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Based on kernel version 3.13. Page generated on 2014-01-20 22:03 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	
46	  4	Configuring procfs
47	  4.1	Mount options
48	
49	------------------------------------------------------------------------------
50	Preface
51	------------------------------------------------------------------------------
52	
53	0.1 Introduction/Credits
54	------------------------
55	
56	This documentation is  part of a soon (or  so we hope) to be  released book on
57	the SuSE  Linux distribution. As  there is  no complete documentation  for the
58	/proc file system and we've used  many freely available sources to write these
59	chapters, it  seems only fair  to give the work  back to the  Linux community.
60	This work is  based on the 2.2.*  kernel version and the  upcoming 2.4.*. I'm
61	afraid it's still far from complete, but we  hope it will be useful. As far as
62	we know, it is the first 'all-in-one' document about the /proc file system. It
63	is focused  on the Intel  x86 hardware,  so if you  are looking for  PPC, ARM,
64	SPARC, AXP, etc., features, you probably  won't find what you are looking for.
65	It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
66	additions and patches  are welcome and will  be added to this  document if you
67	mail them to Bodo.
68	
69	We'd like  to  thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
70	other people for help compiling this documentation. We'd also like to extend a
71	special thank  you to Andi Kleen for documentation, which we relied on heavily
72	to create  this  document,  as well as the additional information he provided.
73	Thanks to  everybody  else  who contributed source or docs to the Linux kernel
74	and helped create a great piece of software... :)
75	
76	If you  have  any comments, corrections or additions, please don't hesitate to
77	contact Bodo  Bauer  at  bb@ricochet.net.  We'll  be happy to add them to this
78	document.
79	
80	The   latest   version    of   this   document   is    available   online   at
81	http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html
82	
83	If  the above  direction does  not works  for you,  you could  try the  kernel
84	mailing  list  at  linux-kernel@vger.kernel.org  and/or try  to  reach  me  at
85	comandante@zaralinux.com.
86	
87	0.2 Legal Stuff
88	---------------
89	
90	We don't  guarantee  the  correctness  of this document, and if you come to us
91	complaining about  how  you  screwed  up  your  system  because  of  incorrect
92	documentation, we won't feel responsible...
93	
94	------------------------------------------------------------------------------
95	CHAPTER 1: COLLECTING SYSTEM INFORMATION
96	------------------------------------------------------------------------------
97	
98	------------------------------------------------------------------------------
99	In This Chapter
100	------------------------------------------------------------------------------
101	* Investigating  the  properties  of  the  pseudo  file  system  /proc and its
102	  ability to provide information on the running Linux system
103	* Examining /proc's structure
104	* Uncovering  various  information  about the kernel and the processes running
105	  on the system
106	------------------------------------------------------------------------------
107	
108	
109	The proc  file  system acts as an interface to internal data structures in the
110	kernel. It  can  be  used to obtain information about the system and to change
111	certain kernel parameters at runtime (sysctl).
112	
113	First, we'll  take  a  look  at the read-only parts of /proc. In Chapter 2, we
114	show you how you can use /proc/sys to change settings.
115	
116	1.1 Process-Specific Subdirectories
117	-----------------------------------
118	
119	The directory  /proc  contains  (among other things) one subdirectory for each
120	process running on the system, which is named after the process ID (PID).
121	
122	The link  self  points  to  the  process reading the file system. Each process
123	subdirectory has the entries listed in Table 1-1.
124	
125	
126	Table 1-1: Process specific entries in /proc
127	..............................................................................
128	 File		Content
129	 clear_refs	Clears page referenced bits shown in smaps output
130	 cmdline	Command line arguments
131	 cpu		Current and last cpu in which it was executed	(2.4)(smp)
132	 cwd		Link to the current working directory
133	 environ	Values of environment variables
134	 exe		Link to the executable of this process
135	 fd		Directory, which contains all file descriptors
136	 maps		Memory maps to executables and library files	(2.4)
137	 mem		Memory held by this process
138	 root		Link to the root directory of this process
139	 stat		Process status
140	 statm		Process memory status information
141	 status		Process status in human readable form
142	 wchan		If CONFIG_KALLSYMS is set, a pre-decoded wchan
143	 pagemap	Page table
144	 stack		Report full stack trace, enable via CONFIG_STACKTRACE
145	 smaps		a extension based on maps, showing the memory consumption of
146			each mapping and flags associated with it
147	..............................................................................
148	
149	For example, to get the status information of a process, all you have to do is
150	read the file /proc/PID/status:
151	
152	  >cat /proc/self/status
153	  Name:   cat
154	  State:  R (running)
155	  Tgid:   5452
156	  Pid:    5452
157	  PPid:   743
158	  TracerPid:      0						(2.4)
159	  Uid:    501     501     501     501
160	  Gid:    100     100     100     100
161	  FDSize: 256
162	  Groups: 100 14 16
163	  VmPeak:     5004 kB
164	  VmSize:     5004 kB
165	  VmLck:         0 kB
166	  VmHWM:       476 kB
167	  VmRSS:       476 kB
168	  VmData:      156 kB
169	  VmStk:        88 kB
170	  VmExe:        68 kB
171	  VmLib:      1412 kB
172	  VmPTE:        20 kb
173	  VmSwap:        0 kB
174	  Threads:        1
175	  SigQ:   0/28578
176	  SigPnd: 0000000000000000
177	  ShdPnd: 0000000000000000
178	  SigBlk: 0000000000000000
179	  SigIgn: 0000000000000000
180	  SigCgt: 0000000000000000
181	  CapInh: 00000000fffffeff
182	  CapPrm: 0000000000000000
183	  CapEff: 0000000000000000
184	  CapBnd: ffffffffffffffff
185	  Seccomp:        0
186	  voluntary_ctxt_switches:        0
187	  nonvoluntary_ctxt_switches:     1
188	
189	This shows you nearly the same information you would get if you viewed it with
190	the ps  command.  In  fact,  ps  uses  the  proc  file  system  to  obtain its
191	information.  But you get a more detailed  view of the  process by reading the
192	file /proc/PID/status. It fields are described in table 1-2.
193	
194	The  statm  file  contains  more  detailed  information about the process
195	memory usage. Its seven fields are explained in Table 1-3.  The stat file
196	contains details information about the process itself.  Its fields are
197	explained in Table 1-4.
198	
199	(for SMP CONFIG users)
200	For making accounting scalable, RSS related information are handled in
201	asynchronous manner and the vaule may not be very precise. To see a precise
202	snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
203	It's slow but very precise.
204	
205	Table 1-2: Contents of the status files (as of 2.6.30-rc7)
206	..............................................................................
207	 Field                       Content
208	 Name                        filename of the executable
209	 State                       state (R is running, S is sleeping, D is sleeping
210	                             in an uninterruptible wait, Z is zombie,
211				     T is traced or stopped)
212	 Tgid                        thread group ID
213	 Pid                         process id
214	 PPid                        process id of the parent process
215	 TracerPid                   PID of process tracing this process (0 if not)
216	 Uid                         Real, effective, saved set, and  file system UIDs
217	 Gid                         Real, effective, saved set, and  file system GIDs
218	 FDSize                      number of file descriptor slots currently allocated
219	 Groups                      supplementary group list
220	 VmPeak                      peak virtual memory size
221	 VmSize                      total program size
222	 VmLck                       locked memory size
223	 VmHWM                       peak resident set size ("high water mark")
224	 VmRSS                       size of memory portions
225	 VmData                      size of data, stack, and text segments
226	 VmStk                       size of data, stack, and text segments
227	 VmExe                       size of text segment
228	 VmLib                       size of shared library code
229	 VmPTE                       size of page table entries
230	 VmSwap                      size of swap usage (the number of referred swapents)
231	 Threads                     number of threads
232	 SigQ                        number of signals queued/max. number for queue
233	 SigPnd                      bitmap of pending signals for the thread
234	 ShdPnd                      bitmap of shared pending signals for the process
235	 SigBlk                      bitmap of blocked signals
236	 SigIgn                      bitmap of ignored signals
237	 SigCgt                      bitmap of catched signals
238	 CapInh                      bitmap of inheritable capabilities
239	 CapPrm                      bitmap of permitted capabilities
240	 CapEff                      bitmap of effective capabilities
241	 CapBnd                      bitmap of capabilities bounding set
242	 Seccomp                     seccomp mode, like prctl(PR_GET_SECCOMP, ...)
243	 Cpus_allowed                mask of CPUs on which this process may run
244	 Cpus_allowed_list           Same as previous, but in "list format"
245	 Mems_allowed                mask of memory nodes allowed to this process
246	 Mems_allowed_list           Same as previous, but in "list format"
247	 voluntary_ctxt_switches     number of voluntary context switches
248	 nonvoluntary_ctxt_switches  number of non voluntary context switches
249	..............................................................................
250	
251	Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
252	..............................................................................
