diff options
Diffstat (limited to 'Documentation/admin-guide/sysctl')
| -rw-r--r-- | Documentation/admin-guide/sysctl/abi.rst | 73 | ||||
| -rw-r--r-- | Documentation/admin-guide/sysctl/fs.rst | 294 | ||||
| -rw-r--r-- | Documentation/admin-guide/sysctl/kernel.rst | 524 | ||||
| -rw-r--r-- | Documentation/admin-guide/sysctl/net.rst | 112 | ||||
| -rw-r--r-- | Documentation/admin-guide/sysctl/vm.rst | 261 |
5 files changed, 858 insertions, 406 deletions
diff --git a/Documentation/admin-guide/sysctl/abi.rst b/Documentation/admin-guide/sysctl/abi.rst index 599bcde7f0b7..4e6db0a2a4c0 100644 --- a/Documentation/admin-guide/sysctl/abi.rst +++ b/Documentation/admin-guide/sysctl/abi.rst @@ -1,67 +1,34 @@ +.. SPDX-License-Identifier: GPL-2.0+ + ================================ Documentation for /proc/sys/abi/ ================================ -kernel version 2.6.0.test2 +.. See scripts/check-sysctl-docs to keep this up to date: +.. scripts/check-sysctl-docs -vtable="abi" \ +.. Documentation/admin-guide/sysctl/abi.rst \ +.. $(git grep -l register_sysctl_) -Copyright (c) 2003, Fabian Frederick <ffrederick@users.sourceforge.net> +Copyright (c) 2020, Stephen Kitt -For general info: index.rst. +For general info, see Documentation/admin-guide/sysctl/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:: +The files in ``/proc/sys/abi`` can be used to see and modify +ABI-related settings. - 0x0001 | STICKY_TIMEOUTS | MMAP_PAGE_ZERO, +Currently, these files might (depending on your configuration) +show up in ``/proc/sys/kernel``: -fake_utsname ------------- +.. contents:: :local: -Unused +vsyscall32 (x86) +================ -trace ------ +Determines whether the kernels maps a vDSO page into 32-bit processes; +can be set to 1 to enable, or 0 to disable. Defaults to enabled if +``CONFIG_COMPAT_VDSO`` is set, disabled otherwise. -Unused +This controls the same setting as the ``vdso32`` kernel boot +parameter. diff --git a/Documentation/admin-guide/sysctl/fs.rst b/Documentation/admin-guide/sysctl/fs.rst index 2a45119e3331..6c54718c9d04 100644 --- a/Documentation/admin-guide/sysctl/fs.rst +++ b/Documentation/admin-guide/sysctl/fs.rst @@ -2,8 +2,6 @@ Documentation for /proc/sys/fs/ =============================== -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> @@ -12,159 +10,135 @@ 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. +This file contains documentation for the sysctl files and directories +in ``/proc/sys/fs/``. The files in this directory can be used to tune and monitor miscellaneous and general things in the operation of the Linux -kernel. Since some of the files _can_ be used to screw up your +kernel. Since some of the files *can* be used to screw up your system, it is advisable to read both documentation and source before actually making adjustments. 1. /proc/sys/fs =============== -Currently, these files are in /proc/sys/fs: - -- aio-max-nr -- aio-nr -- dentry-state -- dquot-max -- dquot-nr -- file-max -- file-nr -- inode-max -- inode-nr -- inode-state -- nr_open -- overflowuid -- overflowgid -- pipe-user-pages-hard -- pipe-user-pages-soft -- protected_fifos -- protected_hardlinks -- protected_regular -- protected_symlinks -- suid_dumpable -- super-max -- super-nr +Currently, these files might (depending on your configuration) +show up in ``/proc/sys/fs``: + +.. contents:: :local: 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 -reaches aio-max-nr then io_setup will fail with EAGAIN. Note that -raising aio-max-nr does not result in the pre-allocation or re-sizing -of any kernel data structures. +``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. If ``aio-nr`` reaches ``aio-nr-max`` then +``io_setup`` will fail with ``EAGAIN``. Note that raising +``aio-max-nr`` does not result in the +pre-allocation or re-sizing of any kernel data structures. +dentry-negative +---------------------------- + +Policy for negative dentries. Set to 1 to always delete the dentry when a +file is removed, and 0 to disable it. By default, this behavior is disabled. dentry-state ------------ -From linux/include/linux/dcache.h:: +This file shows the values in ``struct dentry_stat_t``, as defined in +``fs/dcache.c``:: 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 */ + long nr_dentry; + long nr_unused; + long age_limit; /* age in seconds */ + long want_pages; /* pages requested by system */ + long nr_negative; /* # of unused negative dentries */ + long dummy; /* Reserved for future use */ }; Dentries are dynamically allocated and deallocated. -nr_dentry shows the total number of dentries allocated (active -+ unused). nr_unused shows the number of dentries that are not +``nr_dentry`` shows the total number of dentries allocated (active ++ unused). ``nr_unused shows`` the number of dentries that are not actively used, but are saved in the LRU list for future reuse. -Age_limit is the age in seconds after which dcache entries -can be reclaimed when memory is short and want_pages is -nonzero when shrink_dcache_pages() has been called and the +``age_limit`` is the age in seconds after which dcache entries +can be reclaimed when memory is short and ``want_pages`` is +nonzero when ``shrink_dcache_pages()`` has been called and the dcache isn't pruned yet. -nr_negative shows the number of unused dentries that are also +``nr_negative`` shows the number of unused dentries that are also negative dentries which do not map to any files. Instead, they help speeding up rejection of non-existing files provided by the users. -dquot-max & dquot-nr --------------------- - -The file dquot-max shows the maximum number of cached disk -quota entries. - -The file dquot-nr shows the number of allocated disk quota -entries and the number of free disk quota entries. - -If the number of free cached disk quotas is very low and -you have some awesome number of simultaneous system users, -you might want to raise the limit. - - file-max & file-nr ------------------ -The value in file-max denotes the maximum number of file- +The value in ``file-max`` denotes the maximum number of file- handles that the Linux kernel will allocate. When you get lots of error messages about running out of file handles, you might want to increase this limit. Historically,the kernel was able to allocate file handles dynamically, but not to free them again. The three values in -file-nr denote the number of allocated file handles, the number +``file-nr`` denote the number of allocated file handles, the number of allocated but unused file handles, and the maximum number of -file handles. Linux 2.6 always reports 0 as the number of free +file handles. Linux 2.6 and later always reports 0 as the number of free file handles -- this is not an error, it just means that the number of allocated file handles exactly matches the number of used file handles. -Attempts to allocate more file descriptors than file-max are -reported with printk, look for "VFS: file-max limit <number> -reached". +Attempts to allocate more file descriptors than ``file-max`` are +reported with ``printk``, look for:: + VFS: file-max limit <number> reached -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. +in the kernel logs. -inode-max, inode-nr & inode-state ---------------------------------- +inode-nr & inode-state +---------------------- As with file handles, the kernel allocates the inode structures dynamically, but can't free them yet. -The value in inode-max denotes the maximum number of inode -handlers. This value should be 3-4 times larger than the value -in file-max, since stdin, stdout and network sockets also -need an inode struct to handle them. When you regularly run -out of inodes, you need to increase this value. - -The file inode-nr contains the first two items from -inode-state, so we'll skip to that file... +The file ``inode-nr`` contains the first two items from +``inode-state``, so we'll skip to that file... -Inode-state contains three actual numbers and four dummies. -The actual numbers are, in order of appearance, nr_inodes, -nr_free_inodes and preshrink. +``inode-state`` contains three actual numbers and four dummies. +The actual numbers are, in order of appearance, ``nr_inodes``, +``nr_free_inodes`` and ``preshrink``. -Nr_inodes stands for the number of inodes the system has -allocated, this can be slightly more than inode-max because -Linux allocates them one pageful at a time. +``nr_inodes`` stands for the number of inodes the system has +allocated. -Nr_free_inodes represents the number of free inodes (?) and -preshrink is nonzero when the nr_inodes > inode-max and the +``nr_free_inodes`` represents the number of free inodes (?) and +preshrink is nonzero when the system needs to prune the inode list instead of allocating more. +mount-max +--------- + +This