Version:  2.0.40 2.2.26 2.4.37 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5

Linux/Documentation/filesystems/proc.txt

  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 
  7 2.4.x update      Jorge Nerin <comandante@zaralinux.com>      November 14 2000
  8 move /proc/sys    Shen Feng <shen@cn.fujitsu.com>                 April 1 2009
  9 ------------------------------------------------------------------------------
 10 Version 1.3                                              Kernel version 2.2.12
 11                                               Kernel version 2.4.0-test11-pre4
 12 ------------------------------------------------------------------------------
 13 fixes/update part 1.1  Stefani Seibold <stefani@seibold.net>       June 9 2009
 14 
 15 Table 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   3.9   /proc/<pid>/map_files - Information about memory mapped files
 46 
 47   4     Configuring procfs
 48   4.1   Mount options
 49 
 50 ------------------------------------------------------------------------------
 51 Preface
 52 ------------------------------------------------------------------------------
 53 
 54 0.1 Introduction/Credits
 55 ------------------------
 56 
 57 This documentation is  part of a soon (or  so we hope) to be  released book on
 58 the SuSE  Linux distribution. As  there is  no complete documentation  for the
 59 /proc file system and we've used  many freely available sources to write these
 60 chapters, it  seems only fair  to give the work  back to the  Linux community.
 61 This work is  based on the 2.2.*  kernel version and the  upcoming 2.4.*. I'm
 62 afraid it's still far from complete, but we  hope it will be useful. As far as
 63 we know, it is the first 'all-in-one' document about the /proc file system. It
 64 is focused  on the Intel  x86 hardware,  so if you  are looking for  PPC, ARM,
 65 SPARC, AXP, etc., features, you probably  won't find what you are looking for.
 66 It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
 67 additions and patches  are welcome and will  be added to this  document if you
 68 mail them to Bodo.
 69 
 70 We'd like  to  thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
 71 other people for help compiling this documentation. We'd also like to extend a
 72 special thank  you to Andi Kleen for documentation, which we relied on heavily
 73 to create  this  document,  as well as the additional information he provided.
 74 Thanks to  everybody  else  who contributed source or docs to the Linux kernel
 75 and helped create a great piece of software... :)
 76 
 77 If you  have  any comments, corrections or additions, please don't hesitate to
 78 contact Bodo  Bauer  at  bb@ricochet.net.  We'll  be happy to add them to this
 79 document.
 80 
 81 The   latest   version    of   this   document   is    available   online   at
 82 http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html
 83 
 84 If  the above  direction does  not works  for you,  you could  try the  kernel
 85 mailing  list  at  linux-kernel@vger.kernel.org  and/or try  to  reach  me  at
 86 comandante@zaralinux.com.
 87 
 88 0.2 Legal Stuff
 89 ---------------
 90 
 91 We don't  guarantee  the  correctness  of this document, and if you come to us
 92 complaining about  how  you  screwed  up  your  system  because  of  incorrect
 93 documentation, we won't feel responsible...
 94 
 95 ------------------------------------------------------------------------------
 96 CHAPTER 1: COLLECTING SYSTEM INFORMATION
 97 ------------------------------------------------------------------------------
 98 
 99 ------------------------------------------------------------------------------
100 In This Chapter
101 ------------------------------------------------------------------------------
102 * Investigating  the  properties  of  the  pseudo  file  system  /proc and its
103   ability to provide information on the running Linux system
104 * Examining /proc's structure
105 * Uncovering  various  information  about the kernel and the processes running
106   on the system
107 ------------------------------------------------------------------------------
108 
109 
110 The proc  file  system acts as an interface to internal data structures in the
111 kernel. It  can  be  used to obtain information about the system and to change
112 certain kernel parameters at runtime (sysctl).
113 
114 First, we'll  take  a  look  at the read-only parts of /proc. In Chapter 2, we
115 show you how you can use /proc/sys to change settings.
116 
117 1.1 Process-Specific Subdirectories
118 -----------------------------------
119 
120 The directory  /proc  contains  (among other things) one subdirectory for each
121 process running on the system, which is named after the process ID (PID).
122 
123 The link  self  points  to  the  process reading the file system. Each process
124 subdirectory has the entries listed in Table 1-1.
125 
126 
127 Table 1-1: Process specific entries in /proc
128 ..............................................................................
129  File           Content
130  clear_refs     Clears page referenced bits shown in smaps output
131  cmdline        Command line arguments
132  cpu            Current and last cpu in which it was executed   (2.4)(smp)
133  cwd            Link to the current working directory
134  environ        Values of environment variables
135  exe            Link to the executable of this process
136  fd             Directory, which contains all file descriptors
137  maps           Memory maps to executables and library files    (2.4)
138  mem            Memory held by this process
139  root           Link to the root directory of this process
140  stat           Process status
141  statm          Process memory status information
142  status         Process status in human readable form
143  wchan          Present with CONFIG_KALLSYMS=y: it shows the kernel function
144                 symbol the task is blocked in - or "0" if not blocked.
145  pagemap        Page table
146  stack          Report full stack trace, enable via CONFIG_STACKTRACE
147  smaps          a extension based on maps, showing the memory consumption of
148                 each mapping and flags associated with it
149  numa_maps      an extension based on maps, showing the memory locality and
150                 binding policy as well as mem usage (in pages) of each mapping.
151 ..............................................................................
152 
153 For example, to get the status information of a process, all you have to do is
154 read the file /proc/PID/status:
155 
156   >cat /proc/self/status
157   Name:   cat
158   State:  R (running)
159   Tgid:   5452
160   Pid:    5452
161   PPid:   743
162   TracerPid:      0                                             (2.4)
163   Uid:    501     501     501     501
164   Gid:    100     100     100     100
165   FDSize: 256
166   Groups: 100 14 16
167   VmPeak:     5004 kB
168   VmSize:     5004 kB
169   VmLck:         0 kB
170   VmHWM:       476 kB
171   VmRSS:       476 kB
172   RssAnon:             352 kB
173   RssFile:             120 kB
174   RssShmem:              4 kB
175   VmData:      156 kB
176   VmStk:        88 kB
177   VmExe:        68 kB
178   VmLib:      1412 kB
179   VmPTE:        20 kb
180   VmSwap:        0 kB
181   HugetlbPages:          0 kB
182   Threads:        1
183   SigQ:   0/28578
184   SigPnd: 0000000000000000
185   ShdPnd: 0000000000000000
186   SigBlk: 0000000000000000
187   SigIgn: 0000000000000000
188   SigCgt: 0000000000000000
189   CapInh: 00000000fffffeff
190   CapPrm: 0000000000000000
191   CapEff: 0000000000000000
192   CapBnd: ffffffffffffffff
193   Seccomp:        0
194   voluntary_ctxt_switches:        0
195   nonvoluntary_ctxt_switches:     1
196 
197 This shows you nearly the same information you would get if you viewed it with
198 the ps  command.  In  fact,  ps  uses  the  proc  file  system  to  obtain its
199 information.  But you get a more detailed  view of the  process by reading the
200 file /proc/PID/status. It fields are described in table 1-2.
201 
202 The  statm  file  contains  more  detailed  information about the process
203 memory usage. Its seven fields are explained in Table 1-3.  The stat file
204 contains details information about the process itself.  Its fields are
205 explained in Table 1-4.
206 
207 (for SMP CONFIG users)
208 For making accounting scalable, RSS related information are handled in an
209 asynchronous manner and the value may not be very precise. To see a precise
210 snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
211 It's slow but very precise.
212 
213 Table 1-2: Contents of the status files (as of 4.1)
214 ..............................................................................
215  Field                       Content
216  Name                        filename of the executable
217  State                       state (R is running, S is sleeping, D is sleeping
218                              in an uninterruptible wait, Z is zombie,
219                              T is traced or stopped)
220  Tgid                        thread group ID
221  Ngid                        NUMA group ID (0 if none)
222  Pid                         process id
223  PPid                        process id of the parent process
224  TracerPid                   PID of process tracing this process (0 if not)
225  Uid                         Real, effective, saved set, and  file system UIDs
226  Gid                         Real, effective, saved set, and  file system GIDs
227  FDSize                      number of file descriptor slots currently allocated
228  Groups                      supplementary group list
229  NStgid                      descendant namespace thread group ID hierarchy
230  NSpid                       descendant namespace process ID hierarchy
231  NSpgid                      descendant namespace process group ID hierarchy
232  NSsid                       descendant namespace session ID hierarchy
233  VmPeak                      peak virtual memory size
234  VmSize                      total program size
235  VmLck                       locked memory size
236  VmHWM                       peak resident set size ("high water mark")
237  VmRSS                       size of memory portions. It contains the three
238                              following parts (VmRSS = RssAnon + RssFile + RssShmem)
239  RssAnon                     size of resident anonymous memory
240  RssFile                     size of resident file mappings
241  RssShmem                    size of resident shmem memory (includes SysV shm,
242                              mapping of tmpfs and shared anonymous mappings)
243  VmData                      size of private data segments
244  VmStk                       size of stack segments
245  VmExe                       size of text segment
246  VmLib                       size of shared library code
247  VmPTE                       size of page table entries
248  VmPMD                       size of second level page tables
249  VmSwap                      amount of swap used by anonymous private data
250                              (shmem swap usage is not included)
251  HugetlbPages                size of hugetlb memory portions
252  Threads                     number of threads
253  SigQ                        number of signals queued/max. number for queue
254  SigPnd                      bitmap of pending signals for the thread
255  ShdPnd                      bitmap of shared pending signals for the process
256  SigBlk                      bitmap of blocked signals
257  SigIgn                      bitmap of ignored signals
258  SigCgt                      bitmap of caught signals
259  CapInh                      bitmap of inheritable capabilities
260  CapPrm                      bitmap of permitted capabilities
261  CapEff                      bitmap of effective capabilities
262  CapBnd                      bitmap of capabilities bounding set
263  Seccomp                     seccomp mode, like prctl(PR_GET_SECCOMP, ...)
264  Cpus_allowed                mask of CPUs on which this process may run
265  Cpus_allowed_list           Same as previous, but in "list format"
266  Mems_allowed                mask of memory nodes allowed to this process
267  Mems_allowed_list           Same as previous, but in "list format"
268  voluntary_ctxt_switches     number of voluntary context switches
269  nonvoluntary_ctxt_switches  number of non voluntary context switches
270 ..............................................................................
