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diff --git a/man7/bootparam.7 b/man7/bootparam.7 new file mode 100644 index 0000000..5514aca --- /dev/null +++ b/man7/bootparam.7 @@ -0,0 +1,664 @@ +.\" Copyright (c) 1995,1997 Paul Gortmaker and Andries Brouwer +.\" +.\" SPDX-License-Identifier: GPL-2.0-or-later +.\" +.\" This man page written 950814 by aeb, based on Paul Gortmaker's HOWTO +.\" (dated v1.0.1, 15/08/95). +.\" Major update, aeb, 970114. +.\" +.TH bootparam 7 2023-02-05 "Linux man-pages 6.05.01" +.SH NAME +bootparam \- introduction to boot time parameters of the Linux kernel +.SH DESCRIPTION +The Linux kernel accepts certain 'command-line options' or 'boot time +parameters' at the moment it is started. +In general, this is used to +supply the kernel with information about hardware parameters that +the kernel would not be able to determine on its own, or to avoid/override +the values that the kernel would otherwise detect. +.PP +When the kernel is booted directly by the BIOS, +you have no opportunity to specify any parameters. +So, in order to take advantage of this possibility you have to +use a boot loader that is able to pass parameters, such as GRUB. +.SS The argument list +The kernel command line is parsed into a list of strings +(boot arguments) separated by spaces. +Most of the boot arguments have the form: +.PP +.in +4n +.EX +name[=value_1][,value_2]...[,value_10] +.EE +.in +.PP +where 'name' is a unique keyword that is used to identify what part of +the kernel the associated values (if any) are to be given to. +Note the limit of 10 is real, as the present code handles only 10 comma +separated parameters per keyword. +(However, you can reuse the same +keyword with up to an additional 10 parameters in unusually +complicated situations, assuming the setup function supports it.) +.PP +Most of the sorting is coded in the kernel source file +.IR init/main.c . +First, the kernel +checks to see if the argument is any of the special arguments 'root=', +\&'nfsroot=', 'nfsaddrs=', 'ro', 'rw', 'debug', or 'init'. +The meaning of these special arguments is described below. +.PP +Then it walks a list of setup functions +to see if the specified argument string (such as 'foo') has +been associated with a setup function ('foo_setup()') for a particular +device or part of the kernel. +If you passed the kernel the line +foo=3,4,5,6 then the kernel would search the bootsetups array to see +if 'foo' was registered. +If it was, then it would call the setup +function associated with 'foo' (foo_setup()) and hand it the arguments +3, 4, 5, and 6 as given on the kernel command line. +.PP +Anything of the form 'foo=bar' that is not accepted as a setup function +as described above is then interpreted as an environment variable to +be set. +A (useless?) example would be to use 'TERM=vt100' as a boot +argument. +.PP +Any remaining arguments that were not picked up by the kernel and were +not interpreted as environment variables are then passed onto PID 1, +which is usually the +.BR init (1) +program. +The most common argument that +is passed to the +.I init +process is the word 'single' which instructs it +to boot the computer in single user mode, and not launch all the usual +daemons. +Check the manual page for the version of +.BR init (1) +installed on +your system to see what arguments it accepts. +.SS General non-device-specific boot arguments +.TP +.B "'init=...'" +This sets the initial command to be executed by the kernel. +If this is not set, or cannot be found, the kernel will try +.IR /sbin/init , +then +.IR /etc/init , +then +.IR /bin/init , +then +.I /bin/sh +and panic if all of this fails. +.TP +.B "'nfsaddrs=...'" +This sets the NFS boot address to the given string. +This boot address is used in case of a net boot. +.TP +.B "'nfsroot=...'" +This sets the NFS root name to the given string. +If this string +does not begin with '/' or ',' or a digit, then it is prefixed by +\&'/tftpboot/'. +This root name is used in case of a net boot. +.TP +.B "'root=...'" +This argument tells the kernel what device is to be used as the root +filesystem while booting. +The default of this setting is determined +at compile time, and usually is the value of the root device of the +system that the kernel was built on. +To override this value, and +select the second floppy drive as the root