numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
'node', 'default' can be specified
This can be set from sysctl after boot.
- See Documentation/sysctl/vm.txt for details.
+ See Documentation/sysctl/vm.rst for details.
ohci1394_dma=early [HW] enable debugging via the ohci1394 driver.
See Documentation/debugging-via-ohci1394.txt for more
Linux memory management is a complex system with many configurable
settings. Most of these settings are available via ``/proc``
filesystem and can be quired and adjusted using ``sysctl``. These APIs
-are described in Documentation/sysctl/vm.txt and in `man 5 proc`_.
+are described in Documentation/sysctl/vm.rst and in `man 5 proc`_.
.. _man 5 proc: http://man7.org/linux/man-pages/man5/proc.5.html
If a region of memory must be split into at least one new MADV_MERGEABLE
or MADV_UNMERGEABLE region, the madvise may return ENOMEM if the process
-will exceed ``vm.max_map_count`` (see Documentation/sysctl/vm.txt).
+will exceed ``vm.max_map_count`` (see Documentation/sysctl/vm.rst).
Like other madvise calls, they are intended for use on mapped areas of
the user address space: they will report ENOMEM if the specified range
For printing kernel pointers which should be hidden from unprivileged
users. The behaviour of %pK depends on the kptr_restrict sysctl - see
-Documentation/sysctl/kernel.txt for more details.
+Documentation/sysctl/kernel.rst for more details.
Unmodified Addresses
--------------------
/proc/sys/net/core/*
- Please see: Documentation/sysctl/net.txt for descriptions of these entries.
+ Please see: Documentation/sysctl/net.rst for descriptions of these entries.
/proc/sys/net/unix/*
--- /dev/null
+================================
+Documentation for /proc/sys/abi/
+================================
+
+kernel version 2.6.0.test2
+
+Copyright (c) 2003, Fabian Frederick <ffrederick@users.sourceforge.net>
+
+For general info: index.rst.
+
+------------------------------------------------------------------------------
+
+This path is binary emulation relevant aka personality types aka abi.
+When a process is executed, it's linked to an exec_domain whose
+personality is defined using values available from /proc/sys/abi.
+You can find further details about abi in include/linux/personality.h.
+
+Here are the files featuring in 2.6 kernel:
+
+- defhandler_coff
+- defhandler_elf
+- defhandler_lcall7
+- defhandler_libcso
+- fake_utsname
+- trace
+
+defhandler_coff
+---------------
+
+defined value:
+ PER_SCOSVR3::
+
+ 0x0003 | STICKY_TIMEOUTS | WHOLE_SECONDS | SHORT_INODE
+
+defhandler_elf
+--------------
+
+defined value:
+ PER_LINUX::
+
+ 0
+
+defhandler_lcall7
+-----------------
+
+defined value :
+ PER_SVR4::
+
+ 0x0001 | STICKY_TIMEOUTS | MMAP_PAGE_ZERO,
+
+defhandler_libsco
+-----------------
+
+defined value:
+ PER_SVR4::
+
+ 0x0001 | STICKY_TIMEOUTS | MMAP_PAGE_ZERO,
+
+fake_utsname
+------------
+
+Unused
+
+trace
+-----
+
+Unused
+++ /dev/null
-Documentation for /proc/sys/abi/* kernel version 2.6.0.test2
- (c) 2003, Fabian Frederick <ffrederick@users.sourceforge.net>
-
-For general info : README.
-
-==============================================================
-
-This path is binary emulation relevant aka personality types aka abi.
-When a process is executed, it's linked to an exec_domain whose
-personality is defined using values available from /proc/sys/abi.
-You can find further details about abi in include/linux/personality.h.
-
-Here are the files featuring in 2.6 kernel :
-
-- defhandler_coff
-- defhandler_elf
-- defhandler_lcall7
-- defhandler_libcso
-- fake_utsname
-- trace
-
-===========================================================
-defhandler_coff:
-defined value :
-PER_SCOSVR3
-0x0003 | STICKY_TIMEOUTS | WHOLE_SECONDS | SHORT_INODE
-
-===========================================================
-defhandler_elf:
-defined value :
-PER_LINUX
-0
-
-===========================================================
-defhandler_lcall7:
-defined value :
-PER_SVR4
-0x0001 | STICKY_TIMEOUTS | MMAP_PAGE_ZERO,
-
-===========================================================
-defhandler_libsco:
-defined value:
-PER_SVR4
-0x0001 | STICKY_TIMEOUTS | MMAP_PAGE_ZERO,
-
-===========================================================
-fake_utsname:
-Unused
-
-===========================================================
-trace:
-Unused
-
-===========================================================
-Documentation for /proc/sys/fs/* kernel version 2.2.10
- (c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
- (c) 2009, Shen Feng<shen@cn.fujitsu.com>
+===============================
+Documentation for /proc/sys/fs/
+===============================
-For general info and legal blurb, please look in README.
+kernel version 2.2.10
-==============================================================
+Copyright (c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
+
+Copyright (c) 2009, Shen Feng<shen@cn.fujitsu.com>
+
+For general info and legal blurb, please look in intro.rst.
+
+------------------------------------------------------------------------------
This file contains documentation for the sysctl files in
/proc/sys/fs/ and is valid for Linux kernel version 2.2.
before actually making adjustments.
1. /proc/sys/fs
-----------------------------------------------------------
+===============
Currently, these files are in /proc/sys/fs:
+
- aio-max-nr
- aio-nr
- dentry-state
- super-max
- super-nr
-==============================================================
-aio-nr & aio-max-nr:
+aio-nr & aio-max-nr
+-------------------
aio-nr is the running total of the number of events specified on the
io_setup system call for all currently active aio contexts. If aio-nr
raising aio-max-nr does not result in the pre-allocation or re-sizing
of any kernel data structures.
-==============================================================
-dentry-state:
+dentry-state
+------------
-From linux/include/linux/dcache.h:
---------------------------------------------------------------
-struct dentry_stat_t dentry_stat {
+From linux/include/linux/dcache.h::
+
+ struct dentry_stat_t dentry_stat {
int nr_dentry;
int nr_unused;
int age_limit; /* age in seconds */
int want_pages; /* pages requested by system */
int nr_negative; /* # of unused negative dentries */
int dummy; /* Reserved for future use */
-};
---------------------------------------------------------------
+ };
Dentries are dynamically allocated and deallocated.
they help speeding up rejection of non-existing files provided
by the users.
-==============================================================
-dquot-max & dquot-nr:
+dquot-max & dquot-nr
+--------------------
The file dquot-max shows the maximum number of cached disk
quota entries.
you have some awesome number of simultaneous system users,
you might want to raise the limit.
-==============================================================
-file-max & file-nr:
+file-max & file-nr
+------------------
The value in file-max denotes the maximum number of file-
handles that the Linux kernel will allocate. When you get lots
Attempts to allocate more file descriptors than file-max are
reported with printk, look for "VFS: file-max limit <number>
reached".
-==============================================================
-nr_open:
+
+nr_open
+-------
This denotes the maximum number of file-handles a process can
allocate. Default value is 1024*1024 (1048576) which should be
enough for most machines. Actual limit depends on RLIMIT_NOFILE
resource limit.
-==============================================================
-inode-max, inode-nr & inode-state:
+inode-max, inode-nr & inode-state
+---------------------------------
As with file handles, the kernel allocates the inode structures
dynamically, but can't free them yet.
system needs to prune the inode list instead of allocating
more.
-==============================================================
-overflowgid & overflowuid:
+overflowgid & overflowuid
+-------------------------
Some filesystems only support 16-bit UIDs and GIDs, although in Linux
UIDs and GIDs are 32 bits. When one of these filesystems is mounted
These sysctls allow you to change the value of the fixed UID and GID.
The default is 65534.
-==============================================================
-pipe-user-pages-hard:
+pipe-user-pages-hard
+--------------------
Maximum total number of pages a non-privileged user may allocate for pipes.
Once this limit is reached, no new pipes may be allocated until usage goes
below the limit again. When set to 0, no limit is applied, which is the default
setting.
-==============================================================
-pipe-user-pages-soft:
+pipe-user-pages-soft
+--------------------
Maximum total number of pages a non-privileged user may allocate for pipes
before the pipe size gets limited to a single page. Once this limit is reached,
allocate up to 1024 pipes at their default size. When set to 0, no limit is
applied.
-==============================================================
-protected_fifos:
+protected_fifos
+---------------
The intent of this protection is to avoid unintentional writes to
an attacker-controlled FIFO, where a program expected to create a regular
This protection is based on the restrictions in Openwall.
