1Documentation 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 5For general info and legal blurb, please look in README. 6 7============================================================== 8 9This file contains documentation for the sysctl files in 10/proc/sys/kernel/ and is valid for Linux kernel version 2.2. 11 12The files in this directory can be used to tune and monitor 13miscellaneous and general things in the operation of the Linux 14kernel. Since some of the files _can_ be used to screw up your 15system, it is advisable to read both documentation and source 16before actually making adjustments. 17 18Currently, these files might (depending on your configuration) 19show 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- perf_cpu_time_max_percent 62- perf_event_paranoid 63- pid_max 64- powersave-nap [ PPC only ] 65- printk 66- printk_delay 67- printk_ratelimit 68- printk_ratelimit_burst 69- randomize_va_space 70- real-root-dev ==> Documentation/initrd.txt 71- reboot-cmd [ SPARC only ] 72- rtsig-max 73- rtsig-nr 74- sem 75- sem_next_id [ sysv ipc ] 76- sg-big-buff [ generic SCSI device (sg) ] 77- shm_next_id [ sysv ipc ] 78- shm_rmid_forced 79- shmall 80- shmmax [ sysv ipc ] 81- shmmni 82- softlockup_all_cpu_backtrace 83- soft_watchdog 84- stop-a [ SPARC only ] 85- sysrq ==> Documentation/sysrq.txt 86- sysctl_writes_strict 87- tainted 88- threads-max 89- unknown_nmi_panic 90- watchdog 91- watchdog_thresh 92- version 93 94============================================================== 95 96acct: 97 98highwater lowwater frequency 99 100If BSD-style process accounting is enabled these values control 101its behaviour. If free space on filesystem where the log lives 102goes below <lowwater>% accounting suspends. If free space gets 103above <highwater>% accounting resumes. <Frequency> determines 104how often do we check the amount of free space (value is in 105seconds). Default: 1064 2 30 107That is, suspend accounting if there left <= 2% free; resume it 108if we got >=4%; consider information about amount of free space 109valid for 30 seconds. 110 111============================================================== 112 113acpi_video_flags: 114 115flags 116 117See Doc*/kernel/power/video.txt, it allows mode of video boot to be 118set during run time. 119 120============================================================== 121 122auto_msgmni: 123 124This variable has no effect and may be removed in future kernel 125releases. Reading it always returns 0. 126Up to Linux 3.17, it enabled/disabled automatic recomputing of msgmni 127upon memory add/remove or upon ipc namespace creation/removal. 128Echoing "1" into this file enabled msgmni automatic recomputing. 129Echoing "0" turned it off. auto_msgmni default value was 1. 130 131 132============================================================== 133 134bootloader_type: 135 136x86 bootloader identification 137 138This gives the bootloader type number as indicated by the bootloader, 139shifted left by 4, and OR'd with the low four bits of the bootloader 140version. The reason for this encoding is that this used to match the 141type_of_loader field in the kernel header; the encoding is kept for 142backwards compatibility. That is, if the full bootloader type number 143is 0x15 and the full version number is 0x234, this file will contain 144the value 340 = 0x154. 145 146See the type_of_loader and ext_loader_type fields in 147Documentation/x86/boot.txt for additional information. 148 149============================================================== 150 151bootloader_version: 152 153x86 bootloader version 154 155The complete bootloader version number. In the example above, this 156file will contain the value 564 = 0x234. 157 158See the type_of_loader and ext_loader_ver fields in 159Documentation/x86/boot.txt for additional information. 160 161============================================================== 162 163callhome: 164 165Controls the kernel's callhome behavior in case of a kernel panic. 166 167The s390 hardware allows an operating system to send a notification 168to a service organization (callhome) in case of an operating system panic. 169 170When the value in this file is 0 (which is the default behavior) 171nothing happens in case of a kernel panic. If this value is set to "1" 172the complete kernel oops message is send to the IBM customer service 173organization in case the mainframe the Linux operating system is running 174on has a service contract with IBM. 175 176============================================================== 177 178cap_last_cap 179 180Highest valid capability of the running kernel. Exports 181CAP_LAST_CAP from the kernel. 