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+===================================
+Documentation for /proc/sys/kernel/
+===================================
+
+.. See scripts/check-sysctl-docs to keep this up to date
+
+
+Copyright (c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
+
+Copyright (c) 2009, Shen Feng<shen@cn.fujitsu.com>
+
+For general info and legal blurb, please look in :doc:`index`.
+
+------------------------------------------------------------------------------
+
+This file contains documentation for the sysctl files in
+``/proc/sys/kernel/`` and is valid for Linux kernel version 2.2.
+
+The files in this directory can be used to tune and monitor
+miscellaneous and general things in the operation of the Linux
+kernel. Since some of the files *can* be used to screw up your
+system, it is advisable to read both documentation and source
+before actually making adjustments.
+
+Currently, these files might (depending on your configuration)
+show up in ``/proc/sys/kernel``:
+
+.. contents:: :local:
+
+
+acct
+====
+
+::
+
+ highwater lowwater frequency
+
+If BSD-style process accounting is enabled these values control
+its behaviour. If free space on filesystem where the log lives
+goes below ``lowwater``% accounting suspends. If free space gets
+above ``highwater``% accounting resumes. ``frequency`` determines
+how often do we check the amount of free space (value is in
+seconds). Default:
+
+::
+
+ 4 2 30
+
+That is, suspend accounting if free space drops below 2%; resume it
+if it increases to at least 4%; consider information about amount of
+free space valid for 30 seconds.
+
+
+acpi_video_flags
+================
+
+See :doc:`/power/video`. This allows the video resume mode to be set,
+in a similar fashion to the ``acpi_sleep`` kernel parameter, by
+combining the following values:
+
+= =======
+1 s3_bios
+2 s3_mode
+4 s3_beep
+= =======
+
+
+auto_msgmni
+===========
+
+This variable has no effect and may be removed in future kernel
+releases. Reading it always returns 0.
+Up to Linux 3.17, it enabled/disabled automatic recomputing of
+`msgmni`_
+upon memory add/remove or upon IPC namespace creation/removal.
+Echoing "1" into this file enabled msgmni automatic recomputing.
+Echoing "0" turned it off. The default value was 1.
+
+
+bootloader_type (x86 only)
+==========================
+
+This gives the bootloader type number as indicated by the bootloader,
+shifted left by 4, and OR'd with the low four bits of the bootloader
+version. The reason for this encoding is that this used to match the
+``type_of_loader`` field in the kernel header; the encoding is kept for
+backwards compatibility. That is, if the full bootloader type number
+is 0x15 and the full version number is 0x234, this file will contain
+the value 340 = 0x154.
+
+See the ``type_of_loader`` and ``ext_loader_type`` fields in
+:doc:`/x86/boot` for additional information.
+
+
+bootloader_version (x86 only)
+=============================
+
+The complete bootloader version number. In the example above, this
+file will contain the value 564 = 0x234.
+
+See the ``type_of_loader`` and ``ext_loader_ver`` fields in
+:doc:`/x86/boot` for additional information.
+
+
+bpf_stats_enabled
+=================
+
+Controls whether the kernel should collect statistics on BPF programs
+(total time spent running, number of times run...). Enabling
+statistics causes a slight reduction in performance on each program
+run. The statistics can be seen using ``bpftool``.
+
+= ===================================
+0 Don't collect statistics (default).
+1 Collect statistics.
+= ===================================
+
+
+cad_pid
+=======
+
+This is the pid which will be signalled on reboot (notably, by
+Ctrl-Alt-Delete). Writing a value to this file which doesn't
+correspond to a running process will result in ``-ESRCH``.
+
+See also `ctrl-alt-del`_.
+
+
+cap_last_cap
+============
+
+Highest valid capability of the running kernel. Exports
+``CAP_LAST_CAP`` from the kernel.
+
+
+core_pattern
+============
+
+``core_pattern`` is used to specify a core dumpfile pattern name.
+
+* max length 127 characters; default value is "core"
+* ``core_pattern`` is used as a pattern template for the output
+ filename; certain string patterns (beginning with '%') are
+ substituted with their actual values.
+* backward compatibility with ``core_uses_pid``:
+
+ If ``core_pattern`` does not include "%p" (default does not)
+ and ``core_uses_pid`` is set, then .PID will be appended to
+ the filename.
+
+* corename format specifiers
+
+ ======== ==========================================
+ %<NUL> '%' is dropped
+ %% output one '%'
+ %p pid
+ %P global pid (init PID namespace)
+ %i tid
+ %I global tid (init PID namespace)
+ %u uid (in initial user namespace)
+ %g gid (in initial user namespace)
+ %d dump mode, matches ``PR_SET_DUMPABLE`` and
+ ``/proc/sys/fs/suid_dumpable``
+ %s signal number
+ %t UNIX time of dump
+ %h hostname
+ %e executable filename (may be shortened, could be changed by prctl etc)
+ %f executable filename
+ %E executable path
+ %c maximum size of core file by resource limit RLIMIT_CORE
+ %<OTHER> both are dropped
+ ======== ==========================================
+
+* If the first character of the pattern is a '|', the kernel will treat
+ the rest of the pattern as a command to run. The core dump will be
+ written to the standard input of that program instead of to a file.
+
+
+core_pipe_limit
+===============
+
+This sysctl is only applicable when `core_pattern`_ is configured to
+pipe core files to a user space helper (when the first character of
+``core_pattern`` is a '|', see above).
+When collecting cores via a pipe to an application, it is occasionally
+useful for the collecting application to gather data about the
+crashing process from its ``/proc/pid`` directory.
+In order to do this safely, the kernel must wait for the collecting
+process to exit, so as not to remove the crashing processes proc files
+prematurely.
+This in turn creates the possibility that a misbehaving userspace
+collecting process can block the reaping of a crashed process simply
+by never exiting.
+This sysctl defends against that.
+It defines how many concurrent crashing processes may be piped to user
+space applications in parallel.
+If this value is exceeded, then those crashing processes above that
+value are noted via the kernel log and their cores are skipped.
+0 is a special value, indicating that unlimited processes may be
+captured in parallel, but that no waiting will take place (i.e. the
+collecting process is not guaranteed access to ``/proc/<crashing
+pid>/``).
