proc.txt

《嵌入式系统设计与实例开发实验教材二源码》Linux内核移植与编译实验

This subdirectory  contains  specific  file system, file handle, inode, dentry
and quota information.

Currently, these files are in /proc/sys/fs:

dentry-state
------------

Status of  the  directory  cache.  Since  directory  entries  are  dynamically
allocated and  deallocated,  this  file indicates the current status. It holds
six values, in which the last two are not used and are always zero. The others
are listed in table 2-1.


Table 2-1: Status files of the directory cache 
..............................................................................
 File       Content                                                            
 nr_dentry  Almost always zero                                                 
 nr_unused  Number of unused cache entries                                     
 age_limit  
            in seconds after the entry may be reclaimed, when memory is short 
 want_pages internally                                                         
..............................................................................

dquot-nr and dquot-max
----------------------

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 available cached disk quotas is very low and you have a large
number of simultaneous system users, you might want to raise the limit.

file-nr and file-max
--------------------

The kernel  allocates file handles dynamically, but doesn't free them again at
this time.

The value  in  file-max  denotes  the  maximum number of file handles that the
Linux kernel will allocate. When you get a lot of error messages about running
out of  file handles, you might want to raise this limit. The default value is
4096. To change it, just write the new number into the file:

  # cat /proc/sys/fs/file-max 
  4096 
  # echo 8192 > /proc/sys/fs/file-max 
  # cat /proc/sys/fs/file-max 
  8192 


This method  of  revision  is  useful  for  all customizable parameters of the
kernel - simply echo the new value to the corresponding file.

The three  values  in file-nr denote the number of allocated file handles, the
number of  used file handles, and the maximum number of file handles. When the
allocated file  handles  come close to the maximum, but the number of actually
used ones  is  far  behind,  you've  encountered  a peak in your usage of file
handles and you don't need to increase the maximum.

inode-state, inode-nr and inode-max
-----------------------------------

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 to 4 times larger than the value in file-max, since stdin,
stdout, and  network  sockets also need an inode struct to handle them. If you
regularly run out of inodes, you should 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 dummy values. The numbers
are nr_inodes, nr_free_inodes, and preshrink (in order of appearance).

