2005-04-17 00:20:36 +02:00
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Documentation for /proc/sys/kernel/* kernel version 2.2.10
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(c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
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2009-04-03 01:57:20 +02:00
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(c) 2009, Shen Feng<shen@cn.fujitsu.com>
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2005-04-17 00:20:36 +02:00
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For general info and legal blurb, please look in README.
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==============================================================
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This file contains documentation for the sysctl files in
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/proc/sys/kernel/ and is valid for Linux kernel version 2.2.
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The files in this directory can be used to tune and monitor
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miscellaneous and general things in the operation of the Linux
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kernel. Since some of the files _can_ be used to screw up your
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system, it is advisable to read both documentation and source
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before actually making adjustments.
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Currently, these files might (depending on your configuration)
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show up in /proc/sys/kernel:
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2011-07-23 19:39:29 +02:00
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2005-04-17 00:20:36 +02:00
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- acct
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2011-07-23 19:39:29 +02:00
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- acpi_video_flags
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- auto_msgmni
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2009-12-11 23:23:44 +01:00
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- bootloader_type [ X86 only ]
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- bootloader_version [ X86 only ]
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2009-09-11 10:28:47 +02:00
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- callhome [ S390 only ]
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2011-11-01 01:11:20 +01:00
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- cap_last_cap
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2005-04-17 00:20:36 +02:00
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- core_pattern
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2009-09-24 00:56:56 +02:00
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- core_pipe_limit
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2005-04-17 00:20:36 +02:00
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- core_uses_pid
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- ctrl-alt-del
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2010-11-11 23:05:18 +01:00
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- dmesg_restrict
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2005-04-17 00:20:36 +02:00
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- domainname
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- hostname
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- hotplug
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2015-11-06 03:44:41 +01:00
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- hardlockup_all_cpu_backtrace
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2017-12-10 08:48:46 +01:00
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- hardlockup_panic
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2014-01-20 18:34:13 +01:00
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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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2018-08-22 06:55:52 +02:00
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- hung_task_check_interval_secs
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2014-01-20 18:34:13 +01:00
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- hung_task_warnings
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2018-07-08 04:56:51 +02:00
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- hyperv_record_panic_msg
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kexec: add sysctl to disable kexec_load
For general-purpose (i.e. distro) kernel builds it makes sense to build
with CONFIG_KEXEC to allow end users to choose what kind of things they
want to do with kexec. However, in the face of trying to lock down a
system with such a kernel, there needs to be a way to disable kexec_load
(much like module loading can be disabled). Without this, it is too easy
for the root user to modify kernel memory even when CONFIG_STRICT_DEVMEM
and modules_disabled are set. With this change, it is still possible to
load an image for use later, then disable kexec_load so the image (or lack
of image) can't be altered.
The intention is for using this in environments where "perfect"
enforcement is hard. Without a verified boot, along with verified
modules, and along with verified kexec, this is trying to give a system a
better chance to defend itself (or at least grow the window of
discoverability) against attack in the face of a privilege escalation.
In my mind, I consider several boot scenarios:
1) Verified boot of read-only verified root fs loading fd-based
verification of kexec images.
2) Secure boot of writable root fs loading signed kexec images.
3) Regular boot loading kexec (e.g. kcrash) image early and locking it.
4) Regular boot with no control of kexec image at all.
1 and 2 don't exist yet, but will soon once the verified kexec series has
landed. 4 is the state of things now. The gap between 2 and 4 is too
large, so this change creates scenario 3, a middle-ground above 4 when 2
and 1 are not possible for a system.
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-01-24 00:55:59 +01:00
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- kexec_load_disabled
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kptr_restrict for hiding kernel pointers from unprivileged users
Add the %pK printk format specifier and the /proc/sys/kernel/kptr_restrict
sysctl.
The %pK format specifier is designed to hide exposed kernel pointers,
specifically via /proc interfaces. Exposing these pointers provides an
easy target for kernel write vulnerabilities, since they reveal the
locations of writable structures containing easily triggerable function
pointers. The behavior of %pK depends on the kptr_restrict sysctl.
If kptr_restrict is set to 0, no deviation from the standard %p behavior
occurs. If kptr_restrict is set to 1, the default, if the current user
(intended to be a reader via seq_printf(), etc.) does not have CAP_SYSLOG
(currently in the LSM tree), kernel pointers using %pK are printed as 0's.
If kptr_restrict is set to 2, kernel pointers using %pK are printed as
0's regardless of privileges. Replacing with 0's was chosen over the
default "(null)", which cannot be parsed by userland %p, which expects
"(nil)".
