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Based on kernel version 2.6.33. Page generated on 2010-02-24 15:36 EST.

	------------------------------------------------------------------------------
	                       T H E  /proc   F I L E S Y S T E M
	------------------------------------------------------------------------------
	/proc/sys         Terrehon Bowden <terrehon[AT]pacbell[DOT]net>        October 7 1999
	                  Bodo Bauer <bb[AT]ricochet[DOT]net>
	
	2.4.x update	  Jorge Nerin <comandante[AT]zaralinux[DOT]com>      November 14 2000
	move /proc/sys	  Shen Feng <shen[AT]cn.fujitsu[DOT]com>		  April 1 2009
	------------------------------------------------------------------------------
	Version 1.3                                              Kernel version 2.2.12
						      Kernel version 2.4.0-test11-pre4
	------------------------------------------------------------------------------
	fixes/update part 1.1  Stefani Seibold <stefani[AT]seibold[DOT]net>       June 9 2009
	
	Table of Contents
	-----------------
	
	  0     Preface
	  0.1	Introduction/Credits
	  0.2	Legal Stuff
	
	  1	Collecting System Information
	  1.1	Process-Specific Subdirectories
	  1.2	Kernel data
	  1.3	IDE devices in /proc/ide
	  1.4	Networking info in /proc/net
	  1.5	SCSI info
	  1.6	Parallel port info in /proc/parport
	  1.7	TTY info in /proc/tty
	  1.8	Miscellaneous kernel statistics in /proc/stat
	  1.9 Ext4 file system parameters
	
	  2	Modifying System Parameters
	
	  3	Per-Process Parameters
	  3.1	/proc/<pid>/oom_adj - Adjust the oom-killer score
	  3.2	/proc/<pid>/oom_score - Display current oom-killer score
	  3.3	/proc/<pid>/io - Display the IO accounting fields
	  3.4	/proc/<pid>/coredump_filter - Core dump filtering settings
	  3.5	/proc/<pid>/mountinfo - Information about mounts
	  3.6	/proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
	
	
	------------------------------------------------------------------------------
	Preface
	------------------------------------------------------------------------------
	
	0.1 Introduction/Credits
	------------------------
	
	This documentation is  part of a soon (or  so we hope) to be  released book on
	the SuSE  Linux distribution. As  there is  no complete documentation  for the
	/proc file system and we've used  many freely available sources to write these
	chapters, it  seems only fair  to give the work  back to the  Linux community.
	This work is  based on the 2.2.*  kernel version and the  upcoming 2.4.*. I'm
	afraid it's still far from complete, but we  hope it will be useful. As far as
	we know, it is the first 'all-in-one' document about the /proc file system. It
	is focused  on the Intel  x86 hardware,  so if you  are looking for  PPC, ARM,
	SPARC, AXP, etc., features, you probably  won't find what you are looking for.
	It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
	additions and patches  are welcome and will  be added to this  document if you
	mail them to Bodo.
	
	We'd like  to  thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
	other people for help compiling this documentation. We'd also like to extend a
	special thank  you to Andi Kleen for documentation, which we relied on heavily
	to create  this  document,  as well as the additional information he provided.
	Thanks to  everybody  else  who contributed source or docs to the Linux kernel
	and helped create a great piece of software... :)
	
	If you  have  any comments, corrections or additions, please don't hesitate to
	contact Bodo  Bauer  at  bb[AT]ricochet.net[DOT]  We'll  be happy to add them to this
	document.
	
	The   latest   version    of   this   document   is    available   online   at
	http://skaro.nightcrawler.com/~bb/Docs/Proc as HTML version.
	
	If  the above  direction does  not works  for you,  ypu could  try the  kernel
	mailing  list  at  linux-kernel[AT]vger.kernel[DOT]org  and/or try  to  reach  me  at
	comandante[AT]zaralinux.com[DOT]
	
	0.2 Legal Stuff
	---------------
	
	We don't  guarantee  the  correctness  of this document, and if you come to us
	complaining about  how  you  screwed  up  your  system  because  of  incorrect
	documentation, we won't feel responsible...
	
	------------------------------------------------------------------------------
	CHAPTER 1: COLLECTING SYSTEM INFORMATION
	------------------------------------------------------------------------------
	
	------------------------------------------------------------------------------
	In This Chapter
	------------------------------------------------------------------------------
	* Investigating  the  properties  of  the  pseudo  file  system  /proc and its
	  ability to provide information on the running Linux system
	* Examining /proc's structure
	* Uncovering  various  information  about the kernel and the processes running
	  on the system
	------------------------------------------------------------------------------
	
	
	The proc  file  system acts as an interface to internal data structures in the
	kernel. It  can  be  used to obtain information about the system and to change
	certain kernel parameters at runtime (sysctl).
	
	First, we'll  take  a  look  at the read-only parts of /proc. In Chapter 2, we
	show you how you can use /proc/sys to change settings.
	
	1.1 Process-Specific Subdirectories
	-----------------------------------
	
	The directory  /proc  contains  (among other things) one subdirectory for each
	process running on the system, which is named after the process ID (PID).
	
	The link  self  points  to  the  process reading the file system. Each process
	subdirectory has the entries listed in Table 1-1.
	
	
	Table 1-1: Process specific entries in /proc
	..............................................................................
	 File		Content
	 clear_refs	Clears page referenced bits shown in smaps output
	 cmdline	Command line arguments
	 cpu		Current and last cpu in which it was executed	(2.4)(smp)
	 cwd		Link to the current working directory
	 environ	Values of environment variables
	 exe		Link to the executable of this process
	 fd		Directory, which contains all file descriptors
	 maps		Memory maps to executables and library files	(2.4)
	 mem		Memory held by this process
	 root		Link to the root directory of this process
	 stat		Process status
	 statm		Process memory status information
	 status		Process status in human readable form
	 wchan		If CONFIG_KALLSYMS is set, a pre-decoded wchan
	 stack		Report full stack trace, enable via CONFIG_STACKTRACE
	 smaps		a extension based on maps, showing the memory consumption of
			each mapping
	..............................................................................
	
	For example, to get the status information of a process, all you have to do is
	read the file /proc/PID/status:
	
	  >cat /proc/self/status
	  Name:   cat
	  State:  R (running)
	  Tgid:   5452
	  Pid:    5452
	  PPid:   743
	  TracerPid:      0						(2.4)
	  Uid:    501     501     501     501
	  Gid:    100     100     100     100
	  FDSize: 256
	  Groups: 100 14 16
	  VmPeak:     5004 kB
	  VmSize:     5004 kB
	  VmLck:         0 kB
	  VmHWM:       476 kB
	  VmRSS:       476 kB
	  VmData:      156 kB
	  VmStk:        88 kB
	  VmExe:        68 kB
	  VmLib:      1412 kB
	  VmPTE:        20 kb
	  Threads:        1
	  SigQ:   0/28578
	  SigPnd: 0000000000000000
	  ShdPnd: 0000000000000000
	  SigBlk: 0000000000000000
	  SigIgn: 0000000000000000
	  SigCgt: 0000000000000000
	  CapInh: 00000000fffffeff
	  CapPrm: 0000000000000000
	  CapEff: 0000000000000000
	  CapBnd: ffffffffffffffff
	  voluntary_ctxt_switches:        0
	  nonvoluntary_ctxt_switches:     1
	
	This shows you nearly the same information you would get if you viewed it with
	the ps  command.  In  fact,  ps  uses  the  proc  file  system  to  obtain its
	information.  But you get a more detailed  view of the  process by reading the
	file /proc/PID/status. It fields are described in table 1-2.
	
