summaryrefslogtreecommitdiffstats
path: root/Documentation/filesystems/proc.rst
blob: 898c99eae8e44630b459a2adca8b84ebb1423d8f (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
2018
2019
2020
2021
2022
2023
2024
2025
2026
2027
2028
2029
2030
2031
2032
2033
2034
2035
2036
2037
2038
2039
2040
2041
2042
2043
2044
2045
2046
2047
2048
2049
2050
2051
2052
2053
2054
2055
2056
2057
2058
2059
2060
2061
2062
2063
2064
2065
2066
2067
2068
2069
2070
2071
2072
2073
2074
2075
2076
2077
2078
2079
2080
2081
2082
2083
2084
2085
2086
2087
2088
2089
2090
2091
2092
2093
2094
2095
2096
2097
2098
2099
2100
2101
2102
2103
2104
2105
2106
2107
2108
2109
2110
2111
2112
2113
2114
2115
2116
2117
2118
2119
2120
2121
2122
2123
2124
2125
2126
2127
2128
2129
2130
2131
2132
2133
2134
2135
2136
2137
2138
2139
2140
2141
2142
2143
2144
2145
2146
2147
2148
2149
2150
2151
2152
2153
2154
2155
2156
2157
2158
2159
2160
2161
2162
2163
2164
2165
2166
2167
2168
2169
2170
2171
2172
2173
2174
2175
2176
2177
2178
2179
2180
2181
2182
2183
2184
2185
2186
2187
2188
2189
2190
2191
2192
2193
2194
2195
2196
2197
2198
2199
2200
2201
2202
2203
2204
2205
2206
2207
2208
2209
2210
2211
2212
2213
2214
2215
2216
2217
2218
2219
2220
2221
2222
2223
2224
2225
2226
2227
2228
2229
2230
2231
2232
2233
2234
2235
2236
2237
.. SPDX-License-Identifier: GPL-2.0

====================
The /proc Filesystem
====================

=====================  =======================================  ================
/proc/sys              Terrehon Bowden <terrehon@pacbell.net>,  October 7 1999
                       Bodo Bauer <bb@ricochet.net>
2.4.x update	       Jorge Nerin <comandante@zaralinux.com>   November 14 2000
move /proc/sys	       Shen Feng <shen@cn.fujitsu.com>	        April 1 2009
fixes/update part 1.1  Stefani Seibold <stefani@seibold.net>    June 9 2009
=====================  =======================================  ================



.. Table of Contents

  0     Preface
  0.1	Introduction/Credits
  0.2	Legal Stuff

  1	Collecting System Information
  1.1	Process-Specific Subdirectories
  1.2	Kernel data
  1.3	IDE devices in /proc/ide
  1.4	Networking info in /proc/net
  1.5	SCSI info
  1.6	Parallel port info in /proc/parport
  1.7	TTY info in /proc/tty
  1.8	Miscellaneous kernel statistics in /proc/stat
  1.9	Ext4 file system parameters

  2	Modifying System Parameters

  3	Per-Process Parameters
  3.1	/proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj - Adjust the oom-killer
								score
  3.2	/proc/<pid>/oom_score - Display current oom-killer score
  3.3	/proc/<pid>/io - Display the IO accounting fields
  3.4	/proc/<pid>/coredump_filter - Core dump filtering settings
  3.5	/proc/<pid>/mountinfo - Information about mounts
  3.6	/proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
  3.7   /proc/<pid>/task/<tid>/children - Information about task children
  3.8   /proc/<pid>/fdinfo/<fd> - Information about opened file
  3.9   /proc/<pid>/map_files - Information about memory mapped files
  3.10  /proc/<pid>/timerslack_ns - Task timerslack value
  3.11	/proc/<pid>/patch_state - Livepatch patch operation state
  3.12	/proc/<pid>/arch_status - Task architecture specific information

  4	Configuring procfs
  4.1	Mount options

  5	Filesystem behavior

Preface
=======

0.1 Introduction/Credits
------------------------

This documentation is  part of a soon (or  so we hope) to be  released book on
the SuSE  Linux distribution. As  there is  no complete documentation  for the
/proc file system and we've used  many freely available sources to write these
chapters, it  seems only fair  to give the work  back to the  Linux community.
This work is  based on the 2.2.*  kernel version and the  upcoming 2.4.*. I'm
afraid it's still far from complete, but we  hope it will be useful. As far as
we know, it is the first 'all-in-one' document about the /proc file system. It
is focused  on the Intel  x86 hardware,  so if you  are looking for  PPC, ARM,
SPARC, AXP, etc., features, you probably  won't find what you are looking for.
It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
additions and patches  are welcome and will  be added to this  document if you
mail them to Bodo.

We'd like  to  thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
other people for help compiling this documentation. We'd also like to extend a
special thank  you to Andi Kleen for documentation, which we relied on heavily
to create  this  document,  as well as the additional information he provided.
Thanks to  everybody  else  who contributed source or docs to the Linux kernel
and helped create a great piece of software... :)

If you  have  any comments, corrections or additions, please don't hesitate to
contact Bodo  Bauer  at  bb@ricochet.net.  We'll  be happy to add them to this
document.

The   latest   version    of   this   document   is    available   online   at
http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html

If  the above  direction does  not works  for you,  you could  try the  kernel
mailing  list  at  linux-kernel@vger.kernel.org  and/or try  to  reach  me  at
comandante@zaralinux.com.

0.2 Legal Stuff
---------------

We don't  guarantee  the  correctness  of this document, and if you come to us
complaining about  how  you  screwed  up  your  system  because  of  incorrect
documentation, we won't feel responsible...

Chapter 1: Collecting System Information
========================================

In This Chapter
---------------
* Investigating  the  properties  of  the  pseudo  file  system  /proc and its
  ability to provide information on the running Linux system
* Examining /proc's structure
* Uncovering  various  information  about the kernel and the processes running
  on the system

------------------------------------------------------------------------------

The proc  file  system acts as an interface to internal data structures in the
kernel. It  can  be  used to obtain information about the system and to change
certain kernel parameters at runtime (sysctl).

First, we'll  take  a  look  at the read-only parts of /proc. In Chapter 2, we
show you how you can use /proc/sys to change settings.

1.1 Process-Specific Subdirectories
-----------------------------------

The directory  /proc  contains  (among other things) one subdirectory for each
process running on the system, which is named after the process ID (PID).

The link  'self'  points to  the process reading the file system. Each process
subdirectory has the entries listed in Table 1-1.

Note that an open file descriptor to /proc/<pid> or to any of its
contained files or subdirectories does not prevent <pid> being reused
for some other process in the event that <pid> exits. Operations on
open /proc/<pid> file descriptors corresponding to dead processes
never act on any new process that the kernel may, through chance, have
also assigned the process ID <pid>. Instead, operations on these FDs
usually fail with ESRCH.

.. table:: Table 1-1: Process specific entries in /proc

 =============  ===============================================================
 File		Content
 =============  ===============================================================
 clear_refs	Clears page referenced bits shown in smaps output
 cmdline	Command line arguments
 cpu		Current and last cpu in which it was executed	(2.4)(smp)
 cwd		Link to the current working directory
 environ	Values of environment variables
 exe		Link to the executable of this process
 fd		Directory, which contains all file descriptors
 maps		Memory maps to executables and library files	(2.4)
 mem		Memory held by this process
 root		Link to the root directory of this process
 stat		Process status
 statm		Process memory status information
 status		Process status in human readable form
 wchan		Present with CONFIG_KALLSYMS=y: it shows the kernel function
		symbol the task is blocked in - or "0" if not blocked.
 pagemap	Page table
 stack		Report full stack trace, enable via CONFIG_STACKTRACE
 smaps		An extension based on maps, showing the memory consumption of
		each mapping and flags associated with it
 smaps_rollup	Accumulated smaps stats for all mappings of the process.  This
		can be derived from smaps, but is faster and more convenient
 numa_maps	An extension based on maps, showing the memory locality and
		binding policy as well as mem usage (in pages) of each mapping.
 =============  ===============================================================

For example, to get the status information of a process, all you have to do is
read the file /proc/PID/status::

  >cat /proc/self/status
  Name:   cat
  State:  R (running)
  Tgid:   5452
  Pid:    5452
  PPid:   743
  TracerPid:      0						(2.4)
  Uid:    501     501     501     501
  Gid:    100     100     100     100
  FDSize: 256
  Groups: 100 14 16
  VmPeak:     5004 kB
  VmSize:     5004 kB
  VmLck:         0 kB
  VmHWM:       476 kB
  VmRSS:       476 kB
  RssAnon:             352 kB
  RssFile:             120 kB
  RssShmem:              4 kB
  VmData:      156 kB
  VmStk:        88 kB
  VmExe:        68 kB
  VmLib:      1412 kB
  VmPTE:        20 kb
  VmSwap:        0 kB
  HugetlbPages:          0 kB
  CoreDumping:    0
  THP_enabled:	  1
  Threads:        1
  SigQ:   0/28578
  SigPnd: 0000000000000000
  ShdPnd: 0000000000000000
  SigBlk: 0000000000000000
  SigIgn: 0000000000000000
  SigCgt: 0000000000000000
  CapInh: 00000000fffffeff
  CapPrm: 0000000000000000
  CapEff: 0000000000000000
  CapBnd: ffffffffffffffff
  CapAmb: 0000000000000000
  NoNewPrivs:     0
  Seccomp:        0
  Speculation_Store_Bypass:       thread vulnerable
  SpeculationIndirectBranch:      conditional enabled
  voluntary_ctxt_switches:        0
  nonvoluntary_ctxt_switches:     1

This shows you nearly the same information you would get if you viewed it with
the ps  command.  In  fact,  ps  uses  the  proc  file  system  to  obtain its
information.  But you get a more detailed  view of the  process by reading the
file /proc/PID/status. It fields are described in table 1-2.

The  statm  file  contains  more  detailed  information about the process
memory usage. Its seven fields are explained in Table 1-3.  The stat file
contains detailed information about the process itself.  Its fields are
explained in Table 1-4.

