498 lines
17 KiB
Plaintext
498 lines
17 KiB
Plaintext
Documentation for /proc/sys/kernel/* kernel version 2.2.10
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(c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
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(c) 2009, Shen Feng<shen@cn.fujitsu.com>
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For general info and legal blurb, please look in README.
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==============================================================
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This file contains documentation for the sysctl files in
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/proc/sys/kernel/ and is valid for Linux kernel version 2.2.
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The files in this directory can be used to tune and monitor
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miscellaneous and general things in the operation of the Linux
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kernel. Since some of the files _can_ be used to screw up your
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system, it is advisable to read both documentation and source
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before actually making adjustments.
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Currently, these files might (depending on your configuration)
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show up in /proc/sys/kernel:
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- acpi_video_flags
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- acct
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- callhome [ S390 only ]
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- auto_msgmni
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- core_pattern
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- core_pipe_limit
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- core_uses_pid
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- ctrl-alt-del
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- dentry-state
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- domainname
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- hostname
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- hotplug
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- java-appletviewer [ binfmt_java, obsolete ]
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- java-interpreter [ binfmt_java, obsolete ]
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- kstack_depth_to_print [ X86 only ]
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- l2cr [ PPC only ]
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- modprobe ==> Documentation/debugging-modules.txt
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- modules_disabled
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- msgmax
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- msgmnb
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- msgmni
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- nmi_watchdog
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- osrelease
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- ostype
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- overflowgid
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- overflowuid
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- panic
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- pid_max
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- powersave-nap [ PPC only ]
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- panic_on_unrecovered_nmi
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- printk
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- randomize_va_space
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- real-root-dev ==> Documentation/initrd.txt
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- reboot-cmd [ SPARC only ]
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- rtsig-max
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- rtsig-nr
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- sem
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- sg-big-buff [ generic SCSI device (sg) ]
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- shmall
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- shmmax [ sysv ipc ]
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- shmmni
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- stop-a [ SPARC only ]
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- sysrq ==> Documentation/sysrq.txt
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- tainted
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- threads-max
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- unknown_nmi_panic
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- version
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==============================================================
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acpi_video_flags:
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flags
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See Doc*/kernel/power/video.txt, it allows mode of video boot to be
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set during run time.
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==============================================================
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acct:
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highwater lowwater frequency
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If BSD-style process accounting is enabled these values control
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its behaviour. If free space on filesystem where the log lives
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goes below <lowwater>% accounting suspends. If free space gets
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above <highwater>% accounting resumes. <Frequency> determines
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how often do we check the amount of free space (value is in
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seconds). Default:
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4 2 30
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That is, suspend accounting if there left <= 2% free; resume it
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if we got >=4%; consider information about amount of free space
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valid for 30 seconds.
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==============================================================
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callhome:
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Controls the kernel's callhome behavior in case of a kernel panic.
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The s390 hardware allows an operating system to send a notification
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to a service organization (callhome) in case of an operating system panic.
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When the value in this file is 0 (which is the default behavior)
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nothing happens in case of a kernel panic. If this value is set to "1"
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the complete kernel oops message is send to the IBM customer service
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organization in case the mainframe the Linux operating system is running
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on has a service contract with IBM.
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==============================================================
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core_pattern:
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core_pattern is used to specify a core dumpfile pattern name.
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. max length 128 characters; default value is "core"
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. core_pattern is used as a pattern template for the output filename;
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certain string patterns (beginning with '%') are substituted with
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their actual values.
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. backward compatibility with core_uses_pid:
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If core_pattern does not include "%p" (default does not)
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and core_uses_pid is set, then .PID will be appended to
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the filename.
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. corename format specifiers:
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%<NUL> '%' is dropped
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%% output one '%'
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%p pid
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%u uid
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%g gid
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%s signal number
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%t UNIX time of dump
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%h hostname
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%e executable filename
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%<OTHER> both are dropped
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. If the first character of the pattern is a '|', the kernel will treat
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the rest of the pattern as a command to run. The core dump will be
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written to the standard input of that program instead of to a file.
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==============================================================
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core_pipe_limit:
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This sysctl is only applicable when core_pattern is configured to pipe core
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files to user space helper a (when the first character of core_pattern is a '|',
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see above). When collecting cores via a pipe to an application, it is
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occasionally usefull for the collecting application to gather data about the
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crashing process from its /proc/pid directory. In order to do this safely, the
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kernel must wait for the collecting process to exit, so as not to remove the
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crashing processes proc files prematurely. This in turn creates the possibility
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that a misbehaving userspace collecting process can block the reaping of a
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crashed process simply by never exiting. This sysctl defends against that. It
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defines how many concurrent crashing processes may be piped to user space
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applications in parallel. If this value is exceeded, then those crashing
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processes above that value are noted via the kernel log and their cores are
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skipped. 0 is a special value, indicating that unlimited processes may be
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captured in parallel, but that no waiting will take place (i.e. the collecting
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process is not guaranteed access to /proc/<crahing pid>/). This value defaults
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to 0.
