Can I copy my Ubuntu OS off my hard drive to a USB stick and boot from that stick with all my programs?

I've been doing this for years. I'm writing now from a PC which does not even contain an internal hard drive. I don't even carry a laptop, just this high performance USB flash media.

I will now outline the two components you need to buy if you want decent performance. Most flash drives are too slow for most people, and they can also become unstable due to overuse of the type they get running operating systems and particularly swapspace.

I use this USB3 to mSATA SSD flash media adapter, priced here at US$19.

And inside it, I use an mSATA SSD drive originally made for today's tablet and netbook computers. Though I manage to get by on just 64 GB myself, you may choose to buy something with greater capacity. Last I checked, the capacity of these drives was up to around 1 TB. I remember when the largest available was just 32 GB.

If you would like something still more rugged, I can recommend this similar USB3-mSATA adapter which is made from a solid section of extruded aluminum. It is almost exactly the same price. Whereas the model I previously recommended is only 2/3 the thickness, it would probably cave if stepped on. This one might tolerate a car driving over it.

To the best of my knowledge, nobody has made a waterproof model yet, but it's only a matter of time. The strange thing is that as obvious as these appear as portable operating system environments, apparently all references to these regard their use entirely for portable data.

One last detail. It is my practice to keep a 128 GB common slow flash drive in one of the more regularly used computers and have the portable drive automatically back up critical data to it when it is used there. The automatic backup software I'm using is that which is included with Ubuntu and it encrypts its backups. This way whether I lose the boot drive, or my home is robbed, the odds of actually losing all my current personal data are incredibly low.

This should be possible; your flash drive just needs to have enough memory for the OS and whatever files you'll be using. The limitations are based on the flash drive and/or the computer you run it (but most likely the read/write speed of the flash drive will have a larger impact on speed).

The stick is used as memory similar to any other harddrive in a laptop or desktop computer. You could probably boot from one flash drive with Ubuntu flashed onto it and select your other flash drive as the destination hard disk drive for the OS.

I'm no expert in this, but it should be do-able, just slow.

Yes, this is completely possible. First and foremost, you will need at least 2 USB ports available, or 1 USB port and 1 CD-Drive.

You start by booting into a Live-CD version of Ubuntu with your hard-drive where it is and the target device plugged into USB. Mount your internal drive and target USB to any paths you like.

Open up a terminal and enter the following commands:

tar cp --xattrs /path/to/internal | tar x /path/to/target/usb

You can also look into doing this through a live installation and a utility called CloneZilla, but I am unsure of exactly how to use CloneZilla. The above method is what I used to copy my 128GB hard-drive's installation of Ubuntu to a 64GB flash drive.

I'm adding ANOTHER ANSWER to answer your OTHER QUESTION, which you added to your first question after I offered my original answer, chosen above:

you wrote:

Update: Thanks so much for the thoughtful responses! At this point, I'm wondering how I should go about keeping my system backed up to a bootable external drive.

What you are asking can be answered different ways depending on what you are trying to do. I can think of four possible ways, I will explain in outline format below:

1) Synchronize data-only across two bootable drives:

This seems to be what you want to do, but I believe you will run into a problem which will impede data security. I will explain.

It seems to me that you seek to SYNCHRONIZE data files between two (or more) bootable operating systems. Though I've never actually done this, I know that it is only a google-search away, and very likely explained on this site. However for that to work, you'd almost have to turn encryption off, or rather, never turn encryption on. In my opinion, if you are going to have portable bootable external drive, they should always have data encryption turned on, so unless you discover a drive synchronize that can also accept password data, or unless you decide to travel without data encryption, this is not a viable solution.

2) Clone again the internal or external drive in its entirety to another drive:

Use the "Clonezilla" utility, mentioned in the very last paragraph of my original answer, to clone the original internal drive to another external drive to make two such external bootable drives to keep track of.

3) Use the backup utility included with Ubuntu with your external bootable drive:

This is what I do. I boot (nearly) ALL MY COMPUTERS to a single external drive which travels with me, and when I am home, the 128gb slow usb flash drive, which remains plugged in my home computer, makes incremental backups of changed files on the traveling boot drive.

In your case, I would recommend that in the interest of data security, that you physically remove your internal hard drive and leave it at home. It will frustrate the heck out of anyone who steals your laptop, in fact if they get to try it before they steal it, they might even decide it is broken and leave it alone. If the thought of having only one bootable external drive frightens you, bring two and mark the spare clearly as such so it is never used unless the first one is lost or destroyed. As long as you create the backup drive on the first external drive before cloning it to make a second external drive the incremental backup drive will continue to work with the spare bootable drive.

4) Use the backup utility included with Ubuntu in the traditional method:

Use the backup utility to backup just the data from the internal drive to an ENCRYPTED data-only external drive. You can configure it to make "incremental" backups of any changed files on your internal hard drive to the external, non bootable, SSD.

Yes you can copy a full Ubuntu OS (with Programs, customizations and all ) from your Desktop or Laptop Hard drive to an external USB Flash Drive or external Hard drive. I just did it for Ubuntu 14.04 LTS to an external Hard drive (but equally applicable to USB Flash drive as well) Required software / hardware:

1 Destination External Hard Drive / Destination USB Flash Drive to have the cloned OS

1 Source OS (Ubuntu or any other OS that needs to be cloned)

1 USB Drive (with at least with as much capacity (256 MB - 1 GB) as a clonezilla live USB requires)

1 computer / laptop having Windows which can run Live Linux USB creator

Steps:

1. Download Clonezilla from http://clonezilla.org/downloads/download.php?branch=stable (download the ISO)

2. Download Live Linux USB Creator (Lili) from http://www.linuxliveusb.com/en/download

3. Create a bootable Clonezilla (Live Clonezilla) on USB by running Live Linux USB Creator.

4. Configure your Source desktop / laptop to boot from a USB drive

5. Insert both, the destination external hard drive or destination USB Flash drive in 1 USB Slot and the Clonezilla Live USB drive in other slot and boot.

6. Clonezilla will take some time to read partition info When the Clonezilla UI appears, select default menu entries.

7. [With Caution] select Source Partition info and Destination partition info It may be noted that Clonezilla would require space on destination USB Flash drive or external hard disk which is equivalent of the source Hard disk and it will erase all data from the destination USB Flash drive / external hard drive.

8. Once all is selected, Clonezilla will create a live OS on the destination drive / flash drive

9. Test the cloned OS by removing Clonezilla Live USB drive and booting from the Live OS which has been cloned onto the destination External drive / USB Flash drive.

Enjoy !