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:
28 - java-appletviewer [ binfmt_java, obsolete ]
29 - java-interpreter [ binfmt_java, obsolete ]
30 - kstack_depth_to_print [ X86 only ]
32 - modprobe ==> Documentation/debugging-modules.txt
43 - powersave-nap [ PPC only ]
46 - real-root-dev ==> Documentation/initrd.txt
47 - reboot-cmd [ SPARC only ]
51 - sg-big-buff [ generic SCSI device (sg) ]
55 - stop-a [ SPARC only ]
56 - sysrq ==> Documentation/sysrq.txt
61 ==============================================================
67 See Doc*/kernel/power/video.txt, it allows mode of video boot to be
70 ==============================================================
74 highwater lowwater frequency
76 If BSD-style process accounting is enabled these values control
77 its behaviour. If free space on filesystem where the log lives
78 goes below <lowwater>% accounting suspends. If free space gets
79 above <highwater>% accounting resumes. <Frequency> determines
80 how often do we check the amount of free space (value is in
83 That is, suspend accounting if there left <= 2% free; resume it
84 if we got >=4%; consider information about amount of free space
87 ==============================================================
91 core_pattern is used to specify a core dumpfile pattern name.
92 . max length 128 characters; default value is "core"
93 . core_pattern is used as a pattern template for the output filename;
94 certain string patterns (beginning with '%') are substituted with
96 . backward compatibility with core_uses_pid:
97 If core_pattern does not include "%p" (default does not)
98 and core_uses_pid is set, then .PID will be appended to
100 . corename format specifiers:
101 %<NUL> '%' is dropped
109 %e executable filename
110 %<OTHER> both are dropped
111 . If the first character of the pattern is a '|', the kernel will treat
112 the rest of the pattern as a command to run. The core dump will be
113 written to the standard input of that program instead of to a file.
115 ==============================================================
119 The default coredump filename is "core". By setting
120 core_uses_pid to 1, the coredump filename becomes core.PID.
121 If core_pattern does not include "%p" (default does not)
122 and core_uses_pid is set, then .PID will be appended to
125 ==============================================================
129 When the value in this file is 0, ctrl-alt-del is trapped and
130 sent to the init(1) program to handle a graceful restart.
131 When, however, the value is > 0, Linux's reaction to a Vulcan
132 Nerve Pinch (tm) will be an immediate reboot, without even
133 syncing its dirty buffers.
135 Note: when a program (like dosemu) has the keyboard in 'raw'
136 mode, the ctrl-alt-del is intercepted by the program before it
137 ever reaches the kernel tty layer, and it's up to the program
138 to decide what to do with it.
140 ==============================================================
142 domainname & hostname:
144 These files can be used to set the NIS/YP domainname and the
145 hostname of your box in exactly the same way as the commands
146 domainname and hostname, i.e.:
147 # echo "darkstar" > /proc/sys/kernel/hostname
148 # echo "mydomain" > /proc/sys/kernel/domainname
149 has the same effect as
150 # hostname "darkstar"
151 # domainname "mydomain"
153 Note, however, that the classic darkstar.frop.org has the
154 hostname "darkstar" and DNS (Internet Domain Name Server)
155 domainname "frop.org", not to be confused with the NIS (Network
156 Information Service) or YP (Yellow Pages) domainname. These two
157 domain names are in general different. For a detailed discussion
158 see the hostname(1) man page.
160 ==============================================================
164 Path for the hotplug policy agent.
165 Default value is "/sbin/hotplug".
167 ==============================================================
171 This flag controls the L2 cache of G3 processor boards. If
172 0, the cache is disabled. Enabled if nonzero.
174 ==============================================================
176 kstack_depth_to_print: (X86 only)
178 Controls the number of words to print when dumping the raw
181 ==============================================================
185 A toggle value indicating if modules are allowed to be loaded
186 in an otherwise modular kernel. This toggle defaults to off
187 (0), but can be set true (1). Once true, modules can be
188 neither loaded nor unloaded, and the toggle cannot be set back
191 ==============================================================
193 osrelease, ostype & version:
200 #5 Wed Feb 25 21:49:24 MET 1998
202 The files osrelease and ostype should be clear enough. Version
203 needs a little more clarification however. The '#5' means that
204 this is the fifth kernel built from this source base and the
205 date behind it indicates the time the kernel was built.
206 The only way to tune these values is to rebuild the kernel :-)
208 ==============================================================
210 overflowgid & overflowuid:
212 if your architecture did not always support 32-bit UIDs (i.e. arm, i386,
213 m68k, sh, and sparc32), a fixed UID and GID will be returned to
214 applications that use the old 16-bit UID/GID system calls, if the actual
215 UID or GID would exceed 65535.
217 These sysctls allow you to change the value of the fixed UID and GID.
218 The default is 65534.
220 ==============================================================
224 The value in this file represents the number of seconds the
225 kernel waits before rebooting on a panic. When you use the
226 software watchdog, the recommended setting is 60.
