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Based on kernel version 4.8. Page generated on 2016-10-06 23:19 EST.

1	Documentation for /proc/sys/kernel/*	kernel version 2.2.10
2		(c) 1998, 1999,  Rik van Riel <riel@nl.linux.org>
3		(c) 2009,        Shen Feng<shen@cn.fujitsu.com>
4	
5	For general info and legal blurb, please look in README.
6	
7	==============================================================
8	
9	This file contains documentation for the sysctl files in
10	/proc/sys/kernel/ and is valid for Linux kernel version 2.2.
11	
12	The files in this directory can be used to tune and monitor
13	miscellaneous and general things in the operation of the Linux
14	kernel. Since some of the files _can_ be used to screw up your
15	system, it is advisable to read both documentation and source
16	before actually making adjustments.
17	
18	Currently, these files might (depending on your configuration)
19	show up in /proc/sys/kernel:
20	
21	- acct
22	- acpi_video_flags
23	- auto_msgmni
24	- bootloader_type	     [ X86 only ]
25	- bootloader_version	     [ X86 only ]
26	- callhome		     [ S390 only ]
27	- cap_last_cap
28	- core_pattern
29	- core_pipe_limit
30	- core_uses_pid
31	- ctrl-alt-del
32	- dmesg_restrict
33	- domainname
34	- hostname
35	- hotplug
36	- hardlockup_all_cpu_backtrace
37	- hung_task_panic
38	- hung_task_check_count
39	- hung_task_timeout_secs
40	- hung_task_warnings
41	- kexec_load_disabled
42	- kptr_restrict
43	- kstack_depth_to_print       [ X86 only ]
44	- l2cr                        [ PPC only ]
45	- modprobe                    ==> Documentation/debugging-modules.txt
46	- modules_disabled
47	- msg_next_id		      [ sysv ipc ]
48	- msgmax
49	- msgmnb
50	- msgmni
51	- nmi_watchdog
52	- osrelease
53	- ostype
54	- overflowgid
55	- overflowuid
56	- panic
57	- panic_on_oops
58	- panic_on_stackoverflow
59	- panic_on_unrecovered_nmi
60	- panic_on_warn
61	- panic_on_rcu_stall
62	- perf_cpu_time_max_percent
63	- perf_event_paranoid
64	- perf_event_max_stack
65	- perf_event_max_contexts_per_stack
66	- pid_max
67	- powersave-nap               [ PPC only ]
68	- printk
69	- printk_delay
70	- printk_ratelimit
71	- printk_ratelimit_burst
72	- pty                         ==> Documentation/filesystems/devpts.txt
73	- randomize_va_space
74	- real-root-dev               ==> Documentation/initrd.txt
75	- reboot-cmd                  [ SPARC only ]
76	- rtsig-max
77	- rtsig-nr
78	- sem
79	- sem_next_id		      [ sysv ipc ]
80	- sg-big-buff                 [ generic SCSI device (sg) ]
81	- shm_next_id		      [ sysv ipc ]
82	- shm_rmid_forced
83	- shmall
84	- shmmax                      [ sysv ipc ]
85	- shmmni
86	- softlockup_all_cpu_backtrace
87	- soft_watchdog
88	- stop-a                      [ SPARC only ]
89	- sysrq                       ==> Documentation/sysrq.txt
90	- sysctl_writes_strict
91	- tainted
92	- threads-max
93	- unknown_nmi_panic
94	- watchdog
95	- watchdog_thresh
96	- version
97	
98	==============================================================
99	
100	acct:
101	
102	highwater lowwater frequency
103	
104	If BSD-style process accounting is enabled these values control
105	its behaviour. If free space on filesystem where the log lives
106	goes below <lowwater>% accounting suspends. If free space gets
107	above <highwater>% accounting resumes. <Frequency> determines
108	how often do we check the amount of free space (value is in
109	seconds). Default:
110	4 2 30
111	That is, suspend accounting if there left <= 2% free; resume it
112	if we got >=4%; consider information about amount of free space
113	valid for 30 seconds.
114	
115	==============================================================
116	
117	acpi_video_flags:
118	
119	flags
120	
121	See Doc*/kernel/power/video.txt, it allows mode of video boot to be
122	set during run time.
123	
124	==============================================================
125	
126	auto_msgmni:
127	
128	This variable has no effect and may be removed in future kernel
129	releases. Reading it always returns 0.
130	Up to Linux 3.17, it enabled/disabled automatic recomputing of msgmni
131	upon memory add/remove or upon ipc namespace creation/removal.
