1 Documentation for /proc/sys/kernel/* kernel version 2.2.10
2 (c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
4 For general info and legal blurb, please look in README.
6 ==============================================================
8 This file contains documentation for the sysctl files in
9 /proc/sys/kernel/ and is valid for Linux kernel version 2.2.
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.
17 Currently, these files might (depending on your configuration)
18 show up in /proc/sys/kernel:
26 - htab-reclaim [ PPC only ]
28 - java-appletviewer [ binfmt_java, obsolete ]
29 - java-interpreter [ binfmt_java, obsolete ]
31 - modprobe ==> Documentation/kmod.txt
41 - powersave-nap [ PPC only ]
43 - real-root-dev ==> Documentation/initrd.txt
44 - reboot-cmd [ SPARC only ]
48 - sg-big-buff [ generic SCSI device (sg) ]
52 - stop-a [ SPARC only ]
53 - sysrq ==> Documentation/sysrq.txt
57 - zero-paged [ PPC only ]
59 ==============================================================
63 highwater lowwater frequency
65 If BSD-style process accounting is enabled these values control
66 its behaviour. If free space on filesystem where the log lives
67 goes below <lowwater>% accounting suspends. If free space gets
68 above <highwater>% accounting resumes. <Frequency> determines
69 how often do we check the amount of free space (value is in
72 That is, suspend accounting if there left <= 2% free; resume it
73 if we got >=4%; consider information about amount of free space
76 ==============================================================
80 core_pattern is used to specify a core dumpfile pattern name.
81 . max length 64 characters; default value is "core"
82 . core_pattern is used as a pattern template for the output filename;
83 certain string patterns (beginning with '%') are substituted with
85 . backward compatibility with core_uses_pid:
86 If core_pattern does not include "%p" (default does not)
87 and core_uses_pid is set, then .PID will be appended to
89 . corename format specifiers:
98 %e executable filename
99 %<OTHER> both are dropped
101 ==============================================================
105 The default coredump filename is "core". By setting
106 core_uses_pid to 1, the coredump filename becomes core.PID.
107 If core_pattern does not include "%p" (default does not)
108 and core_uses_pid is set, then .PID will be appended to
111 ==============================================================
115 When the value in this file is 0, ctrl-alt-del is trapped and
116 sent to the init(1) program to handle a graceful restart.
117 When, however, the value is > 0, Linux's reaction to a Vulcan
118 Nerve Pinch (tm) will be an immediate reboot, without even
119 syncing its dirty buffers.
121 Note: when a program (like dosemu) has the keyboard in 'raw'
122 mode, the ctrl-alt-del is intercepted by the program before it
123 ever reaches the kernel tty layer, and it's up to the program
124 to decide what to do with it.
126 ==============================================================
128 domainname & hostname:
130 These files can be used to set the NIS/YP domainname and the
131 hostname of your box in exactly the same way as the commands
132 domainname and hostname, i.e.:
133 # echo "darkstar" > /proc/sys/kernel/hostname
134 # echo "mydomain" > /proc/sys/kernel/domainname
135 has the same effect as
136 # hostname "darkstar" > /proc/sys/kernel/hostname
137 # domainname "mydomain" > /proc/sys/kernel/domainname
139 Note, however, that the classic darkstar.frop.org has the
140 hostname "darkstar" and DNS (Internet Domain Name Server)
141 domainname "frop.org", not to be confused with the NIS (Network
142 Information Service) or YP (Yellow Pages) domainname. These two
143 domain names are in general different. For a detailed discussion
144 see the hostname(1) man page.
146 ==============================================================
148 htab-reclaim: (PPC only)
150 Setting this to a non-zero value, the PowerPC htab
151 (see Documentation/powerpc/ppc_htab.txt) is pruned
152 each time the system hits the idle loop.
154 ==============================================================
158 Path for the hotplug policy agent.
159 Default value is "/sbin/hotplug".
161 ==============================================================
165 This flag controls the L2 cache of G3 processor boards. If
166 0, the cache is disabled. Enabled if nonzero.
168 ==============================================================
170 osrelease, ostype & version:
177 #5 Wed Feb 25 21:49:24 MET 1998
179 The files osrelease and ostype should be clear enough. Version
180 needs a little more clarification however. The '#5' means that
181 this is the fifth kernel built from this source base and the
182 date behind it indicates the time the kernel was built.
