Adding upstream version 4.19.249.upstream/4.19.249upstream

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

1 files changed, 1156 insertions, 0 deletions

diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt
new file mode 100644
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--- /dev/null
+++ b/Documentation/sysctl/kernel.txt
@@ -0,0 +1,1156 @@
+Documentation for /proc/sys/kernel/*	kernel version 2.2.10
+	(c) 1998, 1999,  Rik van Riel <riel@nl.linux.org>
+	(c) 2009,        Shen Feng<shen@cn.fujitsu.com>
+
+For general info and legal blurb, please look in README.
+
+==============================================================
+
+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:
+
+- acct
+- acpi_video_flags
+- auto_msgmni
+- bootloader_type	     [ X86 only ]
+- bootloader_version	     [ X86 only ]
+- callhome		     [ S390 only ]
+- cap_last_cap
+- core_pattern
+- core_pipe_limit
+- core_uses_pid
+- ctrl-alt-del
+- dmesg_restrict
+- domainname
+- hostname
+- hotplug
+- hardlockup_all_cpu_backtrace
+- hardlockup_panic
+- hung_task_panic
+- hung_task_check_count
+- hung_task_timeout_secs
+- hung_task_check_interval_secs
+- hung_task_warnings
+- hyperv_record_panic_msg
+- kexec_load_disabled
+- kptr_restrict
+- l2cr                        [ PPC only ]
+- modprobe                    ==> Documentation/debugging-modules.txt
+- modules_disabled
+- msg_next_id		      [ sysv ipc ]
+- msgmax
+- msgmnb
+- msgmni
+- nmi_watchdog
+- osrelease
+- ostype
+- overflowgid
+- overflowuid
+- panic
+- panic_on_oops
+- panic_on_stackoverflow
+- panic_on_unrecovered_nmi
+- panic_on_warn
+- panic_on_rcu_stall
+- perf_cpu_time_max_percent
+- perf_event_paranoid
+- perf_event_max_stack
+- perf_event_mlock_kb
+- perf_event_max_contexts_per_stack
+- pid_max
+- powersave-nap               [ PPC only ]
+- printk
+- printk_delay
+- printk_ratelimit
+- printk_ratelimit_burst
+- pty                         ==> Documentation/filesystems/devpts.txt
+- randomize_va_space
+- real-root-dev               ==> Documentation/admin-guide/initrd.rst
+- reboot-cmd                  [ SPARC only ]
+- rtsig-max
+- rtsig-nr
+- seccomp/                    ==> Documentation/userspace-api/seccomp_filter.rst
+- sem
+- sem_next_id		      [ sysv ipc ]
+- sg-big-buff                 [ generic SCSI device (sg) ]
+- shm_next_id		      [ sysv ipc ]
+- shm_rmid_forced
+- shmall
+- shmmax                      [ sysv ipc ]
+- shmmni
+- softlockup_all_cpu_backtrace
+- soft_watchdog
+- stop-a                      [ SPARC only ]
+- sysrq                       ==> Documentation/admin-guide/sysrq.rst
+- sysctl_writes_strict
+- tainted
+- threads-max
+- unprivileged_bpf_disabled
+- unknown_nmi_panic
+- watchdog
+- watchdog_thresh
+- version
+
+==============================================================
+
+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 there left <= 2% free; resume it
+if we got >=4%; consider information about amount of free space
+valid for 30 seconds.
+
+==============================================================
+
+acpi_video_flags:
+
+flags
+
+See Doc*/kernel/power/video.txt, it allows mode of video boot to be
+set during run time.
+
+==============================================================
+
+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. auto_msgmni default value was 1.
+
+
+==============================================================
+
+bootloader_type:
+
+x86 bootloader identification
+
+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
+Documentation/x86/boot.txt for additional information.
+
+==============================================================
+
+bootloader_version:
+
+x86 bootloader version
+
+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
+Documentation/x86/boot.txt for additional information.
+
+==============================================================
+
+callhome:
+
+Controls the kernel's callhome behavior in case of a kernel panic.
+
+The s390 hardware allows an operating system to send a notification
+to a service organization (callhome) in case of an operating system panic.
+
+When the value in this file is 0 (which is the default behavior)
+nothing happens in case of a kernel panic. If this value is set to "1"
+the complete kernel oops message is send to the IBM customer service
+organization in case the mainframe the Linux operating system is running
+on has a service contract with IBM.
+
+==============================================================
+
+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 128 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)
+	%E	executable path
+	%<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 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.
+
+==============================================================
+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 Documentation/lockup-watchdogs.txt 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_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 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.
+
+==============================================================
+
+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 0's 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 0's regardless of privileges.