-==============================================================
-protected_hardlinks:
+protected_hardlinks
+--------------------
A long-standing class of security issues is the hardlink-based
time-of-check-time-of-use race, most commonly seen in world-writable
This protection is based on the restrictions in Openwall and grsecurity.
-==============================================================
-protected_regular:
+protected_regular
+-----------------
This protection is similar to protected_fifos, but it
avoids writes to an attacker-controlled regular file, where a program
When set to "2" it also applies to group writable sticky directories.
-==============================================================
-protected_symlinks:
+protected_symlinks
+------------------
A long-standing class of security issues is the symlink-based
time-of-check-time-of-use race, most commonly seen in world-writable
This protection is based on the restrictions in Openwall and grsecurity.
-==============================================================
suid_dumpable:
+--------------
This value can be used to query and set the core dump mode for setuid
or otherwise protected/tainted binaries. The modes are
-0 - (default) - traditional behaviour. Any process which has changed
- privilege levels or is execute only will not be dumped.
-1 - (debug) - all processes dump core when possible. The core dump is
- owned by the current user and no security is applied. This is
- intended for system debugging situations only. Ptrace is unchecked.
- This is insecure as it allows regular users to examine the memory
- contents of privileged processes.
-2 - (suidsafe) - any binary which normally would not be dumped is dumped
- anyway, but only if the "core_pattern" kernel sysctl is set to
- either a pipe handler or a fully qualified path. (For more details
- on this limitation, see CVE-2006-2451.) This mode is appropriate
- when administrators are attempting to debug problems in a normal
- environment, and either have a core dump pipe handler that knows
- to treat privileged core dumps with care, or specific directory
- defined for catching core dumps. If a core dump happens without
- a pipe handler or fully qualifid path, a message will be emitted
- to syslog warning about the lack of a correct setting.
-
-==============================================================
-
-super-max & super-nr:
+= ========== ===============================================================
+0 (default) traditional behaviour. Any process which has changed
+ privilege levels or is execute only will not be dumped.
+1 (debug) all processes dump core when possible. The core dump is
+ owned by the current user and no security is applied. This is
+ intended for system debugging situations only.
+ Ptrace is unchecked.
+ This is insecure as it allows regular users to examine the
+ memory contents of privileged processes.
+2 (suidsafe) any binary which normally would not be dumped is dumped
+ anyway, but only if the "core_pattern" kernel sysctl is set to
+ either a pipe handler or a fully qualified path. (For more
+ details on this limitation, see CVE-2006-2451.) This mode is
+ appropriate when administrators are attempting to debug
+ problems in a normal environment, and either have a core dump
+ pipe handler that knows to treat privileged core dumps with
+ care, or specific directory defined for catching core dumps.
+ If a core dump happens without a pipe handler or fully
+ qualified path, a message will be emitted to syslog warning
+ about the lack of a correct setting.
+= ========== ===============================================================
+
+
+super-max & super-nr
+--------------------
These numbers control the maximum number of superblocks, and
thus the maximum number of mounted filesystems the kernel
mount more filesystems than the current value in super-max
allows you to.
-==============================================================
-aio-nr & aio-max-nr:
+aio-nr & aio-max-nr
+-------------------
aio-nr shows the current system-wide number of asynchronous io
requests. aio-max-nr allows you to change the maximum value
aio-nr can grow to.
-==============================================================
-mount-max:
+mount-max
+---------
This denotes the maximum number of mounts that may exist
in a mount namespace.
-==============================================================
2. /proc/sys/fs/binfmt_misc
-----------------------------------------------------------
+===========================
Documentation for the files in /proc/sys/fs/binfmt_misc is
in Documentation/admin-guide/binfmt-misc.rst.
3. /proc/sys/fs/mqueue - POSIX message queues filesystem
-----------------------------------------------------------
+========================================================
+
The "mqueue" filesystem provides the necessary kernel features to enable the
creation of a user space library that implements the POSIX message queues
exceed msgsize_max, the default value is initialized msgsize_max.
4. /proc/sys/fs/epoll - Configuration options for the epoll interface
---------------------------------------------------------
+=====================================================================
This directory contains configuration options for the epoll(7) interface.
on a 64bit one.
The current default value for max_user_watches is the 1/32 of the available
low memory, divided for the "watch" cost in bytes.
-
-Documentation for /proc/sys/ kernel version 2.2.10
- (c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
+:orphan:
+
+===========================
+Documentation for /proc/sys
+===========================
+
+Copyright (c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
+
+------------------------------------------------------------------------------
'Why', I hear you ask, 'would anyone even _want_ documentation
for them sysctl files? If anybody really needs it, it's all in
Furthermore, the programmers who built sysctl have built it to
be actually used, not just for the fun of programming it :-)
-==============================================================
+------------------------------------------------------------------------------
Legal blurb:
As usual, there are two main things to consider:
+
1. you get what you pay for
2. it's free
Rik van Riel.
-==============================================================
+--------------------------------------------------------------
-Introduction:
+Introduction
+============
Sysctl is a means of configuring certain aspects of the kernel
at run-time, and the /proc/sys/ directory is there so that you
don't even need special tools to do it!
In fact, there are only four things needed to use these config
facilities:
+
- a running Linux system
- root access
- common sense (this is especially hard to come by these days)
one part of the kernel, so you can do configuration on a piece
by piece basis, or just some 'thematic frobbing'.
-The subdirs are about:
+This documentation is about:
+
+=============== ===============================================================
abi/ execution domains & personalities
debug/ <empty>
dev/ device specific information (eg dev/cdrom/info)
vm/ memory management tuning
buffer and cache management
user/ Per user per user namespace limits
+=============== ===============================================================
These are the subdirs I have on my system. There might be more
or other subdirs in another setup. If you see another dir, I'd
really like to hear about it :-)
+
+.. toctree::
+ :maxdepth: 1
+
+ abi
+ fs
+ kernel
+ net
+ sunrpc
+ user
+ vm
-Documentation for /proc/sys/kernel/* kernel version 2.2.10
- (c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
- (c) 2009, Shen Feng<shen@cn.fujitsu.com>
+===================================
+Documentation for /proc/sys/kernel/
+===================================
-For general info and legal blurb, please look in README.
+kernel version 2.2.10
-==============================================================
+Copyright (c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
+
+Copyright (c) 2009, Shen Feng<shen@cn.fujitsu.com>
+
+For general info and legal blurb, please look in index.rst.
+
+------------------------------------------------------------------------------
This file contains documentation for the sysctl files in
/proc/sys/kernel/ and is valid for Linux kernel version 2.2.
- watchdog_thresh
- version
-==============================================================
acct:
+=====
highwater lowwater frequency
if we got >=4%; consider information about amount of free space
valid for 30 seconds.
-==============================================================
acpi_video_flags:
+=================
flags
See Doc*/kernel/power/video.txt, it allows mode of video boot to be
set during run time.
-==============================================================
auto_msgmni:
+============
This variable has no effect and may be removed in future kernel
releases. Reading it always returns 0.
Echoing "0" turned it off. auto_msgmni default value was 1.
-==============================================================
-
bootloader_type:
+================
x86 bootloader identification
See the type_of_loader and ext_loader_type fields in
Documentation/x86/boot.rst for additional information.
-==============================================================
bootloader_version:
+===================
x86 bootloader version
See the type_of_loader and ext_loader_ver fields in
Documentation/x86/boot.rst for additional information.
-==============================================================
-cap_last_cap
+cap_last_cap:
+=============
Highest valid capability of the running kernel. Exports
CAP_LAST_CAP from the kernel.
-==============================================================
core_pattern:
+=============
core_pattern is used to specify a core dumpfile pattern name.
-. max length 127 characters; default value is "core"
-. core_pattern is used as a pattern template for the output filename;
+
+* max length 127 characters; default value is "core"
+* core_pattern is used as a pattern template for the output filename;
certain string patterns (beginning with '%') are substituted with
their actual values.
-. backward compatibility with core_uses_pid:
+* backward compatibility with core_uses_pid:
+
If core_pattern does not include "%p" (default does not)
and core_uses_pid is set, then .PID will be appended to
the filename.
-. corename format specifiers:
+
+* corename format specifiers::
+
%<NUL> '%' is dropped
%% output one '%'
%p pid
%e executable filename (may be shortened)
%E executable path
%<OTHER> both are dropped
-. If the first character of the pattern is a '|', the kernel will treat
+
+* If the first character of the pattern is a '|', the kernel will treat
the rest of the pattern as a command to run. The core dump will be
written to the standard input of that program instead of to a file.
