accept_memory=eager can be used to accept all memory
at once during boot.
- acpi= [HW,ACPI,X86,ARM64,RISCV64]
+ acpi= [HW,ACPI,X86,ARM64,RISCV64,EARLY]
Advanced Configuration and Power Interface
Format: { force | on | off | strict | noirq | rsdt |
copy_dsdt }
See also Documentation/power/runtime_pm.rst, pci=noacpi
- acpi_apic_instance= [ACPI, IOAPIC]
+ acpi_apic_instance= [ACPI,IOAPIC,EARLY]
Format: <int>
2: use 2nd APIC table, if available
1,0: use 1st APIC table
If set to native, use the device's native backlight mode.
If set to none, disable the ACPI backlight interface.
- acpi_force_32bit_fadt_addr
+ acpi_force_32bit_fadt_addr [ACPI,EARLY]
force FADT to use 32 bit addresses rather than the
64 bit X_* addresses. Some firmware have broken 64
bit addresses for force ACPI ignore these and use
no: ACPI OperationRegions are not marked as reserved,
no further checks are performed.
- acpi_force_table_verification [HW,ACPI]
+ acpi_force_table_verification [HW,ACPI,EARLY]
Enable table checksum verification during early stage.
By default, this is disabled due to x86 early mapping
size limitation.
acpi_no_memhotplug [ACPI] Disable memory hotplug. Useful for kdump
kernels.
- acpi_no_static_ssdt [HW,ACPI]
+ acpi_no_static_ssdt [HW,ACPI,EARLY]
Disable installation of static SSDTs at early boot time
By default, SSDTs contained in the RSDT/XSDT will be
installed automatically and they will appear under
Ignore the ACPI-based watchdog interface (WDAT) and let
a native driver control the watchdog device instead.
- acpi_rsdp= [ACPI,EFI,KEXEC]
+ acpi_rsdp= [ACPI,EFI,KEXEC,EARLY]
Pass the RSDP address to the kernel, mostly used
on machines running EFI runtime service to boot the
second kernel for kdump.
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
+ acpi_sci= [HW,ACPI,EARLY] ACPI System Control Interrupt trigger mode
Format: { level | edge | high | low }
- acpi_skip_timer_override [HW,ACPI]
+ acpi_skip_timer_override [HW,ACPI,EARLY]
Recognize and ignore IRQ0/pin2 Interrupt Override.
For broken nForce2 BIOS resulting in XT-PIC timer.
behave incorrectly in some ways with respect to system
suspend and resume to be ignored (use wisely).
- acpi_use_timer_override [HW,ACPI]
+ acpi_use_timer_override [HW,ACPI,EARLY]
Use timer override. For some broken Nvidia NF5 boards
that require a timer override, but don't have HPET
- add_efi_memmap [EFI; X86] Include EFI memory map in
+ add_efi_memmap [EFI,X86,EARLY] Include EFI memory map in
kernel's map of available physical RAM.
agp= [AGP]
do not want to use tracing_snapshot_alloc() as it needs
to be done where GFP_KERNEL allocations are allowed.
- allow_mismatched_32bit_el0 [ARM64]
+ allow_mismatched_32bit_el0 [ARM64,EARLY]
Allow execve() of 32-bit applications and setting of the
PER_LINUX32 personality on systems where only a strict
subset of the CPUs support 32-bit EL0. When this
This mode requires kvm-amd.avic=1.
(Default when IOMMU HW support is present.)
- amd_pstate= [X86]
+ amd_pstate= [X86,EARLY]
disable
Do not enable amd_pstate as the default
scaling driver for the supported processors
not play well with APC CPU idle - disable it if you have
APC and your system crashes randomly.
- apic= [APIC,X86] Advanced Programmable Interrupt Controller
+ apic= [APIC,X86,EARLY] Advanced Programmable Interrupt Controller
Change the output verbosity while booting
Format: { quiet (default) | verbose | debug }
Change the amount of debugging information output
Format: apic=driver_name
Examples: apic=bigsmp
- apic_extnmi= [APIC,X86] External NMI delivery setting
+ apic_extnmi= [APIC,X86,EARLY] External NMI delivery setting
Format: { bsp (default) | all | none }
bsp: External NMI is delivered only to CPU 0
all: External NMIs are broadcast to all CPUs as a
bert_disable [ACPI]
Disable BERT OS support on buggy BIOSes.
- bgrt_disable [ACPI][X86]
+ bgrt_disable [ACPI,X86,EARLY]
Disable BGRT to avoid flickering OEM logo.
blkdevparts= Manual partition parsing of block device(s) for
embedded devices based on command line input.
See Documentation/block/cmdline-partition.rst
- boot_delay= Milliseconds to delay each printk during boot.
+ boot_delay= [KNL,EARLY]
+ Milliseconds to delay each printk during boot.
Only works if CONFIG_BOOT_PRINTK_DELAY is enabled,
and you may also have to specify "lpj=". Boot_delay
values larger than 10 seconds (10000) are assumed
erroneous and ignored.
Format: integer
- bootconfig [KNL]
+ bootconfig [KNL,EARLY]
Extended command line options can be added to an initrd
and this will cause the kernel to look for it.
trust validation.
format: { id:<keyid> | builtin }
- cca= [MIPS] Override the kernel pages' cache coherency
+ cca= [MIPS,EARLY] Override the kernel pages' cache coherency
algorithm. Accepted values range from 0 to 7
inclusive. See arch/mips/include/asm/pgtable-bits.h
for platform specific values (SB1, Loongson3 and
[X86-64] hpet,tsc
clocksource.arm_arch_timer.evtstrm=
- [ARM,ARM64]
+ [ARM,ARM64,EARLY]
Format: <bool>
Enable/disable the eventstream feature of the ARM
architected timer so that code using WFE-based polling
10 seconds when built into the kernel.
cma=nn[MG]@[start[MG][-end[MG]]]
- [KNL,CMA]
+ [KNL,CMA,EARLY]
Sets the size of kernel global memory area for
contiguous memory allocations and optionally the
placement constraint by the physical address range of
kernel/dma/contiguous.c
cma_pernuma=nn[MG]
- [KNL,CMA]
+ [KNL,CMA,EARLY]
Sets the size of kernel per-numa memory area for
contiguous memory allocations. A value of 0 disables
per-numa CMA altogether. And If this option is not
they will fallback to the global default memory area.
numa_cma=<node>:nn[MG][,<node>:nn[MG]]
- [KNL,CMA]
+ [KNL,CMA,EARLY]
Sets the size of kernel numa memory area for
contiguous memory allocations. It will reserve CMA
area for the specified node.
a hypervisor.
Default: yes
- coherent_pool=nn[KMG] [ARM,KNL]
+ coherent_pool=nn[KMG] [ARM,KNL,EARLY]
Sets the size of memory pool for coherent, atomic dma
allocations, by default set to 256K.
condev= [HW,S390] console device
conmode=
- con3215_drop= [S390] 3215 console drop mode.
+ con3215_drop= [S390,EARLY] 3215 console drop mode.
Format: y|n|Y|N|1|0
When set to true, drop data on the 3215 console when
the console buffer is full. In this case the
kernel before the cpufreq driver probes.
cpu_init_udelay=N
- [X86] Delay for N microsec between assert and de-assert
+ [X86,EARLY] Delay for N microsec between assert and de-assert
of APIC INIT to start processors. This delay occurs
on every CPU online, such as boot, and resume from suspend.
Default: 10000
kernel more unstable.
crashkernel=size[KMG][@offset[KMG]]
- [KNL] Using kexec, Linux can switch to a 'crash kernel'
+ [KNL,EARLY] Using kexec, Linux can switch to a 'crash kernel'
upon panic. This parameter reserves the physical
memory region [offset, offset + size] for that kernel
image. If '@offset' is omitted, then a suitable offset
is selected automatically.
