linux/Documentation/filesystems/proc.txt
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   1------------------------------------------------------------------------------
   2                       T H E  /proc   F I L E S Y S T E M
   3------------------------------------------------------------------------------
   4/proc/sys         Terrehon Bowden <terrehon@pacbell.net>        October 7 1999
   5                  Bodo Bauer <bb@ricochet.net>
   6
   72.4.x update      Jorge Nerin <comandante@zaralinux.com>      November 14 2000
   8move /proc/sys    Shen Feng <shen@cn.fujitsu.com>                 April 1 2009
   9------------------------------------------------------------------------------
  10Version 1.3                                              Kernel version 2.2.12
  11                                              Kernel version 2.4.0-test11-pre4
  12------------------------------------------------------------------------------
  13fixes/update part 1.1  Stefani Seibold <stefani@seibold.net>       June 9 2009
  14
  15Table of Contents
  16-----------------
  17
  18  0     Preface
  19  0.1   Introduction/Credits
  20  0.2   Legal Stuff
  21
  22  1     Collecting System Information
  23  1.1   Process-Specific Subdirectories
  24  1.2   Kernel data
  25  1.3   IDE devices in /proc/ide
  26  1.4   Networking info in /proc/net
  27  1.5   SCSI info
  28  1.6   Parallel port info in /proc/parport
  29  1.7   TTY info in /proc/tty
  30  1.8   Miscellaneous kernel statistics in /proc/stat
  31  1.9 Ext4 file system parameters
  32
  33  2     Modifying System Parameters
  34
  35  3     Per-Process Parameters
  36  3.1   /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj - Adjust the oom-killer
  37                                                                score
  38  3.2   /proc/<pid>/oom_score - Display current oom-killer score
  39  3.3   /proc/<pid>/io - Display the IO accounting fields
  40  3.4   /proc/<pid>/coredump_filter - Core dump filtering settings
  41  3.5   /proc/<pid>/mountinfo - Information about mounts
  42  3.6   /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
  43  3.7   /proc/<pid>/task/<tid>/children - Information about task children
  44  3.8   /proc/<pid>/fdinfo/<fd> - Information about opened file
  45
  46  4     Configuring procfs
  47  4.1   Mount options
  48
  49------------------------------------------------------------------------------
  50Preface
  51------------------------------------------------------------------------------
  52
  530.1 Introduction/Credits
  54------------------------
  55
  56This documentation is  part of a soon (or  so we hope) to be  released book on
  57the SuSE  Linux distribution. As  there is  no complete documentation  for the
  58/proc file system and we've used  many freely available sources to write these
  59chapters, it  seems only fair  to give the work  back to the  Linux community.
  60This work is  based on the 2.2.*  kernel version and the  upcoming 2.4.*. I'm
  61afraid it's still far from complete, but we  hope it will be useful. As far as
  62we know, it is the first 'all-in-one' document about the /proc file system. It
  63is focused  on the Intel  x86 hardware,  so if you  are looking for  PPC, ARM,
  64SPARC, AXP, etc., features, you probably  won't find what you are looking for.
  65It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
  66additions and patches  are welcome and will  be added to this  document if you
  67mail them to Bodo.
  68
  69We'd like  to  thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
  70other people for help compiling this documentation. We'd also like to extend a
  71special thank  you to Andi Kleen for documentation, which we relied on heavily
  72to create  this  document,  as well as the additional information he provided.
  73Thanks to  everybody  else  who contributed source or docs to the Linux kernel
  74and helped create a great piece of software... :)
  75
  76If you  have  any comments, corrections or additions, please don't hesitate to
  77contact Bodo  Bauer  at  bb@ricochet.net.  We'll  be happy to add them to this
  78document.
  79
  80The   latest   version    of   this   document   is    available   online   at
  81http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html
  82
  83If  the above  direction does  not works  for you,  you could  try the  kernel
  84mailing  list  at  linux-kernel@vger.kernel.org  and/or try  to  reach  me  at
  85comandante@zaralinux.com.
  86
  870.2 Legal Stuff
  88---------------
  89
  90We don't  guarantee  the  correctness  of this document, and if you come to us
  91complaining about  how  you  screwed  up  your  system  because  of  incorrect
  92documentation, we won't feel responsible...
  93
  94------------------------------------------------------------------------------
  95CHAPTER 1: COLLECTING SYSTEM INFORMATION
  96------------------------------------------------------------------------------
  97
  98------------------------------------------------------------------------------
  99In This Chapter
 100------------------------------------------------------------------------------
 101* Investigating  the  properties  of  the  pseudo  file  system  /proc and its
 102  ability to provide information on the running Linux system
 103* Examining /proc's structure
 104* Uncovering  various  information  about the kernel and the processes running
 105  on the system
 106------------------------------------------------------------------------------
 107
 108
 109The proc  file  system acts as an interface to internal data structures in the
 110kernel. It  can  be  used to obtain information about the system and to change
 111certain kernel parameters at runtime (sysctl).
 112
 113First, we'll  take  a  look  at the read-only parts of /proc. In Chapter 2, we
 114show you how you can use /proc/sys to change settings.
 115
 1161.1 Process-Specific Subdirectories
 117-----------------------------------
 118
 119The directory  /proc  contains  (among other things) one subdirectory for each
 120process running on the system, which is named after the process ID (PID).
 121
 122The link  self  points  to  the  process reading the file system. Each process
 123subdirectory has the entries listed in Table 1-1.
 124
 125
 126Table 1-1: Process specific entries in /proc
 127..............................................................................
 128 File           Content
 129 clear_refs     Clears page referenced bits shown in smaps output
 130 cmdline        Command line arguments
 131 cpu            Current and last cpu in which it was executed   (2.4)(smp)
 132 cwd            Link to the current working directory
 133 environ        Values of environment variables
 134 exe            Link to the executable of this process
 135 fd             Directory, which contains all file descriptors
 136 maps           Memory maps to executables and library files    (2.4)
 137 mem            Memory held by this process
 138 root           Link to the root directory of this process
 139 stat           Process status
 140 statm          Process memory status information
 141 status         Process status in human readable form
 142 wchan          If CONFIG_KALLSYMS is set, a pre-decoded wchan
 143 pagemap        Page table
 144 stack          Report full stack trace, enable via CONFIG_STACKTRACE
 145 smaps          a extension based on maps, showing the memory consumption of
 146                each mapping and flags associated with it
 147..............................................................................
 148
 149For example, to get the status information of a process, all you have to do is
 150read the file /proc/PID/status:
 151
 152  >cat /proc/self/status
 153  Name:   cat
 154  State:  R (running)
 155  Tgid:   5452
 156  Pid:    5452
 157  PPid:   743
 158  TracerPid:      0                                             (2.4)
 159  Uid:    501     501     501     501
 160  Gid:    100     100     100     100
 161  FDSize: 256
 162  Groups: 100 14 16
 163  VmPeak:     5004 kB
 164  VmSize:     5004 kB
 165  VmLck:         0 kB
 166  VmHWM:       476 kB
 167  VmRSS:       476 kB
 168  VmData:      156 kB
 169  VmStk:        88 kB
 170  VmExe:        68 kB
 171  VmLib:      1412 kB
 172  VmPTE:        20 kb
 173  VmSwap:        0 kB
 174  Threads:        1
 175  SigQ:   0/28578
 176  SigPnd: 0000000000000000
 177  ShdPnd: 0000000000000000
 178  SigBlk: 0000000000000000
 179  SigIgn: 0000000000000000
 180  SigCgt: 0000000000000000
 181  CapInh: 00000000fffffeff
 182  CapPrm: 0000000000000000
 183  CapEff: 0000000000000000
 184  CapBnd: ffffffffffffffff
 185  Seccomp:        0
 186  voluntary_ctxt_switches:        0
 187  nonvoluntary_ctxt_switches:     1
 188
 189This shows you nearly the same information you would get if you viewed it with
 190the ps  command.  In  fact,  ps  uses  the  proc  file  system  to  obtain its
 191information.  But you get a more detailed  view of the  process by reading the
 192file /proc/PID/status. It fields are described in table 1-2.
 193
 194The  statm  file  contains  more  detailed  information about the process
 195memory usage. Its seven fields are explained in Table 1-3.  The stat file
 196contains details information about the process itself.  Its fields are
 197explained in Table 1-4.
 198
 199(for SMP CONFIG users)
 200For making accounting scalable, RSS related information are handled in
 201asynchronous manner and the vaule may not be very precise. To see a precise
 202snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
 203It's slow but very precise.
 204
 205Table 1-2: Contents of the status files (as of 2.6.30-rc7)
 206..............................................................................
