytes
 255 heads, 63 sectors/track, 19457 cylinders
 Units = cylinders of 16065 * 512 = 8225280 bytes
 
    Device Boot      Start         End      Blocks   Id  System
 ''/dev/sdx1''   *           1       19456   156280288+  '''c  W95 FAT32 (LBA)'''
 
* '''Solution''' can be to correct your partition type to 83 (Linux) using [https://www.howtogeek.com/106873/how-to-use-fdisk-to-manage-partitions-on-linux/ fdisk].

== Edit your initial ramdisk ==
The initial ramdisk ([[initrd]]) must contain the modules needed to load usb storage. We will use [[mkinitrd]] to rebuild your initial ramdisk. First, change to your system on the USB disk:
 cd ''/mnt/sdx1''
 chroot .
 mount /proc
Now have a look at the drivers that are loaded by the initial ramdisk.

=== SUSE ===
For SUSE, your drivers file is /etc/sysconfig/kernel.
You will find a line starting with INITRD_MODULES= in /etc/sysconfig/kernel. It should look like this:
 INITRD_MODULES="jbd reiserfs ext3 usbcore usb_storage scsi_mod sd_mod uhci_hcd ehci-hcd sbp2 sr_mod"
it can also contain more modules. Verify this line exists, then, create the initial ramdisk:
 mkinitrd

=== Ubuntu ===
For Ubuntu, your drivers file is /etc/modules. It should look at least like this (it can also contain more modules):
<pre>
# /etc/modules: kernel modules to load at boot time.
#
# This file contains the names of kernel modules that should be loaded
# at boot time, one per line. Lines beginning with "#" are ignored.

fuse
lp
usb_storage
uhci_hcd
usbcore
usbhid
sr_mod
sd_mod
scsi_mod
</pre>
After you verified the file exists, create your [[initrd]] with the command:
 mkinitramfs -o /boot/initrd.img

== Use a unique device name ==
If you now boot from your USB disk, it might be that it appears under another name than /dev/sda. To circumvent this problem, we will now use the disk's unique ID instead of /dev/sda. Try
 [[hwinfo]] --partition
You will get a line similar to the following:
   Device Files: ''/dev/sda1'', /dev/disk/by-id/usb-CompanyXXXXXX,_Inc._USB_Mass_Stor
 age_Device_100-part1, /dev/disk/by-path/pci-0000:00:1d.7-usb-0:3:1.0-scsi-0:0:0:
 0-part1, ''/dev/disk/by-uuid/84ff6790-9b69-4401-9ba2-43d044af1d30'', /dev/disk/by-la
 bel/Whatever
Now you know your partition is not only accessible via ''/dev/sda1'', but also via ''/dev/disk/by-uuid/84ff6790-9b69-4401-9ba2-43d044af1d30''. 

=== /etc/fstab ===
You can now edit the [[fstab]] on your USB disk:
 [http://userbase.kde.org/KWrite kwrite] /mnt/sda1/etc/fstab
there is one line for the mountpoint '''/''', maybe:    
 ''/dev/sda1''               /               ext2            defaults        1  1
In our example, you would change this line to 
 ''/dev/disk/by-uuid/84ff6790-9b69-4401-9ba2-43d044af1d30''  /   ext2   defaults   1  1

=== /boot/grub/menu.lst ===
In /mnt/sda1/boot/grub/menu.lst, you will find some lines telling the kernel where to find the root (/) file system, maybe:
 kernel          /boot/vmlinuz-2.6.20-16-generic root=''/dev/sda1'' ro quiet splash
not to boot from the wrong partition, you can also replace them:
 kernel          /boot/vmlinuz-2.6.20-16-generic root=UUID=''84ff6790-9b69-4401-9ba2-43d044af1d30'' ro quiet splash

== Try booting from your disk ==
If there are problems, continue with TroubleShooting.

== TroubleShooting ==
=== GRUB - nothing else ===
* When booting from USB, I get a line saying 
 GRUB
nothing else.
: This can be a problem with your device map. Keep in mind that, when booting from USB, your USB disk corresponds to (hd0), the first harddisk. grub-install will tell you where its device map is - try correcting it.

=== Error 17 after boot menu ===
* After choosing an item from the [[grub]] menu, I get a line saying 
 Error 17: Cannot mount selected partition
: most probably, your device order has changed. For example, if you [[installed linux]] from CD and your IDE harddisk was device 0, it may now be device 1 after [[Booting from USB]]. In this case change 
 root (hd''1'',1)
to 
 root (hd''0'',1)
Please note that ''1'' is simply an example for a partition, it may also be any other number.

=== Error 17 before boot menu ===
* Instead of getting the [[grub]] menu, I get a line saying nothing else but
 Error 17
: most probably, your device order has changed and grub searches its menu (stage) on the wrong disk. You will have to do grub-install again.

=== Error 21 before boot menu ===
* instead of getting the [[grub]] menu, I get a line saying
 Error 21
: Solution was to correct ''/mnt/sda3''/boot/grub/device.map and ''/mnt/sda3''/boot/grub/menu.lst, the re-do a grub-install.

=== Waiting for /dev/sda to appear ===
* After selecting the boot entry in the [[grub]] menu, you get some lines of messages then the boot process stops with the message 
 Waiting for ''/dev/sda'' to appear
: your USB disk is recognized and supported by your BIOS, but your initrd's drivers do not recognize it. You will have to edit your initial ramdisk to contain the correct drivers, as discussed under initrd.

=== No bootable partition in table ===
* After starting the computer, you get a line saying 
 No bootable partition in table
: you do not have a partition that is marked as bootable. Use [https://www.howtogeek.com/106873/how-to-use-fdisk-to-manage-partitions-on-linux/ fdisk]'s "a" command to set the bootable flag of ''/dev/sda1''.

== What comes next ==
Now that you can boot from your USB disk, you should be aware that you cannot write very often to a specific sector, so you should make /tmp a [[ramdisk]] like this:
 mount -t tmpfs tmpfs /tmp -o size=512M