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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 ] |
1da177e4 | 27 | - core_pattern |
a293980c | 28 | - core_pipe_limit |
1da177e4 LT |
29 | - core_uses_pid |
30 | - ctrl-alt-del | |
eaf06b24 | 31 | - dmesg_restrict |
1da177e4 LT |
32 | - domainname |
33 | - hostname | |
34 | - hotplug | |
455cd5ab | 35 | - kptr_restrict |
0741f4d2 | 36 | - kstack_depth_to_print [ X86 only ] |
1da177e4 | 37 | - l2cr [ PPC only ] |
ac76cff2 | 38 | - modprobe ==> Documentation/debugging-modules.txt |
3d43321b | 39 | - modules_disabled |
1da177e4 LT |
40 | - msgmax |
41 | - msgmnb | |
42 | - msgmni | |
760df93e | 43 | - nmi_watchdog |
1da177e4 LT |
44 | - osrelease |
45 | - ostype | |
46 | - overflowgid | |
47 | - overflowuid | |
48 | - panic | |
807094c0 BP |
49 | - panic_on_oops |
50 | - panic_on_unrecovered_nmi | |
1da177e4 LT |
51 | - pid_max |
52 | - powersave-nap [ PPC only ] | |
53 | - printk | |
807094c0 BP |
54 | - printk_delay |
55 | - printk_ratelimit | |
56 | - printk_ratelimit_burst | |
1ec7fd50 | 57 | - randomize_va_space |
1da177e4 LT |
58 | - real-root-dev ==> Documentation/initrd.txt |
59 | - reboot-cmd [ SPARC only ] | |
60 | - rtsig-max | |
61 | - rtsig-nr | |
62 | - sem | |
63 | - sg-big-buff [ generic SCSI device (sg) ] | |
64 | - shmall | |
65 | - shmmax [ sysv ipc ] | |
66 | - shmmni | |
807094c0 | 67 | - softlockup_thresh |
1da177e4 LT |
68 | - stop-a [ SPARC only ] |
69 | - sysrq ==> Documentation/sysrq.txt | |
70 | - tainted | |
71 | - threads-max | |
760df93e | 72 | - unknown_nmi_panic |
1da177e4 LT |
73 | - version |
74 | ||
75 | ============================================================== | |
76 | ||
77 | acct: | |
78 | ||
79 | highwater lowwater frequency | |
80 | ||
81 | If BSD-style process accounting is enabled these values control | |
82 | its behaviour. If free space on filesystem where the log lives | |
83 | goes below <lowwater>% accounting suspends. If free space gets | |
84 | above <highwater>% accounting resumes. <Frequency> determines | |
85 | how often do we check the amount of free space (value is in | |
86 | seconds). Default: | |
87 | 4 2 30 | |
88 | That is, suspend accounting if there left <= 2% free; resume it | |
89 | if we got >=4%; consider information about amount of free space | |
90 | valid for 30 seconds. | |
91 | ||
807094c0 BP |
92 | ============================================================== |
93 | ||
94 | acpi_video_flags: | |
95 | ||
96 | flags | |
97 | ||
98 | See Doc*/kernel/power/video.txt, it allows mode of video boot to be | |
99 | set during run time. | |
100 | ||
101 | ============================================================== | |
102 | ||
103 | auto_msgmni: | |
104 | ||
105 | Enables/Disables automatic recomputing of msgmni upon memory add/remove | |
106 | or upon ipc namespace creation/removal (see the msgmni description | |
107 | above). Echoing "1" into this file enables msgmni automatic recomputing. | |
108 | Echoing "0" turns it off. auto_msgmni default value is 1. | |
109 | ||
110 | ||
1da177e4 LT |
111 | ============================================================== |
112 | ||
d75757ab PA |
113 | bootloader_type: |
114 | ||
115 | x86 bootloader identification | |
116 | ||
117 | This gives the bootloader type number as indicated by the bootloader, | |
118 | shifted left by 4, and OR'd with the low four bits of the bootloader | |
119 | version. The reason for this encoding is that this used to match the | |
120 | type_of_loader field in the kernel header; the encoding is kept for | |
121 | backwards compatibility. That is, if the full bootloader type number | |
122 | is 0x15 and the full version number is 0x234, this file will contain | |
123 | the value 340 = 0x154. | |
124 | ||
125 | See the type_of_loader and ext_loader_type fields in | |
126 | Documentation/x86/boot.txt for additional information. | |
127 | ||
128 | ============================================================== | |
129 | ||
130 | bootloader_version: | |
131 | ||
