在Linux中，给kernel传递参数以控制其行为总共有三种方法：
1.build kernel之时的各个configuration选项。
2.当kernel启动之时，可以参数在kernel被GRUB或LILO等启动程序调用之时传递给kernel。
3.在kernel运行时，修改/proc或/sys目录下的文件。
这里我简单讲的就是第二种方式了，kernel在grub中配置的启动参数。
首先，kernel有哪些参数呢？ 在linux的源代码中，有这样的一个文档Documentation/kernel-parameters.txt，它介绍了kernel的各个参数及其意义。
其次，kernel启动参数以空格分隔，而且是严格区分大小写的（如：mem和MEM是不一样的）。
再次，对于module特有的kernel参数写法是这样的，[module name].[parameter=XX]，例如，igb.max_vfs=7这个kernel启动参数的效果就是相当于这样来动态加载module: modprobe igb max_vfs=7
另外，kernel是怎样处理这些启动参数的呢？ 启动参数通常是这样的形式： name[=value_1][,value_2]…[,value_10]
“name”是关键字，内核用它来识别应该把”关键字”后面的值传递给谁，也就是如何处理这个值，是传递给处理进程还是作为环境变量或者抛给”init”。值的个数限制为10，你可以通过再次使用该关键字使用超过10个的参数。 首先，kernel检查关键字是不是 ‘root=’, ‘nfsroot=’, ‘nfsaddrs=’, ‘ro’, ‘rw’, ‘debug’或’init’，然后内核在bootsetups数组里搜索于该关键字相关联的已注册的处理函数，如果找到相关的已注册的处理函数，则调用这些函数并把关键字后面的值作为参数传递给这些函数。比如，你在启动时设置参数name＝a,b,c,d，内核搜索bootsetups数组，如果发现”name”已注册，则调用”name”的设置函数如name_setup()，并把a,b,c,d传递给name_setup()执行。 所有型如”name＝value”参数，如果没有被上面所述的设置函数接收，将被解释为系统启动后的环境变量，比如”TERM=vt100″启动参数就会被作为一个启动后的环境变量。所有没有被内核设置函数接收也没又被设置成环境变量的参数都将留给init进程处理，比如”single”。
下面简单总结一下我在工作中常用到的一些kernel启动参数吧。
根磁盘相关启动参数：
root #指出启动的根文件系统 如：root=/dev/sda1
ro #指定根设备在启动过程中为read-only，默认情况下一般都是这样配的
rw #和ro类似，它是规定为read-write，可写
rootfstype #根文件系统类型，如：rootfstype=ext4
Console和kernel log相关启动参数：
console #console的设备和选项，如：console=tty0 console=ttyS0
debug #enable kernel debugging 启动中的所有debug信息都会打印到console上
quiet #disable all log messages 将kernel log level设置为KERN_WARNING，在启动中只非常严重的信息
loglevel #设置默认的console日志级别，如：loglevel=7 （0~7的数字分别为：KERN_EMERG,..,KERN_DEBUG）
time #设置在每条kernel log信息前加一个时间戳
内存相关的启动参数：
mem #指定kernel使用的内存量，mem=n[KMG]
hugepages #设置大页表页（4MB大小）的最多个数，hugepages=n
CPU相关的启动参数：
mce # Enable the machine check exception feature.
nosmp #Run as a single-processor machine. 不使用SMP（多处理器）
max_cpus #max_cpus=n, SMP系统最多能使用的CPU个数（即使系统中有大于n个的CPU）
Ramdisk相关的启动参数：
initrd #指定初始化ramdisk的位置，initrd=filename
noinitrd #不使用initrd的配置，即使配置了initrd参数
初始化相关启动参数：
init #在启动时去执行的程序，init=filename，默认值为/sbin/init
PCI相关的启动参数：
pci #pci相关的选项，我常使用pci=assign_buses，也使用过pci=nomsi
SELinux相关启动参数：
enforcing #SELinux enforcing状态的开关，enforcing=0表示仅仅是记录危险而不是阻止访问，enforcing=1完全enable，默认值是0
selinux #在启动时关闭或开启SELinux，selinux=0表示关闭，selinux=1表示开启selinux
另外，还是用max_loop来指定最多可使用的回路设备。
在Redhat的系统中，还有个经常看到的kernel启动参数——rhgb，rhgb表示redhat graphics boot，就是会看到图片来代替启动过程中显示的文本信息，这些信息在启动后用dmesg也可以看到
rhgb = redhat graphical boot – This is a GUI mode booting screen with most of the information hidden while the user sees a rotating activity icon spining and brief information as to what the computer is doing.
quiet = hides the majority of boot messages before rhgb starts. These are supposed to make the common user more comfortable. They get alarmed about seeing the kernel and initializing messages, so they hide them for their comfort.
参考资料:
linux kernel documents
《Linux kernel in a nutshell》
Kernel Parameters ~~~~~~~~~~~~~~~~~ The following is a consolidated list of the kernel parameters as implemented (mostly) by the __setup() macro and sorted into English Dictionary order (defined as ignoring all punctuation and sorting digits before letters in a case insensitive manner), and with descriptions where known. Module parameters for loadable modules are specified only as the parameter name with optional '=' and value as appropriate, such as: modprobe usbcore blinkenlights=1 Module parameters for modules that are built into the kernel image are specified on the kernel command line with the module name plus '.' plus parameter name, with '=' and value if appropriate, such as: usbcore.blinkenlights=1 Hyphens (dashes) and underscores are equivalent in parameter names, so log_buf_len=1M print-fatal-signals=1 can also be entered as log-buf-len=1M print_fatal_signals=1 This document may not be entirely up to date and comprehensive. The command "modinfo -p ${modulename}" shows a current list of all parameters of a loadable module. Loadable modules, after being loaded into the running kernel, also reveal their parameters in /sys/module/${modulename}/parameters/. Some of these parameters may be changed at runtime by the command "echo -n ${value} > /sys/module/${modulename}/parameters/${parm}". The parameters listed below are only valid if certain kernel build options were enabled and if respective hardware is present. The text in square brackets at the beginning of each description states the restrictions within which a parameter is applicable: ACPI ACPI support is enabled. AGP AGP (Accelerated Graphics Port) is enabled. ALSA ALSA sound support is enabled. APIC APIC support is enabled. APM Advanced Power Management support is enabled. AVR32 AVR32 architecture is enabled. AX25 Appropriate AX.25 support is enabled. BLACKFIN Blackfin architecture is enabled. DRM Direct Rendering Management support is enabled. EDD BIOS Enhanced Disk Drive Services (EDD) is enabled EFI EFI Partitioning (GPT) is enabled EIDE EIDE/ATAPI support is enabled. FB The frame buffer device is enabled. GCOV GCOV profiling is enabled. HW Appropriate hardware is enabled. IA-64 IA-64 architecture is enabled. IMA Integrity measurement architecture is enabled. IOSCHED More than one I/O scheduler is enabled. IP_PNP IP DHCP, BOOTP, or RARP is enabled. ISAPNP ISA PnP code is enabled. ISDN Appropriate ISDN support is enabled. JOY Appropriate joystick support is enabled. KVM Kernel Virtual Machine support is enabled. LIBATA Libata driver is enabled LP Printer support is enabled. LOOP Loopback device support is enabled. M68k M68k architecture is enabled. These options have more detailed description inside of Documentation/m68k/kernel-options.txt. MCA MCA bus support is enabled. MDA MDA console support is enabled. MOUSE Appropriate mouse support is enabled. MSI Message Signaled Interrupts (PCI). MTD MTD (Memory Technology Device) support is enabled. NET Appropriate network support is enabled. NUMA NUMA support is enabled. GENERIC_TIME The generic timeofday code is enabled. NFS Appropriate NFS support is enabled. OSS OSS sound support is enabled. PV_OPS A paravirtualized kernel is enabled. PARIDE The ParIDE (parallel port IDE) subsystem is enabled. PARISC The PA-RISC architecture is enabled. PCI PCI bus support is enabled. PCIE PCI Express support is enabled. PCMCIA The PCMCIA subsystem is enabled. PNP Plug & Play support is enabled. PPC PowerPC architecture is enabled. PPT Parallel port support is enabled. PS2 Appropriate PS/2 support is enabled. RAM RAM disk support is enabled. ROOTPLUG The example Root Plug LSM is enabled. S390 S390 architecture is enabled. SCSI Appropriate SCSI support is enabled. A lot of drivers has their options described inside of Documentation/scsi/. SECURITY Different security models are enabled. SELINUX SELinux support is enabled. SERIAL Serial support is enabled. SH SuperH architecture is enabled. SMP The kernel is an SMP kernel. SPARC Sparc architecture is enabled. SWSUSP Software suspend (hibernation) is enabled. SUSPEND System suspend states are enabled. FTRACE Function tracing enabled. TS Appropriate touchscreen support is enabled. UMS USB Mass Storage support is enabled. USB USB support is enabled. USBHID USB Human Interface Device support is enabled. V4L Video For Linux support is enabled. VGA The VGA console has been enabled. VT Virtual terminal support is enabled. WDT Watchdog support is enabled. XT IBM PC/XT MFM hard disk support is enabled. X86-32 X86-32, aka i386 architecture is enabled. X86-64 X86-64 architecture is enabled. More X86-64 boot options can be found in Documentation/x86/x86_64/boot-options.txt . X86 Either 32bit or 64bit x86 (same as X86-32+X86-64) In addition, the following text indicates that the option: BUGS= Relates to possible processor bugs on the said processor. KNL Is a kernel start-up parameter. BOOT Is a boot loader parameter. Parameters denoted with BOOT are actually interpreted by the boot loader, and have no meaning to the kernel directly. Do not modify the syntax of boot loader parameters without extreme need or coordination with <Documentation/x86/boot.txt>. There are also arch-specific kernel-parameters not documented here. See for example <Documentation/x86/x86_64/boot-options.txt>. Note that ALL kernel parameters listed below are CASE SENSITIVE, and that a trailing = on the name of any parameter states that that parameter will be entered as an environment variable, whereas its absence indicates that it will appear as a kernel argument readable via /proc/cmdline by programs running once the system is up. The number of kernel parameters is not limited, but the length of the complete command line (parameters including spaces etc.) is limited to a fixed number of characters. This limit depends on the architecture and is between 256 and 4096 characters. It is defined in the file ./include/asm/setup.h as COMMAND_LINE_SIZE. acpi= [HW,ACPI,X86] Advanced Configuration and Power Interface Format: { force | off | ht | strict | noirq | rsdt } force -- enable ACPI if default was off off -- disable ACPI if default was on noirq -- do not use ACPI for IRQ routing ht -- run only enough ACPI to enable Hyper Threading strict -- Be less tolerant of platforms that are not strictly ACPI specification compliant. rsdt -- prefer RSDT over (default) XSDT See also Documentation/power/pm.txt, pci=noacpi acpi_apic_instance= [ACPI, IOAPIC] Format: <int> 2: use 2nd APIC table, if available 1,0: use 1st APIC table default: 0 acpi_backlight= [HW,ACPI] acpi_backlight=vendor acpi_backlight=video If set to vendor, prefer vendor specific driver (e.g. thinkpad_acpi, sony_acpi, etc.) instead of the ACPI video.ko driver. acpi.debug_layer= [HW,ACPI,ACPI_DEBUG] acpi.debug_level= [HW,ACPI,ACPI_DEBUG] Format: <int> CONFIG_ACPI_DEBUG must be enabled to produce any ACPI debug output. Bits in debug_layer correspond to a _COMPONENT in an ACPI source file, e.g., #define _COMPONENT ACPI_PCI_COMPONENT Bits in debug_level correspond to a level in ACPI_DEBUG_PRINT statements, e.g., ACPI_DEBUG_PRINT((ACPI_DB_INFO, ... The debug_level mask defaults to "info". See Documentation/acpi/debug.txt for more information about debug layers and levels. Enable processor driver info messages: acpi.debug_layer=0x20000000 Enable PCI/PCI interrupt routing info messages: acpi.debug_layer=0x400000 Enable AML "Debug" output, i.e., stores to the Debug object while interpreting AML: acpi.debug_layer=0xffffffff acpi.debug_level=0x2 Enable all messages related to ACPI hardware: acpi.debug_layer=0x2 acpi.debug_level=0xffffffff Some values produce so much output that the system is unusable. The "log_buf_len" parameter may be useful if you need to capture more output. acpi_display_output= [HW,ACPI] acpi_display_output=vendor acpi_display_output=video See above. acpi_irq_balance [HW,ACPI] ACPI will balance active IRQs default in APIC mode acpi_irq_nobalance [HW,ACPI] ACPI will not move active IRQs (default) default