xref: /linux/Documentation/filesystems/proc.rst (revision afcd48134c58d6af45fb3fdb648f1260b20f2326)
1.. SPDX-License-Identifier: GPL-2.0
2
3====================
4The /proc Filesystem
5====================
6
7=====================  =======================================  ================
8/proc/sys              Terrehon Bowden <terrehon@pacbell.net>,  October 7 1999
9                       Bodo Bauer <bb@ricochet.net>
102.4.x update	       Jorge Nerin <comandante@zaralinux.com>   November 14 2000
11move /proc/sys	       Shen Feng <shen@cn.fujitsu.com>	        April 1 2009
12fixes/update part 1.1  Stefani Seibold <stefani@seibold.net>    June 9 2009
13=====================  =======================================  ================
14
15
16
17.. Table of Contents
18
19  0     Preface
20  0.1	Introduction/Credits
21  0.2	Legal Stuff
22
23  1	Collecting System Information
24  1.1	Process-Specific Subdirectories
25  1.2	Kernel data
26  1.3	IDE devices in /proc/ide
27  1.4	Networking info in /proc/net
28  1.5	SCSI info
29  1.6	Parallel port info in /proc/parport
30  1.7	TTY info in /proc/tty
31  1.8	Miscellaneous kernel statistics in /proc/stat
32  1.9	Ext4 file system parameters
33
34  2	Modifying System Parameters
35
36  3	Per-Process Parameters
37  3.1	/proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj - Adjust the oom-killer
38								score
39  3.2	/proc/<pid>/oom_score - Display current oom-killer score
40  3.3	/proc/<pid>/io - Display the IO accounting fields
41  3.4	/proc/<pid>/coredump_filter - Core dump filtering settings
42  3.5	/proc/<pid>/mountinfo - Information about mounts
43  3.6	/proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
44  3.7   /proc/<pid>/task/<tid>/children - Information about task children
45  3.8   /proc/<pid>/fdinfo/<fd> - Information about opened file
46  3.9   /proc/<pid>/map_files - Information about memory mapped files
47  3.10  /proc/<pid>/timerslack_ns - Task timerslack value
48  3.11	/proc/<pid>/patch_state - Livepatch patch operation state
49  3.12	/proc/<pid>/arch_status - Task architecture specific information
50  3.13  /proc/<pid>/fd - List of symlinks to open files
51
52  4	Configuring procfs
53  4.1	Mount options
54
55  5	Filesystem behavior
56
57Preface
58=======
59
600.1 Introduction/Credits
61------------------------
62
63This documentation is  part of a soon (or  so we hope) to be  released book on
64the SuSE  Linux distribution. As  there is  no complete documentation  for the
65/proc file system and we've used  many freely available sources to write these
66chapters, it  seems only fair  to give the work  back to the  Linux community.
67This work is  based on the 2.2.*  kernel version and the  upcoming 2.4.*. I'm
68afraid it's still far from complete, but we  hope it will be useful. As far as
69we know, it is the first 'all-in-one' document about the /proc file system. It
70is focused  on the Intel  x86 hardware,  so if you  are looking for  PPC, ARM,
71SPARC, AXP, etc., features, you probably  won't find what you are looking for.
72It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
73additions and patches  are welcome and will  be added to this  document if you
74mail them to Bodo.
75
76We'd like  to  thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
77other people for help compiling this documentation. We'd also like to extend a
78special thank  you to Andi Kleen for documentation, which we relied on heavily
79to create  this  document,  as well as the additional information he provided.
80Thanks to  everybody  else  who contributed source or docs to the Linux kernel
81and helped create a great piece of software... :)
82
83If you  have  any comments, corrections or additions, please don't hesitate to
84contact Bodo  Bauer  at  bb@ricochet.net.  We'll  be happy to add them to this
85document.
86
87The   latest   version    of   this   document   is    available   online   at
88https://www.kernel.org/doc/html/latest/filesystems/proc.html
89
90If  the above  direction does  not works  for you,  you could  try the  kernel
91mailing  list  at  linux-kernel@vger.kernel.org  and/or try  to  reach  me  at
92comandante@zaralinux.com.
93
940.2 Legal Stuff
95---------------
96
97We don't  guarantee  the  correctness  of this document, and if you come to us
98complaining about  how  you  screwed  up  your  system  because  of  incorrect
99documentation, we won't feel responsible...
100
101Chapter 1: Collecting System Information
102========================================
103
104In This Chapter
105---------------
106* Investigating  the  properties  of  the  pseudo  file  system  /proc and its
107  ability to provide information on the running Linux system
108* Examining /proc's structure
109* Uncovering  various  information  about the kernel and the processes running
110  on the system
111
112------------------------------------------------------------------------------
113
114The proc  file  system acts as an interface to internal data structures in the
115kernel. It  can  be  used to obtain information about the system and to change
116certain kernel parameters at runtime (sysctl).
117
118First, we'll  take  a  look  at the read-only parts of /proc. In Chapter 2, we
119show you how you can use /proc/sys to change settings.
120
1211.1 Process-Specific Subdirectories
122-----------------------------------
123
124The directory  /proc  contains  (among other things) one subdirectory for each
125process running on the system, which is named after the process ID (PID).
126
127The link  'self'  points to  the process reading the file system. Each process
128subdirectory has the entries listed in Table 1-1.
129
130Note that an open file descriptor to /proc/<pid> or to any of its
131contained files or subdirectories does not prevent <pid> being reused
132for some other process in the event that <pid> exits. Operations on
133open /proc/<pid> file descriptors corresponding to dead processes
134never act on any new process that the kernel may, through chance, have
135also assigned the process ID <pid>. Instead, operations on these FDs
136usually fail with ESRCH.
137
138.. table:: Table 1-1: Process specific entries in /proc
139
140 =============  ===============================================================
141 File		Content
142 =============  ===============================================================
143 clear_refs	Clears page referenced bits shown in smaps output
144 cmdline	Command line arguments
145 cpu		Current and last cpu in which it was executed	(2.4)(smp)
146 cwd		Link to the current working directory
147 environ	Values of environment variables
148 exe		Link to the executable of this process
149 fd		Directory, which contains all file descriptors
150 maps		Memory maps to executables and library files	(2.4)
151 mem		Memory held by this process
152 root		Link to the root directory of this process
153 stat		Process status
154 statm		Process memory status information
155 status		Process status in human readable form
156 wchan		Present with CONFIG_KALLSYMS=y: it shows the kernel function
157		symbol the task is blocked in - or "0" if not blocked.
158 pagemap	Page table
159 stack		Report full stack trace, enable via CONFIG_STACKTRACE
160 smaps		An extension based on maps, showing the memory consumption of
161		each mapping and flags associated with it
162 smaps_rollup	Accumulated smaps stats for all mappings of the process.  This
163		can be derived from smaps, but is faster and more convenient
164 numa_maps	An extension based on maps, showing the memory locality and
165		binding policy as well as mem usage (in pages) of each mapping.
166 =============  ===============================================================
167
168For example, to get the status information of a process, all you have to do is
169read the file /proc/PID/status::
170
171  >cat /proc/self/status
172  Name:   cat
173  State:  R (running)
174  Tgid:   5452
175  Pid:    5452
176  PPid:   743
177  TracerPid:      0						(2.4)
178  Uid:    501     501     501     501
179  Gid:    100     100     100     100
180  FDSize: 256
181  Groups: 100 14 16
182  Kthread:    0
183  VmPeak:     5004 kB
184  VmSize:     5004 kB
185  VmLck:         0 kB
186  VmHWM:       476 kB
187  VmRSS:       476 kB
188  RssAnon:             352 kB
189  RssFile:             120 kB
190  RssShmem:              4 kB
191  VmData:      156 kB
192  VmStk:        88 kB
193  VmExe:        68 kB
194  VmLib:      1412 kB
195  VmPTE:        20 kb
196  VmSwap:        0 kB
197  HugetlbPages:          0 kB
198  CoreDumping:    0
199  THP_enabled:	  1
200  Threads:        1
201  SigQ:   0/28578
202  SigPnd: 0000000000000000
203  ShdPnd: 0000000000000000
204  SigBlk: 0000000000000000
205  SigIgn: 0000000000000000
206  SigCgt: 0000000000000000
207  CapInh: 00000000fffffeff
208  CapPrm: 0000000000000000
209  CapEff: 0000000000000000
210  CapBnd: ffffffffffffffff
211  CapAmb: 0000000000000000
212  NoNewPrivs:     0
213  Seccomp:        0
214  Speculation_Store_Bypass:       thread vulnerable
215  SpeculationIndirectBranch:      conditional enabled
216  voluntary_ctxt_switches:        0
217  nonvoluntary_ctxt_switches:     1
218
219This shows you nearly the same information you would get if you viewed it with
220the ps  command.  In  fact,  ps  uses  the  proc  file  system  to  obtain its
221information.  But you get a more detailed  view of the  process by reading the
222file /proc/PID/status. It fields are described in table 1-2.
223
224The  statm  file  contains  more  detailed  information about the process
225memory usage. Its seven fields are explained in Table 1-3.  The stat file
226contains detailed information about the process itself.  Its fields are
227explained in Table 1-4.
228
229(for SMP CONFIG users)
230
231For making accounting scalable, RSS related information are handled in an
232asynchronous manner and the value may not be very precise. To see a precise
233snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
234It's slow but very precise.
235
236.. table:: Table 1-2: Contents of the status fields (as of 4.19)
237
238 ==========================  ===================================================
239 Field                       Content
240 ==========================  ===================================================
241 Name                        filename of the executable
242 Umask                       file mode creation mask
243 State                       state (R is running, S is sleeping, D is sleeping
244                             in an uninterruptible wait, Z is zombie,
245			     T is traced or stopped)
246 Tgid                        thread group ID
247 Ngid                        NUMA group ID (0 if none)
248 Pid                         process id
249 PPid                        process id of the parent process
250 TracerPid                   PID of process tracing this process (0 if not, or
251                             the tracer is outside of the current pid namespace)
252 Uid                         Real, effective, saved set, and  file system UIDs
253 Gid                         Real, effective, saved set, and  file system GIDs
254 FDSize                      number of file descriptor slots currently allocated
255 Groups                      supplementary group list
256 NStgid                      descendant namespace thread group ID hierarchy
257 NSpid                       descendant namespace process ID hierarchy
258 NSpgid                      descendant namespace process group ID hierarchy
259 NSsid                       descendant namespace session ID hierarchy
260 Kthread                     kernel thread flag, 1 is yes, 0 is no
261 VmPeak                      peak virtual memory size
262 VmSize                      total program size
263 VmLck                       locked memory size
264 VmPin                       pinned memory size
265 VmHWM                       peak resident set size ("high water mark")
266 VmRSS                       size of memory portions. It contains the three
267                             following parts
268                             (VmRSS = RssAnon + RssFile + RssShmem)
269 RssAnon                     size of resident anonymous memory
270 RssFile                     size of resident file mappings
271 RssShmem                    size of resident shmem memory (includes SysV shm,
272                             mapping of tmpfs and shared anonymous mappings)
273 VmData                      size of private data segments
274 VmStk                       size of stack segments
275 VmExe                       size of text segment
276 VmLib                       size of shared library code
277 VmPTE                       size of page table entries
278 VmSwap                      amount of swap used by anonymous private data
279                             (shmem swap usage is not included)
280 HugetlbPages                size of hugetlb memory portions
281 CoreDumping                 process's memory is currently being dumped
282                             (killing the process may lead to a corrupted core)