+This value defaults to 0.
+
+
+core_uses_pid
+=============
+
+The default coredump filename is "core". By setting
+``core_uses_pid`` to 1, the coredump filename becomes core.PID.
+If `core_pattern`_ does not include "%p" (default does not)
+and ``core_uses_pid`` is set, then .PID will be appended to
+the filename.
+
+
+ctrl-alt-del
+============
+
+When the value in this file is 0, ctrl-alt-del is trapped and
+sent to the ``init(1)`` program to handle a graceful restart.
+When, however, the value is > 0, Linux's reaction to a Vulcan
+Nerve Pinch (tm) will be an immediate reboot, without even
+syncing its dirty buffers.
+
+Note:
+ when a program (like dosemu) has the keyboard in 'raw'
+ mode, the ctrl-alt-del is intercepted by the program before it
+ ever reaches the kernel tty layer, and it's up to the program
+ to decide what to do with it.
+
+
+dmesg_restrict
+==============
+
+This toggle indicates whether unprivileged users are prevented
+from using ``dmesg(8)`` to view messages from the kernel's log
+buffer.
+When ``dmesg_restrict`` is set to 0 there are no restrictions.
+When ``dmesg_restrict`` is set to 1, users must have
+``CAP_SYSLOG`` to use ``dmesg(8)``.
+
+The kernel config option ``CONFIG_SECURITY_DMESG_RESTRICT`` sets the
+default value of ``dmesg_restrict``.
+
+
+domainname & hostname
+=====================
+
+These files can be used to set the NIS/YP domainname and the
+hostname of your box in exactly the same way as the commands
+domainname and hostname, i.e.::
+
+ # echo "darkstar" > /proc/sys/kernel/hostname
+ # echo "mydomain" > /proc/sys/kernel/domainname
+
+has the same effect as::
+
+ # hostname "darkstar"
+ # domainname "mydomain"
+
+Note, however, that the classic darkstar.frop.org has the
+hostname "darkstar" and DNS (Internet Domain Name Server)
+domainname "frop.org", not to be confused with the NIS (Network
+Information Service) or YP (Yellow Pages) domainname. These two
+domain names are in general different. For a detailed discussion
+see the ``hostname(1)`` man page.
+
+
+firmware_config
+===============
+
+See :doc:`/driver-api/firmware/fallback-mechanisms`.
+
+The entries in this directory allow the firmware loader helper
+fallback to be controlled:
+
+* ``force_sysfs_fallback``, when set to 1, forces the use of the
+ fallback;
+* ``ignore_sysfs_fallback``, when set to 1, ignores any fallback.
+
+
+ftrace_dump_on_oops
+===================
+
+Determines whether ``ftrace_dump()`` should be called on an oops (or
+kernel panic). This will output the contents of the ftrace buffers to
+the console. This is very useful for capturing traces that lead to
+crashes and outputting them to a serial console.
+
+= ===================================================
+0 Disabled (default).
+1 Dump buffers of all CPUs.
+2 Dump the buffer of the CPU that triggered the oops.
+= ===================================================
+
+
+ftrace_enabled, stack_tracer_enabled
+====================================
+
+See :doc:`/trace/ftrace`.
+
+
+hardlockup_all_cpu_backtrace
+============================
+
+This value controls the hard lockup detector behavior when a hard
+lockup condition is detected as to whether or not to gather further
+debug information. If enabled, arch-specific all-CPU stack dumping
+will be initiated.
+
+= ============================================
+0 Do nothing. This is the default behavior.
+1 On detection capture more debug information.
+= ============================================
+
+
+hardlockup_panic
+================
+
+This parameter can be used to control whether the kernel panics
+when a hard lockup is detected.
+
+= ===========================
+0 Don't panic on hard lockup.
+1 Panic on hard lockup.
+= ===========================
+
+See :doc:`/admin-guide/lockup-watchdogs` for more information.
+This can also be set using the nmi_watchdog kernel parameter.
+
+
+hotplug
+=======
+
+Path for the hotplug policy agent.
+Default value is "``/sbin/hotplug``".
+
+
+hung_task_all_cpu_backtrace
+===========================
+
+If this option is set, the kernel will send an NMI to all CPUs to dump
+their backtraces when a hung task is detected. This file shows up if
+CONFIG_DETECT_HUNG_TASK and CONFIG_SMP are enabled.
+
+0: Won't show all CPUs backtraces when a hung task is detected.
+This is the default behavior.
+
+1: Will non-maskably interrupt all CPUs and dump their backtraces when
+a hung task is detected.
+
+
+hung_task_panic
+===============
+
+Controls the kernel's behavior when a hung task is detected.
+This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled.
+
+= =================================================
+0 Continue operation. This is the default behavior.
+1 Panic immediately.
+= =================================================
+
+
+hung_task_check_count
+=====================
+
+The upper bound on the number of tasks that are checked.
+This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled.
+
+
+hung_task_timeout_secs
+======================
+
+When a task in D state did not get scheduled
+for more than this value report a warning.
+This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled.
+
+0 means infinite timeout, no checking is done.
+
+Possible values to set are in range {0:``LONG_MAX``/``HZ``}.
+
+
+hung_task_check_interval_secs
+=============================
+
+Hung task check interval. If hung task checking is enabled
+(see `hung_task_timeout_secs`_), the check is done every
+``hung_task_check_interval_secs`` seconds.
+This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled.
+
+0 (default) means use ``hung_task_timeout_secs`` as checking
+interval.
+
+Possible values to set are in range {0:``LONG_MAX``/``HZ``}.
+
+
+hung_task_warnings
+==================
+
+The maximum number of warnings to report. During a check interval
+if a hung task is detected, this value is decreased by 1.
+When this value reaches 0, no more warnings will be reported.
+This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled.
+
+-1: report an infinite number of warnings.
+
+
+hyperv_record_panic_msg
+=======================
+
+Controls whether the panic kmsg data should be reported to Hyper-V.
+
+= =========================================================
+0 Do not report panic kmsg data.
+1 Report the panic kmsg data. This is the default behavior.
