![Dave Hansen](/assets/img/avatar_default.png)
This patch keeps track of how long perf's NMI handler is taking, and also calculates how many samples perf can take a second. If the sample length times the expected max number of samples exceeds a configurable threshold, it drops the sample rate. This way, we don't have a runaway sampling process eating up the CPU. This patch can tend to drop the sample rate down to level where perf doesn't work very well. *BUT* the alternative is that my system hangs because it spends all of its time handling NMIs. I'll take a busted performance tool over an entire system that's busted and undebuggable any day. BTW, my suspicion is that there's still an underlying bug here. Using the HPET instead of the TSC is definitely a contributing factor, but I suspect there are some other things going on. But, I can't go dig down on a bug like that with my machine hanging all the time. Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: paulus@samba.org Cc: acme@ghostprotocols.net Cc: Dave Hansen <dave@sr71.net> [ Prettified it a bit. ] Signed-off-by: Ingo Molnar <mingo@kernel.org>
681 lines
23 KiB
Plaintext
681 lines
23 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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- acct
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- acpi_video_flags
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- auto_msgmni
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- bootloader_type [ X86 only ]
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- bootloader_version [ X86 only ]
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- callhome [ S390 only ]
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- cap_last_cap
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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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- dmesg_restrict
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- domainname
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- hostname
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- hotplug
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- kptr_restrict
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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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- msg_next_id [ sysv ipc ]
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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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- panic_on_oops
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- panic_on_unrecovered_nmi
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- panic_on_stackoverflow
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- pid_max
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- powersave-nap [ PPC only ]
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- printk
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- printk_delay
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- printk_ratelimit
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- printk_ratelimit_burst
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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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- sem_next_id [ sysv ipc ]
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- sg-big-buff [ generic SCSI device (sg) ]
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- shm_next_id [ sysv ipc ]
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- shm_rmid_forced
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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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- watchdog_thresh
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- version
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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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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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auto_msgmni:
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Enables/Disables automatic recomputing of msgmni upon memory add/remove
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or upon ipc namespace creation/removal (see the msgmni description
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above). Echoing "1" into this file enables msgmni automatic recomputing.
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Echoing "0" turns it off. auto_msgmni default value is 1.
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==============================================================
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bootloader_type:
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x86 bootloader identification
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This gives the bootloader type number as indicated by the bootloader,
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shifted left by 4, and OR'd with the low four bits of the bootloader
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version. The reason for this encoding is that this used to match the
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type_of_loader field in the kernel header; the encoding is kept for
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backwards compatibility. That is, if the full bootloader type number
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is 0x15 and the full version number is 0x234, this file will contain
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the value 340 = 0x154.
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See the type_of_loader and ext_loader_type fields in
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Documentation/x86/boot.txt for additional information.
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==============================================================
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bootloader_version:
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x86 bootloader version
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The complete bootloader version number. In the example above, this
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file will contain the value 564 = 0x234.
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See the type_of_loader and ext_loader_ver fields in
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Documentation/x86/boot.txt for additional information.
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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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cap_last_cap
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Highest valid capability of the running kernel. Exports
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CAP_LAST_CAP from the kernel.
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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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%d dump mode, matches PR_SET_DUMPABLE and
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/proc/sys/fs/suid_dumpable
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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 (may be shortened)
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%E executable path
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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
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core files to a user space helper (when the first character of
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core_pattern is a '|', see above). When collecting cores via a pipe
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to an application, it is occasionally useful for the collecting
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application to gather data about the crashing process from its
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/proc/pid directory. In order to do this safely, the kernel must wait
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for the collecting process to exit, so as not to remove the crashing
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processes proc files prematurely. This in turn creates the
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possibility that a misbehaving userspace collecting process can block
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the reaping of a crashed process simply by never exiting. This sysctl
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defends against that. It defines how many concurrent crashing
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processes may be piped to user space applications in parallel. If
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this value is exceeded, then those crashing processes above that value
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are noted via the kernel log and their cores are skipped. 0 is a
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special value, indicating that unlimited processes may be captured in
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parallel, but that no waiting will take place (i.e. the collecting
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process is not guaranteed access to /proc/<crashing pid>/). This
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value defaults 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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dmesg_restrict:
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This toggle indicates whether unprivileged users are prevented
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from using dmesg(8) to view messages from the kernel's log buffer.
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When dmesg_restrict is set to (0) there are no restrictions. When
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dmesg_restrict is set set to (1), users must have CAP_SYSLOG to use
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dmesg(8).
