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-Documentation for /proc/sys/kernel/* kernel version 2.2.10
- (c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
- (c) 2009, Shen Feng<shen@cn.fujitsu.com>
-
-For general info and legal blurb, please look in README.
-
-==============================================================
-
-This file contains documentation for the sysctl files in
-/proc/sys/kernel/ and is valid for Linux kernel version 2.2.
-
-The files in this directory can be used to tune and monitor
-miscellaneous and general things in the operation of the Linux
-kernel. Since some of the files _can_ be used to screw up your
-system, it is advisable to read both documentation and source
-before actually making adjustments.
-
-Currently, these files might (depending on your configuration)
-show up in /proc/sys/kernel:
-
-- acct
-- acpi_video_flags
-- auto_msgmni
-- bootloader_type [ X86 only ]
-- bootloader_version [ X86 only ]
-- callhome [ S390 only ]
-- cap_last_cap
-- core_pattern
-- core_pipe_limit
-- core_uses_pid
-- ctrl-alt-del
-- dmesg_restrict
-- domainname
-- hostname
-- hotplug
-- kptr_restrict
-- kstack_depth_to_print [ X86 only ]
-- l2cr [ PPC only ]
-- modprobe ==> Documentation/debugging-modules.txt
-- modules_disabled
-- msgmax
-- msgmnb
-- msgmni
-- nmi_watchdog
-- osrelease
-- ostype
-- overflowgid
-- overflowuid
-- panic
-- panic_on_oops
-- panic_on_unrecovered_nmi
-- panic_on_stackoverflow
-- pid_max
-- powersave-nap [ PPC only ]
-- printk
-- printk_delay
-- printk_ratelimit
-- printk_ratelimit_burst
-- randomize_va_space
-- real-root-dev ==> Documentation/initrd.txt
-- reboot-cmd [ SPARC only ]
-- rtsig-max
-- rtsig-nr
-- sem
-- sg-big-buff [ generic SCSI device (sg) ]
-- shm_rmid_forced
-- shmall
-- shmmax [ sysv ipc ]
-- shmmni
-- softlockup_thresh
-- stop-a [ SPARC only ]
-- sysrq ==> Documentation/sysrq.txt
-- tainted
-- threads-max
-- unknown_nmi_panic
-- version
-
-==============================================================
-
-acct:
-
-highwater lowwater frequency
-
-If BSD-style process accounting is enabled these values control
-its behaviour. If free space on filesystem where the log lives
-goes below <lowwater>% accounting suspends. If free space gets
-above <highwater>% accounting resumes. <Frequency> determines
-how often do we check the amount of free space (value is in
-seconds). Default:
-4 2 30
-That is, suspend accounting if there left <= 2% free; resume it
-if we got >=4%; consider information about amount of free space
-valid for 30 seconds.
-
-==============================================================
-
-acpi_video_flags:
-
-flags
-
-See Doc*/kernel/power/video.txt, it allows mode of video boot to be
-set during run time.
-
-==============================================================
-
-auto_msgmni:
-
-Enables/Disables automatic recomputing of msgmni upon memory add/remove
-or upon ipc namespace creation/removal (see the msgmni description
-above). Echoing "1" into this file enables msgmni automatic recomputing.
-Echoing "0" turns it off. auto_msgmni default value is 1.
-
-
-==============================================================
-
-bootloader_type:
-
-x86 bootloader identification
-
-This gives the bootloader type number as indicated by the bootloader,
-shifted left by 4, and OR'd with the low four bits of the bootloader
-version. The reason for this encoding is that this used to match the
-type_of_loader field in the kernel header; the encoding is kept for
-backwards compatibility. That is, if the full bootloader type number
-is 0x15 and the full version number is 0x234, this file will contain
-the value 340 = 0x154.
-
-See the type_of_loader and ext_loader_type fields in
-Documentation/x86/boot.txt for additional information.