253	 Field    Content
254	 size     total program size (pages)		(same as VmSize in status)
255	 resident size of memory portions (pages)	(same as VmRSS in status)
256	 shared   number of pages that are shared	(i.e. backed by a file)
257	 trs      number of pages that are 'code'	(not including libs; broken,
258								includes data segment)
259	 lrs      number of pages of library		(always 0 on 2.6)
260	 drs      number of pages of data/stack		(including libs; broken,
261								includes library text)
262	 dt       number of dirty pages			(always 0 on 2.6)
263	..............................................................................
264	
265	
266	Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
267	..............................................................................
268	 Field          Content
269	  pid           process id
270	  tcomm         filename of the executable
271	  state         state (R is running, S is sleeping, D is sleeping in an
272	                uninterruptible wait, Z is zombie, T is traced or stopped)
273	  ppid          process id of the parent process
274	  pgrp          pgrp of the process
275	  sid           session id
276	  tty_nr        tty the process uses
277	  tty_pgrp      pgrp of the tty
278	  flags         task flags
279	  min_flt       number of minor faults
280	  cmin_flt      number of minor faults with child's
281	  maj_flt       number of major faults
282	  cmaj_flt      number of major faults with child's
283	  utime         user mode jiffies
284	  stime         kernel mode jiffies
285	  cutime        user mode jiffies with child's
286	  cstime        kernel mode jiffies with child's
287	  priority      priority level
288	  nice          nice level
289	  num_threads   number of threads
290	  it_real_value	(obsolete, always 0)
291	  start_time    time the process started after system boot
292	  vsize         virtual memory size
293	  rss           resident set memory size
294	  rsslim        current limit in bytes on the rss
295	  start_code    address above which program text can run
296	  end_code      address below which program text can run
297	  start_stack   address of the start of the main process stack
298	  esp           current value of ESP
299	  eip           current value of EIP
300	  pending       bitmap of pending signals
301	  blocked       bitmap of blocked signals
302	  sigign        bitmap of ignored signals
303	  sigcatch      bitmap of catched signals
304	  wchan         address where process went to sleep
305	  0             (place holder)
306	  0             (place holder)
307	  exit_signal   signal to send to parent thread on exit
308	  task_cpu      which CPU the task is scheduled on
309	  rt_priority   realtime priority
310	  policy        scheduling policy (man sched_setscheduler)
311	  blkio_ticks   time spent waiting for block IO
312	  gtime         guest time of the task in jiffies
313	  cgtime        guest time of the task children in jiffies
314	  start_data    address above which program data+bss is placed
315	  end_data      address below which program data+bss is placed
316	  start_brk     address above which program heap can be expanded with brk()
317	  arg_start     address above which program command line is placed
318	  arg_end       address below which program command line is placed
319	  env_start     address above which program environment is placed
320	  env_end       address below which program environment is placed
321	  exit_code     the thread's exit_code in the form reported by the waitpid system call
322	..............................................................................
323	
324	The /proc/PID/maps file containing the currently mapped memory regions and
325	their access permissions.
326	
327	The format is:
328	
329	address           perms offset  dev   inode      pathname
330	
331	08048000-08049000 r-xp 00000000 03:00 8312       /opt/test
332	08049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
333	0804a000-0806b000 rw-p 00000000 00:00 0          [heap]
334	a7cb1000-a7cb2000 ---p 00000000 00:00 0
335	a7cb2000-a7eb2000 rw-p 00000000 00:00 0
336	a7eb2000-a7eb3000 ---p 00000000 00:00 0
337	a7eb3000-a7ed5000 rw-p 00000000 00:00 0          [stack:1001]
338	a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/libc.so.6
339	a8008000-a800a000 r--p 00133000 03:00 4222       /lib/libc.so.6
340	a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/libc.so.6
341	a800b000-a800e000 rw-p 00000000 00:00 0
342	a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/libpthread.so.0
343	a8022000-a8023000 r--p 00013000 03:00 14462      /lib/libpthread.so.0
344	a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/libpthread.so.0
345	a8024000-a8027000 rw-p 00000000 00:00 0
346	a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/ld-linux.so.2
347	a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/ld-linux.so.2
348	a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/ld-linux.so.2
349	aff35000-aff4a000 rw-p 00000000 00:00 0          [stack]
350	ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
351	
352	where "address" is the address space in the process that it occupies, "perms"
353	is a set of permissions:
354	
355	 r = read
356	 w = write
357	 x = execute
358	 s = shared
359	 p = private (copy on write)
360	
361	"offset" is the offset into the mapping, "dev" is the device (major:minor), and
362	"inode" is the inode  on that device.  0 indicates that  no inode is associated
363	with the memory region, as the case would be with BSS (uninitialized data).
364	The "pathname" shows the name associated file for this mapping.  If the mapping
365	is not associated with a file:
366	
367	 [heap]                   = the heap of the program
368	 [stack]                  = the stack of the main process
369	 [stack:1001]             = the stack of the thread with tid 1001
370	 [vdso]                   = the "virtual dynamic shared object",
371	                            the kernel system call handler
372	
373	 or if empty, the mapping is anonymous.
374	
375	The /proc/PID/task/TID/maps is a view of the virtual memory from the viewpoint
376	of the individual tasks of a process. In this file you will see a mapping marked
377	as [stack] if that task sees it as a stack. This is a key difference from the
378	content of /proc/PID/maps, where you will see all mappings that are being used
379	as stack by all of those tasks. Hence, for the example above, the task-level
380	map, i.e. /proc/PID/task/TID/maps for thread 1001 will look like this:
381	
382	08048000-08049000 r-xp 00000000 03:00 8312       /opt/test
383	08049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
384	0804a000-0806b000 rw-p 00000000 00:00 0          [heap]
385	a7cb1000-a7cb2000 ---p 00000000 00:00 0
386	a7cb2000-a7eb2000 rw-p 00000000 00:00 0
387	a7eb2000-a7eb3000 ---p 00000000 00:00 0
388	a7eb3000-a7ed5000 rw-p 00000000 00:00 0          [stack]
389	a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/libc.so.6
390	a8008000-a800a000 r--p 00133000 03:00 4222       /lib/libc.so.6
391	a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/libc.so.6
392	a800b000-a800e000 rw-p 00000000 00:00 0
393	a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/libpthread.so.0
394	a8022000-a8023000 r--p 00013000 03:00 14462      /lib/libpthread.so.0
395	a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/libpthread.so.0
396	a8024000-a8027000 rw-p 00000000 00:00 0
397	a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/ld-linux.so.2
398	a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/ld-linux.so.2
399	a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/ld-linux.so.2
400	aff35000-aff4a000 rw-p 00000000 00:00 0
401	ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
402	
403	The /proc/PID/smaps is an extension based on maps, showing the memory
404	consumption for each of the process's mappings. For each of mappings there
405	is a series of lines such as the following:
406	
407	08048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
408	Size:               1084 kB
409	Rss:                 892 kB
410	Pss:                 374 kB
411	Shared_Clean:        892 kB
412	Shared_Dirty:          0 kB
413	Private_Clean:         0 kB
414	Private_Dirty:         0 kB
415	Referenced:          892 kB
416	Anonymous:             0 kB
417	Swap:                  0 kB
418	KernelPageSize:        4 kB
419	MMUPageSize:           4 kB
420	Locked:              374 kB
421	VmFlags: rd ex mr mw me de
422	
423	the first of these lines shows the same information as is displayed for the
424	mapping in /proc/PID/maps.  The remaining lines show the size of the mapping
425	(size), the amount of the mapping that is currently resident in RAM (RSS), the
426	process' proportional share of this mapping (PSS), the number of clean and
427	dirty private pages in the mapping.  Note that even a page which is part of a
428	MAP_SHARED mapping, but has only a single pte mapped, i.e.  is currently used
429	by only one process, is accounted as private and not as shared.  "Referenced"
430	indicates the amount of memory currently marked as referenced or accessed.
431	"Anonymous" shows the amount of memory that does not belong to any file.  Even
432	a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
433	and a page is modified, the file page is replaced by a private anonymous copy.
434	"Swap" shows how much would-be-anonymous memory is also used, but out on
435	swap.
436	
437	"VmFlags" field deserves a separate description. This member represents the kernel
438	flags associated with the particular virtual memory area in two letter encoded
439	manner. The codes are the following:
440	    rd  - readable
441	    wr  - writeable
442	    ex  - executable
443	    sh  - shared
444	    mr  - may read
445	    mw  - may write
446	    me  - may execute
447	    ms  - may share
448	    gd  - stack segment growns down
449	    pf  - pure PFN range
450	    dw  - disabled write to the mapped file
451	    lo  - pages are locked in memory
452	    io  - memory mapped I/O area
453	    sr  - sequential read advise provided
454	    rr  - random read advise provided
455	    dc  - do not copy area on fork
456	    de  - do not expand area on remapping
457	    ac  - area is accountable
458	    nr  - swap space is not reserved for the area
459	    ht  - area uses huge tlb pages
460	    nl  - non-linear mapping
461	    ar  - architecture specific flag
462	    dd  - do not include area into core dump
463	    sd  - soft-dirty flag
464	    mm  - mixed map area
465	    hg  - huge page advise flag
466	    nh  - no-huge page advise flag
467	    mg  - mergable advise flag
468	
469	Note that there is no guarantee that every flag and associated mnemonic will
470	be present in all further kernel releases. Things get changed, the flags may
471	be vanished or the reverse -- new added.
