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1da177e4 LT |
1 | Documentation for /proc/sys/kernel/* kernel version 2.2.10 |
2 | (c) 1998, 1999, Rik van Riel <riel@nl.linux.org> | |
760df93e | 3 | (c) 2009, Shen Feng<shen@cn.fujitsu.com> |
1da177e4 LT |
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: | |
807094c0 | 20 | |
1da177e4 | 21 | - acct |
807094c0 BP |
22 | - acpi_video_flags |
23 | - auto_msgmni | |
d75757ab PA |
24 | - bootloader_type [ X86 only ] |
25 | - bootloader_version [ X86 only ] | |
c114728a | 26 | - callhome [ S390 only ] |
73efc039 | 27 | - cap_last_cap |
1da177e4 | 28 | - core_pattern |
a293980c | 29 | - core_pipe_limit |
1da177e4 LT |
30 | - core_uses_pid |
31 | - ctrl-alt-del | |
eaf06b24 | 32 | - dmesg_restrict |
1da177e4 LT |
33 | - domainname |
34 | - hostname | |
35 | - hotplug | |
455cd5ab | 36 | - kptr_restrict |
0741f4d2 | 37 | - kstack_depth_to_print [ X86 only ] |
1da177e4 | 38 | - l2cr [ PPC only ] |
ac76cff2 | 39 | - modprobe ==> Documentation/debugging-modules.txt |
3d43321b | 40 | - modules_disabled |
03f59566 | 41 | - msg_next_id [ sysv ipc ] |
1da177e4 LT |
42 | - msgmax |
43 | - msgmnb | |
44 | - msgmni | |
760df93e | 45 | - nmi_watchdog |
1da177e4 LT |
46 | - osrelease |
47 | - ostype | |
48 | - overflowgid | |
49 | - overflowuid | |
50 | - panic | |
807094c0 BP |
51 | - panic_on_oops |
52 | - panic_on_unrecovered_nmi | |
55af7796 | 53 | - panic_on_stackoverflow |
1da177e4 LT |
54 | - pid_max |
55 | - powersave-nap [ PPC only ] | |
56 | - printk | |
807094c0 BP |
57 | - printk_delay |
58 | - printk_ratelimit | |
59 | - printk_ratelimit_burst | |
1ec7fd50 | 60 | - randomize_va_space |
1da177e4 LT |
61 | - real-root-dev ==> Documentation/initrd.txt |
62 | - reboot-cmd [ SPARC only ] | |
63 | - rtsig-max | |
64 | - rtsig-nr | |
65 | - sem | |
03f59566 | 66 | - sem_next_id [ sysv ipc ] |
1da177e4 | 67 | - sg-big-buff [ generic SCSI device (sg) ] |
03f59566 | 68 | - shm_next_id [ sysv ipc ] |
b34a6b1d | 69 | - shm_rmid_forced |
1da177e4 LT |
70 | - shmall |
71 | - shmmax [ sysv ipc ] | |
72 | - shmmni | |
73 | - stop-a [ SPARC only ] | |
74 | - sysrq ==> Documentation/sysrq.txt | |
75 | - tainted | |
76 | - threads-max | |
760df93e | 77 | - unknown_nmi_panic |
08825c90 | 78 | - watchdog_thresh |
1da177e4 LT |
79 | - version |
80 | ||
81 | ============================================================== | |
82 | ||
83 | acct: | |
84 | ||
85 | highwater lowwater frequency | |
86 | ||
87 | If BSD-style process accounting is enabled these values control | |
88 | its behaviour. If free space on filesystem where the log lives | |
89 | goes below <lowwater>% accounting suspends. If free space gets | |
90 | above <highwater>% accounting resumes. <Frequency> determines | |
91 | how often do we check the amount of free space (value is in | |
92 | seconds). Default: | |
93 | 4 2 30 | |
94 | That is, suspend accounting if there left <= 2% free; resume it | |
95 | if we got >=4%; consider information about amount of free space | |
96 | valid for 30 seconds. | |
97 | ||
807094c0 BP |
98 | ============================================================== |
99 | ||
100 | acpi_video_flags: | |
101 | ||
102 | flags | |
103 | ||
104 | See Doc*/kernel/power/video.txt, it allows mode of video boot to be | |
105 | set during run time. | |
106 | ||
107 | ============================================================== | |
108 | ||
109 | auto_msgmni: | |
110 | ||
111 | Enables/Disables automatic recomputing of msgmni upon memory add/remove | |
112 | or upon ipc namespace creation/removal (see the msgmni description | |
113 | above). Echoing "1" into this file enables msgmni automatic recomputing. | |
114 | Echoing "0" turns it off. auto_msgmni default value is 1. | |
115 | ||
116 | ||
1da177e4 LT |
117 | ============================================================== |
118 | ||
d75757ab PA |
119 | bootloader_type: |
120 | ||
121 | x86 bootloader identification | |
122 | ||
123 | This gives the bootloader type number as indicated by the bootloader, | |
124 | shifted left by 4, and OR'd with the low four bits of the bootloader | |
125 | version. The reason for this encoding is that this used to match the | |
126 | type_of_loader field in the kernel header; the encoding is kept for | |
127 | backwards compatibility. That is, if the full bootloader type number | |
128 | is 0x15 and the full version number is 0x234, this file will contain | |
