Version:  2.0.40 2.2.26 2.4.37 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1

Linux/Documentation/filesystems/proc.txt

  1 ------------------------------------------------------------------------------
  2                        T H E  /proc   F I L E S Y S T E M
  3 ------------------------------------------------------------------------------
  4 /proc/sys         Terrehon Bowden <terrehon@pacbell.net>        October 7 1999
  5                   Bodo Bauer <bb@ricochet.net>
  6 
  7 2.4.x update      Jorge Nerin <comandante@zaralinux.com>      November 14 2000
  8 move /proc/sys    Shen Feng <shen@cn.fujitsu.com>                 April 1 2009
  9 ------------------------------------------------------------------------------
 10 Version 1.3                                              Kernel version 2.2.12
 11                                               Kernel version 2.4.0-test11-pre4
 12 ------------------------------------------------------------------------------
 13 fixes/update part 1.1  Stefani Seibold <stefani@seibold.net>       June 9 2009
 14 
 15 Table of Contents
 16 -----------------
 17 
 18   0     Preface
 19   0.1   Introduction/Credits
 20   0.2   Legal Stuff
 21 
 22   1     Collecting System Information
 23   1.1   Process-Specific Subdirectories
 24   1.2   Kernel data
 25   1.3   IDE devices in /proc/ide
 26   1.4   Networking info in /proc/net
 27   1.5   SCSI info
 28   1.6   Parallel port info in /proc/parport
 29   1.7   TTY info in /proc/tty
 30   1.8   Miscellaneous kernel statistics in /proc/stat
 31   1.9   Ext4 file system parameters
 32 
 33   2     Modifying System Parameters
 34 
 35   3     Per-Process Parameters
 36   3.1   /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj - Adjust the oom-killer
 37                                                                 score
 38   3.2   /proc/<pid>/oom_score - Display current oom-killer score
 39   3.3   /proc/<pid>/io - Display the IO accounting fields
 40   3.4   /proc/<pid>/coredump_filter - Core dump filtering settings
 41   3.5   /proc/<pid>/mountinfo - Information about mounts
 42   3.6   /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
 43   3.7   /proc/<pid>/task/<tid>/children - Information about task children
 44   3.8   /proc/<pid>/fdinfo/<fd> - Information about opened file
 45   3.9   /proc/<pid>/map_files - Information about memory mapped files
 46 
 47   4     Configuring procfs
 48   4.1   Mount options
 49 
 50 ------------------------------------------------------------------------------
 51 Preface
 52 ------------------------------------------------------------------------------
 53 
 54 0.1 Introduction/Credits
 55 ------------------------
 56 
 57 This documentation is  part of a soon (or  so we hope) to be  released book on
 58 the SuSE  Linux distribution. As  there is  no complete documentation  for the
 59 /proc file system and we've used  many freely available sources to write these
 60 chapters, it  seems only fair  to give the work  back to the  Linux community.
 61 This work is  based on the 2.2.*  kernel version and the  upcoming 2.4.*. I'm
 62 afraid it's still far from complete, but we  hope it will be useful. As far as
 63 we know, it is the first 'all-in-one' document about the /proc file system. It
 64 is focused  on the Intel  x86 hardware,  so if you  are looking for  PPC, ARM,
 65 SPARC, AXP, etc., features, you probably  won't find what you are looking for.
 66 It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
 67 additions and patches  are welcome and will  be added to this  document if you
 68 mail them to Bodo.
 69 
 70 We'd like  to  thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
 71 other people for help compiling this documentation. We'd also like to extend a
 72 special thank  you to Andi Kleen for documentation, which we relied on heavily
 73 to create  this  document,  as well as the additional information he provided.
 74 Thanks to  everybody  else  who contributed source or docs to the Linux kernel
 75 and helped create a great piece of software... :)
 76 
 77 If you  have  any comments, corrections or additions, please don't hesitate to
 78 contact Bodo  Bauer  at  bb@ricochet.net.  We'll  be happy to add them to this
 79 document.
 80 
 81 The   latest   version    of   this   document   is    available   online   at
 82 http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html
 83 
 84 If  the above  direction does  not works  for you,  you could  try the  kernel
 85 mailing  list  at  linux-kernel@vger.kernel.org  and/or try  to  reach  me  at
 86 comandante@zaralinux.com.
 87 
 88 0.2 Legal Stuff
 89 ---------------
 90 
 91 We don't  guarantee  the  correctness  of this document, and if you come to us
 92 complaining about  how  you  screwed  up  your  system  because  of  incorrect
 93 documentation, we won't feel responsible...
 94 
 95 ------------------------------------------------------------------------------
 96 CHAPTER 1: COLLECTING SYSTEM INFORMATION
 97 ------------------------------------------------------------------------------
 98 
 99 ------------------------------------------------------------------------------
100 In This Chapter
101 ------------------------------------------------------------------------------
102 * Investigating  the  properties  of  the  pseudo  file  system  /proc and its
103   ability to provide information on the running Linux system
104 * Examining /proc's structure
105 * Uncovering  various  information  about the kernel and the processes running
106   on the system
107 ------------------------------------------------------------------------------
108 
109 
110 The proc  file  system acts as an interface to internal data structures in the
111 kernel. It  can  be  used to obtain information about the system and to change
112 certain kernel parameters at runtime (sysctl).
113 
114 First, we'll  take  a  look  at the read-only parts of /proc. In Chapter 2, we
115 show you how you can use /proc/sys to change settings.
116 
117 1.1 Process-Specific Subdirectories
118 -----------------------------------
119 
120 The directory  /proc  contains  (among other things) one subdirectory for each
121 process running on the system, which is named after the process ID (PID).
122 
123 The link  self  points  to  the  process reading the file system. Each process
124 subdirectory has the entries listed in Table 1-1.
125 
126 
127 Table 1-1: Process specific entries in /proc
128 ..............................................................................
129  File           Content
130  clear_refs     Clears page referenced bits shown in smaps output
131  cmdline        Command line arguments
132  cpu            Current and last cpu in which it was executed   (2.4)(smp)
133  cwd            Link to the current working directory
134  environ        Values of environment variables
135  exe            Link to the executable of this process
136  fd             Directory, which contains all file descriptors
137  maps           Memory maps to executables and library files    (2.4)
138  mem            Memory held by this process
139  root           Link to the root directory of this process
140  stat           Process status
141  statm          Process memory status information
142  status         Process status in human readable form
143  wchan          If CONFIG_KALLSYMS is set, a pre-decoded wchan
144  pagemap        Page table
145  stack          Report full stack trace, enable via CONFIG_STACKTRACE
146  smaps          a extension based on maps, showing the memory consumption of
147                 each mapping and flags associated with it
148  numa_maps      an extension based on maps, showing the memory locality and
149                 binding policy as well as mem usage (in pages) of each mapping.
150 ..............................................................................
151 
152 For example, to get the status information of a process, all you have to do is
153 read the file /proc/PID/status:
154 
155   >cat /proc/self/status
156   Name:   cat
157   State:  R (running)
158   Tgid:   5452
159   Pid:    5452
160   PPid:   743
161   TracerPid:      0                                             (2.4)
162   Uid:    501     501     501     501
163   Gid:    100     100     100     100
164   FDSize: 256
165   Groups: 100 14 16
166   VmPeak:     5004 kB
167   VmSize:     5004 kB
168   VmLck:         0 kB
169   VmHWM:       476 kB
170   VmRSS:       476 kB
171   VmData:      156 kB
172   VmStk:        88 kB
173   VmExe:        68 kB
174   VmLib:      1412 kB
175   VmPTE:        20 kb
176   VmSwap:        0 kB
177   Threads:        1
178   SigQ:   0/28578
179   SigPnd: 0000000000000000
180   ShdPnd: 0000000000000000
181   SigBlk: 0000000000000000
182   SigIgn: 0000000000000000
183   SigCgt: 0000000000000000
184   CapInh: 00000000fffffeff
185   CapPrm: 0000000000000000
186   CapEff: 0000000000000000
187   CapBnd: ffffffffffffffff
188   Seccomp:        0
189   voluntary_ctxt_switches:        0
190   nonvoluntary_ctxt_switches:     1
191 
192 This shows you nearly the same information you would get if you viewed it with
193 the ps  command.  In  fact,  ps  uses  the  proc  file  system  to  obtain its
194 information.  But you get a more detailed  view of the  process by reading the
195 file /proc/PID/status. It fields are described in table 1-2.
196 
197 The  statm  file  contains  more  detailed  information about the process
198 memory usage. Its seven fields are explained in Table 1-3.  The stat file
199 contains details information about the process itself.  Its fields are
200 explained in Table 1-4.
201 
202 (for SMP CONFIG users)
203 For making accounting scalable, RSS related information are handled in an
204 asynchronous manner and the value may not be very precise. To see a precise
205 snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
206 It's slow but very precise.
207 
208 Table 1-2: Contents of the status files (as of 3.20.0)
209 ..............................................................................