+
+==============================================================
+
+l2cr: (PPC only)
+
+This flag controls the L2 cache of G3 processor boards. If
+0, the cache is disabled. Enabled if nonzero.
+
+==============================================================
+
+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.
+
+==============================================================
+
+msg_next_id, sem_next_id, and shm_next_id:
+
+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.
+
+==============================================================
+
+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 Documentation/admin-guide/kernel-parameters.rst).
+
+==============================================================
+
+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.
+
+==============================================================
+
+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 represents the number of seconds the kernel
+waits before rebooting on a panic. 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 NMI's 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_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_SYS_ADMIN).  The default value is 2.
+
+ -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_SYS_ADMIN
+     Disallow raw tracepoint access by users without CAP_SYS_ADMIN
+>=1: Disallow CPU event access by users without CAP_SYS_ADMIN
+>=2: Disallow kernel profiling by users without CAP_SYS_ADMIN
+
+==============================================================
+
+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 jiffies), by
+default we allow one every 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.
+
+==============================================================
+
+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.
+
+==============================================================
+
+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. ???
+
+==============================================================
+
+rtsig-max & rtsig-nr:
+
+The file rtsig-max can be used to tune the maximum number
+of POSIX realtime (queued) signals that can be outstanding
+in the system.
+
+rtsig-nr shows the number of RT signals currently queued.
+
+==============================================================
+
+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.
+
+==============================================================
+
+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.
+
+==============================================================
+
+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.
+
+==============================================================
+
+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.
+
+==============================================================
+
+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):  A module with a non-GPL license has been loaded, this
+             includes modules with no license.
+             Set by modutils >= 2.4.9 and module-init-tools.
+     2 (F): A module was force loaded by insmod -f.
+            Set by modutils >= 2.4.9 and module-init-tools.
+     4 (S): Unsafe SMP processors: SMP with CPUs not designed for SMP.
+     8 (R): A module was forcibly unloaded from the system by rmmod -f.
+    16 (M): A hardware machine check error occurred on the system.
+    32 (B): A bad page was discovered on the system.
+    64 (U): The user has asked that the system be marked "tainted". This
+            could be because they are running software that directly modifies
+            the hardware, or for other reasons.
+   128 (D): The system has died.
+   256 (A): The ACPI DSDT has been overridden with one supplied by the user
+            instead of using the one provided by the hardware.
+   512 (W): A kernel warning has occurred.
+  1024 (C): A module from drivers/staging was loaded.
+  2048 (I): The system is working around a severe firmware bug.
+  4096 (O): An out-of-tree module has been loaded.
+  8192 (E): An unsigned module has been loaded in a kernel supporting module
+            signature.
+ 16384 (L): A soft lockup has previously occurred on the system.
+ 32768 (K): The 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.
+
+==============================================================
+
+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 20.
+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 error
+EINVAL occurs.
+
+The value written is checked against the available RAM pages. If the
+thread structures would occupy too much (more than 1/8th) of the
+available RAM pages threads-max is reduced accordingly.
+
+==============================================================
+
+unprivileged_bpf_disabled:
+
+Writing 1 to this entry will disable unprivileged calls to bpf();
+once disabled, calling bpf() without CAP_SYS_ADMIN 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
+
+==============================================================
+
+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.
+
+==============================================================
+
+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.
+
+==============================================================