 207 Field                       Content
 208 Name                        filename of the executable
 209 State                       state (R is running, S is sleeping, D is sleeping
 210                             in an uninterruptible wait, Z is zombie,
 211                             T is traced or stopped)
 212 Tgid                        thread group ID
 213 Pid                         process id
 214 PPid                        process id of the parent process
 215 TracerPid                   PID of process tracing this process (0 if not)
 216 Uid                         Real, effective, saved set, and  file system UIDs
 217 Gid                         Real, effective, saved set, and  file system GIDs
 218 FDSize                      number of file descriptor slots currently allocated
 219 Groups                      supplementary group list
 220 VmPeak                      peak virtual memory size
 221 VmSize                      total program size
 222 VmLck                       locked memory size
 223 VmHWM                       peak resident set size ("high water mark")
 224 VmRSS                       size of memory portions
 225 VmData                      size of data, stack, and text segments
 226 VmStk                       size of data, stack, and text segments
 227 VmExe                       size of text segment
 228 VmLib                       size of shared library code
 229 VmPTE                       size of page table entries
 230 VmSwap                      size of swap usage (the number of referred swapents)
 231 Threads                     number of threads
 232 SigQ                        number of signals queued/max. number for queue
 233 SigPnd                      bitmap of pending signals for the thread
 234 ShdPnd                      bitmap of shared pending signals for the process
 235 SigBlk                      bitmap of blocked signals
 236 SigIgn                      bitmap of ignored signals
 237 SigCgt                      bitmap of catched signals
 238 CapInh                      bitmap of inheritable capabilities
 239 CapPrm                      bitmap of permitted capabilities
 240 CapEff                      bitmap of effective capabilities
 241 CapBnd                      bitmap of capabilities bounding set
 242 Seccomp                     seccomp mode, like prctl(PR_GET_SECCOMP, ...)
 243 Cpus_allowed                mask of CPUs on which this process may run
 244 Cpus_allowed_list           Same as previous, but in "list format"
 245 Mems_allowed                mask of memory nodes allowed to this process
 246 Mems_allowed_list           Same as previous, but in "list format"
 247 voluntary_ctxt_switches     number of voluntary context switches
 248 nonvoluntary_ctxt_switches  number of non voluntary context switches
 249..............................................................................
 250
 251Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
 252..............................................................................
 253 Field    Content
 254 size     total program size (pages)            (same as VmSize in status)
 255 resident size of memory portions (pages)       (same as VmRSS in status)
 256 shared   number of pages that are shared       (i.e. backed by a file)
 257 trs      number of pages that are 'code'       (not including libs; broken,
 258                                                        includes data segment)
 259 lrs      number of pages of library            (always 0 on 2.6)
 260 drs      number of pages of data/stack         (including libs; broken,
 261                                                        includes library text)
 262 dt       number of dirty pages                 (always 0 on 2.6)
 263..............................................................................
 264
 265
 266Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
 267..............................................................................
 268 Field          Content
 269  pid           process id
 270  tcomm         filename of the executable
 271  state         state (R is running, S is sleeping, D is sleeping in an
 272                uninterruptible wait, Z is zombie, T is traced or stopped)
 273  ppid          process id of the parent process
 274  pgrp          pgrp of the process
 275  sid           session id
 276  tty_nr        tty the process uses
 277  tty_pgrp      pgrp of the tty
 278  flags         task flags
 279  min_flt       number of minor faults
 280  cmin_flt      number of minor faults with child's
 281  maj_flt       number of major faults
 282  cmaj_flt      number of major faults with child's
 283  utime         user mode jiffies
 284  stime         kernel mode jiffies
 285  cutime        user mode jiffies with child's
 286  cstime        kernel mode jiffies with child's
 287  priority      priority level
 288  nice          nice level
 289  num_threads   number of threads
 290  it_real_value (obsolete, always 0)
 291  start_time    time the process started after system boot
 292  vsize         virtual memory size
 293  rss           resident set memory size
 294  rsslim        current limit in bytes on the rss
 295  start_code    address above which program text can run
 296  end_code      address below which program text can run
 297  start_stack   address of the start of the main process stack
 298  esp           current value of ESP
 299  eip           current value of EIP
 300  pending       bitmap of pending signals
 301  blocked       bitmap of blocked signals
 302  sigign        bitmap of ignored signals
 303  sigcatch      bitmap of catched signals
 304  wchan         address where process went to sleep
 305  0             (place holder)
 306  0             (place holder)
 307  exit_signal   signal to send to parent thread on exit
 308  task_cpu      which CPU the task is scheduled on
 309  rt_priority   realtime priority
 310  policy        scheduling policy (man sched_setscheduler)
 311  blkio_ticks   time spent waiting for block IO
 312  gtime         guest time of the task in jiffies
 313  cgtime        guest time of the task children in jiffies
 314  start_data    address above which program data+bss is placed
 315  end_data      address below which program data+bss is placed
 316  start_brk     address above which program heap can be expanded with brk()
 317  arg_start     address above which program command line is placed
 318  arg_end       address below which program command line is placed
 319  env_start     address above which program environment is placed
 320  env_end       address below which program environment is placed
 321  exit_code     the thread's exit_code in the form reported by the waitpid system call
 322..............................................................................
 323
 324The /proc/PID/maps file containing the currently mapped memory regions and
 325their access permissions.
 326
 327The format is:
 328
 329address           perms offset  dev   inode      pathname
 330
 33108048000-08049000 r-xp 00000000 03:00 8312       /opt/test
 33208049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
 3330804a000-0806b000 rw-p 00000000 00:00 0          [heap]
 334a7cb1000-a7cb2000 ---p 00000000 00:00 0
 335a7cb2000-a7eb2000 rw-p 00000000 00:00 0
 336a7eb2000-a7eb3000 ---p 00000000 00:00 0
 337a7eb3000-a7ed5000 rw-p 00000000 00:00 0          [stack:1001]
 338a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/libc.so.6
 339a8008000-a800a000 r--p 00133000 03:00 4222       /lib/libc.so.6
 340a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/libc.so.6
 341a800b000-a800e000 rw-p 00000000 00:00 0
 342a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/libpthread.so.0
 343a8022000-a8023000 r--p 00013000 03:00 14462      /lib/libpthread.so.0
 344a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/libpthread.so.0
 345a8024000-a8027000 rw-p 00000000 00:00 0
 346a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/ld-linux.so.2
 347a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/ld-linux.so.2
 348a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/ld-linux.so.2
 349aff35000-aff4a000 rw-p 00000000 00:00 0          [stack]
 350ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
 351
 352where "address" is the address space in the process that it occupies, "perms"
 353is a set of permissions:
 354
 355 r = read
 356 w = write
 357 x = execute
 358 s = shared
 359 p = private (copy on write)
 360
 361"offset" is the offset into the mapping, "dev" is the device (major:minor), and
 362"inode" is the inode  on that device.  0 indicates that  no inode is associated
 363with the memory region, as the case would be with BSS (uninitialized data).
 364The "pathname" shows the name associated file for this mapping.  If the mapping
 365is not associated with a file:
 366
 367 [heap]                   = the heap of the program
 368 [stack]                  = the stack of the main process
 369 [stack:1001]             = the stack of the thread with tid 1001
 370 [vdso]                   = the "virtual dynamic shared object",
 371                            the kernel system call handler
 372
 373 or if empty, the mapping is anonymous.
 374
 375The /proc/PID/task/TID/maps is a view of the virtual memory from the viewpoint
 376of the individual tasks of a process. In this file you will see a mapping marked
 377as [stack] if that task sees it as a stack. This is a key difference from the
 378content of /proc/PID/maps, where you will see all mappings that are being used
 379as stack by all of those tasks. Hence, for the example above, the task-level
 380map, i.e. /proc/PID/task/TID/maps for thread 1001 will look like this:
 381
 38208048000-08049000 r-xp 00000000 03:00 8312       /opt/test
 38308049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
 3840804a000-0806b000 rw-p 00000000 00:00 0          [heap]
 385a7cb1000-a7cb2000 ---p 00000000 00:00 0
 386a7cb2000-a7eb2000 rw-p 00000000 00:00 0
 387a7eb2000-a7eb3000 ---p 00000000 00:00 0
 388a7eb3000-a7ed5000 rw-p 00000000 00:00 0          [stack]
 389a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/libc.so.6
 390a8008000-a800a000 r--p 00133000 03:00 4222       /lib/libc.so.6
 391a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/libc.so.6
 392a800b000-a800e000 rw-p 00000000 00:00 0
 393a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/libpthread.so.0
 394a8022000-a8023000 r--p 00013000 03:00 14462      /lib/libpthread.so.0
 395a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/libpthread.so.0
 396a8024000-a8027000 rw-p 00000000 00:00 0
 397a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/ld-linux.so.2
 398a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/ld-linux.so.2
 399a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/ld-linux.so.2
 400aff35000-aff4a000 rw-p 00000000 00:00 0
 401ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
 402
 403The /proc/PID/smaps is an extension based on maps, showing the memory
 404consumption for each of the process's mappings. For each of mappings there
 405is a series of lines such as the following:
 406
 40708048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
 408Size:               1084 kB
 409Rss:                 892 kB
 410Pss:                 374 kB
 411Shared_Clean:        892 kB
 412Shared_Dirty:          0 kB
 413Private_Clean:         0 kB
 414Private_Dirty:         0 kB
 415Referenced:          892 kB
 416Anonymous:             0 kB
 417Swap:                  0 kB
 418KernelPageSize:        4 kB
 419MMUPageSize:           4 kB
 420Locked:              374 kB
 421VmFlags: rd ex mr mw me de
 422
 423the first of these lines shows the same information as is displayed for the
 424mapping in /proc/PID/maps.  The remaining lines show the size of the mapping
 425(size), the amount of the mapping that is currently resident in RAM (RSS), the
 426process' proportional share of this mapping (PSS), the number of clean and
 427dirty private pages in the mapping.  Note that even a page which is part of a
 428MAP_SHARED mapping, but has only a single pte mapped, i.e.  is currently used
 429by only one process, is accounted as private and not as shared.  "Referenced"
 430indicates the amount of memory currently marked as referenced or accessed.
