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>
5 For general info and legal blurb, please look in README.
7 ==============================================================
9 This file contains documentation for the sysctl files in
10 /proc/sys/kernel/ and is valid for Linux kernel version 2.2.
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.
18 Currently, these files might (depending on your configuration)
19 show up in /proc/sys/kernel:
24 - bootloader_type [ X86 only ]
25 - bootloader_version [ X86 only ]
26 - callhome [ S390 only ]
36 - hardlockup_all_cpu_backtrace
38 - hung_task_check_count
39 - hung_task_timeout_secs
44 - modprobe ==> Documentation/debugging-modules.txt
46 - msg_next_id [ sysv ipc ]
57 - panic_on_stackoverflow
58 - panic_on_unrecovered_nmi
61 - perf_cpu_time_max_percent
63 - perf_event_max_stack
64 - perf_event_max_contexts_per_stack
66 - powersave-nap [ PPC only ]
70 - printk_ratelimit_burst
71 - pty ==> Documentation/filesystems/devpts.txt
73 - real-root-dev ==> Documentation/admin-guide/initrd.rst
74 - reboot-cmd [ SPARC only ]
77 - seccomp/ ==> Documentation/userspace-api/seccomp_filter.rst
79 - sem_next_id [ sysv ipc ]
80 - sg-big-buff [ generic SCSI device (sg) ]
81 - shm_next_id [ sysv ipc ]
86 - softlockup_all_cpu_backtrace
88 - stop-a [ SPARC only ]
89 - sysrq ==> Documentation/admin-guide/sysrq.rst
90 - sysctl_writes_strict
98 ==============================================================
102 highwater lowwater frequency
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
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.
115 ==============================================================
121 See Doc*/kernel/power/video.txt, it allows mode of video boot to be
124 ==============================================================
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.
136 ==============================================================
140 x86 bootloader identification
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.
150 See the type_of_loader and ext_loader_type fields in
151 Documentation/x86/boot.txt for additional information.
153 ==============================================================
157 x86 bootloader version
159 The complete bootloader version number. In the example above, this
160 file will contain the value 564 = 0x234.
162 See the type_of_loader and ext_loader_ver fields in
163 Documentation/x86/boot.txt for additional information.
165 ==============================================================
169 Controls the kernel's callhome behavior in case of a kernel panic.
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.
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.
180 ==============================================================
184 Highest valid capability of the running kernel. Exports
185 CAP_LAST_CAP from the kernel.
187 ==============================================================
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
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
200 . corename format specifiers:
201 %<NUL> '%' is dropped
204 %P global pid (init PID namespace)
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
214 %e executable filename (may be shortened)
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.
221 ==============================================================
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
244 ==============================================================
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
254 ==============================================================
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.
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.
269 ==============================================================
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
279 The kernel config option CONFIG_SECURITY_DMESG_RESTRICT sets the
280 default value of dmesg_restrict.
282 ==============================================================
284 domainname & hostname:
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"
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.
302 ==============================================================
303 hardlockup_all_cpu_backtrace:
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
310 0: do nothing. This is the default behavior.
312 1: on detection capture more debug information.
313 ==============================================================
317 Path for the hotplug policy agent.
318 Default value is "/sbin/hotplug".
320 ==============================================================
324 Controls the kernel's behavior when a hung task is detected.
325 This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.
327 0: continue operation. This is the default behavior.
329 1: panic immediately.
331 ==============================================================
333 hung_task_check_count:
335 The upper bound on the number of tasks that are checked.
336 This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.
338 ==============================================================
340 hung_task_timeout_secs:
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.
346 0: means infinite timeout - no checking done.
347 Possible values to set are in range {0..LONG_MAX/HZ}.
349 ==============================================================
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.
358 -1: report an infinite number of warnings.
360 ==============================================================
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.
372 ==============================================================
376 This toggle indicates whether restrictions are placed on
377 exposing kernel addresses via /proc and other interfaces.
379 When kptr_restrict is set to (0), the default, there are no restrictions.
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.
393 When kptr_restrict is set to (2), kernel pointers printed using
394 %pK will be replaced with 0's regardless of privileges.