(for SMP CONFIG users)

For making accounting scalable, RSS related information are handled in an
asynchronous manner and the value may not be very precise. To see a precise
snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
It's slow but very precise.

.. table:: Table 1-2: Contents of the status files (as of 4.19)

 ==========================  ===================================================
 Field                       Content
 ==========================  ===================================================
 Name                        filename of the executable
 Umask                       file mode creation mask
 State                       state (R is running, S is sleeping, D is sleeping
                             in an uninterruptible wait, Z is zombie,
			     T is traced or stopped)
 Tgid                        thread group ID
 Ngid                        NUMA group ID (0 if none)
 Pid                         process id
 PPid                        process id of the parent process
 TracerPid                   PID of process tracing this process (0 if not)
 Uid                         Real, effective, saved set, and  file system UIDs
 Gid                         Real, effective, saved set, and  file system GIDs
 FDSize                      number of file descriptor slots currently allocated
 Groups                      supplementary group list
 NStgid                      descendant namespace thread group ID hierarchy
 NSpid                       descendant namespace process ID hierarchy
 NSpgid                      descendant namespace process group ID hierarchy
 NSsid                       descendant namespace session ID hierarchy
 VmPeak                      peak virtual memory size
 VmSize                      total program size
 VmLck                       locked memory size
 VmPin                       pinned memory size
 VmHWM                       peak resident set size ("high water mark")
 VmRSS                       size of memory portions. It contains the three
                             following parts
                             (VmRSS = RssAnon + RssFile + RssShmem)
 RssAnon                     size of resident anonymous memory
 RssFile                     size of resident file mappings
 RssShmem                    size of resident shmem memory (includes SysV shm,
                             mapping of tmpfs and shared anonymous mappings)
 VmData                      size of private data segments
 VmStk                       size of stack segments
 VmExe                       size of text segment
 VmLib                       size of shared library code
 VmPTE                       size of page table entries
 VmSwap                      amount of swap used by anonymous private data
                             (shmem swap usage is not included)
 HugetlbPages                size of hugetlb memory portions
 CoreDumping                 process's memory is currently being dumped
                             (killing the process may lead to a corrupted core)
 THP_enabled		     process is allowed to use THP (returns 0 when
			     PR_SET_THP_DISABLE is set on the process
 Threads                     number of threads
 SigQ                        number of signals queued/max. number for queue
 SigPnd                      bitmap of pending signals for the thread
 ShdPnd                      bitmap of shared pending signals for the process
 SigBlk                      bitmap of blocked signals
 SigIgn                      bitmap of ignored signals
 SigCgt                      bitmap of caught signals
 CapInh                      bitmap of inheritable capabilities
 CapPrm                      bitmap of permitted capabilities
 CapEff                      bitmap of effective capabilities
 CapBnd                      bitmap of capabilities bounding set
 CapAmb                      bitmap of ambient capabilities
 NoNewPrivs                  no_new_privs, like prctl(PR_GET_NO_NEW_PRIV, ...)
 Seccomp                     seccomp mode, like prctl(PR_GET_SECCOMP, ...)
 Speculation_Store_Bypass    speculative store bypass mitigation status
 SpeculationIndirectBranch   indirect branch speculation mode
 Cpus_allowed                mask of CPUs on which this process may run
 Cpus_allowed_list           Same as previous, but in "list format"
 Mems_allowed                mask of memory nodes allowed to this process
 Mems_allowed_list           Same as previous, but in "list format"
 voluntary_ctxt_switches     number of voluntary context switches
 nonvoluntary_ctxt_switches  number of non voluntary context switches
 ==========================  ===================================================


.. table:: Table 1-3: Contents of the statm files (as of 2.6.8-rc3)

 ======== ===============================	==============================
 Field    Content
 ======== ===============================	==============================
 size     total program size (pages)		(same as VmSize in status)
 resident size of memory portions (pages)	(same as VmRSS in status)
 shared   number of pages that are shared	(i.e. backed by a file, same
						as RssFile+RssShmem in status)
 trs      number of pages that are 'code'	(not including libs; broken,
						includes data segment)
 lrs      number of pages of library		(always 0 on 2.6)
 drs      number of pages of data/stack		(including libs; broken,
						includes library text)
 dt       number of dirty pages			(always 0 on 2.6)
 ======== ===============================	==============================


.. table:: Table 1-4: Contents of the stat files (as of 2.6.30-rc7)

  ============= ===============================================================
  Field         Content
  ============= ===============================================================
  pid           process id
  tcomm         filename of the executable
  state         state (R is running, S is sleeping, D is sleeping in an
                uninterruptible wait, Z is zombie, T is traced or stopped)
  ppid          process id of the parent process
  pgrp          pgrp of the process
  sid           session id
  tty_nr        tty the process uses
  tty_pgrp      pgrp of the tty
  flags         task flags
  min_flt       number of minor faults
  cmin_flt      number of minor faults with child's
  maj_flt       number of major faults
  cmaj_flt      number of major faults with child's
  utime         user mode jiffies
  stime         kernel mode jiffies
  cutime        user mode jiffies with child's
  cstime        kernel mode jiffies with child's
  priority      priority level
  nice          nice level
  num_threads   number of threads
  it_real_value	(obsolete, always 0)
  start_time    time the process started after system boot
  vsize         virtual memory size
  rss           resident set memory size
  rsslim        current limit in bytes on the rss
  start_code    address above which program text can run
  end_code      address below which program text can run
  start_stack   address of the start of the main process stack
  esp           current value of ESP
  eip           current value of EIP
  pending       bitmap of pending signals
  blocked       bitmap of blocked signals
  sigign        bitmap of ignored signals
  sigcatch      bitmap of caught signals
  0		(place holder, used to be the wchan address,
		use /proc/PID/wchan instead)
  0             (place holder)
  0             (place holder)
  exit_signal   signal to send to parent thread on exit
  task_cpu      which CPU the task is scheduled on
  rt_priority   realtime priority
  policy        scheduling policy (man sched_setscheduler)
  blkio_ticks   time spent waiting for block IO
  gtime         guest time of the task in jiffies
  cgtime        guest time of the task children in jiffies
  start_data    address above which program data+bss is placed
  end_data      address below which program data+bss is placed
  start_brk     address above which program heap can be expanded with brk()
  arg_start     address above which program command line is placed
  arg_end       address below which program command line is placed
  env_start     address above which program environment is placed
  env_end       address below which program environment is placed
  exit_code     the thread's exit_code in the form reported by the waitpid
		system call
  ============= ===============================================================

The /proc/PID/maps file contains the currently mapped memory regions and
their access permissions.

The format is::

    address           perms offset  dev   inode      pathname

    08048000-08049000 r-xp 00000000 03:00 8312       /opt/test
    08049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
    0804a000-0806b000 rw-p 00000000 00:00 0          [heap]
    a7cb1000-a7cb2000 ---p 00000000 00:00 0
    a7cb2000-a7eb2000 rw-p 00000000 00:00 0
    a7eb2000-a7eb3000 ---p 00000000 00:00 0
    a7eb3000-a7ed5000 rw-p 00000000 00:00 0
    a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/libc.so.6
    a8008000-a800a000 r--p 00133000 03:00 4222       /lib/libc.so.6
    a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/libc.so.6
    a800b000-a800e000 rw-p 00000000 00:00 0
    a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/libpthread.so.0
    a8022000-a8023000 r--p 00013000 03:00 14462      /lib/libpthread.so.0
    a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/libpthread.so.0
    a8024000-a8027000 rw-p 00000000 00:00 0
    a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/ld-linux.so.2
    a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/ld-linux.so.2
    a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/ld-linux.so.2
    aff35000-aff4a000 rw-p 00000000 00:00 0          [stack]
    ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]

where "address" is the address space in the process that it occupies, "perms"
is a set of permissions::

 r = read
 w = write
 x = execute
 s = shared
 p = private (copy on write)

"offset" is the offset into the mapping, "dev" is the device (major:minor), and
"inode" is the inode  on that device.  0 indicates that  no inode is associated
with the memory region, as the case would be with BSS (uninitialized data).
The "pathname" shows the name associated file for this mapping.  If the mapping
is not associated with a file:

 =============              ====================================
 [heap]                     the heap of the program
 [stack]                    the stack of the main process
 [vdso]                     the "virtual dynamic shared object",
                            the kernel system call handler
 [anon:<name>]              an anonymous mapping that has been
                            named by userspace
 =============              ====================================

 or if empty, the mapping is anonymous.

The /proc/PID/smaps is an extension based on maps, showing the memory
consumption for each of the process's mappings. For each mapping (aka Virtual
Memory Area, or VMA) there is a series of lines such as the following::

    08048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash

    Size:               1084 kB
    KernelPageSize:        4 kB
    MMUPageSize:           4 kB
    Rss:                 892 kB
    Pss:                 374 kB
    Pss_Dirty:             0 kB
    Shared_Clean:        892 kB
    Shared_Dirty:          0 kB
    Private_Clean:         0 kB
    Private_Dirty:         0 kB
    Referenced:          892 kB
    Anonymous:             0 kB
    LazyFree:              0 kB
    AnonHugePages:         0 kB
    ShmemPmdMapped:        0 kB
    Shared_Hugetlb:        0 kB
    Private_Hugetlb:       0 kB
    Swap:                  0 kB
    SwapPss:               0 kB
    KernelPageSize:        4 kB
    MMUPageSize:           4 kB
    Locked:                0 kB
    THPeligible:           0
    VmFlags: rd ex mr mw me dw

The first of these lines shows the same information as is displayed for the
mapping in /proc/PID/maps.  Following lines show the size of the mapping
(size); the size of each page allocated when backing a VMA (KernelPageSize),
which is usually the same as the size in the page table entries; the page size
used by the MMU when backing a VMA (in most cases, the same as KernelPageSize);
the amount of the mapping that is currently resident in RAM (RSS); the
process' proportional share of this mapping (PSS); and the number of clean and
dirty shared and private pages in the mapping.