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==============================================================
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core_uses_pid:
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The default coredump filename is "core". By setting
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core_uses_pid to 1, the coredump filename becomes core.PID.
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If core_pattern does not include "%p" (default does not)
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and core_uses_pid is set, then .PID will be appended to
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the filename.
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==============================================================
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ctrl-alt-del:
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When the value in this file is 0, ctrl-alt-del is trapped and
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sent to the init(1) program to handle a graceful restart.
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When, however, the value is > 0, Linux's reaction to a Vulcan
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Nerve Pinch (tm) will be an immediate reboot, without even
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syncing its dirty buffers.
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Note: when a program (like dosemu) has the keyboard in 'raw'
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mode, the ctrl-alt-del is intercepted by the program before it
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ever reaches the kernel tty layer, and it's up to the program
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to decide what to do with it.
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==============================================================
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domainname & hostname:
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These files can be used to set the NIS/YP domainname and the
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hostname of your box in exactly the same way as the commands
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domainname and hostname, i.e.:
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# echo "darkstar" > /proc/sys/kernel/hostname
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# echo "mydomain" > /proc/sys/kernel/domainname
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has the same effect as
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# hostname "darkstar"
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# domainname "mydomain"
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Note, however, that the classic darkstar.frop.org has the
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hostname "darkstar" and DNS (Internet Domain Name Server)
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domainname "frop.org", not to be confused with the NIS (Network
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Information Service) or YP (Yellow Pages) domainname. These two
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domain names are in general different. For a detailed discussion
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see the hostname(1) man page.
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==============================================================
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hotplug:
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Path for the hotplug policy agent.
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Default value is "/sbin/hotplug".
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==============================================================
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l2cr: (PPC only)
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This flag controls the L2 cache of G3 processor boards. If
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0, the cache is disabled. Enabled if nonzero.
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==============================================================
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kstack_depth_to_print: (X86 only)
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Controls the number of words to print when dumping the raw
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kernel stack.
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==============================================================
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modules_disabled:
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A toggle value indicating if modules are allowed to be loaded
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in an otherwise modular kernel. This toggle defaults to off
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(0), but can be set true (1). Once true, modules can be
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neither loaded nor unloaded, and the toggle cannot be set back
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to false.
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==============================================================
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osrelease, ostype & version:
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# cat osrelease
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2.1.88
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# cat ostype
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Linux
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# cat version
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#5 Wed Feb 25 21:49:24 MET 1998
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The files osrelease and ostype should be clear enough. Version
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needs a little more clarification however. The '#5' means that
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this is the fifth kernel built from this source base and the
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date behind it indicates the time the kernel was built.
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The only way to tune these values is to rebuild the kernel :-)
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==============================================================
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overflowgid & overflowuid:
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if your architecture did not always support 32-bit UIDs (i.e. arm, i386,
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m68k, sh, and sparc32), a fixed UID and GID will be returned to
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applications that use the old 16-bit UID/GID system calls, if the actual
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UID or GID would exceed 65535.
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These sysctls allow you to change the value of the fixed UID and GID.
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The default is 65534.
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==============================================================
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panic:
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The value in this file represents the number of seconds the
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kernel waits before rebooting on a panic. When you use the
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software watchdog, the recommended setting is 60.
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==============================================================
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panic_on_oops:
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Controls the kernel's behaviour when an oops or BUG is encountered.
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0: try to continue operation
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1: panic immediately. If the `panic' sysctl is also non-zero then the
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machine will be rebooted.
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==============================================================
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pid_max:
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PID allocation wrap value. When the kernel's next PID value
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reaches this value, it wraps back to a minimum PID value.
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PIDs of value pid_max or larger are not allocated.
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==============================================================
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powersave-nap: (PPC only)
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If set, Linux-PPC will use the 'nap' mode of powersaving,
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otherwise the 'doze' mode will be used.
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==============================================================
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printk:
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The four values in printk denote: console_loglevel,
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default_message_loglevel, minimum_console_loglevel and
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default_console_loglevel respectively.
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These values influence printk() behavior when printing or
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logging error messages. See 'man 2 syslog' for more info on
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the different loglevels.
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- console_loglevel: messages with a higher priority than
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this will be printed to the console
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- default_message_level: messages without an explicit priority
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will be printed with this priority
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- minimum_console_loglevel: minimum (highest) value to which
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console_loglevel can be set
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- default_console_loglevel: default value for console_loglevel
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==============================================================
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printk_ratelimit:
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Some warning messages are rate limited. printk_ratelimit specifies
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the minimum length of time between these messages (in jiffies), by
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default we allow one every 5 seconds.
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A value of 0 will disable rate limiting.
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==============================================================
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printk_ratelimit_burst:
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While long term we enforce one message per printk_ratelimit
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seconds, we do allow a burst of messages to pass through.
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printk_ratelimit_burst specifies the number of messages we can
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send before ratelimiting kicks in.
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==============================================================
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printk_delay:
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Delay each printk message in printk_delay milliseconds
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Value from 0 - 10000 is allowed.
