Version:  2.0.40 2.2.26 2.4.37 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 4.6

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   3.10  /proc/<pid>/timerslack_ns - Task timerslack value
 47 
 48   4     Configuring procfs
 49   4.1   Mount options
 50 
 51 ------------------------------------------------------------------------------
 52 Preface
 53 ------------------------------------------------------------------------------
 54 
 55 0.1 Introduction/Credits
 56 ------------------------
 57 
 58 This documentation is  part of a soon (or  so we hope) to be  released book on
 59 the SuSE  Linux distribution. As  there is  no complete documentation  for the
 60 /proc file system and we've used  many freely available sources to write these
 61 chapters, it  seems only fair  to give the work  back to the  Linux community.
 62 This work is  based on the 2.2.*  kernel version and the  upcoming 2.4.*. I'm
 63 afraid it's still far from complete, but we  hope it will be useful. As far as
 64 we know, it is the first 'all-in-one' document about the /proc file system. It
 65 is focused  on the Intel  x86 hardware,  so if you  are looking for  PPC, ARM,
 66 SPARC, AXP, etc., features, you probably  won't find what you are looking for.
 67 It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
 68 additions and patches  are welcome and will  be added to this  document if you
 69 mail them to Bodo.
 70 
 71 We'd like  to  thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
 72 other people for help compiling this documentation. We'd also like to extend a
 73 special thank  you to Andi Kleen for documentation, which we relied on heavily
 74 to create  this  document,  as well as the additional information he provided.
 75 Thanks to  everybody  else  who contributed source or docs to the Linux kernel
 76 and helped create a great piece of software... :)
 77 
 78 If you  have  any comments, corrections or additions, please don't hesitate to
 79 contact Bodo  Bauer  at  bb@ricochet.net.  We'll  be happy to add them to this
 80 document.
 81 
 82 The   latest   version    of   this   document   is    available   online   at
 83 http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html
 84 
 85 If  the above  direction does  not works  for you,  you could  try the  kernel
 86 mailing  list  at  linux-kernel@vger.kernel.org  and/or try  to  reach  me  at
 87 comandante@zaralinux.com.
 88 
 89 0.2 Legal Stuff
 90 ---------------
 91 
 92 We don't  guarantee  the  correctness  of this document, and if you come to us
 93 complaining about  how  you  screwed  up  your  system  because  of  incorrect
 94 documentation, we won't feel responsible...
 95 
 96 ------------------------------------------------------------------------------
 97 CHAPTER 1: COLLECTING SYSTEM INFORMATION
 98 ------------------------------------------------------------------------------
 99 
100 ------------------------------------------------------------------------------
101 In This Chapter
102 ------------------------------------------------------------------------------
103 * Investigating  the  properties  of  the  pseudo  file  system  /proc and its
104   ability to provide information on the running Linux system
105 * Examining /proc's structure
106 * Uncovering  various  information  about the kernel and the processes running
107   on the system
108 ------------------------------------------------------------------------------
109 
110 
111 The proc  file  system acts as an interface to internal data structures in the
112 kernel. It  can  be  used to obtain information about the system and to change
113 certain kernel parameters at runtime (sysctl).
114 
115 First, we'll  take  a  look  at the read-only parts of /proc. In Chapter 2, we
116 show you how you can use /proc/sys to change settings.
117 
118 1.1 Process-Specific Subdirectories
119 -----------------------------------
120 
121 The directory  /proc  contains  (among other things) one subdirectory for each
122 process running on the system, which is named after the process ID (PID).
123 
124 The link  self  points  to  the  process reading the file system. Each process
125 subdirectory has the entries listed in Table 1-1.
126 
127 
128 Table 1-1: Process specific entries in /proc
129 ..............................................................................
130  File           Content
131  clear_refs     Clears page referenced bits shown in smaps output
132  cmdline        Command line arguments
133  cpu            Current and last cpu in which it was executed   (2.4)(smp)
134  cwd            Link to the current working directory
135  environ        Values of environment variables
136  exe            Link to the executable of this process
137  fd             Directory, which contains all file descriptors
138  maps           Memory maps to executables and library files    (2.4)
139  mem            Memory held by this process
140  root           Link to the root directory of this process
141  stat           Process status
142  statm          Process memory status information
143  status         Process status in human readable form
144  wchan          Present with CONFIG_KALLSYMS=y: it shows the kernel function
145                 symbol the task is blocked in - or "0" if not blocked.
146  pagemap        Page table
147  stack          Report full stack trace, enable via CONFIG_STACKTRACE
148  smaps          a extension based on maps, showing the memory consumption of
149                 each mapping and flags associated with it
150  numa_maps      an extension based on maps, showing the memory locality and
151                 binding policy as well as mem usage (in pages) of each mapping.
152 ..............................................................................
153 
154 For example, to get the status information of a process, all you have to do is
155 read the file /proc/PID/status:
156 
157   >cat /proc/self/status
158   Name:   cat
159   State:  R (running)
160   Tgid:   5452
161   Pid:    5452
162   PPid:   743
163   TracerPid:      0                                             (2.4)
164   Uid:    501     501     501     501
165   Gid:    100     100     100     100
166   FDSize: 256
167   Groups: 100 14 16
168   VmPeak:     5004 kB
169   VmSize:     5004 kB
170   VmLck:         0 kB
171   VmHWM:       476 kB
172   VmRSS:       476 kB
173   RssAnon:             352 kB
174   RssFile:             120 kB
175   RssShmem:              4 kB
176   VmData:      156 kB
177   VmStk:        88 kB
178   VmExe:        68 kB
179   VmLib:      1412 kB
180   VmPTE:        20 kb
181   VmSwap:        0 kB
182   HugetlbPages:          0 kB
183   Threads:        1
184   SigQ:   0/28578
185   SigPnd: 0000000000000000
186   ShdPnd: 0000000000000000
187   SigBlk: 0000000000000000
188   SigIgn: 0000000000000000
189   SigCgt: 0000000000000000
190   CapInh: 00000000fffffeff
191   CapPrm: 0000000000000000
192   CapEff: 0000000000000000
193   CapBnd: ffffffffffffffff
194   Seccomp:        0
195   voluntary_ctxt_switches:        0
196   nonvoluntary_ctxt_switches:     1
197 
198 This shows you nearly the same information you would get if you viewed it with
199 the ps  command.  In  fact,  ps  uses  the  proc  file  system  to  obtain its
200 information.  But you get a more detailed  view of the  process by reading the
201 file /proc/PID/status. It fields are described in table 1-2.
202 
203 The  statm  file  contains  more  detailed  information about the process
204 memory usage. Its seven fields are explained in Table 1-3.  The stat file
205 contains details information about the process itself.  Its fields are
206 explained in Table 1-4.
207 
208 (for SMP CONFIG users)
209 For making accounting scalable, RSS related information are handled in an
210 asynchronous manner and the value may not be very precise. To see a precise
211 snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
212 It's slow but very precise.
213 
214 Table 1-2: Contents of the status files (as of 4.1)
215 ..............................................................................
216  Field                       Content
217  Name                        filename of the executable
218  State                       state (R is running, S is sleeping, D is sleeping
219                              in an uninterruptible wait, Z is zombie,
220                              T is traced or stopped)
221  Tgid                        thread group ID
222  Ngid                        NUMA group ID (0 if none)
223  Pid                         process id
224  PPid                        process id of the parent process
225  TracerPid                   PID of process tracing this process (0 if not)
226  Uid                         Real, effective, saved set, and  file system UIDs
227  Gid                         Real, effective, saved set, and  file system GIDs
228  FDSize                      number of file descriptor slots currently allocated
229  Groups                      supplementary group list
230  NStgid                      descendant namespace thread group ID hierarchy
231  NSpid                       descendant namespace process ID hierarchy
232  NSpgid                      descendant namespace process group ID hierarchy
233  NSsid                       descendant namespace session ID hierarchy
234  VmPeak                      peak virtual memory size
235  VmSize                      total program size
236  VmLck                       locked memory size
237  VmHWM                       peak resident set size ("high water mark")
238  VmRSS                       size of memory portions. It contains the three
239                              following parts (VmRSS = RssAnon + RssFile + RssShmem)
240  RssAnon                     size of resident anonymous memory
241  RssFile                     size of resident file mappings
242  RssShmem                    size of resident shmem memory (includes SysV shm,
243                              mapping of tmpfs and shared anonymous mappings)
244  VmData                      size of private data segments
245  VmStk                       size of stack segments
246  VmExe                       size of text segment
247  VmLib                       size of shared library code
248  VmPTE                       size of page table entries
249  VmPMD                       size of second level page tables
250  VmSwap                      amount of swap used by anonymous private data
251                              (shmem swap usage is not included)
252  HugetlbPages                size of hugetlb memory portions
253  Threads                     number of threads
254  SigQ                        number of signals queued/max. number for queue
255  SigPnd                      bitmap of pending signals for the thread
256  ShdPnd                      bitmap of shared pending signals for the process
257  SigBlk                      bitmap of blocked signals
258  SigIgn                      bitmap of ignored signals
259  SigCgt                      bitmap of caught signals
260  CapInh                      bitmap of inheritable capabilities
261  CapPrm                      bitmap of permitted capabilities
262  CapEff                      bitmap of effective capabilities
263  CapBnd                      bitmap of capabilities bounding set
264  Seccomp                     seccomp mode, like prctl(PR_GET_SECCOMP, ...)
265  Cpus_allowed                mask of CPUs on which this process may run
266  Cpus_allowed_list           Same as previous, but in "list format"
267  Mems_allowed                mask of memory nodes allowed to this process
268  Mems_allowed_list           Same as previous, but in "list format"
269  voluntary_ctxt_switches     number of voluntary context switches
270  nonvoluntary_ctxt_switches  number of non voluntary context switches
271 ..............................................................................