182 183============================================================== 184 185core_pattern: 186 187core_pattern is used to specify a core dumpfile pattern name. 188. max length 128 characters; default value is "core" 189. core_pattern is used as a pattern template for the output filename; 190 certain string patterns (beginning with '%') are substituted with 191 their actual values. 192. backward compatibility with core_uses_pid: 193 If core_pattern does not include "%p" (default does not) 194 and core_uses_pid is set, then .PID will be appended to 195 the filename. 196. corename format specifiers: 197 %<NUL> '%' is dropped 198 %% output one '%' 199 %p pid 200 %P global pid (init PID namespace) 201 %i tid 202 %I global tid (init PID namespace) 203 %u uid (in initial user namespace) 204 %g gid (in initial user namespace) 205 %d dump mode, matches PR_SET_DUMPABLE and 206 /proc/sys/fs/suid_dumpable 207 %s signal number 208 %t UNIX time of dump 209 %h hostname 210 %e executable filename (may be shortened) 211 %E executable path 212 %<OTHER> both are dropped 213. If the first character of the pattern is a '|', the kernel will treat 214 the rest of the pattern as a command to run. The core dump will be 215 written to the standard input of that program instead of to a file. 216 217============================================================== 218 219core_pipe_limit: 220 221This sysctl is only applicable when core_pattern is configured to pipe 222core files to a user space helper (when the first character of 223core_pattern is a '|', see above). When collecting cores via a pipe 224to an application, it is occasionally useful for the collecting 225application to gather data about the crashing process from its 226/proc/pid directory. In order to do this safely, the kernel must wait 227for the collecting process to exit, so as not to remove the crashing 228processes proc files prematurely. This in turn creates the 229possibility that a misbehaving userspace collecting process can block 230the reaping of a crashed process simply by never exiting. This sysctl 231defends against that. It defines how many concurrent crashing 232processes may be piped to user space applications in parallel. If 233this value is exceeded, then those crashing processes above that value 234are noted via the kernel log and their cores are skipped. 0 is a 235special value, indicating that unlimited processes may be captured in 236parallel, but that no waiting will take place (i.e. the collecting 237process is not guaranteed access to /proc/<crashing pid>/). This 238value defaults to 0. 239 240============================================================== 241 242core_uses_pid: 243 244The default coredump filename is "core". By setting 245core_uses_pid to 1, the coredump filename becomes core.PID. 246If core_pattern does not include "%p" (default does not) 247and core_uses_pid is set, then .PID will be appended to 248the filename. 249 250============================================================== 251 252ctrl-alt-del: 253 254When the value in this file is 0, ctrl-alt-del is trapped and 255sent to the init(1) program to handle a graceful restart. 256When, however, the value is > 0, Linux's reaction to a Vulcan 257Nerve Pinch (tm) will be an immediate reboot, without even 258syncing its dirty buffers. 259 260Note: when a program (like dosemu) has the keyboard in 'raw' 261mode, the ctrl-alt-del is intercepted by the program before it 262ever reaches the kernel tty layer, and it's up to the program 263to decide what to do with it. 264 265============================================================== 266 267dmesg_restrict: 268 269This toggle indicates whether unprivileged users are prevented 270from using dmesg(8) to view messages from the kernel's log buffer. 271When dmesg_restrict is set to (0) there are no restrictions. When 272dmesg_restrict is set set to (1), users must have CAP_SYSLOG to use 273dmesg(8). 274 275The kernel config option CONFIG_SECURITY_DMESG_RESTRICT sets the 276default value of dmesg_restrict. 277 278============================================================== 279 280domainname & hostname: 281 282These files can be used to set the NIS/YP domainname and the 283hostname of your box in exactly the same way as the commands 284domainname and hostname, i.e.: 285# echo "darkstar" > /proc/sys/kernel/hostname 286# echo "mydomain" > /proc/sys/kernel/domainname 287has the same effect as 288# hostname "darkstar" 289# domainname "mydomain" 290 291Note, however, that the classic darkstar.frop.org has the 292hostname "darkstar" and DNS (Internet Domain Name Server) 293domainname "frop.org", not to be confused with the NIS (Network 294Information Service) or YP (Yellow Pages) domainname. These two 295domain names are in general different. For a detailed discussion 296see the hostname(1) man page. 297 298============================================================== 299hardlockup_all_cpu_backtrace: 300 301This value controls the hard lockup detector behavior when a hard 302lockup condition is detected as to whether or not to gather further 303debug information. If enabled, arch-specific all-CPU stack dumping 304will be initiated. 