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1 | Documentation for /proc/sys/kernel/* kernel version 2.2.10 |
2 | (c) 1998, 1999, Rik van Riel <riel@nl.linux.org> | |
3 | ||
4 | For general info and legal blurb, please look in README. | |
5 | ||
6 | ============================================================== | |
7 | ||
8 | This file contains documentation for the sysctl files in | |
9 | /proc/sys/kernel/ and is valid for Linux kernel version 2.2. | |
10 | ||
11 | The files in this directory can be used to tune and monitor | |
12 | miscellaneous and general things in the operation of the Linux | |
13 | kernel. Since some of the files _can_ be used to screw up your | |
14 | system, it is advisable to read both documentation and source | |
15 | before actually making adjustments. | |
16 | ||
17 | Currently, these files might (depending on your configuration) | |
18 | show up in /proc/sys/kernel: | |
c255d844 | 19 | - acpi_video_flags |
1da177e4 LT |
20 | - acct |
21 | - core_pattern | |
22 | - core_uses_pid | |
23 | - ctrl-alt-del | |
24 | - dentry-state | |
25 | - domainname | |
26 | - hostname | |
27 | - hotplug | |
28 | - java-appletviewer [ binfmt_java, obsolete ] | |
29 | - java-interpreter [ binfmt_java, obsolete ] | |
0741f4d2 | 30 | - kstack_depth_to_print [ X86 only ] |
1da177e4 | 31 | - l2cr [ PPC only ] |
ac76cff2 | 32 | - modprobe ==> Documentation/debugging-modules.txt |
3d43321b | 33 | - modules_disabled |
1da177e4 LT |
34 | - msgmax |
35 | - msgmnb | |
36 | - msgmni | |
37 | - osrelease | |
38 | - ostype | |
39 | - overflowgid | |
40 | - overflowuid | |
41 | - panic | |
42 | - pid_max | |
43 | - powersave-nap [ PPC only ] | |
44 | - printk | |
1ec7fd50 | 45 | - randomize_va_space |
1da177e4 LT |
46 | - real-root-dev ==> Documentation/initrd.txt |
47 | - reboot-cmd [ SPARC only ] | |
48 | - rtsig-max | |
49 | - rtsig-nr | |
50 | - sem | |
51 | - sg-big-buff [ generic SCSI device (sg) ] | |
52 | - shmall | |
53 | - shmmax [ sysv ipc ] | |
54 | - shmmni | |
55 | - stop-a [ SPARC only ] | |
56 | - sysrq ==> Documentation/sysrq.txt | |
57 | - tainted | |
58 | - threads-max | |
59 | - version | |
60 | ||
61 | ============================================================== | |
62 | ||
c255d844 PM |
63 | acpi_video_flags: |
64 | ||
65 | flags | |
66 | ||
67 | See Doc*/kernel/power/video.txt, it allows mode of video boot to be | |
68 | set during run time. | |
69 | ||
70 | ============================================================== | |
71 | ||
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72 | acct: |
73 | ||
74 | highwater lowwater frequency | |
75 | ||
76 | If BSD-style process accounting is enabled these values control | |
77 | its behaviour. If free space on filesystem where the log lives | |
78 | goes below <lowwater>% accounting suspends. If free space gets | |
79 | above <highwater>% accounting resumes. <Frequency> determines | |
80 | how often do we check the amount of free space (value is in | |
81 | seconds). Default: | |
82 | 4 2 30 | |
83 | That is, suspend accounting if there left <= 2% free; resume it | |
84 | if we got >=4%; consider information about amount of free space | |
85 | valid for 30 seconds. | |
86 | ||
87 | ============================================================== | |
88 | ||
89 | core_pattern: | |
90 | ||
91 | core_pattern is used to specify a core dumpfile pattern name. | |
cd081041 | 92 | . max length 128 characters; default value is "core" |
1da177e4 LT |
93 | . core_pattern is used as a pattern template for the output filename; |
94 | certain string patterns (beginning with '%') are substituted with | |
95 | their actual values. | |
96 | . backward compatibility with core_uses_pid: | |
97 | If core_pattern does not include "%p" (default does not) | |
98 | and core_uses_pid is set, then .PID will be appended to | |
99 | the filename. | |
100 | . corename format specifiers: | |
101 | %<NUL> '%' is dropped | |
102 | %% output one '%' | |
103 | %p pid | |
104 | %u uid | |
105 | %g gid | |
106 | %s signal number | |
107 | %t UNIX time of dump | |
108 | %h hostname | |
109 | %e executable filename | |
110 | %<OTHER> both are dropped | |
cd081041 MU |