272 
273 Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
274 ..............................................................................
275  Field    Content
276  size     total program size (pages)            (same as VmSize in status)
277  resident size of memory portions (pages)       (same as VmRSS in status)
278  shared   number of pages that are shared       (i.e. backed by a file, same
279                                                 as RssFile+RssShmem in status)
280  trs      number of pages that are 'code'       (not including libs; broken,
281                                                         includes data segment)
282  lrs      number of pages of library            (always 0 on 2.6)
283  drs      number of pages of data/stack         (including libs; broken,
284                                                         includes library text)
285  dt       number of dirty pages                 (always 0 on 2.6)
286 ..............................................................................
287 
288 
289 Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
290 ..............................................................................
291  Field          Content
292   pid           process id
293   tcomm         filename of the executable
294   state         state (R is running, S is sleeping, D is sleeping in an
295                 uninterruptible wait, Z is zombie, T is traced or stopped)
296   ppid          process id of the parent process
297   pgrp          pgrp of the process
298   sid           session id
299   tty_nr        tty the process uses
300   tty_pgrp      pgrp of the tty
301   flags         task flags
302   min_flt       number of minor faults
303   cmin_flt      number of minor faults with child's
304   maj_flt       number of major faults
305   cmaj_flt      number of major faults with child's
306   utime         user mode jiffies
307   stime         kernel mode jiffies
308   cutime        user mode jiffies with child's
309   cstime        kernel mode jiffies with child's
310   priority      priority level
311   nice          nice level
312   num_threads   number of threads
313   it_real_value (obsolete, always 0)
314   start_time    time the process started after system boot
315   vsize         virtual memory size
316   rss           resident set memory size
317   rsslim        current limit in bytes on the rss
318   start_code    address above which program text can run
319   end_code      address below which program text can run
320   start_stack   address of the start of the main process stack
321   esp           current value of ESP
322   eip           current value of EIP
323   pending       bitmap of pending signals
324   blocked       bitmap of blocked signals
325   sigign        bitmap of ignored signals
326   sigcatch      bitmap of caught signals
327   0             (place holder, used to be the wchan address, use /proc/PID/wchan instead)
328   0             (place holder)
329   0             (place holder)
330   exit_signal   signal to send to parent thread on exit
331   task_cpu      which CPU the task is scheduled on
332   rt_priority   realtime priority
333   policy        scheduling policy (man sched_setscheduler)
334   blkio_ticks   time spent waiting for block IO
335   gtime         guest time of the task in jiffies
336   cgtime        guest time of the task children in jiffies
337   start_data    address above which program data+bss is placed
338   end_data      address below which program data+bss is placed
339   start_brk     address above which program heap can be expanded with brk()
340   arg_start     address above which program command line is placed
341   arg_end       address below which program command line is placed
342   env_start     address above which program environment is placed
343   env_end       address below which program environment is placed
344   exit_code     the thread's exit_code in the form reported by the waitpid system call
345 ..............................................................................
346 
347 The /proc/PID/maps file containing the currently mapped memory regions and
348 their access permissions.
349 
350 The format is:
351 
352 address           perms offset  dev   inode      pathname
353 
354 08048000-08049000 r-xp 00000000 03:00 8312       /opt/test
355 08049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
356 0804a000-0806b000 rw-p 00000000 00:00 0          [heap]
357 a7cb1000-a7cb2000 ---p 00000000 00:00 0
358 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
359 a7eb2000-a7eb3000 ---p 00000000 00:00 0
360 a7eb3000-a7ed5000 rw-p 00000000 00:00 0
361 a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/libc.so.6
362 a8008000-a800a000 r--p 00133000 03:00 4222       /lib/libc.so.6
363 a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/libc.so.6
364 a800b000-a800e000 rw-p 00000000 00:00 0
365 a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/libpthread.so.0
366 a8022000-a8023000 r--p 00013000 03:00 14462      /lib/libpthread.so.0
367 a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/libpthread.so.0
368 a8024000-a8027000 rw-p 00000000 00:00 0
369 a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/ld-linux.so.2
370 a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/ld-linux.so.2
371 a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/ld-linux.so.2
372 aff35000-aff4a000 rw-p 00000000 00:00 0          [stack]
373 ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
374 
375 where "address" is the address space in the process that it occupies, "perms"
376 is a set of permissions:
377 
378  r = read
379  w = write
380  x = execute
381  s = shared
382  p = private (copy on write)
383 
384 "offset" is the offset into the mapping, "dev" is the device (major:minor), and
385 "inode" is the inode  on that device.  0 indicates that  no inode is associated
386 with the memory region, as the case would be with BSS (uninitialized data).
387 The "pathname" shows the name associated file for this mapping.  If the mapping
388 is not associated with a file:
389 
390  [heap]                   = the heap of the program
391  [stack]                  = the stack of the main process
392  [vdso]                   = the "virtual dynamic shared object",
393                             the kernel system call handler
394 
395  or if empty, the mapping is anonymous.
396 
397 The /proc/PID/task/TID/maps is a view of the virtual memory from the viewpoint
398 of the individual tasks of a process. In this file you will see a mapping marked
399 as [stack] if that task sees it as a stack. Hence, for the example above, the
400 task-level map, i.e. /proc/PID/task/TID/maps for thread 1001 will look like this:
401 
402 08048000-08049000 r-xp 00000000 03:00 8312       /opt/test
403 08049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
404 0804a000-0806b000 rw-p 00000000 00:00 0          [heap]
405 a7cb1000-a7cb2000 ---p 00000000 00:00 0
406 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
407 a7eb2000-a7eb3000 ---p 00000000 00:00 0
408 a7eb3000-a7ed5000 rw-p 00000000 00:00 0          [stack]
409 a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/libc.so.6
410 a8008000-a800a000 r--p 00133000 03:00 4222       /lib/libc.so.6
411 a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/libc.so.6
412 a800b000-a800e000 rw-p 00000000 00:00 0
413 a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/libpthread.so.0
414 a8022000-a8023000 r--p 00013000 03:00 14462      /lib/libpthread.so.0
415 a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/libpthread.so.0
416 a8024000-a8027000 rw-p 00000000 00:00 0
417 a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/ld-linux.so.2
418 a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/ld-linux.so.2
419 a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/ld-linux.so.2
420 aff35000-aff4a000 rw-p 00000000 00:00 0
421 ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
422 
423 The /proc/PID/smaps is an extension based on maps, showing the memory
424 consumption for each of the process's mappings. For each of mappings there
425 is a series of lines such as the following:
426 
427 08048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
428 Size:               1084 kB
429 Rss:                 892 kB
430 Pss:                 374 kB
431 Shared_Clean:        892 kB
432 Shared_Dirty:          0 kB
433 Private_Clean:         0 kB
434 Private_Dirty:         0 kB
435 Referenced:          892 kB
436 Anonymous:             0 kB
437 AnonHugePages:         0 kB
438 Shared_Hugetlb:        0 kB
439 Private_Hugetlb:       0 kB
440 Swap:                  0 kB
441 SwapPss:               0 kB
442 KernelPageSize:        4 kB
443 MMUPageSize:           4 kB
444 Locked:                0 kB
445 VmFlags: rd ex mr mw me dw
446 
447 the first of these lines shows the same information as is displayed for the
448 mapping in /proc/PID/maps.  The remaining lines show the size of the mapping
449 (size), the amount of the mapping that is currently resident in RAM (RSS), the
450 process' proportional share of this mapping (PSS), the number of clean and
451 dirty private pages in the mapping.
452 
453 The "proportional set size" (PSS) of a process is the count of pages it has
454 in memory, where each page is divided by the number of processes sharing it.
455 So if a process has 1000 pages all to itself, and 1000 shared with one other
456 process, its PSS will be 1500.
457 Note that even a page which is part of a MAP_SHARED mapping, but has only
458 a single pte mapped, i.e.  is currently used by only one process, is accounted
459 as private and not as shared.
460 "Referenced" indicates the amount of memory currently marked as referenced or
461 accessed.
462 "Anonymous" shows the amount of memory that does not belong to any file.  Even
463 a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
464 and a page is modified, the file page is replaced by a private anonymous copy.
465 "AnonHugePages" shows the ammount of memory backed by transparent hugepage.
466 "Shared_Hugetlb" and "Private_Hugetlb" show the ammounts of memory backed by
467 hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical
468 reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field.
469 "Swap" shows how much would-be-anonymous memory is also used, but out on swap.
470 For shmem mappings, "Swap" includes also the size of the mapped (and not
471 replaced by copy-on-write) part of the underlying shmem object out on swap.
472 "SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
473 does not take into account swapped out page of underlying shmem objects.
474 "Locked" indicates whether the mapping is locked in memory or not.
475 
476 "VmFlags" field deserves a separate description. This member represents the kernel
477 flags associated with the particular virtual memory area in two letter encoded
478 manner. The codes are the following:
479     rd  - readable
480     wr  - writeable
481     ex  - executable
482     sh  - shared
483     mr  - may read
484     mw  - may write
485     me  - may execute
486     ms  - may share
487     gd  - stack segment growns down
488     pf  - pure PFN range
489     dw  - disabled write to the mapped file
490     lo  - pages are locked in memory
491     io  - memory mapped I/O area
492     sr  - sequential read advise provided
493     rr  - random read advise provided
494     dc  - do not copy area on fork
495     de  - do not expand area on remapping
496     ac  - area is accountable
497     nr  - swap space is not reserved for the area
498     ht  - area uses huge tlb pages
499     ar  - architecture specific flag
500     dd  - do not include area into core dump
501     sd  - soft-dirty flag
502     mm  - mixed map area
503     hg  - huge page advise flag
504     nh  - no-huge page advise flag
505     mg  - mergable advise flag
506 
507 Note that there is no guarantee that every flag and associated mnemonic will
508 be present in all further kernel releases. Things get changed, the flags may
509 be vanished or the reverse -- new added.