396 ==============================================================
400 This flag controls the L2 cache of G3 processor boards. If
401 0, the cache is disabled. Enabled if nonzero.
403 ==============================================================
407 A toggle value indicating if modules are allowed to be loaded
408 in an otherwise modular kernel. This toggle defaults to off
409 (0), but can be set true (1). Once true, modules can be
410 neither loaded nor unloaded, and the toggle cannot be set back
411 to false. Generally used with the "kexec_load_disabled" toggle.
413 ==============================================================
415 msg_next_id, sem_next_id, and shm_next_id:
417 These three toggles allows to specify desired id for next allocated IPC
418 object: message, semaphore or shared memory respectively.
420 By default they are equal to -1, which means generic allocation logic.
421 Possible values to set are in range {0..INT_MAX}.
424 1) kernel doesn't guarantee, that new object will have desired id. So,
425 it's up to userspace, how to handle an object with "wrong" id.
426 2) Toggle with non-default value will be set back to -1 by kernel after
427 successful IPC object allocation.
429 ==============================================================
433 This parameter can be used to control the NMI watchdog
434 (i.e. the hard lockup detector) on x86 systems.
436 0 - disable the hard lockup detector
437 1 - enable the hard lockup detector
439 The hard lockup detector monitors each CPU for its ability to respond to
440 timer interrupts. The mechanism utilizes CPU performance counter registers
441 that are programmed to generate Non-Maskable Interrupts (NMIs) periodically
442 while a CPU is busy. Hence, the alternative name 'NMI watchdog'.
444 The NMI watchdog is disabled by default if the kernel is running as a guest
445 in a KVM virtual machine. This default can be overridden by adding
449 to the guest kernel command line (see Documentation/admin-guide/kernel-parameters.rst).
451 ==============================================================
455 Enables/disables automatic page fault based NUMA memory
456 balancing. Memory is moved automatically to nodes
457 that access it often.
459 Enables/disables automatic NUMA memory balancing. On NUMA machines, there
460 is a performance penalty if remote memory is accessed by a CPU. When this
461 feature is enabled the kernel samples what task thread is accessing memory
462 by periodically unmapping pages and later trapping a page fault. At the
463 time of the page fault, it is determined if the data being accessed should
464 be migrated to a local memory node.
466 The unmapping of pages and trapping faults incur additional overhead that
467 ideally is offset by improved memory locality but there is no universal
468 guarantee. If the target workload is already bound to NUMA nodes then this
469 feature should be disabled. Otherwise, if the system overhead from the
470 feature is too high then the rate the kernel samples for NUMA hinting
471 faults may be controlled by the numa_balancing_scan_period_min_ms,
472 numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms,
473 numa_balancing_scan_size_mb, and numa_balancing_settle_count sysctls.
475 ==============================================================
477 numa_balancing_scan_period_min_ms, numa_balancing_scan_delay_ms,
478 numa_balancing_scan_period_max_ms, numa_balancing_scan_size_mb
480 Automatic NUMA balancing scans tasks address space and unmaps pages to
481 detect if pages are properly placed or if the data should be migrated to a
482 memory node local to where the task is running. Every "scan delay" the task
483 scans the next "scan size" number of pages in its address space. When the
484 end of the address space is reached the scanner restarts from the beginning.
486 In combination, the "scan delay" and "scan size" determine the scan rate.
487 When "scan delay" decreases, the scan rate increases. The scan delay and
488 hence the scan rate of every task is adaptive and depends on historical
489 behaviour. If pages are properly placed then the scan delay increases,
490 otherwise the scan delay decreases. The "scan size" is not adaptive but
491 the higher the "scan size", the higher the scan rate.
493 Higher scan rates incur higher system overhead as page faults must be
494 trapped and potentially data must be migrated. However, the higher the scan
495 rate, the more quickly a tasks memory is migrated to a local node if the
496 workload pattern changes and minimises performance impact due to remote
497 memory accesses. These sysctls control the thresholds for scan delays and
498 the number of pages scanned.
500 numa_balancing_scan_period_min_ms is the minimum time in milliseconds to
501 scan a tasks virtual memory. It effectively controls the maximum scanning
504 numa_balancing_scan_delay_ms is the starting "scan delay" used for a task
505 when it initially forks.