271 
272 Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
273 ..............................................................................
274  Field    Content
275  size     total program size (pages)            (same as VmSize in status)
276  resident size of memory portions (pages)       (same as VmRSS in status)
277  shared   number of pages that are shared       (i.e. backed by a file, same
278                                                 as RssFile+RssShmem in status)
279  trs      number of pages that are 'code'       (not including libs; broken,
280                                                         includes data segment)
281  lrs      number of pages of library            (always 0 on 2.6)
282  drs      number of pages of data/stack         (including libs; broken,
283                                                         includes library text)
284  dt       number of dirty pages                 (always 0 on 2.6)
285 ..............................................................................
286 
287 
288 Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
289 ..............................................................................
290  Field          Content
291   pid           process id
292   tcomm         filename of the executable
293   state         state (R is running, S is sleeping, D is sleeping in an
294                 uninterruptible wait, Z is zombie, T is traced or stopped)
295   ppid          process id of the parent process
296   pgrp          pgrp of the process
297   sid           session id
298   tty_nr        tty the process uses
299   tty_pgrp      pgrp of the tty
300   flags         task flags
301   min_flt       number of minor faults
302   cmin_flt      number of minor faults with child's
303   maj_flt       number of major faults
304   cmaj_flt      number of major faults with child's
305   utime         user mode jiffies
306   stime         kernel mode jiffies
307   cutime        user mode jiffies with child's
308   cstime        kernel mode jiffies with child's
309   priority      priority level
310   nice          nice level
311   num_threads   number of threads
312   it_real_value (obsolete, always 0)
313   start_time    time the process started after system boot
314   vsize         virtual memory size
315   rss           resident set memory size
316   rsslim        current limit in bytes on the rss
317   start_code    address above which program text can run
318   end_code      address below which program text can run
319   start_stack   address of the start of the main process stack
320   esp           current value of ESP
321   eip           current value of EIP
322   pending       bitmap of pending signals
323   blocked       bitmap of blocked signals
324   sigign        bitmap of ignored signals
325   sigcatch      bitmap of caught signals
326   0             (place holder, used to be the wchan address, use /proc/PID/wchan instead)
327   0             (place holder)
328   0             (place holder)
329   exit_signal   signal to send to parent thread on exit
330   task_cpu      which CPU the task is scheduled on
331   rt_priority   realtime priority
332   policy        scheduling policy (man sched_setscheduler)
333   blkio_ticks   time spent waiting for block IO
334   gtime         guest time of the task in jiffies
335   cgtime        guest time of the task children in jiffies
336   start_data    address above which program data+bss is placed
337   end_data      address below which program data+bss is placed
338   start_brk     address above which program heap can be expanded with brk()
339   arg_start     address above which program command line is placed
340   arg_end       address below which program command line is placed
341   env_start     address above which program environment is placed
342   env_end       address below which program environment is placed
343   exit_code     the thread's exit_code in the form reported by the waitpid system call
344 ..............................................................................
345 
346 The /proc/PID/maps file containing the currently mapped memory regions and
347 their access permissions.
348 
349 The format is:
350 
351 address           perms offset  dev   inode      pathname
352 
353 08048000-08049000 r-xp 00000000 03:00 8312       /opt/test
354 08049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
355 0804a000-0806b000 rw-p 00000000 00:00 0          [heap]
356 a7cb1000-a7cb2000 ---p 00000000 00:00 0
357 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
358 a7eb2000-a7eb3000 ---p 00000000 00:00 0
359 a7eb3000-a7ed5000 rw-p 00000000 00:00 0
360 a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/libc.so.6
361 a8008000-a800a000 r--p 00133000 03:00 4222       /lib/libc.so.6
362 a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/libc.so.6
363 a800b000-a800e000 rw-p 00000000 00:00 0
364 a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/libpthread.so.0
365 a8022000-a8023000 r--p 00013000 03:00 14462      /lib/libpthread.so.0
366 a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/libpthread.so.0
367 a8024000-a8027000 rw-p 00000000 00:00 0
368 a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/ld-linux.so.2
369 a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/ld-linux.so.2
370 a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/ld-linux.so.2
371 aff35000-aff4a000 rw-p 00000000 00:00 0          [stack]
372 ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
373 
374 where "address" is the address space in the process that it occupies, "perms"
375 is a set of permissions:
376 
377  r = read
378  w = write
379  x = execute
380  s = shared
381  p = private (copy on write)
382 
383 "offset" is the offset into the mapping, "dev" is the device (major:minor), and
384 "inode" is the inode  on that device.  0 indicates that  no inode is associated
385 with the memory region, as the case would be with BSS (uninitialized data).
386 The "pathname" shows the name associated file for this mapping.  If the mapping
387 is not associated with a file:
388 
389  [heap]                   = the heap of the program
390  [stack]                  = the stack of the main process
391  [vdso]                   = the "virtual dynamic shared object",
392                             the kernel system call handler
393 
394  or if empty, the mapping is anonymous.
395 
396 The /proc/PID/task/TID/maps is a view of the virtual memory from the viewpoint
397 of the individual tasks of a process. In this file you will see a mapping marked
398 as [stack] if that task sees it as a stack. Hence, for the example above, the
399 task-level map, i.e. /proc/PID/task/TID/maps for thread 1001 will look like this:
400 
401 08048000-08049000 r-xp 00000000 03:00 8312       /opt/test
402 08049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
403 0804a000-0806b000 rw-p 00000000 00:00 0          [heap]
404 a7cb1000-a7cb2000 ---p 00000000 00:00 0
405 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
406 a7eb2000-a7eb3000 ---p 00000000 00:00 0
407 a7eb3000-a7ed5000 rw-p 00000000 00:00 0          [stack]
408 a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/libc.so.6
409 a8008000-a800a000 r--p 00133000 03:00 4222       /lib/libc.so.6
410 a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/libc.so.6
411 a800b000-a800e000 rw-p 00000000 00:00 0
412 a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/libpthread.so.0
413 a8022000-a8023000 r--p 00013000 03:00 14462      /lib/libpthread.so.0
414 a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/libpthread.so.0
415 a8024000-a8027000 rw-p 00000000 00:00 0
416 a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/ld-linux.so.2
417 a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/ld-linux.so.2
418 a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/ld-linux.so.2
419 aff35000-aff4a000 rw-p 00000000 00:00 0
420 ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
421 
422 The /proc/PID/smaps is an extension based on maps, showing the memory
423 consumption for each of the process's mappings. For each of mappings there
424 is a series of lines such as the following:
425 
426 08048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
427 Size:               1084 kB
428 Rss:                 892 kB
429 Pss:                 374 kB
430 Shared_Clean:        892 kB
431 Shared_Dirty:          0 kB
432 Private_Clean:         0 kB
433 Private_Dirty:         0 kB
434 Referenced:          892 kB
435 Anonymous:             0 kB
436 AnonHugePages:         0 kB
437 Shared_Hugetlb:        0 kB
438 Private_Hugetlb:       0 kB
439 Swap:                  0 kB
440 SwapPss:               0 kB
441 KernelPageSize:        4 kB
442 MMUPageSize:           4 kB
443 Locked:                0 kB
444 VmFlags: rd ex mr mw me dw
445 
446 the first of these lines shows the same information as is displayed for the
447 mapping in /proc/PID/maps.  The remaining lines show the size of the mapping
448 (size), the amount of the mapping that is currently resident in RAM (RSS), the
449 process' proportional share of this mapping (PSS), the number of clean and
450 dirty private pages in the mapping.
451 
452 The "proportional set size" (PSS) of a process is the count of pages it has
453 in memory, where each page is divided by the number of processes sharing it.
454 So if a process has 1000 pages all to itself, and 1000 shared with one other
455 process, its PSS will be 1500.
456 Note that even a page which is part of a MAP_SHARED mapping, but has only
457 a single pte mapped, i.e.  is currently used by only one process, is accounted
458 as private and not as shared.
459 "Referenced" indicates the amount of memory currently marked as referenced or
460 accessed.
461 "Anonymous" shows the amount of memory that does not belong to any file.  Even
462 a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
463 and a page is modified, the file page is replaced by a private anonymous copy.
464 "AnonHugePages" shows the ammount of memory backed by transparent hugepage.
465 "Shared_Hugetlb" and "Private_Hugetlb" show the ammounts of memory backed by
466 hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical
467 reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field.
468 "Swap" shows how much would-be-anonymous memory is also used, but out on swap.
469 For shmem mappings, "Swap" includes also the size of the mapped (and not
470 replaced by copy-on-write) part of the underlying shmem object out on swap.
471 "SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
472 does not take into account swapped out page of underlying shmem objects.
473 "Locked" indicates whether the mapping is locked in memory or not.
