Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 1 | Documentation for /proc/sys/kernel/* kernel version 2.2.10 |
| 2 | (c) 1998, 1999, Rik van Riel <riel@nl.linux.org> |
Shen Feng | 760df93 | 2009-04-02 16:57:20 -0700 | [diff] [blame] | 3 | (c) 2009, Shen Feng<shen@cn.fujitsu.com> |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 4 | |
| 5 | For general info and legal blurb, please look in README. |
| 6 | |
| 7 | ============================================================== |
| 8 | |
| 9 | This file contains documentation for the sysctl files in |
| 10 | /proc/sys/kernel/ and is valid for Linux kernel version 2.2. |
| 11 | |
| 12 | The files in this directory can be used to tune and monitor |
| 13 | miscellaneous and general things in the operation of the Linux |
| 14 | kernel. Since some of the files _can_ be used to screw up your |
| 15 | system, it is advisable to read both documentation and source |
| 16 | before actually making adjustments. |
| 17 | |
| 18 | Currently, these files might (depending on your configuration) |
| 19 | show up in /proc/sys/kernel: |
Borislav Petkov | 807094c | 2011-07-23 10:39:29 -0700 | [diff] [blame] | 20 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 21 | - acct |
Borislav Petkov | 807094c | 2011-07-23 10:39:29 -0700 | [diff] [blame] | 22 | - acpi_video_flags |
| 23 | - auto_msgmni |
H. Peter Anvin | d75757a | 2009-12-11 14:23:44 -0800 | [diff] [blame] | 24 | - bootloader_type [ X86 only ] |
| 25 | - bootloader_version [ X86 only ] |
Hans-Joachim Picht | c114728a | 2009-09-11 10:28:47 +0200 | [diff] [blame] | 26 | - callhome [ S390 only ] |
Dan Ballard | 73efc03 | 2011-10-31 17:11:20 -0700 | [diff] [blame] | 27 | - cap_last_cap |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 28 | - core_pattern |
Neil Horman | a293980 | 2009-09-23 15:56:56 -0700 | [diff] [blame] | 29 | - core_pipe_limit |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 30 | - core_uses_pid |
| 31 | - ctrl-alt-del |
Dan Rosenberg | eaf06b2 | 2010-11-11 14:05:18 -0800 | [diff] [blame] | 32 | - dmesg_restrict |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 33 | - domainname |
| 34 | - hostname |
| 35 | - hotplug |
Dan Rosenberg | 455cd5a | 2011-01-12 16:59:41 -0800 | [diff] [blame] | 36 | - kptr_restrict |
Chuck Ebbert | 0741f4d | 2006-12-07 02:14:11 +0100 | [diff] [blame] | 37 | - kstack_depth_to_print [ X86 only ] |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 38 | - l2cr [ PPC only ] |
Michael Opdenacker | ac76cff | 2008-02-13 15:03:32 -0800 | [diff] [blame] | 39 | - modprobe ==> Documentation/debugging-modules.txt |
Kees Cook | 3d43321 | 2009-04-02 15:49:29 -0700 | [diff] [blame] | 40 | - modules_disabled |
Stanislav Kinsbursky | 03f5956 | 2013-01-04 15:34:50 -0800 | [diff] [blame] | 41 | - msg_next_id [ sysv ipc ] |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 42 | - msgmax |
| 43 | - msgmnb |
| 44 | - msgmni |
Shen Feng | 760df93 | 2009-04-02 16:57:20 -0700 | [diff] [blame] | 45 | - nmi_watchdog |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 46 | - osrelease |
| 47 | - ostype |
| 48 | - overflowgid |
| 49 | - overflowuid |
| 50 | - panic |
Borislav Petkov | 807094c | 2011-07-23 10:39:29 -0700 | [diff] [blame] | 51 | - panic_on_oops |
| 52 | - panic_on_unrecovered_nmi |
Mitsuo Hayasaka | 55af779 | 2011-11-29 15:08:36 +0900 | [diff] [blame] | 53 | - panic_on_stackoverflow |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 54 | - pid_max |
| 55 | - powersave-nap [ PPC only ] |
| 56 | - printk |
Borislav Petkov | 807094c | 2011-07-23 10:39:29 -0700 | [diff] [blame] | 57 | - printk_delay |
| 58 | - printk_ratelimit |
| 59 | - printk_ratelimit_burst |
Jiri Kosina | 1ec7fd5 | 2008-02-09 23:24:08 +0100 | [diff] [blame] | 60 | - randomize_va_space |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 61 | - real-root-dev ==> Documentation/initrd.txt |
| 62 | - reboot-cmd [ SPARC only ] |
| 63 | - rtsig-max |
| 64 | - rtsig-nr |
| 65 | - sem |
Stanislav Kinsbursky | 03f5956 | 2013-01-04 15:34:50 -0800 | [diff] [blame] | 66 | - sem_next_id [ sysv ipc ] |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 67 | - sg-big-buff [ generic SCSI device (sg) ] |
Stanislav Kinsbursky | 03f5956 | 2013-01-04 15:34:50 -0800 | [diff] [blame] | 68 | - shm_next_id [ sysv ipc ] |
Vasiliy Kulikov | b34a6b1 | 2011-07-26 16:08:48 -0700 | [diff] [blame] | 69 | - shm_rmid_forced |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 70 | - shmall |
| 71 | - shmmax [ sysv ipc ] |
| 72 | - shmmni |
| 73 | - stop-a [ SPARC only ] |
| 74 | - sysrq ==> Documentation/sysrq.txt |
| 75 | - tainted |
| 76 | - threads-max |