472	
473	This file is only present if the CONFIG_MMU kernel configuration option is
474	enabled.
475	
476	The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
477	bits on both physical and virtual pages associated with a process, and the
478	soft-dirty bit on pte (see Documentation/vm/soft-dirty.txt for details).
479	To clear the bits for all the pages associated with the process
480	    > echo 1 > /proc/PID/clear_refs
481	
482	To clear the bits for the anonymous pages associated with the process
483	    > echo 2 > /proc/PID/clear_refs
484	
485	To clear the bits for the file mapped pages associated with the process
486	    > echo 3 > /proc/PID/clear_refs
487	
488	To clear the soft-dirty bit
489	    > echo 4 > /proc/PID/clear_refs
490	
491	Any other value written to /proc/PID/clear_refs will have no effect.
492	
493	The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
494	using /proc/kpageflags and number of times a page is mapped using
495	/proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt.
496	
497	1.2 Kernel data
498	---------------
499	
500	Similar to  the  process entries, the kernel data files give information about
501	the running kernel. The files used to obtain this information are contained in
502	/proc and  are  listed  in Table 1-5. Not all of these will be present in your
503	system. It  depends  on the kernel configuration and the loaded modules, which
504	files are there, and which are missing.
505	
506	Table 1-5: Kernel info in /proc
507	..............................................................................
508	 File        Content                                           
509	 apm         Advanced power management info                    
510	 buddyinfo   Kernel memory allocator information (see text)	(2.5)
511	 bus         Directory containing bus specific information     
512	 cmdline     Kernel command line                               
513	 cpuinfo     Info about the CPU                                
514	 devices     Available devices (block and character)           
515	 dma         Used DMS channels                                 
516	 filesystems Supported filesystems                             
517	 driver	     Various drivers grouped here, currently rtc (2.4)
518	 execdomains Execdomains, related to security			(2.4)
519	 fb	     Frame Buffer devices				(2.4)
520	 fs	     File system parameters, currently nfs/exports	(2.4)
521	 ide         Directory containing info about the IDE subsystem 
522	 interrupts  Interrupt usage                                   
523	 iomem	     Memory map						(2.4)
524	 ioports     I/O port usage                                    
525	 irq	     Masks for irq to cpu affinity			(2.4)(smp?)
526	 isapnp	     ISA PnP (Plug&Play) Info				(2.4)
527	 kcore       Kernel core image (can be ELF or A.OUT(deprecated in 2.4))   
528	 kmsg        Kernel messages                                   
529	 ksyms       Kernel symbol table                               
530	 loadavg     Load average of last 1, 5 & 15 minutes                
531	 locks       Kernel locks                                      
532	 meminfo     Memory info                                       
533	 misc        Miscellaneous                                     
534	 modules     List of loaded modules                            
535	 mounts      Mounted filesystems                               
536	 net         Networking info (see text)                        
537	 pagetypeinfo Additional page allocator information (see text)  (2.5)
538	 partitions  Table of partitions known to the system           
539	 pci	     Deprecated info of PCI bus (new way -> /proc/bus/pci/,
540	             decoupled by lspci					(2.4)
541	 rtc         Real time clock                                   
542	 scsi        SCSI info (see text)                              
543	 slabinfo    Slab pool info                                    
544	 softirqs    softirq usage
545	 stat        Overall statistics                                
546	 swaps       Swap space utilization                            
547	 sys         See chapter 2                                     
548	 sysvipc     Info of SysVIPC Resources (msg, sem, shm)		(2.4)
549	 tty	     Info of tty drivers
550	 uptime      System uptime                                     
551	 version     Kernel version                                    
552	 video	     bttv info of video resources			(2.4)
553	 vmallocinfo Show vmalloced areas
554	..............................................................................
555	
556	You can,  for  example,  check  which interrupts are currently in use and what
557	they are used for by looking in the file /proc/interrupts:
558	
559	  > cat /proc/interrupts 
560	             CPU0        
561	    0:    8728810          XT-PIC  timer 
562	    1:        895          XT-PIC  keyboard 
563	    2:          0          XT-PIC  cascade 
564	    3:     531695          XT-PIC  aha152x 
565	    4:    2014133          XT-PIC  serial 
566	    5:      44401          XT-PIC  pcnet_cs 
567	    8:          2          XT-PIC  rtc 
568	   11:          8          XT-PIC  i82365 
569	   12:     182918          XT-PIC  PS/2 Mouse 
570	   13:          1          XT-PIC  fpu 
571	   14:    1232265          XT-PIC  ide0 
572	   15:          7          XT-PIC  ide1 
573	  NMI:          0 
574	
575	In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
576	output of a SMP machine):
577	
578	  > cat /proc/interrupts 
579	
580	             CPU0       CPU1       
581	    0:    1243498    1214548    IO-APIC-edge  timer
582	    1:       8949       8958    IO-APIC-edge  keyboard
583	    2:          0          0          XT-PIC  cascade
584	    5:      11286      10161    IO-APIC-edge  soundblaster
585	    8:          1          0    IO-APIC-edge  rtc
586	    9:      27422      27407    IO-APIC-edge  3c503
587	   12:     113645     113873    IO-APIC-edge  PS/2 Mouse
588	   13:          0          0          XT-PIC  fpu
589	   14:      22491      24012    IO-APIC-edge  ide0
590	   15:       2183       2415    IO-APIC-edge  ide1
591	   17:      30564      30414   IO-APIC-level  eth0
592	   18:        177        164   IO-APIC-level  bttv
593	  NMI:    2457961    2457959 
594	  LOC:    2457882    2457881 
595	  ERR:       2155
596	
597	NMI is incremented in this case because every timer interrupt generates a NMI
598	(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
599	
600	LOC is the local interrupt counter of the internal APIC of every CPU.
601	
602	ERR is incremented in the case of errors in the IO-APIC bus (the bus that
603	connects the CPUs in a SMP system. This means that an error has been detected,
604	the IO-APIC automatically retry the transmission, so it should not be a big
605	problem, but you should read the SMP-FAQ.
606	
607	In 2.6.2* /proc/interrupts was expanded again.  This time the goal was for
608	/proc/interrupts to display every IRQ vector in use by the system, not
609	just those considered 'most important'.  The new vectors are:
610	
611	  THR -- interrupt raised when a machine check threshold counter
612	  (typically counting ECC corrected errors of memory or cache) exceeds
613	  a configurable threshold.  Only available on some systems.
614	
615	  TRM -- a thermal event interrupt occurs when a temperature threshold
616	  has been exceeded for the CPU.  This interrupt may also be generated
617	  when the temperature drops back to normal.
618	
619	  SPU -- a spurious interrupt is some interrupt that was raised then lowered
620	  by some IO device before it could be fully processed by the APIC.  Hence
621	  the APIC sees the interrupt but does not know what device it came from.
622	  For this case the APIC will generate the interrupt with a IRQ vector
623	  of 0xff. This might also be generated by chipset bugs.
624	
625	  RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
626	  sent from one CPU to another per the needs of the OS.  Typically,
627	  their statistics are used by kernel developers and interested users to
628	  determine the occurrence of interrupts of the given type.
629	
630	The above IRQ vectors are displayed only when relevant.  For example,
631	the threshold vector does not exist on x86_64 platforms.  Others are
632	suppressed when the system is a uniprocessor.  As of this writing, only
633	i386 and x86_64 platforms support the new IRQ vector displays.
634	
635	Of some interest is the introduction of the /proc/irq directory to 2.4.
636	It could be used to set IRQ to CPU affinity, this means that you can "hook" an
637	IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
638	irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
639	prof_cpu_mask.
640	
641	For example 
642	  > ls /proc/irq/
643	  0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
644	  1  11  13  15  17  19  3  5  7  9  default_smp_affinity
645	  > ls /proc/irq/0/
646	  smp_affinity
647	
648	smp_affinity is a bitmask, in which you can specify which CPUs can handle the
649	IRQ, you can set it by doing:
650	
651	  > echo 1 > /proc/irq/10/smp_affinity
652	
653	This means that only the first CPU will handle the IRQ, but you can also echo
654	5 which means that only the first and fourth CPU can handle the IRQ.
655	
656	The contents of each smp_affinity file is the same by default:
657	
658	  > cat /proc/irq/0/smp_affinity
659	  ffffffff
660	
661	There is an alternate interface, smp_affinity_list which allows specifying
662	a cpu range instead of a bitmask:
663	
664	  > cat /proc/irq/0/smp_affinity_list
665	  1024-1031
666	
667	The default_smp_affinity mask applies to all non-active IRQs, which are the
668	IRQs which have not yet been allocated/activated, and hence which lack a
669	/proc/irq/[0-9]* directory.
670	
671	The node file on an SMP system shows the node to which the device using the IRQ
672	reports itself as being attached. This hardware locality information does not
673	include information about any possible driver locality preference.
674	
675	prof_cpu_mask specifies which CPUs are to be profiled by the system wide
676	profiler. Default value is ffffffff (all cpus if there are only 32 of them).
