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 THP
532pages as well as the THP is PMD mappable or not - 1 if true, 0 otherwise.
533It just shows the current status.
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    ==    =======================================
575
576Note that there is no guarantee that every flag and associated mnemonic will
577be present in all further kernel releases. Things get changed, the flags may
578be vanished or the reverse -- new added. Interpretation of their meaning
579might change in future as well. So each consumer of these flags has to
580follow each specific kernel version for the exact semantic.
581
582This file is only present if the CONFIG_MMU kernel configuration option is
583enabled.
584
585Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy (consistent
586output can be achieved only in the single read call).
587
588This typically manifests when doing partial reads of these files while the
589memory map is being modified.  Despite the races, we do provide the following
590guarantees:
591
5921) The mapped addresses never go backwards, which implies no two
593   regions will ever overlap.
5942) If there is something at a given vaddr during the entirety of the
595   life of the smaps/maps walk, there will be some output for it.
596
597The /proc/PID/smaps_rollup file includes the same fields as /proc/PID/smaps,
598but their values are the sums of the corresponding values for all mappings of
599the process.  Additionally, it contains these fields:
600
601- Pss_Anon
602- Pss_File
603- Pss_Shmem
604
605They represent the proportional shares of anonymous, file, and shmem pages, as
606described for smaps above.  These fields are omitted in smaps since each
607mapping identifies the type (anon, file, or shmem) of all pages it contains.
608Thus all information in smaps_rollup can be derived from smaps, but at a
609significantly higher cost.
610
611The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
612bits on both physical and virtual pages associated with a process, and the
613soft-dirty bit on pte (see Documentation/admin-guide/mm/soft-dirty.rst
614for details).
615To clear the bits for all the pages associated with the process::
616
617    > echo 1 > /proc/PID/clear_refs
618
619To clear the bits for the anonymous pages associated with the process::
620
621    > echo 2 > /proc/PID/clear_refs
622
623To clear the bits for the file mapped pages associated with the process::
624
625    > echo 3 > /proc/PID/clear_refs
626
627To clear the soft-dirty bit::
628
629    > echo 4 > /proc/PID/clear_refs
630
631To reset the peak resident set size ("high water mark") to the process's
632current value::
633
634    > echo 5 > /proc/PID/clear_refs
635
636Any other value written to /proc/PID/clear_refs will have no effect.
637
638The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
639using /proc/kpageflags and number of times a page is mapped using
640/proc/kpagecount. For detailed explanation, see
641Documentation/admin-guide/mm/pagemap.rst.
642
643The /proc/pid/numa_maps is an extension based on maps, showing the memory
644locality and binding policy, as well as the memory usage (in pages) of
645each mapping. The output follows a general format where mapping details get
646summarized separated by blank spaces, one mapping per each file line::
647
648    address   policy    mapping details
649
650    00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
651    00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
652    3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
653    320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
654    3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
655    3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
656    3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
657    320698b000 default file=/lib64/libc-2.12.so
658    3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4
659    3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
660    3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
661    7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
662    7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
663    7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
664    7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
665    7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4
666
667Where:
668
669"address" is the starting address for the mapping;
670
671"policy" reports the NUMA memory policy set for the mapping (see Documentation/admin-guide/mm/numa_memory_policy.rst);
672
673"mapping details" summarizes mapping data such as mapping type, page usage counters,
674node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
675size, in KB, that is backing the mapping up.
676
6771.2 Kernel data
678---------------
679
680Similar to  the  process entries, the kernel data files give information about
681the running kernel. The files used to obtain this information are contained in
682/proc and  are  listed  in Table 1-5. Not all of these will be present in your
683system. It  depends  on the kernel configuration and the loaded modules, which
684files are there, and which are missing.
685
686.. table:: Table 1-5: Kernel info in /proc
687
688 ============ ===============================================================
689 File         Content
690 ============ ===============================================================
691 apm          Advanced power management info
692 buddyinfo    Kernel memory allocator information (see text)	(2.5)
693 bus          Directory containing bus specific information
694 cmdline      Kernel command line
695 cpuinfo      Info about the CPU
696 devices      Available devices (block and character)
697 dma          Used DMS channels
698 filesystems  Supported filesystems
699 driver       Various drivers grouped here, currently rtc	(2.4)
700 execdomains  Execdomains, related to security			(2.4)
701 fb 	      Frame Buffer devices				(2.4)
702 fs 	      File system parameters, currently nfs/exports	(2.4)
703 ide          Directory containing info about the IDE subsystem
704 interrupts   Interrupt usage
705 iomem 	      Memory map					(2.4)
706 ioports      I/O port usage
707 irq 	      Masks for irq to cpu affinity			(2.4)(smp?)
708 isapnp       ISA PnP (Plug&Play) Info				(2.4)
709 kcore        Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
710 kmsg         Kernel messages
711 ksyms        Kernel symbol table
712 loadavg      Load average of last 1, 5 & 15 minutes;
713                number of processes currently runnable (running or on ready queue);
714                total number of processes in system;
715                last pid created.
716                All fields are separated by one space except "number of
717                processes currently runnable" and "total number of processes
718                in system", which are separated by a slash ('/'). Example:
719                0.61 0.61 0.55 3/828 22084
720 locks        Kernel locks
721 meminfo      Memory info
722 misc         Miscellaneous
723 modules      List of loaded modules
724 mounts       Mounted filesystems
725 net          Networking info (see text)
726 pagetypeinfo Additional page allocator information (see text)  (2.5)
727 partitions   Table of partitions known to the system
728 pci 	      Deprecated info of PCI bus (new way -> /proc/bus/pci/,
729              decoupled by lspci				(2.4)
730 rtc          Real time clock
731 scsi         SCSI info (see text)
732 slabinfo     Slab pool info
733 softirqs     softirq usage
734 stat         Overall statistics
735 swaps        Swap space utilization
736 sys          See chapter 2
737 sysvipc      Info of SysVIPC Resources (msg, sem, shm)		(2.4)
738 tty 	      Info of tty drivers
739 uptime       Wall clock since boot, combined idle time of all cpus
740 version      Kernel version
741 video 	      bttv info of video resources			(2.4)
742 vmallocinfo  Show vmalloced areas
743 ============ ===============================================================
744
745You can,  for  example,  check  which interrupts are currently in use and what
746they are used for by looking in the file /proc/interrupts::
747
748  > cat /proc/interrupts
749             CPU0
750    0:    8728810          XT-PIC  timer
751    1:        895          XT-PIC  keyboard
752    2:          0          XT-PIC  cascade
753    3:     531695          XT-PIC  aha152x
754    4:    2014133          XT-PIC  serial
755    5:      44401          XT-PIC  pcnet_cs
756    8:          2          XT-PIC  rtc
757   11:          8          XT-PIC  i82365
758   12:     182918          XT-PIC  PS/2 Mouse
759   13:          1          XT-PIC  fpu
760   14:    1232265          XT-PIC  ide0
761   15:          7          XT-PIC  ide1
762  NMI:          0
763
764In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
765output of a SMP machine)::
766
767  > cat /proc/interrupts
768
769             CPU0       CPU1
770    0:    1243498    1214548    IO-APIC-edge  timer
771    1:       8949       8958    IO-APIC-edge  keyboard
772    2:          0          0          XT-PIC  cascade
773    5:      11286      10161    IO-APIC-edge  soundblaster
774    8:          1          0    IO-APIC-edge  rtc
775    9:      27422      27407    IO-APIC-edge  3c503
776   12:     113645     113873    IO-APIC-edge  PS/2 Mouse
777   13:          0          0          XT-PIC  fpu
778   14:      22491      24012    IO-APIC-edge  ide0
779   15:       2183       2415    IO-APIC-edge  ide1
780   17:      30564      30414   IO-APIC-level  eth0
781   18:        177        164   IO-APIC-level  bttv
782  NMI:    2457961    2457959
783  LOC:    2457882    2457881
784  ERR:       2155
785
786NMI is incremented in this case because every timer interrupt generates a NMI
787(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
788
789LOC is the local interrupt counter of the internal APIC of every CPU.