- [KNL, X86-64, ARM64, RISCV] Select a region under 4G first, and
- fall back to reserve region above 4G when '@offset'
- hasn't been specified.
+ [KNL, X86-64, ARM64, RISCV, LoongArch] Select a region
+ under 4G first, and fall back to reserve region above
+ 4G when '@offset' hasn't been specified.
See Documentation/admin-guide/kdump/kdump.rst for further details.
crashkernel=range1:size1[,range2:size2,...][@offset]
Documentation/admin-guide/kdump/kdump.rst for an example.
crashkernel=size[KMG],high
- [KNL, X86-64, ARM64, RISCV] range could be above 4G.
+ [KNL, X86-64, ARM64, RISCV, LoongArch] range could be
+ above 4G.
Allow kernel to allocate physical memory region from top,
so could be above 4G if system have more than 4G ram
installed. Otherwise memory region will be allocated
below 4G, if available.
It will be ignored if crashkernel=X is specified.
crashkernel=size[KMG],low
- [KNL, X86-64, ARM64, RISCV] range under 4G. When crashkernel=X,high
- is passed, kernel could allocate physical memory region
- above 4G, that cause second kernel crash on system
- that require some amount of low memory, e.g. swiotlb
- requires at least 64M+32K low memory, also enough extra
- low memory is needed to make sure DMA buffers for 32-bit
- devices won't run out. Kernel would try to allocate
+ [KNL, X86-64, ARM64, RISCV, LoongArch] range under 4G.
+ When crashkernel=X,high is passed, kernel could allocate
+ physical memory region above 4G, that cause second kernel
+ crash on system that require some amount of low memory,
+ e.g. swiotlb requires at least 64M+32K low memory, also
+ enough extra low memory is needed to make sure DMA buffers
+ for 32-bit devices won't run out. Kernel would try to allocate
default size of memory below 4G automatically. The default
size is platform dependent.
--> x86: max(swiotlb_size_or_default() + 8MiB, 256MiB)
--> arm64: 128MiB
--> riscv: 128MiB
+ --> loongarch: 128MiB
This one lets the user specify own low range under 4G
for second kernel instead.
0: to disable low allocation.
Format: <port#>,<type>
See also Documentation/input/devices/joystick-parport.rst
- debug [KNL] Enable kernel debugging (events log level).
+ debug [KNL,EARLY] Enable kernel debugging (events log level).
debug_boot_weak_hash
- [KNL] Enable printing [hashed] pointers early in the
+ [KNL,EARLY] Enable printing [hashed] pointers early in the
boot sequence. If enabled, we use a weak hash instead
of siphash to hash pointers. Use this option if you are
seeing instances of '(___ptrval___)') and need to see a
will print _a_lot_ more information - normally only
useful to lockdep developers.
- debug_objects [KNL] Enable object debugging
+ debug_objects [KNL,EARLY] Enable object debugging
debug_guardpage_minorder=
- [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this
+ [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this
parameter allows control of the order of pages that will
be intentionally kept free (and hence protected) by the
buddy allocator. Bigger value increase the probability
help tracking down these problems.
debug_pagealloc=
- [KNL] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
+ [KNL,EARLY] When CONFIG_DEBUG_PAGEALLOC is set, this parameter
enables the feature at boot time. By default, it is
disabled and the system will work mostly the same as a
kernel built without CONFIG_DEBUG_PAGEALLOC.
useful to also enable the page_owner functionality.
on: enable the feature
- debugfs= [KNL] This parameter enables what is exposed to userspace
- and debugfs internal clients.
+ debugfs= [KNL,EARLY] This parameter enables what is exposed to
+ userspace and debugfs internal clients.
Format: { on, no-mount, off }
on: All functions are enabled.
no-mount:
dhash_entries= [KNL]
Set number of hash buckets for dentry cache.
- disable_1tb_segments [PPC]
+ disable_1tb_segments [PPC,EARLY]
Disables the use of 1TB hash page table segments. This
causes the kernel to fall back to 256MB segments which
can be useful when debugging issues that require an SLB
disable= [IPV6]
See Documentation/networking/ipv6.rst.
- disable_radix [PPC]
+ disable_radix [PPC,EARLY]
Disable RADIX MMU mode on POWER9
disable_tlbie [PPC]
causing system reset or hang due to sending
INIT from AP to BSP.
- disable_ddw [PPC/PSERIES]
+ disable_ddw [PPC/PSERIES,EARLY]
Disable Dynamic DMA Window support. Use this
to workaround buggy firmware.
disable_ipv6= [IPV6]
See Documentation/networking/ipv6.rst.
- disable_mtrr_cleanup [X86]
+ disable_mtrr_cleanup [X86,EARLY]
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]
+ disable_mtrr_trim [X86, Intel and AMD only,EARLY]
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_timer_pin_1 [X86,EARLY]
Disable PIN 1 of APIC timer
Can be useful to work around chipset bugs.
dscc4.setup= [NET]
- dt_cpu_ftrs= [PPC]
+ dt_cpu_ftrs= [PPC,EARLY]
Format: {"off" | "known"}
Control how the dt_cpu_ftrs device-tree binding is
used for CPU feature discovery and setup (if it
Documentation/admin-guide/dynamic-debug-howto.rst
for details.
- early_ioremap_debug [KNL]
+ early_ioremap_debug [KNL,EARLY]
Enable debug messages in early_ioremap support. This
is useful for tracking down temporary early mappings
which are not unmapped.
- earlycon= [KNL] Output early console device and options.
+ earlycon= [KNL,EARLY] Output early console device and options.
When used with no options, the early console is
determined by stdout-path property in device tree's
address must be provided, and the serial port must
already be setup and configured.
- earlyprintk= [X86,SH,ARM,M68k,S390]
+ earlyprintk= [X86,SH,ARM,M68k,S390,UM,EARLY]
earlyprintk=vga
earlyprintk=sclp
earlyprintk=xen
edd= [EDD]
Format: {"off" | "on" | "skip[mbr]"}
- efi= [EFI]
+ efi= [EFI,EARLY]
Format: { "debug", "disable_early_pci_dma",
"nochunk", "noruntime", "nosoftreserve",
"novamap", "no_disable_early_pci_dma" }
no_disable_early_pci_dma: Leave the busmaster bit set
on all PCI bridges while in the EFI boot stub
- efi_no_storage_paranoia [EFI; X86]
+ efi_no_storage_paranoia [EFI,X86,EARLY]
Using this parameter you can use more than 50% of
your efi variable storage. Use this parameter only if
you are really sure that your UEFI does sane gc and
fulfills the spec otherwise your board may brick.
- efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI; X86]
+ efi_fake_mem= nn[KMG]@ss[KMG]:aa[,nn[KMG]@ss[KMG]:aa,..] [EFI,X86,EARLY]
Add arbitrary attribute to specific memory range by
updating original EFI memory map.
Region of memory which aa attribute is added to is
eisa_irq_edge= [PARISC,HW]
See header of drivers/parisc/eisa.c.
- ekgdboc= [X86,KGDB] Allow early kernel console debugging
+ ekgdboc= [X86,KGDB,EARLY] Allow early kernel console debugging
Format: ekgdboc=kbd
This is designed to be used in conjunction with
See comment before function elanfreq_setup() in
arch/x86/kernel/cpu/cpufreq/elanfreq.c.
- elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390]
+ elfcorehdr=[size[KMG]@]offset[KMG] [PPC,SH,X86,S390,EARLY]
Specifies physical address of start of kernel core
image elf header and optionally the size. Generally
kexec loader will pass this option to capture kernel.
See Documentation/admin-guide/kdump/kdump.rst for details.
- enable_mtrr_cleanup [X86]
+ enable_mtrr_cleanup [X86,EARLY]
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.
Permit 'security.evm' to be updated regardless of
current integrity status.