210  Field                       Content
211  Name                        filename of the executable
212  State                       state (R is running, S is sleeping, D is sleeping
213                              in an uninterruptible wait, Z is zombie,
214                              T is traced or stopped)
215  Tgid                        thread group ID
216  Ngid                        NUMA group ID (0 if none)
217  Pid                         process id
218  PPid                        process id of the parent process
219  TracerPid                   PID of process tracing this process (0 if not)
220  Uid                         Real, effective, saved set, and  file system UIDs
221  Gid                         Real, effective, saved set, and  file system GIDs
222  FDSize                      number of file descriptor slots currently allocated
223  Groups                      supplementary group list
224  NStgid                      descendant namespace thread group ID hierarchy
225  NSpid                       descendant namespace process ID hierarchy
226  NSpgid                      descendant namespace process group ID hierarchy
227  NSsid                       descendant namespace session ID hierarchy
228  VmPeak                      peak virtual memory size
229  VmSize                      total program size
230  VmLck                       locked memory size
231  VmHWM                       peak resident set size ("high water mark")
232  VmRSS                       size of memory portions
233  VmData                      size of data, stack, and text segments
234  VmStk                       size of data, stack, and text segments
235  VmExe                       size of text segment
236  VmLib                       size of shared library code
237  VmPTE                       size of page table entries
238  VmSwap                      size of swap usage (the number of referred swapents)
239  Threads                     number of threads
240  SigQ                        number of signals queued/max. number for queue
241  SigPnd                      bitmap of pending signals for the thread
242  ShdPnd                      bitmap of shared pending signals for the process
243  SigBlk                      bitmap of blocked signals
244  SigIgn                      bitmap of ignored signals
245  SigCgt                      bitmap of caught signals
246  CapInh                      bitmap of inheritable capabilities
247  CapPrm                      bitmap of permitted capabilities
248  CapEff                      bitmap of effective capabilities
249  CapBnd                      bitmap of capabilities bounding set
250  Seccomp                     seccomp mode, like prctl(PR_GET_SECCOMP, ...)
251  Cpus_allowed                mask of CPUs on which this process may run
252  Cpus_allowed_list           Same as previous, but in "list format"
253  Mems_allowed                mask of memory nodes allowed to this process
254  Mems_allowed_list           Same as previous, but in "list format"
255  voluntary_ctxt_switches     number of voluntary context switches
256  nonvoluntary_ctxt_switches  number of non voluntary context switches
257 ..............................................................................
258 
259 Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
260 ..............................................................................
261  Field    Content
262  size     total program size (pages)            (same as VmSize in status)
263  resident size of memory portions (pages)       (same as VmRSS in status)
264  shared   number of pages that are shared       (i.e. backed by a file)
265  trs      number of pages that are 'code'       (not including libs; broken,
266                                                         includes data segment)
267  lrs      number of pages of library            (always 0 on 2.6)
268  drs      number of pages of data/stack         (including libs; broken,
269                                                         includes library text)
270  dt       number of dirty pages                 (always 0 on 2.6)
271 ..............................................................................
272 
273 
274 Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
275 ..............................................................................
276  Field          Content
277   pid           process id
278   tcomm         filename of the executable
279   state         state (R is running, S is sleeping, D is sleeping in an
280                 uninterruptible wait, Z is zombie, T is traced or stopped)
281   ppid          process id of the parent process
282   pgrp          pgrp of the process
283   sid           session id
284   tty_nr        tty the process uses
285   tty_pgrp      pgrp of the tty
286   flags         task flags
287   min_flt       number of minor faults
288   cmin_flt      number of minor faults with child's
289   maj_flt       number of major faults
290   cmaj_flt      number of major faults with child's
291   utime         user mode jiffies
292   stime         kernel mode jiffies
293   cutime        user mode jiffies with child's
294   cstime        kernel mode jiffies with child's
295   priority      priority level
296   nice          nice level
297   num_threads   number of threads
298   it_real_value (obsolete, always 0)
299   start_time    time the process started after system boot
300   vsize         virtual memory size
301   rss           resident set memory size
302   rsslim        current limit in bytes on the rss
303   start_code    address above which program text can run
304   end_code      address below which program text can run
305   start_stack   address of the start of the main process stack
306   esp           current value of ESP
307   eip           current value of EIP
308   pending       bitmap of pending signals
309   blocked       bitmap of blocked signals
310   sigign        bitmap of ignored signals
311   sigcatch      bitmap of caught signals
312   wchan         address where process went to sleep
313   0             (place holder)
314   0             (place holder)
315   exit_signal   signal to send to parent thread on exit
316   task_cpu      which CPU the task is scheduled on
317   rt_priority   realtime priority
318   policy        scheduling policy (man sched_setscheduler)
319   blkio_ticks   time spent waiting for block IO
320   gtime         guest time of the task in jiffies
321   cgtime        guest time of the task children in jiffies
322   start_data    address above which program data+bss is placed
323   end_data      address below which program data+bss is placed
324   start_brk     address above which program heap can be expanded with brk()
325   arg_start     address above which program command line is placed
326   arg_end       address below which program command line is placed
327   env_start     address above which program environment is placed
328   env_end       address below which program environment is placed
329   exit_code     the thread's exit_code in the form reported by the waitpid system call
330 ..............................................................................
331 
332 The /proc/PID/maps file containing the currently mapped memory regions and
333 their access permissions.
334 
335 The format is:
336 
337 address           perms offset  dev   inode      pathname
338 
339 08048000-08049000 r-xp 00000000 03:00 8312       /opt/test
340 08049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
341 0804a000-0806b000 rw-p 00000000 00:00 0          [heap]
342 a7cb1000-a7cb2000 ---p 00000000 00:00 0
343 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
344 a7eb2000-a7eb3000 ---p 00000000 00:00 0
345 a7eb3000-a7ed5000 rw-p 00000000 00:00 0          [stack:1001]
346 a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/libc.so.6
347 a8008000-a800a000 r--p 00133000 03:00 4222       /lib/libc.so.6
348 a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/libc.so.6
349 a800b000-a800e000 rw-p 00000000 00:00 0
350 a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/libpthread.so.0
351 a8022000-a8023000 r--p 00013000 03:00 14462      /lib/libpthread.so.0
352 a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/libpthread.so.0
353 a8024000-a8027000 rw-p 00000000 00:00 0
354 a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/ld-linux.so.2
355 a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/ld-linux.so.2
356 a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/ld-linux.so.2
357 aff35000-aff4a000 rw-p 00000000 00:00 0          [stack]
358 ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
359 
360 where "address" is the address space in the process that it occupies, "perms"
361 is a set of permissions:
362 
363  r = read
364  w = write
365  x = execute
366  s = shared
367  p = private (copy on write)
368 
369 "offset" is the offset into the mapping, "dev" is the device (major:minor), and
370 "inode" is the inode  on that device.  0 indicates that  no inode is associated
371 with the memory region, as the case would be with BSS (uninitialized data).
372 The "pathname" shows the name associated file for this mapping.  If the mapping
373 is not associated with a file:
374 
375  [heap]                   = the heap of the program
376  [stack]                  = the stack of the main process
377  [stack:1001]             = the stack of the thread with tid 1001
378  [vdso]                   = the "virtual dynamic shared object",
379                             the kernel system call handler
380 
381  or if empty, the mapping is anonymous.
382 
383 The /proc/PID/task/TID/maps is a view of the virtual memory from the viewpoint
384 of the individual tasks of a process. In this file you will see a mapping marked
385 as [stack] if that task sees it as a stack. This is a key difference from the
386 content of /proc/PID/maps, where you will see all mappings that are being used
387 as stack by all of those tasks. Hence, for the example above, the task-level
388 map, i.e. /proc/PID/task/TID/maps for thread 1001 will look like this:
389 
390 08048000-08049000 r-xp 00000000 03:00 8312       /opt/test
391 08049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
392 0804a000-0806b000 rw-p 00000000 00:00 0          [heap]
393 a7cb1000-a7cb2000 ---p 00000000 00:00 0
394 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
395 a7eb2000-a7eb3000 ---p 00000000 00:00 0
396 a7eb3000-a7ed5000 rw-p 00000000 00:00 0          [stack]
397 a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/libc.so.6
398 a8008000-a800a000 r--p 00133000 03:00 4222       /lib/libc.so.6
399 a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/libc.so.6
400 a800b000-a800e000 rw-p 00000000 00:00 0
401 a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/libpthread.so.0
402 a8022000-a8023000 r--p 00013000 03:00 14462      /lib/libpthread.so.0
403 a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/libpthread.so.0
404 a8024000-a8027000 rw-p 00000000 00:00 0
405 a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/ld-linux.so.2
406 a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/ld-linux.so.2
407 a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/ld-linux.so.2
408 aff35000-aff4a000 rw-p 00000000 00:00 0
409 ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
410 
411 The /proc/PID/smaps is an extension based on maps, showing the memory
412 consumption for each of the process's mappings. For each of mappings there
413 is a series of lines such as the following:
414 
415 08048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
416 Size:               1084 kB
417 Rss:                 892 kB
418 Pss:                 374 kB
419 Shared_Clean:        892 kB
420 Shared_Dirty:          0 kB
421 Private_Clean:         0 kB
422 Private_Dirty:         0 kB
423 Referenced:          892 kB
424 Anonymous:             0 kB
425 Swap:                  0 kB
426 KernelPageSize:        4 kB
427 MMUPageSize:           4 kB
428 Locked:              374 kB
429 VmFlags: rd ex mr mw me de
430 
431 the first of these lines shows the same information as is displayed for the
432 mapping in /proc/PID/maps.  The remaining lines show the size of the mapping
433 (size), the amount of the mapping that is currently resident in RAM (RSS), the
434 process' proportional share of this mapping (PSS), the number of clean and
435 dirty private pages in the mapping.  Note that even a page which is part of a
436 MAP_SHARED mapping, but has only a single pte mapped, i.e.  is currently used
437 by only one process, is accounted as private and not as shared.  "Referenced"
438 indicates the amount of memory currently marked as referenced or accessed.
439 "Anonymous" shows the amount of memory that does not belong to any file.  Even
440 a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
441 and a page is modified, the file page is replaced by a private anonymous copy.
442 "Swap" shows how much would-be-anonymous memory is also used, but out on
443 swap.