 431"Anonymous" shows the amount of memory that does not belong to any file.  Even
 432a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
 433and a page is modified, the file page is replaced by a private anonymous copy.
 434"Swap" shows how much would-be-anonymous memory is also used, but out on
 435swap.
 436
 437"VmFlags" field deserves a separate description. This member represents the kernel
 438flags associated with the particular virtual memory area in two letter encoded
 439manner. The codes are the following:
 440    rd  - readable
 441    wr  - writeable
 442    ex  - executable
 443    sh  - shared
 444    mr  - may read
 445    mw  - may write
 446    me  - may execute
 447    ms  - may share
 448    gd  - stack segment growns down
 449    pf  - pure PFN range
 450    dw  - disabled write to the mapped file
 451    lo  - pages are locked in memory
 452    io  - memory mapped I/O area
 453    sr  - sequential read advise provided
 454    rr  - random read advise provided
 455    dc  - do not copy area on fork
 456    de  - do not expand area on remapping
 457    ac  - area is accountable
 458    nr  - swap space is not reserved for the area
 459    ht  - area uses huge tlb pages
 460    nl  - non-linear mapping
 461    ar  - architecture specific flag
 462    dd  - do not include area into core dump
 463    mm  - mixed map area
 464    hg  - huge page advise flag
 465    nh  - no-huge page advise flag
 466    mg  - mergable advise flag
 467
 468Note that there is no guarantee that every flag and associated mnemonic will
 469be present in all further kernel releases. Things get changed, the flags may
 470be vanished or the reverse -- new added.
 471
 472This file is only present if the CONFIG_MMU kernel configuration option is
 473enabled.
 474
 475The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
 476bits on both physical and virtual pages associated with a process.
 477To clear the bits for all the pages associated with the process
 478    > echo 1 > /proc/PID/clear_refs
 479
 480To clear the bits for the anonymous pages associated with the process
 481    > echo 2 > /proc/PID/clear_refs
 482
 483To clear the bits for the file mapped pages associated with the process
 484    > echo 3 > /proc/PID/clear_refs
 485Any other value written to /proc/PID/clear_refs will have no effect.
 486
 487The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
 488using /proc/kpageflags and number of times a page is mapped using
 489/proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt.
 490
 4911.2 Kernel data
 492---------------
 493
 494Similar to  the  process entries, the kernel data files give information about
 495the running kernel. The files used to obtain this information are contained in
 496/proc and  are  listed  in Table 1-5. Not all of these will be present in your
 497system. It  depends  on the kernel configuration and the loaded modules, which
 498files are there, and which are missing.
 499
 500Table 1-5: Kernel info in /proc
 501..............................................................................
 502 File        Content                                           
 503 apm         Advanced power management info                    
 504 buddyinfo   Kernel memory allocator information (see text)     (2.5)
 505 bus         Directory containing bus specific information     
 506 cmdline     Kernel command line                               
 507 cpuinfo     Info about the CPU                                
 508 devices     Available devices (block and character)           
 509 dma         Used DMS channels                                 
 510 filesystems Supported filesystems                             
 511 driver      Various drivers grouped here, currently rtc (2.4)
 512 execdomains Execdomains, related to security                   (2.4)
 513 fb          Frame Buffer devices                               (2.4)
 514 fs          File system parameters, currently nfs/exports      (2.4)
 515 ide         Directory containing info about the IDE subsystem 
 516 interrupts  Interrupt usage                                   
 517 iomem       Memory map                                         (2.4)
 518 ioports     I/O port usage                                    
 519 irq         Masks for irq to cpu affinity                      (2.4)(smp?)
 520 isapnp      ISA PnP (Plug&Play) Info                           (2.4)
 521 kcore       Kernel core image (can be ELF or A.OUT(deprecated in 2.4))   
 522 kmsg        Kernel messages                                   
 523 ksyms       Kernel symbol table                               
 524 loadavg     Load average of last 1, 5 & 15 minutes                
 525 locks       Kernel locks                                      
 526 meminfo     Memory info                                       
 527 misc        Miscellaneous                                     
 528 modules     List of loaded modules                            
 529 mounts      Mounted filesystems                               
 530 net         Networking info (see text)                        
 531 pagetypeinfo Additional page allocator information (see text)  (2.5)
 532 partitions  Table of partitions known to the system           
 533 pci         Deprecated info of PCI bus (new way -> /proc/bus/pci/,
 534             decoupled by lspci                                 (2.4)
 535 rtc         Real time clock                                   
 536 scsi        SCSI info (see text)                              
 537 slabinfo    Slab pool info                                    
 538 softirqs    softirq usage
 539 stat        Overall statistics                                
 540 swaps       Swap space utilization                            
 541 sys         See chapter 2                                     
 542 sysvipc     Info of SysVIPC Resources (msg, sem, shm)          (2.4)
 543 tty         Info of tty drivers
 544 uptime      System uptime                                     
 545 version     Kernel version                                    
 546 video       bttv info of video resources                       (2.4)
 547 vmallocinfo Show vmalloced areas
 548..............................................................................
 549
 550You can,  for  example,  check  which interrupts are currently in use and what
 551they are used for by looking in the file /proc/interrupts:
 552
 553  > cat /proc/interrupts 
 554             CPU0        
 555    0:    8728810          XT-PIC  timer 
 556    1:        895          XT-PIC  keyboard 
 557    2:          0          XT-PIC  cascade 
 558    3:     531695          XT-PIC  aha152x 
 559    4:    2014133          XT-PIC  serial 
 560    5:      44401          XT-PIC  pcnet_cs 
 561    8:          2          XT-PIC  rtc 
 562   11:          8          XT-PIC  i82365 
 563   12:     182918          XT-PIC  PS/2 Mouse 
 564   13:          1          XT-PIC  fpu 
 565   14:    1232265          XT-PIC  ide0 
 566   15:          7          XT-PIC  ide1 
 567  NMI:          0 
 568
 569In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
 570output of a SMP machine):
 571
 572  > cat /proc/interrupts 
 573
 574             CPU0       CPU1       
 575    0:    1243498    1214548    IO-APIC-edge  timer
 576    1:       8949       8958    IO-APIC-edge  keyboard
 577    2:          0          0          XT-PIC  cascade
 578    5:      11286      10161    IO-APIC-edge  soundblaster
 579    8:          1          0    IO-APIC-edge  rtc
 580    9:      27422      27407    IO-APIC-edge  3c503
 581   12:     113645     113873    IO-APIC-edge  PS/2 Mouse
 582   13:          0          0          XT-PIC  fpu
 583   14:      22491      24012    IO-APIC-edge  ide0
 584   15:       2183       2415    IO-APIC-edge  ide1
 585   17:      30564      30414   IO-APIC-level  eth0
 586   18:        177        164   IO-APIC-level  bttv
 587  NMI:    2457961    2457959 
 588  LOC:    2457882    2457881 
 589  ERR:       2155
 590
 591NMI is incremented in this case because every timer interrupt generates a NMI
 592(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
 593
 594LOC is the local interrupt counter of the internal APIC of every CPU.
 595
 596ERR is incremented in the case of errors in the IO-APIC bus (the bus that
 597connects the CPUs in a SMP system. This means that an error has been detected,
 598the IO-APIC automatically retry the transmission, so it should not be a big
 599problem, but you should read the SMP-FAQ.
 600
 601In 2.6.2* /proc/interrupts was expanded again.  This time the goal was for
 602/proc/interrupts to display every IRQ vector in use by the system, not
 603just those considered 'most important'.  The new vectors are:
 604
 605  THR -- interrupt raised when a machine check threshold counter
 606  (typically counting ECC corrected errors of memory or cache) exceeds
 607  a configurable threshold.  Only available on some systems.
 608
 609  TRM -- a thermal event interrupt occurs when a temperature threshold
 610  has been exceeded for the CPU.  This interrupt may also be generated
 611  when the temperature drops back to normal.
 612
 613  SPU -- a spurious interrupt is some interrupt that was raised then lowered
 614  by some IO device before it could be fully processed by the APIC.  Hence
 615  the APIC sees the interrupt but does not know what device it came from.
 616  For this case the APIC will generate the interrupt with a IRQ vector
 617  of 0xff. This might also be generated by chipset bugs.
 618
 619  RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
 620  sent from one CPU to another per the needs of the OS.  Typically,
 621  their statistics are used by kernel developers and interested users to
 622  determine the occurrence of interrupts of the given type.
 623
 624The above IRQ vectors are displayed only when relevant.  For example,
 625the threshold vector does not exist on x86_64 platforms.  Others are
 626suppressed when the system is a uniprocessor.  As of this writing, only
 627i386 and x86_64 platforms support the new IRQ vector displays.
