Version:  2.0.40 2.2.26 2.4.37 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 4.8

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 ShmemPmdMapped:        0 kB
440 Shared_Hugetlb:        0 kB
441 Private_Hugetlb:       0 kB
442 Swap:                  0 kB
443 SwapPss:               0 kB
444 KernelPageSize:        4 kB
445 MMUPageSize:           4 kB
446 Locked:                0 kB
447 VmFlags: rd ex mr mw me dw
448 
449 the first of these lines shows the same information as is displayed for the
450 mapping in /proc/PID/maps.  The remaining lines show the size of the mapping
451 (size), the amount of the mapping that is currently resident in RAM (RSS), the
452 process' proportional share of this mapping (PSS), the number of clean and
453 dirty private pages in the mapping.
454 
455 The "proportional set size" (PSS) of a process is the count of pages it has
456 in memory, where each page is divided by the number of processes sharing it.
457 So if a process has 1000 pages all to itself, and 1000 shared with one other
458 process, its PSS will be 1500.
459 Note that even a page which is part of a MAP_SHARED mapping, but has only
460 a single pte mapped, i.e.  is currently used by only one process, is accounted
461 as private and not as shared.
462 "Referenced" indicates the amount of memory currently marked as referenced or
463 accessed.
464 "Anonymous" shows the amount of memory that does not belong to any file.  Even
465 a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
466 and a page is modified, the file page is replaced by a private anonymous copy.
467 "AnonHugePages" shows the ammount of memory backed by transparent hugepage.
468 "ShmemPmdMapped" shows the ammount of shared (shmem/tmpfs) memory backed by
469 huge pages.
470 "Shared_Hugetlb" and "Private_Hugetlb" show the ammounts of memory backed by
471 hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical
472 reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field.
473 "Swap" shows how much would-be-anonymous memory is also used, but out on swap.
474 For shmem mappings, "Swap" includes also the size of the mapped (and not
475 replaced by copy-on-write) part of the underlying shmem object out on swap.
476 "SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
477 does not take into account swapped out page of underlying shmem objects.
478 "Locked" indicates whether the mapping is locked in memory or not.
479 
480 "VmFlags" field deserves a separate description. This member represents the kernel
481 flags associated with the particular virtual memory area in two letter encoded
482 manner. The codes are the following:
483     rd  - readable
484     wr  - writeable
485     ex  - executable
486     sh  - shared
487     mr  - may read
488     mw  - may write
489     me  - may execute
490     ms  - may share
491     gd  - stack segment growns down
492     pf  - pure PFN range
493     dw  - disabled write to the mapped file
494     lo  - pages are locked in memory
495     io  - memory mapped I/O area
496     sr  - sequential read advise provided
497     rr  - random read advise provided
498     dc  - do not copy area on fork
499     de  - do not expand area on remapping
500     ac  - area is accountable
501     nr  - swap space is not reserved for the area
502     ht  - area uses huge tlb pages
503     ar  - architecture specific flag
504     dd  - do not include area into core dump
505     sd  - soft-dirty flag
506     mm  - mixed map area
507     hg  - huge page advise flag
508     nh  - no-huge page advise flag
509     mg  - mergable advise flag
510 
511 Note that there is no guarantee that every flag and associated mnemonic will
512 be present in all further kernel releases. Things get changed, the flags may
513 be vanished or the reverse -- new added.
514 
515 This file is only present if the CONFIG_MMU kernel configuration option is
516 enabled.
517 
518 The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
519 bits on both physical and virtual pages associated with a process, and the
520 soft-dirty bit on pte (see Documentation/vm/soft-dirty.txt for details).
521 To clear the bits for all the pages associated with the process
522     > echo 1 > /proc/PID/clear_refs
523 
524 To clear the bits for the anonymous pages associated with the process
525     > echo 2 > /proc/PID/clear_refs
526 
527 To clear the bits for the file mapped pages associated with the process
528     > echo 3 > /proc/PID/clear_refs
529 
530 To clear the soft-dirty bit
531     > echo 4 > /proc/PID/clear_refs
532 
533 To reset the peak resident set size ("high water mark") to the process's
534 current value:
535     > echo 5 > /proc/PID/clear_refs
536 
537 Any other value written to /proc/PID/clear_refs will have no effect.
538 
539 The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
540 using /proc/kpageflags and number of times a page is mapped using
541 /proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt.
542 
543 The /proc/pid/numa_maps is an extension based on maps, showing the memory
544 locality and binding policy, as well as the memory usage (in pages) of
545 each mapping. The output follows a general format where mapping details get
546 summarized separated by blank spaces, one mapping per each file line:
547 
548 address   policy    mapping details
549 
550 00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
551 00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
552 3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
553 320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
554 3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
555 3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
556 3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
557 320698b000 default file=/lib64/libc-2.12.so
558 3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4
559 3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
560 3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
561 7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
562 7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
563 7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
564 7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
565 7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4
566 
567 Where:
568 "address" is the starting address for the mapping;
569 "policy" reports the NUMA memory policy set for the mapping (see vm/numa_memory_policy.txt);
570 "mapping details" summarizes mapping data such as mapping type, page usage counters,
571 node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
572 size, in KB, that is backing the mapping up.
573 
574 1.2 Kernel data
575 ---------------
576 
577 Similar to  the  process entries, the kernel data files give information about
578 the running kernel. The files used to obtain this information are contained in
579 /proc and  are  listed  in Table 1-5. Not all of these will be present in your
580 system. It  depends  on the kernel configuration and the loaded modules, which
581 files are there, and which are missing.
582 
583 Table 1-5: Kernel info in /proc
584 ..............................................................................
585  File        Content                                           
586  apm         Advanced power management info                    
587  buddyinfo   Kernel memory allocator information (see text)     (2.5)
588  bus         Directory containing bus specific information     
589  cmdline     Kernel command line                               
590  cpuinfo     Info about the CPU                                
591  devices     Available devices (block and character)           
592  dma         Used DMS channels                                 
593  filesystems Supported filesystems                             
594  driver      Various drivers grouped here, currently rtc (2.4)
595  execdomains Execdomains, related to security                   (2.4)
596  fb          Frame Buffer devices                               (2.4)
597  fs          File system parameters, currently nfs/exports      (2.4)
598  ide         Directory containing info about the IDE subsystem 
599  interrupts  Interrupt usage                                   
600  iomem       Memory map                                         (2.4)
601  ioports     I/O port usage                                    
602  irq         Masks for irq to cpu affinity                      (2.4)(smp?)
603  isapnp      ISA PnP (Plug&Play) Info                           (2.4)
604  kcore       Kernel core image (can be ELF or A.OUT(deprecated in 2.4))   
605  kmsg        Kernel messages                                   
606  ksyms       Kernel symbol table                               
607  loadavg     Load average of last 1, 5 & 15 minutes                
608  locks       Kernel locks                                      
609  meminfo     Memory info                                       
610  misc        Miscellaneous                                     
611  modules     List of loaded modules                            
612  mounts      Mounted filesystems                               
613  net         Networking info (see text)                        
614  pagetypeinfo Additional page allocator information (see text)  (2.5)
615  partitions  Table of partitions known to the system           
616  pci         Deprecated info of PCI bus (new way -> /proc/bus/pci/,
617              decoupled by lspci                                 (2.4)
618  rtc         Real time clock                                   
619  scsi        SCSI info (see text)                              
620  slabinfo    Slab pool info                                    
621  softirqs    softirq usage
622  stat        Overall statistics                                
623  swaps       Swap space utilization                            
624  sys         See chapter 2                                     
625  sysvipc     Info of SysVIPC Resources (msg, sem, shm)          (2.4)
626  tty         Info of tty drivers
627  uptime      Wall clock since boot, combined idle time of all cpus
628  version     Kernel version                                    
629  video       bttv info of video resources                       (2.4)
630  vmallocinfo Show vmalloced areas
631 ..............................................................................