283 THP_enabled		     process is allowed to use THP (returns 0 when
284			     PR_SET_THP_DISABLE is set on the process
285 Threads                     number of threads
286 SigQ                        number of signals queued/max. number for queue
287 SigPnd                      bitmap of pending signals for the thread
288 ShdPnd                      bitmap of shared pending signals for the process
289 SigBlk                      bitmap of blocked signals
290 SigIgn                      bitmap of ignored signals
291 SigCgt                      bitmap of caught signals
292 CapInh                      bitmap of inheritable capabilities
293 CapPrm                      bitmap of permitted capabilities
294 CapEff                      bitmap of effective capabilities
295 CapBnd                      bitmap of capabilities bounding set
296 CapAmb                      bitmap of ambient capabilities
297 NoNewPrivs                  no_new_privs, like prctl(PR_GET_NO_NEW_PRIV, ...)
298 Seccomp                     seccomp mode, like prctl(PR_GET_SECCOMP, ...)
299 Speculation_Store_Bypass    speculative store bypass mitigation status
300 SpeculationIndirectBranch   indirect branch speculation mode
301 Cpus_allowed                mask of CPUs on which this process may run
302 Cpus_allowed_list           Same as previous, but in "list format"
303 Mems_allowed                mask of memory nodes allowed to this process
304 Mems_allowed_list           Same as previous, but in "list format"
305 voluntary_ctxt_switches     number of voluntary context switches
306 nonvoluntary_ctxt_switches  number of non voluntary context switches
307 ==========================  ===================================================
308
309
310.. table:: Table 1-3: Contents of the statm fields (as of 2.6.8-rc3)
311
312 ======== ===============================	==============================
313 Field    Content
314 ======== ===============================	==============================
315 size     total program size (pages)		(same as VmSize in status)
316 resident size of memory portions (pages)	(same as VmRSS in status)
317 shared   number of pages that are shared	(i.e. backed by a file, same
318						as RssFile+RssShmem in status)
319 trs      number of pages that are 'code'	(not including libs; broken,
320						includes data segment)
321 lrs      number of pages of library		(always 0 on 2.6)
322 drs      number of pages of data/stack		(including libs; broken,
323						includes library text)
324 dt       number of dirty pages			(always 0 on 2.6)
325 ======== ===============================	==============================
326
327
328.. table:: Table 1-4: Contents of the stat fields (as of 2.6.30-rc7)
329
330  ============= ===============================================================
331  Field         Content
332  ============= ===============================================================
333  pid           process id
334  tcomm         filename of the executable
335  state         state (R is running, S is sleeping, D is sleeping in an
336                uninterruptible wait, Z is zombie, T is traced or stopped)
337  ppid          process id of the parent process
338  pgrp          pgrp of the process
339  sid           session id
340  tty_nr        tty the process uses
341  tty_pgrp      pgrp of the tty
342  flags         task flags
343  min_flt       number of minor faults
344  cmin_flt      number of minor faults with child's
345  maj_flt       number of major faults
346  cmaj_flt      number of major faults with child's
347  utime         user mode jiffies
348  stime         kernel mode jiffies
349  cutime        user mode jiffies with child's
350  cstime        kernel mode jiffies with child's
351  priority      priority level
352  nice          nice level
353  num_threads   number of threads
354  it_real_value	(obsolete, always 0)
355  start_time    time the process started after system boot
356  vsize         virtual memory size
357  rss           resident set memory size
358  rsslim        current limit in bytes on the rss
359  start_code    address above which program text can run
360  end_code      address below which program text can run
361  start_stack   address of the start of the main process stack
362  esp           current value of ESP
363  eip           current value of EIP
364  pending       bitmap of pending signals
365  blocked       bitmap of blocked signals
366  sigign        bitmap of ignored signals
367  sigcatch      bitmap of caught signals
368  0		(place holder, used to be the wchan address,
369		use /proc/PID/wchan instead)
370  0             (place holder)
371  0             (place holder)
372  exit_signal   signal to send to parent thread on exit
373  task_cpu      which CPU the task is scheduled on
374  rt_priority   realtime priority
375  policy        scheduling policy (man sched_setscheduler)
376  blkio_ticks   time spent waiting for block IO
377  gtime         guest time of the task in jiffies
378  cgtime        guest time of the task children in jiffies
379  start_data    address above which program data+bss is placed
380  end_data      address below which program data+bss is placed
381  start_brk     address above which program heap can be expanded with brk()
382  arg_start     address above which program command line is placed
383  arg_end       address below which program command line is placed
384  env_start     address above which program environment is placed
385  env_end       address below which program environment is placed
386  exit_code     the thread's exit_code in the form reported by the waitpid
387		system call
388  ============= ===============================================================
389
390The /proc/PID/maps file contains the currently mapped memory regions and
391their access permissions.
392
393The format is::
394
395    address           perms offset  dev   inode      pathname
396
397    08048000-08049000 r-xp 00000000 03:00 8312       /opt/test
398    08049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
399    0804a000-0806b000 rw-p 00000000 00:00 0          [heap]
400    a7cb1000-a7cb2000 ---p 00000000 00:00 0
401    a7cb2000-a7eb2000 rw-p 00000000 00:00 0
402    a7eb2000-a7eb3000 ---p 00000000 00:00 0
403    a7eb3000-a7ed5000 rw-p 00000000 00:00 0
404    a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/libc.so.6
405    a8008000-a800a000 r--p 00133000 03:00 4222       /lib/libc.so.6
406    a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/libc.so.6
407    a800b000-a800e000 rw-p 00000000 00:00 0
408    a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/libpthread.so.0
409    a8022000-a8023000 r--p 00013000 03:00 14462      /lib/libpthread.so.0
410    a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/libpthread.so.0
411    a8024000-a8027000 rw-p 00000000 00:00 0
412    a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/ld-linux.so.2
413    a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/ld-linux.so.2
414    a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/ld-linux.so.2
415    aff35000-aff4a000 rw-p 00000000 00:00 0          [stack]
416    ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
417
418where "address" is the address space in the process that it occupies, "perms"
419is a set of permissions::
420
421 r = read
422 w = write
423 x = execute
424 s = shared
425 p = private (copy on write)
426
427"offset" is the offset into the mapping, "dev" is the device (major:minor), and
428"inode" is the inode  on that device.  0 indicates that  no inode is associated
429with the memory region, as the case would be with BSS (uninitialized data).
430The "pathname" shows the name associated file for this mapping.  If the mapping
431is not associated with a file:
432
433 ===================        ===========================================
434 [heap]                     the heap of the program
435 [stack]                    the stack of the main process
436 [vdso]                     the "virtual dynamic shared object",
437                            the kernel system call handler
438 [anon:<name>]              a private anonymous mapping that has been
439                            named by userspace
440 [anon_shmem:<name>]        an anonymous shared memory mapping that has
441                            been named by userspace
442 ===================        ===========================================
443
444 or if empty, the mapping is anonymous.
445
446The /proc/PID/smaps is an extension based on maps, showing the memory
447consumption for each of the process's mappings. For each mapping (aka Virtual
448Memory Area, or VMA) there is a series of lines such as the following::
449
450    08048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
451
452    Size:               1084 kB
453    KernelPageSize:        4 kB
454    MMUPageSize:           4 kB
455    Rss:                 892 kB
456    Pss:                 374 kB
457    Pss_Dirty:             0 kB
458    Shared_Clean:        892 kB
459    Shared_Dirty:          0 kB
460    Private_Clean:         0 kB
461    Private_Dirty:         0 kB
462    Referenced:          892 kB
463    Anonymous:             0 kB
464    KSM:                   0 kB
465    LazyFree:              0 kB
466    AnonHugePages:         0 kB
467    ShmemPmdMapped:        0 kB
468    Shared_Hugetlb:        0 kB
469    Private_Hugetlb:       0 kB
470    Swap:                  0 kB
471    SwapPss:               0 kB
472    KernelPageSize:        4 kB
473    MMUPageSize:           4 kB
474    Locked:                0 kB
475    THPeligible:           0
476    VmFlags: rd ex mr mw me dw
477
478The first of these lines shows the same information as is displayed for the
479mapping in /proc/PID/maps.  Following lines show the size of the mapping
480(size); the size of each page allocated when backing a VMA (KernelPageSize),
481which is usually the same as the size in the page table entries; the page size
482used by the MMU when backing a VMA (in most cases, the same as KernelPageSize);
483the amount of the mapping that is currently resident in RAM (RSS); the
484process' proportional share of this mapping (PSS); and the number of clean and
485dirty shared and private pages in the mapping.
486
487The "proportional set size" (PSS) of a process is the count of pages it has
488in memory, where each page is divided by the number of processes sharing it.
489So if a process has 1000 pages all to itself, and 1000 shared with one other
490process, its PSS will be 1500.  "Pss_Dirty" is the portion of PSS which
491consists of dirty pages.  ("Pss_Clean" is not included, but it can be
492calculated by subtracting "Pss_Dirty" from "Pss".)
493
494Note that even a page which is part of a MAP_SHARED mapping, but has only
495a single pte mapped, i.e.  is currently used by only one process, is accounted
496as private and not as shared.
497
498"Referenced" indicates the amount of memory currently marked as referenced or
499accessed.
500
501"Anonymous" shows the amount of memory that does not belong to any file.  Even
502a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
503and a page is modified, the file page is replaced by a private anonymous copy.
504
505"KSM" reports how many of the pages are KSM pages. Note that KSM-placed zeropages
506are not included, only actual KSM pages.
507
508"LazyFree" shows the amount of memory which is marked by madvise(MADV_FREE).
509The memory isn't freed immediately with madvise(). It's freed in memory
510pressure if the memory is clean. Please note that the printed value might
511be lower than the real value due to optimizations used in the current
512implementation. If this is not desirable please file a bug report.
513
514"AnonHugePages" shows the amount of memory backed by transparent hugepage.
515
516"ShmemPmdMapped" shows the amount of shared (shmem/tmpfs) memory backed by
517huge pages.
518
519"Shared_Hugetlb" and "Private_Hugetlb" show the amounts of memory backed by
520hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical
521reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field.
522
523"Swap" shows how much would-be-anonymous memory is also used, but out on swap.
524
525For shmem mappings, "Swap" includes also the size of the mapped (and not
526replaced by copy-on-write) part of the underlying shmem object out on swap.
527"SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
528does not take into account swapped out page of underlying shmem objects.
529"Locked" indicates whether the mapping is locked in memory or not.
530
531"THPeligible" indicates whether the mapping is eligible for allocating
532naturally aligned THP pages of any currently enabled size. 1 if true, 0
533otherwise.
534
535"VmFlags" field deserves a separate description. This member represents the
536kernel flags associated with the particular virtual memory area in two letter
537encoded manner. The codes are the following:
538
539    ==    =======================================
540    rd    readable
541    wr    writeable
542    ex    executable
543    sh    shared
544    mr    may read
545    mw    may write
546    me    may execute
547    ms    may share
548    gd    stack segment growns down
549    pf    pure PFN range
550    dw    disabled write to the mapped file
551    lo    pages are locked in memory
552    io    memory mapped I/O area
553    sr    sequential read advise provided
554    rr    random read advise provided
555    dc    do not copy area on fork
556    de    do not expand area on remapping
557    ac    area is accountable
558    nr    swap space is not reserved for the area
559    ht    area uses huge tlb pages
560    sf    synchronous page fault
561    ar    architecture specific flag
562    wf    wipe on fork
563    dd    do not include area into core dump
564    sd    soft dirty flag
565    mm    mixed map area
566    hg    huge page advise flag
567    nh    no huge page advise flag
568    mg    mergeable advise flag
569    bt    arm64 BTI guarded page
570    mt    arm64 MTE allocation tags are enabled
571    um    userfaultfd missing tracking
572    uw    userfaultfd wr-protect tracking
573    ss    shadow stack page
574    sl    sealed
575    ==    =======================================
576
577Note that there is no guarantee that every flag and associated mnemonic will
578be present in all further kernel releases. Things get changed, the flags may
579be vanished or the reverse -- new added. Interpretation of their meaning
580might change in future as well. So each consumer of these flags has to
581follow each specific kernel version for the exact semantic.