in PIC mode acpi_irq_isa= [HW,ACPI] If irq_balance, mark listed IRQs used by ISA Format: <irq>,<irq>... acpi_irq_pci= [HW,ACPI] If irq_balance, clear listed IRQs for use by PCI Format: <irq>,<irq>... acpi_no_auto_ssdt [HW,ACPI] Disable automatic loading of SSDT acpi_os_name= [HW,ACPI] Tell ACPI BIOS the name of the OS Format: To spoof as Windows 98: ="Microsoft Windows" acpi_osi= [HW,ACPI] Modify list of supported OS interface strings acpi_osi="string1" # add string1 -- only one string acpi_osi="!string2" # remove built-in string2 acpi_osi= # disable all strings acpi_pm_good [X86] Override the pmtimer bug detection: force the kernel to assume that this machine's pmtimer latches its value and always returns good values. acpi_sci= [HW,ACPI] ACPI System Control Interrupt trigger mode Format: { level | edge | high | low } acpi_serialize [HW,ACPI] force serialization of AML methods acpi_skip_timer_override [HW,ACPI] Recognize and ignore IRQ0/pin2 Interrupt Override. For broken nForce2 BIOS resulting in XT-PIC timer. acpi_sleep= [HW,ACPI] Sleep options Format: { s3_bios, s3_mode, s3_beep, s4_nohwsig, old_ordering, s4_nonvs } See Documentation/power/video.txt for information on s3_bios and s3_mode. s3_beep is for debugging; it makes the PC's speaker beep as soon as the kernel's real-mode entry point is called. s4_nohwsig prevents ACPI hardware signature from being used during resume from hibernation. old_ordering causes the ACPI 1.0 ordering of the _PTS control method, with respect to putting devices into low power states, to be enforced (the ACPI 2.0 ordering of _PTS is used by default). s4_nonvs prevents the kernel from saving/restoring the ACPI NVS memory during hibernation. acpi_use_timer_override [HW,ACPI] Use timer override. For some broken Nvidia NF5 boards that require a timer override, but don't have HPET acpi_enforce_resources= [ACPI] { strict | lax | no } Check for resource conflicts between native drivers and ACPI OperationRegions (SystemIO and SystemMemory only). IO ports and memory declared in ACPI might be used by the ACPI subsystem in arbitrary AML code and can interfere with legacy drivers. strict (default): access to resources claimed by ACPI is denied; legacy drivers trying to access reserved resources will fail to bind to device using them. lax: access to resources claimed by ACPI is allowed; legacy drivers trying to access reserved resources will bind successfully but a warning message is logged. no: ACPI OperationRegions are not marked as reserved, no further checks are performed. ad1848= [HW,OSS] Format: <io>,<irq>,<dma>,<dma2>,<type> add_efi_memmap [EFI; X86] Include EFI memory map in kernel's map of available physical RAM. advansys= [HW,SCSI] See header of drivers/scsi/advansys.c. advwdt= [HW,WDT] Advantech WDT Format: <iostart>,<iostop> aedsp16= [HW,OSS] Audio Excel DSP 16 Format: <io>,<irq>,<dma>,<mss_io>,<mpu_io>,<mpu_irq> See also header of sound/oss/aedsp16.c. agp= [AGP] { off | try_unsupported } off: disable AGP support try_unsupported: try to drive unsupported chipsets (may crash computer or cause data corruption) aha152x= [HW,SCSI] See Documentation/scsi/aha152x.txt. aha1542= [HW,SCSI] Format: <portbase>[,<buson>,<busoff>[,<dmaspeed>]] aic7xxx= [HW,SCSI] See Documentation/scsi/aic7xxx.txt. aic79xx= [HW,SCSI] See Documentation/scsi/aic79xx.txt. amd_iommu= [HW,X86-84] Pass parameters to the AMD IOMMU driver in the system. Possible values are: isolate - enable device isolation (each device, as far as possible, will get its own protection domain) [default] share - put every device behind one IOMMU into the same protection domain fullflush - enable flushing of IO/TLB entries when they are unmapped. Otherwise they are flushed before they will be reused, which is a lot of faster amijoy.map= [HW,JOY] Amiga joystick support Map of devices attached to JOY0DAT and JOY1DAT Format: <a>,<b> See also Documentation/kernel/input/joystick.txt analog.map= [HW,JOY] Analog joystick and gamepad support Specifies type or capabilities of an analog joystick connected to one of 16 gameports Format: <type1>,<type2>,..<type16> apc= [HW,SPARC] Power management functions (SPARCstation-4/5 + deriv.) Format: noidle Disable APC CPU standby support. SPARCstation-Fox does not play well with APC CPU idle - disable it if you have APC and your system crashes randomly. apic= [APIC,X86-32] Advanced Programmable Interrupt Controller Change the output verbosity whilst booting Format: { quiet (default) | verbose | debug } Change the amount of debugging information output when initialising the APIC and IO-APIC components. apm= [APM] Advanced Power Management See header of arch/x86/kernel/apm_32.c. arcrimi= [HW,NET] ARCnet - "RIM I" (entirely mem-mapped) cards Format: <io>,<irq>,<nodeID> ataflop= [HW,M68k] atarimouse= [HW,MOUSE] Atari Mouse atascsi= [HW,SCSI] Atari SCSI atkbd.extra= [HW] Enable extra LEDs and keys on IBM RapidAccess, EzKey and similar keyboards atkbd.reset= [HW] Reset keyboard during initialization atkbd.set= [HW] Select keyboard code set Format: <int> (2 = AT (default), 3 = PS/2) atkbd.scroll= [HW] Enable scroll wheel on MS Office and similar keyboards atkbd.softraw= [HW] Choose between synthetic and real raw mode Format: <bool> (0 = real, 1 = synthetic (default)) atkbd.softrepeat= [HW] Use software keyboard repeat autotest [IA64] baycom_epp= [HW,AX25] Format: <io>,<mode> baycom_par= [HW,AX25] BayCom Parallel Port AX.25 Modem Format: <io>,<mode> See header of drivers/net/hamradio/baycom_par.c. baycom_ser_fdx= [HW,AX25] BayCom Serial Port AX.25 Modem (Full Duplex Mode) Format: <io>,<irq>,<mode>[,<baud>] See header of drivers/net/hamradio/baycom_ser_fdx.c. baycom_ser_hdx= [HW,AX25] BayCom Serial Port AX.25 Modem (Half Duplex Mode) Format: <io>,<irq>,<mode> See header of drivers/net/hamradio/baycom_ser_hdx.c. boot_delay= Milliseconds to delay each printk during boot. Values larger than 10 seconds (10000) are changed to no delay (0). Format: integer bootmem_debug [KNL] Enable bootmem allocator debug messages. bttv.card= [HW,V4L] bttv (bt848 + bt878 based grabber cards) bttv.radio= Most important insmod options are available as kernel args too. bttv.pll= See Documentation/video4linux/bttv/Insmod-options bttv.tuner= and Documentation/video4linux/bttv/CARDLIST BusLogic= [HW,SCSI] See drivers/scsi/BusLogic.c, comment before function BusLogic_ParseDriverOptions(). c101= [NET] Moxa C101 synchronous serial card cachesize= [BUGS=X86-32] Override level 2 CPU cache size detection. Sometimes CPU hardware bugs make them report the cache size incorrectly. The kernel will attempt work arounds to fix known problems, but for some CPUs it is not possible to determine what the correct size should be. This option provides an override for these situations. capability.disable= [SECURITY] Disable capabilities. This would normally be used only if an alternative security model is to be configured. Potentially dangerous and should only be used if you are entirely sure of the consequences. ccw_timeout_log [S390] See Documentation/s390/CommonIO for details. cgroup_disable= [KNL] Disable a particular controller Format: {name of the controller(s) to disable} {Currently supported controllers - "memory"} checkreqprot [SELINUX] Set initial checkreqprot flag value. Format: { "0" | "1" } See security/selinux/Kconfig help text. 0 -- check protection applied by kernel (includes any implied execute protection). 1 -- check protection requested by application. Default value is set via a kernel config option. Value can be changed at runtime via /selinux/checkreqprot. cio_ignore= [S390] See Documentation/s390/CommonIO for details. clock= [BUGS=X86-32, HW] gettimeofday clocksource override. [Deprecated] Forces specified clocksource (if available) to be used when calculating gettimeofday(). If specified clocksource is not available, it defaults to PIT. Format: { pit | tsc | cyclone | pmtmr } clocksource= [GENERIC_TIME] Override the default clocksource Format: <string> Override the default clocksource and use the clocksource with the name specified. Some clocksource names to choose from, depending on the platform: [all] jiffies (this is the base, fallback clocksource) [ACPI] acpi_pm [ARM] imx_timer1,OSTS,netx_timer,mpu_timer2, pxa_timer,timer3,32k_counter,timer0_1 [AVR32] avr32 [X86-32] pit,hpet,tsc,vmi-timer; scx200_hrt on Geode; cyclone on IBM x440 [MIPS] MIPS [PARISC] cr16 [S390] tod [SH] SuperH [SPARC64] tick [X86-64] hpet,tsc clearcpuid=BITNUM [X86] Disable CPUID feature X for the kernel. See arch/x86/include/asm/cpufeature.h for the valid bit numbers. Note the Linux specific bits are not necessarily stable over kernel options, but the vendor specific ones should be. Also note that user programs calling CPUID directly or using the feature without checking anything will still see it. This just prevents it from being used by the kernel or shown in /proc/cpuinfo. Also note the kernel might malfunction if you disable some critical bits. cmo_free_hint= [PPC] Format: { yes | no } Specify whether pages are marked as being inactive when they are freed. This is used in CMO environments to determine OS memory pressure for page stealing by a hypervisor. Default: yes code_bytes [X86] How many bytes of object code to print in an oops report. Range: 0 - 8192 Default: 64 com20020= [HW,NET] ARCnet - COM20020 chipset Format: <io>[,<irq>[,<nodeID>[,<backplane>[,<ckp>[,<timeout>]]]]] com90io= [HW,NET] ARCnet - COM90xx chipset (IO-mapped buffers) Format: <io>[,<irq>] com90xx= [HW,NET] ARCnet - COM90xx chipset (memory-mapped buffers) Format: <io>[,<irq>[,<memstart>]] condev= [HW,S390] console device conmode= console= [KNL] Output console device and options. tty<n> Use the virtual console device <n>. ttyS<n>[,options] ttyUSB0[,options] Use the specified serial port. The options are of the form "bbbbpnf", where "bbbb" is the baud rate, "p" is parity ("n", "o", or "e"), "n" is number of bits, and "f" is flow control ("r" for RTS or omit it). Default is "9600n8". See Documentation/serial-console.txt for more information. See Documentation/networking/netconsole.txt for an alternative. uart[8250],io,<addr>[,options] uart[8250],mmio,<addr>[,options] Start an early, polled-mode console on the 8250/16550 UART at the specified I/O port or MMIO address, switching to the matching ttyS device later. The options are the same as for ttyS, above. If the device connected to the port is not a TTY but a braille device, prepend "brl," before the device type, for instance console=brl,ttyS0 For now, only VisioBraille is supported. consoleblank= [KNL] The console blank (screen saver) timeout in seconds. Defaults to 10*60 = 10mins. A value of 0 disables the blank timer. coredump_filter= [KNL] Change the default value for /proc/<pid>/coredump_filter. See also Documentation/filesystems/proc.txt. cpcihp_generic= [HW,PCI] Generic