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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 64 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
109==============================================================
110
111core_uses_pid:
112
113The default coredump filename is "core". By setting
114core_uses_pid to 1, the coredump filename becomes core.PID.
115If core_pattern does not include "%p" (default does not)
116and core_uses_pid is set, then .PID will be appended to
117the filename.
118
119==============================================================
120
121ctrl-alt-del:
122
123When the value in this file is 0, ctrl-alt-del is trapped and
124sent to the init(1) program to handle a graceful restart.
125When, however, the value is > 0, Linux's reaction to a Vulcan
126Nerve Pinch (tm) will be an immediate reboot, without even
127syncing its dirty buffers.
128
129Note: when a program (like dosemu) has the keyboard in 'raw'
130mode, the ctrl-alt-del is intercepted by the program before it
131ever reaches the kernel tty layer, and it's up to the program
132to decide what to do with it.
133
134==============================================================
135
136domainname & hostname:
137
138These files can be used to set the NIS/YP domainname and the
139hostname of your box in exactly the same way as the commands
140domainname and hostname, i.e.:
141# echo "darkstar" > /proc/sys/kernel/hostname
142# echo "mydomain" > /proc/sys/kernel/domainname
143has the same effect as
144# hostname "darkstar"
145# domainname "mydomain"
146
147Note, however, that the classic darkstar.frop.org has the
148hostname "darkstar" and DNS (Internet Domain Name Server)
149domainname "frop.org", not to be confused with the NIS (Network
150Information Service) or YP (Yellow Pages) domainname. These two
151domain names are in general different. For a detailed discussion
152see the hostname(1) man page.
153
154==============================================================
155
156hotplug:
157
158Path for the hotplug policy agent.
159Default value is "/sbin/hotplug".
160
161==============================================================
162
163l2cr: (PPC only)
164
165This flag controls the L2 cache of G3 processor boards. If
1660, the cache is disabled. Enabled if nonzero.
167
168==============================================================
169
170osrelease, ostype & version:
171
172# cat osrelease
1732.1.88
174# cat ostype
175Linux
176# cat version
177#5 Wed Feb 25 21:49:24 MET 1998
178
179The files osrelease and ostype should be clear enough. Version
180needs a little more clarification however. The '#5' means that
181this is the fifth kernel built from this source base and the
182date behind it indicates the time the kernel was built.
183The only way to tune these values is to rebuild the kernel :-)
184
185==============================================================
186
187overflowgid & overflowuid:
188
189if your architecture did not always support 32-bit UIDs (i.e. arm, i386,
190m68k, sh, and sparc32), a fixed UID and GID will be returned to
191applications that use the old 16-bit UID/GID system calls, if the actual
192UID or GID would exceed 65535.
193
194These sysctls allow you to change the value of the fixed UID and GID.
195The default is 65534.
196
197==============================================================
198
199panic:
200
201The value in this file represents the number of seconds the
202kernel waits before rebooting on a panic. When you use the
203software watchdog, the recommended setting is 60.
204
205==============================================================
206
207panic_on_oops:
208
209Controls the kernel's behaviour when an oops or BUG is encountered.
210
2110: try to continue operation
212
2131: panic immediatly. If the `panic' sysctl is also non-zero then the
214 machine will be rebooted.
215
216==============================================================
217
218pid_max:
219
220PID allocation wrap value. When the kenrel's next PID value
221reaches this value, it wraps back to a minimum PID value.
222PIDs of value pid_max or larger are not allocated.
223
224==============================================================
225
226powersave-nap: (PPC only)
227
228If set, Linux-PPC will use the 'nap' mode of powersaving,
229otherwise the 'doze' mode will be used.
230
231==============================================================
232
233printk:
234
235The four values in printk denote: console_loglevel,
236default_message_loglevel, minimum_console_loglevel and
237default_console_loglevel respectively.
238
239These values influence printk() behavior when printing or
240logging error messages. See 'man 2 syslog' for more info on
241the different loglevels.
242
243- console_loglevel: messages with a higher priority than
244 this will be printed to the console
245- default_message_level: messages without an explicit priority
246 will be printed with this priority
247- minimum_console_loglevel: minimum (highest) value to which
248 console_loglevel can be set
249- default_console_loglevel: default value for console_loglevel
250
251==============================================================
252
253printk_ratelimit:
254
255Some warning messages are rate limited. printk_ratelimit specifies
256the minimum length of time between these messages (in jiffies), by
257default we allow one every 5 seconds.
258
259A value of 0 will disable rate limiting.
260
261==============================================================
262
263printk_ratelimit_burst:
264
265While long term we enforce one message per printk_ratelimit
266seconds, we do allow a burst of messages to pass through.
267printk_ratelimit_burst specifies the number of messages we can
268send before ratelimiting kicks in.
269
270==============================================================
271
272reboot-cmd: (Sparc only)
273
274??? This seems to be a way to give an argument to the Sparc
275ROM/Flash boot loader. Maybe to tell it what to do after
276rebooting. ???
277
278==============================================================
279
280rtsig-max & rtsig-nr:
281
282The file rtsig-max can be used to tune the maximum number
283of POSIX realtime (queued) signals that can be outstanding
284in the system.
285
286rtsig-nr shows the number of RT signals currently queued.
287
288==============================================================
289
290sg-big-buff:
291
292This file shows the size of the generic SCSI (sg) buffer.
293You can't tune it just yet, but you could change it on
294compile time by editing include/scsi/sg.h and changing
295the value of SG_BIG_BUFF.
296
297There shouldn't be any reason to change this value. If
298you can come up with one, you probably know what you
299are doing anyway :)
300
301==============================================================
302
303shmmax:
304
305This value can be used to query and set the run time limit
306on the maximum shared memory segment size that can be created.
307Shared memory segments up to 1Gb are now supported in the
308kernel. This value defaults to SHMMAX.
309
310==============================================================
311
312tainted:
313
314Non-zero if the kernel has been tainted. Numeric values, which
315can be ORed together:
316
317 1 - A module with a non-GPL license has been loaded, this
318 includes modules with no license.
319 Set by modutils >= 2.4.9 and module-init-tools.
320 2 - A module was force loaded by insmod -f.
321 Set by modutils >= 2.4.9 and module-init-tools.
322 4 - Unsafe SMP processors: SMP with CPUs not designed for SMP.
323