	The  statm  file  contains  more  detailed  information about the process
	memory usage. Its seven fields are explained in Table 1-3.  The stat file
	contains details information about the process itself.  Its fields are
	explained in Table 1-4.
	
	Table 1-2: Contents of the statm files (as of 2.6.30-rc7)
	..............................................................................
	 Field                       Content
	 Name                        filename of the executable
	 State                       state (R is running, S is sleeping, D is sleeping
	                             in an uninterruptible wait, Z is zombie,
				     T is traced or stopped)
	 Tgid                        thread group ID
	 Pid                         process id
	 PPid                        process id of the parent process
	 TracerPid                   PID of process tracing this process (0 if not)
	 Uid                         Real, effective, saved set, and  file system UIDs
	 Gid                         Real, effective, saved set, and  file system GIDs
	 FDSize                      number of file descriptor slots currently allocated
	 Groups                      supplementary group list
	 VmPeak                      peak virtual memory size
	 VmSize                      total program size
	 VmLck                       locked memory size
	 VmHWM                       peak resident set size ("high water mark")
	 VmRSS                       size of memory portions
	 VmData                      size of data, stack, and text segments
	 VmStk                       size of data, stack, and text segments
	 VmExe                       size of text segment
	 VmLib                       size of shared library code
	 VmPTE                       size of page table entries
	 Threads                     number of threads
	 SigQ                        number of signals queued/max. number for queue
	 SigPnd                      bitmap of pending signals for the thread
	 ShdPnd                      bitmap of shared pending signals for the process
	 SigBlk                      bitmap of blocked signals
	 SigIgn                      bitmap of ignored signals
	 SigCgt                      bitmap of catched signals
	 CapInh                      bitmap of inheritable capabilities
	 CapPrm                      bitmap of permitted capabilities
	 CapEff                      bitmap of effective capabilities
	 CapBnd                      bitmap of capabilities bounding set
	 Cpus_allowed                mask of CPUs on which this process may run
	 Cpus_allowed_list           Same as previous, but in "list format"
	 Mems_allowed                mask of memory nodes allowed to this process
	 Mems_allowed_list           Same as previous, but in "list format"
	 voluntary_ctxt_switches     number of voluntary context switches
	 nonvoluntary_ctxt_switches  number of non voluntary context switches
	..............................................................................
	
	Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
	..............................................................................
	 Field    Content
	 size     total program size (pages)		(same as VmSize in status)
	 resident size of memory portions (pages)	(same as VmRSS in status)
	 shared   number of pages that are shared	(i.e. backed by a file)
	 trs      number of pages that are 'code'	(not including libs; broken,
								includes data segment)
	 lrs      number of pages of library		(always 0 on 2.6)
	 drs      number of pages of data/stack		(including libs; broken,
								includes library text)
	 dt       number of dirty pages			(always 0 on 2.6)
	..............................................................................
	
	
	Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
	..............................................................................
	 Field          Content
	  pid           process id
	  tcomm         filename of the executable
	  state         state (R is running, S is sleeping, D is sleeping in an
	                uninterruptible wait, Z is zombie, T is traced or stopped)
	  ppid          process id of the parent process
	  pgrp          pgrp of the process
	  sid           session id
	  tty_nr        tty the process uses
	  tty_pgrp      pgrp of the tty
	  flags         task flags
	  min_flt       number of minor faults
	  cmin_flt      number of minor faults with child's
	  maj_flt       number of major faults
	  cmaj_flt      number of major faults with child's
	  utime         user mode jiffies
	  stime         kernel mode jiffies
	  cutime        user mode jiffies with child's
	  cstime        kernel mode jiffies with child's
	  priority      priority level
	  nice          nice level
	  num_threads   number of threads
	  it_real_value	(obsolete, always 0)
	  start_time    time the process started after system boot
	  vsize         virtual memory size
	  rss           resident set memory size
	  rsslim        current limit in bytes on the rss
	  start_code    address above which program text can run
	  end_code      address below which program text can run
	  start_stack   address of the start of the stack
	  esp           current value of ESP
	  eip           current value of EIP
	  pending       bitmap of pending signals
	  blocked       bitmap of blocked signals
	  sigign        bitmap of ignored signals
	  sigcatch      bitmap of catched signals
	  wchan         address where process went to sleep
	  0             (place holder)
	  0             (place holder)
	  exit_signal   signal to send to parent thread on exit
	  task_cpu      which CPU the task is scheduled on
	  rt_priority   realtime priority
	  policy        scheduling policy (man sched_setscheduler)
	  blkio_ticks   time spent waiting for block IO
	  gtime         guest time of the task in jiffies
	  cgtime        guest time of the task children in jiffies
	..............................................................................
	
	The /proc/PID/map file containing the currently mapped memory regions and
	their access permissions.
	
	The format is:
	
	address           perms offset  dev   inode      pathname
	
	08048000-08049000 r-xp 00000000 03:00 8312       /opt/test
	08049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
	0804a000-0806b000 rw-p 00000000 00:00 0          [heap]
	a7cb1000-a7cb2000 ---p 00000000 00:00 0
	a7cb2000-a7eb2000 rw-p 00000000 00:00 0          [threadstack:001ff4b4]
	a7eb2000-a7eb3000 ---p 00000000 00:00 0
	a7eb3000-a7ed5000 rw-p 00000000 00:00 0
	a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/libc.so.6
	a8008000-a800a000 r--p 00133000 03:00 4222       /lib/libc.so.6
	a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/libc.so.6
	a800b000-a800e000 rw-p 00000000 00:00 0
	a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/libpthread.so.0
	a8022000-a8023000 r--p 00013000 03:00 14462      /lib/libpthread.so.0
	a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/libpthread.so.0
	a8024000-a8027000 rw-p 00000000 00:00 0
	a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/ld-linux.so.2
	a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/ld-linux.so.2
	a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/ld-linux.so.2
	aff35000-aff4a000 rw-p 00000000 00:00 0          [stack]
	ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
	
	where "address" is the address space in the process that it occupies, "perms"
	is a set of permissions:
	
	 r = read
	 w = write
	 x = execute
	 s = shared
	 p = private (copy on write)
	
	"offset" is the offset into the mapping, "dev" is the device (major:minor), and
	"inode" is the inode  on that device.  0 indicates that  no inode is associated
	with the memory region, as the case would be with BSS (uninitialized data).
	The "pathname" shows the name associated file for this mapping.  If the mapping
	is not associated with a file:
	
	 [heap]                   = the heap of the program
	 [stack]                  = the stack of the main process
	 [vdso]                   = the "virtual dynamic shared object",
	                            the kernel system call handler
	 [threadstack:xxxxxxxx]   = the stack of the thread, xxxxxxxx is the stack size
	
	 or if empty, the mapping is anonymous.
	