228 ==============================================================
232 Controls the kernel's behaviour when an oops or BUG is encountered.
234 0: try to continue operation
236 1: panic immediately. If the `panic' sysctl is also non-zero then the
237 machine will be rebooted.
239 ==============================================================
243 PID allocation wrap value. When the kernel's next PID value
244 reaches this value, it wraps back to a minimum PID value.
245 PIDs of value pid_max or larger are not allocated.
247 ==============================================================
249 powersave-nap: (PPC only)
251 If set, Linux-PPC will use the 'nap' mode of powersaving,
252 otherwise the 'doze' mode will be used.
254 ==============================================================
258 The four values in printk denote: console_loglevel,
259 default_message_loglevel, minimum_console_loglevel and
260 default_console_loglevel respectively.
262 These values influence printk() behavior when printing or
263 logging error messages. See 'man 2 syslog' for more info on
264 the different loglevels.
266 - console_loglevel: messages with a higher priority than
267 this will be printed to the console
268 - default_message_level: messages without an explicit priority
269 will be printed with this priority
270 - minimum_console_loglevel: minimum (highest) value to which
271 console_loglevel can be set
272 - default_console_loglevel: default value for console_loglevel
274 ==============================================================
278 Some warning messages are rate limited. printk_ratelimit specifies
279 the minimum length of time between these messages (in jiffies), by
280 default we allow one every 5 seconds.
282 A value of 0 will disable rate limiting.
284 ==============================================================
286 printk_ratelimit_burst:
288 While long term we enforce one message per printk_ratelimit
289 seconds, we do allow a burst of messages to pass through.
290 printk_ratelimit_burst specifies the number of messages we can
291 send before ratelimiting kicks in.
293 ==============================================================
297 This option can be used to select the type of process address
298 space randomization that is used in the system, for architectures
299 that support this feature.
301 0 - Turn the process address space randomization off by default.
303 1 - Make the addresses of mmap base, stack and VDSO page randomized.
304 This, among other things, implies that shared libraries will be
305 loaded to random addresses. Also for PIE-linked binaries, the location
306 of code start is randomized.
308 With heap randomization, the situation is a little bit more
310 There a few legacy applications out there (such as some ancient
311 versions of libc.so.5 from 1996) that assume that brk area starts
312 just after the end of the code+bss. These applications break when
313 start of the brk area is randomized. There are however no known
314 non-legacy applications that would be broken this way, so for most
315 systems it is safe to choose full randomization. However there is
316 a CONFIG_COMPAT_BRK option for systems with ancient and/or broken
317 binaries, that makes heap non-randomized, but keeps all other
318 parts of process address space randomized if randomize_va_space
321 ==============================================================
323 reboot-cmd: (Sparc only)
325 ??? This seems to be a way to give an argument to the Sparc
326 ROM/Flash boot loader. Maybe to tell it what to do after
329 ==============================================================
331 rtsig-max & rtsig-nr:
333 The file rtsig-max can be used to tune the maximum number
334 of POSIX realtime (queued) signals that can be outstanding
337 rtsig-nr shows the number of RT signals currently queued.
339 ==============================================================
343 This file shows the size of the generic SCSI (sg) buffer.
344 You can't tune it just yet, but you could change it on
345 compile time by editing include/scsi/sg.h and changing
346 the value of SG_BIG_BUFF.
348 There shouldn't be any reason to change this value. If
349 you can come up with one, you probably know what you
352 ==============================================================
356 This value can be used to query and set the run time limit
357 on the maximum shared memory segment size that can be created.
358 Shared memory segments up to 1Gb are now supported in the
359 kernel. This value defaults to SHMMAX.
361 ==============================================================
365 This value can be used to lower the softlockup tolerance threshold. The
366 default threshold is 60 seconds. If a cpu is locked up for 60 seconds,
367 the kernel complains. Valid values are 1-60 seconds. Setting this
368 tunable to zero will disable the softlockup detection altogether.
370 ==============================================================
374 Non-zero if the kernel has been tainted. Numeric values, which
375 can be ORed together:
377 1 - A module with a non-GPL license has been loaded, this
378 includes modules with no license.
379 Set by modutils >= 2.4.9 and module-init-tools.
380 2 - A module was force loaded by insmod -f.
381 Set by modutils >= 2.4.9 and module-init-tools.
382 4 - Unsafe SMP processors: SMP with CPUs not designed for SMP.
383 8 - A module was forcibly unloaded from the system by rmmod -f.
384 16 - A hardware machine check error occurred on the system.
385 32 - A bad page was discovered on the system.
386 64 - The user has asked that the system be marked "tainted". This
387 could be because they are running software that directly modifies
388 the hardware, or for other reasons.
389 128 - The system has died.
390 256 - The ACPI DSDT has been overridden with one supplied by the user
391 instead of using the one provided by the hardware.
392 512 - A kernel warning has occurred.
393 1024 - A module from drivers/staging was loaded.