129 | the value 340 = 0x154. | |
130 | ||
131 | See the type_of_loader and ext_loader_type fields in | |
132 | Documentation/x86/boot.txt for additional information. | |
133 | ||
134 | ============================================================== | |
135 | ||
136 | bootloader_version: | |
137 | ||
138 | x86 bootloader version | |
139 | ||
140 | The complete bootloader version number. In the example above, this | |
141 | file will contain the value 564 = 0x234. | |
142 | ||
143 | See the type_of_loader and ext_loader_ver fields in | |
144 | Documentation/x86/boot.txt for additional information. | |
145 | ||
146 | ============================================================== | |
147 | ||
c114728a HJP |
148 | callhome: |
149 | ||
150 | Controls the kernel's callhome behavior in case of a kernel panic. | |
151 | ||
152 | The s390 hardware allows an operating system to send a notification | |
153 | to a service organization (callhome) in case of an operating system panic. | |
154 | ||
155 | When the value in this file is 0 (which is the default behavior) | |
156 | nothing happens in case of a kernel panic. If this value is set to "1" | |
157 | the complete kernel oops message is send to the IBM customer service | |
158 | organization in case the mainframe the Linux operating system is running | |
159 | on has a service contract with IBM. | |
160 | ||
161 | ============================================================== | |
162 | ||
73efc039 DB |
163 | cap_last_cap |
164 | ||
165 | Highest valid capability of the running kernel. Exports | |
166 | CAP_LAST_CAP from the kernel. | |
167 | ||
168 | ============================================================== | |
169 | ||
1da177e4 LT |
170 | core_pattern: |
171 | ||
172 | core_pattern is used to specify a core dumpfile pattern name. | |
cd081041 | 173 | . max length 128 characters; default value is "core" |
1da177e4 LT |
174 | . core_pattern is used as a pattern template for the output filename; |
175 | certain string patterns (beginning with '%') are substituted with | |
176 | their actual values. | |
177 | . backward compatibility with core_uses_pid: | |
178 | If core_pattern does not include "%p" (default does not) | |
179 | and core_uses_pid is set, then .PID will be appended to | |
180 | the filename. | |
181 | . corename format specifiers: | |
182 | %<NUL> '%' is dropped | |
183 | %% output one '%' | |
184 | %p pid | |
65aafb1e | 185 | %P global pid (init PID namespace) |
1da177e4 LT |
186 | %u uid |
187 | %g gid | |
12a2b4b2 ON |
188 | %d dump mode, matches PR_SET_DUMPABLE and |
189 | /proc/sys/fs/suid_dumpable | |
1da177e4 LT |
190 | %s signal number |
191 | %t UNIX time of dump | |
192 | %h hostname | |
57cc083a JS |
193 | %e executable filename (may be shortened) |
194 | %E executable path | |
1da177e4 | 195 | %<OTHER> both are dropped |
cd081041 MU |
196 | . If the first character of the pattern is a '|', the kernel will treat |
197 | the rest of the pattern as a command to run. The core dump will be | |
198 | written to the standard input of that program instead of to a file. | |
1da177e4 LT |
199 | |
200 | ============================================================== | |
201 | ||
a293980c NH |
202 | core_pipe_limit: |
203 | ||
807094c0 BP |
204 | This sysctl is only applicable when core_pattern is configured to pipe |
205 | core files to a user space helper (when the first character of | |
206 | core_pattern is a '|', see above). When collecting cores via a pipe | |
207 | to an application, it is occasionally useful for the collecting | |
208 | application to gather data about the crashing process from its | |
209 | /proc/pid directory. In order to do this safely, the kernel must wait | |
210 | for the collecting process to exit, so as not to remove the crashing | |
211 | processes proc files prematurely. This in turn creates the | |
212 | possibility that a misbehaving userspace collecting process can block | |
213 | the reaping of a crashed process simply by never exiting. This sysctl | |
214 | defends against that. It defines how many concurrent crashing | |
215 | processes may be piped to user space applications in parallel. If | |
216 | this value is exceeded, then those crashing processes above that value | |
217 | are noted via the kernel log and their cores are skipped. 0 is a | |
218 | special value, indicating that unlimited processes may be captured in | |
219 | parallel, but that no waiting will take place (i.e. the collecting | |