	
	The /proc/PID/smaps is an extension based on maps, showing the memory
	consumption for each of the process's mappings. For each of mappings there
	is a series of lines such as the following:
	
	08048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
	Size:               1084 kB
	Rss:                 892 kB
	Pss:                 374 kB
	Shared_Clean:        892 kB
	Shared_Dirty:          0 kB
	Private_Clean:         0 kB
	Private_Dirty:         0 kB
	Referenced:          892 kB
	Swap:                  0 kB
	KernelPageSize:        4 kB
	MMUPageSize:           4 kB
	
	The first  of these lines shows  the same information  as is displayed for the
	mapping in /proc/PID/maps.  The remaining lines show  the size of the mapping,
	the amount of the mapping that is currently resident in RAM, the "proportional
	set size� (divide each shared page by the number of processes sharing it), the
	number of clean and dirty shared pages in the mapping, and the number of clean
	and dirty private pages in the mapping.  The "Referenced" indicates the amount
	of memory currently marked as referenced or accessed.
	
	This file is only present if the CONFIG_MMU kernel configuration option is
	enabled.
	
	The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
	bits on both physical and virtual pages associated with a process.
	To clear the bits for all the pages associated with the process
	    > echo 1 > /proc/PID/clear_refs
	
	To clear the bits for the anonymous pages associated with the process
	    > echo 2 > /proc/PID/clear_refs
	
	To clear the bits for the file mapped pages associated with the process
	    > echo 3 > /proc/PID/clear_refs
	Any other value written to /proc/PID/clear_refs will have no effect.
	
	
	1.2 Kernel data
	---------------
	
	Similar to  the  process entries, the kernel data files give information about
	the running kernel. The files used to obtain this information are contained in
	/proc and  are  listed  in Table 1-5. Not all of these will be present in your
	system. It  depends  on the kernel configuration and the loaded modules, which
	files are there, and which are missing.
	
	Table 1-5: Kernel info in /proc
	..............................................................................
	 File        Content                                           
	 apm         Advanced power management info                    
	 buddyinfo   Kernel memory allocator information (see text)	(2.5)
	 bus         Directory containing bus specific information     
	 cmdline     Kernel command line                               
	 cpuinfo     Info about the CPU                                
	 devices     Available devices (block and character)           
	 dma         Used DMS channels                                 
	 filesystems Supported filesystems                             
	 driver	     Various drivers grouped here, currently rtc (2.4)
	 execdomains Execdomains, related to security			(2.4)
	 fb	     Frame Buffer devices				(2.4)
	 fs	     File system parameters, currently nfs/exports	(2.4)
	 ide         Directory containing info about the IDE subsystem 
	 interrupts  Interrupt usage                                   
	 iomem	     Memory map						(2.4)
	 ioports     I/O port usage                                    
	 irq	     Masks for irq to cpu affinity			(2.4)(smp?)
	 isapnp	     ISA PnP (Plug&Play) Info				(2.4)
	 kcore       Kernel core image (can be ELF or A.OUT(deprecated in 2.4))   
	 kmsg        Kernel messages                                   
	 ksyms       Kernel symbol table                               
	 loadavg     Load average of last 1, 5 & 15 minutes                
	 locks       Kernel locks                                      
	 meminfo     Memory info                                       
	 misc        Miscellaneous                                     
	 modules     List of loaded modules                            
	 mounts      Mounted filesystems                               
	 net         Networking info (see text)                        
	 partitions  Table of partitions known to the system           
	 pci	     Deprecated info of PCI bus (new way -> /proc/bus/pci/,
	             decoupled by lspci					(2.4)
	 rtc         Real time clock                                   
	 scsi        SCSI info (see text)                              
	 slabinfo    Slab pool info                                    
	 softirqs    softirq usage
	 stat        Overall statistics                                
	 swaps       Swap space utilization                            
	 sys         See chapter 2                                     
	 sysvipc     Info of SysVIPC Resources (msg, sem, shm)		(2.4)
	 tty	     Info of tty drivers
	 uptime      System uptime                                     
	 version     Kernel version                                    
	 video	     bttv info of video resources			(2.4)
	 vmallocinfo Show vmalloced areas
	..............................................................................
	
	You can,  for  example,  check  which interrupts are currently in use and what
	they are used for by looking in the file /proc/interrupts:
	
	  > cat /proc/interrupts 
	             CPU0        
	    0:    8728810          XT-PIC  timer 
	    1:        895          XT-PIC  keyboard 
	    2:          0          XT-PIC  cascade 
	    3:     531695          XT-PIC  aha152x 
	    4:    2014133          XT-PIC  serial 
	    5:      44401          XT-PIC  pcnet_cs 
	    8:          2          XT-PIC  rtc 
	   11:          8          XT-PIC  i82365 
	   12:     182918          XT-PIC  PS/2 Mouse 
	   13:          1          XT-PIC  fpu 
	   14:    1232265          XT-PIC  ide0 
	   15:          7          XT-PIC  ide1 
	  NMI:          0 
	
	In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
	output of a SMP machine):
	
	  > cat /proc/interrupts 
	
	             CPU0       CPU1       
	    0:    1243498    1214548    IO-APIC-edge  timer
	    1:       8949       8958    IO-APIC-edge  keyboard
	    2:          0          0          XT-PIC  cascade
	    5:      11286      10161    IO-APIC-edge  soundblaster
	    8:          1          0    IO-APIC-edge  rtc
	    9:      27422      27407    IO-APIC-edge  3c503
	   12:     113645     113873    IO-APIC-edge  PS/2 Mouse
	   13:          0          0          XT-PIC  fpu
	   14:      22491      24012    IO-APIC-edge  ide0
	   15:       2183       2415    IO-APIC-edge  ide1
	   17:      30564      30414   IO-APIC-level  eth0
	   18:        177        164   IO-APIC-level  bttv
	  NMI:    2457961    2457959 
	  LOC:    2457882    2457881 
	  ERR:       2155
	
	NMI is incremented in this case because every timer interrupt generates a NMI
	(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
	
	LOC is the local interrupt counter of the internal APIC of every CPU.
	
	ERR is incremented in the case of errors in the IO-APIC bus (the bus that
	connects the CPUs in a SMP system. This means that an error has been detected,
	the IO-APIC automatically retry the transmission, so it should not be a big
	problem, but you should read the SMP-FAQ.
	
	In 2.6.2* /proc/interrupts was expanded again.  This time the goal was for
	/proc/interrupts to display every IRQ vector in use by the system, not
	just those considered 'most important'.  The new vectors are:
	
	  THR -- interrupt raised when a machine check threshold counter
	  (typically counting ECC corrected errors of memory or cache) exceeds
	  a configurable threshold.  Only available on some systems.
	
	  TRM -- a thermal event interrupt occurs when a temperature threshold
	  has been exceeded for the CPU.  This interrupt may also be generated
	  when the temperature drops back to normal.
	
	  SPU -- a spurious interrupt is some interrupt that was raised then lowered
	  by some IO device before it could be fully processed by the APIC.  Hence
	  the APIC sees the interrupt but does not know what device it came from.
	  For this case the APIC will generate the interrupt with a IRQ vector
	  of 0xff. This might also be generated by chipset bugs.
	
	  RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
	  sent from one CPU to another per the needs of the OS.  Typically,
	  their statistics are used by kernel developers and interested users to
	  determine the occurrence of interrupts of the given type.
	
	The above IRQ vectors are displayed only when relevent.  For example,
	the threshold vector does not exist on x86_64 platforms.  Others are
	suppressed when the system is a uniprocessor.  As of this writing, only
	i386 and x86_64 platforms support the new IRQ vector displays.
	
