1176 lines
37 KiB
ReStructuredText
1176 lines
37 KiB
ReStructuredText
===================================
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Documentation for /proc/sys/kernel/
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===================================
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kernel version 2.2.10
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Copyright (c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
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Copyright (c) 2009, Shen Feng<shen@cn.fujitsu.com>
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For general info and legal blurb, please look in index.rst.
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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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- 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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- hardlockup_all_cpu_backtrace
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- hardlockup_panic
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- hung_task_panic
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- hung_task_check_count
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- hung_task_timeout_secs
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- hung_task_check_interval_secs
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- hung_task_warnings
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- hyperv_record_panic_msg
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- kexec_load_disabled
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- kptr_restrict
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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_stackoverflow
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- panic_on_unrecovered_nmi
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- panic_on_warn
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- panic_print
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- panic_on_rcu_stall
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- perf_cpu_time_max_percent
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- perf_event_paranoid
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- perf_event_max_stack
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- perf_event_mlock_kb
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- perf_event_max_contexts_per_stack
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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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- pty ==> Documentation/filesystems/devpts.txt
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- randomize_va_space
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- real-root-dev ==> Documentation/admin-guide/initrd.rst
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- reboot-cmd [ SPARC only ]
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- rtsig-max
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- rtsig-nr
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- sched_energy_aware
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- seccomp/ ==> Documentation/userspace-api/seccomp_filter.rst
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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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- softlockup_all_cpu_backtrace
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- soft_watchdog
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- stack_erasing
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- stop-a [ SPARC only ]
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- sysrq ==> Documentation/admin-guide/sysrq.rst
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- sysctl_writes_strict
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- tainted ==> Documentation/admin-guide/tainted-kernels.rst
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- threads-max
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- unknown_nmi_panic
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- watchdog
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- watchdog_thresh
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- version
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acct:
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=====
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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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acpi_video_flags:
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=================
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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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auto_msgmni:
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============
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This variable has no effect and may be removed in future kernel
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releases. Reading it always returns 0.
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Up to Linux 3.17, it enabled/disabled automatic recomputing of msgmni
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upon memory add/remove or upon ipc namespace creation/removal.
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Echoing "1" into this file enabled msgmni automatic recomputing.
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Echoing "0" turned it off. auto_msgmni default value was 1.
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bootloader_type:
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================
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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.rst for additional information.
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bootloader_version:
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===================
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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.rst for additional information.
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cap_last_cap:
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=============
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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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core_pattern:
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=============
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core_pattern is used to specify a core dumpfile pattern name.
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* max length 127 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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%P global pid (init PID namespace)
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%i tid
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%I global tid (init PID namespace)
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%u uid (in initial user namespace)
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%g gid (in initial user namespace)
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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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core_pipe_limit:
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================
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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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core_uses_pid:
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==============
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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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ctrl-alt-del:
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=============
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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:
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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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dmesg_restrict:
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===============
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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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domainname & hostname:
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======================
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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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hardlockup_all_cpu_backtrace:
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=============================
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This value controls the hard lockup detector behavior when a hard
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lockup condition is detected as to whether or not to gather further
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debug information. If enabled, arch-specific all-CPU stack dumping
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will be initiated.
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0: do nothing. This is the default behavior.
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1: on detection capture more debug information.
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hardlockup_panic:
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=================
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This parameter can be used to control whether the kernel panics
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when a hard lockup is detected.
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0 - don't panic on hard lockup
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1 - panic on hard lockup
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See Documentation/admin-guide/lockup-watchdogs.rst for more information. This can
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also be set using the nmi_watchdog kernel parameter.
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hotplug:
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========
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Path for the hotplug policy agent.
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Default value is "/sbin/hotplug".
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hung_task_panic:
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================
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Controls the kernel's behavior when a hung task is detected.
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This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.
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0: continue operation. This is the default behavior.
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1: panic immediately.
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hung_task_check_count:
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======================
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The upper bound on the number of tasks that are checked.
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This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.