111 | . If the first character of the pattern is a '|', the kernel will treat |
112 | the rest of the pattern as a command to run. The core dump will be | |
113 | written to the standard input of that program instead of to a file. | |
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114 | |
115 | ============================================================== | |
116 | ||
117 | core_uses_pid: | |
118 | ||
119 | The default coredump filename is "core". By setting | |
120 | core_uses_pid to 1, the coredump filename becomes core.PID. | |
121 | If core_pattern does not include "%p" (default does not) | |
122 | and core_uses_pid is set, then .PID will be appended to | |
123 | the filename. | |
124 | ||
125 | ============================================================== | |
126 | ||
127 | ctrl-alt-del: | |
128 | ||
129 | When the value in this file is 0, ctrl-alt-del is trapped and | |
130 | sent to the init(1) program to handle a graceful restart. | |
131 | When, however, the value is > 0, Linux's reaction to a Vulcan | |
132 | Nerve Pinch (tm) will be an immediate reboot, without even | |
133 | syncing its dirty buffers. | |
134 | ||
135 | Note: when a program (like dosemu) has the keyboard in 'raw' | |
136 | mode, the ctrl-alt-del is intercepted by the program before it | |
137 | ever reaches the kernel tty layer, and it's up to the program | |
138 | to decide what to do with it. | |
139 | ||
140 | ============================================================== | |
141 | ||
142 | domainname & hostname: | |
143 | ||
144 | These files can be used to set the NIS/YP domainname and the | |
145 | hostname of your box in exactly the same way as the commands | |
146 | domainname and hostname, i.e.: | |
147 | # echo "darkstar" > /proc/sys/kernel/hostname | |
148 | # echo "mydomain" > /proc/sys/kernel/domainname | |
149 | has the same effect as | |
150 | # hostname "darkstar" | |
151 | # domainname "mydomain" | |
152 | ||
153 | Note, however, that the classic darkstar.frop.org has the | |
154 | hostname "darkstar" and DNS (Internet Domain Name Server) | |
155 | domainname "frop.org", not to be confused with the NIS (Network | |
156 | Information Service) or YP (Yellow Pages) domainname. These two | |
157 | domain names are in general different. For a detailed discussion | |
158 | see the hostname(1) man page. | |
159 | ||
160 | ============================================================== | |
161 | ||
162 | hotplug: | |
163 | ||
164 | Path for the hotplug policy agent. | |
165 | Default value is "/sbin/hotplug". | |
166 | ||
167 | ============================================================== | |
168 | ||
169 | l2cr: (PPC only) | |
170 | ||
171 | This flag controls the L2 cache of G3 processor boards. If | |
172 | 0, the cache is disabled. Enabled if nonzero. | |
173 | ||
174 | ============================================================== | |
175 | ||
0741f4d2 CE |
176 | kstack_depth_to_print: (X86 only) |
177 | ||
178 | Controls the number of words to print when dumping the raw | |
179 | kernel stack. | |
180 | ||
181 | ============================================================== | |
182 | ||
3d43321b KC |
183 | modules_disabled: |
184 | ||
185 | A toggle value indicating if modules are allowed to be loaded | |
186 | in an otherwise modular kernel. This toggle defaults to off | |
187 | (0), but can be set true (1). Once true, modules can be | |
188 | neither loaded nor unloaded, and the toggle cannot be set back | |
189 | to false. | |
190 | ||
191 | ============================================================== | |
192 | ||
1da177e4 LT |
193 | osrelease, ostype & version: |
194 | ||
195 | # cat osrelease | |
196 | 2.1.88 | |
197 | # cat ostype | |
198 | Linux | |
199 | # cat version | |
200 | #5 Wed Feb 25 21:49:24 MET 1998 | |
201 | ||
202 | The files osrelease and ostype should be clear enough. Version | |
203 | needs a little more clarification however. The '#5' means that | |
204 | this is the fifth kernel built from this source base and the | |
205 | date behind it indicates the time the kernel was built. | |
206 | The only way to tune these values is to rebuild the kernel :-) | |
207 | ||