Shen Feng | 760df93 | 2009-04-02 16:57:20 -0700 | [diff] [blame] | 77 | - unknown_nmi_panic |
Li Zefan | 08825c9 | 2013-05-17 10:31:20 +0800 | [diff] [blame] | 78 | - watchdog_thresh |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 79 | - version |
| 80 | |
| 81 | ============================================================== |
| 82 | |
| 83 | acct: |
| 84 | |
| 85 | highwater lowwater frequency |
| 86 | |
| 87 | If BSD-style process accounting is enabled these values control |
| 88 | its behaviour. If free space on filesystem where the log lives |
| 89 | goes below <lowwater>% accounting suspends. If free space gets |
| 90 | above <highwater>% accounting resumes. <Frequency> determines |
| 91 | how often do we check the amount of free space (value is in |
| 92 | seconds). Default: |
| 93 | 4 2 30 |
| 94 | That is, suspend accounting if there left <= 2% free; resume it |
| 95 | if we got >=4%; consider information about amount of free space |
| 96 | valid for 30 seconds. |
| 97 | |
| 98 | ============================================================== |
| 99 | |
Borislav Petkov | 807094c | 2011-07-23 10:39:29 -0700 | [diff] [blame] | 100 | acpi_video_flags: |
| 101 | |
| 102 | flags |
| 103 | |
| 104 | See Doc*/kernel/power/video.txt, it allows mode of video boot to be |
| 105 | set during run time. |
| 106 | |
| 107 | ============================================================== |
| 108 | |
| 109 | auto_msgmni: |
| 110 | |
| 111 | Enables/Disables automatic recomputing of msgmni upon memory add/remove |
| 112 | or upon ipc namespace creation/removal (see the msgmni description |
| 113 | above). Echoing "1" into this file enables msgmni automatic recomputing. |
| 114 | Echoing "0" turns it off. auto_msgmni default value is 1. |
| 115 | |
| 116 | |
| 117 | ============================================================== |
| 118 | |
H. Peter Anvin | d75757a | 2009-12-11 14:23:44 -0800 | [diff] [blame] | 119 | bootloader_type: |
| 120 | |
| 121 | x86 bootloader identification |
| 122 | |
| 123 | This gives the bootloader type number as indicated by the bootloader, |
| 124 | shifted left by 4, and OR'd with the low four bits of the bootloader |
| 125 | version. The reason for this encoding is that this used to match the |
| 126 | type_of_loader field in the kernel header; the encoding is kept for |
| 127 | backwards compatibility. That is, if the full bootloader type number |
| 128 | is 0x15 and the full version number is 0x234, this file will contain |
| 129 | the value 340 = 0x154. |
| 130 | |
| 131 | See the type_of_loader and ext_loader_type fields in |
| 132 | Documentation/x86/boot.txt for additional information. |
| 133 | |
| 134 | ============================================================== |
| 135 | |
| 136 | bootloader_version: |
| 137 | |
| 138 | x86 bootloader version |
| 139 | |
| 140 | The complete bootloader version number. In the example above, this |
| 141 | file will contain the value 564 = 0x234. |
| 142 | |
| 143 | See the type_of_loader and ext_loader_ver fields in |
| 144 | Documentation/x86/boot.txt for additional information. |
| 145 | |
| 146 | ============================================================== |
| 147 | |
Hans-Joachim Picht | c114728a | 2009-09-11 10:28:47 +0200 | [diff] [blame] | 148 | callhome: |
| 149 | |
| 150 | Controls the kernel's callhome behavior in case of a kernel panic. |
| 151 | |
| 152 | The s390 hardware allows an operating system to send a notification |
| 153 | to a service organization (callhome) in case of an operating system panic. |
| 154 | |
| 155 | When the value in this file is 0 (which is the default behavior) |
| 156 | nothing happens in case of a kernel panic. If this value is set to "1" |
| 157 | the complete kernel oops message is send to the IBM customer service |
| 158 | organization in case the mainframe the Linux operating system is running |
| 159 | on has a service contract with IBM. |
| 160 | |
| 161 | ============================================================== |
| 162 | |
Dan Ballard | 73efc03 | 2011-10-31 17:11:20 -0700 | [diff] [blame] | 163 | cap_last_cap |
| 164 | |
| 165 | Highest valid capability of the running kernel. Exports |
| 166 | CAP_LAST_CAP from the kernel. |
| 167 | |
| 168 | ============================================================== |
| 169 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 170 | core_pattern: |
| 171 | |
| 172 | core_pattern is used to specify a core dumpfile pattern name. |
Matthias Urlichs | cd08104 | 2006-10-11 01:21:57 -0700 | [diff] [blame] | 173 | . max length 128 characters; default value is "core" |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 174 | . core_pattern is used as a pattern template for the output filename; |