507 numa_balancing_scan_period_max_ms is the maximum time in milliseconds to
508 scan a tasks virtual memory. It effectively controls the minimum scanning
511 numa_balancing_scan_size_mb is how many megabytes worth of pages are
512 scanned for a given scan.
514 ==============================================================
516 osrelease, ostype & version:
523 #5 Wed Feb 25 21:49:24 MET 1998
525 The files osrelease and ostype should be clear enough. Version
526 needs a little more clarification however. The '#5' means that
527 this is the fifth kernel built from this source base and the
528 date behind it indicates the time the kernel was built.
529 The only way to tune these values is to rebuild the kernel :-)
531 ==============================================================
533 overflowgid & overflowuid:
535 if your architecture did not always support 32-bit UIDs (i.e. arm,
536 i386, m68k, sh, and sparc32), a fixed UID and GID will be returned to
537 applications that use the old 16-bit UID/GID system calls, if the
538 actual UID or GID would exceed 65535.
540 These sysctls allow you to change the value of the fixed UID and GID.
541 The default is 65534.
543 ==============================================================
547 The value in this file represents the number of seconds the kernel
548 waits before rebooting on a panic. When you use the software watchdog,
549 the recommended setting is 60.
551 ==============================================================
555 Controls the kernel's behavior when a CPU receives an NMI caused by
558 0: try to continue operation (default)
560 1: panic immediately. The IO error triggered an NMI. This indicates a
561 serious system condition which could result in IO data corruption.
562 Rather than continuing, panicking might be a better choice. Some
563 servers issue this sort of NMI when the dump button is pushed,
564 and you can use this option to take a crash dump.
566 ==============================================================
570 Controls the kernel's behaviour when an oops or BUG is encountered.
572 0: try to continue operation
574 1: panic immediately. If the `panic' sysctl is also non-zero then the
575 machine will be rebooted.
577 ==============================================================
579 panic_on_stackoverflow:
581 Controls the kernel's behavior when detecting the overflows of
582 kernel, IRQ and exception stacks except a user stack.
583 This file shows up if CONFIG_DEBUG_STACKOVERFLOW is enabled.
585 0: try to continue operation.
587 1: panic immediately.
589 ==============================================================
591 panic_on_unrecovered_nmi:
593 The default Linux behaviour on an NMI of either memory or unknown is
594 to continue operation. For many environments such as scientific
595 computing it is preferable that the box is taken out and the error
596 dealt with than an uncorrected parity/ECC error get propagated.
598 A small number of systems do generate NMI's for bizarre random reasons
599 such as power management so the default is off. That sysctl works like
600 the existing panic controls already in that directory.
602 ==============================================================
606 Calls panic() in the WARN() path when set to 1. This is useful to avoid
607 a kernel rebuild when attempting to kdump at the location of a WARN().
609 0: only WARN(), default behaviour.
611 1: call panic() after printing out WARN() location.
613 ==============================================================
617 When set to 1, calls panic() after RCU stall detection messages. This
618 is useful to define the root cause of RCU stalls using a vmcore.
620 0: do not panic() when RCU stall takes place, default behavior.
622 1: panic() after printing RCU stall messages.
624 ==============================================================
626 perf_cpu_time_max_percent:
628 Hints to the kernel how much CPU time it should be allowed to
629 use to handle perf sampling events. If the perf subsystem
630 is informed that its samples are exceeding this limit, it
631 will drop its sampling frequency to attempt to reduce its CPU
634 Some perf sampling happens in NMIs. If these samples
635 unexpectedly take too long to execute, the NMIs can become
636 stacked up next to each other so much that nothing else is
639 0: disable the mechanism. Do not monitor or correct perf's
640 sampling rate no matter how CPU time it takes.
642 1-100: attempt to throttle perf's sample rate to this
643 percentage of CPU. Note: the kernel calculates an
644 "expected" length of each sample event. 100 here means
645 100% of that expected length. Even if this is set to
646 100, you may still see sample throttling if this
647 length is exceeded. Set to 0 if you truly do not care
648 how much CPU is consumed.
650 ==============================================================
654 Controls use of the performance events system by unprivileged
655 users (without CAP_SYS_ADMIN). The default value is 2.