132	Echoing "1" into this file enabled msgmni automatic recomputing.
133	Echoing "0" turned it off. auto_msgmni default value was 1.
134	
135	
136	==============================================================
137	
138	bootloader_type:
139	
140	x86 bootloader identification
141	
142	This gives the bootloader type number as indicated by the bootloader,
143	shifted left by 4, and OR'd with the low four bits of the bootloader
144	version.  The reason for this encoding is that this used to match the
145	type_of_loader field in the kernel header; the encoding is kept for
146	backwards compatibility.  That is, if the full bootloader type number
147	is 0x15 and the full version number is 0x234, this file will contain
148	the value 340 = 0x154.
149	
150	See the type_of_loader and ext_loader_type fields in
151	Documentation/x86/boot.txt for additional information.
152	
153	==============================================================
154	
155	bootloader_version:
156	
157	x86 bootloader version
158	
159	The complete bootloader version number.  In the example above, this
160	file will contain the value 564 = 0x234.
161	
162	See the type_of_loader and ext_loader_ver fields in
163	Documentation/x86/boot.txt for additional information.
164	
165	==============================================================
166	
167	callhome:
168	
169	Controls the kernel's callhome behavior in case of a kernel panic.
170	
171	The s390 hardware allows an operating system to send a notification
172	to a service organization (callhome) in case of an operating system panic.
173	
174	When the value in this file is 0 (which is the default behavior)
175	nothing happens in case of a kernel panic. If this value is set to "1"
176	the complete kernel oops message is send to the IBM customer service
177	organization in case the mainframe the Linux operating system is running
178	on has a service contract with IBM.
179	
180	==============================================================
181	
182	cap_last_cap
183	
184	Highest valid capability of the running kernel.  Exports
185	CAP_LAST_CAP from the kernel.
186	
187	==============================================================
188	
189	core_pattern:
190	
191	core_pattern is used to specify a core dumpfile pattern name.
192	. max length 128 characters; default value is "core"
193	. core_pattern is used as a pattern template for the output filename;
194	  certain string patterns (beginning with '%') are substituted with
195	  their actual values.
196	. backward compatibility with core_uses_pid:
197		If core_pattern does not include "%p" (default does not)
198		and core_uses_pid is set, then .PID will be appended to
199		the filename.
200	. corename format specifiers:
201		%<NUL>	'%' is dropped
202		%%	output one '%'
203		%p	pid
204		%P	global pid (init PID namespace)
205		%i	tid
206		%I	global tid (init PID namespace)
207		%u	uid (in initial user namespace)
208		%g	gid (in initial user namespace)
209		%d	dump mode, matches PR_SET_DUMPABLE and
210			/proc/sys/fs/suid_dumpable
211		%s	signal number
212		%t	UNIX time of dump
213		%h	hostname
214		%e	executable filename (may be shortened)
215		%E	executable path
216		%<OTHER> both are dropped
217	. If the first character of the pattern is a '|', the kernel will treat
218	  the rest of the pattern as a command to run.  The core dump will be
219	  written to the standard input of that program instead of to a file.
220	
221	==============================================================
222	
223	core_pipe_limit:
224	
225	This sysctl is only applicable when core_pattern is configured to pipe
226	core files to a user space helper (when the first character of
227	core_pattern is a '|', see above).  When collecting cores via a pipe
228	to an application, it is occasionally useful for the collecting
229	application to gather data about the crashing process from its
230	/proc/pid directory.  In order to do this safely, the kernel must wait
231	for the collecting process to exit, so as not to remove the crashing
232	processes proc files prematurely.  This in turn creates the
233	possibility that a misbehaving userspace collecting process can block
234	the reaping of a crashed process simply by never exiting.  This sysctl
235	defends against that.  It defines how many concurrent crashing
236	processes may be piped to user space applications in parallel.  If
237	this value is exceeded, then those crashing processes above that value
238	are noted via the kernel log and their cores are skipped.  0 is a
239	special value, indicating that unlimited processes may be captured in
240	parallel, but that no waiting will take place (i.e. the collecting
241	process is not guaranteed access to /proc/<crashing pid>/).  This
242	value defaults to 0.
243	
244	==============================================================
245	
246	core_uses_pid:
247	
248	The default coredump filename is "core".  By setting
249	core_uses_pid to 1, the coredump filename becomes core.PID.
250	If core_pattern does not include "%p" (default does not)
251	and core_uses_pid is set, then .PID will be appended to
252	the filename.
253	
254	==============================================================
255	
256	ctrl-alt-del:
257	
258	When the value in this file is 0, ctrl-alt-del is trapped and
259	sent to the init(1) program to handle a graceful restart.
260	When, however, the value is > 0, Linux's reaction to a Vulcan
261	Nerve Pinch (tm) will be an immediate reboot, without even
262	syncing its dirty buffers.
263	
264	Note: when a program (like dosemu) has the keyboard in 'raw'
265	mode, the ctrl-alt-del is intercepted by the program before it
266	ever reaches the kernel tty layer, and it's up to the program
267	to decide what to do with it.