790
791ERR is incremented in the case of errors in the IO-APIC bus (the bus that
792connects the CPUs in a SMP system. This means that an error has been detected,
793the IO-APIC automatically retry the transmission, so it should not be a big
794problem, but you should read the SMP-FAQ.
795
796In 2.6.2* /proc/interrupts was expanded again.  This time the goal was for
797/proc/interrupts to display every IRQ vector in use by the system, not
798just those considered 'most important'.  The new vectors are:
799
800THR
801  interrupt raised when a machine check threshold counter
802  (typically counting ECC corrected errors of memory or cache) exceeds
803  a configurable threshold.  Only available on some systems.
804
805TRM
806  a thermal event interrupt occurs when a temperature threshold
807  has been exceeded for the CPU.  This interrupt may also be generated
808  when the temperature drops back to normal.
809
810SPU
811  a spurious interrupt is some interrupt that was raised then lowered
812  by some IO device before it could be fully processed by the APIC.  Hence
813  the APIC sees the interrupt but does not know what device it came from.
814  For this case the APIC will generate the interrupt with a IRQ vector
815  of 0xff. This might also be generated by chipset bugs.
816
817RES, CAL, TLB
818  rescheduling, call and TLB flush interrupts are
819  sent from one CPU to another per the needs of the OS.  Typically,
820  their statistics are used by kernel developers and interested users to
821  determine the occurrence of interrupts of the given type.
822
823The above IRQ vectors are displayed only when relevant.  For example,
824the threshold vector does not exist on x86_64 platforms.  Others are
825suppressed when the system is a uniprocessor.  As of this writing, only
826i386 and x86_64 platforms support the new IRQ vector displays.
827
828Of some interest is the introduction of the /proc/irq directory to 2.4.
829It could be used to set IRQ to CPU affinity. This means that you can "hook" an
830IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
831irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
832prof_cpu_mask.
833
834For example::
835
836  > ls /proc/irq/
837  0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
838  1  11  13  15  17  19  3  5  7  9  default_smp_affinity
839  > ls /proc/irq/0/
840  smp_affinity
841
842smp_affinity is a bitmask, in which you can specify which CPUs can handle the
843IRQ. You can set it by doing::
844
845  > echo 1 > /proc/irq/10/smp_affinity
846
847This means that only the first CPU will handle the IRQ, but you can also echo
8485 which means that only the first and third CPU can handle the IRQ.
849
850The contents of each smp_affinity file is the same by default::
851
852  > cat /proc/irq/0/smp_affinity
853  ffffffff
854
855There is an alternate interface, smp_affinity_list which allows specifying
856a CPU range instead of a bitmask::
857
858  > cat /proc/irq/0/smp_affinity_list
859  1024-1031
860
861The default_smp_affinity mask applies to all non-active IRQs, which are the
862IRQs which have not yet been allocated/activated, and hence which lack a
863/proc/irq/[0-9]* directory.
864
865The node file on an SMP system shows the node to which the device using the IRQ
866reports itself as being attached. This hardware locality information does not
867include information about any possible driver locality preference.
868
869prof_cpu_mask specifies which CPUs are to be profiled by the system wide
870profiler. Default value is ffffffff (all CPUs if there are only 32 of them).
871
872The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
873between all the CPUs which are allowed to handle it. As usual the kernel has
874more info than you and does a better job than you, so the defaults are the
875best choice for almost everyone.  [Note this applies only to those IO-APIC's
876that support "Round Robin" interrupt distribution.]
877
878There are  three  more  important subdirectories in /proc: net, scsi, and sys.
879The general  rule  is  that  the  contents,  or  even  the  existence of these
880directories, depend  on your kernel configuration. If SCSI is not enabled, the
881directory scsi  may  not  exist. The same is true with the net, which is there
882only when networking support is present in the running kernel.
883
884The slabinfo  file  gives  information  about  memory usage at the slab level.
885Linux uses  slab  pools for memory management above page level in version 2.2.
886Commonly used  objects  have  their  own  slab  pool (such as network buffers,
887directory cache, and so on).
888
889::
890
891    > cat /proc/buddyinfo
892
893    Node 0, zone      DMA      0      4      5      4      4      3 ...
894    Node 0, zone   Normal      1      0      0      1    101      8 ...
895    Node 0, zone  HighMem      2      0      0      1      1      0 ...
896
897External fragmentation is a problem under some workloads, and buddyinfo is a
898useful tool for helping diagnose these problems.  Buddyinfo will give you a
899clue as to how big an area you can safely allocate, or why a previous
900allocation failed.
901
902Each column represents the number of pages of a certain order which are
903available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
904ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
905available in ZONE_NORMAL, etc...
906
907More information relevant to external fragmentation can be found in
908pagetypeinfo::
909
910    > cat /proc/pagetypeinfo
911    Page block order: 9
912    Pages per block:  512
913
914    Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
915    Node    0, zone      DMA, type    Unmovable      0      0      0      1      1      1      1      1      1      1      0
916    Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0
917    Node    0, zone      DMA, type      Movable      1      1      2      1      2      1      1      0      1      0      2
918    Node    0, zone      DMA, type      Reserve      0      0      0      0      0      0      0      0      0      1      0
919    Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
920    Node    0, zone    DMA32, type    Unmovable    103     54     77      1      1      1     11      8      7      1      9
921    Node    0, zone    DMA32, type  Reclaimable      0      0      2      1      0      0      0      0      1      0      0
922    Node    0, zone    DMA32, type      Movable    169    152    113     91     77     54     39     13      6      1    452
923    Node    0, zone    DMA32, type      Reserve      1      2      2      2      2      0      1      1      1      1      0
924    Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
925
926    Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate
927    Node 0, zone      DMA            2            0            5            1            0
928    Node 0, zone    DMA32           41            6          967            2            0
929
930Fragmentation avoidance in the kernel works by grouping pages of different
931migrate types into the same contiguous regions of memory called page blocks.
932A page block is typically the size of the default hugepage size, e.g. 2MB on
933X86-64. By keeping pages grouped based on their ability to move, the kernel
934can reclaim pages within a page block to satisfy a high-order allocation.
935
936The pagetypinfo begins with information on the size of a page block. It
937then gives the same type of information as buddyinfo except broken down
938by migrate-type and finishes with details on how many page blocks of each
939type exist.
940
941If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
942from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can
943make an estimate of the likely number of huge pages that can be allocated
944at a given point in time. All the "Movable" blocks should be allocatable
945unless memory has been mlock()'d. Some of the Reclaimable blocks should
946also be allocatable although a lot of filesystem metadata may have to be
947reclaimed to achieve this.
