Version:  2.0.40 2.2.26 2.4.37 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17 3.18 3.19 4.0 4.1 4.2 4.3 4.4 4.5 4.6 4.7

Linux/Documentation/filesystems/proc.txt

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

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