268	
269	==============================================================
270	
271	dmesg_restrict:
272	
273	This toggle indicates whether unprivileged users are prevented
274	from using dmesg(8) to view messages from the kernel's log buffer.
275	When dmesg_restrict is set to (0) there are no restrictions. When
276	dmesg_restrict is set set to (1), users must have CAP_SYSLOG to use
277	dmesg(8).
278	
279	The kernel config option CONFIG_SECURITY_DMESG_RESTRICT sets the
280	default value of dmesg_restrict.
281	
282	==============================================================
283	
284	domainname & hostname:
285	
286	These files can be used to set the NIS/YP domainname and the
287	hostname of your box in exactly the same way as the commands
288	domainname and hostname, i.e.:
289	# echo "darkstar" > /proc/sys/kernel/hostname
290	# echo "mydomain" > /proc/sys/kernel/domainname
291	has the same effect as
292	# hostname "darkstar"
293	# domainname "mydomain"
294	
295	Note, however, that the classic darkstar.frop.org has the
296	hostname "darkstar" and DNS (Internet Domain Name Server)
297	domainname "frop.org", not to be confused with the NIS (Network
298	Information Service) or YP (Yellow Pages) domainname. These two
299	domain names are in general different. For a detailed discussion
300	see the hostname(1) man page.
301	
302	==============================================================
303	hardlockup_all_cpu_backtrace:
304	
305	This value controls the hard lockup detector behavior when a hard
306	lockup condition is detected as to whether or not to gather further
307	debug information. If enabled, arch-specific all-CPU stack dumping
308	will be initiated.
309	
310	0: do nothing. This is the default behavior.
311	
312	1: on detection capture more debug information.
313	==============================================================
314	
315	hotplug:
316	
317	Path for the hotplug policy agent.
318	Default value is "/sbin/hotplug".
319	
320	==============================================================
321	
322	hung_task_panic:
323	
324	Controls the kernel's behavior when a hung task is detected.
325	This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.
326	
327	0: continue operation. This is the default behavior.
328	
329	1: panic immediately.
330	
331	==============================================================
332	
333	hung_task_check_count:
334	
335	The upper bound on the number of tasks that are checked.
336	This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.
337	
338	==============================================================
339	
340	hung_task_timeout_secs:
341	
342	Check interval. When a task in D state did not get scheduled
343	for more than this value report a warning.
344	This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.
345	
346	0: means infinite timeout - no checking done.
347	Possible values to set are in range {0..LONG_MAX/HZ}.
348	
349	==============================================================
350	
351	hung_task_warnings:
352	
353	The maximum number of warnings to report. During a check interval
354	if a hung task is detected, this value is decreased by 1.
355	When this value reaches 0, no more warnings will be reported.
356	This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.
357	
358	-1: report an infinite number of warnings.
359	
360	==============================================================
361	
362	kexec_load_disabled:
363	
364	A toggle indicating if the kexec_load syscall has been disabled. This
365	value defaults to 0 (false: kexec_load enabled), but can be set to 1
366	(true: kexec_load disabled). Once true, kexec can no longer be used, and
367	the toggle cannot be set back to false. This allows a kexec image to be
368	loaded before disabling the syscall, allowing a system to set up (and
369	later use) an image without it being altered. Generally used together
370	with the "modules_disabled" sysctl.
371	
372	==============================================================
373	
374	kptr_restrict:
375	
376	This toggle indicates whether restrictions are placed on
377	exposing kernel addresses via /proc and other interfaces.
378	
379	When kptr_restrict is set to (0), the default, there are no restrictions.
380	
381	When kptr_restrict is set to (1), kernel pointers printed using the %pK
382	format specifier will be replaced with 0's unless the user has CAP_SYSLOG
383	and effective user and group ids are equal to the real ids. This is
384	because %pK checks are done at read() time rather than open() time, so
385	if permissions are elevated between the open() and the read() (e.g via
386	a setuid binary) then %pK will not leak kernel pointers to unprivileged
387	users. Note, this is a temporary solution only. The correct long-term
388	solution is to do the permission checks at open() time. Consider removing
389	world read permissions from files that use %pK, and using dmesg_restrict
390	to protect against uses of %pK in dmesg(8) if leaking kernel pointer
391	values to unprivileged users is a concern.
392	
393	When kptr_restrict is set to (2), kernel pointers printed using
394	%pK will be replaced with 0's regardless of privileges.
395	
396	==============================================================
397	
398	kstack_depth_to_print: (X86 only)
399	
400	Controls the number of words to print when dumping the raw
401	kernel stack.
402	
403	==============================================================
404	
405	l2cr: (PPC only)
406	
407	This flag controls the L2 cache of G3 processor boards. If
408	0, the cache is disabled. Enabled if nonzero.
