Documentation/sysctl/kernel.txt - kernel/msm-4.9 - Gitiles

 Documentation for /proc/sys/kernel/*	kernel version 2.2.10
 	(c) 1998, 1999,  Rik van Riel <riel@nl.linux.org>

 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:
 - acpi_video_flags
 - acct
 - core_pattern
 - core_uses_pid
 - ctrl-alt-del
 - dentry-state
 - domainname
 - hostname
 - hotplug
 - java-appletviewer           [ binfmt_java, obsolete ]
 - java-interpreter            [ binfmt_java, obsolete ]
 - kstack_depth_to_print       [ X86 only ]
 - l2cr                        [ PPC only ]
 - modprobe                    ==> Documentation/kmod.txt
 - msgmax
 - msgmnb
 - msgmni
 - osrelease
 - ostype
 - overflowgid
 - overflowuid
 - panic
 - pid_max
 - powersave-nap               [ PPC only ]
 - printk
 - real-root-dev               ==> Documentation/initrd.txt
 - reboot-cmd                  [ SPARC only ]
 - rtsig-max
 - rtsig-nr
 - sem
 - sg-big-buff                 [ generic SCSI device (sg) ]
 - shmall
 - shmmax                      [ sysv ipc ]
 - shmmni
 - stop-a                      [ SPARC only ]
 - sysrq                       ==> Documentation/sysrq.txt
 - tainted
 - threads-max
 - version

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

 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 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.

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

 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
 	%<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_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.

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

 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".

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

 l2cr: (PPC only)

 This flag controls the L2 cache of G3 processor boards. If
 0, the cache is disabled. Enabled if nonzero.

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

 kstack_depth_to_print: (X86 only)

 Controls the number of words to print when dumping the raw
 kernel stack.

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

 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_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.

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

 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.

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

 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_level: 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_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.

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

 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.

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

 softlockup_thresh:

 This value can be used to lower the softlockup tolerance
 threshold. The default threshold is 10s.  If a cpu is locked up
 for 10s, the kernel complains.  Valid values are 1-60s.

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

 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.
	Documentation for /proc/sys/kernel/* kernel version 2.2.10
	(c) 1998, 1999, Rik van Riel <riel@nl.linux.org>

	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:
	- acpi_video_flags
	- acct
	- core_pattern
	- core_uses_pid
	- ctrl-alt-del
	- dentry-state
	- domainname
	- hostname
	- hotplug
	- java-appletviewer [ binfmt_java, obsolete ]
	- java-interpreter [ binfmt_java, obsolete ]
	- kstack_depth_to_print [ X86 only ]
	- l2cr [ PPC only ]
	- modprobe ==> Documentation/kmod.txt
	- msgmax
	- msgmnb
	- msgmni
	- osrelease
	- ostype
	- overflowgid
	- overflowuid
	- panic
	- pid_max
	- powersave-nap [ PPC only ]
	- printk
	- real-root-dev ==> Documentation/initrd.txt
	- reboot-cmd [ SPARC only ]
	- rtsig-max
	- rtsig-nr
	- sem
	- sg-big-buff [ generic SCSI device (sg) ]
	- shmall
	- shmmax [ sysv ipc ]
	- shmmni
	- stop-a [ SPARC only ]
	- sysrq ==> Documentation/sysrq.txt
	- tainted
	- threads-max
	- version

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

	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 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.

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

	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
	%<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_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.

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

	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".

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

	l2cr: (PPC only)

	This flag controls the L2 cache of G3 processor boards. If
	0, the cache is disabled. Enabled if nonzero.

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

	kstack_depth_to_print: (X86 only)

	Controls the number of words to print when dumping the raw
	kernel stack.

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

	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_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.

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

	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.

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

	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_level: 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_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.

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

	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.

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

	softlockup_thresh:

	This value can be used to lower the softlockup tolerance
	threshold. The default threshold is 10s. If a cpu is locked up
	for 10s, the kernel complains. Valid values are 1-60s.

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

	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.