Version:  2.0.40 2.2.26 2.4.37 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10

Linux/Documentation/filesystems/proc.txt

  1 ------------------------------------------------------------------------------
  2                        T H E  /proc   F I L E S Y S T E M
  3 ------------------------------------------------------------------------------
  4 /proc/sys         Terrehon Bowden <terrehon@pacbell.net>        October 7 1999
  5                   Bodo Bauer <bb@ricochet.net>
  6 
  7 2.4.x update      Jorge Nerin <comandante@zaralinux.com>      November 14 2000
  8 move /proc/sys    Shen Feng <shen@cn.fujitsu.com>                 April 1 2009
  9 ------------------------------------------------------------------------------
 10 Version 1.3                                              Kernel version 2.2.12
 11                                               Kernel version 2.4.0-test11-pre4
 12 ------------------------------------------------------------------------------
 13 fixes/update part 1.1  Stefani Seibold <stefani@seibold.net>       June 9 2009
 14 
 15 Table of Contents
 16 -----------------
 17 
 18   0     Preface
 19   0.1   Introduction/Credits
 20   0.2   Legal Stuff
 21 
 22   1     Collecting System Information
 23   1.1   Process-Specific Subdirectories
 24   1.2   Kernel data
 25   1.3   IDE devices in /proc/ide
 26   1.4   Networking info in /proc/net
 27   1.5   SCSI info
 28   1.6   Parallel port info in /proc/parport
 29   1.7   TTY info in /proc/tty
 30   1.8   Miscellaneous kernel statistics in /proc/stat
 31   1.9   Ext4 file system parameters
 32 
 33   2     Modifying System Parameters
 34 
 35   3     Per-Process Parameters
 36   3.1   /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj - Adjust the oom-killer
 37                                                                 score
 38   3.2   /proc/<pid>/oom_score - Display current oom-killer score
 39   3.3   /proc/<pid>/io - Display the IO accounting fields
 40   3.4   /proc/<pid>/coredump_filter - Core dump filtering settings
 41   3.5   /proc/<pid>/mountinfo - Information about mounts
 42   3.6   /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
 43   3.7   /proc/<pid>/task/<tid>/children - Information about task children
 44   3.8   /proc/<pid>/fdinfo/<fd> - Information about opened file
 45   3.9   /proc/<pid>/map_files - Information about memory mapped files
 46   3.10  /proc/<pid>/timerslack_ns - Task timerslack value
 47 
 48   4     Configuring procfs
 49   4.1   Mount options
 50 
 51 ------------------------------------------------------------------------------
 52 Preface
 53 ------------------------------------------------------------------------------
 54 
 55 0.1 Introduction/Credits
 56 ------------------------
 57 
 58 This documentation is  part of a soon (or  so we hope) to be  released book on
 59 the SuSE  Linux distribution. As  there is  no complete documentation  for the
 60 /proc file system and we've used  many freely available sources to write these
 61 chapters, it  seems only fair  to give the work  back to the  Linux community.
 62 This work is  based on the 2.2.*  kernel version and the  upcoming 2.4.*. I'm
 63 afraid it's still far from complete, but we  hope it will be useful. As far as
 64 we know, it is the first 'all-in-one' document about the /proc file system. It
 65 is focused  on the Intel  x86 hardware,  so if you  are looking for  PPC, ARM,
 66 SPARC, AXP, etc., features, you probably  won't find what you are looking for.
 67 It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
 68 additions and patches  are welcome and will  be added to this  document if you
 69 mail them to Bodo.
 70 
 71 We'd like  to  thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
 72 other people for help compiling this documentation. We'd also like to extend a
 73 special thank  you to Andi Kleen for documentation, which we relied on heavily
 74 to create  this  document,  as well as the additional information he provided.
 75 Thanks to  everybody  else  who contributed source or docs to the Linux kernel
 76 and helped create a great piece of software... :)
 77 
 78 If you  have  any comments, corrections or additions, please don't hesitate to
 79 contact Bodo  Bauer  at  bb@ricochet.net.  We'll  be happy to add them to this
 80 document.
 81 
 82 The   latest   version    of   this   document   is    available   online   at
 83 http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html
 84 
 85 If  the above  direction does  not works  for you,  you could  try the  kernel
 86 mailing  list  at  linux-kernel@vger.kernel.org  and/or try  to  reach  me  at
 87 comandante@zaralinux.com.
 88 
 89 0.2 Legal Stuff
 90 ---------------
 91 
 92 We don't  guarantee  the  correctness  of this document, and if you come to us
 93 complaining about  how  you  screwed  up  your  system  because  of  incorrect
 94 documentation, we won't feel responsible...
 95 
 96 ------------------------------------------------------------------------------
 97 CHAPTER 1: COLLECTING SYSTEM INFORMATION
 98 ------------------------------------------------------------------------------
 99 
100 ------------------------------------------------------------------------------
101 In This Chapter
102 ------------------------------------------------------------------------------
103 * Investigating  the  properties  of  the  pseudo  file  system  /proc and its
104   ability to provide information on the running Linux system
105 * Examining /proc's structure
106 * Uncovering  various  information  about the kernel and the processes running
107   on the system
108 ------------------------------------------------------------------------------
109 
110 
111 The proc  file  system acts as an interface to internal data structures in the
112 kernel. It  can  be  used to obtain information about the system and to change
113 certain kernel parameters at runtime (sysctl).
114 
115 First, we'll  take  a  look  at the read-only parts of /proc. In Chapter 2, we
116 show you how you can use /proc/sys to change settings.
117 
118 1.1 Process-Specific Subdirectories
119 -----------------------------------
120 
121 The directory  /proc  contains  (among other things) one subdirectory for each
122 process running on the system, which is named after the process ID (PID).
123 
124 The link  self  points  to  the  process reading the file system. Each process
125 subdirectory has the entries listed in Table 1-1.
126 
127 
128 Table 1-1: Process specific entries in /proc
129 ..............................................................................
130  File           Content
131  clear_refs     Clears page referenced bits shown in smaps output
132  cmdline        Command line arguments
133  cpu            Current and last cpu in which it was executed   (2.4)(smp)
134  cwd            Link to the current working directory
135  environ        Values of environment variables
136  exe            Link to the executable of this process
137  fd             Directory, which contains all file descriptors
138  maps           Memory maps to executables and library files    (2.4)
139  mem            Memory held by this process
140  root           Link to the root directory of this process
141  stat           Process status
142  statm          Process memory status information
143  status         Process status in human readable form
144  wchan          Present with CONFIG_KALLSYMS=y: it shows the kernel function
145                 symbol the task is blocked in - or "0" if not blocked.
146  pagemap        Page table
147  stack          Report full stack trace, enable via CONFIG_STACKTRACE
148  smaps          an extension based on maps, showing the memory consumption of
149                 each mapping and flags associated with it
150  numa_maps      an extension based on maps, showing the memory locality and
151                 binding policy as well as mem usage (in pages) of each mapping.
152 ..............................................................................
153 
154 For example, to get the status information of a process, all you have to do is
155 read the file /proc/PID/status:
156 
157   >cat /proc/self/status
158   Name:   cat
159   State:  R (running)
160   Tgid:   5452
161   Pid:    5452
162   PPid:   743
163   TracerPid:      0                                             (2.4)
164   Uid:    501     501     501     501
165   Gid:    100     100     100     100
166   FDSize: 256
167   Groups: 100 14 16
168   VmPeak:     5004 kB
169   VmSize:     5004 kB
170   VmLck:         0 kB
171   VmHWM:       476 kB
172   VmRSS:       476 kB
173   RssAnon:             352 kB
174   RssFile:             120 kB
175   RssShmem:              4 kB
176   VmData:      156 kB
177   VmStk:        88 kB
178   VmExe:        68 kB
179   VmLib:      1412 kB
180   VmPTE:        20 kb
181   VmSwap:        0 kB
182   HugetlbPages:          0 kB
183   Threads:        1
184   SigQ:   0/28578
185   SigPnd: 0000000000000000
186   ShdPnd: 0000000000000000
187   SigBlk: 0000000000000000
188   SigIgn: 0000000000000000
189   SigCgt: 0000000000000000
190   CapInh: 00000000fffffeff
191   CapPrm: 0000000000000000
192   CapEff: 0000000000000000
193   CapBnd: ffffffffffffffff
194   NoNewPrivs:     0
195   Seccomp:        0
196   voluntary_ctxt_switches:        0
197   nonvoluntary_ctxt_switches:     1
198 
199 This shows you nearly the same information you would get if you viewed it with
200 the ps  command.  In  fact,  ps  uses  the  proc  file  system  to  obtain its
201 information.  But you get a more detailed  view of the  process by reading the
202 file /proc/PID/status. It fields are described in table 1-2.
203 
204 The  statm  file  contains  more  detailed  information about the process
205 memory usage. Its seven fields are explained in Table 1-3.  The stat file
206 contains details information about the process itself.  Its fields are
207 explained in Table 1-4.
208 
209 (for SMP CONFIG users)
210 For making accounting scalable, RSS related information are handled in an
211 asynchronous manner and the value may not be very precise. To see a precise
212 snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
213 It's slow but very precise.
214 
215 Table 1-2: Contents of the status files (as of 4.8)
216 ..............................................................................
