Commit | Line | Data |
---|---|---|
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 | |
270750db AT |
36 | - hung_task_panic |
37 | - hung_task_check_count | |
38 | - hung_task_timeout_secs | |
39 | - hung_task_warnings | |
455cd5ab | 40 | - kptr_restrict |
0741f4d2 | 41 | - kstack_depth_to_print [ X86 only ] |
1da177e4 | 42 | - l2cr [ PPC only ] |
ac76cff2 | 43 | - modprobe ==> Documentation/debugging-modules.txt |
3d43321b | 44 | - modules_disabled |
03f59566 | 45 | - msg_next_id [ sysv ipc ] |
1da177e4 LT |
46 | - msgmax |
47 | - msgmnb | |
48 | - msgmni | |
760df93e | 49 | - nmi_watchdog |
1da177e4 LT |
50 | - osrelease |
51 | - ostype | |
52 | - overflowgid | |
53 | - overflowuid | |
54 | - panic | |
807094c0 BP |
55 | - panic_on_oops |
56 | - panic_on_unrecovered_nmi | |
55af7796 | 57 | - panic_on_stackoverflow |
1da177e4 LT |
58 | - pid_max |
59 | - powersave-nap [ PPC only ] | |
60 | - printk | |
807094c0 BP |
61 | - printk_delay |
62 | - printk_ratelimit | |
63 | - printk_ratelimit_burst | |
1ec7fd50 | 64 | - randomize_va_space |
1da177e4 LT |
65 | - real-root-dev ==> Documentation/initrd.txt |
66 | - reboot-cmd [ SPARC only ] | |
67 | - rtsig-max | |
68 | - rtsig-nr | |
69 | - sem | |
03f59566 | 70 | - sem_next_id [ sysv ipc ] |
1da177e4 | 71 | - sg-big-buff [ generic SCSI device (sg) ] |
03f59566 | 72 | - shm_next_id [ sysv ipc ] |
b34a6b1d | 73 | - shm_rmid_forced |
1da177e4 LT |
74 | - shmall |
75 | - shmmax [ sysv ipc ] | |
76 | - shmmni | |
77 | - stop-a [ SPARC only ] | |
78 | - sysrq ==> Documentation/sysrq.txt | |
79 | - tainted | |
80 | - threads-max | |
760df93e | 81 | - unknown_nmi_panic |
08825c90 | 82 | - watchdog_thresh |
1da177e4 LT |
83 | - version |
84 | ||
85 | ============================================================== | |
86 | ||
87 | acct: | |
88 | ||
89 | highwater lowwater frequency | |
90 | ||
91 | If BSD-style process accounting is enabled these values control | |
92 | its behaviour. If free space on filesystem where the log lives | |
93 | goes below <lowwater>% accounting suspends. If free space gets | |
94 | above <highwater>% accounting resumes. <Frequency> determines | |
95 | how often do we check the amount of free space (value is in | |
96 | seconds). Default: | |
97 | 4 2 30 | |
98 | That is, suspend accounting if there left <= 2% free; resume it | |
99 | if we got >=4%; consider information about amount of free space | |
100 | valid for 30 seconds. | |
101 | ||
807094c0 BP |
102 | ============================================================== |
103 | ||
104 | acpi_video_flags: | |
105 | ||
106 | flags | |
107 | ||
108 | See Doc*/kernel/power/video.txt, it allows mode of video boot to be | |
109 | set during run time. | |
110 | ||
111 | ============================================================== | |
112 | ||
113 | auto_msgmni: | |
114 | ||
115 | Enables/Disables automatic recomputing of msgmni upon memory add/remove | |
116 | or upon ipc namespace creation/removal (see the msgmni description | |
117 | above). Echoing "1" into this file enables msgmni automatic recomputing. | |
118 | Echoing "0" turns it off. auto_msgmni default value is 1. | |
119 | ||
120 | ||
1da177e4 LT |
121 | ============================================================== |
122 | ||
d75757ab PA |
123 | bootloader_type: |
124 | ||
125 | x86 bootloader identification | |
126 | ||
127 | This gives the bootloader type number as indicated by the bootloader, | |
128 | shifted left by 4, and OR'd with the low four bits of the bootloader | |
129 | version. The reason for this encoding is that this used to match the | |
130 | type_of_loader field in the kernel header; the encoding is kept for | |
131 | backwards compatibility. That is, if the full bootloader type number | |
132 | is 0x15 and the full version number is 0x234, this file will contain | |
133 | the value 340 = 0x154. | |
134 | ||
135 | See the type_of_loader and ext_loader_type fields in | |
136 | Documentation/x86/boot.txt for additional information. | |
137 | ||
138 | ============================================================== | |
139 | ||
140 | bootloader_version: | |
141 | ||
142 | x86 bootloader version | |
143 | ||
144 | The complete bootloader version number. In the example above, this | |
145 | file will contain the value 564 = 0x234. | |
146 | ||
147 | See the type_of_loader and ext_loader_ver fields in | |
148 | Documentation/x86/boot.txt for additional information. | |
149 | ||
150 | ============================================================== | |