632 
633 You can,  for  example,  check  which interrupts are currently in use and what
634 they are used for by looking in the file /proc/interrupts:
635 
636   > cat /proc/interrupts 
637              CPU0        
638     0:    8728810          XT-PIC  timer 
639     1:        895          XT-PIC  keyboard 
640     2:          0          XT-PIC  cascade 
641     3:     531695          XT-PIC  aha152x 
642     4:    2014133          XT-PIC  serial 
643     5:      44401          XT-PIC  pcnet_cs 
644     8:          2          XT-PIC  rtc 
645    11:          8          XT-PIC  i82365 
646    12:     182918          XT-PIC  PS/2 Mouse 
647    13:          1          XT-PIC  fpu 
648    14:    1232265          XT-PIC  ide0 
649    15:          7          XT-PIC  ide1 
650   NMI:          0 
651 
652 In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
653 output of a SMP machine):
654 
655   > cat /proc/interrupts 
656 
657              CPU0       CPU1       
658     0:    1243498    1214548    IO-APIC-edge  timer
659     1:       8949       8958    IO-APIC-edge  keyboard
660     2:          0          0          XT-PIC  cascade
661     5:      11286      10161    IO-APIC-edge  soundblaster
662     8:          1          0    IO-APIC-edge  rtc
663     9:      27422      27407    IO-APIC-edge  3c503
664    12:     113645     113873    IO-APIC-edge  PS/2 Mouse
665    13:          0          0          XT-PIC  fpu
666    14:      22491      24012    IO-APIC-edge  ide0
667    15:       2183       2415    IO-APIC-edge  ide1
668    17:      30564      30414   IO-APIC-level  eth0
669    18:        177        164   IO-APIC-level  bttv
670   NMI:    2457961    2457959 
671   LOC:    2457882    2457881 
672   ERR:       2155
673 
674 NMI is incremented in this case because every timer interrupt generates a NMI
675 (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
676 
677 LOC is the local interrupt counter of the internal APIC of every CPU.
678 
679 ERR is incremented in the case of errors in the IO-APIC bus (the bus that
680 connects the CPUs in a SMP system. This means that an error has been detected,
681 the IO-APIC automatically retry the transmission, so it should not be a big
682 problem, but you should read the SMP-FAQ.
683 
684 In 2.6.2* /proc/interrupts was expanded again.  This time the goal was for
685 /proc/interrupts to display every IRQ vector in use by the system, not
686 just those considered 'most important'.  The new vectors are:
687 
688   THR -- interrupt raised when a machine check threshold counter
689   (typically counting ECC corrected errors of memory or cache) exceeds
690   a configurable threshold.  Only available on some systems.
691 
692   TRM -- a thermal event interrupt occurs when a temperature threshold
693   has been exceeded for the CPU.  This interrupt may also be generated
694   when the temperature drops back to normal.
695 
696   SPU -- a spurious interrupt is some interrupt that was raised then lowered
697   by some IO device before it could be fully processed by the APIC.  Hence
698   the APIC sees the interrupt but does not know what device it came from.
699   For this case the APIC will generate the interrupt with a IRQ vector
700   of 0xff. This might also be generated by chipset bugs.
701 
702   RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
703   sent from one CPU to another per the needs of the OS.  Typically,
704   their statistics are used by kernel developers and interested users to
705   determine the occurrence of interrupts of the given type.
706 
707 The above IRQ vectors are displayed only when relevant.  For example,
708 the threshold vector does not exist on x86_64 platforms.  Others are
709 suppressed when the system is a uniprocessor.  As of this writing, only
710 i386 and x86_64 platforms support the new IRQ vector displays.
711 
712 Of some interest is the introduction of the /proc/irq directory to 2.4.
713 It could be used to set IRQ to CPU affinity, this means that you can "hook" an
714 IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
715 irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
716 prof_cpu_mask.
717 
718 For example 
719   > ls /proc/irq/
720   0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
721   1  11  13  15  17  19  3  5  7  9  default_smp_affinity
722   > ls /proc/irq/0/
723   smp_affinity
724 
725 smp_affinity is a bitmask, in which you can specify which CPUs can handle the
726 IRQ, you can set it by doing:
727 
728   > echo 1 > /proc/irq/10/smp_affinity
729 
730 This means that only the first CPU will handle the IRQ, but you can also echo
731 5 which means that only the first and third CPU can handle the IRQ.
732 
733 The contents of each smp_affinity file is the same by default:
734 
735   > cat /proc/irq/0/smp_affinity
736   ffffffff
737 
738 There is an alternate interface, smp_affinity_list which allows specifying
739 a cpu range instead of a bitmask:
740 
741   > cat /proc/irq/0/smp_affinity_list
742   1024-1031
743 
744 The default_smp_affinity mask applies to all non-active IRQs, which are the
745 IRQs which have not yet been allocated/activated, and hence which lack a
746 /proc/irq/[0-9]* directory.
747 
748 The node file on an SMP system shows the node to which the device using the IRQ
749 reports itself as being attached. This hardware locality information does not
750 include information about any possible driver locality preference.
751 
752 prof_cpu_mask specifies which CPUs are to be profiled by the system wide
753 profiler. Default value is ffffffff (all cpus if there are only 32 of them).
754 
755 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
756 between all the CPUs which are allowed to handle it. As usual the kernel has
757 more info than you and does a better job than you, so the defaults are the
758 best choice for almost everyone.  [Note this applies only to those IO-APIC's
759 that support "Round Robin" interrupt distribution.]
760 
761 There are  three  more  important subdirectories in /proc: net, scsi, and sys.
762 The general  rule  is  that  the  contents,  or  even  the  existence of these
763 directories, depend  on your kernel configuration. If SCSI is not enabled, the
764 directory scsi  may  not  exist. The same is true with the net, which is there
765 only when networking support is present in the running kernel.
766 
767 The slabinfo  file  gives  information  about  memory usage at the slab level.
768 Linux uses  slab  pools for memory management above page level in version 2.2.
769 Commonly used  objects  have  their  own  slab  pool (such as network buffers,
770 directory cache, and so on).
771 
772 ..............................................................................
773 
774 > cat /proc/buddyinfo
775 
776 Node 0, zone      DMA      0      4      5      4      4      3 ...
777 Node 0, zone   Normal      1      0      0      1    101      8 ...
778 Node 0, zone  HighMem      2      0      0      1      1      0 ...
779 
780 External fragmentation is a problem under some workloads, and buddyinfo is a
781 useful tool for helping diagnose these problems.  Buddyinfo will give you a 
782 clue as to how big an area you can safely allocate, or why a previous
783 allocation failed.
784 
785 Each column represents the number of pages of a certain order which are 
786 available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in 
787 ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE 
788 available in ZONE_NORMAL, etc... 
789 
790 More information relevant to external fragmentation can be found in
791 pagetypeinfo.
792 
793 > cat /proc/pagetypeinfo
794 Page block order: 9
795 Pages per block:  512
796 
797 Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
798 Node    0, zone      DMA, type    Unmovable      0      0      0      1      1      1      1      1      1      1      0
799 Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0
800 Node    0, zone      DMA, type      Movable      1      1      2      1      2      1      1      0      1      0      2
801 Node    0, zone      DMA, type      Reserve      0      0      0      0      0      0      0      0      0      1      0
802 Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
803 Node    0, zone    DMA32, type    Unmovable    103     54     77      1      1      1     11      8      7      1      9
804 Node    0, zone    DMA32, type  Reclaimable      0      0      2      1      0      0      0      0      1      0      0
805 Node    0, zone    DMA32, type      Movable    169    152    113     91     77     54     39     13      6      1    452
806 Node    0, zone    DMA32, type      Reserve      1      2      2      2      2      0      1      1      1      1      0
807 Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
808 
809 Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate
810 Node 0, zone      DMA            2            0            5            1            0
811 Node 0, zone    DMA32           41            6          967            2            0
812 
813 Fragmentation avoidance in the kernel works by grouping pages of different
814 migrate types into the same contiguous regions of memory called page blocks.