220 | process is not guaranteed access to /proc/<crashing pid>/). This | |
221 | value defaults to 0. | |
a293980c NH |
222 | |
223 | ============================================================== | |
224 | ||
1da177e4 LT |
225 | core_uses_pid: |
226 | ||
227 | The default coredump filename is "core". By setting | |
228 | core_uses_pid to 1, the coredump filename becomes core.PID. | |
229 | If core_pattern does not include "%p" (default does not) | |
230 | and core_uses_pid is set, then .PID will be appended to | |
231 | the filename. | |
232 | ||
233 | ============================================================== | |
234 | ||
235 | ctrl-alt-del: | |
236 | ||
237 | When the value in this file is 0, ctrl-alt-del is trapped and | |
238 | sent to the init(1) program to handle a graceful restart. | |
239 | When, however, the value is > 0, Linux's reaction to a Vulcan | |
240 | Nerve Pinch (tm) will be an immediate reboot, without even | |
241 | syncing its dirty buffers. | |
242 | ||
243 | Note: when a program (like dosemu) has the keyboard in 'raw' | |
244 | mode, the ctrl-alt-del is intercepted by the program before it | |
245 | ever reaches the kernel tty layer, and it's up to the program | |
246 | to decide what to do with it. | |
247 | ||
248 | ============================================================== | |
249 | ||
eaf06b24 DR |
250 | dmesg_restrict: |
251 | ||
807094c0 BP |
252 | This toggle indicates whether unprivileged users are prevented |
253 | from using dmesg(8) to view messages from the kernel's log buffer. | |
254 | When dmesg_restrict is set to (0) there are no restrictions. When | |
38ef4c2e | 255 | dmesg_restrict is set set to (1), users must have CAP_SYSLOG to use |
eaf06b24 DR |
256 | dmesg(8). |
257 | ||
807094c0 BP |
258 | The kernel config option CONFIG_SECURITY_DMESG_RESTRICT sets the |
259 | default value of dmesg_restrict. | |
eaf06b24 DR |
260 | |
261 | ============================================================== | |
262 | ||
1da177e4 LT |
263 | domainname & hostname: |
264 | ||
265 | These files can be used to set the NIS/YP domainname and the | |
266 | hostname of your box in exactly the same way as the commands | |
267 | domainname and hostname, i.e.: | |
268 | # echo "darkstar" > /proc/sys/kernel/hostname | |
269 | # echo "mydomain" > /proc/sys/kernel/domainname | |
270 | has the same effect as | |
271 | # hostname "darkstar" | |
272 | # domainname "mydomain" | |
273 | ||
274 | Note, however, that the classic darkstar.frop.org has the | |
275 | hostname "darkstar" and DNS (Internet Domain Name Server) | |
276 | domainname "frop.org", not to be confused with the NIS (Network | |
277 | Information Service) or YP (Yellow Pages) domainname. These two | |
278 | domain names are in general different. For a detailed discussion | |
279 | see the hostname(1) man page. | |
280 | ||
281 | ============================================================== | |
282 | ||
283 | hotplug: | |
284 | ||
285 | Path for the hotplug policy agent. | |
286 | Default value is "/sbin/hotplug". | |
287 | ||
288 | ============================================================== | |
289 | ||
455cd5ab DR |
290 | kptr_restrict: |
291 | ||
292 | This toggle indicates whether restrictions are placed on | |
312b4e22 RM |
293 | exposing kernel addresses via /proc and other interfaces. |
294 | ||
295 | When kptr_restrict is set to (0), the default, there are no restrictions. | |
296 | ||
297 | When kptr_restrict is set to (1), kernel pointers printed using the %pK | |
298 | format specifier will be replaced with 0's unless the user has CAP_SYSLOG | |
299 | and effective user and group ids are equal to the real ids. This is | |
300 | because %pK checks are done at read() time rather than open() time, so | |
301 | if permissions are elevated between the open() and the read() (e.g via | |
302 | a setuid binary) then %pK will not leak kernel pointers to unprivileged | |
303 | users. Note, this is a temporary solution only. The correct long-term | |
304 | solution is to do the permission checks at open() time. Consider removing | |
305 | world read permissions from files that use %pK, and using dmesg_restrict | |
306 | to protect against uses of %pK in dmesg(8) if leaking kernel pointer | |
307 | values to unprivileged users is a concern. | |
308 | ||
309 | When kptr_restrict is set to (2), kernel pointers printed using | |
310 | %pK will be replaced with 0's regardless of privileges. | |