nr_inodes
~~~~~~~~~

Denotes 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 nr_inodes
is greater than inode-max and the system needs to prune the inode list instead
of allocating more.


super-nr and super-max
----------------------

Again, super  block structures are allocated by the kernel, but not freed. The
file super-max  contains  the  maximum  number  of super block handlers, where
super-nr shows the number of currently allocated ones.

Every mounted file system needs a super block, so if you plan to mount lots of
file systems, you may want to increase these numbers.

2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats
-----------------------------------------------------------

Besides these  files, there is the subdirectory /proc/sys/fs/binfmt_misc. This
handles the kernel support for miscellaneous binary formats.

Binfmt_misc provides  the ability to register additional binary formats to the
Kernel without  compiling  an additional module/kernel. Therefore, binfmt_misc
needs to  know magic numbers at the beginning or the filename extension of the
binary.

It works by maintaining a linked list of structs that contain a description of
a binary  format,  including  a  magic  with size (or the filename extension),
offset and  mask,  and  the  interpreter name. On request it invokes the given
interpreter with  the  original  program  as  argument,  as  binfmt_java  and
binfmt_em86 and  binfmt_mz  do.  Since binfmt_misc does not define any default
binary-formats, you have to register an additional binary-format.

There are two general files in binfmt_misc and one file per registered format.
The two general files are register and status.

Registering a new binary format
-------------------------------

To register a new binary format you have to issue the command

  echo :name:type:offset:magic:mask:interpreter: > /proc/sys/fs/binfmt_misc/register 



with appropriate  name (the name for the /proc-dir entry), offset (defaults to
0, if  omitted),  magic, mask (which can be omitted, defaults to all 0xff) and
last but  not  least,  the  interpreter that is to be invoked (for example and
testing /bin/echo).  Type  can be M for usual magic matching or E for filename
extension matching (give extension in place of magic).

Check or reset the status of the binary format handler
------------------------------------------------------

If you  do a cat on the file /proc/sys/fs/binfmt_misc/status, you will get the
current status (enabled/disabled) of binfmt_misc. Change the status by echoing
0 (disables)  or  1  (enables)  or  -1  (caution:  this  clears all previously
registered binary  formats)  to status. For example echo 0 > status to disable
binfmt_misc (temporarily).

Status of a single handler
--------------------------

Each registered  handler has an entry in /proc/sys/fs/binfmt_misc. These files
perform the  same function as status, but their scope is limited to the actual
binary format.  By  cating this file, you also receive all related information
about the interpreter/magic of the binfmt.

Example usage of binfmt_misc (emulate binfmt_java)
--------------------------------------------------

  cd /proc/sys/fs/binfmt_misc  
  echo ':Java:M::\xca\xfe\xba\xbe::/usr/local/java/bin/javawrapper:' > register  
  echo ':HTML:E::html::/usr/local/java/bin/appletviewer:' > register  
  echo ':Applet:M::<!--applet::/usr/local/java/bin/appletviewer:' > register 
  echo ':DEXE:M::\x0eDEX::/usr/bin/dosexec:' > register 


These four  lines  add  support  for  Java  executables and Java applets (like
binfmt_java, additionally  recognizing the .html extension with no need to put
<!--applet> to  every  applet  file).  You  have  to  install  the JDK and the
shell-script /usr/local/java/bin/javawrapper  too.  It  works  around  the
brokenness of  the Java filename handling. To add a Java binary, just create a
link to the class-file somewhere in the path.

2.3 /proc/sys/kernel - general kernel parameters
------------------------------------------------

This directory  reflects  general  kernel  behaviors. As I've said before, the
contents depend  on  your  configuration.  Here you'll find the most important
files, along with descriptions of what they mean and how to use them.

acct
----

The file contains three values; highwater, lowwater, and frequency.

It exists  only  when  BSD-style  process  accounting is enabled. These values
control its behavior. If the free space on the file system where the log lives
goes below  lowwater  percentage,  accounting  suspends.  If  it  goes  above
highwater percentage,  accounting  resumes. Frequency determines how often you
check the amount of free space (value is in seconds). Default settings are: 4,
2, and  30.  That is, suspend accounting if there is less than 2 percent free;
resume it  if we have a value of 3 or more percent; consider information about
the amount of free space valid for 30 seconds

ctrl-alt-del
------------

When the value in this file is 0, ctrl-alt-del is trapped and sent to the init
program to  handle a graceful restart. However, when the value is greater that
zero, Linux's  reaction  to  this key combination will be an immediate reboot,
without syncing its dirty buffers.

[NOTE]
    When a  program  (like  dosemu)  has  the  keyboard  in  raw  mode,  the
    ctrl-alt-del is  intercepted  by  the  program  before it ever reaches the
    kernel tty  layer,  and  it is up to the program to decide what to do with
    it.

domainname and hostname
-----------------------

These files  can  be controlled to set the NIS domainname and hostname of your
box. For the classic darkstar.frop.org a simple:

  # echo "darkstar" > /proc/sys/kernel/hostname 
  # echo "frop.org" > /proc/sys/kernel/domainname 


would suffice to set your hostname and NIS domainname.

osrelease, ostype and version
-----------------------------

The names make it pretty obvious what these fields contain:

  > cat /proc/sys/kernel/osrelease 
  2.2.12 
   
  > cat /proc/sys/kernel/ostype 
  Linux 
   
  > cat /proc/sys/kernel/version 
  #4 Fri Oct 1 12:41:14 PDT 1999 


The files  osrelease and ostype should be clear enough. Version needs a little
more clarification.  The  #4 means that this is the 4th kernel built from this
source base and the date after it indicates the time the kernel was built. The
only way to tune these values is to rebuild the kernel.

panic
-----

The value  in  this  file  represents  the  number of seconds the kernel waits
before rebooting  on  a  panic.  When  you  use  the  software  watchdog,  the
recommended setting  is  60. If set to 0, the auto reboot after a kernel panic
is disabled, which is the default setting.

printk
------

The four values in printk denote
* console_loglevel,
* default_message_loglevel,
* minimum_console_level and
* default_console_loglevel
respectively.

These values  influence  printk()  behavior  when  printing  or  logging error
messages, which  come  from  inside  the  kernel.  See  syslog(2)  for  more
information on the different log levels.

console_loglevel
----------------

Messages with a higher priority than this will be printed to the console.

default_message_level
---------------------

Messages without an explicit priority will be printed with this priority.

minimum_console_loglevel
------------------------

Minimum (highest) value to which the console_loglevel can be set.

default_console_loglevel
------------------------

Default value for console_loglevel.

sg-big-buff
-----------

This file  shows  the size of the generic SCSI (sg) buffer. At this point, you
can't tune  it  yet,  but  you  can  change  it  at  compile  time  by editing
include/scsi/sg.h and changing the value of SG_BIG_BUFF.

If you use a scanner with SANE (Scanner Access Now Easy) you might want to set
this to a higher value. Refer to the SANE documentation on this issue.

modprobe
--------

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

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.  In addition, one of the files
(bdflush) has some influence on disk usage.

bdflush
-------

This file  controls  the  operation of the bdflush kernel daemon. It currently
contains nine  integer  values,  six of which are actually used by the kernel.
They are listed in table 2-2.


Table 2-2: Parameters in /proc/sys/vm/bdflush 
..............................................................................
 Value      Meaning                                                            
 nfract     Percentage of buffer cache dirty to  activate bdflush              
 ndirty     Maximum number of dirty blocks to  write out per wake-cycle        
 nrefill    Number of clean buffers to try to obtain  each time we call refill 
 nref_dirt  buffer threshold for activating bdflush when trying to refill
            buffers. 
 dummy      Unused                                                             
 age_buffer Time for normal buffer to age before we flush it                   
 age_super  Time for superblock to age before we flush it