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Limit the number of requests that the server will
process in parallel from a single connection.
The default value is 0 (no limit).

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)

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.

Sets the number of seconds to remain in a suspend test
mode before resuming the system (see
/sys/power/pm_test). Only available when CONFIG_PM_DEBUG
is set. Default value is 5.

[KNL] Enable accounting of swap in memory resource
controller if no parameter or 1 is given or disable
it if 0 is given (See Documentation/cgroup-v1/memory.txt)

swiotlb= [ARM,IA-64,PPC,MIPS,X86]
Format: { <int> | force | noforce }
<int> -- Number of I/O TLB slabs
force -- force using of bounce buffers even if they
wouldn't be automatically used by the kernel
noforce -- Never use bounce buffers (for debugging)

switches= [HW,M68k]

sysfs.deprecated=0|1 [KNL]
Enable/disable old style sysfs layout for old udev
on older distributions. When this option is enabled
very new udev will not work anymore. When this option
is disabled (or CONFIG_SYSFS_DEPRECATED not compiled)
in older udev will not work anymore.
Default depends on CONFIG_SYSFS_DEPRECATED_V2 set in
the kernel configuration.

Ignore sysrq setting - this boot parameter will
neutralize any effect of /proc/sys/kernel/sysrq.
Useful for debugging.

tcpmhash_entries= [KNL,NET]
Set the number of tcp_metrics_hash slots.
Default value is 8192 or 16384 depending on total
ram pages. This is used to specify the TCP metrics
cache size. See Documentation/networking/ip-sysctl.txt
"tcp_no_metrics_save" section for more details.

tdfx= [HW,DRM]

test_suspend= [SUSPEND][,N]
Specify "mem" (for Suspend-to-RAM) or "standby" (for
standby suspend) or "freeze" (for suspend type freeze)
as the system sleep state during system startup with
the optional capability to repeat N number of times.
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. [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

thermal.tzp= [HW,ACPI]
Specify global default ACPI thermal zone polling rate
<deci-seconds>: poll all this frequency
0: no polling (default)

threadirqs [KNL]
Force threading of all interrupt handlers except those
marked explicitly IRQF_NO_THREAD.

tmem [KNL,XEN]
Enable the Transcendent memory driver if built-in.

tmem.cleancache=0|1 [KNL, XEN]
Default is on (1). Disable the usage of the cleancache
API to send anonymous pages to the hypervisor.

tmem.frontswap=0|1 [KNL, XEN]
Default is on (1). Disable the usage of the frontswap
API to send swap pages to the hypervisor. If disabled
the selfballooning and selfshrinking are force disabled.

tmem.selfballooning=0|1 [KNL, XEN]
Default is on (1). Disable the driving of swap pages
to the hypervisor.

tmem.selfshrinking=0|1 [KNL, XEN]
Default is on (1). Partial swapoff that immediately
transfers pages from Xen hypervisor back to the
kernel based on different criteria.

topology= [S390]
Format: {off | on}
Specify if the kernel should make use of the cpu
topology information if the hardware supports this.
The scheduler will make use of this information and
e.g. base its process migration decisions on it.
Default is on.

topology_updates= [KNL, PPC, NUMA]
Format: {off}
Specify if the kernel should ignore (off)
topology updates sent by the hypervisor to this

tp720= [HW,PS2]

Format: integer pcr id
Specify that at suspend time, the tpm driver
should extend the specified pcr with zeros,
as a workaround for some chips which fail to
flush the last written pcr on TPM_SaveState.
This will guarantee that all the other pcrs
are saved.

[FTRACE] will set tracing buffer size on each cpu.