+= =========================================================
+
+
+ignore-unaligned-usertrap
+=========================
+
+On architectures where unaligned accesses cause traps, and where this
+feature is supported (``CONFIG_SYSCTL_ARCH_UNALIGN_NO_WARN``;
+currently, ``arc`` and ``ia64``), controls whether all unaligned traps
+are logged.
+
+= =============================================================
+0 Log all unaligned accesses.
+1 Only warn the first time a process traps. This is the default
+ setting.
+= =============================================================
+
+See also `unaligned-trap`_ and `unaligned-dump-stack`_. On ``ia64``,
+this allows system administrators to override the
+``IA64_THREAD_UAC_NOPRINT`` ``prctl`` and avoid logs being flooded.
+
+
+kexec_load_disabled
+===================
+
+A toggle indicating if the ``kexec_load`` syscall has been disabled.
+This value defaults to 0 (false: ``kexec_load`` enabled), but can be
+set to 1 (true: ``kexec_load`` disabled).
+Once true, kexec can no longer be used, and the toggle cannot be set
+back to false.
+This allows a kexec image to be loaded before disabling the syscall,
+allowing a system to set up (and later use) an image without it being
+altered.
+Generally used together with the `modules_disabled`_ sysctl.
+
+
+kptr_restrict
+=============
+
+This toggle indicates whether restrictions are placed on
+exposing kernel addresses via ``/proc`` and other interfaces.
+
+When ``kptr_restrict`` is set to 0 (the default) the address is hashed
+before printing.
+(This is the equivalent to %p.)
+
+When ``kptr_restrict`` is set to 1, kernel pointers printed using the
+%pK format specifier will be replaced with 0s unless the user has
+``CAP_SYSLOG`` and effective user and group ids are equal to the real
+ids.
+This is because %pK checks are done at read() time rather than open()
+time, so if permissions are elevated between the open() and the read()
+(e.g via a setuid binary) then %pK will not leak kernel pointers to
+unprivileged users.
+Note, this is a temporary solution only.
+The correct long-term solution is to do the permission checks at
+open() time.
+Consider removing world read permissions from files that use %pK, and
+using `dmesg_restrict`_ to protect against uses of %pK in ``dmesg(8)``
+if leaking kernel pointer values to unprivileged users is a concern.
+
+When ``kptr_restrict`` is set to 2, kernel pointers printed using
+%pK will be replaced with 0s regardless of privileges.
+
+
+modprobe
+========
+
+The full path to the usermode helper for autoloading kernel modules,
+by default "/sbin/modprobe". This binary is executed when the kernel
+requests a module. For example, if userspace passes an unknown
+filesystem type to mount(), then the kernel will automatically request
+the corresponding filesystem module by executing this usermode helper.
+This usermode helper should insert the needed module into the kernel.
+
+This sysctl only affects module autoloading. It has no effect on the
+ability to explicitly insert modules.
+
+This sysctl can be used to debug module loading requests::
+
+ echo '#! /bin/sh' > /tmp/modprobe
+ echo 'echo "$@" >> /tmp/modprobe.log' >> /tmp/modprobe
+ echo 'exec /sbin/modprobe "$@"' >> /tmp/modprobe
+ chmod a+x /tmp/modprobe
+ echo /tmp/modprobe > /proc/sys/kernel/modprobe
+
+Alternatively, if this sysctl is set to the empty string, then module
+autoloading is completely disabled. The kernel will not try to
+execute a usermode helper at all, nor will it call the
+kernel_module_request LSM hook.
+
+If CONFIG_STATIC_USERMODEHELPER=y is set in the kernel configuration,
+then the configured static usermode helper overrides this sysctl,
+except that the empty string is still accepted to completely disable
+module autoloading as described above.
+
+modules_disabled
+================
+
+A toggle value indicating if modules are allowed to be loaded
+in an otherwise modular kernel. This toggle defaults to off
+(0), but can be set true (1). Once true, modules can be
+neither loaded nor unloaded, and the toggle cannot be set back
+to false. Generally used with the `kexec_load_disabled`_ toggle.
+
+
+.. _msgmni:
+
+msgmax, msgmnb, and msgmni
+==========================
+
+``msgmax`` is the maximum size of an IPC message, in bytes. 8192 by
+default (``MSGMAX``).
+
+``msgmnb`` is the maximum size of an IPC queue, in bytes. 16384 by
+default (``MSGMNB``).
+
+``msgmni`` is the maximum number of IPC queues. 32000 by default
+(``MSGMNI``).
+
+
+msg_next_id, sem_next_id, and shm_next_id (System V IPC)
+========================================================
+
+These three toggles allows to specify desired id for next allocated IPC
+object: message, semaphore or shared memory respectively.
+
+By default they are equal to -1, which means generic allocation logic.
+Possible values to set are in range {0:``INT_MAX``}.
+
+Notes:
+ 1) kernel doesn't guarantee, that new object will have desired id. So,
+ it's up to userspace, how to handle an object with "wrong" id.
+ 2) Toggle with non-default value will be set back to -1 by kernel after
+ successful IPC object allocation. If an IPC object allocation syscall
+ fails, it is undefined if the value remains unmodified or is reset to -1.
+
+
+ngroups_max
+===========
+
+Maximum number of supplementary groups, _i.e._ the maximum size which
+``setgroups`` will accept. Exports ``NGROUPS_MAX`` from the kernel.
+
+
+
+nmi_watchdog
+============
+
+This parameter can be used to control the NMI watchdog
+(i.e. the hard lockup detector) on x86 systems.
+
+= =================================
+0 Disable the hard lockup detector.
+1 Enable the hard lockup detector.
+= =================================
+
+The hard lockup detector monitors each CPU for its ability to respond to
+timer interrupts. The mechanism utilizes CPU performance counter registers
+that are programmed to generate Non-Maskable Interrupts (NMIs) periodically
+while a CPU is busy. Hence, the alternative name 'NMI watchdog'.
+
+The NMI watchdog is disabled by default if the kernel is running as a guest
+in a KVM virtual machine. This default can be overridden by adding::
+
+ nmi_watchdog=1
+
+to the guest kernel command line (see :doc:`/admin-guide/kernel-parameters`).