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==============================================================
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randomize-va-space:
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This option can be used to select the type of process address
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space randomization that is used in the system, for architectures
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that support this feature.
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0 - Turn the process address space randomization off. This is the
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default for architectures that do not support this feature anyways,
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and kernels that are booted with the "norandmaps" parameter.
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1 - Make the addresses of mmap base, stack and VDSO page randomized.
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This, among other things, implies that shared libraries will be
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loaded to random addresses. Also for PIE-linked binaries, the
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location of code start is randomized. This is the default if the
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CONFIG_COMPAT_BRK option is enabled.
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2 - Additionally enable heap randomization. This is the default if
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CONFIG_COMPAT_BRK is disabled.
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There are a few legacy applications out there (such as some ancient
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versions of libc.so.5 from 1996) that assume that brk area starts
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just after the end of the code+bss. These applications break when
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start of the brk area is randomized. There are however no known
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non-legacy applications that would be broken this way, so for most
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systems it is safe to choose full randomization.
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Systems with ancient and/or broken binaries should be configured
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with CONFIG_COMPAT_BRK enabled, which excludes the heap from process
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address space randomization.
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==============================================================
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reboot-cmd: (Sparc only)
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??? This seems to be a way to give an argument to the Sparc
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ROM/Flash boot loader. Maybe to tell it what to do after
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rebooting. ???
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==============================================================
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rtsig-max & rtsig-nr:
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The file rtsig-max can be used to tune the maximum number
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of POSIX realtime (queued) signals that can be outstanding
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in the system.
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rtsig-nr shows the number of RT signals currently queued.
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==============================================================
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sg-big-buff:
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This file shows the size of the generic SCSI (sg) buffer.
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You can't tune it just yet, but you could change it on
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compile time by editing include/scsi/sg.h and changing
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the value of SG_BIG_BUFF.
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There shouldn't be any reason to change this value. If
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you can come up with one, you probably know what you
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are doing anyway :)
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==============================================================
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shmmax:
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This value can be used to query and set the run time limit
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on the maximum shared memory segment size that can be created.
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Shared memory segments up to 1Gb are now supported in the
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kernel. This value defaults to SHMMAX.
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==============================================================
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softlockup_thresh:
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This value can be used to lower the softlockup tolerance threshold. The
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default threshold is 60 seconds. If a cpu is locked up for 60 seconds,
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the kernel complains. Valid values are 1-60 seconds. Setting this
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tunable to zero will disable the softlockup detection altogether.
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==============================================================
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tainted:
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Non-zero if the kernel has been tainted. Numeric values, which
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can be ORed together:
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1 - A module with a non-GPL license has been loaded, this
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includes modules with no license.
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Set by modutils >= 2.4.9 and module-init-tools.
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2 - A module was force loaded by insmod -f.
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Set by modutils >= 2.4.9 and module-init-tools.
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4 - Unsafe SMP processors: SMP with CPUs not designed for SMP.
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8 - A module was forcibly unloaded from the system by rmmod -f.
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16 - A hardware machine check error occurred on the system.
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32 - A bad page was discovered on the system.
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64 - The user has asked that the system be marked "tainted". This
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could be because they are running software that directly modifies
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the hardware, or for other reasons.
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128 - The system has died.
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256 - The ACPI DSDT has been overridden with one supplied by the user
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instead of using the one provided by the hardware.
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512 - A kernel warning has occurred.
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1024 - A module from drivers/staging was loaded.
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==============================================================
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auto_msgmni:
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Enables/Disables automatic recomputing of msgmni upon memory add/remove or
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upon ipc namespace creation/removal (see the msgmni description above).
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Echoing "1" into this file enables msgmni automatic recomputing.
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Echoing "0" turns it off.
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auto_msgmni default value is 1.
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==============================================================
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nmi_watchdog:
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Enables/Disables the NMI watchdog on x86 systems. When the value is non-zero
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the NMI watchdog is enabled and will continuously test all online cpus to
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determine whether or not they are still functioning properly. Currently,
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passing "nmi_watchdog=" parameter at boot time is required for this function
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to work.
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If LAPIC NMI watchdog method is in use (nmi_watchdog=2 kernel parameter), the
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NMI watchdog shares registers with oprofile. By disabling the NMI watchdog,
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oprofile may have more registers to utilize.
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==============================================================
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unknown_nmi_panic:
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The value in this file affects behavior of handling NMI. When the value is
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non-zero, unknown NMI is trapped and then panic occurs. At that time, kernel
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debugging information is displayed on console.
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NMI switch that most IA32 servers have fires unknown NMI up, for example.
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If a system hangs up, try pressing the NMI switch.
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==============================================================
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panic_on_unrecovered_nmi:
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The default Linux behaviour on an NMI of either memory or unknown is to continue
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operation. For many environments such as scientific computing it is preferable
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that the box is taken out and the error dealt with than an uncorrected
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parity/ECC error get propogated.
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A small number of systems do generate NMI's for bizarre random reasons such as
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power management so the default is off. That sysctl works like the existing
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panic controls already in that directory.
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