device, one would +use 'root=/dev/fd1'. +.IP +The root device can be specified symbolically or numerically. +A symbolic specification has the form +.IR /dev/XXYN , +where XX designates +the device type (e.g., 'hd' for ST-506 compatible hard disk, with Y in +\&'a'\[en]'d'; 'sd' for SCSI compatible disk, with Y in 'a'\[en]'e'), +Y the driver letter or +number, and N the number (in decimal) of the partition on this device. +.IP +Note that this has nothing to do with the designation of these +devices on your filesystem. +The '/dev/' part is purely conventional. +.IP +The more awkward and less portable numeric specification of the above +possible root devices in major/minor format is also accepted. +(For example, +.I /dev/sda3 +is major 8, minor 3, so you could use 'root=0x803' as an +alternative.) +.TP +.B 'rootdelay=' +This parameter sets the delay (in seconds) to pause before attempting +to mount the root filesystem. +.TP +.B 'rootflags=...' +This parameter sets the mount option string for the root filesystem +(see also +.BR fstab (5)). +.TP +.B 'rootfstype=...' +The 'rootfstype' option tells the kernel to mount the root filesystem as +if it where of the type specified. +This can be useful (for example) to +mount an ext3 filesystem as ext2 and then remove the journal in the root +filesystem, in fact reverting its format from ext3 to ext2 without the +need to boot the box from alternate media. +.TP +.BR 'ro' " and " 'rw' +The 'ro' option tells the kernel to mount the root filesystem +as 'read-only' so that filesystem consistency check programs (fsck) +can do their work on a quiescent filesystem. +No processes can +write to files on the filesystem in question until it is 'remounted' +as read/write capable, for example, by 'mount \-w \-n \-o remount /'. +(See also +.BR mount (8).) +.IP +The 'rw' option tells the kernel to mount the root filesystem read/write. +This is the default. +.TP +.B "'resume=...'" +This tells the kernel the location of +the suspend-to-disk data that you want the machine to resume from +after hibernation. +Usually, it is the same as your swap partition or file. +Example: +.IP +.in +4n +.EX +resume=/dev/hda2 +.EE +.in +.TP +.B "'reserve=...'" +This is used to protect I/O port regions from probes. +The form of the command is: +.IP +.in +4n +.EX +.BI reserve= iobase,extent[,iobase,extent]... +.EE +.in +.IP +In some machines it may be necessary to prevent device drivers from +checking for devices (auto-probing) in a specific region. +This may be +because of hardware that reacts badly to the probing, or hardware +that would be mistakenly identified, or merely +hardware you don't want the kernel to initialize. +.IP +The reserve boot-time argument specifies an I/O port region that +shouldn't be probed. +A device driver will not probe a reserved region, +unless another boot argument explicitly specifies that it do so. +.IP +For example, the boot line +.IP +.in +4n +.EX +reserve=0x300,32 blah=0x300 +.EE +.in +.IP +keeps all device drivers except the driver for 'blah' from probing +0x300\-0x31f. +.TP +.B "'panic=N'" +By default, the kernel will not reboot after a panic, but this option +will cause a kernel reboot after N seconds (if N is greater than zero). +This panic timeout can also be set by +.IP +.in +4n +.EX +echo N > /proc/sys/kernel/panic +.EE +.in +.TP +.B "'reboot=[warm|cold][,[bios|hard]]'" +Since Linux 2.0.22, a reboot is by default a cold reboot. +One asks for the old default with 'reboot=warm'. +(A cold reboot may be required to reset certain hardware, +but might destroy not yet written data in a disk cache. +A warm reboot may be faster.) +By default, a reboot is hard, by asking the keyboard controller +to pulse the reset line low, but there is at least one type +of motherboard where that doesn't work. +The option 'reboot=bios' will +instead jump through the BIOS. +.TP +.BR 'nosmp' " and " 'maxcpus=N' +(Only when __SMP__ is defined.) +A command-line option of 'nosmp' or 'maxcpus=0' will disable SMP +activation entirely; an option 'maxcpus=N' limits the maximum number +of CPUs activated in SMP mode to N. +.SS Boot arguments for use by kernel developers +.TP +.B "'debug'" +Kernel messages are handed off to a daemon (e.g., +.BR klogd (8) +or similar) so that they may be logged to disk. +Messages with a priority above +.I console_loglevel +are also printed