948
949
950meminfo
951~~~~~~~
952
953Provides information about distribution and utilization of memory.  This
954varies by architecture and compile options.  Some of the counters reported
955here overlap.  The memory reported by the non overlapping counters may not
956add up to the overall memory usage and the difference for some workloads
957can be substantial.  In many cases there are other means to find out
958additional memory using subsystem specific interfaces, for instance
959/proc/net/sockstat for TCP memory allocations.
960
961Example output. You may not have all of these fields.
962
963::
964
965    > cat /proc/meminfo
966
967    MemTotal:       32858820 kB
968    MemFree:        21001236 kB
969    MemAvailable:   27214312 kB
970    Buffers:          581092 kB
971    Cached:          5587612 kB
972    SwapCached:            0 kB
973    Active:          3237152 kB
974    Inactive:        7586256 kB
975    Active(anon):      94064 kB
976    Inactive(anon):  4570616 kB
977    Active(file):    3143088 kB
978    Inactive(file):  3015640 kB
979    Unevictable:           0 kB
980    Mlocked:               0 kB
981    SwapTotal:             0 kB
982    SwapFree:              0 kB
983    Zswap:              1904 kB
984    Zswapped:           7792 kB
985    Dirty:                12 kB
986    Writeback:             0 kB
987    AnonPages:       4654780 kB
988    Mapped:           266244 kB
989    Shmem:              9976 kB
990    KReclaimable:     517708 kB
991    Slab:             660044 kB
992    SReclaimable:     517708 kB
993    SUnreclaim:       142336 kB
994    KernelStack:       11168 kB
995    PageTables:        20540 kB
996    SecPageTables:         0 kB
997    NFS_Unstable:          0 kB
998    Bounce:                0 kB
999    WritebackTmp:          0 kB
1000    CommitLimit:    16429408 kB
1001    Committed_AS:    7715148 kB
1002    VmallocTotal:   34359738367 kB
1003    VmallocUsed:       40444 kB
1004    VmallocChunk:          0 kB
1005    Percpu:            29312 kB
1006    EarlyMemtestBad:       0 kB
1007    HardwareCorrupted:     0 kB
1008    AnonHugePages:   4149248 kB
1009    ShmemHugePages:        0 kB
1010    ShmemPmdMapped:        0 kB
1011    FileHugePages:         0 kB
1012    FilePmdMapped:         0 kB
1013    CmaTotal:              0 kB
1014    CmaFree:               0 kB
1015    HugePages_Total:       0
1016    HugePages_Free:        0
1017    HugePages_Rsvd:        0
1018    HugePages_Surp:        0
1019    Hugepagesize:       2048 kB
1020    Hugetlb:               0 kB
1021    DirectMap4k:      401152 kB
1022    DirectMap2M:    10008576 kB
1023    DirectMap1G:    24117248 kB
1024
1025MemTotal
1026              Total usable RAM (i.e. physical RAM minus a few reserved
1027              bits and the kernel binary code)
1028MemFree
1029              Total free RAM. On highmem systems, the sum of LowFree+HighFree
1030MemAvailable
1031              An estimate of how much memory is available for starting new
1032              applications, without swapping. Calculated from MemFree,
1033              SReclaimable, the size of the file LRU lists, and the low
1034              watermarks in each zone.
1035              The estimate takes into account that the system needs some
1036              page cache to function well, and that not all reclaimable
1037              slab will be reclaimable, due to items being in use. The
1038              impact of those factors will vary from system to system.
1039Buffers
1040              Relatively temporary storage for raw disk blocks
1041              shouldn't get tremendously large (20MB or so)
1042Cached
1043              In-memory cache for files read from the disk (the
1044              pagecache) as well as tmpfs & shmem.
1045              Doesn't include SwapCached.
1046SwapCached
1047              Memory that once was swapped out, is swapped back in but
1048              still also is in the swapfile (if memory is needed it
1049              doesn't need to be swapped out AGAIN because it is already
1050              in the swapfile. This saves I/O)
1051Active
1052              Memory that has been used more recently and usually not
1053              reclaimed unless absolutely necessary.
1054Inactive
1055              Memory which has been less recently used.  It is more
1056              eligible to be reclaimed for other purposes
1057Unevictable
1058              Memory allocated for userspace which cannot be reclaimed, such
1059              as mlocked pages, ramfs backing pages, secret memfd pages etc.
1060Mlocked
1061              Memory locked with mlock().
1062HighTotal, HighFree
1063              Highmem is all memory above ~860MB of physical memory.
1064              Highmem areas are for use by userspace programs, or
1065              for the pagecache.  The kernel must use tricks to access
1066              this memory, making it slower to access than lowmem.
1067LowTotal, LowFree
1068              Lowmem is memory which can be used for everything that
1069              highmem can be used for, but it is also available for the
1070              kernel's use for its own data structures.  Among many
1071              other things, it is where everything from the Slab is
1072              allocated.  Bad things happen when you're out of lowmem.
1073SwapTotal
1074              total amount of swap space available
1075SwapFree
1076              Memory which has been evicted from RAM, and is temporarily
1077              on the disk
1078Zswap
1079              Memory consumed by the zswap backend (compressed size)
1080Zswapped
1081              Amount of anonymous memory stored in zswap (original size)
1082Dirty
1083              Memory which is waiting to get written back to the disk
1084Writeback
1085              Memory which is actively being written back to the disk
1086AnonPages
1087              Non-file backed pages mapped into userspace page tables
1088Mapped
1089              files which have been mmapped, such as libraries
1090Shmem
1091              Total memory used by shared memory (shmem) and tmpfs
1092KReclaimable
1093              Kernel allocations that the kernel will attempt to reclaim
1094              under memory pressure. Includes SReclaimable (below), and other
1095              direct allocations with a shrinker.
1096Slab
1097              in-kernel data structures cache
1098SReclaimable
1099              Part of Slab, that might be reclaimed, such as caches
1100SUnreclaim
1101              Part of Slab, that cannot be reclaimed on memory pressure
1102KernelStack
1103              Memory consumed by the kernel stacks of all tasks
1104PageTables
1105              Memory consumed by userspace page tables
1106SecPageTables
1107              Memory consumed by secondary page tables, this currently
1108              currently includes KVM mmu allocations on x86 and arm64.
1109NFS_Unstable
1110              Always zero. Previous counted pages which had been written to
1111              the server, but has not been committed to stable storage.
1112Bounce
1113              Memory used for block device "bounce buffers"
1114WritebackTmp
1115              Memory used by FUSE for temporary writeback buffers
1116CommitLimit
1117              Based on the overcommit ratio ('vm.overcommit_ratio'),
1118              this is the total amount of  memory currently available to
1119              be allocated on the system. This limit is only adhered to
1120              if strict overcommit accounting is enabled (mode 2 in
1121              'vm.overcommit_memory').
1122
1123              The CommitLimit is calculated with the following formula::
1124
1125                CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
1126                               overcommit_ratio / 100 + [total swap pages]
1127
1128              For example, on a system with 1G of physical RAM and 7G
1129              of swap with a `vm.overcommit_ratio` of 30 it would
1130              yield a CommitLimit of 7.3G.
1131
1132              For more details, see the memory overcommit documentation
1133              in mm/overcommit-accounting.