444 
445 "VmFlags" field deserves a separate description. This member represents the kernel
446 flags associated with the particular virtual memory area in two letter encoded
447 manner. The codes are the following:
448     rd  - readable
449     wr  - writeable
450     ex  - executable
451     sh  - shared
452     mr  - may read
453     mw  - may write
454     me  - may execute
455     ms  - may share
456     gd  - stack segment growns down
457     pf  - pure PFN range
458     dw  - disabled write to the mapped file
459     lo  - pages are locked in memory
460     io  - memory mapped I/O area
461     sr  - sequential read advise provided
462     rr  - random read advise provided
463     dc  - do not copy area on fork
464     de  - do not expand area on remapping
465     ac  - area is accountable
466     nr  - swap space is not reserved for the area
467     ht  - area uses huge tlb pages
468     nl  - non-linear mapping
469     ar  - architecture specific flag
470     dd  - do not include area into core dump
471     sd  - soft-dirty flag
472     mm  - mixed map area
473     hg  - huge page advise flag
474     nh  - no-huge page advise flag
475     mg  - mergable advise flag
476 
477 Note that there is no guarantee that every flag and associated mnemonic will
478 be present in all further kernel releases. Things get changed, the flags may
479 be vanished or the reverse -- new added.
480 
481 This file is only present if the CONFIG_MMU kernel configuration option is
482 enabled.
483 
484 The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
485 bits on both physical and virtual pages associated with a process, and the
486 soft-dirty bit on pte (see Documentation/vm/soft-dirty.txt for details).
487 To clear the bits for all the pages associated with the process
488     > echo 1 > /proc/PID/clear_refs
489 
490 To clear the bits for the anonymous pages associated with the process
491     > echo 2 > /proc/PID/clear_refs
492 
493 To clear the bits for the file mapped pages associated with the process
494     > echo 3 > /proc/PID/clear_refs
495 
496 To clear the soft-dirty bit
497     > echo 4 > /proc/PID/clear_refs
498 
499 To reset the peak resident set size ("high water mark") to the process's
500 current value:
501     > echo 5 > /proc/PID/clear_refs
502 
503 Any other value written to /proc/PID/clear_refs will have no effect.
504 
505 The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
506 using /proc/kpageflags and number of times a page is mapped using
507 /proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt.
508 
509 The /proc/pid/numa_maps is an extension based on maps, showing the memory
510 locality and binding policy, as well as the memory usage (in pages) of
511 each mapping. The output follows a general format where mapping details get
512 summarized separated by blank spaces, one mapping per each file line:
513 
514 address   policy    mapping details
515 
516 00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
517 00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
518 3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
519 320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
520 3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
521 3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
522 3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
523 320698b000 default file=/lib64/libc-2.12.so
524 3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4
525 3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
526 3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
527 7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
528 7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
529 7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
530 7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
531 7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4
532 
533 Where:
534 "address" is the starting address for the mapping;
535 "policy" reports the NUMA memory policy set for the mapping (see vm/numa_memory_policy.txt);
536 "mapping details" summarizes mapping data such as mapping type, page usage counters,
537 node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
538 size, in KB, that is backing the mapping up.
539 
540 1.2 Kernel data
541 ---------------
542 
543 Similar to  the  process entries, the kernel data files give information about
544 the running kernel. The files used to obtain this information are contained in
545 /proc and  are  listed  in Table 1-5. Not all of these will be present in your
546 system. It  depends  on the kernel configuration and the loaded modules, which
547 files are there, and which are missing.
548 
549 Table 1-5: Kernel info in /proc
550 ..............................................................................
551  File        Content                                           
552  apm         Advanced power management info                    
553  buddyinfo   Kernel memory allocator information (see text)     (2.5)
554  bus         Directory containing bus specific information     
555  cmdline     Kernel command line                               
556  cpuinfo     Info about the CPU                                
557  devices     Available devices (block and character)           
558  dma         Used DMS channels                                 
559  filesystems Supported filesystems                             
560  driver      Various drivers grouped here, currently rtc (2.4)
561  execdomains Execdomains, related to security                   (2.4)
562  fb          Frame Buffer devices                               (2.4)
563  fs          File system parameters, currently nfs/exports      (2.4)
564  ide         Directory containing info about the IDE subsystem 
565  interrupts  Interrupt usage                                   
566  iomem       Memory map                                         (2.4)
567  ioports     I/O port usage                                    
568  irq         Masks for irq to cpu affinity                      (2.4)(smp?)
569  isapnp      ISA PnP (Plug&Play) Info                           (2.4)
570  kcore       Kernel core image (can be ELF or A.OUT(deprecated in 2.4))   
571  kmsg        Kernel messages                                   
572  ksyms       Kernel symbol table                               
573  loadavg     Load average of last 1, 5 & 15 minutes                
574  locks       Kernel locks                                      
575  meminfo     Memory info                                       
576  misc        Miscellaneous                                     
577  modules     List of loaded modules                            
578  mounts      Mounted filesystems                               
579  net         Networking info (see text)                        
580  pagetypeinfo Additional page allocator information (see text)  (2.5)
581  partitions  Table of partitions known to the system           
582  pci         Deprecated info of PCI bus (new way -> /proc/bus/pci/,
583              decoupled by lspci                                 (2.4)
584  rtc         Real time clock                                   
585  scsi        SCSI info (see text)                              
586  slabinfo    Slab pool info                                    
587  softirqs    softirq usage
588  stat        Overall statistics                                
589  swaps       Swap space utilization                            
590  sys         See chapter 2                                     
591  sysvipc     Info of SysVIPC Resources (msg, sem, shm)          (2.4)
592  tty         Info of tty drivers
593  uptime      Wall clock since boot, combined idle time of all cpus
594  version     Kernel version                                    
595  video       bttv info of video resources                       (2.4)
596  vmallocinfo Show vmalloced areas
597 ..............................................................................
598 
599 You can,  for  example,  check  which interrupts are currently in use and what
600 they are used for by looking in the file /proc/interrupts:
601 
602   > cat /proc/interrupts 
603              CPU0        
604     0:    8728810          XT-PIC  timer 
605     1:        895          XT-PIC  keyboard 
606     2:          0          XT-PIC  cascade 
607     3:     531695          XT-PIC  aha152x 
608     4:    2014133          XT-PIC  serial 
609     5:      44401          XT-PIC  pcnet_cs 
610     8:          2          XT-PIC  rtc 
611    11:          8          XT-PIC  i82365 
612    12:     182918          XT-PIC  PS/2 Mouse 
613    13:          1          XT-PIC  fpu 
614    14:    1232265          XT-PIC  ide0 
615    15:          7          XT-PIC  ide1 
616   NMI:          0 
617 
618 In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
619 output of a SMP machine):
620 
621   > cat /proc/interrupts 
622 
623              CPU0       CPU1       
624     0:    1243498    1214548    IO-APIC-edge  timer
625     1:       8949       8958    IO-APIC-edge  keyboard
626     2:          0          0          XT-PIC  cascade
627     5:      11286      10161    IO-APIC-edge  soundblaster
628     8:          1          0    IO-APIC-edge  rtc
629     9:      27422      27407    IO-APIC-edge  3c503
630    12:     113645     113873    IO-APIC-edge  PS/2 Mouse
631    13:          0          0          XT-PIC  fpu
632    14:      22491      24012    IO-APIC-edge  ide0
633    15:       2183       2415    IO-APIC-edge  ide1
634    17:      30564      30414   IO-APIC-level  eth0
635    18:        177        164   IO-APIC-level  bttv
636   NMI:    2457961    2457959 
637   LOC:    2457882    2457881 
638   ERR:       2155
639 
640 NMI is incremented in this case because every timer interrupt generates a NMI
641 (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
642 
643 LOC is the local interrupt counter of the internal APIC of every CPU.
644 
645 ERR is incremented in the case of errors in the IO-APIC bus (the bus that
646 connects the CPUs in a SMP system. This means that an error has been detected,
647 the IO-APIC automatically retry the transmission, so it should not be a big
648 problem, but you should read the SMP-FAQ.
649 
650 In 2.6.2* /proc/interrupts was expanded again.  This time the goal was for
651 /proc/interrupts to display every IRQ vector in use by the system, not
652 just those considered 'most important'.  The new vectors are:
653 
654   THR -- interrupt raised when a machine check threshold counter
655   (typically counting ECC corrected errors of memory or cache) exceeds
656   a configurable threshold.  Only available on some systems.
657 
658   TRM -- a thermal event interrupt occurs when a temperature threshold
659   has been exceeded for the CPU.  This interrupt may also be generated
660   when the temperature drops back to normal.
661 
662   SPU -- a spurious interrupt is some interrupt that was raised then lowered
663   by some IO device before it could be fully processed by the APIC.  Hence
664   the APIC sees the interrupt but does not know what device it came from.
665   For this case the APIC will generate the interrupt with a IRQ vector
666   of 0xff. This might also be generated by chipset bugs.
667 
668   RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
669   sent from one CPU to another per the needs of the OS.  Typically,
670   their statistics are used by kernel developers and interested users to
671   determine the occurrence of interrupts of the given type.
672 
673 The above IRQ vectors are displayed only when relevant.  For example,
674 the threshold vector does not exist on x86_64 platforms.  Others are
675 suppressed when the system is a uniprocessor.  As of this writing, only
676 i386 and x86_64 platforms support the new IRQ vector displays.
677 
678 Of some interest is the introduction of the /proc/irq directory to 2.4.
679 It could be used to set IRQ to CPU affinity, this means that you can "hook" an
680 IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
681 irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
682 prof_cpu_mask.
683 
684 For example 
685   > ls /proc/irq/
686   0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
687   1  11  13  15  17  19  3  5  7  9  default_smp_affinity
688   > ls /proc/irq/0/
689   smp_affinity
690 
691 smp_affinity is a bitmask, in which you can specify which CPUs can handle the
692 IRQ, you can set it by doing:
693 
694   > echo 1 > /proc/irq/10/smp_affinity
695 
696 This means that only the first CPU will handle the IRQ, but you can also echo
697 5 which means that only the first and fourth CPU can handle the IRQ.
