a0e881b7c1
Pull second vfs pile from Al Viro:
"The stuff in there: fsfreeze deadlock fixes by Jan (essentially, the
deadlock reproduced by xfstests 068), symlink and hardlink restriction
patches, plus assorted cleanups and fixes.
Note that another fsfreeze deadlock (emergency thaw one) is *not*
dealt with - the series by Fernando conflicts a lot with Jan's, breaks
userland ABI (FIFREEZE semantics gets changed) and trades the deadlock
for massive vfsmount leak; this is going to be handled next cycle.
There probably will be another pull request, but that stuff won't be
in it."
Fix up trivial conflicts due to unrelated changes next to each other in
drivers/{staging/gdm72xx/usb_boot.c, usb/gadget/storage_common.c}
* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs: (54 commits)
delousing target_core_file a bit
Documentation: Correct s_umount state for freeze_fs/unfreeze_fs
fs: Remove old freezing mechanism
ext2: Implement freezing
btrfs: Convert to new freezing mechanism
nilfs2: Convert to new freezing mechanism
ntfs: Convert to new freezing mechanism
fuse: Convert to new freezing mechanism
gfs2: Convert to new freezing mechanism
ocfs2: Convert to new freezing mechanism
xfs: Convert to new freezing code
ext4: Convert to new freezing mechanism
fs: Protect write paths by sb_start_write - sb_end_write
fs: Skip atime update on frozen filesystem
fs: Add freezing handling to mnt_want_write() / mnt_drop_write()
fs: Improve filesystem freezing handling
switch the protection of percpu_counter list to spinlock
nfsd: Push mnt_want_write() outside of i_mutex
btrfs: Push mnt_want_write() outside of i_mutex
fat: Push mnt_want_write() outside of i_mutex
...
301 lines
11 KiB
Plaintext
301 lines
11 KiB
Plaintext
Documentation for /proc/sys/fs/* kernel version 2.2.10
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(c) 1998, 1999, Rik van Riel <riel@nl.linux.org>
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(c) 2009, Shen Feng<shen@cn.fujitsu.com>
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For general info and legal blurb, please look in README.
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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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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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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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- aio-max-nr
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- aio-nr
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- dentry-state
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- dquot-max
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- dquot-nr
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- file-max
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- file-nr
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- inode-max
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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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- protected_hardlinks
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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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==============================================================
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aio-nr & aio-max-nr:
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aio-nr is the running total of the number of events specified on the
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io_setup system call for all currently active aio contexts. If aio-nr
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reaches aio-max-nr then io_setup will fail with EAGAIN. Note that
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raising aio-max-nr does not result in the pre-allocation or re-sizing
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of any kernel data structures.
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==============================================================
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dentry-state:
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From linux/fs/dentry.c:
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--------------------------------------------------------------
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struct {
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int nr_dentry;
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int nr_unused;
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int age_limit; /* age in seconds */
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int want_pages; /* pages requested by system */
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int dummy[2];
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} dentry_stat = {0, 0, 45, 0,};
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--------------------------------------------------------------
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Dentries are dynamically allocated and deallocated, and
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nr_dentry seems to be 0 all the time. Hence it's safe to
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assume that only nr_unused, age_limit and want_pages are
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used. Nr_unused seems to be exactly what its name says.
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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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==============================================================
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dquot-max & dquot-nr:
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The file dquot-max shows the maximum number of cached disk
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quota entries.
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The file dquot-nr shows the number of allocated disk quota
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entries and the number of free disk quota entries.
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If the number of free cached disk quotas is very low and
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you have some awesome number of simultaneous system users,
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you might want to raise the limit.
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==============================================================
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file-max & file-nr:
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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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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 -- 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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==============================================================
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nr_open:
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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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==============================================================
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inode-max, 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 value in inode-max denotes the maximum number of inode
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handlers. This value should be 3-4 times larger than the value
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in file-max, since stdin, stdout and network sockets also
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need an inode struct to handle them. When you regularly run
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out of inodes, you need to increase this value.
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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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Nr_inodes stands for the number of inodes the system has
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allocated, this can be slightly more than inode-max because
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Linux allocates them one pageful at a time.
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Nr_free_inodes represents the number of free inodes (?) and
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preshrink is nonzero when the nr_inodes > inode-max and the
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system needs to prune the inode list instead of allocating
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more.
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==============================================================
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overflowgid & overflowuid:
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Some filesystems only support 16-bit UIDs and GIDs, although in Linux
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UIDs and GIDs are 32 bits. When one of these filesystems is mounted
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with writes enabled, any UID or GID that would exceed 65535 is translated
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to a fixed value before being written to disk.
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These sysctls allow you to change the value of the fixed UID and GID.
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The default is 65534.
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==============================================================
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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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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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from "pinning" vulnerable setuid/setgid files against being upgraded by
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the administrator, or linking to special files.
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When set to "0", hardlink creation behavior is unrestricted.
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When set to "1" hardlinks cannot be created by users if they do not
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already own the source file, or do not have read/write access to it.
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This protection is based on the restrictions in Openwall and grsecurity.
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==============================================================
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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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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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http://cve.mitre.org/cgi-bin/cvekey.cgi?keyword=/tmp
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When set to "0", symlink following behavior is unrestricted.
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When set to "1" symlinks are permitted to be followed only when outside
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a sticky world-writable directory, or when the uid of the symlink and
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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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==============================================================
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suid_dumpable:
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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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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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owned by the current user and no security is applied. This is
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intended for system debugging situations only. Ptrace is unchecked.
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This is insecure as it allows regular users to examine the memory
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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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either a pipe handler or a fully qualified path. (For more details
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on this limitation, see CVE-2006-2451.) This mode is appropriate
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when administrators are attempting to debug problems in a normal
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environment, and either have a core dump pipe handler that knows
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to treat privileged core dumps with care, or specific directory
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defined for catching core dumps. If a core dump happens without
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a pipe handler or fully qualifid path, a message will be emitted
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to syslog warning about the lack of a correct setting.
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==============================================================
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super-max & super-nr:
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These numbers control the maximum number of superblocks, and
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thus the maximum number of mounted filesystems the kernel
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can have. You only need to increase super-max if you need to
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mount more filesystems than the current value in super-max
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allows you to.
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==============================================================
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aio-nr & aio-max-nr:
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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.
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==============================================================
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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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in Documentation/binfmt_misc.txt.
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3. /proc/sys/fs/mqueue - POSIX message queues filesystem
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----------------------------------------------------------
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The "mqueue" filesystem provides the necessary kernel features to enable the
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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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/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/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/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/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/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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4. /proc/sys/fs/epoll - Configuration options for the epoll interface
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--------------------------------------------------------
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This directory contains configuration options for the epoll(7) interface.
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max_user_watches
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----------------
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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 1/32 of the available
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low memory, divided for the "watch" cost in bytes.
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