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hung_task_timeout_secs:
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=======================
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When a task in D state did not get scheduled
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for more than this value report a warning.
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This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.
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0: means infinite timeout - no checking done.
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Possible values to set are in range {0..LONG_MAX/HZ}.
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hung_task_check_interval_secs:
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==============================
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Hung task check interval. If hung task checking is enabled
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(see hung_task_timeout_secs), the check is done every
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hung_task_check_interval_secs seconds.
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This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.
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0 (default): means use hung_task_timeout_secs as checking interval.
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Possible values to set are in range {0..LONG_MAX/HZ}.
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hung_task_warnings:
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===================
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The maximum number of warnings to report. During a check interval
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if a hung task is detected, this value is decreased by 1.
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When this value reaches 0, no more warnings will be reported.
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This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.
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-1: report an infinite number of warnings.
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hyperv_record_panic_msg:
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========================
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Controls whether the panic kmsg data should be reported to Hyper-V.
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0: do not report panic kmsg data.
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1: report the panic kmsg data. This is the default behavior.
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kexec_load_disabled:
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====================
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A toggle indicating if the kexec_load syscall has been disabled. This
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value defaults to 0 (false: kexec_load enabled), but can be set to 1
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(true: kexec_load disabled). Once true, kexec can no longer be used, and
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the toggle cannot be set back to false. This allows a kexec image to be
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loaded before disabling the syscall, allowing a system to set up (and
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later use) an image without it being altered. Generally used together
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with the "modules_disabled" sysctl.
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kptr_restrict:
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==============
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This toggle indicates whether restrictions are placed on
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exposing kernel addresses via /proc and other interfaces.
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When kptr_restrict is set to 0 (the default) the address is hashed before
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printing. (This is the equivalent to %p.)
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When kptr_restrict is set to (1), kernel pointers printed using the %pK
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format specifier will be replaced with 0's unless the user has CAP_SYSLOG
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and effective user and group ids are equal to the real ids. This is
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because %pK checks are done at read() time rather than open() time, so
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if permissions are elevated between the open() and the read() (e.g via
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a setuid binary) then %pK will not leak kernel pointers to unprivileged
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users. Note, this is a temporary solution only. The correct long-term
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solution is to do the permission checks at open() time. Consider removing
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world read permissions from files that use %pK, and using dmesg_restrict
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to protect against uses of %pK in dmesg(8) if leaking kernel pointer
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values to unprivileged users is a concern.
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When kptr_restrict is set to (2), kernel pointers printed using
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%pK will be replaced with 0's regardless of privileges.
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l2cr: (PPC only)
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================
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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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modules_disabled:
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=================
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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. Generally used with the "kexec_load_disabled" toggle.
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msg_next_id, sem_next_id, and shm_next_id:
|
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==========================================
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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. If an IPC object allocation syscall
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fails, it is undefined if the value remains unmodified or is reset to -1.
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nmi_watchdog:
|
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=============
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This parameter can be used to control the NMI watchdog
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(i.e. the hard lockup detector) on x86 systems.
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0 - disable the hard lockup detector
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1 - enable the hard lockup detector
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The hard lockup detector monitors each CPU for its ability to respond to
|
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timer interrupts. The mechanism utilizes CPU performance counter registers
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that are programmed to generate Non-Maskable Interrupts (NMIs) periodically
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while a CPU is busy. Hence, the alternative name 'NMI watchdog'.
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The NMI watchdog is disabled by default if the kernel is running as a guest
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in a KVM virtual machine. This default can be overridden by adding::
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nmi_watchdog=1
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to the guest kernel command line (see Documentation/admin-guide/kernel-parameters.rst).
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numa_balancing:
|
|
===============
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Enables/disables automatic page fault based NUMA memory
|
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balancing. Memory is moved automatically to nodes
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that access it often.
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Enables/disables automatic NUMA memory balancing. On NUMA machines, there
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is a performance penalty if remote memory is accessed by a CPU. When this
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feature is enabled the kernel samples what task thread is accessing memory
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by periodically unmapping pages and later trapping a page fault. At the
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time of the page fault, it is determined if the data being accessed should
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be migrated to a local memory node.