474 
475 "VmFlags" field deserves a separate description. This member represents the kernel
476 flags associated with the particular virtual memory area in two letter encoded
477 manner. The codes are the following:
478     rd  - readable
479     wr  - writeable
480     ex  - executable
481     sh  - shared
482     mr  - may read
483     mw  - may write
484     me  - may execute
485     ms  - may share
486     gd  - stack segment growns down
487     pf  - pure PFN range
488     dw  - disabled write to the mapped file
489     lo  - pages are locked in memory
490     io  - memory mapped I/O area
491     sr  - sequential read advise provided
492     rr  - random read advise provided
493     dc  - do not copy area on fork
494     de  - do not expand area on remapping
495     ac  - area is accountable
496     nr  - swap space is not reserved for the area
497     ht  - area uses huge tlb pages
498     ar  - architecture specific flag
499     dd  - do not include area into core dump
500     sd  - soft-dirty flag
501     mm  - mixed map area
502     hg  - huge page advise flag
503     nh  - no-huge page advise flag
504     mg  - mergable advise flag
505 
506 Note that there is no guarantee that every flag and associated mnemonic will
507 be present in all further kernel releases. Things get changed, the flags may
508 be vanished or the reverse -- new added.
509 
510 This file is only present if the CONFIG_MMU kernel configuration option is
511 enabled.
512 
513 The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
514 bits on both physical and virtual pages associated with a process, and the
515 soft-dirty bit on pte (see Documentation/vm/soft-dirty.txt for details).
516 To clear the bits for all the pages associated with the process
517     > echo 1 > /proc/PID/clear_refs
518 
519 To clear the bits for the anonymous pages associated with the process
520     > echo 2 > /proc/PID/clear_refs
521 
522 To clear the bits for the file mapped pages associated with the process
523     > echo 3 > /proc/PID/clear_refs
524 
525 To clear the soft-dirty bit
526     > echo 4 > /proc/PID/clear_refs
527 
528 To reset the peak resident set size ("high water mark") to the process's
529 current value:
530     > echo 5 > /proc/PID/clear_refs
531 
532 Any other value written to /proc/PID/clear_refs will have no effect.
533 
534 The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
535 using /proc/kpageflags and number of times a page is mapped using
536 /proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt.
537 
538 The /proc/pid/numa_maps is an extension based on maps, showing the memory
539 locality and binding policy, as well as the memory usage (in pages) of
540 each mapping. The output follows a general format where mapping details get
541 summarized separated by blank spaces, one mapping per each file line:
542 
543 address   policy    mapping details
544 
545 00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
546 00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
547 3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
548 320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
549 3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
550 3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
551 3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
552 320698b000 default file=/lib64/libc-2.12.so
553 3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4
554 3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
555 3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
556 7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
557 7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
558 7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
559 7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
560 7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4
561 
562 Where:
563 "address" is the starting address for the mapping;
564 "policy" reports the NUMA memory policy set for the mapping (see vm/numa_memory_policy.txt);
565 "mapping details" summarizes mapping data such as mapping type, page usage counters,
566 node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
567 size, in KB, that is backing the mapping up.
568 
569 1.2 Kernel data
570 ---------------
571 
572 Similar to  the  process entries, the kernel data files give information about
573 the running kernel. The files used to obtain this information are contained in
574 /proc and  are  listed  in Table 1-5. Not all of these will be present in your
575 system. It  depends  on the kernel configuration and the loaded modules, which
576 files are there, and which are missing.
577 
578 Table 1-5: Kernel info in /proc
579 ..............................................................................
580  File        Content                                           
581  apm         Advanced power management info                    
582  buddyinfo   Kernel memory allocator information (see text)     (2.5)
583  bus         Directory containing bus specific information     
584  cmdline     Kernel command line                               
585  cpuinfo     Info about the CPU                                
586  devices     Available devices (block and character)           
587  dma         Used DMS channels                                 
588  filesystems Supported filesystems                             
589  driver      Various drivers grouped here, currently rtc (2.4)
590  execdomains Execdomains, related to security                   (2.4)
591  fb          Frame Buffer devices                               (2.4)
592  fs          File system parameters, currently nfs/exports      (2.4)
593  ide         Directory containing info about the IDE subsystem 
594  interrupts  Interrupt usage                                   
595  iomem       Memory map                                         (2.4)
596  ioports     I/O port usage                                    
597  irq         Masks for irq to cpu affinity                      (2.4)(smp?)
598  isapnp      ISA PnP (Plug&Play) Info                           (2.4)
599  kcore       Kernel core image (can be ELF or A.OUT(deprecated in 2.4))   
600  kmsg        Kernel messages                                   
601  ksyms       Kernel symbol table                               
602  loadavg     Load average of last 1, 5 & 15 minutes                
603  locks       Kernel locks                                      
604  meminfo     Memory info                                       
605  misc        Miscellaneous                                     
606  modules     List of loaded modules                            
607  mounts      Mounted filesystems                               
608  net         Networking info (see text)                        
609  pagetypeinfo Additional page allocator information (see text)  (2.5)
610  partitions  Table of partitions known to the system           
611  pci         Deprecated info of PCI bus (new way -> /proc/bus/pci/,
612              decoupled by lspci                                 (2.4)
613  rtc         Real time clock                                   
614  scsi        SCSI info (see text)                              
615  slabinfo    Slab pool info                                    
616  softirqs    softirq usage
617  stat        Overall statistics                                
618  swaps       Swap space utilization                            
619  sys         See chapter 2                                     
620  sysvipc     Info of SysVIPC Resources (msg, sem, shm)          (2.4)
621  tty         Info of tty drivers
622  uptime      Wall clock since boot, combined idle time of all cpus
623  version     Kernel version                                    
624  video       bttv info of video resources                       (2.4)
625  vmallocinfo Show vmalloced areas
626 ..............................................................................
627 
628 You can,  for  example,  check  which interrupts are currently in use and what
629 they are used for by looking in the file /proc/interrupts:
630 
631   > cat /proc/interrupts 
632              CPU0        
633     0:    8728810          XT-PIC  timer 
634     1:        895          XT-PIC  keyboard 
635     2:          0          XT-PIC  cascade 
636     3:     531695          XT-PIC  aha152x 
637     4:    2014133          XT-PIC  serial 
638     5:      44401          XT-PIC  pcnet_cs 
639     8:          2          XT-PIC  rtc 
640    11:          8          XT-PIC  i82365 
641    12:     182918          XT-PIC  PS/2 Mouse 
642    13:          1          XT-PIC  fpu 
643    14:    1232265          XT-PIC  ide0 
644    15:          7          XT-PIC  ide1 
645   NMI:          0 
646 
647 In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
648 output of a SMP machine):
649 
650   > cat /proc/interrupts 
651 
652              CPU0       CPU1       
653     0:    1243498    1214548    IO-APIC-edge  timer
654     1:       8949       8958    IO-APIC-edge  keyboard
655     2:          0          0          XT-PIC  cascade
656     5:      11286      10161    IO-APIC-edge  soundblaster
657     8:          1          0    IO-APIC-edge  rtc
658     9:      27422      27407    IO-APIC-edge  3c503
659    12:     113645     113873    IO-APIC-edge  PS/2 Mouse
660    13:          0          0          XT-PIC  fpu
661    14:      22491      24012    IO-APIC-edge  ide0
662    15:       2183       2415    IO-APIC-edge  ide1
663    17:      30564      30414   IO-APIC-level  eth0
664    18:        177        164   IO-APIC-level  bttv
665   NMI:    2457961    2457959 
666   LOC:    2457882    2457881 
667   ERR:       2155
668 
669 NMI is incremented in this case because every timer interrupt generates a NMI
670 (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
671 
672 LOC is the local interrupt counter of the internal APIC of every CPU.
673 
674 ERR is incremented in the case of errors in the IO-APIC bus (the bus that
675 connects the CPUs in a SMP system. This means that an error has been detected,
676 the IO-APIC automatically retry the transmission, so it should not be a big
677 problem, but you should read the SMP-FAQ.
678 
679 In 2.6.2* /proc/interrupts was expanded again.  This time the goal was for
680 /proc/interrupts to display every IRQ vector in use by the system, not
681 just those considered 'most important'.  The new vectors are:
682 
683   THR -- interrupt raised when a machine check threshold counter
684   (typically counting ECC corrected errors of memory or cache) exceeds
685   a configurable threshold.  Only available on some systems.
686 
687   TRM -- a thermal event interrupt occurs when a temperature threshold
688   has been exceeded for the CPU.  This interrupt may also be generated
689   when the temperature drops back to normal.
690 
691   SPU -- a spurious interrupt is some interrupt that was raised then lowered
692   by some IO device before it could be fully processed by the APIC.  Hence
693   the APIC sees the interrupt but does not know what device it came from.
694   For this case the APIC will generate the interrupt with a IRQ vector
695   of 0xff. This might also be generated by chipset bugs.
696 
697   RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
698   sent from one CPU to another per the needs of the OS.  Typically,
699   their statistics are used by kernel developers and interested users to
700   determine the occurrence of interrupts of the given type.
701 
702 The above IRQ vectors are displayed only when relevant.  For example,
703 the threshold vector does not exist on x86_64 platforms.  Others are
704 suppressed when the system is a uniprocessor.  As of this writing, only
705 i386 and x86_64 platforms support the new IRQ vector displays.
706 
707 Of some interest is the introduction of the /proc/irq directory to 2.4.
708 It could be used to set IRQ to CPU affinity, this means that you can "hook" an
709 IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
710 irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
711 prof_cpu_mask.
712 
713 For example 
714   > ls /proc/irq/
715   0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
716   1  11  13  15  17  19  3  5  7  9  default_smp_affinity
717   > ls /proc/irq/0/
718   smp_affinity
719 
720 smp_affinity is a bitmask, in which you can specify which CPUs can handle the
721 IRQ, you can set it by doing:
722 
723   > echo 1 > /proc/irq/10/smp_affinity
724 
725 This means that only the first CPU will handle the IRQ, but you can also echo
726 5 which means that only the first and fourth CPU can handle the IRQ.
