Possible Duplicate:
How do I install Ubuntu to a USB key?
Two issues: (1) cannot get Ubuntu to automatically boot from memory stick (nor am I offered a choice of OS to run in BIOS menu); 2) Cannot save changes/additions to Ubuntu persistence file. Working on HP desktop w/ Windows 7
the first is typically set in your BIOS somewhere.
Second, how did you set up your persistence ? Here is how I do it.
Mount your usb device, and cd to the root of the device. Assuming it is mounted at /media/Live
cd /media/Live
# this will make a 1 Gb file for storage
# increase / decrease the count as needed
dd if=/dev/zero of=./home-rw bs=1M count=1000
# Make a file system.
mkfs.ext4 home-rw
mke2fs 1.41.14 (22-Dec-2010)
home-rw is not a block special device.
# Answer ‘yes’ here
Proceed anyway? (y,n) y
#Remove the reserved blocks
tune2fs -m 0 -L home-rw home-rw
When you boot, you need to add the boot option persistent to the options.
NOTE the file nema home-rw is for a persistent /home directory only (IMO it works better). If you want a persistent / directory, change the name from home-rw to casper-rw. Take care with a persistent /, I would not advise you install or upgrade a bunch of packages, it takes a lot of space and is not always reliable, IMO better to remaster the live CD.
See
https://help.ubuntu.com/community/LiveCD/Persistence#Booting_the_Live_CD_in_Persistent_Mode