698 
699 The contents of each smp_affinity file is the same by default:
700 
701   > cat /proc/irq/0/smp_affinity
702   ffffffff
703 
704 There is an alternate interface, smp_affinity_list which allows specifying
705 a cpu range instead of a bitmask:
706 
707   > cat /proc/irq/0/smp_affinity_list
708   1024-1031
709 
710 The default_smp_affinity mask applies to all non-active IRQs, which are the
711 IRQs which have not yet been allocated/activated, and hence which lack a
712 /proc/irq/[0-9]* directory.
713 
714 The node file on an SMP system shows the node to which the device using the IRQ
715 reports itself as being attached. This hardware locality information does not
716 include information about any possible driver locality preference.
717 
718 prof_cpu_mask specifies which CPUs are to be profiled by the system wide
719 profiler. Default value is ffffffff (all cpus if there are only 32 of them).
720 
721 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
722 between all the CPUs which are allowed to handle it. As usual the kernel has
723 more info than you and does a better job than you, so the defaults are the
724 best choice for almost everyone.  [Note this applies only to those IO-APIC's
725 that support "Round Robin" interrupt distribution.]
726 
727 There are  three  more  important subdirectories in /proc: net, scsi, and sys.
728 The general  rule  is  that  the  contents,  or  even  the  existence of these
729 directories, depend  on your kernel configuration. If SCSI is not enabled, the
730 directory scsi  may  not  exist. The same is true with the net, which is there
731 only when networking support is present in the running kernel.
732 
733 The slabinfo  file  gives  information  about  memory usage at the slab level.
734 Linux uses  slab  pools for memory management above page level in version 2.2.
735 Commonly used  objects  have  their  own  slab  pool (such as network buffers,
736 directory cache, and so on).
737 
738 ..............................................................................
739 
740 > cat /proc/buddyinfo
741 
742 Node 0, zone      DMA      0      4      5      4      4      3 ...
743 Node 0, zone   Normal      1      0      0      1    101      8 ...
744 Node 0, zone  HighMem      2      0      0      1      1      0 ...
745 
746 External fragmentation is a problem under some workloads, and buddyinfo is a
747 useful tool for helping diagnose these problems.  Buddyinfo will give you a 
748 clue as to how big an area you can safely allocate, or why a previous
749 allocation failed.
750 
751 Each column represents the number of pages of a certain order which are 
752 available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in 
753 ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE 
754 available in ZONE_NORMAL, etc... 
755 
756 More information relevant to external fragmentation can be found in
757 pagetypeinfo.
758 
759 > cat /proc/pagetypeinfo
760 Page block order: 9
761 Pages per block:  512
762 
763 Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
764 Node    0, zone      DMA, type    Unmovable      0      0      0      1      1      1      1      1      1      1      0
765 Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0
766 Node    0, zone      DMA, type      Movable      1      1      2      1      2      1      1      0      1      0      2
767 Node    0, zone      DMA, type      Reserve      0      0      0      0      0      0      0      0      0      1      0
768 Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
769 Node    0, zone    DMA32, type    Unmovable    103     54     77      1      1      1     11      8      7      1      9
770 Node    0, zone    DMA32, type  Reclaimable      0      0      2      1      0      0      0      0      1      0      0
771 Node    0, zone    DMA32, type      Movable    169    152    113     91     77     54     39     13      6      1    452
772 Node    0, zone    DMA32, type      Reserve      1      2      2      2      2      0      1      1      1      1      0
773 Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
774 
775 Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate
776 Node 0, zone      DMA            2            0            5            1            0
777 Node 0, zone    DMA32           41            6          967            2            0
778 
779 Fragmentation avoidance in the kernel works by grouping pages of different
780 migrate types into the same contiguous regions of memory called page blocks.
781 A page block is typically the size of the default hugepage size e.g. 2MB on
782 X86-64. By keeping pages grouped based on their ability to move, the kernel
783 can reclaim pages within a page block to satisfy a high-order allocation.
784 
785 The pagetypinfo begins with information on the size of a page block. It
786 then gives the same type of information as buddyinfo except broken down
787 by migrate-type and finishes with details on how many page blocks of each
788 type exist.
789 
790 If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
791 from libhugetlbfs http://sourceforge.net/projects/libhugetlbfs/), one can
792 make an estimate of the likely number of huge pages that can be allocated
793 at a given point in time. All the "Movable" blocks should be allocatable
794 unless memory has been mlock()'d. Some of the Reclaimable blocks should
795 also be allocatable although a lot of filesystem metadata may have to be
796 reclaimed to achieve this.
797 
798 ..............................................................................
799 
800 meminfo:
801 
802 Provides information about distribution and utilization of memory.  This
803 varies by architecture and compile options.  The following is from a
804 16GB PIII, which has highmem enabled.  You may not have all of these fields.
805 
806 > cat /proc/meminfo
807 
808 The "Locked" indicates whether the mapping is locked in memory or not.
809 
810 
811 MemTotal:     16344972 kB
812 MemFree:      13634064 kB
813 MemAvailable: 14836172 kB
814 Buffers:          3656 kB
815 Cached:        1195708 kB
816 SwapCached:          0 kB
817 Active:         891636 kB
818 Inactive:      1077224 kB
819 HighTotal:    15597528 kB
820 HighFree:     13629632 kB
821 LowTotal:       747444 kB
822 LowFree:          4432 kB
823 SwapTotal:           0 kB
824 SwapFree:            0 kB
825 Dirty:             968 kB
826 Writeback:           0 kB
827 AnonPages:      861800 kB
828 Mapped:         280372 kB
829 Slab:           284364 kB
830 SReclaimable:   159856 kB
831 SUnreclaim:     124508 kB
832 PageTables:      24448 kB
833 NFS_Unstable:        0 kB
834 Bounce:              0 kB
835 WritebackTmp:        0 kB
836 CommitLimit:   7669796 kB
837 Committed_AS:   100056 kB
838 VmallocTotal:   112216 kB
839 VmallocUsed:       428 kB
840 VmallocChunk:   111088 kB
841 AnonHugePages:   49152 kB
842 
843     MemTotal: Total usable ram (i.e. physical ram minus a few reserved
844               bits and the kernel binary code)
845      MemFree: The sum of LowFree+HighFree
846 MemAvailable: An estimate of how much memory is available for starting new
847               applications, without swapping. Calculated from MemFree,
848               SReclaimable, the size of the file LRU lists, and the low
849               watermarks in each zone.
850               The estimate takes into account that the system needs some
851               page cache to function well, and that not all reclaimable
852               slab will be reclaimable, due to items being in use. The
853               impact of those factors will vary from system to system.
854      Buffers: Relatively temporary storage for raw disk blocks
855               shouldn't get tremendously large (20MB or so)
856       Cached: in-memory cache for files read from the disk (the
857               pagecache).  Doesn't include SwapCached
858   SwapCached: Memory that once was swapped out, is swapped back in but
859               still also is in the swapfile (if memory is needed it
860               doesn't need to be swapped out AGAIN because it is already
861               in the swapfile. This saves I/O)
862       Active: Memory that has been used more recently and usually not
863               reclaimed unless absolutely necessary.
864     Inactive: Memory which has been less recently used.  It is more
865               eligible to be reclaimed for other purposes
866    HighTotal:
867     HighFree: Highmem is all memory above ~860MB of physical memory
868               Highmem areas are for use by userspace programs, or
869               for the pagecache.  The kernel must use tricks to access
870               this memory, making it slower to access than lowmem.
871     LowTotal:
872      LowFree: Lowmem is memory which can be used for everything that
873               highmem can be used for, but it is also available for the
874               kernel's use for its own data structures.  Among many
875               other things, it is where everything from the Slab is
876               allocated.  Bad things happen when you're out of lowmem.
877    SwapTotal: total amount of swap space available
878     SwapFree: Memory which has been evicted from RAM, and is temporarily
879               on the disk
880        Dirty: Memory which is waiting to get written back to the disk
881    Writeback: Memory which is actively being written back to the disk
882    AnonPages: Non-file backed pages mapped into userspace page tables
883 AnonHugePages: Non-file backed huge pages mapped into userspace page tables
884       Mapped: files which have been mmaped, such as libraries
885         Slab: in-kernel data structures cache
886 SReclaimable: Part of Slab, that might be reclaimed, such as caches
887   SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
888   PageTables: amount of memory dedicated to the lowest level of page
889               tables.
890 NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
891               storage
892       Bounce: Memory used for block device "bounce buffers"
893 WritebackTmp: Memory used by FUSE for temporary writeback buffers
894  CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
895               this is the total amount of  memory currently available to
896               be allocated on the system. This limit is only adhered to
897               if strict overcommit accounting is enabled (mode 2 in
898               'vm.overcommit_memory').
899               The CommitLimit is calculated with the following formula:
900               CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
901                              overcommit_ratio / 100 + [total swap pages]
902               For example, on a system with 1G of physical RAM and 7G
903               of swap with a `vm.overcommit_ratio` of 30 it would
904               yield a CommitLimit of 7.3G.
905               For more details, see the memory overcommit documentation
906               in vm/overcommit-accounting.
907 Committed_AS: The amount of memory presently allocated on the system.
908               The committed memory is a sum of all of the memory which
909               has been allocated by processes, even if it has not been
910               "used" by them as of yet. A process which malloc()'s 1G
911               of memory, but only touches 300M of it will show up as
912               using 1G. This 1G is memory which has been "committed" to
913               by the VM and can be used at any time by the allocating
914               application. With strict overcommit enabled on the system
915               (mode 2 in 'vm.overcommit_memory'),allocations which would
916               exceed the CommitLimit (detailed above) will not be permitted.