409	
410	==============================================================
411	
412	modules_disabled:
413	
414	A toggle value indicating if modules are allowed to be loaded
415	in an otherwise modular kernel.  This toggle defaults to off
416	(0), but can be set true (1).  Once true, modules can be
417	neither loaded nor unloaded, and the toggle cannot be set back
418	to false.  Generally used with the "kexec_load_disabled" toggle.
419	
420	==============================================================
421	
422	msg_next_id, sem_next_id, and shm_next_id:
423	
424	These three toggles allows to specify desired id for next allocated IPC
425	object: message, semaphore or shared memory respectively.
426	
427	By default they are equal to -1, which means generic allocation logic.
428	Possible values to set are in range {0..INT_MAX}.
429	
430	Notes:
431	1) kernel doesn't guarantee, that new object will have desired id. So,
432	it's up to userspace, how to handle an object with "wrong" id.
433	2) Toggle with non-default value will be set back to -1 by kernel after
434	successful IPC object allocation.
435	
436	==============================================================
437	
438	nmi_watchdog:
439	
440	This parameter can be used to control the NMI watchdog
441	(i.e. the hard lockup detector) on x86 systems.
442	
443	   0 - disable the hard lockup detector
444	   1 - enable the hard lockup detector
445	
446	The hard lockup detector monitors each CPU for its ability to respond to
447	timer interrupts. The mechanism utilizes CPU performance counter registers
448	that are programmed to generate Non-Maskable Interrupts (NMIs) periodically
449	while a CPU is busy. Hence, the alternative name 'NMI watchdog'.
450	
451	The NMI watchdog is disabled by default if the kernel is running as a guest
452	in a KVM virtual machine. This default can be overridden by adding
453	
454	   nmi_watchdog=1
455	
456	to the guest kernel command line (see Documentation/kernel-parameters.txt).
457	
458	==============================================================
459	
460	numa_balancing
461	
462	Enables/disables automatic page fault based NUMA memory
463	balancing. Memory is moved automatically to nodes
464	that access it often.
465	
466	Enables/disables automatic NUMA memory balancing. On NUMA machines, there
467	is a performance penalty if remote memory is accessed by a CPU. When this
468	feature is enabled the kernel samples what task thread is accessing memory
469	by periodically unmapping pages and later trapping a page fault. At the
470	time of the page fault, it is determined if the data being accessed should
471	be migrated to a local memory node.
472	
473	The unmapping of pages and trapping faults incur additional overhead that
474	ideally is offset by improved memory locality but there is no universal
475	guarantee. If the target workload is already bound to NUMA nodes then this
476	feature should be disabled. Otherwise, if the system overhead from the
477	feature is too high then the rate the kernel samples for NUMA hinting
478	faults may be controlled by the numa_balancing_scan_period_min_ms,
479	numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms,
480	numa_balancing_scan_size_mb, and numa_balancing_settle_count sysctls.
481	
482	==============================================================
483	
484	numa_balancing_scan_period_min_ms, numa_balancing_scan_delay_ms,
485	numa_balancing_scan_period_max_ms, numa_balancing_scan_size_mb
486	
487	Automatic NUMA balancing scans tasks address space and unmaps pages to
488	detect if pages are properly placed or if the data should be migrated to a
489	memory node local to where the task is running.  Every "scan delay" the task
490	scans the next "scan size" number of pages in its address space. When the
491	end of the address space is reached the scanner restarts from the beginning.
492	
493	In combination, the "scan delay" and "scan size" determine the scan rate.
494	When "scan delay" decreases, the scan rate increases.  The scan delay and
495	hence the scan rate of every task is adaptive and depends on historical
496	behaviour. If pages are properly placed then the scan delay increases,
497	otherwise the scan delay decreases.  The "scan size" is not adaptive but
498	the higher the "scan size", the higher the scan rate.
499	
500	Higher scan rates incur higher system overhead as page faults must be
501	trapped and potentially data must be migrated. However, the higher the scan
502	rate, the more quickly a tasks memory is migrated to a local node if the
503	workload pattern changes and minimises performance impact due to remote
504	memory accesses. These sysctls control the thresholds for scan delays and
505	the number of pages scanned.
506	
507	numa_balancing_scan_period_min_ms is the minimum time in milliseconds to
508	scan a tasks virtual memory. It effectively controls the maximum scanning
509	rate for each task.
510	
511	numa_balancing_scan_delay_ms is the starting "scan delay" used for a task
512	when it initially forks.
513	
514	numa_balancing_scan_period_max_ms is the maximum time in milliseconds to
515	scan a tasks virtual memory. It effectively controls the minimum scanning
516	rate for each task.
517	
518	numa_balancing_scan_size_mb is how many megabytes worth of pages are
519	scanned for a given scan.