port I/O CompactPCI driver Format: <first_slot>,<last_slot>,<port>,<enum_bit>[,<debug>] crashkernel=nn[KMG]@ss[KMG] [KNL] Reserve a chunk of physical memory to hold a kernel to switch to with kexec on panic. crashkernel=range1:size1[,range2:size2,...][@offset] [KNL] Same as above, but depends on the memory in the running system. The syntax of range is start-[end] where start and end are both a memory unit (amount[KMG]). See also Documentation/kdump/kdump.txt for a example. cs89x0_dma= [HW,NET] Format: <dma> cs89x0_media= [HW,NET] Format: { rj45 | aui | bnc } dasd= [HW,NET] See header of drivers/s390/block/dasd_devmap.c. db9.dev[2|3]= [HW,JOY] Multisystem joystick support via parallel port (one device per port) Format: <port#>,<type> See also Documentation/input/joystick-parport.txt debug [KNL] Enable kernel debugging (events log level). debug_locks_verbose= [KNL] verbose self-tests Format=<0|1> Print debugging info while doing the locking API self-tests. We default to 0 (no extra messages), setting it to 1 will print _a lot_ more information - normally only useful to kernel developers. debug_objects [KNL] Enable object debugging no_debug_objects [KNL] Disable object debugging debugpat [X86] Enable PAT debugging decnet.addr= [HW,NET] Format: <area>[,<node>] See also Documentation/networking/decnet.txt. default_hugepagesz= [same as hugepagesz=] The size of the default HugeTLB page size. This is the size represented by the legacy /proc/ hugepages APIs, used for SHM, and default size when mounting hugetlbfs filesystems. Defaults to the default architecture's huge page size if not specified. dhash_entries= [KNL] Set number of hash buckets for dentry cache. digi= [HW,SERIAL] IO parameters + enable/disable command. digiepca= [HW,SERIAL] See drivers/char/README.epca and Documentation/serial/digiepca.txt. disable_mtrr_cleanup [X86] The kernel tries to adjust MTRR layout from continuous to discrete, to make X server driver able to add WB entry later. This parameter disables that. disable_mtrr_trim [X86, Intel and AMD only] By default the kernel will trim any uncacheable memory out of your available memory pool based on MTRR settings. This parameter disables that behavior, possibly causing your machine to run very slowly. disable_timer_pin_1 [X86] Disable PIN 1 of APIC timer Can be useful to work around chipset bugs. dmasound= [HW,OSS] Sound subsystem buffers dma_debug=off If the kernel is compiled with DMA_API_DEBUG support, this option disables the debugging code at boot. dma_debug_entries=<number> This option allows to tune the number of preallocated entries for DMA-API debugging code. One entry is required per DMA-API allocation. Use this if the DMA-API debugging code disables itself because the architectural default is too low. dma_debug_driver=<driver_name> With this option the DMA-API debugging driver filter feature can be enabled at boot time. Just pass the driver to filter for as the parameter. The filter can be disabled or changed to another driver later using sysfs. dscc4.setup= [NET] dtc3181e= [HW,SCSI] dynamic_printk Enables pr_debug()/dev_dbg() calls if CONFIG_DYNAMIC_PRINTK_DEBUG has been enabled. These can also be switched on/off via <debugfs>/dynamic_printk/modules earlycon= [KNL] Output early console device and options. uart[8250],io,<addr>[,options] uart[8250],mmio,<addr>[,options] Start an early, polled-mode console on the 8250/16550 UART at the specified I/O port or MMIO address. The options are the same as for ttyS, above. earlyprintk= [X86,SH,BLACKFIN] earlyprintk=vga earlyprintk=serial[,ttySn[,baudrate]] earlyprintk=ttySn[,baudrate] earlyprintk=dbgp[debugController#] Append ",keep" to not disable it when the real console takes over. Only vga or serial or usb debug port at a time. Currently only ttyS0 and ttyS1 are supported. Interaction with the standard serial driver is not very good. The VGA output is eventually overwritten by the real console. eata= [HW,SCSI] edd= [EDD] Format: {"off" | "on" | "skip[mbr]"} eisa_irq_edge= [PARISC,HW] See header of drivers/parisc/eisa.c. elanfreq= [X86-32] See comment before function elanfreq_setup() in arch/x86/kernel/cpu/cpufreq/elanfreq.c. elevator= [IOSCHED] Format: {"anticipatory" | "cfq" | "deadline" | "noop"} See Documentation/block/as-iosched.txt and Documentation/block/deadline-iosched.txt for details. elfcorehdr= [IA64,PPC,SH,X86] Specifies physical address of start of kernel core image elf header. Generally kexec loader will pass this option to capture kernel. See Documentation/kdump/kdump.txt for details. enable_mtrr_cleanup [X86] The kernel tries to adjust MTRR layout from continuous to discrete, to make X server driver able to add WB entry later. This parameter enables that. enable_timer_pin_1 [X86] Enable PIN 1 of APIC timer Can be useful to work around chipset bugs (in particular on some ATI chipsets). The kernel tries to set a reasonable default. enforcing [SELINUX] Set initial enforcing status. Format: {"0" | "1"} See security/selinux/Kconfig help text. 0 -- permissive (log only, no denials). 1 -- enforcing (deny and log). Default value is 0. Value can be changed at runtime via /selinux/enforce. ether= [HW,NET] Ethernet cards parameters This option is obsoleted by the "netdev=" option, which has equivalent usage. See its documentation for details. eurwdt= [HW,WDT] Eurotech CPU-1220/1410 onboard watchdog. Format: <io>[,<irq>] failslab= fail_page_alloc= fail_make_request=[KNL] General fault injection mechanism. Format: <interval>,<probability>,<space>,<times> See also /Documentation/fault-injection/. fd_mcs= [HW,SCSI] See header of drivers/scsi/fd_mcs.c. fdomain= [HW,SCSI] See header of drivers/scsi/fdomain.c. floppy= [HW] See Documentation/blockdev/floppy.txt. force_pal_cache_flush [IA-64] Avoid check_sal_cache_flush which may hang on buggy SAL_CACHE_FLUSH implementations. Using this parameter will force ia64_sal_cache_flush to call ia64_pal_cache_flush instead of SAL_CACHE_FLUSH. ftrace=[tracer] [FTRACE] will set and start the specified tracer as early as possible in order to facilitate early boot debugging. ftrace_dump_on_oops [FTRACE] will dump the trace buffers on oops. ftrace_filter=[function-list] [FTRACE] Limit the functions traced by the function tracer at boot up. function-list is a comma separated list of functions. This list can be changed at run time by the set_ftrace_filter file in the debugfs tracing directory. ftrace_notrace=[function-list] [FTRACE] Do not trace the functions specified in function-list. This list can be changed at run time by the set_ftrace_notrace file in the debugfs tracing directory. gamecon.map[2|3]= [HW,JOY] Multisystem joystick and NES/SNES/PSX pad support via parallel port (up to 5 devices per port) Format: <port#>,<pad1>,<pad2>,<pad3>,<pad4>,<pad5> See also Documentation/input/joystick-parport.txt gamma= [HW,DRM] gart_fix_e820= [X86_64] disable the fix e820 for K8 GART Format: off | on default: on gcov_persist= [GCOV] When non-zero (default), profiling data for kernel modules is saved and remains accessible via debugfs, even when the module is unloaded/reloaded. When zero, profiling data is discarded and associated debugfs files are removed at module unload time. gdth= [HW,SCSI] See header of drivers/scsi/gdth.c. gpt [EFI] Forces disk with valid GPT signature but invalid Protective MBR to be treated as GPT. gvp11= [HW,SCSI] hashdist= [KNL,NUMA] Large hashes allocated during boot are distributed across NUMA nodes. Defaults on for 64bit NUMA, off otherwise. Format: 0 | 1 (for off | on) hcl= [IA-64] SGI's Hardware Graph compatibility layer hd= [EIDE] (E)IDE hard drive subsystem geometry Format: <cyl>,<head>,<sect> highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact size of <nn>. This works even on boxes that have no highmem otherwise. This also works to reduce highmem size on bigger boxes. highres= [KNL] Enable/disable high resolution timer mode. Valid parameters: "on", "off" Default: "on" hisax= [HW,ISDN] See Documentation/isdn/README.HiSax. hlt [BUGS=ARM,SH] hpet= [X86-32,HPET] option to control HPET usage Format: { enable (default) | disable | force | verbose } disable: disable HPET and use PIT instead force: allow force enabled of undocumented chips (ICH4, VIA, nVidia) verbose: show contents of HPET registers during setup hugepages= [HW,X86-32,IA-64] HugeTLB pages to allocate at boot. hugepagesz= [HW,IA-64,PPC,X86-64] The size of the HugeTLB pages. On x86-64 and powerpc, this option can be specified multiple times interleaved with hugepages= to reserve huge pages of different sizes. Valid pages sizes on x86-64 are 2M (when the CPU supports "pse") and 1G (when the CPU supports the "pdpe1gb" cpuinfo flag) Note that 1GB pages can only be allocated at boot time using hugepages= and not freed afterwards. hvc_iucv= [S390] Number of z/VM IUCV hypervisor console (HVC) terminal devices. Valid values: 0..8 hvc_iucv_allow= [S390] Comma-separated list of z/VM user IDs. If specified, z/VM IUCV HVC accepts connections from listed z/VM user IDs only. i2c_bus= [HW] Override the default board specific I2C bus speed or register an additional I2C bus that is not registered from board initialization code. Format: <bus_id>,<clkrate> i8042.debug [HW] Toggle i8042 debug mode i8042.direct [HW] Put keyboard port into non-translated mode i8042.dumbkbd [HW] Pretend that controller can only read data from keyboard and cannot control its state (Don't attempt to blink the leds) i8042.noaux [HW] Don't check for auxiliary (== mouse) port i8042.nokbd [HW] Don't check/create keyboard port i8042.noloop [HW] Disable the AUX Loopback command while probing for the AUX port i8042.nomux [HW] Don't check presence of an active multiplexing controller i8042.nopnp [HW] Don't use ACPIPnP / PnPBIOS to discover KBD/AUX controllers i8042.panicblink= [HW] Frequency with which keyboard LEDs should blink when kernel panics (default is 0.5 sec) i8042.reset [HW] Reset the controller during init and cleanup i8042.unlock [HW] Unlock (ignore) the keylock i810= [HW,DRM] i8k.ignore_dmi [HW] Continue probing hardware even if DMI data indicates that the driver is running on unsupported hardware. i8k.force [HW] Activate i8k driver even if SMM BIOS signature does not match list of supported models. i8k.power_status [HW] Report power status in /proc/i8k (disabled by default) i8k.restricted [HW] Allow controlling fans only if SYS_ADMIN capability is set. ibmmcascsi= [HW,MCA,SCSI] IBM MicroChannel SCSI adapter See Documentation/mca.txt. icn= [HW,ISDN] Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]] ide-core.nodma= [HW] (E)IDE subsystem Format: =0.0 to prevent dma on hda, =0.1 hdb =1.0 hdc .vlb_clock .pci_clock .noflush .nohpa .noprobe .nowerr .cdrom .chs .ignore_cable are additional options See Documentation/ide/ide.txt. ide-pci-generic.all-generic-ide [HW] (E)IDE subsystem Claim all