| 175 | certain string patterns (beginning with '%') are substituted with |
| 176 | their actual values. |
| 177 | . backward compatibility with core_uses_pid: |
| 178 | If core_pattern does not include "%p" (default does not) |
| 179 | and core_uses_pid is set, then .PID will be appended to |
| 180 | the filename. |
| 181 | . corename format specifiers: |
| 182 | %<NUL> '%' is dropped |
| 183 | %% output one '%' |
| 184 | %p pid |
| 185 | %u uid |
| 186 | %g gid |
Oleg Nesterov | 12a2b4b | 2012-10-04 17:15:25 -0700 | [diff] [blame] | 187 | %d dump mode, matches PR_SET_DUMPABLE and |
| 188 | /proc/sys/fs/suid_dumpable |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 189 | %s signal number |
| 190 | %t UNIX time of dump |
| 191 | %h hostname |
Jiri Slaby | 57cc083 | 2011-05-26 16:25:46 -0700 | [diff] [blame] | 192 | %e executable filename (may be shortened) |
| 193 | %E executable path |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 194 | %<OTHER> both are dropped |
Matthias Urlichs | cd08104 | 2006-10-11 01:21:57 -0700 | [diff] [blame] | 195 | . If the first character of the pattern is a '|', the kernel will treat |
| 196 | the rest of the pattern as a command to run. The core dump will be |
| 197 | written to the standard input of that program instead of to a file. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 198 | |
| 199 | ============================================================== |
| 200 | |
Neil Horman | a293980 | 2009-09-23 15:56:56 -0700 | [diff] [blame] | 201 | core_pipe_limit: |
| 202 | |
Borislav Petkov | 807094c | 2011-07-23 10:39:29 -0700 | [diff] [blame] | 203 | This sysctl is only applicable when core_pattern is configured to pipe |
| 204 | core files to a user space helper (when the first character of |
| 205 | core_pattern is a '|', see above). When collecting cores via a pipe |
| 206 | to an application, it is occasionally useful for the collecting |
| 207 | application to gather data about the crashing process from its |
| 208 | /proc/pid directory. In order to do this safely, the kernel must wait |
| 209 | for the collecting process to exit, so as not to remove the crashing |
| 210 | processes proc files prematurely. This in turn creates the |
| 211 | possibility that a misbehaving userspace collecting process can block |
| 212 | the reaping of a crashed process simply by never exiting. This sysctl |
| 213 | defends against that. It defines how many concurrent crashing |
| 214 | processes may be piped to user space applications in parallel. If |
| 215 | this value is exceeded, then those crashing processes above that value |
| 216 | are noted via the kernel log and their cores are skipped. 0 is a |
| 217 | special value, indicating that unlimited processes may be captured in |
| 218 | parallel, but that no waiting will take place (i.e. the collecting |
| 219 | process is not guaranteed access to /proc/<crashing pid>/). This |
| 220 | value defaults to 0. |
Neil Horman | a293980 | 2009-09-23 15:56:56 -0700 | [diff] [blame] | 221 | |
| 222 | ============================================================== |
| 223 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 224 | core_uses_pid: |
| 225 | |
| 226 | The default coredump filename is "core". By setting |
| 227 | core_uses_pid to 1, the coredump filename becomes core.PID. |
| 228 | If core_pattern does not include "%p" (default does not) |
| 229 | and core_uses_pid is set, then .PID will be appended to |
| 230 | the filename. |
| 231 | |
| 232 | ============================================================== |
| 233 | |
| 234 | ctrl-alt-del: |
| 235 | |
| 236 | When the value in this file is 0, ctrl-alt-del is trapped and |
| 237 | sent to the init(1) program to handle a graceful restart. |
| 238 | When, however, the value is > 0, Linux's reaction to a Vulcan |
| 239 | Nerve Pinch (tm) will be an immediate reboot, without even |
| 240 | syncing its dirty buffers. |
| 241 | |
| 242 | Note: when a program (like dosemu) has the keyboard in 'raw' |
| 243 | mode, the ctrl-alt-del is intercepted by the program before it |
| 244 | ever reaches the kernel tty layer, and it's up to the program |
| 245 | to decide what to do with it. |
| 246 | |
| 247 | ============================================================== |
| 248 | |
Dan Rosenberg | eaf06b2 | 2010-11-11 14:05:18 -0800 | [diff] [blame] | 249 | dmesg_restrict: |
| 250 | |
Borislav Petkov | 807094c | 2011-07-23 10:39:29 -0700 | [diff] [blame] | 251 | This toggle indicates whether unprivileged users are prevented |