183 The only way to tune these values is to rebuild the kernel :-)
185 ==============================================================
187 overflowgid & overflowuid:
189 if your architecture did not always support 32-bit UIDs (i.e. arm, i386,
190 m68k, sh, and sparc32), a fixed UID and GID will be returned to
191 applications that use the old 16-bit UID/GID system calls, if the actual
192 UID or GID would exceed 65535.
194 These sysctls allow you to change the value of the fixed UID and GID.
195 The default is 65534.
197 ==============================================================
201 The value in this file represents the number of seconds the
202 kernel waits before rebooting on a panic. When you use the
203 software watchdog, the recommended setting is 60.
205 ==============================================================
209 Controls the kernel's behaviour when an oops or BUG is encountered.
211 0: try to continue operation
213 1: delay a few seconds (to give klogd time to record the oops output) and
214 then panic. If the `panic' sysctl is also non-zero then the machine will
217 ==============================================================
221 PID allocation wrap value. When the kenrel's next PID value
222 reaches this value, it wraps back to a minimum PID value.
223 PIDs of value pid_max or larger are not allocated.
225 ==============================================================
227 powersave-nap: (PPC only)
229 If set, Linux-PPC will use the 'nap' mode of powersaving,
230 otherwise the 'doze' mode will be used.
232 ==============================================================
236 The four values in printk denote: console_loglevel,
237 default_message_loglevel, minimum_console_loglevel and
238 default_console_loglevel respectively.
240 These values influence printk() behavior when printing or
241 logging error messages. See 'man 2 syslog' for more info on
242 the different loglevels.
244 - console_loglevel: messages with a higher priority than
245 this will be printed to the console
246 - default_message_level: messages without an explicit priority
247 will be printed with this priority
248 - minimum_console_loglevel: minimum (highest) value to which
249 console_loglevel can be set
250 - default_console_loglevel: default value for console_loglevel
252 ==============================================================
256 Some warning messages are rate limited. printk_ratelimit specifies
257 the minimum length of time between these messages (in jiffies), by
258 default we allow one every 5 seconds.
260 A value of 0 will disable rate limiting.
262 ==============================================================
264 printk_ratelimit_burst:
266 While long term we enforce one message per printk_ratelimit
267 seconds, we do allow a burst of messages to pass through.
268 printk_ratelimit_burst specifies the number of messages we can
269 send before ratelimiting kicks in.
271 ==============================================================
273 reboot-cmd: (Sparc only)
275 ??? This seems to be a way to give an argument to the Sparc
276 ROM/Flash boot loader. Maybe to tell it what to do after
279 ==============================================================
281 rtsig-max & rtsig-nr:
283 The file rtsig-max can be used to tune the maximum number
284 of POSIX realtime (queued) signals that can be outstanding
287 rtsig-nr shows the number of RT signals currently queued.
289 ==============================================================
293 This file shows the size of the generic SCSI (sg) buffer.
294 You can't tune it just yet, but you could change it on
295 compile time by editing include/scsi/sg.h and changing
296 the value of SG_BIG_BUFF.
298 There shouldn't be any reason to change this value. If
299 you can come up with one, you probably know what you
302 ==============================================================
306 This value can be used to query and set the run time limit
307 on the maximum shared memory segment size that can be created.
308 Shared memory segments up to 1Gb are now supported in the
309 kernel. This value defaults to SHMMAX.
311 ==============================================================
315 Non-zero if the kernel has been tainted. Numeric values, which
316 can be ORed together:
318 1 - A module with a non-GPL license has been loaded, this
319 includes modules with no license.
320 Set by modutils >= 2.4.9 and module-init-tools.
321 2 - A module was force loaded by insmod -f.
322 Set by modutils >= 2.4.9 and module-init-tools.
323 4 - Unsafe SMP processors: SMP with CPUs not designed for SMP.
325 ==============================================================
327 zero-paged: (PPC only)
329 When enabled (non-zero), Linux-PPC will pre-zero pages in
330 the idle loop, possibly speeding up get_free_pages. Since
331 this only affects what the idle loop is doing, you should
332 enable this and see if anything changes.