582
583This file is only present if the CONFIG_MMU kernel configuration option is
584enabled.
585
586Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy (consistent
587output can be achieved only in the single read call).
588
589This typically manifests when doing partial reads of these files while the
590memory map is being modified.  Despite the races, we do provide the following
591guarantees:
592
5931) The mapped addresses never go backwards, which implies no two
594   regions will ever overlap.
5952) If there is something at a given vaddr during the entirety of the
596   life of the smaps/maps walk, there will be some output for it.
597
598The /proc/PID/smaps_rollup file includes the same fields as /proc/PID/smaps,
599but their values are the sums of the corresponding values for all mappings of
600the process.  Additionally, it contains these fields:
601
602- Pss_Anon
603- Pss_File
604- Pss_Shmem
605
606They represent the proportional shares of anonymous, file, and shmem pages, as
607described for smaps above.  These fields are omitted in smaps since each
608mapping identifies the type (anon, file, or shmem) of all pages it contains.
609Thus all information in smaps_rollup can be derived from smaps, but at a
610significantly higher cost.
611
612The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
613bits on both physical and virtual pages associated with a process, and the
614soft-dirty bit on pte (see Documentation/admin-guide/mm/soft-dirty.rst
615for details).
616To clear the bits for all the pages associated with the process::
617
618    > echo 1 > /proc/PID/clear_refs
619
620To clear the bits for the anonymous pages associated with the process::
621
622    > echo 2 > /proc/PID/clear_refs
623
624To clear the bits for the file mapped pages associated with the process::
625
626    > echo 3 > /proc/PID/clear_refs
627
628To clear the soft-dirty bit::
629
630    > echo 4 > /proc/PID/clear_refs
631
632To reset the peak resident set size ("high water mark") to the process's
633current value::
634
635    > echo 5 > /proc/PID/clear_refs
636
637Any other value written to /proc/PID/clear_refs will have no effect.
638
639The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
640using /proc/kpageflags and number of times a page is mapped using
641/proc/kpagecount. For detailed explanation, see
642Documentation/admin-guide/mm/pagemap.rst.
643
644The /proc/pid/numa_maps is an extension based on maps, showing the memory
645locality and binding policy, as well as the memory usage (in pages) of
646each mapping. The output follows a general format where mapping details get
647summarized separated by blank spaces, one mapping per each file line::
648
649    address   policy    mapping details
650
651    00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
652    00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
653    3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
654    320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
655    3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
656    3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
657    3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
658    320698b000 default file=/lib64/libc-2.12.so
659    3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4
660    3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
661    3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
662    7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
663    7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
664    7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
665    7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
666    7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4
667
668Where:
669
670"address" is the starting address for the mapping;
671
672"policy" reports the NUMA memory policy set for the mapping (see Documentation/admin-guide/mm/numa_memory_policy.rst);
673
674"mapping details" summarizes mapping data such as mapping type, page usage counters,
675node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
676size, in KB, that is backing the mapping up.
677
6781.2 Kernel data
679---------------
680
681Similar to  the  process entries, the kernel data files give information about
682the running kernel. The files used to obtain this information are contained in
683/proc and  are  listed  in Table 1-5. Not all of these will be present in your
684system. It  depends  on the kernel configuration and the loaded modules, which
685files are there, and which are missing.
686
687.. table:: Table 1-5: Kernel info in /proc
688
689 ============ ===============================================================
690 File         Content
691 ============ ===============================================================
692 allocinfo    Memory allocations profiling information
693 apm          Advanced power management info
694 bootconfig   Kernel command line obtained from boot config,
695 	      and, if there were kernel parameters from the
696	      boot loader, a "# Parameters from bootloader:"
697	      line followed by a line containing those
698	      parameters prefixed by "# ".			(5.5)
699 buddyinfo    Kernel memory allocator information (see text)	(2.5)
700 bus          Directory containing bus specific information
701 cmdline      Kernel command line, both from bootloader and embedded
702              in the kernel image
703 cpuinfo      Info about the CPU
704 devices      Available devices (block and character)
705 dma          Used DMS channels
706 filesystems  Supported filesystems
707 driver       Various drivers grouped here, currently rtc	(2.4)
708 execdomains  Execdomains, related to security			(2.4)
709 fb 	      Frame Buffer devices				(2.4)
710 fs 	      File system parameters, currently nfs/exports	(2.4)
711 ide          Directory containing info about the IDE subsystem
712 interrupts   Interrupt usage
713 iomem 	      Memory map					(2.4)
714 ioports      I/O port usage
715 irq 	      Masks for irq to cpu affinity			(2.4)(smp?)
716 isapnp       ISA PnP (Plug&Play) Info				(2.4)
717 kcore        Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
718 kmsg         Kernel messages
719 ksyms        Kernel symbol table
720 loadavg      Load average of last 1, 5 & 15 minutes;
721                number of processes currently runnable (running or on ready queue);
722                total number of processes in system;
723                last pid created.
724                All fields are separated by one space except "number of
725                processes currently runnable" and "total number of processes
726                in system", which are separated by a slash ('/'). Example:
727                0.61 0.61 0.55 3/828 22084
728 locks        Kernel locks
729 meminfo      Memory info
730 misc         Miscellaneous
731 modules      List of loaded modules
732 mounts       Mounted filesystems
733 net          Networking info (see text)
734 pagetypeinfo Additional page allocator information (see text)  (2.5)
735 partitions   Table of partitions known to the system
736 pci 	      Deprecated info of PCI bus (new way -> /proc/bus/pci/,
737              decoupled by lspci				(2.4)
738 rtc          Real time clock
739 scsi         SCSI info (see text)
740 slabinfo     Slab pool info
741 softirqs     softirq usage
742 stat         Overall statistics
743 swaps        Swap space utilization
744 sys          See chapter 2
745 sysvipc      Info of SysVIPC Resources (msg, sem, shm)		(2.4)
746 tty 	      Info of tty drivers
747 uptime       Wall clock since boot, combined idle time of all cpus
748 version      Kernel version
749 video 	      bttv info of video resources			(2.4)
750 vmallocinfo  Show vmalloced areas
751 ============ ===============================================================
752
753You can,  for  example,  check  which interrupts are currently in use and what
754they are used for by looking in the file /proc/interrupts::
755
756  > cat /proc/interrupts
757             CPU0
758    0:    8728810          XT-PIC  timer
759    1:        895          XT-PIC  keyboard
760    2:          0          XT-PIC  cascade
761    3:     531695          XT-PIC  aha152x
762    4:    2014133          XT-PIC  serial
763    5:      44401          XT-PIC  pcnet_cs
764    8:          2          XT-PIC  rtc
765   11:          8          XT-PIC  i82365
766   12:     182918          XT-PIC  PS/2 Mouse
767   13:          1          XT-PIC  fpu
768   14:    1232265          XT-PIC  ide0
769   15:          7          XT-PIC  ide1
770  NMI:          0
771
772In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
773output of a SMP machine)::
774
775  > cat /proc/interrupts
776
777             CPU0       CPU1
778    0:    1243498    1214548    IO-APIC-edge  timer
779    1:       8949       8958    IO-APIC-edge  keyboard
780    2:          0          0          XT-PIC  cascade
781    5:      11286      10161    IO-APIC-edge  soundblaster
782    8:          1          0    IO-APIC-edge  rtc
783    9:      27422      27407    IO-APIC-edge  3c503
784   12:     113645     113873    IO-APIC-edge  PS/2 Mouse
785   13:          0          0          XT-PIC  fpu
786   14:      22491      24012    IO-APIC-edge  ide0
787   15:       2183       2415    IO-APIC-edge  ide1
788   17:      30564      30414   IO-APIC-level  eth0
789   18:        177        164   IO-APIC-level  bttv
790  NMI:    2457961    2457959
791  LOC:    2457882    2457881
792  ERR:       2155
793
794NMI is incremented in this case because every timer interrupt generates a NMI
795(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
796
797LOC is the local interrupt counter of the internal APIC of every CPU.
798
799ERR is incremented in the case of errors in the IO-APIC bus (the bus that
800connects the CPUs in a SMP system. This means that an error has been detected,
801the IO-APIC automatically retry the transmission, so it should not be a big
802problem, but you should read the SMP-FAQ.
803
804In 2.6.2* /proc/interrupts was expanded again.  This time the goal was for
805/proc/interrupts to display every IRQ vector in use by the system, not
806just those considered 'most important'.  The new vectors are:
807
808THR
809  interrupt raised when a machine check threshold counter
810  (typically counting ECC corrected errors of memory or cache) exceeds
811  a configurable threshold.  Only available on some systems.
812
813TRM
814  a thermal event interrupt occurs when a temperature threshold
815  has been exceeded for the CPU.  This interrupt may also be generated
816  when the temperature drops back to normal.
817
818SPU
819  a spurious interrupt is some interrupt that was raised then lowered
820  by some IO device before it could be fully processed by the APIC.  Hence
821  the APIC sees the interrupt but does not know what device it came from.
822  For this case the APIC will generate the interrupt with a IRQ vector
823  of 0xff. This might also be generated by chipset bugs.
824
825RES, CAL, TLB
826  rescheduling, call and TLB flush interrupts are
827  sent from one CPU to another per the needs of the OS.  Typically,
828  their statistics are used by kernel developers and interested users to
829  determine the occurrence of interrupts of the given type.
830
831The above IRQ vectors are displayed only when relevant.  For example,
832the threshold vector does not exist on x86_64 platforms.  Others are
833suppressed when the system is a uniprocessor.  As of this writing, only
834i386 and x86_64 platforms support the new IRQ vector displays.
835
836Of some interest is the introduction of the /proc/irq directory to 2.4.
837It could be used to set IRQ to CPU affinity. This means that you can "hook" an
838IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
839irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
840prof_cpu_mask.
841
842For example::
843
844  > ls /proc/irq/
845  0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
846  1  11  13  15  17  19  3  5  7  9  default_smp_affinity
847  > ls /proc/irq/0/
848  smp_affinity
849
850smp_affinity is a bitmask, in which you can specify which CPUs can handle the
851IRQ. You can set it by doing::
852
853  > echo 1 > /proc/irq/10/smp_affinity
854
855This means that only the first CPU will handle the IRQ, but you can also echo
8565 which means that only the first and third CPU can handle the IRQ.
857
858The contents of each smp_affinity file is the same by default::
859
860  > cat /proc/irq/0/smp_affinity
861  ffffffff
862
863There is an alternate interface, smp_affinity_list which allows specifying
864a CPU range instead of a bitmask::
865
866  > cat /proc/irq/0/smp_affinity_list
867  1024-1031
868
869The default_smp_affinity mask applies to all non-active IRQs, which are the
870IRQs which have not yet been allocated/activated, and hence which lack a
871/proc/irq/[0-9]* directory.
872
873The node file on an SMP system shows the node to which the device using the IRQ
874reports itself as being attached. This hardware locality information does not
875include information about any possible driver locality preference.