151 | ||
c114728a HJP |
152 | callhome: |
153 | ||
154 | Controls the kernel's callhome behavior in case of a kernel panic. | |
155 | ||
156 | The s390 hardware allows an operating system to send a notification | |
157 | to a service organization (callhome) in case of an operating system panic. | |
158 | ||
159 | When the value in this file is 0 (which is the default behavior) | |
160 | nothing happens in case of a kernel panic. If this value is set to "1" | |
161 | the complete kernel oops message is send to the IBM customer service | |
162 | organization in case the mainframe the Linux operating system is running | |
163 | on has a service contract with IBM. | |
164 | ||
165 | ============================================================== | |
166 | ||
73efc039 DB |
167 | cap_last_cap |
168 | ||
169 | Highest valid capability of the running kernel. Exports | |
170 | CAP_LAST_CAP from the kernel. | |
171 | ||
172 | ============================================================== | |
173 | ||
1da177e4 LT |
174 | core_pattern: |
175 | ||
176 | core_pattern is used to specify a core dumpfile pattern name. | |
cd081041 | 177 | . max length 128 characters; default value is "core" |
1da177e4 LT |
178 | . core_pattern is used as a pattern template for the output filename; |
179 | certain string patterns (beginning with '%') are substituted with | |
180 | their actual values. | |
181 | . backward compatibility with core_uses_pid: | |
182 | If core_pattern does not include "%p" (default does not) | |
183 | and core_uses_pid is set, then .PID will be appended to | |
184 | the filename. | |
185 | . corename format specifiers: | |
186 | %<NUL> '%' is dropped | |
187 | %% output one '%' | |
188 | %p pid | |
65aafb1e | 189 | %P global pid (init PID namespace) |
1da177e4 LT |
190 | %u uid |
191 | %g gid | |
12a2b4b2 ON |
192 | %d dump mode, matches PR_SET_DUMPABLE and |
193 | /proc/sys/fs/suid_dumpable | |
1da177e4 LT |
194 | %s signal number |
195 | %t UNIX time of dump | |
196 | %h hostname | |
57cc083a JS |
197 | %e executable filename (may be shortened) |
198 | %E executable path | |
1da177e4 | 199 | %<OTHER> both are dropped |
cd081041 MU |
200 | . If the first character of the pattern is a '|', the kernel will treat |
201 | the rest of the pattern as a command to run. The core dump will be | |
202 | written to the standard input of that program instead of to a file. | |
1da177e4 LT |
203 | |
204 | ============================================================== | |
205 | ||
a293980c NH |
206 | core_pipe_limit: |
207 | ||
807094c0 BP |
208 | This sysctl is only applicable when core_pattern is configured to pipe |
209 | core files to a user space helper (when the first character of | |
210 | core_pattern is a '|', see above). When collecting cores via a pipe | |
211 | to an application, it is occasionally useful for the collecting | |
212 | application to gather data about the crashing process from its | |
213 | /proc/pid directory. In order to do this safely, the kernel must wait | |
214 | for the collecting process to exit, so as not to remove the crashing | |
215 | processes proc files prematurely. This in turn creates the | |
216 | possibility that a misbehaving userspace collecting process can block | |
217 | the reaping of a crashed process simply by never exiting. This sysctl | |
218 | defends against that. It defines how many concurrent crashing | |
219 | processes may be piped to user space applications in parallel. If | |
220 | this value is exceeded, then those crashing processes above that value | |
221 | are noted via the kernel log and their cores are skipped. 0 is a | |
222 | special value, indicating that unlimited processes may be captured in | |
223 | parallel, but that no waiting will take place (i.e. the collecting | |
224 | process is not guaranteed access to /proc/<crashing pid>/). This | |
225 | value defaults to 0. | |
a293980c NH |
226 | |
227 | ============================================================== | |
228 | ||
1da177e4 LT |
229 | core_uses_pid: |
230 | ||
231 | The default coredump filename is "core". By setting | |
232 | core_uses_pid to 1, the coredump filename becomes core.PID. | |
233 | If core_pattern does not include "%p" (default does not) | |
234 | and core_uses_pid is set, then .PID will be appended to | |
235 | the filename. | |
236 | ||
237 | ============================================================== | |
238 | ||
239 | ctrl-alt-del: | |
240 | ||
241 | When the value in this file is 0, ctrl-alt-del is trapped and | |