520	
521	==============================================================
522	
523	osrelease, ostype & version:
524	
525	# cat osrelease
526	2.1.88
527	# cat ostype
528	Linux
529	# cat version
530	#5 Wed Feb 25 21:49:24 MET 1998
531	
532	The files osrelease and ostype should be clear enough. Version
533	needs a little more clarification however. The '#5' means that
534	this is the fifth kernel built from this source base and the
535	date behind it indicates the time the kernel was built.
536	The only way to tune these values is to rebuild the kernel :-)
537	
538	==============================================================
539	
540	overflowgid & overflowuid:
541	
542	if your architecture did not always support 32-bit UIDs (i.e. arm,
543	i386, m68k, sh, and sparc32), a fixed UID and GID will be returned to
544	applications that use the old 16-bit UID/GID system calls, if the
545	actual UID or GID would exceed 65535.
546	
547	These sysctls allow you to change the value of the fixed UID and GID.
548	The default is 65534.
549	
550	==============================================================
551	
552	panic:
553	
554	The value in this file represents the number of seconds the kernel
555	waits before rebooting on a panic. When you use the software watchdog,
556	the recommended setting is 60.
557	
558	==============================================================
559	
560	panic_on_io_nmi:
561	
562	Controls the kernel's behavior when a CPU receives an NMI caused by
563	an IO error.
564	
565	0: try to continue operation (default)
566	
567	1: panic immediately. The IO error triggered an NMI. This indicates a
568	   serious system condition which could result in IO data corruption.
569	   Rather than continuing, panicking might be a better choice. Some
570	   servers issue this sort of NMI when the dump button is pushed,
571	   and you can use this option to take a crash dump.
572	
573	==============================================================
574	
575	panic_on_oops:
576	
577	Controls the kernel's behaviour when an oops or BUG is encountered.
578	
579	0: try to continue operation
580	
581	1: panic immediately.  If the `panic' sysctl is also non-zero then the
582	   machine will be rebooted.
583	
584	==============================================================
585	
586	panic_on_stackoverflow:
587	
588	Controls the kernel's behavior when detecting the overflows of
589	kernel, IRQ and exception stacks except a user stack.
590	This file shows up if CONFIG_DEBUG_STACKOVERFLOW is enabled.
591	
592	0: try to continue operation.
593	
594	1: panic immediately.
595	
596	==============================================================
597	
598	panic_on_unrecovered_nmi:
599	
600	The default Linux behaviour on an NMI of either memory or unknown is
601	to continue operation. For many environments such as scientific
602	computing it is preferable that the box is taken out and the error
603	dealt with than an uncorrected parity/ECC error get propagated.
604	
605	A small number of systems do generate NMI's for bizarre random reasons
606	such as power management so the default is off. That sysctl works like
607	the existing panic controls already in that directory.
608	
609	==============================================================
610	
611	panic_on_warn:
612	
613	Calls panic() in the WARN() path when set to 1.  This is useful to avoid
614	a kernel rebuild when attempting to kdump at the location of a WARN().
615	
616	0: only WARN(), default behaviour.
617	
618	1: call panic() after printing out WARN() location.
619	
620	==============================================================
621	
622	panic_on_rcu_stall:
623	
624	When set to 1, calls panic() after RCU stall detection messages. This
625	is useful to define the root cause of RCU stalls using a vmcore.
626	
627	0: do not panic() when RCU stall takes place, default behavior.
628	
629	1: panic() after printing RCU stall messages.
630	
631	==============================================================
632	
633	perf_cpu_time_max_percent:
634	
635	Hints to the kernel how much CPU time it should be allowed to
636	use to handle perf sampling events.  If the perf subsystem
637	is informed that its samples are exceeding this limit, it
638	will drop its sampling frequency to attempt to reduce its CPU
639	usage.
640	
641	Some perf sampling happens in NMIs.  If these samples
642	unexpectedly take too long to execute, the NMIs can become
643	stacked up next to each other so much that nothing else is
644	allowed to execute.
645	
646	0: disable the mechanism.  Do not monitor or correct perf's
647	   sampling rate no matter how CPU time it takes.
648	
649	1-100: attempt to throttle perf's sample rate to this
650	   percentage of CPU.  Note: the kernel calculates an
651	   "expected" length of each sample event.  100 here means
652	   100% of that expected length.  Even if this is set to
653	   100, you may still see sample throttling if this
654	   length is exceeded.  Set to 0 if you truly do not care
655	   how much CPU is consumed.
656	
657	==============================================================
658	
659	perf_event_paranoid:
660	
661	Controls use of the performance events system by unprivileged
662	users (without CAP_SYS_ADMIN).  The default value is 2.
