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-Documentation for /proc/sys/fs/* kernel version 2.2.10
- (c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
- (c) 2009, Shen Feng<shen@cn.fujitsu.com>
-
-For general info and legal blurb, please look in README.
-
-==============================================================
-
-This file contains documentation for the sysctl files in
-/proc/sys/fs/ and is valid for Linux kernel version 2.2.
-
-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
-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
-- suid_dumpable
-- super-max
-- super-nr
-
-==============================================================
-
-aio-nr & aio-max-nr:
-
-aio-nr is the running total of the number of events specified on the
-io_setup system call for all currently active aio contexts. If aio-nr
-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.
-
-==============================================================
-
-dentry-state:
-
-From linux/fs/dentry.c:
---------------------------------------------------------------
-struct {
- int nr_dentry;
- int nr_unused;
- int age_limit; /* age in seconds */
- int want_pages; /* pages requested by system */
- int dummy[2];
-} dentry_stat = {0, 0, 45, 0,};
---------------------------------------------------------------
-
-Dentries are dynamically allocated and deallocated, and
-nr_dentry seems to be 0 all the time. Hence it's safe to
-assume that only nr_unused, age_limit and want_pages are
-used. Nr_unused seems to be exactly what its name says.
-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.
-
-==============================================================
-
-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-
-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
-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 -- 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".
-==============================================================
-
-nr_open:
-
-This denotes the maximum number of file-handles a process can
-allocate. Default value is 1024*1024 (1048576) which should be
-enough for most machines. Actual limit depends on RLIMIT_NOFILE
-resource limit.
-
-==============================================================
-
-inode-max, inode-nr & inode-state:
-
-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...
-
-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_free_inodes represents the number of free inodes (?) and
-preshrink is nonzero when the nr_inodes > inode-max and the
-system needs to prune the inode list instead of allocating
-more.
-
-==============================================================
-
-overflowgid & overflowuid:
-
-Some filesystems only support 16-bit UIDs and GIDs, although in Linux
-UIDs and GIDs are 32 bits. When one of these filesystems is mounted
-with writes enabled, any UID or GID that would exceed 65535 is translated
-to a fixed value before being written to disk.
-
-These sysctls allow you to change the value of the fixed UID and GID.
-The default is 65534.
-
-==============================================================
-
-suid_dumpable:
-
-This value can be used to query and set the core dump mode for setuid
-or otherwise protected/tainted binaries. The modes are
-
-0 - (default) - traditional behaviour. Any process which has changed
- privilege levels or is execute only will not be dumped
-1 - (debug) - all processes dump core when possible. The core dump is
- owned by the current user and no security is applied. This is
- intended for system debugging situations only. Ptrace is unchecked.
-2 - (suidsafe) - any binary which normally would not be dumped is dumped
- readable by root only. This allows the end user to remove
- such a dump but not access it directly. For security reasons
- core dumps in this mode will not overwrite one another or
- other files. This mode is appropriate when administrators are
- attempting to debug problems in a normal environment.
-
-==============================================================
-
-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.
-
-==============================================================
-
-
-2. /proc/sys/fs/binfmt_misc
-----------------------------------------------------------
-
-Documentation for the files in /proc/sys/fs/binfmt_misc is
-in Documentation/binfmt_misc.txt.
-
-
-3. /proc/sys/fs/mqueue - POSIX message queues filesystem
-----------------------------------------------------------
-
-The "mqueue" filesystem provides the necessary kernel features to enable the
-creation of a user space library that implements the POSIX message queues
-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.
-
-/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/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/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/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.
-
-4. /proc/sys/fs/epoll - Configuration options for the epoll interface
---------------------------------------------------------
-
-This directory contains configuration options for the epoll(7) interface.
-
-max_user_watches
-----------------
-
-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.
-