The "proportional set size" (PSS) of a process is the count of pages it has
in memory, where each page is divided by the number of processes sharing it.
So if a process has 1000 pages all to itself, and 1000 shared with one other
process, its PSS will be 1500.  "Pss_Dirty" is the portion of PSS which
consists of dirty pages.  ("Pss_Clean" is not included, but it can be
calculated by subtracting "Pss_Dirty" from "Pss".)

Note that even a page which is part of a MAP_SHARED mapping, but has only
a single pte mapped, i.e.  is currently used by only one process, is accounted
as private and not as shared.

"Referenced" indicates the amount of memory currently marked as referenced or
accessed.

"Anonymous" shows the amount of memory that does not belong to any file.  Even
a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
and a page is modified, the file page is replaced by a private anonymous copy.

"LazyFree" shows the amount of memory which is marked by madvise(MADV_FREE).
The memory isn't freed immediately with madvise(). It's freed in memory
pressure if the memory is clean. Please note that the printed value might
be lower than the real value due to optimizations used in the current
implementation. If this is not desirable please file a bug report.

"AnonHugePages" shows the ammount of memory backed by transparent hugepage.

"ShmemPmdMapped" shows the ammount of shared (shmem/tmpfs) memory backed by
huge pages.

"Shared_Hugetlb" and "Private_Hugetlb" show the ammounts of memory backed by
hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical
reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field.

"Swap" shows how much would-be-anonymous memory is also used, but out on swap.

For shmem mappings, "Swap" includes also the size of the mapped (and not
replaced by copy-on-write) part of the underlying shmem object out on swap.
"SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
does not take into account swapped out page of underlying shmem objects.
"Locked" indicates whether the mapping is locked in memory or not.

"THPeligible" indicates whether the mapping is eligible for allocating THP
pages as well as the THP is PMD mappable or not - 1 if true, 0 otherwise.
It just shows the current status.

"VmFlags" field deserves a separate description. This member represents the
kernel flags associated with the particular virtual memory area in two letter
encoded manner. The codes are the following:

    ==    =======================================
    rd    readable
    wr    writeable
    ex    executable
    sh    shared
    mr    may read
    mw    may write
    me    may execute
    ms    may share
    gd    stack segment growns down
    pf    pure PFN range
    dw    disabled write to the mapped file
    lo    pages are locked in memory
    io    memory mapped I/O area
    sr    sequential read advise provided
    rr    random read advise provided
    dc    do not copy area on fork
    de    do not expand area on remapping
    ac    area is accountable
    nr    swap space is not reserved for the area
    ht    area uses huge tlb pages
    sf    synchronous page fault
    ar    architecture specific flag
    wf    wipe on fork
    dd    do not include area into core dump
    sd    soft dirty flag
    mm    mixed map area
    hg    huge page advise flag
    nh    no huge page advise flag
    mg    mergable advise flag
    bt    arm64 BTI guarded page
    mt    arm64 MTE allocation tags are enabled
    um    userfaultfd missing tracking
    uw    userfaultfd wr-protect tracking
    ==    =======================================

Note that there is no guarantee that every flag and associated mnemonic will
be present in all further kernel releases. Things get changed, the flags may
be vanished or the reverse -- new added. Interpretation of their meaning
might change in future as well. So each consumer of these flags has to
follow each specific kernel version for the exact semantic.

This file is only present if the CONFIG_MMU kernel configuration option is
enabled.

Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy (consistent
output can be achieved only in the single read call).

This typically manifests when doing partial reads of these files while the
memory map is being modified.  Despite the races, we do provide the following
guarantees:

1) The mapped addresses never go backwards, which implies no two
   regions will ever overlap.
2) If there is something at a given vaddr during the entirety of the
   life of the smaps/maps walk, there will be some output for it.

The /proc/PID/smaps_rollup file includes the same fields as /proc/PID/smaps,
but their values are the sums of the corresponding values for all mappings of
the process.  Additionally, it contains these fields:

- Pss_Anon
- Pss_File
- Pss_Shmem

They represent the proportional shares of anonymous, file, and shmem pages, as
described for smaps above.  These fields are omitted in smaps since each
mapping identifies the type (anon, file, or shmem) of all pages it contains.
Thus all information in smaps_rollup can be derived from smaps, but at a
significantly higher cost.

The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
bits on both physical and virtual pages associated with a process, and the
soft-dirty bit on pte (see Documentation/admin-guide/mm/soft-dirty.rst
for details).
To clear the bits for all the pages associated with the process::

    > echo 1 > /proc/PID/clear_refs

To clear the bits for the anonymous pages associated with the process::

    > echo 2 > /proc/PID/clear_refs

To clear the bits for the file mapped pages associated with the process::

    > echo 3 > /proc/PID/clear_refs

To clear the soft-dirty bit::

    > echo 4 > /proc/PID/clear_refs

To reset the peak resident set size ("high water mark") to the process's
current value::

    > echo 5 > /proc/PID/clear_refs

Any other value written to /proc/PID/clear_refs will have no effect.

The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
using /proc/kpageflags and number of times a page is mapped using
/proc/kpagecount. For detailed explanation, see
Documentation/admin-guide/mm/pagemap.rst.

The /proc/pid/numa_maps is an extension based on maps, showing the memory
locality and binding policy, as well as the memory usage (in pages) of
each mapping. The output follows a general format where mapping details get
summarized separated by blank spaces, one mapping per each file line::

    address   policy    mapping details

    00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
    00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
    3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
    320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
    3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
    3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
    3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
    320698b000 default file=/lib64/libc-2.12.so
    3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4
    3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
    3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
    7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
    7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
    7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
    7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
    7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4

Where:

"address" is the starting address for the mapping;

"policy" reports the NUMA memory policy set for the mapping (see Documentation/admin-guide/mm/numa_memory_policy.rst);

"mapping details" summarizes mapping data such as mapping type, page usage counters,
node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
size, in KB, that is backing the mapping up.

1.2 Kernel data
---------------

Similar to  the  process entries, the kernel data files give information about
the running kernel. The files used to obtain this information are contained in
/proc and  are  listed  in Table 1-5. Not all of these will be present in your
system. It  depends  on the kernel configuration and the loaded modules, which
files are there, and which are missing.

.. table:: Table 1-5: Kernel info in /proc

 ============ ===============================================================
 File         Content
 ============ ===============================================================
 apm          Advanced power management info
 buddyinfo    Kernel memory allocator information (see text)	(2.5)
 bus          Directory containing bus specific information
 cmdline      Kernel command line
 cpuinfo      Info about the CPU
 devices      Available devices (block and character)
 dma          Used DMS channels
 filesystems  Supported filesystems
 driver       Various drivers grouped here, currently rtc	(2.4)
 execdomains  Execdomains, related to security			(2.4)
 fb 	      Frame Buffer devices				(2.4)
 fs 	      File system parameters, currently nfs/exports	(2.4)
 ide          Directory containing info about the IDE subsystem
 interrupts   Interrupt usage
 iomem 	      Memory map					(2.4)
 ioports      I/O port usage
 irq 	      Masks for irq to cpu affinity			(2.4)(smp?)
 isapnp       ISA PnP (Plug&Play) Info				(2.4)
 kcore        Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
 kmsg         Kernel messages
 ksyms        Kernel symbol table
 loadavg      Load average of last 1, 5 & 15 minutes;
                number of processes currently runnable (running or on ready queue);
                total number of processes in system;
                last pid created.
                All fields are separated by one space except "number of
                processes currently runnable" and "total number of processes
                in system", which are separated by a slash ('/'). Example:
                0.61 0.61 0.55 3/828 22084
 locks        Kernel locks
 meminfo      Memory info
 misc         Miscellaneous
 modules      List of loaded modules
 mounts       Mounted filesystems
 net          Networking info (see text)
 pagetypeinfo Additional page allocator information (see text)  (2.5)
 partitions   Table of partitions known to the system
 pci 	      Deprecated info of PCI bus (new way -> /proc/bus/pci/,
              decoupled by lspci				(2.4)
 rtc          Real time clock
 scsi         SCSI info (see text)
 slabinfo     Slab pool info
 softirqs     softirq usage
 stat         Overall statistics
 swaps        Swap space utilization
 sys          See chapter 2
 sysvipc      Info of SysVIPC Resources (msg, sem, shm)		(2.4)
 tty 	      Info of tty drivers
 uptime       Wall clock since boot, combined idle time of all cpus
 version      Kernel version
 video 	      bttv info of video resources			(2.4)
 vmallocinfo  Show vmalloced areas
 ============ ===============================================================

You can,  for  example,  check  which interrupts are currently in use and what
they are used for by looking in the file /proc/interrupts::

  > cat /proc/interrupts
             CPU0
    0:    8728810          XT-PIC  timer
    1:        895          XT-PIC  keyboard
    2:          0          XT-PIC  cascade
    3:     531695          XT-PIC  aha152x
    4:    2014133          XT-PIC  serial
    5:      44401          XT-PIC  pcnet_cs
    8:          2          XT-PIC  rtc
   11:          8          XT-PIC  i82365
   12:     182918          XT-PIC  PS/2 Mouse
   13:          1          XT-PIC  fpu
   14:    1232265          XT-PIC  ide0
   15:          7          XT-PIC  ide1
  NMI:          0

In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
output of a SMP machine)::

  > cat /proc/interrupts

             CPU0       CPU1
    0:    1243498    1214548    IO-APIC-edge  timer
    1:       8949       8958    IO-APIC-edge  keyboard
    2:          0          0          XT-PIC  cascade
    5:      11286      10161    IO-APIC-edge  soundblaster
    8:          1          0    IO-APIC-edge  rtc
    9:      27422      27407    IO-APIC-edge  3c503
   12:     113645     113873    IO-APIC-edge  PS/2 Mouse
   13:          0          0          XT-PIC  fpu
   14:      22491      24012    IO-APIC-edge  ide0
   15:       2183       2415    IO-APIC-edge  ide1
   17:      30564      30414   IO-APIC-level  eth0
   18:        177        164   IO-APIC-level  bttv
  NMI:    2457961    2457959
  LOC:    2457882    2457881
  ERR:       2155

NMI is incremented in this case because every timer interrupt generates a NMI
(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.