217  Field                       Content
218  Name                        filename of the executable
219  Umask                       file mode creation mask
220  State                       state (R is running, S is sleeping, D is sleeping
221                              in an uninterruptible wait, Z is zombie,
222                              T is traced or stopped)
223  Tgid                        thread group ID
224  Ngid                        NUMA group ID (0 if none)
225  Pid                         process id
226  PPid                        process id of the parent process
227  TracerPid                   PID of process tracing this process (0 if not)
228  Uid                         Real, effective, saved set, and  file system UIDs
229  Gid                         Real, effective, saved set, and  file system GIDs
230  FDSize                      number of file descriptor slots currently allocated
231  Groups                      supplementary group list
232  NStgid                      descendant namespace thread group ID hierarchy
233  NSpid                       descendant namespace process ID hierarchy
234  NSpgid                      descendant namespace process group ID hierarchy
235  NSsid                       descendant namespace session ID hierarchy
236  VmPeak                      peak virtual memory size
237  VmSize                      total program size
238  VmLck                       locked memory size
239  VmPin                       pinned memory size
240  VmHWM                       peak resident set size ("high water mark")
241  VmRSS                       size of memory portions. It contains the three
242                              following parts (VmRSS = RssAnon + RssFile + RssShmem)
243  RssAnon                     size of resident anonymous memory
244  RssFile                     size of resident file mappings
245  RssShmem                    size of resident shmem memory (includes SysV shm,
246                              mapping of tmpfs and shared anonymous mappings)
247  VmData                      size of private data segments
248  VmStk                       size of stack segments
249  VmExe                       size of text segment
250  VmLib                       size of shared library code
251  VmPTE                       size of page table entries
252  VmPMD                       size of second level page tables
253  VmSwap                      amount of swap used by anonymous private data
254                              (shmem swap usage is not included)
255  HugetlbPages                size of hugetlb memory portions
256  Threads                     number of threads
257  SigQ                        number of signals queued/max. number for queue
258  SigPnd                      bitmap of pending signals for the thread
259  ShdPnd                      bitmap of shared pending signals for the process
260  SigBlk                      bitmap of blocked signals
261  SigIgn                      bitmap of ignored signals
262  SigCgt                      bitmap of caught signals
263  CapInh                      bitmap of inheritable capabilities
264  CapPrm                      bitmap of permitted capabilities
265  CapEff                      bitmap of effective capabilities
266  CapBnd                      bitmap of capabilities bounding set
267  NoNewPrivs                  no_new_privs, like prctl(PR_GET_NO_NEW_PRIV, ...)
268  Seccomp                     seccomp mode, like prctl(PR_GET_SECCOMP, ...)
269  Cpus_allowed                mask of CPUs on which this process may run
270  Cpus_allowed_list           Same as previous, but in "list format"
271  Mems_allowed                mask of memory nodes allowed to this process
272  Mems_allowed_list           Same as previous, but in "list format"
273  voluntary_ctxt_switches     number of voluntary context switches
274  nonvoluntary_ctxt_switches  number of non voluntary context switches
275 ..............................................................................
276 
277 Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
278 ..............................................................................
279  Field    Content
280  size     total program size (pages)            (same as VmSize in status)
281  resident size of memory portions (pages)       (same as VmRSS in status)
282  shared   number of pages that are shared       (i.e. backed by a file, same
283                                                 as RssFile+RssShmem in status)
284  trs      number of pages that are 'code'       (not including libs; broken,
285                                                         includes data segment)
286  lrs      number of pages of library            (always 0 on 2.6)
287  drs      number of pages of data/stack         (including libs; broken,
288                                                         includes library text)
289  dt       number of dirty pages                 (always 0 on 2.6)
290 ..............................................................................
291 
292 
293 Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
294 ..............................................................................
295  Field          Content
296   pid           process id
297   tcomm         filename of the executable
298   state         state (R is running, S is sleeping, D is sleeping in an
299                 uninterruptible wait, Z is zombie, T is traced or stopped)
300   ppid          process id of the parent process
301   pgrp          pgrp of the process
302   sid           session id
303   tty_nr        tty the process uses
304   tty_pgrp      pgrp of the tty
305   flags         task flags
306   min_flt       number of minor faults
307   cmin_flt      number of minor faults with child's
308   maj_flt       number of major faults
309   cmaj_flt      number of major faults with child's
310   utime         user mode jiffies
311   stime         kernel mode jiffies
312   cutime        user mode jiffies with child's
313   cstime        kernel mode jiffies with child's
314   priority      priority level
315   nice          nice level
316   num_threads   number of threads
317   it_real_value (obsolete, always 0)
318   start_time    time the process started after system boot
319   vsize         virtual memory size
320   rss           resident set memory size
321   rsslim        current limit in bytes on the rss
322   start_code    address above which program text can run
323   end_code      address below which program text can run
324   start_stack   address of the start of the main process stack
325   esp           current value of ESP
326   eip           current value of EIP
327   pending       bitmap of pending signals
328   blocked       bitmap of blocked signals
329   sigign        bitmap of ignored signals
330   sigcatch      bitmap of caught signals
331   0             (place holder, used to be the wchan address, use /proc/PID/wchan instead)
332   0             (place holder)
333   0             (place holder)
334   exit_signal   signal to send to parent thread on exit
335   task_cpu      which CPU the task is scheduled on
336   rt_priority   realtime priority
337   policy        scheduling policy (man sched_setscheduler)
338   blkio_ticks   time spent waiting for block IO
339   gtime         guest time of the task in jiffies
340   cgtime        guest time of the task children in jiffies
341   start_data    address above which program data+bss is placed
342   end_data      address below which program data+bss is placed
343   start_brk     address above which program heap can be expanded with brk()
344   arg_start     address above which program command line is placed
345   arg_end       address below which program command line is placed
346   env_start     address above which program environment is placed
347   env_end       address below which program environment is placed
348   exit_code     the thread's exit_code in the form reported by the waitpid system call
349 ..............................................................................
350 
351 The /proc/PID/maps file containing the currently mapped memory regions and
352 their access permissions.
353 
354 The format is:
355 
356 address           perms offset  dev   inode      pathname
357 
358 08048000-08049000 r-xp 00000000 03:00 8312       /opt/test
359 08049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
360 0804a000-0806b000 rw-p 00000000 00:00 0          [heap]
361 a7cb1000-a7cb2000 ---p 00000000 00:00 0
362 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
363 a7eb2000-a7eb3000 ---p 00000000 00:00 0
364 a7eb3000-a7ed5000 rw-p 00000000 00:00 0
365 a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/libc.so.6
366 a8008000-a800a000 r--p 00133000 03:00 4222       /lib/libc.so.6
367 a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/libc.so.6
368 a800b000-a800e000 rw-p 00000000 00:00 0
369 a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/libpthread.so.0
370 a8022000-a8023000 r--p 00013000 03:00 14462      /lib/libpthread.so.0
371 a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/libpthread.so.0
372 a8024000-a8027000 rw-p 00000000 00:00 0
373 a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/ld-linux.so.2
374 a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/ld-linux.so.2
375 a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/ld-linux.so.2
376 aff35000-aff4a000 rw-p 00000000 00:00 0          [stack]
377 ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
378 
379 where "address" is the address space in the process that it occupies, "perms"
380 is a set of permissions:
381 
382  r = read
383  w = write
384  x = execute
385  s = shared
386  p = private (copy on write)
387 
388 "offset" is the offset into the mapping, "dev" is the device (major:minor), and
389 "inode" is the inode  on that device.  0 indicates that  no inode is associated
390 with the memory region, as the case would be with BSS (uninitialized data).
391 The "pathname" shows the name associated file for this mapping.  If the mapping
392 is not associated with a file:
393 
394  [heap]                   = the heap of the program
395  [stack]                  = the stack of the main process
396  [vdso]                   = the "virtual dynamic shared object",
397                             the kernel system call handler
398 
399  or if empty, the mapping is anonymous.
400 
401 The /proc/PID/smaps is an extension based on maps, showing the memory
402 consumption for each of the process's mappings. For each of mappings there
403 is a series of lines such as the following:
404 
405 08048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
406 Size:               1084 kB
407 Rss:                 892 kB
408 Pss:                 374 kB
409 Shared_Clean:        892 kB
410 Shared_Dirty:          0 kB
411 Private_Clean:         0 kB
412 Private_Dirty:         0 kB
413 Referenced:          892 kB
414 Anonymous:             0 kB
415 AnonHugePages:         0 kB
416 ShmemPmdMapped:        0 kB
417 Shared_Hugetlb:        0 kB
418 Private_Hugetlb:       0 kB
419 Swap:                  0 kB
420 SwapPss:               0 kB
421 KernelPageSize:        4 kB
422 MMUPageSize:           4 kB
423 Locked:                0 kB
424 VmFlags: rd ex mr mw me dw
425 
426 the first of these lines shows the same information as is displayed for the
427 mapping in /proc/PID/maps.  The remaining lines show the size of the mapping
428 (size), the amount of the mapping that is currently resident in RAM (RSS), the
429 process' proportional share of this mapping (PSS), the number of clean and
430 dirty private pages in the mapping.
431 
432 The "proportional set size" (PSS) of a process is the count of pages it has
433 in memory, where each page is divided by the number of processes sharing it.
434 So if a process has 1000 pages all to itself, and 1000 shared with one other
435 process, its PSS will be 1500.
436 Note that even a page which is part of a MAP_SHARED mapping, but has only
437 a single pte mapped, i.e.  is currently used by only one process, is accounted
438 as private and not as shared.
439 "Referenced" indicates the amount of memory currently marked as referenced or
440 accessed.
441 "Anonymous" shows the amount of memory that does not belong to any file.  Even
442 a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
443 and a page is modified, the file page is replaced by a private anonymous copy.
444 "AnonHugePages" shows the ammount of memory backed by transparent hugepage.
445 "ShmemPmdMapped" shows the ammount of shared (shmem/tmpfs) memory backed by
446 huge pages.
447 "Shared_Hugetlb" and "Private_Hugetlb" show the ammounts of memory backed by
448 hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical
449 reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field.
450 "Swap" shows how much would-be-anonymous memory is also used, but out on swap.
451 For shmem mappings, "Swap" includes also the size of the mapped (and not
452 replaced by copy-on-write) part of the underlying shmem object out on swap.
453 "SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
454 does not take into account swapped out page of underlying shmem objects.
455 "Locked" indicates whether the mapping is locked in memory or not.
