[Appendix D] D.5 Boot Parameters

D.5 Boot Parameters

When you boot your system by using loadlin, you can specify several parameters that control the boot process. Such parameters are sometimes needed to take advantage of unusual hardware devices, large amounts of RAM (more than 128 MB), and so on. Similarly, when you boot by using lilo, you can also boot parameters to control the boot process; you can specify lilo's boot parameters by using linuxconf or by editing lilo's configuration file. You can also specify boot parameters to lilo by typing them in response to lilo's prompt.

Boot parameters are specified using a two-part directive that includes:

the name of the parameter
an optional list of options, which consists of an equals sign (=) followed by a comma-separated list of option values

No spaces may appear in the directive. As an example, the following directive specifies the identity of the Linux root partition:

 root=/dev/hda1

You can specify multiple directives by separating them with a space. For example, the following specifies the identity of the Linux root partition and specifies that the root partition is initially mounted read-only, so that a thorough check of its filesystem can be performed:

 root=/dev/hda1 ro

Most directives are interpreted by the kernel, though lilo is also capable of processing directives. If you specify a directive that neither the kernel nor lilo understands (assuming you're using lilo), a directive that includes an equals sign is passed to the init process as an environment variable. You've learned about environment variables in Chapter 13, Conquering the BASH Shell . A non-kernel directive that doesn't include an equals sign is passed to the init process. An example of this usage is specifying the directive single, which causes init to start your system in single-user mode:

 root=/dev/hda1 ro single

This directive is especially useful when booting your system using lilo; by specifying the single directive in response to lilo's command prompt, you can boot your system in single-user mode.

D.5.1 General Boot Arguments

Table D.2 describes some of the most popular and useful boot arguments. These arguments apply to your system as a whole; in subsequent sections you'll learn about other boot arguments that apply to specific devices or functions. In addition to boot arguments previously introduced, the table describes the reserve argument, which is helpful in avoided system memory conflicts.

Table D.2: Selected General Boot Arguments
Argument	Description and options
`init=`	Specifies arguments passed by the kernel to the `init` process.
`mem=`	Specifies the amount of physical memory available to Linux; lets you instruct Linux to avoid high memory areas used by some systems for BIOS or caching. You can specify the amount as a hexadecimal number, or as a decimal number followed by k or M, denoting kilobytes or megabytes, respectively.
`reserve=`	Specifies I/O ports that must not be probed. The port number is specified by using a hexadecimal number and the range is specified by using a decimal number. For example, `reserve=0x320,32` specifies the I/O ports `320-33f` must not be probed.
`ro`	Initially mount the root filesystem in read-only mode, so that a more effective filesystem check can be done.
`root=`	Identifies the root filesystem: `/dev/fd` `n`, floppy disk n (0 or 1) `/dev/hd` `xn`, partition n of IDE drive x (a to d) `/dev/sd` `xn`, partition n of SCSI drive x (a to e)
`rw`	Initially mount the root filesystem in read-write mode; do not perform a filesystem check.
`vga=`	Specifies the default display mode set before booting. Specifying `vga=ask` will cause `lilo` to list the available video modes. You can then specify the desired mode in place of ask. Note: This argument is interpreted by `lilo` and will have no effect if another loader is used.

D.5.2 RAM Disk Boot Arguments

Table D.3 describes several boot arguments used in working with RAM disks. You won't likely need to specify any of these; but knowing about them may help you understand boot specifications written by others, including those used by Debian GNU/Linux.

Table D.3: Selected RAM Disk Arguments
Argument	Description and options
`load_ramdisk=`	Specifies that a ramdisk is not to be loaded (0) or is to be loaded (1).
`prompt_ramdisk=`	Specifies whether to provide a prompt instructing the user to insert a floppy containing a ramdisk (1) or provide no such prompt (0).
`ramdisk_size=`	Specifies the amount of RAM to be allocated to a ramdisk. If not specified, the default value is 4 MB.
`ramdisk_start=`	Specifies the offset (in disk blocks from the start of the boot media) of the ramdisk data; lets a kernel and ramdisk data occupy the same floppy disk.

D.5.3 SCSI Host Adapter Boot Arguments

Table D.4 describes the most often used boot arguments related to SCSI host adapters. Table D.5 describes the options used by the SCSI host adapter boot arguments and other boot arguments.