unknown PCI IDE storage controllers. idle= [X86] Format: idle=poll, idle=mwait, idle=halt, idle=nomwait Poll forces a polling idle loop that can slightly improve the performance of waking up a idle CPU, but will use a lot of power and make the system run hot. Not recommended. idle=mwait: On systems which support MONITOR/MWAIT but the kernel chose to not use it because it doesn't save as much power as a normal idle loop, use the MONITOR/MWAIT idle loop anyways. Performance should be the same as idle=poll. idle=halt: Halt is forced to be used for CPU idle. In such case C2/C3 won't be used again. idle=nomwait: Disable mwait for CPU C-states ignore_loglevel [KNL] Ignore loglevel setting - this will print /all/ kernel messages to the console. Useful for debugging. ihash_entries= [KNL] Set number of hash buckets for inode cache. ima_audit= [IMA] Format: { "0" | "1" } 0 -- integrity auditing messages. (Default) 1 -- enable informational integrity auditing messages. ima_hash= [IMA] Format: { "sha1" | "md5" } default: "sha1" ima_tcb [IMA] Load a policy which meets the needs of the Trusted Computing Base. This means IMA will measure all programs exec'd, files mmap'd for exec, and all files opened for read by uid=0. in2000= [HW,SCSI] See header of drivers/scsi/in2000.c. init= [KNL] Format: <full_path> Run specified binary instead of /sbin/init as init process. initcall_debug [KNL] Trace initcalls as they are executed. Useful for working out where the kernel is dying during startup. initrd= [BOOT] Specify the location of the initial ramdisk inport.irq= [HW] Inport (ATI XL and Microsoft) busmouse driver Format: <irq> intel_iommu= [DMAR] Intel IOMMU driver (DMAR) option on Enable intel iommu driver. off Disable intel iommu driver. igfx_off [Default Off] By default, gfx is mapped as normal device. If a gfx device has a dedicated DMAR unit, the DMAR unit is bypassed by not enabling DMAR with this option. In this case, gfx device will use physical address for DMA. forcedac [x86_64] With this option iommu will not optimize to look for io virtual address below 32 bit forcing dual address cycle on pci bus for cards supporting greater than 32 bit addressing. The default is to look for translation below 32 bit and if not available then look in the higher range. strict [Default Off] With this option on every unmap_single operation will result in a hardware IOTLB flush operation as opposed to batching them for performance. inttest= [IA64] iomem= Disable strict checking of access to MMIO memory strict regions from userspace. relaxed iommu= [x86] off force noforce biomerge panic nopanic merge nomerge forcesac soft pt [x86, IA64] io7= [HW] IO7 for Marvel based alpha systems See comment before marvel_specify_io7 in arch/alpha/kernel/core_marvel.c. io_delay= [X86] I/O delay method 0x80 Standard port 0x80 based delay 0xed Alternate port 0xed based delay (needed on some systems) udelay Simple two microseconds delay none No delay ip= [IP_PNP] See Documentation/filesystems/nfsroot.txt. ip2= [HW] Set IO/IRQ pairs for up to 4 IntelliPort boards See comment before ip2_setup() in drivers/char/ip2/ip2base.c. ips= [HW,SCSI] Adaptec / IBM ServeRAID controller See header of drivers/scsi/ips.c. irqfixup [HW] When an interrupt is not handled search all handlers for it. Intended to get systems with badly broken firmware running. irqpoll [HW] When an interrupt is not handled search all handlers for it. Also check all handlers each timer interrupt. Intended to get systems with badly broken firmware running. isapnp= [ISAPNP] Format: <RDP>,<reset>,<pci_scan>,<verbosity> isolcpus= [KNL,SMP] Isolate CPUs from the general scheduler. Format: <cpu number>,...,<cpu number> or <cpu number>-<cpu number> (must be a positive range in ascending order) or a mixture <cpu number>,...,<cpu number>-<cpu number> This option can be used to specify one or more CPUs to isolate from the general SMP balancing and scheduling algorithms. You can move a process onto or off an "isolated" CPU via the CPU affinity syscalls or cpuset. <cpu number> begins at 0 and the maximum value is "number of CPUs in system - 1". This option is the preferred way to isolate CPUs. The alternative -- manually setting the CPU mask of all tasks in the system -- can cause problems and suboptimal load balancer performance. iucv= [HW,NET] js= [HW,JOY] Analog joystick See Documentation/input/joystick.txt. keepinitrd [HW,ARM] kernelcore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter specifies the amount of memory usable by the kernel for non-movable allocations. The requested amount is spread evenly throughout all nodes in the system. The remaining memory in each node is used for Movable pages. In the event, a node is too small to have both kernelcore and Movable pages, kernelcore pages will take priority and other nodes will have a larger number of kernelcore pages. The Movable zone is used for the allocation of pages that may be reclaimed or moved by the page migration subsystem. This means that HugeTLB pages may not be allocated from this zone. Note that allocations like PTEs-from-HighMem still use the HighMem zone if it exists, and the Normal zone if it does not. kgdboc= [HW] kgdb over consoles. Requires a tty driver that supports console polling. (only serial supported for now) Format: <serial_device>[,baud] kmac= [MIPS] korina ethernet MAC address. Configure the RouterBoard 532 series on-chip Ethernet adapter MAC address. kmemleak= [KNL] Boot-time kmemleak enable/disable Valid arguments: on, off Default: on kstack=N [X86] Print N words from the kernel stack in oops dumps. kvm.ignore_msrs=[KVM] Ignore guest accesses to unhandled MSRs. Default is 0 (don't ignore, but inject #GP) kvm.oos_shadow= [KVM] Disable out-of-sync shadow paging. Default is 1 (enabled) kvm-amd.nested= [KVM,AMD] Allow nested virtualization in KVM/SVM. Default is 0 (off) kvm-amd.npt= [KVM,AMD] Disable nested paging (virtualized MMU) for all guests. Default is 1 (enabled) if in 64bit or 32bit-PAE mode kvm-intel.bypass_guest_pf= [KVM,Intel] Disables bypassing of guest page faults on Intel chips. Default is 1 (enabled) kvm-intel.ept= [KVM,Intel] Disable extended page tables (virtualized MMU) support on capable Intel chips. Default is 1 (enabled) kvm-intel.emulate_invalid_guest_state= [KVM,Intel] Enable emulation of invalid guest states Default is 0 (disabled) kvm-intel.flexpriority= [KVM,Intel] Disable FlexPriority feature (TPR shadow). Default is 1 (enabled) kvm-intel.unrestricted_guest= [KVM,Intel] Disable unrestricted guest feature (virtualized real and unpaged mode) on capable Intel chips. Default is 1 (enabled) kvm-intel.vpid= [KVM,Intel] Disable Virtual Processor Identification feature (tagged TLBs) on capable Intel chips. Default is 1 (enabled) l2cr= [PPC] l3cr= [PPC] lapic [X86-32,APIC] Enable the local APIC even if BIOS disabled it. lapic_timer_c2_ok [X86,APIC] trust the local apic timer in C2 power state. libata.dma= [LIBATA] DMA control libata.dma=0 Disable all PATA and SATA DMA libata.dma=1 PATA and SATA Disk DMA only libata.dma=2 ATAPI (CDROM) DMA only libata.dma=4 Compact Flash DMA only Combinations also work, so libata.dma=3 enables DMA for disks and CDROMs, but not CFs. libata.ignore_hpa= [LIBATA] Ignore HPA limit libata.ignore_hpa=0 keep BIOS limits (default) libata.ignore_hpa=1 ignore limits, using full disk libata.noacpi [LIBATA] Disables use of ACPI in libata suspend/resume when set. Format: <int> libata.force= [LIBATA] Force configurations. The format is comma separated list of "[ID:]VAL" where ID is PORT[:DEVICE]. PORT and DEVICE are decimal numbers matching port, link or device. Basically, it matches the ATA ID string printed on console by libata. If the whole ID part is omitted, the last PORT and DEVICE values are used. If ID hasn't been specified yet, the configuration applies to all ports, links and devices. If only DEVICE is omitted, the parameter applies to the port and all links and devices behind it. DEVICE number of 0 either selects the first device or the first fan-out link behind PMP device. It does not select the host link. DEVICE number of 15 selects the host link and device attached to it. The VAL specifies the configuration to force. As long as there's no ambiguity shortcut notation is allowed. For example, both 1.5 and 1.5G would work for 1.5Gbps. The following configurations can be forced. * Cable type: 40c, 80c, short40c, unk, ign or sata. Any ID with matching PORT is used. * SATA link speed limit: 1.5Gbps or 3.0Gbps. * Transfer mode: pio[0-7], mwdma[0-4] and udma[0-7]. udma[/][16,25,33,44,66,100,133] notation is also allowed. * [no]ncq: Turn on or off NCQ. * nohrst, nosrst, norst: suppress hard, soft and both resets. If there are multiple matching configurations changing the same attribute, the last one is used. lmb=debug [KNL] Enable lmb debug messages. load_ramdisk= [RAM] List of ramdisks to load from floppy See Documentation/blockdev/ramdisk.txt. lockd.nlm_grace_period=P [NFS] Assign grace period. Format: <integer> lockd.nlm_tcpport=N [NFS] Assign TCP port. Format: <integer> lockd.nlm_timeout=T [NFS] Assign timeout value. Format: <integer> lockd.nlm_udpport=M [NFS] Assign UDP port. Format: <integer> logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver Format: <irq> loglevel= All Kernel Messages with a loglevel smaller than the console loglevel will be printed to the console. It can also be changed with klogd or other programs. The loglevels are defined as follows: 0 (KERN_EMERG) system is unusable 1 (KERN_ALERT) action must be taken immediately 2 (KERN_CRIT) critical conditions 3 (KERN_ERR) error conditions 4 (KERN_WARNING) warning conditions 5 (KERN_NOTICE) normal but significant condition 6 (KERN_INFO) informational 7 (KERN_DEBUG) debug-level messages log_buf_len=n Sets the size of the printk ring buffer, in bytes. Format: { n | nk | nM } n must be a power of two. The default size is set in the kernel config file. logo.nologo [FB] Disables display of the built-in Linux logo. This may be used to provide more screen space for kernel log messages and is useful when debugging kernel boot problems. lp=0 [LP] Specify parallel ports to use, e.g, lp=port[,port...] lp=none,parport0 (lp0 not configured, lp1 uses lp=reset first parallel port). 'lp=0' disables the lp=auto printer driver. 'lp=reset' (which can be specified in addition to the ports) causes attached printers to be reset. Using lp=port1,port2,... specifies the parallel ports to associate lp devices with, starting with lp0. A port specification may be 'none' to skip that lp device, or a parport name such as 'parport0'. Specifying 'lp=auto' instead of a port specification list means that device IDs from each port should be examined, to see if an IEEE 1284-compliant printer is attached; if so, the driver will manage that printer. See also header of drivers/char/lp.c. lpj=n [KNL] Sets loops_per_jiffy to given constant, thus avoiding time-consuming boot-time autodetection (up to 250 ms per CPU). 