 628
 629Of some interest is the introduction of the /proc/irq directory to 2.4.
 630It could be used to set IRQ to CPU affinity, this means that you can "hook" an
 631IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
 632irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
 633prof_cpu_mask.
 634
 635For example 
 636  > ls /proc/irq/
 637  0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
 638  1  11  13  15  17  19  3  5  7  9  default_smp_affinity
 639  > ls /proc/irq/0/
 640  smp_affinity
 641
 642smp_affinity is a bitmask, in which you can specify which CPUs can handle the
 643IRQ, you can set it by doing:
 644
 645  > echo 1 > /proc/irq/10/smp_affinity
 646
 647This means that only the first CPU will handle the IRQ, but you can also echo
 6485 which means that only the first and fourth CPU can handle the IRQ.
 649
 650The contents of each smp_affinity file is the same by default:
 651
 652  > cat /proc/irq/0/smp_affinity
 653  ffffffff
 654
 655There is an alternate interface, smp_affinity_list which allows specifying
 656a cpu range instead of a bitmask:
 657
 658  > cat /proc/irq/0/smp_affinity_list
 659  1024-1031
 660
 661The default_smp_affinity mask applies to all non-active IRQs, which are the
 662IRQs which have not yet been allocated/activated, and hence which lack a
 663/proc/irq/[0-9]* directory.
 664
 665The node file on an SMP system shows the node to which the device using the IRQ
 666reports itself as being attached. This hardware locality information does not
 667include information about any possible driver locality preference.
 668
 669prof_cpu_mask specifies which CPUs are to be profiled by the system wide
 670profiler. Default value is ffffffff (all cpus if there are only 32 of them).
 671
 672The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
 673between all the CPUs which are allowed to handle it. As usual the kernel has
 674more info than you and does a better job than you, so the defaults are the
 675best choice for almost everyone.  [Note this applies only to those IO-APIC's
 676that support "Round Robin" interrupt distribution.]
 677
 678There are  three  more  important subdirectories in /proc: net, scsi, and sys.
 679The general  rule  is  that  the  contents,  or  even  the  existence of these
 680directories, depend  on your kernel configuration. If SCSI is not enabled, the
 681directory scsi  may  not  exist. The same is true with the net, which is there
 682only when networking support is present in the running kernel.
 683
 684The slabinfo  file  gives  information  about  memory usage at the slab level.
 685Linux uses  slab  pools for memory management above page level in version 2.2.
 686Commonly used  objects  have  their  own  slab  pool (such as network buffers,
 687directory cache, and so on).
 688
 689..............................................................................
 690
 691> cat /proc/buddyinfo
 692
 693Node 0, zone      DMA      0      4      5      4      4      3 ...
 694Node 0, zone   Normal      1      0      0      1    101      8 ...
 695Node 0, zone  HighMem      2      0      0      1      1      0 ...
 696
 697External fragmentation is a problem under some workloads, and buddyinfo is a
 698useful tool for helping diagnose these problems.  Buddyinfo will give you a 
 699clue as to how big an area you can safely allocate, or why a previous
 700allocation failed.
 701
 702Each column represents the number of pages of a certain order which are 
 703available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in 
 704ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE 
 705available in ZONE_NORMAL, etc... 
 706
 707More information relevant to external fragmentation can be found in
 708pagetypeinfo.
 709
 710> cat /proc/pagetypeinfo
 711Page block order: 9
 712Pages per block:  512
 713
 714Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
 715Node    0, zone      DMA, type    Unmovable      0      0      0      1      1      1      1      1      1      1      0
 716Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0
 717Node    0, zone      DMA, type      Movable      1      1      2      1      2      1      1      0      1      0      2
 718Node    0, zone      DMA, type      Reserve      0      0      0      0      0      0      0      0      0      1      0
 719Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
 720Node    0, zone    DMA32, type    Unmovable    103     54     77      1      1      1     11      8      7      1      9
 721Node    0, zone    DMA32, type  Reclaimable      0      0      2      1      0      0      0      0      1      0      0
 722Node    0, zone    DMA32, type      Movable    169    152    113     91     77     54     39     13      6      1    452
 723Node    0, zone    DMA32, type      Reserve      1      2      2      2      2      0      1      1      1      1      0
 724Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
 725
 726Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate
 727Node 0, zone      DMA            2            0            5            1            0
 728Node 0, zone    DMA32           41            6          967            2            0
 729
 730Fragmentation avoidance in the kernel works by grouping pages of different
 731migrate types into the same contiguous regions of memory called page blocks.
 732A page block is typically the size of the default hugepage size e.g. 2MB on
 733X86-64. By keeping pages grouped based on their ability to move, the kernel
 734can reclaim pages within a page block to satisfy a high-order allocation.
 735
 736The pagetypinfo begins with information on the size of a page block. It
 737then gives the same type of information as buddyinfo except broken down
 738by migrate-type and finishes with details on how many page blocks of each
 739type exist.
 740
 741If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
 742from libhugetlbfs http://sourceforge.net/projects/libhugetlbfs/), one can
 743make an estimate of the likely number of huge pages that can be allocated
 744at a given point in time. All the "Movable" blocks should be allocatable
 745unless memory has been mlock()'d. Some of the Reclaimable blocks should
 746also be allocatable although a lot of filesystem metadata may have to be
 747reclaimed to achieve this.
 748
 749..............................................................................
 750
 751meminfo:
 752
 753Provides information about distribution and utilization of memory.  This
 754varies by architecture and compile options.  The following is from a
 75516GB PIII, which has highmem enabled.  You may not have all of these fields.
 756
 757> cat /proc/meminfo
 758
 759The "Locked" indicates whether the mapping is locked in memory or not.
 760
 761
 762MemTotal:     16344972 kB
 763MemFree:      13634064 kB
 764Buffers:          3656 kB
 765Cached:        1195708 kB
 766SwapCached:          0 kB
 767Active:         891636 kB
 768Inactive:      1077224 kB
 769HighTotal:    15597528 kB
 770HighFree:     13629632 kB
 771LowTotal:       747444 kB
 772LowFree:          4432 kB
 773SwapTotal:           0 kB
 774SwapFree:            0 kB
 775Dirty:             968 kB
 776Writeback:           0 kB
 777AnonPages:      861800 kB
 778Mapped:         280372 kB
 779Slab:           284364 kB
 780SReclaimable:   159856 kB
 781SUnreclaim:     124508 kB
 782PageTables:      24448 kB
 783NFS_Unstable:        0 kB
 784Bounce:              0 kB
 785WritebackTmp:        0 kB
 786CommitLimit:   7669796 kB
 787Committed_AS:   100056 kB
 788VmallocTotal:   112216 kB
 789VmallocUsed:       428 kB
 790VmallocChunk:   111088 kB
 791AnonHugePages:   49152 kB
 792
 793    MemTotal: Total usable ram (i.e. physical ram minus a few reserved
 794              bits and the kernel binary code)
 795     MemFree: The sum of LowFree+HighFree
 796     Buffers: Relatively temporary storage for raw disk blocks
 797              shouldn't get tremendously large (20MB or so)
 798      Cached: in-memory cache for files read from the disk (the
 799              pagecache).  Doesn't include SwapCached
 800  SwapCached: Memory that once was swapped out, is swapped back in but
 801              still also is in the swapfile (if memory is needed it
 802              doesn't need to be swapped out AGAIN because it is already
 803              in the swapfile. This saves I/O)
 804      Active: Memory that has been used more recently and usually not
 805              reclaimed unless absolutely necessary.
 806    Inactive: Memory which has been less recently used.  It is more
 807              eligible to be reclaimed for other purposes
 808   HighTotal:
 809    HighFree: Highmem is all memory above ~860MB of physical memory
 810              Highmem areas are for use by userspace programs, or
 811              for the pagecache.  The kernel must use tricks to access
 812              this memory, making it slower to access than lowmem.
 813    LowTotal:
 814     LowFree: Lowmem is memory which can be used for everything that
 815              highmem can be used for, but it is also available for the
 816              kernel's use for its own data structures.  Among many
 817              other things, it is where everything from the Slab is
 818              allocated.  Bad things happen when you're out of lowmem.
 819   SwapTotal: total amount of swap space available
 820    SwapFree: Memory which has been evicted from RAM, and is temporarily
 821              on the disk
 822       Dirty: Memory which is waiting to get written back to the disk
 823   Writeback: Memory which is actively being written back to the disk
 824   AnonPages: Non-file backed pages mapped into userspace page tables
 825AnonHugePages: Non-file backed huge pages mapped into userspace page tables
 826      Mapped: files which have been mmaped, such as libraries
 827        Slab: in-kernel data structures cache
 828SReclaimable: Part of Slab, that might be reclaimed, such as caches
 829  SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
 830  PageTables: amount of memory dedicated to the lowest level of page
 831              tables.
 832NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
 833              storage
 834      Bounce: Memory used for block device "bounce buffers"
 835WritebackTmp: Memory used by FUSE for temporary writeback buffers
 836 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
 837              this is the total amount of  memory currently available to
 838              be allocated on the system. This limit is only adhered to
 839              if strict overcommit accounting is enabled (mode 2 in
 840              'vm.overcommit_memory').