917               This is useful if one needs to guarantee that processes will
918               not fail due to lack of memory once that memory has been
919               successfully allocated.
920 VmallocTotal: total size of vmalloc memory area
921  VmallocUsed: amount of vmalloc area which is used
922 VmallocChunk: largest contiguous block of vmalloc area which is free
923 
924 ..............................................................................
925 
926 vmallocinfo:
927 
928 Provides information about vmalloced/vmaped areas. One line per area,
929 containing the virtual address range of the area, size in bytes,
930 caller information of the creator, and optional information depending
931 on the kind of area :
932 
933  pages=nr    number of pages
934  phys=addr   if a physical address was specified
935  ioremap     I/O mapping (ioremap() and friends)
936  vmalloc     vmalloc() area
937  vmap        vmap()ed pages
938  user        VM_USERMAP area
939  vpages      buffer for pages pointers was vmalloced (huge area)
940  N<node>=nr  (Only on NUMA kernels)
941              Number of pages allocated on memory node <node>
942 
943 > cat /proc/vmallocinfo
944 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
945   /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
946 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
947   /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
948 0xffffc20000302000-0xffffc20000304000    8192 acpi_tb_verify_table+0x21/0x4f...
949   phys=7fee8000 ioremap
950 0xffffc20000304000-0xffffc20000307000   12288 acpi_tb_verify_table+0x21/0x4f...
951   phys=7fee7000 ioremap
952 0xffffc2000031d000-0xffffc2000031f000    8192 init_vdso_vars+0x112/0x210
953 0xffffc2000031f000-0xffffc2000032b000   49152 cramfs_uncompress_init+0x2e ...
954   /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
955 0xffffc2000033a000-0xffffc2000033d000   12288 sys_swapon+0x640/0xac0      ...
956   pages=2 vmalloc N1=2
957 0xffffc20000347000-0xffffc2000034c000   20480 xt_alloc_table_info+0xfe ...
958   /0x130 [x_tables] pages=4 vmalloc N0=4
959 0xffffffffa0000000-0xffffffffa000f000   61440 sys_init_module+0xc27/0x1d00 ...
960    pages=14 vmalloc N2=14
961 0xffffffffa000f000-0xffffffffa0014000   20480 sys_init_module+0xc27/0x1d00 ...
962    pages=4 vmalloc N1=4
963 0xffffffffa0014000-0xffffffffa0017000   12288 sys_init_module+0xc27/0x1d00 ...
964    pages=2 vmalloc N1=2
965 0xffffffffa0017000-0xffffffffa0022000   45056 sys_init_module+0xc27/0x1d00 ...
966    pages=10 vmalloc N0=10
967 
968 ..............................................................................
969 
970 softirqs:
971 
972 Provides counts of softirq handlers serviced since boot time, for each cpu.
973 
974 > cat /proc/softirqs
975                 CPU0       CPU1       CPU2       CPU3
976       HI:          0          0          0          0
977    TIMER:      27166      27120      27097      27034
978   NET_TX:          0          0          0         17
979   NET_RX:         42          0          0         39
980    BLOCK:          0          0        107       1121
981  TASKLET:          0          0          0        290
982    SCHED:      27035      26983      26971      26746
983  HRTIMER:          0          0          0          0
984      RCU:       1678       1769       2178       2250
985 
986 
987 1.3 IDE devices in /proc/ide
988 ----------------------------
989 
990 The subdirectory /proc/ide contains information about all IDE devices of which
991 the kernel  is  aware.  There is one subdirectory for each IDE controller, the
992 file drivers  and a link for each IDE device, pointing to the device directory
993 in the controller specific subtree.
994 
995 The file  drivers  contains general information about the drivers used for the
996 IDE devices:
997 
998   > cat /proc/ide/drivers
999   ide-cdrom version 4.53
1000   ide-disk version 1.08
1001 
1002 More detailed  information  can  be  found  in  the  controller  specific
1003 subdirectories. These  are  named  ide0,  ide1  and  so  on.  Each  of  these
1004 directories contains the files shown in table 1-6.
1005 
1006 
1007 Table 1-6: IDE controller info in  /proc/ide/ide?
1008 ..............................................................................
1009  File    Content                                 
1010  channel IDE channel (0 or 1)                    
1011  config  Configuration (only for PCI/IDE bridge) 
1012  mate    Mate name                               
1013  model   Type/Chipset of IDE controller          
1014 ..............................................................................
1015 
1016 Each device  connected  to  a  controller  has  a separate subdirectory in the
1017 controllers directory.  The  files  listed in table 1-7 are contained in these
1018 directories.
1019 
1020 
1021 Table 1-7: IDE device information
1022 ..............................................................................
1023  File             Content                                    
1024  cache            The cache                                  
1025  capacity         Capacity of the medium (in 512Byte blocks) 
1026  driver           driver and version                         
1027  geometry         physical and logical geometry              
1028  identify         device identify block                      
1029  media            media type                                 
1030  model            device identifier                          
1031  settings         device setup                               
1032  smart_thresholds IDE disk management thresholds             
1033  smart_values     IDE disk management values                 
1034 ..............................................................................
1035 
1036 The most  interesting  file is settings. This file contains a nice overview of
1037 the drive parameters:
1038 
1039   # cat /proc/ide/ide0/hda/settings 
1040   name                    value           min             max             mode 
1041   ----                    -----           ---             ---             ---- 
1042   bios_cyl                526             0               65535           rw 
1043   bios_head               255             0               255             rw 
1044   bios_sect               63              0               63              rw 
1045   breada_readahead        4               0               127             rw 
1046   bswap                   0               0               1               r 
1047   file_readahead          72              0               2097151         rw 
1048   io_32bit                0               0               3               rw 
1049   keepsettings            0               0               1               rw 
1050   max_kb_per_request      122             1               127             rw 
1051   multcount               0               0               8               rw 
1052   nice1                   1               0               1               rw 
1053   nowerr                  0               0               1               rw 
1054   pio_mode                write-only      0               255             w 
1055   slow                    0               0               1               rw 
1056   unmaskirq               0               0               1               rw 
1057   using_dma               0               0               1               rw 
1058 
1059 
1060 1.4 Networking info in /proc/net
1061 --------------------------------
1062 
1063 The subdirectory  /proc/net  follows  the  usual  pattern. Table 1-8 shows the
1064 additional values  you  get  for  IP  version 6 if you configure the kernel to
1065 support this. Table 1-9 lists the files and their meaning.
1066 
1067 
1068 Table 1-8: IPv6 info in /proc/net
1069 ..............................................................................
1070  File       Content                                               
1071  udp6       UDP sockets (IPv6)                                    
1072  tcp6       TCP sockets (IPv6)                                    
1073  raw6       Raw device statistics (IPv6)                          
1074  igmp6      IP multicast addresses, which this host joined (IPv6) 
1075  if_inet6   List of IPv6 interface addresses                      
1076  ipv6_route Kernel routing table for IPv6                         
1077  rt6_stats  Global IPv6 routing tables statistics                 
1078  sockstat6  Socket statistics (IPv6)                              
1079  snmp6      Snmp data (IPv6)                                      
1080 ..............................................................................
1081 
1082 
1083 Table 1-9: Network info in /proc/net
1084 ..............................................................................
1085  File          Content                                                         
1086  arp           Kernel  ARP table                                               
1087  dev           network devices with statistics                                 
1088  dev_mcast     the Layer2 multicast groups a device is listening too
1089                (interface index, label, number of references, number of bound
1090                addresses). 
1091  dev_stat      network device status                                           
1092  ip_fwchains   Firewall chain linkage                                          
1093  ip_fwnames    Firewall chain names                                            
1094  ip_masq       Directory containing the masquerading tables                    
1095  ip_masquerade Major masquerading table                                        
1096  netstat       Network statistics                                              
1097  raw           raw device statistics                                           
1098  route         Kernel routing table                                            
1099  rpc           Directory containing rpc info                                   
1100  rt_cache      Routing cache                                                   
1101  snmp          SNMP data                                                       
1102  sockstat      Socket statistics                                               
1103  tcp           TCP  sockets                                                    
1104  udp           UDP sockets                                                     
1105  unix          UNIX domain sockets                                             
1106  wireless      Wireless interface data (Wavelan etc)                           
1107  igmp          IP multicast addresses, which this host joined                  
1108  psched        Global packet scheduler parameters.                             
1109  netlink       List of PF_NETLINK sockets                                      
1110  ip_mr_vifs    List of multicast virtual interfaces                            
1111  ip_mr_cache   List of multicast routing cache                                 
1112 ..............................................................................
1113 
1114 You can  use  this  information  to see which network devices are available in
1115 your system and how much traffic was routed over those devices:
1116 
1117   > cat /proc/net/dev 
1118   Inter-|Receive                                                   |[... 
1119    face |bytes    packets errs drop fifo frame compressed multicast|[... 
1120       lo:  908188   5596     0    0    0     0          0         0 [...         
1121     ppp0:15475140  20721   410    0    0   410          0         0 [...  
1122     eth0:  614530   7085     0    0    0     0          0         1 [... 
1123    
1124   ...] Transmit 
1125   ...] bytes    packets errs drop fifo colls carrier compressed 
1126   ...]  908188     5596    0    0    0     0       0          0 
1127   ...] 1375103    17405    0    0    0     0       0          0 
1128   ...] 1703981     5535    0    0    0     3       0          0 
1129 
1130 In addition, each Channel Bond interface has its own directory.  For
1131 example, the bond0 device will have a directory called /proc/net/bond0/.
1132 It will contain information that is specific to that bond, such as the
1133 current slaves of the bond, the link status of the slaves, and how
1134 many times the slaves link has failed.