456 
457 "VmFlags" field deserves a separate description. This member represents the kernel
458 flags associated with the particular virtual memory area in two letter encoded
459 manner. The codes are the following:
460     rd  - readable
461     wr  - writeable
462     ex  - executable
463     sh  - shared
464     mr  - may read
465     mw  - may write
466     me  - may execute
467     ms  - may share
468     gd  - stack segment growns down
469     pf  - pure PFN range
470     dw  - disabled write to the mapped file
471     lo  - pages are locked in memory
472     io  - memory mapped I/O area
473     sr  - sequential read advise provided
474     rr  - random read advise provided
475     dc  - do not copy area on fork
476     de  - do not expand area on remapping
477     ac  - area is accountable
478     nr  - swap space is not reserved for the area
479     ht  - area uses huge tlb pages
480     ar  - architecture specific flag
481     dd  - do not include area into core dump
482     sd  - soft-dirty flag
483     mm  - mixed map area
484     hg  - huge page advise flag
485     nh  - no-huge page advise flag
486     mg  - mergable advise flag
487 
488 Note that there is no guarantee that every flag and associated mnemonic will
489 be present in all further kernel releases. Things get changed, the flags may
490 be vanished or the reverse -- new added.
491 
492 This file is only present if the CONFIG_MMU kernel configuration option is
493 enabled.
494 
495 Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy (consistent
496 output can be achieved only in the single read call).
497 This typically manifests when doing partial reads of these files while the
498 memory map is being modified.  Despite the races, we do provide the following
499 guarantees:
500 
501 1) The mapped addresses never go backwards, which implies no two
502    regions will ever overlap.
503 2) If there is something at a given vaddr during the entirety of the
504    life of the smaps/maps walk, there will be some output for it.
505 
506 
507 The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
508 bits on both physical and virtual pages associated with a process, and the
509 soft-dirty bit on pte (see Documentation/vm/soft-dirty.txt for details).
510 To clear the bits for all the pages associated with the process
511     > echo 1 > /proc/PID/clear_refs
512 
513 To clear the bits for the anonymous pages associated with the process
514     > echo 2 > /proc/PID/clear_refs
515 
516 To clear the bits for the file mapped pages associated with the process
517     > echo 3 > /proc/PID/clear_refs
518 
519 To clear the soft-dirty bit
520     > echo 4 > /proc/PID/clear_refs
521 
522 To reset the peak resident set size ("high water mark") to the process's
523 current value:
524     > echo 5 > /proc/PID/clear_refs
525 
526 Any other value written to /proc/PID/clear_refs will have no effect.
527 
528 The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
529 using /proc/kpageflags and number of times a page is mapped using
530 /proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt.
531 
532 The /proc/pid/numa_maps is an extension based on maps, showing the memory
533 locality and binding policy, as well as the memory usage (in pages) of
534 each mapping. The output follows a general format where mapping details get
535 summarized separated by blank spaces, one mapping per each file line:
536 
537 address   policy    mapping details
538 
539 00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
540 00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
541 3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
542 320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
543 3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
544 3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
545 3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
546 320698b000 default file=/lib64/libc-2.12.so
547 3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4
548 3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
549 3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
550 7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
551 7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
552 7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
553 7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
554 7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4
555 
556 Where:
557 "address" is the starting address for the mapping;
558 "policy" reports the NUMA memory policy set for the mapping (see vm/numa_memory_policy.txt);
559 "mapping details" summarizes mapping data such as mapping type, page usage counters,
560 node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
561 size, in KB, that is backing the mapping up.
562 
563 1.2 Kernel data
564 ---------------
565 
566 Similar to  the  process entries, the kernel data files give information about
567 the running kernel. The files used to obtain this information are contained in
568 /proc and  are  listed  in Table 1-5. Not all of these will be present in your
569 system. It  depends  on the kernel configuration and the loaded modules, which
570 files are there, and which are missing.
571 
572 Table 1-5: Kernel info in /proc
573 ..............................................................................
574  File        Content                                           
575  apm         Advanced power management info                    
576  buddyinfo   Kernel memory allocator information (see text)     (2.5)
577  bus         Directory containing bus specific information     
578  cmdline     Kernel command line                               
579  cpuinfo     Info about the CPU                                
580  devices     Available devices (block and character)           
581  dma         Used DMS channels                                 
582  filesystems Supported filesystems                             
583  driver      Various drivers grouped here, currently rtc (2.4)
584  execdomains Execdomains, related to security                   (2.4)
585  fb          Frame Buffer devices                               (2.4)
586  fs          File system parameters, currently nfs/exports      (2.4)
587  ide         Directory containing info about the IDE subsystem 
588  interrupts  Interrupt usage                                   
589  iomem       Memory map                                         (2.4)
590  ioports     I/O port usage                                    
591  irq         Masks for irq to cpu affinity                      (2.4)(smp?)
592  isapnp      ISA PnP (Plug&Play) Info                           (2.4)
593  kcore       Kernel core image (can be ELF or A.OUT(deprecated in 2.4))   
594  kmsg        Kernel messages                                   
595  ksyms       Kernel symbol table                               
596  loadavg     Load average of last 1, 5 & 15 minutes                
597  locks       Kernel locks                                      
598  meminfo     Memory info                                       
599  misc        Miscellaneous                                     
600  modules     List of loaded modules                            
601  mounts      Mounted filesystems                               
602  net         Networking info (see text)                        
603  pagetypeinfo Additional page allocator information (see text)  (2.5)
604  partitions  Table of partitions known to the system           
605  pci         Deprecated info of PCI bus (new way -> /proc/bus/pci/,
606              decoupled by lspci                                 (2.4)
607  rtc         Real time clock                                   
608  scsi        SCSI info (see text)                              
609  slabinfo    Slab pool info                                    
610  softirqs    softirq usage
611  stat        Overall statistics                                
612  swaps       Swap space utilization                            
613  sys         See chapter 2                                     
614  sysvipc     Info of SysVIPC Resources (msg, sem, shm)          (2.4)
615  tty         Info of tty drivers
616  uptime      Wall clock since boot, combined idle time of all cpus
617  version     Kernel version                                    
618  video       bttv info of video resources                       (2.4)
619  vmallocinfo Show vmalloced areas
620 ..............................................................................
621 
622 You can,  for  example,  check  which interrupts are currently in use and what
623 they are used for by looking in the file /proc/interrupts:
624 
625   > cat /proc/interrupts 
626              CPU0        
627     0:    8728810          XT-PIC  timer 
628     1:        895          XT-PIC  keyboard 
629     2:          0          XT-PIC  cascade 
630     3:     531695          XT-PIC  aha152x 
631     4:    2014133          XT-PIC  serial 
632     5:      44401          XT-PIC  pcnet_cs 
633     8:          2          XT-PIC  rtc 
634    11:          8          XT-PIC  i82365 
635    12:     182918          XT-PIC  PS/2 Mouse 
636    13:          1          XT-PIC  fpu 
637    14:    1232265          XT-PIC  ide0 
638    15:          7          XT-PIC  ide1 
639   NMI:          0 
640 
641 In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
642 output of a SMP machine):
643 
644   > cat /proc/interrupts 
645 
646              CPU0       CPU1       
647     0:    1243498    1214548    IO-APIC-edge  timer
648     1:       8949       8958    IO-APIC-edge  keyboard
649     2:          0          0          XT-PIC  cascade
650     5:      11286      10161    IO-APIC-edge  soundblaster
651     8:          1          0    IO-APIC-edge  rtc
652     9:      27422      27407    IO-APIC-edge  3c503
653    12:     113645     113873    IO-APIC-edge  PS/2 Mouse
654    13:          0          0          XT-PIC  fpu
655    14:      22491      24012    IO-APIC-edge  ide0
656    15:       2183       2415    IO-APIC-edge  ide1
657    17:      30564      30414   IO-APIC-level  eth0
658    18:        177        164   IO-APIC-level  bttv
659   NMI:    2457961    2457959 
660   LOC:    2457882    2457881 
661   ERR:       2155
662 
663 NMI is incremented in this case because every timer interrupt generates a NMI
664 (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
665 
666 LOC is the local interrupt counter of the internal APIC of every CPU.
667 
668 ERR is incremented in the case of errors in the IO-APIC bus (the bus that
669 connects the CPUs in a SMP system. This means that an error has been detected,
670 the IO-APIC automatically retry the transmission, so it should not be a big
671 problem, but you should read the SMP-FAQ.
672 
673 In 2.6.2* /proc/interrupts was expanded again.  This time the goal was for
674 /proc/interrupts to display every IRQ vector in use by the system, not
675 just those considered 'most important'.  The new vectors are:
676 
677   THR -- interrupt raised when a machine check threshold counter
678   (typically counting ECC corrected errors of memory or cache) exceeds
679   a configurable threshold.  Only available on some systems.
680 
681   TRM -- a thermal event interrupt occurs when a temperature threshold
682   has been exceeded for the CPU.  This interrupt may also be generated
683   when the temperature drops back to normal.
684 
685   SPU -- a spurious interrupt is some interrupt that was raised then lowered
686   by some IO device before it could be fully processed by the APIC.  Hence
687   the APIC sees the interrupt but does not know what device it came from.
688   For this case the APIC will generate the interrupt with a IRQ vector
689   of 0xff. This might also be generated by chipset bugs.
690 
691   RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
692   sent from one CPU to another per the needs of the OS.  Typically,
693   their statistics are used by kernel developers and interested users to
694   determine the occurrence of interrupts of the given type.
695 
696 The above IRQ vectors are displayed only when relevant.  For example,
697 the threshold vector does not exist on x86_64 platforms.  Others are
698 suppressed when the system is a uniprocessor.  As of this writing, only
699 i386 and x86_64 platforms support the new IRQ vector displays.
700 
701 Of some interest is the introduction of the /proc/irq directory to 2.4.
702 It could be used to set IRQ to CPU affinity, this means that you can "hook" an
703 IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
704 irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
705 prof_cpu_mask.
706 
707 For example 
708   > ls /proc/irq/
709   0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
710   1  11  13  15  17  19  3  5  7  9  default_smp_affinity
711   > ls /proc/irq/0/
712   smp_affinity
713 
714 smp_affinity is a bitmask, in which you can specify which CPUs can handle the
715 IRQ, you can set it by doing:
716 
717   > echo 1 > /proc/irq/10/smp_affinity
718 
719 This means that only the first CPU will handle the IRQ, but you can also echo
720 5 which means that only the first and third CPU can handle the IRQ.