876
877prof_cpu_mask specifies which CPUs are to be profiled by the system wide
878profiler. Default value is ffffffff (all CPUs if there are only 32 of them).
879
880The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
881between all the CPUs which are allowed to handle it. As usual the kernel has
882more info than you and does a better job than you, so the defaults are the
883best choice for almost everyone.  [Note this applies only to those IO-APIC's
884that support "Round Robin" interrupt distribution.]
885
886There are  three  more  important subdirectories in /proc: net, scsi, and sys.
887The general  rule  is  that  the  contents,  or  even  the  existence of these
888directories, depend  on your kernel configuration. If SCSI is not enabled, the
889directory scsi  may  not  exist. The same is true with the net, which is there
890only when networking support is present in the running kernel.
891
892The slabinfo  file  gives  information  about  memory usage at the slab level.
893Linux uses  slab  pools for memory management above page level in version 2.2.
894Commonly used  objects  have  their  own  slab  pool (such as network buffers,
895directory cache, and so on).
896
897::
898
899    > cat /proc/buddyinfo
900
901    Node 0, zone      DMA      0      4      5      4      4      3 ...
902    Node 0, zone   Normal      1      0      0      1    101      8 ...
903    Node 0, zone  HighMem      2      0      0      1      1      0 ...
904
905External fragmentation is a problem under some workloads, and buddyinfo is a
906useful tool for helping diagnose these problems.  Buddyinfo will give you a
907clue as to how big an area you can safely allocate, or why a previous
908allocation failed.
909
910Each column represents the number of pages of a certain order which are
911available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
912ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
913available in ZONE_NORMAL, etc...
914
915More information relevant to external fragmentation can be found in
916pagetypeinfo::
917
918    > cat /proc/pagetypeinfo
919    Page block order: 9
920    Pages per block:  512
921
922    Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
923    Node    0, zone      DMA, type    Unmovable      0      0      0      1      1      1      1      1      1      1      0
924    Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0
925    Node    0, zone      DMA, type      Movable      1      1      2      1      2      1      1      0      1      0      2
926    Node    0, zone      DMA, type      Reserve      0      0      0      0      0      0      0      0      0      1      0
927    Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
928    Node    0, zone    DMA32, type    Unmovable    103     54     77      1      1      1     11      8      7      1      9
929    Node    0, zone    DMA32, type  Reclaimable      0      0      2      1      0      0      0      0      1      0      0
930    Node    0, zone    DMA32, type      Movable    169    152    113     91     77     54     39     13      6      1    452
931    Node    0, zone    DMA32, type      Reserve      1      2      2      2      2      0      1      1      1      1      0
932    Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
933
934    Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate
935    Node 0, zone      DMA            2            0            5            1            0
936    Node 0, zone    DMA32           41            6          967            2            0
937
938Fragmentation avoidance in the kernel works by grouping pages of different
939migrate types into the same contiguous regions of memory called page blocks.
940A page block is typically the size of the default hugepage size, e.g. 2MB on
941X86-64. By keeping pages grouped based on their ability to move, the kernel
942can reclaim pages within a page block to satisfy a high-order allocation.
943
944The pagetypinfo begins with information on the size of a page block. It
945then gives the same type of information as buddyinfo except broken down
946by migrate-type and finishes with details on how many page blocks of each
947type exist.
948
949If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
950from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can
951make an estimate of the likely number of huge pages that can be allocated
952at a given point in time. All the "Movable" blocks should be allocatable
953unless memory has been mlock()'d. Some of the Reclaimable blocks should
954also be allocatable although a lot of filesystem metadata may have to be
955reclaimed to achieve this.
956
957
958allocinfo
959~~~~~~~~~
960
961Provides information about memory allocations at all locations in the code
962base. Each allocation in the code is identified by its source file, line
963number, module (if originates from a loadable module) and the function calling
964the allocation. The number of bytes allocated and number of calls at each
965location are reported. The first line indicates the version of the file, the
966second line is the header listing fields in the file.
967
968Example output.
969
970::
971
972    > tail -n +3 /proc/allocinfo | sort -rn
973   127664128    31168 mm/page_ext.c:270 func:alloc_page_ext
974    56373248     4737 mm/slub.c:2259 func:alloc_slab_page
975    14880768     3633 mm/readahead.c:247 func:page_cache_ra_unbounded
976    14417920     3520 mm/mm_init.c:2530 func:alloc_large_system_hash
977    13377536      234 block/blk-mq.c:3421 func:blk_mq_alloc_rqs
978    11718656     2861 mm/filemap.c:1919 func:__filemap_get_folio
979     9192960     2800 kernel/fork.c:307 func:alloc_thread_stack_node
980     4206592        4 net/netfilter/nf_conntrack_core.c:2567 func:nf_ct_alloc_hashtable
981     4136960     1010 drivers/staging/ctagmod/ctagmod.c:20 [ctagmod] func:ctagmod_start
982     3940352      962 mm/memory.c:4214 func:alloc_anon_folio
983     2894464    22613 fs/kernfs/dir.c:615 func:__kernfs_new_node
984     ...
985
986
987meminfo
988~~~~~~~
989
990Provides information about distribution and utilization of memory.  This
991varies by architecture and compile options.  Some of the counters reported
992here overlap.  The memory reported by the non overlapping counters may not
993add up to the overall memory usage and the difference for some workloads
994can be substantial.  In many cases there are other means to find out
995additional memory using subsystem specific interfaces, for instance
996/proc/net/sockstat for TCP memory allocations.
997
998Example output. You may not have all of these fields.
999
1000::
1001
1002    > cat /proc/meminfo
1003
1004    MemTotal:       32858820 kB
1005    MemFree:        21001236 kB
1006    MemAvailable:   27214312 kB
1007    Buffers:          581092 kB
1008    Cached:          5587612 kB
1009    SwapCached:            0 kB
1010    Active:          3237152 kB
1011    Inactive:        7586256 kB
1012    Active(anon):      94064 kB
1013    Inactive(anon):  4570616 kB
1014    Active(file):    3143088 kB
1015    Inactive(file):  3015640 kB
1016    Unevictable:           0 kB
1017    Mlocked:               0 kB
1018    SwapTotal:             0 kB
1019    SwapFree:              0 kB
1020    Zswap:              1904 kB
1021    Zswapped:           7792 kB
1022    Dirty:                12 kB
1023    Writeback:             0 kB
1024    AnonPages:       4654780 kB
1025    Mapped:           266244 kB
1026    Shmem:              9976 kB
1027    KReclaimable:     517708 kB
1028    Slab:             660044 kB
1029    SReclaimable:     517708 kB
1030    SUnreclaim:       142336 kB
1031    KernelStack:       11168 kB
1032    PageTables:        20540 kB
1033    SecPageTables:         0 kB
1034    NFS_Unstable:          0 kB
1035    Bounce:                0 kB
1036    WritebackTmp:          0 kB
1037    CommitLimit:    16429408 kB
1038    Committed_AS:    7715148 kB
1039    VmallocTotal:   34359738367 kB
1040    VmallocUsed:       40444 kB
1041    VmallocChunk:          0 kB
1042    Percpu:            29312 kB
1043    EarlyMemtestBad:       0 kB
1044    HardwareCorrupted:     0 kB
1045    AnonHugePages:   4149248 kB
1046    ShmemHugePages:        0 kB
1047    ShmemPmdMapped:        0 kB
1048    FileHugePages:         0 kB
1049    FilePmdMapped:         0 kB
1050    CmaTotal:              0 kB
1051    CmaFree:               0 kB
1052    HugePages_Total:       0
1053    HugePages_Free:        0
1054    HugePages_Rsvd:        0
1055    HugePages_Surp:        0
1056    Hugepagesize:       2048 kB
1057    Hugetlb:               0 kB
1058    DirectMap4k:      401152 kB
1059    DirectMap2M:    10008576 kB
1060    DirectMap1G:    24117248 kB
1061
1062MemTotal
1063              Total usable RAM (i.e. physical RAM minus a few reserved
1064              bits and the kernel binary code)
1065MemFree
1066              Total free RAM. On highmem systems, the sum of LowFree+HighFree
1067MemAvailable
1068              An estimate of how much memory is available for starting new
1069              applications, without swapping. Calculated from MemFree,
1070              SReclaimable, the size of the file LRU lists, and the low
1071              watermarks in each zone.
1072              The estimate takes into account that the system needs some
1073              page cache to function well, and that not all reclaimable
1074              slab will be reclaimable, due to items being in use. The
1075              impact of those factors will vary from system to system.
1076Buffers
1077              Relatively temporary storage for raw disk blocks
1078              shouldn't get tremendously large (20MB or so)
1079Cached
1080              In-memory cache for files read from the disk (the
1081              pagecache) as well as tmpfs & shmem.
1082              Doesn't include SwapCached.
1083SwapCached
1084              Memory that once was swapped out, is swapped back in but
1085              still also is in the swapfile (if memory is needed it
1086              doesn't need to be swapped out AGAIN because it is already
1087              in the swapfile. This saves I/O)
1088Active
1089              Memory that has been used more recently and usually not
1090              reclaimed unless absolutely necessary.
1091Inactive
1092              Memory which has been less recently used.  It is more
1093              eligible to be reclaimed for other purposes
1094Unevictable
1095              Memory allocated for userspace which cannot be reclaimed, such
1096              as mlocked pages, ramfs backing pages, secret memfd pages etc.
1097Mlocked
1098              Memory locked with mlock().
1099HighTotal, HighFree
1100              Highmem is all memory above ~860MB of physical memory.
1101              Highmem areas are for use by userspace programs, or
1102              for the pagecache.  The kernel must use tricks to access
1103              this memory, making it slower to access than lowmem.
1104LowTotal, LowFree
1105              Lowmem is memory which can be used for everything that
1106              highmem can be used for, but it is also available for the
1107              kernel's use for its own data structures.  Among many
1108              other things, it is where everything from the Slab is
1109              allocated.  Bad things happen when you're out of lowmem.
1110SwapTotal
1111              total amount of swap space available
1112SwapFree
1113              Memory which has been evicted from RAM, and is temporarily
1114              on the disk
1115Zswap
1116              Memory consumed by the zswap backend (compressed size)
1117Zswapped
1118              Amount of anonymous memory stored in zswap (original size)
1119Dirty
1120              Memory which is waiting to get written back to the disk
1121Writeback
1122              Memory which is actively being written back to the disk
1123AnonPages
1124              Non-file backed pages mapped into userspace page tables
1125Mapped
1126              files which have been mmapped, such as libraries
1127Shmem
1128              Total memory used by shared memory (shmem) and tmpfs
1129KReclaimable
1130              Kernel allocations that the kernel will attempt to reclaim
1131              under memory pressure. Includes SReclaimable (below), and other
1132              direct allocations with a shrinker.
1133Slab
1134              in-kernel data structures cache
1135SReclaimable
1136              Part of Slab, that might be reclaimed, such as caches
1137SUnreclaim
1138              Part of Slab, that cannot be reclaimed on memory pressure
1139KernelStack
1140              Memory consumed by the kernel stacks of all tasks
1141PageTables
1142              Memory consumed by userspace page tables
1143SecPageTables
1144              Memory consumed by secondary page tables, this currently includes
1145              KVM mmu and IOMMU allocations on x86 and arm64.
1146NFS_Unstable
1147              Always zero. Previous counted pages which had been written to
1148              the server, but has not been committed to stable storage.