	Of some interest is the introduction of the /proc/irq directory to 2.4.
	It could be used to set IRQ to CPU affinity, this means that you can "hook" an
	IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
	irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
	prof_cpu_mask.
	
	For example 
	  > ls /proc/irq/
	  0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
	  1  11  13  15  17  19  3  5  7  9  default_smp_affinity
	  > ls /proc/irq/0/
	  smp_affinity
	
	smp_affinity is a bitmask, in which you can specify which CPUs can handle the
	IRQ, you can set it by doing:
	
	  > echo 1 > /proc/irq/10/smp_affinity
	
	This means that only the first CPU will handle the IRQ, but you can also echo
	5 which means that only the first and fourth CPU can handle the IRQ.
	
	The contents of each smp_affinity file is the same by default:
	
	  > cat /proc/irq/0/smp_affinity
	  ffffffff
	
	The default_smp_affinity mask applies to all non-active IRQs, which are the
	IRQs which have not yet been allocated/activated, and hence which lack a
	/proc/irq/[0-9]* directory.
	
	prof_cpu_mask specifies which CPUs are to be profiled by the system wide
	profiler. Default value is ffffffff (all cpus).
	
	The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
	between all the CPUs which are allowed to handle it. As usual the kernel has
	more info than you and does a better job than you, so the defaults are the
	best choice for almost everyone.
	
	There are  three  more  important subdirectories in /proc: net, scsi, and sys.
	The general  rule  is  that  the  contents,  or  even  the  existence of these
	directories, depend  on your kernel configuration. If SCSI is not enabled, the
	directory scsi  may  not  exist. The same is true with the net, which is there
	only when networking support is present in the running kernel.
	
	The slabinfo  file  gives  information  about  memory usage at the slab level.
	Linux uses  slab  pools for memory management above page level in version 2.2.
	Commonly used  objects  have  their  own  slab  pool (such as network buffers,
	directory cache, and so on).
	
	..............................................................................
	
	> cat /proc/buddyinfo
	
	Node 0, zone      DMA      0      4      5      4      4      3 ...
	Node 0, zone   Normal      1      0      0      1    101      8 ...
	Node 0, zone  HighMem      2      0      0      1      1      0 ...
	
	Memory fragmentation is a problem under some workloads, and buddyinfo is a 
	useful tool for helping diagnose these problems.  Buddyinfo will give you a 
	clue as to how big an area you can safely allocate, or why a previous
	allocation failed.
	
	Each column represents the number of pages of a certain order which are 
	available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in 
	ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE 
	available in ZONE_NORMAL, etc... 
	
	..............................................................................
	
	meminfo:
	
	Provides information about distribution and utilization of memory.  This
	varies by architecture and compile options.  The following is from a
	16GB PIII, which has highmem enabled.  You may not have all of these fields.
	
	> cat /proc/meminfo
	
	
	MemTotal:     16344972 kB
	MemFree:      13634064 kB
	Buffers:          3656 kB
	Cached:        1195708 kB
	SwapCached:          0 kB
	Active:         891636 kB
	Inactive:      1077224 kB
	HighTotal:    15597528 kB
	HighFree:     13629632 kB
	LowTotal:       747444 kB
	LowFree:          4432 kB
	SwapTotal:           0 kB
	SwapFree:            0 kB
	Dirty:             968 kB
	Writeback:           0 kB
	AnonPages:      861800 kB
	Mapped:         280372 kB
	Slab:           284364 kB
	SReclaimable:   159856 kB
	SUnreclaim:     124508 kB
	PageTables:      24448 kB
	NFS_Unstable:        0 kB
	Bounce:              0 kB
	WritebackTmp:        0 kB
	CommitLimit:   7669796 kB
	Committed_AS:   100056 kB
	VmallocTotal:   112216 kB
	VmallocUsed:       428 kB
	VmallocChunk:   111088 kB
	
	    MemTotal: Total usable ram (i.e. physical ram minus a few reserved
	              bits and the kernel binary code)
	     MemFree: The sum of LowFree+HighFree
	     Buffers: Relatively temporary storage for raw disk blocks
	              shouldn't get tremendously large (20MB or so)
	      Cached: in-memory cache for files read from the disk (the
	              pagecache).  Doesn't include SwapCached
	  SwapCached: Memory that once was swapped out, is swapped back in but
	              still also is in the swapfile (if memory is needed it
	              doesn't need to be swapped out AGAIN because it is already
	              in the swapfile. This saves I/O)
	      Active: Memory that has been used more recently and usually not
	              reclaimed unless absolutely necessary.
	    Inactive: Memory which has been less recently used.  It is more
	              eligible to be reclaimed for other purposes
	   HighTotal:
	    HighFree: Highmem is all memory above ~860MB of physical memory
	              Highmem areas are for use by userspace programs, or
	              for the pagecache.  The kernel must use tricks to access
	              this memory, making it slower to access than lowmem.
	    LowTotal:
	     LowFree: Lowmem is memory which can be used for everything that
	              highmem can be used for, but it is also available for the
	              kernel's use for its own data structures.  Among many
	              other things, it is where everything from the Slab is
	              allocated.  Bad things happen when you're out of lowmem.
	   SwapTotal: total amount of swap space available
	    SwapFree: Memory which has been evicted from RAM, and is temporarily
	              on the disk
	       Dirty: Memory which is waiting to get written back to the disk
	   Writeback: Memory which is actively being written back to the disk
	   AnonPages: Non-file backed pages mapped into userspace page tables
	      Mapped: files which have been mmaped, such as libraries
	        Slab: in-kernel data structures cache
	SReclaimable: Part of Slab, that might be reclaimed, such as caches
	  SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
	  PageTables: amount of memory dedicated to the lowest level of page
	              tables.
	NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
		      storage
	      Bounce: Memory used for block device "bounce buffers"
	WritebackTmp: Memory used by FUSE for temporary writeback buffers
	 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
	              this is the total amount of  memory currently available to
	              be allocated on the system. This limit is only adhered to
	              if strict overcommit accounting is enabled (mode 2 in
	              'vm.overcommit_memory').
	              The CommitLimit is calculated with the following formula:
	              CommitLimit = ('vm.overcommit_ratio' * Physical RAM) + Swap
	              For example, on a system with 1G of physical RAM and 7G
	              of swap with a `vm.overcommit_ratio` of 30 it would
	              yield a CommitLimit of 7.3G.
	              For more details, see the memory overcommit documentation
	              in vm/overcommit-accounting.
	Committed_AS: The amount of memory presently allocated on the system.
	              The committed memory is a sum of all of the memory which
	              has been allocated by processes, even if it has not been
	              "used" by them as of yet. A process which malloc()'s 1G
	              of memory, but only touches 300M of it will only show up
	              as using 300M of memory even if it has the address space
	              allocated for the entire 1G. This 1G is memory which has
	              been "committed" to by the VM and can be used at any time
	              by the allocating application. With strict overcommit
	              enabled on the system (mode 2 in 'vm.overcommit_memory'),
	              allocations which would exceed the CommitLimit (detailed
	              above) will not be permitted. This is useful if one needs
	              to guarantee that processes will not fail due to lack of
	              memory once that memory has been successfully allocated.
	VmallocTotal: total size of vmalloc memory area
	 VmallocUsed: amount of vmalloc area which is used
	VmallocChunk: largest contiguous block of vmalloc area which is free
	