| 252 | from using dmesg(8) to view messages from the kernel's log buffer. |
| 253 | When dmesg_restrict is set to (0) there are no restrictions. When |
Serge E. Hallyn | 38ef4c2 | 2010-12-08 15:19:01 +0000 | [diff] [blame] | 254 | dmesg_restrict is set set to (1), users must have CAP_SYSLOG to use |
Dan Rosenberg | eaf06b2 | 2010-11-11 14:05:18 -0800 | [diff] [blame] | 255 | dmesg(8). |
| 256 | |
Borislav Petkov | 807094c | 2011-07-23 10:39:29 -0700 | [diff] [blame] | 257 | The kernel config option CONFIG_SECURITY_DMESG_RESTRICT sets the |
| 258 | default value of dmesg_restrict. |
Dan Rosenberg | eaf06b2 | 2010-11-11 14:05:18 -0800 | [diff] [blame] | 259 | |
| 260 | ============================================================== |
| 261 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 262 | domainname & hostname: |
| 263 | |
| 264 | These files can be used to set the NIS/YP domainname and the |
| 265 | hostname of your box in exactly the same way as the commands |
| 266 | domainname and hostname, i.e.: |
| 267 | # echo "darkstar" > /proc/sys/kernel/hostname |
| 268 | # echo "mydomain" > /proc/sys/kernel/domainname |
| 269 | has the same effect as |
| 270 | # hostname "darkstar" |
| 271 | # domainname "mydomain" |
| 272 | |
| 273 | Note, however, that the classic darkstar.frop.org has the |
| 274 | hostname "darkstar" and DNS (Internet Domain Name Server) |
| 275 | domainname "frop.org", not to be confused with the NIS (Network |
| 276 | Information Service) or YP (Yellow Pages) domainname. These two |
| 277 | domain names are in general different. For a detailed discussion |
| 278 | see the hostname(1) man page. |
| 279 | |
| 280 | ============================================================== |
| 281 | |
| 282 | hotplug: |
| 283 | |
| 284 | Path for the hotplug policy agent. |
| 285 | Default value is "/sbin/hotplug". |
| 286 | |
| 287 | ============================================================== |
| 288 | |
Dan Rosenberg | 455cd5a | 2011-01-12 16:59:41 -0800 | [diff] [blame] | 289 | kptr_restrict: |
| 290 | |
| 291 | This toggle indicates whether restrictions are placed on |
| 292 | exposing kernel addresses via /proc and other interfaces. When |
| 293 | kptr_restrict is set to (0), there are no restrictions. When |
| 294 | kptr_restrict is set to (1), the default, kernel pointers |
| 295 | printed using the %pK format specifier will be replaced with 0's |
| 296 | unless the user has CAP_SYSLOG. When kptr_restrict is set to |
| 297 | (2), kernel pointers printed using %pK will be replaced with 0's |
| 298 | regardless of privileges. |
| 299 | |
| 300 | ============================================================== |
| 301 | |
Chuck Ebbert | 0741f4d | 2006-12-07 02:14:11 +0100 | [diff] [blame] | 302 | kstack_depth_to_print: (X86 only) |
| 303 | |
| 304 | Controls the number of words to print when dumping the raw |
| 305 | kernel stack. |
| 306 | |
| 307 | ============================================================== |
| 308 | |
Borislav Petkov | 807094c | 2011-07-23 10:39:29 -0700 | [diff] [blame] | 309 | l2cr: (PPC only) |
| 310 | |
| 311 | This flag controls the L2 cache of G3 processor boards. If |
| 312 | 0, the cache is disabled. Enabled if nonzero. |
| 313 | |
| 314 | ============================================================== |
| 315 | |
Kees Cook | 3d43321 | 2009-04-02 15:49:29 -0700 | [diff] [blame] | 316 | modules_disabled: |
| 317 | |
| 318 | A toggle value indicating if modules are allowed to be loaded |
| 319 | in an otherwise modular kernel. This toggle defaults to off |
| 320 | (0), but can be set true (1). Once true, modules can be |
| 321 | neither loaded nor unloaded, and the toggle cannot be set back |
| 322 | to false. |
| 323 | |
| 324 | ============================================================== |
| 325 | |
Stanislav Kinsbursky | 03f5956 | 2013-01-04 15:34:50 -0800 | [diff] [blame] | 326 | msg_next_id, sem_next_id, and shm_next_id: |
| 327 | |
| 328 | These three toggles allows to specify desired id for next allocated IPC |
| 329 | object: message, semaphore or shared memory respectively. |
| 330 | |
| 331 | By default they are equal to -1, which means generic allocation logic. |
| 332 | Possible values to set are in range {0..INT_MAX}. |
| 333 | |
| 334 | Notes: |
| 335 | 1) kernel doesn't guarantee, that new object will have desired id. So, |
| 336 | it's up to userspace, how to handle an object with "wrong" id. |
| 337 | 2) Toggle with non-default value will be set back to -1 by kernel after |
| 338 | successful IPC object allocation. |
| 339 | |
| 340 | ============================================================== |