[FTRACE] Set and start specified trace events in order
to facilitate early boot debugging. The event-list is a
comma separated list of trace events to enable. See
also Documentation/trace/events.txt

[FTRACE] Enable or disable tracer options at boot.
The option-list is a comma delimited list of options
that can be enabled or disabled just as if you were
to echo the option name into


For example, to enable stacktrace option (to dump the
stack trace of each event), add to the command line:


See also Documentation/trace/ftrace.txt "trace options"

Have the tracepoints sent to printk as well as the
tracing ring buffer. This is useful for early boot up
where the system hangs or reboots and does not give the
option for reading the tracing buffer or performing a

To turn off having tracepoints sent to printk,
echo 0 > /proc/sys/kernel/tracepoint_printk
Note, echoing 1 into this file without the
tracepoint_printk kernel cmdline option has no effect.


Having tracepoints sent to printk() and activating high
frequency tracepoints such as irq or sched, can cause
the system to live lock.

[FTRACE] enable this option to disable tracing when a
warning is hit. This turns off "tracing_on". Tracing can
be enabled again by echoing '1' into the "tracing_on"
file located in /sys/kernel/debug/tracing/

This option is useful, as it disables the trace before
the WARNING dump is called, which prevents the trace to
be filled with content caused by the warning output.

This option can also be set at run time via the sysctl
option: kernel/traceoff_on_warning

Format: [always|madvise|never]
Can be used to control the default behavior of the system
with respect to transparent hugepages.
See Documentation/vm/transhuge.txt for more details.

tsc= Disable clocksource stability checks for TSC.
Format: <string>
[x86] reliable: mark tsc clocksource as reliable, this
disables clocksource verification at runtime, as well
as the stability checks done at bootup. Used to enable
high-resolution timer mode on older hardware, and in
virtualized environment.
[x86] noirqtime: Do not use TSC to do irq accounting.
Used to run time disable IRQ_TIME_ACCOUNTING on any
platforms where RDTSC is slow and this accounting
can add overhead.
[x86] unstable: mark the TSC clocksource as unstable, this
marks the TSC unconditionally unstable at bootup and
avoids any further wobbles once the TSC watchdog notices.[2|3]= [HW,JOY]
TurboGraFX parallel port interface
See also Documentation/input/devices/joystick-parport.rst

udbg-immortal [PPC] When debugging early kernel crashes that
happen after console_init() and before a proper
console driver takes over, this boot options might
help "seeing" what's going on.

uhash_entries= [KNL,NET]
Set number of hash buckets for UDP/UDP-Lite connections

[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.

[X86] Cause panic on unknown NMI.

[USB] Default USB device authorization:
(default -1 = authorized except for wireless USB,
0 = not authorized, 1 = authorized)

[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.

[USB] Set to log all usbfs traffic (default 0 = off).

[USB] Maximum number of bytes to snoop in each URB
(default = 65536).

[USB] Set to cycle leds on hubs (default 0 = off).

[USB] Start with the old device initialization
scheme (default 0 = off).

[USB] Memory limit (in MB) for buffers allocated by
usbfs (default = 16, 0 = max = 2047).

[USB] Try the other device initialization scheme
if the first one fails (default 1 = enabled).

[USB] Specifies timeout for the initial 64-byte
USB_REQ_GET_DESCRIPTOR request in milliseconds
(default 5000 = 5.0 seconds).

usbcore.nousb [USB] Disable the USB subsystem

[USB] A list of quirk entries to augment the built-in
usb core quirk list. List entries are separated by
commas. Each entry has the form
VendorID:ProductID:Flags. The IDs are 4-digit hex
numbers and Flags is a set of letters. Each letter
will change the built-in quirk; setting it if it is
clear and clearing it if it is set. The letters have
the following meanings:
a = USB_QUIRK_STRING_FETCH_255 (string
descriptors must not be fetched using
a 255-byte read);
b = USB_QUIRK_RESET_RESUME (device can't resume
correctly so reset it instead);
c = USB_QUIRK_NO_SET_INTF (device can't handle
Set-Interface requests);
handle its Configuration or Interface
e = USB_QUIRK_RESET (device can't be reset
(e.g morph devices), don't use reset);
more interface descriptions than the
bNumInterfaces count, and can't handle
talking to these interfaces);
g = USB_QUIRK_DELAY_INIT (device needs a pause
during initialization, after we read
the device descriptor);
high speed and super speed interrupt
endpoints, the USB 2.0 and USB 3.0 spec
require the interval in microframes (1
microframe = 125 microseconds) to be
calculated as interval = 2 ^
Devices with this quirk report their
bInterval as the result of this
calculation instead of the exponent
variable used in the calculation);
handle device_qualifier descriptor
generates spurious wakeup, ignore
remote wakeup capability);
k = USB_QUIRK_NO_LPM (device can't handle Link
Power Management);
(Device reports its bInterval as linear
frames instead of the USB 2.0
to be disconnected before suspend to
prevent spurious wakeup);
n = USB_QUIRK_DELAY_CTRL_MSG (Device needs a
pause after every control message);
Example: quirks=0781:5580:bk,0a5c:5834:gij