- early_page_ext [KNL] Enforces page_ext initialization to earlier
+ early_page_ext [KNL,EARLY] Enforces page_ext initialization to earlier
stages so cover more early boot allocations.
Please note that as side effect some optimizations
might be disabled to achieve that (e.g. parallelized
can be changed at run time by the max_graph_depth file
in the tracefs tracing directory. default: 0 (no limit)
- fw_devlink= [KNL] Create device links between consumer and supplier
+ fw_devlink= [KNL,EARLY] Create device links between consumer and supplier
devices by scanning the firmware to infer the
consumer/supplier relationships. This feature is
especially useful when drivers are loaded as modules as
rpm -- Like "on", but also use to order runtime PM.
fw_devlink.strict=<bool>
- [KNL] Treat all inferred dependencies as mandatory
+ [KNL,EARLY] Treat all inferred dependencies as mandatory
dependencies. This only applies for fw_devlink=on|rpm.
Format: <bool>
fw_devlink.sync_state =
- [KNL] When all devices that could probe have finished
+ [KNL,EARLY] When all devices that could probe have finished
probing, this parameter controls what to do with
devices that haven't yet received their sync_state()
calls.
gamma= [HW,DRM]
- gart_fix_e820= [X86-64] disable the fix e820 for K8 GART
+ gart_fix_e820= [X86-64,EARLY] disable the fix e820 for K8 GART
Format: off | on
default: on
gather_data_sampling=
- [X86,INTEL] Control the Gather Data Sampling (GDS)
+ [X86,INTEL,EARLY] Control the Gather Data Sampling (GDS)
mitigation.
Gather Data Sampling is a hardware vulnerability which
(that will set all pages holding image data
during restoration read-only).
- highmem=nn[KMG] [KNL,BOOT] forces the highmem zone to have an exact
+ highmem=nn[KMG] [KNL,BOOT,EARLY] 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.
hlt [BUGS=ARM,SH]
- hostname= [KNL] Set the hostname (aka UTS nodename).
+ hostname= [KNL,EARLY] Set the hostname (aka UTS nodename).
Format: <string>
This allows setting the system's hostname during early
startup. This sets the name returned by gethostname.
Documentation/admin-guide/mm/hugetlbpage.rst.
Format: size[KMG]
- hugetlb_cma= [HW,CMA] The size of a CMA area used for allocation
+ hugetlb_cma= [HW,CMA,EARLY] The size of a CMA area used for allocation
of gigantic hugepages. Or using node format, the size
of a CMA area per node can be specified.
Format: nn[KMGTPE] or (node format)
If specified, z/VM IUCV HVC accepts connections
from listed z/VM user IDs only.
- hv_nopvspin [X86,HYPER_V] Disables the paravirt spinlock optimizations
- which allow the hypervisor to 'idle' the
- guest on lock contention.
+ hv_nopvspin [X86,HYPER_V,EARLY]
+ Disables the paravirt spinlock optimizations
+ which allow the hypervisor to 'idle' the guest
+ on lock contention.
i2c_bus= [HW] Override the default board specific I2C bus speed
or register an additional I2C bus that is not
Format: <io>[,<membase>[,<icn_id>[,<icn_id2>]]]
- idle= [X86]
+ idle= [X86,EARLY]
Format: idle=poll, idle=halt, idle=nomwait
Poll forces a polling idle loop that can slightly
improve the performance of waking up a idle CPU, but
mode generally follows that for the NaN encoding,
except where unsupported by hardware.
- ignore_loglevel [KNL]
+ ignore_loglevel [KNL,EARLY]
Ignore loglevel setting - this will print /all/
kernel messages to the console. Useful for debugging.
We also add it as printk module parameter, so users
unpacking being completed before device_ and
late_ initcalls.
- initrd= [BOOT] Specify the location of the initial ramdisk
+ initrd= [BOOT,EARLY] Specify the location of the initial ramdisk
- initrdmem= [KNL] Specify a physical address and size from which to
+ initrdmem= [KNL,EARLY] Specify a physical address and size from which to
load the initrd. If an initrd is compiled in or
specified in the bootparams, it takes priority over this
setting.
Format: ss[KMG],nn[KMG]
Default is 0, 0
- init_on_alloc= [MM] Fill newly allocated pages and heap objects with
+ init_on_alloc= [MM,EARLY] Fill newly allocated pages and heap objects with
zeroes.
Format: 0 | 1
Default set by CONFIG_INIT_ON_ALLOC_DEFAULT_ON.
- init_on_free= [MM] Fill freed pages and heap objects with zeroes.
+ init_on_free= [MM,EARLY] Fill freed pages and heap objects with zeroes.
Format: 0 | 1
Default set by CONFIG_INIT_ON_FREE_DEFAULT_ON.
0 disables intel_idle and fall back on acpi_idle.
1 to 9 specify maximum depth of C-state.
- intel_pstate= [X86]
+ intel_pstate= [X86,EARLY]
disable
Do not enable intel_pstate as the default
scaling driver for the supported processors
Allow per-logical-CPU P-State performance control limits using
cpufreq sysfs interface
- intremap= [X86-64, Intel-IOMMU]
+ intremap= [X86-64,Intel-IOMMU,EARLY]
on enable Interrupt Remapping (default)
off disable Interrupt Remapping
nosid disable Source ID checking
strict regions from userspace.
relaxed
- iommu= [X86]
+ iommu= [X86,EARLY]
off
force
noforce
nobypass [PPC/POWERNV]
Disable IOMMU bypass, using IOMMU for PCI devices.
- iommu.forcedac= [ARM64, X86] Control IOVA allocation for PCI devices.
+ iommu.forcedac= [ARM64,X86,EARLY] Control IOVA allocation for PCI devices.
Format: { "0" | "1" }
0 - Try to allocate a 32-bit DMA address first, before
falling back to the full range if needed.
forcing Dual Address Cycle for PCI cards supporting
greater than 32-bit addressing.
- iommu.strict= [ARM64, X86, S390] Configure TLB invalidation behaviour
+ iommu.strict= [ARM64,X86,S390,EARLY] Configure TLB invalidation behaviour
Format: { "0" | "1" }
0 - Lazy mode.
Request that DMA unmap operations use deferred
legacy driver-specific options takes precedence.
iommu.passthrough=
- [ARM64, X86] Configure DMA to bypass the IOMMU by default.
+ [ARM64,X86,EARLY] Configure DMA to bypass the IOMMU by default.
Format: { "0" | "1" }
0 - Use IOMMU translation for DMA.
1 - Bypass the IOMMU for DMA.
See comment before marvel_specify_io7 in
arch/alpha/kernel/core_marvel.c.
- io_delay= [X86] I/O delay method
+ io_delay= [X86,EARLY] I/O delay method
0x80
Standard port 0x80 based delay
0xed
ip= [IP_PNP]
See Documentation/admin-guide/nfs/nfsroot.rst.
- ipcmni_extend [KNL] Extend the maximum number of unique System V
+ ipcmni_extend [KNL,EARLY] Extend the maximum number of unique System V
IPC identifiers from 32,768 to 16,777,216.
irqaffinity= [SMP] Set the default irq affinity mask
The argument is a cpu list, as described above.
irqchip.gicv2_force_probe=
- [ARM, ARM64]
+ [ARM,ARM64,EARLY]
Format: <bool>
Force the kernel to look for the second 4kB page
of a GICv2 controller even if the memory range
exposed by the device tree is too small.
irqchip.gicv3_nolpi=
- [ARM, ARM64]
+ [ARM,ARM64,EARLY]
Force the kernel to ignore the availability of
LPIs (and by consequence ITSs). Intended for system
that use the kernel as a bootloader, and thus want
to let secondary kernels in charge of setting up
LPIs.
- irqchip.gicv3_pseudo_nmi= [ARM64]
+ irqchip.gicv3_pseudo_nmi= [ARM64,EARLY]
Enables support for pseudo-NMIs in the kernel. This
requires the kernel to be built with
CONFIG_ARM64_PSEUDO_NMI.
parameter KASAN will print report only for the first
invalid access.
