admin-guide/sysctl/kernel.rst

5 .. See scripts/check-sysctl-docs to keep this up to date
13 Documentation/admin-guide/sysctl/index.rst.
15 ------------------------------------------------------------------------------
39 If BSD-style process accounting is enabled these values control
71 The machine hardware name, the same output as ``uname -m``
129 Ctrl-Alt-Delete). Writing a value to this file which doesn't
130 correspond to a running process will result in ``-ESRCH``.
132 See also `ctrl-alt-del`_.
225 ctrl-alt-del
228 When the value in this file is 0, ctrl-alt-del is trapped and
236   mode, the ctrl-alt-del is intercepted by the program before it
281 See Documentation/driver-api/firmware/fallback-mechanisms.rst.
315 This value controls the hard lockup detector behavior when a hard
317 debug information. If enabled, arch-specific all-CPU stack dumping
337 See Documentation/admin-guide/lockup-watchdogs.rst for more information.
349 modern systems rely exclusively on the netlink-based uevent source and
363 1: Will non-maskably interrupt all CPUs and dump their backtraces when
420 -1: report an infinite number of warnings.
426 Controls whether the panic kmsg data should be reported to Hyper-V.
434 ignore-unaligned-usertrap
448 See also `unaligned-trap`_ and `unaligned-dump-stack`_. On ``ia64``,
463   -EPERM) for unprivileged processes not in the io_uring_group group.
467   always fails with -EPERM. Existing io_uring instances can still be
477 to create an io_uring instance.  If io_uring_group is set to -1 (the
505 -1 Unlimited calls to kexec. This is the default setting.
534 The correct long-term solution is to do the permission checks at
607 By default they are equal to -1, which means generic allocation logic.
613   2) Toggle with non-default value will be set back to -1 by kernel after
615      fails, it is undefined if the value remains unmodified or is reset to -1.
630 (i.e. the hard lockup detector) on x86 systems.
633 0 Disable the hard lockup detector.
634 1 Enable the hard lockup detector.
637 The hard lockup detector monitors each CPU for its ability to respond to
639 that are programmed to generate Non-Maskable Interrupts (NMIs) periodically
648 Documentation/admin-guide/kernel-parameters.rst).
699 promotion throughput.  The per-node max promotion throughput in MB/s
717 1: Will non-maskably interrupt all CPUs and dump their backtraces when
747 The only way to tune these values is to rebuild the kernel :-)
753 if your architecture did not always support 32-bit UIDs (i.e. arm,
755 applications that use the old 16-bit UID/GID system calls, if the
799 1 Panic immediately.  If the `panic` sysctl is also non-zero then the
900 1-100 Attempt to throttle perf's sample rate to this
923  -1  Allow use of (almost) all events by all users.
944 '``perf record -g``' or '``perf trace --call-graph fp``'.
947 enabled, otherwise writing to this file will return ``-EBUSY``.
955 Control size of per-cpu ring buffer not counted against mlock limit.
965 instance, when using '``perf record -g``' or '``perf trace --call-graph fp``'.
968 enabled, otherwise writing to this file will return ``-EBUSY``.
1019 powersave-nap (PPC only)
1022 If set, Linux-PPC will use the 'nap' mode of powersaving,
1055 Value from 0 - 10000 is allowed.
1091 a one-time setting until next reboot: once set, it cannot be changed by
1143     loaded to random addresses.  Also for PIE-linked binaries, the
1154     non-legacy applications that would be broken this way, so for most
1163 real-root-dev
1166 See Documentation/admin-guide/initrd.rst.
1169 reboot-cmd (SPARC only)
1191 Documentation/accounting/delay-accounting.rst. Enabling this feature incurs
1260 See Documentation/userspace-api/seccomp_filter.rst.
1263 sg-big-buff
1333   -1   Legacy per-write sysctl value handling, with no printk warnings.
1350 This value controls the soft lockup detector thread's behavior
1381 This parameter can be used to control the soft lockup detector.
1384 0 Disable the soft lockup detector.
1385 1 Enable the soft lockup detector.
1388 The soft lockup detector monitors CPUs for threads that are hogging the CPUs
1399 On x86, each "split lock" imposes a system-wide performance penalty. On larger
1401 denials of service to well-behaved and potentially more important users.
1412 0 Disable the mitigation mode - just warns the split lock on kernel log
1414 1 Enable the mitigation mode (this is the default) - penalizes the split
1437 stop-a (SPARC only)
1440 Controls Stop-A:
1443 0 Stop-A has no effect.
1444 1 Stop-A breaks to the PROM (default).
1447 Stop-A is always enabled on a panic, so that the user can return to
1454 See Documentation/admin-guide/sysrq.rst.
1460 Non-zero if the kernel has been tainted. Numeric values, which can be
1476   4096  `(O)`  externally-built ("out-of-tree") module was loaded
1484 See Documentation/admin-guide/tainted-kernels.rst for more information.
1491   See Documentation/admin-guide/kernel-parameters.rst for more details on
1495 threads-max
1505 The minimum value that can be written to ``threads-max`` is 1.
1507 The maximum value that can be written to ``threads-max`` is given by the
1510 If a value outside of this range is written to ``threads-max`` an
1537 See Documentation/admin-guide/kernel-parameters.rst and
1538 Documentation/trace/boottime-trace.rst.
1541 .. _unaligned-dump-stack:
1543 unaligned-dump-stack (ia64)
1554 See also `ignore-unaligned-usertrap`_.
1557 unaligned-trap
1570 See also `ignore-unaligned-usertrap`_.
1577 value is non-zero, unknown NMI is trapped and then panic occurs. At
1589 will return ``-EPERM``. Once set to 1, this can't be cleared from the
1618 This parameter can be used to disable or enable the soft lockup detector
1619 *and* the NMI watchdog (i.e. the hard lockup detector) at the same time.
1626 The soft lockup detector and the NMI watchdog can also be disabled or
1648 to re-enable cores that by default were not running the watchdog,
1655   echo 0,2-4 > /proc/sys/kernel/watchdog_cpumask
1662 events and the soft and hard lockup thresholds. The default threshold
1665 The softlockup threshold is (``2 * watchdog_thresh``). Setting this