815 A page block is typically the size of the default hugepage size e.g. 2MB on
816 X86-64. By keeping pages grouped based on their ability to move, the kernel
817 can reclaim pages within a page block to satisfy a high-order allocation.
818 
819 The pagetypinfo begins with information on the size of a page block. It
820 then gives the same type of information as buddyinfo except broken down
821 by migrate-type and finishes with details on how many page blocks of each
822 type exist.
823 
824 If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
825 from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can
826 make an estimate of the likely number of huge pages that can be allocated
827 at a given point in time. All the "Movable" blocks should be allocatable
828 unless memory has been mlock()'d. Some of the Reclaimable blocks should
829 also be allocatable although a lot of filesystem metadata may have to be
830 reclaimed to achieve this.
831 
832 ..............................................................................
833 
834 meminfo:
835 
836 Provides information about distribution and utilization of memory.  This
837 varies by architecture and compile options.  The following is from a
838 16GB PIII, which has highmem enabled.  You may not have all of these fields.
839 
840 > cat /proc/meminfo
841 
842 MemTotal:     16344972 kB
843 MemFree:      13634064 kB
844 MemAvailable: 14836172 kB
845 Buffers:          3656 kB
846 Cached:        1195708 kB
847 SwapCached:          0 kB
848 Active:         891636 kB
849 Inactive:      1077224 kB
850 HighTotal:    15597528 kB
851 HighFree:     13629632 kB
852 LowTotal:       747444 kB
853 LowFree:          4432 kB
854 SwapTotal:           0 kB
855 SwapFree:            0 kB
856 Dirty:             968 kB
857 Writeback:           0 kB
858 AnonPages:      861800 kB
859 Mapped:         280372 kB
860 Shmem:             644 kB
861 Slab:           284364 kB
862 SReclaimable:   159856 kB
863 SUnreclaim:     124508 kB
864 PageTables:      24448 kB
865 NFS_Unstable:        0 kB
866 Bounce:              0 kB
867 WritebackTmp:        0 kB
868 CommitLimit:   7669796 kB
869 Committed_AS:   100056 kB
870 VmallocTotal:   112216 kB
871 VmallocUsed:       428 kB
872 VmallocChunk:   111088 kB
873 AnonHugePages:   49152 kB
874 ShmemHugePages:      0 kB
875 ShmemPmdMapped:      0 kB
876 
877 
878     MemTotal: Total usable ram (i.e. physical ram minus a few reserved
879               bits and the kernel binary code)
880      MemFree: The sum of LowFree+HighFree
881 MemAvailable: An estimate of how much memory is available for starting new
882               applications, without swapping. Calculated from MemFree,
883               SReclaimable, the size of the file LRU lists, and the low
884               watermarks in each zone.
885               The estimate takes into account that the system needs some
886               page cache to function well, and that not all reclaimable
887               slab will be reclaimable, due to items being in use. The
888               impact of those factors will vary from system to system.
889      Buffers: Relatively temporary storage for raw disk blocks
890               shouldn't get tremendously large (20MB or so)
891       Cached: in-memory cache for files read from the disk (the
892               pagecache).  Doesn't include SwapCached
893   SwapCached: Memory that once was swapped out, is swapped back in but
894               still also is in the swapfile (if memory is needed it
895               doesn't need to be swapped out AGAIN because it is already
896               in the swapfile. This saves I/O)
897       Active: Memory that has been used more recently and usually not
898               reclaimed unless absolutely necessary.
899     Inactive: Memory which has been less recently used.  It is more
900               eligible to be reclaimed for other purposes
901    HighTotal:
902     HighFree: Highmem is all memory above ~860MB of physical memory
903               Highmem areas are for use by userspace programs, or
904               for the pagecache.  The kernel must use tricks to access
905               this memory, making it slower to access than lowmem.
906     LowTotal:
907      LowFree: Lowmem is memory which can be used for everything that
908               highmem can be used for, but it is also available for the
909               kernel's use for its own data structures.  Among many
910               other things, it is where everything from the Slab is
911               allocated.  Bad things happen when you're out of lowmem.
912    SwapTotal: total amount of swap space available
913     SwapFree: Memory which has been evicted from RAM, and is temporarily
914               on the disk
915        Dirty: Memory which is waiting to get written back to the disk
916    Writeback: Memory which is actively being written back to the disk
917    AnonPages: Non-file backed pages mapped into userspace page tables
918 AnonHugePages: Non-file backed huge pages mapped into userspace page tables
919       Mapped: files which have been mmaped, such as libraries
920        Shmem: Total memory used by shared memory (shmem) and tmpfs
921 ShmemHugePages: Memory used by shared memory (shmem) and tmpfs allocated
922               with huge pages
923 ShmemPmdMapped: Shared memory mapped into userspace with huge pages
924         Slab: in-kernel data structures cache
925 SReclaimable: Part of Slab, that might be reclaimed, such as caches
926   SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
927   PageTables: amount of memory dedicated to the lowest level of page
928               tables.
929 NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
930               storage
931       Bounce: Memory used for block device "bounce buffers"
932 WritebackTmp: Memory used by FUSE for temporary writeback buffers
933  CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
934               this is the total amount of  memory currently available to
935               be allocated on the system. This limit is only adhered to
936               if strict overcommit accounting is enabled (mode 2 in
937               'vm.overcommit_memory').
938               The CommitLimit is calculated with the following formula:
939               CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
940                              overcommit_ratio / 100 + [total swap pages]
941               For example, on a system with 1G of physical RAM and 7G
942               of swap with a `vm.overcommit_ratio` of 30 it would
943               yield a CommitLimit of 7.3G.
944               For more details, see the memory overcommit documentation
945               in vm/overcommit-accounting.
946 Committed_AS: The amount of memory presently allocated on the system.
947               The committed memory is a sum of all of the memory which
948               has been allocated by processes, even if it has not been
949               "used" by them as of yet. A process which malloc()'s 1G
950               of memory, but only touches 300M of it will show up as
951               using 1G. This 1G is memory which has been "committed" to
952               by the VM and can be used at any time by the allocating
953               application. With strict overcommit enabled on the system
954               (mode 2 in 'vm.overcommit_memory'),allocations which would
955               exceed the CommitLimit (detailed above) will not be permitted.
956               This is useful if one needs to guarantee that processes will
957               not fail due to lack of memory once that memory has been
958               successfully allocated.
959 VmallocTotal: total size of vmalloc memory area
960  VmallocUsed: amount of vmalloc area which is used
961 VmallocChunk: largest contiguous block of vmalloc area which is free
962 
963 ..............................................................................
964 
965 vmallocinfo:
966 
967 Provides information about vmalloced/vmaped areas. One line per area,
968 containing the virtual address range of the area, size in bytes,
969 caller information of the creator, and optional information depending
970 on the kind of area :
971 
972  pages=nr    number of pages
973  phys=addr   if a physical address was specified
974  ioremap     I/O mapping (ioremap() and friends)
975  vmalloc     vmalloc() area
976  vmap        vmap()ed pages
977  user        VM_USERMAP area
978  vpages      buffer for pages pointers was vmalloced (huge area)
979  N<node>=nr  (Only on NUMA kernels)
980              Number of pages allocated on memory node <node>
981 
982 > cat /proc/vmallocinfo
983 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
984   /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
985 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
986   /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
987 0xffffc20000302000-0xffffc20000304000    8192 acpi_tb_verify_table+0x21/0x4f...