-==============================================================
core_pipe_limit:
+================
This sysctl is only applicable when core_pattern is configured to pipe
core files to a user space helper (when the first character of
process is not guaranteed access to /proc/<crashing pid>/). This
value defaults to 0.
-==============================================================
core_uses_pid:
+==============
The default coredump filename is "core". By setting
core_uses_pid to 1, the coredump filename becomes core.PID.
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.
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.
+Note:
+ when a program (like dosemu) has the keyboard in 'raw'
+ mode, the ctrl-alt-del is intercepted by the program before it
+ ever reaches the kernel tty layer, and it's up to the program
+ to decide what to do with it.
-==============================================================
dmesg_restrict:
+===============
This toggle indicates whether unprivileged users are prevented
from using dmesg(8) to view messages from the kernel's log buffer.
The kernel config option CONFIG_SECURITY_DMESG_RESTRICT sets the
default value of dmesg_restrict.
-==============================================================
domainname & hostname:
+======================
These files can be used to set the NIS/YP domainname and the
hostname of your box in exactly the same way as the commands
-domainname and hostname, i.e.:
-# echo "darkstar" > /proc/sys/kernel/hostname
-# echo "mydomain" > /proc/sys/kernel/domainname
-has the same effect as
-# hostname "darkstar"
-# domainname "mydomain"
+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)
domain names are in general different. For a detailed discussion
see the hostname(1) man page.
-==============================================================
+
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
0: do nothing. This is the default behavior.
1: on detection capture more debug information.
-==============================================================
+
hardlockup_panic:
+=================
This parameter can be used to control whether the kernel panics
when a hard lockup is detected.
See Documentation/lockup-watchdogs.txt for more information. This can
also be set using the nmi_watchdog kernel parameter.
-==============================================================
hotplug:
+========
Path for the hotplug policy agent.
Default value is "/sbin/hotplug".
-==============================================================
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.
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:
+=======================
When a task in D state did not get scheduled
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.
+
Possible values to set are in range {0..LONG_MAX/HZ}.
-==============================================================
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
0 (default): means use hung_task_timeout_secs as checking interval.
Possible values to set are in range {0..LONG_MAX/HZ}.
-==============================================================
hung_task_warnings:
+===================
The maximum number of warnings to report. During a check interval
if a hung task is detected, this value is decreased by 1.
-1: report an infinite number of warnings.
-==============================================================
hyperv_record_panic_msg:
+========================
Controls whether the panic kmsg data should be reported to Hyper-V.
1: report the panic kmsg data. This is the default behavior.
-==============================================================
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
later use) an image without it being altered. Generally used together
with the "modules_disabled" sysctl.
-==============================================================
kptr_restrict:
+==============
This toggle indicates whether restrictions are placed on
exposing kernel addresses via /proc and other interfaces.
When kptr_restrict is set to (2), kernel pointers printed using
%pK will be replaced with 0's regardless of privileges.
-==============================================================
l2cr: (PPC only)
+================
This flag controls the L2 cache of G3 processor boards. If
0, the cache is disabled. Enabled if nonzero.
-==============================================================
modules_disabled:
+=================
A toggle value indicating if modules are allowed to be loaded
in an otherwise modular kernel. This toggle defaults to off
neither loaded nor unloaded, and the toggle cannot be set back
to false. Generally used with the "kexec_load_disabled" toggle.
-==============================================================
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.
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
-successful IPC object allocation. If an IPC object allocation syscall
-fails, it is undefined if the value remains unmodified or is reset to -1.
+ 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
+ successful IPC object allocation. If an IPC object allocation syscall
+ fails, it is undefined if the value remains unmodified or is reset to -1.
-==============================================================
nmi_watchdog:
+=============
This parameter can be used to control the NMI watchdog
(i.e. the hard lockup detector) on x86 systems.
- 0 - disable the hard lockup detector
- 1 - enable the hard lockup detector
+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
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
+in a KVM virtual machine. This default can be overridden by adding::
nmi_watchdog=1
to the guest kernel command line (see Documentation/admin-guide/kernel-parameters.rst).
-==============================================================
-numa_balancing
+numa_balancing:
+===============
Enables/disables automatic page fault based NUMA memory
balancing. Memory is moved automatically to nodes
numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms,
numa_balancing_scan_size_mb, and numa_balancing_settle_count sysctls.
-==============================================================
+numa_balancing_scan_period_min_ms, numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms, numa_balancing_scan_size_mb
+===============================================================================================================================
-numa_balancing_scan_period_min_ms, numa_balancing_scan_delay_ms,
-numa_balancing_scan_period_max_ms, numa_balancing_scan_size_mb
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
numa_balancing_scan_size_mb is how many megabytes worth of pages are
scanned for a given scan.
-==============================================================
osrelease, ostype & version:
+============================
+
+::
-# cat osrelease
-2.1.88
-# cat ostype
-Linux
-# cat version
-#5 Wed Feb 25 21:49:24 MET 1998
+ # 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
date behind it indicates the time the kernel was built.
The only way to tune these values is to rebuild the kernel :-)
-==============================================================
overflowgid & overflowuid:
+==========================
if your architecture did not always support 32-bit UIDs (i.e. arm,
i386, m68k, sh, and sparc32), a fixed UID and GID will be returned to
These sysctls allow you to change the value of the fixed UID and GID.
The default is 65534.
-==============================================================
panic:
+======
The value in this file represents the number of seconds the kernel
waits before rebooting on a panic. When you use the software watchdog,
the recommended setting is 60.
-==============================================================
panic_on_io_nmi:
+================
Controls the kernel's behavior when a CPU receives an NMI caused by
an IO error.
servers issue this sort of NMI when the dump button is pushed,
and you can use this option to take a crash dump.
-==============================================================
panic_on_oops:
+==============
Controls the kernel's behaviour when an oops or BUG is encountered.
0: try to continue operation
-1: panic immediately. If the `panic' sysctl is also non-zero then the
+1: panic immediately. If the `panic` sysctl is also non-zero then the
machine will be rebooted.
-==============================================================
panic_on_stackoverflow:
+=======================
Controls the kernel's behavior when detecting the overflows of
kernel, IRQ and exception stacks except a user stack.
1: panic immediately.
-==============================================================
panic_on_unrecovered_nmi:
+=========================
The default Linux behaviour on an NMI of either memory or unknown is
to continue operation. For many environments such as scientific
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().
1: call panic() after printing out WARN() location.
-==============================================================
panic_print:
+============
Bitmask for printing system info when panic happens. User can chose
combination of the following bits:
-bit 0: print all tasks info
-bit 1: print system memory info
-bit 2: print timer info
-bit 3: print locks info if CONFIG_LOCKDEP is on
-bit 4: print ftrace buffer
+===== ========================================
+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::
-So for example to print tasks and memory info on panic, user can:
echo 3 > /proc/sys/kernel/panic_print
-==============================================================
panic_on_rcu_stall:
+===================
When set to 1, calls panic() after RCU stall detection messages. This
is useful to define the root cause of RCU stalls using a vmcore.
1: panic() after printing RCU stall messages.
-==============================================================
perf_cpu_time_max_percent:
+==========================
Hints to the kernel how much CPU time it should be allowed to
use to handle perf sampling events. If the perf subsystem
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
+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
+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
length is exceeded. Set to 0 if you truly do not care
how much CPU is consumed.
-==============================================================
perf_event_paranoid:
+====================
Controls use of the performance events system by unprivileged
users (without CAP_SYS_ADMIN). The default value is 2.
- -1: Allow use of (almost) all events by all users
+=== ==================================================================
+ -1 Allow use of (almost) all events by all users
+
Ignore mlock limit after perf_event_mlock_kb without CAP_IPC_LOCK
->=0: Disallow ftrace function tracepoint by users without CAP_SYS_ADMIN
+
+>=0 Disallow ftrace function tracepoint by users without CAP_SYS_ADMIN
+
Disallow raw tracepoint access by users without CAP_SYS_ADMIN
->=1: Disallow CPU event access by users without CAP_SYS_ADMIN
->=2: Disallow kernel profiling by users without CAP_SYS_ADMIN
-==============================================================
+>=1 Disallow CPU event access by users without CAP_SYS_ADMIN
+
+>=2 Disallow kernel profiling by users without CAP_SYS_ADMIN
+=== ==================================================================
+
perf_event_max_stack:
+=====================
Controls maximum number of stack frames to copy for (attr.sample_type &
PERF_SAMPLE_CALLCHAIN) configured events, for instance, when using
The default value is 127.