1149Bounce
1150              Memory used for block device "bounce buffers"
1151WritebackTmp
1152              Memory used by FUSE for temporary writeback buffers
1153CommitLimit
1154              Based on the overcommit ratio ('vm.overcommit_ratio'),
1155              this is the total amount of  memory currently available to
1156              be allocated on the system. This limit is only adhered to
1157              if strict overcommit accounting is enabled (mode 2 in
1158              'vm.overcommit_memory').
1159
1160              The CommitLimit is calculated with the following formula::
1161
1162                CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
1163                               overcommit_ratio / 100 + [total swap pages]
1164
1165              For example, on a system with 1G of physical RAM and 7G
1166              of swap with a `vm.overcommit_ratio` of 30 it would
1167              yield a CommitLimit of 7.3G.
1168
1169              For more details, see the memory overcommit documentation
1170              in mm/overcommit-accounting.
1171Committed_AS
1172              The amount of memory presently allocated on the system.
1173              The committed memory is a sum of all of the memory which
1174              has been allocated by processes, even if it has not been
1175              "used" by them as of yet. A process which malloc()'s 1G
1176              of memory, but only touches 300M of it will show up as
1177              using 1G. This 1G is memory which has been "committed" to
1178              by the VM and can be used at any time by the allocating
1179              application. With strict overcommit enabled on the system
1180              (mode 2 in 'vm.overcommit_memory'), allocations which would
1181              exceed the CommitLimit (detailed above) will not be permitted.
1182              This is useful if one needs to guarantee that processes will
1183              not fail due to lack of memory once that memory has been
1184              successfully allocated.
1185VmallocTotal
1186              total size of vmalloc virtual address space
1187VmallocUsed
1188              amount of vmalloc area which is used
1189VmallocChunk
1190              largest contiguous block of vmalloc area which is free
1191Percpu
1192              Memory allocated to the percpu allocator used to back percpu
1193              allocations. This stat excludes the cost of metadata.
1194EarlyMemtestBad
1195              The amount of RAM/memory in kB, that was identified as corrupted
1196              by early memtest. If memtest was not run, this field will not
1197              be displayed at all. Size is never rounded down to 0 kB.
1198              That means if 0 kB is reported, you can safely assume
1199              there was at least one pass of memtest and none of the passes
1200              found a single faulty byte of RAM.
1201HardwareCorrupted
1202              The amount of RAM/memory in KB, the kernel identifies as
1203              corrupted.
1204AnonHugePages
1205              Non-file backed huge pages mapped into userspace page tables
1206ShmemHugePages
1207              Memory used by shared memory (shmem) and tmpfs allocated
1208              with huge pages
1209ShmemPmdMapped
1210              Shared memory mapped into userspace with huge pages
1211FileHugePages
1212              Memory used for filesystem data (page cache) allocated
1213              with huge pages
1214FilePmdMapped
1215              Page cache mapped into userspace with huge pages
1216CmaTotal
1217              Memory reserved for the Contiguous Memory Allocator (CMA)
1218CmaFree
1219              Free remaining memory in the CMA reserves
1220HugePages_Total, HugePages_Free, HugePages_Rsvd, HugePages_Surp, Hugepagesize, Hugetlb
1221              See Documentation/admin-guide/mm/hugetlbpage.rst.
1222DirectMap4k, DirectMap2M, DirectMap1G
1223              Breakdown of page table sizes used in the kernel's
1224              identity mapping of RAM
1225
1226vmallocinfo
1227~~~~~~~~~~~
1228
1229Provides information about vmalloced/vmaped areas. One line per area,
1230containing the virtual address range of the area, size in bytes,
1231caller information of the creator, and optional information depending
1232on the kind of area:
1233
1234 ==========  ===================================================
1235 pages=nr    number of pages
1236 phys=addr   if a physical address was specified
1237 ioremap     I/O mapping (ioremap() and friends)
1238 vmalloc     vmalloc() area
1239 vmap        vmap()ed pages
1240 user        VM_USERMAP area
1241 vpages      buffer for pages pointers was vmalloced (huge area)
1242 N<node>=nr  (Only on NUMA kernels)
1243             Number of pages allocated on memory node <node>
1244 ==========  ===================================================
1245
1246::
1247
1248    > cat /proc/vmallocinfo
1249    0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
1250    /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
1251    0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
1252    /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
1253    0xffffc20000302000-0xffffc20000304000    8192 acpi_tb_verify_table+0x21/0x4f...
1254    phys=7fee8000 ioremap
1255    0xffffc20000304000-0xffffc20000307000   12288 acpi_tb_verify_table+0x21/0x4f...
1256    phys=7fee7000 ioremap
1257    0xffffc2000031d000-0xffffc2000031f000    8192 init_vdso_vars+0x112/0x210
1258    0xffffc2000031f000-0xffffc2000032b000   49152 cramfs_uncompress_init+0x2e ...
1259    /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
1260    0xffffc2000033a000-0xffffc2000033d000   12288 sys_swapon+0x640/0xac0      ...
1261    pages=2 vmalloc N1=2
1262    0xffffc20000347000-0xffffc2000034c000   20480 xt_alloc_table_info+0xfe ...
1263    /0x130 [x_tables] pages=4 vmalloc N0=4
1264    0xffffffffa0000000-0xffffffffa000f000   61440 sys_init_module+0xc27/0x1d00 ...
1265    pages=14 vmalloc N2=14
1266    0xffffffffa000f000-0xffffffffa0014000   20480 sys_init_module+0xc27/0x1d00 ...
1267    pages=4 vmalloc N1=4
1268    0xffffffffa0014000-0xffffffffa0017000   12288 sys_init_module+0xc27/0x1d00 ...
1269    pages=2 vmalloc N1=2
1270    0xffffffffa0017000-0xffffffffa0022000   45056 sys_init_module+0xc27/0x1d00 ...
1271    pages=10 vmalloc N0=10
1272
1273
1274softirqs
1275~~~~~~~~
1276
1277Provides counts of softirq handlers serviced since boot time, for each CPU.
1278
1279::
1280
1281    > cat /proc/softirqs
1282		  CPU0       CPU1       CPU2       CPU3
1283	HI:          0          0          0          0
1284    TIMER:       27166      27120      27097      27034
1285    NET_TX:          0          0          0         17
1286    NET_RX:         42          0          0         39
1287    BLOCK:           0          0        107       1121
1288    TASKLET:         0          0          0        290
1289    SCHED:       27035      26983      26971      26746
1290    HRTIMER:         0          0          0          0
1291	RCU:      1678       1769       2178       2250
1292
12931.3 Networking info in /proc/net
1294--------------------------------
1295
1296The subdirectory  /proc/net  follows  the  usual  pattern. Table 1-8 shows the
1297additional values  you  get  for  IP  version 6 if you configure the kernel to
1298support this. Table 1-9 lists the files and their meaning.
1299
1300
1301.. table:: Table 1-8: IPv6 info in /proc/net
1302
1303 ========== =====================================================
1304 File       Content
1305 ========== =====================================================
1306 udp6       UDP sockets (IPv6)
1307 tcp6       TCP sockets (IPv6)
1308 raw6       Raw device statistics (IPv6)
1309 igmp6      IP multicast addresses, which this host joined (IPv6)
1310 if_inet6   List of IPv6 interface addresses
1311 ipv6_route Kernel routing table for IPv6
1312 rt6_stats  Global IPv6 routing tables statistics
1313 sockstat6  Socket statistics (IPv6)
1314 snmp6      Snmp data (IPv6)
1315 ========== =====================================================
1316
1317.. table:: Table 1-9: Network info in /proc/net
1318
1319 ============= ================================================================
1320 File          Content
1321 ============= ================================================================
1322 arp           Kernel  ARP table
1323 dev           network devices with statistics
1324 dev_mcast     the Layer2 multicast groups a device is listening too
1325               (interface index, label, number of references, number of bound
1326               addresses).
1327 dev_stat      network device status
1328 ip_fwchains   Firewall chain linkage
1329 ip_fwnames    Firewall chain names
1330 ip_masq       Directory containing the masquerading tables
1331 ip_masquerade Major masquerading table
1332 netstat       Network statistics
1333 raw           raw device statistics
1334 route         Kernel routing table
1335 rpc           Directory containing rpc info
1336 rt_cache      Routing cache
1337 snmp          SNMP data
1338 sockstat      Socket statistics
1339 softnet_stat  Per-CPU incoming packets queues statistics of online CPUs
1340 tcp           TCP  sockets
1341 udp           UDP sockets
1342 unix          UNIX domain sockets
1343 wireless      Wireless interface data (Wavelan etc)
1344 igmp          IP multicast addresses, which this host joined
1345 psched        Global packet scheduler parameters.
1346 netlink       List of PF_NETLINK sockets
1347 ip_mr_vifs    List of multicast virtual interfaces
1348 ip_mr_cache   List of multicast routing cache
1349 ============= ================================================================
1350
1351You can  use  this  information  to see which network devices are available in
1352your system and how much traffic was routed over those devices::
1353
1354  > cat /proc/net/dev
1355  Inter-|Receive                                                   |[...
1356   face |bytes    packets errs drop fifo frame compressed multicast|[...
1357      lo:  908188   5596     0    0    0     0          0         0 [...
1358    ppp0:15475140  20721   410    0    0   410          0         0 [...
1359    eth0:  614530   7085     0    0    0     0          0         1 [...
1360
1361  ...] Transmit
1362  ...] bytes    packets errs drop fifo colls carrier compressed
1363  ...]  908188     5596    0    0    0     0       0          0
1364  ...] 1375103    17405    0    0    0     0       0          0
1365  ...] 1703981     5535    0    0    0     3       0          0
1366
1367In addition, each Channel Bond interface has its own directory.  For
1368example, the bond0 device will have a directory called /proc/net/bond0/.
1369It will contain information that is specific to that bond, such as the
1370current slaves of the bond, the link status of the slaves, and how
1371many times the slaves link has failed.
1372
13731.4 SCSI info
1374-------------
1375
1376If you have a SCSI or ATA host adapter in your system, you'll find a
1377subdirectory named after the driver for this adapter in /proc/scsi.
1378You'll also see a list of all recognized SCSI devices in /proc/scsi::
1379
1380  >cat /proc/scsi/scsi
1381  Attached devices:
1382  Host: scsi0 Channel: 00 Id: 00 Lun: 00
1383    Vendor: IBM      Model: DGHS09U          Rev: 03E0
1384    Type:   Direct-Access                    ANSI SCSI revision: 03
1385  Host: scsi0 Channel: 00 Id: 06 Lun: 00
1386    Vendor: PIONEER  Model: CD-ROM DR-U06S   Rev: 1.04
1387    Type:   CD-ROM                           ANSI SCSI revision: 02
1388
1389
1390The directory  named  after  the driver has one file for each adapter found in
1391the system.  These  files  contain information about the controller, including
1392the used  IRQ  and  the  IO  address range. The amount of information shown is
1393dependent on  the adapter you use. The example shows the output for an Adaptec
1394AHA-2940 SCSI adapter::
1395
1396  > cat /proc/scsi/aic7xxx/0
1397
1398  Adaptec AIC7xxx driver version: 5.1.19/3.2.4
1399  Compile Options:
1400    TCQ Enabled By Default : Disabled
1401    AIC7XXX_PROC_STATS     : Disabled
1402    AIC7XXX_RESET_DELAY    : 5
1403  Adapter Configuration:
1404             SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
1405                             Ultra Wide Controller
1406      PCI MMAPed I/O Base: 0xeb001000
1407   Adapter SEEPROM Config: SEEPROM found and used.
1408        Adaptec SCSI BIOS: Enabled
1409                      IRQ: 10
1410                     SCBs: Active 0, Max Active 2,
1411                           Allocated 15, HW 16, Page 255
1412               Interrupts: 160328
1413        BIOS Control Word: 0x18b6
1414     Adapter Control Word: 0x005b
1415     Extended Translation: Enabled
1416  Disconnect Enable Flags: 0xffff
1417       Ultra Enable Flags: 0x0001
1418   Tag Queue Enable Flags: 0x0000
1419  Ordered Queue Tag Flags: 0x0000
1420  Default Tag Queue Depth: 8
1421      Tagged Queue By Device array for aic7xxx host instance 0:
1422        {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
1423      Actual queue depth per device for aic7xxx host instance 0:
1424        {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
1425  Statistics:
1426  (scsi0:0:0:0)
1427    Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
1428    Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
1429    Total transfers 160151 (74577 reads and 85574 writes)
1430  (scsi0:0:6:0)
1431    Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
1432    Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
1433    Total transfers 0 (0 reads and 0 writes)
1434
1435
14361.5 Parallel port info in /proc/parport
1437---------------------------------------
1438
1439The directory  /proc/parport  contains information about the parallel ports of
1440your system.  It  has  one  subdirectory  for  each port, named after the port
1441number (0,1,2,...).