510 
511 This file is only present if the CONFIG_MMU kernel configuration option is
512 enabled.
513 
514 The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
515 bits on both physical and virtual pages associated with a process, and the
516 soft-dirty bit on pte (see Documentation/vm/soft-dirty.txt for details).
517 To clear the bits for all the pages associated with the process
518     > echo 1 > /proc/PID/clear_refs
519 
520 To clear the bits for the anonymous pages associated with the process
521     > echo 2 > /proc/PID/clear_refs
522 
523 To clear the bits for the file mapped pages associated with the process
524     > echo 3 > /proc/PID/clear_refs
525 
526 To clear the soft-dirty bit
527     > echo 4 > /proc/PID/clear_refs
528 
529 To reset the peak resident set size ("high water mark") to the process's
530 current value:
531     > echo 5 > /proc/PID/clear_refs
532 
533 Any other value written to /proc/PID/clear_refs will have no effect.
534 
535 The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
536 using /proc/kpageflags and number of times a page is mapped using
537 /proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt.
538 
539 The /proc/pid/numa_maps is an extension based on maps, showing the memory
540 locality and binding policy, as well as the memory usage (in pages) of
541 each mapping. The output follows a general format where mapping details get
542 summarized separated by blank spaces, one mapping per each file line:
543 
544 address   policy    mapping details
545 
546 00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
547 00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
548 3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
549 320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
550 3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
551 3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
552 3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
553 320698b000 default file=/lib64/libc-2.12.so
554 3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4
555 3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
556 3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
557 7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
558 7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
559 7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
560 7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
561 7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4
562 
563 Where:
564 "address" is the starting address for the mapping;
565 "policy" reports the NUMA memory policy set for the mapping (see vm/numa_memory_policy.txt);
566 "mapping details" summarizes mapping data such as mapping type, page usage counters,
567 node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
568 size, in KB, that is backing the mapping up.
569 
570 1.2 Kernel data
571 ---------------
572 
573 Similar to  the  process entries, the kernel data files give information about
574 the running kernel. The files used to obtain this information are contained in
575 /proc and  are  listed  in Table 1-5. Not all of these will be present in your
576 system. It  depends  on the kernel configuration and the loaded modules, which
577 files are there, and which are missing.
578 
579 Table 1-5: Kernel info in /proc
580 ..............................................................................
581  File        Content                                           
582  apm         Advanced power management info                    
583  buddyinfo   Kernel memory allocator information (see text)     (2.5)
584  bus         Directory containing bus specific information     
585  cmdline     Kernel command line                               
586  cpuinfo     Info about the CPU                                
587  devices     Available devices (block and character)           
588  dma         Used DMS channels                                 
589  filesystems Supported filesystems                             
590  driver      Various drivers grouped here, currently rtc (2.4)
591  execdomains Execdomains, related to security                   (2.4)
592  fb          Frame Buffer devices                               (2.4)
593  fs          File system parameters, currently nfs/exports      (2.4)
594  ide         Directory containing info about the IDE subsystem 
595  interrupts  Interrupt usage                                   
596  iomem       Memory map                                         (2.4)
597  ioports     I/O port usage                                    
598  irq         Masks for irq to cpu affinity                      (2.4)(smp?)
599  isapnp      ISA PnP (Plug&Play) Info                           (2.4)
600  kcore       Kernel core image (can be ELF or A.OUT(deprecated in 2.4))   
601  kmsg        Kernel messages                                   
602  ksyms       Kernel symbol table                               
603  loadavg     Load average of last 1, 5 & 15 minutes                
604  locks       Kernel locks                                      
605  meminfo     Memory info                                       
606  misc        Miscellaneous                                     
607  modules     List of loaded modules                            
608  mounts      Mounted filesystems                               
609  net         Networking info (see text)                        
610  pagetypeinfo Additional page allocator information (see text)  (2.5)
611  partitions  Table of partitions known to the system           
612  pci         Deprecated info of PCI bus (new way -> /proc/bus/pci/,
613              decoupled by lspci                                 (2.4)
614  rtc         Real time clock                                   
615  scsi        SCSI info (see text)                              
616  slabinfo    Slab pool info                                    
617  softirqs    softirq usage
618  stat        Overall statistics                                
619  swaps       Swap space utilization                            
620  sys         See chapter 2                                     
621  sysvipc     Info of SysVIPC Resources (msg, sem, shm)          (2.4)
622  tty         Info of tty drivers
623  uptime      Wall clock since boot, combined idle time of all cpus
624  version     Kernel version                                    
625  video       bttv info of video resources                       (2.4)
626  vmallocinfo Show vmalloced areas
627 ..............................................................................
628 
629 You can,  for  example,  check  which interrupts are currently in use and what
630 they are used for by looking in the file /proc/interrupts:
631 
632   > cat /proc/interrupts 
633              CPU0        
634     0:    8728810          XT-PIC  timer 
635     1:        895          XT-PIC  keyboard 
636     2:          0          XT-PIC  cascade 
637     3:     531695          XT-PIC  aha152x 
638     4:    2014133          XT-PIC  serial 
639     5:      44401          XT-PIC  pcnet_cs 
640     8:          2          XT-PIC  rtc 
641    11:          8          XT-PIC  i82365 
642    12:     182918          XT-PIC  PS/2 Mouse 
643    13:          1          XT-PIC  fpu 
644    14:    1232265          XT-PIC  ide0 
645    15:          7          XT-PIC  ide1 
646   NMI:          0 
647 
648 In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
649 output of a SMP machine):
650 
651   > cat /proc/interrupts 
652 
653              CPU0       CPU1       
654     0:    1243498    1214548    IO-APIC-edge  timer
655     1:       8949       8958    IO-APIC-edge  keyboard
656     2:          0          0          XT-PIC  cascade
657     5:      11286      10161    IO-APIC-edge  soundblaster
658     8:          1          0    IO-APIC-edge  rtc
659     9:      27422      27407    IO-APIC-edge  3c503
660    12:     113645     113873    IO-APIC-edge  PS/2 Mouse
661    13:          0          0          XT-PIC  fpu
662    14:      22491      24012    IO-APIC-edge  ide0
663    15:       2183       2415    IO-APIC-edge  ide1
664    17:      30564      30414   IO-APIC-level  eth0
665    18:        177        164   IO-APIC-level  bttv
666   NMI:    2457961    2457959 
667   LOC:    2457882    2457881 
668   ERR:       2155
669 
670 NMI is incremented in this case because every timer interrupt generates a NMI
671 (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
672 
673 LOC is the local interrupt counter of the internal APIC of every CPU.
674 
675 ERR is incremented in the case of errors in the IO-APIC bus (the bus that
676 connects the CPUs in a SMP system. This means that an error has been detected,
677 the IO-APIC automatically retry the transmission, so it should not be a big
678 problem, but you should read the SMP-FAQ.
679 
680 In 2.6.2* /proc/interrupts was expanded again.  This time the goal was for
681 /proc/interrupts to display every IRQ vector in use by the system, not
682 just those considered 'most important'.  The new vectors are:
683 
684   THR -- interrupt raised when a machine check threshold counter
685   (typically counting ECC corrected errors of memory or cache) exceeds
686   a configurable threshold.  Only available on some systems.
687 
688   TRM -- a thermal event interrupt occurs when a temperature threshold
689   has been exceeded for the CPU.  This interrupt may also be generated
690   when the temperature drops back to normal.
691 
692   SPU -- a spurious interrupt is some interrupt that was raised then lowered
693   by some IO device before it could be fully processed by the APIC.  Hence
694   the APIC sees the interrupt but does not know what device it came from.
695   For this case the APIC will generate the interrupt with a IRQ vector
696   of 0xff. This might also be generated by chipset bugs.
697 
698   RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
699   sent from one CPU to another per the needs of the OS.  Typically,
700   their statistics are used by kernel developers and interested users to
701   determine the occurrence of interrupts of the given type.
702 
703 The above IRQ vectors are displayed only when relevant.  For example,
704 the threshold vector does not exist on x86_64 platforms.  Others are
705 suppressed when the system is a uniprocessor.  As of this writing, only
706 i386 and x86_64 platforms support the new IRQ vector displays.
707 
708 Of some interest is the introduction of the /proc/irq directory to 2.4.
709 It could be used to set IRQ to CPU affinity, this means that you can "hook" an
710 IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
711 irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
712 prof_cpu_mask.
713 
714 For example 
715   > ls /proc/irq/
716   0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
717   1  11  13  15  17  19  3  5  7  9  default_smp_affinity
718   > ls /proc/irq/0/
719   smp_affinity
720 
721 smp_affinity is a bitmask, in which you can specify which CPUs can handle the
722 IRQ, you can set it by doing:
723 
724   > echo 1 > /proc/irq/10/smp_affinity
725 
726 This means that only the first CPU will handle the IRQ, but you can also echo
727 5 which means that only the first and fourth CPU can handle the IRQ.
728 
729 The contents of each smp_affinity file is the same by default:
730 
731   > cat /proc/irq/0/smp_affinity
732   ffffffff
733 
734 There is an alternate interface, smp_affinity_list which allows specifying
735 a cpu range instead of a bitmask:
736 
737   > cat /proc/irq/0/smp_affinity_list
738   1024-1031
739 
740 The default_smp_affinity mask applies to all non-active IRQs, which are the
741 IRQs which have not yet been allocated/activated, and hence which lack a
742 /proc/irq/[0-9]* directory.