LOC is the local interrupt counter of the internal APIC of every CPU.

ERR is incremented in the case of errors in the IO-APIC bus (the bus that
connects the CPUs in a SMP system. This means that an error has been detected,
the IO-APIC automatically retry the transmission, so it should not be a big
problem, but you should read the SMP-FAQ.

In 2.6.2* /proc/interrupts was expanded again.  This time the goal was for
/proc/interrupts to display every IRQ vector in use by the system, not
just those considered 'most important'.  The new vectors are:

THR
  interrupt raised when a machine check threshold counter
  (typically counting ECC corrected errors of memory or cache) exceeds
  a configurable threshold.  Only available on some systems.

TRM
  a thermal event interrupt occurs when a temperature threshold
  has been exceeded for the CPU.  This interrupt may also be generated
  when the temperature drops back to normal.

SPU
  a spurious interrupt is some interrupt that was raised then lowered
  by some IO device before it could be fully processed by the APIC.  Hence
  the APIC sees the interrupt but does not know what device it came from.
  For this case the APIC will generate the interrupt with a IRQ vector
  of 0xff. This might also be generated by chipset bugs.

RES, CAL, TLB
  rescheduling, call and TLB flush interrupts are
  sent from one CPU to another per the needs of the OS.  Typically,
  their statistics are used by kernel developers and interested users to
  determine the occurrence of interrupts of the given type.

The above IRQ vectors are displayed only when relevant.  For example,
the threshold vector does not exist on x86_64 platforms.  Others are
suppressed when the system is a uniprocessor.  As of this writing, only
i386 and x86_64 platforms support the new IRQ vector displays.

Of some interest is the introduction of the /proc/irq directory to 2.4.
It could be used to set IRQ to CPU affinity. This means that you can "hook" an
IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
prof_cpu_mask.

For example::

  > ls /proc/irq/
  0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
  1  11  13  15  17  19  3  5  7  9  default_smp_affinity
  > ls /proc/irq/0/
  smp_affinity

smp_affinity is a bitmask, in which you can specify which CPUs can handle the
IRQ. You can set it by doing::

  > echo 1 > /proc/irq/10/smp_affinity

This means that only the first CPU will handle the IRQ, but you can also echo
5 which means that only the first and third CPU can handle the IRQ.

The contents of each smp_affinity file is the same by default::

  > cat /proc/irq/0/smp_affinity
  ffffffff

There is an alternate interface, smp_affinity_list which allows specifying
a CPU range instead of a bitmask::

  > cat /proc/irq/0/smp_affinity_list
  1024-1031

The default_smp_affinity mask applies to all non-active IRQs, which are the
IRQs which have not yet been allocated/activated, and hence which lack a
/proc/irq/[0-9]* directory.

The node file on an SMP system shows the node to which the device using the IRQ
reports itself as being attached. This hardware locality information does not
include information about any possible driver locality preference.

prof_cpu_mask specifies which CPUs are to be profiled by the system wide
profiler. Default value is ffffffff (all CPUs if there are only 32 of them).

The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
between all the CPUs which are allowed to handle it. As usual the kernel has
more info than you and does a better job than you, so the defaults are the
best choice for almost everyone.  [Note this applies only to those IO-APIC's
that support "Round Robin" interrupt distribution.]

There are  three  more  important subdirectories in /proc: net, scsi, and sys.
The general  rule  is  that  the  contents,  or  even  the  existence of these
directories, depend  on your kernel configuration. If SCSI is not enabled, the
directory scsi  may  not  exist. The same is true with the net, which is there
only when networking support is present in the running kernel.

The slabinfo  file  gives  information  about  memory usage at the slab level.
Linux uses  slab  pools for memory management above page level in version 2.2.
Commonly used  objects  have  their  own  slab  pool (such as network buffers,
directory cache, and so on).

::

    > cat /proc/buddyinfo

    Node 0, zone      DMA      0      4      5      4      4      3 ...
    Node 0, zone   Normal      1      0      0      1    101      8 ...
    Node 0, zone  HighMem      2      0      0      1      1      0 ...

External fragmentation is a problem under some workloads, and buddyinfo is a
useful tool for helping diagnose these problems.  Buddyinfo will give you a
clue as to how big an area you can safely allocate, or why a previous
allocation failed.

Each column represents the number of pages of a certain order which are
available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
available in ZONE_NORMAL, etc...

More information relevant to external fragmentation can be found in
pagetypeinfo::

    > cat /proc/pagetypeinfo
    Page block order: 9
    Pages per block:  512

    Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
    Node    0, zone      DMA, type    Unmovable      0      0      0      1      1      1      1      1      1      1      0
    Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0
    Node    0, zone      DMA, type      Movable      1      1      2      1      2      1      1      0      1      0      2
    Node    0, zone      DMA, type      Reserve      0      0      0      0      0      0      0      0      0      1      0
    Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
    Node    0, zone    DMA32, type    Unmovable    103     54     77      1      1      1     11      8      7      1      9
    Node    0, zone    DMA32, type  Reclaimable      0      0      2      1      0      0      0      0      1      0      0
    Node    0, zone    DMA32, type      Movable    169    152    113     91     77     54     39     13      6      1    452
    Node    0, zone    DMA32, type      Reserve      1      2      2      2      2      0      1      1      1      1      0
    Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0

    Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate
    Node 0, zone      DMA            2            0            5            1            0
    Node 0, zone    DMA32           41            6          967            2            0

Fragmentation avoidance in the kernel works by grouping pages of different
migrate types into the same contiguous regions of memory called page blocks.
A page block is typically the size of the default hugepage size, e.g. 2MB on
X86-64. By keeping pages grouped based on their ability to move, the kernel
can reclaim pages within a page block to satisfy a high-order allocation.

The pagetypinfo begins with information on the size of a page block. It
then gives the same type of information as buddyinfo except broken down
by migrate-type and finishes with details on how many page blocks of each
type exist.

If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can
make an estimate of the likely number of huge pages that can be allocated
at a given point in time. All the "Movable" blocks should be allocatable
unless memory has been mlock()'d. Some of the Reclaimable blocks should
also be allocatable although a lot of filesystem metadata may have to be
reclaimed to achieve this.