 841              The CommitLimit is calculated with the following formula:
 842              CommitLimit = ('vm.overcommit_ratio' * Physical RAM) + Swap
 843              For example, on a system with 1G of physical RAM and 7G
 844              of swap with a `vm.overcommit_ratio` of 30 it would
 845              yield a CommitLimit of 7.3G.
 846              For more details, see the memory overcommit documentation
 847              in vm/overcommit-accounting.
 848Committed_AS: The amount of memory presently allocated on the system.
 849              The committed memory is a sum of all of the memory which
 850              has been allocated by processes, even if it has not been
 851              "used" by them as of yet. A process which malloc()'s 1G
 852              of memory, but only touches 300M of it will only show up
 853              as using 300M of memory even if it has the address space
 854              allocated for the entire 1G. This 1G is memory which has
 855              been "committed" to by the VM and can be used at any time
 856              by the allocating application. With strict overcommit
 857              enabled on the system (mode 2 in 'vm.overcommit_memory'),
 858              allocations which would exceed the CommitLimit (detailed
 859              above) will not be permitted. This is useful if one needs
 860              to guarantee that processes will not fail due to lack of
 861              memory once that memory has been successfully allocated.
 862VmallocTotal: total size of vmalloc memory area
 863 VmallocUsed: amount of vmalloc area which is used
 864VmallocChunk: largest contiguous block of vmalloc area which is free
 865
 866..............................................................................
 867
 868vmallocinfo:
 869
 870Provides information about vmalloced/vmaped areas. One line per area,
 871containing the virtual address range of the area, size in bytes,
 872caller information of the creator, and optional information depending
 873on the kind of area :
 874
 875 pages=nr    number of pages
 876 phys=addr   if a physical address was specified
 877 ioremap     I/O mapping (ioremap() and friends)
 878 vmalloc     vmalloc() area
 879 vmap        vmap()ed pages
 880 user        VM_USERMAP area
 881 vpages      buffer for pages pointers was vmalloced (huge area)
 882 N<node>=nr  (Only on NUMA kernels)
 883             Number of pages allocated on memory node <node>
 884
 885> cat /proc/vmallocinfo
 8860xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
 887  /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
 8880xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
 889  /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
 8900xffffc20000302000-0xffffc20000304000    8192 acpi_tb_verify_table+0x21/0x4f...
 891  phys=7fee8000 ioremap
 8920xffffc20000304000-0xffffc20000307000   12288 acpi_tb_verify_table+0x21/0x4f...
 893  phys=7fee7000 ioremap
 8940xffffc2000031d000-0xffffc2000031f000    8192 init_vdso_vars+0x112/0x210
 8950xffffc2000031f000-0xffffc2000032b000   49152 cramfs_uncompress_init+0x2e ...
 896  /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
 8970xffffc2000033a000-0xffffc2000033d000   12288 sys_swapon+0x640/0xac0      ...
 898  pages=2 vmalloc N1=2
 8990xffffc20000347000-0xffffc2000034c000   20480 xt_alloc_table_info+0xfe ...
 900  /0x130 [x_tables] pages=4 vmalloc N0=4
 9010xffffffffa0000000-0xffffffffa000f000   61440 sys_init_module+0xc27/0x1d00 ...
 902   pages=14 vmalloc N2=14
 9030xffffffffa000f000-0xffffffffa0014000   20480 sys_init_module+0xc27/0x1d00 ...
 904   pages=4 vmalloc N1=4
 9050xffffffffa0014000-0xffffffffa0017000   12288 sys_init_module+0xc27/0x1d00 ...
 906   pages=2 vmalloc N1=2
 9070xffffffffa0017000-0xffffffffa0022000   45056 sys_init_module+0xc27/0x1d00 ...
 908   pages=10 vmalloc N0=10
 909
 910..............................................................................
 911
 912softirqs:
 913
 914Provides counts of softirq handlers serviced since boot time, for each cpu.
 915
 916> cat /proc/softirqs
 917                CPU0       CPU1       CPU2       CPU3
 918      HI:          0          0          0          0
 919   TIMER:      27166      27120      27097      27034
 920  NET_TX:          0          0          0         17
 921  NET_RX:         42          0          0         39
 922   BLOCK:          0          0        107       1121
 923 TASKLET:          0          0          0        290
 924   SCHED:      27035      26983      26971      26746
 925 HRTIMER:          0          0          0          0
 926     RCU:       1678       1769       2178       2250
 927
 928
 9291.3 IDE devices in /proc/ide
 930----------------------------
 931
 932The subdirectory /proc/ide contains information about all IDE devices of which
 933the kernel  is  aware.  There is one subdirectory for each IDE controller, the
 934file drivers  and a link for each IDE device, pointing to the device directory
 935in the controller specific subtree.
 936
 937The file  drivers  contains general information about the drivers used for the
 938IDE devices:
 939
 940  > cat /proc/ide/drivers
 941  ide-cdrom version 4.53
 942  ide-disk version 1.08
 943
 944More detailed  information  can  be  found  in  the  controller  specific
 945subdirectories. These  are  named  ide0,  ide1  and  so  on.  Each  of  these
 946directories contains the files shown in table 1-6.
 947
 948
 949Table 1-6: IDE controller info in  /proc/ide/ide?
 950..............................................................................
 951 File    Content                                 
 952 channel IDE channel (0 or 1)                    
 953 config  Configuration (only for PCI/IDE bridge) 
 954 mate    Mate name                               
 955 model   Type/Chipset of IDE controller          
 956..............................................................................
 957
 958Each device  connected  to  a  controller  has  a separate subdirectory in the
 959controllers directory.  The  files  listed in table 1-7 are contained in these
 960directories.
 961
 962
 963Table 1-7: IDE device information
 964..............................................................................
 965 File             Content                                    
 966 cache            The cache                                  
 967 capacity         Capacity of the medium (in 512Byte blocks) 
 968 driver           driver and version                         
 969 geometry         physical and logical geometry              
 970 identify         device identify block                      
 971 media            media type                                 
 972 model            device identifier                          
 973 settings         device setup                               
 974 smart_thresholds IDE disk management thresholds             
 975 smart_values     IDE disk management values                 
 976..............................................................................
 977
 978The most  interesting  file is settings. This file contains a nice overview of
 979the drive parameters:
 980
 981  # cat /proc/ide/ide0/hda/settings 
 982  name                    value           min             max             mode 
 983  ----                    -----           ---             ---             ---- 
 984  bios_cyl                526             0               65535           rw 
 985  bios_head               255             0               255             rw 
 986  bios_sect               63              0               63              rw 
 987  breada_readahead        4               0               127             rw 
 988  bswap                   0               0               1               r 
 989  file_readahead          72              0               2097151         rw 
 990  io_32bit                0               0               3               rw 
 991  keepsettings            0               0               1               rw 
 992  max_kb_per_request      122             1               127             rw 
 993  multcount               0               0               8               rw 
 994  nice1                   1               0               1               rw 
 995  nowerr                  0               0               1               rw 
 996  pio_mode                write-only      0               255             w 
 997  slow                    0               0               1               rw 
 998  unmaskirq               0               0               1               rw 
 999  using_dma               0               0               1               rw 
1000
1001
10021.4 Networking info in /proc/net
1003--------------------------------
1004
1005The subdirectory  /proc/net  follows  the  usual  pattern. Table 1-8 shows the
1006additional values  you  get  for  IP  version 6 if you configure the kernel to
1007support this. Table 1-9 lists the files and their meaning.
1008
1009
1010Table 1-8: IPv6 info in /proc/net
1011..............................................................................
1012 File       Content                                               
1013 udp6       UDP sockets (IPv6)                                    
1014 tcp6       TCP sockets (IPv6)                                    
1015 raw6       Raw device statistics (IPv6)                          
1016 igmp6      IP multicast addresses, which this host joined (IPv6) 
1017 if_inet6   List of IPv6 interface addresses                      
1018 ipv6_route Kernel routing table for IPv6                         
1019 rt6_stats  Global IPv6 routing tables statistics                 
1020 sockstat6  Socket statistics (IPv6)                              
1021 snmp6      Snmp data (IPv6)                                      
1022..............................................................................
1023
1024
1025Table 1-9: Network info in /proc/net
1026..............................................................................
1027 File          Content                                                         
1028 arp           Kernel  ARP table                                               
1029 dev           network devices with statistics                                 
1030 dev_mcast     the Layer2 multicast groups a device is listening too
1031               (interface index, label, number of references, number of bound
1032               addresses). 
1033 dev_stat      network device status                                           
1034 ip_fwchains   Firewall chain linkage                                          
1035 ip_fwnames    Firewall chain names                                            
1036 ip_masq       Directory containing the masquerading tables                    
1037 ip_masquerade Major masquerading table                                        
1038 netstat       Network statistics                                              
1039 raw           raw device statistics                                           
1040 route         Kernel routing table                                            
1041 rpc           Directory containing rpc info                                   
1042 rt_cache      Routing cache                                                   
1043 snmp          SNMP data                                                       
1044 sockstat      Socket statistics                                               
1045 tcp           TCP  sockets                                                    
1046 udp           UDP sockets                                                     
1047 unix          UNIX domain sockets                                             
1048 wireless      Wireless interface data (Wavelan etc)                           
1049 igmp          IP multicast addresses, which this host joined                  
1050 psched        Global packet scheduler parameters.                             