-
-==============================================================
-
-bootloader_version:
-
-x86 bootloader version
-
-The complete bootloader version number. In the example above, this
-file will contain the value 564 = 0x234.
-
-See the type_of_loader and ext_loader_ver fields in
-Documentation/x86/boot.txt for additional information.
-
-==============================================================
-
-callhome:
-
-Controls the kernel's callhome behavior in case of a kernel panic.
-
-The s390 hardware allows an operating system to send a notification
-to a service organization (callhome) in case of an operating system panic.
-
-When the value in this file is 0 (which is the default behavior)
-nothing happens in case of a kernel panic. If this value is set to "1"
-the complete kernel oops message is send to the IBM customer service
-organization in case the mainframe the Linux operating system is running
-on has a service contract with IBM.
-
-==============================================================
-
-cap_last_cap
-
-Highest valid capability of the running kernel. Exports
-CAP_LAST_CAP from the kernel.
-
-==============================================================
-
-core_pattern:
-
-core_pattern is used to specify a core dumpfile pattern name.
-. max length 128 characters; default value is "core"
-. core_pattern is used as a pattern template for the output filename;
- certain string patterns (beginning with '%') are substituted with
- their actual values.
-. backward compatibility with core_uses_pid:
- If core_pattern does not include "%p" (default does not)
- and core_uses_pid is set, then .PID will be appended to
- the filename.
-. corename format specifiers:
- %<NUL> '%' is dropped
- %% output one '%'
- %p pid
- %u uid
- %g gid
- %s signal number
- %t UNIX time of dump
- %h hostname
- %e executable filename (may be shortened)
- %E executable path
- %<OTHER> both are dropped
-. If the first character of the pattern is a '|', the kernel will treat
- the rest of the pattern as a command to run. The core dump will be
- written to the standard input of that program instead of to a file.
-
-==============================================================
-
-core_pipe_limit:
-
-This sysctl is only applicable when core_pattern is configured to pipe
-core files to a user space helper (when the first character of
-core_pattern is a '|', see above). When collecting cores via a pipe
-to an application, it is occasionally useful for the collecting
-application to gather data about the crashing process from its
-/proc/pid directory. In order to do this safely, the kernel must wait
-for the collecting process to exit, so as not to remove the crashing
-processes proc files prematurely. This in turn creates the
-possibility that a misbehaving userspace collecting process can block
-the reaping of a crashed process simply by never exiting. This sysctl
-defends against that. It defines how many concurrent crashing
-processes may be piped to user space applications in parallel. If
-this value is exceeded, then those crashing processes above that value
-are noted via the kernel log and their cores are skipped. 0 is a
-special value, indicating that unlimited processes may be captured in
-parallel, but that no waiting will take place (i.e. the collecting
-process is not guaranteed access to /proc/<crashing pid>/). This
-value defaults to 0.
-
-==============================================================
-
-core_uses_pid:
-
-The default coredump filename is "core". By setting
-core_uses_pid to 1, the coredump filename becomes core.PID.
-If core_pattern does not include "%p" (default does not)
-and core_uses_pid is set, then .PID will be appended to
-the filename.
-
-==============================================================
-
-ctrl-alt-del:
-
-When the value in this file is 0, ctrl-alt-del is trapped and
-sent to the init(1) program to handle a graceful restart.
-When, however, the value is > 0, Linux's reaction to a Vulcan
-Nerve Pinch (tm) will be an immediate reboot, without even
-syncing its dirty buffers.
-
-Note: when a program (like dosemu) has the keyboard in 'raw'
-mode, the ctrl-alt-del is intercepted by the program before it
-ever reaches the kernel tty layer, and it's up to the program
-to decide what to do with it.
-
-==============================================================
-
-dmesg_restrict:
-
-This toggle indicates whether unprivileged users are prevented
-from using dmesg(8) to view messages from the kernel's log buffer.