meminfo
~~~~~~~

Provides information about distribution and utilization of memory.  This
varies by architecture and compile options.  Some of the counters reported
here overlap.  The memory reported by the non overlapping counters may not
add up to the overall memory usage and the difference for some workloads
can be substantial.  In many cases there are other means to find out
additional memory using subsystem specific interfaces, for instance
/proc/net/sockstat for TCP memory allocations.

Example output. You may not have all of these fields.

::

    > cat /proc/meminfo

    MemTotal:       32858820 kB
    MemFree:        21001236 kB
    MemAvailable:   27214312 kB
    Buffers:          581092 kB
    Cached:          5587612 kB
    SwapCached:            0 kB
    Active:          3237152 kB
    Inactive:        7586256 kB
    Active(anon):      94064 kB
    Inactive(anon):  4570616 kB
    Active(file):    3143088 kB
    Inactive(file):  3015640 kB
    Unevictable:           0 kB
    Mlocked:               0 kB
    SwapTotal:             0 kB
    SwapFree:              0 kB
    Zswap:              1904 kB
    Zswapped:           7792 kB
    Dirty:                12 kB
    Writeback:             0 kB
    AnonPages:       4654780 kB
    Mapped:           266244 kB
    Shmem:              9976 kB
    KReclaimable:     517708 kB
    Slab:             660044 kB
    SReclaimable:     517708 kB
    SUnreclaim:       142336 kB
    KernelStack:       11168 kB
    PageTables:        20540 kB
    SecPageTables:         0 kB
    NFS_Unstable:          0 kB
    Bounce:                0 kB
    WritebackTmp:          0 kB
    CommitLimit:    16429408 kB
    Committed_AS:    7715148 kB
    VmallocTotal:   34359738367 kB
    VmallocUsed:       40444 kB
    VmallocChunk:          0 kB
    Percpu:            29312 kB
    HardwareCorrupted:     0 kB
    AnonHugePages:   4149248 kB
    ShmemHugePages:        0 kB
    ShmemPmdMapped:        0 kB
    FileHugePages:         0 kB
    FilePmdMapped:         0 kB
    CmaTotal:              0 kB
    CmaFree:               0 kB
    HugePages_Total:       0
    HugePages_Free:        0
    HugePages_Rsvd:        0
    HugePages_Surp:        0
    Hugepagesize:       2048 kB
    Hugetlb:               0 kB
    DirectMap4k:      401152 kB
    DirectMap2M:    10008576 kB
    DirectMap1G:    24117248 kB

MemTotal
              Total usable RAM (i.e. physical RAM minus a few reserved
              bits and the kernel binary code)
MemFree
              Total free RAM. On highmem systems, the sum of LowFree+HighFree
MemAvailable
              An estimate of how much memory is available for starting new
              applications, without swapping. Calculated from MemFree,
              SReclaimable, the size of the file LRU lists, and the low
              watermarks in each zone.
              The estimate takes into account that the system needs some
              page cache to function well, and that not all reclaimable
              slab will be reclaimable, due to items being in use. The
              impact of those factors will vary from system to system.
Buffers
              Relatively temporary storage for raw disk blocks
              shouldn't get tremendously large (20MB or so)
Cached
              In-memory cache for files read from the disk (the
              pagecache) as well as tmpfs & shmem.
              Doesn't include SwapCached.
SwapCached
              Memory that once was swapped out, is swapped back in but
              still also is in the swapfile (if memory is needed it
              doesn't need to be swapped out AGAIN because it is already
              in the swapfile. This saves I/O)
Active
              Memory that has been used more recently and usually not
              reclaimed unless absolutely necessary.
Inactive
              Memory which has been less recently used.  It is more
              eligible to be reclaimed for other purposes
Unevictable
              Memory allocated for userspace which cannot be reclaimed, such
              as mlocked pages, ramfs backing pages, secret memfd pages etc.
Mlocked
              Memory locked with mlock().
HighTotal, HighFree
              Highmem is all memory above ~860MB of physical memory.
              Highmem areas are for use by userspace programs, or
              for the pagecache.  The kernel must use tricks to access
              this memory, making it slower to access than lowmem.
LowTotal, LowFree
              Lowmem is memory which can be used for everything that
              highmem can be used for, but it is also available for the
              kernel's use for its own data structures.  Among many
              other things, it is where everything from the Slab is
              allocated.  Bad things happen when you're out of lowmem.
SwapTotal
              total amount of swap space available
SwapFree
              Memory which has been evicted from RAM, and is temporarily
              on the disk
Zswap
              Memory consumed by the zswap backend (compressed size)
Zswapped
              Amount of anonymous memory stored in zswap (original size)
Dirty
              Memory which is waiting to get written back to the disk
Writeback
              Memory which is actively being written back to the disk
AnonPages
              Non-file backed pages mapped into userspace page tables
Mapped
              files which have been mmaped, such as libraries
Shmem
              Total memory used by shared memory (shmem) and tmpfs
KReclaimable
              Kernel allocations that the kernel will attempt to reclaim
              under memory pressure. Includes SReclaimable (below), and other
              direct allocations with a shrinker.
Slab
              in-kernel data structures cache
SReclaimable
              Part of Slab, that might be reclaimed, such as caches
SUnreclaim
              Part of Slab, that cannot be reclaimed on memory pressure
KernelStack
              Memory consumed by the kernel stacks of all tasks
PageTables
              Memory consumed by userspace page tables
SecPageTables
              Memory consumed by secondary page tables, this currently
              currently includes KVM mmu allocations on x86 and arm64.
NFS_Unstable
              Always zero. Previous counted pages which had been written to
              the server, but has not been committed to stable storage.
Bounce
              Memory used for block device "bounce buffers"
WritebackTmp
              Memory used by FUSE for temporary writeback buffers
CommitLimit
              Based on the overcommit ratio ('vm.overcommit_ratio'),
              this is the total amount of  memory currently available to
              be allocated on the system. This limit is only adhered to
              if strict overcommit accounting is enabled (mode 2 in
              'vm.overcommit_memory').

              The CommitLimit is calculated with the following formula::

                CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
                               overcommit_ratio / 100 + [total swap pages]

              For example, on a system with 1G of physical RAM and 7G
              of swap with a `vm.overcommit_ratio` of 30 it would
              yield a CommitLimit of 7.3G.

              For more details, see the memory overcommit documentation
              in mm/overcommit-accounting.
Committed_AS
              The amount of memory presently allocated on the system.
              The committed memory is a sum of all of the memory which
              has been allocated by processes, even if it has not been
              "used" by them as of yet. A process which malloc()'s 1G
              of memory, but only touches 300M of it will show up as
              using 1G. This 1G is memory which has been "committed" to
              by the VM and can be used at any time by the allocating
              application. With strict overcommit enabled on the system
              (mode 2 in 'vm.overcommit_memory'), allocations which would
              exceed the CommitLimit (detailed above) will not be permitted.
              This is useful if one needs to guarantee that processes will
              not fail due to lack of memory once that memory has been
              successfully allocated.
VmallocTotal
              total size of vmalloc virtual address space
VmallocUsed
              amount of vmalloc area which is used
VmallocChunk
              largest contiguous block of vmalloc area which is free
Percpu
              Memory allocated to the percpu allocator used to back percpu
              allocations. This stat excludes the cost of metadata.
HardwareCorrupted
              The amount of RAM/memory in KB, the kernel identifies as
              corrupted.
AnonHugePages
              Non-file backed huge pages mapped into userspace page tables
ShmemHugePages
              Memory used by shared memory (shmem) and tmpfs allocated
              with huge pages
ShmemPmdMapped
              Shared memory mapped into userspace with huge pages
FileHugePages
              Memory used for filesystem data (page cache) allocated
              with huge pages
FilePmdMapped
              Page cache mapped into userspace with huge pages
CmaTotal
              Memory reserved for the Contiguous Memory Allocator (CMA)
CmaFree
              Free remaining memory in the CMA reserves
HugePages_Total, HugePages_Free, HugePages_Rsvd, HugePages_Surp, Hugepagesize, Hugetlb
              See Documentation/admin-guide/mm/hugetlbpage.rst.
DirectMap4k, DirectMap2M, DirectMap1G
              Breakdown of page table sizes used in the kernel's
              identity mapping of RAM

vmallocinfo
~~~~~~~~~~~

Provides information about vmalloced/vmaped areas. One line per area,
containing the virtual address range of the area, size in bytes,
caller information of the creator, and optional information depending
on the kind of area:

 ==========  ===================================================
 pages=nr    number of pages
 phys=addr   if a physical address was specified
 ioremap     I/O mapping (ioremap() and friends)
 vmalloc     vmalloc() area
 vmap        vmap()ed pages
 user        VM_USERMAP area
 vpages      buffer for pages pointers was vmalloced (huge area)
 N<node>=nr  (Only on NUMA kernels)
             Number of pages allocated on memory node <node>
 ==========  ===================================================

::

    > cat /proc/vmallocinfo
    0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
    /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
    0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
    /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
    0xffffc20000302000-0xffffc20000304000    8192 acpi_tb_verify_table+0x21/0x4f...
    phys=7fee8000 ioremap
    0xffffc20000304000-0xffffc20000307000   12288 acpi_tb_verify_table+0x21/0x4f...
    phys=7fee7000 ioremap
    0xffffc2000031d000-0xffffc2000031f000    8192 init_vdso_vars+0x112/0x210
    0xffffc2000031f000-0xffffc2000032b000   49152 cramfs_uncompress_init+0x2e ...
    /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
    0xffffc2000033a000-0xffffc2000033d000   12288 sys_swapon+0x640/0xac0      ...
    pages=2 vmalloc N1=2
    0xffffc20000347000-0xffffc2000034c000   20480 xt_alloc_table_info+0xfe ...
    /0x130 [x_tables] pages=4 vmalloc N0=4
    0xffffffffa0000000-0xffffffffa000f000   61440 sys_init_module+0xc27/0x1d00 ...
    pages=14 vmalloc N2=14
    0xffffffffa000f000-0xffffffffa0014000   20480 sys_init_module+0xc27/0x1d00 ...
    pages=4 vmalloc N1=4
    0xffffffffa0014000-0xffffffffa0017000   12288 sys_init_module+0xc27/0x1d00 ...
    pages=2 vmalloc N1=2
    0xffffffffa0017000-0xffffffffa0022000   45056 sys_init_module+0xc27/0x1d00 ...
    pages=10 vmalloc N0=10