677	
678	The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
679	between all the CPUs which are allowed to handle it. As usual the kernel has
680	more info than you and does a better job than you, so the defaults are the
681	best choice for almost everyone.  [Note this applies only to those IO-APIC's
682	that support "Round Robin" interrupt distribution.]
683	
684	There are  three  more  important subdirectories in /proc: net, scsi, and sys.
685	The general  rule  is  that  the  contents,  or  even  the  existence of these
686	directories, depend  on your kernel configuration. If SCSI is not enabled, the
687	directory scsi  may  not  exist. The same is true with the net, which is there
688	only when networking support is present in the running kernel.
689	
690	The slabinfo  file  gives  information  about  memory usage at the slab level.
691	Linux uses  slab  pools for memory management above page level in version 2.2.
692	Commonly used  objects  have  their  own  slab  pool (such as network buffers,
693	directory cache, and so on).
694	
695	..............................................................................
696	
697	> cat /proc/buddyinfo
698	
699	Node 0, zone      DMA      0      4      5      4      4      3 ...
700	Node 0, zone   Normal      1      0      0      1    101      8 ...
701	Node 0, zone  HighMem      2      0      0      1      1      0 ...
702	
703	External fragmentation is a problem under some workloads, and buddyinfo is a
704	useful tool for helping diagnose these problems.  Buddyinfo will give you a 
705	clue as to how big an area you can safely allocate, or why a previous
706	allocation failed.
707	
708	Each column represents the number of pages of a certain order which are 
709	available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in 
710	ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE 
711	available in ZONE_NORMAL, etc... 
712	
713	More information relevant to external fragmentation can be found in
714	pagetypeinfo.
715	
716	> cat /proc/pagetypeinfo
717	Page block order: 9
718	Pages per block:  512
719	
720	Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
721	Node    0, zone      DMA, type    Unmovable      0      0      0      1      1      1      1      1      1      1      0
722	Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0
723	Node    0, zone      DMA, type      Movable      1      1      2      1      2      1      1      0      1      0      2
724	Node    0, zone      DMA, type      Reserve      0      0      0      0      0      0      0      0      0      1      0
725	Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
726	Node    0, zone    DMA32, type    Unmovable    103     54     77      1      1      1     11      8      7      1      9
727	Node    0, zone    DMA32, type  Reclaimable      0      0      2      1      0      0      0      0      1      0      0
728	Node    0, zone    DMA32, type      Movable    169    152    113     91     77     54     39     13      6      1    452
729	Node    0, zone    DMA32, type      Reserve      1      2      2      2      2      0      1      1      1      1      0
730	Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
731	
732	Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate
733	Node 0, zone      DMA            2            0            5            1            0
734	Node 0, zone    DMA32           41            6          967            2            0
735	
736	Fragmentation avoidance in the kernel works by grouping pages of different
737	migrate types into the same contiguous regions of memory called page blocks.
738	A page block is typically the size of the default hugepage size e.g. 2MB on
739	X86-64. By keeping pages grouped based on their ability to move, the kernel
740	can reclaim pages within a page block to satisfy a high-order allocation.
741	
742	The pagetypinfo begins with information on the size of a page block. It
743	then gives the same type of information as buddyinfo except broken down
744	by migrate-type and finishes with details on how many page blocks of each
745	type exist.
746	
747	If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
748	from libhugetlbfs http://sourceforge.net/projects/libhugetlbfs/), one can
749	make an estimate of the likely number of huge pages that can be allocated
750	at a given point in time. All the "Movable" blocks should be allocatable
751	unless memory has been mlock()'d. Some of the Reclaimable blocks should
752	also be allocatable although a lot of filesystem metadata may have to be
753	reclaimed to achieve this.
754	
755	..............................................................................
756	
757	meminfo:
758	
759	Provides information about distribution and utilization of memory.  This
760	varies by architecture and compile options.  The following is from a
761	16GB PIII, which has highmem enabled.  You may not have all of these fields.
762	
763	> cat /proc/meminfo
764	
765	The "Locked" indicates whether the mapping is locked in memory or not.
766	
767	
768	MemTotal:     16344972 kB
769	MemFree:      13634064 kB
770	Buffers:          3656 kB
771	Cached:        1195708 kB
772	SwapCached:          0 kB
773	Active:         891636 kB
774	Inactive:      1077224 kB
775	HighTotal:    15597528 kB
776	HighFree:     13629632 kB
777	LowTotal:       747444 kB
778	LowFree:          4432 kB
779	SwapTotal:           0 kB
780	SwapFree:            0 kB
781	Dirty:             968 kB
782	Writeback:           0 kB
783	AnonPages:      861800 kB
784	Mapped:         280372 kB
785	Slab:           284364 kB
786	SReclaimable:   159856 kB
787	SUnreclaim:     124508 kB
788	PageTables:      24448 kB
789	NFS_Unstable:        0 kB
790	Bounce:              0 kB
791	WritebackTmp:        0 kB
792	CommitLimit:   7669796 kB
793	Committed_AS:   100056 kB
794	VmallocTotal:   112216 kB
795	VmallocUsed:       428 kB
796	VmallocChunk:   111088 kB
797	AnonHugePages:   49152 kB
798	
799	    MemTotal: Total usable ram (i.e. physical ram minus a few reserved
800	              bits and the kernel binary code)
801	     MemFree: The sum of LowFree+HighFree
802	     Buffers: Relatively temporary storage for raw disk blocks
803	              shouldn't get tremendously large (20MB or so)
804	      Cached: in-memory cache for files read from the disk (the
805	              pagecache).  Doesn't include SwapCached
806	  SwapCached: Memory that once was swapped out, is swapped back in but
807	              still also is in the swapfile (if memory is needed it
808	              doesn't need to be swapped out AGAIN because it is already
809	              in the swapfile. This saves I/O)
810	      Active: Memory that has been used more recently and usually not
811	              reclaimed unless absolutely necessary.
812	    Inactive: Memory which has been less recently used.  It is more
813	              eligible to be reclaimed for other purposes
814	   HighTotal:
815	    HighFree: Highmem is all memory above ~860MB of physical memory
816	              Highmem areas are for use by userspace programs, or
817	              for the pagecache.  The kernel must use tricks to access
818	              this memory, making it slower to access than lowmem.
819	    LowTotal:
820	     LowFree: Lowmem is memory which can be used for everything that
821	              highmem can be used for, but it is also available for the
822	              kernel's use for its own data structures.  Among many
823	              other things, it is where everything from the Slab is
824	              allocated.  Bad things happen when you're out of lowmem.
825	   SwapTotal: total amount of swap space available
826	    SwapFree: Memory which has been evicted from RAM, and is temporarily
827	              on the disk
828	       Dirty: Memory which is waiting to get written back to the disk
829	   Writeback: Memory which is actively being written back to the disk
830	   AnonPages: Non-file backed pages mapped into userspace page tables
831	AnonHugePages: Non-file backed huge pages mapped into userspace page tables
832	      Mapped: files which have been mmaped, such as libraries
833	        Slab: in-kernel data structures cache
834	SReclaimable: Part of Slab, that might be reclaimed, such as caches
835	  SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
836	  PageTables: amount of memory dedicated to the lowest level of page
837	              tables.
838	NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
839		      storage
840	      Bounce: Memory used for block device "bounce buffers"
841	WritebackTmp: Memory used by FUSE for temporary writeback buffers
842	 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
843	              this is the total amount of  memory currently available to
844	              be allocated on the system. This limit is only adhered to
845	              if strict overcommit accounting is enabled (mode 2 in
846	              'vm.overcommit_memory').
847	              The CommitLimit is calculated with the following formula:
848	              CommitLimit = ('vm.overcommit_ratio' * Physical RAM) + Swap
849	              For example, on a system with 1G of physical RAM and 7G
850	              of swap with a `vm.overcommit_ratio` of 30 it would
851	              yield a CommitLimit of 7.3G.
852	              For more details, see the memory overcommit documentation
853	              in vm/overcommit-accounting.
854	Committed_AS: The amount of memory presently allocated on the system.
855	              The committed memory is a sum of all of the memory which
856	              has been allocated by processes, even if it has not been
857	              "used" by them as of yet. A process which malloc()'s 1G
858	              of memory, but only touches 300M of it will show up as
859		      using 1G. This 1G is memory which has been "committed" to
860	              by the VM and can be used at any time by the allocating
861	              application. With strict overcommit enabled on the system
862	              (mode 2 in 'vm.overcommit_memory'),allocations which would
863	              exceed the CommitLimit (detailed above) will not be permitted.
864	              This is useful if one needs to guarantee that processes will
865	              not fail due to lack of memory once that memory has been
866	              successfully allocated.
867	VmallocTotal: total size of vmalloc memory area
868	 VmallocUsed: amount of vmalloc area which is used
869	VmallocChunk: largest contiguous block of vmalloc area which is free
870	
871	..............................................................................