| 341 | |
Borislav Petkov | 807094c | 2011-07-23 10:39:29 -0700 | [diff] [blame] | 342 | nmi_watchdog: |
| 343 | |
| 344 | Enables/Disables the NMI watchdog on x86 systems. When the value is |
| 345 | non-zero the NMI watchdog is enabled and will continuously test all |
| 346 | online cpus to determine whether or not they are still functioning |
| 347 | properly. Currently, passing "nmi_watchdog=" parameter at boot time is |
| 348 | required for this function to work. |
| 349 | |
| 350 | If LAPIC NMI watchdog method is in use (nmi_watchdog=2 kernel |
| 351 | parameter), the NMI watchdog shares registers with oprofile. By |
| 352 | disabling the NMI watchdog, oprofile may have more registers to |
| 353 | utilize. |
| 354 | |
| 355 | ============================================================== |
| 356 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 357 | osrelease, ostype & version: |
| 358 | |
| 359 | # cat osrelease |
| 360 | 2.1.88 |
| 361 | # cat ostype |
| 362 | Linux |
| 363 | # cat version |
| 364 | #5 Wed Feb 25 21:49:24 MET 1998 |
| 365 | |
| 366 | The files osrelease and ostype should be clear enough. Version |
| 367 | needs a little more clarification however. The '#5' means that |
| 368 | this is the fifth kernel built from this source base and the |
| 369 | date behind it indicates the time the kernel was built. |
| 370 | The only way to tune these values is to rebuild the kernel :-) |
| 371 | |
| 372 | ============================================================== |
| 373 | |
| 374 | overflowgid & overflowuid: |
| 375 | |
Borislav Petkov | 807094c | 2011-07-23 10:39:29 -0700 | [diff] [blame] | 376 | if your architecture did not always support 32-bit UIDs (i.e. arm, |
| 377 | i386, m68k, sh, and sparc32), a fixed UID and GID will be returned to |
| 378 | applications that use the old 16-bit UID/GID system calls, if the |
| 379 | actual UID or GID would exceed 65535. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 380 | |
| 381 | These sysctls allow you to change the value of the fixed UID and GID. |
| 382 | The default is 65534. |
| 383 | |
| 384 | ============================================================== |
| 385 | |
| 386 | panic: |
| 387 | |
Borislav Petkov | 807094c | 2011-07-23 10:39:29 -0700 | [diff] [blame] | 388 | The value in this file represents the number of seconds the kernel |
| 389 | waits before rebooting on a panic. When you use the software watchdog, |
| 390 | the recommended setting is 60. |
| 391 | |
| 392 | ============================================================== |
| 393 | |
| 394 | panic_on_unrecovered_nmi: |
| 395 | |
| 396 | The default Linux behaviour on an NMI of either memory or unknown is |
| 397 | to continue operation. For many environments such as scientific |
| 398 | computing it is preferable that the box is taken out and the error |
| 399 | dealt with than an uncorrected parity/ECC error get propagated. |
| 400 | |
| 401 | A small number of systems do generate NMI's for bizarre random reasons |
| 402 | such as power management so the default is off. That sysctl works like |
| 403 | the existing panic controls already in that directory. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 404 | |
| 405 | ============================================================== |
| 406 | |
| 407 | panic_on_oops: |
| 408 | |
| 409 | Controls the kernel's behaviour when an oops or BUG is encountered. |
| 410 | |
| 411 | 0: try to continue operation |
| 412 | |
Matt LaPlante | a982ac0 | 2007-05-09 07:35:06 +0200 | [diff] [blame] | 413 | 1: panic immediately. If the `panic' sysctl is also non-zero then the |
Maxime Bizon | 8b23d04d | 2006-08-05 12:14:32 -0700 | [diff] [blame] | 414 | machine will be rebooted. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 415 | |
| 416 | ============================================================== |
| 417 | |
Mitsuo Hayasaka | 55af779 | 2011-11-29 15:08:36 +0900 | [diff] [blame] | 418 | panic_on_stackoverflow: |
| 419 | |
| 420 | Controls the kernel's behavior when detecting the overflows of |
| 421 | kernel, IRQ and exception stacks except a user stack. |
| 422 | This file shows up if CONFIG_DEBUG_STACKOVERFLOW is enabled. |
| 423 | |
| 424 | 0: try to continue operation. |
| 425 | |
| 426 | 1: panic immediately. |
| 427 | |
| 428 | ============================================================== |
| 429 | |
Dave Hansen | 14c63f1 | 2013-06-21 08:51:36 -0700 | [diff] [blame] | 430 | perf_cpu_time_max_percent: |
| 431 | |
| 432 | Hints to the kernel how much CPU time it should be allowed to |
| 433 | use to handle perf sampling events. If the perf subsystem |