- keep_bootcon [KNL]
+ keep_bootcon [KNL,EARLY]
Do not unregister boot console at start. This is only
useful for debugging when something happens in the window
between unregistering the boot console and initializing
the real console.
- keepinitrd [HW,ARM]
+ keepinitrd [HW,ARM] See retain_initrd.
- kernelcore= [KNL,X86,IA-64,PPC]
+ kernelcore= [KNL,X86,IA-64,PPC,EARLY]
Format: nn[KMGTPE] | nn% | "mirror"
This parameter specifies the amount of memory usable by
the kernel for non-movable allocations. The requested
for Movable pages. "nn[KMGTPE]", "nn%", and "mirror"
are exclusive, so you cannot specify multiple forms.
- kgdbdbgp= [KGDB,HW] kgdb over EHCI usb debug port.
+ kgdbdbgp= [KGDB,HW,EARLY] kgdb over EHCI usb debug port.
Format: <Controller#>[,poll interval]
The controller # is the number of the ehci usb debug
port as it is probed via PCI. The poll interval is
kms, kbd format: kms,kbd
kms, kbd and serial format: kms,kbd,<ser_dev>[,baud]
- kgdboc_earlycon= [KGDB,HW]
+ kgdboc_earlycon= [KGDB,HW,EARLY]
If the boot console provides the ability to read
characters and can work in polling mode, you can use
this parameter to tell kgdb to use it as a backend
blank and the first boot console that implements
read() will be picked.
- kgdbwait [KGDB] Stop kernel execution and enter the
+ kgdbwait [KGDB,EARLY] Stop kernel execution and enter the
kernel debugger at the earliest opportunity.
kmac= [MIPS] Korina ethernet MAC address.
Configure the RouterBoard 532 series on-chip
Ethernet adapter MAC address.
- kmemleak= [KNL] Boot-time kmemleak enable/disable
+ kmemleak= [KNL,EARLY] Boot-time kmemleak enable/disable
Valid arguments: on, off
Default: on
Built with CONFIG_DEBUG_KMEMLEAK_DEFAULT_OFF=y,
See also Documentation/trace/kprobetrace.rst "Kernel
Boot Parameter" section.
- kpti= [ARM64] Control page table isolation of user
- and kernel address spaces.
+ kpti= [ARM64,EARLY] Control page table isolation of
+ user and kernel address spaces.
Default: enabled on cores which need mitigation.
0: force disabled
1: force enabled
for NPT.
kvm-arm.mode=
- [KVM,ARM] Select one of KVM/arm64's modes of operation.
+ [KVM,ARM,EARLY] Select one of KVM/arm64's modes of
+ operation.
none: Forcefully disable KVM.
used with extreme caution.
kvm-arm.vgic_v3_group0_trap=
- [KVM,ARM] Trap guest accesses to GICv3 group-0
+ [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-0
system registers
kvm-arm.vgic_v3_group1_trap=
- [KVM,ARM] Trap guest accesses to GICv3 group-1
+ [KVM,ARM,EARLY] Trap guest accesses to GICv3 group-1
system registers
kvm-arm.vgic_v3_common_trap=
- [KVM,ARM] Trap guest accesses to GICv3 common
+ [KVM,ARM,EARLY] Trap guest accesses to GICv3 common
system registers
kvm-arm.vgic_v4_enable=
- [KVM,ARM] Allow use of GICv4 for direct injection of
- LPIs.
+ [KVM,ARM,EARLY] Allow use of GICv4 for direct
+ injection of LPIs.
- kvm_cma_resv_ratio=n [PPC]
+ kvm_cma_resv_ratio=n [PPC,EARLY]
Reserves given percentage from system memory area for
contiguous memory allocation for KVM hash pagetable
allocation.
(enabled). Disable by KVM if hardware lacks support
for it.
- l1d_flush= [X86,INTEL]
+ l1d_flush= [X86,INTEL,EARLY]
Control mitigation for L1D based snooping vulnerability.
Certain CPUs are vulnerable to an exploit against CPU
on - enable the interface for the mitigation
- l1tf= [X86] Control mitigation of the L1TF vulnerability on
+ l1tf= [X86,EARLY] Control mitigation of the L1TF vulnerability on
affected CPUs
The kernel PTE inversion protection is unconditionally
l3cr= [PPC]
- lapic [X86-32,APIC] Enable the local APIC even if BIOS
+ lapic [X86-32,APIC,EARLY] Enable the local APIC even if BIOS
disabled it.
lapic= [X86,APIC] Do not use TSC deadline
back to the programmable timer unit in the LAPIC.
Format: notscdeadline
- lapic_timer_c2_ok [X86,APIC] trust the local apic timer
+ lapic_timer_c2_ok [X86,APIC,EARLY] trust the local apic timer
in C2 power state.
libata.dma= [LIBATA] DMA control
lockd.nlm_udpport=M [NFS] Assign UDP port.
Format: <integer>
- lockdown= [SECURITY]
+ lockdown= [SECURITY,EARLY]
{ integrity | confidentiality }
Enable the kernel lockdown feature. If set to
integrity, kernel features that allow userland to
logibm.irq= [HW,MOUSE] Logitech Bus Mouse Driver
Format: <irq>
- loglevel= All Kernel Messages with a loglevel smaller than the
+ loglevel= [KNL,EARLY]
+ 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:
6 (KERN_INFO) informational
7 (KERN_DEBUG) debug-level messages
- log_buf_len=n[KMG] Sets the size of the printk ring buffer,
- in bytes. n must be a power of two and greater
- than the minimal size. The minimal size is defined
- by LOG_BUF_SHIFT kernel config parameter. There is
- also CONFIG_LOG_CPU_MAX_BUF_SHIFT config parameter
- that allows to increase the default size depending on
- the number of CPUs. See init/Kconfig for more details.
+ log_buf_len=n[KMG] [KNL,EARLY]
+ Sets the size of the printk ring buffer, in bytes.
+ n must be a power of two and greater than the
+ minimal size. The minimal size is defined by
+ LOG_BUF_SHIFT kernel config parameter. There
+ is also CONFIG_LOG_CPU_MAX_BUF_SHIFT config
+ parameter that allows to increase the default size
+ depending on the number of CPUs. See init/Kconfig
+ for more details.
logo.nologo [FB] Disables display of the built-in Linux logo.
This may be used to provide more screen space for
max_addr=nn[KMG] [KNL,BOOT,IA-64] All physical memory greater
than or equal to this physical address is ignored.
- maxcpus= [SMP] Maximum number of processors that an SMP kernel
+ maxcpus= [SMP,EARLY] Maximum number of processors that an SMP kernel
will bring up during bootup. maxcpus=n : n >= 0 limits
the kernel to bring up 'n' processors. Surely after
bootup you can bring up the other plugged cpu by executing
Format: <first>,<last>
Specifies range of consoles to be captured by the MDA.
- mds= [X86,INTEL]
+ mds= [X86,INTEL,EARLY]
Control mitigation for the Micro-architectural Data
Sampling (MDS) vulnerability.
For details see: Documentation/admin-guide/hw-vuln/mds.rst
- mem=nn[KMG] [HEXAGON] Set the memory size.
+ mem=nn[KMG] [HEXAGON,EARLY] Set the memory size.
Must be specified, otherwise memory size will be 0.
- mem=nn[KMG] [KNL,BOOT] Force usage of a specific amount of memory
- Amount of memory to be used in cases as follows:
+ mem=nn[KMG] [KNL,BOOT,EARLY] Force usage of a specific amount
+ of memory Amount of memory to be used in cases
+ as follows:
1 for test;
2 when the kernel is not able to see the whole system memory;
if system memory of hypervisor is not sufficient.
mem=nn[KMG]@ss[KMG]
- [ARM,MIPS] - override the memory layout reported by
- firmware.
