sinty-initramfs

The initramfs init of SintyOS. It runs before the real init and decides which root filesystem the machine boots: the one whose dm-verity tree matches the root hash in the signed kernel command line.

Why it exists

The boot itself is the Atom Loops boot package: root selection by the signed hash, loop devices and dm-verity through the kernel interfaces, the persistent /var, the verified firmware bundles and the switch to the real init. Atom Loops defines that contract, so SintyOS builds on the package instead of keeping its own copy of the logic.

This program is the part that is particular to SintyOS. The initramfs holds no shell interpreter, no BusyBox and no device-mapper tools: one Go binary does the boot.

What it adds

• The SintyOS command line: sing.roothash=, sing.live, sing.portable (portable roots on the partitions named sing-portable-root and sing-portable-hash), init= and sinit.debug, which is passed on to sinit.
• The first-boot login setup. On an installed system whose first-boot setup has not completed, the login configuration of the setup is put back, so a device wiped by a bootloader unlock still starts the setup and gets an account.
• Boot diagnostics. A boot that cannot continue saves the reason, the command line, the block devices and the tail of the kernel log to SINTYRESCUE.txt on the SINTYLOGS partition and says so on the screen.
• Unlock. sintykey tells whether the owner unlocked the bootloader. A locked device that cannot boot powers off; an unlocked one offers a root shell after the phrase OPEN DEBUG SHELL is typed.

Build

make build            # ./sinty-initramfs
make static           # stripped static binary for the initramfs
make test
go build ./...        # plain build

Requires Go >= 1.26 and Linux. The initramfs carries the static binary as /init.