132 | x86 bootloader version | |
133 | ||
134 | The complete bootloader version number. In the example above, this | |
135 | file will contain the value 564 = 0x234. | |
136 | ||
137 | See the type_of_loader and ext_loader_ver fields in | |
138 | Documentation/x86/boot.txt for additional information. | |
139 | ||
140 | ============================================================== | |
141 | ||
c114728a HJP |
142 | callhome: |
143 | ||
144 | Controls the kernel's callhome behavior in case of a kernel panic. | |
145 | ||
146 | The s390 hardware allows an operating system to send a notification | |
147 | to a service organization (callhome) in case of an operating system panic. | |
148 | ||
149 | When the value in this file is 0 (which is the default behavior) | |
150 | nothing happens in case of a kernel panic. If this value is set to "1" | |
151 | the complete kernel oops message is send to the IBM customer service | |
152 | organization in case the mainframe the Linux operating system is running | |
153 | on has a service contract with IBM. | |
154 | ||
155 | ============================================================== | |
156 | ||
1da177e4 LT |
157 | core_pattern: |
158 | ||
159 | core_pattern is used to specify a core dumpfile pattern name. | |
cd081041 | 160 | . max length 128 characters; default value is "core" |
1da177e4 LT |
161 | . core_pattern is used as a pattern template for the output filename; |
162 | certain string patterns (beginning with '%') are substituted with | |
163 | their actual values. | |
164 | . backward compatibility with core_uses_pid: | |
165 | If core_pattern does not include "%p" (default does not) | |
166 | and core_uses_pid is set, then .PID will be appended to | |
167 | the filename. | |
168 | . corename format specifiers: | |
169 | %<NUL> '%' is dropped | |
170 | %% output one '%' | |
171 | %p pid | |
172 | %u uid | |
173 | %g gid | |
174 | %s signal number | |
175 | %t UNIX time of dump | |
176 | %h hostname | |
57cc083a JS |
177 | %e executable filename (may be shortened) |
178 | %E executable path | |
1da177e4 | 179 | %<OTHER> both are dropped |
cd081041 MU |
180 | . If the first character of the pattern is a '|', the kernel will treat |
181 | the rest of the pattern as a command to run. The core dump will be | |
182 | written to the standard input of that program instead of to a file. | |
1da177e4 LT |
183 | |
184 | ============================================================== | |
185 | ||
a293980c NH |
186 | core_pipe_limit: |
187 | ||
807094c0 BP |
188 | This sysctl is only applicable when core_pattern is configured to pipe |
189 | core files to a user space helper (when the first character of | |
190 | core_pattern is a '|', see above). When collecting cores via a pipe | |
191 | to an application, it is occasionally useful for the collecting | |
192 | application to gather data about the crashing process from its | |
193 | /proc/pid directory. In order to do this safely, the kernel must wait | |
194 | for the collecting process to exit, so as not to remove the crashing | |
195 | processes proc files prematurely. This in turn creates the | |
196 | possibility that a misbehaving userspace collecting process can block | |
197 | the reaping of a crashed process simply by never exiting. This sysctl | |
198 | defends against that. It defines how many concurrent crashing | |
199 | processes may be piped to user space applications in parallel. If | |
200 | this value is exceeded, then those crashing processes above that value | |
201 | are noted via the kernel log and their cores are skipped. 0 is a | |
202 | special value, indicating that unlimited processes may be captured in | |
203 | parallel, but that no waiting will take place (i.e. the collecting | |
204 | process is not guaranteed access to /proc/<crashing pid>/). This | |
205 | value defaults to 0. | |
a293980c NH |
206 | |
207 | ============================================================== | |
208 | ||
1da177e4 LT |
209 | core_uses_pid: |
210 | ||
211 | The default coredump filename is "core". By setting | |