on the console. +(For a discussion of log levels, see +.BR syslog (2).) +By default, +.I console_loglevel +is set to log messages at levels higher than +.BR KERN_DEBUG . +This boot argument will cause the kernel to also +print messages logged at level +.BR KERN_DEBUG . +The console loglevel can also be set on a booted system via the +.I /proc/sys/kernel/printk +file (described in +.BR syslog (2)), +the +.BR syslog (2) +.B SYSLOG_ACTION_CONSOLE_LEVEL +operation, or +.BR dmesg (8). +.TP +.B "'profile=N'" +It is possible to enable a kernel profiling function, +if one wishes to find out where the kernel is spending its CPU cycles. +Profiling is enabled by setting the variable +.I prof_shift +to a nonzero value. +This is done either by specifying +.B CONFIG_PROFILE +at compile time, or by giving the 'profile=' option. +Now the value that +.I prof_shift +gets will be N, when given, or +.BR CONFIG_PROFILE_SHIFT , +when that is given, or 2, the default. +The significance of this variable is that it +gives the granularity of the profiling: each clock tick, if the +system was executing kernel code, a counter is incremented: +.IP +.in +4n +.EX +profile[address >> prof_shift]++; +.EE +.in +.IP +The raw profiling information can be read from +.IR /proc/profile . +Probably you'll want to use a tool such as readprofile.c to digest it. +Writing to +.I /proc/profile +will clear the counters. +.SS Boot arguments for ramdisk use +(Only if the kernel was compiled with +.BR CONFIG_BLK_DEV_RAM .) +In general it is a bad idea to use a ramdisk under Linux\[em]the +system will use available memory more efficiently itself. +But while booting, +it is often useful to load the floppy contents into a +ramdisk. +One might also have a system in which first +some modules (for filesystem or hardware) must be loaded +before the main disk can be accessed. +.IP +In Linux 1.3.48, ramdisk handling was changed drastically. +Earlier, the memory was allocated statically, and there was +a 'ramdisk=N' parameter to tell its size. +(This could also be set in the kernel image at compile time.) +These days ram disks use the buffer cache, and grow dynamically. +For a lot of information on the current ramdisk +setup, see the kernel source file +.I Documentation/blockdev/ramdisk.txt +.RI ( Documentation/ramdisk.txt +in older kernels). +.IP +There are four parameters, two boolean and two integral. +.TP +.B "'load_ramdisk=N'" +If N=1, do load a ramdisk. +If N=0, do not load a ramdisk. +(This is the default.) +.TP +.B "'prompt_ramdisk=N'" +If N=1, do prompt for insertion of the floppy. +(This is the default.) +If N=0, do not prompt. +(Thus, this parameter is never needed.) +.TP +.BR 'ramdisk_size=N' " or (obsolete) " 'ramdisk=N' +Set the maximal size of the ramdisk(s) to N kB. +The default is 4096 (4\ MB). +.TP +.B "'ramdisk_start=N'" +Sets the starting block number (the offset on the floppy where +the ramdisk starts) to N. +This is needed in case the ramdisk follows a kernel image. +.TP +.B "'noinitrd'" +(Only if the kernel was compiled with +.B CONFIG_BLK_DEV_RAM +and +.BR CONFIG_BLK_DEV_INITRD .) +These days it is possible to compile the kernel to use initrd. +When this feature is enabled, the boot process will load the kernel +and an initial ramdisk; then the kernel converts initrd into +a "normal" ramdisk, which is mounted read-write as root device; +then +.I /linuxrc +is executed; afterward the "real" root filesystem is mounted, +and the initrd filesystem is moved over to +.IR /initrd ; +finally +the usual boot sequence (e.g., invocation of +.IR /sbin/init ) +is performed. +.IP +For a detailed description of the initrd feature, see the kernel source file +.I Documentation/admin\-guide/initrd.rst +.