How Android works

The Linux kernel

The engine under everything — and what Android bolted onto it.

4 pages62 min4 interactive9700 words

01Android's kernel, and its androidismsAndroid runs on Linux, but not quite the Linux you would install on a server. This page is about the four jobs the kernel does for Android, the handful of features Android bolted on, and what happened to each of them.intermediate15 mininteractive
02Branches, GKI and the KMIFor years every phone shipped a different kernel, and a security fix could take years to arrive. GKI made the kernel a single signed binary and moved board support into loadable modules behind a frozen interface.nerd15 mininteractive
03Wakelocks and the art of sleepingA phone must sleep to survive, and must wake to be useful. The machinery that decides which is a story about a rejected kernel patch, a userspace dialect, and the cheapest way to keep a CPU alive.intermediate15 mininteractive
04The kernel features Android leans onSeven kernel facilities Android could not work without: Binder, memfd, cgroups and PSI, SELinux, seccomp, DMA-BUF heaps and eBPF — plus the filesystems that make read-only system images cheap.nerd17 mininteractive

Test yourself

Test yourself: The Linux kernel

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Order the steps of the SystemSuspend suspend thread's loop, from first to last.

Drag, or use the arrows to reorder.

1Wait for the wake lock counter to reach zero
2Write the saved value back to /sys/power/wakeup_count
3Write mem to /sys/power/state
4Read /sys/power/wakeup_count