743 
744 The node file on an SMP system shows the node to which the device using the IRQ
745 reports itself as being attached. This hardware locality information does not
746 include information about any possible driver locality preference.
747 
748 prof_cpu_mask specifies which CPUs are to be profiled by the system wide
749 profiler. Default value is ffffffff (all cpus if there are only 32 of them).
750 
751 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
752 between all the CPUs which are allowed to handle it. As usual the kernel has
753 more info than you and does a better job than you, so the defaults are the
754 best choice for almost everyone.  [Note this applies only to those IO-APIC's
755 that support "Round Robin" interrupt distribution.]
756 
757 There are  three  more  important subdirectories in /proc: net, scsi, and sys.
758 The general  rule  is  that  the  contents,  or  even  the  existence of these
759 directories, depend  on your kernel configuration. If SCSI is not enabled, the
760 directory scsi  may  not  exist. The same is true with the net, which is there
761 only when networking support is present in the running kernel.
762 
763 The slabinfo  file  gives  information  about  memory usage at the slab level.
764 Linux uses  slab  pools for memory management above page level in version 2.2.
765 Commonly used  objects  have  their  own  slab  pool (such as network buffers,
766 directory cache, and so on).
767 
768 ..............................................................................
769 
770 > cat /proc/buddyinfo
771 
772 Node 0, zone      DMA      0      4      5      4      4      3 ...
773 Node 0, zone   Normal      1      0      0      1    101      8 ...
774 Node 0, zone  HighMem      2      0      0      1      1      0 ...
775 
776 External fragmentation is a problem under some workloads, and buddyinfo is a
777 useful tool for helping diagnose these problems.  Buddyinfo will give you a 
778 clue as to how big an area you can safely allocate, or why a previous
779 allocation failed.
780 
781 Each column represents the number of pages of a certain order which are 
782 available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in 
783 ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE 
784 available in ZONE_NORMAL, etc... 
785 
786 More information relevant to external fragmentation can be found in
787 pagetypeinfo.
788 
789 > cat /proc/pagetypeinfo
790 Page block order: 9
791 Pages per block:  512
792 
793 Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
794 Node    0, zone      DMA, type    Unmovable      0      0      0      1      1      1      1      1      1      1      0
795 Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0
796 Node    0, zone      DMA, type      Movable      1      1      2      1      2      1      1      0      1      0      2
797 Node    0, zone      DMA, type      Reserve      0      0      0      0      0      0      0      0      0      1      0
798 Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
799 Node    0, zone    DMA32, type    Unmovable    103     54     77      1      1      1     11      8      7      1      9
800 Node    0, zone    DMA32, type  Reclaimable      0      0      2      1      0      0      0      0      1      0      0
801 Node    0, zone    DMA32, type      Movable    169    152    113     91     77     54     39     13      6      1    452
802 Node    0, zone    DMA32, type      Reserve      1      2      2      2      2      0      1      1      1      1      0
803 Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
804 
805 Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate
806 Node 0, zone      DMA            2            0            5            1            0
807 Node 0, zone    DMA32           41            6          967            2            0
808 
809 Fragmentation avoidance in the kernel works by grouping pages of different
810 migrate types into the same contiguous regions of memory called page blocks.
811 A page block is typically the size of the default hugepage size e.g. 2MB on
812 X86-64. By keeping pages grouped based on their ability to move, the kernel
813 can reclaim pages within a page block to satisfy a high-order allocation.
814 
815 The pagetypinfo begins with information on the size of a page block. It
816 then gives the same type of information as buddyinfo except broken down
817 by migrate-type and finishes with details on how many page blocks of each
818 type exist.
819 
820 If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
821 from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can
822 make an estimate of the likely number of huge pages that can be allocated
823 at a given point in time. All the "Movable" blocks should be allocatable
824 unless memory has been mlock()'d. Some of the Reclaimable blocks should
825 also be allocatable although a lot of filesystem metadata may have to be
826 reclaimed to achieve this.
827 
828 ..............................................................................
829 
830 meminfo:
831 
832 Provides information about distribution and utilization of memory.  This
833 varies by architecture and compile options.  The following is from a
834 16GB PIII, which has highmem enabled.  You may not have all of these fields.
835 
836 > cat /proc/meminfo
837 
838 MemTotal:     16344972 kB
839 MemFree:      13634064 kB
840 MemAvailable: 14836172 kB
841 Buffers:          3656 kB
842 Cached:        1195708 kB
843 SwapCached:          0 kB
844 Active:         891636 kB
845 Inactive:      1077224 kB
846 HighTotal:    15597528 kB
847 HighFree:     13629632 kB
848 LowTotal:       747444 kB
849 LowFree:          4432 kB
850 SwapTotal:           0 kB
851 SwapFree:            0 kB
852 Dirty:             968 kB
853 Writeback:           0 kB
854 AnonPages:      861800 kB
855 Mapped:         280372 kB
856 Shmem:             644 kB
857 Slab:           284364 kB
858 SReclaimable:   159856 kB
859 SUnreclaim:     124508 kB
860 PageTables:      24448 kB
861 NFS_Unstable:        0 kB
862 Bounce:              0 kB
863 WritebackTmp:        0 kB
864 CommitLimit:   7669796 kB
865 Committed_AS:   100056 kB
866 VmallocTotal:   112216 kB
867 VmallocUsed:       428 kB
868 VmallocChunk:   111088 kB
869 AnonHugePages:   49152 kB
870 
871     MemTotal: Total usable ram (i.e. physical ram minus a few reserved
872               bits and the kernel binary code)
873      MemFree: The sum of LowFree+HighFree
874 MemAvailable: An estimate of how much memory is available for starting new
875               applications, without swapping. Calculated from MemFree,
876               SReclaimable, the size of the file LRU lists, and the low
877               watermarks in each zone.
878               The estimate takes into account that the system needs some
879               page cache to function well, and that not all reclaimable
880               slab will be reclaimable, due to items being in use. The
881               impact of those factors will vary from system to system.
882      Buffers: Relatively temporary storage for raw disk blocks
883               shouldn't get tremendously large (20MB or so)
884       Cached: in-memory cache for files read from the disk (the
885               pagecache).  Doesn't include SwapCached
886   SwapCached: Memory that once was swapped out, is swapped back in but
887               still also is in the swapfile (if memory is needed it
888               doesn't need to be swapped out AGAIN because it is already
889               in the swapfile. This saves I/O)
890       Active: Memory that has been used more recently and usually not
891               reclaimed unless absolutely necessary.
892     Inactive: Memory which has been less recently used.  It is more
893               eligible to be reclaimed for other purposes
894    HighTotal:
895     HighFree: Highmem is all memory above ~860MB of physical memory
896               Highmem areas are for use by userspace programs, or
897               for the pagecache.  The kernel must use tricks to access
898               this memory, making it slower to access than lowmem.
899     LowTotal:
900      LowFree: Lowmem is memory which can be used for everything that
901               highmem can be used for, but it is also available for the
902               kernel's use for its own data structures.  Among many
903               other things, it is where everything from the Slab is
904               allocated.  Bad things happen when you're out of lowmem.
905    SwapTotal: total amount of swap space available
906     SwapFree: Memory which has been evicted from RAM, and is temporarily
907               on the disk
908        Dirty: Memory which is waiting to get written back to the disk
909    Writeback: Memory which is actively being written back to the disk
910    AnonPages: Non-file backed pages mapped into userspace page tables
911 AnonHugePages: Non-file backed huge pages mapped into userspace page tables
912       Mapped: files which have been mmaped, such as libraries
913        Shmem: Total memory used by shared memory (shmem) and tmpfs
914         Slab: in-kernel data structures cache
915 SReclaimable: Part of Slab, that might be reclaimed, such as caches
916   SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
917   PageTables: amount of memory dedicated to the lowest level of page
918               tables.
919 NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
920               storage
921       Bounce: Memory used for block device "bounce buffers"
922 WritebackTmp: Memory used by FUSE for temporary writeback buffers
923  CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
924               this is the total amount of  memory currently available to
925               be allocated on the system. This limit is only adhered to
926               if strict overcommit accounting is enabled (mode 2 in
927               'vm.overcommit_memory').
928               The CommitLimit is calculated with the following formula:
929               CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
930                              overcommit_ratio / 100 + [total swap pages]
931               For example, on a system with 1G of physical RAM and 7G
932               of swap with a `vm.overcommit_ratio` of 30 it would
933               yield a CommitLimit of 7.3G.
934               For more details, see the memory overcommit documentation
935               in vm/overcommit-accounting.
936 Committed_AS: The amount of memory presently allocated on the system.
937               The committed memory is a sum of all of the memory which
938               has been allocated by processes, even if it has not been
939               "used" by them as of yet. A process which malloc()'s 1G
940               of memory, but only touches 300M of it will show up as
941               using 1G. This 1G is memory which has been "committed" to
942               by the VM and can be used at any time by the allocating
943               application. With strict overcommit enabled on the system
944               (mode 2 in 'vm.overcommit_memory'),allocations which would
945               exceed the CommitLimit (detailed above) will not be permitted.
946               This is useful if one needs to guarantee that processes will
947               not fail due to lack of memory once that memory has been
948               successfully allocated.
949 VmallocTotal: total size of vmalloc memory area
950  VmallocUsed: amount of vmalloc area which is used
951 VmallocChunk: largest contiguous block of vmalloc area which is free
952 
953 ..............................................................................