denotes the maximum number of mounts that may exist +in a mount namespace. + + +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. + + overflowgid & overflowuid ------------------------- @@ -192,7 +166,7 @@ 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, new pipes will be limited to a single page in size for this user in order to -limit total memory usage, and trying to increase them using fcntl() will be +limit total memory usage, and trying to increase them using ``fcntl()`` will be denied until usage goes below the limit again. The default value allows to allocate up to 1024 pipes at their default size. When set to 0, no limit is applied. @@ -207,7 +181,7 @@ file. When set to "0", writing to FIFOs is unrestricted. -When set to "1" don't allow O_CREAT open on FIFOs that we don't own +When set to "1" don't allow ``O_CREAT`` open on FIFOs that we don't own in world writable sticky directories, unless they are owned by the owner of the directory. @@ -221,7 +195,7 @@ 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 -directories like /tmp. The common method of exploitation of this flaw +directories like ``/tmp``. The common method of exploitation of this flaw is to cross privilege boundaries when following a given hardlink (i.e. a root process follows a hardlink created by another user). Additionally, on systems without separated partitions, this stops unauthorized users @@ -239,13 +213,13 @@ This protection is based on the restrictions in Openwall and grsecurity. protected_regular ----------------- -This protection is similar to protected_fifos, but it +This protection is similar to `protected_fifos`_, but it avoids writes to an attacker-controlled regular file, where a program expected to create one. When set to "0", writing to regular files is unrestricted. -When set to "1" don't allow O_CREAT open on regular files that we +When set to "1" don't allow ``O_CREAT`` open on regular files that we don't own in world writable sticky directories, unless they are owned by the owner of the directory. @@ -257,11 +231,11 @@ 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 -directories like /tmp. The common method of exploitation of this flaw +directories like ``/tmp``. The common method of exploitation of this flaw is to cross privilege boundaries when following a given symlink (i.e. a root process follows a symlink belonging to another user). For a likely incomplete list of hundreds of examples across the years, please see: -http://cve.mitre.org/cgi-bin/cvekey.cgi?keyword=/tmp +https://cve.mitre.org/cgi-bin/cvekey.cgi?keyword=/tmp When set to "0", symlink following behavior is unrestricted. @@ -272,23 +246,25 @@ follower match, or when the directory owner matches the symlink's owner. This protection is based on the restrictions in Openwall and grsecurity. -suid_dumpable: --------------- +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 +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 +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 +2 (suidsafe) Any binary which normally would not be dumped is dumped + anyway, but only if the ``core_pattern`` kernel sysctl (see + :ref:`Documentation/admin-guide/sysctl/kernel.rst <core_pattern>`) + 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 @@ -301,36 +277,11 @@ or otherwise protected/tainted binaries. The modes are = ========== =============================================================== -super-max & super-nr --------------------- - -These numbers control the maximum number of superblocks, and -thus the maximum number of mounted filesystems the kernel -can have. You only need to increase super-max if you need to -mount more filesystems than the current value in super-max -allows you to. - - -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 ---------- - -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 +Documentation for the files in ``/proc/sys/fs/binfmt_misc`` is in Documentation/admin-guide/binfmt-misc.rst. @@ -343,28 +294,32 @@ creation of a user space library that implements the POSIX message queues API (as noted by the MSG tag in the POSIX 1003.1-2001 version of the System Interfaces specification.) -The "mqueue" filesystem contains values for determining/setting the amount of -resources used by the file system. +The "mqueue" filesystem contains values for determining/setting the +amount of resources used by the file system. -/proc/sys/fs/mqueue/queues_max is a read/write file for setting/getting the -maximum number of message queues allowed on the system. +``/proc/sys/fs/mqueue/queues_max`` is a read/write file for +setting/getting the maximum number of message queues allowed on the +system. -/proc/sys/fs/mqueue/msg_max is a read/write file for setting/getting the -maximum number of messages in a queue value. In fact it is the limiting value -for another (user) limit which is set in mq_open invocation. This attribute of -a queue must be less or equal then msg_max. +``/proc/sys/fs/mqueue/msg_max`` is a read/write file for +setting/getting the maximum number of messages in a queue value. In +fact it is the limiting value for another (user) limit which is set in +``mq_open`` invocation. This attribute of a queue must be less than +or equal to ``msg_max``. -/proc/sys/fs/mqueue/msgsize_max is a read/write file for setting/getting the -maximum message size value (it is every message queue's attribute set during -its creation). +``/proc/sys/fs/mqueue/msgsize_max`` is a read/write file for +setting/getting the maximum message size value (it is an attribute of +every message queue, set during its creation). -/proc/sys/fs/mqueue/msg_default is a read/write file for setting/getting the -default number of messages in a queue value if attr parameter of mq_open(2) is -NULL. If it exceed msg_max, the default value is initialized msg_max. +``/proc/sys/fs/mqueue/msg_default`` is a read/write file for +setting/getting the default number of messages in a queue value if the +``attr`` parameter of ``mq_open(2)`` is ``NULL``. If it exceeds +``msg_max``, the default value is initialized to ``msg_max``. -/proc/sys/fs/mqueue/msgsize_default is a read/write file for setting/getting -the default message size value if attr parameter of mq_open(2) is NULL. If it -exceed msgsize_max, the default value is initialized msgsize_max. +``/proc/sys/fs/mqueue/msgsize_default`` is a read/write file for +setting/getting the default message size value if the ``attr`` +parameter of ``mq_open(2)`` is ``NULL``. If it exceeds +``msgsize_max``, the default value is initialized to ``msgsize_max``. 4. /proc/sys/fs/epoll - Configuration options for the epoll interface ===================================================================== @@ -378,7 +333,42 @@ Every epoll file descriptor can store a number of files to be monitored for event readiness. Each one of these monitored files constitutes a "watch". This configuration option sets the maximum number of "watches" that are allowed for each user. -Each "watch" costs roughly 90 bytes on a 32bit kernel, and roughly 160 bytes -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. +Each "watch" costs roughly 90 bytes on a 32-bit kernel, and roughly 160 bytes +on a 64-bit one. +The current default value for ``max_user_watches`` is 4% of the +available low memory, divided by the "watch" cost in bytes. + +5. /proc/sys/fs/fuse - Configuration options for FUSE filesystems +===================================================================== + +This directory contains the following configuration options for FUSE +filesystems: + +``/proc/sys/fs/fuse/max_pages_limit`` is a read/write file for +setting/getting the maximum number of pages that can be used for servicing +requests in FUSE. + +``/proc/sys/fs/fuse/default_request_timeout`` is a read/write file for +setting/getting the default timeout (in seconds) for a fuse server to +reply to a kernel-issued request in the event where the server did not +specify a timeout at mount. If the server set a timeout, +then default_request_timeout will be ignored. The default +"default_request_timeout" is set to 0. 0 indicates no default timeout. +The maximum value that can be set is 65535. + +``/proc/sys/fs/fuse/max_request_timeout`` is a read/write file for +setting/getting the maximum timeout (in seconds) for a fuse server to +reply to a kernel-issued request. A value greater than 0 automatically opts +the server into a timeout that will be set to at most "max_request_timeout", +even if the server did not specify a timeout and default_request_timeout is +set to 0. If max_request_timeout is greater than 0 and the server set a timeout +greater than max_request_timeout or default_request_timeout is set to a value +greater than max_request_timeout, the system will use max_request_timeout as the +timeout. 