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The unmapping of pages and trapping faults incur additional overhead that
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ideally is offset by improved memory locality but there is no universal
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guarantee. If the target workload is already bound to NUMA nodes then this
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feature should be disabled. Otherwise, if the system overhead from the
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feature is too high then the rate the kernel samples for NUMA hinting
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faults may be controlled by the numa_balancing_scan_period_min_ms,
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numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms,
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numa_balancing_scan_size_mb, and numa_balancing_settle_count sysctls.
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numa_balancing_scan_period_min_ms, numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms, numa_balancing_scan_size_mb
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===============================================================================================================================
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Automatic NUMA balancing scans tasks address space and unmaps pages to
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detect if pages are properly placed or if the data should be migrated to a
|
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memory node local to where the task is running. Every "scan delay" the task
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scans the next "scan size" number of pages in its address space. When the
|
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end of the address space is reached the scanner restarts from the beginning.
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In combination, the "scan delay" and "scan size" determine the scan rate.
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|
When "scan delay" decreases, the scan rate increases. The scan delay and
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hence the scan rate of every task is adaptive and depends on historical
|
|
behaviour. If pages are properly placed then the scan delay increases,
|
|
otherwise the scan delay decreases. The "scan size" is not adaptive but
|
|
the higher the "scan size", the higher the scan rate.
|
|
|
|
Higher scan rates incur higher system overhead as page faults must be
|
|
trapped and potentially data must be migrated. However, the higher the scan
|
|
rate, the more quickly a tasks memory is migrated to a local node if the
|
|
workload pattern changes and minimises performance impact due to remote
|
|
memory accesses. These sysctls control the thresholds for scan delays and
|
|
the number of pages scanned.
|
|
|
|
numa_balancing_scan_period_min_ms is the minimum time in milliseconds to
|
|
scan a tasks virtual memory. It effectively controls the maximum scanning
|
|
rate for each task.
|
|
|
|
numa_balancing_scan_delay_ms is the starting "scan delay" used for a task
|
|
when it initially forks.
|
|
|
|
numa_balancing_scan_period_max_ms is the maximum time in milliseconds to
|
|
scan a tasks virtual memory. It effectively controls the minimum scanning
|
|
rate for each task.
|
|
|
|
numa_balancing_scan_size_mb is how many megabytes worth of pages are
|
|
scanned for a given scan.
|
|
|
|
|
|
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_io_nmi:
|
|
================
|
|
|
|
Controls the kernel's behavior when a CPU receives an NMI caused by
|
|
an IO error.
|
|
|
|
0: try to continue operation (default)
|
|
|
|
1: panic immediately. The IO error triggered an NMI. This indicates a
|
|
serious system condition which could result in IO data corruption.
|
|
Rather than continuing, panicking might be a better choice. Some
|
|
servers issue this sort of NMI when the dump button is pushed,
|
|
and you can use this option to take a crash dump.
|
|
|
|
|
|
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.
|
|
|
|
|
|
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_warn:
|
|
==============
|
|
|
|
Calls panic() in the WARN() path when set to 1. This is useful to avoid
|
|
a kernel rebuild when attempting to kdump at the location of a WARN().
|
|
|
|
0: only WARN(), default behaviour.
|
|
|
|
1: call panic() after printing out WARN() location.
|
|
|
|
|
|
panic_print:
|
|
============
|
|
|
|
Bitmask for printing system info when panic happens. User can chose
|
|
combination of the following bits:
|
|
|
|
===== ========================================
|
|
bit 0 print all tasks info
|
|
bit 1 print system memory info
|
|
bit 2 print timer info
|
|
bit 3 print locks info if CONFIG_LOCKDEP is on
|
|
bit 4 print ftrace buffer
|
|
===== ========================================
|
|
|
|
So for example to print tasks and memory info on panic, user can::
|
|
|
|
echo 3 > /proc/sys/kernel/panic_print
|
|
|
|
|
|
panic_on_rcu_stall:
|
|
===================
|
|
|
|
When set to 1, calls panic() after RCU stall detection messages. This
|
|
is useful to define the root cause of RCU stalls using a vmcore.