872	
873	vmallocinfo:
874	
875	Provides information about vmalloced/vmaped areas. One line per area,
876	containing the virtual address range of the area, size in bytes,
877	caller information of the creator, and optional information depending
878	on the kind of area :
879	
880	 pages=nr    number of pages
881	 phys=addr   if a physical address was specified
882	 ioremap     I/O mapping (ioremap() and friends)
883	 vmalloc     vmalloc() area
884	 vmap        vmap()ed pages
885	 user        VM_USERMAP area
886	 vpages      buffer for pages pointers was vmalloced (huge area)
887	 N<node>=nr  (Only on NUMA kernels)
888	             Number of pages allocated on memory node <node>
889	
890	> cat /proc/vmallocinfo
891	0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
892	  /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
893	0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
894	  /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
895	0xffffc20000302000-0xffffc20000304000    8192 acpi_tb_verify_table+0x21/0x4f...
896	  phys=7fee8000 ioremap
897	0xffffc20000304000-0xffffc20000307000   12288 acpi_tb_verify_table+0x21/0x4f...
898	  phys=7fee7000 ioremap
899	0xffffc2000031d000-0xffffc2000031f000    8192 init_vdso_vars+0x112/0x210
900	0xffffc2000031f000-0xffffc2000032b000   49152 cramfs_uncompress_init+0x2e ...
901	  /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
902	0xffffc2000033a000-0xffffc2000033d000   12288 sys_swapon+0x640/0xac0      ...
903	  pages=2 vmalloc N1=2
904	0xffffc20000347000-0xffffc2000034c000   20480 xt_alloc_table_info+0xfe ...
905	  /0x130 [x_tables] pages=4 vmalloc N0=4
906	0xffffffffa0000000-0xffffffffa000f000   61440 sys_init_module+0xc27/0x1d00 ...
907	   pages=14 vmalloc N2=14
908	0xffffffffa000f000-0xffffffffa0014000   20480 sys_init_module+0xc27/0x1d00 ...
909	   pages=4 vmalloc N1=4
910	0xffffffffa0014000-0xffffffffa0017000   12288 sys_init_module+0xc27/0x1d00 ...
911	   pages=2 vmalloc N1=2
912	0xffffffffa0017000-0xffffffffa0022000   45056 sys_init_module+0xc27/0x1d00 ...
913	   pages=10 vmalloc N0=10
914	
915	..............................................................................
916	
917	softirqs:
918	
919	Provides counts of softirq handlers serviced since boot time, for each cpu.
920	
921	> cat /proc/softirqs
922	                CPU0       CPU1       CPU2       CPU3
923	      HI:          0          0          0          0
924	   TIMER:      27166      27120      27097      27034
925	  NET_TX:          0          0          0         17
926	  NET_RX:         42          0          0         39
927	   BLOCK:          0          0        107       1121
928	 TASKLET:          0          0          0        290
929	   SCHED:      27035      26983      26971      26746
930	 HRTIMER:          0          0          0          0
931	     RCU:       1678       1769       2178       2250
932	
933	
934	1.3 IDE devices in /proc/ide
935	----------------------------
936	
937	The subdirectory /proc/ide contains information about all IDE devices of which
938	the kernel  is  aware.  There is one subdirectory for each IDE controller, the
939	file drivers  and a link for each IDE device, pointing to the device directory
940	in the controller specific subtree.
941	
942	The file  drivers  contains general information about the drivers used for the
943	IDE devices:
944	
945	  > cat /proc/ide/drivers
946	  ide-cdrom version 4.53
947	  ide-disk version 1.08
948	
949	More detailed  information  can  be  found  in  the  controller  specific
950	subdirectories. These  are  named  ide0,  ide1  and  so  on.  Each  of  these
951	directories contains the files shown in table 1-6.
952	
953	
954	Table 1-6: IDE controller info in  /proc/ide/ide?
955	..............................................................................
956	 File    Content                                 
957	 channel IDE channel (0 or 1)                    
958	 config  Configuration (only for PCI/IDE bridge) 
959	 mate    Mate name                               
960	 model   Type/Chipset of IDE controller          
961	..............................................................................
962	
963	Each device  connected  to  a  controller  has  a separate subdirectory in the
964	controllers directory.  The  files  listed in table 1-7 are contained in these
965	directories.
966	
967	
968	Table 1-7: IDE device information
969	..............................................................................
970	 File             Content                                    
971	 cache            The cache                                  
972	 capacity         Capacity of the medium (in 512Byte blocks) 
973	 driver           driver and version                         
974	 geometry         physical and logical geometry              
975	 identify         device identify block                      
976	 media            media type                                 
977	 model            device identifier                          
978	 settings         device setup                               
979	 smart_thresholds IDE disk management thresholds             
980	 smart_values     IDE disk management values                 
981	..............................................................................
982	
983	The most  interesting  file is settings. This file contains a nice overview of
984	the drive parameters:
985	
986	  # cat /proc/ide/ide0/hda/settings 
987	  name                    value           min             max             mode 
988	  ----                    -----           ---             ---             ---- 
989	  bios_cyl                526             0               65535           rw 
990	  bios_head               255             0               255             rw 
991	  bios_sect               63              0               63              rw 
992	  breada_readahead        4               0               127             rw 
993	  bswap                   0               0               1               r 
994	  file_readahead          72              0               2097151         rw 
995	  io_32bit                0               0               3               rw 
996	  keepsettings            0               0               1               rw 
997	  max_kb_per_request      122             1               127             rw 
998	  multcount               0               0               8               rw 
999	  nice1                   1               0               1               rw 
1000	  nowerr                  0               0               1               rw 
1001	  pio_mode                write-only      0               255             w 
1002	  slow                    0               0               1               rw 
1003	  unmaskirq               0               0               1               rw 
1004	  using_dma               0               0               1               rw 
1005	
1006	
1007	1.4 Networking info in /proc/net
1008	--------------------------------
1009	
1010	The subdirectory  /proc/net  follows  the  usual  pattern. Table 1-8 shows the
1011	additional values  you  get  for  IP  version 6 if you configure the kernel to
1012	support this. Table 1-9 lists the files and their meaning.
1013	
1014	
1015	Table 1-8: IPv6 info in /proc/net
1016	..............................................................................
1017	 File       Content                                               
1018	 udp6       UDP sockets (IPv6)                                    
1019	 tcp6       TCP sockets (IPv6)                                    
1020	 raw6       Raw device statistics (IPv6)                          
1021	 igmp6      IP multicast addresses, which this host joined (IPv6) 
1022	 if_inet6   List of IPv6 interface addresses                      
1023	 ipv6_route Kernel routing table for IPv6                         
1024	 rt6_stats  Global IPv6 routing tables statistics                 
1025	 sockstat6  Socket statistics (IPv6)                              
1026	 snmp6      Snmp data (IPv6)                                      
1027	..............................................................................
1028	
1029	
1030	Table 1-9: Network info in /proc/net
1031	..............................................................................
1032	 File          Content                                                         
1033	 arp           Kernel  ARP table                                               
1034	 dev           network devices with statistics                                 
1035	 dev_mcast     the Layer2 multicast groups a device is listening too
1036	               (interface index, label, number of references, number of bound
1037	               addresses). 
1038	 dev_stat      network device status                                           
1039	 ip_fwchains   Firewall chain linkage                                          
1040	 ip_fwnames    Firewall chain names                                            
1041	 ip_masq       Directory containing the masquerading tables                    
1042	 ip_masquerade Major masquerading table                                        
1043	 netstat       Network statistics                                              
1044	 raw           raw device statistics                                           
1045	 route         Kernel routing table                                            
1046	 rpc           Directory containing rpc info                                   
1047	 rt_cache      Routing cache                                                   
1048	 snmp          SNMP data                                                       
1049	 sockstat      Socket statistics                                               
1050	 tcp           TCP  sockets                                                    
1051	 udp           UDP sockets                                                     
1052	 unix          UNIX domain sockets                                             
1053	 wireless      Wireless interface data (Wavelan etc)                           
1054	 igmp          IP multicast addresses, which this host joined                  
1055	 psched        Global packet scheduler parameters.                             
1056	 netlink       List of PF_NETLINK sockets                                      
1057	 ip_mr_vifs    List of multicast virtual interfaces                            
1058	 ip_mr_cache   List of multicast routing cache                                 
1059	..............................................................................
1060	
1061	You can  use  this  information  to see which network devices are available in
1062	your system and how much traffic was routed over those devices:
1063	
1064	  > cat /proc/net/dev 
1065	  Inter-|Receive                                                   |[... 
1066	   face |bytes    packets errs drop fifo frame compressed multicast|[... 
1067	      lo:  908188   5596     0    0    0     0          0         0 [...         
1068	    ppp0:15475140  20721   410    0    0   410          0         0 [...  
1069	    eth0:  614530   7085     0    0    0     0          0         1 [... 
1070	   
1071	  ...] Transmit 
1072	  ...] bytes    packets errs drop fifo colls carrier compressed 
1073	  ...]  908188     5596    0    0    0     0       0          0 
1074	  ...] 1375103    17405    0    0    0     0       0          0 
1075	  ...] 1703981     5535    0    0    0     3       0          0 
1076	
1077	In addition, each Channel Bond interface has its own directory.  For
1078	example, the bond0 device will have a directory called /proc/net/bond0/.
