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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 ] | |
30 | - l2cr [ PPC only ] | |
31 | - modprobe ==> Documentation/kmod.txt | |
32 | - msgmax | |
33 | - msgmnb | |
34 | - msgmni | |
35 | - osrelease | |
36 | - ostype | |
37 | - overflowgid | |
38 | - overflowuid | |
39 | - panic | |
40 | - pid_max | |
41 | - powersave-nap [ PPC only ] | |
42 | - printk | |
43 | - real-root-dev ==> Documentation/initrd.txt | |
44 | - reboot-cmd [ SPARC only ] | |
45 | - rtsig-max | |
46 | - rtsig-nr | |
47 | - sem | |
48 | - sg-big-buff [ generic SCSI device (sg) ] | |
49 | - shmall | |
50 | - shmmax [ sysv ipc ] | |
51 | - shmmni | |
52 | - stop-a [ SPARC only ] | |
d6e71144 | 53 | - suid_dumpable |
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54 | - sysrq ==> Documentation/sysrq.txt |
55 | - tainted | |
56 | - threads-max | |
57 | - version | |
58 | ||
59 | ============================================================== | |
60 | ||
c255d844 PM |
61 | acpi_video_flags: |
62 | ||
63 | flags | |
64 | ||
65 | See Doc*/kernel/power/video.txt, it allows mode of video boot to be | |
66 | set during run time. | |
67 | ||
68 | ============================================================== | |
69 | ||
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70 | acct: |
71 | ||
72 | highwater lowwater frequency | |
73 | ||
74 | If BSD-style process accounting is enabled these values control | |
75 | its behaviour. If free space on filesystem where the log lives | |
76 | goes below <lowwater>% accounting suspends. If free space gets | |
77 | above <highwater>% accounting resumes. <Frequency> determines | |
78 | how often do we check the amount of free space (value is in | |
79 | seconds). Default: | |
80 | 4 2 30 | |
81 | That is, suspend accounting if there left <= 2% free; resume it | |
82 | if we got >=4%; consider information about amount of free space | |
83 | valid for 30 seconds. | |
84 | ||
85 | ============================================================== | |
86 | ||
87 | core_pattern: | |
88 | ||
89 | core_pattern is used to specify a core dumpfile pattern name. | |
90 | . max length 64 characters; default value is "core" | |
91 | . core_pattern is used as a pattern template for the output filename; | |
92 | certain string patterns (beginning with '%') are substituted with | |
93 | their actual values. | |
94 | . backward compatibility with core_uses_pid: | |
95 | If core_pattern does not include "%p" (default does not) | |
96 | and core_uses_pid is set, then .PID will be appended to | |
97 | the filename. | |
98 | . corename format specifiers: | |
99 | %<NUL> '%' is dropped | |
100 | %% output one '%' | |
101 | %p pid | |
102 | %u uid | |
103 | %g gid | |
104 | %s signal number | |
105 | %t UNIX time of dump | |
106 | %h hostname | |
107 | %e executable filename | |
108 | %<OTHER> both are dropped | |
109 | ||
110 | ============================================================== | |
111 | ||
112 | core_uses_pid: | |
113 | ||
114 | The default coredump filename is "core". By setting | |
115 | core_uses_pid to 1, the coredump filename becomes core.PID. | |
116 | If core_pattern does not include "%p" (default does not) | |
117 | and core_uses_pid is set, then .PID will be appended to | |
118 | the filename. | |
119 | ||
120 | ============================================================== | |
121 | ||
122 | ctrl-alt-del: | |
123 | ||
124 | When the value in this file is 0, ctrl-alt-del is trapped and | |
125 | sent to the init(1) program to handle a graceful restart. | |
126 | When, however, the value is > 0, Linux's reaction to a Vulcan | |
127 | Nerve Pinch (tm) will be an immediate reboot, without even | |
128 | syncing its dirty buffers. | |
129 | ||
130 | Note: when a program (like dosemu) has the keyboard in 'raw' | |
131 | mode, the ctrl-alt-del is intercepted by the program before it | |
132 | ever reaches the kernel tty layer, and it's up to the program | |
133 | to decide what to do with it. | |
134 | ||
135 | ============================================================== | |
136 | ||
137 | domainname & hostname: | |
138 | ||
139 | These files can be used to set the NIS/YP domainname and the | |
140 | hostname of your box in exactly the same way as the commands | |