1051 netlink       List of PF_NETLINK sockets                                      
1052 ip_mr_vifs    List of multicast virtual interfaces                            
1053 ip_mr_cache   List of multicast routing cache                                 
1054..............................................................................
1055
1056You can  use  this  information  to see which network devices are available in
1057your system and how much traffic was routed over those devices:
1058
1059  > cat /proc/net/dev 
1060  Inter-|Receive                                                   |[... 
1061   face |bytes    packets errs drop fifo frame compressed multicast|[... 
1062      lo:  908188   5596     0    0    0     0          0         0 [...         
1063    ppp0:15475140  20721   410    0    0   410          0         0 [...  
1064    eth0:  614530   7085     0    0    0     0          0         1 [... 
1065   
1066  ...] Transmit 
1067  ...] bytes    packets errs drop fifo colls carrier compressed 
1068  ...]  908188     5596    0    0    0     0       0          0 
1069  ...] 1375103    17405    0    0    0     0       0          0 
1070  ...] 1703981     5535    0    0    0     3       0          0 
1071
1072In addition, each Channel Bond interface has its own directory.  For
1073example, the bond0 device will have a directory called /proc/net/bond0/.
1074It will contain information that is specific to that bond, such as the
1075current slaves of the bond, the link status of the slaves, and how
1076many times the slaves link has failed.
1077
10781.5 SCSI info
1079-------------
1080
1081If you  have  a  SCSI  host adapter in your system, you'll find a subdirectory
1082named after  the driver for this adapter in /proc/scsi. You'll also see a list
1083of all recognized SCSI devices in /proc/scsi:
1084
1085  >cat /proc/scsi/scsi 
1086  Attached devices: 
1087  Host: scsi0 Channel: 00 Id: 00 Lun: 00 
1088    Vendor: IBM      Model: DGHS09U          Rev: 03E0 
1089    Type:   Direct-Access                    ANSI SCSI revision: 03 
1090  Host: scsi0 Channel: 00 Id: 06 Lun: 00 
1091    Vendor: PIONEER  Model: CD-ROM DR-U06S   Rev: 1.04 
1092    Type:   CD-ROM                           ANSI SCSI revision: 02 
1093
1094
1095The directory  named  after  the driver has one file for each adapter found in
1096the system.  These  files  contain information about the controller, including
1097the used  IRQ  and  the  IO  address range. The amount of information shown is
1098dependent on  the adapter you use. The example shows the output for an Adaptec
1099AHA-2940 SCSI adapter:
1100
1101  > cat /proc/scsi/aic7xxx/0 
1102   
1103  Adaptec AIC7xxx driver version: 5.1.19/3.2.4 
1104  Compile Options: 
1105    TCQ Enabled By Default : Disabled 
1106    AIC7XXX_PROC_STATS     : Disabled 
1107    AIC7XXX_RESET_DELAY    : 5 
1108  Adapter Configuration: 
1109             SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter 
1110                             Ultra Wide Controller 
1111      PCI MMAPed I/O Base: 0xeb001000 
1112   Adapter SEEPROM Config: SEEPROM found and used. 
1113        Adaptec SCSI BIOS: Enabled 
1114                      IRQ: 10 
1115                     SCBs: Active 0, Max Active 2, 
1116                           Allocated 15, HW 16, Page 255 
1117               Interrupts: 160328 
1118        BIOS Control Word: 0x18b6 
1119     Adapter Control Word: 0x005b 
1120     Extended Translation: Enabled 
1121  Disconnect Enable Flags: 0xffff 
1122       Ultra Enable Flags: 0x0001 
1123   Tag Queue Enable Flags: 0x0000 
1124  Ordered Queue Tag Flags: 0x0000 
1125  Default Tag Queue Depth: 8 
1126      Tagged Queue By Device array for aic7xxx host instance 0: 
1127        {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} 
1128      Actual queue depth per device for aic7xxx host instance 0: 
1129        {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} 
1130  Statistics: 
1131  (scsi0:0:0:0) 
1132    Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 
1133    Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) 
1134    Total transfers 160151 (74577 reads and 85574 writes) 
1135  (scsi0:0:6:0) 
1136    Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 
1137    Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) 
1138    Total transfers 0 (0 reads and 0 writes) 
1139
1140
11411.6 Parallel port info in /proc/parport
1142---------------------------------------
1143
1144The directory  /proc/parport  contains information about the parallel ports of
1145your system.  It  has  one  subdirectory  for  each port, named after the port
1146number (0,1,2,...).
1147
1148These directories contain the four files shown in Table 1-10.
1149
1150
1151Table 1-10: Files in /proc/parport
1152..............................................................................
1153 File      Content                                                             
1154 autoprobe Any IEEE-1284 device ID information that has been acquired.         
1155 devices   list of the device drivers using that port. A + will appear by the
1156           name of the device currently using the port (it might not appear
1157           against any). 
1158 hardware  Parallel port's base address, IRQ line and DMA channel.             
1159 irq       IRQ that parport is using for that port. This is in a separate
1160           file to allow you to alter it by writing a new value in (IRQ
1161           number or none). 
1162..............................................................................
1163
11641.7 TTY info in /proc/tty
1165-------------------------
1166
1167Information about  the  available  and actually used tty's can be found in the
1168directory /proc/tty.You'll  find  entries  for drivers and line disciplines in
1169this directory, as shown in Table 1-11.
1170
1171
1172Table 1-11: Files in /proc/tty
1173..............................................................................
1174 File          Content                                        
1175 drivers       list of drivers and their usage                
1176 ldiscs        registered line disciplines                    
1177 driver/serial usage statistic and status of single tty lines 
1178..............................................................................
1179
1180To see  which  tty's  are  currently in use, you can simply look into the file
1181/proc/tty/drivers:
1182
1183  > cat /proc/tty/drivers 
1184  pty_slave            /dev/pts      136   0-255 pty:slave 
1185  pty_master           /dev/ptm      128   0-255 pty:master 
1186  pty_slave            /dev/ttyp       3   0-255 pty:slave 
1187  pty_master           /dev/pty        2   0-255 pty:master 
1188  serial               /dev/cua        5   64-67 serial:callout 
1189  serial               /dev/ttyS       4   64-67 serial 
1190  /dev/tty0            /dev/tty0       4       0 system:vtmaster 
1191  /dev/ptmx            /dev/ptmx       5       2 system 
1192  /dev/console         /dev/console    5       1 system:console 
1193  /dev/tty             /dev/tty        5       0 system:/dev/tty 
1194  unknown              /dev/tty        4    1-63 console 
1195
1196
11971.8 Miscellaneous kernel statistics in /proc/stat
1198-------------------------------------------------
1199
1200Various pieces   of  information about  kernel activity  are  available in the
1201/proc/stat file.  All  of  the numbers reported  in  this file are  aggregates
1202since the system first booted.  For a quick look, simply cat the file:
1203
1204  > cat /proc/stat
1205  cpu  2255 34 2290 22625563 6290 127 456 0 0
1206  cpu0 1132 34 1441 11311718 3675 127 438 0 0
1207  cpu1 1123 0 849 11313845 2614 0 18 0 0
1208  intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1209  ctxt 1990473
1210  btime 1062191376
1211  processes 2915
1212  procs_running 1
1213  procs_blocked 0
1214  softirq 183433 0 21755 12 39 1137 231 21459 2263
1215
1216The very first  "cpu" line aggregates the  numbers in all  of the other "cpuN"
1217lines.  These numbers identify the amount of time the CPU has spent performing
1218different kinds of work.  Time units are in USER_HZ (typically hundredths of a
1219second).  The meanings of the columns are as follows, from left to right:
1220
1221- user: normal processes executing in user mode
1222- nice: niced processes executing in user mode
1223- system: processes executing in kernel mode
1224- idle: twiddling thumbs
1225- iowait: waiting for I/O to complete
1226- irq: servicing interrupts
1227- softirq: servicing softirqs
1228- steal: involuntary wait
1229- guest: running a normal guest
1230- guest_nice: running a niced guest
1231
1232The "intr" line gives counts of interrupts  serviced since boot time, for each
1233of the  possible system interrupts.   The first  column  is the  total of  all
1234interrupts serviced; each  subsequent column is the  total for that particular
1235interrupt.
1236
1237The "ctxt" line gives the total number of context switches across all CPUs.
1238
1239The "btime" line gives  the time at which the  system booted, in seconds since
1240the Unix epoch.
1241
1242The "processes" line gives the number  of processes and threads created, which
1243includes (but  is not limited  to) those  created by  calls to the  fork() and
1244clone() system calls.
1245
1246The "procs_running" line gives the total number of threads that are
1247running or ready to run (i.e., the total number of runnable threads).