+
+
+numa_balancing
+==============
+
+Enables/disables automatic page fault based NUMA memory
+balancing. Memory is moved automatically to nodes
+that access it often.
+
+Enables/disables automatic NUMA memory balancing. On NUMA machines, there
+is a performance penalty if remote memory is accessed by a CPU. When this
+feature is enabled the kernel samples what task thread is accessing memory
+by periodically unmapping pages and later trapping a page fault. At the
+time of the page fault, it is determined if the data being accessed should
+be migrated to a local memory node.
+
+The unmapping of pages and trapping faults incur additional overhead that
+ideally is offset by improved memory locality but there is no universal
+guarantee. If the target workload is already bound to NUMA nodes then this
+feature should be disabled. Otherwise, if the system overhead from the
+feature is too high then the rate the kernel samples for NUMA hinting
+faults may be controlled by the `numa_balancing_scan_period_min_ms,
+numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms,
+numa_balancing_scan_size_mb`_, and numa_balancing_settle_count sysctls.
+
+
+numa_balancing_scan_period_min_ms, numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms, numa_balancing_scan_size_mb
+===============================================================================================================================
+
+
+Automatic NUMA balancing scans tasks address space and unmaps pages to
+detect if pages are properly placed or if the data should be migrated to a
+memory node local to where the task is running. Every "scan delay" the task
+scans the next "scan size" number of pages in its address space. When the
+end of the address space is reached the scanner restarts from the beginning.
+
+In combination, the "scan delay" and "scan size" determine the scan rate.
+When "scan delay" decreases, the scan rate increases. The scan delay and
+hence the scan rate of every task is adaptive and depends on historical
+behaviour. If pages are properly placed then the scan delay increases,
+otherwise the scan delay decreases. The "scan size" is not adaptive but
+the higher the "scan size", the higher the scan rate.
+
+Higher scan rates incur higher system overhead as page faults must be
+trapped and potentially data must be migrated. However, the higher the scan
+rate, the more quickly a tasks memory is migrated to a local node if the
+workload pattern changes and minimises performance impact due to remote
+memory accesses. These sysctls control the thresholds for scan delays and
+the number of pages scanned.
+
+``numa_balancing_scan_period_min_ms`` is the minimum time in milliseconds to
+scan a tasks virtual memory. It effectively controls the maximum scanning
+rate for each task.
+
+``numa_balancing_scan_delay_ms`` is the starting "scan delay" used for a task
+when it initially forks.
+
+``numa_balancing_scan_period_max_ms`` is the maximum time in milliseconds to
+scan a tasks virtual memory. It effectively controls the minimum scanning
+rate for each task.
+
+``numa_balancing_scan_size_mb`` is how many megabytes worth of pages are
+scanned for a given scan.
+
+
+oops_all_cpu_backtrace
+======================
+
+If this option is set, the kernel will send an NMI to all CPUs to dump
+their backtraces when an oops event occurs. It should be used as a last
+resort in case a panic cannot be triggered (to protect VMs running, for
+example) or kdump can't be collected. This file shows up if CONFIG_SMP
+is enabled.
+
+0: Won't show all CPUs backtraces when an oops is detected.
+This is the default behavior.
+
+1: Will non-maskably interrupt all CPUs and dump their backtraces when
+an oops event is detected.
+
+
+oops_limit
+==========
+
+Number of kernel oopses after which the kernel should panic when
+``panic_on_oops`` is not set. Setting this to 0 disables checking
+the count. Setting this to 1 has the same effect as setting
+``panic_on_oops=1``. The default value is 10000.
+
+
+osrelease, ostype & version
+===========================
+
+::
+
+ # cat osrelease
+ 2.1.88
+ # cat ostype
+ Linux
+ # cat version
+ #5 Wed Feb 25 21:49:24 MET 1998
+
+The files ``osrelease`` and ``ostype`` should be clear enough.
+``version``
+needs a little more clarification however. The '#5' means that
+this is the fifth kernel built from this source base and the
+date behind it indicates the time the kernel was built.
+The only way to tune these values is to rebuild the kernel :-)
+
+
+overflowgid & overflowuid
+=========================
+
+if your architecture did not always support 32-bit UIDs (i.e. arm,
+i386, m68k, sh, and sparc32), a fixed UID and GID will be returned to
+applications that use the old 16-bit UID/GID system calls, if the
+actual UID or GID would exceed 65535.
+
+These sysctls allow you to change the value of the fixed UID and GID.
+The default is 65534.
+
+
+panic
+=====
+
+The value in this file determines the behaviour of the kernel on a
+panic:
+
+* if zero, the kernel will loop forever;
+* if negative, the kernel will reboot immediately;
+* if positive, the kernel will reboot after the corresponding number
+ of seconds.
+
+When you use the software watchdog, the recommended setting is 60.
+
+
+panic_on_io_nmi
+===============
+
+Controls the kernel's behavior when a CPU receives an NMI caused by
+an IO error.
+
+= ==================================================================
+0 Try to continue operation (default).
+1 Panic immediately. The IO error triggered an NMI. This indicates a
+ serious system condition which could result in IO data corruption.
+ Rather than continuing, panicking might be a better choice. Some
+ servers issue this sort of NMI when the dump button is pushed,
+ and you can use this option to take a crash dump.
+= ==================================================================
+
+
+panic_on_oops
+=============
+
+Controls the kernel's behaviour when an oops or BUG is encountered.
+
+= ===================================================================
+0 Try to continue operation.
+1 Panic immediately. If the `panic` sysctl is also non-zero then the
+ machine will be rebooted.
+= ===================================================================
+
+
+panic_on_stackoverflow
+======================
+
+Controls the kernel's behavior when detecting the overflows of
+kernel, IRQ and exception stacks except a user stack.
+This file shows up if ``CONFIG_DEBUG_STACKOVERFLOW`` is enabled.
+
+= ==========================
+0 Try to continue operation.
+1 Panic immediately.
+= ==========================
+
+
+panic_on_unrecovered_nmi
+========================
+
+The default Linux behaviour on an NMI of either memory or unknown is
+to continue operation. For many environments such as scientific
+computing it is preferable that the box is taken out and the error
+dealt with than an uncorrected parity/ECC error get propagated.
