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Diffstat (limited to 'Documentation/sysctl/kernel.txt')
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diff --git a/Documentation/sysctl/kernel.txt b/Documentation/sysctl/kernel.txt new file mode 100644 index 00000000..6d78841f --- /dev/null +++ b/Documentation/sysctl/kernel.txt @@ -0,0 +1,616 @@ +Documentation for /proc/sys/kernel/* kernel version 2.2.10 + (c) 1998, 1999, Rik van Riel <riel@nl.linux.org> + (c) 2009, Shen Feng<shen@cn.fujitsu.com> + +For general info and legal blurb, please look in README. + +============================================================== + +This file contains documentation for the sysctl files in +/proc/sys/kernel/ and is valid for Linux kernel version 2.2. + +The files in this directory can be used to tune and monitor +miscellaneous and general things in the operation of the Linux +kernel. Since some of the files _can_ be used to screw up your +system, it is advisable to read both documentation and source +before actually making adjustments. + +Currently, these files might (depending on your configuration) +show up in /proc/sys/kernel: + +- acct +- acpi_video_flags +- auto_msgmni +- bootloader_type [ X86 only ] +- bootloader_version [ X86 only ] +- callhome [ S390 only ] +- cap_last_cap +- core_pattern +- core_pipe_limit +- core_uses_pid +- ctrl-alt-del +- dmesg_restrict +- domainname +- hostname +- hotplug +- kptr_restrict +- kstack_depth_to_print [ X86 only ] +- l2cr [ PPC only ] +- modprobe ==> Documentation/debugging-modules.txt +- modules_disabled +- msgmax +- msgmnb +- msgmni +- nmi_watchdog +- osrelease +- ostype +- overflowgid +- overflowuid +- panic +- panic_on_oops +- panic_on_unrecovered_nmi +- panic_on_stackoverflow +- pid_max +- powersave-nap [ PPC only ] +- printk +- printk_delay +- printk_ratelimit +- printk_ratelimit_burst +- randomize_va_space +- real-root-dev ==> Documentation/initrd.txt +- reboot-cmd [ SPARC only ] +- rtsig-max +- rtsig-nr +- sem +- sg-big-buff [ generic SCSI device (sg) ] +- shm_rmid_forced +- shmall +- shmmax [ sysv ipc ] +- shmmni +- softlockup_thresh +- stop-a [ SPARC only ] +- sysrq ==> Documentation/sysrq.txt +- tainted +- threads-max +- unknown_nmi_panic +- version + +============================================================== + +acct: + +highwater lowwater frequency + +If BSD-style process accounting is enabled these values control +its behaviour. If free space on filesystem where the log lives +goes below <lowwater>% accounting suspends. If free space gets +above <highwater>% accounting resumes. <Frequency> determines +how often do we check the amount of free space (value is in +seconds). Default: +4 2 30 +That is, suspend accounting if there left <= 2% free; resume it +if we got >=4%; consider information about amount of free space +valid for 30 seconds. + +============================================================== + +acpi_video_flags: + +flags + +See Doc*/kernel/power/video.txt, it allows mode of video boot to be +set during run time. + +============================================================== + +auto_msgmni: + +Enables/Disables automatic recomputing of msgmni upon memory add/remove +or upon ipc namespace creation/removal (see the msgmni description +above). Echoing "1" into this file enables msgmni automatic recomputing. +Echoing "0" turns it off. auto_msgmni default value is 1. + + +============================================================== + +bootloader_type: + +x86 bootloader identification + +This gives the bootloader type number as indicated by the bootloader, +shifted left by 4, and OR'd with the low four bits of the bootloader +version. The reason for this encoding is that this used to match the +type_of_loader field in the kernel header; the encoding is kept for +backwards compatibility. That is, if the full bootloader type number +is 0x15 and the full version number is 0x234, this file will contain +the value 340 = 0x154. + +See the type_of_loader and ext_loader_type fields in +Documentation/x86/boot.txt for additional information. + +============================================================== + +bootloader_version: + +x86 bootloader version + +The complete bootloader version number. In the example above, this +file will contain the value 564 = 0x234. + +See the type_of_loader and ext_loader_ver fields in +Documentation/x86/boot.txt for additional information. + +============================================================== + +callhome: + +Controls the kernel's callhome behavior in case of a kernel panic. + +The s390 hardware allows an operating system to send a notification +to a service organization (callhome) in case of an operating system panic. + +When the value in this file is 0 (which is the default behavior) +nothing happens in case of a kernel panic. If this value is set to "1" +the complete kernel oops message is send to the IBM customer service +organization in case the mainframe the Linux operating system is running +on has a service contract with IBM. + +============================================================== + +cap_last_cap + +Highest valid capability of the running kernel. Exports +CAP_LAST_CAP from the kernel. + +============================================================== + +core_pattern: + +core_pattern is used to specify a core dumpfile pattern name. +. max length 128 characters; default value is "core" +. core_pattern is used as a pattern template for the output filename; + certain string patterns (beginning with '%') are substituted with + their actual values. +. backward compatibility with core_uses_pid: + If core_pattern does not include "%p" (default does not) + and core_uses_pid is set, then .PID will be appended to + the filename. +. corename format specifiers: + %<NUL> '%' is dropped + %% output one '%' + %p pid + %u uid + %g gid + %s signal number + %t UNIX time of dump + %h hostname + %e executable filename (may be shortened) + %E executable path + %<OTHER> both are dropped +. If the first character of the pattern is a '|', the kernel will treat + the rest of the pattern as a command to run. The core dump will be + written to the standard input of that program instead of to a file. + +============================================================== + +core_pipe_limit: + +This sysctl is only applicable when core_pattern is configured to pipe +core files to a user space helper (when the first character of +core_pattern is a '|', see above). When collecting cores via a pipe +to an application, it is occasionally useful for the collecting +application to gather data about the crashing process from its +/proc/pid directory. In order to do this safely, the kernel must wait +for the collecting process to exit, so as not to remove the crashing +processes proc files prematurely. This in turn creates the +possibility that a misbehaving userspace collecting process can block +the reaping of a crashed process simply by never exiting. This sysctl +defends against that. It defines how many concurrent crashing +processes may be piped to user space applications in parallel. If +this value is exceeded, then those crashing processes above that value +are noted via the kernel log and their cores are skipped. 0 is a +special value, indicating that unlimited processes may be captured in +parallel, but that no waiting will take place (i.e. the collecting +process is not guaranteed access to /proc/<crashing pid>/). This +value defaults to 0. + +============================================================== + +core_uses_pid: + +The default coredump filename is "core". By setting +core_uses_pid to 1, the coredump filename becomes core.PID. +If core_pattern does not include "%p" (default does not) +and core_uses_pid is set, then .PID will be appended to +the filename. + +============================================================== + +ctrl-alt-del: + +When the value in this file is 0, ctrl-alt-del is trapped and +sent to the init(1) program to handle a graceful restart. +When, however, the value is > 0, Linux's reaction to a Vulcan +Nerve Pinch (tm) will be an immediate reboot, without even +syncing its dirty buffers. + +Note: when a program (like dosemu) has the keyboard in 'raw' +mode, the ctrl-alt-del is intercepted by the program before it +ever reaches the kernel tty layer, and it's up to the program +to decide what to do with it. + +============================================================== + +dmesg_restrict: + +This toggle indicates whether unprivileged users are prevented +from using dmesg(8) to view messages from the kernel's log buffer. +When dmesg_restrict is set to (0) there are no restrictions. When +dmesg_restrict is set set to (1), users must have CAP_SYSLOG to use +dmesg(8). + +The kernel config option CONFIG_SECURITY_DMESG_RESTRICT sets the +default value of dmesg_restrict. + +============================================================== + +domainname & hostname: + +These files can be used to set the NIS/YP domainname and the +hostname of your box in exactly the same way as the commands +domainname and hostname, i.e.: +# echo "darkstar" > /proc/sys/kernel/hostname +# echo "mydomain" > /proc/sys/kernel/domainname +has the same effect as +# hostname "darkstar" +# domainname "mydomain" + +Note, however, that the classic darkstar.frop.org has the +hostname "darkstar" and DNS (Internet Domain Name Server) +domainname "frop.org", not to be confused with the NIS (Network +Information Service) or YP (Yellow Pages) domainname. These two +domain names are in general different. For a detailed discussion +see the hostname(1) man page. + +============================================================== + +hotplug: + +Path for the hotplug policy agent. +Default value is "/sbin/hotplug". + +============================================================== + +kptr_restrict: + +This toggle indicates whether restrictions are placed on +exposing kernel addresses via /proc and other interfaces. When +kptr_restrict is set to (0), there are no restrictions. When +kptr_restrict is set to (1), the default, kernel pointers +printed using the %pK format specifier will be replaced with 0's +unless the user has CAP_SYSLOG. When kptr_restrict is set to +(2), kernel pointers printed using %pK will be replaced with 0's +regardless of privileges. + +============================================================== + +kstack_depth_to_print: (X86 only) + +Controls the number of words to print when dumping the raw +kernel stack. + +============================================================== + +l2cr: (PPC only) + +This flag controls the L2 cache of G3 processor boards. If +0, the cache is disabled. Enabled if nonzero. + +============================================================== + +modules_disabled: + +A toggle value indicating if modules are allowed to be loaded +in an otherwise modular kernel. This toggle defaults to off +(0), but can be set true (1). Once true, modules can be +neither loaded nor unloaded, and the toggle