With 2GB RAM & 1.3Ghz processor, is using Ubuntu via USB practicable?
With your hardware running Ubuntu from a live USB is possible, but I wouldn't go so far as to say that it is practical because of slow, laggy performance. A dual boot of a lightweight Ubuntu flavor like Xubuntu 18.04 or Lubuntu 18.04 alongside your existing operating system would be a better alternative.
I answered this question because it is a niche question, and there seems to be no other way to prevent frustrating user experiences caused by trying to run Ubuntu from a live USB on a computer that has limited hardware. There are flavors like Lubuntu that work well on this hardware1, but the read/write speed limitations of the USB flash drive would still be a performance bottleneck.
The limitations of live USB performance on the flash drive form factor are purely physical, not the result of any corporate paywall.
A live USB on a pocket-sized portable SSD has OK performance, but trying to run Ubuntu on an expensive toy like that is a waste of money for most people.
Lightweight live Linux distros that are designed to run on a USB flash drive such as Boot-Repair, GParted, Clonezilla and grml work just fine on ordinary USB flash drives.
Answer to the edited question
Booting and running from a USB pendrive can be slow
In a low-spec computer
- If there are 'only' USB 2 ports on the computer
- If the pendrive is a USB 2 pendrive
- If the pendrive is a slow USB 3 pendrive. The flash hardware (electronics and memory cells) is often the bottleneck, slower than the USB 3 interface.
- It is always an advantage to use a fast USB 3 pendrive, even when there are 'only' USB 2 ports on the computer
- For this reason you should select an Ubuntu family flavour with a light desktop environment, for example Lubuntu or Xubuntu. (Standard Ubuntu may be slow, and if the graphics chip/card cannot manage 3D graphics, it might not work at all or very slowly.)
Live, persistent live or installed system in the USB pendrive
A live (live-only) Lubuntu or Xubuntu system is the simplest system to install and it is the fastest alternative with a computer and pendrive, where the communication via USB is slow. But the modifications of the system and documents will not survive shutdown and reboot. The data are stored in RAM which is fast but not persistent.
A persistent live Lubuntu or Xubuntu system uses and overlay system, where the storage in RAM is overlayed with a
casper-rwfile or a
casper-rwpartition. This means that the modifications of the system and documents will survive shutdown and reboot, they will persist.
You can install programs and tweak the system, but you cannot use an upgraded kernel and its hardware drivers, because the overlay system is started after the linux kernel has started.
Very portable between computers.
- Rather sensitive to corruption. You need frequent backups
An installed system, installed like into an internal drive, but installed into a USB drive. In order to be fairly fast you should use a fast USB 3 pendrive with size at least 16 GB or an SSD connected via an external adapter or box.
You can install programs and tweak the system only limited by the size of the USB drive. It works just like any installed system.
Portable between computers, much more so than Windows. You should avoid proprietary drivers if you want portability, otherwise, when used in a single computer you can install proprietary drivers (usually for graphics and wifi).
Rather robust, but the USB connection and the pendrive hardware increase the risk of corruption and failure due to wear of memory cells. You need frequent backups.
The following was written to answer the original question
The original question gave the impression that the OP does not know how to boot into a USB pendrie, but after editing it seems no longer relevant.
Small tips how to boot into a USB pendrive
Boot (or reboot) your computer,
and at once during boot either press or tap repeatedly (depending on computer brand and model) the hotkey, that should give you a temporary menu: ESC, F2, F9, F12 ...,
and in the temporary menu select USB to start Ubuntu from the USB pendrive instead of the installed operating system.