212 | core_uses_pid to 1, the coredump filename becomes core.PID. | |
213 | If core_pattern does not include "%p" (default does not) | |
214 | and core_uses_pid is set, then .PID will be appended to | |
215 | the filename. | |
216 | ||
217 | ============================================================== | |
218 | ||
219 | ctrl-alt-del: | |
220 | ||
221 | When the value in this file is 0, ctrl-alt-del is trapped and | |
222 | sent to the init(1) program to handle a graceful restart. | |
223 | When, however, the value is > 0, Linux's reaction to a Vulcan | |
224 | Nerve Pinch (tm) will be an immediate reboot, without even | |
225 | syncing its dirty buffers. | |
226 | ||
227 | Note: when a program (like dosemu) has the keyboard in 'raw' | |
228 | mode, the ctrl-alt-del is intercepted by the program before it | |
229 | ever reaches the kernel tty layer, and it's up to the program | |
230 | to decide what to do with it. | |
231 | ||
232 | ============================================================== | |
233 | ||
eaf06b24 DR |
234 | dmesg_restrict: |
235 | ||
807094c0 BP |
236 | This toggle indicates whether unprivileged users are prevented |
237 | from using dmesg(8) to view messages from the kernel's log buffer. | |
238 | When dmesg_restrict is set to (0) there are no restrictions. When | |
38ef4c2e | 239 | dmesg_restrict is set set to (1), users must have CAP_SYSLOG to use |
eaf06b24 DR |
240 | dmesg(8). |
241 | ||
807094c0 BP |
242 | The kernel config option CONFIG_SECURITY_DMESG_RESTRICT sets the |
243 | default value of dmesg_restrict. | |
eaf06b24 DR |
244 | |
245 | ============================================================== | |
246 | ||
1da177e4 LT |
247 | domainname & hostname: |
248 | ||
249 | These files can be used to set the NIS/YP domainname and the | |
250 | hostname of your box in exactly the same way as the commands | |
251 | domainname and hostname, i.e.: | |
252 | # echo "darkstar" > /proc/sys/kernel/hostname | |
253 | # echo "mydomain" > /proc/sys/kernel/domainname | |
254 | has the same effect as | |
255 | # hostname "darkstar" | |
256 | # domainname "mydomain" | |
257 | ||
258 | Note, however, that the classic darkstar.frop.org has the | |
259 | hostname "darkstar" and DNS (Internet Domain Name Server) | |
260 | domainname "frop.org", not to be confused with the NIS (Network | |
261 | Information Service) or YP (Yellow Pages) domainname. These two | |
262 | domain names are in general different. For a detailed discussion | |
263 | see the hostname(1) man page. | |
264 | ||
265 | ============================================================== | |
266 | ||
267 | hotplug: | |
268 | ||
269 | Path for the hotplug policy agent. | |
270 | Default value is "/sbin/hotplug". | |
271 | ||
272 | ============================================================== | |
273 | ||
455cd5ab DR |
274 | kptr_restrict: |
275 | ||
276 | This toggle indicates whether restrictions are placed on | |
277 | exposing kernel addresses via /proc and other interfaces. When | |
278 | kptr_restrict is set to (0), there are no restrictions. When | |
279 | kptr_restrict is set to (1), the default, kernel pointers | |
280 | printed using the %pK format specifier will be replaced with 0's | |
281 | unless the user has CAP_SYSLOG. When kptr_restrict is set to | |
282 | (2), kernel pointers printed using %pK will be replaced with 0's | |
283 | regardless of privileges. | |
284 | ||
285 | ============================================================== | |
286 | ||
0741f4d2 CE |
287 | kstack_depth_to_print: (X86 only) |
288 | ||
289 | Controls the number of words to print when dumping the raw | |
290 | kernel stack. | |
291 | ||
292 | ============================================================== | |
293 | ||
807094c0 BP |
294 | l2cr: (PPC only) |
295 | ||
296 | This flag controls the L2 cache of G3 processor boards. If | |
297 | 0, the cache is disabled. Enabled if nonzero. | |
298 | ||
299 | ============================================================== | |
300 | ||