| 434 | is informed that its samples are exceeding this limit, it |
| 435 | will drop its sampling frequency to attempt to reduce its CPU |
| 436 | usage. |
| 437 | |
| 438 | Some perf sampling happens in NMIs. If these samples |
| 439 | unexpectedly take too long to execute, the NMIs can become |
| 440 | stacked up next to each other so much that nothing else is |
| 441 | allowed to execute. |
| 442 | |
| 443 | 0: disable the mechanism. Do not monitor or correct perf's |
| 444 | sampling rate no matter how CPU time it takes. |
| 445 | |
| 446 | 1-100: attempt to throttle perf's sample rate to this |
| 447 | percentage of CPU. Note: the kernel calculates an |
| 448 | "expected" length of each sample event. 100 here means |
| 449 | 100% of that expected length. Even if this is set to |
| 450 | 100, you may still see sample throttling if this |
| 451 | length is exceeded. Set to 0 if you truly do not care |
| 452 | how much CPU is consumed. |
| 453 | |
| 454 | ============================================================== |
| 455 | |
Mitsuo Hayasaka | 55af779 | 2011-11-29 15:08:36 +0900 | [diff] [blame] | 456 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 457 | pid_max: |
| 458 | |
Robert P. J. Day | beb7dd8 | 2007-05-09 07:14:03 +0200 | [diff] [blame] | 459 | PID allocation wrap value. When the kernel's next PID value |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 460 | reaches this value, it wraps back to a minimum PID value. |
| 461 | PIDs of value pid_max or larger are not allocated. |
| 462 | |
| 463 | ============================================================== |
| 464 | |
Pavel Emelyanov | b8f566b | 2012-01-12 17:20:27 -0800 | [diff] [blame] | 465 | ns_last_pid: |
| 466 | |
| 467 | The last pid allocated in the current (the one task using this sysctl |
| 468 | lives in) pid namespace. When selecting a pid for a next task on fork |
| 469 | kernel tries to allocate a number starting from this one. |
| 470 | |
| 471 | ============================================================== |
| 472 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 473 | powersave-nap: (PPC only) |
| 474 | |
| 475 | If set, Linux-PPC will use the 'nap' mode of powersaving, |
| 476 | otherwise the 'doze' mode will be used. |
| 477 | |
| 478 | ============================================================== |
| 479 | |
| 480 | printk: |
| 481 | |
| 482 | The four values in printk denote: console_loglevel, |
| 483 | default_message_loglevel, minimum_console_loglevel and |
| 484 | default_console_loglevel respectively. |
| 485 | |
| 486 | These values influence printk() behavior when printing or |
| 487 | logging error messages. See 'man 2 syslog' for more info on |
| 488 | the different loglevels. |
| 489 | |
| 490 | - console_loglevel: messages with a higher priority than |
| 491 | this will be printed to the console |
Paul Bolle | 87889e1 | 2011-02-06 21:00:41 +0100 | [diff] [blame] | 492 | - default_message_loglevel: messages without an explicit priority |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 493 | will be printed with this priority |
| 494 | - minimum_console_loglevel: minimum (highest) value to which |
| 495 | console_loglevel can be set |
| 496 | - default_console_loglevel: default value for console_loglevel |
| 497 | |
| 498 | ============================================================== |
| 499 | |
Borislav Petkov | 807094c | 2011-07-23 10:39:29 -0700 | [diff] [blame] | 500 | printk_delay: |
| 501 | |
| 502 | Delay each printk message in printk_delay milliseconds |
| 503 | |
| 504 | Value from 0 - 10000 is allowed. |
| 505 | |
| 506 | ============================================================== |
| 507 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 508 | printk_ratelimit: |
| 509 | |
| 510 | Some warning messages are rate limited. printk_ratelimit specifies |
| 511 | the minimum length of time between these messages (in jiffies), by |
| 512 | default we allow one every 5 seconds. |
| 513 | |
| 514 | A value of 0 will disable rate limiting. |
| 515 | |
| 516 | ============================================================== |
| 517 | |
| 518 | printk_ratelimit_burst: |
| 519 | |
| 520 | While long term we enforce one message per printk_ratelimit |
| 521 | seconds, we do allow a burst of messages to pass through. |
| 522 | printk_ratelimit_burst specifies the number of messages we can |
| 523 | send before ratelimiting kicks in. |
| 524 | |
| 525 | ============================================================== |
| 526 | |
Borislav Petkov | 807094c | 2011-07-23 10:39:29 -0700 | [diff] [blame] | 527 | randomize_va_space: |