0 indicates no max request timeout. The maximum value that can be set +is 65535. + +For timeouts, if the server does not respond to the request by the time +the set timeout elapses, then the connection to the fuse server will be aborted. +Please note that the timeouts are not 100% precise (eg you may set 60 seconds but +the timeout may kick in after 70 seconds). The upper margin of error for the +timeout is roughly FUSE_TIMEOUT_TIMER_FREQ seconds. diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst index 83acf5025488..dd49a89a62d3 100644 --- a/Documentation/admin-guide/sysctl/kernel.rst +++ b/Documentation/admin-guide/sysctl/kernel.rst @@ -9,12 +9,13 @@ 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 :doc:`index`. +For general info and legal blurb, please look in +Documentation/admin-guide/sysctl/index.rst. ------------------------------------------------------------------------------ This file contains documentation for the sysctl files in -``/proc/sys/kernel/`` and is valid for Linux kernel version 2.2. +``/proc/sys/kernel/``. The files in this directory can be used to tune and monitor miscellaneous and general things in the operation of the Linux @@ -37,8 +38,8 @@ acct If BSD-style process accounting is enabled these values control its behaviour. If free space on filesystem where the log lives -goes below ``lowwater``% accounting suspends. If free space gets -above ``highwater``% accounting resumes. ``frequency`` determines +goes below ``lowwater``\ % accounting suspends. If free space gets +above ``highwater``\ % accounting resumes. ``frequency`` determines how often do we check the amount of free space (value is in seconds). Default: @@ -54,7 +55,7 @@ free space valid for 30 seconds. acpi_video_flags ================ -See :doc:`/power/video`. This allows the video resume mode to be set, +See Documentation/power/video.rst. This allows the video resume mode to be set, in a similar fashion to the ``acpi_sleep`` kernel parameter, by combining the following values: @@ -64,6 +65,11 @@ combining the following values: 4 s3_beep = ======= +arch +==== + +The machine hardware name, the same output as ``uname -m`` +(e.g. ``x86_64`` or ``aarch64``). auto_msgmni =========== @@ -89,7 +95,7 @@ is 0x15 and the full version number is 0x234, this file will contain the value 340 = 0x154. See the ``type_of_loader`` and ``ext_loader_type`` fields in -:doc:`/x86/boot` for additional information. +Documentation/arch/x86/boot.rst for additional information. bootloader_version (x86 only) @@ -99,7 +105,7 @@ The complete bootloader version number. In the example above, this file will contain the value 564 = 0x234. See the ``type_of_loader`` and ``ext_loader_ver`` fields in -:doc:`/x86/boot` for additional information. +Documentation/arch/x86/boot.rst for additional information. bpf_stats_enabled @@ -133,6 +139,8 @@ Highest valid capability of the running kernel. Exports ``CAP_LAST_CAP`` from the kernel. +.. _core_pattern: + core_pattern ============ @@ -164,9 +172,11 @@ core_pattern %s signal number %t UNIX time of dump %h hostname - %e executable filename (may be shortened) + %e executable filename (may be shortened, could be changed by prctl etc) + %f executable filename %E executable path %c maximum size of core file by resource limit RLIMIT_CORE + %C CPU the task ran on %<OTHER> both are dropped ======== ========================================== @@ -202,6 +212,17 @@ pid>/``). This value defaults to 0. +core_sort_vma +============= + +The default coredump writes VMAs in address order. By setting +``core_sort_vma`` to 1, VMAs will be written from smallest size +to largest size. This is known to break at least elfutils, but +can be handy when dealing with very large (and truncated) +coredumps where the more useful debugging details are included +in the smaller VMAs. + + core_uses_pid ============= @@ -235,7 +256,7 @@ This toggle indicates whether unprivileged users are prevented from using ``dmesg(8)`` to view messages from the kernel's log buffer. When ``dmesg_restrict`` is set to 0 there are no restrictions. -When ``dmesg_restrict`` is set set to 1, users must have +When ``dmesg_restrict`` is set to 1, users must have ``CAP_SYSLOG`` to use ``dmesg(8)``. The kernel config option ``CONFIG_SECURITY_DMESG_RESTRICT`` sets the @@ -268,7 +289,7 @@ see the ``hostname(1)`` man page. firmware_config =============== -See :doc:`/driver-api/firmware/fallback-mechanisms`. +See Documentation/driver-api/firmware/fallback-mechanisms.rst. The entries in this directory allow the firmware loader helper fallback to be controlled: @@ -286,17 +307,35 @@ kernel panic). This will output the contents of the ftrace buffers to the console. This is very useful for capturing traces that lead to crashes and outputting them to a serial console. -= =================================================== -0 Disabled (default). -1 Dump buffers of all CPUs. -2 Dump the buffer of the CPU that triggered the oops. -= =================================================== +======================= =========================================== +0 Disabled (default). +1 Dump buffers of all CPUs. +2(orig_cpu) Dump the buffer of the CPU that triggered the + oops. +<instance> Dump the specific instance buffer on all CPUs. +<instance>=2(orig_cpu) Dump the specific instance buffer on the CPU + that triggered the oops. +======================= =========================================== + +Multiple instance dump is also supported, and instances are separated +by commas. If global buffer also needs to be dumped, please specify +the dump mode (1/2/orig_cpu) first for global buffer. +So for example to dump "foo" and "bar" instance buffer on all CPUs, +user can:: + + echo "foo,bar" > /proc/sys/kernel/ftrace_dump_on_oops + +To dump global buffer and "foo" instance buffer on all +CPUs along with the "bar" instance buffer on CPU that triggered the +oops, user can:: + + echo "1,foo,bar=2" > /proc/sys/kernel/ftrace_dump_on_oops ftrace_enabled, stack_tracer_enabled ==================================== -See :doc:`/trace/ftrace`. +See Documentation/trace/ftrace.rst. hardlockup_all_cpu_backtrace @@ -324,7 +363,7 @@ when a hard lockup is detected. 1 Panic on hard lockup. = =========================== -See :doc:`/admin-guide/lockup-watchdogs` for more information. +See Documentation/admin-guide/lockup-watchdogs.rst for more information. This can also be set using the nmi_watchdog kernel parameter. @@ -332,11 +371,16 @@ hotplug ======= Path for the hotplug policy agent. -Default value is "``/sbin/hotplug``". +Default value is ``CONFIG_UEVENT_HELPER_PATH``, which in turn defaults +to the empty string. +This file only exists when ``CONFIG_UEVENT_HELPER`` is enabled. Most +modern systems rely exclusively on the netlink-based uevent source and +don't need this. -hung_task_all_cpu_backtrace: -================ + +hung_task_all_cpu_backtrace +=========================== If this option is set, the kernel will send an NMI to all CPUs to dump their backtraces when a hung task is detected. This file shows up if @@ -368,6 +412,15 @@ The upper bound on the number of tasks that are checked. This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled. +hung_task_detect_count +====================== + +Indicates the total number of tasks that have been detected as hung since +the system boot. + +This file shows up if ``CONFIG_DETECT_HUNG_TASK`` is enabled. + + hung_task_timeout_secs ====================== @@ -421,8 +474,8 @@ ignore-unaligned-usertrap On architectures where unaligned accesses cause traps, and where this feature is supported (``CONFIG_SYSCTL_ARCH_UNALIGN_NO_WARN``; -currently, ``arc`` and ``ia64``), controls whether all unaligned traps -are logged. +currently, ``arc``, ``parisc`` and ``loongarch``), controls whether all +unaligned traps are logged. = ============================================================= 0 Log all unaligned accesses. @@ -430,17 +483,44 @@ are logged. setting. = ============================================================= -See also `unaligned-trap`_ and `unaligned-dump-stack`_. On ``ia64``, -this allows system administrators to override the -``IA64_THREAD_UAC_NOPRINT`` ``prctl`` and avoid logs being flooded. +See also `unaligned-trap`_. + +io_uring_disabled +================= + +Prevents all processes from creating new io_uring instances. Enabling this +shrinks the kernel's attack surface. + += ====================================================================== +0 All processes can create io_uring instances as normal. This is the + default setting. +1 io_uring creation is disabled (io_uring_setup() will fail with + -EPERM) for unprivileged processes not in the io_uring_group group. + Existing io_uring instances can still be used. See the + documentation for io_uring_group for more information. +2 io_uring creation is disabled for all processes. io_uring_setup() + always fails with -EPERM. Existing io_uring instances can still be + used. += ====================================================================== + + +io_uring_group +============== + +When io_uring_disabled is set to 1, a process must either be +privileged (CAP_SYS_ADMIN) or be in the io_uring_group group in order +to create an io_uring instance. If io_uring_group is set to -1 (the +default), only processes with the CAP_SYS_ADMIN capability may create +io_uring instances. 