	..............................................................................
	
	vmallocinfo:
	
	Provides information about vmalloced/vmaped areas. One line per area,
	containing the virtual address range of the area, size in bytes,
	caller information of the creator, and optional information depending
	on the kind of area :
	
	 pages=nr    number of pages
	 phys=addr   if a physical address was specified
	 ioremap     I/O mapping (ioremap() and friends)
	 vmalloc     vmalloc() area
	 vmap        vmap()ed pages
	 user        VM_USERMAP area
	 vpages      buffer for pages pointers was vmalloced (huge area)
	 N<node>=nr  (Only on NUMA kernels)
	             Number of pages allocated on memory node <node>
	
	> cat /proc/vmallocinfo
	0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
	  /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
	0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
	  /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
	0xffffc20000302000-0xffffc20000304000    8192 acpi_tb_verify_table+0x21/0x4f...
	  phys=7fee8000 ioremap
	0xffffc20000304000-0xffffc20000307000   12288 acpi_tb_verify_table+0x21/0x4f...
	  phys=7fee7000 ioremap
	0xffffc2000031d000-0xffffc2000031f000    8192 init_vdso_vars+0x112/0x210
	0xffffc2000031f000-0xffffc2000032b000   49152 cramfs_uncompress_init+0x2e ...
	  /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
	0xffffc2000033a000-0xffffc2000033d000   12288 sys_swapon+0x640/0xac0      ...
	  pages=2 vmalloc N1=2
	0xffffc20000347000-0xffffc2000034c000   20480 xt_alloc_table_info+0xfe ...
	  /0x130 [x_tables] pages=4 vmalloc N0=4
	0xffffffffa0000000-0xffffffffa000f000   61440 sys_init_module+0xc27/0x1d00 ...
	   pages=14 vmalloc N2=14
	0xffffffffa000f000-0xffffffffa0014000   20480 sys_init_module+0xc27/0x1d00 ...
	   pages=4 vmalloc N1=4
	0xffffffffa0014000-0xffffffffa0017000   12288 sys_init_module+0xc27/0x1d00 ...
	   pages=2 vmalloc N1=2
	0xffffffffa0017000-0xffffffffa0022000   45056 sys_init_module+0xc27/0x1d00 ...
	   pages=10 vmalloc N0=10
	
	..............................................................................
	
	softirqs:
	
	Provides counts of softirq handlers serviced since boot time, for each cpu.
	
	> cat /proc/softirqs
	                CPU0       CPU1       CPU2       CPU3
	      HI:          0          0          0          0
	   TIMER:      27166      27120      27097      27034
	  NET_TX:          0          0          0         17
	  NET_RX:         42          0          0         39
	   BLOCK:          0          0        107       1121
	 TASKLET:          0          0          0        290
	   SCHED:      27035      26983      26971      26746
	 HRTIMER:          0          0          0          0
	     RCU:       1678       1769       2178       2250
	
	
	1.3 IDE devices in /proc/ide
	----------------------------
	
	The subdirectory /proc/ide contains information about all IDE devices of which
	the kernel  is  aware.  There is one subdirectory for each IDE controller, the
	file drivers  and a link for each IDE device, pointing to the device directory
	in the controller specific subtree.
	
	The file  drivers  contains general information about the drivers used for the
	IDE devices:
	
	  > cat /proc/ide/drivers
	  ide-cdrom version 4.53
	  ide-disk version 1.08
	
	More detailed  information  can  be  found  in  the  controller  specific
	subdirectories. These  are  named  ide0,  ide1  and  so  on.  Each  of  these
	directories contains the files shown in table 1-6.
	
	
	Table 1-6: IDE controller info in  /proc/ide/ide?
	..............................................................................
	 File    Content                                 
	 channel IDE channel (0 or 1)                    
	 config  Configuration (only for PCI/IDE bridge) 
	 mate    Mate name                               
	 model   Type/Chipset of IDE controller          
	..............................................................................
	
	Each device  connected  to  a  controller  has  a separate subdirectory in the
	controllers directory.  The  files  listed in table 1-7 are contained in these
	directories.
	
	
	Table 1-7: IDE device information
	..............................................................................
	 File             Content                                    
	 cache            The cache                                  
	 capacity         Capacity of the medium (in 512Byte blocks) 
	 driver           driver and version                         
	 geometry         physical and logical geometry              
	 identify         device identify block                      
	 media            media type                                 
	 model            device identifier                          
	 settings         device setup                               
	 smart_thresholds IDE disk management thresholds             
	 smart_values     IDE disk management values                 
	..............................................................................
	
	The most  interesting  file is settings. This file contains a nice overview of
	the drive parameters:
	
	  # cat /proc/ide/ide0/hda/settings 
	  name                    value           min             max             mode 
	  ----                    -----           ---             ---             ---- 
	  bios_cyl                526             0               65535           rw 
	  bios_head               255             0               255             rw 
	  bios_sect               63              0               63              rw 
	  breada_readahead        4               0               127             rw 
	  bswap                   0               0               1               r 
	  file_readahead          72              0               2097151         rw 
	  io_32bit                0               0               3               rw 
	  keepsettings            0               0               1               rw 
	  max_kb_per_request      122             1               127             rw 
	  multcount               0               0               8               rw 
	  nice1                   1               0               1               rw 
	  nowerr                  0               0               1               rw 
	  pio_mode                write-only      0               255             w 
	  slow                    0               0               1               rw 
	  unmaskirq               0               0               1               rw 
	  using_dma               0               0               1               rw 
	
	
	1.4 Networking info in /proc/net
	--------------------------------
	
	The subdirectory  /proc/net  follows  the  usual  pattern. Table 1-8 shows the
	additional values  you  get  for  IP  version 6 if you configure the kernel to
	support this. Table 1-9 lists the files and their meaning.
	
	
	Table 1-8: IPv6 info in /proc/net
	..............................................................................
	 File       Content                                               
	 udp6       UDP sockets (IPv6)                                    
	 tcp6       TCP sockets (IPv6)                                    
	 raw6       Raw device statistics (IPv6)                          
	 igmp6      IP multicast addresses, which this host joined (IPv6) 
	 if_inet6   List of IPv6 interface addresses                      
	 ipv6_route Kernel routing table for IPv6                         
	 rt6_stats  Global IPv6 routing tables statistics                 
	 sockstat6  Socket statistics (IPv6)                              
	 snmp6      Snmp data (IPv6)                                      
	..............................................................................
	