1134Committed_AS
1135              The amount of memory presently allocated on the system.
1136              The committed memory is a sum of all of the memory which
1137              has been allocated by processes, even if it has not been
1138              "used" by them as of yet. A process which malloc()'s 1G
1139              of memory, but only touches 300M of it will show up as
1140              using 1G. This 1G is memory which has been "committed" to
1141              by the VM and can be used at any time by the allocating
1142              application. With strict overcommit enabled on the system
1143              (mode 2 in 'vm.overcommit_memory'), allocations which would
1144              exceed the CommitLimit (detailed above) will not be permitted.
1145              This is useful if one needs to guarantee that processes will
1146              not fail due to lack of memory once that memory has been
1147              successfully allocated.
1148VmallocTotal
1149              total size of vmalloc virtual address space
1150VmallocUsed
1151              amount of vmalloc area which is used
1152VmallocChunk
1153              largest contiguous block of vmalloc area which is free
1154Percpu
1155              Memory allocated to the percpu allocator used to back percpu
1156              allocations. This stat excludes the cost of metadata.
1157EarlyMemtestBad
1158              The amount of RAM/memory in kB, that was identified as corrupted
1159              by early memtest. If memtest was not run, this field will not
1160              be displayed at all. Size is never rounded down to 0 kB.
1161              That means if 0 kB is reported, you can safely assume
1162              there was at least one pass of memtest and none of the passes
1163              found a single faulty byte of RAM.
1164HardwareCorrupted
1165              The amount of RAM/memory in KB, the kernel identifies as
1166              corrupted.
1167AnonHugePages
1168              Non-file backed huge pages mapped into userspace page tables
1169ShmemHugePages
1170              Memory used by shared memory (shmem) and tmpfs allocated
1171              with huge pages
1172ShmemPmdMapped
1173              Shared memory mapped into userspace with huge pages
1174FileHugePages
1175              Memory used for filesystem data (page cache) allocated
1176              with huge pages
1177FilePmdMapped
1178              Page cache mapped into userspace with huge pages
1179CmaTotal
1180              Memory reserved for the Contiguous Memory Allocator (CMA)
1181CmaFree
1182              Free remaining memory in the CMA reserves
1183HugePages_Total, HugePages_Free, HugePages_Rsvd, HugePages_Surp, Hugepagesize, Hugetlb
1184              See Documentation/admin-guide/mm/hugetlbpage.rst.
1185DirectMap4k, DirectMap2M, DirectMap1G
1186              Breakdown of page table sizes used in the kernel's
1187              identity mapping of RAM
1188
1189vmallocinfo
1190~~~~~~~~~~~
1191
1192Provides information about vmalloced/vmaped areas. One line per area,
1193containing the virtual address range of the area, size in bytes,
1194caller information of the creator, and optional information depending
1195on the kind of area:
1196
1197 ==========  ===================================================
1198 pages=nr    number of pages
1199 phys=addr   if a physical address was specified
1200 ioremap     I/O mapping (ioremap() and friends)
1201 vmalloc     vmalloc() area
1202 vmap        vmap()ed pages
1203 user        VM_USERMAP area
1204 vpages      buffer for pages pointers was vmalloced (huge area)
1205 N<node>=nr  (Only on NUMA kernels)
1206             Number of pages allocated on memory node <node>
1207 ==========  ===================================================
1208
1209::
1210
1211    > cat /proc/vmallocinfo
1212    0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
1213    /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
1214    0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
1215    /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
1216    0xffffc20000302000-0xffffc20000304000    8192 acpi_tb_verify_table+0x21/0x4f...
1217    phys=7fee8000 ioremap
1218    0xffffc20000304000-0xffffc20000307000   12288 acpi_tb_verify_table+0x21/0x4f...
1219    phys=7fee7000 ioremap
1220    0xffffc2000031d000-0xffffc2000031f000    8192 init_vdso_vars+0x112/0x210
1221    0xffffc2000031f000-0xffffc2000032b000   49152 cramfs_uncompress_init+0x2e ...
1222    /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
1223    0xffffc2000033a000-0xffffc2000033d000   12288 sys_swapon+0x640/0xac0      ...
1224    pages=2 vmalloc N1=2
1225    0xffffc20000347000-0xffffc2000034c000   20480 xt_alloc_table_info+0xfe ...
1226    /0x130 [x_tables] pages=4 vmalloc N0=4
1227    0xffffffffa0000000-0xffffffffa000f000   61440 sys_init_module+0xc27/0x1d00 ...
1228    pages=14 vmalloc N2=14
1229    0xffffffffa000f000-0xffffffffa0014000   20480 sys_init_module+0xc27/0x1d00 ...
1230    pages=4 vmalloc N1=4
1231    0xffffffffa0014000-0xffffffffa0017000   12288 sys_init_module+0xc27/0x1d00 ...
1232    pages=2 vmalloc N1=2
1233    0xffffffffa0017000-0xffffffffa0022000   45056 sys_init_module+0xc27/0x1d00 ...
1234    pages=10 vmalloc N0=10
1235
1236
1237softirqs
1238~~~~~~~~
1239
1240Provides counts of softirq handlers serviced since boot time, for each CPU.
1241
1242::
1243
1244    > cat /proc/softirqs
1245		  CPU0       CPU1       CPU2       CPU3
1246	HI:          0          0          0          0
1247    TIMER:       27166      27120      27097      27034
1248    NET_TX:          0          0          0         17
1249    NET_RX:         42          0          0         39
1250    BLOCK:           0          0        107       1121
1251    TASKLET:         0          0          0        290
1252    SCHED:       27035      26983      26971      26746
1253    HRTIMER:         0          0          0          0
1254	RCU:      1678       1769       2178       2250
1255
12561.3 Networking info in /proc/net
1257--------------------------------
1258
1259The subdirectory  /proc/net  follows  the  usual  pattern. Table 1-8 shows the
1260additional values  you  get  for  IP  version 6 if you configure the kernel to
1261support this. Table 1-9 lists the files and their meaning.
1262
1263
1264.. table:: Table 1-8: IPv6 info in /proc/net
1265
1266 ========== =====================================================
1267 File       Content
1268 ========== =====================================================
1269 udp6       UDP sockets (IPv6)
1270 tcp6       TCP sockets (IPv6)
1271 raw6       Raw device statistics (IPv6)
1272 igmp6      IP multicast addresses, which this host joined (IPv6)
1273 if_inet6   List of IPv6 interface addresses
1274 ipv6_route Kernel routing table for IPv6
1275 rt6_stats  Global IPv6 routing tables statistics
1276 sockstat6  Socket statistics (IPv6)
1277 snmp6      Snmp data (IPv6)
1278 ========== =====================================================
1279
1280.. table:: Table 1-9: Network info in /proc/net
1281
1282 ============= ================================================================
1283 File          Content
1284 ============= ================================================================
1285 arp           Kernel  ARP table
1286 dev           network devices with statistics
1287 dev_mcast     the Layer2 multicast groups a device is listening too
1288               (interface index, label, number of references, number of bound
1289               addresses).