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). +A toggle indicating if the syscalls ``kexec_load`` and +``kexec_file_load`` have 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, @@ -448,6 +528,24 @@ allowing a system to set up (and later use) an image without it being altered. Generally used together with the `modules_disabled`_ sysctl. +kexec_load_limit_panic +====================== + +This parameter specifies a limit to the number of times the syscalls +``kexec_load`` and ``kexec_file_load`` can be called with a crash +image. It can only be set with a more restrictive value than the +current one. + +== ====================================================== +-1 Unlimited calls to kexec. This is the default setting. +N Number of calls left. +== ====================================================== + +kexec_load_limit_reboot +======================= + +Similar functionality as ``kexec_load_limit_panic``, but for a normal +image. kptr_restrict ============= @@ -482,10 +580,11 @@ modprobe ======== The full path to the usermode helper for autoloading kernel modules, -by default "/sbin/modprobe". This binary is executed when the kernel -requests a module. For example, if userspace passes an unknown -filesystem type to mount(), then the kernel will automatically request -the corresponding filesystem module by executing this usermode helper. +by default ``CONFIG_MODPROBE_PATH``, which in turn defaults to +"/sbin/modprobe". This binary is executed when the kernel requests a +module. For example, if userspace passes an unknown filesystem type +to mount(), then the kernel will automatically request the +corresponding filesystem module by executing this usermode helper. This usermode helper should insert the needed module into the kernel. This sysctl only affects module autoloading. It has no effect on the @@ -533,6 +632,9 @@ default (``MSGMNB``). ``msgmni`` is the maximum number of IPC queues. 32000 by default (``MSGMNI``). +All of these parameters are set per ipc namespace. The maximum number of bytes +in POSIX message queues is limited by ``RLIMIT_MSGQUEUE``. This limit is +respected hierarchically in the each user namespace. msg_next_id, sem_next_id, and shm_next_id (System V IPC) ======================================================== @@ -580,74 +682,66 @@ in a KVM virtual machine. This default can be overridden by adding:: nmi_watchdog=1 -to the guest kernel command line (see :doc:`/admin-guide/kernel-parameters`). - - -numa_balancing -============== +to the guest kernel command line (see +Documentation/admin-guide/kernel-parameters.rst). -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. +nmi_wd_lpm_factor (PPC only) +============================ -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, -numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms, -numa_balancing_scan_size_mb`_, and numa_balancing_settle_count sysctls. +Factor to apply to the NMI watchdog timeout (only when ``nmi_watchdog`` is +set to 1). This factor represents the percentage added to +``watchdog_thresh`` when calculating the NMI watchdog timeout during an +LPM. The soft lockup timeout is not impacted. +A value of 0 means no change. The default value is 200 meaning the NMI +watchdog is set to 30s (based on ``watchdog_thresh`` equal to 10). -numa_balancing_scan_period_min_ms, numa_balancing_scan_delay_ms, numa_balancing_scan_period_max_ms, numa_balancing_scan_size_mb -=============================================================================================================================== +numa_balancing +============== -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. +Enables/disables and configures automatic page fault based NUMA memory +balancing. Memory is moved automatically to nodes that access it often. +The value to set can be the result of ORing the following: -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. += ================================= +0 NUMA_BALANCING_DISABLED +1 NUMA_BALANCING_NORMAL +2 NUMA_BALANCING_MEMORY_TIERING += ================================= -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. +Or NUMA_BALANCING_NORMAL to optimize page placement among different +NUMA nodes to reduce remote accessing. 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. -``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. +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. -``numa_balancing_scan_delay_ms`` is the starting "scan delay" used for a task -when it initially forks. +Or NUMA_BALANCING_MEMORY_TIERING to optimize page placement among +different types of memory (represented as different NUMA nodes) to +place the hot pages in the fast memory. This is implemented based on +unmapping and page fault too. -``numa_balancing_scan_period_max_ms`` is the maximum time in milliseconds to -scan a tasks virtual memory. It effectively controls the minimum scanning -rate for each task. +numa_balancing_promote_rate_limit_MBps +====================================== -``numa_balancing_scan_size_mb`` is how many megabytes worth of pages are -scanned for a given scan. +Too high promotion/demotion throughput between different memory types +may hurt application latency. This can be used to rate limit the +promotion throughput. The per-node max promotion throughput in MB/s +will be limited to be no more than the set value. +A rule of thumb is to set this to less than 1/10 of the PMEM node +write bandwidth. -oops_all_cpu_backtrace: -================ +oops_all_cpu_backtrace +====================== If this option is set, the kernel will send an NMI to all CPUs to dump their backtraces when an oops event occurs. It should be used as a last @@ -662,6 +756,15 @@ This is the default behavior. an oops event is detected. +oops_limit +========== + +Number of kernel oopses after which the kernel should panic when +``panic_on_oops`` is not set. Setting this to 0 disables checking +the count. Setting this to 1 has the same effect as setting +``panic_on_oops=1``. The default value is 10000. + + osrelease, ostype & version =========================== @@ -786,6 +889,9 @@ 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 5 print all printk messages in buffer +bit 6 print all CPUs backtrace (if available in the arch) +bit 7 print only tasks in uninterruptible (blocked) state ===== ============================================ So for example to print tasks and memory info on panic, user can:: @@ -804,6 +910,13 @@ is useful to define the root cause of RCU stalls using a vmcore. 1 panic() after printing RCU stall messages. = ============================================================ +max_rcu_stall_to_panic +====================== + +When ``panic_on_rcu_stall`` is set to 1, this value determines the +number of times that RCU can stall before panic() is called. + +When ``panic_on_rcu_stall`` is set to 0, this value is has no effect. perf_cpu_time_max_percent ========================= @@ -878,7 +991,7 @@ The default value is 127. perf_event_mlock_kb =================== -Control size of per-cpu ring buffer not counted agains mlock limit. +Control size of per-cpu ring buffer not counted against mlock limit. The default value is 512 + 1 page @@ -896,6 +1009,36 @@ enabled, otherwise writing to this file will return ``-EBUSY``. The default value is 8. +perf_user_access (arm64 and riscv only) +======================================= + +Controls user space access for reading perf event counters. + +arm64 +===== + +The default value is 0 (access disabled). + +When set to 1, user space can read performance monitor counter registers +directly. + +See Documentation/arch/arm64/perf.rst for more information. + +riscv +===== + +When set to 0, user space access is disabled. + +The default value is 1, user space can read performance monitor counter +registers through perf, any direct access without perf intervention will trigger +an illegal instruction. + +When set to 2, which enables legacy mode (user space has direct access to cycle +and insret CSRs only). Note that this legacy value is deprecated and will be +removed once all user space applications are fixed. + +Note that