988   phys=7fee8000 ioremap
989 0xffffc20000304000-0xffffc20000307000   12288 acpi_tb_verify_table+0x21/0x4f...
990   phys=7fee7000 ioremap
991 0xffffc2000031d000-0xffffc2000031f000    8192 init_vdso_vars+0x112/0x210
992 0xffffc2000031f000-0xffffc2000032b000   49152 cramfs_uncompress_init+0x2e ...
993   /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
994 0xffffc2000033a000-0xffffc2000033d000   12288 sys_swapon+0x640/0xac0      ...
995   pages=2 vmalloc N1=2
996 0xffffc20000347000-0xffffc2000034c000   20480 xt_alloc_table_info+0xfe ...
997   /0x130 [x_tables] pages=4 vmalloc N0=4
998 0xffffffffa0000000-0xffffffffa000f000   61440 sys_init_module+0xc27/0x1d00 ...
999    pages=14 vmalloc N2=14
1000 0xffffffffa000f000-0xffffffffa0014000   20480 sys_init_module+0xc27/0x1d00 ...
1001    pages=4 vmalloc N1=4
1002 0xffffffffa0014000-0xffffffffa0017000   12288 sys_init_module+0xc27/0x1d00 ...
1003    pages=2 vmalloc N1=2
1004 0xffffffffa0017000-0xffffffffa0022000   45056 sys_init_module+0xc27/0x1d00 ...
1005    pages=10 vmalloc N0=10
1006 
1007 ..............................................................................
1008 
1009 softirqs:
1010 
1011 Provides counts of softirq handlers serviced since boot time, for each cpu.
1012 
1013 > cat /proc/softirqs
1014                 CPU0       CPU1       CPU2       CPU3
1015       HI:          0          0          0          0
1016    TIMER:      27166      27120      27097      27034
1017   NET_TX:          0          0          0         17
1018   NET_RX:         42          0          0         39
1019    BLOCK:          0          0        107       1121
1020  TASKLET:          0          0          0        290
1021    SCHED:      27035      26983      26971      26746
1022  HRTIMER:          0          0          0          0
1023      RCU:       1678       1769       2178       2250
1024 
1025 
1026 1.3 IDE devices in /proc/ide
1027 ----------------------------
1028 
1029 The subdirectory /proc/ide contains information about all IDE devices of which
1030 the kernel  is  aware.  There is one subdirectory for each IDE controller, the
1031 file drivers  and a link for each IDE device, pointing to the device directory
1032 in the controller specific subtree.
1033 
1034 The file  drivers  contains general information about the drivers used for the
1035 IDE devices:
1036 
1037   > cat /proc/ide/drivers
1038   ide-cdrom version 4.53
1039   ide-disk version 1.08
1040 
1041 More detailed  information  can  be  found  in  the  controller  specific
1042 subdirectories. These  are  named  ide0,  ide1  and  so  on.  Each  of  these
1043 directories contains the files shown in table 1-6.
1044 
1045 
1046 Table 1-6: IDE controller info in  /proc/ide/ide?
1047 ..............................................................................
1048  File    Content                                 
1049  channel IDE channel (0 or 1)                    
1050  config  Configuration (only for PCI/IDE bridge) 
1051  mate    Mate name                               
1052  model   Type/Chipset of IDE controller          
1053 ..............................................................................
1054 
1055 Each device  connected  to  a  controller  has  a separate subdirectory in the
1056 controllers directory.  The  files  listed in table 1-7 are contained in these
1057 directories.
1058 
1059 
1060 Table 1-7: IDE device information
1061 ..............................................................................
1062  File             Content                                    
1063  cache            The cache                                  
1064  capacity         Capacity of the medium (in 512Byte blocks) 
1065  driver           driver and version                         
1066  geometry         physical and logical geometry              
1067  identify         device identify block                      
1068  media            media type                                 
1069  model            device identifier                          
1070  settings         device setup                               
1071  smart_thresholds IDE disk management thresholds             
1072  smart_values     IDE disk management values                 
1073 ..............................................................................
1074 
1075 The most  interesting  file is settings. This file contains a nice overview of
1076 the drive parameters:
1077 
1078   # cat /proc/ide/ide0/hda/settings 
1079   name                    value           min             max             mode 
1080   ----                    -----           ---             ---             ---- 
1081   bios_cyl                526             0               65535           rw 
1082   bios_head               255             0               255             rw 
1083   bios_sect               63              0               63              rw 
1084   breada_readahead        4               0               127             rw 
1085   bswap                   0               0               1               r 
1086   file_readahead          72              0               2097151         rw 
1087   io_32bit                0               0               3               rw 
1088   keepsettings            0               0               1               rw 
1089   max_kb_per_request      122             1               127             rw 
1090   multcount               0               0               8               rw 
1091   nice1                   1               0               1               rw 
1092   nowerr                  0               0               1               rw 
1093   pio_mode                write-only      0               255             w 
1094   slow                    0               0               1               rw 
1095   unmaskirq               0               0               1               rw 
1096   using_dma               0               0               1               rw 
1097 
1098 
1099 1.4 Networking info in /proc/net
1100 --------------------------------
1101 
1102 The subdirectory  /proc/net  follows  the  usual  pattern. Table 1-8 shows the
1103 additional values  you  get  for  IP  version 6 if you configure the kernel to
1104 support this. Table 1-9 lists the files and their meaning.
1105 
1106 
1107 Table 1-8: IPv6 info in /proc/net
1108 ..............................................................................
1109  File       Content                                               
1110  udp6       UDP sockets (IPv6)                                    
1111  tcp6       TCP sockets (IPv6)                                    
1112  raw6       Raw device statistics (IPv6)                          
1113  igmp6      IP multicast addresses, which this host joined (IPv6) 
1114  if_inet6   List of IPv6 interface addresses                      
1115  ipv6_route Kernel routing table for IPv6                         
1116  rt6_stats  Global IPv6 routing tables statistics                 
1117  sockstat6  Socket statistics (IPv6)                              
1118  snmp6      Snmp data (IPv6)                                      
1119 ..............................................................................
1120 
1121 
1122 Table 1-9: Network info in /proc/net
1123 ..............................................................................
1124  File          Content                                                         
1125  arp           Kernel  ARP table                                               
1126  dev           network devices with statistics                                 
1127  dev_mcast     the Layer2 multicast groups a device is listening too
1128                (interface index, label, number of references, number of bound
1129                addresses). 
1130  dev_stat      network device status                                           
1131  ip_fwchains   Firewall chain linkage                                          
1132  ip_fwnames    Firewall chain names                                            
1133  ip_masq       Directory containing the masquerading tables                    
1134  ip_masquerade Major masquerading table                                        
1135  netstat       Network statistics                                              
1136  raw           raw device statistics                                           
1137  route         Kernel routing table                                            
1138  rpc           Directory containing rpc info                                   
1139  rt_cache      Routing cache                                                   
1140  snmp          SNMP data                                                       
1141  sockstat      Socket statistics                                               
1142  tcp           TCP  sockets                                                    
1143  udp           UDP sockets                                                     
1144  unix          UNIX domain sockets                                             
1145  wireless      Wireless interface data (Wavelan etc)                           
1146  igmp          IP multicast addresses, which this host joined                  
1147  psched        Global packet scheduler parameters.                             
1148  netlink       List of PF_NETLINK sockets                                      
1149  ip_mr_vifs    List of multicast virtual interfaces                            
1150  ip_mr_cache   List of multicast routing cache                                 
1151 ..............................................................................
1152 
1153 You can  use  this  information  to see which network devices are available in
1154 your system and how much traffic was routed over those devices:
1155 
1156   > cat /proc/net/dev 
1157   Inter-|Receive                                                   |[... 
1158    face |bytes    packets errs drop fifo frame compressed multicast|[... 