	
	Table 1-9: Network info in /proc/net
	..............................................................................
	 File          Content                                                         
	 arp           Kernel  ARP table                                               
	 dev           network devices with statistics                                 
	 dev_mcast     the Layer2 multicast groups a device is listening too
	               (interface index, label, number of references, number of bound
	               addresses). 
	 dev_stat      network device status                                           
	 ip_fwchains   Firewall chain linkage                                          
	 ip_fwnames    Firewall chain names                                            
	 ip_masq       Directory containing the masquerading tables                    
	 ip_masquerade Major masquerading table                                        
	 netstat       Network statistics                                              
	 raw           raw device statistics                                           
	 route         Kernel routing table                                            
	 rpc           Directory containing rpc info                                   
	 rt_cache      Routing cache                                                   
	 snmp          SNMP data                                                       
	 sockstat      Socket statistics                                               
	 tcp           TCP  sockets                                                    
	 tr_rif        Token ring RIF routing table                                    
	 udp           UDP sockets                                                     
	 unix          UNIX domain sockets                                             
	 wireless      Wireless interface data (Wavelan etc)                           
	 igmp          IP multicast addresses, which this host joined                  
	 psched        Global packet scheduler parameters.                             
	 netlink       List of PF_NETLINK sockets                                      
	 ip_mr_vifs    List of multicast virtual interfaces                            
	 ip_mr_cache   List of multicast routing cache                                 
	..............................................................................
	
	You can  use  this  information  to see which network devices are available in
	your system and how much traffic was routed over those devices:
	
	  > cat /proc/net/dev 
	  Inter-|Receive                                                   |[... 
	   face |bytes    packets errs drop fifo frame compressed multicast|[... 
	      lo:  908188   5596     0    0    0     0          0         0 [...         
	    ppp0:15475140  20721   410    0    0   410          0         0 [...  
	    eth0:  614530   7085     0    0    0     0          0         1 [... 
	   
	  ...] Transmit 
	  ...] bytes    packets errs drop fifo colls carrier compressed 
	  ...]  908188     5596    0    0    0     0       0          0 
	  ...] 1375103    17405    0    0    0     0       0          0 
	  ...] 1703981     5535    0    0    0     3       0          0 
	
	In addition, each Channel Bond interface has it's own directory.  For
	example, the bond0 device will have a directory called /proc/net/bond0/.
	It will contain information that is specific to that bond, such as the
	current slaves of the bond, the link status of the slaves, and how
	many times the slaves link has failed.
	
	1.5 SCSI info
	-------------
	
	If you  have  a  SCSI  host adapter in your system, you'll find a subdirectory
	named after  the driver for this adapter in /proc/scsi. You'll also see a list
	of all recognized SCSI devices in /proc/scsi:
	
	  >cat /proc/scsi/scsi 
	  Attached devices: 
	  Host: scsi0 Channel: 00 Id: 00 Lun: 00 
	    Vendor: IBM      Model: DGHS09U          Rev: 03E0 
	    Type:   Direct-Access                    ANSI SCSI revision: 03 
	  Host: scsi0 Channel: 00 Id: 06 Lun: 00 
	    Vendor: PIONEER  Model: CD-ROM DR-U06S   Rev: 1.04 
	    Type:   CD-ROM                           ANSI SCSI revision: 02 
	
	
	The directory  named  after  the driver has one file for each adapter found in
	the system.  These  files  contain information about the controller, including
	the used  IRQ  and  the  IO  address range. The amount of information shown is
	dependent on  the adapter you use. The example shows the output for an Adaptec
	AHA-2940 SCSI adapter:
	
	  > cat /proc/scsi/aic7xxx/0 
	   
	  Adaptec AIC7xxx driver version: 5.1.19/3.2.4 
	  Compile Options: 
	    TCQ Enabled By Default : Disabled 
	    AIC7XXX_PROC_STATS     : Disabled 
	    AIC7XXX_RESET_DELAY    : 5 
	  Adapter Configuration: 
	             SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter 
	                             Ultra Wide Controller 
	      PCI MMAPed I/O Base: 0xeb001000 
	   Adapter SEEPROM Config: SEEPROM found and used. 
	        Adaptec SCSI BIOS: Enabled 
	                      IRQ: 10 
	                     SCBs: Active 0, Max Active 2, 
	                           Allocated 15, HW 16, Page 255 
	               Interrupts: 160328 
	        BIOS Control Word: 0x18b6 
	     Adapter Control Word: 0x005b 
	     Extended Translation: Enabled 
	  Disconnect Enable Flags: 0xffff 
	       Ultra Enable Flags: 0x0001 
	   Tag Queue Enable Flags: 0x0000 
	  Ordered Queue Tag Flags: 0x0000 
	  Default Tag Queue Depth: 8 
	      Tagged Queue By Device array for aic7xxx host instance 0: 
	        {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} 
	      Actual queue depth per device for aic7xxx host instance 0: 
	        {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} 
	  Statistics: 
	  (scsi0:0:0:0) 
	    Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 
	    Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) 
	    Total transfers 160151 (74577 reads and 85574 writes) 
	  (scsi0:0:6:0) 
	    Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 
	    Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) 
	    Total transfers 0 (0 reads and 0 writes) 
	
	
	1.6 Parallel port info in /proc/parport
	---------------------------------------
	
	The directory  /proc/parport  contains information about the parallel ports of
	your system.  It  has  one  subdirectory  for  each port, named after the port
	number (0,1,2,...).
	
	These directories contain the four files shown in Table 1-10.
	
	
	Table 1-10: Files in /proc/parport
	..............................................................................
	 File      Content                                                             
	 autoprobe Any IEEE-1284 device ID information that has been acquired.         
	 devices   list of the device drivers using that port. A + will appear by the
	           name of the device currently using the port (it might not appear
	           against any). 
	 hardware  Parallel port's base address, IRQ line and DMA channel.             
	 irq       IRQ that parport is using for that port. This is in a separate
	           file to allow you to alter it by writing a new value in (IRQ
	           number or none). 
	..............................................................................
	
	1.7 TTY info in /proc/tty
	-------------------------
	
	Information about  the  available  and actually used tty's can be found in the
	directory /proc/tty.You'll  find  entries  for drivers and line disciplines in
	this directory, as shown in Table 1-11.
	
	
	Table 1-11: Files in /proc/tty
	..............................................................................
	 File          Content                                        
	 drivers       list of drivers and their usage                
	 ldiscs        registered line disciplines                    
	 driver/serial usage statistic and status of single tty lines 
	..............................................................................
	
	To see  which  tty's  are  currently in use, you can simply look into the file
	/proc/tty/drivers:
	
	  > cat /proc/tty/drivers 
	  pty_slave            /dev/pts      136   0-255 pty:slave 
	  pty_master           /dev/ptm      128   0-255 pty:master 
	  pty_slave            /dev/ttyp       3   0-255 pty:slave 
	  pty_master           /dev/pty        2   0-255 pty:master 
	  serial               /dev/cua        5   64-67 serial:callout 
	  serial               /dev/ttyS       4   64-67 serial 
	  /dev/tty0            /dev/tty0       4       0 system:vtmaster 
	  /dev/ptmx            /dev/ptmx       5       2 system 
	  /dev/console         /dev/console    5       1 system:console 
	  /dev/tty             /dev/tty        5       0 system:/dev/tty 
	  unknown              /dev/tty        4    1-63 console 
	
	
	1.8 Miscellaneous kernel statistics in /proc/stat
	-------------------------------------------------
	
	Various pieces   of  information about  kernel activity  are  available in the
	/proc/stat file.  All  of  the numbers reported  in  this file are  aggregates
	since the system first booted.  For a quick look, simply cat the file:
	
	  > cat /proc/stat
	  cpu  2255 34 2290 22625563 6290 127 456 0 0
	  cpu0 1132 34 1441 11311718 3675 127 438 0 0
	  cpu1 1123 0 849 11313845 2614 0 18 0 0
	  intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
	  ctxt 1990473
	  btime 1062191376
	  processes 2915
	  procs_running 1
	  procs_blocked 0
	  softirq 183433 0 21755 12 39 1137 231 21459 2263
	
	The very first  "cpu" line aggregates the  numbers in all  of the other "cpuN"
	lines.  These numbers identify the amount of time the CPU has spent performing
	different kinds of work.  Time units are in USER_HZ (typically hundredths of a
	second).  The meanings of the columns are as follows, from left to right:
	
	- user: normal processes executing in user mode
	- nice: niced processes executing in user mode
	- system: processes executing in kernel mode
	- idle: twiddling thumbs
	- iowait: waiting for I/O to complete
	- irq: servicing interrupts
	- softirq: servicing softirqs
	- steal: involuntary wait
	- guest: running a normal guest
	- guest_nice: running a niced guest
	
	The "intr" line gives counts of interrupts  serviced since boot time, for each
	of the  possible system interrupts.   The first  column  is the  total of  all
	interrupts serviced; each  subsequent column is the  total for that particular
	interrupt.
	
