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docs: sysctl/fs: re-order, prettify
This brings the text markup in line with sysctl/abi and sysctl/kernel: * the entries are ordered alphabetically * the table of contents is automatically generated * markup is used as appropriate for constants etc. The content isn't fully up-to-date but the obsolete entries are gone, so remove the kernel version mention. Signed-off-by: Stephen Kitt <steve@sk2.org> Link: https://lore.kernel.org/r/20220930102937.135841-6-steve@sk2.org Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Stephen Kitt
Jonathan Corbet
parent
4ce463179a
commit
aadc0cd52f
@ -2,8 +2,6 @@
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Documentation for /proc/sys/fs/
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===============================
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kernel version 2.2.10
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Copyright (c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
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Copyright (c) 2009, Shen Feng<shen@cn.fujitsu.com>
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@ -12,55 +10,40 @@ For general info and legal blurb, please look in intro.rst.
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------------------------------------------------------------------------------
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This file contains documentation for the sysctl files in
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/proc/sys/fs/ and is valid for Linux kernel version 2.2.
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This file contains documentation for the sysctl files and directories
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in ``/proc/sys/fs/``.
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The files in this directory can be used to tune and monitor
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miscellaneous and general things in the operation of the Linux
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kernel. Since some of the files _can_ be used to screw up your
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kernel. Since some of the files *can* be used to screw up your
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system, it is advisable to read both documentation and source
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before actually making adjustments.
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1. /proc/sys/fs
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===============
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Currently, these files are in /proc/sys/fs:
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Currently, these files might (depending on your configuration)
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show up in ``/proc/sys/fs``:
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- aio-max-nr
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- aio-nr
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- dentry-state
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- file-max
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- file-nr
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- inode-nr
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- inode-state
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- nr_open
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- overflowuid
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- overflowgid
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- pipe-user-pages-hard
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- pipe-user-pages-soft
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- protected_fifos
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- protected_hardlinks
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- protected_regular
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- protected_symlinks
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- suid_dumpable
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- super-max
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- super-nr
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.. contents:: :local:
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aio-nr & aio-max-nr
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-------------------
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aio-nr shows the current system-wide number of asynchronous io
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requests. aio-max-nr allows you to change the maximum value
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aio-nr can grow to. If aio-nr reaches aio-nr-max then io_setup will
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fail with EAGAIN. Note that raising aio-max-nr does not result in the
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``aio-nr`` shows the current system-wide number of asynchronous io
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requests. ``aio-max-nr`` allows you to change the maximum value
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``aio-nr`` can grow to. If ``aio-nr`` reaches ``aio-nr-max`` then
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``io_setup`` will fail with ``EAGAIN``. Note that raising
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``aio-max-nr`` does not result in the
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pre-allocation or re-sizing of any kernel data structures.
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dentry-state
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------------
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From linux/include/linux/dcache.h::
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This file shows the values in ``struct dentry_stat``, as defined in
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``linux/include/linux/dcache.h``::
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struct dentry_stat_t dentry_stat {
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int nr_dentry;
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@ -73,16 +56,16 @@ From linux/include/linux/dcache.h::
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Dentries are dynamically allocated and deallocated.
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nr_dentry shows the total number of dentries allocated (active
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+ unused). nr_unused shows the number of dentries that are not
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``nr_dentry`` shows the total number of dentries allocated (active
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+ unused). ``nr_unused shows`` the number of dentries that are not
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actively used, but are saved in the LRU list for future reuse.
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Age_limit is the age in seconds after which dcache entries
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can be reclaimed when memory is short and want_pages is
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nonzero when shrink_dcache_pages() has been called and the
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``age_limit`` is the age in seconds after which dcache entries
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can be reclaimed when memory is short and ``want_pages`` is
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nonzero when ``shrink_dcache_pages()`` has been called and the
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dcache isn't pruned yet.
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nr_negative shows the number of unused dentries that are also
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``nr_negative`` shows the number of unused dentries that are also
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negative dentries which do not map to any files. Instead,
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they help speeding up rejection of non-existing files provided
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by the users.
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@ -91,32 +74,26 @@ by the users.
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file-max & file-nr
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------------------
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The value in file-max denotes the maximum number of file-
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The value in ``file-max`` denotes the maximum number of file-
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handles that the Linux kernel will allocate. When you get lots
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of error messages about running out of file handles, you might
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want to increase this limit.
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Historically,the kernel was able to allocate file handles
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dynamically, but not to free them again. The three values in
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file-nr denote the number of allocated file handles, the number
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``file-nr`` denote the number of allocated file handles, the number
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of allocated but unused file handles, and the maximum number of
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file handles. Linux 2.6 always reports 0 as the number of free
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file handles. Linux 2.6 and later always reports 0 as the number of free
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file handles -- this is not an error, it just means that the
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number of allocated file handles exactly matches the number of
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used file handles.