the time CSR is always directly accessible to all modes. + pid_max ======= @@ -996,6 +1139,32 @@ pty See Documentation/filesystems/devpts.rst. +random +====== + +This is a directory, with the following entries: + +* ``boot_id``: a UUID generated the first time this is retrieved, and + unvarying after that; + +* ``uuid``: a UUID generated every time this is retrieved (this can + thus be used to generate UUIDs at will); + +* ``entropy_avail``: the pool's entropy count, in bits; + +* ``poolsize``: the entropy pool size, in bits; + +* ``urandom_min_reseed_secs``: obsolete (used to determine the minimum + number of seconds between urandom pool reseeding). This file is + writable for compatibility purposes, but writing to it has no effect + on any RNG behavior; + +* ``write_wakeup_threshold``: when the entropy count drops below this + (as a number of bits), processes waiting to write to ``/dev/random`` + are woken up. This file is writable for compatibility purposes, but + writing to it has no effect on any RNG behavior. + + randomize_va_space ================== @@ -1033,7 +1202,7 @@ that support this feature. real-root-dev ============= -See :doc:`/admin-guide/initrd`. +See Documentation/admin-guide/initrd.rst. reboot-cmd (SPARC only) @@ -1052,8 +1221,16 @@ 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. +this value to 0. On Non-EAS platforms, write operation fails and +read doesn't return anything. + +task_delayacct +=============== +Enables/disables task delay accounting (see +Documentation/accounting/delay-accounting.rst. Enabling this feature incurs +a small amount of overhead in the scheduler but is useful for debugging +and performance tuning. It is required by some tools such as iotop. sched_schedstats ================ @@ -1062,11 +1239,65 @@ Enables/disables scheduler statistics. Enabling this feature incurs a small amount of overhead in the scheduler but is useful for debugging and performance tuning. +sched_util_clamp_min +==================== + +Max allowed *minimum* utilization. + +Default value is 1024, which is the maximum possible value. + +It means that any requested uclamp.min value cannot be greater than +sched_util_clamp_min, i.e., it is restricted to the range +[0:sched_util_clamp_min]. + +sched_util_clamp_max +==================== + +Max allowed *maximum* utilization. + +Default value is 1024, which is the maximum possible value. + +It means that any requested uclamp.max value cannot be greater than +sched_util_clamp_max, i.e., it is restricted to the range +[0:sched_util_clamp_max]. + +sched_util_clamp_min_rt_default +=============================== + +By default Linux is tuned for performance. Which means that RT tasks always run +at the highest frequency and most capable (highest capacity) CPU (in +heterogeneous systems). + +Uclamp achieves this by setting the requested uclamp.min of all RT tasks to +1024 by default, which effectively boosts the tasks to run at the highest +frequency and biases them to run on the biggest CPU. + +This knob allows admins to change the default behavior when uclamp is being +used. In battery powered devices particularly, running at the maximum +capacity and frequency will increase energy consumption and shorten the battery +life. + +This knob is only effective for RT tasks which the user hasn't modified their +requested uclamp.min value via sched_setattr() syscall. + +This knob will not escape the range constraint imposed by sched_util_clamp_min +defined above. + +For example if + + sched_util_clamp_min_rt_default = 800 + sched_util_clamp_min = 600 + +Then the boost will be clamped to 600 because 800 is outside of the permissible +range of [0:600]. This could happen for instance if a powersave mode will +restrict all boosts temporarily by modifying sched_util_clamp_min. As soon as +this restriction is lifted, the requested sched_util_clamp_min_rt_default +will take effect. seccomp ======= -See :doc:`/userspace-api/seccomp_filter`. +See Documentation/userspace-api/seccomp_filter.rst. sg-big-buff @@ -1085,15 +1316,20 @@ are doing anyway :) shmall ====== -This parameter sets the total amount of shared memory pages that -can be used system wide. Hence, ``shmall`` should always be at least -``ceil(shmmax/PAGE_SIZE)``. +This parameter sets the total amount of shared memory pages that can be used +inside ipc namespace. The shared memory pages counting occurs for each ipc +namespace separately and is not inherited. 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 +To reduce or disable the ability to allocate shared memory, you must create a +new ipc namespace, set this parameter to the required value and prohibit the +creation of a new ipc namespace in the current user namespace or cgroups can +be used. shmmax ====== @@ -1195,11 +1431,34 @@ This parameter can be used to control 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. +without rescheduling voluntarily, and thus prevent the 'migration/N' threads +from running, causing the watchdog work fail to execute. The mechanism depends +on the CPUs ability to respond to timer interrupts which are needed for the +watchdog work to be queued by the watchdog timer function, otherwise the NMI +watchdog — if enabled — can detect a hard lockup condition. + + +split_lock_mitigate (x86 only) +============================== + +On x86, each "split lock" imposes a system-wide performance penalty. On larger +systems, large numbers of split locks from unprivileged users can result in +denials of service to well-behaved and potentially more important users. + +The kernel mitigates these bad users by detecting split locks and imposing +penalties: forcing them to wait and only allowing one core to execute split +locks at a time. + +These mitigations can make those bad applications unbearably slow. Setting +split_lock_mitigate=0 may restore some application performance, but will also +increase system exposure to denial of service attacks from split lock users. + += =================================================================== +0 Disable the mitigation mode - just warns the split lock on kernel log + and exposes the system to denials of service from the split lockers. +1 Enable the mitigation mode (this is the default) - penalizes the split + lockers with intentional performance degradation. += =================================================================== stack_erasing @@ -1237,7 +1496,7 @@ the boot PROM. sysrq ===== -See :doc:`/admin-guide/sysrq`. +See Documentation/admin-guide/sysrq.rst. tainted @@ -1249,7 +1508,7 @@ 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 + 4 `(S)` kernel running on an out of specification system 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 @@ -1267,15 +1526,16 @@ ORed together. The letters are seen in "Tainted" line of Oops reports. 131072 `(T)` The kernel was built with the struct randomization plugin ====== ===== ============================================================== -See :doc:`/admin-guide/tainted-kernels` for more information. +See Documentation/admin-guide/tainted-kernels.rst for more information. Note: writes to this sysctl interface will fail with ``EINVAL`` if the kernel is booted with the command line option ``panic_on_taint=<bitmask>,nousertaint`` and any of the ORed together values being written to ``tainted`` match with the bitmask declared on panic_on_taint. - See :doc:`/admin-guide/kernel-parameters` for more details on that particular - kernel command line option and its optional ``nousertaint`` switch. + See Documentation/admin-guide/kernel-parameters.rst for more details on + that particular kernel command line option and its optional + ``nousertaint`` switch. threads-max =========== @@ -1295,11 +1555,18 @@ constant ``FUTEX_TID_MASK`` (0x3fffffff). If a value outside of this range is written to ``threads-max`` an ``EINVAL`` error occurs. +timer_migration +=============== + +When set to a non-zero value, attempt to migrate timers away from idle cpus to +allow them to remain in low power states longer. + +Default is set (1). traceoff_on_warning =================== -When set, disables tracing (see :doc:`/trace/ftrace`) when a +When set, disables tracing (see Documentation/trace/ftrace.rst) when a ``WARN()`` is hit. @@ -1319,24 +1586,8 @@ will send them to printk() again. This only works if the kernel was booted with ``tp_printk`` enabled. -See :doc:`/admin-guide/kernel-parameters` and -:doc:`/trace/boottime-trace`. - - -.. _unaligned-dump-stack: - -unaligned-dump-stack (ia64) -=========================== - -When logging unaligned accesses, controls whether the stack is -dumped. - -= =================================================== -0 Do not dump the stack. This is the default setting. -1 Dump the