Merge tag 'docs-6.2' of git://git.lwn.net/linux

	@$(srctree)/scripts/sphinx-pre-install --version-check

	@+$(foreach var,$(SPHINXDIRS),$(call loop_cmd,sphinx,html,$(var),,$(var)))

texinfodocs:

	@$(srctree)/scripts/sphinx-pre-install --version-check

	@+$(foreach var,$(SPHINXDIRS),$(call loop_cmd,sphinx,texinfo,$(var),texinfo,$(var)))

# Note: the 'info' Make target is generated by sphinx itself when

# running the texinfodocs target define above.

infodocs: texinfodocs

	$(MAKE) -C $(BUILDDIR)/texinfo info

linkcheckdocs:

	@$(foreach var,$(SPHINXDIRS),$(call loop_cmd,sphinx,linkcheck,$(var),,$(var)))

dochelp:

	@echo  ' Linux kernel internal documentation in different formats from ReST:'

	@echo  '  htmldocs        - HTML'

	@echo  '  texinfodocs     - Texinfo'

	@echo  '  infodocs        - Info'

	@echo  '  latexdocs       - LaTeX'

	@echo  '  pdfdocs         - PDF'

	@echo  '  epubdocs        - EPUB'

passing the kernel parameters. All the key-value pairs under ``kernel``

key will be passed to kernel cmdline directly. Moreover, the key-value

pairs under ``init`` will be passed to init process via the cmdline.

The parameters are concatinated with user-given kernel cmdline string

The parameters are concatenated with user-given kernel cmdline string

as the following order, so that the command line parameter can override

bootconfig parameters (this depends on how the subsystem handles parameters

but in general, earlier parameter will be overwritten by later one.)::

==========================================================

Linux support for random number generator in i8xx chipsets

==========================================================

=================================

Hardware random number generators

=================================

Introduction

============

significant performance improvement if reads from the compressed cache are

faster than reads from a swap device.

.. note::

   Zswap is a new feature as of v3.11 and interacts heavily with memory

   reclaim.  This interaction has not been fully explored on the large set of

   potential configurations and workloads that exist.  For this reason, zswap

   is a work in progress and should be considered experimental.

Some potential benefits:

* Desktop/laptop users with limited RAM capacities can mitigate the

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>

------------------------------------------------------------------------------

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-state

------------

From linux/include/linux/dcache.h::

This file shows the values in ``struct dentry_stat``, as defined in

``linux/include/linux/dcache.h``::

  struct dentry_stat_t dentry_stat {

        int nr_dentry;

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

-------------------------

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.

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.

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

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.

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:

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

=   ==========  ===============================================================

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.

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

=====================================================================

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 1/25 (4%) 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.