+ [ARM,MIPS,EARLY] - override the memory layout
+ reported by firmware.
Define a memory region of size nn[KMG] starting at
ss[KMG].
Multiple different regions can be specified with
mem=nopentium [BUGS=X86-32] Disable usage of 4MB pages for kernel
memory.
- memblock=debug [KNL] Enable memblock debug messages.
+ memblock=debug [KNL,EARLY] Enable memblock debug messages.
memchunk=nn[KMG]
[KNL,SH] Allow user to override the default size for
option.
See Documentation/admin-guide/mm/memory-hotplug.rst.
- memmap=exactmap [KNL,X86] Enable setting of an exact
+ memmap=exactmap [KNL,X86,EARLY] 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, X86, MIPS, XTENSA] Force usage of a specific region of memory.
+ [KNL, X86,MIPS,XTENSA,EARLY] Force usage of a specific region of memory.
Region of memory to be used is from ss to ss+nn.
If @ss[KMG] is omitted, it is equivalent to mem=nn[KMG],
which limits max address to nn[KMG].
memmap=100M@2G,100M#3G,1G!1024G
memmap=nn[KMG]#ss[KMG]
- [KNL,ACPI] Mark specific memory as ACPI data.
+ [KNL,ACPI,EARLY] Mark specific memory as ACPI data.
Region of memory to be marked is from ss to ss+nn.
memmap=nn[KMG]$ss[KMG]
- [KNL,ACPI] Mark specific memory as reserved.
+ [KNL,ACPI,EARLY] Mark specific memory as reserved.
Region of memory to be reserved is from ss to ss+nn.
Example: Exclude memory from 0x18690000-0x1869ffff
memmap=64K$0x18690000
like Grub2, otherwise '$' and the following number
will be eaten.
- memmap=nn[KMG]!ss[KMG]
+ memmap=nn[KMG]!ss[KMG,EARLY]
[KNL,X86] Mark specific memory as protected.
Region of memory to be used, from ss to ss+nn.
The memory region may be marked as e820 type 12 (0xc)
and is NVDIMM or ADR memory.
memmap=<size>%<offset>-<oldtype>+<newtype>
- [KNL,ACPI] Convert memory within the specified region
+ [KNL,ACPI,EARLY] Convert memory within the specified region
from <oldtype> to <newtype>. If "-<oldtype>" is left
out, the whole region will be marked as <newtype>,
even if previously unavailable. If "+<newtype>" is left
specified as e820 types, e.g., 1 = RAM, 2 = reserved,
3 = ACPI, 12 = PRAM.
- memory_corruption_check=0/1 [X86]
+ memory_corruption_check=0/1 [X86,EARLY]
Some BIOSes seem to corrupt the first 64k of
memory when doing things like suspend/resume.
Setting this option will scan the memory
affects the same memory, you can use memmap=
to prevent the kernel from using that memory.
- memory_corruption_check_size=size [X86]
+ memory_corruption_check_size=size [X86,EARLY]
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]
+ memory_corruption_check_period=seconds [X86,EARLY]
By default it checks for corruption every 60
seconds. Use this parameter to check at some
other rate. 0 disables periodic checking.
Note that even when enabled, there are a few cases where
the feature is not effective.
- memtest= [KNL,X86,ARM,M68K,PPC,RISCV] Enable memtest
+ memtest= [KNL,X86,ARM,M68K,PPC,RISCV,EARLY] Enable memtest
Format: <integer>
default : 0 <disable>
Specifies the number of memtest passes to be
https://repo.or.cz/w/linux-2.6/mini2440.git
mitigations=
- [X86,PPC,S390,ARM64] Control optional mitigations for
+ [X86,PPC,S390,ARM64,EARLY] Control optional mitigations for
CPU vulnerabilities. This is a set of curated,
arch-independent options, each of which is an
aggregation of existing arch-specific options.
retbleed=auto,nosmt [X86]
mminit_loglevel=
- [KNL] When CONFIG_DEBUG_MEMORY_INIT is set, this
+ [KNL,EARLY] 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
so loglevel=8 may also need to be specified.
mmio_stale_data=
- [X86,INTEL] Control mitigation for the Processor
+ [X86,INTEL,EARLY] Control mitigation for the Processor
MMIO Stale Data vulnerabilities.
Processor MMIO Stale Data is a class of
mousedev.yres= [MOUSE] Vertical screen resolution, used for devices
reporting absolute coordinates, such as tablets
- movablecore= [KNL,X86,IA-64,PPC]
+ movablecore= [KNL,X86,IA-64,PPC,EARLY]
Format: nn[KMGTPE] | nn%
This parameter is the complement to kernelcore=, it
specifies the amount of memory used for migratable
that the amount of memory usable for all allocations
is not too small.
- movable_node [KNL] Boot-time switch to make hotplugable memory
+ movable_node [KNL,EARLY] Boot-time switch to make hotplugable memory
NUMA nodes to be movable. This means that the memory
of such nodes will be usable only for movable
allocations which rules out almost all kernel
[HW] Make the MicroTouch USB driver use raw coordinates
('y', default) or cooked coordinates ('n')
- mtrr=debug [X86]
+ mtrr=debug [X86,EARLY]
Enable printing debug information related to MTRR
registers at boot time.
- mtrr_chunk_size=nn[KMG] [X86]
+ mtrr_chunk_size=nn[KMG,X86,EARLY]
used for mtrr cleanup. It is largest continuous chunk
that could hold holes aka. UC entries.
- mtrr_gran_size=nn[KMG] [X86]
+ mtrr_gran_size=nn[KMG,X86,EARLY]
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]
+ mtrr_spare_reg_nr=n [X86,EARLY]
Format: <integer>
Range: 0,7 : spare reg number
Default : 1
emulation library even if a 387 maths coprocessor
is present.
- no4lvl [RISCV] Disable 4-level and 5-level paging modes. Forces
- kernel to use 3-level paging instead.
+ no4lvl [RISCV,EARLY] Disable 4-level and 5-level paging modes.
+ Forces kernel to use 3-level paging instead.
- no5lvl [X86-64,RISCV] Disable 5-level paging mode. Forces
+ no5lvl [X86-64,RISCV,EARLY] Disable 5-level paging mode. Forces
kernel to use 4-level paging instead.
noaliencache [MM, NUMA, SLAB] Disables the allocation of alien
noalign [KNL,ARM]
- noaltinstr [S390] Disables alternative instructions patching
- (CPU alternatives feature).
+ noaltinstr [S390,EARLY] Disables alternative instructions
+ patching (CPU alternatives feature).
- noapic [SMP,APIC] Tells the kernel to not make use of any
+ noapic [SMP,APIC,EARLY] Tells the kernel to not make use of any
IOAPICs that may be present in the system.
noautogroup Disable scheduler automatic task group creation.
- nocache [ARM]
+ nocache [ARM,EARLY]
no_console_suspend
[HW] Never suspend the console
turn on/off it dynamically.
no_debug_objects
- [KNL] Disable object debugging
+ [KNL,EARLY] Disable object debugging
nodsp [SH] Disable hardware DSP at boot time.
- noefi Disable EFI runtime services support.
+ noefi [EFI,EARLY] Disable EFI runtime services support.
- no_entry_flush [PPC] Don't flush the L1-D cache when entering the kernel.
+ no_entry_flush [PPC,EARLY] Don't flush the L1-D cache when entering the kernel.
noexec [IA-64]
real-time systems.
no_hash_pointers
+ [KNL,EARLY]
Force pointers printed to the console or buffers to be
unhashed. By default, when a pointer is printed via %p
format string, that pointer is "hashed", i.e. obscured
the impact of the sleep instructions. This is also
useful when using JTAG debugger.
- nohugeiomap [KNL,X86,PPC,ARM64] Disable kernel huge I/O mappings.
+ nohugeiomap [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge I/O mappings.