[akpm@linux-foundation.org: check for IRQ context when !kptr_restrict, save an indent level, s/WARN/WARN_ONCE/]
[akpm@linux-foundation.org: coding-style fixup]
[randy.dunlap@oracle.com: fix kernel/sysctl.c warning]
Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: James Morris <jmorris@namei.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Thomas Graf <tgraf@infradead.org>
Cc: Eugene Teo <eugeneteo@kernel.org>
Cc: Kees Cook <kees.cook@canonical.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: David S. Miller <davem@davemloft.net>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Eric Paris <eparis@parisplace.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-01-13 01:59:41 +01:00
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- kptr_restrict
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2005-04-17 00:20:36 +02:00
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- l2cr [ PPC only ]
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2008-02-14 00:03:32 +01:00
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- modprobe ==> Documentation/debugging-modules.txt
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2009-04-03 00:49:29 +02:00
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- modules_disabled
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2013-01-05 00:34:50 +01:00
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- msg_next_id [ sysv ipc ]
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2005-04-17 00:20:36 +02:00
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- msgmax
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- msgmnb
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- msgmni
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2009-04-03 01:57:20 +02:00
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- nmi_watchdog
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2005-04-17 00:20:36 +02:00
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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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2011-07-23 19:39:29 +02:00
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- panic_on_oops
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2011-11-29 07:08:36 +01:00
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- panic_on_stackoverflow
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2014-12-11 00:45:50 +01:00
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- panic_on_unrecovered_nmi
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- panic_on_warn
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2019-01-04 00:28:20 +01:00
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- panic_print
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2016-06-02 18:51:41 +02:00
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- panic_on_rcu_stall
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2016-01-19 22:35:15 +01:00
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- perf_cpu_time_max_percent
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- perf_event_paranoid
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2016-04-21 17:28:50 +02:00
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- perf_event_max_stack
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2017-08-20 13:39:20 +02:00
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- perf_event_mlock_kb
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2016-05-12 18:06:21 +02:00
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- perf_event_max_contexts_per_stack
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2005-04-17 00:20:36 +02:00
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- pid_max
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- powersave-nap [ PPC only ]
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- printk
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2011-07-23 19:39:29 +02:00
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- printk_delay
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- printk_ratelimit
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- printk_ratelimit_burst
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2016-02-21 08:06:14 +01:00
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- pty ==> Documentation/filesystems/devpts.txt
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2008-02-09 23:24:08 +01:00
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- randomize_va_space
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2016-10-18 14:12:27 +02:00
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- real-root-dev ==> Documentation/admin-guide/initrd.rst
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2005-04-17 00:20:36 +02:00
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- reboot-cmd [ SPARC only ]
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- rtsig-max
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- rtsig-nr
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2018-12-03 10:56:23 +01:00
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- sched_energy_aware
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2017-08-11 06:33:52 +02:00
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- seccomp/ ==> Documentation/userspace-api/seccomp_filter.rst
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2005-04-17 00:20:36 +02:00
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- sem
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2013-01-05 00:34:50 +01:00
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- sem_next_id [ sysv ipc ]
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2005-04-17 00:20:36 +02:00
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- sg-big-buff [ generic SCSI device (sg) ]
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2013-01-05 00:34:50 +01:00
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- shm_next_id [ sysv ipc ]
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2011-07-27 01:08:48 +02:00
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- shm_rmid_forced
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2005-04-17 00:20:36 +02:00
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- shmall
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- shmmax [ sysv ipc ]
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- shmmni
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2014-06-23 22:22:05 +02:00
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- softlockup_all_cpu_backtrace
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2015-04-15 00:44:13 +02:00
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- soft_watchdog
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2018-08-17 00:17:03 +02:00
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- stack_erasing
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2005-04-17 00:20:36 +02:00
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- stop-a [ SPARC only ]
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2017-02-24 09:42:14 +01:00
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- sysrq ==> Documentation/admin-guide/sysrq.rst
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sysctl: allow for strict write position handling
When writing to a sysctl string, each write, regardless of VFS position,
begins writing the string from the start. This means the contents of
the last write to the sysctl controls the string contents instead of the
first:
open("/proc/sys/kernel/modprobe", O_WRONLY) = 1
write(1, "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"..., 4096) = 4096
write(1, "/bin/true", 9) = 9
close(1) = 0
$ cat /proc/sys/kernel/modprobe
/bin/true
Expected behaviour would be to have the sysctl be "AAAA..." capped at
maxlen (in this case KMOD_PATH_LEN: 256), instead of truncating to the
contents of the second write. Similarly, multiple short writes would
not append to the sysctl.
The old behavior is unlike regular POSIX files enough that doing audits
of software that interact with sysctls can end up in unexpected or
dangerous situations. For example, "as long as the input starts with a
trusted path" turns out to be an insufficient filter, as what must also
happen is for the input to be entirely contained in a single write
syscall -- not a common consideration, especially for high level tools.
This provides kernel.sysctl_writes_strict as a way to make this behavior
act in a less surprising manner for strings, and disallows non-zero file
position when writing numeric sysctls (similar to what is already done
when reading from non-zero file positions). For now, the default (0) is
to warn about non-zero file position use, but retain the legacy
behavior. Setting this to -1 disables the warning, and setting this to
1 enables the file position respecting behavior.
[akpm@linux-foundation.org: fix build]
[akpm@linux-foundation.org: move misplaced hunk, per Randy]
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-06-06 23:37:19 +02:00
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- sysctl_writes_strict
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2019-01-08 20:40:07 +01:00
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- tainted ==> Documentation/admin-guide/tainted-kernels.rst
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2005-04-17 00:20:36 +02:00
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- threads-max
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2009-04-03 01:57:20 +02:00
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- unknown_nmi_panic
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2015-04-15 00:44:13 +02:00
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- watchdog
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2013-05-17 04:31:20 +02:00
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- watchdog_thresh
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2005-04-17 00:20:36 +02:00
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- version
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==============================================================
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acct:
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highwater lowwater frequency
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If BSD-style process accounting is enabled these values control
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its behaviour. If free space on filesystem where the log lives
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goes below <lowwater>% accounting suspends. If free space gets
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above <highwater>% accounting resumes. <Frequency> determines
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how often do we check the amount of free space (value is in
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seconds). Default:
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4 2 30
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That is, suspend accounting if there left <= 2% free; resume it
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if we got >=4%; consider information about amount of free space
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valid for 30 seconds.
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2011-07-23 19:39:29 +02:00
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==============================================================
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acpi_video_flags:
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flags
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See Doc*/kernel/power/video.txt, it allows mode of video boot to be
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set during run time.
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==============================================================
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auto_msgmni:
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2014-12-13 01:58:17 +01:00
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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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2011-07-23 19:39:29 +02:00
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2005-04-17 00:20:36 +02:00
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==============================================================
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2009-12-11 23:23:44 +01:00
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bootloader_type:
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x86 bootloader identification
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This gives the bootloader type number as indicated by the bootloader,
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shifted left by 4, and OR'd with the low four bits of the bootloader
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version. The reason for this encoding is that this used to match the
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type_of_loader field in the kernel header; the encoding is kept for
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backwards compatibility. That is, if the full bootloader type number
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is 0x15 and the full version number is 0x234, this file will contain
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the value 340 = 0x154.