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Attempts to allocate more file descriptors than file-max are
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reported with printk, look for "VFS: file-max limit <number>
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reached".
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Attempts to allocate more file descriptors than ``file-max`` are
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reported with ``printk``, look for::
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VFS: file-max limit <number> reached
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nr_open
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-------
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This denotes the maximum number of file-handles a process can
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allocate. Default value is 1024*1024 (1048576) which should be
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enough for most machines. Actual limit depends on RLIMIT_NOFILE
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resource limit.
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in the kernel logs.
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inode-nr & inode-state
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@ -125,22 +102,38 @@ inode-nr & inode-state
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As with file handles, the kernel allocates the inode structures
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dynamically, but can't free them yet.
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The file inode-nr contains the first two items from
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inode-state, so we'll skip to that file...
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The file ``inode-nr`` contains the first two items from
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``inode-state``, so we'll skip to that file...
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Inode-state contains three actual numbers and four dummies.
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The actual numbers are, in order of appearance, nr_inodes,
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nr_free_inodes and preshrink.
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``inode-state`` contains three actual numbers and four dummies.
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The actual numbers are, in order of appearance, ``nr_inodes``,
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``nr_free_inodes`` and ``preshrink``.
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Nr_inodes stands for the number of inodes the system has
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``nr_inodes`` stands for the number of inodes the system has
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allocated.
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Nr_free_inodes represents the number of free inodes (?) and
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``nr_free_inodes`` represents the number of free inodes (?) and
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preshrink is nonzero when the
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system needs to prune the inode list instead of allocating
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more.
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mount-max
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---------
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This denotes the maximum number of mounts that may exist
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in a mount namespace.
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nr_open
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-------
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This denotes the maximum number of file-handles a process can
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allocate. Default value is 1024*1024 (1048576) which should be
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enough for most machines. Actual limit depends on ``RLIMIT_NOFILE``
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resource limit.
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overflowgid & overflowuid
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-------------------------
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@ -168,7 +161,7 @@ pipe-user-pages-soft
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Maximum total number of pages a non-privileged user may allocate for pipes
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before the pipe size gets limited to a single page. Once this limit is reached,
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new pipes will be limited to a single page in size for this user in order to
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limit total memory usage, and trying to increase them using fcntl() will be
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limit total memory usage, and trying to increase them using ``fcntl()`` will be
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denied until usage goes below the limit again. The default value allows to
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allocate up to 1024 pipes at their default size. When set to 0, no limit is
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applied.
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@ -183,7 +176,7 @@ file.
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When set to "0", writing to FIFOs is unrestricted.
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When set to "1" don't allow O_CREAT open on FIFOs that we don't own
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When set to "1" don't allow ``O_CREAT`` open on FIFOs that we don't own
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in world writable sticky directories, unless they are owned by the
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owner of the directory.
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@ -197,7 +190,7 @@ protected_hardlinks
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A long-standing class of security issues is the hardlink-based
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time-of-check-time-of-use race, most commonly seen in world-writable
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directories like /tmp. The common method of exploitation of this flaw
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directories like ``/tmp``. The common method of exploitation of this flaw
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is to cross privilege boundaries when following a given hardlink (i.e. a
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root process follows a hardlink created by another user). Additionally,
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on systems without separated partitions, this stops unauthorized users
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@ -215,13 +208,13 @@ This protection is based on the restrictions in Openwall and grsecurity.
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protected_regular
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-----------------
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This protection is similar to protected_fifos, but it
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This protection is similar to `protected_fifos`_, but it
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avoids writes to an attacker-controlled regular file, where a program
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expected to create one.
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When set to "0", writing to regular files is unrestricted.
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When set to "1" don't allow O_CREAT open on regular files that we
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When set to "1" don't allow ``O_CREAT`` open on regular files that we
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don't own in world writable sticky directories, unless they are
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owned by the owner of the directory.
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@ -233,7 +226,7 @@ protected_symlinks
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A long-standing class of security issues is the symlink-based
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time-of-check-time-of-use race, most commonly seen in world-writable
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directories like /tmp. The common method of exploitation of this flaw
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directories like ``/tmp``. The common method of exploitation of this flaw
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is to cross privilege boundaries when following a given symlink (i.e. a
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root process follows a symlink belonging to another user). For a likely
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incomplete list of hundreds of examples across the years, please see:
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@ -248,23 +241,25 @@ follower match, or when the directory owner matches the symlink's owner.
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This protection is based on the restrictions in Openwall and grsecurity.
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suid_dumpable:
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--------------
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suid_dumpable
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-------------
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This value can be used to query and set the core dump mode for setuid
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or otherwise protected/tainted binaries. The modes are
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= ========== ===============================================================
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0 (default) traditional behaviour. Any process which has changed
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0 (default) Traditional behaviour. Any process which has changed
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privilege levels or is execute only will not be dumped.