1248
1249The   "procs_blocked" line gives  the  number of  processes currently blocked,
1250waiting for I/O to complete.
1251
1252The "softirq" line gives counts of softirqs serviced since boot time, for each
1253of the possible system softirqs. The first column is the total of all
1254softirqs serviced; each subsequent column is the total for that particular
1255softirq.
1256
1257
12581.9 Ext4 file system parameters
1259------------------------------
1260
1261Information about mounted ext4 file systems can be found in
1262/proc/fs/ext4.  Each mounted filesystem will have a directory in
1263/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1264/proc/fs/ext4/dm-0).   The files in each per-device directory are shown
1265in Table 1-12, below.
1266
1267Table 1-12: Files in /proc/fs/ext4/<devname>
1268..............................................................................
1269 File            Content                                        
1270 mb_groups       details of multiblock allocator buddy cache of free blocks
1271..............................................................................
1272
12732.0 /proc/consoles
1274------------------
1275Shows registered system console lines.
1276
1277To see which character device lines are currently used for the system console
1278/dev/console, you may simply look into the file /proc/consoles:
1279
1280  > cat /proc/consoles
1281  tty0                 -WU (ECp)       4:7
1282  ttyS0                -W- (Ep)        4:64
1283
1284The columns are:
1285
1286  device               name of the device
1287  operations           R = can do read operations
1288                       W = can do write operations
1289                       U = can do unblank
1290  flags                E = it is enabled
1291                       C = it is preferred console
1292                       B = it is primary boot console
1293                       p = it is used for printk buffer
1294                       b = it is not a TTY but a Braille device
1295                       a = it is safe to use when cpu is offline
1296  major:minor          major and minor number of the device separated by a colon
1297
1298------------------------------------------------------------------------------
1299Summary
1300------------------------------------------------------------------------------
1301The /proc file system serves information about the running system. It not only
1302allows access to process data but also allows you to request the kernel status
1303by reading files in the hierarchy.
1304
1305The directory  structure  of /proc reflects the types of information and makes
1306it easy, if not obvious, where to look for specific data.
1307------------------------------------------------------------------------------
1308
1309------------------------------------------------------------------------------
1310CHAPTER 2: MODIFYING SYSTEM PARAMETERS
1311------------------------------------------------------------------------------
1312
1313------------------------------------------------------------------------------
1314In This Chapter
1315------------------------------------------------------------------------------
1316* Modifying kernel parameters by writing into files found in /proc/sys
1317* Exploring the files which modify certain parameters
1318* Review of the /proc/sys file tree
1319------------------------------------------------------------------------------
1320
1321
1322A very  interesting part of /proc is the directory /proc/sys. This is not only
1323a source  of  information,  it also allows you to change parameters within the
1324kernel. Be  very  careful  when attempting this. You can optimize your system,
1325but you  can  also  cause  it  to  crash.  Never  alter kernel parameters on a
1326production system.  Set  up  a  development machine and test to make sure that
1327everything works  the  way  you want it to. You may have no alternative but to
1328reboot the machine once an error has been made.
1329
1330To change  a  value,  simply  echo  the new value into the file. An example is
1331given below  in the section on the file system data. You need to be root to do
1332this. You  can  create  your  own  boot script to perform this every time your
1333system boots.
1334
1335The files  in /proc/sys can be used to fine tune and monitor miscellaneous and
1336general things  in  the operation of the Linux kernel. Since some of the files
1337can inadvertently  disrupt  your  system,  it  is  advisable  to  read  both
1338documentation and  source  before actually making adjustments. In any case, be
1339very careful  when  writing  to  any  of these files. The entries in /proc may
1340change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1341review the kernel documentation in the directory /usr/src/linux/Documentation.
1342This chapter  is  heavily  based  on the documentation included in the pre 2.2
1343kernels, and became part of it in version 2.2.1 of the Linux kernel.
1344
1345Please see: Documentation/sysctl/ directory for descriptions of these
1346entries.
1347
1348------------------------------------------------------------------------------
1349Summary
1350------------------------------------------------------------------------------
1351Certain aspects  of  kernel  behavior  can be modified at runtime, without the
1352need to  recompile  the kernel, or even to reboot the system. The files in the
1353/proc/sys tree  can  not only be read, but also modified. You can use the echo
1354command to write value into these files, thereby changing the default settings
1355of the kernel.
1356------------------------------------------------------------------------------
1357
1358------------------------------------------------------------------------------
1359CHAPTER 3: PER-PROCESS PARAMETERS
1360------------------------------------------------------------------------------
1361
13623.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1363--------------------------------------------------------------------------------
1364
1365These file can be used to adjust the badness heuristic used to select which
1366process gets killed in out of memory conditions.
1367
1368The badness heuristic assigns a value to each candidate task ranging from 0
1369(never kill) to 1000 (always kill) to determine which process is targeted.  The
1370units are roughly a proportion along that range of allowed memory the process
1371may allocate from based on an estimation of its current memory and swap use.
1372For example, if a task is using all allowed memory, its badness score will be
13731000.  If it is using half of its allowed memory, its score will be 500.
1374
1375There is an additional factor included in the badness score: the current memory
1376and swap usage is discounted by 3% for root processes.
1377
1378The amount of "allowed" memory depends on the context in which the oom killer
1379was called.  If it is due to the memory assigned to the allocating task's cpuset
1380being exhausted, the allowed memory represents the set of mems assigned to that
1381cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
1382memory represents the set of mempolicy nodes.  If it is due to a memory
1383limit (or swap limit) being reached, the allowed memory is that configured
1384limit.  Finally, if it is due to the entire system being out of memory, the
1385allowed memory represents all allocatable resources.
1386
1387The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1388is used to determine which task to kill.  Acceptable values range from -1000
1389(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
1390polarize the preference for oom killing either by always preferring a certain
1391task or completely disabling it.  The lowest possible value, -1000, is
1392equivalent to disabling oom killing entirely for that task since it will always
1393report a badness score of 0.
1394
1395Consequently, it is very simple for userspace to define the amount of memory to
1396consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
1397example, is roughly equivalent to allowing the remainder of tasks sharing the
1398same system, cpuset, mempolicy, or memory controller resources to use at least
139950% more memory.  A value of -500, on the other hand, would be roughly
1400equivalent to discounting 50% of the task's allowed memory from being considered
1401as scoring against the task.
1402
1403For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1404be used to tune the badness score.  Its acceptable values range from -16
1405(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1406(OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
1407scaled linearly with /proc/<pid>/oom_score_adj.
1408
1409The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1410value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1411requires CAP_SYS_RESOURCE.
1412
1413Caveat: when a parent task is selected, the oom killer will sacrifice any first
1414generation children with separate address spaces instead, if possible.  This
1415avoids servers and important system daemons from being killed and loses the
1416minimal amount of work.
1417
1418
14193.2 /proc/<pid>/oom_score - Display current oom-killer score
1420-------------------------------------------------------------
1421
1422This file can be used to check the current score used by the oom-killer is for
1423any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1424process should be killed in an out-of-memory situation.
1425
1426
14273.3  /proc/<pid>/io - Display the IO accounting fields
1428-------------------------------------------------------
1429
1430This file contains IO statistics for each running process
1431
1432Example
1433-------
1434
1435test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1436[1] 3828
1437
1438test:/tmp # cat /proc/3828/io
1439rchar: 323934931
1440wchar: 323929600
1441syscr: 632687
1442syscw: 632675
1443read_bytes: 0
1444write_bytes: 323932160
1445cancelled_write_bytes: 0
1446
1447
1448Description
1449-----------
1450
1451rchar
1452-----
1453
1454I/O counter: chars read
1455The number of bytes which this task has caused to be read from storage. This
1456is simply the sum of bytes which this process passed to read() and pread().
1457It includes things like tty IO and it is unaffected by whether or not actual
1458physical disk IO was required (the read might have been satisfied from
1459pagecache)
1460
1461
1462wchar
1463-----
1464
1465I/O counter: chars written
1466The number of bytes which this task has caused, or shall cause to be written
1467to disk. Similar caveats apply here as with rchar.
1468
1469
1470syscr
1471-----
1472
1473I/O counter: read syscalls
1474Attempt to count the number of read I/O operations, i.e. syscalls like read()
1475and pread().
1476
1477
1478syscw
1479-----
1480
1481I/O counter: write syscalls
1482Attempt to count the number of write I/O operations, i.e. syscalls like
1483write() and pwrite().
1484
1485
1486read_bytes
1487----------
1488
1489I/O counter: bytes read
1490Attempt to count the number of bytes which this process really did cause to
1491be fetched from the storage layer. Done at the submit_bio() level, so it is
1492accurate for block-backed filesystems. <please add status regarding NFS and
1493CIFS at a later time>
1494
1495
1496write_bytes
1497-----------
1498
1499I/O counter: bytes written
1500Attempt to count the number of bytes which this process caused to be sent to
1501the storage layer. This is done at page-dirtying time.
1502
1503
1504cancelled_write_bytes
1505---------------------
1506
1507The big inaccuracy here is truncate. If a process writes 1MB to a file and
1508then deletes the file, it will in fact perform no writeout. But it will have
1509been accounted as having caused 1MB of write.