3d43321b KC |
301 | modules_disabled: |
302 | ||
303 | A toggle value indicating if modules are allowed to be loaded | |
304 | in an otherwise modular kernel. This toggle defaults to off | |
305 | (0), but can be set true (1). Once true, modules can be | |
306 | neither loaded nor unloaded, and the toggle cannot be set back | |
307 | to false. | |
308 | ||
309 | ============================================================== | |
310 | ||
807094c0 BP |
311 | nmi_watchdog: |
312 | ||
313 | Enables/Disables the NMI watchdog on x86 systems. When the value is | |
314 | non-zero the NMI watchdog is enabled and will continuously test all | |
315 | online cpus to determine whether or not they are still functioning | |
316 | properly. Currently, passing "nmi_watchdog=" parameter at boot time is | |
317 | required for this function to work. | |
318 | ||
319 | If LAPIC NMI watchdog method is in use (nmi_watchdog=2 kernel | |
320 | parameter), the NMI watchdog shares registers with oprofile. By | |
321 | disabling the NMI watchdog, oprofile may have more registers to | |
322 | utilize. | |
323 | ||
324 | ============================================================== | |
325 | ||
1da177e4 LT |
326 | osrelease, ostype & version: |
327 | ||
328 | # cat osrelease | |
329 | 2.1.88 | |
330 | # cat ostype | |
331 | Linux | |
332 | # cat version | |
333 | #5 Wed Feb 25 21:49:24 MET 1998 | |
334 | ||
335 | The files osrelease and ostype should be clear enough. Version | |
336 | needs a little more clarification however. The '#5' means that | |
337 | this is the fifth kernel built from this source base and the | |
338 | date behind it indicates the time the kernel was built. | |
339 | The only way to tune these values is to rebuild the kernel :-) | |
340 | ||
341 | ============================================================== | |
342 | ||
343 | overflowgid & overflowuid: | |
344 | ||
807094c0 BP |
345 | if your architecture did not always support 32-bit UIDs (i.e. arm, |
346 | i386, m68k, sh, and sparc32), a fixed UID and GID will be returned to | |
347 | applications that use the old 16-bit UID/GID system calls, if the | |
348 | actual UID or GID would exceed 65535. | |
1da177e4 LT |
349 | |
350 | These sysctls allow you to change the value of the fixed UID and GID. | |
351 | The default is 65534. | |
352 | ||
353 | ============================================================== | |
354 | ||
355 | panic: | |
356 | ||
807094c0 BP |
357 | The value in this file represents the number of seconds the kernel |
358 | waits before rebooting on a panic. When you use the software watchdog, | |
359 | the recommended setting is 60. | |
360 | ||
361 | ============================================================== | |
362 | ||
363 | panic_on_unrecovered_nmi: | |
364 | ||
365 | The default Linux behaviour on an NMI of either memory or unknown is | |
366 | to continue operation. For many environments such as scientific | |
367 | computing it is preferable that the box is taken out and the error | |
368 | dealt with than an uncorrected parity/ECC error get propagated. | |
369 | ||
370 | A small number of systems do generate NMI's for bizarre random reasons | |
371 | such as power management so the default is off. That sysctl works like | |
372 | the existing panic controls already in that directory. | |
1da177e4 LT |
373 | |
374 | ============================================================== | |
375 | ||
376 | panic_on_oops: | |
377 | ||
378 | Controls the kernel's behaviour when an oops or BUG is encountered. | |
379 | ||
380 | 0: try to continue operation | |
381 | ||
a982ac06 | 382 | 1: panic immediately. If the `panic' sysctl is also non-zero then the |
8b23d04d | 383 | machine will be rebooted. |
1da177e4 LT |
384 | |
385 | ============================================================== | |
386 | ||
387 | pid_max: | |
388 | ||
beb7dd86 | 389 | PID allocation wrap value. When the kernel's next PID value |
1da177e4 LT |
390 | reaches this value, it wraps back to a minimum PID value. |