1159       lo:  908188   5596     0    0    0     0          0         0 [...         
1160     ppp0:15475140  20721   410    0    0   410          0         0 [...  
1161     eth0:  614530   7085     0    0    0     0          0         1 [... 
1162    
1163   ...] Transmit 
1164   ...] bytes    packets errs drop fifo colls carrier compressed 
1165   ...]  908188     5596    0    0    0     0       0          0 
1166   ...] 1375103    17405    0    0    0     0       0          0 
1167   ...] 1703981     5535    0    0    0     3       0          0 
1168 
1169 In addition, each Channel Bond interface has its own directory.  For
1170 example, the bond0 device will have a directory called /proc/net/bond0/.
1171 It will contain information that is specific to that bond, such as the
1172 current slaves of the bond, the link status of the slaves, and how
1173 many times the slaves link has failed.
1174 
1175 1.5 SCSI info
1176 -------------
1177 
1178 If you  have  a  SCSI  host adapter in your system, you'll find a subdirectory
1179 named after  the driver for this adapter in /proc/scsi. You'll also see a list
1180 of all recognized SCSI devices in /proc/scsi:
1181 
1182   >cat /proc/scsi/scsi 
1183   Attached devices: 
1184   Host: scsi0 Channel: 00 Id: 00 Lun: 00 
1185     Vendor: IBM      Model: DGHS09U          Rev: 03E0 
1186     Type:   Direct-Access                    ANSI SCSI revision: 03 
1187   Host: scsi0 Channel: 00 Id: 06 Lun: 00 
1188     Vendor: PIONEER  Model: CD-ROM DR-U06S   Rev: 1.04 
1189     Type:   CD-ROM                           ANSI SCSI revision: 02 
1190 
1191 
1192 The directory  named  after  the driver has one file for each adapter found in
1193 the system.  These  files  contain information about the controller, including
1194 the used  IRQ  and  the  IO  address range. The amount of information shown is
1195 dependent on  the adapter you use. The example shows the output for an Adaptec
1196 AHA-2940 SCSI adapter:
1197 
1198   > cat /proc/scsi/aic7xxx/0 
1199    
1200   Adaptec AIC7xxx driver version: 5.1.19/3.2.4 
1201   Compile Options: 
1202     TCQ Enabled By Default : Disabled 
1203     AIC7XXX_PROC_STATS     : Disabled 
1204     AIC7XXX_RESET_DELAY    : 5 
1205   Adapter Configuration: 
1206              SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter 
1207                              Ultra Wide Controller 
1208       PCI MMAPed I/O Base: 0xeb001000 
1209    Adapter SEEPROM Config: SEEPROM found and used. 
1210         Adaptec SCSI BIOS: Enabled 
1211                       IRQ: 10 
1212                      SCBs: Active 0, Max Active 2, 
1213                            Allocated 15, HW 16, Page 255 
1214                Interrupts: 160328 
1215         BIOS Control Word: 0x18b6 
1216      Adapter Control Word: 0x005b 
1217      Extended Translation: Enabled 
1218   Disconnect Enable Flags: 0xffff 
1219        Ultra Enable Flags: 0x0001 
1220    Tag Queue Enable Flags: 0x0000 
1221   Ordered Queue Tag Flags: 0x0000 
1222   Default Tag Queue Depth: 8 
1223       Tagged Queue By Device array for aic7xxx host instance 0: 
1224         {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} 
1225       Actual queue depth per device for aic7xxx host instance 0: 
1226         {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} 
1227   Statistics: 
1228   (scsi0:0:0:0) 
1229     Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 
1230     Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) 
1231     Total transfers 160151 (74577 reads and 85574 writes) 
1232   (scsi0:0:6:0) 
1233     Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 
1234     Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) 
1235     Total transfers 0 (0 reads and 0 writes) 
1236 
1237 
1238 1.6 Parallel port info in /proc/parport
1239 ---------------------------------------
1240 
1241 The directory  /proc/parport  contains information about the parallel ports of
1242 your system.  It  has  one  subdirectory  for  each port, named after the port
1243 number (0,1,2,...).
1244 
1245 These directories contain the four files shown in Table 1-10.
1246 
1247 
1248 Table 1-10: Files in /proc/parport
1249 ..............................................................................
1250  File      Content                                                             
1251  autoprobe Any IEEE-1284 device ID information that has been acquired.         
1252  devices   list of the device drivers using that port. A + will appear by the
1253            name of the device currently using the port (it might not appear
1254            against any). 
1255  hardware  Parallel port's base address, IRQ line and DMA channel.             
1256  irq       IRQ that parport is using for that port. This is in a separate
1257            file to allow you to alter it by writing a new value in (IRQ
1258            number or none). 
1259 ..............................................................................
1260 
1261 1.7 TTY info in /proc/tty
1262 -------------------------
1263 
1264 Information about  the  available  and actually used tty's can be found in the
1265 directory /proc/tty.You'll  find  entries  for drivers and line disciplines in
1266 this directory, as shown in Table 1-11.
1267 
1268 
1269 Table 1-11: Files in /proc/tty
1270 ..............................................................................
1271  File          Content                                        
1272  drivers       list of drivers and their usage                
1273  ldiscs        registered line disciplines                    
1274  driver/serial usage statistic and status of single tty lines 
1275 ..............................................................................
1276 
1277 To see  which  tty's  are  currently in use, you can simply look into the file
1278 /proc/tty/drivers:
1279 
1280   > cat /proc/tty/drivers 
1281   pty_slave            /dev/pts      136   0-255 pty:slave 
1282   pty_master           /dev/ptm      128   0-255 pty:master 
1283   pty_slave            /dev/ttyp       3   0-255 pty:slave 
1284   pty_master           /dev/pty        2   0-255 pty:master 
1285   serial               /dev/cua        5   64-67 serial:callout 
1286   serial               /dev/ttyS       4   64-67 serial 
1287   /dev/tty0            /dev/tty0       4       0 system:vtmaster 
1288   /dev/ptmx            /dev/ptmx       5       2 system 
1289   /dev/console         /dev/console    5       1 system:console 
1290   /dev/tty             /dev/tty        5       0 system:/dev/tty 
1291   unknown              /dev/tty        4    1-63 console 
1292 
1293 
1294 1.8 Miscellaneous kernel statistics in /proc/stat
1295 -------------------------------------------------
1296 
1297 Various pieces   of  information about  kernel activity  are  available in the
1298 /proc/stat file.  All  of  the numbers reported  in  this file are  aggregates
1299 since the system first booted.  For a quick look, simply cat the file:
1300 
1301   > cat /proc/stat
1302   cpu  2255 34 2290 22625563 6290 127 456 0 0 0
1303   cpu0 1132 34 1441 11311718 3675 127 438 0 0 0
1304   cpu1 1123 0 849 11313845 2614 0 18 0 0 0
1305   intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1306   ctxt 1990473
1307   btime 1062191376
1308   processes 2915
1309   procs_running 1
1310   procs_blocked 0
1311   softirq 183433 0 21755 12 39 1137 231 21459 2263
1312 
1313 The very first  "cpu" line aggregates the  numbers in all  of the other "cpuN"
1314 lines.  These numbers identify the amount of time the CPU has spent performing
1315 different kinds of work.  Time units are in USER_HZ (typically hundredths of a
1316 second).  The meanings of the columns are as follows, from left to right:
1317 
1318 - user: normal processes executing in user mode
1319 - nice: niced processes executing in user mode
1320 - system: processes executing in kernel mode
1321 - idle: twiddling thumbs
1322 - iowait: waiting for I/O to complete
1323 - irq: servicing interrupts
1324 - softirq: servicing softirqs
1325 - steal: involuntary wait
1326 - guest: running a normal guest
1327 - guest_nice: running a niced guest
1328 
1329 The "intr" line gives counts of interrupts  serviced since boot time, for each
1330 of the  possible system interrupts.   The first  column  is the  total of  all
1331 interrupts serviced  including  unnumbered  architecture specific  interrupts;
1332 each  subsequent column is the  total for that particular numbered interrupt.