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1 (debug) all processes dump core when possible. The core dump is
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1 (debug) All processes dump core when possible. The core dump is
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owned by the current user and no security is applied. This is
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intended for system debugging situations only.
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Ptrace is unchecked.
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This is insecure as it allows regular users to examine the
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memory contents of privileged processes.
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2 (suidsafe) any binary which normally would not be dumped is dumped
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anyway, but only if the "core_pattern" kernel sysctl is set to
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2 (suidsafe) Any binary which normally would not be dumped is dumped
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anyway, but only if the ``core_pattern`` kernel sysctl (see
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:ref:`Documentation/admin-guide/sysctl/kernel.rst <core_pattern>`)
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is set to
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either a pipe handler or a fully qualified path. (For more
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details on this limitation, see CVE-2006-2451.) This mode is
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appropriate when administrators are attempting to debug
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@ -277,18 +272,11 @@ or otherwise protected/tainted binaries. The modes are
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= ========== ===============================================================
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mount-max
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---------
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This denotes the maximum number of mounts that may exist
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in a mount namespace.
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2. /proc/sys/fs/binfmt_misc
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===========================
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Documentation for the files in /proc/sys/fs/binfmt_misc is
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Documentation for the files in ``/proc/sys/fs/binfmt_misc`` is
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in Documentation/admin-guide/binfmt-misc.rst.
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@ -301,28 +289,32 @@ creation of a user space library that implements the POSIX message queues
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API (as noted by the MSG tag in the POSIX 1003.1-2001 version of the System
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Interfaces specification.)
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The "mqueue" filesystem contains values for determining/setting the amount of
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resources used by the file system.
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The "mqueue" filesystem contains values for determining/setting the
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amount of resources used by the file system.
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/proc/sys/fs/mqueue/queues_max is a read/write file for setting/getting the
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maximum number of message queues allowed on the system.
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``/proc/sys/fs/mqueue/queues_max`` is a read/write file for
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setting/getting the maximum number of message queues allowed on the
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system.
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/proc/sys/fs/mqueue/msg_max is a read/write file for setting/getting the
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maximum number of messages in a queue value. In fact it is the limiting value
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for another (user) limit which is set in mq_open invocation. This attribute of
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a queue must be less or equal then msg_max.
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``/proc/sys/fs/mqueue/msg_max`` is a read/write file for
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setting/getting the maximum number of messages in a queue value. In
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fact it is the limiting value for another (user) limit which is set in
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``mq_open`` invocation. This attribute of a queue must be less than
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or equal to ``msg_max``.
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/proc/sys/fs/mqueue/msgsize_max is a read/write file for setting/getting the
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maximum message size value (it is every message queue's attribute set during
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its creation).
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``/proc/sys/fs/mqueue/msgsize_max`` is a read/write file for
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setting/getting the maximum message size value (it is an attribute of
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every message queue, set during its creation).
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/proc/sys/fs/mqueue/msg_default is a read/write file for setting/getting the
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default number of messages in a queue value if attr parameter of mq_open(2) is
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NULL. If it exceed msg_max, the default value is initialized msg_max.
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``/proc/sys/fs/mqueue/msg_default`` is a read/write file for
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setting/getting the default number of messages in a queue value if the
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``attr`` parameter of ``mq_open(2)`` is ``NULL``. If it exceeds
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``msg_max``, the default value is initialized to ``msg_max``.
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/proc/sys/fs/mqueue/msgsize_default is a read/write file for setting/getting
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the default message size value if attr parameter of mq_open(2) is NULL. If it
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exceed msgsize_max, the default value is initialized msgsize_max.
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``/proc/sys/fs/mqueue/msgsize_default`` is a read/write file for
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setting/getting the default message size value if the ``attr``
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parameter of ``mq_open(2)`` is ``NULL``. If it exceeds
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``msgsize_max``, the default value is initialized to ``msgsize_max``.
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4. /proc/sys/fs/epoll - Configuration options for the epoll interface
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=====================================================================
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@ -336,7 +328,7 @@ Every epoll file descriptor can store a number of files to be monitored
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for event readiness. Each one of these monitored files constitutes a "watch".
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This configuration option sets the maximum number of "watches" that are
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allowed for each user.
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Each "watch" costs roughly 90 bytes on a 32bit kernel, and roughly 160 bytes
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on a 64bit one.
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The current default value for max_user_watches is the 1/25 (4%) of the
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available low memory, divided for the "watch" cost in bytes.
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Each "watch" costs roughly 90 bytes on a 32-bit kernel, and roughly 160 bytes
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on a 64-bit one.
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The current default value for ``max_user_watches`` is 4% of the
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available low memory, divided by the "watch" cost in bytes.
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@ -139,6 +139,8 @@ Highest valid capability of the running kernel. Exports
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``CAP_LAST_CAP`` from the kernel.
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.. _core_pattern:
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core_pattern
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============
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