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1Documentation for /proc/sys/kernel/* kernel version 2.2.10
2 (c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
3
4For general info and legal blurb, please look in README.
5
6==============================================================
7
8This file contains documentation for the sysctl files in
9/proc/sys/kernel/ and is valid for Linux kernel version 2.2.
10
11The files in this directory can be used to tune and monitor
12miscellaneous and general things in the operation of the Linux
13kernel. Since some of the files _can_ be used to screw up your
14system, it is advisable to read both documentation and source
15before actually making adjustments.
16
17Currently, these files might (depending on your configuration)
18show 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- kstack_depth_to_print [ X86 only ]
31- l2cr [ PPC only ]
32- modprobe ==> Documentation/kmod.txt
33- msgmax
34- msgmnb
35- msgmni
36- osrelease
37- ostype
38- overflowgid
39- overflowuid
40- panic
41- pid_max
42- powersave-nap [ PPC only ]
43- printk
44- real-root-dev ==> Documentation/initrd.txt
45- reboot-cmd [ SPARC only ]
46- rtsig-max
47- rtsig-nr
48- sem
49- sg-big-buff [ generic SCSI device (sg) ]
50- shmall
51- shmmax [ sysv ipc ]
52- shmmni
53- stop-a [ SPARC only ]
54- sysrq ==> Documentation/sysrq.txt
55- tainted
56- threads-max
57- version
58
59==============================================================
60
61acpi_video_flags:
62
63flags
64
65See Doc*/kernel/power/video.txt, it allows mode of video boot to be
66set during run time.
67
68==============================================================
69
70acct:
71
72highwater lowwater frequency
73
74If BSD-style process accounting is enabled these values control
75its behaviour. If free space on filesystem where the log lives
76goes below <lowwater>% accounting suspends. If free space gets
77above <highwater>% accounting resumes. <Frequency> determines
78how often do we check the amount of free space (value is in
79seconds). Default:
804 2 30
81That is, suspend accounting if there left <= 2% free; resume it
82if we got >=4%; consider information about amount of free space
83valid for 30 seconds.
84
85==============================================================
86
87core_pattern:
88
89core_pattern is used to specify a core dumpfile pattern name.
90. max length 128 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. If the first character of the pattern is a '|', the kernel will treat
110 the rest of the pattern as a command to run. The core dump will be
111 written to the standard input of that program instead of to a file.
112
113==============================================================
114
115core_uses_pid:
116
117The default coredump filename is "core". By setting
118core_uses_pid to 1, the coredump filename becomes core.PID.
119If core_pattern does not include "%p" (default does not)
120and core_uses_pid is set, then .PID will be appended to
121the filename.
122
123==============================================================
124
125ctrl-alt-del:
126
127When the value in this file is 0, ctrl-alt-del is trapped and
128sent to the init(1) program to handle a graceful restart.
129When, however, the value is > 0, Linux's reaction to a Vulcan
130Nerve Pinch (tm) will be an immediate reboot, without even
131syncing its dirty buffers.
132
133Note: when a program (like dosemu) has the keyboard in 'raw'
134mode, the ctrl-alt-del is intercepted by the program before it
135ever reaches the kernel tty layer, and it's up to the program
136to decide what to do with it.
137
138==============================================================
139
140domainname & hostname:
141
142These files can be used to set the NIS/YP domainname and the
143hostname of your box in exactly the same way as the commands
144domainname and hostname, i.e.:
145# echo "darkstar" > /proc/sys/kernel/hostname
146# echo "mydomain" > /proc/sys/kernel/domainname
147has the same effect as
148# hostname "darkstar"
149# domainname "mydomain"
150
151Note, however, that the classic darkstar.frop.org has the
152hostname "darkstar" and DNS (Internet Domain Name Server)
153domainname "frop.org", not to be confused with the NIS (Network
154Information Service) or YP (Yellow Pages) domainname. These two
155domain names are in general different. For a detailed discussion
156see the hostname(1) man page.
157
158==============================================================
159
160hotplug:
161
162Path for the hotplug policy agent.
163Default value is "/sbin/hotplug".
164
165==============================================================
166
167l2cr: (PPC only)
168
169This flag controls the L2 cache of G3 processor boards. If
1700, the cache is disabled. Enabled if nonzero.