242 | sent to the init(1) program to handle a graceful restart. | |
243 | When, however, the value is > 0, Linux's reaction to a Vulcan | |
244 | Nerve Pinch (tm) will be an immediate reboot, without even | |
245 | syncing its dirty buffers. | |
246 | ||
247 | Note: when a program (like dosemu) has the keyboard in 'raw' | |
248 | mode, the ctrl-alt-del is intercepted by the program before it | |
249 | ever reaches the kernel tty layer, and it's up to the program | |
250 | to decide what to do with it. | |
251 | ||
252 | ============================================================== | |
253 | ||
eaf06b24 DR |
254 | dmesg_restrict: |
255 | ||
807094c0 BP |
256 | This toggle indicates whether unprivileged users are prevented |
257 | from using dmesg(8) to view messages from the kernel's log buffer. | |
258 | When dmesg_restrict is set to (0) there are no restrictions. When | |
38ef4c2e | 259 | dmesg_restrict is set set to (1), users must have CAP_SYSLOG to use |
eaf06b24 DR |
260 | dmesg(8). |
261 | ||
807094c0 BP |
262 | The kernel config option CONFIG_SECURITY_DMESG_RESTRICT sets the |
263 | default value of dmesg_restrict. | |
eaf06b24 DR |
264 | |
265 | ============================================================== | |
266 | ||
1da177e4 LT |
267 | domainname & hostname: |
268 | ||
269 | These files can be used to set the NIS/YP domainname and the | |
270 | hostname of your box in exactly the same way as the commands | |
271 | domainname and hostname, i.e.: | |
272 | # echo "darkstar" > /proc/sys/kernel/hostname | |
273 | # echo "mydomain" > /proc/sys/kernel/domainname | |
274 | has the same effect as | |
275 | # hostname "darkstar" | |
276 | # domainname "mydomain" | |
277 | ||
278 | Note, however, that the classic darkstar.frop.org has the | |
279 | hostname "darkstar" and DNS (Internet Domain Name Server) | |
280 | domainname "frop.org", not to be confused with the NIS (Network | |
281 | Information Service) or YP (Yellow Pages) domainname. These two | |
282 | domain names are in general different. For a detailed discussion | |
283 | see the hostname(1) man page. | |
284 | ||
285 | ============================================================== | |
286 | ||
287 | hotplug: | |
288 | ||
289 | Path for the hotplug policy agent. | |
290 | Default value is "/sbin/hotplug". | |
291 | ||
292 | ============================================================== | |
293 | ||
270750db AT |
294 | hung_task_panic: |
295 | ||
296 | Controls the kernel's behavior when a hung task is detected. | |
297 | This file shows up if CONFIG_DETECT_HUNG_TASK is enabled. | |
298 | ||
299 | 0: continue operation. This is the default behavior. | |
300 | ||
301 | 1: panic immediately. | |
302 | ||
303 | ============================================================== | |
304 | ||
305 | hung_task_check_count: | |
306 | ||
307 | The upper bound on the number of tasks that are checked. | |
308 | This file shows up if CONFIG_DETECT_HUNG_TASK is enabled. | |
309 | ||
310 | ============================================================== | |
311 | ||
312 | hung_task_timeout_secs: | |
313 | ||
314 | Check interval. When a task in D state did not get scheduled | |
315 | for more than this value report a warning. | |
316 | This file shows up if CONFIG_DETECT_HUNG_TASK is enabled. | |
317 | ||
318 | 0: means infinite timeout - no checking done. | |
319 | ||
320 | ============================================================== | |
321 | ||
322 | hung_task_warning: | |
323 | ||
324 | The maximum number of warnings to report. During a check interval | |
325 | When this value is reached, no more the warnings will be reported. | |
326 | This file shows up if CONFIG_DETECT_HUNG_TASK is enabled. | |
327 | ||
328 | -1: report an infinite number of warnings. | |
329 | ||
330 | ============================================================== | |
331 | ||
455cd5ab DR |
332 | kptr_restrict: |
333 | ||
334 | This toggle indicates whether restrictions are placed on | |
312b4e22 RM |
335 | exposing kernel addresses via /proc and other interfaces. |
336 | ||
337 | When kptr_restrict is set to (0), the default, there are no restrictions. | |
338 | ||
339 | When kptr_restrict is set to (1), kernel pointers printed using the %pK | |
340 | format specifier will be replaced with 0's unless the user has CAP_SYSLOG | |
341 | and effective user and group ids are equal to the real ids. This is | |
342 | because %pK checks are done at read() time rather than open() time, so | |