1135 
1136 1.5 SCSI info
1137 -------------
1138 
1139 If you  have  a  SCSI  host adapter in your system, you'll find a subdirectory
1140 named after  the driver for this adapter in /proc/scsi. You'll also see a list
1141 of all recognized SCSI devices in /proc/scsi:
1142 
1143   >cat /proc/scsi/scsi 
1144   Attached devices: 
1145   Host: scsi0 Channel: 00 Id: 00 Lun: 00 
1146     Vendor: IBM      Model: DGHS09U          Rev: 03E0 
1147     Type:   Direct-Access                    ANSI SCSI revision: 03 
1148   Host: scsi0 Channel: 00 Id: 06 Lun: 00 
1149     Vendor: PIONEER  Model: CD-ROM DR-U06S   Rev: 1.04 
1150     Type:   CD-ROM                           ANSI SCSI revision: 02 
1151 
1152 
1153 The directory  named  after  the driver has one file for each adapter found in
1154 the system.  These  files  contain information about the controller, including
1155 the used  IRQ  and  the  IO  address range. The amount of information shown is
1156 dependent on  the adapter you use. The example shows the output for an Adaptec
1157 AHA-2940 SCSI adapter:
1158 
1159   > cat /proc/scsi/aic7xxx/0 
1160    
1161   Adaptec AIC7xxx driver version: 5.1.19/3.2.4 
1162   Compile Options: 
1163     TCQ Enabled By Default : Disabled 
1164     AIC7XXX_PROC_STATS     : Disabled 
1165     AIC7XXX_RESET_DELAY    : 5 
1166   Adapter Configuration: 
1167              SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter 
1168                              Ultra Wide Controller 
1169       PCI MMAPed I/O Base: 0xeb001000 
1170    Adapter SEEPROM Config: SEEPROM found and used. 
1171         Adaptec SCSI BIOS: Enabled 
1172                       IRQ: 10 
1173                      SCBs: Active 0, Max Active 2, 
1174                            Allocated 15, HW 16, Page 255 
1175                Interrupts: 160328 
1176         BIOS Control Word: 0x18b6 
1177      Adapter Control Word: 0x005b 
1178      Extended Translation: Enabled 
1179   Disconnect Enable Flags: 0xffff 
1180        Ultra Enable Flags: 0x0001 
1181    Tag Queue Enable Flags: 0x0000 
1182   Ordered Queue Tag Flags: 0x0000 
1183   Default Tag Queue Depth: 8 
1184       Tagged Queue By Device array for aic7xxx host instance 0: 
1185         {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} 
1186       Actual queue depth per device for aic7xxx host instance 0: 
1187         {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} 
1188   Statistics: 
1189   (scsi0:0:0:0) 
1190     Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 
1191     Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) 
1192     Total transfers 160151 (74577 reads and 85574 writes) 
1193   (scsi0:0:6:0) 
1194     Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 
1195     Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) 
1196     Total transfers 0 (0 reads and 0 writes) 
1197 
1198 
1199 1.6 Parallel port info in /proc/parport
1200 ---------------------------------------
1201 
1202 The directory  /proc/parport  contains information about the parallel ports of
1203 your system.  It  has  one  subdirectory  for  each port, named after the port
1204 number (0,1,2,...).
1205 
1206 These directories contain the four files shown in Table 1-10.
1207 
1208 
1209 Table 1-10: Files in /proc/parport
1210 ..............................................................................
1211  File      Content                                                             
1212  autoprobe Any IEEE-1284 device ID information that has been acquired.         
1213  devices   list of the device drivers using that port. A + will appear by the
1214            name of the device currently using the port (it might not appear
1215            against any). 
1216  hardware  Parallel port's base address, IRQ line and DMA channel.             
1217  irq       IRQ that parport is using for that port. This is in a separate
1218            file to allow you to alter it by writing a new value in (IRQ
1219            number or none). 
1220 ..............................................................................
1221 
1222 1.7 TTY info in /proc/tty
1223 -------------------------
1224 
1225 Information about  the  available  and actually used tty's can be found in the
1226 directory /proc/tty.You'll  find  entries  for drivers and line disciplines in
1227 this directory, as shown in Table 1-11.
1228 
1229 
1230 Table 1-11: Files in /proc/tty
1231 ..............................................................................
1232  File          Content                                        
1233  drivers       list of drivers and their usage                
1234  ldiscs        registered line disciplines                    
1235  driver/serial usage statistic and status of single tty lines 
1236 ..............................................................................
1237 
1238 To see  which  tty's  are  currently in use, you can simply look into the file
1239 /proc/tty/drivers:
1240 
1241   > cat /proc/tty/drivers 
1242   pty_slave            /dev/pts      136   0-255 pty:slave 
1243   pty_master           /dev/ptm      128   0-255 pty:master 
1244   pty_slave            /dev/ttyp       3   0-255 pty:slave 
1245   pty_master           /dev/pty        2   0-255 pty:master 
1246   serial               /dev/cua        5   64-67 serial:callout 
1247   serial               /dev/ttyS       4   64-67 serial 
1248   /dev/tty0            /dev/tty0       4       0 system:vtmaster 
1249   /dev/ptmx            /dev/ptmx       5       2 system 
1250   /dev/console         /dev/console    5       1 system:console 
1251   /dev/tty             /dev/tty        5       0 system:/dev/tty 
1252   unknown              /dev/tty        4    1-63 console 
1253 
1254 
1255 1.8 Miscellaneous kernel statistics in /proc/stat
1256 -------------------------------------------------
1257 
1258 Various pieces   of  information about  kernel activity  are  available in the
1259 /proc/stat file.  All  of  the numbers reported  in  this file are  aggregates
1260 since the system first booted.  For a quick look, simply cat the file:
1261 
1262   > cat /proc/stat
1263   cpu  2255 34 2290 22625563 6290 127 456 0 0 0
1264   cpu0 1132 34 1441 11311718 3675 127 438 0 0 0
1265   cpu1 1123 0 849 11313845 2614 0 18 0 0 0
1266   intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1267   ctxt 1990473
1268   btime 1062191376
1269   processes 2915
1270   procs_running 1
1271   procs_blocked 0
1272   softirq 183433 0 21755 12 39 1137 231 21459 2263
1273 
1274 The very first  "cpu" line aggregates the  numbers in all  of the other "cpuN"
1275 lines.  These numbers identify the amount of time the CPU has spent performing
1276 different kinds of work.  Time units are in USER_HZ (typically hundredths of a
1277 second).  The meanings of the columns are as follows, from left to right:
1278 
1279 - user: normal processes executing in user mode
1280 - nice: niced processes executing in user mode
1281 - system: processes executing in kernel mode
1282 - idle: twiddling thumbs
1283 - iowait: waiting for I/O to complete
1284 - irq: servicing interrupts
1285 - softirq: servicing softirqs
1286 - steal: involuntary wait
1287 - guest: running a normal guest
1288 - guest_nice: running a niced guest
1289 
1290 The "intr" line gives counts of interrupts  serviced since boot time, for each
1291 of the  possible system interrupts.   The first  column  is the  total of  all
1292 interrupts serviced  including  unnumbered  architecture specific  interrupts;
1293 each  subsequent column is the  total for that particular numbered interrupt.
1294 Unnumbered interrupts are not shown, only summed into the total.
1295 
1296 The "ctxt" line gives the total number of context switches across all CPUs.
1297 
1298 The "btime" line gives  the time at which the  system booted, in seconds since
1299 the Unix epoch.
1300 
1301 The "processes" line gives the number  of processes and threads created, which
1302 includes (but  is not limited  to) those  created by  calls to the  fork() and
1303 clone() system calls.
1304 
1305 The "procs_running" line gives the total number of threads that are
1306 running or ready to run (i.e., the total number of runnable threads).
1307 
1308 The   "procs_blocked" line gives  the  number of  processes currently blocked,
1309 waiting for I/O to complete.
1310 
1311 The "softirq" line gives counts of softirqs serviced since boot time, for each
1312 of the possible system softirqs. The first column is the total of all
1313 softirqs serviced; each subsequent column is the total for that particular
1314 softirq.
1315 
1316 
1317 1.9 Ext4 file system parameters
1318 -------------------------------
1319 
1320 Information about mounted ext4 file systems can be found in
1321 /proc/fs/ext4.  Each mounted filesystem will have a directory in
1322 /proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1323 /proc/fs/ext4/dm-0).   The files in each per-device directory are shown
1324 in Table 1-12, below.
1325 
1326 Table 1-12: Files in /proc/fs/ext4/<devname>
1327 ..............................................................................
1328  File            Content                                        
1329  mb_groups       details of multiblock allocator buddy cache of free blocks
1330 ..............................................................................
1331 
1332 2.0 /proc/consoles
1333 ------------------
1334 Shows registered system console lines.
1335 
1336 To see which character device lines are currently used for the system console
1337 /dev/console, you may simply look into the file /proc/consoles:
1338 
1339   > cat /proc/consoles
1340   tty0                 -WU (ECp)       4:7
1341   ttyS0                -W- (Ep)        4:64
1342 
1343 The columns are:
1344 
1345   device               name of the device
1346   operations           R = can do read operations
1347                        W = can do write operations
1348                        U = can do unblank
1349   flags                E = it is enabled
1350                        C = it is preferred console
1351                        B = it is primary boot console
1352                        p = it is used for printk buffer
1353                        b = it is not a TTY but a Braille device
1354                        a = it is safe to use when cpu is offline
1355   major:minor          major and minor number of the device separated by a colon
1356 
1357 ------------------------------------------------------------------------------
1358 Summary
1359 ------------------------------------------------------------------------------
1360 The /proc file system serves information about the running system. It not only
1361 allows access to process data but also allows you to request the kernel status
1362 by reading files in the hierarchy.