Table D.4: Selected SCSI Host Adapter Arguments
Argument	Description and options
`advansys=`	Advansys SCSI host adapter: iobase,[ iobase,[ iobase,[ iobase]]]
`aha152x=`	Adaptec aha151x, ada152x, aic6260, aic6360, and SB16-SCSI SCSI host adapters: iobase[, irq[, scsi_id[, reconnect[, parity]]]]
`aha1542=`	Adaptec aha154x SCSI host adapter: iobase[, buson,busoff[, dmaspeed]]
`aic7xxx=`	Adaptec aha274x, aha284x, aic7xxx SCSI host adapters: extended, no_reset
`AM53C974=`	AMD AM53C974-based SCSI host adapters: scsi-id, dev_id, dmaspeed, offset See the file linux/drivers/scsi/README.AM53C974.
`buslogic=`	BusLogic SCSI controller: Many options are available. See the BootPrompt-HOWTO.
`eata=`	EATA SCSI host adapter: iobase,[ iobase,[ iobase,[ iobase]]]
`fdomain=`	Future Domain SCSI controller: iobase, irq[, scsi_id]
`in2000=`	Always SCSI host adapter: The driver for the Always SCSI controller accepts options in somewhat different format than other drivers. See the BootPrompt-HOWTO.
`max-scsi-luns=`	Specifies the maximum number of SCSI logical units to be probed; lets you avoid probing devices that might lock up the SCSI bus.
`ncr5380=`	NCR 5380-based SCSI host adapters: iobase, irq, dma membase, irq, dma
`ncr53c400=`	NCR 53c400-based SCSI host adapters: iobase, irq membase, irq
`ncr53c406a=`	NCR 53c406a-based SCSI host adapters: iobase, irq, pio membase, irq, pio
`ppa=`	IOMEGA parallel port SCSI adapter for ZIP drive: iobase, speed_high, speed_low, nybble
`pas16=`	Pro Audio Spectrum SCSI host adapter: iobase, irq
`st0x=`	Seagate ST-0x SCSI host adapter: membase, irq
`t128=`	Trantor T128 SCSI host adapter: membase, irq
`tmc8xx=`	Future Domain TMC-8xx and TMC-950 SCSI host adapters: membase, irq
`u14-34f=`	Ultrastor SCSI host adapter: iobase,[ iobase,[ iobase,[ iobase]]]
`wd7000=`	Western Digital WD7000 SCSI host adapter: irq, dma, iobase

For example, from Table D.4 you can learn that Adaptec aha154x SCSI host adapters use a boot argument having the form:

  iobase[, buson,busoff[, dmaspeed]]

Table D.5 helps you understand the form of the iobase option and the other italicized options. The iobase option, for example, lets you specify the I/O port associated with the SCSI host adapter. Don't include the square brackets in your boot argument; they merely indicate which options must be present. For example, you can specify a boot argument for an Adaptec aha154x SCSI host adapter by writing only an iobase option; the remaining options are optional. However, as indicated by the square brackets, if you include a buson option, you must include a busoffoption. Similarly, to include the dmaspeed option, you must include each of the other options. Here's an example of a complete boot argument:

 aha1542=0x300,11,4

Table D.5: Selected Boot Prompt Options
Option	Description and options
`busoff`	The interval (number of microseconds) during which the device will relinquish the ISA bus, specified as a decimal integer; for example, `4`.
`buson`	The interval (number of microseconds) during which the device will dominate the ISA bus, specified as a decimal integer; for example, `11`.
`ctl`	The I/O port used for control, specified as a hexadecimal number; for example, `0x300`.
`cyl,head,sect`	The geometry of the storage device, specified as three integers denoting the number of cylinders, heads, and sectors, respectively.
`dev_id`	A SCSI device with which the host adapter communicates, specified as a decimal integer; for example, `2`.
`dma`	The DMA (direct memory access) channel by used by the device, specified as a decimal integer; for example, `3`.
`dmaspeed`	The rate (in MB/sec.) at which DMA transfers are performed, specified as a decimal integer; for example, `5`.
`extended`	Specifies whether extended translation for large disks is enabled ( `1`) or not ( `0`).
`magic_number`	Specifying the value `79` causes the driver to attempt to work, even if the firmware version is unknown; other values are ignored.
`no_reset`	Specifies whether the driver should reset the SCSI bus when setting up the host adapter at boot ( `1`) or not ( `0`).
`iobase`	An I/O port, specified as a hexadecimal number; for example, `0x300`.
`irq`	A hardware interrupt number, specified as a decimal integer; for example, `5`.
`is_pas_card`	Specifies whether a Pro Audio Spectrum card is used ( `PAS`); otherwise, do not specify this option.
`membase`	The base address of a memory region used for memory-mapped I/O, specified as a hexadecimal number; for example, `0x2000`.
`parity`	Specifies whether the SCSI host adapter uses parity ( `1`) or does not use parity ( `0`).
`pio`	Specifies whether `insl` and `outsl` multi-byte instructions ( `1`) or `inb` and `outb` single-byte instructions ( `0`) are used.
`reconnect`	Specifies whether the SCSI host adapter is allowed to disconnect and reconnect ( `1`) or holds a connection until the operation is complete ( `0`).
`scsi_id`	The ID by which the SCSI host adapter identifies itself, specified as a decimal integer; for example, `7`.

To determine a proper value for options described in Table D.5, you must often know something about the hardware structure of your system. The procedures described in Chapter 2, Preparing to Install Linux will help you.