+
+A small number of systems do generate NMIs for bizarre random reasons
+such as power management so the default is off. That sysctl works like
+the existing panic controls already in that directory.
+
+
+panic_on_warn
+=============
+
+Calls panic() in the WARN() path when set to 1. This is useful to avoid
+a kernel rebuild when attempting to kdump at the location of a WARN().
+
+= ================================================
+0 Only WARN(), default behaviour.
+1 Call panic() after printing out WARN() location.
+= ================================================
+
+
+panic_print
+===========
+
+Bitmask for printing system info when panic happens. User can chose
+combination of the following bits:
+
+===== ============================================
+bit 0 print all tasks info
+bit 1 print system memory info
+bit 2 print timer info
+bit 3 print locks info if ``CONFIG_LOCKDEP`` is on
+bit 4 print ftrace buffer
+bit 5 print all printk messages in buffer
+===== ============================================
+
+So for example to print tasks and memory info on panic, user can::
+
+ echo 3 > /proc/sys/kernel/panic_print
+
+
+panic_on_rcu_stall
+==================
+
+When set to 1, calls panic() after RCU stall detection messages. This
+is useful to define the root cause of RCU stalls using a vmcore.
+
+= ============================================================
+0 Do not panic() when RCU stall takes place, default behavior.
+1 panic() after printing RCU stall messages.
+= ============================================================
+
+
+perf_cpu_time_max_percent
+=========================
+
+Hints to the kernel how much CPU time it should be allowed to
+use to handle perf sampling events. If the perf subsystem
+is informed that its samples are exceeding this limit, it
+will drop its sampling frequency to attempt to reduce its CPU
+usage.
+
+Some perf sampling happens in NMIs. If these samples
+unexpectedly take too long to execute, the NMIs can become
+stacked up next to each other so much that nothing else is
+allowed to execute.
+
+===== ========================================================
+0 Disable the mechanism. Do not monitor or correct perf's
+ sampling rate no matter how CPU time it takes.
+
+1-100 Attempt to throttle perf's sample rate to this
+ percentage of CPU. Note: the kernel calculates an
+ "expected" length of each sample event. 100 here means
+ 100% of that expected length. Even if this is set to
+ 100, you may still see sample throttling if this
+ length is exceeded. Set to 0 if you truly do not care
+ how much CPU is consumed.
+===== ========================================================
+
+
+perf_event_paranoid
+===================
+
+Controls use of the performance events system by unprivileged
+users (without CAP_PERFMON). The default value is 2.
+
+For backward compatibility reasons access to system performance
+monitoring and observability remains open for CAP_SYS_ADMIN
+privileged processes but CAP_SYS_ADMIN usage for secure system
+performance monitoring and observability operations is discouraged
+with respect to CAP_PERFMON use cases.
+
+=== ==================================================================
+ -1 Allow use of (almost) all events by all users.
+
+ Ignore mlock limit after perf_event_mlock_kb without
+ ``CAP_IPC_LOCK``.
+
+>=0 Disallow ftrace function tracepoint by users without
+ ``CAP_PERFMON``.
+
+ Disallow raw tracepoint access by users without ``CAP_PERFMON``.
+
+>=1 Disallow CPU event access by users without ``CAP_PERFMON``.
+
+>=2 Disallow kernel profiling by users without ``CAP_PERFMON``.
+=== ==================================================================
+
+
+perf_event_max_stack
+====================
+
+Controls maximum number of stack frames to copy for (``attr.sample_type &
+PERF_SAMPLE_CALLCHAIN``) configured events, for instance, when using
+'``perf record -g``' or '``perf trace --call-graph fp``'.
+
+This can only be done when no events are in use that have callchains
+enabled, otherwise writing to this file will return ``-EBUSY``.
+
+The default value is 127.
+
+
+perf_event_mlock_kb
+===================
+
+Control size of per-cpu ring buffer not counted agains mlock limit.
+
+The default value is 512 + 1 page
+
+
+perf_event_max_contexts_per_stack
+=================================
+
+Controls maximum number of stack frame context entries for
+(``attr.sample_type & PERF_SAMPLE_CALLCHAIN``) configured events, for
+instance, when using '``perf record -g``' or '``perf trace --call-graph fp``'.
+
+This can only be done when no events are in use that have callchains
+enabled, otherwise writing to this file will return ``-EBUSY``.
+
+The default value is 8.
+
+
+pid_max
+=======
+
+PID allocation wrap value. When the kernel's next PID value
+reaches this value, it wraps back to a minimum PID value.
+PIDs of value ``pid_max`` or larger are not allocated.
+
+
+ns_last_pid
+===========
+
+The last pid allocated in the current (the one task using this sysctl
+lives in) pid namespace. When selecting a pid for a next task on fork
+kernel tries to allocate a number starting from this one.
+
+
+powersave-nap (PPC only)
+========================
+
+If set, Linux-PPC will use the 'nap' mode of powersaving,
+otherwise the 'doze' mode will be used.
+
+
+==============================================================
+
+printk
+======
+
+The four values in printk denote: ``console_loglevel``,
+``default_message_loglevel``, ``minimum_console_loglevel`` and
+``default_console_loglevel`` respectively.
+
+These values influence printk() behavior when printing or
+logging error messages. See '``man 2 syslog``' for more info on
+the different loglevels.
+
+======================== =====================================
+console_loglevel messages with a higher priority than
+ this will be printed to the console
+default_message_loglevel messages without an explicit priority
+ will be printed with this priority
+minimum_console_loglevel minimum (highest) value to which
+ console_loglevel can be set
+default_console_loglevel default value for console_loglevel
+======================== =====================================
+
+
+printk_delay
+============
+
+Delay each printk message in ``printk_delay`` milliseconds
+
+Value from 0 - 10000 is allowed.
+
+
+printk_ratelimit
+================
+
+Some warning messages are rate limited. ``printk_ratelimit`` specifies
+the minimum length of time between these messages (in seconds).
+The default value is 5 seconds.
+
+A value of 0 will disable rate limiting.