-==============================================================
perf_event_mlock_kb:
+====================
Control size of per-cpu ring buffer not counted agains mlock limit.
The default value is 512 + 1 page
-==============================================================
perf_event_max_contexts_per_stack:
+==================================
Controls maximum number of stack frame context entries for
(attr.sample_type & PERF_SAMPLE_CALLCHAIN) configured events, for
The default value is 8.
-==============================================================
pid_max:
+========
PID allocation wrap value. When the kernel's next PID value
reaches this value, it wraps back to a minimum PID value.
PIDs of value pid_max or larger are not allocated.
-==============================================================
ns_last_pid:
+============
The last pid allocated in the current (the one task using this sysctl
lives in) pid namespace. When selecting a pid for a next task on fork
kernel tries to allocate a number starting from this one.
-==============================================================
powersave-nap: (PPC only)
+=========================
If set, Linux-PPC will use the 'nap' mode of powersaving,
otherwise the 'doze' mode will be used.
==============================================================
printk:
+=======
The four values in printk denote: console_loglevel,
default_message_loglevel, minimum_console_loglevel and
logging error messages. See 'man 2 syslog' for more info on
the different loglevels.
-- console_loglevel: messages with a higher priority than
- this will be printed to the console
-- default_message_loglevel: messages without an explicit priority
- will be printed with this priority
-- minimum_console_loglevel: minimum (highest) value to which
- console_loglevel can be set
-- default_console_loglevel: default value for console_loglevel
+- console_loglevel:
+ messages with a higher priority than
+ this will be printed to the console
+- default_message_loglevel:
+ messages without an explicit priority
+ will be printed with this priority
+- minimum_console_loglevel:
+ minimum (highest) value to which
+ console_loglevel can be set
+- default_console_loglevel:
+ default value for console_loglevel
-==============================================================
printk_delay:
+=============
Delay each printk message in printk_delay milliseconds
Value from 0 - 10000 is allowed.
-==============================================================
printk_ratelimit:
+=================
Some warning messages are rate limited. printk_ratelimit specifies
the minimum length of time between these messages (in jiffies), by
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.
-==============================================================
printk_devkmsg:
+===============
Control the logging to /dev/kmsg from userspace:
-ratelimit: default, ratelimited
+ratelimit:
+ default, ratelimited
+
on: unlimited logging to /dev/kmsg from userspace
+
off: logging to /dev/kmsg disabled
The kernel command line parameter printk.devkmsg= overrides this and is
a one-time setting until next reboot: once set, it cannot be changed by
this sysctl interface anymore.
-==============================================================
randomize_va_space:
+===================
This option can be used to select the type of process address
space randomization that is used in the system, for architectures
that support this feature.
-0 - Turn the process address space randomization off. This is the
+== ===========================================================================
+0 Turn the process address space randomization off. This is the
default for architectures that do not support this feature anyways,
and kernels that are booted with the "norandmaps" parameter.
-1 - Make the addresses of mmap base, stack and VDSO page randomized.
+1 Make the addresses of mmap base, stack and VDSO page randomized.
This, among other things, implies that shared libraries will be
loaded to random addresses. Also for PIE-linked binaries, the
location of code start is randomized. This is the default if the
CONFIG_COMPAT_BRK option is enabled.
-2 - Additionally enable heap randomization. This is the default if
+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
Systems with ancient and/or broken binaries should be configured
with CONFIG_COMPAT_BRK enabled, which excludes the heap from process
address space randomization.
+== ===========================================================================
-==============================================================
reboot-cmd: (Sparc only)
+========================
??? This seems to be a way to give an argument to the Sparc
ROM/Flash boot loader. Maybe to tell it what to do after
rebooting. ???
-==============================================================
rtsig-max & rtsig-nr:
+=====================
The file rtsig-max can be used to tune the maximum number
of POSIX realtime (queued) signals that can be outstanding
rtsig-nr shows the number of RT signals currently queued.
-==============================================================
sched_energy_aware:
+===================
Enables/disables Energy Aware Scheduling (EAS). EAS starts
automatically on platforms where it can run (that is,
requirements for EAS but you do not want to use it, change
this value to 0.
-==============================================================
sched_schedstats:
+=================
Enables/disables scheduler statistics. Enabling this feature
incurs a small amount of overhead in the scheduler but is
useful for debugging and performance tuning.
-==============================================================
sg-big-buff:
+============
This file shows the size of the generic SCSI (sg) buffer.
You can't tune it just yet, but you could change it on
you can come up with one, you probably know what you
are doing anyway :)
-==============================================================
shmall:
+=======
This parameter sets the total amount of shared memory pages that
can be used system wide. Hence, SHMALL should always be at least
If you are not sure what the default PAGE_SIZE is on your Linux
system, you can run the following command:
-# getconf PAGE_SIZE
+ # getconf PAGE_SIZE
-==============================================================
shmmax:
+=======
This value can be used to query and set the run time limit
on the maximum shared memory segment size that can be created.
Shared memory segments up to 1Gb are now supported in the
kernel. This value defaults to SHMMAX.
-==============================================================
shm_rmid_forced:
+================
Linux lets you set resource limits, including how much memory one
process can consume, via setrlimit(2). Unfortunately, shared memory
Note that if you change this from 0 to 1, already created segments
without users and with a dead originative process will be destroyed.
-==============================================================
sysctl_writes_strict:
+=====================
Control how file position affects the behavior of updating sysctl values
via the /proc/sys interface:
- -1 - Legacy per-write sysctl value handling, with no printk warnings.
+ == ======================================================================
+ -1 Legacy per-write sysctl value handling, with no printk warnings.
Each write syscall must fully contain the sysctl value to be
written, and multiple writes on the same sysctl file descriptor
will rewrite the sysctl value, regardless of file position.
- 0 - Same behavior as above, but warn about processes that perform writes
+ 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
+ 1 (default) Respect file position when writing sysctl strings. Multiple
writes will append to the sysctl value buffer. Anything past the max
length of the sysctl value buffer will be ignored. Writes to numeric
sysctl entries must always be at file position 0 and the value must
be fully contained in the buffer sent in the write syscall.
+ == ======================================================================
-==============================================================
softlockup_all_cpu_backtrace:
+=============================
This value controls the soft lockup detector thread's behavior
when a soft lockup condition is detected as to whether or not
1: on detection capture more debug information.
-==============================================================
-soft_watchdog
+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
the watchdog timer function, otherwise the NMI watchdog - if enabled - can
detect a hard lockup condition.
-==============================================================
-stack_erasing
+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.
1: kernel stack erasing is enabled (default), it is performed before
returning to the userspace at the end of syscalls.
-==============================================================
+
tainted
+=======
Non-zero if the kernel has been tainted. Numeric values, which can be
ORed together. The letters are seen in "Tainted" line of Oops reports.
- 1 (P): proprietary module was loaded
- 2 (F): module was force loaded
- 4 (S): SMP kernel oops on an officially SMP incapable processor
- 8 (R): module was force unloaded
- 16 (M): processor reported a Machine Check Exception (MCE)
- 32 (B): bad page referenced or some unexpected page flags
- 64 (U): taint requested by userspace application
- 128 (D): kernel died recently, i.e. there was an OOPS or BUG
- 256 (A): an ACPI table was overridden by user
- 512 (W): kernel issued warning
- 1024 (C): staging driver was loaded
- 2048 (I): workaround for bug in platform firmware applied
- 4096 (O): externally-built ("out-of-tree") module was loaded
- 8192 (E): unsigned module was loaded
- 16384 (L): soft lockup occurred
- 32768 (K): kernel has been live patched
- 65536 (X): Auxiliary taint, defined and used by for distros
-131072 (T): The kernel was built with the struct randomization plugin
+====== ===== ==============================================================
+ 1 `(P)` proprietary module was loaded
+ 2 `(F)` module was force loaded
+ 4 `(S)` SMP kernel oops on an officially SMP incapable processor
+ 8 `(R)` module was force unloaded
+ 16 `(M)` processor reported a Machine Check Exception (MCE)
+ 32 `(B)` bad page referenced or some unexpected page flags
+ 64 `(U)` taint requested by userspace application
+ 128 `(D)` kernel died recently, i.e. there was an OOPS or BUG
+ 256 `(A)` an ACPI table was overridden by user
+ 512 `(W)` kernel issued warning
+ 1024 `(C)` staging driver was loaded
+ 2048 `(I)` workaround for bug in platform firmware applied
+ 4096 `(O)` externally-built ("out-of-tree") module was loaded
+ 8192 `(E)` unsigned module was loaded
+ 16384 `(L)` soft lockup occurred
+ 32768 `(K)` kernel has been live patched
+ 65536 `(X)` Auxiliary taint, defined and used by for distros
+131072 `(T)` The kernel was built with the struct randomization plugin
+====== ===== ==============================================================
See Documentation/admin-guide/tainted-kernels.rst for more information.