1442
1443These directories contain the four files shown in Table 1-10.
1444
1445
1446.. table:: Table 1-10: Files in /proc/parport
1447
1448 ========= ====================================================================
1449 File      Content
1450 ========= ====================================================================
1451 autoprobe Any IEEE-1284 device ID information that has been acquired.
1452 devices   list of the device drivers using that port. A + will appear by the
1453           name of the device currently using the port (it might not appear
1454           against any).
1455 hardware  Parallel port's base address, IRQ line and DMA channel.
1456 irq       IRQ that parport is using for that port. This is in a separate
1457           file to allow you to alter it by writing a new value in (IRQ
1458           number or none).
1459 ========= ====================================================================
1460
14611.6 TTY info in /proc/tty
1462-------------------------
1463
1464Information about  the  available  and actually used tty's can be found in the
1465directory /proc/tty. You'll find  entries  for drivers and line disciplines in
1466this directory, as shown in Table 1-11.
1467
1468
1469.. table:: Table 1-11: Files in /proc/tty
1470
1471 ============= ==============================================
1472 File          Content
1473 ============= ==============================================
1474 drivers       list of drivers and their usage
1475 ldiscs        registered line disciplines
1476 driver/serial usage statistic and status of single tty lines
1477 ============= ==============================================
1478
1479To see  which  tty's  are  currently in use, you can simply look into the file
1480/proc/tty/drivers::
1481
1482  > cat /proc/tty/drivers
1483  pty_slave            /dev/pts      136   0-255 pty:slave
1484  pty_master           /dev/ptm      128   0-255 pty:master
1485  pty_slave            /dev/ttyp       3   0-255 pty:slave
1486  pty_master           /dev/pty        2   0-255 pty:master
1487  serial               /dev/cua        5   64-67 serial:callout
1488  serial               /dev/ttyS       4   64-67 serial
1489  /dev/tty0            /dev/tty0       4       0 system:vtmaster
1490  /dev/ptmx            /dev/ptmx       5       2 system
1491  /dev/console         /dev/console    5       1 system:console
1492  /dev/tty             /dev/tty        5       0 system:/dev/tty
1493  unknown              /dev/tty        4    1-63 console
1494
1495
14961.7 Miscellaneous kernel statistics in /proc/stat
1497-------------------------------------------------
1498
1499Various pieces   of  information about  kernel activity  are  available in the
1500/proc/stat file.  All  of  the numbers reported  in  this file are  aggregates
1501since the system first booted.  For a quick look, simply cat the file::
1502
1503  > cat /proc/stat
1504  cpu  237902850 368826709 106375398 1873517540 1135548 0 14507935 0 0 0
1505  cpu0 60045249 91891769 26331539 468411416 495718 0 5739640 0 0 0
1506  cpu1 59746288 91759249 26609887 468860630 312281 0 4384817 0 0 0
1507  cpu2 59489247 92985423 26904446 467808813 171668 0 2268998 0 0 0
1508  cpu3 58622065 92190267 26529524 468436680 155879 0 2114478 0 0 0
1509  intr 8688370575 8 3373 0 0 0 0 0 0 1 40791 0 0 353317 0 0 0 0 224789828 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 190974333 41958554 123983334 43 0 224593 0 0 0 <more 0's deleted>
1510  ctxt 22848221062
1511  btime 1605316999
1512  processes 746787147
1513  procs_running 2
1514  procs_blocked 0
1515  softirq 12121874454 100099120 3938138295 127375644 2795979 187870761 0 173808342 3072582055 52608 224184354
1516
1517The very first  "cpu" line aggregates the  numbers in all  of the other "cpuN"
1518lines.  These numbers identify the amount of time the CPU has spent performing
1519different kinds of work.  Time units are in USER_HZ (typically hundredths of a
1520second).  The meanings of the columns are as follows, from left to right:
1521
1522- user: normal processes executing in user mode
1523- nice: niced processes executing in user mode
1524- system: processes executing in kernel mode
1525- idle: twiddling thumbs
1526- iowait: In a word, iowait stands for waiting for I/O to complete. But there
1527  are several problems:
1528
1529  1. CPU will not wait for I/O to complete, iowait is the time that a task is
1530     waiting for I/O to complete. When CPU goes into idle state for
1531     outstanding task I/O, another task will be scheduled on this CPU.
1532  2. In a multi-core CPU, the task waiting for I/O to complete is not running
1533     on any CPU, so the iowait of each CPU is difficult to calculate.
1534  3. The value of iowait field in /proc/stat will decrease in certain
1535     conditions.
1536
1537  So, the iowait is not reliable by reading from /proc/stat.
1538- irq: servicing interrupts
1539- softirq: servicing softirqs
1540- steal: involuntary wait
1541- guest: running a normal guest
1542- guest_nice: running a niced guest
1543
1544The "intr" line gives counts of interrupts  serviced since boot time, for each
1545of the  possible system interrupts.   The first  column  is the  total of  all
1546interrupts serviced  including  unnumbered  architecture specific  interrupts;
1547each  subsequent column is the  total for that particular numbered interrupt.
1548Unnumbered interrupts are not shown, only summed into the total.
1549
1550The "ctxt" line gives the total number of context switches across all CPUs.
1551
1552The "btime" line gives  the time at which the  system booted, in seconds since
1553the Unix epoch.
1554
1555The "processes" line gives the number  of processes and threads created, which
1556includes (but  is not limited  to) those  created by  calls to the  fork() and
1557clone() system calls.
1558
1559The "procs_running" line gives the total number of threads that are
1560running or ready to run (i.e., the total number of runnable threads).
1561
1562The   "procs_blocked" line gives  the  number of  processes currently blocked,
1563waiting for I/O to complete.
1564
1565The "softirq" line gives counts of softirqs serviced since boot time, for each
1566of the possible system softirqs. The first column is the total of all
1567softirqs serviced; each subsequent column is the total for that particular
1568softirq.
1569
1570
15711.8 Ext4 file system parameters
1572-------------------------------
1573
1574Information about mounted ext4 file systems can be found in
1575/proc/fs/ext4.  Each mounted filesystem will have a directory in
1576/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1577/proc/fs/ext4/sda9 or /proc/fs/ext4/dm-0).   The files in each per-device
1578directory are shown in Table 1-12, below.
1579
1580.. table:: Table 1-12: Files in /proc/fs/ext4/<devname>
1581
1582 ==============  ==========================================================
1583 File            Content
1584 mb_groups       details of multiblock allocator buddy cache of free blocks
1585 ==============  ==========================================================
1586
15871.9 /proc/consoles
1588-------------------
1589Shows registered system console lines.
1590
1591To see which character device lines are currently used for the system console
1592/dev/console, you may simply look into the file /proc/consoles::
1593
1594  > cat /proc/consoles
1595  tty0                 -WU (ECp)       4:7
1596  ttyS0                -W- (Ep)        4:64
1597
1598The columns are:
1599
1600+--------------------+-------------------------------------------------------+
1601| device             | name of the device                                    |
1602+====================+=======================================================+
1603| operations         | * R = can do read operations                          |
1604|                    | * W = can do write operations                         |
1605|                    | * U = can do unblank                                  |
1606+--------------------+-------------------------------------------------------+
1607| flags              | * E = it is enabled                                   |
1608|                    | * C = it is preferred console                         |
1609|                    | * B = it is primary boot console                      |
1610|                    | * p = it is used for printk buffer                    |
1611|                    | * b = it is not a TTY but a Braille device            |
1612|                    | * a = it is safe to use when cpu is offline           |
1613+--------------------+-------------------------------------------------------+
1614| major:minor        | major and minor number of the device separated by a   |
1615|                    | colon                                                 |
1616+--------------------+-------------------------------------------------------+
1617
1618Summary
1619-------
1620
1621The /proc file system serves information about the running system. It not only
1622allows access to process data but also allows you to request the kernel status
1623by reading files in the hierarchy.
1624
1625The directory  structure  of /proc reflects the types of information and makes
1626it easy, if not obvious, where to look for specific data.
1627
1628Chapter 2: Modifying System Parameters
1629======================================
1630
1631In This Chapter
1632---------------
1633
1634* Modifying kernel parameters by writing into files found in /proc/sys
1635* Exploring the files which modify certain parameters
1636* Review of the /proc/sys file tree
1637
1638------------------------------------------------------------------------------
1639
1640A very  interesting part of /proc is the directory /proc/sys. This is not only
1641a source  of  information,  it also allows you to change parameters within the
1642kernel. Be  very  careful  when attempting this. You can optimize your system,
1643but you  can  also  cause  it  to  crash.  Never  alter kernel parameters on a
1644production system.  Set  up  a  development machine and test to make sure that
1645everything works  the  way  you want it to. You may have no alternative but to
1646reboot the machine once an error has been made.
1647
1648To change  a  value,  simply  echo  the new value into the file.
1649You need to be root to do this. You  can  create  your  own  boot script
1650to perform this every time your system boots.
1651
1652The files  in /proc/sys can be used to fine tune and monitor miscellaneous and
1653general things  in  the operation of the Linux kernel. Since some of the files
1654can inadvertently  disrupt  your  system,  it  is  advisable  to  read  both
1655documentation and  source  before actually making adjustments. In any case, be
1656very careful  when  writing  to  any  of these files. The entries in /proc may
1657change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1658review the kernel documentation in the directory linux/Documentation.
1659This chapter  is  heavily  based  on the documentation included in the pre 2.2
1660kernels, and became part of it in version 2.2.1 of the Linux kernel.
1661
1662Please see: Documentation/admin-guide/sysctl/ directory for descriptions of
1663these entries.
1664
1665Summary
1666-------
1667
1668Certain aspects  of  kernel  behavior  can be modified at runtime, without the
1669need to  recompile  the kernel, or even to reboot the system. The files in the
1670/proc/sys tree  can  not only be read, but also modified. You can use the echo
1671command to write value into these files, thereby changing the default settings
1672of the kernel.
1673
1674
1675Chapter 3: Per-process Parameters
1676=================================
1677
16783.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1679--------------------------------------------------------------------------------
1680
1681These files can be used to adjust the badness heuristic used to select which
1682process gets killed in out of memory (oom) conditions.