1079	It will contain information that is specific to that bond, such as the
1080	current slaves of the bond, the link status of the slaves, and how
1081	many times the slaves link has failed.
1082	
1083	1.5 SCSI info
1084	-------------
1085	
1086	If you  have  a  SCSI  host adapter in your system, you'll find a subdirectory
1087	named after  the driver for this adapter in /proc/scsi. You'll also see a list
1088	of all recognized SCSI devices in /proc/scsi:
1089	
1090	  >cat /proc/scsi/scsi 
1091	  Attached devices: 
1092	  Host: scsi0 Channel: 00 Id: 00 Lun: 00 
1093	    Vendor: IBM      Model: DGHS09U          Rev: 03E0 
1094	    Type:   Direct-Access                    ANSI SCSI revision: 03 
1095	  Host: scsi0 Channel: 00 Id: 06 Lun: 00 
1096	    Vendor: PIONEER  Model: CD-ROM DR-U06S   Rev: 1.04 
1097	    Type:   CD-ROM                           ANSI SCSI revision: 02 
1098	
1099	
1100	The directory  named  after  the driver has one file for each adapter found in
1101	the system.  These  files  contain information about the controller, including
1102	the used  IRQ  and  the  IO  address range. The amount of information shown is
1103	dependent on  the adapter you use. The example shows the output for an Adaptec
1104	AHA-2940 SCSI adapter:
1105	
1106	  > cat /proc/scsi/aic7xxx/0 
1107	   
1108	  Adaptec AIC7xxx driver version: 5.1.19/3.2.4 
1109	  Compile Options: 
1110	    TCQ Enabled By Default : Disabled 
1111	    AIC7XXX_PROC_STATS     : Disabled 
1112	    AIC7XXX_RESET_DELAY    : 5 
1113	  Adapter Configuration: 
1114	             SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter 
1115	                             Ultra Wide Controller 
1116	      PCI MMAPed I/O Base: 0xeb001000 
1117	   Adapter SEEPROM Config: SEEPROM found and used. 
1118	        Adaptec SCSI BIOS: Enabled 
1119	                      IRQ: 10 
1120	                     SCBs: Active 0, Max Active 2, 
1121	                           Allocated 15, HW 16, Page 255 
1122	               Interrupts: 160328 
1123	        BIOS Control Word: 0x18b6 
1124	     Adapter Control Word: 0x005b 
1125	     Extended Translation: Enabled 
1126	  Disconnect Enable Flags: 0xffff 
1127	       Ultra Enable Flags: 0x0001 
1128	   Tag Queue Enable Flags: 0x0000 
1129	  Ordered Queue Tag Flags: 0x0000 
1130	  Default Tag Queue Depth: 8 
1131	      Tagged Queue By Device array for aic7xxx host instance 0: 
1132	        {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} 
1133	      Actual queue depth per device for aic7xxx host instance 0: 
1134	        {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} 
1135	  Statistics: 
1136	  (scsi0:0:0:0) 
1137	    Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 
1138	    Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) 
1139	    Total transfers 160151 (74577 reads and 85574 writes) 
1140	  (scsi0:0:6:0) 
1141	    Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 
1142	    Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) 
1143	    Total transfers 0 (0 reads and 0 writes) 
1144	
1145	
1146	1.6 Parallel port info in /proc/parport
1147	---------------------------------------
1148	
1149	The directory  /proc/parport  contains information about the parallel ports of
1150	your system.  It  has  one  subdirectory  for  each port, named after the port
1151	number (0,1,2,...).
1152	
1153	These directories contain the four files shown in Table 1-10.
1154	
1155	
1156	Table 1-10: Files in /proc/parport
1157	..............................................................................
1158	 File      Content                                                             
1159	 autoprobe Any IEEE-1284 device ID information that has been acquired.         
1160	 devices   list of the device drivers using that port. A + will appear by the
1161	           name of the device currently using the port (it might not appear
1162	           against any). 
1163	 hardware  Parallel port's base address, IRQ line and DMA channel.             
1164	 irq       IRQ that parport is using for that port. This is in a separate
1165	           file to allow you to alter it by writing a new value in (IRQ
1166	           number or none). 
1167	..............................................................................
1168	
1169	1.7 TTY info in /proc/tty
1170	-------------------------
1171	
1172	Information about  the  available  and actually used tty's can be found in the
1173	directory /proc/tty.You'll  find  entries  for drivers and line disciplines in
1174	this directory, as shown in Table 1-11.
1175	
1176	
1177	Table 1-11: Files in /proc/tty
1178	..............................................................................
1179	 File          Content                                        
1180	 drivers       list of drivers and their usage                
1181	 ldiscs        registered line disciplines                    
1182	 driver/serial usage statistic and status of single tty lines 
1183	..............................................................................
1184	
1185	To see  which  tty's  are  currently in use, you can simply look into the file
1186	/proc/tty/drivers:
1187	
1188	  > cat /proc/tty/drivers 
1189	  pty_slave            /dev/pts      136   0-255 pty:slave 
1190	  pty_master           /dev/ptm      128   0-255 pty:master 
1191	  pty_slave            /dev/ttyp       3   0-255 pty:slave 
1192	  pty_master           /dev/pty        2   0-255 pty:master 
1193	  serial               /dev/cua        5   64-67 serial:callout 
1194	  serial               /dev/ttyS       4   64-67 serial 
1195	  /dev/tty0            /dev/tty0       4       0 system:vtmaster 
1196	  /dev/ptmx            /dev/ptmx       5       2 system 
1197	  /dev/console         /dev/console    5       1 system:console 
1198	  /dev/tty             /dev/tty        5       0 system:/dev/tty 
1199	  unknown              /dev/tty        4    1-63 console 
1200	
1201	
1202	1.8 Miscellaneous kernel statistics in /proc/stat
1203	-------------------------------------------------
1204	
1205	Various pieces   of  information about  kernel activity  are  available in the
1206	/proc/stat file.  All  of  the numbers reported  in  this file are  aggregates
1207	since the system first booted.  For a quick look, simply cat the file:
1208	
1209	  > cat /proc/stat
1210	  cpu  2255 34 2290 22625563 6290 127 456 0 0
1211	  cpu0 1132 34 1441 11311718 3675 127 438 0 0
1212	  cpu1 1123 0 849 11313845 2614 0 18 0 0
1213	  intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1214	  ctxt 1990473
1215	  btime 1062191376
1216	  processes 2915
1217	  procs_running 1
1218	  procs_blocked 0
1219	  softirq 183433 0 21755 12 39 1137 231 21459 2263
1220	
1221	The very first  "cpu" line aggregates the  numbers in all  of the other "cpuN"
1222	lines.  These numbers identify the amount of time the CPU has spent performing
1223	different kinds of work.  Time units are in USER_HZ (typically hundredths of a
1224	second).  The meanings of the columns are as follows, from left to right:
1225	
1226	- user: normal processes executing in user mode
1227	- nice: niced processes executing in user mode
1228	- system: processes executing in kernel mode
1229	- idle: twiddling thumbs
1230	- iowait: waiting for I/O to complete
1231	- irq: servicing interrupts
1232	- softirq: servicing softirqs
1233	- steal: involuntary wait
1234	- guest: running a normal guest
1235	- guest_nice: running a niced guest
1236	
1237	The "intr" line gives counts of interrupts  serviced since boot time, for each
1238	of the  possible system interrupts.   The first  column  is the  total of  all
1239	interrupts serviced; each  subsequent column is the  total for that particular
1240	interrupt.
1241	
1242	The "ctxt" line gives the total number of context switches across all CPUs.
1243	
1244	The "btime" line gives  the time at which the  system booted, in seconds since
1245	the Unix epoch.
1246	
1247	The "processes" line gives the number  of processes and threads created, which
1248	includes (but  is not limited  to) those  created by  calls to the  fork() and
1249	clone() system calls.
1250	
1251	The "procs_running" line gives the total number of threads that are
1252	running or ready to run (i.e., the total number of runnable threads).
1253	
1254	The   "procs_blocked" line gives  the  number of  processes currently blocked,
1255	waiting for I/O to complete.
1256	
1257	The "softirq" line gives counts of softirqs serviced since boot time, for each
1258	of the possible system softirqs. The first column is the total of all
1259	softirqs serviced; each subsequent column is the total for that particular
1260	softirq.
1261	
1262	
1263	1.9 Ext4 file system parameters
1264	------------------------------
1265	
1266	Information about mounted ext4 file systems can be found in
1267	/proc/fs/ext4.  Each mounted filesystem will have a directory in
1268	/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1269	/proc/fs/ext4/dm-0).   The files in each per-device directory are shown
1270	in Table 1-12, below.
1271	
1272	Table 1-12: Files in /proc/fs/ext4/<devname>
1273	..............................................................................
1274	 File            Content                                        
1275	 mb_groups       details of multiblock allocator buddy cache of free blocks
1276	..............................................................................