stack. -= =================================================== - -See also `ignore-unaligned-usertrap`_. +See Documentation/admin-guide/kernel-parameters.rst and +Documentation/trace/boottime-trace.rst. unaligned-trap @@ -1344,8 +1595,8 @@ unaligned-trap On architectures where unaligned accesses cause traps, and where this feature is supported (``CONFIG_SYSCTL_ARCH_UNALIGN_ALLOW``; currently, -``arc`` and ``parisc``), controls whether unaligned traps are caught -and emulated (instead of failing). +``arc``, ``parisc`` and ``loongarch``), controls whether unaligned traps +are caught and emulated (instead of failing). = ======================================================== 0 Do not emulate unaligned accesses. @@ -1370,10 +1621,31 @@ unprivileged_bpf_disabled ========================= Writing 1 to this entry will disable unprivileged calls to ``bpf()``; -once disabled, calling ``bpf()`` without ``CAP_SYS_ADMIN`` will return -``-EPERM``. +once disabled, calling ``bpf()`` without ``CAP_SYS_ADMIN`` or ``CAP_BPF`` +will return ``-EPERM``. Once set to 1, this can't be cleared from the +running kernel anymore. + +Writing 2 to this entry will also disable unprivileged calls to ``bpf()``, +however, an admin can still change this setting later on, if needed, by +writing 0 or 1 to this entry. + +If ``BPF_UNPRIV_DEFAULT_OFF`` is enabled in the kernel config, then this +entry will default to 2 instead of 0. + += ============================================================= +0 Unprivileged calls to ``bpf()`` are enabled +1 Unprivileged calls to ``bpf()`` are disabled without recovery +2 Unprivileged calls to ``bpf()`` are disabled += ============================================================= + + +warn_limit +========== -Once set, this can't be cleared. +Number of kernel warnings after which the kernel should panic when +``panic_on_warn`` is not set. Setting this to 0 disables checking +the warning count. Setting this to 1 has the same effect as setting +``panic_on_warn=1``. The default value is 0. watchdog diff --git a/Documentation/admin-guide/sysctl/net.rst b/Documentation/admin-guide/sysctl/net.rst index 42cd04bca548..7b0c4291c686 100644 --- a/Documentation/admin-guide/sysctl/net.rst +++ b/Documentation/admin-guide/sysctl/net.rst @@ -31,17 +31,18 @@ see only some of them, depending on your kernel's configuration. 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 + ========= =================== = ========== =================== + 802 E802 protocol mptcp Multipath TCP + appletalk Appletalk protocol netfilter Network Filter + ax25 AX25 netrom NET/ROM + bridge Bridging rose X.25 PLP layer + core General parameter tipc TIPC + ethernet Ethernet protocol unix Unix domain sockets ipv4 IP version 4 x25 X.25 protocol - bridge Bridging decnet DEC net - ipv6 IP version 6 tipc TIPC - ========= =================== = ========== ================== + ipv6 IP version 6 + ========= =================== = ========== =================== 1. /proc/sys/net/core - Network core options ============================================ @@ -64,16 +65,18 @@ two flavors of JITs, the newer eBPF JIT currently supported on: - arm64 - arm32 - ppc64 + - ppc32 - sparc64 - mips64 - s390x - riscv64 - riscv32 + - loongarch64 + - arc And the older cBPF JIT supported on the following archs: - mips - - ppc - sparc eBPF JITs are a superset of cBPF JITs, meaning the kernel will @@ -101,6 +104,9 @@ Values: - 1 - enable JIT hardening for unprivileged users only - 2 - enable JIT hardening for all users +where "privileged user" in this context means a process having +CAP_BPF or CAP_SYS_ADMIN in the root user name space. + bpf_jit_kallsyms ---------------- @@ -201,6 +207,11 @@ Will increase power usage. Default: 0 (off) +mem_pcpu_rsv +------------ + +Per-cpu reserved forward alloc cache size in page units. Default 1MB per CPU. + rmem_default ------------ @@ -211,6 +222,12 @@ rmem_max The maximum receive socket buffer size in bytes. +rps_default_mask +---------------- + +The default RPS CPU mask used on newly created network devices. An empty +mask means RPS disabled by default. + tstamp_allow_data ----------------- Allow processes to receive tx timestamps looped together with the original @@ -271,7 +288,7 @@ poll cycle or the number of packets processed reaches netdev_budget. netdev_max_backlog ------------------ -Maximum number of packets, queued on the INPUT side, when the interface +Maximum number of packets, queued on the INPUT side, when the interface receives packets faster than kernel can process them. netdev_rss_key @@ -311,21 +328,52 @@ permit to distribute the load on several cpus. If set to 1 (default), timestamps are sampled as soon as possible, before queueing. +netdev_unregister_timeout_secs +------------------------------ + +Unregister network device timeout in seconds. +This option controls the timeout (in seconds) used to issue a warning while +waiting for a network device refcount to drop to 0 during device +unregistration. A lower value may be useful during bisection to detect +a leaked reference faster. A larger value may be useful to prevent false +warnings on slow/loaded systems. +Default value is 10, minimum 1, maximum 3600. + +skb_defer_max +------------- + +Max size (in skbs) of the per-cpu list of skbs being freed +by the cpu which allocated them. Used by TCP stack so far. + +Default: 64 + optmem_max ---------- Maximum ancillary buffer size allowed per socket. Ancillary data is a sequence -of struct cmsghdr structures with appended data. +of struct cmsghdr structures with appended data. TCP tx zerocopy also uses +optmem_max as a limit for its internal structures. + +Default : 128 KB fb_tunnels_only_for_init_net ---------------------------- Controls if fallback tunnels (like tunl0, gre0, gretap0, erspan0, -sit0, ip6tnl0, ip6gre0) are automatically created when a new -network namespace is created, if corresponding tunnel is present -in initial network namespace. -If set to 1, these devices are not automatically created, and -user space is responsible for creating them if needed. +sit0, ip6tnl0, ip6gre0) are automatically created. There are 3 possibilities +(a) value = 0; respective fallback tunnels are created when module is +loaded in every net namespaces (backward compatible behavior). +(b) value = 1; [kcmd value: initns] respective fallback tunnels are +created only in init net namespace and every other net namespace will +not have them. +(c) value = 2; [kcmd value: none] fallback tunnels are not created +when a module is loaded in any of the net namespace. Setting value to +"2" is pointless after boot if these modules are built-in, so there is +a kernel command-line option that can change this default. Please refer to +Documentation/admin-guide/kernel-parameters.txt for additional details. + +Not creating fallback tunnels gives control to userspace to create +whatever is needed only and avoid creating devices which are redundant. Default : 0 (for compatibility reasons) @@ -345,6 +393,36 @@ new netns has been created. Default : 0 (for compatibility reasons) +txrehash +-------- + +Controls default hash rethink behaviour on socket when SO_TXREHASH option is set +to SOCK_TXREHASH_DEFAULT (i. e. not overridden by setsockopt). + +If set to 1 (default), hash rethink is performed on listening socket. +If set to 0, hash rethink is not performed. + +gro_normal_batch +---------------- + +Maximum number of the segments to batch up on output of GRO. When a packet +exits GRO, either as a coalesced superframe or as an original packet which +GRO has decided not to coalesce, it is placed on a per-NAPI list. This +list is then passed to the stack when the number of segments reaches the +gro_normal_batch limit. + +high_order_alloc_disable +------------------------ + +By default the allocator for page frags tries to use high order pages (order-3 +on x86). While the default behavior gives good results in most cases, some users +might have hit a contention in page allocations/freeing. This was especially +true on older kernels (< 5.14) when high-order pages were not stored on per-cpu +lists. This allows to opt-in for order-0 allocation instead but is now mostly of +historical importance. + +Default: 0 + 2. /proc/sys/net/unix - Parameters for Unix domain sockets ---------------------------------------------------------- diff --git a/Documentation/admin-guide/sysctl/vm.rst b/Documentation/admin-guide/sysctl/vm.rst index d46d5b7013c6..9bef46151d53 100644 --- a/Documentation/admin-guide/sysctl/vm.rst +++ b/Documentation/admin-guide/sysctl/vm.rst @@ -25,9 +25,10 @@ files can be found in mm/swap.c. Currently, these files are in /proc/sys/vm: - admin_reserve_kbytes -- block_dump - compact_memory +- compaction_proactiveness - compact_unevictable_allowed +- defrag_mode - dirty_background_bytes - dirty_background_ratio - dirty_bytes @@ -36,12 +37,15 @@ Currently, these files are in /proc/sys/vm: - dirtytime_expire_seconds - dirty_writeback_centisecs - drop_caches +- enable_soft_offline - extfrag_threshold +- highmem_is_dirtyable - hugetlb_shm_group - laptop_mode - legacy_va_layout - lowmem_reserve_ratio - max_map_count +- mem_profiling (only if CONFIG_MEM_ALLOC_PROFILING=y) - memory_failure_early_kill - memory_failure_recovery - min_free_kbytes @@ -61,8 +65,9 @@ Currently, these files are in /proc/sys/vm: - overcommit_memory - overcommit_ratio - page-cluster +- page_lock_unfairness - panic_on_oom -- percpu_pagelist_fraction +- percpu_pagelist_high_fraction - stat_interval - stat_refresh - numa_stat @@ -70,6 +75,7 @@ Currently, these files are in /proc/sys/vm: - unprivileged_userfaultfd - user_reserve_kbytes - vfs_cache_pressure +- vfs_cache_pressure_denom - watermark_boost_factor - watermark_scale_factor - zone_reclaim_mode @@ -104,13 +110,6 @@ On x86_64 this is about 128MB. 