727 
728 The contents of each smp_affinity file is the same by default:
729 
730   > cat /proc/irq/0/smp_affinity
731   ffffffff
732 
733 There is an alternate interface, smp_affinity_list which allows specifying
734 a cpu range instead of a bitmask:
735 
736   > cat /proc/irq/0/smp_affinity_list
737   1024-1031
738 
739 The default_smp_affinity mask applies to all non-active IRQs, which are the
740 IRQs which have not yet been allocated/activated, and hence which lack a
741 /proc/irq/[0-9]* directory.
742 
743 The node file on an SMP system shows the node to which the device using the IRQ
744 reports itself as being attached. This hardware locality information does not
745 include information about any possible driver locality preference.
746 
747 prof_cpu_mask specifies which CPUs are to be profiled by the system wide
748 profiler. Default value is ffffffff (all cpus if there are only 32 of them).
749 
750 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
751 between all the CPUs which are allowed to handle it. As usual the kernel has
752 more info than you and does a better job than you, so the defaults are the
753 best choice for almost everyone.  [Note this applies only to those IO-APIC's
754 that support "Round Robin" interrupt distribution.]
755 
756 There are  three  more  important subdirectories in /proc: net, scsi, and sys.
757 The general  rule  is  that  the  contents,  or  even  the  existence of these
758 directories, depend  on your kernel configuration. If SCSI is not enabled, the
759 directory scsi  may  not  exist. The same is true with the net, which is there
760 only when networking support is present in the running kernel.
761 
762 The slabinfo  file  gives  information  about  memory usage at the slab level.
763 Linux uses  slab  pools for memory management above page level in version 2.2.
764 Commonly used  objects  have  their  own  slab  pool (such as network buffers,
765 directory cache, and so on).
766 
767 ..............................................................................
768 
769 > cat /proc/buddyinfo
770 
771 Node 0, zone      DMA      0      4      5      4      4      3 ...
772 Node 0, zone   Normal      1      0      0      1    101      8 ...
773 Node 0, zone  HighMem      2      0      0      1      1      0 ...
774 
775 External fragmentation is a problem under some workloads, and buddyinfo is a
776 useful tool for helping diagnose these problems.  Buddyinfo will give you a 
777 clue as to how big an area you can safely allocate, or why a previous
778 allocation failed.
779 
780 Each column represents the number of pages of a certain order which are 
781 available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in 
782 ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE 
783 available in ZONE_NORMAL, etc... 
784 
785 More information relevant to external fragmentation can be found in
786 pagetypeinfo.
787 
788 > cat /proc/pagetypeinfo
789 Page block order: 9
790 Pages per block:  512
791 
792 Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
793 Node    0, zone      DMA, type    Unmovable      0      0      0      1      1      1      1      1      1      1      0
794 Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0
795 Node    0, zone      DMA, type      Movable      1      1      2      1      2      1      1      0      1      0      2
796 Node    0, zone      DMA, type      Reserve      0      0      0      0      0      0      0      0      0      1      0
797 Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
798 Node    0, zone    DMA32, type    Unmovable    103     54     77      1      1      1     11      8      7      1      9
799 Node    0, zone    DMA32, type  Reclaimable      0      0      2      1      0      0      0      0      1      0      0
800 Node    0, zone    DMA32, type      Movable    169    152    113     91     77     54     39     13      6      1    452
801 Node    0, zone    DMA32, type      Reserve      1      2      2      2      2      0      1      1      1      1      0
802 Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
803 
804 Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate
805 Node 0, zone      DMA            2            0            5            1            0
806 Node 0, zone    DMA32           41            6          967            2            0
807 
808 Fragmentation avoidance in the kernel works by grouping pages of different
809 migrate types into the same contiguous regions of memory called page blocks.
810 A page block is typically the size of the default hugepage size e.g. 2MB on
811 X86-64. By keeping pages grouped based on their ability to move, the kernel
812 can reclaim pages within a page block to satisfy a high-order allocation.
813 
814 The pagetypinfo begins with information on the size of a page block. It
815 then gives the same type of information as buddyinfo except broken down
816 by migrate-type and finishes with details on how many page blocks of each
817 type exist.
818 
819 If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
820 from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can
821 make an estimate of the likely number of huge pages that can be allocated
822 at a given point in time. All the "Movable" blocks should be allocatable
823 unless memory has been mlock()'d. Some of the Reclaimable blocks should
824 also be allocatable although a lot of filesystem metadata may have to be
825 reclaimed to achieve this.
826 
827 ..............................................................................
828 
829 meminfo:
830 
831 Provides information about distribution and utilization of memory.  This
832 varies by architecture and compile options.  The following is from a
833 16GB PIII, which has highmem enabled.  You may not have all of these fields.
834 
835 > cat /proc/meminfo
836 
837 MemTotal:     16344972 kB
838 MemFree:      13634064 kB
839 MemAvailable: 14836172 kB
840 Buffers:          3656 kB
841 Cached:        1195708 kB
842 SwapCached:          0 kB
843 Active:         891636 kB
844 Inactive:      1077224 kB
845 HighTotal:    15597528 kB
846 HighFree:     13629632 kB
847 LowTotal:       747444 kB
848 LowFree:          4432 kB
849 SwapTotal:           0 kB
850 SwapFree:            0 kB
851 Dirty:             968 kB
852 Writeback:           0 kB
853 AnonPages:      861800 kB
854 Mapped:         280372 kB
855 Shmem:             644 kB
856 Slab:           284364 kB
857 SReclaimable:   159856 kB
858 SUnreclaim:     124508 kB
859 PageTables:      24448 kB
860 NFS_Unstable:        0 kB
861 Bounce:              0 kB
862 WritebackTmp:        0 kB
863 CommitLimit:   7669796 kB
864 Committed_AS:   100056 kB
865 VmallocTotal:   112216 kB
866 VmallocUsed:       428 kB
867 VmallocChunk:   111088 kB
868 AnonHugePages:   49152 kB
869 
870     MemTotal: Total usable ram (i.e. physical ram minus a few reserved
871               bits and the kernel binary code)
872      MemFree: The sum of LowFree+HighFree
873 MemAvailable: An estimate of how much memory is available for starting new
874               applications, without swapping. Calculated from MemFree,
875               SReclaimable, the size of the file LRU lists, and the low
876               watermarks in each zone.
877               The estimate takes into account that the system needs some
878               page cache to function well, and that not all reclaimable
879               slab will be reclaimable, due to items being in use. The
880               impact of those factors will vary from system to system.
881      Buffers: Relatively temporary storage for raw disk blocks
882               shouldn't get tremendously large (20MB or so)
883       Cached: in-memory cache for files read from the disk (the
884               pagecache).  Doesn't include SwapCached
885   SwapCached: Memory that once was swapped out, is swapped back in but
886               still also is in the swapfile (if memory is needed it
887               doesn't need to be swapped out AGAIN because it is already
888               in the swapfile. This saves I/O)
889       Active: Memory that has been used more recently and usually not
890               reclaimed unless absolutely necessary.
891     Inactive: Memory which has been less recently used.  It is more
892               eligible to be reclaimed for other purposes
893    HighTotal:
894     HighFree: Highmem is all memory above ~860MB of physical memory
895               Highmem areas are for use by userspace programs, or
896               for the pagecache.  The kernel must use tricks to access
897               this memory, making it slower to access than lowmem.
898     LowTotal:
899      LowFree: Lowmem is memory which can be used for everything that
900               highmem can be used for, but it is also available for the
901               kernel's use for its own data structures.  Among many
902               other things, it is where everything from the Slab is
903               allocated.  Bad things happen when you're out of lowmem.
904    SwapTotal: total amount of swap space available
905     SwapFree: Memory which has been evicted from RAM, and is temporarily
906               on the disk
907        Dirty: Memory which is waiting to get written back to the disk
908    Writeback: Memory which is actively being written back to the disk
909    AnonPages: Non-file backed pages mapped into userspace page tables
910 AnonHugePages: Non-file backed huge pages mapped into userspace page tables
911       Mapped: files which have been mmaped, such as libraries
912        Shmem: Total memory used by shared memory (shmem) and tmpfs
913         Slab: in-kernel data structures cache
914 SReclaimable: Part of Slab, that might be reclaimed, such as caches
915   SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
916   PageTables: amount of memory dedicated to the lowest level of page
917               tables.
918 NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
919               storage
920       Bounce: Memory used for block device "bounce buffers"
921 WritebackTmp: Memory used by FUSE for temporary writeback buffers
922  CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
923               this is the total amount of  memory currently available to
924               be allocated on the system. This limit is only adhered to
925               if strict overcommit accounting is enabled (mode 2 in
926               'vm.overcommit_memory').
927               The CommitLimit is calculated with the following formula:
928               CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
929                              overcommit_ratio / 100 + [total swap pages]
930               For example, on a system with 1G of physical RAM and 7G
931               of swap with a `vm.overcommit_ratio` of 30 it would
932               yield a CommitLimit of 7.3G.
933               For more details, see the memory overcommit documentation
934               in vm/overcommit-accounting.
935 Committed_AS: The amount of memory presently allocated on the system.
936               The committed memory is a sum of all of the memory which
937               has been allocated by processes, even if it has not been
938               "used" by them as of yet. A process which malloc()'s 1G
939               of memory, but only touches 300M of it will show up as
940               using 1G. This 1G is memory which has been "committed" to
941               by the VM and can be used at any time by the allocating
942               application. With strict overcommit enabled on the system
943               (mode 2 in 'vm.overcommit_memory'),allocations which would
944               exceed the CommitLimit (detailed above) will not be permitted.
945               This is useful if one needs to guarantee that processes will
946               not fail due to lack of memory once that memory has been
947               successfully allocated.