305 3060: do nothing. This is the default behavior. 307 3081: on detection capture more debug information. 309============================================================== 310 311hotplug: 312 313Path for the hotplug policy agent. 314Default value is "/sbin/hotplug". 315 316============================================================== 317 318hung_task_panic: 319 320Controls the kernel's behavior when a hung task is detected. 321This file shows up if CONFIG_DETECT_HUNG_TASK is enabled. 322 3230: continue operation. This is the default behavior. 324 3251: panic immediately. 326 327============================================================== 328 329hung_task_check_count: 330 331The upper bound on the number of tasks that are checked. 332This file shows up if CONFIG_DETECT_HUNG_TASK is enabled. 333 334============================================================== 335 336hung_task_timeout_secs: 337 338Check interval. When a task in D state did not get scheduled 339for more than this value report a warning. 340This file shows up if CONFIG_DETECT_HUNG_TASK is enabled. 341 3420: means infinite timeout - no checking done. 343Possible values to set are in range {0..LONG_MAX/HZ}. 344 345============================================================== 346 347hung_task_warnings: 348 349The maximum number of warnings to report. During a check interval 350if a hung task is detected, this value is decreased by 1. 351When this value reaches 0, no more warnings will be reported. 352This file shows up if CONFIG_DETECT_HUNG_TASK is enabled. 353 354-1: report an infinite number of warnings. 355 356============================================================== 357 358kexec_load_disabled: 359 360A toggle indicating if the kexec_load syscall has been disabled. This 361value defaults to 0 (false: kexec_load enabled), but can be set to 1 362(true: kexec_load disabled). Once true, kexec can no longer be used, and 363the toggle cannot be set back to false. This allows a kexec image to be 364loaded before disabling the syscall, allowing a system to set up (and 365later use) an image without it being altered. Generally used together 366with the "modules_disabled" sysctl. 367 368============================================================== 369 370kptr_restrict: 371 372This toggle indicates whether restrictions are placed on 373exposing kernel addresses via /proc and other interfaces. 374 375When kptr_restrict is set to (0), the default, there are no restrictions. 376 377When kptr_restrict is set to (1), kernel pointers printed using the %pK 378format specifier will be replaced with 0's unless the user has CAP_SYSLOG 379and effective user and group ids are equal to the real ids. This is 380because %pK checks are done at read() time rather than open() time, so 381if permissions are elevated between the open() and the read() (e.g via 382a setuid binary) then %pK will not leak kernel pointers to unprivileged 383users. Note, this is a temporary solution only. The correct long-term 384solution is to do the permission checks at open() time. Consider removing 385world read permissions from files that use %pK, and using dmesg_restrict 386to protect against uses of %pK in dmesg(8) if leaking kernel pointer 387values to unprivileged users is a concern. 388 389When kptr_restrict is set to (2), kernel pointers printed using 390%pK will be replaced with 0's regardless of privileges. 391 392============================================================== 393 394kstack_depth_to_print: (X86 only) 395 396Controls the number of words to print when dumping the raw 397kernel stack. 398 399============================================================== 400 401l2cr: (PPC only) 402 403This flag controls the L2 cache of G3 processor boards. If 4040, the cache is disabled. Enabled if nonzero. 405 406============================================================== 407 408modules_disabled: 409 410A toggle value indicating if modules are allowed to be loaded 411in an otherwise modular kernel. This toggle defaults to off 412(0), but can be set true (1). Once true, modules can be 413neither loaded nor unloaded, and the toggle cannot be set back 414to false. Generally used with the "kexec_load_disabled" toggle. 