- nohugevmalloc [KNL,X86,PPC,ARM64] Disable kernel huge vmalloc mappings.
+ nohugevmalloc [KNL,X86,PPC,ARM64,EARLY] Disable kernel huge vmalloc mappings.
nohz= [KNL] Boottime enable/disable dynamic ticks
Valid arguments: on, off
noinitrd [RAM] Tells the kernel not to load any configured
initial RAM disk.
- nointremap [X86-64, Intel-IOMMU] Do not enable interrupt
+ nointremap [X86-64,Intel-IOMMU,EARLY] Do not enable interrupt
remapping.
[Deprecated - use intremap=off]
nointroute [IA-64]
- noinvpcid [X86] Disable the INVPCID cpu feature.
+ noinvpcid [X86,EARLY] Disable the INVPCID cpu feature.
noiotrap [SH] Disables trapped I/O port accesses.
nojitter [IA-64] Disables jitter checking for ITC timers.
- nokaslr [KNL]
+ nokaslr [KNL,EARLY]
When CONFIG_RANDOMIZE_BASE is set, this disables
kernel and module base offset ASLR (Address Space
Layout Randomization).
- no-kvmapf [X86,KVM] Disable paravirtualized asynchronous page
+ no-kvmapf [X86,KVM,EARLY] Disable paravirtualized asynchronous page
fault handling.
- no-kvmclock [X86,KVM] Disable paravirtualized KVM clock driver
+ no-kvmclock [X86,KVM,EARLY] Disable paravirtualized KVM clock driver
- nolapic [X86-32,APIC] Do not enable or use the local APIC.
+ nolapic [X86-32,APIC,EARLY] Do not enable or use the local APIC.
- nolapic_timer [X86-32,APIC] Do not use the local APIC timer.
+ nolapic_timer [X86-32,APIC,EARLY] Do not use the local APIC timer.
nomca [IA-64] Disable machine check abort handling
shutdown the other cpus. Instead use the REBOOT_VECTOR
irq.
- nopat [X86] Disable PAT (page attribute table extension of
+ nopat [X86,EARLY] Disable PAT (page attribute table extension of
pagetables) support.
- nopcid [X86-64] Disable the PCID cpu feature.
+ nopcid [X86-64,EARLY] Disable the PCID cpu feature.
nopku [X86] Disable Memory Protection Keys CPU feature found
in some Intel CPUs.
- nopti [X86-64]
+ nopti [X86-64,EARLY]
Equivalent to pti=off
- nopv= [X86,XEN,KVM,HYPER_V,VMWARE]
+ nopv= [X86,XEN,KVM,HYPER_V,VMWARE,EARLY]
Disables the PV optimizations forcing the guest to run
as generic guest with no PV drivers. Currently support
XEN HVM, KVM, HYPER_V and VMWARE guest.
- nopvspin [X86,XEN,KVM]
+ nopvspin [X86,XEN,KVM,EARLY]
Disables the qspinlock slow path using PV optimizations
which allow the hypervisor to 'idle' the guest on lock
contention.
This is required for the Braillex ib80-piezo Braille
reader made by F.H. Papenmeier (Germany).
- nosgx [X86-64,SGX] Disables Intel SGX kernel support.
+ nosgx [X86-64,SGX,EARLY] Disables Intel SGX kernel support.
- nosmap [PPC]
+ nosmap [PPC,EARLY]
Disable SMAP (Supervisor Mode Access Prevention)
even if it is supported by processor.
- nosmep [PPC64s]
+ nosmep [PPC64s,EARLY]
Disable SMEP (Supervisor Mode Execution Prevention)
even if it is supported by processor.
- nosmp [SMP] Tells an SMP kernel to act as a UP kernel,
+ nosmp [SMP,EARLY] Tells an SMP kernel to act as a UP kernel,
and disable the IO APIC. legacy for "maxcpus=0".
- nosmt [KNL,MIPS,PPC,S390] Disable symmetric multithreading (SMT).
+ nosmt [KNL,MIPS,PPC,S390,EARLY] Disable symmetric multithreading (SMT).
Equivalent to smt=1.
[KNL,X86,PPC] Disable symmetric multithreading (SMT).
nosoftlockup [KNL] Disable the soft-lockup detector.
nospec_store_bypass_disable
- [HW] Disable all mitigations for the Speculative Store Bypass vulnerability
+ [HW,EARLY] Disable all mitigations for the Speculative
+ Store Bypass vulnerability
- nospectre_bhb [ARM64] Disable all mitigations for Spectre-BHB (branch
+ nospectre_bhb [ARM64,EARLY] Disable all mitigations for Spectre-BHB (branch
history injection) vulnerability. System may allow data leaks
with this option.
- nospectre_v1 [X86,PPC] Disable mitigations for Spectre Variant 1
+ nospectre_v1 [X86,PPC,EARLY] Disable mitigations for Spectre Variant 1
(bounds check bypass). With this option data leaks are
possible in the system.
- nospectre_v2 [X86,PPC_E500,ARM64] Disable all mitigations for
- the Spectre variant 2 (indirect branch prediction)
- vulnerability. System may allow data leaks with this
- option.
+ nospectre_v2 [X86,PPC_E500,ARM64,EARLY] Disable all mitigations
+ for the Spectre variant 2 (indirect branch
+ prediction) vulnerability. System may allow data
+ leaks with this option.
- no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES] Disable paravirtualized
- steal time accounting. steal time is computed, but
- won't influence scheduler behaviour
+ no-steal-acc [X86,PV_OPS,ARM64,PPC/PSERIES,RISCV,EARLY] Disable
+ paravirtualized steal time accounting. steal time is
+ computed, but won't influence scheduler behaviour
nosync [HW,M68K] Disables sync negotiation for all devices.
broken timer IRQ sources.
no_uaccess_flush
- [PPC] Don't flush the L1-D cache after accessing user data.
+ [PPC,EARLY] Don't flush the L1-D cache after accessing user data.
novmcoredd [KNL,KDUMP]
Disable device dump. Device dump allows drivers to
is set.
no-vmw-sched-clock
- [X86,PV_OPS] Disable paravirtualized VMware scheduler
- clock and use the default one.
+ [X86,PV_OPS,EARLY] Disable paravirtualized VMware
+ scheduler clock and use the default one.
nowatchdog [KNL] Disable both lockup detectors, i.e.
soft-lockup and NMI watchdog (hard-lockup).
- nowb [ARM]
+ nowb [ARM,EARLY]
- nox2apic [X86-64,APIC] Do not enable x2APIC mode.
+ nox2apic [X86-64,APIC,EARLY] Do not enable x2APIC mode.
NOTE: this parameter will be ignored on systems with the
LEGACY_XAPIC_DISABLED bit set in the
purges which is reported from either PAL_VM_SUMMARY or
SAL PALO.
- nr_cpus= [SMP] Maximum number of processors that an SMP kernel
+ nr_cpus= [SMP,EARLY] Maximum number of processors that an SMP kernel
could support. nr_cpus=n : n >= 1 limits the kernel to
support 'n' processors. It could be larger than the
number of already plugged CPU during bootup, later in
nr_uarts= [SERIAL] maximum number of UARTs to be registered.
- numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86] Disable NUMA, Only
- set up a single NUMA node spanning all memory.
+ numa=off [KNL, ARM64, PPC, RISCV, SPARC, X86, EARLY]
+ Disable NUMA, Only set up a single NUMA node
+ spanning all memory.
numa_balancing= [KNL,ARM64,PPC,RISCV,S390,X86] Enable or disable automatic
NUMA balancing.
This can be set from sysctl after boot.
See Documentation/admin-guide/sysctl/vm.rst for details.
- ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
+ ohci1394_dma=early [HW,EARLY] enable debugging via the ohci1394 driver.
See Documentation/core-api/debugging-via-ohci1394.rst for more
info.