663	
664	 -1: Allow use of (almost) all events by all users
665	>=0: Disallow raw tracepoint access by users without CAP_IOC_LOCK
666	>=1: Disallow CPU event access by users without CAP_SYS_ADMIN
667	>=2: Disallow kernel profiling by users without CAP_SYS_ADMIN
668	
669	==============================================================
670	
671	perf_event_max_stack:
672	
673	Controls maximum number of stack frames to copy for (attr.sample_type &
674	PERF_SAMPLE_CALLCHAIN) configured events, for instance, when using
675	'perf record -g' or 'perf trace --call-graph fp'.
676	
677	This can only be done when no events are in use that have callchains
678	enabled, otherwise writing to this file will return -EBUSY.
679	
680	The default value is 127.
681	
682	==============================================================
683	
684	perf_event_max_contexts_per_stack:
685	
686	Controls maximum number of stack frame context entries for
687	(attr.sample_type & PERF_SAMPLE_CALLCHAIN) configured events, for
688	instance, when using 'perf record -g' or 'perf trace --call-graph fp'.
689	
690	This can only be done when no events are in use that have callchains
691	enabled, otherwise writing to this file will return -EBUSY.
692	
693	The default value is 8.
694	
695	==============================================================
696	
697	pid_max:
698	
699	PID allocation wrap value.  When the kernel's next PID value
700	reaches this value, it wraps back to a minimum PID value.
701	PIDs of value pid_max or larger are not allocated.
702	
703	==============================================================
704	
705	ns_last_pid:
706	
707	The last pid allocated in the current (the one task using this sysctl
708	lives in) pid namespace. When selecting a pid for a next task on fork
709	kernel tries to allocate a number starting from this one.
710	
711	==============================================================
712	
713	powersave-nap: (PPC only)
714	
715	If set, Linux-PPC will use the 'nap' mode of powersaving,
716	otherwise the 'doze' mode will be used.
717	
718	==============================================================
719	
720	printk:
721	
722	The four values in printk denote: console_loglevel,
723	default_message_loglevel, minimum_console_loglevel and
724	default_console_loglevel respectively.
725	
726	These values influence printk() behavior when printing or
727	logging error messages. See 'man 2 syslog' for more info on
728	the different loglevels.
729	
730	- console_loglevel: messages with a higher priority than
731	  this will be printed to the console
732	- default_message_loglevel: messages without an explicit priority
733	  will be printed with this priority
734	- minimum_console_loglevel: minimum (highest) value to which
735	  console_loglevel can be set
736	- default_console_loglevel: default value for console_loglevel
737	
738	==============================================================
739	
740	printk_delay:
741	
742	Delay each printk message in printk_delay milliseconds
743	
744	Value from 0 - 10000 is allowed.
745	
746	==============================================================
747	
748	printk_ratelimit:
749	
750	Some warning messages are rate limited. printk_ratelimit specifies
751	the minimum length of time between these messages (in jiffies), by
752	default we allow one every 5 seconds.
753	
754	A value of 0 will disable rate limiting.
755	
756	==============================================================
757	
758	printk_ratelimit_burst:
759	
760	While long term we enforce one message per printk_ratelimit
761	seconds, we do allow a burst of messages to pass through.
762	printk_ratelimit_burst specifies the number of messages we can
763	send before ratelimiting kicks in.
764	
765	==============================================================
766	
767	printk_devkmsg:
768	
769	Control the logging to /dev/kmsg from userspace:
770	
771	ratelimit: default, ratelimited
772	on: unlimited logging to /dev/kmsg from userspace
773	off: logging to /dev/kmsg disabled
774	
775	The kernel command line parameter printk.devkmsg= overrides this and is
776	a one-time setting until next reboot: once set, it cannot be changed by
777	this sysctl interface anymore.
778	
779	==============================================================
780	
781	randomize_va_space:
782	
783	This option can be used to select the type of process address
784	space randomization that is used in the system, for architectures
785	that support this feature.
786	
787	0 - Turn the process address space randomization off.  This is the
788	    default for architectures that do not support this feature anyways,
789	    and kernels that are booted with the "norandmaps" parameter.
790	
791	1 - Make the addresses of mmap base, stack and VDSO page randomized.
792	    This, among other things, implies that shared libraries will be
793	    loaded to random addresses.  Also for PIE-linked binaries, the
794	    location of code start is randomized.  This is the default if the
795	    CONFIG_COMPAT_BRK option is enabled.
796	
797	2 - Additionally enable heap randomization.  This is the default if
798	    CONFIG_COMPAT_BRK is disabled.
799	
800	    There are a few legacy applications out there (such as some ancient
801	    versions of libc.so.5 from 1996) that assume that brk area starts
802	    just after the end of the code+bss.  These applications break when
803	    start of the brk area is randomized.  There are however no known
804	    non-legacy applications that would be broken this way, so for most
805	    systems it is safe to choose full randomization.