1290 dev_stat      network device status
1291 ip_fwchains   Firewall chain linkage
1292 ip_fwnames    Firewall chain names
1293 ip_masq       Directory containing the masquerading tables
1294 ip_masquerade Major masquerading table
1295 netstat       Network statistics
1296 raw           raw device statistics
1297 route         Kernel routing table
1298 rpc           Directory containing rpc info
1299 rt_cache      Routing cache
1300 snmp          SNMP data
1301 sockstat      Socket statistics
1302 softnet_stat  Per-CPU incoming packets queues statistics of online CPUs
1303 tcp           TCP  sockets
1304 udp           UDP sockets
1305 unix          UNIX domain sockets
1306 wireless      Wireless interface data (Wavelan etc)
1307 igmp          IP multicast addresses, which this host joined
1308 psched        Global packet scheduler parameters.
1309 netlink       List of PF_NETLINK sockets
1310 ip_mr_vifs    List of multicast virtual interfaces
1311 ip_mr_cache   List of multicast routing cache
1312 ============= ================================================================
1313
1314You can  use  this  information  to see which network devices are available in
1315your system and how much traffic was routed over those devices::
1316
1317  > cat /proc/net/dev
1318  Inter-|Receive                                                   |[...
1319   face |bytes    packets errs drop fifo frame compressed multicast|[...
1320      lo:  908188   5596     0    0    0     0          0         0 [...
1321    ppp0:15475140  20721   410    0    0   410          0         0 [...
1322    eth0:  614530   7085     0    0    0     0          0         1 [...
1323
1324  ...] Transmit
1325  ...] bytes    packets errs drop fifo colls carrier compressed
1326  ...]  908188     5596    0    0    0     0       0          0
1327  ...] 1375103    17405    0    0    0     0       0          0
1328  ...] 1703981     5535    0    0    0     3       0          0
1329
1330In addition, each Channel Bond interface has its own directory.  For
1331example, the bond0 device will have a directory called /proc/net/bond0/.
1332It will contain information that is specific to that bond, such as the
1333current slaves of the bond, the link status of the slaves, and how
1334many times the slaves link has failed.
1335
13361.4 SCSI info
1337-------------
1338
1339If you have a SCSI or ATA host adapter in your system, you'll find a
1340subdirectory named after the driver for this adapter in /proc/scsi.
1341You'll also see a list of all recognized SCSI devices in /proc/scsi::
1342
1343  >cat /proc/scsi/scsi
1344  Attached devices:
1345  Host: scsi0 Channel: 00 Id: 00 Lun: 00
1346    Vendor: IBM      Model: DGHS09U          Rev: 03E0
1347    Type:   Direct-Access                    ANSI SCSI revision: 03
1348  Host: scsi0 Channel: 00 Id: 06 Lun: 00
1349    Vendor: PIONEER  Model: CD-ROM DR-U06S   Rev: 1.04
1350    Type:   CD-ROM                           ANSI SCSI revision: 02
1351
1352
1353The directory  named  after  the driver has one file for each adapter found in
1354the system.  These  files  contain information about the controller, including
1355the used  IRQ  and  the  IO  address range. The amount of information shown is
1356dependent on  the adapter you use. The example shows the output for an Adaptec
1357AHA-2940 SCSI adapter::
1358
1359  > cat /proc/scsi/aic7xxx/0
1360
1361  Adaptec AIC7xxx driver version: 5.1.19/3.2.4
1362  Compile Options:
1363    TCQ Enabled By Default : Disabled
1364    AIC7XXX_PROC_STATS     : Disabled
1365    AIC7XXX_RESET_DELAY    : 5
1366  Adapter Configuration:
1367             SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
1368                             Ultra Wide Controller
1369      PCI MMAPed I/O Base: 0xeb001000
1370   Adapter SEEPROM Config: SEEPROM found and used.
1371        Adaptec SCSI BIOS: Enabled
1372                      IRQ: 10
1373                     SCBs: Active 0, Max Active 2,
1374                           Allocated 15, HW 16, Page 255
1375               Interrupts: 160328
1376        BIOS Control Word: 0x18b6
1377     Adapter Control Word: 0x005b
1378     Extended Translation: Enabled
1379  Disconnect Enable Flags: 0xffff
1380       Ultra Enable Flags: 0x0001
1381   Tag Queue Enable Flags: 0x0000
1382  Ordered Queue Tag Flags: 0x0000
1383  Default Tag Queue Depth: 8
1384      Tagged Queue By Device array for aic7xxx host instance 0:
1385        {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
1386      Actual queue depth per device for aic7xxx host instance 0:
1387        {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
1388  Statistics:
1389  (scsi0:0:0:0)
1390    Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
1391    Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
1392    Total transfers 160151 (74577 reads and 85574 writes)
1393  (scsi0:0:6:0)
1394    Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
1395    Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
1396    Total transfers 0 (0 reads and 0 writes)
1397
1398
13991.5 Parallel port info in /proc/parport
1400---------------------------------------
1401
1402The directory  /proc/parport  contains information about the parallel ports of
1403your system.  It  has  one  subdirectory  for  each port, named after the port
1404number (0,1,2,...).
1405
1406These directories contain the four files shown in Table 1-10.
1407
1408
1409.. table:: Table 1-10: Files in /proc/parport
1410
1411 ========= ====================================================================
1412 File      Content
1413 ========= ====================================================================
1414 autoprobe Any IEEE-1284 device ID information that has been acquired.
1415 devices   list of the device drivers using that port. A + will appear by the
1416           name of the device currently using the port (it might not appear
1417           against any).
1418 hardware  Parallel port's base address, IRQ line and DMA channel.
1419 irq       IRQ that parport is using for that port. This is in a separate
1420           file to allow you to alter it by writing a new value in (IRQ
1421           number or none).
1422 ========= ====================================================================
1423
14241.6 TTY info in /proc/tty
1425-------------------------
1426
1427Information about  the  available  and actually used tty's can be found in the
1428directory /proc/tty. You'll find  entries  for drivers and line disciplines in
1429this directory, as shown in Table 1-11.