954 
955 vmallocinfo:
956 
957 Provides information about vmalloced/vmaped areas. One line per area,
958 containing the virtual address range of the area, size in bytes,
959 caller information of the creator, and optional information depending
960 on the kind of area :
961 
962  pages=nr    number of pages
963  phys=addr   if a physical address was specified
964  ioremap     I/O mapping (ioremap() and friends)
965  vmalloc     vmalloc() area
966  vmap        vmap()ed pages
967  user        VM_USERMAP area
968  vpages      buffer for pages pointers was vmalloced (huge area)
969  N<node>=nr  (Only on NUMA kernels)
970              Number of pages allocated on memory node <node>
971 
972 > cat /proc/vmallocinfo
973 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
974   /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
975 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
976   /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
977 0xffffc20000302000-0xffffc20000304000    8192 acpi_tb_verify_table+0x21/0x4f...
978   phys=7fee8000 ioremap
979 0xffffc20000304000-0xffffc20000307000   12288 acpi_tb_verify_table+0x21/0x4f...
980   phys=7fee7000 ioremap
981 0xffffc2000031d000-0xffffc2000031f000    8192 init_vdso_vars+0x112/0x210
982 0xffffc2000031f000-0xffffc2000032b000   49152 cramfs_uncompress_init+0x2e ...
983   /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
984 0xffffc2000033a000-0xffffc2000033d000   12288 sys_swapon+0x640/0xac0      ...
985   pages=2 vmalloc N1=2
986 0xffffc20000347000-0xffffc2000034c000   20480 xt_alloc_table_info+0xfe ...
987   /0x130 [x_tables] pages=4 vmalloc N0=4
988 0xffffffffa0000000-0xffffffffa000f000   61440 sys_init_module+0xc27/0x1d00 ...
989    pages=14 vmalloc N2=14
990 0xffffffffa000f000-0xffffffffa0014000   20480 sys_init_module+0xc27/0x1d00 ...
991    pages=4 vmalloc N1=4
992 0xffffffffa0014000-0xffffffffa0017000   12288 sys_init_module+0xc27/0x1d00 ...
993    pages=2 vmalloc N1=2
994 0xffffffffa0017000-0xffffffffa0022000   45056 sys_init_module+0xc27/0x1d00 ...
995    pages=10 vmalloc N0=10
996 
997 ..............................................................................
998 
999 softirqs:
1000 
1001 Provides counts of softirq handlers serviced since boot time, for each cpu.
1002 
1003 > cat /proc/softirqs
1004                 CPU0       CPU1       CPU2       CPU3
1005       HI:          0          0          0          0
1006    TIMER:      27166      27120      27097      27034
1007   NET_TX:          0          0          0         17
1008   NET_RX:         42          0          0         39
1009    BLOCK:          0          0        107       1121
1010  TASKLET:          0          0          0        290
1011    SCHED:      27035      26983      26971      26746
1012  HRTIMER:          0          0          0          0
1013      RCU:       1678       1769       2178       2250
1014 
1015 
1016 1.3 IDE devices in /proc/ide
1017 ----------------------------
1018 
1019 The subdirectory /proc/ide contains information about all IDE devices of which
1020 the kernel  is  aware.  There is one subdirectory for each IDE controller, the
1021 file drivers  and a link for each IDE device, pointing to the device directory
1022 in the controller specific subtree.
1023 
1024 The file  drivers  contains general information about the drivers used for the
1025 IDE devices:
1026 
1027   > cat /proc/ide/drivers
1028   ide-cdrom version 4.53
1029   ide-disk version 1.08
1030 
1031 More detailed  information  can  be  found  in  the  controller  specific
1032 subdirectories. These  are  named  ide0,  ide1  and  so  on.  Each  of  these
1033 directories contains the files shown in table 1-6.
1034 
1035 
1036 Table 1-6: IDE controller info in  /proc/ide/ide?
1037 ..............................................................................
1038  File    Content                                 
1039  channel IDE channel (0 or 1)                    
1040  config  Configuration (only for PCI/IDE bridge) 
1041  mate    Mate name                               
1042  model   Type/Chipset of IDE controller          
1043 ..............................................................................
1044 
1045 Each device  connected  to  a  controller  has  a separate subdirectory in the
1046 controllers directory.  The  files  listed in table 1-7 are contained in these
1047 directories.
1048 
1049 
1050 Table 1-7: IDE device information
1051 ..............................................................................
1052  File             Content                                    
1053  cache            The cache                                  
1054  capacity         Capacity of the medium (in 512Byte blocks) 
1055  driver           driver and version                         
1056  geometry         physical and logical geometry              
1057  identify         device identify block                      
1058  media            media type                                 
1059  model            device identifier                          
1060  settings         device setup                               
1061  smart_thresholds IDE disk management thresholds             
1062  smart_values     IDE disk management values                 
1063 ..............................................................................
1064 
1065 The most  interesting  file is settings. This file contains a nice overview of
1066 the drive parameters:
1067 
1068   # cat /proc/ide/ide0/hda/settings 
1069   name                    value           min             max             mode 
1070   ----                    -----           ---             ---             ---- 
1071   bios_cyl                526             0               65535           rw 
1072   bios_head               255             0               255             rw 
1073   bios_sect               63              0               63              rw 
1074   breada_readahead        4               0               127             rw 
1075   bswap                   0               0               1               r 
1076   file_readahead          72              0               2097151         rw 
1077   io_32bit                0               0               3               rw 
1078   keepsettings            0               0               1               rw 
1079   max_kb_per_request      122             1               127             rw 
1080   multcount               0               0               8               rw 
1081   nice1                   1               0               1               rw 
1082   nowerr                  0               0               1               rw 
1083   pio_mode                write-only      0               255             w 
1084   slow                    0               0               1               rw 
1085   unmaskirq               0               0               1               rw 
1086   using_dma               0               0               1               rw 
1087 
1088 
1089 1.4 Networking info in /proc/net
1090 --------------------------------
1091 
1092 The subdirectory  /proc/net  follows  the  usual  pattern. Table 1-8 shows the
1093 additional values  you  get  for  IP  version 6 if you configure the kernel to
1094 support this. Table 1-9 lists the files and their meaning.
1095 
1096 
1097 Table 1-8: IPv6 info in /proc/net
1098 ..............................................................................
1099  File       Content                                               
1100  udp6       UDP sockets (IPv6)                                    
1101  tcp6       TCP sockets (IPv6)                                    
1102  raw6       Raw device statistics (IPv6)                          
1103  igmp6      IP multicast addresses, which this host joined (IPv6) 
1104  if_inet6   List of IPv6 interface addresses                      
1105  ipv6_route Kernel routing table for IPv6                         
1106  rt6_stats  Global IPv6 routing tables statistics                 
1107  sockstat6  Socket statistics (IPv6)                              
1108  snmp6      Snmp data (IPv6)                                      
1109 ..............................................................................
1110 
1111 
1112 Table 1-9: Network info in /proc/net
1113 ..............................................................................
1114  File          Content                                                         
1115  arp           Kernel  ARP table                                               
1116  dev           network devices with statistics                                 
1117  dev_mcast     the Layer2 multicast groups a device is listening too
1118                (interface index, label, number of references, number of bound
1119                addresses). 
1120  dev_stat      network device status                                           
1121  ip_fwchains   Firewall chain linkage                                          
1122  ip_fwnames    Firewall chain names                                            
1123  ip_masq       Directory containing the masquerading tables                    
1124  ip_masquerade Major masquerading table                                        
1125  netstat       Network statistics                                              
1126  raw           raw device statistics                                           
1127  route         Kernel routing table                                            
1128  rpc           Directory containing rpc info                                   
1129  rt_cache      Routing cache                                                   
1130  snmp          SNMP data                                                       
1131  sockstat      Socket statistics                                               
1132  tcp           TCP  sockets                                                    
1133  udp           UDP sockets                                                     
1134  unix          UNIX domain sockets                                             
1135  wireless      Wireless interface data (Wavelan etc)                           
1136  igmp          IP multicast addresses, which this host joined                  
1137  psched        Global packet scheduler parameters.                             
1138  netlink       List of PF_NETLINK sockets                                      
1139  ip_mr_vifs    List of multicast virtual interfaces                            
1140  ip_mr_cache   List of multicast routing cache                                 
1141 ..............................................................................
1142 
1143 You can  use  this  information  to see which network devices are available in
1144 your system and how much traffic was routed over those devices:
1145 
1146   > cat /proc/net/dev 
1147   Inter-|Receive                                                   |[... 
1148    face |bytes    packets errs drop fifo frame compressed multicast|[... 
1149       lo:  908188   5596     0    0    0     0          0         0 [...         
1150     ppp0:15475140  20721   410    0    0   410          0         0 [...  
1151     eth0:  614530   7085     0    0    0     0          0         1 [... 
1152    
1153   ...] Transmit 
1154   ...] bytes    packets errs drop fifo colls carrier compressed 
1155   ...]  908188     5596    0    0    0     0       0          0 
1156   ...] 1375103    17405    0    0    0     0       0          0 
1157   ...] 1703981     5535    0    0    0     3       0          0 
1158 
1159 In addition, each Channel Bond interface has its own directory.  For
1160 example, the bond0 device will have a directory called /proc/net/bond0/.
1161 It will contain information that is specific to that bond, such as the
1162 current slaves of the bond, the link status of the slaves, and how
1163 many times the slaves link has failed.