806	
807	    Systems with ancient and/or broken binaries should be configured
808	    with CONFIG_COMPAT_BRK enabled, which excludes the heap from process
809	    address space randomization.
810	
811	==============================================================
812	
813	reboot-cmd: (Sparc only)
814	
815	??? This seems to be a way to give an argument to the Sparc
816	ROM/Flash boot loader. Maybe to tell it what to do after
817	rebooting. ???
818	
819	==============================================================
820	
821	rtsig-max & rtsig-nr:
822	
823	The file rtsig-max can be used to tune the maximum number
824	of POSIX realtime (queued) signals that can be outstanding
825	in the system.
826	
827	rtsig-nr shows the number of RT signals currently queued.
828	
829	==============================================================
830	
831	sched_schedstats:
832	
833	Enables/disables scheduler statistics. Enabling this feature
834	incurs a small amount of overhead in the scheduler but is
835	useful for debugging and performance tuning.
836	
837	==============================================================
838	
839	sg-big-buff:
840	
841	This file shows the size of the generic SCSI (sg) buffer.
842	You can't tune it just yet, but you could change it on
843	compile time by editing include/scsi/sg.h and changing
844	the value of SG_BIG_BUFF.
845	
846	There shouldn't be any reason to change this value. If
847	you can come up with one, you probably know what you
848	are doing anyway :)
849	
850	==============================================================
851	
852	shmall:
853	
854	This parameter sets the total amount of shared memory pages that
855	can be used system wide. Hence, SHMALL should always be at least
856	ceil(shmmax/PAGE_SIZE).
857	
858	If you are not sure what the default PAGE_SIZE is on your Linux
859	system, you can run the following command:
860	
861	# getconf PAGE_SIZE
862	
863	==============================================================
864	
865	shmmax:
866	
867	This value can be used to query and set the run time limit
868	on the maximum shared memory segment size that can be created.
869	Shared memory segments up to 1Gb are now supported in the
870	kernel.  This value defaults to SHMMAX.
871	
872	==============================================================
873	
874	shm_rmid_forced:
875	
876	Linux lets you set resource limits, including how much memory one
877	process can consume, via setrlimit(2).  Unfortunately, shared memory
878	segments are allowed to exist without association with any process, and
879	thus might not be counted against any resource limits.  If enabled,
880	shared memory segments are automatically destroyed when their attach
881	count becomes zero after a detach or a process termination.  It will
882	also destroy segments that were created, but never attached to, on exit
883	from the process.  The only use left for IPC_RMID is to immediately
884	destroy an unattached segment.  Of course, this breaks the way things are
885	defined, so some applications might stop working.  Note that this
886	feature will do you no good unless you also configure your resource
887	limits (in particular, RLIMIT_AS and RLIMIT_NPROC).  Most systems don't
888	need this.
889	
890	Note that if you change this from 0 to 1, already created segments
891	without users and with a dead originative process will be destroyed.
892	
893	==============================================================
894	
895	sysctl_writes_strict:
896	
897	Control how file position affects the behavior of updating sysctl values
898	via the /proc/sys interface:
899	
900	  -1 - Legacy per-write sysctl value handling, with no printk warnings.
901	       Each write syscall must fully contain the sysctl value to be
902	       written, and multiple writes on the same sysctl file descriptor
903	       will rewrite the sysctl value, regardless of file position.
904	   0 - Same behavior as above, but warn about processes that perform writes
905	       to a sysctl file descriptor when the file position is not 0.
906	   1 - (default) Respect file position when writing sysctl strings. Multiple
907	       writes will append to the sysctl value buffer. Anything past the max
908	       length of the sysctl value buffer will be ignored. Writes to numeric
909	       sysctl entries must always be at file position 0 and the value must
910	       be fully contained in the buffer sent in the write syscall.
911	
912	==============================================================
913	
914	softlockup_all_cpu_backtrace:
915	
916	This value controls the soft lockup detector thread's behavior
917	when a soft lockup condition is detected as to whether or not
918	to gather further debug information. If enabled, each cpu will
919	be issued an NMI and instructed to capture stack trace.
920	
921	This feature is only applicable for architectures which support
922	NMI.
923	
924	0: do nothing. This is the default behavior.
925	
926	1: on detection capture more debug information.
927	
928	==============================================================
929	
930	soft_watchdog
931	
932	This parameter can be used to control the soft lockup detector.
933	
934	   0 - disable the soft lockup detector
935	   1 - enable the soft lockup detector
936	
937	The soft lockup detector monitors CPUs for threads that are hogging the CPUs
938	without rescheduling voluntarily, and thus prevent the 'watchdog/N' threads
939	from running. The mechanism depends on the CPUs ability to respond to timer
940	interrupts which are needed for the 'watchdog/N' threads to be woken up by
941	the watchdog timer function, otherwise the NMI watchdog - if enabled - can
942	detect a hard lockup condition.
