proc.txt

linux 内核源代码

The location  where  the  modprobe  binary  is  located.  The kernel uses this
program to load modules on demand.

unknown_nmi_panic
-----------------

The value in this file affects behavior of handling NMI. When the value is
non-zero, unknown NMI is trapped and then panic occurs. At that time, kernel
debugging information is displayed on console.

NMI switch that most IA32 servers have fires unknown NMI up, for example.
If a system hangs up, try pressing the NMI switch.

nmi_watchdog
------------

Enables/Disables the NMI watchdog on x86 systems.  When the value is non-zero
the NMI watchdog is enabled and will continuously test all online cpus to
determine whether or not they are still functioning properly.

Because the NMI watchdog shares registers with oprofile, by disabling the NMI
watchdog, oprofile may have more registers to utilize.

maps_protect
------------

Enables/Disables the protection of the per-process proc entries "maps" and
"smaps".  When enabled, the contents of these files are visible only to
readers that are allowed to ptrace() the given process.


2.4 /proc/sys/vm - The virtual memory subsystem
-----------------------------------------------

The files  in  this directory can be used to tune the operation of the virtual
memory (VM)  subsystem  of  the  Linux  kernel.

vfs_cache_pressure
------------------

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.  Increasing vfs_cache_pressure beyond 100
causes the kernel to prefer to reclaim dentries and inodes.

dirty_background_ratio
----------------------

Contains, as a percentage of total system memory, the number of pages at which
the pdflush background writeback daemon will start writing out dirty data.

dirty_ratio
-----------------

Contains, as a percentage of total system memory, the number of pages at which
a process which is generating disk writes will itself start writing out dirty
data.

dirty_writeback_centisecs
-------------------------

The pdflush writeback daemons will periodically wake up and write `old' data
out to disk.  This tunable expresses the interval between those wakeups, in
100'ths of a second.

Setting this to zero disables periodic writeback altogether.

dirty_expire_centisecs
----------------------

This tunable is used to define when dirty data is old enough to be eligible
for writeout by the pdflush daemons.  It is expressed in 100'ths of a second. 
Data which has been dirty in-memory for longer than this interval will be
written out next time a pdflush daemon wakes up.

legacy_va_layout
----------------

If non-zero, this sysctl disables the new 32-bit mmap mmap layout - the kernel
will use the legacy (2.4) layout for all processes.

lower_zone_protection
---------------------

For some specialised workloads on highmem machines it is dangerous for
the kernel to allow process memory to be allocated from the "lowmem"
zone.  This is because that memory could then be pinned via the mlock()
system call, or by unavailability of swapspace.

And on large highmem machines this lack of reclaimable lowmem memory
can be fatal.

So the Linux page allocator has a mechanism which prevents allocations
which _could_ use highmem from using too much lowmem.  This means that
a certain amount of lowmem is defended from the possibility of being
captured into pinned user memory.

(The same argument applies to the old 16 megabyte ISA DMA region.  This
mechanism will also defend that region from allocations which could use
highmem or lowmem).

The `lower_zone_protection' tunable determines how aggressive the kernel is
in defending these lower zones.  The default value is zero - no
protection at all.

If you have a machine which uses highmem or ISA DMA and your
applications are using mlock(), or if you are running with no swap then
you probably should increase the lower_zone_protection setting.

The units of this tunable are fairly vague.  It is approximately equal
to "megabytes," so setting lower_zone_protection=100 will protect around 100
megabytes of the lowmem zone from user allocations.  It will also make
those 100 megabytes unavailable for use by applications and by
pagecache, so there is a cost.

The effects of this tunable may be observed by monitoring
/proc/meminfo:LowFree.  Write a single huge file and observe the point
at which LowFree ceases to fall.

A reasonable value for lower_zone_protection is 100.

page-cluster
------------

page-cluster controls the number of pages which are written to swap in
a single attempt.  The swap I/O size.

It is a logarithmic value - setting it to zero means "1 page", setting
it to 1 means "2 pages", setting it to 2 means "4 pages", etc.

The default value is three (eight pages at a time).  There may be some
small benefits in tuning this to a different value if your workload is
swap-intensive.

overcommit_memory
-----------------

Controls overcommit of system memory, possibly allowing processes
to allocate (but not use) more memory than is actually available.


0	-	Heuristic overcommit handling. Obvious overcommits of
		address space are refused. Used for a typical system. It
		ensures a seriously wild allocation fails while allowing
		overcommit to reduce swap usage.  root is allowed to
		allocate slightly more memory in this mode. This is the
		default.