0 enables autodetection (default). To determine the correct value for your kernel, boot with normal autodetection and see what value is printed. Note that on SMP systems the preset will be applied to all CPUs, which is likely to cause problems if your CPUs need significantly divergent settings. An incorrect value will cause delays in the kernel to be wrong, leading to unpredictable I/O errors and other breakage. Although unlikely, in the extreme case this might damage your hardware. ltpc= [NET] Format: <io>,<irq>,<dma> mac5380= [HW,SCSI] Format: <can_queue>,<cmd_per_lun>,<sg_tablesize>,<hostid>,<use_tags> machvec= [IA64] Force the use of a particular machine-vector (machvec) in a generic kernel. Example: machvec=hpzx1_swiotlb machtype= [Loongson] Share the same kernel image file between different yeeloong laptop. Example: machtype=lemote-yeeloong-2f-7inch max_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory greater than or equal to this physical address is ignored. maxcpus= [SMP] Maximum number of processors that an SMP kernel should make use of. maxcpus=n : n >= 0 limits the kernel to using 'n' processors. n=0 is a special case, it is equivalent to "nosmp", which also disables the IO APIC. max_loop= [LOOP] Maximum number of loopback devices that can be mounted Format: <1-256> max_luns= [SCSI] Maximum number of LUNs to probe. Should be between 1 and 2^32-1. max_report_luns= [SCSI] Maximum number of LUNs received. Should be between 1 and 16384. mcatest= [IA-64] mce [X86-32] Machine Check Exception mce=option [X86-64] See Documentation/x86/x86_64/boot-options.txt md= [HW] RAID subsystems devices and level See Documentation/md.txt. mdacon= [MDA] Format: <first>,<last> Specifies range of consoles to be captured by the MDA. mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory Amount of memory to be used when the kernel is not able to see the whole system memory or for test. [X86-32] Use together with memmap= to avoid physical address space collisions. Without memmap= PCI devices could be placed at addresses belonging to unused RAM. mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel memory. memchunk=nn[KMG] [KNL,SH] Allow user to override the default size for per-device physically contiguous DMA buffers. memmap=exactmap [KNL,X86] Enable setting of an exact E820 memory map, as specified by the user. Such memmap=exactmap lines can be constructed based on BIOS output or other requirements. See the memmap=nn@ss option description. memmap=nn[KMG]@ss[KMG] [KNL] Force usage of a specific region of memory Region of memory to be used, from ss to ss+nn. memmap=nn[KMG]#ss[KMG] [KNL,ACPI] Mark specific memory as ACPI data. Region of memory to be used, from ss to ss+nn. memmap=nn[KMG]$ss[KMG] [KNL,ACPI] Mark specific memory as reserved. Region of memory to be used, from ss to ss+nn. Example: Exclude memory from 0x18690000-0x1869ffff memmap=64K$0x18690000 or memmap=0x10000$0x18690000 memory_corruption_check=0/1 [X86] Some BIOSes seem to corrupt the first 64k of memory when doing things like suspend/resume. Setting this option will scan the memory looking for corruption. Enabling this will both detect corruption and prevent the kernel from using the memory being corrupted. However, its intended as a diagnostic tool; if repeatable BIOS-originated corruption always affects the same memory, you can use memmap= to prevent the kernel from using that memory. memory_corruption_check_size=size [X86] By default it checks for corruption in the low 64k, making this memory unavailable for normal use. Use this parameter to scan for corruption in more or less memory. memory_corruption_check_period=seconds [X86] By default it checks for corruption every 60 seconds. Use this parameter to check at some other rate. 0 disables periodic checking. memtest= [KNL,X86] Enable memtest Format: <integer> default : 0 <disable> Specifies the number of memtest passes to be performed. Each pass selects another test pattern from a given set of patterns. Memtest fills the memory with this pattern, validates memory contents and reserves bad memory regions that are detected. meye.*= [HW] Set MotionEye Camera parameters See Documentation/video4linux/meye.txt. mfgpt_irq= [IA-32] Specify the IRQ to use for the Multi-Function General Purpose Timers on AMD Geode platforms. mfgptfix [X86-32] Fix MFGPT timers on AMD Geode platforms when the BIOS has incorrectly applied a workaround. TinyBIOS version 0.98 is known to be affected, 0.99 fixes the problem by letting the user disable the workaround. mga= [HW,DRM] min_addr=nn[KMG] [KNL,BOOT,ia64] All physical memory below this physical address is ignored. mini2440= [ARM,HW,KNL] Format:[0..2][b][c][t] Default: "0tb" MINI2440 configuration specification: 0 - The attached screen is the 3.5" TFT 1 - The attached screen is the 7" TFT 2 - The VGA Shield is attached (1024x768) Leaving out the screen size parameter will not load the TFT driver, and the framebuffer will be left unconfigured. b - Enable backlight. The TFT backlight pin will be linked to the kernel VESA blanking code and a GPIO LED. This parameter is not necessary when using the VGA shield. c - Enable the s3c camera interface. t - Reserved for enabling touchscreen support. The touchscreen support is not enabled in the mainstream kernel as of 2.6.30, a preliminary port can be found in the "bleeding edge" mini2440 support kernel at http://repo.or.cz/w/linux-2.6/mini2440.git mminit_loglevel= [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this parameter allows control of the logging verbosity for the additional memory initialisation checks. A value of 0 disables mminit logging and a level of 4 will log everything. Information is printed at KERN_DEBUG so loglevel=8 may also need to be specified. mousedev.tap_time= [MOUSE] Maximum time between finger touching and leaving touchpad surface for touch to be considered a tap and be reported as a left button click (for touchpads working in absolute mode only). Format: <msecs> mousedev.xres= [MOUSE] Horizontal screen resolution, used for devices reporting absolute coordinates, such as tablets mousedev.yres= [MOUSE] Vertical screen resolution, used for devices reporting absolute coordinates, such as tablets movablecore=nn[KMG] [KNL,X86,IA-64,PPC] This parameter is similar to kernelcore except it specifies the amount of memory used for migratable allocations. If both kernelcore and movablecore is specified, then kernelcore will be at *least* the specified value but may be more. If movablecore on its own is specified, the administrator must be careful that the amount of memory usable for all allocations is not too small. mpu401= [HW,OSS] Format: <io>,<irq> MTD_Partition= [MTD] Format: <name>,<region-number>,<size>,<offset> MTD_Region= [MTD] Format: <name>,<region-number>[,<base>,<size>,<buswidth>,<altbuswidth>] mtdparts= [MTD] See drivers/mtd/cmdlinepart.c. onenand.bdry= [HW,MTD] Flex-OneNAND Boundary Configuration Format: [die0_boundary][,die0_lock][,die1_boundary][,die1_lock] boundary - index of last SLC block on Flex-OneNAND. The remaining blocks are configured as MLC blocks. lock - Configure if Flex-OneNAND boundary should be locked. Once locked, the boundary cannot be changed. 1 indicates lock status, 0 indicates unlock status. mtdset= [ARM] ARM/S3C2412 JIVE boot control See arch/arm/mach-s3c2412/mach-jive.c mtouchusb.raw_coordinates= [HW] Make the MicroTouch USB driver use raw coordinates ('y', default) or cooked coordinates ('n') mtrr_chunk_size=nn[KMG] [X86] used for mtrr cleanup. It is largest continuous chunk that could hold holes aka. UC entries. mtrr_gran_size=nn[KMG] [X86] Used for mtrr cleanup. It is granularity of mtrr block. Default is 1. Large value could prevent small alignment from using up MTRRs. mtrr_spare_reg_nr=n [X86] Format: <integer> Range: 0,7 : spare reg number Default : 1 Used for mtrr cleanup. It is spare mtrr entries number. Set to 2 or more if your graphical card needs more. n2= [NET] SDL Inc. RISCom/N2 synchronous serial card NCR_D700= [HW,SCSI] See header of drivers/scsi/NCR_D700.c. ncr5380= [HW,SCSI] ncr53c400= [HW,SCSI] ncr53c400a= [HW,SCSI] ncr53c406a= [HW,SCSI] ncr53c8xx= [HW,SCSI] netdev= [NET] Network devices parameters Format: <irq>,<io>,<mem_start>,<mem_end>,<name> Note that mem_start is often overloaded to mean something different and driver-specific. This usage is only documented in each driver source file if at all. nf_conntrack.acct= [NETFILTER] Enable connection tracking flow accounting 0 to disable accounting 1 to enable accounting Default value depends on CONFIG_NF_CT_ACCT that is going to be removed in 2.6.29. nfsaddrs= [NFS] See Documentation/filesystems/nfsroot.txt. nfsroot= [NFS] nfs root filesystem for disk-less boxes. See Documentation/filesystems/nfsroot.txt. nfs.callback_tcpport= [NFS] set the TCP port on which the NFSv4 callback channel should listen. nfs.cache_getent= [NFS] sets the pathname to the program which is used to update the NFS client cache entries. nfs.cache_getent_timeout= [NFS] sets the timeout after which an attempt to update a cache entry is deemed to have failed. nfs.idmap_cache_timeout= [NFS] set the maximum lifetime for idmapper cache entries. nfs.enable_ino64= [NFS] enable 64-bit inode numbers. If zero, the NFS client will fake up a 32-bit inode number for the readdir() and stat() syscalls instead of returning the full 64-bit number. The default is to return 64-bit inode numbers. nmi_debug= [KNL,AVR32,SH] Specify one or more actions to take when a NMI is triggered. Format: [state][,regs][,debounce][,die] nmi_watchdog= [KNL,BUGS=X86] Debugging features for SMP kernels Format: [panic,][num] Valid num: 0,1,2 0 - turn nmi_watchdog off 1 - use the IO-APIC timer for the NMI watchdog 2 - use the local APIC for the NMI watchdog using a performance counter. Note: This will use one performance counter and the local APIC's performance vector. When panic is specified, panic when an NMI watchdog timeout occurs. This is useful when you use a panic=... timeout and need the box quickly up again. Instead of 1 and 2 it is possible to use the following symbolic names: lapic and ioapic Example: nmi_watchdog=2 or nmi_watchdog=panic,lapic netpoll.carrier_timeout= [NET] Specifies amount of time (in seconds) that netpoll should wait for a carrier. By default netpoll waits 4 seconds. no387 [BUGS=X86-32] Tells the kernel to use the 387 maths emulation library even if a 387 maths coprocessor is present. no_console_suspend [HW] Never suspend the console Disable suspending of consoles during suspend and hibernate operations. Once disabled, debugging messages can reach various consoles while the rest of the system is being put to sleep (ie, while debugging