343 | if permissions are elevated between the open() and the read() (e.g via | |
344 | a setuid binary) then %pK will not leak kernel pointers to unprivileged | |
345 | users. Note, this is a temporary solution only. The correct long-term | |
346 | solution is to do the permission checks at open() time. Consider removing | |
347 | world read permissions from files that use %pK, and using dmesg_restrict | |
348 | to protect against uses of %pK in dmesg(8) if leaking kernel pointer | |
349 | values to unprivileged users is a concern. | |
350 | ||
351 | When kptr_restrict is set to (2), kernel pointers printed using | |
352 | %pK will be replaced with 0's regardless of privileges. | |
455cd5ab DR |
353 | |
354 | ============================================================== | |
355 | ||
0741f4d2 CE |
356 | kstack_depth_to_print: (X86 only) |
357 | ||
358 | Controls the number of words to print when dumping the raw | |
359 | kernel stack. | |
360 | ||
361 | ============================================================== | |
362 | ||
807094c0 BP |
363 | l2cr: (PPC only) |
364 | ||
365 | This flag controls the L2 cache of G3 processor boards. If | |
366 | 0, the cache is disabled. Enabled if nonzero. | |
367 | ||
368 | ============================================================== | |
369 | ||
3d43321b KC |
370 | modules_disabled: |
371 | ||
372 | A toggle value indicating if modules are allowed to be loaded | |
373 | in an otherwise modular kernel. This toggle defaults to off | |
374 | (0), but can be set true (1). Once true, modules can be | |
375 | neither loaded nor unloaded, and the toggle cannot be set back | |
376 | to false. | |
377 | ||
378 | ============================================================== | |
379 | ||
03f59566 SK |
380 | msg_next_id, sem_next_id, and shm_next_id: |
381 | ||
382 | These three toggles allows to specify desired id for next allocated IPC | |
383 | object: message, semaphore or shared memory respectively. | |
384 | ||
385 | By default they are equal to -1, which means generic allocation logic. | |
386 | Possible values to set are in range {0..INT_MAX}. | |
387 | ||
388 | Notes: | |
389 | 1) kernel doesn't guarantee, that new object will have desired id. So, | |
390 | it's up to userspace, how to handle an object with "wrong" id. | |
391 | 2) Toggle with non-default value will be set back to -1 by kernel after | |
392 | successful IPC object allocation. | |
393 | ||
394 | ============================================================== | |
395 | ||
807094c0 BP |
396 | nmi_watchdog: |
397 | ||
398 | Enables/Disables the NMI watchdog on x86 systems. When the value is | |
399 | non-zero the NMI watchdog is enabled and will continuously test all | |
400 | online cpus to determine whether or not they are still functioning | |
401 | properly. Currently, passing "nmi_watchdog=" parameter at boot time is | |
402 | required for this function to work. | |
403 | ||
404 | If LAPIC NMI watchdog method is in use (nmi_watchdog=2 kernel | |
405 | parameter), the NMI watchdog shares registers with oprofile. By | |
406 | disabling the NMI watchdog, oprofile may have more registers to | |
407 | utilize. | |
408 | ||
409 | ============================================================== | |
410 | ||
10fc05d0 MG |
411 | numa_balancing |
412 | ||
413 | Enables/disables automatic page fault based NUMA memory | |
414 | balancing. Memory is moved automatically to nodes | |
415 | that access it often. | |
416 | ||
417 | Enables/disables automatic NUMA memory balancing. On NUMA machines, there | |
418 | is a performance penalty if remote memory is accessed by a CPU. When this | |
419 | feature is enabled the kernel samples what task thread is accessing memory | |
420 | by periodically unmapping pages and later trapping a page fault. At the | |
421 | time of the page fault, it is determined if the data being accessed should | |
422 | be migrated to a local memory node. | |
423 | ||
424 | The unmapping of pages and trapping faults incur additional overhead that | |
425 | ideally is offset by improved memory locality but there is no universal | |
426 | guarantee. If the target workload is already bound to NUMA nodes then this | |
427 | feature should be disabled. Otherwise, if the system overhead from the | |
428 | feature is too high then the rate the kernel samples for NUMA hinting | |
429 | faults may be controlled by the numa_balancing_scan_period_min_ms, | |
930aa174 | 430 | numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms, |