Jiri Kosina | 1ec7fd5 | 2008-02-09 23:24:08 +0100 | [diff] [blame] | 528 | |
| 529 | This option can be used to select the type of process address |
| 530 | space randomization that is used in the system, for architectures |
| 531 | that support this feature. |
| 532 | |
Horst Schirmeier | b7f5ab6 | 2009-07-03 14:20:17 +0200 | [diff] [blame] | 533 | 0 - Turn the process address space randomization off. This is the |
| 534 | default for architectures that do not support this feature anyways, |
| 535 | and kernels that are booted with the "norandmaps" parameter. |
Jiri Kosina | 1ec7fd5 | 2008-02-09 23:24:08 +0100 | [diff] [blame] | 536 | |
| 537 | 1 - Make the addresses of mmap base, stack and VDSO page randomized. |
| 538 | This, among other things, implies that shared libraries will be |
Horst Schirmeier | b7f5ab6 | 2009-07-03 14:20:17 +0200 | [diff] [blame] | 539 | loaded to random addresses. Also for PIE-linked binaries, the |
| 540 | location of code start is randomized. This is the default if the |
| 541 | CONFIG_COMPAT_BRK option is enabled. |
Jiri Kosina | 1ec7fd5 | 2008-02-09 23:24:08 +0100 | [diff] [blame] | 542 | |
Horst Schirmeier | b7f5ab6 | 2009-07-03 14:20:17 +0200 | [diff] [blame] | 543 | 2 - Additionally enable heap randomization. This is the default if |
| 544 | CONFIG_COMPAT_BRK is disabled. |
| 545 | |
| 546 | There are a few legacy applications out there (such as some ancient |
Jiri Kosina | 1ec7fd5 | 2008-02-09 23:24:08 +0100 | [diff] [blame] | 547 | versions of libc.so.5 from 1996) that assume that brk area starts |
Horst Schirmeier | b7f5ab6 | 2009-07-03 14:20:17 +0200 | [diff] [blame] | 548 | just after the end of the code+bss. These applications break when |
| 549 | start of the brk area is randomized. There are however no known |
Jiri Kosina | 1ec7fd5 | 2008-02-09 23:24:08 +0100 | [diff] [blame] | 550 | non-legacy applications that would be broken this way, so for most |
Horst Schirmeier | b7f5ab6 | 2009-07-03 14:20:17 +0200 | [diff] [blame] | 551 | systems it is safe to choose full randomization. |
| 552 | |
| 553 | Systems with ancient and/or broken binaries should be configured |
| 554 | with CONFIG_COMPAT_BRK enabled, which excludes the heap from process |
| 555 | address space randomization. |
Jiri Kosina | 1ec7fd5 | 2008-02-09 23:24:08 +0100 | [diff] [blame] | 556 | |
| 557 | ============================================================== |
| 558 | |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 559 | reboot-cmd: (Sparc only) |
| 560 | |
| 561 | ??? This seems to be a way to give an argument to the Sparc |
| 562 | ROM/Flash boot loader. Maybe to tell it what to do after |
| 563 | rebooting. ??? |
| 564 | |
| 565 | ============================================================== |
| 566 | |
| 567 | rtsig-max & rtsig-nr: |
| 568 | |
| 569 | The file rtsig-max can be used to tune the maximum number |
| 570 | of POSIX realtime (queued) signals that can be outstanding |
| 571 | in the system. |
| 572 | |
| 573 | rtsig-nr shows the number of RT signals currently queued. |
| 574 | |
| 575 | ============================================================== |
| 576 | |
| 577 | sg-big-buff: |
| 578 | |
| 579 | This file shows the size of the generic SCSI (sg) buffer. |
| 580 | You can't tune it just yet, but you could change it on |
| 581 | compile time by editing include/scsi/sg.h and changing |
| 582 | the value of SG_BIG_BUFF. |
| 583 | |
| 584 | There shouldn't be any reason to change this value. If |
| 585 | you can come up with one, you probably know what you |
| 586 | are doing anyway :) |
| 587 | |
| 588 | ============================================================== |
| 589 | |
Carlos Alberto Lopez Perez | 358e419 | 2013-01-04 15:35:05 -0800 | [diff] [blame] | 590 | shmall: |
| 591 | |
| 592 | This parameter sets the total amount of shared memory pages that |
| 593 | can be used system wide. Hence, SHMALL should always be at least |
| 594 | ceil(shmmax/PAGE_SIZE). |
| 595 | |
| 596 | If you are not sure what the default PAGE_SIZE is on your Linux |
| 597 | system, you can run the following command: |
| 598 | |
| 599 | # getconf PAGE_SIZE |
| 600 | |
| 601 | ============================================================== |
| 602 | |
Borislav Petkov | 807094c | 2011-07-23 10:39:29 -0700 | [diff] [blame] | 603 | shmmax: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 604 | |
| 605 | This value can be used to query and set the run time limit |
| 606 | on the maximum shared memory segment size that can be created. |
Borislav Petkov | 807094c | 2011-07-23 10:39:29 -0700 | [diff] [blame] | 607 | Shared memory segments up to 1Gb are now supported in the |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 608 | kernel. This value defaults to SHMMAX. |