1683
1684The badness heuristic assigns a value to each candidate task ranging from 0
1685(never kill) to 1000 (always kill) to determine which process is targeted.  The
1686units are roughly a proportion along that range of allowed memory the process
1687may allocate from based on an estimation of its current memory and swap use.
1688For example, if a task is using all allowed memory, its badness score will be
16891000.  If it is using half of its allowed memory, its score will be 500.
1690
1691The amount of "allowed" memory depends on the context in which the oom killer
1692was called.  If it is due to the memory assigned to the allocating task's cpuset
1693being exhausted, the allowed memory represents the set of mems assigned to that
1694cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
1695memory represents the set of mempolicy nodes.  If it is due to a memory
1696limit (or swap limit) being reached, the allowed memory is that configured
1697limit.  Finally, if it is due to the entire system being out of memory, the
1698allowed memory represents all allocatable resources.
1699
1700The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1701is used to determine which task to kill.  Acceptable values range from -1000
1702(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
1703polarize the preference for oom killing either by always preferring a certain
1704task or completely disabling it.  The lowest possible value, -1000, is
1705equivalent to disabling oom killing entirely for that task since it will always
1706report a badness score of 0.
1707
1708Consequently, it is very simple for userspace to define the amount of memory to
1709consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
1710example, is roughly equivalent to allowing the remainder of tasks sharing the
1711same system, cpuset, mempolicy, or memory controller resources to use at least
171250% more memory.  A value of -500, on the other hand, would be roughly
1713equivalent to discounting 50% of the task's allowed memory from being considered
1714as scoring against the task.
1715
1716For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1717be used to tune the badness score.  Its acceptable values range from -16
1718(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1719(OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
1720scaled linearly with /proc/<pid>/oom_score_adj.
1721
1722The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1723value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1724requires CAP_SYS_RESOURCE.
1725
1726
17273.2 /proc/<pid>/oom_score - Display current oom-killer score
1728-------------------------------------------------------------
1729
1730This file can be used to check the current score used by the oom-killer for
1731any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1732process should be killed in an out-of-memory situation.
1733
1734Please note that the exported value includes oom_score_adj so it is
1735effectively in range [0,2000].
1736
1737
17383.3  /proc/<pid>/io - Display the IO accounting fields
1739-------------------------------------------------------
1740
1741This file contains IO statistics for each running process.
1742
1743Example
1744~~~~~~~
1745
1746::
1747
1748    test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1749    [1] 3828
1750
1751    test:/tmp # cat /proc/3828/io
1752    rchar: 323934931
1753    wchar: 323929600
1754    syscr: 632687
1755    syscw: 632675
1756    read_bytes: 0
1757    write_bytes: 323932160
1758    cancelled_write_bytes: 0
1759
1760
1761Description
1762~~~~~~~~~~~
1763
1764rchar
1765^^^^^
1766
1767I/O counter: chars read
1768The number of bytes which this task has caused to be read from storage. This
1769is simply the sum of bytes which this process passed to read() and pread().
1770It includes things like tty IO and it is unaffected by whether or not actual
1771physical disk IO was required (the read might have been satisfied from
1772pagecache).
1773
1774
1775wchar
1776^^^^^
1777
1778I/O counter: chars written
1779The number of bytes which this task has caused, or shall cause to be written
1780to disk. Similar caveats apply here as with rchar.
1781
1782
1783syscr
1784^^^^^
1785
1786I/O counter: read syscalls
1787Attempt to count the number of read I/O operations, i.e. syscalls like read()
1788and pread().
1789
1790
1791syscw
1792^^^^^
1793
1794I/O counter: write syscalls
1795Attempt to count the number of write I/O operations, i.e. syscalls like
1796write() and pwrite().
1797
1798
1799read_bytes
1800^^^^^^^^^^
1801
1802I/O counter: bytes read
1803Attempt to count the number of bytes which this process really did cause to
1804be fetched from the storage layer. Done at the submit_bio() level, so it is
1805accurate for block-backed filesystems. <please add status regarding NFS and
1806CIFS at a later time>
1807
1808
1809write_bytes
1810^^^^^^^^^^^
1811
1812I/O counter: bytes written
1813Attempt to count the number of bytes which this process caused to be sent to
1814the storage layer. This is done at page-dirtying time.
1815
1816
1817cancelled_write_bytes
1818^^^^^^^^^^^^^^^^^^^^^
1819
1820The big inaccuracy here is truncate. If a process writes 1MB to a file and
1821then deletes the file, it will in fact perform no writeout. But it will have
1822been accounted as having caused 1MB of write.
1823In other words: The number of bytes which this process caused to not happen,
1824by truncating pagecache. A task can cause "negative" IO too. If this task
1825truncates some dirty pagecache, some IO which another task has been accounted
1826for (in its write_bytes) will not be happening. We _could_ just subtract that
1827from the truncating task's write_bytes, but there is information loss in doing
1828that.
1829
1830
1831.. Note::
1832
1833   At its current implementation state, this is a bit racy on 32-bit machines:
1834   if process A reads process B's /proc/pid/io while process B is updating one
1835   of those 64-bit counters, process A could see an intermediate result.
1836
1837
1838More information about this can be found within the taskstats documentation in
1839Documentation/accounting.
1840
18413.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1842---------------------------------------------------------------
1843When a process is dumped, all anonymous memory is written to a core file as
1844long as the size of the core file isn't limited. But sometimes we don't want
1845to dump some memory segments, for example, huge shared memory or DAX.
1846Conversely, sometimes we want to save file-backed memory segments into a core
1847file, not only the individual files.
1848
1849/proc/<pid>/coredump_filter allows you to customize which memory segments
1850will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1851of memory types. If a bit of the bitmask is set, memory segments of the
1852corresponding memory type are dumped, otherwise they are not dumped.
1853
1854The following 9 memory types are supported:
1855
1856  - (bit 0) anonymous private memory
1857  - (bit 1) anonymous shared memory
1858  - (bit 2) file-backed private memory
1859  - (bit 3) file-backed shared memory
1860  - (bit 4) ELF header pages in file-backed private memory areas (it is
1861    effective only if the bit 2 is cleared)
1862  - (bit 5) hugetlb private memory
1863  - (bit 6) hugetlb shared memory
1864  - (bit 7) DAX private memory
1865  - (bit 8) DAX shared memory
1866
1867  Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1868  are always dumped regardless of the bitmask status.
1869
1870  Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
1871  only affected by bit 5-6, and DAX is only affected by bits 7-8.
1872
1873The default value of coredump_filter is 0x33; this means all anonymous memory
1874segments, ELF header pages and hugetlb private memory are dumped.
1875
1876If you don't want to dump all shared memory segments attached to pid 1234,
1877write 0x31 to the process's proc file::
1878
1879  $ echo 0x31 > /proc/1234/coredump_filter
1880
1881When a new process is created, the process inherits the bitmask status from its
1882parent. It is useful to set up coredump_filter before the program runs.
1883For example::
1884
1885  $ echo 0x7 > /proc/self/coredump_filter
1886  $ ./some_program
1887
18883.5	/proc/<pid>/mountinfo - Information about mounts
1889--------------------------------------------------------
1890
1891This file contains lines of the form::
1892
1893    36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1894    (1)(2)(3)   (4)   (5)      (6)     (n…m) (m+1)(m+2) (m+3)         (m+4)
1895
1896    (1)   mount ID:        unique identifier of the mount (may be reused after umount)
1897    (2)   parent ID:       ID of parent (or of self for the top of the mount tree)
1898    (3)   major:minor:     value of st_dev for files on filesystem
1899    (4)   root:            root of the mount within the filesystem
1900    (5)   mount point:     mount point relative to the process's root
1901    (6)   mount options:   per mount options
1902    (n…m) optional fields: zero or more fields of the form "tag[:value]"
1903    (m+1) separator:       marks the end of the optional fields
1904    (m+2) filesystem type: name of filesystem of the form "type[.subtype]"
1905    (m+3) mount source:    filesystem specific information or "none"
1906    (m+4) super options:   per super block options
1907
1908Parsers should ignore all unrecognised optional fields.  Currently the
1909possible optional fields are:
1910
1911================  ==============================================================
1912shared:X          mount is shared in peer group X
1913master:X          mount is slave to peer group X
1914propagate_from:X  mount is slave and receives propagation from peer group X [#]_
1915unbindable        mount is unbindable
1916================  ==============================================================
1917
1918.. [#] X is the closest dominant peer group under the process's root.  If
1919       X is the immediate master of the mount, or if there's no dominant peer
1920       group under the same root, then only the "master:X" field is present
1921       and not the "propagate_from:X" field.
1922
1923For more information on mount propagation see:
1924
1925  Documentation/filesystems/sharedsubtree.rst
1926
1927
19283.6	/proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
1929--------------------------------------------------------
1930These files provide a method to access a task's comm value. It also allows for
1931a task to set its own or one of its thread siblings comm value. The comm value
1932is limited in size compared to the cmdline value, so writing anything longer
1933then the kernel's TASK_COMM_LEN (currently 16 chars, including the NUL
1934terminator) will result in a truncated comm value.
1935
1936
19373.7	/proc/<pid>/task/<tid>/children - Information about task children
1938-------------------------------------------------------------------------
1939This file provides a fast way to retrieve first level children pids
1940of a task pointed by <pid>/<tid> pair. The format is a space separated
1941stream of pids.
1942
1943Note the "first level" here -- if a child has its own children they will
1944not be listed here; one needs to read /proc/<children-pid>/task/<tid>/children
1945to obtain the descendants.
1946
1947Since this interface is intended to be fast and cheap it doesn't
1948guarantee to provide precise results and some children might be
1949skipped, especially if they've exited right after we printed their
1950pids, so one needs to either stop or freeze processes being inspected
1951if precise results are needed.
1952
1953
19543.8	/proc/<pid>/fdinfo/<fd> - Information about opened file
1955---------------------------------------------------------------
1956This file provides information associated with an opened file. The regular
1957files have at least four fields -- 'pos', 'flags', 'mnt_id' and 'ino'.
1958The 'pos' represents the current offset of the opened file in decimal
1959form [see lseek(2) for details], 'flags' denotes the octal O_xxx mask the
1960file has been created with [see open(2) for details] and 'mnt_id' represents
1961mount ID of the file system containing the opened file [see 3.5
1962/proc/<pid>/mountinfo for details]. 'ino' represents the inode number of
1963the file.
1964
1965A typical output is::
1966
1967	pos:	0
1968	flags:	0100002
1969	mnt_id:	19
1970	ino:	63107
1971
1972All locks associated with a file descriptor are shown in its fdinfo too::
1973
1974    lock:       1: FLOCK  ADVISORY  WRITE 359 00:13:11691 0 EOF
1975
1976The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1977pair provide additional information particular to the objects they represent.
1978
1979Eventfd files
1980~~~~~~~~~~~~~
1981
1982::
1983
1984	pos:	0
1985	flags:	04002
1986	mnt_id:	9
1987	ino:	63107
1988	eventfd-count:	5a
1989
1990where 'eventfd-count' is hex value of a counter.
1991
1992Signalfd files
1993~~~~~~~~~~~~~~
1994
1995::
1996
1997	pos:	0
1998	flags:	04002
1999	mnt_id:	9
2000	ino:	63107
2001	sigmask:	0000000000000200
2002
2003where 'sigmask' is hex value of the signal mask associated
2004with a file.
2005
2006Epoll files
2007~~~~~~~~~~~
2008
2009::
2010
2011	pos:	0
2012	flags:	02
2013	mnt_id:	9
2014	ino:	63107
2015	tfd:        5 events:       1d data: ffffffffffffffff pos:0 ino:61af sdev:7
2016
2017where 'tfd' is a target file descriptor number in decimal form,
2018'events' is events mask being watched and the 'data' is data
2019associated with a target [see epoll(7) for more details].
