Initramfs

The serial log may show a long Linux kernel boot, then end in a panic. The kernel may appear to boot, but the product application never starts. The log may say No working init found or VFS: Unable to mount root fs.

These failures are often treated as application startup problems. But before any application can run, Linux has to cross a more basic boundary: the kernel must find and mount rootfs, then execute the first user-space process.