+
+
+printk_ratelimit_burst
+======================
+
+While long term we enforce one message per `printk_ratelimit`_
+seconds, we do allow a burst of messages to pass through.
+``printk_ratelimit_burst`` specifies the number of messages we can
+send before ratelimiting kicks in.
+
+The default value is 10 messages.
+
+
+printk_devkmsg
+==============
+
+Control the logging to ``/dev/kmsg`` from userspace:
+
+========= =============================================
+ratelimit default, ratelimited
+on unlimited logging to /dev/kmsg from userspace
+off logging to /dev/kmsg disabled
+========= =============================================
+
+The kernel command line parameter ``printk.devkmsg=`` overrides this and is
+a one-time setting until next reboot: once set, it cannot be changed by
+this sysctl interface anymore.
+
+==============================================================
+
+
+pty
+===
+
+See Documentation/filesystems/devpts.rst.
+
+
+random
+======
+
+This is a directory, with the following entries:
+
+* ``boot_id``: a UUID generated the first time this is retrieved, and
+ unvarying after that;
+
+* ``uuid``: a UUID generated every time this is retrieved (this can
+ thus be used to generate UUIDs at will);
+
+* ``entropy_avail``: the pool's entropy count, in bits;
+
+* ``poolsize``: the entropy pool size, in bits;
+
+* ``urandom_min_reseed_secs``: obsolete (used to determine the minimum
+ number of seconds between urandom pool reseeding). This file is
+ writable for compatibility purposes, but writing to it has no effect
+ on any RNG behavior;
+
+* ``write_wakeup_threshold``: when the entropy count drops below this
+ (as a number of bits), processes waiting to write to ``/dev/random``
+ are woken up. This file is writable for compatibility purposes, but
+ writing to it has no effect on any RNG behavior.
+
+
+randomize_va_space
+==================
+
+This option can be used to select the type of process address
+space randomization that is used in the system, for architectures
+that support this feature.
+
+== ===========================================================================
+0 Turn the process address space randomization off. This is the
+ default for architectures that do not support this feature anyways,
+ and kernels that are booted with the "norandmaps" parameter.
+
+1 Make the addresses of mmap base, stack and VDSO page randomized.
+ This, among other things, implies that shared libraries will be
+ loaded to random addresses. Also for PIE-linked binaries, the
+ location of code start is randomized. This is the default if the
+ ``CONFIG_COMPAT_BRK`` option is enabled.
+
+2 Additionally enable heap randomization. This is the default if
+ ``CONFIG_COMPAT_BRK`` is disabled.
+
+ There are a few legacy applications out there (such as some ancient
+ versions of libc.so.5 from 1996) that assume that brk area starts
+ just after the end of the code+bss. These applications break when
+ start of the brk area is randomized. There are however no known
+ non-legacy applications that would be broken this way, so for most
+ systems it is safe to choose full randomization.
+
+ Systems with ancient and/or broken binaries should be configured
+ with ``CONFIG_COMPAT_BRK`` enabled, which excludes the heap from process
+ address space randomization.
+== ===========================================================================
+
+
+real-root-dev
+=============
+
+See :doc:`/admin-guide/initrd`.
+
+
+reboot-cmd (SPARC only)
+=======================
+
+??? This seems to be a way to give an argument to the Sparc
+ROM/Flash boot loader. Maybe to tell it what to do after
+rebooting. ???
+
+
+sched_energy_aware
+==================
+
+Enables/disables Energy Aware Scheduling (EAS). EAS starts
+automatically on platforms where it can run (that is,
+platforms with asymmetric CPU topologies and having an Energy
+Model available). If your platform happens to meet the
+requirements for EAS but you do not want to use it, change
+this value to 0.
+
+
+sched_schedstats
+================
+
+Enables/disables scheduler statistics. Enabling this feature
+incurs a small amount of overhead in the scheduler but is
+useful for debugging and performance tuning.
+
+sched_util_clamp_min:
+=====================
+
+Max allowed *minimum* utilization.
+
+Default value is 1024, which is the maximum possible value.
+
+It means that any requested uclamp.min value cannot be greater than
+sched_util_clamp_min, i.e., it is restricted to the range
+[0:sched_util_clamp_min].
+
+sched_util_clamp_max:
+=====================
+
+Max allowed *maximum* utilization.
+
+Default value is 1024, which is the maximum possible value.
+
+It means that any requested uclamp.max value cannot be greater than
+sched_util_clamp_max, i.e., it is restricted to the range
+[0:sched_util_clamp_max].
+
+sched_util_clamp_min_rt_default:
+================================
+
+By default Linux is tuned for performance. Which means that RT tasks always run
+at the highest frequency and most capable (highest capacity) CPU (in
+heterogeneous systems).
+
+Uclamp achieves this by setting the requested uclamp.min of all RT tasks to
+1024 by default, which effectively boosts the tasks to run at the highest
+frequency and biases them to run on the biggest CPU.
+
+This knob allows admins to change the default behavior when uclamp is being
+used. In battery powered devices particularly, running at the maximum
+capacity and frequency will increase energy consumption and shorten the battery
+life.
+
+This knob is only effective for RT tasks which the user hasn't modified their
+requested uclamp.min value via sched_setattr() syscall.
+
+This knob will not escape the range constraint imposed by sched_util_clamp_min
+defined above.
+
+For example if
+
+ sched_util_clamp_min_rt_default = 800
+ sched_util_clamp_min = 600
+
+Then the boost will be clamped to 600 because 800 is outside of the permissible
+range of [0:600]. This could happen for instance if a powersave mode will
+restrict all boosts temporarily by modifying sched_util_clamp_min. As soon as
+this restriction is lifted, the requested sched_util_clamp_min_rt_default
+will take effect.
+
+seccomp
+=======
+
+See :doc:`/userspace-api/seccomp_filter`.
+
+
+sg-big-buff
+===========
+
+This file shows the size of the generic SCSI (sg) buffer.
+You can't tune it just yet, but you could change it on
+compile time by editing ``include/scsi/sg.h`` and changing
+the value of ``SG_BIG_BUFF``.