softirqs
~~~~~~~~

Provides counts of softirq handlers serviced since boot time, for each CPU.

::

    > cat /proc/softirqs
		  CPU0       CPU1       CPU2       CPU3
	HI:          0          0          0          0
    TIMER:       27166      27120      27097      27034
    NET_TX:          0          0          0         17
    NET_RX:         42          0          0         39
    BLOCK:           0          0        107       1121
    TASKLET:         0          0          0        290
    SCHED:       27035      26983      26971      26746
    HRTIMER:         0          0          0          0
	RCU:      1678       1769       2178       2250

1.3 Networking info in /proc/net
--------------------------------

The subdirectory  /proc/net  follows  the  usual  pattern. Table 1-8 shows the
additional values  you  get  for  IP  version 6 if you configure the kernel to
support this. Table 1-9 lists the files and their meaning.


.. table:: Table 1-8: IPv6 info in /proc/net

 ========== =====================================================
 File       Content
 ========== =====================================================
 udp6       UDP sockets (IPv6)
 tcp6       TCP sockets (IPv6)
 raw6       Raw device statistics (IPv6)
 igmp6      IP multicast addresses, which this host joined (IPv6)
 if_inet6   List of IPv6 interface addresses
 ipv6_route Kernel routing table for IPv6
 rt6_stats  Global IPv6 routing tables statistics
 sockstat6  Socket statistics (IPv6)
 snmp6      Snmp data (IPv6)
 ========== =====================================================

.. table:: Table 1-9: Network info in /proc/net

 ============= ================================================================
 File          Content
 ============= ================================================================
 arp           Kernel  ARP table
 dev           network devices with statistics
 dev_mcast     the Layer2 multicast groups a device is listening too
               (interface index, label, number of references, number of bound
               addresses).
 dev_stat      network device status
 ip_fwchains   Firewall chain linkage
 ip_fwnames    Firewall chain names
 ip_masq       Directory containing the masquerading tables
 ip_masquerade Major masquerading table
 netstat       Network statistics
 raw           raw device statistics
 route         Kernel routing table
 rpc           Directory containing rpc info
 rt_cache      Routing cache
 snmp          SNMP data
 sockstat      Socket statistics
 tcp           TCP  sockets
 udp           UDP sockets
 unix          UNIX domain sockets
 wireless      Wireless interface data (Wavelan etc)
 igmp          IP multicast addresses, which this host joined
 psched        Global packet scheduler parameters.
 netlink       List of PF_NETLINK sockets
 ip_mr_vifs    List of multicast virtual interfaces
 ip_mr_cache   List of multicast routing cache
 ============= ================================================================

You can  use  this  information  to see which network devices are available in
your system and how much traffic was routed over those devices::

  > cat /proc/net/dev
  Inter-|Receive                                                   |[...
   face |bytes    packets errs drop fifo frame compressed multicast|[...
      lo:  908188   5596     0    0    0     0          0         0 [...
    ppp0:15475140  20721   410    0    0   410          0         0 [...
    eth0:  614530   7085     0    0    0     0          0         1 [...

  ...] Transmit
  ...] bytes    packets errs drop fifo colls carrier compressed
  ...]  908188     5596    0    0    0     0       0          0
  ...] 1375103    17405    0    0    0     0       0          0
  ...] 1703981     5535    0    0    0     3       0          0

In addition, each Channel Bond interface has its own directory.  For
example, the bond0 device will have a directory called /proc/net/bond0/.
It will contain information that is specific to that bond, such as the
current slaves of the bond, the link status of the slaves, and how
many times the slaves link has failed.

1.4 SCSI info
-------------

If you  have  a  SCSI  host adapter in your system, you'll find a subdirectory
named after  the driver for this adapter in /proc/scsi. You'll also see a list
of all recognized SCSI devices in /proc/scsi::

  >cat /proc/scsi/scsi
  Attached devices:
  Host: scsi0 Channel: 00 Id: 00 Lun: 00
    Vendor: IBM      Model: DGHS09U          Rev: 03E0
    Type:   Direct-Access                    ANSI SCSI revision: 03
  Host: scsi0 Channel: 00 Id: 06 Lun: 00
    Vendor: PIONEER  Model: CD-ROM DR-U06S   Rev: 1.04
    Type:   CD-ROM                           ANSI SCSI revision: 02


The directory  named  after  the driver has one file for each adapter found in
the system.  These  files  contain information about the controller, including
the used  IRQ  and  the  IO  address range. The amount of information shown is
dependent on  the adapter you use. The example shows the output for an Adaptec
AHA-2940 SCSI adapter::

  > cat /proc/scsi/aic7xxx/0

  Adaptec AIC7xxx driver version: 5.1.19/3.2.4
  Compile Options:
    TCQ Enabled By Default : Disabled
    AIC7XXX_PROC_STATS     : Disabled
    AIC7XXX_RESET_DELAY    : 5
  Adapter Configuration:
             SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
                             Ultra Wide Controller
      PCI MMAPed I/O Base: 0xeb001000
   Adapter SEEPROM Config: SEEPROM found and used.
        Adaptec SCSI BIOS: Enabled
                      IRQ: 10
                     SCBs: Active 0, Max Active 2,
                           Allocated 15, HW 16, Page 255
               Interrupts: 160328
        BIOS Control Word: 0x18b6
     Adapter Control Word: 0x005b
     Extended Translation: Enabled
  Disconnect Enable Flags: 0xffff
       Ultra Enable Flags: 0x0001
   Tag Queue Enable Flags: 0x0000
  Ordered Queue Tag Flags: 0x0000
  Default Tag Queue Depth: 8
      Tagged Queue By Device array for aic7xxx host instance 0:
        {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
      Actual queue depth per device for aic7xxx host instance 0:
        {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
  Statistics:
  (scsi0:0:0:0)
    Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
    Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
    Total transfers 160151 (74577 reads and 85574 writes)
  (scsi0:0:6:0)
    Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
    Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
    Total transfers 0 (0 reads and 0 writes)


1.5 Parallel port info in /proc/parport
---------------------------------------

The directory  /proc/parport  contains information about the parallel ports of
your system.  It  has  one  subdirectory  for  each port, named after the port
number (0,1,2,...).

These directories contain the four files shown in Table 1-10.


.. table:: Table 1-10: Files in /proc/parport

 ========= ====================================================================
 File      Content
 ========= ====================================================================
 autoprobe Any IEEE-1284 device ID information that has been acquired.
 devices   list of the device drivers using that port. A + will appear by the
           name of the device currently using the port (it might not appear
           against any).
 hardware  Parallel port's base address, IRQ line and DMA channel.
 irq       IRQ that parport is using for that port. This is in a separate
           file to allow you to alter it by writing a new value in (IRQ
           number or none).
 ========= ====================================================================

1.6 TTY info in /proc/tty
-------------------------

Information about  the  available  and actually used tty's can be found in the
directory /proc/tty. You'll find  entries  for drivers and line disciplines in
this directory, as shown in Table 1-11.


.. table:: Table 1-11: Files in /proc/tty

 ============= ==============================================
 File          Content
 ============= ==============================================
 drivers       list of drivers and their usage
 ldiscs        registered line disciplines
 driver/serial usage statistic and status of single tty lines
 ============= ==============================================

To see  which  tty's  are  currently in use, you can simply look into the file
/proc/tty/drivers::

  > cat /proc/tty/drivers
  pty_slave            /dev/pts      136   0-255 pty:slave
  pty_master           /dev/ptm      128   0-255 pty:master
  pty_slave            /dev/ttyp       3   0-255 pty:slave
  pty_master           /dev/pty        2   0-255 pty:master
  serial               /dev/cua        5   64-67 serial:callout
  serial               /dev/ttyS       4   64-67 serial
  /dev/tty0            /dev/tty0       4       0 system:vtmaster
  /dev/ptmx            /dev/ptmx       5       2 system
  /dev/console         /dev/console    5       1 system:console
  /dev/tty             /dev/tty        5       0 system:/dev/tty
  unknown              /dev/tty        4    1-63 console


1.7 Miscellaneous kernel statistics in /proc/stat
-------------------------------------------------

Various pieces   of  information about  kernel activity  are  available in the
/proc/stat file.  All  of  the numbers reported  in  this file are  aggregates
since the system first booted.  For a quick look, simply cat the file::

  > cat /proc/stat
  cpu  2255 34 2290 22625563 6290 127 456 0 0 0
  cpu0 1132 34 1441 11311718 3675 127 438 0 0 0
  cpu1 1123 0 849 11313845 2614 0 18 0 0 0
  intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
  ctxt 1990473
  btime 1062191376
  processes 2915
  procs_running 1
  procs_blocked 0
  softirq 183433 0 21755 12 39 1137 231 21459 2263

The very first  "cpu" line aggregates the  numbers in all  of the other "cpuN"
lines.  These numbers identify the amount of time the CPU has spent performing
different kinds of work.  Time units are in USER_HZ (typically hundredths of a
second).  The meanings of the columns are as follows, from left to right:

- user: normal processes executing in user mode
- nice: niced processes executing in user mode
- system: processes executing in kernel mode
- idle: twiddling thumbs
- iowait: In a word, iowait stands for waiting for I/O to complete. But there
  are several problems:

  1. CPU will not wait for I/O to complete, iowait is the time that a task is
     waiting for I/O to complete. When CPU goes into idle state for
     outstanding task I/O, another task will be scheduled on this CPU.
  2. In a multi-core CPU, the task waiting for I/O to complete is not running
     on any CPU, so the iowait of each CPU is difficult to calculate.
  3. The value of iowait field in /proc/stat will decrease in certain
     conditions.

  So, the iowait is not reliable by reading from /proc/stat.
- irq: servicing interrupts
- softirq: servicing softirqs
- steal: involuntary wait
- guest: running a normal guest
- guest_nice: running a niced guest

The "intr" line gives counts of interrupts  serviced since boot time, for each
of the  possible system interrupts.   The first  column  is the  total of  all
interrupts serviced  including  unnumbered  architecture specific  interrupts;
each  subsequent column is the  total for that particular numbered interrupt.
Unnumbered interrupts are not shown, only summed into the total.

The "ctxt" line gives the total number of context switches across all CPUs.

The "btime" line gives  the time at which the  system booted, in seconds since
the Unix epoch.

The "processes" line gives the number  of processes and threads created, which
includes (but  is not limited  to) those  created by  calls to the  fork() and
clone() system calls.

The "procs_running" line gives the total number of threads that are
running or ready to run (i.e., the total number of runnable threads).

The   "procs_blocked" line gives  the  number of  processes currently blocked,
waiting for I/O to complete.

The "softirq" line gives counts of softirqs serviced since boot time, for each
of the possible system softirqs. The first column is the total of all
softirqs serviced; each subsequent column is the total for that particular
softirq.


1.8 Ext4 file system parameters
-------------------------------

Information about mounted ext4 file systems can be found in
/proc/fs/ext4.  Each mounted filesystem will have a directory in
/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
/proc/fs/ext4/dm-0).   The files in each per-device directory are shown
in Table 1-12, below.

.. table:: Table 1-12: Files in /proc/fs/ext4/<devname>

 ==============  ==========================================================
 File            Content
 mb_groups       details of multiblock allocator buddy cache of free blocks
 ==============  ==========================================================

1.9 /proc/consoles
-------------------
Shows registered system console lines.

To see which character device lines are currently used for the system console
/dev/console, you may simply look into the file /proc/consoles::

  > cat /proc/consoles
  tty0                 -WU (ECp)       4:7
  ttyS0                -W- (Ep)        4:64

The columns are:

+--------------------+-------------------------------------------------------+
| device             | name of the device                                    |
+====================+=======================================================+
| operations         | * R = can do read operations                          |
|                    | * W = can do write operations                         |
|                    | * U = can do unblank                                  |
+--------------------+-------------------------------------------------------+
| flags              | * E = it is enabled                                   |
|                    | * C = it is preferred console                         |
|                    | * B = it is primary boot console                      |
|                    | * p = it is used for printk buffer                    |
|                    | * b = it is not a TTY but a Braille device            |
|                    | * a = it is safe to use when cpu is offline           |
+--------------------+-------------------------------------------------------+
| major:minor        | major and minor number of the device separated by a   |
|                    | colon                                                 |
+--------------------+-------------------------------------------------------+

Summary
-------

The /proc file system serves information about the running system. It not only
allows access to process data but also allows you to request the kernel status
by reading files in the hierarchy.

The directory  structure  of /proc reflects the types of information and makes
it easy, if not obvious, where to look for specific data.

Chapter 2: Modifying System Parameters
======================================

In This Chapter
---------------

* Modifying kernel parameters by writing into files found in /proc/sys
* Exploring the files which modify certain parameters
* Review of the /proc/sys file tree

------------------------------------------------------------------------------

A very  interesting part of /proc is the directory /proc/sys. This is not only
a source  of  information,  it also allows you to change parameters within the
kernel. Be  very  careful  when attempting this. You can optimize your system,
but you  can  also  cause  it  to  crash.  Never  alter kernel parameters on a
production system.  Set  up  a  development machine and test to make sure that
everything works  the  way  you want it to. You may have no alternative but to
reboot the machine once an error has been made.

To change  a  value,  simply  echo  the new value into the file.
You need to be root to do this. You  can  create  your  own  boot script
to perform this every time your system boots.

The files  in /proc/sys can be used to fine tune and monitor miscellaneous and
general things  in  the operation of the Linux kernel. Since some of the files
can inadvertently  disrupt  your  system,  it  is  advisable  to  read  both
documentation and  source  before actually making adjustments. In any case, be
very careful  when  writing  to  any  of these files. The entries in /proc may
change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
review the kernel documentation in the directory /usr/src/linux/Documentation.
This chapter  is  heavily  based  on the documentation included in the pre 2.2
kernels, and became part of it in version 2.2.1 of the Linux kernel.

Please see: Documentation/admin-guide/sysctl/ directory for descriptions of these
entries.

Summary
-------

Certain aspects  of  kernel  behavior  can be modified at runtime, without the
need to  recompile  the kernel, or even to reboot the system. The files in the
/proc/sys tree  can  not only be read, but also modified. You can use the echo
command to write value into these files, thereby changing the default settings
of the kernel.


Chapter 3: Per-process Parameters
=================================

3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
--------------------------------------------------------------------------------

These files can be used to adjust the badness heuristic used to select which
process gets killed in out of memory (oom) conditions.

The badness heuristic assigns a value to each candidate task ranging from 0
(never kill) to 1000 (always kill) to determine which process is targeted.  The
units are roughly a proportion along that range of allowed memory the process
may allocate from based on an estimation of its current memory and swap use.
For example, if a task is using all allowed memory, its badness score will be
1000.  If it is using half of its allowed memory, its score will be 500.

The amount of "allowed" memory depends on the context in which the oom killer
was called.  If it is due to the memory assigned to the allocating task's cpuset
being exhausted, the allowed memory represents the set of mems assigned to that
cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
memory represents the set of mempolicy nodes.  If it is due to a memory
limit (or swap limit) being reached, the allowed memory is that configured
limit.  Finally, if it is due to the entire system being out of memory, the
allowed memory represents all allocatable resources.

The value of /proc/<pid>/oom_score_adj is added to the badness score before it
is used to determine which task to kill.  Acceptable values range from -1000
(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
polarize the preference for oom killing either by always preferring a certain
task or completely disabling it.  The lowest possible value, -1000, is
equivalent to disabling oom killing entirely for that task since it will always
report a badness score of 0.

Consequently, it is very simple for userspace to define the amount of memory to
consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
example, is roughly equivalent to allowing the remainder of tasks sharing the
same system, cpuset, mempolicy, or memory controller resources to use at least
50% more memory.  A value of -500, on the other hand, would be roughly
equivalent to discounting 50% of the task's allowed memory from being considered
as scoring against the task.

For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
be used to tune the badness score.  Its acceptable values range from -16
(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
(OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
scaled linearly with /proc/<pid>/oom_score_adj.

The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
requires CAP_SYS_RESOURCE.


3.2 /proc/<pid>/oom_score - Display current oom-killer score
-------------------------------------------------------------

This file can be used to check the current score used by the oom-killer for
any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
process should be killed in an out-of-memory situation.

Please note that the exported value includes oom_score_adj so it is
effectively in range [0,2000].


3.3  /proc/<pid>/io - Display the IO accounting fields
-------------------------------------------------------

This file contains IO statistics for each running process.

Example
~~~~~~~