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/admin-guide/laptops/laptop-mode.rst. - - compact_memory ============== @@ -119,6 +118,28 @@ 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. +compaction_proactiveness +======================== + +This tunable takes a value in the range [0, 100] with a default value of +20. This tunable determines how aggressively compaction is done in the +background. Write of a non zero value to this tunable will immediately +trigger the proactive compaction. Setting it to 0 disables proactive compaction. + +Note that compaction has a non-trivial system-wide impact as pages +belonging to different processes are moved around, which could also lead +to latency spikes in unsuspecting applications. The kernel employs +various heuristics to avoid wasting CPU cycles if it detects that +proactive compaction is not being effective. + +Setting the value above 80 will, in addition to lowering the acceptable level +of fragmentation, make the compaction code more sensitive to increases in +fragmentation, i.e. compaction will trigger more often, but reduce +fragmentation by a smaller amount. +This makes the fragmentation level more stable over time. + +Be careful when setting it to extreme values like 100, as that may +cause excessive background compaction activity. compact_unevictable_allowed =========================== @@ -129,9 +150,17 @@ This should be used on systems where stalls for minor page faults are an acceptable trade for large contiguous free memory. Set to 0 to prevent compaction from moving pages that are unevictable. Default value is 1. On CONFIG_PREEMPT_RT the default value is 0 in order to avoid a page fault, due -to compaction, which would block the task from becomming active until the fault +to compaction, which would block the task from becoming active until the fault is resolved. +defrag_mode +=========== + +When set to 1, the page allocator tries harder to avoid fragmentation +and maintain the ability to produce huge pages / higher-order pages. + +It is recommended to enable this right after boot, as fragmentation, +once it occurred, can be long-lasting or even permanent. dirty_background_bytes ====================== @@ -255,6 +284,43 @@ used:: 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. +enable_soft_offline +=================== +Correctable memory errors are very common on servers. Soft-offline is kernel's +solution for memory pages having (excessive) corrected memory errors. + +For different types of page, soft-offline has different behaviors / costs. + +- For a raw error page, soft-offline migrates the in-use page's content to + a new raw page. + +- For a page that is part of a transparent hugepage, soft-offline splits the + transparent hugepage into raw pages, then migrates only the raw error page. + As a result, user is transparently backed by 1 less hugepage, impacting + memory access performance. + +- For a page that is part of a HugeTLB hugepage, soft-offline first migrates + the entire HugeTLB hugepage, during which a free hugepage will be consumed + as migration target. Then the original hugepage is dissolved into raw + pages without compensation, reducing the capacity of the HugeTLB pool by 1. + +It is user's call to choose between reliability (staying away from fragile +physical memory) vs performance / capacity implications in transparent and +HugeTLB cases. + +For all architectures, enable_soft_offline controls whether to soft offline +memory pages. When set to 1, kernel attempts to soft offline the pages +whenever it thinks needed. When set to 0, kernel returns EOPNOTSUPP to +the request to soft offline the pages. Its default value is 1. + +It is worth mentioning that after setting enable_soft_offline to 0, the +following requests to soft offline pages will not be performed: + +- Request to soft offline pages from RAS Correctable Errors Collector. + +- On ARM, the request to soft offline pages from GHES driver. + +- On PARISC, the request to soft offline pages from Page Deallocation Table. extfrag_threshold ================= @@ -345,7 +411,7 @@ The lowmem_reserve_ratio is an array. You can see them by reading this file:: 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). +in /proc/zoneinfo like the following. (This is an example of x86-64 box). Each zone has an array of protection pages like this:: Node 0, zone DMA @@ -411,7 +477,22 @@ While most applications need less than a thousand maps, certain programs, particularly malloc debuggers, may consume lots of them, e.g., up to one or two maps per allocation. -The default value is 65536. +The default value is 65530. + + +mem_profiling +============== + +Enable memory profiling (when CONFIG_MEM_ALLOC_PROFILING=y) + +1: Enable memory profiling. + +0: Disable memory profiling. + +Enabling memory profiling introduces a small performance overhead for all +memory allocations. + +The default value depends on CONFIG_MEM_ALLOC_PROFILING_ENABLED_BY_DEFAULT. memory_failure_early_kill: @@ -422,7 +503,7 @@ a 2bit error in a memory module) is detected in the background by hardware that cannot be handled by the kernel. In some cases (like the page still having a valid copy on disk) the kernel will handle the failure transparently without affecting any applications. But if there is -no other uptodate copy of the data it will kill to prevent any data +no other up-to-date copy of the data it will kill to prevent any data corruptions from propagating. 1: Kill all processes that have the corrupted and not reloadable page mapped @@ -551,6 +632,43 @@ Change the minimum size of the hugepage pool. See Documentation/admin-guide/mm/hugetlbpage.rst +hugetlb_optimize_vmemmap +======================== + +This knob is not available when the size of 'struct page' (a structure defined +in include/linux/mm_types.h) is not power of two (an unusual system config could +result in this). + +Enable (set to 1) or disable (set to 0) HugeTLB Vmemmap Optimization (HVO). + +Once enabled, the vmemmap pages of subsequent allocation of HugeTLB pages from +buddy allocator will be optimized (7 pages per 2MB HugeTLB page and 4095 pages +per 1GB HugeTLB page), whereas already allocated HugeTLB pages will not be +optimized. When those optimized HugeTLB pages are freed from the HugeTLB pool +to the buddy allocator, the vmemmap pages representing that range needs to be +remapped again and the vmemmap pages discarded earlier need to be rellocated +again. If your use case is that HugeTLB pages are allocated 'on the fly' (e.g. +never explicitly allocating HugeTLB pages with 'nr_hugepages' but only set +'nr_overcommit_hugepages', those overcommitted HugeTLB pages are allocated 'on +the fly') instead of being pulled from the HugeTLB pool, you should weigh the +benefits of memory savings against the more overhead (~2x slower than before) +of allocation or freeing HugeTLB pages between the HugeTLB pool and the buddy +allocator. Another behavior to note is that if the system is under heavy memory +pressure, it could prevent the user from freeing HugeTLB pages from the HugeTLB +pool to the buddy allocator since the allocation of vmemmap pages could be +failed, you have to retry later if your system encounter this situation. + +Once disabled, the vmemmap pages of subsequent allocation of HugeTLB pages from +buddy allocator will not be optimized meaning the extra overhead at allocation +time from buddy allocator disappears, whereas already optimized HugeTLB pages +will not be affected. If you want to make sure there are no optimized HugeTLB +pages, you can set "nr_hugepages" to 0 first and then disable this. Note that +writing 0 to nr_hugepages will make any "in use" HugeTLB pages become surplus +pages. So, those surplus pages are