de1c9ce6 RR |
431 | numa_balancing_scan_size_mb, numa_balancing_settle_count sysctls and |
432 | numa_balancing_migrate_deferred. | |
10fc05d0 MG |
433 | |
434 | ============================================================== | |
435 | ||
436 | numa_balancing_scan_period_min_ms, numa_balancing_scan_delay_ms, | |
930aa174 | 437 | numa_balancing_scan_period_max_ms, numa_balancing_scan_size_mb |
10fc05d0 MG |
438 | |
439 | Automatic NUMA balancing scans tasks address space and unmaps pages to | |
440 | detect if pages are properly placed or if the data should be migrated to a | |
441 | memory node local to where the task is running. Every "scan delay" the task | |
442 | scans the next "scan size" number of pages in its address space. When the | |
443 | end of the address space is reached the scanner restarts from the beginning. | |
444 | ||
445 | In combination, the "scan delay" and "scan size" determine the scan rate. | |
446 | When "scan delay" decreases, the scan rate increases. The scan delay and | |
447 | hence the scan rate of every task is adaptive and depends on historical | |
448 | behaviour. If pages are properly placed then the scan delay increases, | |
449 | otherwise the scan delay decreases. The "scan size" is not adaptive but | |
450 | the higher the "scan size", the higher the scan rate. | |
451 | ||
452 | Higher scan rates incur higher system overhead as page faults must be | |
453 | trapped and potentially data must be migrated. However, the higher the scan | |
454 | rate, the more quickly a tasks memory is migrated to a local node if the | |
455 | workload pattern changes and minimises performance impact due to remote | |
456 | memory accesses. These sysctls control the thresholds for scan delays and | |
457 | the number of pages scanned. | |
458 | ||
598f0ec0 MG |
459 | numa_balancing_scan_period_min_ms is the minimum time in milliseconds to |
460 | scan a tasks virtual memory. It effectively controls the maximum scanning | |
461 | rate for each task. | |
10fc05d0 MG |
462 | |
463 | numa_balancing_scan_delay_ms is the starting "scan delay" used for a task | |
464 | when it initially forks. | |
465 | ||
598f0ec0 MG |
466 | numa_balancing_scan_period_max_ms is the maximum time in milliseconds to |
467 | scan a tasks virtual memory. It effectively controls the minimum scanning | |
468 | rate for each task. | |
10fc05d0 MG |
469 | |
470 | numa_balancing_scan_size_mb is how many megabytes worth of pages are | |
471 | scanned for a given scan. | |
472 | ||
de1c9ce6 RR |
473 | numa_balancing_migrate_deferred is how many page migrations get skipped |
474 | unconditionally, after a page migration is skipped because a page is shared | |
475 | with other tasks. This reduces page migration overhead, and determines | |
476 | how much stronger the "move task near its memory" policy scheduler becomes, | |
477 | versus the "move memory near its task" memory management policy, for workloads | |
478 | with shared memory. | |
479 | ||
10fc05d0 MG |
480 | ============================================================== |
481 | ||
1da177e4 LT |
482 | osrelease, ostype & version: |
483 | ||
484 | # cat osrelease | |
485 | 2.1.88 | |
486 | # cat ostype | |
487 | Linux | |
488 | # cat version | |
489 | #5 Wed Feb 25 21:49:24 MET 1998 | |
490 | ||
491 | The files osrelease and ostype should be clear enough. Version | |
492 | needs a little more clarification however. The '#5' means that | |
493 | this is the fifth kernel built from this source base and the | |
494 | date behind it indicates the time the kernel was built. | |
495 | The only way to tune these values is to rebuild the kernel :-) | |
496 | ||
497 | ============================================================== | |
498 | ||
499 | overflowgid & overflowuid: | |
500 | ||
807094c0 BP |
501 | if your architecture did not always support 32-bit UIDs (i.e. arm, |
502 | i386, m68k, sh, and sparc32), a fixed UID and GID will be returned to | |
503 | applications that use the old 16-bit UID/GID system calls, if the | |
504 | actual UID or GID would exceed 65535. | |
1da177e4 LT |
505 | |
506 | These sysctls allow you to change the value of the fixed UID and GID. | |
507 | The default is 65534. | |
508 | ||
509 | ============================================================== | |
510 | ||
511 | panic: | |
512 | ||
807094c0 BP |
513 | The value in this file represents the number of seconds the kernel |
514 | waits before rebooting on a panic. When you use the software watchdog, | |