415 416============================================================== 417 418msg_next_id, sem_next_id, and shm_next_id: 419 420These three toggles allows to specify desired id for next allocated IPC 421object: message, semaphore or shared memory respectively. 422 423By default they are equal to -1, which means generic allocation logic. 424Possible values to set are in range {0..INT_MAX}. 425 426Notes: 4271) kernel doesn't guarantee, that new object will have desired id. So, 428it's up to userspace, how to handle an object with "wrong" id. 4292) Toggle with non-default value will be set back to -1 by kernel after 430successful IPC object allocation. 431 432============================================================== 433 434nmi_watchdog: 435 436This parameter can be used to control the NMI watchdog 437(i.e. the hard lockup detector) on x86 systems. 438 439 0 - disable the hard lockup detector 440 1 - enable the hard lockup detector 441 442The hard lockup detector monitors each CPU for its ability to respond to 443timer interrupts. The mechanism utilizes CPU performance counter registers 444that are programmed to generate Non-Maskable Interrupts (NMIs) periodically 445while a CPU is busy. Hence, the alternative name 'NMI watchdog'. 446 447The NMI watchdog is disabled by default if the kernel is running as a guest 448in a KVM virtual machine. This default can be overridden by adding 449 450 nmi_watchdog=1 451 452to the guest kernel command line (see Documentation/kernel-parameters.txt). 453 454============================================================== 455 456numa_balancing 457 458Enables/disables automatic page fault based NUMA memory 459balancing. Memory is moved automatically to nodes 460that access it often. 461 462Enables/disables automatic NUMA memory balancing. On NUMA machines, there 463is a performance penalty if remote memory is accessed by a CPU. When this 464feature is enabled the kernel samples what task thread is accessing memory 465by periodically unmapping pages and later trapping a page fault. At the 466time of the page fault, it is determined if the data being accessed should 467be migrated to a local memory node. 468 469The unmapping of pages and trapping faults incur additional overhead that 470ideally is offset by improved memory locality but there is no universal 471guarantee. If the target workload is already bound to NUMA nodes then this 472feature should be disabled. Otherwise, if the system overhead from the 473feature is too high then the rate the kernel samples for NUMA hinting 474faults may be controlled by the numa_balancing_scan_period_min_ms, 475numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms, 476numa_balancing_scan_size_mb, and numa_balancing_settle_count sysctls. 477 478============================================================== 479 480numa_balancing_scan_period_min_ms, numa_balancing_scan_delay_ms, 481numa_balancing_scan_period_max_ms, numa_balancing_scan_size_mb 482 483Automatic NUMA balancing scans tasks address space and unmaps pages to 484detect if pages are properly placed or if the data should be migrated to a 485memory node local to where the task is running. Every "scan delay" the task 486scans the next "scan size" number of pages in its address space. When the 487end of the address space is reached the scanner restarts from the beginning. 488 489In combination, the "scan delay" and "scan size" determine the scan rate. 490When "scan delay" decreases, the scan rate increases. The scan delay and 491hence the scan rate of every task is adaptive and depends on historical 492behaviour. If pages are properly placed then the scan delay increases, 493otherwise the scan delay decreases. The "scan size" is not adaptive but 494the higher the "scan size", the higher the scan rate. 495 496Higher scan rates incur higher system overhead as page faults must be 497trapped and potentially data must be migrated. However, the higher the scan 498rate, the more quickly a tasks memory is migrated to a local node if the 499workload pattern changes and minimises performance impact due to remote 500memory accesses. These sysctls control the thresholds for scan delays and 501the number of pages scanned. 502 503numa_balancing_scan_period_min_ms is the minimum time in milliseconds to 504scan a tasks virtual memory. It effectively controls the maximum scanning 505rate for each task. 506 507numa_balancing_scan_delay_ms is the starting "scan delay" used for a task 508when it initially forks. 