-==============================================================
-threads-max
+threads-max:
+============
This value controls the maximum number of threads that can be created
using fork().
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.
thread structures would occupy too much (more than 1/8th) of the
available RAM pages threads-max is reduced accordingly.
-==============================================================
unknown_nmi_panic:
+==================
The value in this file affects behavior of handling NMI. When the
value is non-zero, unknown NMI is trapped and then panic occurs. At
NMI switch that most IA32 servers have fires unknown NMI up, for
example. If a system hangs up, try pressing the NMI switch.
-==============================================================
watchdog:
+=========
This parameter can be used to disable or enable the soft lockup detector
_and_ the NMI watchdog (i.e. the hard lockup detector) at the same time.
0 - disable both lockup detectors
+
1 - enable both lockup detectors
The soft lockup detector and the NMI watchdog can also be disabled or
enabled individually, using the soft_watchdog and nmi_watchdog parameters.
-If the watchdog parameter is read, for example by executing
+If the watchdog parameter is read, for example by executing::
cat /proc/sys/kernel/watchdog
the output of this command (0 or 1) shows the logical OR of soft_watchdog
and nmi_watchdog.
-==============================================================
watchdog_cpumask:
+=================
This value can be used to control on which cpus the watchdog may run.
The default cpumask is all possible cores, but if NO_HZ_FULL is
The argument value is the standard cpulist format for cpumasks,
so for example to enable the watchdog on cores 0, 2, 3, and 4 you
-might say:
+might say::
echo 0,2-4 > /proc/sys/kernel/watchdog_cpumask
-==============================================================
watchdog_thresh:
+================
This value can be used to control the frequency of hrtimer and NMI
events and the soft and hard lockup thresholds. The default threshold
The softlockup threshold is (2 * watchdog_thresh). Setting this
tunable to zero will disable lockup detection altogether.
-
-==============================================================
-Documentation for /proc/sys/net/*
- (c) 1999 Terrehon Bowden <terrehon@pacbell.net>
- Bodo Bauer <bb@ricochet.net>
- (c) 2000 Jorge Nerin <comandante@zaralinux.com>
- (c) 2009 Shen Feng <shen@cn.fujitsu.com>
+================================
+Documentation for /proc/sys/net/
+================================
-For general info and legal blurb, please look in README.
+Copyright
-==============================================================
+Copyright (c) 1999
+
+ - Terrehon Bowden <terrehon@pacbell.net>
+ - Bodo Bauer <bb@ricochet.net>
+
+Copyright (c) 2000
+
+ - Jorge Nerin <comandante@zaralinux.com>
+
+Copyright (c) 2009
+
+ - Shen Feng <shen@cn.fujitsu.com>
+
+For general info and legal blurb, please look in index.rst.
+
+------------------------------------------------------------------------------
This file contains the documentation for the sysctl files in
/proc/sys/net
Table : Subdirectories in /proc/sys/net
-..............................................................................
- Directory Content Directory Content
- core General parameter appletalk Appletalk protocol
- unix Unix domain sockets netrom NET/ROM
- 802 E802 protocol ax25 AX25
- ethernet Ethernet protocol rose X.25 PLP layer
- ipv4 IP version 4 x25 X.25 protocol
- ipx IPX token-ring IBM token ring
- bridge Bridging decnet DEC net
- ipv6 IP version 6 tipc TIPC
-..............................................................................
+
+ ========= =================== = ========== ==================
+ Directory Content Directory Content
+ ========= =================== = ========== ==================
+ core General parameter appletalk Appletalk protocol
+ unix Unix domain sockets netrom NET/ROM
+ 802 E802 protocol ax25 AX25
+ ethernet Ethernet protocol rose X.25 PLP layer
+ ipv4 IP version 4 x25 X.25 protocol
+ ipx IPX token-ring IBM token ring
+ bridge Bridging decnet DEC net
+ ipv6 IP version 6 tipc TIPC
+ ========= =================== = ========== ==================
1. /proc/sys/net/core - Network core options
--------------------------------------------------------
+============================================
bpf_jit_enable
--------------
through bpf(2) and passing a verifier in the kernel, a JIT will then
translate these BPF proglets into native CPU instructions. There are
two flavors of JITs, the newer eBPF JIT currently supported on:
+
- x86_64
- x86_32
- arm64
- riscv
And the older cBPF JIT supported on the following archs:
+
- mips
- ppc
- sparc
tcpdump filters, seccomp rules, etc, but not mentioned eBPF
programs loaded through bpf(2).
-Values :
- 0 - disable the JIT (default value)
- 1 - enable the JIT
- 2 - enable the JIT and ask the compiler to emit traces on kernel log.
+Values:
+
+ - 0 - disable the JIT (default value)
+ - 1 - enable the JIT
+ - 2 - enable the JIT and ask the compiler to emit traces on kernel log.
bpf_jit_harden
--------------
This enables hardening for the BPF JIT compiler. Supported are eBPF
JIT backends. Enabling hardening trades off performance, but can
mitigate JIT spraying.
-Values :
- 0 - disable JIT hardening (default value)
- 1 - enable JIT hardening for unprivileged users only
- 2 - enable JIT hardening for all users
+
+Values:
+
+ - 0 - disable JIT hardening (default value)
+ - 1 - enable JIT hardening for unprivileged users only
+ - 2 - enable JIT hardening for all users
bpf_jit_kallsyms
----------------
in /proc/kallsyms. This enables export of these addresses, which can
be used for debugging/tracing. If bpf_jit_harden is enabled, this
feature is disabled.
+
Values :
- 0 - disable JIT kallsyms export (default value)
- 1 - enable JIT kallsyms export for privileged users only
+
+ - 0 - disable JIT kallsyms export (default value)
+ - 1 - enable JIT kallsyms export for privileged users only
bpf_jit_limit
-------------
in bytes.
dev_weight
---------------
+----------
The maximum number of packets that kernel can handle on a NAPI interrupt,
it's a Per-CPU variable. For drivers that support LRO or GRO_HW, a hardware
Default: 64
dev_weight_rx_bias
---------------
+------------------
RPS (e.g. RFS, aRFS) processing is competing with the registered NAPI poll function
of the driver for the per softirq cycle netdev_budget. This parameter influences
dev_weight adaptable for asymmetric CPU needs on RX/TX side of the network stack.
(see dev_weight_tx_bias) It is effective on a per CPU basis. Determination is based
on dev_weight and is calculated multiplicative (dev_weight * dev_weight_rx_bias).
+
Default: 1
dev_weight_tx_bias
---------------
+------------------
Scales the maximum number of packets that can be processed during a TX softirq cycle.
Effective on a per CPU basis. Allows scaling of current dev_weight for asymmetric
net stack processing needs. Be careful to avoid making TX softirq processing a CPU hog.
+
Calculation is based on dev_weight (dev_weight * dev_weight_tx_bias).
+
Default: 1
default_qdisc
---------------
+-------------
The default queuing discipline to use for network devices. This allows
overriding the default of pfifo_fast with an alternative. Since the default
interfaces still use mq as root qdisc, which in turn uses this default for its
leaves. Virtual devices (like e.g. lo or veth) ignore this setting and instead
default to noqueue.
+
Default: pfifo_fast
busy_read
-----------------
+---------
+
Low latency busy poll timeout for socket reads. (needs CONFIG_NET_RX_BUSY_POLL)
Approximate time in us to busy loop waiting for packets on the device queue.
This sets the default value of the SO_BUSY_POLL socket option.
Can be set or overridden per socket by setting socket option SO_BUSY_POLL,
which is the preferred method of enabling. If you need to enable the feature
globally via sysctl, a value of 50 is recommended.
+
Will increase power usage.
+
Default: 0 (off)
busy_poll
Note that only sockets with SO_BUSY_POLL set will be busy polled,
so you want to either selectively set SO_BUSY_POLL on those sockets or set
sysctl.net.busy_read globally.
+
Will increase power usage.