721 
722 The contents of each smp_affinity file is the same by default:
723 
724   > cat /proc/irq/0/smp_affinity
725   ffffffff
726 
727 There is an alternate interface, smp_affinity_list which allows specifying
728 a cpu range instead of a bitmask:
729 
730   > cat /proc/irq/0/smp_affinity_list
731   1024-1031
732 
733 The default_smp_affinity mask applies to all non-active IRQs, which are the
734 IRQs which have not yet been allocated/activated, and hence which lack a
735 /proc/irq/[0-9]* directory.
736 
737 The node file on an SMP system shows the node to which the device using the IRQ
738 reports itself as being attached. This hardware locality information does not
739 include information about any possible driver locality preference.
740 
741 prof_cpu_mask specifies which CPUs are to be profiled by the system wide
742 profiler. Default value is ffffffff (all cpus if there are only 32 of them).
743 
744 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
745 between all the CPUs which are allowed to handle it. As usual the kernel has
746 more info than you and does a better job than you, so the defaults are the
747 best choice for almost everyone.  [Note this applies only to those IO-APIC's
748 that support "Round Robin" interrupt distribution.]
749 
750 There are  three  more  important subdirectories in /proc: net, scsi, and sys.
751 The general  rule  is  that  the  contents,  or  even  the  existence of these
752 directories, depend  on your kernel configuration. If SCSI is not enabled, the
753 directory scsi  may  not  exist. The same is true with the net, which is there
754 only when networking support is present in the running kernel.
755 
756 The slabinfo  file  gives  information  about  memory usage at the slab level.
757 Linux uses  slab  pools for memory management above page level in version 2.2.
758 Commonly used  objects  have  their  own  slab  pool (such as network buffers,
759 directory cache, and so on).
760 
761 ..............................................................................
762 
763 > cat /proc/buddyinfo
764 
765 Node 0, zone      DMA      0      4      5      4      4      3 ...
766 Node 0, zone   Normal      1      0      0      1    101      8 ...
767 Node 0, zone  HighMem      2      0      0      1      1      0 ...
768 
769 External fragmentation is a problem under some workloads, and buddyinfo is a
770 useful tool for helping diagnose these problems.  Buddyinfo will give you a 
771 clue as to how big an area you can safely allocate, or why a previous
772 allocation failed.
773 
774 Each column represents the number of pages of a certain order which are 
775 available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in 
776 ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE 
777 available in ZONE_NORMAL, etc... 
778 
779 More information relevant to external fragmentation can be found in
780 pagetypeinfo.
781 
782 > cat /proc/pagetypeinfo
783 Page block order: 9
784 Pages per block:  512
785 
786 Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
787 Node    0, zone      DMA, type    Unmovable      0      0      0      1      1      1      1      1      1      1      0
788 Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0
789 Node    0, zone      DMA, type      Movable      1      1      2      1      2      1      1      0      1      0      2
790 Node    0, zone      DMA, type      Reserve      0      0      0      0      0      0      0      0      0      1      0
791 Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
792 Node    0, zone    DMA32, type    Unmovable    103     54     77      1      1      1     11      8      7      1      9
793 Node    0, zone    DMA32, type  Reclaimable      0      0      2      1      0      0      0      0      1      0      0
794 Node    0, zone    DMA32, type      Movable    169    152    113     91     77     54     39     13      6      1    452
795 Node    0, zone    DMA32, type      Reserve      1      2      2      2      2      0      1      1      1      1      0
796 Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
797 
798 Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate
799 Node 0, zone      DMA            2            0            5            1            0
800 Node 0, zone    DMA32           41            6          967            2            0
801 
802 Fragmentation avoidance in the kernel works by grouping pages of different
803 migrate types into the same contiguous regions of memory called page blocks.
804 A page block is typically the size of the default hugepage size e.g. 2MB on
805 X86-64. By keeping pages grouped based on their ability to move, the kernel
806 can reclaim pages within a page block to satisfy a high-order allocation.
807 
808 The pagetypinfo begins with information on the size of a page block. It
809 then gives the same type of information as buddyinfo except broken down
810 by migrate-type and finishes with details on how many page blocks of each
811 type exist.
812 
813 If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
814 from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can
815 make an estimate of the likely number of huge pages that can be allocated
816 at a given point in time. All the "Movable" blocks should be allocatable
817 unless memory has been mlock()'d. Some of the Reclaimable blocks should
818 also be allocatable although a lot of filesystem metadata may have to be
819 reclaimed to achieve this.
820 
821 ..............................................................................
822 
823 meminfo:
824 
825 Provides information about distribution and utilization of memory.  This
826 varies by architecture and compile options.  The following is from a
827 16GB PIII, which has highmem enabled.  You may not have all of these fields.
828 
829 > cat /proc/meminfo
830 
831 MemTotal:     16344972 kB
832 MemFree:      13634064 kB
833 MemAvailable: 14836172 kB
834 Buffers:          3656 kB
835 Cached:        1195708 kB
836 SwapCached:          0 kB
837 Active:         891636 kB
838 Inactive:      1077224 kB
839 HighTotal:    15597528 kB
840 HighFree:     13629632 kB
841 LowTotal:       747444 kB
842 LowFree:          4432 kB
843 SwapTotal:           0 kB
844 SwapFree:            0 kB
845 Dirty:             968 kB
846 Writeback:           0 kB
847 AnonPages:      861800 kB
848 Mapped:         280372 kB
849 Shmem:             644 kB
850 Slab:           284364 kB
851 SReclaimable:   159856 kB
852 SUnreclaim:     124508 kB
853 PageTables:      24448 kB
854 NFS_Unstable:        0 kB
855 Bounce:              0 kB
856 WritebackTmp:        0 kB
857 CommitLimit:   7669796 kB
858 Committed_AS:   100056 kB
859 VmallocTotal:   112216 kB
860 VmallocUsed:       428 kB
861 VmallocChunk:   111088 kB
862 AnonHugePages:   49152 kB
863 ShmemHugePages:      0 kB
864 ShmemPmdMapped:      0 kB
865 
866 
867     MemTotal: Total usable ram (i.e. physical ram minus a few reserved
868               bits and the kernel binary code)
869      MemFree: The sum of LowFree+HighFree
870 MemAvailable: An estimate of how much memory is available for starting new
871               applications, without swapping. Calculated from MemFree,
872               SReclaimable, the size of the file LRU lists, and the low
873               watermarks in each zone.
874               The estimate takes into account that the system needs some
875               page cache to function well, and that not all reclaimable
876               slab will be reclaimable, due to items being in use. The
877               impact of those factors will vary from system to system.
878      Buffers: Relatively temporary storage for raw disk blocks
879               shouldn't get tremendously large (20MB or so)
880       Cached: in-memory cache for files read from the disk (the
881               pagecache).  Doesn't include SwapCached
882   SwapCached: Memory that once was swapped out, is swapped back in but
883               still also is in the swapfile (if memory is needed it
884               doesn't need to be swapped out AGAIN because it is already
885               in the swapfile. This saves I/O)
886       Active: Memory that has been used more recently and usually not
887               reclaimed unless absolutely necessary.
888     Inactive: Memory which has been less recently used.  It is more
889               eligible to be reclaimed for other purposes
890    HighTotal:
891     HighFree: Highmem is all memory above ~860MB of physical memory
892               Highmem areas are for use by userspace programs, or
893               for the pagecache.  The kernel must use tricks to access
894               this memory, making it slower to access than lowmem.
895     LowTotal:
896      LowFree: Lowmem is memory which can be used for everything that
897               highmem can be used for, but it is also available for the
898               kernel's use for its own data structures.  Among many
899               other things, it is where everything from the Slab is
900               allocated.  Bad things happen when you're out of lowmem.
901    SwapTotal: total amount of swap space available
902     SwapFree: Memory which has been evicted from RAM, and is temporarily
903               on the disk
904        Dirty: Memory which is waiting to get written back to the disk
905    Writeback: Memory which is actively being written back to the disk
906    AnonPages: Non-file backed pages mapped into userspace page tables
907 AnonHugePages: Non-file backed huge pages mapped into userspace page tables
908       Mapped: files which have been mmaped, such as libraries
909        Shmem: Total memory used by shared memory (shmem) and tmpfs
910 ShmemHugePages: Memory used by shared memory (shmem) and tmpfs allocated
911               with huge pages
912 ShmemPmdMapped: Shared memory mapped into userspace with huge pages
913         Slab: in-kernel data structures cache
914 SReclaimable: Part of Slab, that might be reclaimed, such as caches
915   SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
916   PageTables: amount of memory dedicated to the lowest level of page
917               tables.
918 NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
919               storage
920       Bounce: Memory used for block device "bounce buffers"
921 WritebackTmp: Memory used by FUSE for temporary writeback buffers
922  CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
923               this is the total amount of  memory currently available to
924               be allocated on the system. This limit is only adhered to
925               if strict overcommit accounting is enabled (mode 2 in
926               'vm.overcommit_memory').
927               The CommitLimit is calculated with the following formula:
928               CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
929                              overcommit_ratio / 100 + [total swap pages]
930               For example, on a system with 1G of physical RAM and 7G
931               of swap with a `vm.overcommit_ratio` of 30 it would
932               yield a CommitLimit of 7.3G.
933               For more details, see the memory overcommit documentation
934               in vm/overcommit-accounting.
935 Committed_AS: The amount of memory presently allocated on the system.
936               The committed memory is a sum of all of the memory which
937               has been allocated by processes, even if it has not been
938               "used" by them as of yet. A process which malloc()'s 1G
939               of memory, but only touches 300M of it will show up as
940               using 1G. This 1G is memory which has been "committed" to
941               by the VM and can be used at any time by the allocating
942               application. With strict overcommit enabled on the system
943               (mode 2 in 'vm.overcommit_memory'),allocations which would
944               exceed the CommitLimit (detailed above) will not be permitted.
