Almost all Blu-ray players use Linux because of its open-source license. Linux also provides multimedia capabilities necessary for running Blu-ray applications and other media such as running Java binaries and media codecs.

A player's user interface that uses Linux OS.

Linux is often used for personal computers, but Blu-ray players use a customized and embedded (stripped down) version of it, removing unnecessary code that's originally used for computers. It is often compiled to run on ARM-based CPUs; historically, it has also been compiled to MIPS and SuperH CPUs. Most players uses 2.x or 3.x series of the Linux kernel, for example Sony uses the 2.4.x series, Panasonic uses the 3.x series, and Sharp uses the 2.6.x series.

Duke and Tux fight off against an army of clippies!

For Blu-ray developers, Linux is not relevant for BD application development because a BD application uses a virtual machine, making it a independent platform, meaning it does not depend on any specific operating system or hardware architecture.

Firmware

Firmware is a type of software that's embedded into the player's hardware to help function properly and provide low-level control. Unlike DVD players, Blu-ray players will sometimes need a firmware update. It is sometimes needed to fix glitches, security, or other things, because the Blu-ray format is technologically more advanced than the basic DVD. Firmware updates aren't that big, ranging mostly 100 MB.

Bootloader

Blu-ray players either have their own proprietary bootloader or an open-source one such as U-Boot 🔗 used notably on the MediaTek MT8580 SoC. These bootloaders are used to perform low-level hardware initialization tasks and boot the device's operating system kernel. Some players will boot insanely fast, while others can be slow due to poor optimization or have a big sized operating system.

Hacking

Now if you're just a Linux enthusiast, interested on how the Blu-ray player's operating system works, or want to make a player region free, then looking into Linux will interest you. Hacking Blu-ray players is niche and very difficult as Blu-ray players are not computers.

Links about Linux

• Linux Kernel Archives
• Linux Wikipedia Page 

Linux Source Code used on Blu-ray players

• Panasonic Source Code Distribution Service -Blu-ray Players
• Sharp Source Code Components
• Sony Source Code Distribution Service

External Links

• Linux Kernel Archives
• Linux Wikipedia Page 
• Hacking BluRay players just for fun - Part 1 
• How to get local root shell on the LG HR598 Bluray 
• Hacking BD-C5500/XAA
  
• Hacking Samsung BD-P1620A/BD-P3600
• Rip SACD with a Blu-ray player (Talks about Linux on different BD players)