1363 
1364 The directory  structure  of /proc reflects the types of information and makes
1365 it easy, if not obvious, where to look for specific data.
1366 ------------------------------------------------------------------------------
1367 
1368 ------------------------------------------------------------------------------
1369 CHAPTER 2: MODIFYING SYSTEM PARAMETERS
1370 ------------------------------------------------------------------------------
1371 
1372 ------------------------------------------------------------------------------
1373 In This Chapter
1374 ------------------------------------------------------------------------------
1375 * Modifying kernel parameters by writing into files found in /proc/sys
1376 * Exploring the files which modify certain parameters
1377 * Review of the /proc/sys file tree
1378 ------------------------------------------------------------------------------
1379 
1380 
1381 A very  interesting part of /proc is the directory /proc/sys. This is not only
1382 a source  of  information,  it also allows you to change parameters within the
1383 kernel. Be  very  careful  when attempting this. You can optimize your system,
1384 but you  can  also  cause  it  to  crash.  Never  alter kernel parameters on a
1385 production system.  Set  up  a  development machine and test to make sure that
1386 everything works  the  way  you want it to. You may have no alternative but to
1387 reboot the machine once an error has been made.
1388 
1389 To change  a  value,  simply  echo  the new value into the file. An example is
1390 given below  in the section on the file system data. You need to be root to do
1391 this. You  can  create  your  own  boot script to perform this every time your
1392 system boots.
1393 
1394 The files  in /proc/sys can be used to fine tune and monitor miscellaneous and
1395 general things  in  the operation of the Linux kernel. Since some of the files
1396 can inadvertently  disrupt  your  system,  it  is  advisable  to  read  both
1397 documentation and  source  before actually making adjustments. In any case, be
1398 very careful  when  writing  to  any  of these files. The entries in /proc may
1399 change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1400 review the kernel documentation in the directory /usr/src/linux/Documentation.
1401 This chapter  is  heavily  based  on the documentation included in the pre 2.2
1402 kernels, and became part of it in version 2.2.1 of the Linux kernel.
1403 
1404 Please see: Documentation/sysctl/ directory for descriptions of these
1405 entries.
1406 
1407 ------------------------------------------------------------------------------
1408 Summary
1409 ------------------------------------------------------------------------------
1410 Certain aspects  of  kernel  behavior  can be modified at runtime, without the
1411 need to  recompile  the kernel, or even to reboot the system. The files in the
1412 /proc/sys tree  can  not only be read, but also modified. You can use the echo
1413 command to write value into these files, thereby changing the default settings
1414 of the kernel.
1415 ------------------------------------------------------------------------------
1416 
1417 ------------------------------------------------------------------------------
1418 CHAPTER 3: PER-PROCESS PARAMETERS
1419 ------------------------------------------------------------------------------
1420 
1421 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1422 --------------------------------------------------------------------------------
1423 
1424 These file can be used to adjust the badness heuristic used to select which
1425 process gets killed in out of memory conditions.
1426 
1427 The badness heuristic assigns a value to each candidate task ranging from 0
1428 (never kill) to 1000 (always kill) to determine which process is targeted.  The
1429 units are roughly a proportion along that range of allowed memory the process
1430 may allocate from based on an estimation of its current memory and swap use.
1431 For example, if a task is using all allowed memory, its badness score will be
1432 1000.  If it is using half of its allowed memory, its score will be 500.
1433 
1434 There is an additional factor included in the badness score: the current memory
1435 and swap usage is discounted by 3% for root processes.
1436 
1437 The amount of "allowed" memory depends on the context in which the oom killer
1438 was called.  If it is due to the memory assigned to the allocating task's cpuset
1439 being exhausted, the allowed memory represents the set of mems assigned to that
1440 cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
1441 memory represents the set of mempolicy nodes.  If it is due to a memory
1442 limit (or swap limit) being reached, the allowed memory is that configured
1443 limit.  Finally, if it is due to the entire system being out of memory, the
1444 allowed memory represents all allocatable resources.
1445 
1446 The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1447 is used to determine which task to kill.  Acceptable values range from -1000
1448 (OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
1449 polarize the preference for oom killing either by always preferring a certain
1450 task or completely disabling it.  The lowest possible value, -1000, is
1451 equivalent to disabling oom killing entirely for that task since it will always
1452 report a badness score of 0.
1453 
1454 Consequently, it is very simple for userspace to define the amount of memory to
1455 consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
1456 example, is roughly equivalent to allowing the remainder of tasks sharing the
1457 same system, cpuset, mempolicy, or memory controller resources to use at least
1458 50% more memory.  A value of -500, on the other hand, would be roughly
1459 equivalent to discounting 50% of the task's allowed memory from being considered
1460 as scoring against the task.
1461 
1462 For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1463 be used to tune the badness score.  Its acceptable values range from -16
1464 (OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1465 (OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
1466 scaled linearly with /proc/<pid>/oom_score_adj.
1467 
1468 The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1469 value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1470 requires CAP_SYS_RESOURCE.
1471 
1472 Caveat: when a parent task is selected, the oom killer will sacrifice any first
1473 generation children with separate address spaces instead, if possible.  This
1474 avoids servers and important system daemons from being killed and loses the
1475 minimal amount of work.
1476 
1477 
1478 3.2 /proc/<pid>/oom_score - Display current oom-killer score
1479 -------------------------------------------------------------
1480 
1481 This file can be used to check the current score used by the oom-killer is for
1482 any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1483 process should be killed in an out-of-memory situation.
1484 
1485 
1486 3.3  /proc/<pid>/io - Display the IO accounting fields
1487 -------------------------------------------------------
1488 
1489 This file contains IO statistics for each running process
1490 
1491 Example
1492 -------
1493 
1494 test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1495 [1] 3828
1496 
1497 test:/tmp # cat /proc/3828/io
1498 rchar: 323934931
1499 wchar: 323929600
1500 syscr: 632687
1501 syscw: 632675
1502 read_bytes: 0
1503 write_bytes: 323932160
1504 cancelled_write_bytes: 0
1505 
1506 
1507 Description
1508 -----------
1509 
1510 rchar
1511 -----
1512 
1513 I/O counter: chars read
1514 The number of bytes which this task has caused to be read from storage. This
1515 is simply the sum of bytes which this process passed to read() and pread().
1516 It includes things like tty IO and it is unaffected by whether or not actual
1517 physical disk IO was required (the read might have been satisfied from
1518 pagecache)
1519 
1520 
1521 wchar
1522 -----
1523 
1524 I/O counter: chars written
1525 The number of bytes which this task has caused, or shall cause to be written
1526 to disk. Similar caveats apply here as with rchar.
1527 
1528 
1529 syscr
1530 -----
1531 
1532 I/O counter: read syscalls
1533 Attempt to count the number of read I/O operations, i.e. syscalls like read()
1534 and pread().
1535 
1536 
1537 syscw
1538 -----
1539 
1540 I/O counter: write syscalls
1541 Attempt to count the number of write I/O operations, i.e. syscalls like
1542 write() and pwrite().
1543 
1544 
1545 read_bytes
1546 ----------
1547 
1548 I/O counter: bytes read
1549 Attempt to count the number of bytes which this process really did cause to
1550 be fetched from the storage layer. Done at the submit_bio() level, so it is
1551 accurate for block-backed filesystems. <please add status regarding NFS and
1552 CIFS at a later time>
1553 
1554 
1555 write_bytes
1556 -----------
1557 
1558 I/O counter: bytes written
1559 Attempt to count the number of bytes which this process caused to be sent to
1560 the storage layer. This is done at page-dirtying time.
1561 
1562 
1563 cancelled_write_bytes
1564 ---------------------
1565 
1566 The big inaccuracy here is truncate. If a process writes 1MB to a file and
1567 then deletes the file, it will in fact perform no writeout. But it will have
1568 been accounted as having caused 1MB of write.
1569 In other words: The number of bytes which this process caused to not happen,
1570 by truncating pagecache. A task can cause "negative" IO too. If this task
1571 truncates some dirty pagecache, some IO which another task has been accounted
1572 for (in its write_bytes) will not be happening. We _could_ just subtract that
1573 from the truncating task's write_bytes, but there is information loss in doing
1574 that.
1575 
1576 
1577 Note
1578 ----
1579 
1580 At its current implementation state, this is a bit racy on 32-bit machines: if
1581 process A reads process B's /proc/pid/io while process B is updating one of
1582 those 64-bit counters, process A could see an intermediate result.
1583 
1584 
1585 More information about this can be found within the taskstats documentation in
1586 Documentation/accounting.
1587 
1588 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1589 ---------------------------------------------------------------
1590 When a process is dumped, all anonymous memory is written to a core file as
1591 long as the size of the core file isn't limited. But sometimes we don't want
1592 to dump some memory segments, for example, huge shared memory. Conversely,
1593 sometimes we want to save file-backed memory segments into a core file, not
1594 only the individual files.
1595 
1596 /proc/<pid>/coredump_filter allows you to customize which memory segments
1597 will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1598 of memory types. If a bit of the bitmask is set, memory segments of the
1599 corresponding memory type are dumped, otherwise they are not dumped.
1600 
1601 The following 7 memory types are supported:
1602   - (bit 0) anonymous private memory
1603   - (bit 1) anonymous shared memory
1604   - (bit 2) file-backed private memory
1605   - (bit 3) file-backed shared memory
1606   - (bit 4) ELF header pages in file-backed private memory areas (it is
1607             effective only if the bit 2 is cleared)
1608   - (bit 5) hugetlb private memory
1609   - (bit 6) hugetlb shared memory
1610 
1611   Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1612   are always dumped regardless of the bitmask status.