943	
944	==============================================================
945	
946	tainted:
947	
948	Non-zero if the kernel has been tainted.  Numeric values, which
949	can be ORed together:
950	
951	   1 - A module with a non-GPL license has been loaded, this
952	       includes modules with no license.
953	       Set by modutils >= 2.4.9 and module-init-tools.
954	   2 - A module was force loaded by insmod -f.
955	       Set by modutils >= 2.4.9 and module-init-tools.
956	   4 - Unsafe SMP processors: SMP with CPUs not designed for SMP.
957	   8 - A module was forcibly unloaded from the system by rmmod -f.
958	  16 - A hardware machine check error occurred on the system.
959	  32 - A bad page was discovered on the system.
960	  64 - The user has asked that the system be marked "tainted".  This
961	       could be because they are running software that directly modifies
962	       the hardware, or for other reasons.
963	 128 - The system has died.
964	 256 - The ACPI DSDT has been overridden with one supplied by the user
965	        instead of using the one provided by the hardware.
966	 512 - A kernel warning has occurred.
967	1024 - A module from drivers/staging was loaded.
968	2048 - The system is working around a severe firmware bug.
969	4096 - An out-of-tree module has been loaded.
970	8192 - An unsigned module has been loaded in a kernel supporting module
971	       signature.
972	16384 - A soft lockup has previously occurred on the system.
973	32768 - The kernel has been live patched.
974	
975	==============================================================
976	
977	threads-max
978	
979	This value controls the maximum number of threads that can be created
980	using fork().
981	
982	During initialization the kernel sets this value such that even if the
983	maximum number of threads is created, the thread structures occupy only
984	a part (1/8th) of the available RAM pages.
985	
986	The minimum value that can be written to threads-max is 20.
987	The maximum value that can be written to threads-max is given by the
988	constant FUTEX_TID_MASK (0x3fffffff).
989	If a value outside of this range is written to threads-max an error
990	EINVAL occurs.
991	
992	The value written is checked against the available RAM pages. If the
993	thread structures would occupy too much (more than 1/8th) of the
994	available RAM pages threads-max is reduced accordingly.
995	
996	==============================================================
997	
998	unknown_nmi_panic:
999	
1000	The value in this file affects behavior of handling NMI. When the
1001	value is non-zero, unknown NMI is trapped and then panic occurs. At
1002	that time, kernel debugging information is displayed on console.
1003	
1004	NMI switch that most IA32 servers have fires unknown NMI up, for
1005	example.  If a system hangs up, try pressing the NMI switch.
1006	
1007	==============================================================
1008	
1009	watchdog:
1010	
1011	This parameter can be used to disable or enable the soft lockup detector
1012	_and_ the NMI watchdog (i.e. the hard lockup detector) at the same time.
1013	
1014	   0 - disable both lockup detectors
1015	   1 - enable both lockup detectors
1016	
1017	The soft lockup detector and the NMI watchdog can also be disabled or
1018	enabled individually, using the soft_watchdog and nmi_watchdog parameters.
1019	If the watchdog parameter is read, for example by executing
1020	
1021	   cat /proc/sys/kernel/watchdog
1022	
1023	the output of this command (0 or 1) shows the logical OR of soft_watchdog
1024	and nmi_watchdog.
1025	
1026	==============================================================
1027	
1028	watchdog_cpumask:
1029	
1030	This value can be used to control on which cpus the watchdog may run.
1031	The default cpumask is all possible cores, but if NO_HZ_FULL is
1032	enabled in the kernel config, and cores are specified with the
1033	nohz_full= boot argument, those cores are excluded by default.
1034	Offline cores can be included in this mask, and if the core is later
1035	brought online, the watchdog will be started based on the mask value.
1036	
1037	Typically this value would only be touched in the nohz_full case
1038	to re-enable cores that by default were not running the watchdog,
1039	if a kernel lockup was suspected on those cores.
1040	
1041	The argument value is the standard cpulist format for cpumasks,
1042	so for example to enable the watchdog on cores 0, 2, 3, and 4 you
1043	might say:
1044	
1045	  echo 0,2-4 > /proc/sys/kernel/watchdog_cpumask
1046	
1047	==============================================================
1048	
1049	watchdog_thresh:
1050	
1051	This value can be used to control the frequency of hrtimer and NMI
1052	events and the soft and hard lockup thresholds. The default threshold
1053	is 10 seconds.
1054	
1055	The softlockup threshold is (2 * watchdog_thresh). Setting this
1056	tunable to zero will disable lockup detection altogether.
1057	
1058	==============================================================
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