RAM file system

The RAM file system, part of the boot image, is totally memory-resident and contains all programs that allow the boot process to continue. The files in the RAM file system are specific to the type of boot.

A maintenance boot RAM file system might not have the logical volume routines, because the rootvg might not need to be varied on. During a hard disk boot, however, it is desirable that the rootvg be varied on and paging activated as soon as possible. Although there are differences in these two boot scenarios, the structure of the RAM file system does not vary to a great extent.

The init command, which is located on the RAM file system, is a basic boot command interpreter program that is designed for use during the boot process. This boot command interpreter program controls the boot process by calling the rc.boot script. The rc.boot script determines from which device the machine was started. The boot device determines which devices must be configured on the RAM file system. If the machine is started over the network, the network devices need to be configured so that the client file systems can be remotely mounted. In the case of a tape, CD-ROM, or DVD boot, the console is configured to display the base operating system (BOS) installation menus. After the rc.boot script identifies the boot device, the appropriate configuration routines are called from the RAM file system. The rc.boot script is called twice by the boot command interpreter program to match the two configuration phases during the boot process. A third call to rc.boot occurs during a disk or a network boot when the real init command is called. The inittab file contains an rc.boot stanza that completes the final configuration of the machine.

The RAM file system for each boot device is also unique because of the various types of devices to be configured. A prototype file is associated with each type of boot device. The prototype file is a template of files making up the RAM file system. The bosboot command uses the mkfs command to create the RAM file system using the various prototype files. See the bosboot command for more details.