Specifications

2.6 Passing Arguments to the `init' program
Any remaining arguments that were not picked up by the kernel and were not interpreted as environment
variables are then passed onto process one, which is usually the init program. The most common argument
that is passed to the init process is the word single which instructs init to boot the computer in single user
mode, and not launch all the usual daemons. Check the manual page for the version of init installed on your
system to see what arguments it accepts.
3. General Non−Device Specific Boot Args
These are the boot arguments that are not related to any specific device or peripheral. They are instead related
to certain internal kernel parameters, such as memory handling, ramdisk handling, root file system handling
and others.
3.1 Root Filesystem options
The following options all pertain to how the kernel selects and handles the root filesystem.
The `root=' Argument
This argument tells the kernel what device is to be used as the root filesystem while booting. The default of
this setting is the value of the root device of the system that the kernel was built on. For example, if the kernel
in question was built on a system that used `/dev/hda1' as the root partition, then the default root device would
be `/dev/hda1'. To override this default value, and select the second floppy drive as the root device, one would
use `root=/dev/fd1'.
Valid root devices are any of the following devices:
(1) /dev/hdaN to /dev/hddN, which is partition N on ST−506 compatible disk `a to d'.
(2) /dev/sdaN to /dev/sdeN, which is partition N on SCSI compatible disk `a to e'.
(3) /dev/xdaN to /dev/xdbN, which is partition N on XT compatible disk `a to b'.
(4) /dev/fdN, which is floppy disk drive number N. Having N=0 would be the DOS `A:' drive, and N=1 would
be `B:'.
(5) /dev/nfs, which is not really a device, but rather a flag to tell the kernel to get the root fs via the network.
(6) /dev/ram, which is the RAM disk.
The more awkward and less portable numeric specification of the above possible disk devices in major/minor
format is also accepted. (e.g. /dev/sda3 is major 8, minor 3, so you could use root=0x803 as an alternative.)
This is one of the few kernel boot arguments that has its default stored in the kernel image, and which can thus
be altered with the rdev utility.
The Linux BootPrompt−HowTo
2.6 Passing Arguments to the `init' program 7