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kernel

Guest on 31st July 2022 05:16:23 PM

  1. Documentation for /proc/sys/kernel/*    kernel version 2.2.5
  2.         (c) ,Rik van Riel <riel@nl.linux.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. - acct
  20. - ctrl-alt-del
  21. - dentry-state
  22. - domainname
  23. - hostname
  24. - htab-reclaim                [ PPC only ]
  25. - java-appletviewer           [ binfmt_java, obsolete ]
  26. - java-interpreter            [ binfmt_java, obsolete ]
  27. - l2cr                        [ PPC only ]
  28. - modprobe                    ==> Documentation/kmod.txt
  29. - osrelease
  30. - ostype
  31. - panic
  32. - powersave-nap               [ PPC only ]
  33. - printk
  34. - real-root-dev               ==> Documentation/initrd.txt
  35. - reboot-cmd                  [ SPARC only ]
  36. - rtsig-nr
  37. - rtsig-max
  38. - sg-big-buff                 [ generic SCSI device (sg) ]
  39. - shmmax                      [ sysv ipc ]
  40. - version
  41. - zero-paged                  [ PPC only ]
  42.  
  43. ==============================================================
  44.  
  45. acct:
  46.  
  47. highwater lowwater frequency
  48.  
  49. If BSD-style process accounting is enabled these values control
  50. its behaviour. If free space on filesystem where the log lives
  51. goes below <lowwater>% accounting suspends. If free space gets
  52. above <highwater>% accounting resumes. <Frequency> determines
  53. how often do we check the amount of free space (value is in
  54. seconds). Default:
  55. 4 2 30
  56. That is, suspend accounting if there left <= 2% free; resume it
  57. if we got >=4%; consider information about amount of free space
  58. valid for 30 seconds.
  59.  
  60. ==============================================================
  61.  
  62. ctrl-alt-del:
  63.  
  64. When the value in this file is 0, ctrl-alt-del is trapped and
  65. sent to the init(1) program to handle a graceful restart.
  66. When, however, the value is > 0, Linux's reaction to a Vulcan
  67. Nerve Pinch (tm) will be an immediate reboot, without even
  68. syncing its dirty buffers.
  69.  
  70. Note: when a program (like dosemu) has the keyboard in 'raw'
  71. mode, the ctrl-alt-del is intercepted by the program before it
  72. ever reaches the kernel tty layer, and it's up to the program
  73. to decide what to do with it.
  74.  
  75. ==============================================================
  76.  
  77. domainname & hostname:
  78.  
  79. These files can be controlled to set the domainname and
  80. hostname of your box. For the classic darkstar.frop.org
  81. a simple:
  82. # echo "darkstar" > /proc/sys/kernel/hostname
  83. # echo "frop.org" > /proc/sys/kernel/domainname
  84. would suffice to set your hostname and domainname.
  85.  
  86. ==============================================================
  87.  
  88. htab-reclaim: (PPC only)
  89.  
  90. Setting this to a non-zero value, the PowerPC htab
  91. (see Documentation/powerpc/ppc_htab.txt) is pruned
  92. each time the system hits the idle loop.
  93.  
  94. ==============================================================
  95.  
  96. l2cr: (PPC only)
  97.  
  98. This flag controls the L2 cache of G3 processor boards. If
  99. 0, the cache is disabled. Enabled if nonzero.
  100.  
  101. ==============================================================
  102.  
  103. osrelease, ostype & version:
  104.  
  105. # cat osrelease
  106. 2.1.88
  107. # cat ostype
  108. Linux
  109. # cat version
  110. #5 Wed Feb 25 21:49:24 MET
  111.  
  112. The files osrelease and ostype should be clear enough. Version
  113. needs a little more clarification however. The '#5' means that
  114. this is the fifth kernel built from this source base and the
  115. date behind it indicates the time the kernel was built.
  116. The only way to tune these values is to rebuild the kernel :-)
  117.  
  118. ==============================================================
  119.  
  120. panic:
  121.  
  122. The value in this file represents the number of seconds the
  123. kernel waits before rebooting on a panic. When you use the
  124. software watchdog, the recommended setting is 60.
  125.  
  126. ==============================================================
  127.  
  128. powersave-nap: (PPC only)
  129.  
  130. If set, Linux-PPC will use the 'nap' mode of powersaving,
  131. otherwise the 'doze' mode will be used.
  132.  
  133. ==============================================================
  134.  
  135. printk:
  136.  
  137. The four values in printk denote: console_loglevel,
  138. default_message_loglevel, minimum_console_level and
  139. default_console_loglevel respectively.
  140.  
  141. These values influence printk() behavior when printing or
  142. logging error messages. See 'man 2 syslog' for more info on
  143. the different loglevels.
  144.  
  145. - console_loglevel: messages with a higher priority than
  146.   this will be printed to the console
  147. - default_message_level: messages without an explicit priority
  148.   will be printed with this priority
  149. - minimum_console_loglevel: minimum (highest) value to which
  150.   console_loglevel can be set
  151. - default_console_loglevel: default value for console_loglevel
  152.  
  153. Note: a quick look in linux/kernel/printk.c will reveal that
  154. these variables aren't put inside a structure, so their order
  155. in-core isn't formally guaranteed and garbage values _might_
  156. occur when the compiler changes. (???)
  157.  
  158. ==============================================================
  159.  
  160. reboot-cmd: (Sparc only)
  161.  
  162. ??? This seems to be a way to give an argument to the Sparc
  163. ROM/Flash boot loader. Maybe to tell it what to do after
  164. rebooting. ???
  165.  
  166. ==============================================================
  167.  
  168. rtsig-max & rtsig-nr:
  169.  
  170. The file rtsig-max can be used to tune the maximum number
  171. of POSIX realtime (queued) signals that can be outstanding
  172. in the system.
  173.  
  174. Rtsig-nr shows the number of RT signals currently queued.
  175.  
  176. ==============================================================
  177.  
  178. sg-big-buff:
  179.  
  180. This file shows the size of the generic SCSI (sg) buffer.
  181. You can't tune it just yet, but you could change it on
  182. compile time by editing include/scsi/sg.h and changing
  183. the value of SG_BIG_BUFF.
  184.  
  185. There shouldn't be any reason to change this value. If
  186. you can come up with one, you probably know what you
  187. are doing anyway :)
  188.  
  189. ==============================================================
  190.  
  191. shmmax:
  192.  
  193. This value can be used to query and set the run time limit
  194. on the maximum shared memory segment size that can be created.
  195. Shared memory segments up to 1Gb are now supported in the
  196. kernel.  This value defaults to SHMMAX.
  197.  
  198. ==============================================================
  199.  
  200. zero-paged: (PPC only)
  201.  
  202. When enabled (non-zero), Linux-PPC will pre-zero pages in
  203. the idle loop, possibly speeding up get_free_pages. Since
  204. this only affects what the idle loop is doing, you should
  205. enable this and see if anything changes.

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