| 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: |
| - acpi_video_flags |
| - acct |
| - callhome [ S390 only ] |
| - auto_msgmni |
| - 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/debugging-modules.txt |
| - modules_disabled |
| - msgmax |
| - msgmnb |
| - msgmni |
| - nmi_watchdog |
| - osrelease |
| - ostype |
| - overflowgid |
| - overflowuid |
| - panic |
| - pid_max |
| - powersave-nap [ PPC only ] |
| - panic_on_unrecovered_nmi |
| - printk |
| - 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) ] |
| - shmall |
| - shmmax [ sysv ipc ] |
| - shmmni |
| - stop-a [ SPARC only ] |
| - sysrq ==> Documentation/sysrq.txt |
| - tainted |
| - threads-max |
| - unknown_nmi_panic |
| - 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. |
| |
| ============================================================== |
| |
| 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. |
| |
| ============================================================== |
| |
| 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. |
| |
| ============================================================== |
| |
| 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. |
| |
| ============================================================== |
| |
| 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. |
| |
| ============================================================== |
| |
| 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. |
| |
| ============================================================== |
| |
| 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. |
| |
| ============================================================== |
| |
| 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. |
| |