1164 
1165 1.5 SCSI info
1166 -------------
1167 
1168 If you  have  a  SCSI  host adapter in your system, you'll find a subdirectory
1169 named after  the driver for this adapter in /proc/scsi. You'll also see a list
1170 of all recognized SCSI devices in /proc/scsi:
1171 
1172   >cat /proc/scsi/scsi 
1173   Attached devices: 
1174   Host: scsi0 Channel: 00 Id: 00 Lun: 00 
1175     Vendor: IBM      Model: DGHS09U          Rev: 03E0 
1176     Type:   Direct-Access                    ANSI SCSI revision: 03 
1177   Host: scsi0 Channel: 00 Id: 06 Lun: 00 
1178     Vendor: PIONEER  Model: CD-ROM DR-U06S   Rev: 1.04 
1179     Type:   CD-ROM                           ANSI SCSI revision: 02 
1180 
1181 
1182 The directory  named  after  the driver has one file for each adapter found in
1183 the system.  These  files  contain information about the controller, including
1184 the used  IRQ  and  the  IO  address range. The amount of information shown is
1185 dependent on  the adapter you use. The example shows the output for an Adaptec
1186 AHA-2940 SCSI adapter:
1187 
1188   > cat /proc/scsi/aic7xxx/0 
1189    
1190   Adaptec AIC7xxx driver version: 5.1.19/3.2.4 
1191   Compile Options: 
1192     TCQ Enabled By Default : Disabled 
1193     AIC7XXX_PROC_STATS     : Disabled 
1194     AIC7XXX_RESET_DELAY    : 5 
1195   Adapter Configuration: 
1196              SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter 
1197                              Ultra Wide Controller 
1198       PCI MMAPed I/O Base: 0xeb001000 
1199    Adapter SEEPROM Config: SEEPROM found and used. 
1200         Adaptec SCSI BIOS: Enabled 
1201                       IRQ: 10 
1202                      SCBs: Active 0, Max Active 2, 
1203                            Allocated 15, HW 16, Page 255 
1204                Interrupts: 160328 
1205         BIOS Control Word: 0x18b6 
1206      Adapter Control Word: 0x005b 
1207      Extended Translation: Enabled 
1208   Disconnect Enable Flags: 0xffff 
1209        Ultra Enable Flags: 0x0001 
1210    Tag Queue Enable Flags: 0x0000 
1211   Ordered Queue Tag Flags: 0x0000 
1212   Default Tag Queue Depth: 8 
1213       Tagged Queue By Device array for aic7xxx host instance 0: 
1214         {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} 
1215       Actual queue depth per device for aic7xxx host instance 0: 
1216         {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} 
1217   Statistics: 
1218   (scsi0:0:0:0) 
1219     Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 
1220     Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) 
1221     Total transfers 160151 (74577 reads and 85574 writes) 
1222   (scsi0:0:6:0) 
1223     Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 
1224     Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) 
1225     Total transfers 0 (0 reads and 0 writes) 
1226 
1227 
1228 1.6 Parallel port info in /proc/parport
1229 ---------------------------------------
1230 
1231 The directory  /proc/parport  contains information about the parallel ports of
1232 your system.  It  has  one  subdirectory  for  each port, named after the port
1233 number (0,1,2,...).
1234 
1235 These directories contain the four files shown in Table 1-10.
1236 
1237 
1238 Table 1-10: Files in /proc/parport
1239 ..............................................................................
1240  File      Content                                                             
1241  autoprobe Any IEEE-1284 device ID information that has been acquired.         
1242  devices   list of the device drivers using that port. A + will appear by the
1243            name of the device currently using the port (it might not appear
1244            against any). 
1245  hardware  Parallel port's base address, IRQ line and DMA channel.             
1246  irq       IRQ that parport is using for that port. This is in a separate
1247            file to allow you to alter it by writing a new value in (IRQ
1248            number or none). 
1249 ..............................................................................
1250 
1251 1.7 TTY info in /proc/tty
1252 -------------------------
1253 
1254 Information about  the  available  and actually used tty's can be found in the
1255 directory /proc/tty.You'll  find  entries  for drivers and line disciplines in
1256 this directory, as shown in Table 1-11.
1257 
1258 
1259 Table 1-11: Files in /proc/tty
1260 ..............................................................................
1261  File          Content                                        
1262  drivers       list of drivers and their usage                
1263  ldiscs        registered line disciplines                    
1264  driver/serial usage statistic and status of single tty lines 
1265 ..............................................................................
1266 
1267 To see  which  tty's  are  currently in use, you can simply look into the file
1268 /proc/tty/drivers:
1269 
1270   > cat /proc/tty/drivers 
1271   pty_slave            /dev/pts      136   0-255 pty:slave 
1272   pty_master           /dev/ptm      128   0-255 pty:master 
1273   pty_slave            /dev/ttyp       3   0-255 pty:slave 
1274   pty_master           /dev/pty        2   0-255 pty:master 
1275   serial               /dev/cua        5   64-67 serial:callout 
1276   serial               /dev/ttyS       4   64-67 serial 
1277   /dev/tty0            /dev/tty0       4       0 system:vtmaster 
1278   /dev/ptmx            /dev/ptmx       5       2 system 
1279   /dev/console         /dev/console    5       1 system:console 
1280   /dev/tty             /dev/tty        5       0 system:/dev/tty 
1281   unknown              /dev/tty        4    1-63 console 
1282 
1283 
1284 1.8 Miscellaneous kernel statistics in /proc/stat
1285 -------------------------------------------------
1286 
1287 Various pieces   of  information about  kernel activity  are  available in the
1288 /proc/stat file.  All  of  the numbers reported  in  this file are  aggregates
1289 since the system first booted.  For a quick look, simply cat the file:
1290 
1291   > cat /proc/stat
1292   cpu  2255 34 2290 22625563 6290 127 456 0 0 0
1293   cpu0 1132 34 1441 11311718 3675 127 438 0 0 0
1294   cpu1 1123 0 849 11313845 2614 0 18 0 0 0
1295   intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1296   ctxt 1990473
1297   btime 1062191376
1298   processes 2915
1299   procs_running 1
1300   procs_blocked 0
1301   softirq 183433 0 21755 12 39 1137 231 21459 2263
1302 
1303 The very first  "cpu" line aggregates the  numbers in all  of the other "cpuN"
1304 lines.  These numbers identify the amount of time the CPU has spent performing
1305 different kinds of work.  Time units are in USER_HZ (typically hundredths of a
1306 second).  The meanings of the columns are as follows, from left to right:
1307 
1308 - user: normal processes executing in user mode
1309 - nice: niced processes executing in user mode
1310 - system: processes executing in kernel mode
1311 - idle: twiddling thumbs
1312 - iowait: waiting for I/O to complete
1313 - irq: servicing interrupts
1314 - softirq: servicing softirqs
1315 - steal: involuntary wait
1316 - guest: running a normal guest
1317 - guest_nice: running a niced guest
1318 
1319 The "intr" line gives counts of interrupts  serviced since boot time, for each
1320 of the  possible system interrupts.   The first  column  is the  total of  all
1321 interrupts serviced  including  unnumbered  architecture specific  interrupts;
1322 each  subsequent column is the  total for that particular numbered interrupt.
1323 Unnumbered interrupts are not shown, only summed into the total.
1324 
1325 The "ctxt" line gives the total number of context switches across all CPUs.
1326 
1327 The "btime" line gives  the time at which the  system booted, in seconds since
1328 the Unix epoch.
1329 
1330 The "processes" line gives the number  of processes and threads created, which
1331 includes (but  is not limited  to) those  created by  calls to the  fork() and
1332 clone() system calls.
1333 
1334 The "procs_running" line gives the total number of threads that are
1335 running or ready to run (i.e., the total number of runnable threads).
1336 
1337 The   "procs_blocked" line gives  the  number of  processes currently blocked,
1338 waiting for I/O to complete.
1339 
1340 The "softirq" line gives counts of softirqs serviced since boot time, for each
1341 of the possible system softirqs. The first column is the total of all
1342 softirqs serviced; each subsequent column is the total for that particular
1343 softirq.
1344 
1345 
1346 1.9 Ext4 file system parameters
1347 -------------------------------
1348 
1349 Information about mounted ext4 file systems can be found in
1350 /proc/fs/ext4.  Each mounted filesystem will have a directory in
1351 /proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1352 /proc/fs/ext4/dm-0).   The files in each per-device directory are shown
1353 in Table 1-12, below.
1354 
1355 Table 1-12: Files in /proc/fs/ext4/<devname>
1356 ..............................................................................
1357  File            Content                                        
1358  mb_groups       details of multiblock allocator buddy cache of free blocks
1359 ..............................................................................
1360 
1361 2.0 /proc/consoles
1362 ------------------
1363 Shows registered system console lines.
1364 
1365 To see which character device lines are currently used for the system console
1366 /dev/console, you may simply look into the file /proc/consoles:
1367 
1368   > cat /proc/consoles
1369   tty0                 -WU (ECp)       4:7
1370   ttyS0                -W- (Ep)        4:64
1371 
1372 The columns are:
1373 
1374   device               name of the device
1375   operations           R = can do read operations
1376                        W = can do write operations
1377                        U = can do unblank
1378   flags                E = it is enabled
1379                        C = it is preferred console
1380                        B = it is primary boot console
1381                        p = it is used for printk buffer
1382                        b = it is not a TTY but a Braille device
1383                        a = it is safe to use when cpu is offline
1384   major:minor          major and minor number of the device separated by a colon
1385 
1386 ------------------------------------------------------------------------------
1387 Summary
1388 ------------------------------------------------------------------------------
1389 The /proc file system serves information about the running system. It not only
1390 allows access to process data but also allows you to request the kernel status
1391 by reading files in the hierarchy.
1392 
1393 The directory  structure  of /proc reflects the types of information and makes
1394 it easy, if not obvious, where to look for specific data.
1395 ------------------------------------------------------------------------------
1396 
1397 ------------------------------------------------------------------------------
1398 CHAPTER 2: MODIFYING SYSTEM PARAMETERS
1399 ------------------------------------------------------------------------------
1400 
1401 ------------------------------------------------------------------------------
1402 In This Chapter
1403 ------------------------------------------------------------------------------
1404 * Modifying kernel parameters by writing into files found in /proc/sys
1405 * Exploring the files which modify certain parameters
1406 * Review of the /proc/sys file tree
1407 ------------------------------------------------------------------------------
1408 
1409 
1410 A very  interesting part of /proc is the directory /proc/sys. This is not only
1411 a source  of  information,  it also allows you to change parameters within the
1412 kernel. Be  very  careful  when attempting this. You can optimize your system,
1413 but you  can  also  cause  it  to  crash.  Never  alter kernel parameters on a
1414 production system.  Set  up  a  development machine and test to make sure that
1415 everything works  the  way  you want it to. You may have no alternative but to
1416 reboot the machine once an error has been made.