1430
1431
1432.. table:: Table 1-11: Files in /proc/tty
1433
1434 ============= ==============================================
1435 File          Content
1436 ============= ==============================================
1437 drivers       list of drivers and their usage
1438 ldiscs        registered line disciplines
1439 driver/serial usage statistic and status of single tty lines
1440 ============= ==============================================
1441
1442To see  which  tty's  are  currently in use, you can simply look into the file
1443/proc/tty/drivers::
1444
1445  > cat /proc/tty/drivers
1446  pty_slave            /dev/pts      136   0-255 pty:slave
1447  pty_master           /dev/ptm      128   0-255 pty:master
1448  pty_slave            /dev/ttyp       3   0-255 pty:slave
1449  pty_master           /dev/pty        2   0-255 pty:master
1450  serial               /dev/cua        5   64-67 serial:callout
1451  serial               /dev/ttyS       4   64-67 serial
1452  /dev/tty0            /dev/tty0       4       0 system:vtmaster
1453  /dev/ptmx            /dev/ptmx       5       2 system
1454  /dev/console         /dev/console    5       1 system:console
1455  /dev/tty             /dev/tty        5       0 system:/dev/tty
1456  unknown              /dev/tty        4    1-63 console
1457
1458
14591.7 Miscellaneous kernel statistics in /proc/stat
1460-------------------------------------------------
1461
1462Various pieces   of  information about  kernel activity  are  available in the
1463/proc/stat file.  All  of  the numbers reported  in  this file are  aggregates
1464since the system first booted.  For a quick look, simply cat the file::
1465
1466  > cat /proc/stat
1467  cpu  237902850 368826709 106375398 1873517540 1135548 0 14507935 0 0 0
1468  cpu0 60045249 91891769 26331539 468411416 495718 0 5739640 0 0 0
1469  cpu1 59746288 91759249 26609887 468860630 312281 0 4384817 0 0 0
1470  cpu2 59489247 92985423 26904446 467808813 171668 0 2268998 0 0 0
1471  cpu3 58622065 92190267 26529524 468436680 155879 0 2114478 0 0 0
1472  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>
1473  ctxt 22848221062
1474  btime 1605316999
1475  processes 746787147
1476  procs_running 2
1477  procs_blocked 0
1478  softirq 12121874454 100099120 3938138295 127375644 2795979 187870761 0 173808342 3072582055 52608 224184354
1479
1480The very first  "cpu" line aggregates the  numbers in all  of the other "cpuN"
1481lines.  These numbers identify the amount of time the CPU has spent performing
1482different kinds of work.  Time units are in USER_HZ (typically hundredths of a
1483second).  The meanings of the columns are as follows, from left to right:
1484
1485- user: normal processes executing in user mode
1486- nice: niced processes executing in user mode
1487- system: processes executing in kernel mode
1488- idle: twiddling thumbs
1489- iowait: In a word, iowait stands for waiting for I/O to complete. But there
1490  are several problems:
1491
1492  1. CPU will not wait for I/O to complete, iowait is the time that a task is
1493     waiting for I/O to complete. When CPU goes into idle state for
1494     outstanding task I/O, another task will be scheduled on this CPU.
1495  2. In a multi-core CPU, the task waiting for I/O to complete is not running
1496     on any CPU, so the iowait of each CPU is difficult to calculate.
1497  3. The value of iowait field in /proc/stat will decrease in certain
1498     conditions.
1499
1500  So, the iowait is not reliable by reading from /proc/stat.
1501- irq: servicing interrupts
1502- softirq: servicing softirqs
1503- steal: involuntary wait
1504- guest: running a normal guest
1505- guest_nice: running a niced guest
1506
1507The "intr" line gives counts of interrupts  serviced since boot time, for each
1508of the  possible system interrupts.   The first  column  is the  total of  all
1509interrupts serviced  including  unnumbered  architecture specific  interrupts;
1510each  subsequent column is the  total for that particular numbered interrupt.
1511Unnumbered interrupts are not shown, only summed into the total.
1512
1513The "ctxt" line gives the total number of context switches across all CPUs.
1514
1515The "btime" line gives  the time at which the  system booted, in seconds since
1516the Unix epoch.
1517
1518The "processes" line gives the number  of processes and threads created, which
1519includes (but  is not limited  to) those  created by  calls to the  fork() and
1520clone() system calls.
1521
1522The "procs_running" line gives the total number of threads that are
1523running or ready to run (i.e., the total number of runnable threads).
1524
1525The   "procs_blocked" line gives  the  number of  processes currently blocked,
1526waiting for I/O to complete.
1527
1528The "softirq" line gives counts of softirqs serviced since boot time, for each
1529of the possible system softirqs. The first column is the total of all
1530softirqs serviced; each subsequent column is the total for that particular
1531softirq.
1532
1533
15341.8 Ext4 file system parameters
1535-------------------------------
1536
1537Information about mounted ext4 file systems can be found in
1538/proc/fs/ext4.  Each mounted filesystem will have a directory in
1539/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1540/proc/fs/ext4/sda9 or /proc/fs/ext4/dm-0).   The files in each per-device
1541directory are shown in Table 1-12, below.
1542
1543.. table:: Table 1-12: Files in /proc/fs/ext4/<devname>
1544
1545 ==============  ==========================================================
1546 File            Content
1547 mb_groups       details of multiblock allocator buddy cache of free blocks
1548 ==============  ==========================================================
1549
15501.9 /proc/consoles
1551-------------------
1552Shows registered system console lines.
1553
1554To see which character device lines are currently used for the system console
1555/dev/console, you may simply look into the file /proc/consoles::
1556
1557  > cat /proc/consoles
1558  tty0                 -WU (ECp)       4:7
1559  ttyS0                -W- (Ep)        4:64
1560
1561The columns are:
1562
1563+--------------------+-------------------------------------------------------+
1564| device             | name of the device                                    |
1565+====================+=======================================================+
1566| operations         | * R = can do read operations                          |
1567|                    | * W = can do write operations                         |
1568|                    | * U = can do unblank                                  |
1569+--------------------+-------------------------------------------------------+
1570| flags              | * E = it is enabled                                   |
1571|                    | * C = it is preferred console                         |
1572|                    | * B = it is primary boot console                      |
1573|                    | * p = it is used for printk buffer                    |
1574|                    | * b = it is not a TTY but a Braille device            |
1575|                    | * a = it is safe to use when cpu is offline           |
1576+--------------------+-------------------------------------------------------+
1577| major:minor        | major and minor number of the device separated by a   |
1578|                    | colon                                                 |
1579+--------------------+-------------------------------------------------------+
1580
1581Summary
1582-------
1583
1584The /proc file system serves information about the running system. It not only
1585allows access to process data but also allows you to request the kernel status
1586by reading files in the hierarchy.
1587
1588The directory  structure  of /proc reflects the types of information and makes
1589it easy, if not obvious, where to look for specific data.
1590
1591Chapter 2: Modifying System Parameters
1592======================================
1593
1594In This Chapter
1595---------------
1596
1597* Modifying kernel parameters by writing into files found in /proc/sys
1598* Exploring the files which modify certain parameters
1599* Review of the /proc/sys file tree
1600
1601------------------------------------------------------------------------------
1602
1603A very  interesting part of /proc is the directory /proc/sys. This is not only
1604a source  of  information,  it also allows you to change parameters within the
1605kernel. Be  very  careful  when attempting this. You can optimize your system,
1606but you  can  also  cause  it  to  crash.  Never  alter kernel parameters on a
1607production system.  Set  up  a  development machine and test to make sure that
1608everything works  the  way  you want it to. You may have no alternative but to
1609reboot the machine once an error has been made.
1610
1611To change  a  value,  simply  echo  the new value into the file.
1612You need to be root to do this. You  can  create  your  own  boot script
1613to perform this every time your system boots.
1614
1615The files  in /proc/sys can be used to fine tune and monitor miscellaneous and
1616general things  in  the operation of the Linux kernel. Since some of the files
1617can inadvertently  disrupt  your  system,  it  is  advisable  to  read  both
1618documentation and  source  before actually making adjustments. In any case, be
1619very careful  when  writing  to  any  of these files. The entries in /proc may
1620change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1621review the kernel documentation in the directory linux/Documentation.
1622This chapter  is  heavily  based  on the documentation included in the pre 2.2
1623kernels, and became part of it in version 2.2.1 of the Linux kernel.
1624
1625Please see: Documentation/admin-guide/sysctl/ directory for descriptions of
1626these entries.
1627
1628Summary
1629-------
1630
1631Certain aspects  of  kernel  behavior  can be modified at runtime, without the
1632need to  recompile  the kernel, or even to reboot the system. The files in the
1633/proc/sys tree  can  not only be read, but also modified. You can use the echo
1634command to write value into these files, thereby changing the default settings
1635of the kernel.