-When dmesg_restrict is set to (0) there are no restrictions. When
-dmesg_restrict is set set to (1), users must have CAP_SYSLOG to use
-dmesg(8).
-
-The kernel config option CONFIG_SECURITY_DMESG_RESTRICT sets the
-default value of dmesg_restrict.
-
-==============================================================
-
-domainname & hostname:
-
-These files can be used to set the NIS/YP domainname and the
-hostname of your box in exactly the same way as the commands
-domainname and hostname, i.e.:
-# echo "darkstar" > /proc/sys/kernel/hostname
-# echo "mydomain" > /proc/sys/kernel/domainname
-has the same effect as
-# hostname "darkstar"
-# domainname "mydomain"
-
-Note, however, that the classic darkstar.frop.org has the
-hostname "darkstar" and DNS (Internet Domain Name Server)
-domainname "frop.org", not to be confused with the NIS (Network
-Information Service) or YP (Yellow Pages) domainname. These two
-domain names are in general different. For a detailed discussion
-see the hostname(1) man page.
-
-==============================================================
-
-hotplug:
-
-Path for the hotplug policy agent.
-Default value is "/sbin/hotplug".
-
-==============================================================
-
-kptr_restrict:
-
-This toggle indicates whether restrictions are placed on
-exposing kernel addresses via /proc and other interfaces. When
-kptr_restrict is set to (0), there are no restrictions. When
-kptr_restrict is set to (1), the default, kernel pointers
-printed using the %pK format specifier will be replaced with 0's
-unless the user has CAP_SYSLOG. When kptr_restrict is set to
-(2), kernel pointers printed using %pK will be replaced with 0's
-regardless of privileges.
-
-==============================================================
-
-kstack_depth_to_print: (X86 only)
-
-Controls the number of words to print when dumping the raw
-kernel stack.
-
-==============================================================
-
-l2cr: (PPC only)
-
-This flag controls the L2 cache of G3 processor boards. If
-0, the cache is disabled. Enabled if nonzero.
-
-==============================================================
-
-modules_disabled:
-
-A toggle value indicating if modules are allowed to be loaded
-in an otherwise modular kernel. This toggle defaults to off
-(0), but can be set true (1). Once true, modules can be
-neither loaded nor unloaded, and the toggle cannot be set back
-to false.
-
-==============================================================
-
-nmi_watchdog:
-
-Enables/Disables the NMI watchdog on x86 systems. When the value is
-non-zero the NMI watchdog is enabled and will continuously test all
-online cpus to determine whether or not they are still functioning
-properly. Currently, passing "nmi_watchdog=" parameter at boot time is
-required for this function to work.
-
-If LAPIC NMI watchdog method is in use (nmi_watchdog=2 kernel
-parameter), the NMI watchdog shares registers with oprofile. By
-disabling the NMI watchdog, oprofile may have more registers to
-utilize.
-
-==============================================================
-
-osrelease, ostype & version:
-
-# cat osrelease
-2.1.88
-# cat ostype
-Linux
-# cat version
-#5 Wed Feb 25 21:49:24 MET 1998
-
-The files osrelease and ostype should be clear enough. Version
-needs a little more clarification however. The '#5' means that
-this is the fifth kernel built from this source base and the
-date behind it indicates the time the kernel was built.
-The only way to tune these values is to rebuild the kernel :-)
-
-==============================================================
-
-overflowgid & overflowuid:
-
-if your architecture did not always support 32-bit UIDs (i.e. arm,
-i386, m68k, sh, and sparc32), a fixed UID and GID will be returned to
-applications that use the old 16-bit UID/GID system calls, if the
-actual UID or GID would exceed 65535.
-
-These sysctls allow you to change the value of the fixed UID and GID.
-The default is 65534.
-
-==============================================================
-
-panic:
-
-The value in this file represents the number of seconds the kernel
-waits before rebooting on a panic. When you use the software watchdog,
-the recommended setting is 60.