141 | domainname and hostname, i.e.: | |
142 | # echo "darkstar" > /proc/sys/kernel/hostname | |
143 | # echo "mydomain" > /proc/sys/kernel/domainname | |
144 | has the same effect as | |
145 | # hostname "darkstar" | |
146 | # domainname "mydomain" | |
147 | ||
148 | Note, however, that the classic darkstar.frop.org has the | |
149 | hostname "darkstar" and DNS (Internet Domain Name Server) | |
150 | domainname "frop.org", not to be confused with the NIS (Network | |
151 | Information Service) or YP (Yellow Pages) domainname. These two | |
152 | domain names are in general different. For a detailed discussion | |
153 | see the hostname(1) man page. | |
154 | ||
155 | ============================================================== | |
156 | ||
157 | hotplug: | |
158 | ||
159 | Path for the hotplug policy agent. | |
160 | Default value is "/sbin/hotplug". | |
161 | ||
162 | ============================================================== | |
163 | ||
164 | l2cr: (PPC only) | |
165 | ||
166 | This flag controls the L2 cache of G3 processor boards. If | |
167 | 0, the cache is disabled. Enabled if nonzero. | |
168 | ||
169 | ============================================================== | |
170 | ||
171 | osrelease, ostype & version: | |
172 | ||
173 | # cat osrelease | |
174 | 2.1.88 | |
175 | # cat ostype | |
176 | Linux | |
177 | # cat version | |
178 | #5 Wed Feb 25 21:49:24 MET 1998 | |
179 | ||
180 | The files osrelease and ostype should be clear enough. Version | |
181 | needs a little more clarification however. The '#5' means that | |
182 | this is the fifth kernel built from this source base and the | |
183 | date behind it indicates the time the kernel was built. | |
184 | The only way to tune these values is to rebuild the kernel :-) | |
185 | ||
186 | ============================================================== | |
187 | ||
188 | overflowgid & overflowuid: | |
189 | ||
190 | if your architecture did not always support 32-bit UIDs (i.e. arm, i386, | |
191 | m68k, sh, and sparc32), a fixed UID and GID will be returned to | |
192 | applications that use the old 16-bit UID/GID system calls, if the actual | |
193 | UID or GID would exceed 65535. | |
194 | ||
195 | These sysctls allow you to change the value of the fixed UID and GID. | |
196 | The default is 65534. | |
197 | ||
198 | ============================================================== | |
199 | ||
200 | panic: | |
201 | ||
202 | The value in this file represents the number of seconds the | |
203 | kernel waits before rebooting on a panic. When you use the | |
204 | software watchdog, the recommended setting is 60. | |
205 | ||
206 | ============================================================== | |
207 | ||
208 | panic_on_oops: | |
209 | ||
210 | Controls the kernel's behaviour when an oops or BUG is encountered. | |
211 | ||
212 | 0: try to continue operation | |
213 | ||
214 | 1: delay a few seconds (to give klogd time to record the oops output) and | |
215 | then panic. If the `panic' sysctl is also non-zero then the machine will | |
216 | be rebooted. | |
217 | ||
218 | ============================================================== | |
219 | ||
220 | pid_max: | |
221 | ||
222 | PID allocation wrap value. When the kenrel's next PID value | |
223 | reaches this value, it wraps back to a minimum PID value. | |
224 | PIDs of value pid_max or larger are not allocated. | |
225 | ||
226 | ============================================================== | |
227 | ||
228 | powersave-nap: (PPC only) | |
229 | ||
230 | If set, Linux-PPC will use the 'nap' mode of powersaving, | |
231 | otherwise the 'doze' mode will be used. | |
232 | ||
233 | ============================================================== | |
234 | ||
235 | printk: | |
236 | ||
237 | The four values in printk denote: console_loglevel, | |
238 | default_message_loglevel, minimum_console_loglevel and | |
239 | default_console_loglevel respectively. | |
240 | ||
241 | These values influence printk() behavior when printing or | |
242 | logging error messages. See 'man 2 syslog' for more info on | |
243 | the different loglevels. | |
244 | ||
245 | - console_loglevel: messages with a higher priority than | |
246 | this will be printed to the console | |
247 | - default_message_level: messages without an explicit priority | |