+
Default: 0 (off)
rmem_default
Allow processes to receive tx timestamps looped together with the original
packet contents. If disabled, transmit timestamp requests from unprivileged
processes are dropped unless socket option SOF_TIMESTAMPING_OPT_TSONLY is set.
+
Default: 1 (on)
Some user space might need to gather its content even if drivers do not
provide ethtool -x support yet.
-myhost:~# cat /proc/sys/net/core/netdev_rss_key
-84:50:f4:00:a8:15:d1:a7:e9:7f:1d:60:35:c7:47:25:42:97:74:ca:56:bb:b6:a1:d8: ... (52 bytes total)
+::
+
+ myhost:~# cat /proc/sys/net/core/netdev_rss_key
+ 84:50:f4:00:a8:15:d1:a7:e9:7f:1d:60:35:c7:47:25:42:97:74:ca:56:bb:b6:a1:d8: ... (52 bytes total)
File contains nul bytes if no driver ever called netdev_rss_key_fill() function.
+
Note:
-/proc/sys/net/core/netdev_rss_key contains 52 bytes of key,
-but most drivers only use 40 bytes of it.
+ /proc/sys/net/core/netdev_rss_key contains 52 bytes of key,
+ but most drivers only use 40 bytes of it.
+
+::
-myhost:~# ethtool -x eth0
-RX flow hash indirection table for eth0 with 8 RX ring(s):
- 0: 0 1 2 3 4 5 6 7
-RSS hash key:
-84:50:f4:00:a8:15:d1:a7:e9:7f:1d:60:35:c7:47:25:42:97:74:ca:56:bb:b6:a1:d8:43:e3:c9:0c:fd:17:55:c2:3a:4d:69:ed:f1:42:89
+ myhost:~# ethtool -x eth0
+ RX flow hash indirection table for eth0 with 8 RX ring(s):
+ 0: 0 1 2 3 4 5 6 7
+ RSS hash key:
+ 84:50:f4:00:a8:15:d1:a7:e9:7f:1d:60:35:c7:47:25:42:97:74:ca:56:bb:b6:a1:d8:43:e3:c9:0c:fd:17:55:c2:3a:4d:69:ed:f1:42:89
netdev_tstamp_prequeue
----------------------
Default : 0 (for compatibility reasons)
devconf_inherit_init_net
-----------------------------
+------------------------
Controls if a new network namespace should inherit all current
settings under /proc/sys/net/{ipv4,ipv6}/conf/{all,default}/. By
Default : 0 (for compatibility reasons)
2. /proc/sys/net/unix - Parameters for Unix domain sockets
--------------------------------------------------------
+----------------------------------------------------------
There is only one file in this directory.
unix_dgram_qlen limits the max number of datagrams queued in Unix domain
3. /proc/sys/net/ipv4 - IPV4 settings
--------------------------------------------------------
+-------------------------------------
Please see: Documentation/networking/ip-sysctl.txt and ipvs-sysctl.txt for
descriptions of these entries.
4. Appletalk
--------------------------------------------------------
+------------
The /proc/sys/net/appletalk directory holds the Appletalk configuration data
when Appletalk is loaded. The configurable parameters are:
5. IPX
--------------------------------------------------------
+------
The IPX protocol has no tunable values in proc/sys/net.
address of the router (or Connected) for internal networks.
6. TIPC
--------------------------------------------------------
+-------
tipc_rmem
-----------
+---------
The TIPC protocol now has a tunable for the receive memory, similar to the
tcp_rmem - i.e. a vector of 3 INTEGERs: (min, default, max)
+::
+
# cat /proc/sys/net/tipc/tipc_rmem
4252725 34021800 68043600
#
preserved in order to be consistent with things like tcp_rmem.
named_timeout
---------------
+-------------
TIPC name table updates are distributed asynchronously in a cluster, without
any form of transaction handling. This means that different race scenarios are
-Documentation for /proc/sys/sunrpc/* kernel version 2.2.10
- (c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
+===================================
+Documentation for /proc/sys/sunrpc/
+===================================
-For general info and legal blurb, please look in README.
+kernel version 2.2.10
-==============================================================
+Copyright (c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
+
+For general info and legal blurb, please look in index.rst.
+
+------------------------------------------------------------------------------
This file contains the documentation for the sysctl files in
/proc/sys/sunrpc and is valid for Linux kernel version 2.2.
-Documentation for /proc/sys/user/* kernel version 4.9.0
- (c) 2016 Eric Biederman <ebiederm@xmission.com>
+=================================
+Documentation for /proc/sys/user/
+=================================
-==============================================================
+kernel version 4.9.0
+
+Copyright (c) 2016 Eric Biederman <ebiederm@xmission.com>
+
+------------------------------------------------------------------------------
This file contains the documentation for the sysctl files in
/proc/sys/user.
Currently, these files are in /proc/sys/user:
-- max_cgroup_namespaces
+max_cgroup_namespaces
+=====================
The maximum number of cgroup namespaces that any user in the current
user namespace may create.
-- max_ipc_namespaces
+max_ipc_namespaces
+==================
The maximum number of ipc namespaces that any user in the current
user namespace may create.
-- max_mnt_namespaces
+max_mnt_namespaces
+==================
The maximum number of mount namespaces that any user in the current
user namespace may create.
-- max_net_namespaces
+max_net_namespaces
+==================
The maximum number of network namespaces that any user in the
current user namespace may create.
-- max_pid_namespaces
+max_pid_namespaces
+==================
The maximum number of pid namespaces that any user in the current
user namespace may create.
-- max_user_namespaces
+max_user_namespaces
+===================
The maximum number of user namespaces that any user in the current
user namespace may create.
-- max_uts_namespaces
+max_uts_namespaces
+==================
The maximum number of user namespaces that any user in the current
user namespace may create.
-Documentation for /proc/sys/vm/* kernel version 2.6.29
- (c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
- (c) 2008 Peter W. Morreale <pmorreale@novell.com>
+===============================
+Documentation for /proc/sys/vm/
+===============================
-For general info and legal blurb, please look in README.
+kernel version 2.6.29
-==============================================================
+Copyright (c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
+
+Copyright (c) 2008 Peter W. Morreale <pmorreale@novell.com>
+
+For general info and legal blurb, please look in index.rst.
+
+------------------------------------------------------------------------------
This file contains the documentation for the sysctl files in
/proc/sys/vm and is valid for Linux kernel version 2.6.29.
- watermark_scale_factor
- zone_reclaim_mode
-==============================================================
admin_reserve_kbytes
+====================
The amount of free memory in the system that should be reserved for users
with the capability cap_sys_admin.
Changing this takes effect whenever an application requests memory.
-==============================================================
block_dump
+==========
block_dump enables block I/O debugging when set to a nonzero value. More
information on block I/O debugging is in Documentation/laptops/laptop-mode.rst.
-==============================================================
compact_memory
+==============
Available only when CONFIG_COMPACTION is set. When 1 is written to the file,
all zones are compacted such that free memory is available in contiguous
blocks where possible. This can be important for example in the allocation of
huge pages although processes will also directly compact memory as required.
-==============================================================
compact_unevictable_allowed
+===========================
Available only when CONFIG_COMPACTION is set. When set to 1, compaction is
allowed to examine the unevictable lru (mlocked pages) for pages to compact.
acceptable trade for large contiguous free memory. Set to 0 to prevent
compaction from moving pages that are unevictable. Default value is 1.
-==============================================================
dirty_background_bytes
+======================
Contains the amount of dirty memory at which the background kernel
flusher threads will start writeback.
-Note: dirty_background_bytes is the counterpart of dirty_background_ratio. Only
-one of them may be specified at a time. When one sysctl is written it is
-immediately taken into account to evaluate the dirty memory limits and the
-other appears as 0 when read.
+Note:
+ dirty_background_bytes is the counterpart of dirty_background_ratio. Only
+ one of them may be specified at a time. When one sysctl is written it is
+ immediately taken into account to evaluate the dirty memory limits and the
+ other appears as 0 when read.
-==============================================================
dirty_background_ratio
+======================
Contains, as a percentage of total available memory that contains free pages
and reclaimable pages, the number of pages at which the background kernel
The total available memory is not equal to total system memory.
-==============================================================
dirty_bytes
+===========
Contains the amount of dirty memory at which a process generating disk writes
will itself start writeback.
value lower than this limit will be ignored and the old configuration will be
retained.