\" commit 9d85025b0418163fae079c9ba8f8445212de8568 +(or +.I Documentation/initrd.txt +before Linux 4.10). +.IP +The 'noinitrd' option tells the kernel that although it was compiled for +operation with initrd, it should not go through the above steps, but +leave the initrd data under +.IR /dev/initrd . +(This device can be used only once: the data is freed as soon as +the last process that used it has closed +.IR /dev/initrd .) +.SS Boot arguments for SCSI devices +General notation for this section: +.PP +.I iobase +-- the first I/O port that the SCSI host occupies. +These are specified in hexadecimal notation, +and usually lie in the range from 0x200 to 0x3ff. +.PP +.I irq +-- the hardware interrupt that the card is configured to use. +Valid values will be dependent on the card in question, but will +usually be 5, 7, 9, 10, 11, 12, and 15. +The other values are usually +used for common peripherals like IDE hard disks, floppies, serial +ports, and so on. +.PP +.I scsi\-id +-- the ID that the host adapter uses to identify itself on the +SCSI bus. +Only some host adapters allow you to change this value, as +most have it permanently specified internally. +The usual default value +is 7, but the Seagate and Future Domain TMC-950 boards use 6. +.PP +.I parity +-- whether the SCSI host adapter expects the attached devices +to supply a parity value with all information exchanges. +Specifying a one indicates parity checking is enabled, +and a zero disables parity checking. +Again, not all adapters will support selection of parity +behavior as a boot argument. +.TP +.B "'max_scsi_luns=...'" +A SCSI device can have a number of 'subdevices' contained within +itself. +The most common example is one of the new SCSI CD-ROMs that +handle more than one disk at a time. +Each CD is addressed as a +\&'Logical Unit Number' (LUN) of that particular device. +But most +devices, such as hard disks, tape drives, and such are only one device, +and will be assigned to LUN zero. +.IP +Some poorly designed SCSI devices cannot handle being probed for +LUNs not equal to zero. +Therefore, if the compile-time flag +.B CONFIG_SCSI_MULTI_LUN +is not set, newer kernels will by default probe only LUN zero. +.IP +To specify the number of probed LUNs at boot, one enters +\&'max_scsi_luns=n' as a boot arg, where n is a number between one and +eight. +To avoid problems as described above, one would use n=1 to +avoid upsetting such broken devices. +.TP +.B "SCSI tape configuration" +Some boot time configuration of the SCSI tape driver can be achieved +by using the following: +.IP +.in +4n +.EX +.BI st= buf_size[,write_threshold[,max_bufs]] +.EE +.in +.IP +The first two numbers are specified in units of kB. +The default +.I buf_size +is 32k\ B, and the maximum size that can be specified is a +ridiculous 16384\ kB. +The +.I write_threshold +is the value at which the buffer is committed to tape, with a +default value of 30\ kB. +The maximum number of buffers varies +with the number of drives detected, and has a default of two. +An example usage would be: +.IP +.in +4n +.EX +st=32,30,2 +.EE +.in +.IP +Full details can be found in the file +.I Documentation/scsi/st.txt +(or +.I drivers/scsi/README.st +for older kernels) in the Linux kernel source. +.SS Hard disks +.TP +.B "IDE Disk/CD-ROM Driver Parameters" +The IDE driver accepts a number of parameters, which range from disk +geometry specifications, to support for broken controller chips. +Drive-specific options are specified by using 'hdX=' with X in 'a'\[en]'h'. +.IP +Non-drive-specific options are specified with the prefix 'hd='. +Note that using a drive-specific prefix for a non-drive-specific option +will still work, and the option will just be applied as expected. +.IP +Also note that 'hd=' can be used to refer to the next unspecified +drive in the (a, ..., h) sequence. +For the following discussions, +the 'hd=' option will be cited for brevity. +See the file +.I Documentation/ide/ide.txt +(or +.I Documentation/ide.txt +.\" Linux 2.0, 2.2, 2.4 +in older kernels, or +.I drivers/block/README.ide +in ancient kernels) in the Linux kernel source for more details. +.TP +.B "The 'hd=cyls,heads,sects[,wpcom[,irq]]' options" +These options are used to specify the physical geometry of the disk. +Only the first three values are required. +The cylinder/head/sectors +values will be those used by fdisk. +The write precompensation value +is ignored for IDE disks. +The IRQ value specified will be the IRQ +used for the interface that the drive resides on, and is not really a +drive-specific parameter. +.TP +.B "The 'hd=serialize' option" +The dual IDE interface CMD-640 chip is broken as designed such that +when drives on the secondary interface are used at the same time as +drives on the primary interface, it will corrupt your data. +Using this +option tells the driver to make sure that both interfaces are never +used at the same time. +.TP +.B "The 'hd=noprobe' option" +Do not probe for this drive. +For