948 VmallocTotal: total size of vmalloc memory area
949  VmallocUsed: amount of vmalloc area which is used
950 VmallocChunk: largest contiguous block of vmalloc area which is free
951 
952 ..............................................................................
953 
954 vmallocinfo:
955 
956 Provides information about vmalloced/vmaped areas. One line per area,
957 containing the virtual address range of the area, size in bytes,
958 caller information of the creator, and optional information depending
959 on the kind of area :
960 
961  pages=nr    number of pages
962  phys=addr   if a physical address was specified
963  ioremap     I/O mapping (ioremap() and friends)
964  vmalloc     vmalloc() area
965  vmap        vmap()ed pages
966  user        VM_USERMAP area
967  vpages      buffer for pages pointers was vmalloced (huge area)
968  N<node>=nr  (Only on NUMA kernels)
969              Number of pages allocated on memory node <node>
970 
971 > cat /proc/vmallocinfo
972 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
973   /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
974 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
975   /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
976 0xffffc20000302000-0xffffc20000304000    8192 acpi_tb_verify_table+0x21/0x4f...
977   phys=7fee8000 ioremap
978 0xffffc20000304000-0xffffc20000307000   12288 acpi_tb_verify_table+0x21/0x4f...
979   phys=7fee7000 ioremap
980 0xffffc2000031d000-0xffffc2000031f000    8192 init_vdso_vars+0x112/0x210
981 0xffffc2000031f000-0xffffc2000032b000   49152 cramfs_uncompress_init+0x2e ...
982   /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
983 0xffffc2000033a000-0xffffc2000033d000   12288 sys_swapon+0x640/0xac0      ...
984   pages=2 vmalloc N1=2
985 0xffffc20000347000-0xffffc2000034c000   20480 xt_alloc_table_info+0xfe ...
986   /0x130 [x_tables] pages=4 vmalloc N0=4
987 0xffffffffa0000000-0xffffffffa000f000   61440 sys_init_module+0xc27/0x1d00 ...
988    pages=14 vmalloc N2=14
989 0xffffffffa000f000-0xffffffffa0014000   20480 sys_init_module+0xc27/0x1d00 ...
990    pages=4 vmalloc N1=4
991 0xffffffffa0014000-0xffffffffa0017000   12288 sys_init_module+0xc27/0x1d00 ...
992    pages=2 vmalloc N1=2
993 0xffffffffa0017000-0xffffffffa0022000   45056 sys_init_module+0xc27/0x1d00 ...
994    pages=10 vmalloc N0=10
995 
996 ..............................................................................
997 
998 softirqs:
999 
1000 Provides counts of softirq handlers serviced since boot time, for each cpu.
1001 
1002 > cat /proc/softirqs
1003                 CPU0       CPU1       CPU2       CPU3
1004       HI:          0          0          0          0
1005    TIMER:      27166      27120      27097      27034
1006   NET_TX:          0          0          0         17
1007   NET_RX:         42          0          0         39
1008    BLOCK:          0          0        107       1121
1009  TASKLET:          0          0          0        290
1010    SCHED:      27035      26983      26971      26746
1011  HRTIMER:          0          0          0          0
1012      RCU:       1678       1769       2178       2250
1013 
1014 
1015 1.3 IDE devices in /proc/ide
1016 ----------------------------
1017 
1018 The subdirectory /proc/ide contains information about all IDE devices of which
1019 the kernel  is  aware.  There is one subdirectory for each IDE controller, the
1020 file drivers  and a link for each IDE device, pointing to the device directory
1021 in the controller specific subtree.
1022 
1023 The file  drivers  contains general information about the drivers used for the
1024 IDE devices:
1025 
1026   > cat /proc/ide/drivers
1027   ide-cdrom version 4.53
1028   ide-disk version 1.08
1029 
1030 More detailed  information  can  be  found  in  the  controller  specific
1031 subdirectories. These  are  named  ide0,  ide1  and  so  on.  Each  of  these
1032 directories contains the files shown in table 1-6.
1033 
1034 
1035 Table 1-6: IDE controller info in  /proc/ide/ide?
1036 ..............................................................................
1037  File    Content                                 
1038  channel IDE channel (0 or 1)                    
1039  config  Configuration (only for PCI/IDE bridge) 
1040  mate    Mate name                               
1041  model   Type/Chipset of IDE controller          
1042 ..............................................................................
1043 
1044 Each device  connected  to  a  controller  has  a separate subdirectory in the
1045 controllers directory.  The  files  listed in table 1-7 are contained in these
1046 directories.
1047 
1048 
1049 Table 1-7: IDE device information
1050 ..............................................................................
1051  File             Content                                    
1052  cache            The cache                                  
1053  capacity         Capacity of the medium (in 512Byte blocks) 
1054  driver           driver and version                         
1055  geometry         physical and logical geometry              
1056  identify         device identify block                      
1057  media            media type                                 
1058  model            device identifier                          
1059  settings         device setup                               
1060  smart_thresholds IDE disk management thresholds             
1061  smart_values     IDE disk management values                 
1062 ..............................................................................
1063 
1064 The most  interesting  file is settings. This file contains a nice overview of
1065 the drive parameters:
1066 
1067   # cat /proc/ide/ide0/hda/settings 
1068   name                    value           min             max             mode 
1069   ----                    -----           ---             ---             ---- 
1070   bios_cyl                526             0               65535           rw 
1071   bios_head               255             0               255             rw 
1072   bios_sect               63              0               63              rw 
1073   breada_readahead        4               0               127             rw 
1074   bswap                   0               0               1               r 
1075   file_readahead          72              0               2097151         rw 
1076   io_32bit                0               0               3               rw 
1077   keepsettings            0               0               1               rw 
1078   max_kb_per_request      122             1               127             rw 
1079   multcount               0               0               8               rw 
1080   nice1                   1               0               1               rw 
1081   nowerr                  0               0               1               rw 
1082   pio_mode                write-only      0               255             w 
1083   slow                    0               0               1               rw 
1084   unmaskirq               0               0               1               rw 
1085   using_dma               0               0               1               rw 
1086 
1087 
1088 1.4 Networking info in /proc/net
1089 --------------------------------
1090 
1091 The subdirectory  /proc/net  follows  the  usual  pattern. Table 1-8 shows the
1092 additional values  you  get  for  IP  version 6 if you configure the kernel to
1093 support this. Table 1-9 lists the files and their meaning.
1094 
1095 
1096 Table 1-8: IPv6 info in /proc/net
1097 ..............................................................................
1098  File       Content                                               
1099  udp6       UDP sockets (IPv6)                                    
1100  tcp6       TCP sockets (IPv6)                                    
1101  raw6       Raw device statistics (IPv6)                          
1102  igmp6      IP multicast addresses, which this host joined (IPv6) 
1103  if_inet6   List of IPv6 interface addresses                      
1104  ipv6_route Kernel routing table for IPv6                         
1105  rt6_stats  Global IPv6 routing tables statistics                 
1106  sockstat6  Socket statistics (IPv6)                              
1107  snmp6      Snmp data (IPv6)                                      
1108 ..............................................................................
1109 
1110 
1111 Table 1-9: Network info in /proc/net
1112 ..............................................................................
1113  File          Content                                                         
1114  arp           Kernel  ARP table                                               
1115  dev           network devices with statistics                                 
1116  dev_mcast     the Layer2 multicast groups a device is listening too
1117                (interface index, label, number of references, number of bound
1118                addresses). 
1119  dev_stat      network device status                                           
1120  ip_fwchains   Firewall chain linkage                                          
1121  ip_fwnames    Firewall chain names                                            
1122  ip_masq       Directory containing the masquerading tables                    
1123  ip_masquerade Major masquerading table                                        
1124  netstat       Network statistics                                              
1125  raw           raw device statistics                                           
1126  route         Kernel routing table                                            
1127  rpc           Directory containing rpc info                                   
1128  rt_cache      Routing cache                                                   
1129  snmp          SNMP data                                                       
1130  sockstat      Socket statistics                                               
1131  tcp           TCP  sockets                                                    
1132  udp           UDP sockets                                                     
1133  unix          UNIX domain sockets                                             
1134  wireless      Wireless interface data (Wavelan etc)                           
1135  igmp          IP multicast addresses, which this host joined                  
1136  psched        Global packet scheduler parameters.                             
1137  netlink       List of PF_NETLINK sockets                                      
1138  ip_mr_vifs    List of multicast virtual interfaces                            
1139  ip_mr_cache   List of multicast routing cache                                 
1140 ..............................................................................
1141 
1142 You can  use  this  information  to see which network devices are available in
1143 your system and how much traffic was routed over those devices:
1144 
1145   > cat /proc/net/dev 
1146   Inter-|Receive                                                   |[... 
1147    face |bytes    packets errs drop fifo frame compressed multicast|[... 
1148       lo:  908188   5596     0    0    0     0          0         0 [...         
1149     ppp0:15475140  20721   410    0    0   410          0         0 [...  
1150     eth0:  614530   7085     0    0    0     0          0         1 [... 
1151    
1152   ...] Transmit 
1153   ...] bytes    packets errs drop fifo colls carrier compressed 
1154   ...]  908188     5596    0    0    0     0       0          0 
1155   ...] 1375103    17405    0    0    0     0       0          0 
1156   ...] 1703981     5535    0    0    0     3       0          0 
1157 
1158 In addition, each Channel Bond interface has its own directory.  For
1159 example, the bond0 device will have a directory called /proc/net/bond0/.
1160 It will contain information that is specific to that bond, such as the
1161 current slaves of the bond, the link status of the slaves, and how
1162 many times the slaves link has failed.