1277	
1278	2.0 /proc/consoles
1279	------------------
1280	Shows registered system console lines.
1281	
1282	To see which character device lines are currently used for the system console
1283	/dev/console, you may simply look into the file /proc/consoles:
1284	
1285	  > cat /proc/consoles
1286	  tty0                 -WU (ECp)       4:7
1287	  ttyS0                -W- (Ep)        4:64
1288	
1289	The columns are:
1290	
1291	  device               name of the device
1292	  operations           R = can do read operations
1293	                       W = can do write operations
1294	                       U = can do unblank
1295	  flags                E = it is enabled
1296	                       C = it is preferred console
1297	                       B = it is primary boot console
1298	                       p = it is used for printk buffer
1299	                       b = it is not a TTY but a Braille device
1300	                       a = it is safe to use when cpu is offline
1301	  major:minor          major and minor number of the device separated by a colon
1302	
1303	------------------------------------------------------------------------------
1304	Summary
1305	------------------------------------------------------------------------------
1306	The /proc file system serves information about the running system. It not only
1307	allows access to process data but also allows you to request the kernel status
1308	by reading files in the hierarchy.
1309	
1310	The directory  structure  of /proc reflects the types of information and makes
1311	it easy, if not obvious, where to look for specific data.
1312	------------------------------------------------------------------------------
1313	
1314	------------------------------------------------------------------------------
1315	CHAPTER 2: MODIFYING SYSTEM PARAMETERS
1316	------------------------------------------------------------------------------
1317	
1318	------------------------------------------------------------------------------
1319	In This Chapter
1320	------------------------------------------------------------------------------
1321	* Modifying kernel parameters by writing into files found in /proc/sys
1322	* Exploring the files which modify certain parameters
1323	* Review of the /proc/sys file tree
1324	------------------------------------------------------------------------------
1325	
1326	
1327	A very  interesting part of /proc is the directory /proc/sys. This is not only
1328	a source  of  information,  it also allows you to change parameters within the
1329	kernel. Be  very  careful  when attempting this. You can optimize your system,
1330	but you  can  also  cause  it  to  crash.  Never  alter kernel parameters on a
1331	production system.  Set  up  a  development machine and test to make sure that
1332	everything works  the  way  you want it to. You may have no alternative but to
1333	reboot the machine once an error has been made.
1334	
1335	To change  a  value,  simply  echo  the new value into the file. An example is
1336	given below  in the section on the file system data. You need to be root to do
1337	this. You  can  create  your  own  boot script to perform this every time your
1338	system boots.
1339	
1340	The files  in /proc/sys can be used to fine tune and monitor miscellaneous and
1341	general things  in  the operation of the Linux kernel. Since some of the files
1342	can inadvertently  disrupt  your  system,  it  is  advisable  to  read  both
1343	documentation and  source  before actually making adjustments. In any case, be
1344	very careful  when  writing  to  any  of these files. The entries in /proc may
1345	change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1346	review the kernel documentation in the directory /usr/src/linux/Documentation.
1347	This chapter  is  heavily  based  on the documentation included in the pre 2.2
1348	kernels, and became part of it in version 2.2.1 of the Linux kernel.
1349	
1350	Please see: Documentation/sysctl/ directory for descriptions of these
1351	entries.
1352	
1353	------------------------------------------------------------------------------
1354	Summary
1355	------------------------------------------------------------------------------
1356	Certain aspects  of  kernel  behavior  can be modified at runtime, without the
1357	need to  recompile  the kernel, or even to reboot the system. The files in the
1358	/proc/sys tree  can  not only be read, but also modified. You can use the echo
1359	command to write value into these files, thereby changing the default settings
1360	of the kernel.
1361	------------------------------------------------------------------------------
1362	
1363	------------------------------------------------------------------------------
1364	CHAPTER 3: PER-PROCESS PARAMETERS
1365	------------------------------------------------------------------------------
1366	
1367	3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1368	--------------------------------------------------------------------------------
1369	
1370	These file can be used to adjust the badness heuristic used to select which
1371	process gets killed in out of memory conditions.
1372	
1373	The badness heuristic assigns a value to each candidate task ranging from 0
1374	(never kill) to 1000 (always kill) to determine which process is targeted.  The
1375	units are roughly a proportion along that range of allowed memory the process
1376	may allocate from based on an estimation of its current memory and swap use.
1377	For example, if a task is using all allowed memory, its badness score will be
1378	1000.  If it is using half of its allowed memory, its score will be 500.
1379	
1380	There is an additional factor included in the badness score: root
1381	processes are given 3% extra memory over other tasks.
1382	
1383	The amount of "allowed" memory depends on the context in which the oom killer
1384	was called.  If it is due to the memory assigned to the allocating task's cpuset
1385	being exhausted, the allowed memory represents the set of mems assigned to that
1386	cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
1387	memory represents the set of mempolicy nodes.  If it is due to a memory
1388	limit (or swap limit) being reached, the allowed memory is that configured
1389	limit.  Finally, if it is due to the entire system being out of memory, the
1390	allowed memory represents all allocatable resources.
1391	
1392	The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1393	is used to determine which task to kill.  Acceptable values range from -1000
1394	(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
1395	polarize the preference for oom killing either by always preferring a certain
1396	task or completely disabling it.  The lowest possible value, -1000, is
1397	equivalent to disabling oom killing entirely for that task since it will always
1398	report a badness score of 0.
1399	
1400	Consequently, it is very simple for userspace to define the amount of memory to
1401	consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
1402	example, is roughly equivalent to allowing the remainder of tasks sharing the
1403	same system, cpuset, mempolicy, or memory controller resources to use at least
1404	50% more memory.  A value of -500, on the other hand, would be roughly
1405	equivalent to discounting 50% of the task's allowed memory from being considered
1406	as scoring against the task.
1407	
1408	For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1409	be used to tune the badness score.  Its acceptable values range from -16
1410	(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1411	(OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
1412	scaled linearly with /proc/<pid>/oom_score_adj.
1413	
1414	The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1415	value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1416	requires CAP_SYS_RESOURCE.
1417	
1418	Caveat: when a parent task is selected, the oom killer will sacrifice any first
1419	generation children with separate address spaces instead, if possible.  This
1420	avoids servers and important system daemons from being killed and loses the
1421	minimal amount of work.
1422	
1423	
1424	3.2 /proc/<pid>/oom_score - Display current oom-killer score
1425	-------------------------------------------------------------
1426	
1427	This file can be used to check the current score used by the oom-killer is for
1428	any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1429	process should be killed in an out-of-memory situation.
1430	
1431	
1432	3.3  /proc/<pid>/io - Display the IO accounting fields
1433	-------------------------------------------------------
1434	
1435	This file contains IO statistics for each running process
1436	
1437	Example
1438	-------
1439	
1440	test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1441	[1] 3828
1442	
1443	test:/tmp # cat /proc/3828/io
1444	rchar: 323934931
1445	wchar: 323929600
1446	syscr: 632687
1447	syscw: 632675
1448	read_bytes: 0
1449	write_bytes: 323932160
1450	cancelled_write_bytes: 0
1451	
1452	
1453	Description
1454	-----------
1455	
1456	rchar
1457	-----
1458	
1459	I/O counter: chars read
1460	The number of bytes which this task has caused to be read from storage. This
1461	is simply the sum of bytes which this process passed to read() and pread().
1462	It includes things like tty IO and it is unaffected by whether or not actual
1463	physical disk IO was required (the read might have been satisfied from
1464	pagecache)
1465	
1466	
1467	wchar
1468	-----
1469	
1470	I/O counter: chars written
1471	The number of bytes which this task has caused, or shall cause to be written
1472	to disk. Similar caveats apply here as with rchar.
1473	
1474	
1475	syscr
1476	-----
1477	
1478	I/O counter: read syscalls
1479	Attempt to count the number of read I/O operations, i.e. syscalls like read()
1480	and pread().
1481	
1482	
1483	syscw
1484	-----
1485	
1486	I/O counter: write syscalls
1487	Attempt to count the number of write I/O operations, i.e. syscalls like
1488	write() and pwrite().
1489	
1490	
1491	read_bytes
1492	----------
1493	
1494	I/O counter: bytes read
1495	Attempt to count the number of bytes which this process really did cause to
1496	be fetched from the storage layer. Done at the submit_bio() level, so it is
1497	accurate for block-backed filesystems. <please add status regarding NFS and
1498	CIFS at a later time>
1499	
1500	
1501	write_bytes
1502	-----------
1503	
1504	I/O counter: bytes written
1505	Attempt to count the number of bytes which this process caused to be sent to
1506	the storage layer. This is done at page-dirtying time.
1507	
1508	
1509	cancelled_write_bytes
1510	---------------------
1511	
1512	The big inaccuracy here is truncate. If a process writes 1MB to a file and
1513	then deletes the file, it will in fact perform no writeout. But it will have
1514	been accounted as having caused 1MB of write.
1515	In other words: The number of bytes which this process caused to not happen,
1516	by truncating pagecache. A task can cause "negative" IO too. If this task
1517	truncates some dirty pagecache, some IO which another task has been accounted
1518	for (in its write_bytes) will not be happening. We _could_ just subtract that
1519	from the truncating task's write_bytes, but there is information loss in doing
1520	that.