1613 
1614   Note bit 0-4 doesn't effect any hugetlb memory. hugetlb memory are only
1615   effected by bit 5-6.
1616 
1617 Default value of coredump_filter is 0x23; this means all anonymous memory
1618 segments and hugetlb private memory are dumped.
1619 
1620 If you don't want to dump all shared memory segments attached to pid 1234,
1621 write 0x21 to the process's proc file.
1622 
1623   $ echo 0x21 > /proc/1234/coredump_filter
1624 
1625 When a new process is created, the process inherits the bitmask status from its
1626 parent. It is useful to set up coredump_filter before the program runs.
1627 For example:
1628 
1629   $ echo 0x7 > /proc/self/coredump_filter
1630   $ ./some_program
1631 
1632 3.5     /proc/<pid>/mountinfo - Information about mounts
1633 --------------------------------------------------------
1634 
1635 This file contains lines of the form:
1636 
1637 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1638 (1)(2)(3)   (4)   (5)      (6)      (7)   (8) (9)   (10)         (11)
1639 
1640 (1) mount ID:  unique identifier of the mount (may be reused after umount)
1641 (2) parent ID:  ID of parent (or of self for the top of the mount tree)
1642 (3) major:minor:  value of st_dev for files on filesystem
1643 (4) root:  root of the mount within the filesystem
1644 (5) mount point:  mount point relative to the process's root
1645 (6) mount options:  per mount options
1646 (7) optional fields:  zero or more fields of the form "tag[:value]"
1647 (8) separator:  marks the end of the optional fields
1648 (9) filesystem type:  name of filesystem of the form "type[.subtype]"
1649 (10) mount source:  filesystem specific information or "none"
1650 (11) super options:  per super block options
1651 
1652 Parsers should ignore all unrecognised optional fields.  Currently the
1653 possible optional fields are:
1654 
1655 shared:X  mount is shared in peer group X
1656 master:X  mount is slave to peer group X
1657 propagate_from:X  mount is slave and receives propagation from peer group X (*)
1658 unbindable  mount is unbindable
1659 
1660 (*) X is the closest dominant peer group under the process's root.  If
1661 X is the immediate master of the mount, or if there's no dominant peer
1662 group under the same root, then only the "master:X" field is present
1663 and not the "propagate_from:X" field.
1664 
1665 For more information on mount propagation see:
1666 
1667   Documentation/filesystems/sharedsubtree.txt
1668 
1669 
1670 3.6     /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
1671 --------------------------------------------------------
1672 These files provide a method to access a tasks comm value. It also allows for
1673 a task to set its own or one of its thread siblings comm value. The comm value
1674 is limited in size compared to the cmdline value, so writing anything longer
1675 then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1676 comm value.
1677 
1678 
1679 3.7     /proc/<pid>/task/<tid>/children - Information about task children
1680 -------------------------------------------------------------------------
1681 This file provides a fast way to retrieve first level children pids
1682 of a task pointed by <pid>/<tid> pair. The format is a space separated
1683 stream of pids.
1684 
1685 Note the "first level" here -- if a child has own children they will
1686 not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children
1687 to obtain the descendants.
1688 
1689 Since this interface is intended to be fast and cheap it doesn't
1690 guarantee to provide precise results and some children might be
1691 skipped, especially if they've exited right after we printed their
1692 pids, so one need to either stop or freeze processes being inspected
1693 if precise results are needed.
1694 
1695 
1696 3.8     /proc/<pid>/fdinfo/<fd> - Information about opened file
1697 ---------------------------------------------------------------
1698 This file provides information associated with an opened file. The regular
1699 files have at least three fields -- 'pos', 'flags' and mnt_id. The 'pos'
1700 represents the current offset of the opened file in decimal form [see lseek(2)
1701 for details], 'flags' denotes the octal O_xxx mask the file has been
1702 created with [see open(2) for details] and 'mnt_id' represents mount ID of
1703 the file system containing the opened file [see 3.5 /proc/<pid>/mountinfo
1704 for details].
1705 
1706 A typical output is
1707 
1708         pos:    0
1709         flags:  0100002
1710         mnt_id: 19
1711 
1712 All locks associated with a file descriptor are shown in its fdinfo too.
1713 
1714 lock:       1: FLOCK  ADVISORY  WRITE 359 00:13:11691 0 EOF
1715 
1716 The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1717 pair provide additional information particular to the objects they represent.
1718 
1719         Eventfd files
1720         ~~~~~~~~~~~~~
1721         pos:    0
1722         flags:  04002
1723         mnt_id: 9
1724         eventfd-count:  5a
1725 
1726         where 'eventfd-count' is hex value of a counter.
1727 
1728         Signalfd files
1729         ~~~~~~~~~~~~~~
1730         pos:    0
1731         flags:  04002
1732         mnt_id: 9
1733         sigmask:        0000000000000200
1734 
1735         where 'sigmask' is hex value of the signal mask associated
1736         with a file.
1737 
1738         Epoll files
1739         ~~~~~~~~~~~
1740         pos:    0
1741         flags:  02
1742         mnt_id: 9
1743         tfd:        5 events:       1d data: ffffffffffffffff
1744 
1745         where 'tfd' is a target file descriptor number in decimal form,
1746         'events' is events mask being watched and the 'data' is data
1747         associated with a target [see epoll(7) for more details].
1748 
1749         Fsnotify files
1750         ~~~~~~~~~~~~~~
1751         For inotify files the format is the following
1752 
1753         pos:    0
1754         flags:  02000000
1755         inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
1756 
1757         where 'wd' is a watch descriptor in decimal form, ie a target file
1758         descriptor number, 'ino' and 'sdev' are inode and device where the
1759         target file resides and the 'mask' is the mask of events, all in hex
1760         form [see inotify(7) for more details].
1761 
1762         If the kernel was built with exportfs support, the path to the target
1763         file is encoded as a file handle.  The file handle is provided by three
1764         fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
1765         format.
1766 
1767         If the kernel is built without exportfs support the file handle won't be
1768         printed out.
1769 
1770         If there is no inotify mark attached yet the 'inotify' line will be omitted.
1771 
1772         For fanotify files the format is
1773 
1774         pos:    0
1775         flags:  02
1776         mnt_id: 9
1777         fanotify flags:10 event-flags:0
1778         fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
1779         fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
1780 
1781         where fanotify 'flags' and 'event-flags' are values used in fanotify_init
1782         call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
1783         flags associated with mark which are tracked separately from events
1784         mask. 'ino', 'sdev' are target inode and device, 'mask' is the events
1785         mask and 'ignored_mask' is the mask of events which are to be ignored.
1786         All in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
1787         does provide information about flags and mask used in fanotify_mark
1788         call [see fsnotify manpage for details].
1789 
1790         While the first three lines are mandatory and always printed, the rest is
1791         optional and may be omitted if no marks created yet.
1792 
1793         Timerfd files
1794         ~~~~~~~~~~~~~
1795 
1796         pos:    0
1797         flags:  02
1798         mnt_id: 9
1799         clockid: 0
1800         ticks: 0
1801         settime flags: 01
1802         it_value: (0, 49406829)
1803         it_interval: (1, 0)
1804 
1805         where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
1806         that have occurred [see timerfd_create(2) for details]. 'settime flags' are
1807         flags in octal form been used to setup the timer [see timerfd_settime(2) for
1808         details]. 'it_value' is remaining time until the timer exiration.
1809         'it_interval' is the interval for the timer. Note the timer might be set up
1810         with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
1811         still exhibits timer's remaining time.
1812 
1813 3.9     /proc/<pid>/map_files - Information about memory mapped files
1814 ---------------------------------------------------------------------
1815 This directory contains symbolic links which represent memory mapped files
1816 the process is maintaining.  Example output:
1817 
1818      | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
1819      | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
1820      | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
1821      | ...
1822      | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
1823      | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
1824 
1825 The name of a link represents the virtual memory bounds of a mapping, i.e.
1826 vm_area_struct::vm_start-vm_area_struct::vm_end.
1827 
1828 The main purpose of the map_files is to retrieve a set of memory mapped
1829 files in a fast way instead of parsing /proc/<pid>/maps or
1830 /proc/<pid>/smaps, both of which contain many more records.  At the same
1831 time one can open(2) mappings from the listings of two processes and
1832 comparing their inode numbers to figure out which anonymous memory areas
1833 are actually shared.
1834 
1835 ------------------------------------------------------------------------------
1836 Configuring procfs
1837 ------------------------------------------------------------------------------
1838 
1839 4.1     Mount options
1840 ---------------------
1841 
1842 The following mount options are supported:
1843 
1844         hidepid=        Set /proc/<pid>/ access mode.
1845         gid=            Set the group authorized to learn processes information.
1846 
1847 hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
1848 (default).
1849 
1850 hidepid=1 means users may not access any /proc/<pid>/ directories but their
1851 own.  Sensitive files like cmdline, sched*, status are now protected against
1852 other users.  This makes it impossible to learn whether any user runs
1853 specific program (given the program doesn't reveal itself by its behaviour).
1854 As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users,
1855 poorly written programs passing sensitive information via program arguments are
1856 now protected against local eavesdroppers.
1857 
1858 hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other
1859 users.  It doesn't mean that it hides a fact whether a process with a specific
1860 pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"),
1861 but it hides process' uid and gid, which may be learned by stat()'ing
1862 /proc/<pid>/ otherwise.  It greatly complicates an intruder's task of gathering
1863 information about running processes, whether some daemon runs with elevated
1864 privileges, whether other user runs some sensitive program, whether other users
1865 run any program at all, etc.
1866 
1867 gid= defines a group authorized to learn processes information otherwise
1868 prohibited by hidepid=.  If you use some daemon like identd which needs to learn
1869 information about processes information, just add identd to this group.

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