-==============================================================
dirty_expire_centisecs
+======================
This tunable is used to define when dirty data is old enough to be eligible
for writeout by the kernel flusher threads. It is expressed in 100'ths
of a second. Data which has been dirty in-memory for longer than this
interval will be written out next time a flusher thread wakes up.
-==============================================================
dirty_ratio
+===========
Contains, as a percentage of total available memory that contains free pages
and reclaimable pages, the number of pages at which a process which is
The total available memory is not equal to total system memory.
-==============================================================
dirtytime_expire_seconds
+========================
When a lazytime inode is constantly having its pages dirtied, the inode with
an updated timestamp will never get chance to be written out. And, if the
inode is old enough to be eligible for writeback by the kernel flusher threads.
And, it is also used as the interval to wakeup dirtytime_writeback thread.
-==============================================================
dirty_writeback_centisecs
+=========================
-The kernel flusher threads will periodically wake up and write `old' data
+The kernel flusher threads will periodically wake up and write `old` data
out to disk. This tunable expresses the interval between those wakeups, in
100'ths of a second.
Setting this to zero disables periodic writeback altogether.
-==============================================================
drop_caches
+===========
Writing to this will cause the kernel to drop clean caches, as well as
reclaimable slab objects like dentries and inodes. Once dropped, their
memory becomes free.
-To free pagecache:
+To free pagecache::
+
echo 1 > /proc/sys/vm/drop_caches
-To free reclaimable slab objects (includes dentries and inodes):
+
+To free reclaimable slab objects (includes dentries and inodes)::
+
echo 2 > /proc/sys/vm/drop_caches
-To free slab objects and pagecache:
+
+To free slab objects and pagecache::
+
echo 3 > /proc/sys/vm/drop_caches
This is a non-destructive operation and will not free any dirty objects.
To increase the number of objects freed by this operation, the user may run
-`sync' prior to writing to /proc/sys/vm/drop_caches. This will minimize the
+`sync` prior to writing to /proc/sys/vm/drop_caches. This will minimize the
number of dirty objects on the system and create more candidates to be
dropped.
use outside of a testing or debugging environment is not recommended.
You may see informational messages in your kernel log when this file is
-used:
+used::
cat (1234): drop_caches: 3
These are informational only. They do not mean that anything is wrong
with your system. To disable them, echo 4 (bit 2) into drop_caches.
-==============================================================
extfrag_threshold
+=================
This parameter affects whether the kernel will compact memory or direct
reclaim to satisfy a high-order allocation. The extfrag/extfrag_index file in
The kernel will not compact memory in a zone if the
fragmentation index is <= extfrag_threshold. The default value is 500.
-==============================================================
highmem_is_dirtyable
+====================
Available only for systems with CONFIG_HIGHMEM enabled (32b systems).
only use the low memory and they can fill it up with dirty data without
any throttling.
-==============================================================
hugetlb_shm_group
+=================
hugetlb_shm_group contains group id that is allowed to create SysV
shared memory segment using hugetlb page.
-==============================================================
laptop_mode
+===========
laptop_mode is a knob that controls "laptop mode". All the things that are
controlled by this knob are discussed in Documentation/laptops/laptop-mode.rst.
-==============================================================
legacy_va_layout
+================
If non-zero, this sysctl disables the new 32-bit mmap layout - the kernel
will use the legacy (2.4) layout for all processes.
-==============================================================
lowmem_reserve_ratio
+====================
For some specialised workloads on highmem machines it is dangerous for
the kernel to allow process memory to be allocated from the "lowmem"
can be fatal.
So the Linux page allocator has a mechanism which prevents allocations
-which _could_ use highmem from using too much lowmem. This means that
+which *could* use highmem from using too much lowmem. This means that
a certain amount of lowmem is defended from the possibility of being
captured into pinned user memory.
mechanism will also defend that region from allocations which could use
highmem or lowmem).
-The `lowmem_reserve_ratio' tunable determines how aggressive the kernel is
+The `lowmem_reserve_ratio` tunable determines how aggressive the kernel is
in defending these lower zones.
If you have a machine which uses highmem or ISA DMA and your
applications are using mlock(), or if you are running with no swap then
you probably should change the lowmem_reserve_ratio setting.
-The lowmem_reserve_ratio is an array. You can see them by reading this file.
--
-% cat /proc/sys/vm/lowmem_reserve_ratio
-256 256 32
--
+The lowmem_reserve_ratio is an array. You can see them by reading this file::
+
+ % cat /proc/sys/vm/lowmem_reserve_ratio
+ 256 256 32
But, these values are not used directly. The kernel calculates # of protection
pages for each zones from them. These are shown as array of protection pages
in /proc/zoneinfo like followings. (This is an example of x86-64 box).
-Each zone has an array of protection pages like this.
-
--
-Node 0, zone DMA
- pages free 1355
- min 3
- low 3
- high 4
+Each zone has an array of protection pages like this::
+
+ Node 0, zone DMA
+ pages free 1355
+ min 3
+ low 3
+ high 4
:
:
- numa_other 0
- protection: (0, 2004, 2004, 2004)
+ numa_other 0
+ protection: (0, 2004, 2004, 2004)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
- pagesets
- cpu: 0 pcp: 0
- :
--
+ pagesets
+ cpu: 0 pcp: 0
+ :
+
These protections are added to score to judge whether this zone should be used
for page allocation or should be reclaimed.
normal page requirement. If requirement is DMA zone(index=0), protection[0]
(=0) is used.
-zone[i]'s protection[j] is calculated by following expression.
+zone[i]'s protection[j] is calculated by following expression::
-(i < j):
- zone[i]->protection[j]
- = (total sums of managed_pages from zone[i+1] to zone[j] on the node)
- / lowmem_reserve_ratio[i];
-(i = j):
- (should not be protected. = 0;
-(i > j):
- (not necessary, but looks 0)
+ (i < j):
+ zone[i]->protection[j]
+ = (total sums of managed_pages from zone[i+1] to zone[j] on the node)
+ / lowmem_reserve_ratio[i];
+ (i = j):
+ (should not be protected. = 0;
+ (i > j):
+ (not necessary, but looks 0)
The default values of lowmem_reserve_ratio[i] are
+
+ === ====================================
256 (if zone[i] means DMA or DMA32 zone)
- 32 (others).
+ 32 (others)
+ === ====================================
+
As above expression, they are reciprocal number of ratio.
256 means 1/256. # of protection pages becomes about "0.39%" of total managed
pages of higher zones on the node.
The minimum value is 1 (1/1 -> 100%). The value less than 1 completely
disables protection of the pages.
-==============================================================
max_map_count:
+==============
This file contains the maximum number of memory map areas a process
may have. Memory map areas are used as a side-effect of calling
The default value is 65536.
-=============================================================
memory_failure_early_kill:
+==========================
Control how to kill processes when uncorrected memory error (typically
a 2bit error in a memory module) is detected in the background by hardware
Applications can override this setting individually with the PR_MCE_KILL prctl
-==============================================================
memory_failure_recovery
+=======================
Enable memory failure recovery (when supported by the platform)
0: Always panic on a memory failure.
-==============================================================
-min_free_kbytes:
+min_free_kbytes
+===============
This is used to force the Linux VM to keep a minimum number
of kilobytes free. The VM uses this number to compute a
Setting this too high will OOM your machine instantly.
-=============================================================
-min_slab_ratio:
+min_slab_ratio
+==============
This is available only on NUMA kernels.
The process of reclaiming slab memory is currently not node specific
and may not be fast.
-=============================================================
-min_unmapped_ratio:
+min_unmapped_ratio
+==================
This is available only on NUMA kernels.
The default is 1 percent.
-==============================================================
mmap_min_addr
+=============
This file indicates the amount of address space which a user process will
be restricted from mmapping. Since kernel null dereference bugs could
vast majority of applications to work correctly and provide defense in depth
against future potential kernel bugs.
-==============================================================
-mmap_rnd_bits:
+mmap_rnd_bits
+=============
This value can be used to select the number of bits to use to
determine the random offset to the base address of vma regions
This value can be changed after boot using the
/proc/sys/vm/mmap_rnd_bits tunable
-==============================================================
-mmap_rnd_compat_bits:
+mmap_rnd_compat_bits
+====================
This value can be used to select the number of bits to use to
determine the random offset to the base address of vma regions
This value can be changed after boot using the
/proc/sys/vm/mmap_rnd_compat_bits tunable
-==============================================================
nr_hugepages
+============
Change the minimum size of the hugepage pool.
See Documentation/admin-guide/mm/hugetlbpage.rst
-==============================================================
nr_hugepages_mempolicy
+======================
Change the size of the hugepage pool at run-time on a specific
set of NUMA nodes.