|
|
|
|
0: do not panic() when RCU stall takes place, default behavior.
|
|
|
|
1: panic() after printing RCU stall messages.
|
|
|
|
|
|
perf_cpu_time_max_percent:
|
|
==========================
|
|
|
|
Hints to the kernel how much CPU time it should be allowed to
|
|
use to handle perf sampling events. If the perf subsystem
|
|
is informed that its samples are exceeding this limit, it
|
|
will drop its sampling frequency to attempt to reduce its CPU
|
|
usage.
|
|
|
|
Some perf sampling happens in NMIs. If these samples
|
|
unexpectedly take too long to execute, the NMIs can become
|
|
stacked up next to each other so much that nothing else is
|
|
allowed to execute.
|
|
|
|
0:
|
|
disable the mechanism. Do not monitor or correct perf's
|
|
sampling rate no matter how CPU time it takes.
|
|
|
|
1-100:
|
|
attempt to throttle perf's sample rate to this
|
|
percentage of CPU. Note: the kernel calculates an
|
|
"expected" length of each sample event. 100 here means
|
|
100% of that expected length. Even if this is set to
|
|
100, you may still see sample throttling if this
|
|
length is exceeded. Set to 0 if you truly do not care
|
|
how much CPU is consumed.
|
|
|
|
|
|
perf_event_paranoid:
|
|
====================
|
|
|
|
Controls use of the performance events system by unprivileged
|
|
users (without CAP_SYS_ADMIN). The default value is 2.
|
|
|
|
=== ==================================================================
|
|
-1 Allow use of (almost) all events by all users
|
|
|
|
Ignore mlock limit after perf_event_mlock_kb without CAP_IPC_LOCK
|
|
|
|
>=0 Disallow ftrace function tracepoint by users without CAP_SYS_ADMIN
|
|
|
|
Disallow raw tracepoint access by users without CAP_SYS_ADMIN
|
|
|
|
>=1 Disallow CPU event access by users without CAP_SYS_ADMIN
|
|
|
|
>=2 Disallow kernel profiling by users without CAP_SYS_ADMIN
|
|
=== ==================================================================
|
|
|
|
|
|
perf_event_max_stack:
|
|
=====================
|
|
|
|
Controls maximum number of stack frames to copy for (attr.sample_type &
|
|
PERF_SAMPLE_CALLCHAIN) configured events, for instance, when using
|
|
'perf record -g' or 'perf trace --call-graph fp'.
|
|
|
|
This can only be done when no events are in use that have callchains
|
|
enabled, otherwise writing to this file will return -EBUSY.
|
|
|
|
The default value is 127.
|
|
|
|
|
|
perf_event_mlock_kb:
|
|
====================
|
|
|
|
Control size of per-cpu ring buffer not counted agains mlock limit.
|
|
|
|
The default value is 512 + 1 page
|
|
|
|
|
|
perf_event_max_contexts_per_stack:
|
|
==================================
|
|
|
|
Controls maximum number of stack frame context entries for
|
|
(attr.sample_type & PERF_SAMPLE_CALLCHAIN) configured events, for
|
|
instance, when using 'perf record -g' or 'perf trace --call-graph fp'.
|
|
|
|
This can only be done when no events are in use that have callchains
|
|
enabled, otherwise writing to this file will return -EBUSY.
|
|
|
|
The default value is 8.
|
|
|
|
|
|
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 seconds).
|
|
The default value is 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.
|
|
|
|
The default value is 10 messages.