1333 Unnumbered interrupts are not shown, only summed into the total.
1334 
1335 The "ctxt" line gives the total number of context switches across all CPUs.
1336 
1337 The "btime" line gives  the time at which the  system booted, in seconds since
1338 the Unix epoch.
1339 
1340 The "processes" line gives the number  of processes and threads created, which
1341 includes (but  is not limited  to) those  created by  calls to the  fork() and
1342 clone() system calls.
1343 
1344 The "procs_running" line gives the total number of threads that are
1345 running or ready to run (i.e., the total number of runnable threads).
1346 
1347 The   "procs_blocked" line gives  the  number of  processes currently blocked,
1348 waiting for I/O to complete.
1349 
1350 The "softirq" line gives counts of softirqs serviced since boot time, for each
1351 of the possible system softirqs. The first column is the total of all
1352 softirqs serviced; each subsequent column is the total for that particular
1353 softirq.
1354 
1355 
1356 1.9 Ext4 file system parameters
1357 -------------------------------
1358 
1359 Information about mounted ext4 file systems can be found in
1360 /proc/fs/ext4.  Each mounted filesystem will have a directory in
1361 /proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1362 /proc/fs/ext4/dm-0).   The files in each per-device directory are shown
1363 in Table 1-12, below.
1364 
1365 Table 1-12: Files in /proc/fs/ext4/<devname>
1366 ..............................................................................
1367  File            Content                                        
1368  mb_groups       details of multiblock allocator buddy cache of free blocks
1369 ..............................................................................
1370 
1371 2.0 /proc/consoles
1372 ------------------
1373 Shows registered system console lines.
1374 
1375 To see which character device lines are currently used for the system console
1376 /dev/console, you may simply look into the file /proc/consoles:
1377 
1378   > cat /proc/consoles
1379   tty0                 -WU (ECp)       4:7
1380   ttyS0                -W- (Ep)        4:64
1381 
1382 The columns are:
1383 
1384   device               name of the device
1385   operations           R = can do read operations
1386                        W = can do write operations
1387                        U = can do unblank
1388   flags                E = it is enabled
1389                        C = it is preferred console
1390                        B = it is primary boot console
1391                        p = it is used for printk buffer
1392                        b = it is not a TTY but a Braille device
1393                        a = it is safe to use when cpu is offline
1394   major:minor          major and minor number of the device separated by a colon
1395 
1396 ------------------------------------------------------------------------------
1397 Summary
1398 ------------------------------------------------------------------------------
1399 The /proc file system serves information about the running system. It not only
1400 allows access to process data but also allows you to request the kernel status
1401 by reading files in the hierarchy.
1402 
1403 The directory  structure  of /proc reflects the types of information and makes
1404 it easy, if not obvious, where to look for specific data.
1405 ------------------------------------------------------------------------------
1406 
1407 ------------------------------------------------------------------------------
1408 CHAPTER 2: MODIFYING SYSTEM PARAMETERS
1409 ------------------------------------------------------------------------------
1410 
1411 ------------------------------------------------------------------------------
1412 In This Chapter
1413 ------------------------------------------------------------------------------
1414 * Modifying kernel parameters by writing into files found in /proc/sys
1415 * Exploring the files which modify certain parameters
1416 * Review of the /proc/sys file tree
1417 ------------------------------------------------------------------------------
1418 
1419 
1420 A very  interesting part of /proc is the directory /proc/sys. This is not only
1421 a source  of  information,  it also allows you to change parameters within the
1422 kernel. Be  very  careful  when attempting this. You can optimize your system,
1423 but you  can  also  cause  it  to  crash.  Never  alter kernel parameters on a
1424 production system.  Set  up  a  development machine and test to make sure that
1425 everything works  the  way  you want it to. You may have no alternative but to
1426 reboot the machine once an error has been made.
1427 
1428 To change  a  value,  simply  echo  the new value into the file. An example is
1429 given below  in the section on the file system data. You need to be root to do
1430 this. You  can  create  your  own  boot script to perform this every time your
1431 system boots.
1432 
1433 The files  in /proc/sys can be used to fine tune and monitor miscellaneous and
1434 general things  in  the operation of the Linux kernel. Since some of the files
1435 can inadvertently  disrupt  your  system,  it  is  advisable  to  read  both
1436 documentation and  source  before actually making adjustments. In any case, be
1437 very careful  when  writing  to  any  of these files. The entries in /proc may
1438 change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1439 review the kernel documentation in the directory /usr/src/linux/Documentation.
1440 This chapter  is  heavily  based  on the documentation included in the pre 2.2
1441 kernels, and became part of it in version 2.2.1 of the Linux kernel.
1442 
1443 Please see: Documentation/sysctl/ directory for descriptions of these
1444 entries.
1445 
1446 ------------------------------------------------------------------------------
1447 Summary
1448 ------------------------------------------------------------------------------
1449 Certain aspects  of  kernel  behavior  can be modified at runtime, without the
1450 need to  recompile  the kernel, or even to reboot the system. The files in the
1451 /proc/sys tree  can  not only be read, but also modified. You can use the echo
1452 command to write value into these files, thereby changing the default settings
1453 of the kernel.
1454 ------------------------------------------------------------------------------
1455 
1456 ------------------------------------------------------------------------------
1457 CHAPTER 3: PER-PROCESS PARAMETERS
1458 ------------------------------------------------------------------------------
1459 
1460 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1461 --------------------------------------------------------------------------------
1462 
1463 These file can be used to adjust the badness heuristic used to select which
1464 process gets killed in out of memory conditions.
1465 
1466 The badness heuristic assigns a value to each candidate task ranging from 0
1467 (never kill) to 1000 (always kill) to determine which process is targeted.  The
1468 units are roughly a proportion along that range of allowed memory the process
1469 may allocate from based on an estimation of its current memory and swap use.
1470 For example, if a task is using all allowed memory, its badness score will be
1471 1000.  If it is using half of its allowed memory, its score will be 500.
1472 
1473 There is an additional factor included in the badness score: the current memory
1474 and swap usage is discounted by 3% for root processes.
1475 
1476 The amount of "allowed" memory depends on the context in which the oom killer
1477 was called.  If it is due to the memory assigned to the allocating task's cpuset
1478 being exhausted, the allowed memory represents the set of mems assigned to that
1479 cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
1480 memory represents the set of mempolicy nodes.  If it is due to a memory
1481 limit (or swap limit) being reached, the allowed memory is that configured
1482 limit.  Finally, if it is due to the entire system being out of memory, the
1483 allowed memory represents all allocatable resources.
1484 
1485 The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1486 is used to determine which task to kill.  Acceptable values range from -1000
1487 (OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
1488 polarize the preference for oom killing either by always preferring a certain
1489 task or completely disabling it.  The lowest possible value, -1000, is
1490 equivalent to disabling oom killing entirely for that task since it will always
1491 report a badness score of 0.
1492 
1493 Consequently, it is very simple for userspace to define the amount of memory to
1494 consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
1495 example, is roughly equivalent to allowing the remainder of tasks sharing the
1496 same system, cpuset, mempolicy, or memory controller resources to use at least
1497 50% more memory.  A value of -500, on the other hand, would be roughly
1498 equivalent to discounting 50% of the task's allowed memory from being considered
1499 as scoring against the task.