Once locked, the boundary cannot be changed.
1 indicates lock status, 0 indicates unlock status.
- oops=panic Always panic on oopses. Default is to just kill the
+ oops=panic [KNL,EARLY]
+ Always panic on oopses. Default is to just kill the
process, but there is a small probability of
deadlocking the machine.
This will also cause panics on machine check exceptions.
can be read from sysfs at:
/sys/module/page_alloc/parameters/shuffle.
- page_owner= [KNL] Boot-time page_owner enabling option.
+ page_owner= [KNL,EARLY] Boot-time page_owner enabling option.
Storage of the information about who allocated
each page is disabled in default. With this switch,
we can turn it on.
on: enable the feature
- page_poison= [KNL] Boot-time parameter changing the state of
+ page_poison= [KNL,EARLY] Boot-time parameter changing the state of
poisoning on the buddy allocator, available with
CONFIG_PAGE_POISONING=y.
off: turn off poisoning (default)
timeout < 0: reboot immediately
Format: <timeout>
- panic_on_taint= Bitmask for conditionally calling panic() in add_taint()
+ panic_on_taint= [KNL,EARLY]
+ Bitmask for conditionally calling panic() in add_taint()
Format: <hex>[,nousertaint]
Hexadecimal bitmask representing the set of TAINT flags
that will cause the kernel to panic when add_taint() is
pcbit= [HW,ISDN]
- pci=option[,option...] [PCI] various PCI subsystem options.
+ pci=option[,option...] [PCI,EARLY] various PCI subsystem options.
Some options herein operate on a specific device
or a set of devices (<pci_dev>). These are
Format: { 0 | 1 }
See arch/parisc/kernel/pdc_chassis.c
- percpu_alloc= Select which percpu first chunk allocator to use.
+ percpu_alloc= [MM,EARLY]
+ 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
execution priority.
ppc_strict_facility_enable
- [PPC] This option catches any kernel floating point,
+ [PPC,ENABLE] This option catches any kernel floating point,
Altivec, VSX and SPE outside of regions specifically
allowed (eg kernel_enable_fpu()/kernel_disable_fpu()).
There is some performance impact when enabling this.
- ppc_tm= [PPC]
+ ppc_tm= [PPC,EARLY]
Format: {"off"}
Disable Hardware Transactional Memory
[KNL] Number of legacy pty's. Overwrites compiled-in
default number.
- quiet [KNL] Disable most log messages
+ quiet [KNL,EARLY] Disable most log messages
r128= [HW,DRM]
ramdisk_start= [RAM] RAM disk image start address
random.trust_cpu=off
- [KNL] Disable trusting the use of the CPU's
+ [KNL,EARLY] Disable trusting the use of the CPU's
random number generator (if available) to
initialize the kernel's RNG.
random.trust_bootloader=off
- [KNL] Disable trusting the use of the a seed
+ [KNL,EARLY] Disable trusting the use of the a seed
passed by the bootloader (if available) to
initialize the kernel's RNG.
randomize_kstack_offset=
- [KNL] Enable or disable kernel stack offset
+ [KNL,EARLY] Enable or disable kernel stack offset
randomization, which provides roughly 5 bits of
entropy, frustrating memory corruption attacks
that depend on stack address determinism or
this kernel boot parameter, forcibly setting it
to zero.
+ rcutree.enable_rcu_lazy= [KNL]
+ To save power, batch RCU callbacks and flush after
+ delay, memory pressure or callback list growing too
+ big.
+
rcuscale.gp_async= [KNL]
Measure performance of asynchronous
grace-period primitives such as call_rcu().
Run specified binary instead of /init from the ramdisk,
used for early userspace startup. See initrd.
- rdrand= [X86]
+ rdrand= [X86,EARLY]
force - Override the decision by the kernel to hide the
advertisement of RDRAND support (this affects
certain AMD processors because of buggy BIOS
them. If <base> is less than 0x10000, the region
is assumed to be I/O ports; otherwise it is memory.
- reservetop= [X86-32]
+ reservetop= [X86-32,EARLY]
Format: nn[KMG]
Reserves a hole at the top of the kernel virtual
address space.
Useful for devices that are detected asynchronously
(e.g. USB and MMC devices).
- retain_initrd [RAM] Keep initrd memory after extraction
+ retain_initrd [RAM] Keep initrd memory after extraction. After boot, it will
+ be accessible via /sys/firmware/initrd.
retbleed= [X86] Control mitigation of RETBleed (Arbitrary
Speculative Code Execution with Return Instructions)
[KNL] Disable ring 3 MONITOR/MWAIT feature on supported
CPUs.
- riscv_isa_fallback [RISCV]
+ riscv_isa_fallback [RISCV,EARLY]
When CONFIG_RISCV_ISA_FALLBACK is not enabled, permit
falling back to detecting extension support by parsing
"riscv,isa" property on devicetree systems when the
ro [KNL] Mount root device read-only on boot
- rodata= [KNL]
+ rodata= [KNL,EARLY]
on Mark read-only kernel memory as read-only (default).
off Leave read-only kernel memory writable for debugging.
full Mark read-only kernel memory and aliases as read-only
[arm64]
rockchip.usb_uart
+ [EARLY]
Enable the uart passthrough on the designated usb port
on Rockchip SoCs. When active, the signals of the
debug-uart get routed to the D+ and D- pins of the usb
sa1100ir [NET]
See drivers/net/irda/sa1100_ir.c.
- sched_verbose [KNL] Enables verbose scheduler debug messages.
+ sched_verbose [KNL,EARLY] Enables verbose scheduler debug messages.
schedstats= [KNL,X86] Enable or disable scheduled statistics.
Allowed values are enable and disable. This feature
non-zero "wait" parameter. See weight_single
and weight_many.
- skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
+ skew_tick= [KNL,EARLY] Offset the periodic timer tick per cpu to mitigate
xtime_lock contention on larger systems, and/or RCU lock
contention on all systems with CONFIG_MAXSMP set.
Format: { "0" | "1" }
1: Fast pin select (default)
2: ATC IRMode
- smt= [KNL,MIPS,S390] Set the maximum number of threads (logical
- CPUs) to use per physical CPU on systems capable of
- symmetric multithreading (SMT). Will be capped to the
- actual hardware limit.
+ smt= [KNL,MIPS,S390,EARLY] Set the maximum number of threads
+ (logical CPUs) to use per physical CPU on systems
+ capable of symmetric multithreading (SMT). Will
+ be capped to the actual hardware limit.
Format: <integer>
Default: -1 (no limit)
sonypi.*= [HW] Sony Programmable I/O Control Device driver
See Documentation/admin-guide/laptops/sonypi.rst
- spectre_v2= [X86] Control mitigation of Spectre variant 2
+ spectre_v2= [X86,EARLY] Control mitigation of Spectre variant 2
(indirect branch speculation) vulnerability.
The default operation protects the kernel from
user space attacks.
spectre_v2_user=auto.
spec_rstack_overflow=
- [X86] Control RAS overflow mitigation on AMD Zen CPUs
+ [X86,EARLY] Control RAS overflow mitigation on AMD Zen CPUs
off - Disable mitigation
microcode - Enable microcode mitigation only
(cloud-specific mitigation)
spec_store_bypass_disable=
- [HW] Control Speculative Store Bypass (SSB) Disable mitigation
+ [HW,EARLY] Control Speculative Store Bypass (SSB) Disable mitigation
(Speculative Store Bypass vulnerability)
Certain CPUs are vulnerable to an exploit against a
#DB exception for bus lock is triggered only when
CPL > 0.
- srbds= [X86,INTEL]
+ srbds= [X86,INTEL,EARLY]
Control the Special Register Buffer Data Sampling
(SRBDS) mitigation.
srcutree.convert_to_big must have the 0x10 bit
set for contention-based conversions to occur.