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See the type_of_loader and ext_loader_type fields in
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Documentation/x86/boot.txt for additional information.
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==============================================================
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bootloader_version:
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x86 bootloader version
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The complete bootloader version number. In the example above, this
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file will contain the value 564 = 0x234.
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See the type_of_loader and ext_loader_ver fields in
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Documentation/x86/boot.txt for additional information.
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==============================================================
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2009-09-11 10:28:47 +02:00
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callhome:
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Controls the kernel's callhome behavior in case of a kernel panic.
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The s390 hardware allows an operating system to send a notification
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to a service organization (callhome) in case of an operating system panic.
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When the value in this file is 0 (which is the default behavior)
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nothing happens in case of a kernel panic. If this value is set to "1"
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the complete kernel oops message is send to the IBM customer service
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organization in case the mainframe the Linux operating system is running
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on has a service contract with IBM.
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==============================================================
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2011-11-01 01:11:20 +01:00
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cap_last_cap
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Highest valid capability of the running kernel. Exports
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CAP_LAST_CAP from the kernel.
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==============================================================
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2005-04-17 00:20:36 +02:00
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core_pattern:
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core_pattern is used to specify a core dumpfile pattern name.
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2019-03-18 18:34:21 +01:00
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. max length 127 characters; default value is "core"
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2005-04-17 00:20:36 +02:00
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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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2013-09-11 23:24:32 +02:00
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%P global pid (init PID namespace)
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2014-10-14 00:53:35 +02:00
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%i tid
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%I global tid (init PID namespace)
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coredump: use from_kuid/kgid when formatting corename
When adding __printf attribute to cn_printf, gcc reports some issues:
fs/coredump.c:213:5: warning: format '%d' expects argument of type
'int', but argument 3 has type 'kuid_t' [-Wformat=]
err = cn_printf(cn, "%d", cred->uid);
^
fs/coredump.c:217:5: warning: format '%d' expects argument of type
'int', but argument 3 has type 'kgid_t' [-Wformat=]
err = cn_printf(cn, "%d", cred->gid);
^
These warnings come from the fact that the value of uid/gid needs to be
extracted from the kuid_t/kgid_t structure before being used as an
integer. More precisely, cred->uid and cred->gid need to be converted to
either user-namespace uid/gid or to init_user_ns uid/gid.
Use init_user_ns in order not to break existing ABI, and document this in
Documentation/sysctl/kernel.txt.
While at it, format uid and gid values with %u instead of %d because
uid_t/__kernel_uid32_t and gid_t/__kernel_gid32_t are unsigned int.
Signed-off-by: Nicolas Iooss <nicolas.iooss_linux@m4x.org>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2015-06-26 00:03:51 +02:00
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%u uid (in initial user namespace)
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%g gid (in initial user namespace)
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2012-10-05 02:15:25 +02:00
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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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2005-04-17 00:20:36 +02:00
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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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2011-05-27 01:25:46 +02:00
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%e executable filename (may be shortened)
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%E executable path
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2005-04-17 00:20:36 +02:00
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%<OTHER> both are dropped
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2006-10-11 10:21:57 +02:00
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|
|
. 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.
|
2005-04-17 00:20:36 +02:00
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2009-09-24 00:56:56 +02:00
|
|
|
core_pipe_limit:
|
|
|
|
|
2011-07-23 19:39:29 +02:00
|
|
|
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.
|
2009-09-24 00:56:56 +02:00
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2005-04-17 00:20:36 +02:00
|
|
|
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.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2010-11-11 23:05:18 +01:00
|
|
|
dmesg_restrict:
|
|
|
|
|
2011-07-23 19:39:29 +02:00
|
|
|
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
|
2010-12-08 16:19:01 +01:00
|
|
|
dmesg_restrict is set set to (1), users must have CAP_SYSLOG to use
|
2010-11-11 23:05:18 +01:00
|
|
|
dmesg(8).
|
|
|
|
|
2011-07-23 19:39:29 +02:00
|
|
|
The kernel config option CONFIG_SECURITY_DMESG_RESTRICT sets the
|
|
|
|
default value of dmesg_restrict.
|
2010-11-11 23:05:18 +01:00
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2005-04-17 00:20:36 +02:00
|
|
|
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.
|
|
|
|
|
2015-11-06 03:44:41 +01:00
|
|
|
==============================================================
|
|
|
|
hardlockup_all_cpu_backtrace:
|
|
|
|
|
|
|
|
This value controls the hard lockup detector behavior when a hard
|
|
|
|
lockup condition is detected as to whether or not to gather further
|
|
|
|
debug information. If enabled, arch-specific all-CPU stack dumping
|
|
|
|
will be initiated.
|
|
|
|
|
|
|
|
0: do nothing. This is the default behavior.
|
|
|
|
|
|
|
|
1: on detection capture more debug information.
|
2005-04-17 00:20:36 +02:00
|
|
|
==============================================================
|
|
|
|
|
2017-12-10 08:48:46 +01:00
|
|
|
hardlockup_panic:
|
|
|
|
|
|
|
|
This parameter can be used to control whether the kernel panics
|
|
|
|
when a hard lockup is detected.
|
|
|
|
|
|
|
|
0 - don't panic on hard lockup
|
|
|
|
1 - panic on hard lockup
|
|
|
|
|
|
|
|
See Documentation/lockup-watchdogs.txt for more information. This can
|
|
|
|
also be set using the nmi_watchdog kernel parameter.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2005-04-17 00:20:36 +02:00
|
|
|
hotplug:
|
|
|
|
|
|
|
|
Path for the hotplug policy agent.
|
|
|
|
Default value is "/sbin/hotplug".