|
|
|
|
|
|
printk_devkmsg:
|
|
===============
|
|
|
|
Control the logging to /dev/kmsg from userspace:
|
|
|
|
ratelimit:
|
|
default, ratelimited
|
|
|
|
on: unlimited logging to /dev/kmsg from userspace
|
|
|
|
off: logging to /dev/kmsg disabled
|
|
|
|
The kernel command line parameter printk.devkmsg= overrides this and is
|
|
a one-time setting until next reboot: once set, it cannot be changed by
|
|
this sysctl interface anymore.
|
|
|
|
|
|
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.
|
|
|
|
|
|
sched_energy_aware:
|
|
===================
|
|
|
|
Enables/disables Energy Aware Scheduling (EAS). EAS starts
|
|
automatically on platforms where it can run (that is,
|
|
platforms with asymmetric CPU topologies and having an Energy
|
|
Model available). If your platform happens to meet the
|
|
requirements for EAS but you do not want to use it, change
|
|
this value to 0.
|
|
|
|
|
|
sched_schedstats:
|
|
=================
|
|
|
|
Enables/disables scheduler statistics. Enabling this feature
|
|
incurs a small amount of overhead in the scheduler but is
|
|
useful for debugging and performance tuning.
|
|
|
|
|
|
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.
|
|
|
|
|
|
sysctl_writes_strict:
|
|
=====================
|
|
|
|
Control how file position affects the behavior of updating sysctl values
|
|
via the /proc/sys interface:
|
|
|
|
== ======================================================================
|
|
-1 Legacy per-write sysctl value handling, with no printk warnings.
|
|
Each write syscall must fully contain the sysctl value to be
|
|
written, and multiple writes on the same sysctl file descriptor
|
|
will rewrite the sysctl value, regardless of file position.
|
|
0 Same behavior as above, but warn about processes that perform writes
|
|
to a sysctl file descriptor when the file position is not 0.
|
|
1 (default) Respect file position when writing sysctl strings. Multiple
|
|
writes will append to the sysctl value buffer. Anything past the max
|
|
length of the sysctl value buffer will be ignored. Writes to numeric
|
|
sysctl entries must always be at file position 0 and the value must
|
|
be fully contained in the buffer sent in the write syscall.
|
|
== ======================================================================
|
|
|
|
|
|
softlockup_all_cpu_backtrace:
|
|
=============================
|
|
|
|
This value controls the soft lockup detector thread's behavior
|
|
when a soft lockup condition is detected as to whether or not
|
|
to gather further debug information. If enabled, each cpu will
|
|
be issued an NMI and instructed to capture stack trace.
|
|
|
|
This feature is only applicable for architectures which support
|
|
NMI.
|
|
|
|
0: do nothing. This is the default behavior.
|
|
|
|
1: on detection capture more debug information.
|
|
|
|
|
|
soft_watchdog:
|
|
==============
|
|
|
|
This parameter can be used to control the soft lockup detector.
|
|
|
|
0 - disable the soft lockup detector
|
|
|
|
1 - enable the soft lockup detector
|
|
|
|
The soft lockup detector monitors CPUs for threads that are hogging the CPUs
|
|
without rescheduling voluntarily, and thus prevent the 'watchdog/N' threads
|
|
from running. The mechanism depends on the CPUs ability to respond to timer
|
|
interrupts which are needed for the 'watchdog/N' threads to be woken up by
|
|
the watchdog timer function, otherwise the NMI watchdog - if enabled - can
|
|
detect a hard lockup condition.
|
|
|
|
|
|
stack_erasing:
|
|
==============
|
|
|
|
This parameter can be used to control kernel stack erasing at the end
|
|
of syscalls for kernels built with CONFIG_GCC_PLUGIN_STACKLEAK.
|
|
|
|
That erasing reduces the information which kernel stack leak bugs
|
|
can reveal and blocks some uninitialized stack variable attacks.
|
|
The tradeoff is the performance impact: on a single CPU system kernel
|
|
compilation sees a 1% slowdown, other systems and workloads may vary.
|
|
|
|
0: kernel stack erasing is disabled, STACKLEAK_METRICS are not updated.