	The "ctxt" line gives the total number of context switches across all CPUs.
	
	The "btime" line gives  the time at which the  system booted, in seconds since
	the Unix epoch.
	
	The "processes" line gives the number  of processes and threads created, which
	includes (but  is not limited  to) those  created by  calls to the  fork() and
	clone() system calls.
	
	The "procs_running" line gives the total number of threads that are
	running or ready to run (i.e., the total number of runnable threads).
	
	The   "procs_blocked" line gives  the  number of  processes currently blocked,
	waiting for I/O to complete.
	
	The "softirq" line gives counts of softirqs serviced since boot time, for each
	of the possible system softirqs. The first column is the total of all
	softirqs serviced; each subsequent column is the total for that particular
	softirq.
	
	
	1.9 Ext4 file system parameters
	------------------------------
	
	Information about mounted ext4 file systems can be found in
	/proc/fs/ext4.  Each mounted filesystem will have a directory in
	/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
	/proc/fs/ext4/dm-0).   The files in each per-device directory are shown
	in Table 1-12, below.
	
	Table 1-12: Files in /proc/fs/ext4/<devname>
	..............................................................................
	 File            Content                                        
	 mb_groups       details of multiblock allocator buddy cache of free blocks
	..............................................................................
	
	
	------------------------------------------------------------------------------
	Summary
	------------------------------------------------------------------------------
	The /proc file system serves information about the running system. It not only
	allows access to process data but also allows you to request the kernel status
	by reading files in the hierarchy.
	
	The directory  structure  of /proc reflects the types of information and makes
	it easy, if not obvious, where to look for specific data.
	------------------------------------------------------------------------------
	
	------------------------------------------------------------------------------
	CHAPTER 2: MODIFYING SYSTEM PARAMETERS
	------------------------------------------------------------------------------
	
	------------------------------------------------------------------------------
	In This Chapter
	------------------------------------------------------------------------------
	* Modifying kernel parameters by writing into files found in /proc/sys
	* Exploring the files which modify certain parameters
	* Review of the /proc/sys file tree
	------------------------------------------------------------------------------
	
	
	A very  interesting part of /proc is the directory /proc/sys. This is not only
	a source  of  information,  it also allows you to change parameters within the
	kernel. Be  very  careful  when attempting this. You can optimize your system,
	but you  can  also  cause  it  to  crash.  Never  alter kernel parameters on a
	production system.  Set  up  a  development machine and test to make sure that
	everything works  the  way  you want it to. You may have no alternative but to
	reboot the machine once an error has been made.
	
	To change  a  value,  simply  echo  the new value into the file. An example is
	given below  in the section on the file system data. You need to be root to do
	this. You  can  create  your  own  boot script to perform this every time your
	system boots.
	
	The files  in /proc/sys can be used to fine tune and monitor miscellaneous and
	general things  in  the operation of the Linux kernel. Since some of the files
	can inadvertently  disrupt  your  system,  it  is  advisable  to  read  both
	documentation and  source  before actually making adjustments. In any case, be
	very careful  when  writing  to  any  of these files. The entries in /proc may
	change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
	review the kernel documentation in the directory /usr/src/linux/Documentation.
	This chapter  is  heavily  based  on the documentation included in the pre 2.2
	kernels, and became part of it in version 2.2.1 of the Linux kernel.
	
	Please see: Documentation/sysctls/ directory for descriptions of these
	entries.
	
	------------------------------------------------------------------------------
	Summary
	------------------------------------------------------------------------------
	Certain aspects  of  kernel  behavior  can be modified at runtime, without the
	need to  recompile  the kernel, or even to reboot the system. The files in the
	/proc/sys tree  can  not only be read, but also modified. You can use the echo
	command to write value into these files, thereby changing the default settings
	of the kernel.
	------------------------------------------------------------------------------
	
	------------------------------------------------------------------------------
	CHAPTER 3: PER-PROCESS PARAMETERS
	------------------------------------------------------------------------------
	
	3.1 /proc/<pid>/oom_adj - Adjust the oom-killer score
	------------------------------------------------------
	
	This file can be used to adjust the score used to select which processes
	should be killed in an  out-of-memory  situation.  Giving it a high score will
	increase the likelihood of this process being killed by the oom-killer.  Valid
	values are in the range -16 to +15, plus the special value -17, which disables
	oom-killing altogether for this process.
	
	The process to be killed in an out-of-memory situation is selected among all others
	based on its badness score. This value equals the original memory size of the process
	and is then updated according to its CPU time (utime + stime) and the
	run time (uptime - start time). The longer it runs the smaller is the score.
	Badness score is divided by the square root of the CPU time and then by
	the double square root of the run time.
	
	Swapped out tasks are killed first. Half of each child's memory size is added to
	the parent's score if they do not share the same memory. Thus forking servers
	are the prime candidates to be killed. Having only one 'hungry' child will make
	parent less preferable than the child.
	
	/proc/<pid>/oom_score shows process' current badness score.
	
	The following heuristics are then applied:
	 * if the task was reniced, its score doubles
	 * superuser or direct hardware access tasks (CAP_SYS_ADMIN, CAP_SYS_RESOURCE
	 	or CAP_SYS_RAWIO) have their score divided by 4
	 * if oom condition happened in one cpuset and checked process does not belong
	 	to it, its score is divided by 8
	 * the resulting score is multiplied by two to the power of oom_adj, i.e.
		points <<= oom_adj when it is positive and
		points >>= -(oom_adj) otherwise
	
	The task with the highest badness score is then selected and its children
	are killed, process itself will be killed in an OOM situation when it does
	not have children or some of them disabled oom like described above.
	
	3.2 /proc/<pid>/oom_score - Display current oom-killer score
	-------------------------------------------------------------
	
	This file can be used to check the current score used by the oom-killer is for
	any given <pid>. Use it together with /proc/<pid>/oom_adj to tune which
	process should be killed in an out-of-memory situation.
	