509 510numa_balancing_scan_period_max_ms is the maximum time in milliseconds to 511scan a tasks virtual memory. It effectively controls the minimum scanning 512rate for each task. 513 514numa_balancing_scan_size_mb is how many megabytes worth of pages are 515scanned for a given scan. 516 517============================================================== 518 519osrelease, ostype & version: 520 521# cat osrelease 5222.1.88 523# cat ostype 524Linux 525# cat version 526#5 Wed Feb 25 21:49:24 MET 1998 527 528The files osrelease and ostype should be clear enough. Version 529needs a little more clarification however. The '#5' means that 530this is the fifth kernel built from this source base and the 531date behind it indicates the time the kernel was built. 532The only way to tune these values is to rebuild the kernel :-) 533 534============================================================== 535 536overflowgid & overflowuid: 537 538if your architecture did not always support 32-bit UIDs (i.e. arm, 539i386, m68k, sh, and sparc32), a fixed UID and GID will be returned to 540applications that use the old 16-bit UID/GID system calls, if the 541actual UID or GID would exceed 65535. 542 543These sysctls allow you to change the value of the fixed UID and GID. 544The default is 65534. 545 546============================================================== 547 548panic: 549 550The value in this file represents the number of seconds the kernel 551waits before rebooting on a panic. When you use the software watchdog, 552the recommended setting is 60. 553 554============================================================== 555 556panic_on_oops: 557 558Controls the kernel's behaviour when an oops or BUG is encountered. 559 5600: try to continue operation 561 5621: panic immediately. If the `panic' sysctl is also non-zero then the 563 machine will be rebooted. 564 565============================================================== 566 567panic_on_stackoverflow: 568 569Controls the kernel's behavior when detecting the overflows of 570kernel, IRQ and exception stacks except a user stack. 571This file shows up if CONFIG_DEBUG_STACKOVERFLOW is enabled. 572 5730: try to continue operation. 574 5751: panic immediately. 576 577============================================================== 578 579panic_on_unrecovered_nmi: 580 581The default Linux behaviour on an NMI of either memory or unknown is 582to continue operation. For many environments such as scientific 583computing it is preferable that the box is taken out and the error 584dealt with than an uncorrected parity/ECC error get propagated. 585 586A small number of systems do generate NMI's for bizarre random reasons 587such as power management so the default is off. That sysctl works like 588the existing panic controls already in that directory. 589 590============================================================== 591 592panic_on_warn: 593 594Calls panic() in the WARN() path when set to 1. This is useful to avoid 595a kernel rebuild when attempting to kdump at the location of a WARN(). 596 5970: only WARN(), default behaviour. 598 5991: call panic() after printing out WARN() location. 600 601============================================================== 602 603perf_cpu_time_max_percent: 604 605Hints to the kernel how much CPU time it should be allowed to 606use to handle perf sampling events. If the perf subsystem 607is informed that its samples are exceeding this limit, it 608will drop its sampling frequency to attempt to reduce its CPU 609usage. 610 611Some perf sampling happens in NMIs. If these samples 612unexpectedly take too long to execute, the NMIs can become 613stacked up next to each other so much that nothing else is 614allowed to execute. 615 6160: disable the mechanism. Do not monitor or correct perf's 617 sampling rate no matter how CPU time it takes. 618 6191-100: attempt to throttle perf's sample rate to this 620 percentage of CPU. Note: the kernel calculates an 621 "expected" length of each sample event. 100 here means 622 100% of that expected length. Even if this is set to 623 100, you may still see sample throttling if this 624 length is exceeded. Set to 0 if you truly do not care 625 how much CPU is consumed. 626 627============================================================== 628 629perf_event_paranoid: 630 631Controls use of the performance events system by unprivileged 632users (without CAP_SYS_ADMIN). The default value is 3 if 633CONFIG_SECURITY_PERF_EVENTS_RESTRICT is set, or 1 otherwise. 