455cd5ab DR |
311 | |
312 | ============================================================== | |
313 | ||
0741f4d2 CE |
314 | kstack_depth_to_print: (X86 only) |
315 | ||
316 | Controls the number of words to print when dumping the raw | |
317 | kernel stack. | |
318 | ||
319 | ============================================================== | |
320 | ||
807094c0 BP |
321 | l2cr: (PPC only) |
322 | ||
323 | This flag controls the L2 cache of G3 processor boards. If | |
324 | 0, the cache is disabled. Enabled if nonzero. | |
325 | ||
326 | ============================================================== | |
327 | ||
3d43321b KC |
328 | modules_disabled: |
329 | ||
330 | A toggle value indicating if modules are allowed to be loaded | |
331 | in an otherwise modular kernel. This toggle defaults to off | |
332 | (0), but can be set true (1). Once true, modules can be | |
333 | neither loaded nor unloaded, and the toggle cannot be set back | |
334 | to false. | |
335 | ||
336 | ============================================================== | |
337 | ||
03f59566 SK |
338 | msg_next_id, sem_next_id, and shm_next_id: |
339 | ||
340 | These three toggles allows to specify desired id for next allocated IPC | |
341 | object: message, semaphore or shared memory respectively. | |
342 | ||
343 | By default they are equal to -1, which means generic allocation logic. | |
344 | Possible values to set are in range {0..INT_MAX}. | |
345 | ||
346 | Notes: | |
347 | 1) kernel doesn't guarantee, that new object will have desired id. So, | |
348 | it's up to userspace, how to handle an object with "wrong" id. | |
349 | 2) Toggle with non-default value will be set back to -1 by kernel after | |
350 | successful IPC object allocation. | |
351 | ||
352 | ============================================================== | |
353 | ||
807094c0 BP |
354 | nmi_watchdog: |
355 | ||
356 | Enables/Disables the NMI watchdog on x86 systems. When the value is | |
357 | non-zero the NMI watchdog is enabled and will continuously test all | |
358 | online cpus to determine whether or not they are still functioning | |
359 | properly. Currently, passing "nmi_watchdog=" parameter at boot time is | |
360 | required for this function to work. | |
361 | ||
362 | If LAPIC NMI watchdog method is in use (nmi_watchdog=2 kernel | |
363 | parameter), the NMI watchdog shares registers with oprofile. By | |
364 | disabling the NMI watchdog, oprofile may have more registers to | |
365 | utilize. | |
366 | ||
367 | ============================================================== | |
368 | ||
10fc05d0 MG |
369 | numa_balancing |
370 | ||
371 | Enables/disables automatic page fault based NUMA memory | |
372 | balancing. Memory is moved automatically to nodes | |
373 | that access it often. | |
374 | ||
375 | Enables/disables automatic NUMA memory balancing. On NUMA machines, there | |
376 | is a performance penalty if remote memory is accessed by a CPU. When this | |
377 | feature is enabled the kernel samples what task thread is accessing memory | |
378 | by periodically unmapping pages and later trapping a page fault. At the | |
379 | time of the page fault, it is determined if the data being accessed should | |
380 | be migrated to a local memory node. | |
381 | ||
382 | The unmapping of pages and trapping faults incur additional overhead that | |
383 | ideally is offset by improved memory locality but there is no universal | |
384 | guarantee. If the target workload is already bound to NUMA nodes then this | |
385 | feature should be disabled. Otherwise, if the system overhead from the | |
386 | feature is too high then the rate the kernel samples for NUMA hinting | |
387 | faults may be controlled by the numa_balancing_scan_period_min_ms, | |
930aa174 | 388 | numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms, |
de1c9ce6 RR |
389 | numa_balancing_scan_size_mb, numa_balancing_settle_count sysctls and |
390 | numa_balancing_migrate_deferred. | |
10fc05d0 MG |
391 | |
392 | ============================================================== | |
393 | ||
394 | numa_balancing_scan_period_min_ms, numa_balancing_scan_delay_ms, | |
930aa174 | 395 | numa_balancing_scan_period_max_ms, numa_balancing_scan_size_mb |
10fc05d0 MG |
396 | |
397 | Automatic NUMA balancing scans tasks address space and unmaps pages to | |
398 | detect if pages are properly placed or if the data should be migrated to a | |
