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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- 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
59acct:
60
61highwater lowwater frequency
62
63If BSD-style process accounting is enabled these values control
64its behaviour. If free space on filesystem where the log lives
65goes below <lowwater>% accounting suspends. If free space gets
66above <highwater>% accounting resumes. <Frequency> determines
67how often do we check the amount of free space (value is in
68seconds). Default:
694 2 30
70That is, suspend accounting if there left <= 2% free; resume it
71if we got >=4%; consider information about amount of free space
72valid for 30 seconds.
73
74==============================================================
75
76core_pattern:
77
78core_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
101core_uses_pid:
102
103The default coredump filename is "core". By setting
104core_uses_pid to 1, the coredump filename becomes core.PID.
105If core_pattern does not include "%p" (default does not)
106and core_uses_pid is set, then .PID will be appended to
107the filename.
108
109==============================================================
110
111ctrl-alt-del:
112
113When the value in this file is 0, ctrl-alt-del is trapped and
114sent to the init(1) program to handle a graceful restart.
115When, however, the value is > 0, Linux's reaction to a Vulcan
116Nerve Pinch (tm) will be an immediate reboot, without even
117syncing its dirty buffers.
118
119Note: when a program (like dosemu) has the keyboard in 'raw'
120mode, the ctrl-alt-del is intercepted by the program before it
121ever reaches the kernel tty layer, and it's up to the program
122to decide what to do with it.
123
124==============================================================
125
126domainname & hostname:
127
128These files can be used to set the NIS/YP domainname and the
129hostname of your box in exactly the same way as the commands
130domainname and hostname, i.e.:
131# echo "darkstar" > /proc/sys/kernel/hostname
132# echo "mydomain" > /proc/sys/kernel/domainname
133has the same effect as
134# hostname "darkstar"
135# domainname "mydomain"
136
137Note, however, that the classic darkstar.frop.org has the
138hostname "darkstar" and DNS (Internet Domain Name Server)
139domainname "frop.org", not to be confused with the NIS (Network
140Information Service) or YP (Yellow Pages) domainname. These two
141domain names are in general different. For a detailed discussion
142see the hostname(1) man page.
143
144==============================================================
145
146hotplug:
147
148Path for the hotplug policy agent.
149Default value is "/sbin/hotplug".
150
151==============================================================
152
153l2cr: (PPC only)
154
155This flag controls the L2 cache of G3 processor boards. If
1560, the cache is disabled. Enabled if nonzero.
157
158==============================================================
159
160osrelease, ostype & version:
161
162# cat osrelease
1632.1.88
164# cat ostype
165Linux
166# cat version
167#5 Wed Feb 25 21:49:24 MET 1998
168
169The files osrelease and ostype should be clear enough. Version
170needs a little more clarification however. The '#5' means that
171this is the fifth kernel built from this source base and the
172date behind it indicates the time the kernel was built.
173The only way to tune these values is to rebuild the kernel :-)
174
175==============================================================
176
177overflowgid & overflowuid:
178
179if your architecture did not always support 32-bit UIDs (i.e. arm, i386,
180m68k, sh, and sparc32), a fixed UID and GID will be returned to
181applications that use the old 16-bit UID/GID system calls, if the actual
182UID or GID would exceed 65535.
183
184These sysctls allow you to change the value of the fixed UID and GID.
185The default is 65534.
186
187==============================================================
188
189panic:
190
191The value in this file represents the number of seconds the
192kernel waits before rebooting on a panic. When you use the
193software watchdog, the recommended setting is 60.
194
195==============================================================
196
197panic_on_oops:
198
199Controls the kernel's behaviour when an oops or BUG is encountered.
200
2010: try to continue operation
202
2031: 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
209pid_max:
210
211PID allocation wrap value. When the kenrel's next PID value
212reaches this value, it wraps back to a minimum PID value.
213PIDs of value pid_max or larger are not allocated.
214
215==============================================================
216
217powersave-nap: (PPC only)
218
219If set, Linux-PPC will use the 'nap' mode of powersaving,
220otherwise the 'doze' mode will be used.
221
222==============================================================
223
224printk:
225
226The four values in printk denote: console_loglevel,
227default_message_loglevel, minimum_console_loglevel and
228default_console_loglevel respectively.
229
230These values influence printk() behavior when printing or
231logging error messages. See 'man 2 syslog' for more info on
232the 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
244printk_ratelimit:
245
246Some warning messages are rate limited. printk_ratelimit specifies
247the minimum length of time between these messages (in jiffies), by
248default we allow one every 5 seconds.
249
250A value of 0 will disable rate limiting.
251
252==============================================================
253
254printk_ratelimit_burst:
255
256While long term we enforce one message per printk_ratelimit
257seconds, we do allow a burst of messages to pass through.
258printk_ratelimit_burst specifies the number of messages we can
259send before ratelimiting kicks in.
260
261==============================================================
262
263reboot-cmd: (Sparc only)
264
265??? This seems to be a way to give an argument to the Sparc
266ROM/Flash boot loader. Maybe to tell it what to do after
267rebooting. ???
268
269==============================================================
270
271rtsig-max & rtsig-nr:
272
273The file rtsig-max can be used to tune the maximum number
274of POSIX realtime (queued) signals that can be outstanding
275in the system.
276
277rtsig-nr shows the number of RT signals currently queued.
278
279==============================================================
280
281sg-big-buff:
282
283This file shows the size of the generic SCSI (sg) buffer.
284You can't tune it just yet, but you could change it on
285compile time by editing include/scsi/sg.h and changing
286the value of SG_BIG_BUFF.
287
288There shouldn't be any reason to change this value. If
289you can come up with one, you probably know what you
290are doing anyway :)
291
292==============================================================
293
294shmmax:
295
296This value can be used to query and set the run time limit
297on the maximum shared memory segment size that can be created.
298Shared memory segments up to 1Gb are now supported in the
299kernel. This value defaults to SHMMAX.
300
301==============================================================
302
303tainted:
304
305Non-zero if the kernel has been tainted. Numeric values, which
306can 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