Merging upstream version 6.8.

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

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+.\" 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 2024-05-02 "Linux man-pages (unreleased)"
+.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.
+.P
+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:
+.P
+.in +4n
+.EX
+name[=value_1][,value_2]...[,value_10]
+.EE
+.in
+.P
+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.)
+.P
+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.
+.P
+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.
+.P
+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.
+.P
+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:
+.P
+.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.
+.P
+.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.
+.P
+.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.
+.P
+.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:
+.P
+.in +4n
+.EX
+ether=irq,iobase[,param_1[,...param_8]],name
+.EE
+.in
+.P
+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.
+.P
+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:
+.P
+.in +4n
+.EX
+ether=0,0,eth1
+.EE
+.in
+.P
+Note that the values of zero for the IRQ and I/O base in the above
+example tell the driver(s) to autoprobe.
+.P
+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:
+.P
+.in +4n
+.EX
+sound=device1[,device2[,device3...[,device10]]]
+.EE
+.in
+.P
+where each deviceN value is of the following format 0xTaaaId and the
+bytes are used as follows:
+.P
+T \- device type: 1=FM, 2=SB, 3=PAS, 4=GUS, 5=MPU401, 6=SB16,
+7=SB16-MPU401
+.P
+aaa \- I/O address in hex.
+.P
+I \- interrupt line in hex (i.e., 10=a, 11=b, ...)
+.P
+d \- DMA channel.
+.P
+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)
+.P
+For up-to-date information, see the kernel source file
+.IR Documentation/admin\-guide/kernel\-parameters.txt .