399 | memory node local to where the task is running. Every "scan delay" the task | |
400 | scans the next "scan size" number of pages in its address space. When the | |
401 | end of the address space is reached the scanner restarts from the beginning. | |
402 | ||
403 | In combination, the "scan delay" and "scan size" determine the scan rate. | |
404 | When "scan delay" decreases, the scan rate increases. The scan delay and | |
405 | hence the scan rate of every task is adaptive and depends on historical | |
406 | behaviour. If pages are properly placed then the scan delay increases, | |
407 | otherwise the scan delay decreases. The "scan size" is not adaptive but | |
408 | the higher the "scan size", the higher the scan rate. | |
409 | ||
410 | Higher scan rates incur higher system overhead as page faults must be | |
411 | trapped and potentially data must be migrated. However, the higher the scan | |
412 | rate, the more quickly a tasks memory is migrated to a local node if the | |
413 | workload pattern changes and minimises performance impact due to remote | |
414 | memory accesses. These sysctls control the thresholds for scan delays and | |
415 | the number of pages scanned. | |
416 | ||
598f0ec0 MG |
417 | numa_balancing_scan_period_min_ms is the minimum time in milliseconds to |
418 | scan a tasks virtual memory. It effectively controls the maximum scanning | |
419 | rate for each task. | |
10fc05d0 MG |
420 | |
421 | numa_balancing_scan_delay_ms is the starting "scan delay" used for a task | |
422 | when it initially forks. | |
423 | ||
598f0ec0 MG |
424 | numa_balancing_scan_period_max_ms is the maximum time in milliseconds to |
425 | scan a tasks virtual memory. It effectively controls the minimum scanning | |
426 | rate for each task. | |
10fc05d0 MG |
427 | |
428 | numa_balancing_scan_size_mb is how many megabytes worth of pages are | |
429 | scanned for a given scan. | |
430 | ||
3a7053b3 MG |
431 | numa_balancing_settle_count is how many scan periods must complete before |
432 | the schedule balancer stops pushing the task towards a preferred node. This | |
433 | gives the scheduler a chance to place the task on an alternative node if the | |
434 | preferred node is overloaded. | |
435 | ||
de1c9ce6 RR |
436 | numa_balancing_migrate_deferred is how many page migrations get skipped |
437 | unconditionally, after a page migration is skipped because a page is shared | |
438 | with other tasks. This reduces page migration overhead, and determines | |
439 | how much stronger the "move task near its memory" policy scheduler becomes, | |
440 | versus the "move memory near its task" memory management policy, for workloads | |
441 | with shared memory. | |
442 | ||
10fc05d0 MG |
443 | ============================================================== |
444 | ||
1da177e4 LT |
445 | osrelease, ostype & version: |
446 | ||
447 | # cat osrelease | |
448 | 2.1.88 | |
449 | # cat ostype | |
450 | Linux | |
451 | # cat version | |
452 | #5 Wed Feb 25 21:49:24 MET 1998 | |
453 | ||
454 | The files osrelease and ostype should be clear enough. Version | |
455 | needs a little more clarification however. The '#5' means that | |
456 | this is the fifth kernel built from this source base and the | |
457 | date behind it indicates the time the kernel was built. | |
458 | The only way to tune these values is to rebuild the kernel :-) | |
459 | ||
460 | ============================================================== | |
461 | ||
462 | overflowgid & overflowuid: | |
463 | ||
807094c0 BP |
464 | if your architecture did not always support 32-bit UIDs (i.e. arm, |
465 | i386, m68k, sh, and sparc32), a fixed UID and GID will be returned to | |
466 | applications that use the old 16-bit UID/GID system calls, if the | |
467 | actual UID or GID would exceed 65535. | |
1da177e4 LT |
468 | |
469 | These sysctls allow you to change the value of the fixed UID and GID. | |
470 | The default is 65534. | |
471 | ||
472 | ============================================================== | |
473 | ||
474 | panic: | |
475 | ||
807094c0 BP |
476 | The value in this file represents the number of seconds the kernel |
477 | waits before rebooting on a panic. When you use the software watchdog, | |
478 | the recommended setting is 60. | |
479 | ||
480 | ============================================================== | |
481 | ||
482 | panic_on_unrecovered_nmi: | |
483 | ||
484 | The default Linux behaviour on an NMI of either memory or unknown is | |