1500 
1501 For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1502 be used to tune the badness score.  Its acceptable values range from -16
1503 (OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1504 (OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
1505 scaled linearly with /proc/<pid>/oom_score_adj.
1506 
1507 The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1508 value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1509 requires CAP_SYS_RESOURCE.
1510 
1511 Caveat: when a parent task is selected, the oom killer will sacrifice any first
1512 generation children with separate address spaces instead, if possible.  This
1513 avoids servers and important system daemons from being killed and loses the
1514 minimal amount of work.
1515 
1516 
1517 3.2 /proc/<pid>/oom_score - Display current oom-killer score
1518 -------------------------------------------------------------
1519 
1520 This file can be used to check the current score used by the oom-killer is for
1521 any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1522 process should be killed in an out-of-memory situation.
1523 
1524 
1525 3.3  /proc/<pid>/io - Display the IO accounting fields
1526 -------------------------------------------------------
1527 
1528 This file contains IO statistics for each running process
1529 
1530 Example
1531 -------
1532 
1533 test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1534 [1] 3828
1535 
1536 test:/tmp # cat /proc/3828/io
1537 rchar: 323934931
1538 wchar: 323929600
1539 syscr: 632687
1540 syscw: 632675
1541 read_bytes: 0
1542 write_bytes: 323932160
1543 cancelled_write_bytes: 0
1544 
1545 
1546 Description
1547 -----------
1548 
1549 rchar
1550 -----
1551 
1552 I/O counter: chars read
1553 The number of bytes which this task has caused to be read from storage. This
1554 is simply the sum of bytes which this process passed to read() and pread().
1555 It includes things like tty IO and it is unaffected by whether or not actual
1556 physical disk IO was required (the read might have been satisfied from
1557 pagecache)
1558 
1559 
1560 wchar
1561 -----
1562 
1563 I/O counter: chars written
1564 The number of bytes which this task has caused, or shall cause to be written
1565 to disk. Similar caveats apply here as with rchar.
1566 
1567 
1568 syscr
1569 -----
1570 
1571 I/O counter: read syscalls
1572 Attempt to count the number of read I/O operations, i.e. syscalls like read()
1573 and pread().
1574 
1575 
1576 syscw
1577 -----
1578 
1579 I/O counter: write syscalls
1580 Attempt to count the number of write I/O operations, i.e. syscalls like
1581 write() and pwrite().
1582 
1583 
1584 read_bytes
1585 ----------
1586 
1587 I/O counter: bytes read
1588 Attempt to count the number of bytes which this process really did cause to
1589 be fetched from the storage layer. Done at the submit_bio() level, so it is
1590 accurate for block-backed filesystems. <please add status regarding NFS and
1591 CIFS at a later time>
1592 
1593 
1594 write_bytes
1595 -----------
1596 
1597 I/O counter: bytes written
1598 Attempt to count the number of bytes which this process caused to be sent to
1599 the storage layer. This is done at page-dirtying time.
1600 
1601 
1602 cancelled_write_bytes
1603 ---------------------
1604 
1605 The big inaccuracy here is truncate. If a process writes 1MB to a file and
1606 then deletes the file, it will in fact perform no writeout. But it will have
1607 been accounted as having caused 1MB of write.
1608 In other words: The number of bytes which this process caused to not happen,
1609 by truncating pagecache. A task can cause "negative" IO too. If this task
1610 truncates some dirty pagecache, some IO which another task has been accounted
1611 for (in its write_bytes) will not be happening. We _could_ just subtract that
1612 from the truncating task's write_bytes, but there is information loss in doing
1613 that.
1614 
1615 
1616 Note
1617 ----
1618 
1619 At its current implementation state, this is a bit racy on 32-bit machines: if
1620 process A reads process B's /proc/pid/io while process B is updating one of
1621 those 64-bit counters, process A could see an intermediate result.
1622 
1623 
1624 More information about this can be found within the taskstats documentation in
1625 Documentation/accounting.
1626 
1627 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1628 ---------------------------------------------------------------
1629 When a process is dumped, all anonymous memory is written to a core file as
1630 long as the size of the core file isn't limited. But sometimes we don't want
1631 to dump some memory segments, for example, huge shared memory or DAX.
1632 Conversely, sometimes we want to save file-backed memory segments into a core
1633 file, not only the individual files.
1634 
1635 /proc/<pid>/coredump_filter allows you to customize which memory segments
1636 will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1637 of memory types. If a bit of the bitmask is set, memory segments of the
1638 corresponding memory type are dumped, otherwise they are not dumped.
1639 
1640 The following 9 memory types are supported:
1641   - (bit 0) anonymous private memory
1642   - (bit 1) anonymous shared memory
1643   - (bit 2) file-backed private memory
1644   - (bit 3) file-backed shared memory
1645   - (bit 4) ELF header pages in file-backed private memory areas (it is
1646             effective only if the bit 2 is cleared)
1647   - (bit 5) hugetlb private memory
1648   - (bit 6) hugetlb shared memory
1649   - (bit 7) DAX private memory
1650   - (bit 8) DAX shared memory
1651 
1652   Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1653   are always dumped regardless of the bitmask status.
1654 
1655   Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
1656   only affected by bit 5-6, and DAX is only affected by bits 7-8.
1657 
1658 The default value of coredump_filter is 0x33; this means all anonymous memory
1659 segments, ELF header pages and hugetlb private memory are dumped.
1660 
1661 If you don't want to dump all shared memory segments attached to pid 1234,
1662 write 0x31 to the process's proc file.
1663 
1664   $ echo 0x31 > /proc/1234/coredump_filter
1665 
1666 When a new process is created, the process inherits the bitmask status from its
1667 parent. It is useful to set up coredump_filter before the program runs.
1668 For example:
1669 
1670   $ echo 0x7 > /proc/self/coredump_filter
1671   $ ./some_program
1672 
1673 3.5     /proc/<pid>/mountinfo - Information about mounts
1674 --------------------------------------------------------
1675 
1676 This file contains lines of the form:
1677 
1678 36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1679 (1)(2)(3)   (4)   (5)      (6)      (7)   (8) (9)   (10)         (11)
1680 
1681 (1) mount ID:  unique identifier of the mount (may be reused after umount)
1682 (2) parent ID:  ID of parent (or of self for the top of the mount tree)
1683 (3) major:minor:  value of st_dev for files on filesystem
1684 (4) root:  root of the mount within the filesystem
1685 (5) mount point:  mount point relative to the process's root
1686 (6) mount options:  per mount options
1687 (7) optional fields:  zero or more fields of the form "tag[:value]"
1688 (8) separator:  marks the end of the optional fields
1689 (9) filesystem type:  name of filesystem of the form "type[.subtype]"
1690 (10) mount source:  filesystem specific information or "none"
1691 (11) super options:  per super block options
1692 
1693 Parsers should ignore all unrecognised optional fields.  Currently the
1694 possible optional fields are:
1695 
1696 shared:X  mount is shared in peer group X
1697 master:X  mount is slave to peer group X
1698 propagate_from:X  mount is slave and receives propagation from peer group X (*)
1699 unbindable  mount is unbindable
1700 
1701 (*) X is the closest dominant peer group under the process's root.  If
1702 X is the immediate master of the mount, or if there's no dominant peer
1703 group under the same root, then only the "master:X" field is present
1704 and not the "propagate_from:X" field.
1705 
1706 For more information on mount propagation see:
1707 
1708   Documentation/filesystems/sharedsubtree.txt
1709 
1710 
1711 3.6     /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
1712 --------------------------------------------------------
1713 These files provide a method to access a tasks comm value. It also allows for
1714 a task to set its own or one of its thread siblings comm value. The comm value
1715 is limited in size compared to the cmdline value, so writing anything longer
1716 then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1717 comm value.