driver suspend/resume hooks). This may not work reliably with all consoles, but is known to work with serial and VGA consoles. noaliencache [MM, NUMA, SLAB] Disables the allocation of alien caches in the slab allocator. Saves per-node memory, but will impact performance. noalign [KNL,ARM] noapic [SMP,APIC] Tells the kernel to not make use of any IOAPICs that may be present in the system. nobats [PPC] Do not use BATs for mapping kernel lowmem on "Classic" PPC cores. nocache [ARM] noclflush [BUGS=X86] Don't use the CLFLUSH instruction nodelayacct [KNL] Disable per-task delay accounting nodisconnect [HW,SCSI,M68K] Disables SCSI disconnects. nodsp [SH] Disable hardware DSP at boot time. noefi [X86] Disable EFI runtime services support. noexec [IA-64] noexec [X86] On X86-32 available only on PAE configured kernels. noexec=on: enable non-executable mappings (default) noexec=off: disable non-executable mappings noexec32 [X86-64] This affects only 32-bit executables. noexec32=on: enable non-executable mappings (default) read doesn't imply executable mappings noexec32=off: disable non-executable mappings read implies executable mappings nofpu [SH] Disable hardware FPU at boot time. nofxsr [BUGS=X86-32] Disables x86 floating point extended register save and restore. The kernel will only save legacy floating-point registers on task switch. noxsave [BUGS=X86] Disables x86 extended register state save and restore using xsave. The kernel will fallback to enabling legacy floating-point and sse state. nohlt [BUGS=ARM,SH] Tells the kernel that the sleep(SH) or wfi(ARM) instruction doesn't work correctly and not to use it. This is also useful when using JTAG debugger. no-hlt [BUGS=X86-32] Tells the kernel that the hlt instruction doesn't work correctly and not to use it. no_file_caps Tells the kernel not to honor file capabilities. The only way then for a file to be executed with privilege is to be setuid root or executed by root. nohalt [IA-64] Tells the kernel not to use the power saving function PAL_HALT_LIGHT when idle. This increases power-consumption. On the positive side, it reduces interrupt wake-up latency, which may improve performance in certain environments such as networked servers or real-time systems. nohz= [KNL] Boottime enable/disable dynamic ticks Valid arguments: on, off Default: on noiotrap [SH] Disables trapped I/O port accesses. noirqdebug [X86-32] Disables the code which attempts to detect and disable unhandled interrupt sources. no_timer_check [X86,APIC] Disables the code which tests for broken timer IRQ sources. noisapnp [ISAPNP] Disables ISA PnP code. noinitrd [RAM] Tells the kernel not to load any configured initial RAM disk. nointremap [X86-64, Intel-IOMMU] Do not enable interrupt remapping. nointroute [IA-64] nojitter [IA64] Disables jitter checking for ITC timers. nolapic [X86-32,APIC] Do not enable or use the local APIC. nolapic_timer [X86-32,APIC] Do not use the local APIC timer. noltlbs [PPC] Do not use large page/tlb entries for kernel lowmem mapping on PPC40x. nomca [IA-64] Disable machine check abort handling nomce [X86-32] Machine Check Exception nomfgpt [X86-32] Disable Multi-Function General Purpose Timer usage (for AMD Geode machines). norandmaps Don't use address space randomization. Equivalent to echo 0 > /proc/sys/kernel/randomize_va_space noreplace-paravirt [X86-32,PV_OPS] Don't patch paravirt_ops noreplace-smp [X86-32,SMP] Don't replace SMP instructions with UP alternatives noresidual [PPC] Don't use residual data on PReP machines. noresume [SWSUSP] Disables resume and restores original swap space. no-scroll [VGA] Disables scrollback. This is required for the Braillex ib80-piezo Braille reader made by F.H. Papenmeier (Germany). nosbagart [IA-64] nosep [BUGS=X86-32] Disables x86 SYSENTER/SYSEXIT support. nosmp [SMP] Tells an SMP kernel to act as a UP kernel, and disable the IO APIC. legacy for "maxcpus=0". nosoftlockup [KNL] Disable the soft-lockup detector. noswapaccount [KNL] Disable accounting of swap in memory resource controller. (See Documentation/cgroups/memory.txt) nosync [HW,M68K] Disables sync negotiation for all devices. notsc [BUGS=X86-32] Disable Time Stamp Counter nousb [USB] Disable the USB subsystem nowb [ARM] nox2apic [X86-64,APIC] Do not enable x2APIC mode. nptcg= [IA64] Override max number of concurrent global TLB purges which is reported from either PAL_VM_SUMMARY or SAL PALO. nr_uarts= [SERIAL] maximum number of UARTs to be registered. numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA. one of ['zone', 'node', 'default'] can be specified This can be set from sysctl after boot. See Documentation/sysctl/vm.txt for details. ohci1394_dma=early [HW] enable debugging via the ohci1394 driver. See Documentation/debugging-via-ohci1394.txt for more info. olpc_ec_timeout= [OLPC] ms delay when issuing EC commands Rather than timing out after 20 ms if an EC command is not properly ACKed, override the length of the timeout. We have interrupts disabled while waiting for the ACK, so if this is set too high interrupts *may* be lost! opl3= [HW,OSS] Format: <io> oprofile.timer= [HW] Use timer interrupt instead of performance counters oprofile.cpu_type= Force an oprofile cpu type This might be useful if you have an older oprofile userland or if you want common events. Format: { arch_perfmon } arch_perfmon: [X86] Force use of architectural perfmon on Intel CPUs instead of the CPU specific event set. osst= [HW,SCSI] SCSI Tape Driver Format: <buffer_size>,<write_threshold> See also Documentation/scsi/st.txt. panic= [KNL] Kernel behaviour on panic Format: <timeout> parkbd.port= [HW] Parallel port number the keyboard adapter is connected to, default is 0. Format: <parport#> parkbd.mode= [HW] Parallel port keyboard adapter mode of operation, 0 for XT, 1 for AT (default is AT). Format: <mode> parport= [HW,PPT] Specify parallel ports. 0 disables. Format: { 0 | auto | 0xBBB[,IRQ[,DMA]] } Use 'auto' to force the driver to use any IRQ/DMA settings detected (the default is to ignore detected IRQ/DMA settings because of possible conflicts). You can specify the base address, IRQ, and DMA settings; IRQ and DMA should be numbers, or 'auto' (for using detected settings on that particular port), or 'nofifo' (to avoid using a FIFO even if it is detected). Parallel ports are assigned in the order they are specified on the command line, starting with parport0. parport_init_mode= [HW,PPT] Configure VIA parallel port to operate in a specific mode. This is necessary on Pegasos computer where firmware has no options for setting up parallel port mode and sets it to spp. Currently this function knows 686a and 8231 chips. Format: [spp|ps2|epp|ecp|ecpepp] pas2= [HW,OSS] Format: <io>,<irq>,<dma>,<dma16>,<sb_io>,<sb_irq>,<sb_dma>,<sb_dma16> pas16= [HW,SCSI] See header of drivers/scsi/pas16.c. pause_on_oops= Halt all CPUs after the first oops has been printed for the specified number of seconds. This is to be used if your oopses keep scrolling off the screen. pcbit= [HW,ISDN] pcd. [PARIDE] See header of drivers/block/paride/pcd.c. See also Documentation/blockdev/paride.txt. pci=option[,option...] [PCI] various PCI subsystem options: earlydump [X86] dump PCI config space before the kernel changes anything off [X86] don't probe for the PCI bus bios [X86-32] force use of PCI BIOS, don't access the hardware directly. Use this if your machine has a non-standard PCI host bridge. nobios [X86-32] disallow use of PCI BIOS, only direct hardware access methods are allowed. Use this if you experience crashes upon bootup and you suspect they are caused by the BIOS. conf1 [X86] Force use of PCI Configuration Mechanism 1. conf2 [X86] Force use of PCI Configuration Mechanism 2. noaer [PCIE] If the PCIEAER kernel config parameter is enabled, this kernel boot option can be used to disable the use of PCIE advanced error reporting. nodomains [PCI] Disable support for multiple PCI root domains (aka PCI segments, in ACPI-speak). nommconf [X86] Disable use of MMCONFIG for PCI Configuration check_enable_amd_mmconf [X86] check for and enable properly configured MMIO access to PCI config space on AMD family 10h CPU nomsi [MSI] If the PCI_MSI kernel config parameter is enabled, this kernel boot option can be used to disable the use of MSI interrupts system-wide. noioapicquirk [APIC] Disable all boot interrupt quirks. Safety option to keep boot IRQs enabled. This should never be necessary. ioapicreroute [APIC] Enable rerouting of boot IRQs to the primary IO-APIC for bridges that cannot disable boot IRQs. This fixes a source of spurious IRQs when the system masks IRQs. noioapicreroute [APIC] Disable workaround that uses the boot IRQ equivalent of an IRQ that connects to a chipset where boot IRQs cannot be disabled. The opposite of ioapicreroute. biosirq [X86-32] Use PCI BIOS calls to get the interrupt routing table. These calls are known to be buggy on several machines and they hang the machine when used, but on other computers it's the only way to get the interrupt routing table. Try this option if the kernel is unable to allocate IRQs or discover secondary PCI buses on your motherboard. rom [X86] Assign address space to expansion ROMs. Use with caution as certain devices share address decoders between ROMs and other resources. norom [X86] Do not assign address space to expansion ROMs that do not already have BIOS assigned address ranges. irqmask=0xMMMM [X86] Set a bit mask of IRQs allowed to be assigned automatically to PCI devices. You can make the kernel exclude IRQs of your ISA cards this way. pirqaddr=0xAAAAA [X86] Specify the physical address of the PIRQ table (normally generated by the BIOS) if it is outside the F0000h-100000h range. lastbus=N [X86] Scan all buses thru bus #N. Can be useful if the kernel is unable to find your secondary buses and you want to tell it explicitly which ones they are. assign-busses [X86] Always assign all PCI bus numbers ourselves, overriding whatever the firmware may have done. usepirqmask [X86] Honor the possible IRQ mask stored in the BIOS $PIR table. This is needed on some systems with broken BIOSes, notably some HP Pavilion N5400 and Omnibook XE3 notebooks. This will have no effect if ACPI IRQ routing is enabled. noacpi [X86] Do not use ACPI for IRQ routing or for PCI scanning. use_crs [X86] Use _CRS for PCI resource allocation. routeirq Do IRQ routing for all PCI devices. This is normally done in pci_enable_device(), so this option is a temporary workaround for broken drivers that don't call it. skip_isa_align [X86] do not align io start addr, so can handle more pci cards firmware [ARM] Do not re-enumerate the bus but instead just use the configuration from the bootloader. This is currently used on IXP2000 systems where the bus has to be configured a certain way for adjunct CPUs. noearly [X86] Don't do any early type 1 scanning. This might help on some broken boards which machine check when some devices' config space is read. But various workarounds are disabled and some IOMMU drivers will not work. bfsort Sort PCI devices into breadth-first order. This sorting is done to get a device order compatible with older (<= 2.4) kernels. nobfsort Don't sort PCI devices into breadth-first order. cbiosize=nn[KMG] The fixed amount of bus space which is reserved for the CardBus bridge's IO window. The default value is 256 bytes. cbmemsize=nn[KMG] The fixed amount of bus space which is reserved for the CardBus bridge's memory window. The default value is 64 megabytes. resource_alignment= Format: [<order of align>@][<domain>:]<bus>:<slot>.