945               This is useful if one needs to guarantee that processes will
946               not fail due to lack of memory once that memory has been
947               successfully allocated.
948 VmallocTotal: total size of vmalloc memory area
949  VmallocUsed: amount of vmalloc area which is used
950 VmallocChunk: largest contiguous block of vmalloc area which is free
951 
952 ..............................................................................
953 
954 vmallocinfo:
955 
956 Provides information about vmalloced/vmaped areas. One line per area,
957 containing the virtual address range of the area, size in bytes,
958 caller information of the creator, and optional information depending
959 on the kind of area :
960 
961  pages=nr    number of pages
962  phys=addr   if a physical address was specified
963  ioremap     I/O mapping (ioremap() and friends)
964  vmalloc     vmalloc() area
965  vmap        vmap()ed pages
966  user        VM_USERMAP area
967  vpages      buffer for pages pointers was vmalloced (huge area)
968  N<node>=nr  (Only on NUMA kernels)
969              Number of pages allocated on memory node <node>
970 
971 > cat /proc/vmallocinfo
972 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
973   /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
974 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
975   /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
976 0xffffc20000302000-0xffffc20000304000    8192 acpi_tb_verify_table+0x21/0x4f...
977   phys=7fee8000 ioremap
978 0xffffc20000304000-0xffffc20000307000   12288 acpi_tb_verify_table+0x21/0x4f...
979   phys=7fee7000 ioremap
980 0xffffc2000031d000-0xffffc2000031f000    8192 init_vdso_vars+0x112/0x210
981 0xffffc2000031f000-0xffffc2000032b000   49152 cramfs_uncompress_init+0x2e ...
982   /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
983 0xffffc2000033a000-0xffffc2000033d000   12288 sys_swapon+0x640/0xac0      ...
984   pages=2 vmalloc N1=2
985 0xffffc20000347000-0xffffc2000034c000   20480 xt_alloc_table_info+0xfe ...
986   /0x130 [x_tables] pages=4 vmalloc N0=4
987 0xffffffffa0000000-0xffffffffa000f000   61440 sys_init_module+0xc27/0x1d00 ...
988    pages=14 vmalloc N2=14
989 0xffffffffa000f000-0xffffffffa0014000   20480 sys_init_module+0xc27/0x1d00 ...
990    pages=4 vmalloc N1=4
991 0xffffffffa0014000-0xffffffffa0017000   12288 sys_init_module+0xc27/0x1d00 ...
992    pages=2 vmalloc N1=2
993 0xffffffffa0017000-0xffffffffa0022000   45056 sys_init_module+0xc27/0x1d00 ...
994    pages=10 vmalloc N0=10
995 
996 ..............................................................................
997 
998 softirqs:
999 
1000 Provides counts of softirq handlers serviced since boot time, for each cpu.
1001 
1002 > cat /proc/softirqs
1003                 CPU0       CPU1       CPU2       CPU3
1004       HI:          0          0          0          0
1005    TIMER:      27166      27120      27097      27034
1006   NET_TX:          0          0          0         17
1007   NET_RX:         42          0          0         39
1008    BLOCK:          0          0        107       1121
1009  TASKLET:          0          0          0        290
1010    SCHED:      27035      26983      26971      26746
1011  HRTIMER:          0          0          0          0
1012      RCU:       1678       1769       2178       2250
1013 
1014 
1015 1.3 IDE devices in /proc/ide
1016 ----------------------------
1017 
1018 The subdirectory /proc/ide contains information about all IDE devices of which
1019 the kernel  is  aware.  There is one subdirectory for each IDE controller, the
1020 file drivers  and a link for each IDE device, pointing to the device directory
1021 in the controller specific subtree.
1022 
1023 The file  drivers  contains general information about the drivers used for the
1024 IDE devices:
1025 
1026   > cat /proc/ide/drivers
1027   ide-cdrom version 4.53
1028   ide-disk version 1.08
1029 
1030 More detailed  information  can  be  found  in  the  controller  specific
1031 subdirectories. These  are  named  ide0,  ide1  and  so  on.  Each  of  these
1032 directories contains the files shown in table 1-6.
1033 
1034 
1035 Table 1-6: IDE controller info in  /proc/ide/ide?
1036 ..............................................................................
1037  File    Content                                 
1038  channel IDE channel (0 or 1)                    
1039  config  Configuration (only for PCI/IDE bridge) 
1040  mate    Mate name                               
1041  model   Type/Chipset of IDE controller          
1042 ..............................................................................
1043 
1044 Each device  connected  to  a  controller  has  a separate subdirectory in the
1045 controllers directory.  The  files  listed in table 1-7 are contained in these
1046 directories.
1047 
1048 
1049 Table 1-7: IDE device information
1050 ..............................................................................
1051  File             Content                                    
1052  cache            The cache                                  
1053  capacity         Capacity of the medium (in 512Byte blocks) 
1054  driver           driver and version                         
1055  geometry         physical and logical geometry              
1056  identify         device identify block                      
1057  media            media type                                 
1058  model            device identifier                          
1059  settings         device setup                               
1060  smart_thresholds IDE disk management thresholds             
1061  smart_values     IDE disk management values                 
1062 ..............................................................................
1063 
1064 The most  interesting  file is settings. This file contains a nice overview of
1065 the drive parameters:
1066 
1067   # cat /proc/ide/ide0/hda/settings 
1068   name                    value           min             max             mode 
1069   ----                    -----           ---             ---             ---- 
1070   bios_cyl                526             0               65535           rw 
1071   bios_head               255             0               255             rw 
1072   bios_sect               63              0               63              rw 
1073   breada_readahead        4               0               127             rw 
1074   bswap                   0               0               1               r 
1075   file_readahead          72              0               2097151         rw 
1076   io_32bit                0               0               3               rw 
1077   keepsettings            0               0               1               rw 
1078   max_kb_per_request      122             1               127             rw 
1079   multcount               0               0               8               rw 
1080   nice1                   1               0               1               rw 
1081   nowerr                  0               0               1               rw 
1082   pio_mode                write-only      0               255             w 
1083   slow                    0               0               1               rw 
1084   unmaskirq               0               0               1               rw 
1085   using_dma               0               0               1               rw 
1086 
1087 
1088 1.4 Networking info in /proc/net
1089 --------------------------------
1090 
1091 The subdirectory  /proc/net  follows  the  usual  pattern. Table 1-8 shows the
1092 additional values  you  get  for  IP  version 6 if you configure the kernel to
1093 support this. Table 1-9 lists the files and their meaning.
1094 
1095 
1096 Table 1-8: IPv6 info in /proc/net
1097 ..............................................................................
1098  File       Content                                               
1099  udp6       UDP sockets (IPv6)                                    
1100  tcp6       TCP sockets (IPv6)                                    
1101  raw6       Raw device statistics (IPv6)                          
1102  igmp6      IP multicast addresses, which this host joined (IPv6) 
1103  if_inet6   List of IPv6 interface addresses                      
1104  ipv6_route Kernel routing table for IPv6                         
1105  rt6_stats  Global IPv6 routing tables statistics                 
1106  sockstat6  Socket statistics (IPv6)                              
1107  snmp6      Snmp data (IPv6)                                      
1108 ..............................................................................
1109 
1110 
1111 Table 1-9: Network info in /proc/net
1112 ..............................................................................
1113  File          Content                                                         
1114  arp           Kernel  ARP table                                               
1115  dev           network devices with statistics                                 
1116  dev_mcast     the Layer2 multicast groups a device is listening too
1117                (interface index, label, number of references, number of bound
1118                addresses). 
1119  dev_stat      network device status                                           
1120  ip_fwchains   Firewall chain linkage                                          
1121  ip_fwnames    Firewall chain names                                            
1122  ip_masq       Directory containing the masquerading tables                    
1123  ip_masquerade Major masquerading table                                        
1124  netstat       Network statistics                                              
1125  raw           raw device statistics                                           
1126  route         Kernel routing table                                            
1127  rpc           Directory containing rpc info                                   
1128  rt_cache      Routing cache                                                   
1129  snmp          SNMP data                                                       
1130  sockstat      Socket statistics                                               
1131  tcp           TCP  sockets                                                    
1132  udp           UDP sockets                                                     
1133  unix          UNIX domain sockets                                             
1134  wireless      Wireless interface data (Wavelan etc)                           
1135  igmp          IP multicast addresses, which this host joined                  
1136  psched        Global packet scheduler parameters.                             
1137  netlink       List of PF_NETLINK sockets                                      
1138  ip_mr_vifs    List of multicast virtual interfaces                            
1139  ip_mr_cache   List of multicast routing cache                                 
1140 ..............................................................................
1141 
1142 You can  use  this  information  to see which network devices are available in
1143 your system and how much traffic was routed over those devices:
1144 
1145   > cat /proc/net/dev 
1146   Inter-|Receive                                                   |[... 
1147    face |bytes    packets errs drop fifo frame compressed multicast|[... 
1148       lo:  908188   5596     0    0    0     0          0         0 [...         
1149     ppp0:15475140  20721   410    0    0   410          0         0 [...  
1150     eth0:  614530   7085     0    0    0     0          0         1 [... 
1151    
1152   ...] Transmit 
1153   ...] bytes    packets errs drop fifo colls carrier compressed 
1154   ...]  908188     5596    0    0    0     0       0          0 
1155   ...] 1375103    17405    0    0    0     0       0          0 
1156   ...] 1703981     5535    0    0    0     3       0          0 
1157 
1158 In addition, each Channel Bond interface has its own directory.  For
1159 example, the bond0 device will have a directory called /proc/net/bond0/.
1160 It will contain information that is specific to that bond, such as the
1161 current slaves of the bond, the link status of the slaves, and how
1162 many times the slaves link has failed.