	
	3.3  /proc/<pid>/io - Display the IO accounting fields
	-------------------------------------------------------
	
	This file contains IO statistics for each running process
	
	Example
	-------
	
	test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
	[1] 3828
	
	test:/tmp # cat /proc/3828/io
	rchar: 323934931
	wchar: 323929600
	syscr: 632687
	syscw: 632675
	read_bytes: 0
	write_bytes: 323932160
	cancelled_write_bytes: 0
	
	
	Description
	-----------
	
	rchar
	-----
	
	I/O counter: chars read
	The number of bytes which this task has caused to be read from storage. This
	is simply the sum of bytes which this process passed to read() and pread().
	It includes things like tty IO and it is unaffected by whether or not actual
	physical disk IO was required (the read might have been satisfied from
	pagecache)
	
	
	wchar
	-----
	
	I/O counter: chars written
	The number of bytes which this task has caused, or shall cause to be written
	to disk. Similar caveats apply here as with rchar.
	
	
	syscr
	-----
	
	I/O counter: read syscalls
	Attempt to count the number of read I/O operations, i.e. syscalls like read()
	and pread().
	
	
	syscw
	-----
	
	I/O counter: write syscalls
	Attempt to count the number of write I/O operations, i.e. syscalls like
	write() and pwrite().
	
	
	read_bytes
	----------
	
	I/O counter: bytes read
	Attempt to count the number of bytes which this process really did cause to
	be fetched from the storage layer. Done at the submit_bio() level, so it is
	accurate for block-backed filesystems. <please add status regarding NFS and
	CIFS at a later time>
	
	
	write_bytes
	-----------
	
	I/O counter: bytes written
	Attempt to count the number of bytes which this process caused to be sent to
	the storage layer. This is done at page-dirtying time.
	
	
	cancelled_write_bytes
	---------------------
	
	The big inaccuracy here is truncate. If a process writes 1MB to a file and
	then deletes the file, it will in fact perform no writeout. But it will have
	been accounted as having caused 1MB of write.
	In other words: The number of bytes which this process caused to not happen,
	by truncating pagecache. A task can cause "negative" IO too. If this task
	truncates some dirty pagecache, some IO which another task has been accounted
	for (in it's write_bytes) will not be happening. We _could_ just subtract that
	from the truncating task's write_bytes, but there is information loss in doing
	that.
	
	
	Note
	----
	
	At its current implementation state, this is a bit racy on 32-bit machines: if
	process A reads process B's /proc/pid/io while process B is updating one of
	those 64-bit counters, process A could see an intermediate result.
	
	
	More information about this can be found within the taskstats documentation in
	Documentation/accounting.
	
	3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
	---------------------------------------------------------------
	When a process is dumped, all anonymous memory is written to a core file as
	long as the size of the core file isn't limited. But sometimes we don't want
	to dump some memory segments, for example, huge shared memory. Conversely,
	sometimes we want to save file-backed memory segments into a core file, not
	only the individual files.
	
	/proc/<pid>/coredump_filter allows you to customize which memory segments
	will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
	of memory types. If a bit of the bitmask is set, memory segments of the
	corresponding memory type are dumped, otherwise they are not dumped.
	
	The following 7 memory types are supported:
	  - (bit 0) anonymous private memory
	  - (bit 1) anonymous shared memory
	  - (bit 2) file-backed private memory
	  - (bit 3) file-backed shared memory
	  - (bit 4) ELF header pages in file-backed private memory areas (it is
	            effective only if the bit 2 is cleared)
	  - (bit 5) hugetlb private memory
	  - (bit 6) hugetlb shared memory
	
	  Note that MMIO pages such as frame buffer are never dumped and vDSO pages
	  are always dumped regardless of the bitmask status.
	
	  Note bit 0-4 doesn't effect any hugetlb memory. hugetlb memory are only
	  effected by bit 5-6.
	
	Default value of coredump_filter is 0x23; this means all anonymous memory
	segments and hugetlb private memory are dumped.
	
	If you don't want to dump all shared memory segments attached to pid 1234,
	write 0x21 to the process's proc file.
	
	  $ echo 0x21 > /proc/1234/coredump_filter
	
	When a new process is created, the process inherits the bitmask status from its
	parent. It is useful to set up coredump_filter before the program runs.
	For example:
	
	  $ echo 0x7 > /proc/self/coredump_filter
	  $ ./some_program
	
	3.5	/proc/<pid>/mountinfo - Information about mounts
	--------------------------------------------------------
	
	This file contains lines of the form:
	
	36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
	(1)(2)(3)   (4)   (5)      (6)      (7)   (8) (9)   (10)         (11)
	
	(1) mount ID:  unique identifier of the mount (may be reused after umount)
	(2) parent ID:  ID of parent (or of self for the top of the mount tree)
	(3) major:minor:  value of st_dev for files on filesystem
	(4) root:  root of the mount within the filesystem
	(5) mount point:  mount point relative to the process's root
	(6) mount options:  per mount options
	(7) optional fields:  zero or more fields of the form "tag[:value]"
	(8) separator:  marks the end of the optional fields
	(9) filesystem type:  name of filesystem of the form "type[.subtype]"
	(10) mount source:  filesystem specific information or "none"
	(11) super options:  per super block options
	
	Parsers should ignore all unrecognised optional fields.  Currently the
	possible optional fields are:
	
	shared:X  mount is shared in peer group X
	master:X  mount is slave to peer group X
	propagate_from:X  mount is slave and receives propagation from peer group X (*)
	unbindable  mount is unbindable
	
	(*) X is the closest dominant peer group under the process's root.  If
	X is the immediate master of the mount, or if there's no dominant peer
	group under the same root, then only the "master:X" field is present
	and not the "propagate_from:X" field.
	
	For more information on mount propagation see:
	
	  Documentation/filesystems/sharedsubtree.txt
	
	
	3.6	/proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
	--------------------------------------------------------
	These files provide a method to access a tasks comm value. It also allows for
	a task to set its own or one of its thread siblings comm value. The comm value
	is limited in size compared to the cmdline value, so writing anything longer
	then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
	comm value.

• [ filesystems ]
• 00-INDEX
• 9p.txt
• adfs.txt
• affs.txt
• afs.txt
• autofs4-mount-control.txt
• automount-support.txt
• befs.txt
• bfs.txt
• btrfs.txt
• [ caching ]
• cifs.txt
• coda.txt
• [ configfs ]
• cramfs.txt
• debugfs.txt
• dentry-locking.txt
• devpts.txt
• directory-locking
• dlmfs.txt
• dnotify.txt
• ecryptfs.txt
• exofs.txt
• ext2.txt
• ext3.txt
• ext4.txt
• fiemap.txt
• files.txt
• fuse.txt
• gfs2-glocks.txt
• gfs2-uevents.txt
• gfs2.txt
• hfs.txt
• hfsplus.txt
• hpfs.txt
• inotify.txt
• isofs.txt
• jfs.txt
• Locking
• locks.txt
• mandatory-locking.txt
• ncpfs.txt
• [ nfs ]
• nilfs2.txt
• ntfs.txt
• ocfs2.txt
• omfs.txt
• [ pohmelfs ]
• porting
• proc.txt
• quota.txt
• ramfs-rootfs-initramfs.txt
• relay.txt
• romfs.txt
• seq_file.txt
• sharedsubtree.txt
• smbfs.txt
• spufs.txt
• squashfs.txt
• sysfs-pci.txt
• sysfs.txt
• sysv-fs.txt
• tmpfs.txt
• ubifs.txt
• udf.txt
• ufs.txt
• vfat.txt
• vfs.txt
• xfs.txt
• xip.txt
•