634 635 -1: Allow use of (almost) all events by all users 636>=0: Disallow raw tracepoint access by users without CAP_IOC_LOCK 637>=1: Disallow CPU event access by users without CAP_SYS_ADMIN 638>=2: Disallow kernel profiling by users without CAP_SYS_ADMIN 639>=3: Disallow all event access by users without CAP_SYS_ADMIN 640 641============================================================== 642 643pid_max: 644 645PID allocation wrap value. When the kernel's next PID value 646reaches this value, it wraps back to a minimum PID value. 647PIDs of value pid_max or larger are not allocated. 648 649============================================================== 650 651ns_last_pid: 652 653The last pid allocated in the current (the one task using this sysctl 654lives in) pid namespace. When selecting a pid for a next task on fork 655kernel tries to allocate a number starting from this one. 656 657============================================================== 658 659powersave-nap: (PPC only) 660 661If set, Linux-PPC will use the 'nap' mode of powersaving, 662otherwise the 'doze' mode will be used. 663 664============================================================== 665 666printk: 667 668The four values in printk denote: console_loglevel, 669default_message_loglevel, minimum_console_loglevel and 670default_console_loglevel respectively. 671 672These values influence printk() behavior when printing or 673logging error messages. See 'man 2 syslog' for more info on 674the different loglevels. 675 676- console_loglevel: messages with a higher priority than 677 this will be printed to the console 678- default_message_loglevel: messages without an explicit priority 679 will be printed with this priority 680- minimum_console_loglevel: minimum (highest) value to which 681 console_loglevel can be set 682- default_console_loglevel: default value for console_loglevel 683 684============================================================== 685 686printk_delay: 687 688Delay each printk message in printk_delay milliseconds 689 690Value from 0 - 10000 is allowed. 691 692============================================================== 693 694printk_ratelimit: 695 696Some warning messages are rate limited. printk_ratelimit specifies 697the minimum length of time between these messages (in jiffies), by 698default we allow one every 5 seconds. 699 700A value of 0 will disable rate limiting. 701 702============================================================== 703 704printk_ratelimit_burst: 705 706While long term we enforce one message per printk_ratelimit 707seconds, we do allow a burst of messages to pass through. 708printk_ratelimit_burst specifies the number of messages we can 709send before ratelimiting kicks in. 710 711============================================================== 712 713randomize_va_space: 714 715This option can be used to select the type of process address 716space randomization that is used in the system, for architectures 717that support this feature. 718 7190 - Turn the process address space randomization off. This is the 720 default for architectures that do not support this feature anyways, 721 and kernels that are booted with the "norandmaps" parameter. 722 7231 - Make the addresses of mmap base, stack and VDSO page randomized. 724 This, among other things, implies that shared libraries will be 725 loaded to random addresses. Also for PIE-linked binaries, the 726 location of code start is randomized. This is the default if the 727 CONFIG_COMPAT_BRK option is enabled. 728 7292 - Additionally enable heap randomization. This is the default if 730 CONFIG_COMPAT_BRK is disabled. 731 732 There are a few legacy applications out there (such as some ancient 733 versions of libc.so.5 from 1996) that assume that brk area starts 734 just after the end of the code+bss. These applications break when 735 start of the brk area is randomized. There are however no known 736 non-legacy applications that would be broken this way, so for most 737 systems it is safe to choose full randomization. 738 739 Systems with ancient and/or broken binaries should be configured 740 with CONFIG_COMPAT_BRK enabled, which excludes the heap from process 741 address space randomization. 742 743============================================================== 744 745reboot-cmd: (Sparc only) 746 747??? This seems to be a way to give an argument to the Sparc 748ROM/Flash boot loader. Maybe to tell it what to do after 749rebooting. ??? 750 751============================================================== 752 753rtsig-max & rtsig-nr: 754 755The file rtsig-max can be used to tune the maximum number 756of POSIX realtime (queued) signals that can be outstanding 757in the system. 758 759rtsig-nr shows the number of RT signals currently queued. 