Based on kernel version 2.6.26. Page generated on 2008-07-16 21:13 EST.
1 Documentation for /proc/sys/kernel/* kernel version 2.2.10 2 (c) 1998, 1999, Rik van Riel <riel[AT]nl.linux[DOT]org> 3 4 For general info and legal blurb, please look in README. 5 6 ============================================================== 7 8 This file contains documentation for the sysctl files in 9 /proc/sys/kernel/ and is valid for Linux kernel version 2.2. 10 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. 16 17 Currently, these files might (depending on your configuration) 18 show 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 - kstack_depth_to_print [ X86 only ] 31 - l2cr [ PPC only ] 32 - modprobe ==> Documentation/debugging-modules.txt 33 - msgmax 34 - msgmnb 35 - msgmni 36 - osrelease 37 - ostype 38 - overflowgid 39 - overflowuid 40 - panic 41 - pid_max 42 - powersave-nap [ PPC only ] 43 - printk 44 - randomize_va_space 45 - real-root-dev ==> Documentation/initrd.txt 46 - reboot-cmd [ SPARC only ] 47 - rtsig-max 48 - rtsig-nr 49 - sem 50 - sg-big-buff [ generic SCSI device (sg) ] 51 - shmall 52 - shmmax [ sysv ipc ] 53 - shmmni 54 - stop-a [ SPARC only ] 55 - sysrq ==> Documentation/sysrq.txt 56 - tainted 57 - threads-max 58 - version 59 60 ============================================================== 61 62 acpi_video_flags: 63 64 flags 65 66 See Doc*/kernel/power/video.txt, it allows mode of video boot to be 67 set during run time. 68 69 ============================================================== 70 71 acct: 72 73 highwater lowwater frequency 74 75 If BSD-style process accounting is enabled these values control 76 its behaviour. If free space on filesystem where the log lives 77 goes below <lowwater>% accounting suspends. If free space gets 78 above <highwater>% accounting resumes. <Frequency> determines 79 how often do we check the amount of free space (value is in 80 seconds). Default: 81 4 2 30 82 That is, suspend accounting if there left <= 2% free; resume it 83 if we got >=4%; consider information about amount of free space 84 valid for 30 seconds. 85 86 ============================================================== 87 88 core_pattern: 89 90 core_pattern is used to specify a core dumpfile pattern name. 91 . max length 128 characters; default value is "core" 92 . core_pattern is used as a pattern template for the output filename; 93 certain string patterns (beginning with '%') are substituted with 94 their actual values. 95 . backward compatibility with core_uses_pid: 96 If core_pattern does not include "%p" (default does not) 97 and core_uses_pid is set, then .PID will be appended to 98 the filename. 99 . corename format specifiers: 100 %<NUL> '%' is dropped 101 %% output one '%' 102 %p pid 103 %u uid 104 %g gid 105 %s signal number 106 %t UNIX time of dump 107 %h hostname 108 %e executable filename 109 %<OTHER> both are dropped 110 . If the first character of the pattern is a '|', the kernel will treat 111 the rest of the pattern as a command to run. The core dump will be 112 written to the standard input of that program instead of to a file. 113 114 ============================================================== 115 116 core_uses_pid: 117 118 The default coredump filename is "core". By setting 119 core_uses_pid to 1, the coredump filename becomes core.PID. 120 If core_pattern does not include "%p" (default does not) 121 and core_uses_pid is set, then .PID will be appended to 122 the filename. 123 124 ============================================================== 125 126 ctrl-alt-del: 127 128 When the value in this file is 0, ctrl-alt-del is trapped and 129 sent to the init(1) program to handle a graceful restart. 130 When, however, the value is > 0, Linux's reaction to a Vulcan 131 Nerve Pinch (tm) will be an immediate reboot, without even 132 syncing its dirty buffers. 133 134 Note: when a program (like dosemu) has the keyboard in 'raw' 135 mode, the ctrl-alt-del is intercepted by the program before it 136 ever reaches the kernel tty layer, and it's up to the program 137 to decide what to do with it. 138 139 ============================================================== 140 141 domainname & hostname: 142 143 These files can be used to set the NIS/YP domainname and the 144 hostname of your box in exactly the same way as the commands 145 domainname and hostname, i.e.: 146 # echo "darkstar" > /proc/sys/kernel/hostname 147 # echo "mydomain" > /proc/sys/kernel/domainname 148 has the same effect as 149 # hostname "darkstar" 150 # domainname "mydomain" 151 152 Note, however, that the classic darkstar.frop.org has the 153 hostname "darkstar" and DNS (Internet Domain Name Server) 154 domainname "frop.org", not to be confused with the NIS (Network 155 Information Service) or YP (Yellow Pages) domainname. These two 156 domain names are in general different. For a detailed discussion 157 see the hostname(1) man page. 158 159 ============================================================== 160 161 hotplug: 162 163 Path for the hotplug policy agent. 164 Default value is "/sbin/hotplug". 165 166 ============================================================== 167 168 l2cr: (PPC only) 169 170 This flag controls the L2 cache of G3 processor boards. If 171 0, the cache is disabled. Enabled if nonzero. 172 173 ============================================================== 174 175 kstack_depth_to_print: (X86 only) 176 177 Controls the number of words to print when dumping the raw 178 kernel stack. 179 180 ============================================================== 181 182 osrelease, ostype & version: 183 184 # cat osrelease 185 2.1.88 186 # cat ostype 187 Linux 188 # cat version 189 #5 Wed Feb 25 21:49:24 MET 1998 190 191 The files osrelease and ostype should be clear enough. Version 192 needs a little more clarification however. The '#5' means that 193 this is the fifth kernel built from this source base and the 194 date behind it indicates the time the kernel was built. 195 The only way to tune these values is to rebuild the kernel :-) 196 197 ============================================================== 198 199 overflowgid & overflowuid: 200 201 if your architecture did not always support 32-bit UIDs (i.e. arm, i386, 202 m68k, sh, and sparc32), a fixed UID and GID will be returned to 203 applications that use the old 16-bit UID/GID system calls, if the actual 204 UID or GID would exceed 65535. 