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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- 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- sysrq ==> Documentation/sysrq.txt
54- tainted
55- threads-max
56- version
57
58==============================================================
59
60acpi_video_flags:
61
62flags
63
64See Doc*/kernel/power/video.txt, it allows mode of video boot to be
65set during run time.
66
67==============================================================
68
69acct:
70
71highwater lowwater frequency
72
73If BSD-style process accounting is enabled these values control
74its behaviour. If free space on filesystem where the log lives
75goes below <lowwater>% accounting suspends. If free space gets
76above <highwater>% accounting resumes. <Frequency> determines
77how often do we check the amount of free space (value is in
78seconds). Default:
794 2 30
80That is, suspend accounting if there left <= 2% free; resume it
81if we got >=4%; consider information about amount of free space
82valid for 30 seconds.
83
84==============================================================
85
86core_pattern:
87
88core_pattern is used to specify a core dumpfile pattern name.
89. max length 128 characters; default value is "core"
90. core_pattern is used as a pattern template for the output filename;
91 certain string patterns (beginning with '%') are substituted with
92 their actual values.
93. backward compatibility with core_uses_pid:
94 If core_pattern does not include "%p" (default does not)
95 and core_uses_pid is set, then .PID will be appended to
96 the filename.
97. corename format specifiers:
98 %<NUL> '%' is dropped
99 %% output one '%'
100 %p pid
101 %u uid
102 %g gid
103 %s signal number
104 %t UNIX time of dump
105 %h hostname
106 %e executable filename
107 %<OTHER> both are dropped
108. If the first character of the pattern is a '|', the kernel will treat
109 the rest of the pattern as a command to run. The core dump will be
110 written to the standard input of that program instead of to a file.
111
112==============================================================
113
114core_uses_pid:
115
116The default coredump filename is "core". By setting
117core_uses_pid to 1, the coredump filename becomes core.PID.
118If core_pattern does not include "%p" (default does not)
119and core_uses_pid is set, then .PID will be appended to
120the filename.
121
122==============================================================
123
124ctrl-alt-del:
125
126When the value in this file is 0, ctrl-alt-del is trapped and
127sent to the init(1) program to handle a graceful restart.
128When, however, the value is > 0, Linux's reaction to a Vulcan
129Nerve Pinch (tm) will be an immediate reboot, without even
130syncing its dirty buffers.
131
132Note: when a program (like dosemu) has the keyboard in 'raw'
133mode, the ctrl-alt-del is intercepted by the program before it
134ever reaches the kernel tty layer, and it's up to the program
135to decide what to do with it.
136
137==============================================================
138
139domainname & hostname:
140
141These files can be used to set the NIS/YP domainname and the
142hostname of your box in exactly the same way as the commands
143domainname and hostname, i.e.:
144# echo "darkstar" > /proc/sys/kernel/hostname
145# echo "mydomain" > /proc/sys/kernel/domainname
146has the same effect as
147# hostname "darkstar"
148# domainname "mydomain"
149
150Note, however, that the classic darkstar.frop.org has the
151hostname "darkstar" and DNS (Internet Domain Name Server)
152domainname "frop.org", not to be confused with the NIS (Network
153Information Service) or YP (Yellow Pages) domainname. These two
154domain names are in general different. For a detailed discussion
155see the hostname(1) man page.
156
157==============================================================
158
159hotplug:
160
161Path for the hotplug policy agent.
162Default value is "/sbin/hotplug".
163
164==============================================================
165
166l2cr: (PPC only)
167
168This flag controls the L2 cache of G3 processor boards. If
1690, the cache is disabled. Enabled if nonzero.
170
171==============================================================
172
173osrelease, ostype & version:
174
175# cat osrelease
1762.1.88
177# cat ostype
178Linux
179# cat version
180#5 Wed Feb 25 21:49:24 MET 1998
181
182The files osrelease and ostype should be clear enough. Version
183needs a little more clarification however. The '#5' means that
184this is the fifth kernel built from this source base and the
185date behind it indicates the time the kernel was built.