1163 
1164 1.5 SCSI info
1165 -------------
1166 
1167 If you  have  a  SCSI  host adapter in your system, you'll find a subdirectory
1168 named after  the driver for this adapter in /proc/scsi. You'll also see a list
1169 of all recognized SCSI devices in /proc/scsi:
1170 
1171   >cat /proc/scsi/scsi 
1172   Attached devices: 
1173   Host: scsi0 Channel: 00 Id: 00 Lun: 00 
1174     Vendor: IBM      Model: DGHS09U          Rev: 03E0 
1175     Type:   Direct-Access                    ANSI SCSI revision: 03 
1176   Host: scsi0 Channel: 00 Id: 06 Lun: 00 
1177     Vendor: PIONEER  Model: CD-ROM DR-U06S   Rev: 1.04 
1178     Type:   CD-ROM                           ANSI SCSI revision: 02 
1179 
1180 
1181 The directory  named  after  the driver has one file for each adapter found in
1182 the system.  These  files  contain information about the controller, including
1183 the used  IRQ  and  the  IO  address range. The amount of information shown is
1184 dependent on  the adapter you use. The example shows the output for an Adaptec
1185 AHA-2940 SCSI adapter:
1186 
1187   > cat /proc/scsi/aic7xxx/0 
1188    
1189   Adaptec AIC7xxx driver version: 5.1.19/3.2.4 
1190   Compile Options: 
1191     TCQ Enabled By Default : Disabled 
1192     AIC7XXX_PROC_STATS     : Disabled 
1193     AIC7XXX_RESET_DELAY    : 5 
1194   Adapter Configuration: 
1195              SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter 
1196                              Ultra Wide Controller 
1197       PCI MMAPed I/O Base: 0xeb001000 
1198    Adapter SEEPROM Config: SEEPROM found and used. 
1199         Adaptec SCSI BIOS: Enabled 
1200                       IRQ: 10 
1201                      SCBs: Active 0, Max Active 2, 
1202                            Allocated 15, HW 16, Page 255 
1203                Interrupts: 160328 
1204         BIOS Control Word: 0x18b6 
1205      Adapter Control Word: 0x005b 
1206      Extended Translation: Enabled 
1207   Disconnect Enable Flags: 0xffff 
1208        Ultra Enable Flags: 0x0001 
1209    Tag Queue Enable Flags: 0x0000 
1210   Ordered Queue Tag Flags: 0x0000 
1211   Default Tag Queue Depth: 8 
1212       Tagged Queue By Device array for aic7xxx host instance 0: 
1213         {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} 
1214       Actual queue depth per device for aic7xxx host instance 0: 
1215         {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} 
1216   Statistics: 
1217   (scsi0:0:0:0) 
1218     Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 
1219     Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) 
1220     Total transfers 160151 (74577 reads and 85574 writes) 
1221   (scsi0:0:6:0) 
1222     Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 
1223     Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) 
1224     Total transfers 0 (0 reads and 0 writes) 
1225 
1226 
1227 1.6 Parallel port info in /proc/parport
1228 ---------------------------------------
1229 
1230 The directory  /proc/parport  contains information about the parallel ports of
1231 your system.  It  has  one  subdirectory  for  each port, named after the port
1232 number (0,1,2,...).
1233 
1234 These directories contain the four files shown in Table 1-10.
1235 
1236 
1237 Table 1-10: Files in /proc/parport
1238 ..............................................................................
1239  File      Content                                                             
1240  autoprobe Any IEEE-1284 device ID information that has been acquired.         
1241  devices   list of the device drivers using that port. A + will appear by the
1242            name of the device currently using the port (it might not appear
1243            against any). 
1244  hardware  Parallel port's base address, IRQ line and DMA channel.             
1245  irq       IRQ that parport is using for that port. This is in a separate
1246            file to allow you to alter it by writing a new value in (IRQ
1247            number or none). 
1248 ..............................................................................
1249 
1250 1.7 TTY info in /proc/tty
1251 -------------------------
1252 
1253 Information about  the  available  and actually used tty's can be found in the
1254 directory /proc/tty.You'll  find  entries  for drivers and line disciplines in
1255 this directory, as shown in Table 1-11.
1256 
1257 
1258 Table 1-11: Files in /proc/tty
1259 ..............................................................................
1260  File          Content                                        
1261  drivers       list of drivers and their usage                
1262  ldiscs        registered line disciplines                    
1263  driver/serial usage statistic and status of single tty lines 
1264 ..............................................................................
1265 
1266 To see  which  tty's  are  currently in use, you can simply look into the file
1267 /proc/tty/drivers:
1268 
1269   > cat /proc/tty/drivers 
1270   pty_slave            /dev/pts      136   0-255 pty:slave 
1271   pty_master           /dev/ptm      128   0-255 pty:master 
1272   pty_slave            /dev/ttyp       3   0-255 pty:slave 
1273   pty_master           /dev/pty        2   0-255 pty:master 
1274   serial               /dev/cua        5   64-67 serial:callout 
1275   serial               /dev/ttyS       4   64-67 serial 
1276   /dev/tty0            /dev/tty0       4       0 system:vtmaster 
1277   /dev/ptmx            /dev/ptmx       5       2 system 
1278   /dev/console         /dev/console    5       1 system:console 
1279   /dev/tty             /dev/tty        5       0 system:/dev/tty 
1280   unknown              /dev/tty        4    1-63 console 
1281 
1282 
1283 1.8 Miscellaneous kernel statistics in /proc/stat
1284 -------------------------------------------------
1285 
1286 Various pieces   of  information about  kernel activity  are  available in the
1287 /proc/stat file.  All  of  the numbers reported  in  this file are  aggregates
1288 since the system first booted.  For a quick look, simply cat the file:
1289 
1290   > cat /proc/stat
1291   cpu  2255 34 2290 22625563 6290 127 456 0 0 0
1292   cpu0 1132 34 1441 11311718 3675 127 438 0 0 0
1293   cpu1 1123 0 849 11313845 2614 0 18 0 0 0
1294   intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1295   ctxt 1990473
1296   btime 1062191376
1297   processes 2915
1298   procs_running 1
1299   procs_blocked 0
1300   softirq 183433 0 21755 12 39 1137 231 21459 2263
1301 
1302 The very first  "cpu" line aggregates the  numbers in all  of the other "cpuN"
1303 lines.  These numbers identify the amount of time the CPU has spent performing
1304 different kinds of work.  Time units are in USER_HZ (typically hundredths of a
1305 second).  The meanings of the columns are as follows, from left to right:
1306 
1307 - user: normal processes executing in user mode
1308 - nice: niced processes executing in user mode
1309 - system: processes executing in kernel mode
1310 - idle: twiddling thumbs
1311 - iowait: waiting for I/O to complete
1312 - irq: servicing interrupts
1313 - softirq: servicing softirqs
1314 - steal: involuntary wait
1315 - guest: running a normal guest
1316 - guest_nice: running a niced guest
1317 
1318 The "intr" line gives counts of interrupts  serviced since boot time, for each
1319 of the  possible system interrupts.   The first  column  is the  total of  all
1320 interrupts serviced  including  unnumbered  architecture specific  interrupts;
1321 each  subsequent column is the  total for that particular numbered interrupt.
1322 Unnumbered interrupts are not shown, only summed into the total.
1323 
1324 The "ctxt" line gives the total number of context switches across all CPUs.
1325 
1326 The "btime" line gives  the time at which the  system booted, in seconds since
1327 the Unix epoch.
1328 
1329 The "processes" line gives the number  of processes and threads created, which
1330 includes (but  is not limited  to) those  created by  calls to the  fork() and
1331 clone() system calls.
1332 
1333 The "procs_running" line gives the total number of threads that are
1334 running or ready to run (i.e., the total number of runnable threads).
1335 
1336 The   "procs_blocked" line gives  the  number of  processes currently blocked,
1337 waiting for I/O to complete.
1338 
1339 The "softirq" line gives counts of softirqs serviced since boot time, for each
1340 of the possible system softirqs. The first column is the total of all
1341 softirqs serviced; each subsequent column is the total for that particular
1342 softirq.
1343 
1344 
1345 1.9 Ext4 file system parameters
1346 -------------------------------
1347 
1348 Information about mounted ext4 file systems can be found in
1349 /proc/fs/ext4.  Each mounted filesystem will have a directory in
1350 /proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1351 /proc/fs/ext4/dm-0).   The files in each per-device directory are shown
1352 in Table 1-12, below.
1353 
1354 Table 1-12: Files in /proc/fs/ext4/<devname>
1355 ..............................................................................
1356  File            Content                                        
1357  mb_groups       details of multiblock allocator buddy cache of free blocks
1358 ..............................................................................
1359 
1360 2.0 /proc/consoles
1361 ------------------
1362 Shows registered system console lines.
1363 
1364 To see which character device lines are currently used for the system console
1365 /dev/console, you may simply look into the file /proc/consoles:
1366 
1367   > cat /proc/consoles
1368   tty0                 -WU (ECp)       4:7
1369   ttyS0                -W- (Ep)        4:64
1370 
1371 The columns are:
1372 
1373   device               name of the device
1374   operations           R = can do read operations
1375                        W = can do write operations
1376                        U = can do unblank
1377   flags                E = it is enabled
1378                        C = it is preferred console
1379                        B = it is primary boot console
1380                        p = it is used for printk buffer
1381                        b = it is not a TTY but a Braille device
1382                        a = it is safe to use when cpu is offline
1383   major:minor          major and minor number of the device separated by a colon
1384 
1385 ------------------------------------------------------------------------------
1386 Summary
1387 ------------------------------------------------------------------------------
1388 The /proc file system serves information about the running system. It not only
1389 allows access to process data but also allows you to request the kernel status
1390 by reading files in the hierarchy.