485 | to continue operation. For many environments such as scientific | |
486 | computing it is preferable that the box is taken out and the error | |
487 | dealt with than an uncorrected parity/ECC error get propagated. | |
488 | ||
489 | A small number of systems do generate NMI's for bizarre random reasons | |
490 | such as power management so the default is off. That sysctl works like | |
491 | the existing panic controls already in that directory. | |
1da177e4 LT |
492 | |
493 | ============================================================== | |
494 | ||
495 | panic_on_oops: | |
496 | ||
497 | Controls the kernel's behaviour when an oops or BUG is encountered. | |
498 | ||
499 | 0: try to continue operation | |
500 | ||
a982ac06 | 501 | 1: panic immediately. If the `panic' sysctl is also non-zero then the |
8b23d04d | 502 | machine will be rebooted. |
1da177e4 LT |
503 | |
504 | ============================================================== | |
505 | ||
55af7796 MH |
506 | panic_on_stackoverflow: |
507 | ||
508 | Controls the kernel's behavior when detecting the overflows of | |
509 | kernel, IRQ and exception stacks except a user stack. | |
510 | This file shows up if CONFIG_DEBUG_STACKOVERFLOW is enabled. | |
511 | ||
512 | 0: try to continue operation. | |
513 | ||
514 | 1: panic immediately. | |
515 | ||
516 | ============================================================== | |
517 | ||
14c63f17 DH |
518 | perf_cpu_time_max_percent: |
519 | ||
520 | Hints to the kernel how much CPU time it should be allowed to | |
521 | use to handle perf sampling events. If the perf subsystem | |
522 | is informed that its samples are exceeding this limit, it | |
523 | will drop its sampling frequency to attempt to reduce its CPU | |
524 | usage. | |
525 | ||
526 | Some perf sampling happens in NMIs. If these samples | |
527 | unexpectedly take too long to execute, the NMIs can become | |
528 | stacked up next to each other so much that nothing else is | |
529 | allowed to execute. | |
530 | ||
531 | 0: disable the mechanism. Do not monitor or correct perf's | |
532 | sampling rate no matter how CPU time it takes. | |
533 | ||
534 | 1-100: attempt to throttle perf's sample rate to this | |
535 | percentage of CPU. Note: the kernel calculates an | |
536 | "expected" length of each sample event. 100 here means | |
537 | 100% of that expected length. Even if this is set to | |
538 | 100, you may still see sample throttling if this | |
539 | length is exceeded. Set to 0 if you truly do not care | |
540 | how much CPU is consumed. | |
541 | ||
542 | ============================================================== | |
543 | ||
55af7796 | 544 | |
1da177e4 LT |
545 | pid_max: |
546 | ||
beb7dd86 | 547 | PID allocation wrap value. When the kernel's next PID value |
1da177e4 LT |
548 | reaches this value, it wraps back to a minimum PID value. |
549 | PIDs of value pid_max or larger are not allocated. | |
550 | ||
551 | ============================================================== | |
552 | ||
b8f566b0 PE |
553 | ns_last_pid: |
554 | ||
555 | The last pid allocated in the current (the one task using this sysctl | |
556 | lives in) pid namespace. When selecting a pid for a next task on fork | |
557 | kernel tries to allocate a number starting from this one. | |
558 | ||
559 | ============================================================== | |
560 | ||
1da177e4 LT |
561 | powersave-nap: (PPC only) |
562 | ||
563 | If set, Linux-PPC will use the 'nap' mode of powersaving, | |
564 | otherwise the 'doze' mode will be used. | |
565 | ||
566 | ============================================================== | |
567 | ||
568 | printk: | |
569 | ||
570 | The four values in printk denote: console_loglevel, | |
571 | default_message_loglevel, minimum_console_loglevel and | |
572 | default_console_loglevel respectively. | |
573 | ||
574 | These values influence printk() behavior when printing or | |
575 | logging error messages. See 'man 2 syslog' for more info on | |
576 | the different loglevels. | |
577 | ||
578 | - console_loglevel: messages with a higher priority than | |
579 | this will be printed to the console | |
87889e15 | 580 | - default_message_loglevel: messages without an explicit priority |
1da177e4 LT |
581 | will be printed with this priority |
582 | - minimum_console_loglevel: minimum (highest) value to which | |
583 | console_loglevel can be set | |