1163 
1164 1.5 SCSI info
1165 -------------
1166 
1167 If you  have  a  SCSI  host adapter in your system, you'll find a subdirectory
1168 named after  the driver for this adapter in /proc/scsi. You'll also see a list
1169 of all recognized SCSI devices in /proc/scsi:
1170 
1171   >cat /proc/scsi/scsi 
1172   Attached devices: 
1173   Host: scsi0 Channel: 00 Id: 00 Lun: 00 
1174     Vendor: IBM      Model: DGHS09U          Rev: 03E0 
1175     Type:   Direct-Access                    ANSI SCSI revision: 03 
1176   Host: scsi0 Channel: 00 Id: 06 Lun: 00 
1177     Vendor: PIONEER  Model: CD-ROM DR-U06S   Rev: 1.04 
1178     Type:   CD-ROM                           ANSI SCSI revision: 02 
1179 
1180 
1181 The directory  named  after  the driver has one file for each adapter found in
1182 the system.  These  files  contain information about the controller, including
1183 the used  IRQ  and  the  IO  address range. The amount of information shown is
1184 dependent on  the adapter you use. The example shows the output for an Adaptec
1185 AHA-2940 SCSI adapter:
1186 
1187   > cat /proc/scsi/aic7xxx/0 
1188    
1189   Adaptec AIC7xxx driver version: 5.1.19/3.2.4 
1190   Compile Options: 
1191     TCQ Enabled By Default : Disabled 
1192     AIC7XXX_PROC_STATS     : Disabled 
1193     AIC7XXX_RESET_DELAY    : 5 
1194   Adapter Configuration: 
1195              SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter 
1196                              Ultra Wide Controller 
1197       PCI MMAPed I/O Base: 0xeb001000 
1198    Adapter SEEPROM Config: SEEPROM found and used. 
1199         Adaptec SCSI BIOS: Enabled 
1200                       IRQ: 10 
1201                      SCBs: Active 0, Max Active 2, 
1202                            Allocated 15, HW 16, Page 255 
1203                Interrupts: 160328 
1204         BIOS Control Word: 0x18b6 
1205      Adapter Control Word: 0x005b 
1206      Extended Translation: Enabled 
1207   Disconnect Enable Flags: 0xffff 
1208        Ultra Enable Flags: 0x0001 
1209    Tag Queue Enable Flags: 0x0000 
1210   Ordered Queue Tag Flags: 0x0000 
1211   Default Tag Queue Depth: 8 
1212       Tagged Queue By Device array for aic7xxx host instance 0: 
1213         {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} 
1214       Actual queue depth per device for aic7xxx host instance 0: 
1215         {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} 
1216   Statistics: 
1217   (scsi0:0:0:0) 
1218     Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 
1219     Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) 
1220     Total transfers 160151 (74577 reads and 85574 writes) 
1221   (scsi0:0:6:0) 
1222     Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 
1223     Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) 
1224     Total transfers 0 (0 reads and 0 writes) 
1225 
1226 
1227 1.6 Parallel port info in /proc/parport
1228 ---------------------------------------
1229 
1230 The directory  /proc/parport  contains information about the parallel ports of
1231 your system.  It  has  one  subdirectory  for  each port, named after the port
1232 number (0,1,2,...).
1233 
1234 These directories contain the four files shown in Table 1-10.
1235 
1236 
1237 Table 1-10: Files in /proc/parport
1238 ..............................................................................
1239  File      Content                                                             
1240  autoprobe Any IEEE-1284 device ID information that has been acquired.         
1241  devices   list of the device drivers using that port. A + will appear by the
1242            name of the device currently using the port (it might not appear
1243            against any). 
1244  hardware  Parallel port's base address, IRQ line and DMA channel.             
1245  irq       IRQ that parport is using for that port. This is in a separate
1246            file to allow you to alter it by writing a new value in (IRQ
1247            number or none). 
1248 ..............................................................................
1249 
1250 1.7 TTY info in /proc/tty
1251 -------------------------
1252 
1253 Information about  the  available  and actually used tty's can be found in the
1254 directory /proc/tty.You'll  find  entries  for drivers and line disciplines in
1255 this directory, as shown in Table 1-11.
1256 
1257 
1258 Table 1-11: Files in /proc/tty
1259 ..............................................................................
1260  File          Content                                        
1261  drivers       list of drivers and their usage                
1262  ldiscs        registered line disciplines                    
1263  driver/serial usage statistic and status of single tty lines 
1264 ..............................................................................
1265 
1266 To see  which  tty's  are  currently in use, you can simply look into the file
1267 /proc/tty/drivers:
1268 
1269   > cat /proc/tty/drivers 
1270   pty_slave            /dev/pts      136   0-255 pty:slave 
1271   pty_master           /dev/ptm      128   0-255 pty:master 
1272   pty_slave            /dev/ttyp       3   0-255 pty:slave 
1273   pty_master           /dev/pty        2   0-255 pty:master 
1274   serial               /dev/cua        5   64-67 serial:callout 
1275   serial               /dev/ttyS       4   64-67 serial 
1276   /dev/tty0            /dev/tty0       4       0 system:vtmaster 
1277   /dev/ptmx            /dev/ptmx       5       2 system 
1278   /dev/console         /dev/console    5       1 system:console 
1279   /dev/tty             /dev/tty        5       0 system:/dev/tty 
1280   unknown              /dev/tty        4    1-63 console 
1281 
1282 
1283 1.8 Miscellaneous kernel statistics in /proc/stat
1284 -------------------------------------------------
1285 
1286 Various pieces   of  information about  kernel activity  are  available in the
1287 /proc/stat file.  All  of  the numbers reported  in  this file are  aggregates
1288 since the system first booted.  For a quick look, simply cat the file:
1289 
1290   > cat /proc/stat
1291   cpu  2255 34 2290 22625563 6290 127 456 0 0 0
1292   cpu0 1132 34 1441 11311718 3675 127 438 0 0 0
1293   cpu1 1123 0 849 11313845 2614 0 18 0 0 0
1294   intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1295   ctxt 1990473
1296   btime 1062191376
1297   processes 2915
1298   procs_running 1
1299   procs_blocked 0
1300   softirq 183433 0 21755 12 39 1137 231 21459 2263
1301 
1302 The very first  "cpu" line aggregates the  numbers in all  of the other "cpuN"
1303 lines.  These numbers identify the amount of time the CPU has spent performing
1304 different kinds of work.  Time units are in USER_HZ (typically hundredths of a
1305 second).  The meanings of the columns are as follows, from left to right:
1306 
1307 - user: normal processes executing in user mode
1308 - nice: niced processes executing in user mode
1309 - system: processes executing in kernel mode
1310 - idle: twiddling thumbs
1311 - iowait: In a word, iowait stands for waiting for I/O to complete. But there
1312   are several problems:
1313   1. Cpu will not wait for I/O to complete, iowait is the time that a task is
1314      waiting for I/O to complete. When cpu goes into idle state for
1315      outstanding task io, another task will be scheduled on this CPU.
1316   2. In a multi-core CPU, the task waiting for I/O to complete is not running
1317      on any CPU, so the iowait of each CPU is difficult to calculate.
1318   3. The value of iowait field in /proc/stat will decrease in certain
1319      conditions.
1320   So, the iowait is not reliable by reading from /proc/stat.
1321 - irq: servicing interrupts
1322 - softirq: servicing softirqs
1323 - steal: involuntary wait
1324 - guest: running a normal guest
1325 - guest_nice: running a niced guest
1326 
1327 The "intr" line gives counts of interrupts  serviced since boot time, for each
1328 of the  possible system interrupts.   The first  column  is the  total of  all
1329 interrupts serviced  including  unnumbered  architecture specific  interrupts;
1330 each  subsequent column is the  total for that particular numbered interrupt.
1331 Unnumbered interrupts are not shown, only summed into the total.
1332 
1333 The "ctxt" line gives the total number of context switches across all CPUs.
1334 
1335 The "btime" line gives  the time at which the  system booted, in seconds since
1336 the Unix epoch.
1337 
1338 The "processes" line gives the number  of processes and threads created, which
1339 includes (but  is not limited  to) those  created by  calls to the  fork() and
1340 clone() system calls.
1341 
1342 The "procs_running" line gives the total number of threads that are
1343 running or ready to run (i.e., the total number of runnable threads).
1344 
1345 The   "procs_blocked" line gives  the  number of  processes currently blocked,
1346 waiting for I/O to complete.
1347 
1348 The "softirq" line gives counts of softirqs serviced since boot time, for each
1349 of the possible system softirqs. The first column is the total of all
1350 softirqs serviced; each subsequent column is the total for that particular
1351 softirq.
1352 
1353 
1354 1.9 Ext4 file system parameters
1355 -------------------------------
1356 
1357 Information about mounted ext4 file systems can be found in
1358 /proc/fs/ext4.  Each mounted filesystem will have a directory in
1359 /proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1360 /proc/fs/ext4/dm-0).   The files in each per-device directory are shown
1361 in Table 1-12, below.
1362 
1363 Table 1-12: Files in /proc/fs/ext4/<devname>
1364 ..............................................................................
1365  File            Content                                        
1366  mb_groups       details of multiblock allocator buddy cache of free blocks
1367 ..............................................................................
1368 
1369 2.0 /proc/consoles
1370 ------------------
1371 Shows registered system console lines.
1372 
1373 To see which character device lines are currently used for the system console
1374 /dev/console, you may simply look into the file /proc/consoles:
1375 
1376   > cat /proc/consoles
1377   tty0                 -WU (ECp)       4:7
1378   ttyS0                -W- (Ep)        4:64
1379 
1380 The columns are:
1381 
1382   device               name of the device
1383   operations           R = can do read operations
1384                        W = can do write operations
1385                        U = can do unblank
1386   flags                E = it is enabled
1387                        C = it is preferred console
1388                        B = it is primary boot console
1389                        p = it is used for printk buffer
1390                        b = it is not a TTY but a Braille device
1391                        a = it is safe to use when cpu is offline
1392   major:minor          major and minor number of the device separated by a colon
1393 
1394 ------------------------------------------------------------------------------
1395 Summary
1396 ------------------------------------------------------------------------------
1397 The /proc file system serves information about the running system. It not only
1398 allows access to process data but also allows you to request the kernel status
1399 by reading files in the hierarchy.