171
172==============================================================
173
174kstack_depth_to_print: (X86 only)
175
176Controls the number of words to print when dumping the raw
177kernel stack.
178
179==============================================================
180
181osrelease, ostype & version:
182
183# cat osrelease
1842.1.88
185# cat ostype
186Linux
187# cat version
188#5 Wed Feb 25 21:49:24 MET 1998
189
190The files osrelease and ostype should be clear enough. Version
191needs a little more clarification however. The '#5' means that
192this is the fifth kernel built from this source base and the
193date behind it indicates the time the kernel was built.
194The only way to tune these values is to rebuild the kernel :-)
195
196==============================================================
197
198overflowgid & overflowuid:
199
200if your architecture did not always support 32-bit UIDs (i.e. arm, i386,
201m68k, sh, and sparc32), a fixed UID and GID will be returned to
202applications that use the old 16-bit UID/GID system calls, if the actual
203UID or GID would exceed 65535.
204
205These sysctls allow you to change the value of the fixed UID and GID.
206The default is 65534.
207
208==============================================================
209
210panic:
211
212The value in this file represents the number of seconds the
213kernel waits before rebooting on a panic. When you use the
214software watchdog, the recommended setting is 60.
215
216==============================================================
217
218panic_on_oops:
219
220Controls the kernel's behaviour when an oops or BUG is encountered.
221
2220: try to continue operation
223
2241: panic immediatly. If the `panic' sysctl is also non-zero then the
225 machine will be rebooted.
226
227==============================================================
228
229pid_max:
230
231PID allocation wrap value. When the kenrel's next PID value
232reaches this value, it wraps back to a minimum PID value.
233PIDs of value pid_max or larger are not allocated.
234
235==============================================================
236
237powersave-nap: (PPC only)
238
239If set, Linux-PPC will use the 'nap' mode of powersaving,
240otherwise the 'doze' mode will be used.
241
242==============================================================
243
244printk:
245
246The four values in printk denote: console_loglevel,
247default_message_loglevel, minimum_console_loglevel and
248default_console_loglevel respectively.
249
250These values influence printk() behavior when printing or
251logging error messages. See 'man 2 syslog' for more info on
252the different loglevels.
253
254- console_loglevel: messages with a higher priority than
255 this will be printed to the console
256- default_message_level: messages without an explicit priority
257 will be printed with this priority
258- minimum_console_loglevel: minimum (highest) value to which
259 console_loglevel can be set
260- default_console_loglevel: default value for console_loglevel
261
262==============================================================
263
264printk_ratelimit:
265
266Some warning messages are rate limited. printk_ratelimit specifies
267the minimum length of time between these messages (in jiffies), by
268default we allow one every 5 seconds.
269
270A value of 0 will disable rate limiting.
271
272==============================================================
273
274printk_ratelimit_burst:
275
276While long term we enforce one message per printk_ratelimit
277seconds, we do allow a burst of messages to pass through.
278printk_ratelimit_burst specifies the number of messages we can
279send before ratelimiting kicks in.
280
281==============================================================
282
283reboot-cmd: (Sparc only)
284
285??? This seems to be a way to give an argument to the Sparc
286ROM/Flash boot loader. Maybe to tell it what to do after
287rebooting. ???
288
289==============================================================
290
291rtsig-max & rtsig-nr:
292
293The file rtsig-max can be used to tune the maximum number
294of POSIX realtime (queued) signals that can be outstanding
295in the system.
296
297rtsig-nr shows the number of RT signals currently queued.
298
299==============================================================
300
301sg-big-buff:
302
303This file shows the size of the generic SCSI (sg) buffer.
304You can't tune it just yet, but you could change it on
305compile time by editing include/scsi/sg.h and changing
306the value of SG_BIG_BUFF.
307
308There shouldn't be any reason to change this value. If
309you can come up with one, you probably know what you
310are doing anyway :)
311
312==============================================================
313
314shmmax:
315
316This value can be used to query and set the run time limit
317on the maximum shared memory segment size that can be created.
318Shared memory segments up to 1Gb are now supported in the
319kernel. This value defaults to SHMMAX.
320
321==============================================================
322
323tainted:
324
325Non-zero if the kernel has been tainted. Numeric values, which
326can 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