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