Documentation: refresh sysctl/kernel.txt

Currently, these files might (depending on your configuration)

show up in /proc/sys/kernel:

- acpi_video_flags

- acct

- acpi_video_flags

- auto_msgmni

- bootloader_type	     [ X86 only ]

- bootloader_version	     [ X86 only ]

- callhome		     [ S390 only ]

- auto_msgmni

- core_pattern

- core_pipe_limit

- core_uses_pid

- ctrl-alt-del

- dentry-state

- dmesg_restrict

- domainname

- hostname

- hotplug

- java-appletviewer           [ binfmt_java, obsolete ]

- java-interpreter            [ binfmt_java, obsolete ]

- kptr_restrict

- kstack_depth_to_print       [ X86 only ]

- l2cr                        [ PPC only ]

- overflowgid

- overflowuid

- panic

- panic_on_oops

- panic_on_unrecovered_nmi

- pid_max

- powersave-nap               [ PPC only ]

- panic_on_unrecovered_nmi

- printk

- printk_delay

- printk_ratelimit

- printk_ratelimit_burst

- randomize_va_space

- real-root-dev               ==> Documentation/initrd.txt

- reboot-cmd                  [ SPARC only ]

- shmall

- shmmax                      [ sysv ipc ]

- shmmni

- softlockup_thresh

- stop-a                      [ SPARC only ]

- sysrq                       ==> Documentation/sysrq.txt

- tainted

==============================================================

acpi_video_flags:

flags

See Doc*/kernel/power/video.txt, it allows mode of video boot to be

set during run time.

==============================================================

acct:

highwater lowwater frequency

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:

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.

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.

==============================================================

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

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.

The kernel config option CONFIG_SECURITY_DMESG_RESTRICT sets the

default value of dmesg_restrict.

==============================================================

==============================================================

l2cr: (PPC only)

This flag controls the L2 cache of G3 processor boards. If

0, the cache is disabled. Enabled if nonzero.

==============================================================

kptr_restrict:

This toggle indicates whether restrictions are placed on

==============================================================

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

==============================================================

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

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.

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.

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.

==============================================================

==============================================================

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

==============================================================

printk_delay:

Delay each printk message in printk_delay milliseconds

Value from 0 - 10000 is allowed.

==============================================================

randomize-va-space:

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

==============================================================

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.

==============================================================

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.

==============================================================

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.

==============================================================

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 propogated.

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.

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.