1391 
1392 The directory  structure  of /proc reflects the types of information and makes
1393 it easy, if not obvious, where to look for specific data.
1394 ------------------------------------------------------------------------------
1395 
1396 ------------------------------------------------------------------------------
1397 CHAPTER 2: MODIFYING SYSTEM PARAMETERS
1398 ------------------------------------------------------------------------------
1399 
1400 ------------------------------------------------------------------------------
1401 In This Chapter
1402 ------------------------------------------------------------------------------
1403 * Modifying kernel parameters by writing into files found in /proc/sys
1404 * Exploring the files which modify certain parameters
1405 * Review of the /proc/sys file tree
1406 ------------------------------------------------------------------------------
1407 
1408 
1409 A very  interesting part of /proc is the directory /proc/sys. This is not only
1410 a source  of  information,  it also allows you to change parameters within the
1411 kernel. Be  very  careful  when attempting this. You can optimize your system,
1412 but you  can  also  cause  it  to  crash.  Never  alter kernel parameters on a
1413 production system.  Set  up  a  development machine and test to make sure that
1414 everything works  the  way  you want it to. You may have no alternative but to
1415 reboot the machine once an error has been made.
1416 
1417 To change  a  value,  simply  echo  the new value into the file. An example is
1418 given below  in the section on the file system data. You need to be root to do
1419 this. You  can  create  your  own  boot script to perform this every time your
1420 system boots.
1421 
1422 The files  in /proc/sys can be used to fine tune and monitor miscellaneous and
1423 general things  in  the operation of the Linux kernel. Since some of the files
1424 can inadvertently  disrupt  your  system,  it  is  advisable  to  read  both
1425 documentation and  source  before actually making adjustments. In any case, be
1426 very careful  when  writing  to  any  of these files. The entries in /proc may
1427 change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1428 review the kernel documentation in the directory /usr/src/linux/Documentation.
1429 This chapter  is  heavily  based  on the documentation included in the pre 2.2
1430 kernels, and became part of it in version 2.2.1 of the Linux kernel.
1431 
1432 Please see: Documentation/sysctl/ directory for descriptions of these
1433 entries.
1434 
1435 ------------------------------------------------------------------------------
1436 Summary
1437 ------------------------------------------------------------------------------
1438 Certain aspects  of  kernel  behavior  can be modified at runtime, without the
1439 need to  recompile  the kernel, or even to reboot the system. The files in the
1440 /proc/sys tree  can  not only be read, but also modified. You can use the echo
1441 command to write value into these files, thereby changing the default settings
1442 of the kernel.
1443 ------------------------------------------------------------------------------
1444 
1445 ------------------------------------------------------------------------------
1446 CHAPTER 3: PER-PROCESS PARAMETERS
1447 ------------------------------------------------------------------------------
1448 
1449 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1450 --------------------------------------------------------------------------------
1451 
1452 These file can be used to adjust the badness heuristic used to select which
1453 process gets killed in out of memory conditions.
1454 
1455 The badness heuristic assigns a value to each candidate task ranging from 0
1456 (never kill) to 1000 (always kill) to determine which process is targeted.  The
1457 units are roughly a proportion along that range of allowed memory the process
1458 may allocate from based on an estimation of its current memory and swap use.
1459 For example, if a task is using all allowed memory, its badness score will be
1460 1000.  If it is using half of its allowed memory, its score will be 500.
1461 
1462 There is an additional factor included in the badness score: the current memory
1463 and swap usage is discounted by 3% for root processes.
1464 
1465 The amount of "allowed" memory depends on the context in which the oom killer
1466 was called.  If it is due to the memory assigned to the allocating task's cpuset
1467 being exhausted, the allowed memory represents the set of mems assigned to that
1468 cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
1469 memory represents the set of mempolicy nodes.  If it is due to a memory
1470 limit (or swap limit) being reached, the allowed memory is that configured
1471 limit.  Finally, if it is due to the entire system being out of memory, the
1472 allowed memory represents all allocatable resources.
1473 
1474 The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1475 is used to determine which task to kill.  Acceptable values range from -1000
1476 (OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
1477 polarize the preference for oom killing either by always preferring a certain
1478 task or completely disabling it.  The lowest possible value, -1000, is
1479 equivalent to disabling oom killing entirely for that task since it will always
1480 report a badness score of 0.
1481 
1482 Consequently, it is very simple for userspace to define the amount of memory to
1483 consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
1484 example, is roughly equivalent to allowing the remainder of tasks sharing the
1485 same system, cpuset, mempolicy, or memory controller resources to use at least
1486 50% more memory.  A value of -500, on the other hand, would be roughly
1487 equivalent to discounting 50% of the task's allowed memory from being considered
1488 as scoring against the task.
1489 
1490 For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1491 be used to tune the badness score.  Its acceptable values range from -16
1492 (OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1493 (OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
1494 scaled linearly with /proc/<pid>/oom_score_adj.
1495 
1496 The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1497 value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1498 requires CAP_SYS_RESOURCE.
1499 
1500 Caveat: when a parent task is selected, the oom killer will sacrifice any first
1501 generation children with separate address spaces instead, if possible.  This
1502 avoids servers and important system daemons from being killed and loses the
1503 minimal amount of work.
1504 
1505 
1506 3.2 /proc/<pid>/oom_score - Display current oom-killer score
1507 -------------------------------------------------------------
1508 
1509 This file can be used to check the current score used by the oom-killer is for
1510 any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1511 process should be killed in an out-of-memory situation.
1512 
1513 
1514 3.3  /proc/<pid>/io - Display the IO accounting fields
1515 -------------------------------------------------------
1516 
1517 This file contains IO statistics for each running process
1518 
1519 Example
1520 -------
1521 
1522 test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1523 [1] 3828
1524 
1525 test:/tmp # cat /proc/3828/io
1526 rchar: 323934931
1527 wchar: 323929600
1528 syscr: 632687
1529 syscw: 632675
1530 read_bytes: 0
1531 write_bytes: 323932160
1532 cancelled_write_bytes: 0
1533 
1534 
1535 Description
1536 -----------
1537 
1538 rchar
1539 -----
1540 
1541 I/O counter: chars read
1542 The number of bytes which this task has caused to be read from storage. This
1543 is simply the sum of bytes which this process passed to read() and pread().
1544 It includes things like tty IO and it is unaffected by whether or not actual
1545 physical disk IO was required (the read might have been satisfied from
1546 pagecache)
1547 
1548 
1549 wchar
1550 -----
1551 
1552 I/O counter: chars written
1553 The number of bytes which this task has caused, or shall cause to be written
1554 to disk. Similar caveats apply here as with rchar.
1555 
1556 
1557 syscr
1558 -----
1559 
1560 I/O counter: read syscalls
1561 Attempt to count the number of read I/O operations, i.e. syscalls like read()
1562 and pread().
1563 
1564 
1565 syscw
1566 -----
1567 
1568 I/O counter: write syscalls
1569 Attempt to count the number of write I/O operations, i.e. syscalls like
1570 write() and pwrite().
1571 
1572 
1573 read_bytes
1574 ----------
1575 
1576 I/O counter: bytes read
1577 Attempt to count the number of bytes which this process really did cause to
1578 be fetched from the storage layer. Done at the submit_bio() level, so it is
1579 accurate for block-backed filesystems. <please add status regarding NFS and
1580 CIFS at a later time>
1581 
1582 
1583 write_bytes
1584 -----------
1585 
1586 I/O counter: bytes written
1587 Attempt to count the number of bytes which this process caused to be sent to
1588 the storage layer. This is done at page-dirtying time.
1589 
1590 
1591 cancelled_write_bytes
1592 ---------------------
1593 
1594 The big inaccuracy here is truncate. If a process writes 1MB to a file and
1595 then deletes the file, it will in fact perform no writeout. But it will have
1596 been accounted as having caused 1MB of write.
1597 In other words: The number of bytes which this process caused to not happen,
1598 by truncating pagecache. A task can cause "negative" IO too. If this task
1599 truncates some dirty pagecache, some IO which another task has been accounted
1600 for (in its write_bytes) will not be happening. We _could_ just subtract that
1601 from the truncating task's write_bytes, but there is information loss in doing
1602 that.
1603 
1604 
1605 Note
1606 ----
1607 
1608 At its current implementation state, this is a bit racy on 32-bit machines: if
1609 process A reads process B's /proc/pid/io while process B is updating one of
1610 those 64-bit counters, process A could see an intermediate result.
1611 
1612 
1613 More information about this can be found within the taskstats documentation in
1614 Documentation/accounting.
1615 
1616 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1617 ---------------------------------------------------------------
1618 When a process is dumped, all anonymous memory is written to a core file as
1619 long as the size of the core file isn't limited. But sometimes we don't want
1620 to dump some memory segments, for example, huge shared memory or DAX.
1621 Conversely, sometimes we want to save file-backed memory segments into a core
1622 file, not only the individual files.
1623 
1624 /proc/<pid>/coredump_filter allows you to customize which memory segments
1625 will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1626 of memory types. If a bit of the bitmask is set, memory segments of the
1627 corresponding memory type are dumped, otherwise they are not dumped.
1628 
1629 The following 9 memory types are supported:
1630   - (bit 0) anonymous private memory
1631   - (bit 1) anonymous shared memory
1632   - (bit 2) file-backed private memory
1633   - (bit 3) file-backed shared memory
1634   - (bit 4) ELF header pages in file-backed private memory areas (it is
1635             effective only if the bit 2 is cleared)
1636   - (bit 5) hugetlb private memory
1637   - (bit 6) hugetlb shared memory
1638   - (bit 7) DAX private memory
1639   - (bit 8) DAX shared memory
1640 
1641   Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1642   are always dumped regardless of the bitmask status.