+
+There shouldn't be any reason to change this value. If
+you can come up with one, you probably know what you
+are doing anyway :)
+
+
+shmall
+======
+
+This parameter sets the total amount of shared memory pages that
+can be used system wide. Hence, ``shmall`` should always be at least
+``ceil(shmmax/PAGE_SIZE)``.
+
+If you are not sure what the default ``PAGE_SIZE`` is on your Linux
+system, you can run the following command::
+
+ # getconf PAGE_SIZE
+
+
+shmmax
+======
+
+This value can be used to query and set the run time limit
+on the maximum shared memory segment size that can be created.
+Shared memory segments up to 1Gb are now supported in the
+kernel. This value defaults to ``SHMMAX``.
+
+
+shmmni
+======
+
+This value determines the maximum number of shared memory segments.
+4096 by default (``SHMMNI``).
+
+
+shm_rmid_forced
+===============
+
+Linux lets you set resource limits, including how much memory one
+process can consume, via ``setrlimit(2)``. Unfortunately, shared memory
+segments are allowed to exist without association with any process, and
+thus might not be counted against any resource limits. If enabled,
+shared memory segments are automatically destroyed when their attach
+count becomes zero after a detach or a process termination. It will
+also destroy segments that were created, but never attached to, on exit
+from the process. The only use left for ``IPC_RMID`` is to immediately
+destroy an unattached segment. Of course, this breaks the way things are
+defined, so some applications might stop working. Note that this
+feature will do you no good unless you also configure your resource
+limits (in particular, ``RLIMIT_AS`` and ``RLIMIT_NPROC``). Most systems don't
+need this.
+
+Note that if you change this from 0 to 1, already created segments
+without users and with a dead originative process will be destroyed.
+
+
+sysctl_writes_strict
+====================
+
+Control how file position affects the behavior of updating sysctl values
+via the ``/proc/sys`` interface:
+
+ == ======================================================================
+ -1 Legacy per-write sysctl value handling, with no printk warnings.
+ Each write syscall must fully contain the sysctl value to be
+ written, and multiple writes on the same sysctl file descriptor
+ will rewrite the sysctl value, regardless of file position.
+ 0 Same behavior as above, but warn about processes that perform writes
+ to a sysctl file descriptor when the file position is not 0.
+ 1 (default) Respect file position when writing sysctl strings. Multiple
+ writes will append to the sysctl value buffer. Anything past the max
+ length of the sysctl value buffer will be ignored. Writes to numeric
+ sysctl entries must always be at file position 0 and the value must
+ be fully contained in the buffer sent in the write syscall.
+ == ======================================================================
+
+
+softlockup_all_cpu_backtrace
+============================
+
+This value controls the soft lockup detector thread's behavior
+when a soft lockup condition is detected as to whether or not
+to gather further debug information. If enabled, each cpu will
+be issued an NMI and instructed to capture stack trace.
+
+This feature is only applicable for architectures which support
+NMI.
+
+= ============================================
+0 Do nothing. This is the default behavior.
+1 On detection capture more debug information.
+= ============================================
+
+
+softlockup_panic
+=================
+
+This parameter can be used to control whether the kernel panics
+when a soft lockup is detected.
+
+= ============================================
+0 Don't panic on soft lockup.
+1 Panic on soft lockup.
+= ============================================
+
+This can also be set using the softlockup_panic kernel parameter.
+
+
+soft_watchdog
+=============
+
+This parameter can be used to control the soft lockup detector.
+
+= =================================
+0 Disable the soft lockup detector.
+1 Enable the soft lockup detector.
+= =================================
+
+The soft lockup detector monitors CPUs for threads that are hogging the CPUs
+without rescheduling voluntarily, and thus prevent the 'watchdog/N' threads
+from running. The mechanism depends on the CPUs ability to respond to timer
+interrupts which are needed for the 'watchdog/N' threads to be woken up by
+the watchdog timer function, otherwise the NMI watchdog — if enabled — can
+detect a hard lockup condition.
+
+
+stack_erasing
+=============
+
+This parameter can be used to control kernel stack erasing at the end
+of syscalls for kernels built with ``CONFIG_GCC_PLUGIN_STACKLEAK``.
+
+That erasing reduces the information which kernel stack leak bugs
+can reveal and blocks some uninitialized stack variable attacks.
+The tradeoff is the performance impact: on a single CPU system kernel
+compilation sees a 1% slowdown, other systems and workloads may vary.
+
+= ====================================================================
+0 Kernel stack erasing is disabled, STACKLEAK_METRICS are not updated.
+1 Kernel stack erasing is enabled (default), it is performed before
+ returning to the userspace at the end of syscalls.
+= ====================================================================
+
+
+stop-a (SPARC only)
+===================
+
+Controls Stop-A:
+
+= ====================================
+0 Stop-A has no effect.
+1 Stop-A breaks to the PROM (default).
+= ====================================
+
+Stop-A is always enabled on a panic, so that the user can return to
+the boot PROM.
+
+
+sysrq
+=====
+
+See :doc:`/admin-guide/sysrq`.
+
+
+tainted
+=======
+
+Non-zero if the kernel has been tainted. Numeric values, which can be
+ORed together. The letters are seen in "Tainted" line of Oops reports.
+
+====== ===== ==============================================================
+ 1 `(P)` proprietary module was loaded
+ 2 `(F)` module was force loaded
+ 4 `(S)` SMP kernel oops on an officially SMP incapable processor
+ 8 `(R)` module was force unloaded
+ 16 `(M)` processor reported a Machine Check Exception (MCE)
+ 32 `(B)` bad page referenced or some unexpected page flags
+ 64 `(U)` taint requested by userspace application
+ 128 `(D)` kernel died recently, i.e. there was an OOPS or BUG
+ 256 `(A)` an ACPI table was overridden by user
+ 512 `(W)` kernel issued warning
+ 1024 `(C)` staging driver was loaded
+ 2048 `(I)` workaround for bug in platform firmware applied
+ 4096 `(O)` externally-built ("out-of-tree") module was loaded
+ 8192 `(E)` unsigned module was loaded
+ 16384 `(L)` soft lockup occurred
+ 32768 `(K)` kernel has been live patched
+ 65536 `(X)` Auxiliary taint, defined and used by for distros
+131072 `(T)` The kernel was built with the struct randomization plugin
+====== ===== ==============================================================
+
+See :doc:`/admin-guide/tainted-kernels` for more information.
