The short answer is . There is currently no known way to flash a custom ROM like PostmarketOS or Ubuntu Touch directly onto the Q20 hardware because the device will only boot software digitally signed by BlackBerry.

However, there are several "pseudo-Linux" methods that allow you to run Linux environments within the existing OS or use the device as a Linux terminal. 1. The Reality: Can You Replace BB10 with Native Linux?

: You can use native BB10 apps or sideloaded Android equivalents to connect to a Linux VPS or home server.

Installing a native Linux distribution on a BlackBerry Classic (Q20) Go to product viewer dialog for this item.

: The security is rooted in the hardware processor, making it nearly impossible to "jailbreak" or install an alternate kernel.