1636
1637
1638Chapter 3: Per-process Parameters
1639=================================
1640
16413.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1642--------------------------------------------------------------------------------
1643
1644These files can be used to adjust the badness heuristic used to select which
1645process gets killed in out of memory (oom) conditions.
1646
1647The badness heuristic assigns a value to each candidate task ranging from 0
1648(never kill) to 1000 (always kill) to determine which process is targeted.  The
1649units are roughly a proportion along that range of allowed memory the process
1650may allocate from based on an estimation of its current memory and swap use.
1651For example, if a task is using all allowed memory, its badness score will be
16521000.  If it is using half of its allowed memory, its score will be 500.
1653
1654The amount of "allowed" memory depends on the context in which the oom killer
1655was called.  If it is due to the memory assigned to the allocating task's cpuset
1656being exhausted, the allowed memory represents the set of mems assigned to that
1657cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
1658memory represents the set of mempolicy nodes.  If it is due to a memory
1659limit (or swap limit) being reached, the allowed memory is that configured
1660limit.  Finally, if it is due to the entire system being out of memory, the
1661allowed memory represents all allocatable resources.
1662
1663The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1664is used to determine which task to kill.  Acceptable values range from -1000
1665(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
1666polarize the preference for oom killing either by always preferring a certain
1667task or completely disabling it.  The lowest possible value, -1000, is
1668equivalent to disabling oom killing entirely for that task since it will always
1669report a badness score of 0.
1670
1671Consequently, it is very simple for userspace to define the amount of memory to
1672consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
1673example, is roughly equivalent to allowing the remainder of tasks sharing the
1674same system, cpuset, mempolicy, or memory controller resources to use at least
167550% more memory.  A value of -500, on the other hand, would be roughly
1676equivalent to discounting 50% of the task's allowed memory from being considered
1677as scoring against the task.
1678
1679For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1680be used to tune the badness score.  Its acceptable values range from -16
1681(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1682(OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
1683scaled linearly with /proc/<pid>/oom_score_adj.
1684
1685The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1686value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1687requires CAP_SYS_RESOURCE.
1688
1689
16903.2 /proc/<pid>/oom_score - Display current oom-killer score
1691-------------------------------------------------------------
1692
1693This file can be used to check the current score used by the oom-killer for
1694any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1695process should be killed in an out-of-memory situation.
1696
1697Please note that the exported value includes oom_score_adj so it is
1698effectively in range [0,2000].
1699
1700
17013.3  /proc/<pid>/io - Display the IO accounting fields
1702-------------------------------------------------------
1703
1704This file contains IO statistics for each running process.
1705
1706Example
1707~~~~~~~
1708
1709::
1710
1711    test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1712    [1] 3828
1713
1714    test:/tmp # cat /proc/3828/io
1715    rchar: 323934931
1716    wchar: 323929600
1717    syscr: 632687
1718    syscw: 632675
1719    read_bytes: 0
1720    write_bytes: 323932160
1721    cancelled_write_bytes: 0
1722
1723
1724Description
1725~~~~~~~~~~~
1726
1727rchar
1728^^^^^
1729
1730I/O counter: chars read
1731The number of bytes which this task has caused to be read from storage. This
1732is simply the sum of bytes which this process passed to read() and pread().
1733It includes things like tty IO and it is unaffected by whether or not actual
1734physical disk IO was required (the read might have been satisfied from
1735pagecache).
1736
1737
1738wchar
1739^^^^^
1740
1741I/O counter: chars written
1742The number of bytes which this task has caused, or shall cause to be written
1743to disk. Similar caveats apply here as with rchar.
1744
1745
1746syscr
1747^^^^^
1748
1749I/O counter: read syscalls
1750Attempt to count the number of read I/O operations, i.e. syscalls like read()
1751and pread().
1752
1753
1754syscw
1755^^^^^
1756
1757I/O counter: write syscalls
1758Attempt to count the number of write I/O operations, i.e. syscalls like
1759write() and pwrite().
1760
1761
1762read_bytes
1763^^^^^^^^^^
1764
1765I/O counter: bytes read
1766Attempt to count the number of bytes which this process really did cause to
1767be fetched from the storage layer. Done at the submit_bio() level, so it is
1768accurate for block-backed filesystems. <please add status regarding NFS and
1769CIFS at a later time>
1770
1771
1772write_bytes
1773^^^^^^^^^^^
1774
1775I/O counter: bytes written
1776Attempt to count the number of bytes which this process caused to be sent to
1777the storage layer. This is done at page-dirtying time.
1778
1779
1780cancelled_write_bytes
1781^^^^^^^^^^^^^^^^^^^^^
1782
1783The big inaccuracy here is truncate. If a process writes 1MB to a file and
1784then deletes the file, it will in fact perform no writeout. But it will have
1785been accounted as having caused 1MB of write.
1786In other words: The number of bytes which this process caused to not happen,
1787by truncating pagecache. A task can cause "negative" IO too. If this task
1788truncates some dirty pagecache, some IO which another task has been accounted
1789for (in its write_bytes) will not be happening. We _could_ just subtract that
1790from the truncating task's write_bytes, but there is information loss in doing
1791that.
1792
1793
1794.. Note::
1795
1796   At its current implementation state, this is a bit racy on 32-bit machines:
1797   if process A reads process B's /proc/pid/io while process B is updating one
1798   of those 64-bit counters, process A could see an intermediate result.
1799
1800
1801More information about this can be found within the taskstats documentation in
1802Documentation/accounting.
1803
18043.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1805---------------------------------------------------------------
1806When a process is dumped, all anonymous memory is written to a core file as
1807long as the size of the core file isn't limited. But sometimes we don't want
1808to dump some memory segments, for example, huge shared memory or DAX.
1809Conversely, sometimes we want to save file-backed memory segments into a core
1810file, not only the individual files.
1811
1812/proc/<pid>/coredump_filter allows you to customize which memory segments
1813will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1814of memory types. If a bit of the bitmask is set, memory segments of the
1815corresponding memory type are dumped, otherwise they are not dumped.
1816
1817The following 9 memory types are supported:
1818
1819  - (bit 0) anonymous private memory
1820  - (bit 1) anonymous shared memory
1821  - (bit 2) file-backed private memory
1822  - (bit 3) file-backed shared memory
1823  - (bit 4) ELF header pages in file-backed private memory areas (it is
1824    effective only if the bit 2 is cleared)
1825  - (bit 5) hugetlb private memory
1826  - (bit 6) hugetlb shared memory
1827  - (bit 7) DAX private memory
1828  - (bit 8) DAX shared memory
1829
1830  Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1831  are always dumped regardless of the bitmask status.
1832
1833  Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
1834  only affected by bit 5-6, and DAX is only affected by bits 7-8.
1835
1836The default value of coredump_filter is 0x33; this means all anonymous memory
1837segments, ELF header pages and hugetlb private memory are dumped.
1838
1839If you don't want to dump all shared memory segments attached to pid 1234,
1840write 0x31 to the process's proc file::
1841
1842  $ echo 0x31 > /proc/1234/coredump_filter
1843
1844When a new process is created, the process inherits the bitmask status from its
1845parent. It is useful to set up coredump_filter before the program runs.