515 | the recommended setting is 60. | |
516 | ||
517 | ============================================================== | |
518 | ||
519 | panic_on_unrecovered_nmi: | |
520 | ||
521 | The default Linux behaviour on an NMI of either memory or unknown is | |
522 | to continue operation. For many environments such as scientific | |
523 | computing it is preferable that the box is taken out and the error | |
524 | dealt with than an uncorrected parity/ECC error get propagated. | |
525 | ||
526 | A small number of systems do generate NMI's for bizarre random reasons | |
527 | such as power management so the default is off. That sysctl works like | |
528 | the existing panic controls already in that directory. | |
1da177e4 LT |
529 | |
530 | ============================================================== | |
531 | ||
532 | panic_on_oops: | |
533 | ||
534 | Controls the kernel's behaviour when an oops or BUG is encountered. | |
535 | ||
536 | 0: try to continue operation | |
537 | ||
a982ac06 | 538 | 1: panic immediately. If the `panic' sysctl is also non-zero then the |
8b23d04d | 539 | machine will be rebooted. |
1da177e4 LT |
540 | |
541 | ============================================================== | |
542 | ||
55af7796 MH |
543 | panic_on_stackoverflow: |
544 | ||
545 | Controls the kernel's behavior when detecting the overflows of | |
546 | kernel, IRQ and exception stacks except a user stack. | |
547 | This file shows up if CONFIG_DEBUG_STACKOVERFLOW is enabled. | |
548 | ||
549 | 0: try to continue operation. | |
550 | ||
551 | 1: panic immediately. | |
552 | ||
553 | ============================================================== | |
554 | ||
14c63f17 DH |
555 | perf_cpu_time_max_percent: |
556 | ||
557 | Hints to the kernel how much CPU time it should be allowed to | |
558 | use to handle perf sampling events. If the perf subsystem | |
559 | is informed that its samples are exceeding this limit, it | |
560 | will drop its sampling frequency to attempt to reduce its CPU | |
561 | usage. | |
562 | ||
563 | Some perf sampling happens in NMIs. If these samples | |
564 | unexpectedly take too long to execute, the NMIs can become | |
565 | stacked up next to each other so much that nothing else is | |
566 | allowed to execute. | |
567 | ||
568 | 0: disable the mechanism. Do not monitor or correct perf's | |
569 | sampling rate no matter how CPU time it takes. | |
570 | ||
571 | 1-100: attempt to throttle perf's sample rate to this | |
572 | percentage of CPU. Note: the kernel calculates an | |
573 | "expected" length of each sample event. 100 here means | |
574 | 100% of that expected length. Even if this is set to | |
575 | 100, you may still see sample throttling if this | |
576 | length is exceeded. Set to 0 if you truly do not care | |
577 | how much CPU is consumed. | |
578 | ||
579 | ============================================================== | |
580 | ||
55af7796 | 581 | |
1da177e4 LT |
582 | pid_max: |
583 | ||
beb7dd86 | 584 | PID allocation wrap value. When the kernel's next PID value |
1da177e4 LT |
585 | reaches this value, it wraps back to a minimum PID value. |
586 | PIDs of value pid_max or larger are not allocated. | |
587 | ||
588 | ============================================================== | |
589 | ||
b8f566b0 PE |
590 | ns_last_pid: |
591 | ||
592 | The last pid allocated in the current (the one task using this sysctl | |
593 | lives in) pid namespace. When selecting a pid for a next task on fork | |
594 | kernel tries to allocate a number starting from this one. | |
595 | ||
596 | ============================================================== | |
597 | ||
1da177e4 LT |
598 | powersave-nap: (PPC only) |
599 | ||
600 | If set, Linux-PPC will use the 'nap' mode of powersaving, | |
601 | otherwise the 'doze' mode will be used. | |
602 | ||
603 | ============================================================== | |
604 | ||
605 | printk: | |
606 | ||
607 | The four values in printk denote: console_loglevel, | |
608 | default_message_loglevel, minimum_console_loglevel and | |
609 | default_console_loglevel respectively. | |
610 | ||
611 | These values influence printk() behavior when printing or | |
612 | logging error messages. See 'man 2 syslog' for more info on | |
613 | the different loglevels. | |
614 | ||
615 | - console_loglevel: messages with a higher priority than | |
616 | this will be printed to the console | |
87889e15 | 617 | - default_message_loglevel: messages without an explicit priority |
1da177e4 LT |