+
+Note:
+ writes to this sysctl interface will fail with ``EINVAL`` if the kernel is
+ booted with the command line option ``panic_on_taint=<bitmask>,nousertaint``
+ and any of the ORed together values being written to ``tainted`` match with
+ the bitmask declared on panic_on_taint.
+ See :doc:`/admin-guide/kernel-parameters` for more details on that particular
+ kernel command line option and its optional ``nousertaint`` switch.
+
+threads-max
+===========
+
+This value controls the maximum number of threads that can be created
+using ``fork()``.
+
+During initialization the kernel sets this value such that even if the
+maximum number of threads is created, the thread structures occupy only
+a part (1/8th) of the available RAM pages.
+
+The minimum value that can be written to ``threads-max`` is 1.
+
+The maximum value that can be written to ``threads-max`` is given by the
+constant ``FUTEX_TID_MASK`` (0x3fffffff).
+
+If a value outside of this range is written to ``threads-max`` an
+``EINVAL`` error occurs.
+
+
+traceoff_on_warning
+===================
+
+When set, disables tracing (see :doc:`/trace/ftrace`) when a
+``WARN()`` is hit.
+
+
+tracepoint_printk
+=================
+
+When tracepoints are sent to printk() (enabled by the ``tp_printk``
+boot parameter), this entry provides runtime control::
+
+ echo 0 > /proc/sys/kernel/tracepoint_printk
+
+will stop tracepoints from being sent to printk(), and::
+
+ echo 1 > /proc/sys/kernel/tracepoint_printk
+
+will send them to printk() again.
+
+This only works if the kernel was booted with ``tp_printk`` enabled.
+
+See :doc:`/admin-guide/kernel-parameters` and
+:doc:`/trace/boottime-trace`.
+
+
+.. _unaligned-dump-stack:
+
+unaligned-dump-stack (ia64)
+===========================
+
+When logging unaligned accesses, controls whether the stack is
+dumped.
+
+= ===================================================
+0 Do not dump the stack. This is the default setting.
+1 Dump the stack.
+= ===================================================
+
+See also `ignore-unaligned-usertrap`_.
+
+
+unaligned-trap
+==============
+
+On architectures where unaligned accesses cause traps, and where this
+feature is supported (``CONFIG_SYSCTL_ARCH_UNALIGN_ALLOW``; currently,
+``arc`` and ``parisc``), controls whether unaligned traps are caught
+and emulated (instead of failing).
+
+= ========================================================
+0 Do not emulate unaligned accesses.
+1 Emulate unaligned accesses. This is the default setting.
+= ========================================================
+
+See also `ignore-unaligned-usertrap`_.
+
+
+unknown_nmi_panic
+=================
+
+The value in this file affects behavior of handling NMI. When the
+value is non-zero, unknown NMI is trapped and then panic occurs. At
+that time, kernel debugging information is displayed on console.
+
+NMI switch that most IA32 servers have fires unknown NMI up, for
+example. If a system hangs up, try pressing the NMI switch.
+
+
+unprivileged_bpf_disabled
+=========================
+
+Writing 1 to this entry will disable unprivileged calls to ``bpf()``;
+once disabled, calling ``bpf()`` without ``CAP_SYS_ADMIN`` or ``CAP_BPF``
+will return ``-EPERM``. Once set to 1, this can't be cleared from the
+running kernel anymore.
+
+Writing 2 to this entry will also disable unprivileged calls to ``bpf()``,
+however, an admin can still change this setting later on, if needed, by
+writing 0 or 1 to this entry.
+
+If ``BPF_UNPRIV_DEFAULT_OFF`` is enabled in the kernel config, then this
+entry will default to 2 instead of 0.
+
+= =============================================================
+0 Unprivileged calls to ``bpf()`` are enabled
+1 Unprivileged calls to ``bpf()`` are disabled without recovery
+2 Unprivileged calls to ``bpf()`` are disabled
+= =============================================================
+
+
+warn_limit
+==========
+
+Number of kernel warnings after which the kernel should panic when
+``panic_on_warn`` is not set. Setting this to 0 disables checking
+the warning count. Setting this to 1 has the same effect as setting
+``panic_on_warn=1``. The default value is 0.
+
+
+watchdog
+========
+
+This parameter can be used to disable or enable the soft lockup detector
+*and* the NMI watchdog (i.e. the hard lockup detector) at the same time.
+
+= ==============================
+0 Disable both lockup detectors.
+1 Enable both lockup detectors.
+= ==============================
+
+The soft lockup detector and the NMI watchdog can also be disabled or
+enabled individually, using the ``soft_watchdog`` and ``nmi_watchdog``
+parameters.
+If the ``watchdog`` parameter is read, for example by executing::
+
+ cat /proc/sys/kernel/watchdog
+
+the output of this command (0 or 1) shows the logical OR of
+``soft_watchdog`` and ``nmi_watchdog``.
+
+
+watchdog_cpumask
+================
+
+This value can be used to control on which cpus the watchdog may run.
+The default cpumask is all possible cores, but if ``NO_HZ_FULL`` is
+enabled in the kernel config, and cores are specified with the
+``nohz_full=`` boot argument, those cores are excluded by default.
+Offline cores can be included in this mask, and if the core is later
+brought online, the watchdog will be started based on the mask value.
+
+Typically this value would only be touched in the ``nohz_full`` case
+to re-enable cores that by default were not running the watchdog,
+if a kernel lockup was suspected on those cores.
+
+The argument value is the standard cpulist format for cpumasks,
+so for example to enable the watchdog on cores 0, 2, 3, and 4 you
+might say::
+
+ echo 0,2-4 > /proc/sys/kernel/watchdog_cpumask
+
+
+watchdog_thresh
+===============
+
+This value can be used to control the frequency of hrtimer and NMI
+events and the soft and hard lockup thresholds. The default threshold
+is 10 seconds.
+
+The softlockup threshold is (``2 * watchdog_thresh``). Setting this
+tunable to zero will disable lockup detection altogether.