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2014-01-20 18:34:13 +01:00
|
|
|
hung_task_panic:
|
|
|
|
|
|
|
|
Controls the kernel's behavior when a hung task is detected.
|
|
|
|
This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.
|
|
|
|
|
|
|
|
0: continue operation. This is the default behavior.
|
|
|
|
|
|
|
|
1: panic immediately.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
|
|
|
hung_task_check_count:
|
|
|
|
|
|
|
|
The upper bound on the number of tasks that are checked.
|
|
|
|
This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
|
|
|
hung_task_timeout_secs:
|
|
|
|
|
2018-08-22 06:55:52 +02:00
|
|
|
When a task in D state did not get scheduled
|
2014-01-20 18:34:13 +01:00
|
|
|
for more than this value report a warning.
|
|
|
|
This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.
|
|
|
|
|
|
|
|
0: means infinite timeout - no checking done.
|
2014-04-08 00:38:57 +02:00
|
|
|
Possible values to set are in range {0..LONG_MAX/HZ}.
|
2014-01-20 18:34:13 +01:00
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2018-08-22 06:55:52 +02:00
|
|
|
hung_task_check_interval_secs:
|
|
|
|
|
|
|
|
Hung task check interval. If hung task checking is enabled
|
|
|
|
(see hung_task_timeout_secs), the check is done every
|
|
|
|
hung_task_check_interval_secs seconds.
|
|
|
|
This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.
|
|
|
|
|
|
|
|
0 (default): means use hung_task_timeout_secs as checking interval.
|
|
|
|
Possible values to set are in range {0..LONG_MAX/HZ}.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2014-01-27 10:00:57 +01:00
|
|
|
hung_task_warnings:
|
2014-01-20 18:34:13 +01:00
|
|
|
|
|
|
|
The maximum number of warnings to report. During a check interval
|
2014-01-27 10:00:57 +01:00
|
|
|
if a hung task is detected, this value is decreased by 1.
|
|
|
|
When this value reaches 0, no more warnings will be reported.
|
2014-01-20 18:34:13 +01:00
|
|
|
This file shows up if CONFIG_DETECT_HUNG_TASK is enabled.
|
|
|
|
|
|
|
|
-1: report an infinite number of warnings.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2018-07-08 04:56:51 +02:00
|
|
|
hyperv_record_panic_msg:
|
|
|
|
|
|
|
|
Controls whether the panic kmsg data should be reported to Hyper-V.
|
|
|
|
|
|
|
|
0: do not report panic kmsg data.
|
|
|
|
|
|
|
|
1: report the panic kmsg data. This is the default behavior.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
kexec: add sysctl to disable kexec_load
For general-purpose (i.e. distro) kernel builds it makes sense to build
with CONFIG_KEXEC to allow end users to choose what kind of things they
want to do with kexec. However, in the face of trying to lock down a
system with such a kernel, there needs to be a way to disable kexec_load
(much like module loading can be disabled). Without this, it is too easy
for the root user to modify kernel memory even when CONFIG_STRICT_DEVMEM
and modules_disabled are set. With this change, it is still possible to
load an image for use later, then disable kexec_load so the image (or lack
of image) can't be altered.
The intention is for using this in environments where "perfect"
enforcement is hard. Without a verified boot, along with verified
modules, and along with verified kexec, this is trying to give a system a
better chance to defend itself (or at least grow the window of
discoverability) against attack in the face of a privilege escalation.
In my mind, I consider several boot scenarios:
1) Verified boot of read-only verified root fs loading fd-based
verification of kexec images.
2) Secure boot of writable root fs loading signed kexec images.
3) Regular boot loading kexec (e.g. kcrash) image early and locking it.
4) Regular boot with no control of kexec image at all.
1 and 2 don't exist yet, but will soon once the verified kexec series has
landed. 4 is the state of things now. The gap between 2 and 4 is too
large, so this change creates scenario 3, a middle-ground above 4 when 2
and 1 are not possible for a system.
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-01-24 00:55:59 +01:00
|
|
|
kexec_load_disabled:
|
|
|
|
|
|
|
|
A toggle indicating if the kexec_load syscall has been disabled. This
|
|
|
|
value defaults to 0 (false: kexec_load enabled), but can be set to 1
|
|
|
|
(true: kexec_load disabled). Once true, kexec can no longer be used, and
|
|
|
|
the toggle cannot be set back to false. This allows a kexec image to be
|
|
|
|
loaded before disabling the syscall, allowing a system to set up (and
|
|
|
|
later use) an image without it being altered. Generally used together
|
|
|
|
with the "modules_disabled" sysctl.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
kptr_restrict for hiding kernel pointers from unprivileged users
Add the %pK printk format specifier and the /proc/sys/kernel/kptr_restrict
sysctl.
The %pK format specifier is designed to hide exposed kernel pointers,
specifically via /proc interfaces. Exposing these pointers provides an
easy target for kernel write vulnerabilities, since they reveal the
locations of writable structures containing easily triggerable function
pointers. The behavior of %pK depends on the kptr_restrict sysctl.
If kptr_restrict is set to 0, no deviation from the standard %p behavior
occurs. If kptr_restrict is set to 1, the default, if the current user
(intended to be a reader via seq_printf(), etc.) does not have CAP_SYSLOG
(currently in the LSM tree), kernel pointers using %pK are printed as 0's.
If kptr_restrict is set to 2, kernel pointers using %pK are printed as
0's regardless of privileges. Replacing with 0's was chosen over the
default "(null)", which cannot be parsed by userland %p, which expects
"(nil)".