<func>[; ...] Specifies alignment and device to reassign aligned memory resources. If <order of align> is not specified, PAGE_SIZE is used as alignment. PCI-PCI bridge can be specified, if resource windows need to be expanded. ecrc= Enable/disable PCIe ECRC (transaction layer end-to-end CRC checking). bios: Use BIOS/firmware settings. This is the the default. off: Turn ECRC off on: Turn ECRC on. pcie_aspm= [PCIE] Forcibly enable or disable PCIe Active State Power Management. off Disable ASPM. force Enable ASPM even on devices that claim not to support it. WARNING: Forcing ASPM on may cause system lockups. pcmv= [HW,PCMCIA] BadgePAD 4 pd. [PARIDE] See Documentation/blockdev/paride.txt. pdcchassis= [PARISC,HW] Disable/Enable PDC Chassis Status codes at boot time. Format: { 0 | 1 } See arch/parisc/kernel/pdc_chassis.c percpu_alloc= Select which percpu first chunk allocator to use. Currently supported values are "embed" and "page". Archs may support subset or none of the selections. See comments in mm/percpu.c for details on each allocator. This parameter is primarily for debugging and performance comparison. pf. [PARIDE] See Documentation/blockdev/paride.txt. pg. [PARIDE] See Documentation/blockdev/paride.txt. pirq= [SMP,APIC] Manual mp-table setup See Documentation/x86/i386/IO-APIC.txt. plip= [PPT,NET] Parallel port network link Format: { parport<nr> | timid | 0 } See also Documentation/parport.txt. pmtmr= [X86] Manual setup of pmtmr I/O Port. Override pmtimer IOPort with a hex value. e.g. pmtmr=0x508 pnp.debug [PNP] Enable PNP debug messages. This depends on the CONFIG_PNP_DEBUG_MESSAGES option. pnpacpi= [ACPI] { off } pnpbios= [ISAPNP] { on | off | curr | res | no-curr | no-res } pnp_reserve_irq= [ISAPNP] Exclude IRQs for the autoconfiguration pnp_reserve_dma= [ISAPNP] Exclude DMAs for the autoconfiguration pnp_reserve_io= [ISAPNP] Exclude I/O ports for the autoconfiguration Ranges are in pairs (I/O port base and size). pnp_reserve_mem= [ISAPNP] Exclude memory regions for the autoconfiguration. Ranges are in pairs (memory base and size). ports= [IP_VS_FTP] IPVS ftp helper module Default is 21. Up to 8 (IP_VS_APP_MAX_PORTS) ports may be specified. Format: <port>,<port>.... print-fatal-signals= [KNL] debug: print fatal signals print-fatal-signals=1: print segfault info to the kernel console. default: off. printk.time= Show timing data prefixed to each printk message line Format: <bool> (1/Y/y=enable, 0/N/n=disable) processor.max_cstate= [HW,ACPI] Limit processor to maximum C-state max_cstate=9 overrides any DMI blacklist limit. processor.nocst [HW,ACPI] Ignore the _CST method to determine C-states, instead using the legacy FADT method profile= [KNL] Enable kernel profiling via /proc/profile Format: [schedule,]<number> Param: "schedule" - profile schedule points. Param: <number> - step/bucket size as a power of 2 for statistical time based profiling. Param: "sleep" - profile D-state sleeping (millisecs). Requires CONFIG_SCHEDSTATS Param: "kvm" - profile VM exits. prompt_ramdisk= [RAM] List of RAM disks to prompt for floppy disk before loading. See Documentation/blockdev/ramdisk.txt. psmouse.proto= [HW,MOUSE] Highest PS2 mouse protocol extension to probe for; one of (bare|imps|exps|lifebook|any). psmouse.rate= [HW,MOUSE] Set desired mouse report rate, in reports per second. psmouse.resetafter= [HW,MOUSE] Try to reset the device after so many bad packets (0 = never). psmouse.resolution= [HW,MOUSE] Set desired mouse resolution, in dpi. psmouse.smartscroll= [HW,MOUSE] Controls Logitech smartscroll autorepeat. 0 = disabled, 1 = enabled (default). pss= [HW,OSS] Personal Sound System (ECHO ESC614) Format: <io>,<mss_io>,<mss_irq>,<mss_dma>,<mpu_io>,<mpu_irq> pt. [PARIDE] See Documentation/blockdev/paride.txt. pty.legacy_count= [KNL] Number of legacy pty's. Overwrites compiled-in default number. quiet [KNL] Disable most log messages r128= [HW,DRM] raid= [HW,RAID] See Documentation/md.txt. ramdisk_blocksize= [RAM] See Documentation/blockdev/ramdisk.txt. ramdisk_size= [RAM] Sizes of RAM disks in kilobytes See Documentation/blockdev/ramdisk.txt. rcupdate.blimit= [KNL,BOOT] Set maximum number of finished RCU callbacks to process in one batch. rcupdate.qhimark= [KNL,BOOT] Set threshold of queued RCU callbacks over which batch limiting is disabled. rcupdate.qlowmark= [KNL,BOOT] Set threshold of queued RCU callbacks below which batch limiting is re-enabled. rdinit= [KNL] Format: <full_path> Run specified binary instead of /init from the ramdisk, used for early userspace startup. See initrd. reboot= [BUGS=X86-32,BUGS=ARM,BUGS=IA-64] Rebooting mode Format: <reboot_mode>[,<reboot_mode2>[,...]] See arch/*/kernel/reboot.c or arch/*/kernel/process.c relax_domain_level= [KNL, SMP] Set scheduler's default relax_domain_level. See Documentation/cgroups/cpusets.txt. reserve= [KNL,BUGS] Force the kernel to ignore some iomem area reservetop= [X86-32] Format: nn[KMG] Reserves a hole at the top of the kernel virtual address space. reset_devices [KNL] Force drivers to reset the underlying device during initialization. resume= [SWSUSP] Specify the partition device for software suspend resume_offset= [SWSUSP] Specify the offset from the beginning of the partition given by "resume=" at which the swap header is located, in <PAGE_SIZE> units (needed only for swap files). See Documentation/power/swsusp-and-swap-files.txt retain_initrd [RAM] Keep initrd memory after extraction rhash_entries= [KNL,NET] Set number of hash buckets for route cache riscom8= [HW,SERIAL] Format: <io_board1>[,<io_board2>[,...<io_boardN>]] ro [KNL] Mount root device read-only on boot root= [KNL] Root filesystem rootdelay= [KNL] Delay (in seconds) to pause before attempting to mount the root filesystem rootflags= [KNL] Set root filesystem mount option string rootfstype= [KNL] Set root filesystem type rootwait [KNL] Wait (indefinitely) for root device to show up. Useful for devices that are detected asynchronously (e.g. USB and MMC devices). root_plug.vendor_id= [ROOTPLUG] Override the default vendor ID root_plug.product_id= [ROOTPLUG] Override the default product ID root_plug.debug= [ROOTPLUG] Enable debugging output rw [KNL] Mount root device read-write on boot S [KNL] Run init in single mode sa1100ir [NET] See drivers/net/irda/sa1100_ir.c. sbni= [NET] Granch SBNI12 leased line adapter sc1200wdt= [HW,WDT] SC1200 WDT (watchdog) driver Format: <io>[,<timeout>[,<isapnp>]] scsi_debug_*= [SCSI] See drivers/scsi/scsi_debug.c. scsi_default_dev_flags= [SCSI] SCSI default device flags Format: <integer> scsi_dev_flags= [SCSI] Black/white list entry for vendor and model Format: <vendor>:<model>:<flags> (flags are integer value) scsi_logging_level= [SCSI] a bit mask of logging levels See drivers/scsi/scsi_logging.h for bits. Also settable via sysctl at dev.scsi.logging_level (/proc/sys/dev/scsi/logging_level). There is also a nice 'scsi_logging_level' script in the S390-tools package, available for download at http://www-128.ibm.com/developerworks/linux/linux390/s390-tools-1.5.4.html scsi_mod.scan= [SCSI] sync (default) scans SCSI busses as they are discovered. async scans them in kernel threads, allowing boot to proceed. none ignores them, expecting user space to do the scan. security= [SECURITY] Choose a security module to enable at boot. If this boot parameter is not specified, only the first security module asking for security registration will be loaded. An invalid security module name will be treated as if no module has been chosen. selinux= [SELINUX] Disable or enable SELinux at boot time. Format: { "0" | "1" } See security/selinux/Kconfig help text. 0 -- disable. 1 -- enable. Default value is set via kernel config option. If enabled at boot time, /selinux/disable can be used later to disable prior to initial policy load. serialnumber [BUGS=X86-32] shapers= [NET] Maximal number of shapers. show_msr= [x86] show boot-time MSR settings Format: { <integer> } Show boot-time (BIOS-initialized) MSR settings. The parameter means the number of CPUs to show, for example 1 means boot CPU only. sim710= [SCSI,HW] See header of drivers/scsi/sim710.c. simeth= [IA-64] simscsi= slram= [HW,MTD] slub_debug[=options[,slabs]] [MM, SLUB] Enabling slub_debug allows one to determine the culprit if slab objects become corrupted. Enabling slub_debug can create guard zones around objects and may poison objects when not in use. Also tracks the last alloc / free. For more information see Documentation/vm/slub.txt. slub_max_order= [MM, SLUB] Determines the maximum allowed order for slabs. A high setting may cause OOMs due to memory fragmentation. For more information see Documentation/vm/slub.txt. slub_min_objects= [MM, SLUB] The minimum number of objects per slab. SLUB will increase the slab order up to slub_max_order to generate a sufficiently large slab able to contain the number of objects indicated. The higher the number of objects the smaller the overhead of tracking slabs and the less frequently locks need to be acquired. For more information see Documentation/vm/slub.txt. slub_min_order= [MM, SLUB] Determines the mininum page order for slabs. Must be lower than slub_max_order. For more information see Documentation/vm/slub.txt. slub_nomerge [MM, SLUB] Disable merging of slabs with similar size. May be necessary if there is some reason to distinguish allocs to different slabs. Debug options disable merging on their own. For more information see Documentation/vm/slub.txt. smart2= [HW] Format: <io1>[,<io2>[,...,<io8>]] smp-alt-once [X86-32,SMP] On a hotplug CPU system, only attempt to substitute SMP alternatives once at boot. smsc-ircc2.nopnp [HW] Don't use PNP to discover SMC devices smsc-ircc2.ircc_cfg= [HW] Device configuration I/O port smsc-ircc2.ircc_sir= [HW] SIR base I/O port smsc-ircc2.ircc_fir= [HW] FIR base I/O port smsc-ircc2.ircc_irq= [HW] IRQ line smsc-ircc2.ircc_dma= [HW] DMA channel smsc-ircc2.ircc_transceiver= [HW] Transceiver type: 0: Toshiba Satellite 1800 (GP data pin select) 1: Fast pin select (default) 2: ATC IRMode snd-ad1816a= [HW,ALSA] snd-ad1848= [HW,ALSA] snd-ali5451= [HW,ALSA] snd-als100= [HW,ALSA] snd-als4000= [HW,ALSA] snd-azt2320= [HW,ALSA] snd-cmi8330= [HW,ALSA] snd-cmipci= [HW,ALSA] snd-cs4231= [HW,ALSA] snd-cs4232= [HW,ALSA] snd-cs4236= [HW,ALSA] snd-cs4281= [HW,ALSA] snd-cs46xx= [HW,ALSA] snd-dt019x= [HW,ALSA] snd-dummy= [HW,ALSA] snd-emu10k1= [HW,ALSA] snd-ens1370= [HW,ALSA] snd-ens1371= [HW,ALSA] snd-es968= [HW,ALSA] snd-es1688= [HW,ALSA] snd-es18xx= [HW,ALSA] snd-es1938= [HW,ALSA] snd-es1968= [HW,ALSA] snd-fm801= [HW,ALSA] snd-gusclassic= [HW,ALSA] snd-gusextreme= [HW,ALSA] snd-gusmax= [HW,ALSA] snd-hdsp= [HW,ALSA] snd-ice1712= [HW,ALSA] snd-intel8x0= [HW,ALSA] snd-interwave= [HW,ALSA] snd-interwave-stb= [HW,ALSA] snd-korg1212= [HW,ALSA] snd-maestro3= [HW,ALSA] snd-mpu401= [HW,ALSA] snd-mtpav= [HW,ALSA] snd-nm256= [HW,ALSA] snd-opl3sa2= [HW,ALSA] snd-opti92x-ad1848= [HW,ALSA] snd-opti92x-cs4231= [HW,ALSA] snd-opti93x= [HW,ALSA] snd-pmac= [HW,ALSA] snd-rme32= [HW,ALSA] snd-rme96= [HW,ALSA] snd-rme9652= [HW,ALSA] snd-sb8= [HW,ALSA] snd-sb16= [HW,ALSA] snd-sbawe= [HW,ALSA] snd-serial= [HW,ALSA] snd-sgalaxy= [HW,ALSA] snd-sonicvibes= [HW,ALSA] snd-sun-amd7930= [HW,ALSA] snd-sun-cs4231= [HW,ALSA] snd-trident= [HW,ALSA] snd-usb-audio= [HW,ALSA,USB] snd-via82xx= [HW,ALSA] snd-virmidi= [HW,ALSA] snd-wavefront= [HW,ALSA] snd-ymfpci= [HW,ALSA] softlockup_panic= [KNL] Should the soft-lockup detector generate panics. sonypi.