1718 
1719 
1720 3.7     /proc/<pid>/task/<tid>/children - Information about task children
1721 -------------------------------------------------------------------------
1722 This file provides a fast way to retrieve first level children pids
1723 of a task pointed by <pid>/<tid> pair. The format is a space separated
1724 stream of pids.
1725 
1726 Note the "first level" here -- if a child has own children they will
1727 not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children
1728 to obtain the descendants.
1729 
1730 Since this interface is intended to be fast and cheap it doesn't
1731 guarantee to provide precise results and some children might be
1732 skipped, especially if they've exited right after we printed their
1733 pids, so one need to either stop or freeze processes being inspected
1734 if precise results are needed.
1735 
1736 
1737 3.8     /proc/<pid>/fdinfo/<fd> - Information about opened file
1738 ---------------------------------------------------------------
1739 This file provides information associated with an opened file. The regular
1740 files have at least three fields -- 'pos', 'flags' and mnt_id. The 'pos'
1741 represents the current offset of the opened file in decimal form [see lseek(2)
1742 for details], 'flags' denotes the octal O_xxx mask the file has been
1743 created with [see open(2) for details] and 'mnt_id' represents mount ID of
1744 the file system containing the opened file [see 3.5 /proc/<pid>/mountinfo
1745 for details].
1746 
1747 A typical output is
1748 
1749         pos:    0
1750         flags:  0100002
1751         mnt_id: 19
1752 
1753 All locks associated with a file descriptor are shown in its fdinfo too.
1754 
1755 lock:       1: FLOCK  ADVISORY  WRITE 359 00:13:11691 0 EOF
1756 
1757 The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1758 pair provide additional information particular to the objects they represent.
1759 
1760         Eventfd files
1761         ~~~~~~~~~~~~~
1762         pos:    0
1763         flags:  04002
1764         mnt_id: 9
1765         eventfd-count:  5a
1766 
1767         where 'eventfd-count' is hex value of a counter.
1768 
1769         Signalfd files
1770         ~~~~~~~~~~~~~~
1771         pos:    0
1772         flags:  04002
1773         mnt_id: 9
1774         sigmask:        0000000000000200
1775 
1776         where 'sigmask' is hex value of the signal mask associated
1777         with a file.
1778 
1779         Epoll files
1780         ~~~~~~~~~~~
1781         pos:    0
1782         flags:  02
1783         mnt_id: 9
1784         tfd:        5 events:       1d data: ffffffffffffffff
1785 
1786         where 'tfd' is a target file descriptor number in decimal form,
1787         'events' is events mask being watched and the 'data' is data
1788         associated with a target [see epoll(7) for more details].
1789 
1790         Fsnotify files
1791         ~~~~~~~~~~~~~~
1792         For inotify files the format is the following
1793 
1794         pos:    0
1795         flags:  02000000
1796         inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
1797 
1798         where 'wd' is a watch descriptor in decimal form, ie a target file
1799         descriptor number, 'ino' and 'sdev' are inode and device where the
1800         target file resides and the 'mask' is the mask of events, all in hex
1801         form [see inotify(7) for more details].
1802 
1803         If the kernel was built with exportfs support, the path to the target
1804         file is encoded as a file handle.  The file handle is provided by three
1805         fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
1806         format.
1807 
1808         If the kernel is built without exportfs support the file handle won't be
1809         printed out.
1810 
1811         If there is no inotify mark attached yet the 'inotify' line will be omitted.
1812 
1813         For fanotify files the format is
1814 
1815         pos:    0
1816         flags:  02
1817         mnt_id: 9
1818         fanotify flags:10 event-flags:0
1819         fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
1820         fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
1821 
1822         where fanotify 'flags' and 'event-flags' are values used in fanotify_init
1823         call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
1824         flags associated with mark which are tracked separately from events
1825         mask. 'ino', 'sdev' are target inode and device, 'mask' is the events
1826         mask and 'ignored_mask' is the mask of events which are to be ignored.
1827         All in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
1828         does provide information about flags and mask used in fanotify_mark
1829         call [see fsnotify manpage for details].
1830 
1831         While the first three lines are mandatory and always printed, the rest is
1832         optional and may be omitted if no marks created yet.
1833 
1834         Timerfd files
1835         ~~~~~~~~~~~~~
1836 
1837         pos:    0
1838         flags:  02
1839         mnt_id: 9
1840         clockid: 0
1841         ticks: 0
1842         settime flags: 01
1843         it_value: (0, 49406829)
1844         it_interval: (1, 0)
1845 
1846         where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
1847         that have occurred [see timerfd_create(2) for details]. 'settime flags' are
1848         flags in octal form been used to setup the timer [see timerfd_settime(2) for
1849         details]. 'it_value' is remaining time until the timer exiration.
1850         'it_interval' is the interval for the timer. Note the timer might be set up
1851         with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
1852         still exhibits timer's remaining time.
1853 
1854 3.9     /proc/<pid>/map_files - Information about memory mapped files
1855 ---------------------------------------------------------------------
1856 This directory contains symbolic links which represent memory mapped files
1857 the process is maintaining.  Example output:
1858 
1859      | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
1860      | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
1861      | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
1862      | ...
1863      | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
1864      | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
1865 
1866 The name of a link represents the virtual memory bounds of a mapping, i.e.
1867 vm_area_struct::vm_start-vm_area_struct::vm_end.
1868 
1869 The main purpose of the map_files is to retrieve a set of memory mapped
1870 files in a fast way instead of parsing /proc/<pid>/maps or
1871 /proc/<pid>/smaps, both of which contain many more records.  At the same
1872 time one can open(2) mappings from the listings of two processes and
1873 comparing their inode numbers to figure out which anonymous memory areas
1874 are actually shared.
1875 
1876 3.10    /proc/<pid>/timerslack_ns - Task timerslack value
1877 ---------------------------------------------------------
1878 This file provides the value of the task's timerslack value in nanoseconds.
1879 This value specifies a amount of time that normal timers may be deferred
1880 in order to coalesce timers and avoid unnecessary wakeups.
1881 
1882 This allows a task's interactivity vs power consumption trade off to be
1883 adjusted.
1884 
1885 Writing 0 to the file will set the tasks timerslack to the default value.
1886 
1887 Valid values are from 0 - ULLONG_MAX
1888 
1889 An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
1890 permissions on the task specified to change its timerslack_ns value.
1891 
1892 
1893 ------------------------------------------------------------------------------
1894 Configuring procfs
1895 ------------------------------------------------------------------------------
1896 
1897 4.1     Mount options
1898 ---------------------
1899 
1900 The following mount options are supported:
1901 
1902         hidepid=        Set /proc/<pid>/ access mode.
1903         gid=            Set the group authorized to learn processes information.
1904 
1905 hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
1906 (default).
1907 
1908 hidepid=1 means users may not access any /proc/<pid>/ directories but their
1909 own.  Sensitive files like cmdline, sched*, status are now protected against
1910 other users.  This makes it impossible to learn whether any user runs
1911 specific program (given the program doesn't reveal itself by its behaviour).
1912 As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users,
1913 poorly written programs passing sensitive information via program arguments are
1914 now protected against local eavesdroppers.
1915 
1916 hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other
1917 users.  It doesn't mean that it hides a fact whether a process with a specific
1918 pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"),
1919 but it hides process' uid and gid, which may be learned by stat()'ing
1920 /proc/<pid>/ otherwise.  It greatly complicates an intruder's task of gathering
1921 information about running processes, whether some daemon runs with elevated
1922 privileges, whether other user runs some sensitive program, whether other users
1923 run any program at all, etc.
1924 
1925 gid= defines a group authorized to learn processes information otherwise
1926 prohibited by hidepid=.  If you use some daemon like identd which needs to learn
1927 information about processes information, just add identd to this group.

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