760 761============================================================== 762 763sg-big-buff: 764 765This file shows the size of the generic SCSI (sg) buffer. 766You can't tune it just yet, but you could change it on 767compile time by editing include/scsi/sg.h and changing 768the value of SG_BIG_BUFF. 769 770There shouldn't be any reason to change this value. If 771you can come up with one, you probably know what you 772are doing anyway :) 773 774============================================================== 775 776shmall: 777 778This parameter sets the total amount of shared memory pages that 779can be used system wide. Hence, SHMALL should always be at least 780ceil(shmmax/PAGE_SIZE). 781 782If you are not sure what the default PAGE_SIZE is on your Linux 783system, you can run the following command: 784 785# getconf PAGE_SIZE 786 787============================================================== 788 789shmmax: 790 791This value can be used to query and set the run time limit 792on the maximum shared memory segment size that can be created. 793Shared memory segments up to 1Gb are now supported in the 794kernel. This value defaults to SHMMAX. 795 796============================================================== 797 798shm_rmid_forced: 799 800Linux lets you set resource limits, including how much memory one 801process can consume, via setrlimit(2). Unfortunately, shared memory 802segments are allowed to exist without association with any process, and 803thus might not be counted against any resource limits. If enabled, 804shared memory segments are automatically destroyed when their attach 805count becomes zero after a detach or a process termination. It will 806also destroy segments that were created, but never attached to, on exit 807from the process. The only use left for IPC_RMID is to immediately 808destroy an unattached segment. Of course, this breaks the way things are 809defined, so some applications might stop working. Note that this 810feature will do you no good unless you also configure your resource 811limits (in particular, RLIMIT_AS and RLIMIT_NPROC). Most systems don't 812need this. 813 814Note that if you change this from 0 to 1, already created segments 815without users and with a dead originative process will be destroyed. 816 817============================================================== 818 819sysctl_writes_strict: 820 821Control how file position affects the behavior of updating sysctl values 822via the /proc/sys interface: 823 824 -1 - Legacy per-write sysctl value handling, with no printk warnings. 825 Each write syscall must fully contain the sysctl value to be 826 written, and multiple writes on the same sysctl file descriptor 827 will rewrite the sysctl value, regardless of file position. 828 0 - Same behavior as above, but warn about processes that perform writes 829 to a sysctl file descriptor when the file position is not 0. 830 1 - (default) Respect file position when writing sysctl strings. Multiple 831 writes will append to the sysctl value buffer. Anything past the max 832 length of the sysctl value buffer will be ignored. Writes to numeric 833 sysctl entries must always be at file position 0 and the value must 834 be fully contained in the buffer sent in the write syscall. 835 836============================================================== 837 838softlockup_all_cpu_backtrace: 839 840This value controls the soft lockup detector thread's behavior 841when a soft lockup condition is detected as to whether or not 842to gather further debug information. If enabled, each cpu will 843be issued an NMI and instructed to capture stack trace. 844 845This feature is only applicable for architectures which support 846NMI. 847 8480: do nothing. This is the default behavior. 849 8501: on detection capture more debug information. 851 852============================================================== 853 854soft_watchdog 855 856This parameter can be used to control the soft lockup detector. 857 858 0 - disable the soft lockup detector 859 1 - enable the soft lockup detector 860 861The soft lockup detector monitors CPUs for threads that are hogging the CPUs 862without rescheduling voluntarily, and thus prevent the 'watchdog/N' threads 863from running. The mechanism depends on the CPUs ability to respond to timer 864interrupts which are needed for the 'watchdog/N' threads to be woken up by 865the watchdog timer function, otherwise the NMI watchdog - if enabled - can 866detect a hard lockup condition. 