Version:  2.0.40 2.2.26 2.4.37 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 3.10 3.11 3.12 3.13 3.14 3.15 3.16 3.17

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

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