[akpm@linux-foundation.org: check for IRQ context when !kptr_restrict, save an indent level, s/WARN/WARN_ONCE/]
[akpm@linux-foundation.org: coding-style fixup]
[randy.dunlap@oracle.com: fix kernel/sysctl.c warning]
Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: James Morris <jmorris@namei.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Thomas Graf <tgraf@infradead.org>
Cc: Eugene Teo <eugeneteo@kernel.org>
Cc: Kees Cook <kees.cook@canonical.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: David S. Miller <davem@davemloft.net>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Eric Paris <eparis@parisplace.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-01-13 01:59:41 +01:00
|
|
|
kptr_restrict:
|
|
|
|
|
|
|
|
This toggle indicates whether restrictions are placed on
|
2013-11-13 00:08:51 +01:00
|
|
|
exposing kernel addresses via /proc and other interfaces.
|
|
|
|
|
2017-12-19 22:17:16 +01:00
|
|
|
When kptr_restrict is set to 0 (the default) the address is hashed before
|
|
|
|
printing. (This is the equivalent to %p.)
|
2013-11-13 00:08:51 +01:00
|
|
|
|
|
|
|
When kptr_restrict is set to (1), kernel pointers printed using the %pK
|
|
|
|
format specifier will be replaced with 0's unless the user has CAP_SYSLOG
|
|
|
|
and effective user and group ids are equal to the real ids. This is
|
|
|
|
because %pK checks are done at read() time rather than open() time, so
|
|
|
|
if permissions are elevated between the open() and the read() (e.g via
|
|
|
|
a setuid binary) then %pK will not leak kernel pointers to unprivileged
|
|
|
|
users. Note, this is a temporary solution only. The correct long-term
|
|
|
|
solution is to do the permission checks at open() time. Consider removing
|
|
|
|
world read permissions from files that use %pK, and using dmesg_restrict
|
|
|
|
to protect against uses of %pK in dmesg(8) if leaking kernel pointer
|
|
|
|
values to unprivileged users is a concern.
|
|
|
|
|
|
|
|
When kptr_restrict is set to (2), kernel pointers printed using
|
|
|
|
%pK will be replaced with 0's regardless of privileges.
|
kptr_restrict for hiding kernel pointers from unprivileged users
Add the %pK printk format specifier and the /proc/sys/kernel/kptr_restrict
sysctl.
The %pK format specifier is designed to hide exposed kernel pointers,
specifically via /proc interfaces. Exposing these pointers provides an
easy target for kernel write vulnerabilities, since they reveal the
locations of writable structures containing easily triggerable function
pointers. The behavior of %pK depends on the kptr_restrict sysctl.
If kptr_restrict is set to 0, no deviation from the standard %p behavior
occurs. If kptr_restrict is set to 1, the default, if the current user
(intended to be a reader via seq_printf(), etc.) does not have CAP_SYSLOG
(currently in the LSM tree), kernel pointers using %pK are printed as 0's.
If kptr_restrict is set to 2, kernel pointers using %pK are printed as
0's regardless of privileges. Replacing with 0's was chosen over the
default "(null)", which cannot be parsed by userland %p, which expects
"(nil)".
[akpm@linux-foundation.org: check for IRQ context when !kptr_restrict, save an indent level, s/WARN/WARN_ONCE/]
[akpm@linux-foundation.org: coding-style fixup]
[randy.dunlap@oracle.com: fix kernel/sysctl.c warning]
Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: James Morris <jmorris@namei.org>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Thomas Graf <tgraf@infradead.org>
Cc: Eugene Teo <eugeneteo@kernel.org>
Cc: Kees Cook <kees.cook@canonical.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: David S. Miller <davem@davemloft.net>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Eric Paris <eparis@parisplace.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2011-01-13 01:59:41 +01:00
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2011-07-23 19:39:29 +02:00
|
|
|
l2cr: (PPC only)
|
|
|
|
|
|
|
|
This flag controls the L2 cache of G3 processor boards. If
|
|
|
|
0, the cache is disabled. Enabled if nonzero.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2009-04-03 00:49:29 +02:00
|
|
|
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
|
kexec: add sysctl to disable kexec_load
For general-purpose (i.e. distro) kernel builds it makes sense to build
with CONFIG_KEXEC to allow end users to choose what kind of things they
want to do with kexec. However, in the face of trying to lock down a
system with such a kernel, there needs to be a way to disable kexec_load
(much like module loading can be disabled). Without this, it is too easy
for the root user to modify kernel memory even when CONFIG_STRICT_DEVMEM
and modules_disabled are set. With this change, it is still possible to
load an image for use later, then disable kexec_load so the image (or lack
of image) can't be altered.
The intention is for using this in environments where "perfect"
enforcement is hard. Without a verified boot, along with verified
modules, and along with verified kexec, this is trying to give a system a
better chance to defend itself (or at least grow the window of
discoverability) against attack in the face of a privilege escalation.
In my mind, I consider several boot scenarios:
1) Verified boot of read-only verified root fs loading fd-based
verification of kexec images.
2) Secure boot of writable root fs loading signed kexec images.
3) Regular boot loading kexec (e.g. kcrash) image early and locking it.
4) Regular boot with no control of kexec image at all.
1 and 2 don't exist yet, but will soon once the verified kexec series has
landed. 4 is the state of things now. The gap between 2 and 4 is too
large, so this change creates scenario 3, a middle-ground above 4 when 2
and 1 are not possible for a system.
Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Rik van Riel <riel@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-01-24 00:55:59 +01:00
|
|
|
to false. Generally used with the "kexec_load_disabled" toggle.
|
2009-04-03 00:49:29 +02:00
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2013-01-05 00:34:50 +01:00
|
|
|
msg_next_id, sem_next_id, and shm_next_id:
|
|
|
|
|
|
|
|
These three toggles allows to specify desired id for next allocated IPC
|
|
|
|
object: message, semaphore or shared memory respectively.
|
|
|
|
|
|
|
|
By default they are equal to -1, which means generic allocation logic.
|
|
|
|
Possible values to set are in range {0..INT_MAX}.
|
|
|
|
|
|
|
|
Notes:
|
|
|
|
1) kernel doesn't guarantee, that new object will have desired id. So,
|
|
|
|
it's up to userspace, how to handle an object with "wrong" id.
|
|
|
|
2) Toggle with non-default value will be set back to -1 by kernel after
|
2018-08-22 07:01:25 +02:00
|
|
|
successful IPC object allocation. If an IPC object allocation syscall
|
|
|
|
fails, it is undefined if the value remains unmodified or is reset to -1.
|
2013-01-05 00:34:50 +01:00
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2011-07-23 19:39:29 +02:00
|
|
|
nmi_watchdog:
|
|
|
|
|
2015-04-15 00:44:13 +02:00
|
|
|
This parameter can be used to control the NMI watchdog
|
|
|
|
(i.e. the hard lockup detector) on x86 systems.
|
2011-07-23 19:39:29 +02:00
|
|
|
|
2015-04-15 00:44:13 +02:00
|
|
|
0 - disable the hard lockup detector
|
|
|
|
1 - enable the hard lockup detector
|
|
|
|
|
|
|
|
The hard lockup detector monitors each CPU for its ability to respond to
|
|
|
|
timer interrupts. The mechanism utilizes CPU performance counter registers
|
|
|
|
that are programmed to generate Non-Maskable Interrupts (NMIs) periodically
|
|
|
|
while a CPU is busy. Hence, the alternative name 'NMI watchdog'.
|
|
|
|
|
|
|
|
The NMI watchdog is disabled by default if the kernel is running as a guest
|
|
|
|
in a KVM virtual machine. This default can be overridden by adding
|
|
|
|
|
|
|
|
nmi_watchdog=1
|
|
|
|
|
2016-10-18 14:12:27 +02:00
|
|
|
to the guest kernel command line (see Documentation/admin-guide/kernel-parameters.rst).
|
2011-07-23 19:39:29 +02:00
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2013-10-07 12:28:40 +02:00
|
|
|
numa_balancing
|
|
|
|
|
|
|
|
Enables/disables automatic page fault based NUMA memory
|
|
|
|
balancing. Memory is moved automatically to nodes
|
|
|
|
that access it often.
|
|
|
|
|
|
|
|
Enables/disables automatic NUMA memory balancing. On NUMA machines, there
|
|
|
|
is a performance penalty if remote memory is accessed by a CPU. When this
|
|
|
|
feature is enabled the kernel samples what task thread is accessing memory
|
|
|
|
by periodically unmapping pages and later trapping a page fault. At the
|
|
|
|
time of the page fault, it is determined if the data being accessed should
|
|
|
|
be migrated to a local memory node.
|
|
|
|
|
|
|
|
The unmapping of pages and trapping faults incur additional overhead that
|
|
|
|
ideally is offset by improved memory locality but there is no universal
|
|
|
|
guarantee. If the target workload is already bound to NUMA nodes then this
|
|
|
|
feature should be disabled. Otherwise, if the system overhead from the
|
|
|
|
feature is too high then the rate the kernel samples for NUMA hinting
|
|
|
|
faults may be controlled by the numa_balancing_scan_period_min_ms,
|
2013-10-07 12:29:37 +02:00
|
|
|
numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms,
|
2014-01-27 23:03:40 +01:00
|
|
|
numa_balancing_scan_size_mb, and numa_balancing_settle_count sysctls.
|
2013-10-07 12:28:40 +02:00
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
|
|
|
numa_balancing_scan_period_min_ms, numa_balancing_scan_delay_ms,
|
2013-10-07 12:29:37 +02:00
|
|
|
numa_balancing_scan_period_max_ms, numa_balancing_scan_size_mb
|
2013-10-07 12:28:40 +02:00
|
|
|
|
|
|
|
Automatic NUMA balancing scans tasks address space and unmaps pages to
|
|
|
|
detect if pages are properly placed or if the data should be migrated to a
|
|
|
|
memory node local to where the task is running. Every "scan delay" the task
|
|
|
|
scans the next "scan size" number of pages in its address space. When the
|
|
|
|
end of the address space is reached the scanner restarts from the beginning.
|
|
|
|
|
|
|
|
In combination, the "scan delay" and "scan size" determine the scan rate.
|
|
|
|
When "scan delay" decreases, the scan rate increases. The scan delay and
|
|
|
|
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.
|
|
|
|
|
2013-10-07 12:28:55 +02:00
|
|
|
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.
|
2013-10-07 12:28:40 +02:00
|
|
|
|
|
|
|
numa_balancing_scan_delay_ms is the starting "scan delay" used for a task
|
|
|
|
when it initially forks.
|
|
|
|
|
2013-10-07 12:28:55 +02:00
|
|
|
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.
|
2013-10-07 12:28:40 +02:00
|
|
|
|
|
|
|
numa_balancing_scan_size_mb is how many megabytes worth of pages are
|
|
|
|
scanned for a given scan.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2005-04-17 00:20:36 +02:00
|
|
|
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:
|
|
|
|
|
2011-07-23 19:39:29 +02:00
|
|
|
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.
|
2005-04-17 00:20:36 +02:00
|
|
|
|
|
|
|
These sysctls allow you to change the value of the fixed UID and GID.
|
|
|
|
The default is 65534.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
|
|
|
panic:
|
|
|
|
|
2011-07-23 19:39:29 +02:00
|
|
|
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.
|
|
|
|
|
|
|
|
==============================================================
|
2015-12-14 11:19:14 +01:00
|
|
|
|
|
|
|
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.