248 | will be printed with this priority | |
249 | - minimum_console_loglevel: minimum (highest) value to which | |
250 | console_loglevel can be set | |
251 | - default_console_loglevel: default value for console_loglevel | |
252 | ||
253 | ============================================================== | |
254 | ||
255 | printk_ratelimit: | |
256 | ||
257 | Some warning messages are rate limited. printk_ratelimit specifies | |
258 | the minimum length of time between these messages (in jiffies), by | |
259 | default we allow one every 5 seconds. | |
260 | ||
261 | A value of 0 will disable rate limiting. | |
262 | ||
263 | ============================================================== | |
264 | ||
265 | printk_ratelimit_burst: | |
266 | ||
267 | While long term we enforce one message per printk_ratelimit | |
268 | seconds, we do allow a burst of messages to pass through. | |
269 | printk_ratelimit_burst specifies the number of messages we can | |
270 | send before ratelimiting kicks in. | |
271 | ||
272 | ============================================================== | |
273 | ||
274 | reboot-cmd: (Sparc only) | |
275 | ||
276 | ??? This seems to be a way to give an argument to the Sparc | |
277 | ROM/Flash boot loader. Maybe to tell it what to do after | |
278 | rebooting. ??? | |
279 | ||
280 | ============================================================== | |
281 | ||
282 | rtsig-max & rtsig-nr: | |
283 | ||
284 | The file rtsig-max can be used to tune the maximum number | |
285 | of POSIX realtime (queued) signals that can be outstanding | |
286 | in the system. | |
287 | ||
288 | rtsig-nr shows the number of RT signals currently queued. | |
289 | ||
290 | ============================================================== | |
291 | ||
292 | sg-big-buff: | |
293 | ||
294 | This file shows the size of the generic SCSI (sg) buffer. | |
295 | You can't tune it just yet, but you could change it on | |
296 | compile time by editing include/scsi/sg.h and changing | |
297 | the value of SG_BIG_BUFF. | |
298 | ||
299 | There shouldn't be any reason to change this value. If | |
300 | you can come up with one, you probably know what you | |
301 | are doing anyway :) | |
302 | ||
303 | ============================================================== | |
304 | ||
305 | shmmax: | |
306 | ||
307 | This value can be used to query and set the run time limit | |
308 | on the maximum shared memory segment size that can be created. | |
309 | Shared memory segments up to 1Gb are now supported in the | |
310 | kernel. This value defaults to SHMMAX. | |
311 | ||
312 | ============================================================== | |
313 | ||
d6e71144 AC |
314 | suid_dumpable: |
315 | ||
316 | This value can be used to query and set the core dump mode for setuid | |
317 | or otherwise protected/tainted binaries. The modes are | |
318 | ||
319 | 0 - (default) - traditional behaviour. Any process which has changed | |
320 | privilege levels or is execute only will not be dumped | |
321 | 1 - (debug) - all processes dump core when possible. The core dump is | |
322 | owned by the current user and no security is applied. This is | |
323 | intended for system debugging situations only. Ptrace is unchecked. | |
324 | 2 - (suidsafe) - any binary which normally would not be dumped is dumped | |
325 | readable by root only. This allows the end user to remove | |
326 | such a dump but not access it directly. For security reasons | |
327 | core dumps in this mode will not overwrite one another or | |
328 | other files. This mode is appropriate when adminstrators are | |
329 | attempting to debug problems in a normal environment. | |
330 | ||
331 | ============================================================== | |
332 | ||
1da177e4 LT |
333 | tainted: |
334 | ||
335 | Non-zero if the kernel has been tainted. Numeric values, which | |
336 | can be ORed together: | |
337 | ||
338 | 1 - A module with a non-GPL license has been loaded, this | |
339 | includes modules with no license. | |
340 | Set by modutils >= 2.4.9 and module-init-tools. | |
341 | 2 - A module was force loaded by insmod -f. | |
342 | Set by modutils >= 2.4.9 and module-init-tools. | |
343 | 4 - Unsafe SMP processors: SMP with CPUs not designed for SMP. | |
344 |