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Based on kernel version 4.7.2. Page generated on 2016-08-22 22:45 EST.

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