208 | ============================================================== | |
209 | ||
210 | overflowgid & overflowuid: | |
211 | ||
212 | if your architecture did not always support 32-bit UIDs (i.e. arm, i386, | |
213 | m68k, sh, and sparc32), a fixed UID and GID will be returned to | |
214 | applications that use the old 16-bit UID/GID system calls, if the actual | |
215 | UID or GID would exceed 65535. | |
216 | ||
217 | These sysctls allow you to change the value of the fixed UID and GID. | |
218 | The default is 65534. | |
219 | ||
220 | ============================================================== | |
221 | ||
222 | panic: | |
223 | ||
224 | The value in this file represents the number of seconds the | |
225 | kernel waits before rebooting on a panic. When you use the | |
226 | software watchdog, the recommended setting is 60. | |
227 | ||
228 | ============================================================== | |
229 | ||
230 | panic_on_oops: | |
231 | ||
232 | Controls the kernel's behaviour when an oops or BUG is encountered. | |
233 | ||
234 | 0: try to continue operation | |
235 | ||
a982ac06 | 236 | 1: panic immediately. If the `panic' sysctl is also non-zero then the |
8b23d04d | 237 | machine will be rebooted. |
1da177e4 LT |
238 | |
239 | ============================================================== | |
240 | ||
241 | pid_max: | |
242 | ||
beb7dd86 | 243 | PID allocation wrap value. When the kernel's next PID value |
1da177e4 LT |
244 | reaches this value, it wraps back to a minimum PID value. |
245 | PIDs of value pid_max or larger are not allocated. | |
246 | ||
247 | ============================================================== | |
248 | ||
249 | powersave-nap: (PPC only) | |
250 | ||
251 | If set, Linux-PPC will use the 'nap' mode of powersaving, | |
252 | otherwise the 'doze' mode will be used. | |
253 | ||
254 | ============================================================== | |
255 | ||
256 | printk: | |
257 | ||
258 | The four values in printk denote: console_loglevel, | |
259 | default_message_loglevel, minimum_console_loglevel and | |
260 | default_console_loglevel respectively. | |
261 | ||
262 | These values influence printk() behavior when printing or | |
263 | logging error messages. See 'man 2 syslog' for more info on | |
264 | the different loglevels. | |
265 | ||
266 | - console_loglevel: messages with a higher priority than | |
267 | this will be printed to the console | |
268 | - default_message_level: messages without an explicit priority | |
269 | will be printed with this priority | |
270 | - minimum_console_loglevel: minimum (highest) value to which | |
271 | console_loglevel can be set | |
272 | - default_console_loglevel: default value for console_loglevel | |
273 | ||
274 | ============================================================== | |
275 | ||
276 | printk_ratelimit: | |
277 | ||
278 | Some warning messages are rate limited. printk_ratelimit specifies | |
279 | the minimum length of time between these messages (in jiffies), by | |
280 | default we allow one every 5 seconds. | |
281 | ||
282 | A value of 0 will disable rate limiting. | |
283 | ||
284 | ============================================================== | |
285 | ||
286 | printk_ratelimit_burst: | |
287 | ||
288 | While long term we enforce one message per printk_ratelimit | |
289 | seconds, we do allow a burst of messages to pass through. | |
290 | printk_ratelimit_burst specifies the number of messages we can | |
291 | send before ratelimiting kicks in. | |
292 | ||
293 | ============================================================== | |
294 | ||
1ec7fd50 JK |
295 | randomize-va-space: |
296 | ||
297 | This option can be used to select the type of process address | |
298 | space randomization that is used in the system, for architectures | |
299 | that support this feature. | |
300 | ||
301 | 0 - Turn the process address space randomization off by default. | |
302 | ||
303 | 1 - Make the addresses of mmap base, stack and VDSO page randomized. | |
304 | This, among other things, implies that shared libraries will be | |
305 | loaded to random addresses. Also for PIE-linked binaries, the location | |
306 | of code start is randomized. | |