2020
2021The 'pos' is current offset of the target file in decimal form
2022[see lseek(2)], 'ino' and 'sdev' are inode and device numbers
2023where target file resides, all in hex format.
2024
2025Fsnotify files
2026~~~~~~~~~~~~~~
2027For inotify files the format is the following::
2028
2029	pos:	0
2030	flags:	02000000
2031	mnt_id:	9
2032	ino:	63107
2033	inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
2034
2035where 'wd' is a watch descriptor in decimal form, i.e. a target file
2036descriptor number, 'ino' and 'sdev' are inode and device where the
2037target file resides and the 'mask' is the mask of events, all in hex
2038form [see inotify(7) for more details].
2039
2040If the kernel was built with exportfs support, the path to the target
2041file is encoded as a file handle.  The file handle is provided by three
2042fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
2043format.
2044
2045If the kernel is built without exportfs support the file handle won't be
2046printed out.
2047
2048If there is no inotify mark attached yet the 'inotify' line will be omitted.
2049
2050For fanotify files the format is::
2051
2052	pos:	0
2053	flags:	02
2054	mnt_id:	9
2055	ino:	63107
2056	fanotify flags:10 event-flags:0
2057	fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
2058	fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
2059
2060where fanotify 'flags' and 'event-flags' are values used in fanotify_init
2061call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
2062flags associated with mark which are tracked separately from events
2063mask. 'ino' and 'sdev' are target inode and device, 'mask' is the events
2064mask and 'ignored_mask' is the mask of events which are to be ignored.
2065All are in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
2066provide information about flags and mask used in fanotify_mark
2067call [see fsnotify manpage for details].
2068
2069While the first three lines are mandatory and always printed, the rest is
2070optional and may be omitted if no marks created yet.
2071
2072Timerfd files
2073~~~~~~~~~~~~~
2074
2075::
2076
2077	pos:	0
2078	flags:	02
2079	mnt_id:	9
2080	ino:	63107
2081	clockid: 0
2082	ticks: 0
2083	settime flags: 01
2084	it_value: (0, 49406829)
2085	it_interval: (1, 0)
2086
2087where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
2088that have occurred [see timerfd_create(2) for details]. 'settime flags' are
2089flags in octal form been used to setup the timer [see timerfd_settime(2) for
2090details]. 'it_value' is remaining time until the timer expiration.
2091'it_interval' is the interval for the timer. Note the timer might be set up
2092with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
2093still exhibits timer's remaining time.
2094
2095DMA Buffer files
2096~~~~~~~~~~~~~~~~
2097
2098::
2099
2100	pos:	0
2101	flags:	04002
2102	mnt_id:	9
2103	ino:	63107
2104	size:   32768
2105	count:  2
2106	exp_name:  system-heap
2107
2108where 'size' is the size of the DMA buffer in bytes. 'count' is the file count of
2109the DMA buffer file. 'exp_name' is the name of the DMA buffer exporter.
2110
21113.9	/proc/<pid>/map_files - Information about memory mapped files
2112---------------------------------------------------------------------
2113This directory contains symbolic links which represent memory mapped files
2114the process is maintaining.  Example output::
2115
2116     | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
2117     | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
2118     | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
2119     | ...
2120     | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
2121     | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
2122
2123The name of a link represents the virtual memory bounds of a mapping, i.e.
2124vm_area_struct::vm_start-vm_area_struct::vm_end.
2125
2126The main purpose of the map_files is to retrieve a set of memory mapped
2127files in a fast way instead of parsing /proc/<pid>/maps or
2128/proc/<pid>/smaps, both of which contain many more records.  At the same
2129time one can open(2) mappings from the listings of two processes and
2130comparing their inode numbers to figure out which anonymous memory areas
2131are actually shared.
2132
21333.10	/proc/<pid>/timerslack_ns - Task timerslack value
2134---------------------------------------------------------
2135This file provides the value of the task's timerslack value in nanoseconds.
2136This value specifies an amount of time that normal timers may be deferred
2137in order to coalesce timers and avoid unnecessary wakeups.
2138
2139This allows a task's interactivity vs power consumption tradeoff to be
2140adjusted.
2141
2142Writing 0 to the file will set the task's timerslack to the default value.
2143
2144Valid values are from 0 - ULLONG_MAX
2145
2146An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
2147permissions on the task specified to change its timerslack_ns value.
2148
21493.11	/proc/<pid>/patch_state - Livepatch patch operation state
2150-----------------------------------------------------------------
2151When CONFIG_LIVEPATCH is enabled, this file displays the value of the
2152patch state for the task.
2153
2154A value of '-1' indicates that no patch is in transition.
2155
2156A value of '0' indicates that a patch is in transition and the task is
2157unpatched.  If the patch is being enabled, then the task hasn't been
2158patched yet.  If the patch is being disabled, then the task has already
2159been unpatched.
2160
2161A value of '1' indicates that a patch is in transition and the task is
2162patched.  If the patch is being enabled, then the task has already been
2163patched.  If the patch is being disabled, then the task hasn't been
2164unpatched yet.
2165
21663.12 /proc/<pid>/arch_status - task architecture specific status
2167-------------------------------------------------------------------
2168When CONFIG_PROC_PID_ARCH_STATUS is enabled, this file displays the
2169architecture specific status of the task.
2170
2171Example
2172~~~~~~~
2173
2174::
2175
2176 $ cat /proc/6753/arch_status
2177 AVX512_elapsed_ms:      8
2178
2179Description
2180~~~~~~~~~~~
2181
2182x86 specific entries
2183~~~~~~~~~~~~~~~~~~~~~
2184
2185AVX512_elapsed_ms
2186^^^^^^^^^^^^^^^^^^
2187
2188  If AVX512 is supported on the machine, this entry shows the milliseconds
2189  elapsed since the last time AVX512 usage was recorded. The recording
2190  happens on a best effort basis when a task is scheduled out. This means
2191  that the value depends on two factors:
2192
2193    1) The time which the task spent on the CPU without being scheduled
2194       out. With CPU isolation and a single runnable task this can take
2195       several seconds.
2196
2197    2) The time since the task was scheduled out last. Depending on the
2198       reason for being scheduled out (time slice exhausted, syscall ...)
2199       this can be arbitrary long time.
2200
2201  As a consequence the value cannot be considered precise and authoritative
2202  information. The application which uses this information has to be aware
2203  of the overall scenario on the system in order to determine whether a
2204  task is a real AVX512 user or not. Precise information can be obtained
2205  with performance counters.
2206
2207  A special value of '-1' indicates that no AVX512 usage was recorded, thus
2208  the task is unlikely an AVX512 user, but depends on the workload and the
2209  scheduling scenario, it also could be a false negative mentioned above.
2210
22113.13 /proc/<pid>/fd - List of symlinks to open files
2212-------------------------------------------------------
2213This directory contains symbolic links which represent open files
2214the process is maintaining.  Example output::
2215
2216  lr-x------ 1 root root 64 Sep 20 17:53 0 -> /dev/null
2217  l-wx------ 1 root root 64 Sep 20 17:53 1 -> /dev/null
2218  lrwx------ 1 root root 64 Sep 20 17:53 10 -> 'socket:[12539]'
2219  lrwx------ 1 root root 64 Sep 20 17:53 11 -> 'socket:[12540]'
2220  lrwx------ 1 root root 64 Sep 20 17:53 12 -> 'socket:[12542]'
2221
2222The number of open files for the process is stored in 'size' member
2223of stat() output for /proc/<pid>/fd for fast access.
2224-------------------------------------------------------
2225
2226
2227Chapter 4: Configuring procfs
2228=============================
2229
22304.1	Mount options
2231---------------------
2232
2233The following mount options are supported:
2234
2235	=========	========================================================
2236	hidepid=	Set /proc/<pid>/ access mode.
2237	gid=		Set the group authorized to learn processes information.
2238	subset=		Show only the specified subset of procfs.
2239	=========	========================================================
2240
2241hidepid=off or hidepid=0 means classic mode - everybody may access all
2242/proc/<pid>/ directories (default).
2243
2244hidepid=noaccess or hidepid=1 means users may not access any /proc/<pid>/
2245directories but their own.  Sensitive files like cmdline, sched*, status are now
2246protected against other users.  This makes it impossible to learn whether any
2247user runs specific program (given the program doesn't reveal itself by its
2248behaviour).  As an additional bonus, as /proc/<pid>/cmdline is unaccessible for
2249other users, poorly written programs passing sensitive information via program
2250arguments are now protected against local eavesdroppers.
2251
2252hidepid=invisible or hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be
2253fully invisible to other users.  It doesn't mean that it hides a fact whether a
2254process with a specific pid value exists (it can be learned by other means, e.g.
2255by "kill -0 $PID"), but it hides process' uid and gid, which may be learned by
2256stat()'ing /proc/<pid>/ otherwise.  It greatly complicates an intruder's task of
2257gathering information about running processes, whether some daemon runs with
2258elevated privileges, whether other user runs some sensitive program, whether
2259other users run any program at all, etc.
2260
2261hidepid=ptraceable or hidepid=4 means that procfs should only contain
2262/proc/<pid>/ directories that the caller can ptrace.
2263
2264gid= defines a group authorized to learn processes information otherwise
2265prohibited by hidepid=.  If you use some daemon like identd which needs to learn
2266information about processes information, just add identd to this group.
2267
2268subset=pid hides all top level files and directories in the procfs that
2269are not related to tasks.
2270
2271Chapter 5: Filesystem behavior
2272==============================
2273
2274Originally, before the advent of pid namespace, procfs was a global file
2275system. It means that there was only one procfs instance in the system.
2276
2277When pid namespace was added, a separate procfs instance was mounted in
2278each pid namespace. So, procfs mount options are global among all
2279mountpoints within the same namespace::
2280
2281	# grep ^proc /proc/mounts
2282	proc /proc proc rw,relatime,hidepid=2 0 0
2283
2284	# strace -e mount mount -o hidepid=1 -t proc proc /tmp/proc
2285	mount("proc", "/tmp/proc", "proc", 0, "hidepid=1") = 0
2286	+++ exited with 0 +++
2287
2288	# grep ^proc /proc/mounts
2289	proc /proc proc rw,relatime,hidepid=2 0 0
2290	proc /tmp/proc proc rw,relatime,hidepid=2 0 0
2291
2292and only after remounting procfs mount options will change at all
2293mountpoints::
2294
2295	# mount -o remount,hidepid=1 -t proc proc /tmp/proc
2296
2297	# grep ^proc /proc/mounts
2298	proc /proc proc rw,relatime,hidepid=1 0 0
2299	proc /tmp/proc proc rw,relatime,hidepid=1 0 0
2300
2301This behavior is different from the behavior of other filesystems.
2302
2303The new procfs behavior is more like other filesystems. Each procfs mount
2304creates a new procfs instance. Mount options affect own procfs instance.
2305It means that it became possible to have several procfs instances
2306displaying tasks with different filtering options in one pid namespace::
2307
2308	# mount -o hidepid=invisible -t proc proc /proc
2309	# mount -o hidepid=noaccess -t proc proc /tmp/proc
2310	# grep ^proc /proc/mounts
2311	proc /proc proc rw,relatime,hidepid=invisible 0 0
2312	proc /tmp/proc proc rw,relatime,hidepid=noaccess 0 0
2313