|
|
|
|
|
|
|
|
==============================================================
|
2011-07-23 19:39:29 +02:00
|
|
|
|
2005-04-17 00:20:36 +02:00
|
|
|
panic_on_oops:
|
|
|
|
|
|
|
|
Controls the kernel's behaviour when an oops or BUG is encountered.
|
|
|
|
|
|
|
|
0: try to continue operation
|
|
|
|
|
2007-05-09 07:35:06 +02:00
|
|
|
1: panic immediately. If the `panic' sysctl is also non-zero then the
|
2006-08-05 21:14:32 +02:00
|
|
|
machine will be rebooted.
|
2005-04-17 00:20:36 +02:00
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2011-11-29 07:08:36 +01:00
|
|
|
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.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2014-12-11 00:45:50 +01:00
|
|
|
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.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2019-01-04 00:28:20 +01:00
|
|
|
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
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2016-06-02 18:51:41 +02:00
|
|
|
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.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2013-06-21 17:51:36 +02:00
|
|
|
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.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2016-01-19 22:35:15 +01:00
|
|
|
perf_event_paranoid:
|
|
|
|
|
|
|
|
Controls use of the performance events system by unprivileged
|
2016-05-10 00:48:51 +02:00
|
|
|
users (without CAP_SYS_ADMIN). The default value is 2.
|
2016-01-19 22:35:15 +01:00
|
|
|
|
|
|
|
-1: Allow use of (almost) all events by all users
|
2017-08-20 13:39:20 +02:00
|
|
|
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
|
2016-01-19 22:35:15 +01:00
|
|
|
>=1: Disallow CPU event access by users without CAP_SYS_ADMIN
|
|
|
|
>=2: Disallow kernel profiling by users without CAP_SYS_ADMIN
|
|
|
|
|
|
|
|
==============================================================
|
2011-11-29 07:08:36 +01:00
|
|
|
|
2016-04-21 17:28:50 +02:00
|
|
|
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.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2017-08-20 13:39:20 +02:00
|
|
|
perf_event_mlock_kb:
|
|
|
|
|
|
|
|
Control size of per-cpu ring buffer not counted agains mlock limit.
|
|
|
|
|
|
|
|
The default value is 512 + 1 page
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2016-05-12 18:06:21 +02:00
|
|
|
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.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2005-04-17 00:20:36 +02:00
|
|
|
pid_max:
|
|
|
|
|
2007-05-09 07:14:03 +02:00
|
|
|
PID allocation wrap value. When the kernel's next PID value
|
2005-04-17 00:20:36 +02:00
|
|
|
reaches this value, it wraps back to a minimum PID value.
|
|
|
|
PIDs of value pid_max or larger are not allocated.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2012-01-13 02:20:27 +01:00
|
|
|
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.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2005-04-17 00:20:36 +02:00
|
|
|
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
|
2011-02-06 21:00:41 +01:00
|
|
|
- default_message_loglevel: messages without an explicit priority
|
2005-04-17 00:20:36 +02:00
|
|
|
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
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2011-07-23 19:39:29 +02:00
|
|
|
printk_delay:
|
|
|
|
|
|
|
|
Delay each printk message in printk_delay milliseconds
|
|
|
|
|
|
|
|
Value from 0 - 10000 is allowed.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2005-04-17 00:20:36 +02:00
|
|
|
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.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2016-08-02 23:04:07 +02:00
|
|
|
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.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2011-07-23 19:39:29 +02:00
|
|
|
randomize_va_space:
|
2008-02-09 23:24:08 +01:00
|
|
|
|
|
|
|
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.
|
|
|
|
|
2009-07-03 14:20:17 +02:00
|
|
|
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.
|
2008-02-09 23:24:08 +01:00
|
|
|
|
|
|
|
1 - Make the addresses of mmap base, stack and VDSO page randomized.
|
|
|
|
This, among other things, implies that shared libraries will be
|
2009-07-03 14:20:17 +02:00
|
|
|
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.
|
2008-02-09 23:24:08 +01:00
|
|
|
|
2009-07-03 14:20:17 +02:00
|
|
|
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
|
2008-02-09 23:24:08 +01:00
|
|
|
versions of libc.so.5 from 1996) that assume that brk area starts
|
2009-07-03 14:20:17 +02:00
|
|
|
just after the end of the code+bss. These applications break when
|
|
|
|
start of the brk area is randomized. There are however no known
|
2008-02-09 23:24:08 +01:00
|
|
|
non-legacy applications that would be broken this way, so for most
|
2009-07-03 14:20:17 +02:00
|
|
|
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.
|
2008-02-09 23:24:08 +01:00
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2005-04-17 00:20:36 +02:00
|
|
|
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.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2018-12-03 10:56:23 +01:00
|
|
|
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.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2016-02-05 10:08:36 +01:00
|
|
|
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.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2005-04-17 00:20:36 +02:00
|
|
|
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 :)
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2013-01-05 00:35:05 +01:00
|
|
|
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
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2011-07-23 19:39:29 +02:00
|
|
|
shmmax:
|
2005-04-17 00:20:36 +02:00
|
|
|
|
|
|
|
This value can be used to query and set the run time limit
|
|
|
|
on the maximum shared memory segment size that can be created.
|
2011-07-23 19:39:29 +02:00
|
|
|
Shared memory segments up to 1Gb are now supported in the
|
2005-04-17 00:20:36 +02:00
|
|
|
kernel. This value defaults to SHMMAX.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2011-07-27 01:08:48 +02:00
|
|
|
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: allow for strict write position handling
When writing to a sysctl string, each write, regardless of VFS position,
begins writing the string from the start. This means the contents of
the last write to the sysctl controls the string contents instead of the
first:
open("/proc/sys/kernel/modprobe", O_WRONLY) = 1
write(1, "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"..., 4096) = 4096
write(1, "/bin/true", 9) = 9
close(1) = 0
$ cat /proc/sys/kernel/modprobe
/bin/true
Expected behaviour would be to have the sysctl be "AAAA..." capped at
maxlen (in this case KMOD_PATH_LEN: 256), instead of truncating to the
contents of the second write. Similarly, multiple short writes would
not append to the sysctl.