cannot be set back +to false. + +============================================================== + +nmi_watchdog: + +Enables/Disables the NMI watchdog on x86 systems. When the value is +non-zero the NMI watchdog is enabled and will continuously test all +online cpus to determine whether or not they are still functioning +properly. Currently, passing "nmi_watchdog=" parameter at boot time is +required for this function to work. + +If LAPIC NMI watchdog method is in use (nmi_watchdog=2 kernel +parameter), the NMI watchdog shares registers with oprofile. By +disabling the NMI watchdog, oprofile may have more registers to +utilize. + +============================================================== + +osrelease, ostype & version: + +# cat osrelease +2.1.88 +# cat ostype +Linux +# cat version +#5 Wed Feb 25 21:49:24 MET 1998 + +The files osrelease and ostype should be clear enough. Version +needs a little more clarification however. The '#5' means that +this is the fifth kernel built from this source base and the +date behind it indicates the time the kernel was built. +The only way to tune these values is to rebuild the kernel :-) + +============================================================== + +overflowgid & overflowuid: + +if your architecture did not always support 32-bit UIDs (i.e. arm, +i386, m68k, sh, and sparc32), a fixed UID and GID will be returned to +applications that use the old 16-bit UID/GID system calls, if the +actual UID or GID would exceed 65535. + +These sysctls allow you to change the value of the fixed UID and GID. +The default is 65534. + +============================================================== + +panic: + +The value in this file represents the number of seconds the kernel +waits before rebooting on a panic. When you use the software watchdog, +the recommended setting is 60. + +============================================================== + +panic_on_unrecovered_nmi: + +The default Linux behaviour on an NMI of either memory or unknown is +to continue operation. For many environments such as scientific +computing it is preferable that the box is taken out and the error +dealt with than an uncorrected parity/ECC error get propagated. + +A small number of systems do generate NMI's for bizarre random reasons +such as power management so the default is off. That sysctl works like +the existing panic controls already in that directory. + +============================================================== + +panic_on_oops: + +Controls the kernel's behaviour when an oops or BUG is encountered. + +0: try to continue operation + +1: panic immediately. If the `panic' sysctl is also non-zero then the + machine will be rebooted. + +============================================================== + +panic_on_stackoverflow: + +Controls the kernel's behavior when detecting the overflows of +kernel, IRQ and exception stacks except a user stack. +This file shows up if CONFIG_DEBUG_STACKOVERFLOW is enabled. + +0: try to continue operation. + +1: panic immediately. + +============================================================== + + +pid_max: + +PID allocation wrap value. When the kernel's next PID value +reaches this value, it wraps back to a minimum PID value. +PIDs of value pid_max or larger are not allocated. + +============================================================== + +ns_last_pid: + +The last pid allocated in the current (the one task using this sysctl +lives in) pid namespace. When selecting a pid for a next task on fork +kernel tries to allocate a number starting from this one. + +============================================================== + +powersave-nap: (PPC only) + +If set, Linux-PPC will use the 'nap' mode of powersaving, +otherwise the 'doze' mode will be used. + +============================================================== + +printk: + +The four values in printk denote: console_loglevel, +default_message_loglevel, minimum_console_loglevel and +default_console_loglevel respectively. + +These values influence printk() behavior when printing or +logging error messages. See 'man 2 syslog' for more info on +the different loglevels. + +- console_loglevel: messages with a higher priority than + this will be printed to the console +- default_message_loglevel: messages without an explicit priority + will be printed with this priority +- minimum_console_loglevel: minimum (highest) value to which + console_loglevel can be set +- default_console_loglevel: default value for console_loglevel + +============================================================== + +printk_delay: + +Delay each printk message in printk_delay milliseconds + +Value from 0 - 10000 is allowed. + +============================================================== + +printk_ratelimit: + +Some warning messages are rate limited. printk_ratelimit specifies +the minimum length of time between these messages (in jiffies), by +default we allow one every 5 seconds. + +A value of 0 will disable rate limiting. + +============================================================== + +printk_ratelimit_burst: + +While long term we enforce one message per printk_ratelimit +seconds, we do allow a burst of messages to pass through. +printk_ratelimit_burst specifies the number of messages we can +send before ratelimiting kicks in. + +============================================================== + +randomize_va_space: + +This option can be used to select the type of process address +space randomization that is used in the system, for