205 206 These sysctls allow you to change the value of the fixed UID and GID. 207 The default is 65534. 208 209 ============================================================== 210 211 panic: 212 213 The value in this file represents the number of seconds the 214 kernel waits before rebooting on a panic. When you use the 215 software watchdog, the recommended setting is 60. 216 217 ============================================================== 218 219 panic_on_oops: 220 221 Controls the kernel's behaviour when an oops or BUG is encountered. 222 223 0: try to continue operation 224 225 1: panic immediately. If the `panic' sysctl is also non-zero then the 226 machine will be rebooted. 227 228 ============================================================== 229 230 pid_max: 231 232 PID allocation wrap value. When the kernel's next PID value 233 reaches this value, it wraps back to a minimum PID value. 234 PIDs of value pid_max or larger are not allocated. 235 236 ============================================================== 237 238 powersave-nap: (PPC only) 239 240 If set, Linux-PPC will use the 'nap' mode of powersaving, 241 otherwise the 'doze' mode will be used. 242 243 ============================================================== 244 245 printk: 246 247 The four values in printk denote: console_loglevel, 248 default_message_loglevel, minimum_console_loglevel and 249 default_console_loglevel respectively. 250 251 These values influence printk() behavior when printing or 252 logging error messages. See 'man 2 syslog' for more info on 253 the different loglevels. 254 255 - console_loglevel: messages with a higher priority than 256 this will be printed to the console 257 - default_message_level: messages without an explicit priority 258 will be printed with this priority 259 - minimum_console_loglevel: minimum (highest) value to which 260 console_loglevel can be set 261 - default_console_loglevel: default value for console_loglevel 262 263 ============================================================== 264 265 printk_ratelimit: 266 267 Some warning messages are rate limited. printk_ratelimit specifies 268 the minimum length of time between these messages (in jiffies), by 269 default we allow one every 5 seconds. 270 271 A value of 0 will disable rate limiting. 272 273 ============================================================== 274 275 printk_ratelimit_burst: 276 277 While long term we enforce one message per printk_ratelimit 278 seconds, we do allow a burst of messages to pass through. 279 printk_ratelimit_burst specifies the number of messages we can 280 send before ratelimiting kicks in. 281 282 ============================================================== 283 284 randomize-va-space: 285 286 This option can be used to select the type of process address 287 space randomization that is used in the system, for architectures 288 that support this feature. 289 290 0 - Turn the process address space randomization off by default. 291 292 1 - Make the addresses of mmap base, stack and VDSO page randomized. 293 This, among other things, implies that shared libraries will be 294 loaded to random addresses. Also for PIE-linked binaries, the location 295 of code start is randomized. 296 297 With heap randomization, the situation is a little bit more 298 complicated. 299 There a few legacy applications out there (such as some ancient 300 versions of libc.so.5 from 1996) that assume that brk area starts 301 just after the end of the code+bss. These applications break when 302 start of the brk area is randomized. There are however no known 303 non-legacy applications that would be broken this way, so for most 304 systems it is safe to choose full randomization. However there is 305 a CONFIG_COMPAT_BRK option for systems with ancient and/or broken 306 binaries, that makes heap non-randomized, but keeps all other 307 parts of process address space randomized if randomize_va_space 308 sysctl is turned on. 309 310 ============================================================== 311 312 reboot-cmd: (Sparc only) 313 314 ??? This seems to be a way to give an argument to the Sparc 315 ROM/Flash boot loader. Maybe to tell it what to do after 316 rebooting. ??? 317 318 ============================================================== 319 320 rtsig-max & rtsig-nr: 321 322 The file rtsig-max can be used to tune the maximum number 323 of POSIX realtime (queued) signals that can be outstanding 324 in the system. 325 326 rtsig-nr shows the number of RT signals currently queued. 327 328 ============================================================== 329 330 sg-big-buff: 331 332 This file shows the size of the generic SCSI (sg) buffer. 333 You can't tune it just yet, but you could change it on 334 compile time by editing include/scsi/sg.h and changing 335 the value of SG_BIG_BUFF. 336 337 There shouldn't be any reason to change this value. If 338 you can come up with one, you probably know what you 339 are doing anyway :) 340 341 ============================================================== 342 343 shmmax: 344 345 This value can be used to query and set the run time limit 346 on the maximum shared memory segment size that can be created. 347 Shared memory segments up to 1Gb are now supported in the 348 kernel. This value defaults to SHMMAX. 349 350 ============================================================== 351 352 softlockup_thresh: 353 354 This value can be used to lower the softlockup tolerance 355 threshold. The default threshold is 10s. If a cpu is locked up 356 for 10s, the kernel complains. Valid values are 1-60s. 357 358 ============================================================== 359 360 tainted: 361 362 Non-zero if the kernel has been tainted. Numeric values, which 363 can be ORed together: 364 365 1 - A module with a non-GPL license has been loaded, this 366 includes modules with no license. 367 Set by modutils >= 2.4.9 and module-init-tools. 368 2 - A module was force loaded by insmod -f. 369 Set by modutils >= 2.4.9 and module-init-tools. 370 4 - Unsafe SMP processors: SMP with CPUs not designed for SMP.