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The kernel config option CONFIG_SECURITY_DMESG_RESTRICT sets the
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default value of dmesg_restrict.
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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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kptr_restrict:
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This toggle indicates whether restrictions are placed on
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exposing kernel addresses via /proc and other interfaces. When
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kptr_restrict is set to (0), there are no restrictions. When
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kptr_restrict is set to (1), the default, kernel pointers
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printed using the %pK format specifier will be replaced with 0's
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unless the user has CAP_SYSLOG. When kptr_restrict is set to
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(2), kernel pointers printed using %pK will be replaced with 0's
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regardless of privileges.
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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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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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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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msg_next_id, sem_next_id, and shm_next_id:
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These three toggles allows to specify desired id for next allocated IPC
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object: message, semaphore or shared memory respectively.
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By default they are equal to -1, which means generic allocation logic.
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Possible values to set are in range {0..INT_MAX}.
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Notes:
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1) kernel doesn't guarantee, that new object will have desired id. So,
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it's up to userspace, how to handle an object with "wrong" id.
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2) Toggle with non-default value will be set back to -1 by kernel after
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successful IPC object allocation.
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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
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non-zero the NMI watchdog is enabled and will continuously test all
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online cpus to determine whether or not they are still functioning
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properly. Currently, passing "nmi_watchdog=" parameter at boot time is
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required for this function to work.
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If LAPIC NMI watchdog method is in use (nmi_watchdog=2 kernel
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parameter), the NMI watchdog shares registers with oprofile. By
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disabling the NMI watchdog, oprofile may have more registers to
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utilize.
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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,
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i386, 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
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actual 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 kernel
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waits before rebooting on a panic. When you use the software watchdog,
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the recommended setting is 60.
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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
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to continue operation. For many environments such as scientific
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computing it is preferable that the box is taken out and the error
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dealt with than an uncorrected parity/ECC error get propagated.
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A small number of systems do generate NMI's for bizarre random reasons
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such as power management so the default is off. That sysctl works like
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the existing panic controls already in that directory.
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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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panic_on_stackoverflow:
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Controls the kernel's behavior when detecting the overflows of
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kernel, IRQ and exception stacks except a user stack.
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This file shows up if CONFIG_DEBUG_STACKOVERFLOW is enabled.
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0: try to continue operation.
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1: panic immediately.
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==============================================================
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perf_cpu_time_max_percent:
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Hints to the kernel how much CPU time it should be allowed to
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use to handle perf sampling events. If the perf subsystem
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is informed that its samples are exceeding this limit, it
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will drop its sampling frequency to attempt to reduce its CPU
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usage.
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Some perf sampling happens in NMIs. If these samples
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unexpectedly take too long to execute, the NMIs can become
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stacked up next to each other so much that nothing else is
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allowed to execute.
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0: disable the mechanism. Do not monitor or correct perf's
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sampling rate no matter how CPU time it takes.
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1-100: attempt to throttle perf's sample rate to this
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percentage of CPU. Note: the kernel calculates an
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"expected" length of each sample event. 100 here means
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100% of that expected length. Even if this is set to
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100, you may still see sample throttling if this
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length is exceeded. Set to 0 if you truly do not care
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how much CPU is consumed.
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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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ns_last_pid:
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The last pid allocated in the current (the one task using this sysctl
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lives in) pid namespace. When selecting a pid for a next task on fork
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kernel tries to allocate a number starting from this one.
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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_loglevel: 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_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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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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randomize_va_space:
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|
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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.
|
|
|
|
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 :)
|
|
|
|
==============================================================
|
|
|
|
shmall:
|
|
|
|
This parameter sets the total amount of shared memory pages that
|
|
can be used system wide. Hence, SHMALL should always be at least
|
|
ceil(shmmax/PAGE_SIZE).
|
|
|
|
If you are not sure what the default PAGE_SIZE is on your Linux
|
|
system, you can run the following command:
|
|
|
|
# getconf PAGE_SIZE
|
|
|
|
==============================================================
|
|
|
|
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.
|
|
|
|
==============================================================
|
|
|
|
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.
|
|
|
|
==============================================================
|
|
|
|
watchdog_thresh:
|
|
|
|
This value can be used to control the frequency of hrtimer and NMI
|
|
events and the soft and hard lockup thresholds. The default threshold
|
|
is 10 seconds.
|
|
|
|
The softlockup threshold is (2 * watchdog_thresh). Setting this
|
|
tunable to zero will disable lockup detection altogether.
|
|
|
|
==============================================================
|