*= [HW] Sony Programmable I/O Control Device driver See Documentation/sonypi.txt specialix= [HW,SERIAL] Specialix multi-serial port adapter See Documentation/serial/specialix.txt. spia_io_base= [HW,MTD] spia_fio_base= spia_pedr= spia_peddr= sscape= [HW,OSS] Format: <io>,<irq>,<dma>,<mpu_io>,<mpu_irq> st= [HW,SCSI] SCSI tape parameters (buffers, etc.) See Documentation/scsi/st.txt. stacktrace [FTRACE] Enabled the stack tracer on boot up. sti= [PARISC,HW] Format: <num> Set the STI (builtin display/keyboard on the HP-PARISC machines) console (graphic card) which should be used as the initial boot-console. See also comment in drivers/video/console/sticore.c. sti_font= [HW] See comment in drivers/video/console/sticore.c. stifb= [HW] Format: bpp:<bpp1>[:<bpp2>[:<bpp3>...]] sunrpc.min_resvport= sunrpc.max_resvport= [NFS,SUNRPC] SunRPC servers often require that client requests originate from a privileged port (i.e. a port in the range 0 < portnr < 1024). An administrator who wishes to reserve some of these ports for other uses may adjust the range that the kernel's sunrpc client considers to be privileged using these two parameters to set the minimum and maximum port values. sunrpc.pool_mode= [NFS] Control how the NFS server code allocates CPUs to service thread pools. Depending on how many NICs you have and where their interrupts are bound, this option will affect which CPUs will do NFS serving. Note: this parameter cannot be changed while the NFS server is running. auto the server chooses an appropriate mode automatically using heuristics global a single global pool contains all CPUs percpu one pool for each CPU pernode one pool for each NUMA node (equivalent to global on non-NUMA machines) sunrpc.tcp_slot_table_entries= sunrpc.udp_slot_table_entries= [NFS,SUNRPC] Sets the upper limit on the number of simultaneous RPC calls that can be sent from the client to a server. Increasing these values may allow you to improve throughput, but will also increase the amount of memory reserved for use by the client. swiotlb= [IA-64] Number of I/O TLB slabs switches= [HW,M68k] sym53c416= [HW,SCSI] See header of drivers/scsi/sym53c416.c. sysrq_always_enabled [KNL] Ignore sysrq setting - this boot parameter will neutralize any effect of /proc/sys/kernel/sysrq. Useful for debugging. t128= [HW,SCSI] See header of drivers/scsi/t128.c. tdfx= [HW,DRM] test_suspend= [SUSPEND] Specify "mem" (for Suspend-to-RAM) or "standby" (for standby suspend) as the system sleep state to briefly enter during system startup. The system is woken from this state using a wakeup-capable RTC alarm. thash_entries= [KNL,NET] Set number of hash buckets for TCP connection thermal.act= [HW,ACPI] -1: disable all active trip points in all thermal zones <degrees C>: override all lowest active trip points thermal.crt= [HW,ACPI] -1: disable all critical trip points in all thermal zones <degrees C>: override all critical trip points thermal.nocrt= [HW,ACPI] Set to disable actions on ACPI thermal zone critical and hot trip points. thermal.off= [HW,ACPI] 1: disable ACPI thermal control thermal.psv= [HW,ACPI] -1: disable all passive trip points <degrees C>: override all passive trip points to this value thermal.tzp= [HW,ACPI] Specify global default ACPI thermal zone polling rate <deci-seconds>: poll all this frequency 0: no polling (default) tmscsim= [HW,SCSI] See comment before function dc390_setup() in drivers/scsi/tmscsim.c. topology= [S390] Format: {off | on} Specify if the kernel should make use of the cpu topology informations if the hardware supports these. The scheduler will make use of these informations and e.g. base its process migration decisions on it. Default is off. tp720= [HW,PS2] trace_buf_size=nn[KMG] [FTRACE] will set tracing buffer size. trace_event=[event-list] [FTRACE] Set and start specified trace events in order to facilitate early boot debugging. See also Documentation/trace/events.txt trix= [HW,OSS] MediaTrix AudioTrix Pro Format: <io>,<irq>,<dma>,<dma2>,<sb_io>,<sb_irq>,<sb_dma>,<mpu_io>,<mpu_irq> tsc= Disable clocksource-must-verify flag for TSC. Format: <string> [x86] reliable: mark tsc clocksource as reliable, this disables clocksource verification at runtime. Used to enable high-resolution timer mode on older hardware, and in virtualized environment. turbografx.map[2|3]= [HW,JOY] TurboGraFX parallel port interface Format: <port#>,<js1>,<js2>,<js3>,<js4>,<js5>,<js6>,<js7> See also Documentation/input/joystick-parport.txt u14-34f= [HW,SCSI] UltraStor 14F/34F SCSI host adapter See header of drivers/scsi/u14-34f.c. uart401= [HW,OSS] Format: <io>,<irq> uart6850= [HW,OSS] Format: <io>,<irq> uhci-hcd.ignore_oc= [USB] Ignore overcurrent events (default N). Some badly-designed motherboards generate lots of bogus events, for ports that aren't wired to anything. Set this parameter to avoid log spamming. Note that genuine overcurrent events won't be reported either. unknown_nmi_panic [X86] Set unknown_nmi_panic=1 early on boot. usbcore.autosuspend= [USB] The autosuspend time delay (in seconds) used for newly-detected USB devices (default 2). This is the time required before an idle device will be autosuspended. Devices for which the delay is set to a negative value won't be autosuspended at all. usbcore.usbfs_snoop= [USB] Set to log all usbfs traffic (default 0 = off). usbcore.blinkenlights= [USB] Set to cycle leds on hubs (default 0 = off). usbcore.old_scheme_first= [USB] Start with the old device initialization scheme (default 0 = off). usbcore.use_both_schemes= [USB] Try the other device initialization scheme if the first one fails (default 1 = enabled). usbcore.initial_descriptor_timeout= [USB] Specifies timeout for the initial 64-byte USB_REQ_GET_DESCRIPTOR request in milliseconds (default 5000 = 5.0 seconds). usbhid.mousepoll= [USBHID] The interval which mice are to be polled at. usb-storage.delay_use= [UMS] The delay in seconds before a new device is scanned for Logical Units (default 5). usb-storage.quirks= [UMS] A list of quirks entries to supplement or override the built-in unusual_devs list. List entries are separated by commas. Each entry has the form VID:PID:Flags where VID and PID are Vendor and Product ID values (4-digit hex numbers) and Flags is a set of characters, each corresponding to a common usb-storage quirk flag as follows: a = SANE_SENSE (collect more than 18 bytes of sense data); c = FIX_CAPACITY (decrease the reported device capacity by one sector); h = CAPACITY_HEURISTICS (decrease the reported device capacity by one sector if the number is odd); i = IGNORE_DEVICE (don't bind to this device); l = NOT_LOCKABLE (don't try to lock and unlock ejectable media); m = MAX_SECTORS_64 (don't transfer more than 64 sectors = 32 KB at a time); o = CAPACITY_OK (accept the capacity reported by the device); r = IGNORE_RESIDUE (the device reports bogus residue values); s = SINGLE_LUN (the device has only one Logical Unit); w = NO_WP_DETECT (don't test whether the medium is write-protected). Example: quirks=0419:aaf5:rl,0421:0433:rc vdso= [X86,SH] vdso=2: enable compat VDSO (default with COMPAT_VDSO) vdso=1: enable VDSO (default) vdso=0: disable VDSO mapping vdso32= [X86] vdso32=2: enable compat VDSO (default with COMPAT_VDSO) vdso32=1: enable 32-bit VDSO (default) vdso32=0: disable 32-bit VDSO mapping vector= [IA-64,SMP] vector=percpu: enable percpu vector domain video= [FB] Frame buffer configuration See Documentation/fb/modedb.txt. vga= [BOOT,X86-32] Select a particular video mode See Documentation/x86/boot.txt and Documentation/svga.txt. Use vga=ask for menu. This is actually a boot loader parameter; the value is passed to the kernel using a special protocol. vmalloc=nn[KMG] [KNL,BOOT] Forces the vmalloc area to have an exact size of <nn>. This can be used to increase the minimum size (128MB on x86). It can also be used to decrease the size and leave more room for directly mapped kernel RAM. vmhalt= [KNL,S390] Perform z/VM CP command after system halt. Format: <command> vmpanic= [KNL,S390] Perform z/VM CP command after kernel panic. Format: <command> vmpoff= [KNL,S390] Perform z/VM CP command after power off. Format: <command> vt.default_blu= [VT] Format: <blue0>,<blue1>,<blue2>,...,<blue15> Change the default blue palette of the console. This is a 16-member array composed of values ranging from 0-255. vt.default_grn= [VT] Format: <green0>,<green1>,<green2>,...,<green15> Change the default green palette of the console. This is a 16-member array composed of values ranging from 0-255. vt.default_red= [VT] Format: <red0>,<red1>,<red2>,...,<red15> Change the default red palette of the console. This is a 16-member array composed of values ranging from 0-255. vt.default_utf8= [VT] Format=<0|1> Set system-wide default UTF-8 mode for all tty's. Default is 1, i.e. UTF-8 mode is enabled for all newly opened terminals. waveartist= [HW,OSS] Format: <io>,<irq>,<dma>,<dma2> wd33c93= [HW,SCSI] See header of drivers/scsi/wd33c93.c. wd7000= [HW,SCSI] See header of drivers/scsi/wd7000.c. wdt= [WDT] Watchdog See Documentation/watchdog/wdt.txt. x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of default x2apic cluster mode on platforms supporting x2apic. xd= [HW,XT] Original XT pre-IDE (RLL encoded) disks. xd_geo= See header of drivers/block/xd.c. xirc2ps_cs= [NET,PCMCIA] Format: <irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]] ______________________________________________________________________ TODO: Add documentation for ALSA options. Add more DRM drivers.