------------------------------------------------------------------------------
                         T H E  /proc   F I L E S Y S T E M
  ------------------------------------------------------------------------------
  /proc/sys         Terrehon Bowden <terrehon@pacbell.net>        October 7 1999
                    Bodo Bauer <bb@ricochet.net>
  
  2.4.x update	  Jorge Nerin <comandante@zaralinux.com>      November 14 2000

  move /proc/sys	  Shen Feng <shen@cn.fujitsu.com>		    April 1 2009

  ------------------------------------------------------------------------------
  Version 1.3                                              Kernel version 2.2.12
  					      Kernel version 2.4.0-test11-pre4
  ------------------------------------------------------------------------------
  
  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

  
  ------------------------------------------------------------------------------
  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@ricochet.net.  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@vger.kernel.org  and/or try  to  reach  me  at
  comandante@zaralinux.com.
  
  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		Extension based on maps, the rss size for each mapped file

  ..............................................................................
  
  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) 
    Pid:    5452 
    PPid:   743 
    TracerPid:      0						(2.4)
    Uid:    501     501     501     501 
    Gid:    100     100     100     100 
    Groups: 100 14 16 
    VmSize:     1112 kB 
    VmLck:         0 kB 
    VmRSS:       348 kB 
    VmData:       24 kB 
    VmStk:        12 kB 
    VmExe:         8 kB 
    VmLib:      1044 kB 
    SigPnd: 0000000000000000 
    SigBlk: 0000000000000000 
    SigIgn: 0000000000000000 
    SigCgt: 0000000000000000 
    CapInh: 00000000fffffeff 
    CapPrm: 0000000000000000 
    CapEff: 0000000000000000 
  
  
  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. The  statm  file  contains  more  detailed  information about the

  process memory usage. Its seven fields are explained in Table 1-2.  The stat
  file contains details information about the process itself.  Its fields are
  explained in Table 1-3.

  
  
  Table 1-2: 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 1-3: Contents of the stat files (as of 2.6.22-rc3)
  ..............................................................................
   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 (obsolete)
    blocked       bitmap of blocked signals (obsolete)
    sigign        bitmap of ignored signals (obsolete)
    sigcatch      bitmap of catched signals (obsolete)
    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
  ..............................................................................

  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 1-4. 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 1-4: 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                                    
   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 occurance of interrupt 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 contigious 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

  
  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 1-5.

  Table 1-5: 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 1-6 are contained in these

  directories.

  Table 1-6: 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 1-6 shows the
  additional values  you  get  for  IP  version 6 if you configure the kernel to
  support this. Table 1-7 lists the files and their meaning.
  
  
  Table 1-6: 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 1-7: 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 1-8.
  
  
  Table 1-8: 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 1-9.
  
  
  Table 1-9: 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
    cpu0 1132 34 1441 11311718 3675 127 438 0
    cpu1 1123 0 849 11313845 2614 0 18 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
  
  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

  
  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  number of processes  currently running on
  CPUs.
  
  The   "procs_blocked" line gives  the  number of  processes currently blocked,
  waiting for I/O to complete.

  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 1-10, below.
  
  Table 1-10: Files in /proc/fs/ext4/<devname>
  ..............................................................................
   File            Content                                        
   mb_groups       details of multiblock allocator buddy cache of free blocks
   mb_history      multiblock allocation history

  ..............................................................................

  
  ------------------------------------------------------------------------------
  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 task 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