584 | - default_console_loglevel: default value for console_loglevel | |
585 | ||
586 | ============================================================== | |
587 | ||
807094c0 BP |
588 | printk_delay: |
589 | ||
590 | Delay each printk message in printk_delay milliseconds | |
591 | ||
592 | Value from 0 - 10000 is allowed. | |
593 | ||
594 | ============================================================== | |
595 | ||
1da177e4 LT |
596 | printk_ratelimit: |
597 | ||
598 | Some warning messages are rate limited. printk_ratelimit specifies | |
599 | the minimum length of time between these messages (in jiffies), by | |
600 | default we allow one every 5 seconds. | |
601 | ||
602 | A value of 0 will disable rate limiting. | |
603 | ||
604 | ============================================================== | |
605 | ||
606 | printk_ratelimit_burst: | |
607 | ||
608 | While long term we enforce one message per printk_ratelimit | |
609 | seconds, we do allow a burst of messages to pass through. | |
610 | printk_ratelimit_burst specifies the number of messages we can | |
611 | send before ratelimiting kicks in. | |
612 | ||
613 | ============================================================== | |
614 | ||
807094c0 | 615 | randomize_va_space: |
1ec7fd50 JK |
616 | |
617 | This option can be used to select the type of process address | |
618 | space randomization that is used in the system, for architectures | |
619 | that support this feature. | |
620 | ||
b7f5ab6f HS |
621 | 0 - Turn the process address space randomization off. This is the |
622 | default for architectures that do not support this feature anyways, | |
623 | and kernels that are booted with the "norandmaps" parameter. | |
1ec7fd50 JK |
624 | |
625 | 1 - Make the addresses of mmap base, stack and VDSO page randomized. | |
626 | This, among other things, implies that shared libraries will be | |
b7f5ab6f HS |
627 | loaded to random addresses. Also for PIE-linked binaries, the |
628 | location of code start is randomized. This is the default if the | |
629 | CONFIG_COMPAT_BRK option is enabled. | |
1ec7fd50 | 630 | |
b7f5ab6f HS |
631 | 2 - Additionally enable heap randomization. This is the default if |
632 | CONFIG_COMPAT_BRK is disabled. | |
633 | ||
634 | There are a few legacy applications out there (such as some ancient | |
1ec7fd50 | 635 | versions of libc.so.5 from 1996) that assume that brk area starts |
b7f5ab6f HS |
636 | just after the end of the code+bss. These applications break when |
637 | start of the brk area is randomized. There are however no known | |
1ec7fd50 | 638 | non-legacy applications that would be broken this way, so for most |
b7f5ab6f HS |
639 | systems it is safe to choose full randomization. |
640 | ||
641 | Systems with ancient and/or broken binaries should be configured | |
642 | with CONFIG_COMPAT_BRK enabled, which excludes the heap from process | |
643 | address space randomization. | |
1ec7fd50 JK |
644 | |
645 | ============================================================== | |
646 | ||
1da177e4 LT |
647 | reboot-cmd: (Sparc only) |
648 | ||
649 | ??? This seems to be a way to give an argument to the Sparc | |
650 | ROM/Flash boot loader. Maybe to tell it what to do after | |
651 | rebooting. ??? | |
652 | ||
653 | ============================================================== | |
654 | ||
655 | rtsig-max & rtsig-nr: | |
656 | ||
657 | The file rtsig-max can be used to tune the maximum number | |
658 | of POSIX realtime (queued) signals that can be outstanding | |
659 | in the system. | |
660 | ||
661 | rtsig-nr shows the number of RT signals currently queued. | |
662 | ||
663 | ============================================================== | |
664 | ||
665 | sg-big-buff: | |
666 | ||
667 | This file shows the size of the generic SCSI (sg) buffer. | |
668 | You can't tune it just yet, but you could change it on | |
669 | compile time by editing include/scsi/sg.h and changing | |
670 | the value of SG_BIG_BUFF. | |
671 | ||
672 | There shouldn't be any reason to change this value. If | |
673 | you can come up with one, you probably know what you | |
674 | are doing anyway :) | |
675 | ||
676 | ============================================================== | |
677 | ||
358e419f CALP |
678 | shmall: |
679 | ||
680 | This parameter sets the total amount of shared memory pages that | |
681 | can be used system wide. Hence, SHMALL should always be at least | |
682 | ceil(shmmax/PAGE_SIZE). | |