::

    test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
    [1] 3828

    test:/tmp # cat /proc/3828/io
    rchar: 323934931
    wchar: 323929600
    syscr: 632687
    syscw: 632675
    read_bytes: 0
    write_bytes: 323932160
    cancelled_write_bytes: 0


Description
~~~~~~~~~~~

rchar
^^^^^

I/O counter: chars read
The number of bytes which this task has caused to be read from storage. This
is simply the sum of bytes which this process passed to read() and pread().
It includes things like tty IO and it is unaffected by whether or not actual
physical disk IO was required (the read might have been satisfied from
pagecache).


wchar
^^^^^

I/O counter: chars written
The number of bytes which this task has caused, or shall cause to be written
to disk. Similar caveats apply here as with rchar.


syscr
^^^^^

I/O counter: read syscalls
Attempt to count the number of read I/O operations, i.e. syscalls like read()
and pread().


syscw
^^^^^

I/O counter: write syscalls
Attempt to count the number of write I/O operations, i.e. syscalls like
write() and pwrite().


read_bytes
^^^^^^^^^^

I/O counter: bytes read
Attempt to count the number of bytes which this process really did cause to
be fetched from the storage layer. Done at the submit_bio() level, so it is
accurate for block-backed filesystems. <please add status regarding NFS and
CIFS at a later time>


write_bytes
^^^^^^^^^^^

I/O counter: bytes written
Attempt to count the number of bytes which this process caused to be sent to
the storage layer. This is done at page-dirtying time.


cancelled_write_bytes
^^^^^^^^^^^^^^^^^^^^^

The big inaccuracy here is truncate. If a process writes 1MB to a file and
then deletes the file, it will in fact perform no writeout. But it will have
been accounted as having caused 1MB of write.
In other words: The number of bytes which this process caused to not happen,
by truncating pagecache. A task can cause "negative" IO too. If this task
truncates some dirty pagecache, some IO which another task has been accounted
for (in its write_bytes) will not be happening. We _could_ just subtract that
from the truncating task's write_bytes, but there is information loss in doing
that.


.. Note::

   At its current implementation state, this is a bit racy on 32-bit machines:
   if process A reads process B's /proc/pid/io while process B is updating one
   of those 64-bit counters, process A could see an intermediate result.


More information about this can be found within the taskstats documentation in
Documentation/accounting.

3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
---------------------------------------------------------------
When a process is dumped, all anonymous memory is written to a core file as
long as the size of the core file isn't limited. But sometimes we don't want
to dump some memory segments, for example, huge shared memory or DAX.
Conversely, sometimes we want to save file-backed memory segments into a core
file, not only the individual files.

/proc/<pid>/coredump_filter allows you to customize which memory segments
will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
of memory types. If a bit of the bitmask is set, memory segments of the
corresponding memory type are dumped, otherwise they are not dumped.

The following 9 memory types are supported:

  - (bit 0) anonymous private memory
  - (bit 1) anonymous shared memory
  - (bit 2) file-backed private memory
  - (bit 3) file-backed shared memory
  - (bit 4) ELF header pages in file-backed private memory areas (it is
    effective only if the bit 2 is cleared)
  - (bit 5) hugetlb private memory
  - (bit 6) hugetlb shared memory
  - (bit 7) DAX private memory
  - (bit 8) DAX shared memory

  Note that MMIO pages such as frame buffer are never dumped and vDSO pages
  are always dumped regardless of the bitmask status.

  Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
  only affected by bit 5-6, and DAX is only affected by bits 7-8.

The default value of coredump_filter is 0x33; this means all anonymous memory
segments, ELF header pages and hugetlb private memory are dumped.

If you don't want to dump all shared memory segments attached to pid 1234,
write 0x31 to the process's proc file::

  $ echo 0x31 > /proc/1234/coredump_filter

When a new process is created, the process inherits the bitmask status from its
parent. It is useful to set up coredump_filter before the program runs.
For example::

  $ echo 0x7 > /proc/self/coredump_filter
  $ ./some_program

3.5	/proc/<pid>/mountinfo - Information about mounts
--------------------------------------------------------

This file contains lines of the form::

    36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
    (1)(2)(3)   (4)   (5)      (6)     (n…m) (m+1)(m+2) (m+3)         (m+4)

    (1)   mount ID:        unique identifier of the mount (may be reused after umount)
    (2)   parent ID:       ID of parent (or of self for the top of the mount tree)
    (3)   major:minor:     value of st_dev for files on filesystem
    (4)   root:            root of the mount within the filesystem
    (5)   mount point:     mount point relative to the process's root
    (6)   mount options:   per mount options
    (n…m) optional fields: zero or more fields of the form "tag[:value]"
    (m+1) separator:       marks the end of the optional fields
    (m+2) filesystem type: name of filesystem of the form "type[.subtype]"
    (m+3) mount source:    filesystem specific information or "none"
    (m+4) super options:   per super block options

Parsers should ignore all unrecognised optional fields.  Currently the
possible optional fields are:

================  ==============================================================
shared:X          mount is shared in peer group X
master:X          mount is slave to peer group X
propagate_from:X  mount is slave and receives propagation from peer group X [#]_
unbindable        mount is unbindable
================  ==============================================================

.. [#] X is the closest dominant peer group under the process's root.  If
       X is the immediate master of the mount, or if there's no dominant peer
       group under the same root, then only the "master:X" field is present
       and not the "propagate_from:X" field.

For more information on mount propagation see:

  Documentation/filesystems/sharedsubtree.rst


3.6	/proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
--------------------------------------------------------
These files provide a method to access a task's comm value. It also allows for
a task to set its own or one of its thread siblings comm value. The comm value
is limited in size compared to the cmdline value, so writing anything longer
then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
comm value.


3.7	/proc/<pid>/task/<tid>/children - Information about task children
-------------------------------------------------------------------------
This file provides a fast way to retrieve first level children pids
of a task pointed by <pid>/<tid> pair. The format is a space separated
stream of pids.

Note the "first level" here -- if a child has its own children they will
not be listed here; one needs to read /proc/<children-pid>/task/<tid>/children
to obtain the descendants.

Since this interface is intended to be fast and cheap it doesn't
guarantee to provide precise results and some children might be
skipped, especially if they've exited right after we printed their
pids, so one needs to either stop or freeze processes being inspected
if precise results are needed.


3.8	/proc/<pid>/fdinfo/<fd> - Information about opened file
---------------------------------------------------------------
This file provides information associated with an opened file. The regular
files have at least four fields -- 'pos', 'flags', 'mnt_id' and 'ino'.
The 'pos' represents the current offset of the opened file in decimal
form [see lseek(2) for details], 'flags' denotes the octal O_xxx mask the
file has been created with [see open(2) for details] and 'mnt_id' represents
mount ID of the file system containing the opened file [see 3.5
/proc/<pid>/mountinfo for details]. 'ino' represents the inode number of
the file.

A typical output is::

	pos:	0
	flags:	0100002
	mnt_id:	19
	ino:	63107

All locks associated with a file descriptor are shown in its fdinfo too::

    lock:       1: FLOCK  ADVISORY  WRITE 359 00:13:11691 0 EOF

The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
pair provide additional information particular to the objects they represent.

Eventfd files
~~~~~~~~~~~~~

::

	pos:	0
	flags:	04002
	mnt_id:	9
	ino:	63107
	eventfd-count:	5a

where 'eventfd-count' is hex value of a counter.