307 | ||
308 | With heap randomization, the situation is a little bit more | |
309 | complicated. | |
310 | There a few legacy applications out there (such as some ancient | |
311 | versions of libc.so.5 from 1996) that assume that brk area starts | |
312 | just after the end of the code+bss. These applications break when | |
313 | start of the brk area is randomized. There are however no known | |
314 | non-legacy applications that would be broken this way, so for most | |
315 | systems it is safe to choose full randomization. However there is | |
316 | a CONFIG_COMPAT_BRK option for systems with ancient and/or broken | |
317 | binaries, that makes heap non-randomized, but keeps all other | |
318 | parts of process address space randomized if randomize_va_space | |
319 | sysctl is turned on. | |
320 | ||
321 | ============================================================== | |
322 | ||
1da177e4 LT |
323 | reboot-cmd: (Sparc only) |
324 | ||
325 | ??? This seems to be a way to give an argument to the Sparc | |
326 | ROM/Flash boot loader. Maybe to tell it what to do after | |
327 | rebooting. ??? | |
328 | ||
329 | ============================================================== | |
330 | ||
331 | rtsig-max & rtsig-nr: | |
332 | ||
333 | The file rtsig-max can be used to tune the maximum number | |
334 | of POSIX realtime (queued) signals that can be outstanding | |
335 | in the system. | |
336 | ||
337 | rtsig-nr shows the number of RT signals currently queued. | |
338 | ||
339 | ============================================================== | |
340 | ||
341 | sg-big-buff: | |
342 | ||
343 | This file shows the size of the generic SCSI (sg) buffer. | |
344 | You can't tune it just yet, but you could change it on | |
345 | compile time by editing include/scsi/sg.h and changing | |
346 | the value of SG_BIG_BUFF. | |
347 | ||
348 | There shouldn't be any reason to change this value. If | |
349 | you can come up with one, you probably know what you | |
350 | are doing anyway :) | |
351 | ||
352 | ============================================================== | |
353 | ||
354 | shmmax: | |
355 | ||
356 | This value can be used to query and set the run time limit | |
357 | on the maximum shared memory segment size that can be created. | |
358 | Shared memory segments up to 1Gb are now supported in the | |
359 | kernel. This value defaults to SHMMAX. | |
360 | ||
361 | ============================================================== | |
362 | ||
c4f3b63f RT |
363 | softlockup_thresh: |
364 | ||
b4d19cc8 AM |
365 | This value can be used to lower the softlockup tolerance threshold. The |
366 | default threshold is 60 seconds. If a cpu is locked up for 60 seconds, | |
367 | the kernel complains. Valid values are 1-60 seconds. Setting this | |
368 | tunable to zero will disable the softlockup detection altogether. | |
c4f3b63f RT |
369 | |
370 | ============================================================== | |
371 | ||
1da177e4 LT |
372 | tainted: |
373 | ||
374 | Non-zero if the kernel has been tainted. Numeric values, which | |
375 | can be ORed together: | |
376 | ||
bb20698d GKH |
377 | 1 - A module with a non-GPL license has been loaded, this |
378 | includes modules with no license. | |
379 | Set by modutils >= 2.4.9 and module-init-tools. | |
380 | 2 - A module was force loaded by insmod -f. | |
381 | Set by modutils >= 2.4.9 and module-init-tools. | |
382 | 4 - Unsafe SMP processors: SMP with CPUs not designed for SMP. | |
383 | 8 - A module was forcibly unloaded from the system by rmmod -f. | |
384 | 16 - A hardware machine check error occurred on the system. | |
385 | 32 - A bad page was discovered on the system. | |
386 | 64 - The user has asked that the system be marked "tainted". This | |
387 | could be because they are running software that directly modifies | |
388 | the hardware, or for other reasons. | |
389 | 128 - The system has died. | |
390 | 256 - The ACPI DSDT has been overridden with one supplied by the user | |
391 | instead of using the one provided by the hardware. | |
392 | 512 - A kernel warning has occurred. | |
393 | 1024 - A module from drivers/staging was loaded. | |
1da177e4 | 394 |