1417 
1418 To change  a  value,  simply  echo  the new value into the file. An example is
1419 given below  in the section on the file system data. You need to be root to do
1420 this. You  can  create  your  own  boot script to perform this every time your
1421 system boots.
1422 
1423 The files  in /proc/sys can be used to fine tune and monitor miscellaneous and
1424 general things  in  the operation of the Linux kernel. Since some of the files
1425 can inadvertently  disrupt  your  system,  it  is  advisable  to  read  both
1426 documentation and  source  before actually making adjustments. In any case, be
1427 very careful  when  writing  to  any  of these files. The entries in /proc may
1428 change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1429 review the kernel documentation in the directory /usr/src/linux/Documentation.
1430 This chapter  is  heavily  based  on the documentation included in the pre 2.2
1431 kernels, and became part of it in version 2.2.1 of the Linux kernel.
1432 
1433 Please see: Documentation/sysctl/ directory for descriptions of these
1434 entries.
1435 
1436 ------------------------------------------------------------------------------
1437 Summary
1438 ------------------------------------------------------------------------------
1439 Certain aspects  of  kernel  behavior  can be modified at runtime, without the
1440 need to  recompile  the kernel, or even to reboot the system. The files in the
1441 /proc/sys tree  can  not only be read, but also modified. You can use the echo
1442 command to write value into these files, thereby changing the default settings
1443 of the kernel.
1444 ------------------------------------------------------------------------------
1445 
1446 ------------------------------------------------------------------------------
1447 CHAPTER 3: PER-PROCESS PARAMETERS
1448 ------------------------------------------------------------------------------
1449 
1450 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1451 --------------------------------------------------------------------------------
1452 
1453 These file can be used to adjust the badness heuristic used to select which
1454 process gets killed in out of memory conditions.
1455 
1456 The badness heuristic assigns a value to each candidate task ranging from 0
1457 (never kill) to 1000 (always kill) to determine which process is targeted.  The
1458 units are roughly a proportion along that range of allowed memory the process
1459 may allocate from based on an estimation of its current memory and swap use.
1460 For example, if a task is using all allowed memory, its badness score will be
1461 1000.  If it is using half of its allowed memory, its score will be 500.
1462 
1463 There is an additional factor included in the badness score: the current memory
1464 and swap usage is discounted by 3% for root processes.
1465 
1466 The amount of "allowed" memory depends on the context in which the oom killer
1467 was called.  If it is due to the memory assigned to the allocating task's cpuset
1468 being exhausted, the allowed memory represents the set of mems assigned to that
1469 cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
1470 memory represents the set of mempolicy nodes.  If it is due to a memory
1471 limit (or swap limit) being reached, the allowed memory is that configured
1472 limit.  Finally, if it is due to the entire system being out of memory, the
1473 allowed memory represents all allocatable resources.
1474 
1475 The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1476 is used to determine which task to kill.  Acceptable values range from -1000
1477 (OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
1478 polarize the preference for oom killing either by always preferring a certain
1479 task or completely disabling it.  The lowest possible value, -1000, is
1480 equivalent to disabling oom killing entirely for that task since it will always
1481 report a badness score of 0.
1482 
1483 Consequently, it is very simple for userspace to define the amount of memory to
1484 consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
1485 example, is roughly equivalent to allowing the remainder of tasks sharing the
1486 same system, cpuset, mempolicy, or memory controller resources to use at least
1487 50% more memory.  A value of -500, on the other hand, would be roughly
1488 equivalent to discounting 50% of the task's allowed memory from being considered
1489 as scoring against the task.
1490 
1491 For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1492 be used to tune the badness score.  Its acceptable values range from -16
1493 (OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1494 (OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
1495 scaled linearly with /proc/<pid>/oom_score_adj.
1496 
1497 The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1498 value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1499 requires CAP_SYS_RESOURCE.
1500 
1501 Caveat: when a parent task is selected, the oom killer will sacrifice any first
1502 generation children with separate address spaces instead, if possible.  This
1503 avoids servers and important system daemons from being killed and loses the
1504 minimal amount of work.
1505 
1506 
1507 3.2 /proc/<pid>/oom_score - Display current oom-killer score
1508 -------------------------------------------------------------
1509 
1510 This file can be used to check the current score used by the oom-killer is for
1511 any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1512 process should be killed in an out-of-memory situation.
1513 
1514 
1515 3.3  /proc/<pid>/io - Display the IO accounting fields
1516 -------------------------------------------------------
1517 
1518 This file contains IO statistics for each running process
1519 
1520 Example
1521 -------
1522 
1523 test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1524 [1] 3828
1525 
1526 test:/tmp # cat /proc/3828/io
1527 rchar: 323934931
1528 wchar: 323929600
1529 syscr: 632687
1530 syscw: 632675
1531 read_bytes: 0
1532 write_bytes: 323932160
1533 cancelled_write_bytes: 0
1534 
1535 
1536 Description
1537 -----------
1538 
1539 rchar
1540 -----
1541 
1542 I/O counter: chars read
1543 The number of bytes which this task has caused to be read from storage. This
1544 is simply the sum of bytes which this process passed to read() and pread().
1545 It includes things like tty IO and it is unaffected by whether or not actual
1546 physical disk IO was required (the read might have been satisfied from
1547 pagecache)
1548 
1549 
1550 wchar
1551 -----
1552 
1553 I/O counter: chars written
1554 The number of bytes which this task has caused, or shall cause to be written
1555 to disk. Similar caveats apply here as with rchar.
1556 
1557 
1558 syscr
1559 -----
1560 
1561 I/O counter: read syscalls
1562 Attempt to count the number of read I/O operations, i.e. syscalls like read()
1563 and pread().
1564 
1565 
1566 syscw
1567 -----
1568 
1569 I/O counter: write syscalls
1570 Attempt to count the number of write I/O operations, i.e. syscalls like
1571 write() and pwrite().
1572 
1573 
1574 read_bytes
1575 ----------
1576 
1577 I/O counter: bytes read
1578 Attempt to count the number of bytes which this process really did cause to
1579 be fetched from the storage layer. Done at the submit_bio() level, so it is
1580 accurate for block-backed filesystems. <please add status regarding NFS and
1581 CIFS at a later time>
1582 
1583 
1584 write_bytes
1585 -----------
1586 
1587 I/O counter: bytes written
1588 Attempt to count the number of bytes which this process caused to be sent to
1589 the storage layer. This is done at page-dirtying time.
1590 
1591 
1592 cancelled_write_bytes
1593 ---------------------
1594 
1595 The big inaccuracy here is truncate. If a process writes 1MB to a file and
1596 then deletes the file, it will in fact perform no writeout. But it will have
1597 been accounted as having caused 1MB of write.
1598 In other words: The number of bytes which this process caused to not happen,
1599 by truncating pagecache. A task can cause "negative" IO too. If this task
1600 truncates some dirty pagecache, some IO which another task has been accounted
1601 for (in its write_bytes) will not be happening. We _could_ just subtract that
1602 from the truncating task's write_bytes, but there is information loss in doing
1603 that.
1604 
1605 
1606 Note
1607 ----
1608 
1609 At its current implementation state, this is a bit racy on 32-bit machines: if
1610 process A reads process B's /proc/pid/io while process B is updating one of
1611 those 64-bit counters, process A could see an intermediate result.
1612 
1613 
1614 More information about this can be found within the taskstats documentation in
1615 Documentation/accounting.
1616 
1617 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1618 ---------------------------------------------------------------
1619 When a process is dumped, all anonymous memory is written to a core file as
1620 long as the size of the core file isn't limited. But sometimes we don't want
1621 to dump some memory segments, for example, huge shared memory or DAX.
1622 Conversely, sometimes we want to save file-backed memory segments into a core
1623 file, not only the individual files.
1624 
1625 /proc/<pid>/coredump_filter allows you to customize which memory segments
1626 will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1627 of memory types. If a bit of the bitmask is set, memory segments of the
1628 corresponding memory type are dumped, otherwise they are not dumped.
1629 
1630 The following 9 memory types are supported:
1631   - (bit 0) anonymous private memory
1632   - (bit 1) anonymous shared memory
1633   - (bit 2) file-backed private memory
1634   - (bit 3) file-backed shared memory
1635   - (bit 4) ELF header pages in file-backed private memory areas (it is
1636             effective only if the bit 2 is cleared)
1637   - (bit 5) hugetlb private memory
1638   - (bit 6) hugetlb shared memory
1639   - (bit 7) DAX private memory
1640   - (bit 8) DAX shared memory
1641 
1642   Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1643   are always dumped regardless of the bitmask status.
1644 
1645   Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
1646   only affected by bit 5-6, and DAX is only affected by bits 7-8.
1647 
1648 The default value of coredump_filter is 0x33; this means all anonymous memory
1649 segments, ELF header pages and hugetlb private memory are dumped.
1650 
1651 If you don't want to dump all shared memory segments attached to pid 1234,
1652 write 0x31 to the process's proc file.
1653 
1654   $ echo 0x31 > /proc/1234/coredump_filter
1655 
1656 When a new process is created, the process inherits the bitmask status from its
1657 parent. It is useful to set up coredump_filter before the program runs.