391 | PIDs of value pid_max or larger are not allocated. | |
392 | ||
393 | ============================================================== | |
394 | ||
395 | powersave-nap: (PPC only) | |
396 | ||
397 | If set, Linux-PPC will use the 'nap' mode of powersaving, | |
398 | otherwise the 'doze' mode will be used. | |
399 | ||
400 | ============================================================== | |
401 | ||
402 | printk: | |
403 | ||
404 | The four values in printk denote: console_loglevel, | |
405 | default_message_loglevel, minimum_console_loglevel and | |
406 | default_console_loglevel respectively. | |
407 | ||
408 | These values influence printk() behavior when printing or | |
409 | logging error messages. See 'man 2 syslog' for more info on | |
410 | the different loglevels. | |
411 | ||
412 | - console_loglevel: messages with a higher priority than | |
413 | this will be printed to the console | |
87889e15 | 414 | - default_message_loglevel: messages without an explicit priority |
1da177e4 LT |
415 | will be printed with this priority |
416 | - minimum_console_loglevel: minimum (highest) value to which | |
417 | console_loglevel can be set | |
418 | - default_console_loglevel: default value for console_loglevel | |
419 | ||
420 | ============================================================== | |
421 | ||
807094c0 BP |
422 | printk_delay: |
423 | ||
424 | Delay each printk message in printk_delay milliseconds | |
425 | ||
426 | Value from 0 - 10000 is allowed. | |
427 | ||
428 | ============================================================== | |
429 | ||
1da177e4 LT |
430 | printk_ratelimit: |
431 | ||
432 | Some warning messages are rate limited. printk_ratelimit specifies | |
433 | the minimum length of time between these messages (in jiffies), by | |
434 | default we allow one every 5 seconds. | |
435 | ||
436 | A value of 0 will disable rate limiting. | |
437 | ||
438 | ============================================================== | |
439 | ||
440 | printk_ratelimit_burst: | |
441 | ||
442 | While long term we enforce one message per printk_ratelimit | |
443 | seconds, we do allow a burst of messages to pass through. | |
444 | printk_ratelimit_burst specifies the number of messages we can | |
445 | send before ratelimiting kicks in. | |
446 | ||
447 | ============================================================== | |
448 | ||
807094c0 | 449 | randomize_va_space: |
1ec7fd50 JK |
450 | |
451 | This option can be used to select the type of process address | |
452 | space randomization that is used in the system, for architectures | |
453 | that support this feature. | |
454 | ||
b7f5ab6f HS |
455 | 0 - Turn the process address space randomization off. This is the |
456 | default for architectures that do not support this feature anyways, | |
457 | and kernels that are booted with the "norandmaps" parameter. | |
1ec7fd50 JK |
458 | |
459 | 1 - Make the addresses of mmap base, stack and VDSO page randomized. | |
460 | This, among other things, implies that shared libraries will be | |
b7f5ab6f HS |
461 | loaded to random addresses. Also for PIE-linked binaries, the |
462 | location of code start is randomized. This is the default if the | |
463 | CONFIG_COMPAT_BRK option is enabled. | |
1ec7fd50 | 464 | |
b7f5ab6f HS |
465 | 2 - Additionally enable heap randomization. This is the default if |
466 | CONFIG_COMPAT_BRK is disabled. | |
467 | ||
468 | There are a few legacy applications out there (such as some ancient | |
1ec7fd50 | 469 | versions of libc.so.5 from 1996) that assume that brk area starts |
b7f5ab6f HS |
470 | just after the end of the code+bss. These applications break when |
471 | start of the brk area is randomized. There are however no known | |
1ec7fd50 | 472 | non-legacy applications that would be broken this way, so for most |
b7f5ab6f HS |
473 | systems it is safe to choose full randomization. |
474 | ||
475 | Systems with ancient and/or broken binaries should be configured | |
476 | with CONFIG_COMPAT_BRK enabled, which excludes the heap from process | |