1400 
1401 The directory  structure  of /proc reflects the types of information and makes
1402 it easy, if not obvious, where to look for specific data.
1403 ------------------------------------------------------------------------------
1404 
1405 ------------------------------------------------------------------------------
1406 CHAPTER 2: MODIFYING SYSTEM PARAMETERS
1407 ------------------------------------------------------------------------------
1408 
1409 ------------------------------------------------------------------------------
1410 In This Chapter
1411 ------------------------------------------------------------------------------
1412 * Modifying kernel parameters by writing into files found in /proc/sys
1413 * Exploring the files which modify certain parameters
1414 * Review of the /proc/sys file tree
1415 ------------------------------------------------------------------------------
1416 
1417 
1418 A very  interesting part of /proc is the directory /proc/sys. This is not only
1419 a source  of  information,  it also allows you to change parameters within the
1420 kernel. Be  very  careful  when attempting this. You can optimize your system,
1421 but you  can  also  cause  it  to  crash.  Never  alter kernel parameters on a
1422 production system.  Set  up  a  development machine and test to make sure that
1423 everything works  the  way  you want it to. You may have no alternative but to
1424 reboot the machine once an error has been made.
1425 
1426 To change  a  value,  simply  echo  the new value into the file. An example is
1427 given below  in the section on the file system data. You need to be root to do
1428 this. You  can  create  your  own  boot script to perform this every time your
1429 system boots.
1430 
1431 The files  in /proc/sys can be used to fine tune and monitor miscellaneous and
1432 general things  in  the operation of the Linux kernel. Since some of the files
1433 can inadvertently  disrupt  your  system,  it  is  advisable  to  read  both
1434 documentation and  source  before actually making adjustments. In any case, be
1435 very careful  when  writing  to  any  of these files. The entries in /proc may
1436 change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1437 review the kernel documentation in the directory /usr/src/linux/Documentation.
1438 This chapter  is  heavily  based  on the documentation included in the pre 2.2
1439 kernels, and became part of it in version 2.2.1 of the Linux kernel.
1440 
1441 Please see: Documentation/sysctl/ directory for descriptions of these
1442 entries.
1443 
1444 ------------------------------------------------------------------------------
1445 Summary
1446 ------------------------------------------------------------------------------
1447 Certain aspects  of  kernel  behavior  can be modified at runtime, without the
1448 need to  recompile  the kernel, or even to reboot the system. The files in the
1449 /proc/sys tree  can  not only be read, but also modified. You can use the echo
1450 command to write value into these files, thereby changing the default settings
1451 of the kernel.
1452 ------------------------------------------------------------------------------
1453 
1454 ------------------------------------------------------------------------------
1455 CHAPTER 3: PER-PROCESS PARAMETERS
1456 ------------------------------------------------------------------------------
1457 
1458 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1459 --------------------------------------------------------------------------------
1460 
1461 These file can be used to adjust the badness heuristic used to select which
1462 process gets killed in out of memory conditions.
1463 
1464 The badness heuristic assigns a value to each candidate task ranging from 0
1465 (never kill) to 1000 (always kill) to determine which process is targeted.  The
1466 units are roughly a proportion along that range of allowed memory the process
1467 may allocate from based on an estimation of its current memory and swap use.
1468 For example, if a task is using all allowed memory, its badness score will be
1469 1000.  If it is using half of its allowed memory, its score will be 500.
1470 
1471 There is an additional factor included in the badness score: the current memory
1472 and swap usage is discounted by 3% for root processes.
1473 
1474 The amount of "allowed" memory depends on the context in which the oom killer
1475 was called.  If it is due to the memory assigned to the allocating task's cpuset
1476 being exhausted, the allowed memory represents the set of mems assigned to that
1477 cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
1478 memory represents the set of mempolicy nodes.  If it is due to a memory
1479 limit (or swap limit) being reached, the allowed memory is that configured
1480 limit.  Finally, if it is due to the entire system being out of memory, the
1481 allowed memory represents all allocatable resources.
1482 
1483 The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1484 is used to determine which task to kill.  Acceptable values range from -1000
1485 (OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
1486 polarize the preference for oom killing either by always preferring a certain
1487 task or completely disabling it.  The lowest possible value, -1000, is
1488 equivalent to disabling oom killing entirely for that task since it will always
1489 report a badness score of 0.
1490 
1491 Consequently, it is very simple for userspace to define the amount of memory to
1492 consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
1493 example, is roughly equivalent to allowing the remainder of tasks sharing the
1494 same system, cpuset, mempolicy, or memory controller resources to use at least
1495 50% more memory.  A value of -500, on the other hand, would be roughly
1496 equivalent to discounting 50% of the task's allowed memory from being considered
1497 as scoring against the task.
1498 
1499 For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1500 be used to tune the badness score.  Its acceptable values range from -16
1501 (OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1502 (OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
1503 scaled linearly with /proc/<pid>/oom_score_adj.
1504 
1505 The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1506 value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1507 requires CAP_SYS_RESOURCE.
1508 
1509 Caveat: when a parent task is selected, the oom killer will sacrifice any first
1510 generation children with separate address spaces instead, if possible.  This
1511 avoids servers and important system daemons from being killed and loses the
1512 minimal amount of work.
1513 
1514 
1515 3.2 /proc/<pid>/oom_score - Display current oom-killer score
1516 -------------------------------------------------------------
1517 
1518 This file can be used to check the current score used by the oom-killer is for
1519 any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1520 process should be killed in an out-of-memory situation.
1521 
1522 
1523 3.3  /proc/<pid>/io - Display the IO accounting fields
1524 -------------------------------------------------------
1525 
1526 This file contains IO statistics for each running process
1527 
1528 Example
1529 -------
1530 
1531 test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1532 [1] 3828
1533 
1534 test:/tmp # cat /proc/3828/io
1535 rchar: 323934931
1536 wchar: 323929600
1537 syscr: 632687
1538 syscw: 632675
1539 read_bytes: 0
1540 write_bytes: 323932160
1541 cancelled_write_bytes: 0
1542 
1543 
1544 Description
1545 -----------
1546 
1547 rchar
1548 -----
1549 
1550 I/O counter: chars read
1551 The number of bytes which this task has caused to be read from storage. This
1552 is simply the sum of bytes which this process passed to read() and pread().
1553 It includes things like tty IO and it is unaffected by whether or not actual
1554 physical disk IO was required (the read might have been satisfied from
1555 pagecache)
1556 
1557 
1558 wchar
1559 -----
1560 
1561 I/O counter: chars written
1562 The number of bytes which this task has caused, or shall cause to be written
1563 to disk. Similar caveats apply here as with rchar.
1564 
1565 
1566 syscr
1567 -----
1568 
1569 I/O counter: read syscalls
1570 Attempt to count the number of read I/O operations, i.e. syscalls like read()
1571 and pread().
1572 
1573 
1574 syscw
1575 -----
1576 
1577 I/O counter: write syscalls
1578 Attempt to count the number of write I/O operations, i.e. syscalls like
1579 write() and pwrite().
1580 
1581 
1582 read_bytes
1583 ----------
1584 
1585 I/O counter: bytes read
1586 Attempt to count the number of bytes which this process really did cause to
1587 be fetched from the storage layer. Done at the submit_bio() level, so it is
1588 accurate for block-backed filesystems. <please add status regarding NFS and
1589 CIFS at a later time>
1590 
1591 
1592 write_bytes
1593 -----------
1594 
1595 I/O counter: bytes written
1596 Attempt to count the number of bytes which this process caused to be sent to
1597 the storage layer. This is done at page-dirtying time.
1598 
1599 
1600 cancelled_write_bytes
1601 ---------------------
1602 
1603 The big inaccuracy here is truncate. If a process writes 1MB to a file and
1604 then deletes the file, it will in fact perform no writeout. But it will have
1605 been accounted as having caused 1MB of write.
1606 In other words: The number of bytes which this process caused to not happen,
1607 by truncating pagecache. A task can cause "negative" IO too. If this task
1608 truncates some dirty pagecache, some IO which another task has been accounted
1609 for (in its write_bytes) will not be happening. We _could_ just subtract that
1610 from the truncating task's write_bytes, but there is information loss in doing
1611 that.
1612 
1613 
1614 Note
1615 ----
1616 
1617 At its current implementation state, this is a bit racy on 32-bit machines: if
1618 process A reads process B's /proc/pid/io while process B is updating one of
1619 those 64-bit counters, process A could see an intermediate result.
1620 
1621 
1622 More information about this can be found within the taskstats documentation in
1623 Documentation/accounting.
1624 
1625 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1626 ---------------------------------------------------------------
1627 When a process is dumped, all anonymous memory is written to a core file as
1628 long as the size of the core file isn't limited. But sometimes we don't want
1629 to dump some memory segments, for example, huge shared memory or DAX.
1630 Conversely, sometimes we want to save file-backed memory segments into a core
1631 file, not only the individual files.
1632 
1633 /proc/<pid>/coredump_filter allows you to customize which memory segments
1634 will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1635 of memory types. If a bit of the bitmask is set, memory segments of the
1636 corresponding memory type are dumped, otherwise they are not dumped.
1637 
1638 The following 9 memory types are supported:
1639   - (bit 0) anonymous private memory
1640   - (bit 1) anonymous shared memory
1641   - (bit 2) file-backed private memory
1642   - (bit 3) file-backed shared memory
1643   - (bit 4) ELF header pages in file-backed private memory areas (it is
1644             effective only if the bit 2 is cleared)
1645   - (bit 5) hugetlb private memory
1646   - (bit 6) hugetlb shared memory
1647   - (bit 7) DAX private memory
1648   - (bit 8) DAX shared memory
1649 
1650   Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1651   are always dumped regardless of the bitmask status.
1652 
1653   Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
1654   only affected by bit 5-6, and DAX is only affected by bits 7-8.
1655 
1656 The default value of coredump_filter is 0x33; this means all anonymous memory
1657 segments, ELF header pages and hugetlb private memory are dumped.
1658 
1659 If you don't want to dump all shared memory segments attached to pid 1234,
1660 write 0x31 to the process's proc file.