| 609 | |
| 610 | ============================================================== |
| 611 | |
Vasiliy Kulikov | b34a6b1 | 2011-07-26 16:08:48 -0700 | [diff] [blame] | 612 | shm_rmid_forced: |
| 613 | |
| 614 | Linux lets you set resource limits, including how much memory one |
| 615 | process can consume, via setrlimit(2). Unfortunately, shared memory |
| 616 | segments are allowed to exist without association with any process, and |
| 617 | thus might not be counted against any resource limits. If enabled, |
| 618 | shared memory segments are automatically destroyed when their attach |
| 619 | count becomes zero after a detach or a process termination. It will |
| 620 | also destroy segments that were created, but never attached to, on exit |
| 621 | from the process. The only use left for IPC_RMID is to immediately |
| 622 | destroy an unattached segment. Of course, this breaks the way things are |
| 623 | defined, so some applications might stop working. Note that this |
| 624 | feature will do you no good unless you also configure your resource |
| 625 | limits (in particular, RLIMIT_AS and RLIMIT_NPROC). Most systems don't |
| 626 | need this. |
| 627 | |
| 628 | Note that if you change this from 0 to 1, already created segments |
| 629 | without users and with a dead originative process will be destroyed. |
| 630 | |
| 631 | ============================================================== |
| 632 | |
Borislav Petkov | 807094c | 2011-07-23 10:39:29 -0700 | [diff] [blame] | 633 | tainted: |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 634 | |
| 635 | Non-zero if the kernel has been tainted. Numeric values, which |
| 636 | can be ORed together: |
| 637 | |
Greg Kroah-Hartman | bb20698 | 2008-10-17 15:01:07 -0700 | [diff] [blame] | 638 | 1 - A module with a non-GPL license has been loaded, this |
| 639 | includes modules with no license. |
| 640 | Set by modutils >= 2.4.9 and module-init-tools. |
| 641 | 2 - A module was force loaded by insmod -f. |
| 642 | Set by modutils >= 2.4.9 and module-init-tools. |
| 643 | 4 - Unsafe SMP processors: SMP with CPUs not designed for SMP. |
| 644 | 8 - A module was forcibly unloaded from the system by rmmod -f. |
| 645 | 16 - A hardware machine check error occurred on the system. |
| 646 | 32 - A bad page was discovered on the system. |
| 647 | 64 - The user has asked that the system be marked "tainted". This |
| 648 | could be because they are running software that directly modifies |
| 649 | the hardware, or for other reasons. |
| 650 | 128 - The system has died. |
| 651 | 256 - The ACPI DSDT has been overridden with one supplied by the user |
| 652 | instead of using the one provided by the hardware. |
| 653 | 512 - A kernel warning has occurred. |
| 654 | 1024 - A module from drivers/staging was loaded. |
Larry Finger | f5fe184 | 2012-02-06 09:49:50 -0800 | [diff] [blame] | 655 | 2048 - The system is working around a severe firmware bug. |
| 656 | 4096 - An out-of-tree module has been loaded. |
Linus Torvalds | 1da177e | 2005-04-16 15:20:36 -0700 | [diff] [blame] | 657 | |
Shen Feng | 760df93 | 2009-04-02 16:57:20 -0700 | [diff] [blame] | 658 | ============================================================== |
| 659 | |
Shen Feng | 760df93 | 2009-04-02 16:57:20 -0700 | [diff] [blame] | 660 | unknown_nmi_panic: |
| 661 | |
Borislav Petkov | 807094c | 2011-07-23 10:39:29 -0700 | [diff] [blame] | 662 | The value in this file affects behavior of handling NMI. When the |
| 663 | value is non-zero, unknown NMI is trapped and then panic occurs. At |
| 664 | that time, kernel debugging information is displayed on console. |
Shen Feng | 760df93 | 2009-04-02 16:57:20 -0700 | [diff] [blame] | 665 | |
Borislav Petkov | 807094c | 2011-07-23 10:39:29 -0700 | [diff] [blame] | 666 | NMI switch that most IA32 servers have fires unknown NMI up, for |
| 667 | example. If a system hangs up, try pressing the NMI switch. |
Li Zefan | 08825c9 | 2013-05-17 10:31:20 +0800 | [diff] [blame] | 668 | |
| 669 | ============================================================== |
| 670 | |
| 671 | watchdog_thresh: |
| 672 | |
| 673 | This value can be used to control the frequency of hrtimer and NMI |
| 674 | events and the soft and hard lockup thresholds. The default threshold |
| 675 | is 10 seconds. |
| 676 | |
| 677 | The softlockup threshold is (2 * watchdog_thresh). Setting this |
| 678 | tunable to zero will disable lockup detection altogether. |
| 679 | |
| 680 | ============================================================== |