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