-
-==============================================================
-
-panic_on_unrecovered_nmi:
-
-The default Linux behaviour on an NMI of either memory or unknown is
-to continue operation. For many environments such as scientific
-computing it is preferable that the box is taken out and the error
-dealt with than an uncorrected parity/ECC error get propagated.
-
-A small number of systems do generate NMI's for bizarre random reasons
-such as power management so the default is off. That sysctl works like
-the existing panic controls already in that directory.
-
-==============================================================
-
-panic_on_oops:
-
-Controls the kernel's behaviour when an oops or BUG is encountered.
-
-0: try to continue operation
-
-1: panic immediately. If the `panic' sysctl is also non-zero then the
- machine will be rebooted.
-
-==============================================================
-
-panic_on_stackoverflow:
-
-Controls the kernel's behavior when detecting the overflows of
-kernel, IRQ and exception stacks except a user stack.
-This file shows up if CONFIG_DEBUG_STACKOVERFLOW is enabled.
-
-0: try to continue operation.
-
-1: panic immediately.
-
-==============================================================
-
-
-pid_max:
-
-PID allocation wrap value. When the kernel's next PID value
-reaches this value, it wraps back to a minimum PID value.
-PIDs of value pid_max or larger are not allocated.
-
-==============================================================
-
-ns_last_pid:
-
-The last pid allocated in the current (the one task using this sysctl
-lives in) pid namespace. When selecting a pid for a next task on fork
-kernel tries to allocate a number starting from this one.
-
-==============================================================
-
-powersave-nap: (PPC only)
-
-If set, Linux-PPC will use the 'nap' mode of powersaving,
-otherwise the 'doze' mode will be used.
-
-==============================================================
-
-printk:
-
-The four values in printk denote: console_loglevel,
-default_message_loglevel, minimum_console_loglevel and
-default_console_loglevel respectively.
-
-These values influence printk() behavior when printing or
-logging error messages. See 'man 2 syslog' for more info on
-the different loglevels.
-
-- console_loglevel: messages with a higher priority than
- this will be printed to the console
-- default_message_loglevel: messages without an explicit priority
- will be printed with this priority
-- minimum_console_loglevel: minimum (highest) value to which
- console_loglevel can be set
-- default_console_loglevel: default value for console_loglevel
-
-==============================================================
-
-printk_delay:
-
-Delay each printk message in printk_delay milliseconds
-
-Value from 0 - 10000 is allowed.
-
-==============================================================
-
-printk_ratelimit:
-
-Some warning messages are rate limited. printk_ratelimit specifies
-the minimum length of time between these messages (in jiffies), by
-default we allow one every 5 seconds.
-
-A value of 0 will disable rate limiting.
-
-==============================================================
-
-printk_ratelimit_burst:
-
-While long term we enforce one message per printk_ratelimit
-seconds, we do allow a burst of messages to pass through.
-printk_ratelimit_burst specifies the number of messages we can
-send before ratelimiting kicks in.
-
-==============================================================
-
-randomize_va_space:
-
-This option can be used to select the type of process address
-space randomization that is used in the system, for architectures
-that support this feature.
-
-0 - Turn the process address space randomization off. This is the
- default for architectures that do not support this feature anyways,
- and kernels that are booted with the "norandmaps" parameter.
-
-1 - Make the addresses of mmap base, stack and VDSO page randomized.
- This, among other things, implies that shared libraries will be
- loaded to random addresses. Also for PIE-linked binaries, the
- location of code start is randomized. This is the default if the
- CONFIG_COMPAT_BRK option is enabled.
-
-2 - Additionally enable heap randomization. This is the default if
- CONFIG_COMPAT_BRK is disabled.
-
- There are a few legacy applications out there (such as some ancient
- versions of libc.so.5 from 1996) that assume that brk area starts
- just after the end of the code+bss. These applications break when
- start of the brk area is randomized. There are however no known
- non-legacy applications that would be broken this way, so for most
- systems it is safe to choose full randomization.