1521	
1522	
1523	Note
1524	----
1525	
1526	At its current implementation state, this is a bit racy on 32-bit machines: if
1527	process A reads process B's /proc/pid/io while process B is updating one of
1528	those 64-bit counters, process A could see an intermediate result.
1529	
1530	
1531	More information about this can be found within the taskstats documentation in
1532	Documentation/accounting.
1533	
1534	3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1535	---------------------------------------------------------------
1536	When a process is dumped, all anonymous memory is written to a core file as
1537	long as the size of the core file isn't limited. But sometimes we don't want
1538	to dump some memory segments, for example, huge shared memory. Conversely,
1539	sometimes we want to save file-backed memory segments into a core file, not
1540	only the individual files.
1541	
1542	/proc/<pid>/coredump_filter allows you to customize which memory segments
1543	will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1544	of memory types. If a bit of the bitmask is set, memory segments of the
1545	corresponding memory type are dumped, otherwise they are not dumped.
1546	
1547	The following 7 memory types are supported:
1548	  - (bit 0) anonymous private memory
1549	  - (bit 1) anonymous shared memory
1550	  - (bit 2) file-backed private memory
1551	  - (bit 3) file-backed shared memory
1552	  - (bit 4) ELF header pages in file-backed private memory areas (it is
1553	            effective only if the bit 2 is cleared)
1554	  - (bit 5) hugetlb private memory
1555	  - (bit 6) hugetlb shared memory
1556	
1557	  Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1558	  are always dumped regardless of the bitmask status.
1559	
1560	  Note bit 0-4 doesn't effect any hugetlb memory. hugetlb memory are only
1561	  effected by bit 5-6.
1562	
1563	Default value of coredump_filter is 0x23; this means all anonymous memory
1564	segments and hugetlb private memory are dumped.
1565	
1566	If you don't want to dump all shared memory segments attached to pid 1234,
1567	write 0x21 to the process's proc file.
1568	
1569	  $ echo 0x21 > /proc/1234/coredump_filter
1570	
1571	When a new process is created, the process inherits the bitmask status from its
1572	parent. It is useful to set up coredump_filter before the program runs.
1573	For example:
1574	
1575	  $ echo 0x7 > /proc/self/coredump_filter
1576	  $ ./some_program
1577	
1578	3.5	/proc/<pid>/mountinfo - Information about mounts
1579	--------------------------------------------------------
1580	
1581	This file contains lines of the form:
1582	
1583	36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1584	(1)(2)(3)   (4)   (5)      (6)      (7)   (8) (9)   (10)         (11)
1585	
1586	(1) mount ID:  unique identifier of the mount (may be reused after umount)
1587	(2) parent ID:  ID of parent (or of self for the top of the mount tree)
1588	(3) major:minor:  value of st_dev for files on filesystem
1589	(4) root:  root of the mount within the filesystem
1590	(5) mount point:  mount point relative to the process's root
1591	(6) mount options:  per mount options
1592	(7) optional fields:  zero or more fields of the form "tag[:value]"
1593	(8) separator:  marks the end of the optional fields
1594	(9) filesystem type:  name of filesystem of the form "type[.subtype]"
1595	(10) mount source:  filesystem specific information or "none"
1596	(11) super options:  per super block options
1597	
1598	Parsers should ignore all unrecognised optional fields.  Currently the
1599	possible optional fields are:
1600	
1601	shared:X  mount is shared in peer group X
1602	master:X  mount is slave to peer group X
1603	propagate_from:X  mount is slave and receives propagation from peer group X (*)
1604	unbindable  mount is unbindable
1605	
1606	(*) X is the closest dominant peer group under the process's root.  If
1607	X is the immediate master of the mount, or if there's no dominant peer
1608	group under the same root, then only the "master:X" field is present
1609	and not the "propagate_from:X" field.
1610	
1611	For more information on mount propagation see:
1612	
1613	  Documentation/filesystems/sharedsubtree.txt
1614	
1615	
1616	3.6	/proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
1617	--------------------------------------------------------
1618	These files provide a method to access a tasks comm value. It also allows for
1619	a task to set its own or one of its thread siblings comm value. The comm value
1620	is limited in size compared to the cmdline value, so writing anything longer
1621	then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1622	comm value.
1623	
1624	
1625	3.7	/proc/<pid>/task/<tid>/children - Information about task children
1626	-------------------------------------------------------------------------
1627	This file provides a fast way to retrieve first level children pids
1628	of a task pointed by <pid>/<tid> pair. The format is a space separated
1629	stream of pids.
1630	
1631	Note the "first level" here -- if a child has own children they will
1632	not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children
1633	to obtain the descendants.
1634	
1635	Since this interface is intended to be fast and cheap it doesn't
1636	guarantee to provide precise results and some children might be
1637	skipped, especially if they've exited right after we printed their
1638	pids, so one need to either stop or freeze processes being inspected
1639	if precise results are needed.
1640	
1641	
1642	3.7	/proc/<pid>/fdinfo/<fd> - Information about opened file
1643	---------------------------------------------------------------
1644	This file provides information associated with an opened file. The regular
1645	files have at least two fields -- 'pos' and 'flags'. The 'pos' represents
1646	the current offset of the opened file in decimal form [see lseek(2) for
1647	details] and 'flags' denotes the octal O_xxx mask the file has been
1648	created with [see open(2) for details].
1649	
1650	A typical output is
1651	
1652		pos:	0
1653		flags:	0100002
1654	
1655	The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1656	pair provide additional information particular to the objects they represent.
1657	
1658		Eventfd files
1659		~~~~~~~~~~~~~
1660		pos:	0
1661		flags:	04002
1662		eventfd-count:	5a
1663	
1664		where 'eventfd-count' is hex value of a counter.
1665	
1666		Signalfd files
1667		~~~~~~~~~~~~~~
1668		pos:	0
1669		flags:	04002
1670		sigmask:	0000000000000200
1671	
1672		where 'sigmask' is hex value of the signal mask associated
1673		with a file.
1674	
1675		Epoll files
1676		~~~~~~~~~~~
1677		pos:	0
1678		flags:	02
1679		tfd:        5 events:       1d data: ffffffffffffffff
1680	
1681		where 'tfd' is a target file descriptor number in decimal form,
1682		'events' is events mask being watched and the 'data' is data
1683		associated with a target [see epoll(7) for more details].
1684	
1685		Fsnotify files
1686		~~~~~~~~~~~~~~
1687		For inotify files the format is the following
1688	
1689		pos:	0
1690		flags:	02000000
1691		inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
1692	
1693		where 'wd' is a watch descriptor in decimal form, ie a target file
1694		descriptor number, 'ino' and 'sdev' are inode and device where the
1695		target file resides and the 'mask' is the mask of events, all in hex
1696		form [see inotify(7) for more details].
1697	
1698		If the kernel was built with exportfs support, the path to the target
1699		file is encoded as a file handle.  The file handle is provided by three
1700		fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
1701		format.
1702	
1703		If the kernel is built without exportfs support the file handle won't be
1704		printed out.
1705	
1706		If there is no inotify mark attached yet the 'inotify' line will be omitted.
1707	
1708		For fanotify files the format is
1709	
1710		pos:	0
1711		flags:	02
1712		fanotify flags:10 event-flags:0
1713		fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
1714		fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
1715	
1716		where fanotify 'flags' and 'event-flags' are values used in fanotify_init
1717		call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
1718		flags associated with mark which are tracked separately from events
1719		mask. 'ino', 'sdev' are target inode and device, 'mask' is the events
1720		mask and 'ignored_mask' is the mask of events which are to be ignored.
1721		All in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
1722		does provide information about flags and mask used in fanotify_mark
1723		call [see fsnotify manpage for details].
1724	
1725		While the first three lines are mandatory and always printed, the rest is
1726		optional and may be omitted if no marks created yet.
1727	
1728	
1729	------------------------------------------------------------------------------
1730	Configuring procfs
1731	------------------------------------------------------------------------------
1732	
1733	4.1	Mount options
1734	---------------------
1735	
1736	The following mount options are supported:
1737	
1738		hidepid=	Set /proc/<pid>/ access mode.
1739		gid=		Set the group authorized to learn processes information.
1740	
1741	hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
1742	(default).
1743	
1744	hidepid=1 means users may not access any /proc/<pid>/ directories but their
1745	own.  Sensitive files like cmdline, sched*, status are now protected against
1746	other users.  This makes it impossible to learn whether any user runs
1747	specific program (given the program doesn't reveal itself by its behaviour).
1748	As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users,
1749	poorly written programs passing sensitive information via program arguments are
1750	now protected against local eavesdroppers.
1751	
1752	hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other
1753	users.  It doesn't mean that it hides a fact whether a process with a specific
1754	pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"),
1755	but it hides process' uid and gid, which may be learned by stat()'ing
1756	/proc/<pid>/ otherwise.  It greatly complicates an intruder's task of gathering
1757	information about running processes, whether some daemon runs with elevated
1758	privileges, whether other user runs some sensitive program, whether other users
1759	run any program at all, etc.
1760	
1761	gid= defines a group authorized to learn processes information otherwise
1762	prohibited by hidepid=.  If you use some daemon like identd which needs to learn
1763	information about processes information, just add identd to this group.
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