Boot-time configuration

At boot time, a node comes up and determines its hostname, usually in the initramfs via DHCP (with use-host-decl-names set to on). After /sbin/init is run, the system runs the primary oneSIS boot-time configuration script, /sbin/rc.preinit. The rc.preinit script determines which class the node belongs to and builds a RAM disk in /ram appropriate for the node.

The oneSIS RAM disk contains all necessary files and directories configured to help the node function as normal without a writable root filesystem. It has all class-specific and node-specific deviations. If a `login' node needs a different /etc/fstab, rc.preinit creates a /ram/etc/fstab symlink that points to /etc/fstab.login in the master image, if it exists.

If there is no class-specific version of /ram/etc/fstab, that symbolic link will link back to the /etc/fstab.default file. This `linkback' process provides flexibility. Any file in the master image can be changed or deleted on a per-class and per-node basis, allowing for fine-grained control of any file in the master image. All deviations in the filesystem are handled similarly.