still optimized until they are no longer +in use. You would need to wait for those surplus pages to be released before +there are no optimized pages in the system. + + nr_hugepages_mempolicy ====================== @@ -583,7 +701,7 @@ trimming of allocations is initiated. The default value is 1. -See Documentation/nommu-mmap.txt for more information. +See Documentation/admin-guide/mm/nommu-mmap.rst for more information. numa_zonelist_order @@ -694,8 +812,8 @@ overcommit_memory This value contains a flag that enables memory overcommitment. -When this flag is 0, the kernel attempts to estimate the amount -of free memory left when userspace requests more memory. +When this flag is 0, the kernel compares the userspace memory request +size against total memory plus swap and rejects obvious overcommits. When this flag is 1, the kernel pretends there is always enough memory until it actually runs out. @@ -710,7 +828,7 @@ and don't use much of it. The default value is 0. -See Documentation/vm/overcommit-accounting.rst and +See Documentation/mm/overcommit-accounting.rst and mm/util.c::__vm_enough_memory() for more information. @@ -744,6 +862,14 @@ extra faults and I/O delays for following faults if they would have been part of that consecutive pages readahead would have brought in. +page_lock_unfairness +==================== + +This value determines the number of times that the page lock can be +stolen from under a waiter. After the lock is stolen the number of times +specified in this file (default is 5), the "fair lock handoff" semantics +will apply, and the waiter will only be awakened if the lock can be taken. + panic_on_oom ============ @@ -773,22 +899,24 @@ panic_on_oom=2+kdump gives you very strong tool to investigate why oom happens. You can get snapshot. -percpu_pagelist_fraction -======================== +percpu_pagelist_high_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 -means that we don't allow more than 1/8th of pages in each zone to be -allocated in any single per_cpu_pagelist. This entry only changes the value -of hot per cpu pagelists. User can specify a number like 100 to allocate -1/100th of each zone to each per cpu page list. +This is the fraction of pages in each zone that are can be stored to +per-cpu page lists. It is an upper boundary that is divided depending +on the number of online CPUs. The min value for this is 8 which means +that we do not allow more than 1/8th of pages in each zone to be stored +on per-cpu page lists. This entry only changes the value of hot per-cpu +page lists. A user can specify a number like 100 to allocate 1/100th of +each zone between per-cpu lists. -The batch value of each per cpu pagelist is also updated as a result. It is -set to pcp->high/4. The upper limit of batch is (PAGE_SHIFT * 8) +The batch value of each per-cpu page list remains the same regardless of +the value of the high fraction so allocation latencies are unaffected. -The initial value is zero. Kernel does not use this value at boot time to set -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. +The initial value is zero. Kernel uses this value to set the high pcp->high +mark based on the low watermark for the zone and the number of local +online CPUs. If the user writes '0' to this sysctl, it will revert to +this default behavior. stat_interval @@ -856,13 +984,21 @@ file-backed pages is less than the high watermark in a zone. 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 -userfaultfd system calls, or set this to 0 to restrict userfaultfd to only -privileged users (with SYS_CAP_PTRACE capability). +This flag controls the mode in which unprivileged users can use the +userfaultfd system calls. Set this to 0 to restrict unprivileged users +to handle page faults in user mode only. In this case, users without +SYS_CAP_PTRACE must pass UFFD_USER_MODE_ONLY in order for userfaultfd to +succeed. Prohibiting use of userfaultfd for handling faults from kernel +mode may make certain vulnerabilities more difficult to exploit. -The default value is 1. +Set this to 1 to allow unprivileged users to use the userfaultfd system +calls without any restrictions. +The default value is 0. + +Another way to control permissions for userfaultfd is to use +/dev/userfaultfd instead of userfaultfd(2). See +Documentation/admin-guide/mm/userfaultfd.rst. user_reserve_kbytes =================== @@ -888,19 +1024,28 @@ 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. -At the default value of vfs_cache_pressure=100 the kernel will attempt to -reclaim dentries and inodes at a "fair" rate with respect to pagecache and -swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer -to retain dentry and inode caches. When vfs_cache_pressure=0, the kernel will -never reclaim dentries and inodes due to memory pressure and this can easily -lead to out-of-memory conditions. Increasing vfs_cache_pressure beyond 100 -causes the kernel to prefer to reclaim dentries and inodes. +At the default value of vfs_cache_pressure=vfs_cache_pressure_denom the kernel +will attempt to reclaim dentries and inodes at a "fair" rate with respect to +pagecache and swapcache reclaim. Decreasing vfs_cache_pressure causes the +kernel to prefer to retain dentry and inode caches. When vfs_cache_pressure=0, +the kernel will never reclaim dentries and inodes due to memory pressure and +this can easily lead to out-of-memory conditions. Increasing vfs_cache_pressure +beyond vfs_cache_pressure_denom causes the kernel to prefer to reclaim dentries +and inodes. + +Increasing vfs_cache_pressure significantly beyond vfs_cache_pressure_denom may +have negative performance impact. Reclaim code needs to take various locks to +find freeable directory and inode objects. When vfs_cache_pressure equals +(10 * vfs_cache_pressure_denom), it will look for ten times more freeable +objects than there are. -Increasing vfs_cache_pressure significantly beyond 100 may have negative -performance impact. Reclaim code needs to take various locks to find freeable -directory and inode objects. With vfs_cache_pressure=1000, it will look for -ten times more freeable objects than there are. +Note: This setting should always be used together with vfs_cache_pressure_denom. + +vfs_cache_pressure_denom +======================== +Defaults to 100 (minimum allowed value). Requires corresponding +vfs_cache_pressure setting to take effect. watermark_boost_factor ====================== @@ -914,12 +1059,12 @@ allocations, THP and hugetlbfs pages. To make it sensible with respect to the watermark_scale_factor parameter, the unit is in fractions of 10,000. The default value of -15,000 on !DISCONTIGMEM configurations means that up to 150% of the high -watermark will be reclaimed in the event of a pageblock being mixed due -to fragmentation. The level of reclaim is determined by the number of -fragmentation events that occurred in the recent past. If this value is -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. +15,000 means that up to 150% of the high watermark will be reclaimed in the +event of a pageblock being mixed due to fragmentation. The level of reclaim +is determined by the number of fragmentation events that occurred in the +recent past. If this value is 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 @@ -931,7 +1076,7 @@ how much memory needs to be free before kswapd goes back to sleep. The unit is in fractions of 10,000. The default value of 10 means the distances between watermarks are 0.1% of the available memory in the -node/system. The maximum value is 1000, or 10% of memory. +node/system. The maximum value is 3000, or 30% of memory. A high rate of threads entering direct reclaim (allocstall) or kswapd going to sleep prematurely (kswapd_low_wmark_hit_quickly) can indicate @@ -961,11 +1106,11 @@ that benefit from having their data cached, zone_reclaim_mode should be left disabled as the caching effect is likely to be more important than data locality. -zone_reclaim may be enabled if it's known that the workload is partitioned -such that each partition fits within a NUMA node and that accessing remote -memory would cause a measurable performance reduction. The page allocator -will then reclaim easily reusable pages (those page cache pages that are -currently not used) before allocating off node pages. +Consider enabling one or more zone_reclaim mode bits if it's known that the +workload is partitioned such that each partition fits within a NUMA node +and that accessing remote memory would cause a measurable performance +reduction. The page allocator will take additional actions before +allocating off node pages. Allowing zone reclaim to write out pages stops processes that are writing large amounts of data from dirtying pages on other nodes. Zone |