Signalfd files
~~~~~~~~~~~~~~

::

	pos:	0
	flags:	04002
	mnt_id:	9
	ino:	63107
	sigmask:	0000000000000200

where 'sigmask' is hex value of the signal mask associated
with a file.

Epoll files
~~~~~~~~~~~

::

	pos:	0
	flags:	02
	mnt_id:	9
	ino:	63107
	tfd:        5 events:       1d data: ffffffffffffffff pos:0 ino:61af sdev:7

where 'tfd' is a target file descriptor number in decimal form,
'events' is events mask being watched and the 'data' is data
associated with a target [see epoll(7) for more details].

The 'pos' is current offset of the target file in decimal form
[see lseek(2)], 'ino' and 'sdev' are inode and device numbers
where target file resides, all in hex format.

Fsnotify files
~~~~~~~~~~~~~~
For inotify files the format is the following::

	pos:	0
	flags:	02000000
	mnt_id:	9
	ino:	63107
	inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d

where 'wd' is a watch descriptor in decimal form, i.e. a target file
descriptor number, 'ino' and 'sdev' are inode and device where the
target file resides and the 'mask' is the mask of events, all in hex
form [see inotify(7) for more details].

If the kernel was built with exportfs support, the path to the target
file is encoded as a file handle.  The file handle is provided by three
fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
format.

If the kernel is built without exportfs support the file handle won't be
printed out.

If there is no inotify mark attached yet the 'inotify' line will be omitted.

For fanotify files the format is::

	pos:	0
	flags:	02
	mnt_id:	9
	ino:	63107
	fanotify flags:10 event-flags:0
	fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
	fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4

where fanotify 'flags' and 'event-flags' are values used in fanotify_init
call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
flags associated with mark which are tracked separately from events
mask. 'ino' and 'sdev' are target inode and device, 'mask' is the events
mask and 'ignored_mask' is the mask of events which are to be ignored.
All are in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
provide information about flags and mask used in fanotify_mark
call [see fsnotify manpage for details].

While the first three lines are mandatory and always printed, the rest is
optional and may be omitted if no marks created yet.

Timerfd files
~~~~~~~~~~~~~

::

	pos:	0
	flags:	02
	mnt_id:	9
	ino:	63107
	clockid: 0
	ticks: 0
	settime flags: 01
	it_value: (0, 49406829)
	it_interval: (1, 0)

where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
that have occurred [see timerfd_create(2) for details]. 'settime flags' are
flags in octal form been used to setup the timer [see timerfd_settime(2) for
details]. 'it_value' is remaining time until the timer expiration.
'it_interval' is the interval for the timer. Note the timer might be set up
with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
still exhibits timer's remaining time.

DMA Buffer files
~~~~~~~~~~~~~~~~

::

	pos:	0
	flags:	04002
	mnt_id:	9
	ino:	63107
	size:   32768
	count:  2
	exp_name:  system-heap

where 'size' is the size of the DMA buffer in bytes. 'count' is the file count of
the DMA buffer file. 'exp_name' is the name of the DMA buffer exporter.

3.9	/proc/<pid>/map_files - Information about memory mapped files
---------------------------------------------------------------------
This directory contains symbolic links which represent memory mapped files
the process is maintaining.  Example output::

     | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
     | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
     | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
     | ...
     | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
     | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls

The name of a link represents the virtual memory bounds of a mapping, i.e.
vm_area_struct::vm_start-vm_area_struct::vm_end.

The main purpose of the map_files is to retrieve a set of memory mapped
files in a fast way instead of parsing /proc/<pid>/maps or
/proc/<pid>/smaps, both of which contain many more records.  At the same
time one can open(2) mappings from the listings of two processes and
comparing their inode numbers to figure out which anonymous memory areas
are actually shared.

3.10	/proc/<pid>/timerslack_ns - Task timerslack value
---------------------------------------------------------
This file provides the value of the task's timerslack value in nanoseconds.
This value specifies an amount of time that normal timers may be deferred
in order to coalesce timers and avoid unnecessary wakeups.

This allows a task's interactivity vs power consumption tradeoff to be
adjusted.

Writing 0 to the file will set the task's timerslack to the default value.

Valid values are from 0 - ULLONG_MAX

An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
permissions on the task specified to change its timerslack_ns value.

3.11	/proc/<pid>/patch_state - Livepatch patch operation state
-----------------------------------------------------------------
When CONFIG_LIVEPATCH is enabled, this file displays the value of the
patch state for the task.

A value of '-1' indicates that no patch is in transition.

A value of '0' indicates that a patch is in transition and the task is
unpatched.  If the patch is being enabled, then the task hasn't been
patched yet.  If the patch is being disabled, then the task has already
been unpatched.

A value of '1' indicates that a patch is in transition and the task is
patched.  If the patch is being enabled, then the task has already been
patched.  If the patch is being disabled, then the task hasn't been
unpatched yet.

3.12 /proc/<pid>/arch_status - task architecture specific status
-------------------------------------------------------------------
When CONFIG_PROC_PID_ARCH_STATUS is enabled, this file displays the
architecture specific status of the task.

Example
~~~~~~~

::

 $ cat /proc/6753/arch_status
 AVX512_elapsed_ms:      8

Description
~~~~~~~~~~~

x86 specific entries
~~~~~~~~~~~~~~~~~~~~~

AVX512_elapsed_ms
^^^^^^^^^^^^^^^^^^

  If AVX512 is supported on the machine, this entry shows the milliseconds
  elapsed since the last time AVX512 usage was recorded. The recording
  happens on a best effort basis when a task is scheduled out. This means
  that the value depends on two factors:

    1) The time which the task spent on the CPU without being scheduled
       out. With CPU isolation and a single runnable task this can take
       several seconds.

    2) The time since the task was scheduled out last. Depending on the
       reason for being scheduled out (time slice exhausted, syscall ...)
       this can be arbitrary long time.

  As a consequence the value cannot be considered precise and authoritative
  information. The application which uses this information has to be aware
  of the overall scenario on the system in order to determine whether a
  task is a real AVX512 user or not. Precise information can be obtained
  with performance counters.

  A special value of '-1' indicates that no AVX512 usage was recorded, thus
  the task is unlikely an AVX512 user, but depends on the workload and the
  scheduling scenario, it also could be a false negative mentioned above.

Chapter 4: Configuring procfs
=============================

4.1	Mount options
---------------------

The following mount options are supported:

	=========	========================================================
	hidepid=	Set /proc/<pid>/ access mode.
	gid=		Set the group authorized to learn processes information.
	subset=		Show only the specified subset of procfs.
	=========	========================================================

hidepid=off or hidepid=0 means classic mode - everybody may access all
/proc/<pid>/ directories (default).

hidepid=noaccess or hidepid=1 means users may not access any /proc/<pid>/
directories but their own.  Sensitive files like cmdline, sched*, status are now
protected against other users.  This makes it impossible to learn whether any
user runs specific program (given the program doesn't reveal itself by its
behaviour).  As an additional bonus, as /proc/<pid>/cmdline is unaccessible for
other users, poorly written programs passing sensitive information via program
arguments are now protected against local eavesdroppers.

hidepid=invisible or hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be
fully invisible to other users.  It doesn't mean that it hides a fact whether a
process with a specific pid value exists (it can be learned by other means, e.g.
by "kill -0 $PID"), but it hides process' uid and gid, which may be learned by
stat()'ing /proc/<pid>/ otherwise.  It greatly complicates an intruder's task of
gathering information about running processes, whether some daemon runs with
elevated privileges, whether other user runs some sensitive program, whether
other users run any program at all, etc.

hidepid=ptraceable or hidepid=4 means that procfs should only contain
/proc/<pid>/ directories that the caller can ptrace.

gid= defines a group authorized to learn processes information otherwise
prohibited by hidepid=.  If you use some daemon like identd which needs to learn
information about processes information, just add identd to this group.

subset=pid hides all top level files and directories in the procfs that
are not related to tasks.

Chapter 5: Filesystem behavior
==============================

Originally, before the advent of pid namepsace, procfs was a global file
system. It means that there was only one procfs instance in the system.

When pid namespace was added, a separate procfs instance was mounted in
each pid namespace. So, procfs mount options are global among all
mountpoints within the same namespace::

	# grep ^proc /proc/mounts
	proc /proc proc rw,relatime,hidepid=2 0 0

	# strace -e mount mount -o hidepid=1 -t proc proc /tmp/proc
	mount("proc", "/tmp/proc", "proc", 0, "hidepid=1") = 0
	+++ exited with 0 +++

	# grep ^proc /proc/mounts
	proc /proc proc rw,relatime,hidepid=2 0 0
	proc /tmp/proc proc rw,relatime,hidepid=2 0 0

and only after remounting procfs mount options will change at all
mountpoints::

	# mount -o remount,hidepid=1 -t proc proc /tmp/proc

	# grep ^proc /proc/mounts
	proc /proc proc rw,relatime,hidepid=1 0 0
	proc /tmp/proc proc rw,relatime,hidepid=1 0 0

This behavior is different from the behavior of other filesystems.

The new procfs behavior is more like other filesystems. Each procfs mount
creates a new procfs instance. Mount options affect own procfs instance.
It means that it became possible to have several procfs instances
displaying tasks with different filtering options in one pid namespace::

	# mount -o hidepid=invisible -t proc proc /proc
	# mount -o hidepid=noaccess -t proc proc /tmp/proc
	# grep ^proc /proc/mounts
	proc /proc proc rw,relatime,hidepid=invisible 0 0
	proc /tmp/proc proc rw,relatime,hidepid=noaccess 0 0