186The only way to tune these values is to rebuild the kernel :-)
187
188==============================================================
189
190overflowgid & overflowuid:
191
192if your architecture did not always support 32-bit UIDs (i.e. arm, i386,
193m68k, sh, and sparc32), a fixed UID and GID will be returned to
194applications that use the old 16-bit UID/GID system calls, if the actual
195UID or GID would exceed 65535.
196
197These sysctls allow you to change the value of the fixed UID and GID.
198The default is 65534.
199
200==============================================================
201
202panic:
203
204The value in this file represents the number of seconds the
205kernel waits before rebooting on a panic. When you use the
206software watchdog, the recommended setting is 60.
207
208==============================================================
209
210panic_on_oops:
211
212Controls the kernel's behaviour when an oops or BUG is encountered.
213
2140: try to continue operation
215
2161: panic immediatly. If the `panic' sysctl is also non-zero then the
217 machine will be rebooted.
218
219==============================================================
220
221pid_max:
222
223PID allocation wrap value. When the kenrel's next PID value
224reaches this value, it wraps back to a minimum PID value.
225PIDs of value pid_max or larger are not allocated.
226
227==============================================================
228
229powersave-nap: (PPC only)
230
231If set, Linux-PPC will use the 'nap' mode of powersaving,
232otherwise the 'doze' mode will be used.
233
234==============================================================
235
236printk:
237
238The four values in printk denote: console_loglevel,
239default_message_loglevel, minimum_console_loglevel and
240default_console_loglevel respectively.
241
242These values influence printk() behavior when printing or
243logging error messages. See 'man 2 syslog' for more info on
244the different loglevels.
245
246- console_loglevel: messages with a higher priority than
247 this will be printed to the console
248- default_message_level: messages without an explicit priority
249 will be printed with this priority
250- minimum_console_loglevel: minimum (highest) value to which
251 console_loglevel can be set
252- default_console_loglevel: default value for console_loglevel
253
254==============================================================
255
256printk_ratelimit:
257
258Some warning messages are rate limited. printk_ratelimit specifies
259the minimum length of time between these messages (in jiffies), by
260default we allow one every 5 seconds.
261
262A value of 0 will disable rate limiting.
263
264==============================================================
265
266printk_ratelimit_burst:
267
268While long term we enforce one message per printk_ratelimit
269seconds, we do allow a burst of messages to pass through.
270printk_ratelimit_burst specifies the number of messages we can
271send before ratelimiting kicks in.
272
273==============================================================
274
275reboot-cmd: (Sparc only)
276
277??? This seems to be a way to give an argument to the Sparc
278ROM/Flash boot loader. Maybe to tell it what to do after
279rebooting. ???
280
281==============================================================
282
283rtsig-max & rtsig-nr:
284
285The file rtsig-max can be used to tune the maximum number
286of POSIX realtime (queued) signals that can be outstanding
287in the system.
288
289rtsig-nr shows the number of RT signals currently queued.
290
291==============================================================
292
293sg-big-buff:
294
295This file shows the size of the generic SCSI (sg) buffer.
296You can't tune it just yet, but you could change it on
297compile time by editing include/scsi/sg.h and changing
298the value of SG_BIG_BUFF.
299
300There shouldn't be any reason to change this value. If
301you can come up with one, you probably know what you
302are doing anyway :)
303
304==============================================================
305
306shmmax:
307
308This value can be used to query and set the run time limit
309on the maximum shared memory segment size that can be created.
310Shared memory segments up to 1Gb are now supported in the
311kernel. This value defaults to SHMMAX.
312
313==============================================================
314
315tainted:
316
317Non-zero if the kernel has been tainted. Numeric values, which
318can be ORed together:
319
320 1 - A module with a non-GPL license has been loaded, this
321 includes modules with no license.
322 Set by modutils >= 2.4.9 and module-init-tools.
323 2 - A module was force loaded by insmod -f.
324 Set by modutils >= 2.4.9 and module-init-tools.
325 4 - Unsafe SMP processors: SMP with CPUs not designed for SMP.
326