1661 
1662   $ echo 0x31 > /proc/1234/coredump_filter
1663 
1664 When a new process is created, the process inherits the bitmask status from its
1665 parent. It is useful to set up coredump_filter before the program runs.
1666 For example:
1667 
1668   $ echo 0x7 > /proc/self/coredump_filter
1669   $ ./some_program
1670 
1671 3.5     /proc/<pid>/mountinfo - Information about mounts
1672 --------------------------------------------------------
1673 
1674 This file contains lines of the form:
1675 
1676 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1677 (1)(2)(3)   (4)   (5)      (6)      (7)   (8) (9)   (10)         (11)
1678 
1679 (1) mount ID:  unique identifier of the mount (may be reused after umount)
1680 (2) parent ID:  ID of parent (or of self for the top of the mount tree)
1681 (3) major:minor:  value of st_dev for files on filesystem
1682 (4) root:  root of the mount within the filesystem
1683 (5) mount point:  mount point relative to the process's root
1684 (6) mount options:  per mount options
1685 (7) optional fields:  zero or more fields of the form "tag[:value]"
1686 (8) separator:  marks the end of the optional fields
1687 (9) filesystem type:  name of filesystem of the form "type[.subtype]"
1688 (10) mount source:  filesystem specific information or "none"
1689 (11) super options:  per super block options
1690 
1691 Parsers should ignore all unrecognised optional fields.  Currently the
1692 possible optional fields are:
1693 
1694 shared:X  mount is shared in peer group X
1695 master:X  mount is slave to peer group X
1696 propagate_from:X  mount is slave and receives propagation from peer group X (*)
1697 unbindable  mount is unbindable
1698 
1699 (*) X is the closest dominant peer group under the process's root.  If
1700 X is the immediate master of the mount, or if there's no dominant peer
1701 group under the same root, then only the "master:X" field is present
1702 and not the "propagate_from:X" field.
1703 
1704 For more information on mount propagation see:
1705 
1706   Documentation/filesystems/sharedsubtree.txt
1707 
1708 
1709 3.6     /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
1710 --------------------------------------------------------
1711 These files provide a method to access a tasks comm value. It also allows for
1712 a task to set its own or one of its thread siblings comm value. The comm value
1713 is limited in size compared to the cmdline value, so writing anything longer
1714 then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1715 comm value.
1716 
1717 
1718 3.7     /proc/<pid>/task/<tid>/children - Information about task children
1719 -------------------------------------------------------------------------
1720 This file provides a fast way to retrieve first level children pids
1721 of a task pointed by <pid>/<tid> pair. The format is a space separated
1722 stream of pids.
1723 
1724 Note the "first level" here -- if a child has own children they will
1725 not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children
1726 to obtain the descendants.
1727 
1728 Since this interface is intended to be fast and cheap it doesn't
1729 guarantee to provide precise results and some children might be
1730 skipped, especially if they've exited right after we printed their
1731 pids, so one need to either stop or freeze processes being inspected
1732 if precise results are needed.
1733 
1734 
1735 3.8     /proc/<pid>/fdinfo/<fd> - Information about opened file
1736 ---------------------------------------------------------------
1737 This file provides information associated with an opened file. The regular
1738 files have at least three fields -- 'pos', 'flags' and mnt_id. The 'pos'
1739 represents the current offset of the opened file in decimal form [see lseek(2)
1740 for details], 'flags' denotes the octal O_xxx mask the file has been
1741 created with [see open(2) for details] and 'mnt_id' represents mount ID of
1742 the file system containing the opened file [see 3.5 /proc/<pid>/mountinfo
1743 for details].
1744 
1745 A typical output is
1746 
1747         pos:    0
1748         flags:  0100002
1749         mnt_id: 19
1750 
1751 All locks associated with a file descriptor are shown in its fdinfo too.
1752 
1753 lock:       1: FLOCK  ADVISORY  WRITE 359 00:13:11691 0 EOF
1754 
1755 The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1756 pair provide additional information particular to the objects they represent.
1757 
1758         Eventfd files
1759         ~~~~~~~~~~~~~
1760         pos:    0
1761         flags:  04002
1762         mnt_id: 9
1763         eventfd-count:  5a
1764 
1765         where 'eventfd-count' is hex value of a counter.
1766 
1767         Signalfd files
1768         ~~~~~~~~~~~~~~
1769         pos:    0
1770         flags:  04002
1771         mnt_id: 9
1772         sigmask:        0000000000000200
1773 
1774         where 'sigmask' is hex value of the signal mask associated
1775         with a file.
1776 
1777         Epoll files
1778         ~~~~~~~~~~~
1779         pos:    0
1780         flags:  02
1781         mnt_id: 9
1782         tfd:        5 events:       1d data: ffffffffffffffff
1783 
1784         where 'tfd' is a target file descriptor number in decimal form,
1785         'events' is events mask being watched and the 'data' is data
1786         associated with a target [see epoll(7) for more details].
1787 
1788         Fsnotify files
1789         ~~~~~~~~~~~~~~
1790         For inotify files the format is the following
1791 
1792         pos:    0
1793         flags:  02000000
1794         inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
1795 
1796         where 'wd' is a watch descriptor in decimal form, ie a target file
1797         descriptor number, 'ino' and 'sdev' are inode and device where the
1798         target file resides and the 'mask' is the mask of events, all in hex
1799         form [see inotify(7) for more details].
1800 
1801         If the kernel was built with exportfs support, the path to the target
1802         file is encoded as a file handle.  The file handle is provided by three
1803         fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
1804         format.
1805 
1806         If the kernel is built without exportfs support the file handle won't be
1807         printed out.
1808 
1809         If there is no inotify mark attached yet the 'inotify' line will be omitted.
1810 
1811         For fanotify files the format is
1812 
1813         pos:    0
1814         flags:  02
1815         mnt_id: 9
1816         fanotify flags:10 event-flags:0
1817         fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
1818         fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
1819 
1820         where fanotify 'flags' and 'event-flags' are values used in fanotify_init
1821         call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
1822         flags associated with mark which are tracked separately from events
1823         mask. 'ino', 'sdev' are target inode and device, 'mask' is the events
1824         mask and 'ignored_mask' is the mask of events which are to be ignored.
1825         All in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
1826         does provide information about flags and mask used in fanotify_mark
1827         call [see fsnotify manpage for details].
1828 
1829         While the first three lines are mandatory and always printed, the rest is
1830         optional and may be omitted if no marks created yet.
1831 
1832         Timerfd files
1833         ~~~~~~~~~~~~~
1834 
1835         pos:    0
1836         flags:  02
1837         mnt_id: 9
1838         clockid: 0
1839         ticks: 0
1840         settime flags: 01
1841         it_value: (0, 49406829)
1842         it_interval: (1, 0)
1843 
1844         where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
1845         that have occurred [see timerfd_create(2) for details]. 'settime flags' are
1846         flags in octal form been used to setup the timer [see timerfd_settime(2) for
1847         details]. 'it_value' is remaining time until the timer exiration.
1848         'it_interval' is the interval for the timer. Note the timer might be set up
1849         with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
1850         still exhibits timer's remaining time.
1851 
1852 3.9     /proc/<pid>/map_files - Information about memory mapped files
1853 ---------------------------------------------------------------------
1854 This directory contains symbolic links which represent memory mapped files
1855 the process is maintaining.  Example output:
1856 
1857      | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
1858      | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
1859      | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
1860      | ...
1861      | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
1862      | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
1863 
1864 The name of a link represents the virtual memory bounds of a mapping, i.e.
1865 vm_area_struct::vm_start-vm_area_struct::vm_end.
1866 
1867 The main purpose of the map_files is to retrieve a set of memory mapped
1868 files in a fast way instead of parsing /proc/<pid>/maps or
1869 /proc/<pid>/smaps, both of which contain many more records.  At the same
1870 time one can open(2) mappings from the listings of two processes and
1871 comparing their inode numbers to figure out which anonymous memory areas
1872 are actually shared.
1873 
1874 3.10    /proc/<pid>/timerslack_ns - Task timerslack value
1875 ---------------------------------------------------------
1876 This file provides the value of the task's timerslack value in nanoseconds.
1877 This value specifies a amount of time that normal timers may be deferred
1878 in order to coalesce timers and avoid unnecessary wakeups.
1879 
1880 This allows a task's interactivity vs power consumption trade off to be
1881 adjusted.
1882 
1883 Writing 0 to the file will set the tasks timerslack to the default value.
1884 
1885 Valid values are from 0 - ULLONG_MAX
1886 
1887 An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
1888 permissions on the task specified to change its timerslack_ns value.
1889 
1890 
1891 ------------------------------------------------------------------------------
1892 Configuring procfs
1893 ------------------------------------------------------------------------------
1894 
1895 4.1     Mount options
1896 ---------------------
1897 
1898 The following mount options are supported:
1899 
1900         hidepid=        Set /proc/<pid>/ access mode.
1901         gid=            Set the group authorized to learn processes information.
1902 
1903 hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
1904 (default).
1905 
1906 hidepid=1 means users may not access any /proc/<pid>/ directories but their
1907 own.  Sensitive files like cmdline, sched*, status are now protected against
1908 other users.  This makes it impossible to learn whether any user runs
1909 specific program (given the program doesn't reveal itself by its behaviour).
1910 As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users,
1911 poorly written programs passing sensitive information via program arguments are
1912 now protected against local eavesdroppers.
1913 
1914 hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other
1915 users.  It doesn't mean that it hides a fact whether a process with a specific
1916 pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"),
1917 but it hides process' uid and gid, which may be learned by stat()'ing
1918 /proc/<pid>/ otherwise.  It greatly complicates an intruder's task of gathering
1919 information about running processes, whether some daemon runs with elevated
1920 privileges, whether other user runs some sensitive program, whether other users
1921 run any program at all, etc.
1922 
1923 gid= defines a group authorized to learn processes information otherwise
1924 prohibited by hidepid=.  If you use some daemon like identd which needs to learn
1925 information about processes information, just add identd to this group.

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