618 | will be printed with this priority |
619 | - minimum_console_loglevel: minimum (highest) value to which | |
620 | console_loglevel can be set | |
621 | - default_console_loglevel: default value for console_loglevel | |
622 | ||
623 | ============================================================== | |
624 | ||
807094c0 BP |
625 | printk_delay: |
626 | ||
627 | Delay each printk message in printk_delay milliseconds | |
628 | ||
629 | Value from 0 - 10000 is allowed. | |
630 | ||
631 | ============================================================== | |
632 | ||
1da177e4 LT |
633 | printk_ratelimit: |
634 | ||
635 | Some warning messages are rate limited. printk_ratelimit specifies | |
636 | the minimum length of time between these messages (in jiffies), by | |
637 | default we allow one every 5 seconds. | |
638 | ||
639 | A value of 0 will disable rate limiting. | |
640 | ||
641 | ============================================================== | |
642 | ||
643 | printk_ratelimit_burst: | |
644 | ||
645 | While long term we enforce one message per printk_ratelimit | |
646 | seconds, we do allow a burst of messages to pass through. | |
647 | printk_ratelimit_burst specifies the number of messages we can | |
648 | send before ratelimiting kicks in. | |
649 | ||
650 | ============================================================== | |
651 | ||
807094c0 | 652 | randomize_va_space: |
1ec7fd50 JK |
653 | |
654 | This option can be used to select the type of process address | |
655 | space randomization that is used in the system, for architectures | |
656 | that support this feature. | |
657 | ||
b7f5ab6f HS |
658 | 0 - Turn the process address space randomization off. This is the |
659 | default for architectures that do not support this feature anyways, | |
660 | and kernels that are booted with the "norandmaps" parameter. | |
1ec7fd50 JK |
661 | |
662 | 1 - Make the addresses of mmap base, stack and VDSO page randomized. | |
663 | This, among other things, implies that shared libraries will be | |
b7f5ab6f HS |
664 | loaded to random addresses. Also for PIE-linked binaries, the |
665 | location of code start is randomized. This is the default if the | |
666 | CONFIG_COMPAT_BRK option is enabled. | |
1ec7fd50 | 667 | |
b7f5ab6f HS |
668 | 2 - Additionally enable heap randomization. This is the default if |
669 | CONFIG_COMPAT_BRK is disabled. | |
670 | ||
671 | There are a few legacy applications out there (such as some ancient | |
1ec7fd50 | 672 | versions of libc.so.5 from 1996) that assume that brk area starts |
b7f5ab6f HS |
673 | just after the end of the code+bss. These applications break when |
674 | start of the brk area is randomized. There are however no known | |
1ec7fd50 | 675 | non-legacy applications that would be broken this way, so for most |
b7f5ab6f HS |
676 | systems it is safe to choose full randomization. |
677 | ||
678 | Systems with ancient and/or broken binaries should be configured | |
679 | with CONFIG_COMPAT_BRK enabled, which excludes the heap from process | |
680 | address space randomization. | |
1ec7fd50 JK |
681 | |
682 | ============================================================== | |
683 | ||
1da177e4 LT |
684 | reboot-cmd: (Sparc only) |
685 | ||
686 | ??? This seems to be a way to give an argument to the Sparc | |
687 | ROM/Flash boot loader. Maybe to tell it what to do after | |
688 | rebooting. ??? | |
689 | ||
690 | ============================================================== | |
691 | ||
692 | rtsig-max & rtsig-nr: | |
693 | ||
694 | The file rtsig-max can be used to tune the maximum number | |
695 | of POSIX realtime (queued) signals that can be outstanding | |
696 | in the system. | |
697 | ||
698 | rtsig-nr shows the number of RT signals currently queued. | |
699 | ||
700 | ============================================================== | |
701 | ||
702 | sg-big-buff: | |
703 | ||
704 | This file shows the size of the generic SCSI (sg) buffer. | |
705 | You can't tune it just yet, but you could change it on | |
706 | compile time by editing include/scsi/sg.h and changing | |
707 | the value of SG_BIG_BUFF. | |
708 | ||
709 | There shouldn't be any reason to change this value. If | |
710 | you can come up with one, you probably know what you | |
711 | are doing anyway :) | |
712 | ||
713 | ============================================================== | |
714 | ||
358e419f CALP |
715 | shmall: |
716 | ||
717 | This parameter sets the total amount of shared memory pages that | |