example, +.IP +.in +4n +.EX +hdb=noprobe hdb=1166,7,17 +.EE +.in +.IP +would disable the probe, but still specify the drive geometry so +that it would be registered as a valid block device, and hence +usable. +.TP +.B "The 'hd=nowerr' option" +Some drives apparently have the +.B WRERR_STAT +bit stuck on permanently. +This enables a work-around for these broken devices. +.TP +.B "The 'hd=cdrom' option" +This tells the IDE driver that there is an ATAPI compatible CD-ROM +attached in place of a normal IDE hard disk. +In most cases the CD-ROM +is identified automatically, but if it isn't then this may help. +.TP +.B "Standard ST-506 Disk Driver Options ('hd=')" +The standard disk driver can accept geometry arguments for the disks +similar to the IDE driver. +Note however that it expects only three +values (C/H/S); any more or any less and it will silently ignore you. +Also, it accepts only 'hd=' as an argument, that is, 'hda=' +and so on are not valid here. +The format is as follows: +.IP +.in +4n +.EX +hd=cyls,heads,sects +.EE +.in +.IP +If there are two disks installed, the above is repeated with the +geometry parameters of the second disk. +.SS Ethernet devices +Different drivers make use of different parameters, but they all at +least share having an IRQ, an I/O port base value, and a name. +In its most generic form, it looks something like this: +.PP +.in +4n +.EX +ether=irq,iobase[,param_1[,...param_8]],name +.EE +.in +.PP +The first nonnumeric argument is taken as the name. +The param_n values (if applicable) usually have different meanings for each +different card/driver. +Typical param_n values are used to specify +things like shared memory address, interface selection, DMA channel +and the like. +.PP +The most common use of this parameter is to force probing for a second +ethercard, as the default is to probe only for one. +This can be accomplished with a simple: +.PP +.in +4n +.EX +ether=0,0,eth1 +.EE +.in +.PP +Note that the values of zero for the IRQ and I/O base in the above +example tell the driver(s) to autoprobe. +.PP +The Ethernet-HowTo has extensive documentation on using multiple +cards and on the card/driver-specific implementation +of the param_n values where used. +Interested readers should refer to +the section in that document on their particular card. +.SS The floppy disk driver +There are many floppy driver options, and they are all listed in +.I Documentation/blockdev/floppy.txt +(or +.I Documentation/floppy.txt +in older kernels, or +.I drivers/block/README.fd +for ancient kernels) in the Linux kernel source. +See that file for the details. +.SS The sound driver +The sound driver can also accept boot arguments to override the compiled-in +values. +This is not recommended, as it is rather complex. +It is described in the Linux kernel source file +.I Documentation/sound/oss/README.OSS +.RI ( drivers/sound/Readme.linux +in older kernel versions). +It accepts +a boot argument of the form: +.PP +.in +4n +.EX +sound=device1[,device2[,device3...[,device10]]] +.EE +.in +.PP +where each deviceN value is of the following format 0xTaaaId and the +bytes are used as follows: +.PP +T \- device type: 1=FM, 2=SB, 3=PAS, 4=GUS, 5=MPU401, 6=SB16, +7=SB16-MPU401 +.PP +aaa \- I/O address in hex. +.PP +I \- interrupt line in hex (i.e., 10=a, 11=b, ...) +.PP +d \- DMA channel. +.PP +As you can see, it gets pretty messy, and you are better off to compile +in your own personal values as recommended. +Using a boot argument of +\&'sound=0' will disable the sound driver entirely. +.SS The line printer driver +.TP +.B "'lp='" +.br +Syntax: +.IP +.in +4n +.EX +lp=0 +lp=auto +lp=reset +lp=port[,port...] +.EE +.in +.IP +You can tell the printer driver what ports to use and what ports not +to use. +The latter comes in handy if you don't want the printer driver +to claim all available parallel ports, so that other drivers +(e.g., PLIP, PPA) can use them instead. +.IP +The format of the argument is multiple port names. +For example, +lp=none,parport0 would use the first parallel port for lp1, and +disable lp0. +To disable the printer driver entirely, one can use +lp=0. +.\" .SH AUTHORS +.\" Linus Torvalds (and many others) +.SH SEE ALSO +.BR klogd (8), +.BR mount (8) +.PP +For up-to-date information, see the kernel source file +.IR Documentation/admin\-guide/kernel\-parameters.txt . |