The old behavior is unlike regular POSIX files enough that doing audits
of software that interact with sysctls can end up in unexpected or
dangerous situations. For example, "as long as the input starts with a
trusted path" turns out to be an insufficient filter, as what must also
happen is for the input to be entirely contained in a single write
syscall -- not a common consideration, especially for high level tools.
This provides kernel.sysctl_writes_strict as a way to make this behavior
act in a less surprising manner for strings, and disallows non-zero file
position when writing numeric sysctls (similar to what is already done
when reading from non-zero file positions). For now, the default (0) is
to warn about non-zero file position use, but retain the legacy
behavior. Setting this to -1 disables the warning, and setting this to
1 enables the file position respecting behavior.
[akpm@linux-foundation.org: fix build]
[akpm@linux-foundation.org: move misplaced hunk, per Randy]
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-06-06 23:37:19 +02:00
|
|
|
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.
|
2016-01-21 00:00:45 +01:00
|
|
|
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.
|
sysctl: allow for strict write position handling
When writing to a sysctl string, each write, regardless of VFS position,
begins writing the string from the start. This means the contents of
the last write to the sysctl controls the string contents instead of the
first:
open("/proc/sys/kernel/modprobe", O_WRONLY) = 1
write(1, "AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA"..., 4096) = 4096
write(1, "/bin/true", 9) = 9
close(1) = 0
$ cat /proc/sys/kernel/modprobe
/bin/true
Expected behaviour would be to have the sysctl be "AAAA..." capped at
maxlen (in this case KMOD_PATH_LEN: 256), instead of truncating to the
contents of the second write. Similarly, multiple short writes would
not append to the sysctl.
The old behavior is unlike regular POSIX files enough that doing audits
of software that interact with sysctls can end up in unexpected or
dangerous situations. For example, "as long as the input starts with a
trusted path" turns out to be an insufficient filter, as what must also
happen is for the input to be entirely contained in a single write
syscall -- not a common consideration, especially for high level tools.
This provides kernel.sysctl_writes_strict as a way to make this behavior
act in a less surprising manner for strings, and disallows non-zero file
position when writing numeric sysctls (similar to what is already done
when reading from non-zero file positions). For now, the default (0) is
to warn about non-zero file position use, but retain the legacy
behavior. Setting this to -1 disables the warning, and setting this to
1 enables the file position respecting behavior.
[akpm@linux-foundation.org: fix build]
[akpm@linux-foundation.org: move misplaced hunk, per Randy]
Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2014-06-06 23:37:19 +02:00
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2014-06-23 22:22:05 +02:00
|
|
|
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.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2015-04-15 00:44:13 +02:00
|
|
|
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.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2018-08-17 00:17:03 +02:00
|
|
|
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.
|
|
|
|
==============================================================
|
|
|
|
|
2019-01-08 20:40:07 +01:00
|
|
|
tainted
|
2005-04-17 00:20:36 +02:00
|
|
|
|
2018-04-11 01:32:29 +02:00
|
|
|
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.
|
|
|
|
|
2019-01-08 20:40:07 +01:00
|
|
|
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.
|
2005-04-17 00:20:36 +02:00
|
|
|
|
2009-04-03 01:57:20 +02:00
|
|
|
==============================================================
|
|
|
|
|
2015-04-16 21:47:53 +02:00
|
|
|
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 20.
|
|
|
|
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.
|
|
|
|
|
|
|
|
The value written is checked against the available RAM pages. If the
|
|
|
|
thread structures would occupy too much (more than 1/8th) of the
|
|
|
|
available RAM pages threads-max is reduced accordingly.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2009-04-03 01:57:20 +02:00
|
|
|
unknown_nmi_panic:
|
|
|
|
|
2011-07-23 19:39:29 +02:00
|
|
|
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.
|
2009-04-03 01:57:20 +02:00
|
|
|
|
2011-07-23 19:39:29 +02:00
|
|
|
NMI switch that most IA32 servers have fires unknown NMI up, for
|
|
|
|
example. If a system hangs up, try pressing the NMI switch.
|
2013-05-17 04:31:20 +02:00
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2015-04-15 00:44:13 +02:00
|
|
|
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.
|
|
|
|
|
|
|
|
==============================================================
|
|
|
|
|
2015-06-25 01:55:45 +02:00
|
|
|
watchdog_cpumask:
|
|
|
|
|
|
|
|
This value can be used to control on which cpus the watchdog may run.
|
|
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The default cpumask is all possible cores, but if NO_HZ_FULL is
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enabled in the kernel config, and cores are specified with the
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nohz_full= boot argument, those cores are excluded by default.
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Offline cores can be included in this mask, and if the core is later
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brought online, the watchdog will be started based on the mask value.
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Typically this value would only be touched in the nohz_full case
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to re-enable cores that by default were not running the watchdog,
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if a kernel lockup was suspected on those cores.
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The argument value is the standard cpulist format for cpumasks,
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so for example to enable the watchdog on cores 0, 2, 3, and 4 you
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might say:
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echo 0,2-4 > /proc/sys/kernel/watchdog_cpumask
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==============================================================
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2013-05-17 04:31:20 +02:00
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watchdog_thresh:
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This value can be used to control the frequency of hrtimer and NMI
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events and the soft and hard lockup thresholds. The default threshold
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is 10 seconds.
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The softlockup threshold is (2 * watchdog_thresh). Setting this
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tunable to zero will disable lockup detection altogether.
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==============================================================
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