- ssbd= [ARM64,HW]
+ ssbd= [ARM64,HW,EARLY]
Speculative Store Bypass Disable control
On CPUs that are vulnerable to the Speculative
growing up) the main stack are reserved for no other
mapping. Default value is 256 pages.
- stack_depot_disable= [KNL]
+ stack_depot_disable= [KNL,EARLY]
Setting this to true through kernel command line will
disable the stack depot thereby saving the static memory
consumed by the stack hash table. By default this is set
be used to filter out binaries which have
not yet been made aware of AT_MINSIGSTKSZ.
- stress_hpt [PPC]
+ stress_hpt [PPC,EARLY]
Limits the number of kernel HPT entries in the hash
page table to increase the rate of hash page table
faults on kernel addresses.
- stress_slb [PPC]
+ stress_slb [PPC,EARLY]
Limits the number of kernel SLB entries, and flushes
them frequently to increase the rate of SLB faults
on kernel addresses.
This parameter controls use of the Protected
Execution Facility on pSeries.
- swiotlb= [ARM,IA-64,PPC,MIPS,X86]
+ swiotlb= [ARM,IA-64,PPC,MIPS,X86,EARLY]
Format: { <int> [,<int>] | force | noforce }
<int> -- Number of I/O TLB slabs
<int> -- Second integer after comma. Number of swiotlb
wouldn't be automatically used by the kernel
noforce -- Never use bounce buffers (for debugging)
- switches= [HW,M68k]
+ switches= [HW,M68k,EARLY]
sysctl.*= [KNL]
Set a sysctl parameter, right before loading the init
<deci-seconds>: poll all this frequency
0: no polling (default)
- threadirqs [KNL]
+ threadirqs [KNL,EARLY]
Force threading of all interrupt handlers except those
marked explicitly IRQF_NO_THREAD.
- topology= [S390]
+ topology= [S390,EARLY]
Format: {off | on}
Specify if the kernel should make use of the cpu
topology information if the hardware supports this.
can be overridden by a later tsc=nowatchdog. A console
message will flag any such suppression or overriding.
- tsc_early_khz= [X86] Skip early TSC calibration and use the given
+ tsc_early_khz= [X86,EARLY] Skip early TSC calibration and use the given
value instead. Useful when the early TSC frequency discovery
procedure is not reliable, such as on overclocked systems
with CPUID.16h support and partial CPUID.15h support.
See Documentation/admin-guide/hw-vuln/tsx_async_abort.rst
for more details.
- tsx_async_abort= [X86,INTEL] Control mitigation for the TSX Async
+ tsx_async_abort= [X86,INTEL,EARLY] Control mitigation for the TSX Async
Abort (TAA) vulnerability.
Similar to Micro-architectural Data Sampling (MDS)
unknown_nmi_panic
[X86] Cause panic on unknown NMI.
- unwind_debug [X86-64]
+ unwind_debug [X86-64,EARLY]
Enable unwinder debug output. This can be
useful for debugging certain unwinder error
conditions, including corrupt stacks and
pause after every control message);
o = USB_QUIRK_HUB_SLOW_RESET (Hub needs extra
delay after resetting its port);
+ p = USB_QUIRK_SHORT_SET_ADDRESS_REQ_TIMEOUT
+ (Reduce timeout of the SET_ADDRESS
+ request from 5000 ms to 500 ms);
Example: quirks=0781:5580:bk,0a5c:5834:gij
usbhid.mousepoll=
Example: user_debug=31
userpte=
- [X86] Flags controlling user PTE allocations.
+ [X86,EARLY] Flags controlling user PTE allocations.
nohigh = do not allocate PTE pages in
HIGHMEM regardless of setting
vector= [IA-64,SMP]
vector=percpu: enable percpu vector domain
- video= [FB] Frame buffer configuration
+ video= [FB,EARLY] Frame buffer configuration
See Documentation/fb/modedb.rst.
video.brightness_switch_enabled= [ACPI]
P Enable page structure init time poisoning
- Disable all of the above options
- 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.
+ vmalloc=nn[KMG] [KNL,BOOT,EARLY] 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.
- vmcp_cma=nn[MG] [KNL,S390]
+ vmcp_cma=nn[MG] [KNL,S390,EARLY]
Sets the memory size reserved for contiguous memory
allocations for the vmcp device driver.
vmpoff= [KNL,S390] Perform z/VM CP command after power off.
Format: <command>
- vsyscall= [X86-64]
+ vsyscall= [X86-64,EARLY]
Controls the behavior of vsyscalls (i.e. calls to
fixed addresses of 0xffffffffff600x00 from legacy
code). Most statically-linked binaries and older
threshold repeatedly. They are likely good
candidates for using WQ_UNBOUND workqueues instead.
+ workqueue.cpu_intensive_warning_thresh=<uint>
+ If CONFIG_WQ_CPU_INTENSIVE_REPORT is set, the kernel
+ will report the work functions which violate the
+ intensive_threshold_us repeatedly. In order to prevent
+ spurious warnings, start printing only after a work
+ function has violated this threshold number of times.
+
+ The default is 4 times. 0 disables the warning.
+
workqueue.power_efficient
Per-cpu workqueues are generally preferred because
they show better performance thanks to cache
When enabled, memory and cache locality will be
impacted.
- writecombine= [LOONGARCH] Control the MAT (Memory Access Type) of
- ioremap_wc().
+ writecombine= [LOONGARCH,EARLY] Control the MAT (Memory Access
+ Type) of ioremap_wc().
on - Enable writecombine, use WUC for ioremap_wc()
off - Disable writecombine, use SUC for ioremap_wc()
- x2apic_phys [X86-64,APIC] Use x2apic physical mode instead of
+ x2apic_phys [X86-64,APIC,EARLY] Use x2apic physical mode instead of
default x2apic cluster mode on platforms
supporting x2apic.
save/restore/migration must be enabled to handle larger
domains.
- xen_emul_unplug= [HW,X86,XEN]
+ xen_emul_unplug= [HW,X86,XEN,EARLY]
Unplug Xen emulated devices
Format: [unplug0,][unplug1]
ide-disks -- unplug primary master IDE devices
the unplug protocol
never -- do not unplug even if version check succeeds
- xen_legacy_crash [X86,XEN]
+ xen_legacy_crash [X86,XEN,EARLY]
Crash from Xen panic notifier, without executing late
panic() code such as dumping handler.
- xen_msr_safe= [X86,XEN]
+ xen_msr_safe= [X86,XEN,EARLY]
Format: <bool>
Select whether to always use non-faulting (safe) MSR
access functions when running as Xen PV guest. The
default value is controlled by CONFIG_XEN_PV_MSR_SAFE.
- xen_nopvspin [X86,XEN]
+ xen_nopvspin [X86,XEN,EARLY]
Disables the qspinlock slowpath using Xen PV optimizations.
This parameter is obsoleted by "nopvspin" parameter, which
has equivalent effect for XEN platform.
has equivalent effect for XEN platform.
xen_no_vector_callback
- [KNL,X86,XEN] Disable the vector callback for Xen
+ [KNL,X86,XEN,EARLY] Disable the vector callback for Xen
event channel interrupts.
xen_scrub_pages= [XEN]
with /sys/devices/system/xen_memory/xen_memory0/scrub_pages.
Default value controlled with CONFIG_XEN_SCRUB_PAGES_DEFAULT.
- xen_timer_slop= [X86-64,XEN]
+ xen_timer_slop= [X86-64,XEN,EARLY]
Set the timer slop (in nanoseconds) for the virtual Xen
timers (default is 100000). This adjusts the minimum
delta of virtualized Xen timers, where lower values
host controller quirks. Meaning of each bit can be
consulted in header drivers/usb/host/xhci.h.
- xmon [PPC]
+ xmon [PPC,EARLY]
Format: { early | on | rw | ro | off }
Controls if xmon debugger is enabled. Default is off.
Passing only "xmon" is equivalent to "xmon=early".
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