657 -1: Allow use of (almost) all events by all users
658 >=0: Disallow raw tracepoint access by users without CAP_IOC_LOCK
659 >=1: Disallow CPU event access by users without CAP_SYS_ADMIN
660 >=2: Disallow kernel profiling by users without CAP_SYS_ADMIN
662 ==============================================================
664 perf_event_max_stack:
666 Controls maximum number of stack frames to copy for (attr.sample_type &
667 PERF_SAMPLE_CALLCHAIN) configured events, for instance, when using
668 'perf record -g' or 'perf trace --call-graph fp'.
670 This can only be done when no events are in use that have callchains
671 enabled, otherwise writing to this file will return -EBUSY.
673 The default value is 127.
675 ==============================================================
677 perf_event_max_contexts_per_stack:
679 Controls maximum number of stack frame context entries for
680 (attr.sample_type & PERF_SAMPLE_CALLCHAIN) configured events, for
681 instance, when using 'perf record -g' or 'perf trace --call-graph fp'.
683 This can only be done when no events are in use that have callchains
684 enabled, otherwise writing to this file will return -EBUSY.
686 The default value is 8.
688 ==============================================================
692 PID allocation wrap value. When the kernel's next PID value
693 reaches this value, it wraps back to a minimum PID value.
694 PIDs of value pid_max or larger are not allocated.
696 ==============================================================
700 The last pid allocated in the current (the one task using this sysctl
701 lives in) pid namespace. When selecting a pid for a next task on fork
702 kernel tries to allocate a number starting from this one.
704 ==============================================================
706 powersave-nap: (PPC only)
708 If set, Linux-PPC will use the 'nap' mode of powersaving,
709 otherwise the 'doze' mode will be used.
711 ==============================================================
715 The four values in printk denote: console_loglevel,
716 default_message_loglevel, minimum_console_loglevel and
717 default_console_loglevel respectively.
719 These values influence printk() behavior when printing or
720 logging error messages. See 'man 2 syslog' for more info on
721 the different loglevels.
723 - console_loglevel: messages with a higher priority than
724 this will be printed to the console
725 - default_message_loglevel: messages without an explicit priority
726 will be printed with this priority
727 - minimum_console_loglevel: minimum (highest) value to which
728 console_loglevel can be set
729 - default_console_loglevel: default value for console_loglevel
731 ==============================================================
735 Delay each printk message in printk_delay milliseconds
737 Value from 0 - 10000 is allowed.
739 ==============================================================
743 Some warning messages are rate limited. printk_ratelimit specifies
744 the minimum length of time between these messages (in jiffies), by
745 default we allow one every 5 seconds.
747 A value of 0 will disable rate limiting.
749 ==============================================================
751 printk_ratelimit_burst:
753 While long term we enforce one message per printk_ratelimit
754 seconds, we do allow a burst of messages to pass through.
755 printk_ratelimit_burst specifies the number of messages we can
756 send before ratelimiting kicks in.
758 ==============================================================
762 Control the logging to /dev/kmsg from userspace:
764 ratelimit: default, ratelimited
765 on: unlimited logging to /dev/kmsg from userspace
766 off: logging to /dev/kmsg disabled
768 The kernel command line parameter printk.devkmsg= overrides this and is
769 a one-time setting until next reboot: once set, it cannot be changed by
770 this sysctl interface anymore.
772 ==============================================================
776 This option can be used to select the type of process address
777 space randomization that is used in the system, for architectures
778 that support this feature.
780 0 - Turn the process address space randomization off. This is the
781 default for architectures that do not support this feature anyways,
782 and kernels that are booted with the "norandmaps" parameter.
784 1 - Make the addresses of mmap base, stack and VDSO page randomized.
785 This, among other things, implies that shared libraries will be
786 loaded to random addresses. Also for PIE-linked binaries, the
787 location of code start is randomized. This is the default if the
788 CONFIG_COMPAT_BRK option is enabled.
790 2 - Additionally enable heap randomization. This is the default if
791 CONFIG_COMPAT_BRK is disabled.
793 There are a few legacy applications out there (such as some ancient
794 versions of libc.so.5 from 1996) that assume that brk area starts
795 just after the end of the code+bss. These applications break when
796 start of the brk area is randomized. There are however no known
797 non-legacy applications that would be broken this way, so for most
798 systems it is safe to choose full randomization.