[USBHID] The interval which mice are to be polled at.

[USBHID] The interval which joysticks are to be polled at.

[USBHID] The interval which keyboards are to be polled at.

[UMS] The delay in seconds before a new device is
scanned for Logical Units (default 1).

[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);
b = BAD_SENSE (don't collect more than 18
bytes of sense data);
c = FIX_CAPACITY (decrease the reported
device capacity by one sector);
d = NO_READ_DISC_INFO (don't use
READ_DISC_INFO command);
e = NO_READ_CAPACITY_16 (don't use
READ_CAPACITY_16 command);
f = NO_REPORT_OPCODES (don't use report opcodes
command, uas only);
g = MAX_SECTORS_240 (don't transfer more than
240 sectors at a time, uas only);
h = CAPACITY_HEURISTICS (decrease the
reported device capacity by one
sector if the number is odd);
i = IGNORE_DEVICE (don't bind to this
j = NO_REPORT_LUNS (don't use report luns
command, uas only);
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);
n = INITIAL_READ10 (force a retry of the
initial READ(10) command);
o = CAPACITY_OK (accept the capacity
reported by the device);
p = WRITE_CACHE (the device cache is ON
by default);
r = IGNORE_RESIDUE (the device reports
bogus residue values);
s = SINGLE_LUN (the device has only one
Logical Unit);
t = NO_ATA_1X (don't allow ATA(12) and ATA(16)
commands, uas only);
u = IGNORE_UAS (don't bind to the uas driver);
w = NO_WP_DETECT (don't test whether the
medium is write-protected).
even if the device claims no cache)
Example: quirks=0419:aaf5:rl,0421:0433:rc

user_debug= [KNL,ARM]
Format: <int>
See arch/arm/Kconfig.debug help text.
1 - undefined instruction events
2 - system calls
4 - invalid data aborts
8 - SIGSEGV faults
16 - SIGBUS faults
Example: user_debug=31

[X86] Flags controlling user PTE allocations.

nohigh = do not allocate PTE pages in
HIGHMEM regardless of setting

vdso= [X86,SH]
On X86_32, this is an alias for vdso32=. Otherwise:

vdso=1: enable VDSO (the default)
vdso=0: disable VDSO mapping

vdso32= [X86] Control the 32-bit vDSO
vdso32=1: enable 32-bit VDSO
vdso32=0 or vdso32=2: disable 32-bit VDSO

See the help text for CONFIG_COMPAT_VDSO for more
details. If CONFIG_COMPAT_VDSO is set, the default is
vdso32=0; otherwise, the default is vdso32=1.

For compatibility with older kernels, vdso32=2 is an
alias for vdso32=0.

Try vdso32=0 if you encounter an error that says:
dl_main: Assertion `(void *) ph->p_vaddr == _rtld_local._dl_sysinfo_dso' failed!

vector= [IA-64,SMP]
vector=percpu: enable percpu vector domain

video= [FB] Frame buffer configuration
See Documentation/fb/modedb.txt.

video.brightness_switch_enabled= [0,1]
If set to 1, on receiving an ACPI notify event
generated by hotkey, video driver will adjust brightness
level and then send out the event to user space through
the allocated input device; If set to 0, video driver
will only send out the event without touching backlight
brightness level.
default: 1