1510In other words: The number of bytes which this process caused to not happen,
1511by truncating pagecache. A task can cause "negative" IO too. If this task
1512truncates some dirty pagecache, some IO which another task has been accounted
1513for (in its write_bytes) will not be happening. We _could_ just subtract that
1514from the truncating task's write_bytes, but there is information loss in doing
1515that.
1516
1517
1518Note
1519----
1520
1521At its current implementation state, this is a bit racy on 32-bit machines: if
1522process A reads process B's /proc/pid/io while process B is updating one of
1523those 64-bit counters, process A could see an intermediate result.
1524
1525
1526More information about this can be found within the taskstats documentation in
1527Documentation/accounting.
1528
15293.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1530---------------------------------------------------------------
1531When a process is dumped, all anonymous memory is written to a core file as
1532long as the size of the core file isn't limited. But sometimes we don't want
1533to dump some memory segments, for example, huge shared memory. Conversely,
1534sometimes we want to save file-backed memory segments into a core file, not
1535only the individual files.
1536
1537/proc/<pid>/coredump_filter allows you to customize which memory segments
1538will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1539of memory types. If a bit of the bitmask is set, memory segments of the
1540corresponding memory type are dumped, otherwise they are not dumped.
1541
1542The following 7 memory types are supported:
1543  - (bit 0) anonymous private memory
1544  - (bit 1) anonymous shared memory
1545  - (bit 2) file-backed private memory
1546  - (bit 3) file-backed shared memory
1547  - (bit 4) ELF header pages in file-backed private memory areas (it is
1548            effective only if the bit 2 is cleared)
1549  - (bit 5) hugetlb private memory
1550  - (bit 6) hugetlb shared memory
1551
1552  Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1553  are always dumped regardless of the bitmask status.
1554
1555  Note bit 0-4 doesn't effect any hugetlb memory. hugetlb memory are only
1556  effected by bit 5-6.
1557
1558Default value of coredump_filter is 0x23; this means all anonymous memory
1559segments and hugetlb private memory are dumped.
1560
1561If you don't want to dump all shared memory segments attached to pid 1234,
1562write 0x21 to the process's proc file.
1563
1564  $ echo 0x21 > /proc/1234/coredump_filter
1565
1566When a new process is created, the process inherits the bitmask status from its
1567parent. It is useful to set up coredump_filter before the program runs.
1568For example:
1569
1570  $ echo 0x7 > /proc/self/coredump_filter
1571  $ ./some_program
1572
15733.5     /proc/<pid>/mountinfo - Information about mounts
1574--------------------------------------------------------
1575
1576This file contains lines of the form:
1577
157836 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1579(1)(2)(3)   (4)   (5)      (6)      (7)   (8) (9)   (10)         (11)
1580
1581(1) mount ID:  unique identifier of the mount (may be reused after umount)
1582(2) parent ID:  ID of parent (or of self for the top of the mount tree)
1583(3) major:minor:  value of st_dev for files on filesystem
1584(4) root:  root of the mount within the filesystem
1585(5) mount point:  mount point relative to the process's root
1586(6) mount options:  per mount options
1587(7) optional fields:  zero or more fields of the form "tag[:value]"
1588(8) separator:  marks the end of the optional fields
1589(9) filesystem type:  name of filesystem of the form "type[.subtype]"
1590(10) mount source:  filesystem specific information or "none"
1591(11) super options:  per super block options
1592
1593Parsers should ignore all unrecognised optional fields.  Currently the
1594possible optional fields are:
1595
1596shared:X  mount is shared in peer group X
1597master:X  mount is slave to peer group X
1598propagate_from:X  mount is slave and receives propagation from peer group X (*)
1599unbindable  mount is unbindable
1600
1601(*) X is the closest dominant peer group under the process's root.  If
1602X is the immediate master of the mount, or if there's no dominant peer
1603group under the same root, then only the "master:X" field is present
1604and not the "propagate_from:X" field.
1605
1606For more information on mount propagation see:
1607
1608  Documentation/filesystems/sharedsubtree.txt
1609
1610
16113.6     /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
1612--------------------------------------------------------
1613These files provide a method to access a tasks comm value. It also allows for
1614a task to set its own or one of its thread siblings comm value. The comm value
1615is limited in size compared to the cmdline value, so writing anything longer
1616then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1617comm value.
1618
1619
16203.7     /proc/<pid>/task/<tid>/children - Information about task children
1621-------------------------------------------------------------------------
1622This file provides a fast way to retrieve first level children pids
1623of a task pointed by <pid>/<tid> pair. The format is a space separated
1624stream of pids.
1625
1626Note the "first level" here -- if a child has own children they will
1627not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children
1628to obtain the descendants.
1629
1630Since this interface is intended to be fast and cheap it doesn't
1631guarantee to provide precise results and some children might be
1632skipped, especially if they've exited right after we printed their
1633pids, so one need to either stop or freeze processes being inspected
1634if precise results are needed.
1635
1636
16373.7     /proc/<pid>/fdinfo/<fd> - Information about opened file
1638---------------------------------------------------------------
1639This file provides information associated with an opened file. The regular
1640files have at least two fields -- 'pos' and 'flags'. The 'pos' represents
1641the current offset of the opened file in decimal form [see lseek(2) for
1642details] and 'flags' denotes the octal O_xxx mask the file has been
1643created with [see open(2) for details].
1644
1645A typical output is
1646
1647        pos:    0
1648        flags:  0100002
1649
1650The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1651pair provide additional information particular to the objects they represent.
1652
1653        Eventfd files
1654        ~~~~~~~~~~~~~
1655        pos:    0
1656        flags:  04002
1657        eventfd-count:  5a
1658
1659        where 'eventfd-count' is hex value of a counter.
1660
1661        Signalfd files
1662        ~~~~~~~~~~~~~~
1663        pos:    0
1664        flags:  04002
1665        sigmask:        0000000000000200
1666
1667        where 'sigmask' is hex value of the signal mask associated
1668        with a file.
1669
1670        Epoll files
1671        ~~~~~~~~~~~
1672        pos:    0
1673        flags:  02
1674        tfd:        5 events:       1d data: ffffffffffffffff
1675
1676        where 'tfd' is a target file descriptor number in decimal form,
1677        'events' is events mask being watched and the 'data' is data
1678        associated with a target [see epoll(7) for more details].
1679
1680        Fsnotify files
1681        ~~~~~~~~~~~~~~
1682        For inotify files the format is the following
1683
1684        pos:    0
1685        flags:  02000000
1686        inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
1687
1688        where 'wd' is a watch descriptor in decimal form, ie a target file
1689        descriptor number, 'ino' and 'sdev' are inode and device where the
1690        target file resides and the 'mask' is the mask of events, all in hex
1691        form [see inotify(7) for more details].
1692
1693        If the kernel was built with exportfs support, the path to the target
1694        file is encoded as a file handle.  The file handle is provided by three
1695        fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
1696        format.
1697
1698        If the kernel is built without exportfs support the file handle won't be
1699        printed out.
1700
1701        If there is no inotify mark attached yet the 'inotify' line will be omitted.
1702
1703        For fanotify files the format is
1704
1705        pos:    0
1706        flags:  02
1707        fanotify flags:10 event-flags:0
1708        fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
1709        fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
1710
1711        where fanotify 'flags' and 'event-flags' are values used in fanotify_init
1712        call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
1713        flags associated with mark which are tracked separately from events
1714        mask. 'ino', 'sdev' are target inode and device, 'mask' is the events
1715        mask and 'ignored_mask' is the mask of events which are to be ignored.
1716        All in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
1717        does provide information about flags and mask used in fanotify_mark
1718        call [see fsnotify manpage for details].
1719
1720        While the first three lines are mandatory and always printed, the rest is
1721        optional and may be omitted if no marks created yet.
1722
1723
1724------------------------------------------------------------------------------
1725Configuring procfs
1726------------------------------------------------------------------------------
1727
17284.1     Mount options
1729---------------------
1730
1731The following mount options are supported:
1732
1733        hidepid=        Set /proc/<pid>/ access mode.
1734        gid=            Set the group authorized to learn processes information.
1735
1736hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
1737(default).
1738
1739hidepid=1 means users may not access any /proc/<pid>/ directories but their
1740own.  Sensitive files like cmdline, sched*, status are now protected against
1741other users.  This makes it impossible to learn whether any user runs
1742specific program (given the program doesn't reveal itself by its behaviour).
1743As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users,
1744poorly written programs passing sensitive information via program arguments are
1745now protected against local eavesdroppers.
1746
1747hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other
1748users.  It doesn't mean that it hides a fact whether a process with a specific
1749pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"),
1750but it hides process' uid and gid, which may be learned by stat()'ing
1751/proc/<pid>/ otherwise.  It greatly complicates an intruder's task of gathering
1752information about running processes, whether some daemon runs with elevated
1753privileges, whether other user runs some sensitive program, whether other users
1754run any program at all, etc.
1755
1756gid= defines a group authorized to learn processes information otherwise
1757prohibited by hidepid=.  If you use some daemon like identd which needs to learn
1758information about processes information, just add identd to this group.
1759