800 Systems with ancient and/or broken binaries should be configured
801 with CONFIG_COMPAT_BRK enabled, which excludes the heap from process
802 address space randomization.
804 ==============================================================
806 reboot-cmd: (Sparc only)
808 ??? This seems to be a way to give an argument to the Sparc
809 ROM/Flash boot loader. Maybe to tell it what to do after
812 ==============================================================
814 rtsig-max & rtsig-nr:
816 The file rtsig-max can be used to tune the maximum number
817 of POSIX realtime (queued) signals that can be outstanding
820 rtsig-nr shows the number of RT signals currently queued.
822 ==============================================================
826 Enables/disables scheduler statistics. Enabling this feature
827 incurs a small amount of overhead in the scheduler but is
828 useful for debugging and performance tuning.
830 ==============================================================
834 This file shows the size of the generic SCSI (sg) buffer.
835 You can't tune it just yet, but you could change it on
836 compile time by editing include/scsi/sg.h and changing
837 the value of SG_BIG_BUFF.
839 There shouldn't be any reason to change this value. If
840 you can come up with one, you probably know what you
843 ==============================================================
847 This parameter sets the total amount of shared memory pages that
848 can be used system wide. Hence, SHMALL should always be at least
849 ceil(shmmax/PAGE_SIZE).
851 If you are not sure what the default PAGE_SIZE is on your Linux
852 system, you can run the following command:
856 ==============================================================
860 This value can be used to query and set the run time limit
861 on the maximum shared memory segment size that can be created.
862 Shared memory segments up to 1Gb are now supported in the
863 kernel. This value defaults to SHMMAX.
865 ==============================================================
869 Linux lets you set resource limits, including how much memory one
870 process can consume, via setrlimit(2). Unfortunately, shared memory
871 segments are allowed to exist without association with any process, and
872 thus might not be counted against any resource limits. If enabled,
873 shared memory segments are automatically destroyed when their attach
874 count becomes zero after a detach or a process termination. It will
875 also destroy segments that were created, but never attached to, on exit
876 from the process. The only use left for IPC_RMID is to immediately
877 destroy an unattached segment. Of course, this breaks the way things are
878 defined, so some applications might stop working. Note that this
879 feature will do you no good unless you also configure your resource
880 limits (in particular, RLIMIT_AS and RLIMIT_NPROC). Most systems don't
883 Note that if you change this from 0 to 1, already created segments
884 without users and with a dead originative process will be destroyed.
886 ==============================================================
888 sysctl_writes_strict:
890 Control how file position affects the behavior of updating sysctl values
891 via the /proc/sys interface:
893 -1 - Legacy per-write sysctl value handling, with no printk warnings.
894 Each write syscall must fully contain the sysctl value to be
895 written, and multiple writes on the same sysctl file descriptor
896 will rewrite the sysctl value, regardless of file position.
897 0 - Same behavior as above, but warn about processes that perform writes
898 to a sysctl file descriptor when the file position is not 0.
899 1 - (default) Respect file position when writing sysctl strings. Multiple
900 writes will append to the sysctl value buffer. Anything past the max
901 length of the sysctl value buffer will be ignored. Writes to numeric
902 sysctl entries must always be at file position 0 and the value must
903 be fully contained in the buffer sent in the write syscall.
905 ==============================================================
907 softlockup_all_cpu_backtrace:
909 This value controls the soft lockup detector thread's behavior
910 when a soft lockup condition is detected as to whether or not
911 to gather further debug information. If enabled, each cpu will
912 be issued an NMI and instructed to capture stack trace.
914 This feature is only applicable for architectures which support
917 0: do nothing. This is the default behavior.
919 1: on detection capture more debug information.
921 ==============================================================
925 This parameter can be used to control the soft lockup detector.
927 0 - disable the soft lockup detector
928 1 - enable the soft lockup detector
930 The soft lockup detector monitors CPUs for threads that are hogging the CPUs
931 without rescheduling voluntarily, and thus prevent the 'watchdog/N' threads
932 from running. The mechanism depends on the CPUs ability to respond to timer
933 interrupts which are needed for the 'watchdog/N' threads to be woken up by
934 the watchdog timer function, otherwise the NMI watchdog - if enabled - can
935 detect a hard lockup condition.