D.5.4 IDE Hard Drive and CD-ROM Boot Arguments

Table D.6 describes the most commonly used boot arguments associated with IDE hard rives and CD-ROM drives. Refer to Table D.7 to determine the form of the italicized options.

Table D.6: Selected IDE Hard Drive Arguments
`Argument`	Description and Options
`ide0=`	IDE hard drive or CD-ROM: `ali14xx`, probe for, and support, the alil4xx interface. `cmd640_vlb`, probe for, and support, the cmd640 chip (required for controllers using a VLB interface). `dtc2278`, probe for, and support, the dtc2278 interface. `ht6560b`, probe for, and support, the ht6560b interface. `qd6580`, probe for, and support, the qd6580 interface. `umc8672`, probe for, and support, the umc8672 interface.
`hd` `x` `=`	IDE hard drive or CD-ROM (`x` denotes the physical device, and must be a letter from a to h): `autotune`, which specifies that the driver should attempt to tune the interface to the fastest possible mode and speed. `cdrom`, which specifies that the drive is a CD-ROM drive. `cyl`,`head`,`sect`, which specifies the geometry of the drive. `none`, which specifies that the drive is not present - do not probe. `noprobe`, which specifies that the driver should not probe for the device. `nowerr`, which specifies that the `WRERR_STAT` bit should be ignored on this drive.
`ide` `x` `=`	IDE hard drive or CD-ROM (`x` specifies the physical device, and must be a digit from 0 to 3): `autotune`, which specifies that the driver should attempt to tune the interface to the fastest possible mode and speed. `iobase`, which specifies the I/O port used by the drive. `iobase` `,` `ctl`, which specifies the I/O port and control port used by the drive. `iobase` `,` `ctl` `,` `irq`, which specifies the I/O port, control port, and IRQ used by the drive. `noautotune`, which specifies that the driver should not attempt to tune the interface for fastest mode and speed.
	`noprobe`, which specifies that the driver should not probe for the device. `serialize`, which specifies that I/O operations should not be overlapped.

D.5.5 Non-IDE CD-ROM Drive Boot Arguments

Table D.7 describes the most common boot arguments for non-IDE CD-ROM drives. Refer to Table D.5 to determine the form of the italicized options.

Table D.7: Selected CD-ROM Arguments
Argument	Description and Options
`aztcd=`	Aztech CD-ROM: iobase[, magic_number]
`cdu31a=`	Sony CDU-31A or CDU-33A CD-ROM: iobase,[ irq[, is_pas_card]]
`sonycd535=`	Sony CDU-535 CD-ROM: iobase[, irq]
`gscd=`	Goldstar CD-ROM: iobase
`isp16=`	ISP16 CD-ROM: [ port[, irq[, dma]]][[,] drive_type]
`mcd=`	Mitsumi CD-ROM: iobase,[ irq[, wait_value]]
`optcd=`	Optical Storage CD-ROM: iobase
`cm206=`	Phillips CD206 CD-ROM: [ iobase][, irq]
`sjcd=`	Sanyo CD-ROM: iobase[, irq[, dma_channel]]
`sbpcd=`	SoundBlaster Pro CD-ROM: iobase, type

D.5.6 Floppy Drive Boot Arguments

A few systems require special boot arguments to make best use of their floppy drives. Table D.8 describes the most common boot arguments related to floppy drives. The file README.fd in linux/drivers/block describes additional arguments. Floppy drives that are not well behaved may malfunction if you specify the daring option, which you should use only with care.

Table D.8: Selected Floppy Disk Arguments and Options
Argument and Option	Description
`floppy=asus_pci`	Specifies that only units 0 and 1 are allowed, to work around problem with BIOS of certain ASUS motherboards.
`floppy=daring`	Specifies that the floppy controller is well behaved, allowing more efficient operation.
`floppy=0,daring`	Specifies that the floppy controller may not be well behaved (default).
`floppy=thinkpad`	Specifies that the system is an IBM Thinkpad.
`floppy=no_unexpected_interrupts` or `floppy=L40SX`	Specifies that a message should be printed when an unexpected interrupt is received. This is required by IBM L40SX laptops in certain video modes.

D.5.7 Bus Mouse Boot Arguments

Two boot arguments provide bus mouse support. The first supports the Microsoft bus mouse:

 msmouse= irq

The second supports any non-Microsoft bus mouse:

 bmouse= irq

Each argument accepts a single option specifying the IRQ associated with the mouse.

D.5.8 Parallel Port Printer Boot Arguments

The Linux printer driver claims all available parallel ports. If you want to access a device other than a printer attached to a parallel port, you must instruct the printer driver to reserve only the ports associated with printers. To do so, use the lp boot argument, which takes as its options a list of ports and IRQs use to support printers. For example, the following boot argument specifies two printers:

 lp=0x3bc,0,0x378,7

The first printer is on port 0x3bc and the second is on port 0x378. The first printer uses a special IRQ-less mode known as polling, so its IRQ is specified as 0. The second printer uses IRQ 7.

To disable all printers, specify lp=0.