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 - acpi_video_flags
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 ]
53 - suid_dumpable
54 - sysrq ==> Documentation/sysrq.txt
55 - tainted
56 - threads-max
57 - version
58
59 ==============================================================
60
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
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
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
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
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