1643 
1644   Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
1645   only affected by bit 5-6, and DAX is only affected by bits 7-8.
1646 
1647 The default value of coredump_filter is 0x33; this means all anonymous memory
1648 segments, ELF header pages and hugetlb private memory are dumped.
1649 
1650 If you don't want to dump all shared memory segments attached to pid 1234,
1651 write 0x31 to the process's proc file.
1652 
1653   $ echo 0x31 > /proc/1234/coredump_filter
1654 
1655 When a new process is created, the process inherits the bitmask status from its
1656 parent. It is useful to set up coredump_filter before the program runs.
1657 For example:
1658 
1659   $ echo 0x7 > /proc/self/coredump_filter
1660   $ ./some_program
1661 
1662 3.5     /proc/<pid>/mountinfo - Information about mounts
1663 --------------------------------------------------------
1664 
1665 This file contains lines of the form:
1666 
1667 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1668 (1)(2)(3)   (4)   (5)      (6)      (7)   (8) (9)   (10)         (11)
1669 
1670 (1) mount ID:  unique identifier of the mount (may be reused after umount)
1671 (2) parent ID:  ID of parent (or of self for the top of the mount tree)
1672 (3) major:minor:  value of st_dev for files on filesystem
1673 (4) root:  root of the mount within the filesystem
1674 (5) mount point:  mount point relative to the process's root
1675 (6) mount options:  per mount options
1676 (7) optional fields:  zero or more fields of the form "tag[:value]"
1677 (8) separator:  marks the end of the optional fields
1678 (9) filesystem type:  name of filesystem of the form "type[.subtype]"
1679 (10) mount source:  filesystem specific information or "none"
1680 (11) super options:  per super block options
1681 
1682 Parsers should ignore all unrecognised optional fields.  Currently the
1683 possible optional fields are:
1684 
1685 shared:X  mount is shared in peer group X
1686 master:X  mount is slave to peer group X
1687 propagate_from:X  mount is slave and receives propagation from peer group X (*)
1688 unbindable  mount is unbindable
1689 
1690 (*) X is the closest dominant peer group under the process's root.  If
1691 X is the immediate master of the mount, or if there's no dominant peer
1692 group under the same root, then only the "master:X" field is present
1693 and not the "propagate_from:X" field.
1694 
1695 For more information on mount propagation see:
1696 
1697   Documentation/filesystems/sharedsubtree.txt
1698 
1699 
1700 3.6     /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
1701 --------------------------------------------------------
1702 These files provide a method to access a tasks comm value. It also allows for
1703 a task to set its own or one of its thread siblings comm value. The comm value
1704 is limited in size compared to the cmdline value, so writing anything longer
1705 then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1706 comm value.
1707 
1708 
1709 3.7     /proc/<pid>/task/<tid>/children - Information about task children
1710 -------------------------------------------------------------------------
1711 This file provides a fast way to retrieve first level children pids
1712 of a task pointed by <pid>/<tid> pair. The format is a space separated
1713 stream of pids.
1714 
1715 Note the "first level" here -- if a child has own children they will
1716 not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children
1717 to obtain the descendants.
1718 
1719 Since this interface is intended to be fast and cheap it doesn't
1720 guarantee to provide precise results and some children might be
1721 skipped, especially if they've exited right after we printed their
1722 pids, so one need to either stop or freeze processes being inspected
1723 if precise results are needed.
1724 
1725 
1726 3.8     /proc/<pid>/fdinfo/<fd> - Information about opened file
1727 ---------------------------------------------------------------
1728 This file provides information associated with an opened file. The regular
1729 files have at least three fields -- 'pos', 'flags' and mnt_id. The 'pos'
1730 represents the current offset of the opened file in decimal form [see lseek(2)
1731 for details], 'flags' denotes the octal O_xxx mask the file has been
1732 created with [see open(2) for details] and 'mnt_id' represents mount ID of
1733 the file system containing the opened file [see 3.5 /proc/<pid>/mountinfo
1734 for details].
1735 
1736 A typical output is
1737 
1738         pos:    0
1739         flags:  0100002
1740         mnt_id: 19
1741 
1742 All locks associated with a file descriptor are shown in its fdinfo too.
1743 
1744 lock:       1: FLOCK  ADVISORY  WRITE 359 00:13:11691 0 EOF
1745 
1746 The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1747 pair provide additional information particular to the objects they represent.
1748 
1749         Eventfd files
1750         ~~~~~~~~~~~~~
1751         pos:    0
1752         flags:  04002
1753         mnt_id: 9
1754         eventfd-count:  5a
1755 
1756         where 'eventfd-count' is hex value of a counter.
1757 
1758         Signalfd files
1759         ~~~~~~~~~~~~~~
1760         pos:    0
1761         flags:  04002
1762         mnt_id: 9
1763         sigmask:        0000000000000200
1764 
1765         where 'sigmask' is hex value of the signal mask associated
1766         with a file.
1767 
1768         Epoll files
1769         ~~~~~~~~~~~
1770         pos:    0
1771         flags:  02
1772         mnt_id: 9
1773         tfd:        5 events:       1d data: ffffffffffffffff
1774 
1775         where 'tfd' is a target file descriptor number in decimal form,
1776         'events' is events mask being watched and the 'data' is data
1777         associated with a target [see epoll(7) for more details].
1778 
1779         Fsnotify files
1780         ~~~~~~~~~~~~~~
1781         For inotify files the format is the following
1782 
1783         pos:    0
1784         flags:  02000000
1785         inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
1786 
1787         where 'wd' is a watch descriptor in decimal form, ie a target file
1788         descriptor number, 'ino' and 'sdev' are inode and device where the
1789         target file resides and the 'mask' is the mask of events, all in hex
1790         form [see inotify(7) for more details].
1791 
1792         If the kernel was built with exportfs support, the path to the target
1793         file is encoded as a file handle.  The file handle is provided by three
1794         fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
1795         format.
1796 
1797         If the kernel is built without exportfs support the file handle won't be
1798         printed out.
1799 
1800         If there is no inotify mark attached yet the 'inotify' line will be omitted.
1801 
1802         For fanotify files the format is
1803 
1804         pos:    0
1805         flags:  02
1806         mnt_id: 9
1807         fanotify flags:10 event-flags:0
1808         fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
1809         fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
1810 
1811         where fanotify 'flags' and 'event-flags' are values used in fanotify_init
1812         call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
1813         flags associated with mark which are tracked separately from events
1814         mask. 'ino', 'sdev' are target inode and device, 'mask' is the events
1815         mask and 'ignored_mask' is the mask of events which are to be ignored.
1816         All in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
1817         does provide information about flags and mask used in fanotify_mark
1818         call [see fsnotify manpage for details].
1819 
1820         While the first three lines are mandatory and always printed, the rest is
1821         optional and may be omitted if no marks created yet.
1822 
1823         Timerfd files
1824         ~~~~~~~~~~~~~
1825 
1826         pos:    0
1827         flags:  02
1828         mnt_id: 9
1829         clockid: 0
1830         ticks: 0
1831         settime flags: 01
1832         it_value: (0, 49406829)
1833         it_interval: (1, 0)
1834 
1835         where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
1836         that have occurred [see timerfd_create(2) for details]. 'settime flags' are
1837         flags in octal form been used to setup the timer [see timerfd_settime(2) for
1838         details]. 'it_value' is remaining time until the timer exiration.
1839         'it_interval' is the interval for the timer. Note the timer might be set up
1840         with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
1841         still exhibits timer's remaining time.
1842 
1843 3.9     /proc/<pid>/map_files - Information about memory mapped files
1844 ---------------------------------------------------------------------
1845 This directory contains symbolic links which represent memory mapped files
1846 the process is maintaining.  Example output:
1847 
1848      | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
1849      | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
1850      | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
1851      | ...
1852      | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
1853      | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
1854 
1855 The name of a link represents the virtual memory bounds of a mapping, i.e.
1856 vm_area_struct::vm_start-vm_area_struct::vm_end.
1857 
1858 The main purpose of the map_files is to retrieve a set of memory mapped
1859 files in a fast way instead of parsing /proc/<pid>/maps or
1860 /proc/<pid>/smaps, both of which contain many more records.  At the same
1861 time one can open(2) mappings from the listings of two processes and
1862 comparing their inode numbers to figure out which anonymous memory areas
1863 are actually shared.
1864 
1865 ------------------------------------------------------------------------------
1866 Configuring procfs
1867 ------------------------------------------------------------------------------
1868 
1869 4.1     Mount options
1870 ---------------------
1871 
1872 The following mount options are supported:
1873 
1874         hidepid=        Set /proc/<pid>/ access mode.
1875         gid=            Set the group authorized to learn processes information.
1876 
1877 hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
1878 (default).
1879 
1880 hidepid=1 means users may not access any /proc/<pid>/ directories but their
1881 own.  Sensitive files like cmdline, sched*, status are now protected against
1882 other users.  This makes it impossible to learn whether any user runs
1883 specific program (given the program doesn't reveal itself by its behaviour).
1884 As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users,
1885 poorly written programs passing sensitive information via program arguments are
1886 now protected against local eavesdroppers.
1887 
1888 hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other
1889 users.  It doesn't mean that it hides a fact whether a process with a specific
1890 pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"),
1891 but it hides process' uid and gid, which may be learned by stat()'ing
1892 /proc/<pid>/ otherwise.  It greatly complicates an intruder's task of gathering
1893 information about running processes, whether some daemon runs with elevated
1894 privileges, whether other user runs some sensitive program, whether other users
1895 run any program at all, etc.
1896 
1897 gid= defines a group authorized to learn processes information otherwise
1898 prohibited by hidepid=.  If you use some daemon like identd which needs to learn
1899 information about processes information, just add identd to this group.

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