An initramfs (initial ram file system) is used to prepare Linux systems during boot before the init process starts.
The initramfs usually takes care of mounting important file systems (by loading the proper kernel modules and drivers) such as /usr or /var, preparing the /dev file structure, etc. Users who use an encrypted file system will also have the initramfs ask them for the passphrase before it can mount the file systems. When the file systems are mounted, control is passed on to init which then takes care of further starting all necessary services and booting up the remainder of the system.
- Custom Initramfs — the successor of initrd. It provides early userspace which can do things the kernel can't easily do by itself during the boot process.
- Dracut — an initramfs infrastructure and aims to have as little as possible hard-coded into the initramfs.
- Early Userspace Mounting — how to build a custom minimal initramfs that checks the /usr filesystem and pre-mounts /usr.
- Genkernel — a tool created by Gentoo used to automate the build process of the kernel and initramfs.
- Initramfs/Guide — covers the concepts of the initramfs as well as how to properly create and manage initramfs instances.
- Handbook:Parts/Installation/Kernel#Optional: Building an initramfs