1658 For example:
1659 
1660   $ echo 0x7 > /proc/self/coredump_filter
1661   $ ./some_program
1662 
1663 3.5     /proc/<pid>/mountinfo - Information about mounts
1664 --------------------------------------------------------
1665 
1666 This file contains lines of the form:
1667 
1668 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1669 (1)(2)(3)   (4)   (5)      (6)      (7)   (8) (9)   (10)         (11)
1670 
1671 (1) mount ID:  unique identifier of the mount (may be reused after umount)
1672 (2) parent ID:  ID of parent (or of self for the top of the mount tree)
1673 (3) major:minor:  value of st_dev for files on filesystem
1674 (4) root:  root of the mount within the filesystem
1675 (5) mount point:  mount point relative to the process's root
1676 (6) mount options:  per mount options
1677 (7) optional fields:  zero or more fields of the form "tag[:value]"
1678 (8) separator:  marks the end of the optional fields
1679 (9) filesystem type:  name of filesystem of the form "type[.subtype]"
1680 (10) mount source:  filesystem specific information or "none"
1681 (11) super options:  per super block options
1682 
1683 Parsers should ignore all unrecognised optional fields.  Currently the
1684 possible optional fields are:
1685 
1686 shared:X  mount is shared in peer group X
1687 master:X  mount is slave to peer group X
1688 propagate_from:X  mount is slave and receives propagation from peer group X (*)
1689 unbindable  mount is unbindable
1690 
1691 (*) X is the closest dominant peer group under the process's root.  If
1692 X is the immediate master of the mount, or if there's no dominant peer
1693 group under the same root, then only the "master:X" field is present
1694 and not the "propagate_from:X" field.
1695 
1696 For more information on mount propagation see:
1697 
1698   Documentation/filesystems/sharedsubtree.txt
1699 
1700 
1701 3.6     /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
1702 --------------------------------------------------------
1703 These files provide a method to access a tasks comm value. It also allows for
1704 a task to set its own or one of its thread siblings comm value. The comm value
1705 is limited in size compared to the cmdline value, so writing anything longer
1706 then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1707 comm value.
1708 
1709 
1710 3.7     /proc/<pid>/task/<tid>/children - Information about task children
1711 -------------------------------------------------------------------------
1712 This file provides a fast way to retrieve first level children pids
1713 of a task pointed by <pid>/<tid> pair. The format is a space separated
1714 stream of pids.
1715 
1716 Note the "first level" here -- if a child has own children they will
1717 not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children
1718 to obtain the descendants.
1719 
1720 Since this interface is intended to be fast and cheap it doesn't
1721 guarantee to provide precise results and some children might be
1722 skipped, especially if they've exited right after we printed their
1723 pids, so one need to either stop or freeze processes being inspected
1724 if precise results are needed.
1725 
1726 
1727 3.8     /proc/<pid>/fdinfo/<fd> - Information about opened file
1728 ---------------------------------------------------------------
1729 This file provides information associated with an opened file. The regular
1730 files have at least three fields -- 'pos', 'flags' and mnt_id. The 'pos'
1731 represents the current offset of the opened file in decimal form [see lseek(2)
1732 for details], 'flags' denotes the octal O_xxx mask the file has been
1733 created with [see open(2) for details] and 'mnt_id' represents mount ID of
1734 the file system containing the opened file [see 3.5 /proc/<pid>/mountinfo
1735 for details].
1736 
1737 A typical output is
1738 
1739         pos:    0
1740         flags:  0100002
1741         mnt_id: 19
1742 
1743 All locks associated with a file descriptor are shown in its fdinfo too.
1744 
1745 lock:       1: FLOCK  ADVISORY  WRITE 359 00:13:11691 0 EOF
1746 
1747 The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1748 pair provide additional information particular to the objects they represent.
1749 
1750         Eventfd files
1751         ~~~~~~~~~~~~~
1752         pos:    0
1753         flags:  04002
1754         mnt_id: 9
1755         eventfd-count:  5a
1756 
1757         where 'eventfd-count' is hex value of a counter.
1758 
1759         Signalfd files
1760         ~~~~~~~~~~~~~~
1761         pos:    0
1762         flags:  04002
1763         mnt_id: 9
1764         sigmask:        0000000000000200
1765 
1766         where 'sigmask' is hex value of the signal mask associated
1767         with a file.
1768 
1769         Epoll files
1770         ~~~~~~~~~~~
1771         pos:    0
1772         flags:  02
1773         mnt_id: 9
1774         tfd:        5 events:       1d data: ffffffffffffffff
1775 
1776         where 'tfd' is a target file descriptor number in decimal form,
1777         'events' is events mask being watched and the 'data' is data
1778         associated with a target [see epoll(7) for more details].
1779 
1780         Fsnotify files
1781         ~~~~~~~~~~~~~~
1782         For inotify files the format is the following
1783 
1784         pos:    0
1785         flags:  02000000
1786         inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
1787 
1788         where 'wd' is a watch descriptor in decimal form, ie a target file
1789         descriptor number, 'ino' and 'sdev' are inode and device where the
1790         target file resides and the 'mask' is the mask of events, all in hex
1791         form [see inotify(7) for more details].
1792 
1793         If the kernel was built with exportfs support, the path to the target
1794         file is encoded as a file handle.  The file handle is provided by three
1795         fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
1796         format.
1797 
1798         If the kernel is built without exportfs support the file handle won't be
1799         printed out.
1800 
1801         If there is no inotify mark attached yet the 'inotify' line will be omitted.
1802 
1803         For fanotify files the format is
1804 
1805         pos:    0
1806         flags:  02
1807         mnt_id: 9
1808         fanotify flags:10 event-flags:0
1809         fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
1810         fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
1811 
1812         where fanotify 'flags' and 'event-flags' are values used in fanotify_init
1813         call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
1814         flags associated with mark which are tracked separately from events
1815         mask. 'ino', 'sdev' are target inode and device, 'mask' is the events
1816         mask and 'ignored_mask' is the mask of events which are to be ignored.
1817         All in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
1818         does provide information about flags and mask used in fanotify_mark
1819         call [see fsnotify manpage for details].
1820 
1821         While the first three lines are mandatory and always printed, the rest is
1822         optional and may be omitted if no marks created yet.
1823 
1824         Timerfd files
1825         ~~~~~~~~~~~~~
1826 
1827         pos:    0
1828         flags:  02
1829         mnt_id: 9
1830         clockid: 0
1831         ticks: 0
1832         settime flags: 01
1833         it_value: (0, 49406829)
1834         it_interval: (1, 0)
1835 
1836         where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
1837         that have occurred [see timerfd_create(2) for details]. 'settime flags' are
1838         flags in octal form been used to setup the timer [see timerfd_settime(2) for
1839         details]. 'it_value' is remaining time until the timer exiration.
1840         'it_interval' is the interval for the timer. Note the timer might be set up
1841         with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
1842         still exhibits timer's remaining time.
1843 
1844 3.9     /proc/<pid>/map_files - Information about memory mapped files
1845 ---------------------------------------------------------------------
1846 This directory contains symbolic links which represent memory mapped files
1847 the process is maintaining.  Example output:
1848 
1849      | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
1850      | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
1851      | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
1852      | ...
1853      | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
1854      | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
1855 
1856 The name of a link represents the virtual memory bounds of a mapping, i.e.
1857 vm_area_struct::vm_start-vm_area_struct::vm_end.
1858 
1859 The main purpose of the map_files is to retrieve a set of memory mapped
1860 files in a fast way instead of parsing /proc/<pid>/maps or
1861 /proc/<pid>/smaps, both of which contain many more records.  At the same
1862 time one can open(2) mappings from the listings of two processes and
1863 comparing their inode numbers to figure out which anonymous memory areas
1864 are actually shared.
1865 
1866 3.10    /proc/<pid>/timerslack_ns - Task timerslack value
1867 ---------------------------------------------------------
1868 This file provides the value of the task's timerslack value in nanoseconds.
1869 This value specifies a amount of time that normal timers may be deferred
1870 in order to coalesce timers and avoid unnecessary wakeups.
1871 
1872 This allows a task's interactivity vs power consumption trade off to be
1873 adjusted.
1874 
1875 Writing 0 to the file will set the tasks timerslack to the default value.
1876 
1877 Valid values are from 0 - ULLONG_MAX
1878 
1879 An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
1880 permissions on the task specified to change its timerslack_ns value.
1881 
1882 
1883 ------------------------------------------------------------------------------
1884 Configuring procfs
1885 ------------------------------------------------------------------------------
1886 
1887 4.1     Mount options
1888 ---------------------
1889 
1890 The following mount options are supported:
1891 
1892         hidepid=        Set /proc/<pid>/ access mode.
1893         gid=            Set the group authorized to learn processes information.
1894 
1895 hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
1896 (default).
1897 
1898 hidepid=1 means users may not access any /proc/<pid>/ directories but their
1899 own.  Sensitive files like cmdline, sched*, status are now protected against
1900 other users.  This makes it impossible to learn whether any user runs
1901 specific program (given the program doesn't reveal itself by its behaviour).
1902 As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users,
1903 poorly written programs passing sensitive information via program arguments are
1904 now protected against local eavesdroppers.
1905 
1906 hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other
1907 users.  It doesn't mean that it hides a fact whether a process with a specific
1908 pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"),
1909 but it hides process' uid and gid, which may be learned by stat()'ing
1910 /proc/<pid>/ otherwise.  It greatly complicates an intruder's task of gathering
1911 information about running processes, whether some daemon runs with elevated
1912 privileges, whether other user runs some sensitive program, whether other users
1913 run any program at all, etc.
1914 
1915 gid= defines a group authorized to learn processes information otherwise
1916 prohibited by hidepid=.  If you use some daemon like identd which needs to learn
1917 information about processes information, just add identd to this group.

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