See Documentation/admin-guide/mm/hugetlbpage.rst
-==============================================================
nr_overcommit_hugepages
+=======================
Change the maximum size of the hugepage pool. The maximum is
nr_hugepages + nr_overcommit_hugepages.
See Documentation/admin-guide/mm/hugetlbpage.rst
-==============================================================
nr_trim_pages
+=============
This is available only on NOMMU kernels.
See Documentation/nommu-mmap.txt for more information.
-==============================================================
numa_zonelist_order
+===================
This sysctl is only for NUMA and it is deprecated. Anything but
Node order will fail!
'where the memory is allocated from' is controlled by zonelists.
+
(This documentation ignores ZONE_HIGHMEM/ZONE_DMA32 for simple explanation.
- you may be able to read ZONE_DMA as ZONE_DMA32...)
+you may be able to read ZONE_DMA as ZONE_DMA32...)
In non-NUMA case, a zonelist for GFP_KERNEL is ordered as following.
ZONE_NORMAL -> ZONE_DMA
get memory from ZONE_DMA only when ZONE_NORMAL is not available.
In NUMA case, you can think of following 2 types of order.
-Assume 2 node NUMA and below is zonelist of Node(0)'s GFP_KERNEL
+Assume 2 node NUMA and below is zonelist of Node(0)'s GFP_KERNEL::
-(A) Node(0) ZONE_NORMAL -> Node(0) ZONE_DMA -> Node(1) ZONE_NORMAL
-(B) Node(0) ZONE_NORMAL -> Node(1) ZONE_NORMAL -> Node(0) ZONE_DMA.
+ (A) Node(0) ZONE_NORMAL -> Node(0) ZONE_DMA -> Node(1) ZONE_NORMAL
+ (B) Node(0) ZONE_NORMAL -> Node(1) ZONE_NORMAL -> Node(0) ZONE_DMA.
Type(A) offers the best locality for processes on Node(0), but ZONE_DMA
will be used before ZONE_NORMAL exhaustion. This increases possibility of
Default order is recommended unless this is causing problems for your
system/application.
-==============================================================
oom_dump_tasks
+==============
Enables a system-wide task dump (excluding kernel threads) to be produced
when the kernel performs an OOM-killing and includes such information as
The default value is 1 (enabled).
-==============================================================
oom_kill_allocating_task
+========================
This enables or disables killing the OOM-triggering task in
out-of-memory situations.
The default value is 0.
-==============================================================
-overcommit_kbytes:
+overcommit_kbytes
+=================
When overcommit_memory is set to 2, the committed address space is not
permitted to exceed swap plus this amount of physical RAM. See below.
of them may be specified at a time. Setting one disables the other (which
then appears as 0 when read).
-==============================================================
-overcommit_memory:
+overcommit_memory
+=================
This value contains a flag that enables memory overcommitment.
See Documentation/vm/overcommit-accounting.rst and
mm/util.c::__vm_enough_memory() for more information.
-==============================================================
-overcommit_ratio:
+overcommit_ratio
+================
When overcommit_memory is set to 2, the committed address
space is not permitted to exceed swap plus this percentage
of physical RAM. See above.
-==============================================================
page-cluster
+============
page-cluster controls the number of pages up to which consecutive pages
are read in from swap in a single attempt. This is the swap counterpart
extra faults and I/O delays for following faults if they would have been part of
that consecutive pages readahead would have brought in.
-=============================================================
panic_on_oom
+============
This enables or disables panic on out-of-memory feature.
system panics.
The default value is 0.
+
1 and 2 are for failover of clustering. Please select either
according to your policy of failover.
+
panic_on_oom=2+kdump gives you very strong tool to investigate
why oom happens. You can get snapshot.
-=============================================================
percpu_pagelist_fraction
+========================
This is the fraction of pages at most (high mark pcp->high) in each zone that
are allocated for each per cpu page list. The min value for this is 8. It
the high water marks for each per cpu page list. If the user writes '0' to this
sysctl, it will revert to this default behavior.
-==============================================================
stat_interval
+=============
The time interval between which vm statistics are updated. The default
is 1 second.
-==============================================================
stat_refresh
+============
Any read or write (by root only) flushes all the per-cpu vm statistics
into their global totals, for more accurate reports when testing
(At time of writing, a few stats are known sometimes to be found negative,
with no ill effects: errors and warnings on these stats are suppressed.)
-==============================================================
numa_stat
+=========
This interface allows runtime configuration of numa statistics.
When page allocation performance becomes a bottleneck and you can tolerate
some possible tool breakage and decreased numa counter precision, you can
-do:
+do::
+
echo 0 > /proc/sys/vm/numa_stat
When page allocation performance is not a bottleneck and you want all
-tooling to work, you can do:
+tooling to work, you can do::
+
echo 1 > /proc/sys/vm/numa_stat
-==============================================================
swappiness
+==========
This control is used to define how aggressive the kernel will swap
memory pages. Higher values will increase aggressiveness, lower values
The default value is 60.
-==============================================================
unprivileged_userfaultfd
+========================
This flag controls whether unprivileged users can use the userfaultfd
system calls. Set this to 1 to allow unprivileged users to use the
The default value is 1.
-==============================================================
-- user_reserve_kbytes
+user_reserve_kbytes
+===================
When overcommit_memory is set to 2, "never overcommit" mode, reserve
min(3% of current process size, user_reserve_kbytes) of free memory.
Changing this takes effect whenever an application requests memory.
-==============================================================
vfs_cache_pressure
-------------------
+==================
This percentage value controls the tendency of the kernel to reclaim
the memory which is used for caching of directory and inode objects.
directory and inode objects. With vfs_cache_pressure=1000, it will look for
ten times more freeable objects than there are.
-=============================================================
-watermark_boost_factor:
+watermark_boost_factor
+======================
This factor controls the level of reclaim when memory is being fragmented.
It defines the percentage of the high watermark of a zone that will be
smaller than a pageblock then a pageblocks worth of pages will be reclaimed
(e.g. 2MB on 64-bit x86). A boost factor of 0 will disable the feature.
-=============================================================
-watermark_scale_factor:
+watermark_scale_factor
+======================
This factor controls the aggressiveness of kswapd. It defines the
amount of memory left in a node/system before kswapd is woken up and
too small for the allocation bursts occurring in the system. This knob
can then be used to tune kswapd aggressiveness accordingly.
-==============================================================
-zone_reclaim_mode:
+zone_reclaim_mode
+=================
Zone_reclaim_mode allows someone to set more or less aggressive approaches to
reclaim memory when a zone runs out of memory. If it is set to zero then no
zone reclaim occurs. Allocations will be satisfied from other zones / nodes
in the system.
-This is value ORed together of
+This is value OR'ed together of
-1 = Zone reclaim on
-2 = Zone reclaim writes dirty pages out
-4 = Zone reclaim swaps pages
+= ===================================
+1 Zone reclaim on
+2 Zone reclaim writes dirty pages out
+4 Zone reclaim swaps pages
+= ===================================
zone_reclaim_mode is disabled by default. For file servers or workloads
that benefit from having their data cached, zone_reclaim_mode should be
Allowing regular swap effectively restricts allocations to the local
node unless explicitly overridden by memory policies or cpuset
configurations.
-
-============ End of Document =================================
The unevictable LRU can be scanned for compactable regions and the default
behavior is to do so. /proc/sys/vm/compact_unevictable_allowed controls
-this behavior (see Documentation/sysctl/vm.txt). Once scanning of the
+this behavior (see Documentation/sysctl/vm.rst). Once scanning of the
unevictable LRU is enabled, the work of compaction is mostly handled by
the page migration code and the same work flow as described in MIGRATING
MLOCKED PAGES will apply.
/**
* print_tainted - return a string to represent the kernel taint state.
*
- * For individual taint flag meanings, see Documentation/sysctl/kernel.txt
+ * For individual taint flag meanings, see Documentation/sysctl/kernel.rst
*
* The string is overwritten by the next call to print_tainted(),
* but is always NULL terminated.
/*
* This file contains the default values for the operation of the
* Linux VM subsystem. Fine-tuning documentation can be found in
- * Documentation/sysctl/vm.txt.
+ * Documentation/sysctl/vm.rst.
* Started 18.12.91
* Swap aging added 23.2.95, Stephen Tweedie.
* Buffermem limits added 12.3.98, Rik van Riel.
projects / users / hch / xfs.git / commitdiff