477 | address space randomization. | |
1ec7fd50 JK |
478 | |
479 | ============================================================== | |
480 | ||
1da177e4 LT |
481 | reboot-cmd: (Sparc only) |
482 | ||
483 | ??? This seems to be a way to give an argument to the Sparc | |
484 | ROM/Flash boot loader. Maybe to tell it what to do after | |
485 | rebooting. ??? | |
486 | ||
487 | ============================================================== | |
488 | ||
489 | rtsig-max & rtsig-nr: | |
490 | ||
491 | The file rtsig-max can be used to tune the maximum number | |
492 | of POSIX realtime (queued) signals that can be outstanding | |
493 | in the system. | |
494 | ||
495 | rtsig-nr shows the number of RT signals currently queued. | |
496 | ||
497 | ============================================================== | |
498 | ||
499 | sg-big-buff: | |
500 | ||
501 | This file shows the size of the generic SCSI (sg) buffer. | |
502 | You can't tune it just yet, but you could change it on | |
503 | compile time by editing include/scsi/sg.h and changing | |
504 | the value of SG_BIG_BUFF. | |
505 | ||
506 | There shouldn't be any reason to change this value. If | |
507 | you can come up with one, you probably know what you | |
508 | are doing anyway :) | |
509 | ||
510 | ============================================================== | |
511 | ||
807094c0 | 512 | shmmax: |
1da177e4 LT |
513 | |
514 | This value can be used to query and set the run time limit | |
515 | on the maximum shared memory segment size that can be created. | |
807094c0 | 516 | Shared memory segments up to 1Gb are now supported in the |
1da177e4 LT |
517 | kernel. This value defaults to SHMMAX. |
518 | ||
519 | ============================================================== | |
520 | ||
c4f3b63f RT |
521 | softlockup_thresh: |
522 | ||
b4d19cc8 AM |
523 | This value can be used to lower the softlockup tolerance threshold. The |
524 | default threshold is 60 seconds. If a cpu is locked up for 60 seconds, | |
525 | the kernel complains. Valid values are 1-60 seconds. Setting this | |
526 | tunable to zero will disable the softlockup detection altogether. | |
c4f3b63f RT |
527 | |
528 | ============================================================== | |
529 | ||
807094c0 | 530 | tainted: |
1da177e4 LT |
531 | |
532 | Non-zero if the kernel has been tainted. Numeric values, which | |
533 | can be ORed together: | |
534 | ||
bb20698d GKH |
535 | 1 - A module with a non-GPL license has been loaded, this |
536 | includes modules with no license. | |
537 | Set by modutils >= 2.4.9 and module-init-tools. | |
538 | 2 - A module was force loaded by insmod -f. | |
539 | Set by modutils >= 2.4.9 and module-init-tools. | |
540 | 4 - Unsafe SMP processors: SMP with CPUs not designed for SMP. | |
541 | 8 - A module was forcibly unloaded from the system by rmmod -f. | |
542 | 16 - A hardware machine check error occurred on the system. | |
543 | 32 - A bad page was discovered on the system. | |
544 | 64 - The user has asked that the system be marked "tainted". This | |
545 | could be because they are running software that directly modifies | |
546 | the hardware, or for other reasons. | |
547 | 128 - The system has died. | |
548 | 256 - The ACPI DSDT has been overridden with one supplied by the user | |
549 | instead of using the one provided by the hardware. | |
550 | 512 - A kernel warning has occurred. | |
551 | 1024 - A module from drivers/staging was loaded. | |
1da177e4 | 552 | |
760df93e SF |
553 | ============================================================== |
554 | ||
760df93e SF |
555 | unknown_nmi_panic: |
556 | ||
807094c0 BP |
557 | The value in this file affects behavior of handling NMI. When the |
558 | value is non-zero, unknown NMI is trapped and then panic occurs. At | |
559 | that time, kernel debugging information is displayed on console. | |
760df93e | 560 | |
807094c0 BP |
561 | NMI switch that most IA32 servers have fires unknown NMI up, for |
562 | example. If a system hangs up, try pressing the NMI switch. |