|
|
|
|
1: kernel stack erasing is enabled (default), it is performed before
|
|
returning to the userspace at the end of syscalls.
|
|
|
|
|
|
tainted
|
|
=======
|
|
|
|
Non-zero if the kernel has been tainted. Numeric values, which can be
|
|
ORed together. The letters are seen in "Tainted" line of Oops reports.
|
|
|
|
====== ===== ==============================================================
|
|
1 `(P)` proprietary module was loaded
|
|
2 `(F)` module was force loaded
|
|
4 `(S)` SMP kernel oops on an officially SMP incapable processor
|
|
8 `(R)` module was force unloaded
|
|
16 `(M)` processor reported a Machine Check Exception (MCE)
|
|
32 `(B)` bad page referenced or some unexpected page flags
|
|
64 `(U)` taint requested by userspace application
|
|
128 `(D)` kernel died recently, i.e. there was an OOPS or BUG
|
|
256 `(A)` an ACPI table was overridden by user
|
|
512 `(W)` kernel issued warning
|
|
1024 `(C)` staging driver was loaded
|
|
2048 `(I)` workaround for bug in platform firmware applied
|
|
4096 `(O)` externally-built ("out-of-tree") module was loaded
|
|
8192 `(E)` unsigned module was loaded
|
|
16384 `(L)` soft lockup occurred
|
|
32768 `(K)` kernel has been live patched
|
|
65536 `(X)` Auxiliary taint, defined and used by for distros
|
|
131072 `(T)` The kernel was built with the struct randomization plugin
|
|
====== ===== ==============================================================
|
|
|
|
See Documentation/admin-guide/tainted-kernels.rst for more information.
|
|
|
|
|
|
threads-max:
|
|
============
|
|
|
|
This value controls the maximum number of threads that can be created
|
|
using fork().
|
|
|
|
During initialization the kernel sets this value such that even if the
|
|
maximum number of threads is created, the thread structures occupy only
|
|
a part (1/8th) of the available RAM pages.
|
|
|
|
The minimum value that can be written to threads-max is 1.
|
|
|
|
The maximum value that can be written to threads-max is given by the
|
|
constant FUTEX_TID_MASK (0x3fffffff).
|
|
|
|
If a value outside of this range is written to threads-max an error
|
|
EINVAL occurs.
|
|
|
|
|
|
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:
|
|
=========
|
|
|
|
This parameter can be used to disable or enable the soft lockup detector
|
|
_and_ the NMI watchdog (i.e. the hard lockup detector) at the same time.
|
|
|
|
0 - disable both lockup detectors
|
|
|
|
1 - enable both lockup detectors
|
|
|
|
The soft lockup detector and the NMI watchdog can also be disabled or
|
|
enabled individually, using the soft_watchdog and nmi_watchdog parameters.
|
|
If the watchdog parameter is read, for example by executing::
|
|
|
|
cat /proc/sys/kernel/watchdog
|
|
|
|
the output of this command (0 or 1) shows the logical OR of soft_watchdog
|
|
and nmi_watchdog.
|
|
|
|
|
|
watchdog_cpumask:
|
|
=================
|
|
|
|
This value can be used to control on which cpus the watchdog may run.
|
|
The default cpumask is all possible cores, but if NO_HZ_FULL is
|
|
enabled in the kernel config, and cores are specified with the
|
|
nohz_full= boot argument, those cores are excluded by default.
|
|
Offline cores can be included in this mask, and if the core is later
|
|
brought online, the watchdog will be started based on the mask value.
|
|
|
|
Typically this value would only be touched in the nohz_full case
|
|
to re-enable cores that by default were not running the watchdog,
|
|
if a kernel lockup was suspected on those cores.
|
|
|
|
The argument value is the standard cpulist format for cpumasks,
|
|
so for example to enable the watchdog on cores 0, 2, 3, and 4 you
|
|
might say::
|
|
|
|
echo 0,2-4 > /proc/sys/kernel/watchdog_cpumask
|
|
|
|
|
|
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.
|