architectures +that support this feature. + +0 - Turn the process address space randomization off. This is the + default for architectures that do not support this feature anyways, + and kernels that are booted with the "norandmaps" parameter. + +1 - Make the addresses of mmap base, stack and VDSO page randomized. + This, among other things, implies that shared libraries will be + loaded to random addresses. Also for PIE-linked binaries, the + location of code start is randomized. This is the default if the + CONFIG_COMPAT_BRK option is enabled. + +2 - Additionally enable heap randomization. This is the default if + CONFIG_COMPAT_BRK is disabled. + + There are a few legacy applications out there (such as some ancient + versions of libc.so.5 from 1996) that assume that brk area starts + just after the end of the code+bss. These applications break when + start of the brk area is randomized. There are however no known + non-legacy applications that would be broken this way, so for most + systems it is safe to choose full randomization. + + Systems with ancient and/or broken binaries should be configured + with CONFIG_COMPAT_BRK enabled, which excludes the heap from process + address space randomization. + +============================================================== + +reboot-cmd: (Sparc only) + +??? This seems to be a way to give an argument to the Sparc +ROM/Flash boot loader. Maybe to tell it what to do after +rebooting. ??? + +============================================================== + +rtsig-max & rtsig-nr: + +The file rtsig-max can be used to tune the maximum number +of POSIX realtime (queued) signals that can be outstanding +in the system. + +rtsig-nr shows the number of RT signals currently queued. + +============================================================== + +sg-big-buff: + +This file shows the size of the generic SCSI (sg) buffer. +You can't tune it just yet, but you could change it on +compile time by editing include/scsi/sg.h and changing +the value of SG_BIG_BUFF. + +There shouldn't be any reason to change this value. If +you can come up with one, you probably know what you +are doing anyway :) + +============================================================== + +shmmax: + +This value can be used to query and set the run time limit +on the maximum shared memory segment size that can be created. +Shared memory segments up to 1Gb are now supported in the +kernel. This value defaults to SHMMAX. + +============================================================== + +shm_rmid_forced: + +Linux lets you set resource limits, including how much memory one +process can consume, via setrlimit(2). Unfortunately, shared memory +segments are allowed to exist without association with any process, and +thus might not be counted against any resource limits. If enabled, +shared memory segments are automatically destroyed when their attach +count becomes zero after a detach or a process termination. It will +also destroy segments that were created, but never attached to, on exit +from the process. The only use left for IPC_RMID is to immediately +destroy an unattached segment. Of course, this breaks the way things are +defined, so some applications might stop working. Note that this +feature will do you no good unless you also configure your resource +limits (in particular, RLIMIT_AS and RLIMIT_NPROC). Most systems don't +need this. + +Note that if you change this from 0 to 1, already created segments +without users and with a dead originative process will be destroyed. + +============================================================== + +softlockup_thresh: + +This value can be used to lower the softlockup tolerance threshold. The +default threshold is 60 seconds. If a cpu is locked up for 60 seconds, +the kernel complains. Valid values are 1-60 seconds. Setting this +tunable to zero will disable the softlockup detection altogether. + +============================================================== + +tainted: + +Non-zero if the kernel has been tainted. Numeric values, which +can be ORed together: + + 1 - A module with a non-GPL license has been loaded, this + includes modules with no license. + Set by modutils >= 2.4.9 and module-init-tools. + 2 - A module was force loaded by insmod -f. + Set by modutils >= 2.4.9 and module-init-tools. + 4 - Unsafe SMP processors: SMP with CPUs not designed for SMP. + 8 - A module was forcibly unloaded from the system by rmmod -f. + 16 - A hardware machine check error occurred on the system. + 32 - A bad page was discovered on the system. + 64 - The user has asked that the system be marked "tainted". This + could be because they are running software that directly modifies + the hardware, or for other reasons. + 128 - The system has died. + 256 - The ACPI DSDT has been overridden with one supplied by the user + instead of using the one provided by the hardware. + 512 - A kernel warning has occurred. +1024 - A module from drivers/staging was loaded. +2048 - The system is working around a severe firmware bug. +4096 - An out-of-tree module has been loaded. + +============================================================== + +unknown_nmi_panic: + +The value in this file affects behavior of handling NMI. When the +value is non-zero, unknown NMI is trapped and then panic occurs. At +that time, kernel debugging information is displayed on console. + +NMI switch that most IA32 servers have fires unknown NMI up, for +example. If a system hangs up, try pressing the NMI switch. |