683 | ||
684 | If you are not sure what the default PAGE_SIZE is on your Linux | |
685 | system, you can run the following command: | |
686 | ||
687 | # getconf PAGE_SIZE | |
688 | ||
689 | ============================================================== | |
690 | ||
807094c0 | 691 | shmmax: |
1da177e4 LT |
692 | |
693 | This value can be used to query and set the run time limit | |
694 | on the maximum shared memory segment size that can be created. | |
807094c0 | 695 | Shared memory segments up to 1Gb are now supported in the |
1da177e4 LT |
696 | kernel. This value defaults to SHMMAX. |
697 | ||
698 | ============================================================== | |
699 | ||
b34a6b1d VK |
700 | shm_rmid_forced: |
701 | ||
702 | Linux lets you set resource limits, including how much memory one | |
703 | process can consume, via setrlimit(2). Unfortunately, shared memory | |
704 | segments are allowed to exist without association with any process, and | |
705 | thus might not be counted against any resource limits. If enabled, | |
706 | shared memory segments are automatically destroyed when their attach | |
707 | count becomes zero after a detach or a process termination. It will | |
708 | also destroy segments that were created, but never attached to, on exit | |
709 | from the process. The only use left for IPC_RMID is to immediately | |
710 | destroy an unattached segment. Of course, this breaks the way things are | |
711 | defined, so some applications might stop working. Note that this | |
712 | feature will do you no good unless you also configure your resource | |
713 | limits (in particular, RLIMIT_AS and RLIMIT_NPROC). Most systems don't | |
714 | need this. | |
715 | ||
716 | Note that if you change this from 0 to 1, already created segments | |
717 | without users and with a dead originative process will be destroyed. | |
718 | ||
719 | ============================================================== | |
720 | ||
807094c0 | 721 | tainted: |
1da177e4 LT |
722 | |
723 | Non-zero if the kernel has been tainted. Numeric values, which | |
724 | can be ORed together: | |
725 | ||
bb20698d GKH |
726 | 1 - A module with a non-GPL license has been loaded, this |
727 | includes modules with no license. | |
728 | Set by modutils >= 2.4.9 and module-init-tools. | |
729 | 2 - A module was force loaded by insmod -f. | |
730 | Set by modutils >= 2.4.9 and module-init-tools. | |
731 | 4 - Unsafe SMP processors: SMP with CPUs not designed for SMP. | |
732 | 8 - A module was forcibly unloaded from the system by rmmod -f. | |
733 | 16 - A hardware machine check error occurred on the system. | |
734 | 32 - A bad page was discovered on the system. | |
735 | 64 - The user has asked that the system be marked "tainted". This | |
736 | could be because they are running software that directly modifies | |
737 | the hardware, or for other reasons. | |
738 | 128 - The system has died. | |
739 | 256 - The ACPI DSDT has been overridden with one supplied by the user | |
740 | instead of using the one provided by the hardware. | |
741 | 512 - A kernel warning has occurred. | |
742 | 1024 - A module from drivers/staging was loaded. | |
f5fe184b LF |
743 | 2048 - The system is working around a severe firmware bug. |
744 | 4096 - An out-of-tree module has been loaded. | |
1da177e4 | 745 | |
760df93e SF |
746 | ============================================================== |
747 | ||
760df93e SF |
748 | unknown_nmi_panic: |
749 | ||
807094c0 BP |
750 | The value in this file affects behavior of handling NMI. When the |
751 | value is non-zero, unknown NMI is trapped and then panic occurs. At | |
752 | that time, kernel debugging information is displayed on console. | |
760df93e | 753 | |
807094c0 BP |
754 | NMI switch that most IA32 servers have fires unknown NMI up, for |
755 | example. If a system hangs up, try pressing the NMI switch. | |
08825c90 LZ |
756 | |
757 | ============================================================== | |
758 | ||
759 | watchdog_thresh: | |
760 | ||
761 | This value can be used to control the frequency of hrtimer and NMI | |
762 | events and the soft and hard lockup thresholds. The default threshold | |
763 | is 10 seconds. | |
764 | ||
765 | The softlockup threshold is (2 * watchdog_thresh). Setting this | |
766 | tunable to zero will disable lockup detection altogether. | |
767 | ||
768 | ============================================================== |