718 | can be used system wide. Hence, SHMALL should always be at least | |
719 | ceil(shmmax/PAGE_SIZE). | |
720 | ||
721 | If you are not sure what the default PAGE_SIZE is on your Linux | |
722 | system, you can run the following command: | |
723 | ||
724 | # getconf PAGE_SIZE | |
725 | ||
726 | ============================================================== | |
727 | ||
807094c0 | 728 | shmmax: |
1da177e4 LT |
729 | |
730 | This value can be used to query and set the run time limit | |
731 | on the maximum shared memory segment size that can be created. | |
807094c0 | 732 | Shared memory segments up to 1Gb are now supported in the |
1da177e4 LT |
733 | kernel. This value defaults to SHMMAX. |
734 | ||
735 | ============================================================== | |
736 | ||
b34a6b1d VK |
737 | shm_rmid_forced: |
738 | ||
739 | Linux lets you set resource limits, including how much memory one | |
740 | process can consume, via setrlimit(2). Unfortunately, shared memory | |
741 | segments are allowed to exist without association with any process, and | |
742 | thus might not be counted against any resource limits. If enabled, | |
743 | shared memory segments are automatically destroyed when their attach | |
744 | count becomes zero after a detach or a process termination. It will | |
745 | also destroy segments that were created, but never attached to, on exit | |
746 | from the process. The only use left for IPC_RMID is to immediately | |
747 | destroy an unattached segment. Of course, this breaks the way things are | |
748 | defined, so some applications might stop working. Note that this | |
749 | feature will do you no good unless you also configure your resource | |
750 | limits (in particular, RLIMIT_AS and RLIMIT_NPROC). Most systems don't | |
751 | need this. | |
752 | ||
753 | Note that if you change this from 0 to 1, already created segments | |
754 | without users and with a dead originative process will be destroyed. | |
755 | ||
756 | ============================================================== | |
757 | ||
807094c0 | 758 | tainted: |
1da177e4 LT |
759 | |
760 | Non-zero if the kernel has been tainted. Numeric values, which | |
761 | can be ORed together: | |
762 | ||
bb20698d GKH |
763 | 1 - A module with a non-GPL license has been loaded, this |
764 | includes modules with no license. | |
765 | Set by modutils >= 2.4.9 and module-init-tools. | |
766 | 2 - A module was force loaded by insmod -f. | |
767 | Set by modutils >= 2.4.9 and module-init-tools. | |
768 | 4 - Unsafe SMP processors: SMP with CPUs not designed for SMP. | |
769 | 8 - A module was forcibly unloaded from the system by rmmod -f. | |
770 | 16 - A hardware machine check error occurred on the system. | |
771 | 32 - A bad page was discovered on the system. | |
772 | 64 - The user has asked that the system be marked "tainted". This | |
773 | could be because they are running software that directly modifies | |
774 | the hardware, or for other reasons. | |
775 | 128 - The system has died. | |
776 | 256 - The ACPI DSDT has been overridden with one supplied by the user | |
777 | instead of using the one provided by the hardware. | |
778 | 512 - A kernel warning has occurred. | |
779 | 1024 - A module from drivers/staging was loaded. | |
f5fe184b LF |
780 | 2048 - The system is working around a severe firmware bug. |
781 | 4096 - An out-of-tree module has been loaded. | |
1da177e4 | 782 | |
760df93e SF |
783 | ============================================================== |
784 | ||
760df93e SF |
785 | unknown_nmi_panic: |
786 | ||
807094c0 BP |
787 | The value in this file affects behavior of handling NMI. When the |
788 | value is non-zero, unknown NMI is trapped and then panic occurs. At | |
789 | that time, kernel debugging information is displayed on console. | |
760df93e | 790 | |
807094c0 BP |
791 | NMI switch that most IA32 servers have fires unknown NMI up, for |
792 | example. If a system hangs up, try pressing the NMI switch. | |
08825c90 LZ |
793 | |
794 | ============================================================== | |
795 | ||
796 | watchdog_thresh: | |
797 | ||
798 | This value can be used to control the frequency of hrtimer and NMI | |
799 | events and the soft and hard lockup thresholds. The default threshold | |
800 | is 10 seconds. | |
801 | ||
802 | The softlockup threshold is (2 * watchdog_thresh). Setting this | |
803 | tunable to zero will disable lockup detection altogether. | |
804 | ||
805 | ============================================================== |