937 ==============================================================
941 Non-zero if the kernel has been tainted. Numeric values, which
942 can be ORed together:
944 1 - A module with a non-GPL license has been loaded, this
945 includes modules with no license.
946 Set by modutils >= 2.4.9 and module-init-tools.
947 2 - A module was force loaded by insmod -f.
948 Set by modutils >= 2.4.9 and module-init-tools.
949 4 - Unsafe SMP processors: SMP with CPUs not designed for SMP.
950 8 - A module was forcibly unloaded from the system by rmmod -f.
951 16 - A hardware machine check error occurred on the system.
952 32 - A bad page was discovered on the system.
953 64 - The user has asked that the system be marked "tainted". This
954 could be because they are running software that directly modifies
955 the hardware, or for other reasons.
956 128 - The system has died.
957 256 - The ACPI DSDT has been overridden with one supplied by the user
958 instead of using the one provided by the hardware.
959 512 - A kernel warning has occurred.
960 1024 - A module from drivers/staging was loaded.
961 2048 - The system is working around a severe firmware bug.
962 4096 - An out-of-tree module has been loaded.
963 8192 - An unsigned module has been loaded in a kernel supporting module
965 16384 - A soft lockup has previously occurred on the system.
966 32768 - The kernel has been live patched.
968 ==============================================================
972 This value controls the maximum number of threads that can be created
975 During initialization the kernel sets this value such that even if the
976 maximum number of threads is created, the thread structures occupy only
977 a part (1/8th) of the available RAM pages.
979 The minimum value that can be written to threads-max is 20.
980 The maximum value that can be written to threads-max is given by the
981 constant FUTEX_TID_MASK (0x3fffffff).
982 If a value outside of this range is written to threads-max an error
985 The value written is checked against the available RAM pages. If the
986 thread structures would occupy too much (more than 1/8th) of the
987 available RAM pages threads-max is reduced accordingly.
989 ==============================================================
993 The value in this file affects behavior of handling NMI. When the
994 value is non-zero, unknown NMI is trapped and then panic occurs. At
995 that time, kernel debugging information is displayed on console.
997 NMI switch that most IA32 servers have fires unknown NMI up, for
998 example. If a system hangs up, try pressing the NMI switch.
1000 ==============================================================
1004 This parameter can be used to disable or enable the soft lockup detector
1005 _and_ the NMI watchdog (i.e. the hard lockup detector) at the same time.
1007 0 - disable both lockup detectors
1008 1 - enable both lockup detectors
1010 The soft lockup detector and the NMI watchdog can also be disabled or
1011 enabled individually, using the soft_watchdog and nmi_watchdog parameters.
1012 If the watchdog parameter is read, for example by executing
1014 cat /proc/sys/kernel/watchdog
1016 the output of this command (0 or 1) shows the logical OR of soft_watchdog
1019 ==============================================================
1023 This value can be used to control on which cpus the watchdog may run.
1024 The default cpumask is all possible cores, but if NO_HZ_FULL is
1025 enabled in the kernel config, and cores are specified with the
1026 nohz_full= boot argument, those cores are excluded by default.
1027 Offline cores can be included in this mask, and if the core is later
1028 brought online, the watchdog will be started based on the mask value.
1030 Typically this value would only be touched in the nohz_full case
1031 to re-enable cores that by default were not running the watchdog,
1032 if a kernel lockup was suspected on those cores.
1034 The argument value is the standard cpulist format for cpumasks,
1035 so for example to enable the watchdog on cores 0, 2, 3, and 4 you
1038 echo 0,2-4 > /proc/sys/kernel/watchdog_cpumask
1040 ==============================================================
1044 This value can be used to control the frequency of hrtimer and NMI
1045 events and the soft and hard lockup thresholds. The default threshold
1048 The softlockup threshold is (2 * watchdog_thresh). Setting this
1049 tunable to zero will disable lockup detection altogether.
1051 ==============================================================