1	-	Always overcommit. Appropriate for some scientific
		applications.

2	-	Don't overcommit. The total address space commit
		for the system is not permitted to exceed swap plus a
		configurable percentage (default is 50) of physical RAM.
		Depending on the percentage you use, in most situations
		this means a process will not be killed while attempting
		to use already-allocated memory but will receive errors
		on memory allocation as	appropriate.

overcommit_ratio
----------------

Percentage of physical memory size to include in overcommit calculations
(see above.)

Memory allocation limit = swapspace + physmem * (overcommit_ratio / 100)

	swapspace = total size of all swap areas
	physmem = size of physical memory in system

nr_hugepages and hugetlb_shm_group
----------------------------------

nr_hugepages configures number of hugetlb page reserved for the system.

hugetlb_shm_group contains group id that is allowed to create SysV shared
memory segment using hugetlb page.

hugepages_treat_as_movable
--------------------------

This parameter is only useful when kernelcore= is specified at boot time to
create ZONE_MOVABLE for pages that may be reclaimed or migrated. Huge pages
are not movable so are not normally allocated from ZONE_MOVABLE. A non-zero
value written to hugepages_treat_as_movable allows huge pages to be allocated
from ZONE_MOVABLE.

Once enabled, the ZONE_MOVABLE is treated as an area of memory the huge
pages pool can easily grow or shrink within. Assuming that applications are
not running that mlock() a lot of memory, it is likely the huge pages pool
can grow to the size of ZONE_MOVABLE by repeatedly entering the desired value
into nr_hugepages and triggering page reclaim.

laptop_mode
-----------

laptop_mode is a knob that controls "laptop mode". All the things that are
controlled by this knob are discussed in Documentation/laptop-mode.txt.

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/laptop-mode.txt.

swap_token_timeout
------------------

This file contains valid hold time of swap out protection token. The Linux
VM has token based thrashing control mechanism and uses the token to prevent
unnecessary page faults in thrashing situation. The unit of the value is
second. The value would be useful to tune thrashing behavior.

drop_caches
-----------

Writing to this will cause the kernel to drop clean caches, dentries and
inodes from memory, causing that memory to become free.

To free pagecache:
	echo 1 > /proc/sys/vm/drop_caches
To free dentries and inodes:
	echo 2 > /proc/sys/vm/drop_caches
To free pagecache, dentries and inodes:
	echo 3 > /proc/sys/vm/drop_caches

As this is a non-destructive operation and dirty objects are not freeable, the
user should run `sync' first.


2.5 /proc/sys/dev - Device specific parameters
----------------------------------------------

Currently there is only support for CDROM drives, and for those, there is only
one read-only  file containing information about the CD-ROM drives attached to
the system:

  >cat /proc/sys/dev/cdrom/info 
  CD-ROM information, Id: cdrom.c 2.55 1999/04/25 
   
  drive name:             sr0     hdb 
  drive speed:            32      40 
  drive # of slots:       1       0 
  Can close tray:         1       1 
  Can open tray:          1       1 
  Can lock tray:          1       1 
  Can change speed:       1       1 
  Can select disk:        0       1 
  Can read multisession:  1       1 
  Can read MCN:           1       1 
  Reports media changed:  1       1 
  Can play audio:         1       1 


You see two drives, sr0 and hdb, along with a list of their features.

2.6 /proc/sys/sunrpc - Remote procedure calls
---------------------------------------------

This directory  contains four files, which enable or disable debugging for the
RPC functions NFS, NFS-daemon, RPC and NLM. The default values are 0. They can
be set to one to turn debugging on. (The default value is 0 for each)

2.7 /proc/sys/net - Networking stuff
------------------------------------

The interface  to  the  networking  parts  of  the  kernel  is  located  in
/proc/sys/net. Table  2-3  shows all possible subdirectories. You may see only
some of them, depending on your kernel's configuration.


Table 2-3: 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     
 ipv4      IP version 4        x25        X.25 protocol      
 ipx       IPX                 token-ring IBM token ring     
 bridge    Bridging            decnet     DEC net            
 ipv6      IP version 6                   
..............................................................................

We will  concentrate  on IP networking here. Since AX15, X.25, and DEC Net are
only minor players in the Linux world, we'll skip them in this chapter. You'll
find some  short  info on Appletalk and IPX further on in this chapter. Review
the online  documentation  and the kernel source to get a detailed view of the
parameters for  those  protocols.  In  this  section  we'll  discuss  the
subdirectories printed  in  bold letters in the table above. As default values
are suitable for most needs, there is no need to change these values.

/proc/sys/net/core - Network core options
-----------------