867 868============================================================== 869 870tainted: 871 872Non-zero if the kernel has been tainted. Numeric values, which 873can be ORed together: 874 875 1 - A module with a non-GPL license has been loaded, this 876 includes modules with no license. 877 Set by modutils >= 2.4.9 and module-init-tools. 878 2 - A module was force loaded by insmod -f. 879 Set by modutils >= 2.4.9 and module-init-tools. 880 4 - Unsafe SMP processors: SMP with CPUs not designed for SMP. 881 8 - A module was forcibly unloaded from the system by rmmod -f. 882 16 - A hardware machine check error occurred on the system. 883 32 - A bad page was discovered on the system. 884 64 - The user has asked that the system be marked "tainted". This 885 could be because they are running software that directly modifies 886 the hardware, or for other reasons. 887 128 - The system has died. 888 256 - The ACPI DSDT has been overridden with one supplied by the user 889 instead of using the one provided by the hardware. 890 512 - A kernel warning has occurred. 8911024 - A module from drivers/staging was loaded. 8922048 - The system is working around a severe firmware bug. 8934096 - An out-of-tree module has been loaded. 8948192 - An unsigned module has been loaded in a kernel supporting module 895 signature. 89616384 - A soft lockup has previously occurred on the system. 89732768 - The kernel has been live patched. 898 899============================================================== 900 901threads-max 902 903This value controls the maximum number of threads that can be created 904using fork(). 905 906During initialization the kernel sets this value such that even if the 907maximum number of threads is created, the thread structures occupy only 908a part (1/8th) of the available RAM pages. 909 910The minimum value that can be written to threads-max is 20. 911The maximum value that can be written to threads-max is given by the 912constant FUTEX_TID_MASK (0x3fffffff). 913If a value outside of this range is written to threads-max an error 914EINVAL occurs. 915 916The value written is checked against the available RAM pages. If the 917thread structures would occupy too much (more than 1/8th) of the 918available RAM pages threads-max is reduced accordingly. 919 920============================================================== 921 922unknown_nmi_panic: 923 924The value in this file affects behavior of handling NMI. When the 925value is non-zero, unknown NMI is trapped and then panic occurs. At 926that time, kernel debugging information is displayed on console. 927 928NMI switch that most IA32 servers have fires unknown NMI up, for 929example. If a system hangs up, try pressing the NMI switch. 930 931============================================================== 932 933watchdog: 934 935This parameter can be used to disable or enable the soft lockup detector 936_and_ the NMI watchdog (i.e. the hard lockup detector) at the same time. 937 938 0 - disable both lockup detectors 939 1 - enable both lockup detectors 940 941The soft lockup detector and the NMI watchdog can also be disabled or 942enabled individually, using the soft_watchdog and nmi_watchdog parameters. 943If the watchdog parameter is read, for example by executing 944 945 cat /proc/sys/kernel/watchdog 946 947the output of this command (0 or 1) shows the logical OR of soft_watchdog 948and nmi_watchdog. 949 950============================================================== 951 952watchdog_cpumask: 953 954This value can be used to control on which cpus the watchdog may run. 955The default cpumask is all possible cores, but if NO_HZ_FULL is 956enabled in the kernel config, and cores are specified with the 957nohz_full= boot argument, those cores are excluded by default. 958Offline cores can be included in this mask, and if the core is later 959brought online, the watchdog will be started based on the mask value. 960 961Typically this value would only be touched in the nohz_full case 962to re-enable cores that by default were not running the watchdog, 963if a kernel lockup was suspected on those cores. 964 965The argument value is the standard cpulist format for cpumasks, 966so for example to enable the watchdog on cores 0, 2, 3, and 4 you 967might say: 968 969 echo 0,2-4 > /proc/sys/kernel/watchdog_cpumask 970 971============================================================== 972 973watchdog_thresh: 974 975This value can be used to control the frequency of hrtimer and NMI 976events and the soft and hard lockup thresholds. The default threshold 977is 10 seconds. 978 979The softlockup threshold is (2 * watchdog_thresh). Setting this 980tunable to zero will disable lockup detection altogether. 981 982============================================================== 983