-
- Systems with ancient and/or broken binaries should be configured
- with CONFIG_COMPAT_BRK enabled, which excludes the heap from process
- address space randomization.
-
-==============================================================
-
-reboot-cmd: (Sparc only)
-
-??? This seems to be a way to give an argument to the Sparc
-ROM/Flash boot loader. Maybe to tell it what to do after
-rebooting. ???
-
-==============================================================
-
-rtsig-max & rtsig-nr:
-
-The file rtsig-max can be used to tune the maximum number
-of POSIX realtime (queued) signals that can be outstanding
-in the system.
-
-rtsig-nr shows the number of RT signals currently queued.
-
-==============================================================
-
-sg-big-buff:
-
-This file shows the size of the generic SCSI (sg) buffer.
-You can't tune it just yet, but you could change it on
-compile time by editing include/scsi/sg.h and changing
-the value of SG_BIG_BUFF.
-
-There shouldn't be any reason to change this value. If
-you can come up with one, you probably know what you
-are doing anyway :)
-
-==============================================================
-
-shmmax:
-
-This value can be used to query and set the run time limit
-on the maximum shared memory segment size that can be created.
-Shared memory segments up to 1Gb are now supported in the
-kernel. This value defaults to SHMMAX.
-
-==============================================================
-
-shm_rmid_forced:
-
-Linux lets you set resource limits, including how much memory one
-process can consume, via setrlimit(2). Unfortunately, shared memory
-segments are allowed to exist without association with any process, and
-thus might not be counted against any resource limits. If enabled,
-shared memory segments are automatically destroyed when their attach
-count becomes zero after a detach or a process termination. It will
-also destroy segments that were created, but never attached to, on exit
-from the process. The only use left for IPC_RMID is to immediately
-destroy an unattached segment. Of course, this breaks the way things are
-defined, so some applications might stop working. Note that this
-feature will do you no good unless you also configure your resource
-limits (in particular, RLIMIT_AS and RLIMIT_NPROC). Most systems don't
-need this.
-
-Note that if you change this from 0 to 1, already created segments
-without users and with a dead originative process will be destroyed.
-
-==============================================================
-
-softlockup_thresh:
-
-This value can be used to lower the softlockup tolerance threshold. The
-default threshold is 60 seconds. If a cpu is locked up for 60 seconds,
-the kernel complains. Valid values are 1-60 seconds. Setting this
-tunable to zero will disable the softlockup detection altogether.
-
-==============================================================
-
-tainted:
-
-Non-zero if the kernel has been tainted. Numeric values, which
-can be ORed together:
-
- 1 - A module with a non-GPL license has been loaded, this
- includes modules with no license.
- Set by modutils >= 2.4.9 and module-init-tools.
- 2 - A module was force loaded by insmod -f.
- Set by modutils >= 2.4.9 and module-init-tools.
- 4 - Unsafe SMP processors: SMP with CPUs not designed for SMP.
- 8 - A module was forcibly unloaded from the system by rmmod -f.
- 16 - A hardware machine check error occurred on the system.
- 32 - A bad page was discovered on the system.
- 64 - The user has asked that the system be marked "tainted". This
- could be because they are running software that directly modifies
- the hardware, or for other reasons.
- 128 - The system has died.
- 256 - The ACPI DSDT has been overridden with one supplied by the user
- instead of using the one provided by the hardware.
- 512 - A kernel warning has occurred.
-1024 - A module from drivers/staging was loaded.
-2048 - The system is working around a severe firmware bug.
-4096 - An out-of-tree module has been loaded.
-
-==============================================================
-
-unknown_nmi_panic:
-
-The value in this file affects behavior of handling NMI. When the
-value is non-zero, unknown NMI is trapped and then panic occurs. At
-that time, kernel debugging information is displayed on console.
-
-NMI switch that most IA32 servers have fires unknown NMI up, for
-example. If a system hangs up, try pressing the NMI switch.