1846For example::
1847
1848  $ echo 0x7 > /proc/self/coredump_filter
1849  $ ./some_program
1850
18513.5	/proc/<pid>/mountinfo - Information about mounts
1852--------------------------------------------------------
1853
1854This file contains lines of the form::
1855
1856    36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1857    (1)(2)(3)   (4)   (5)      (6)     (n…m) (m+1)(m+2) (m+3)         (m+4)
1858
1859    (1)   mount ID:        unique identifier of the mount (may be reused after umount)
1860    (2)   parent ID:       ID of parent (or of self for the top of the mount tree)
1861    (3)   major:minor:     value of st_dev for files on filesystem
1862    (4)   root:            root of the mount within the filesystem
1863    (5)   mount point:     mount point relative to the process's root
1864    (6)   mount options:   per mount options
1865    (n…m) optional fields: zero or more fields of the form "tag[:value]"
1866    (m+1) separator:       marks the end of the optional fields
1867    (m+2) filesystem type: name of filesystem of the form "type[.subtype]"
1868    (m+3) mount source:    filesystem specific information or "none"
1869    (m+4) super options:   per super block options
1870
1871Parsers should ignore all unrecognised optional fields.  Currently the
1872possible optional fields are:
1873
1874================  ==============================================================
1875shared:X          mount is shared in peer group X
1876master:X          mount is slave to peer group X
1877propagate_from:X  mount is slave and receives propagation from peer group X [#]_
1878unbindable        mount is unbindable
1879================  ==============================================================
1880
1881.. [#] X is the closest dominant peer group under the process's root.  If
1882       X is the immediate master of the mount, or if there's no dominant peer
1883       group under the same root, then only the "master:X" field is present
1884       and not the "propagate_from:X" field.
1885
1886For more information on mount propagation see:
1887
1888  Documentation/filesystems/sharedsubtree.rst
1889
1890
18913.6	/proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
1892--------------------------------------------------------
1893These files provide a method to access a task's comm value. It also allows for
1894a task to set its own or one of its thread siblings comm value. The comm value
1895is limited in size compared to the cmdline value, so writing anything longer
1896then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1897comm value.
1898
1899
19003.7	/proc/<pid>/task/<tid>/children - Information about task children
1901-------------------------------------------------------------------------
1902This file provides a fast way to retrieve first level children pids
1903of a task pointed by <pid>/<tid> pair. The format is a space separated
1904stream of pids.
1905
1906Note the "first level" here -- if a child has its own children they will
1907not be listed here; one needs to read /proc/<children-pid>/task/<tid>/children
1908to obtain the descendants.
1909
1910Since this interface is intended to be fast and cheap it doesn't
1911guarantee to provide precise results and some children might be
1912skipped, especially if they've exited right after we printed their
1913pids, so one needs to either stop or freeze processes being inspected
1914if precise results are needed.
1915
1916
19173.8	/proc/<pid>/fdinfo/<fd> - Information about opened file
1918---------------------------------------------------------------
1919This file provides information associated with an opened file. The regular
1920files have at least four fields -- 'pos', 'flags', 'mnt_id' and 'ino'.
1921The 'pos' represents the current offset of the opened file in decimal
1922form [see lseek(2) for details], 'flags' denotes the octal O_xxx mask the
1923file has been created with [see open(2) for details] and 'mnt_id' represents
1924mount ID of the file system containing the opened file [see 3.5
1925/proc/<pid>/mountinfo for details]. 'ino' represents the inode number of
1926the file.
1927
1928A typical output is::
1929
1930	pos:	0
1931	flags:	0100002
1932	mnt_id:	19
1933	ino:	63107
1934
1935All locks associated with a file descriptor are shown in its fdinfo too::
1936
1937    lock:       1: FLOCK  ADVISORY  WRITE 359 00:13:11691 0 EOF
1938
1939The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1940pair provide additional information particular to the objects they represent.
1941
1942Eventfd files
1943~~~~~~~~~~~~~
1944
1945::
1946
1947	pos:	0
1948	flags:	04002
1949	mnt_id:	9
1950	ino:	63107
1951	eventfd-count:	5a
1952
1953where 'eventfd-count' is hex value of a counter.
1954
1955Signalfd files
1956~~~~~~~~~~~~~~
1957
1958::
1959
1960	pos:	0
1961	flags:	04002
1962	mnt_id:	9
1963	ino:	63107
1964	sigmask:	0000000000000200
1965
1966where 'sigmask' is hex value of the signal mask associated
1967with a file.
1968
1969Epoll files
1970~~~~~~~~~~~
1971
1972::
1973
1974	pos:	0
1975	flags:	02
1976	mnt_id:	9
1977	ino:	63107
1978	tfd:        5 events:       1d data: ffffffffffffffff pos:0 ino:61af sdev:7
1979
1980where 'tfd' is a target file descriptor number in decimal form,
1981'events' is events mask being watched and the 'data' is data
1982associated with a target [see epoll(7) for more details].
1983
1984The 'pos' is current offset of the target file in decimal form
1985[see lseek(2)], 'ino' and 'sdev' are inode and device numbers
1986where target file resides, all in hex format.
1987
1988Fsnotify files
1989~~~~~~~~~~~~~~
1990For inotify files the format is the following::
1991
1992	pos:	0
1993	flags:	02000000
1994	mnt_id:	9
1995	ino:	63107
1996	inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
1997
1998where 'wd' is a watch descriptor in decimal form, i.e. a target file
1999descriptor number, 'ino' and 'sdev' are inode and device where the
2000target file resides and the 'mask' is the mask of events, all in hex
2001form [see inotify(7) for more details].
2002
2003If the kernel was built with exportfs support, the path to the target
2004file is encoded as a file handle.  The file handle is provided by three
2005fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
2006format.
2007
2008If the kernel is built without exportfs support the file handle won't be
2009printed out.
2010
2011If there is no inotify mark attached yet the 'inotify' line will be omitted.
2012
2013For fanotify files the format is::
2014
2015	pos:	0
2016	flags:	02
2017	mnt_id:	9
2018	ino:	63107
2019	fanotify flags:10 event-flags:0
2020	fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
2021	fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
2022
2023where fanotify 'flags' and 'event-flags' are values used in fanotify_init
2024call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
2025flags associated with mark which are tracked separately from events
2026mask. 'ino' and 'sdev' are target inode and device, 'mask' is the events
2027mask and 'ignored_mask' is the mask of events which are to be ignored.
2028All are in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
2029provide information about flags and mask used in fanotify_mark
2030call [see fsnotify manpage for details].
2031
2032While the first three lines are mandatory and always printed, the rest is
2033optional and may be omitted if no marks created yet.
2034
2035Timerfd files
2036~~~~~~~~~~~~~
2037
2038::
2039
2040	pos:	0
2041	flags:	02
2042	mnt_id:	9
2043	ino:	63107
2044	clockid: 0
2045	ticks: 0
2046	settime flags: 01
2047	it_value: (0, 49406829)
2048	it_interval: (1, 0)
2049
2050where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
2051that have occurred [see timerfd_create(2) for details]. 'settime flags' are
2052flags in octal form been used to setup the timer [see timerfd_settime(2) for
2053details]. 'it_value' is remaining time until the timer expiration.
2054'it_interval' is the interval for the timer. Note the timer might be set up
2055with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
2056still exhibits timer's remaining time.
2057
2058DMA Buffer files
2059~~~~~~~~~~~~~~~~
2060
2061::
2062
2063	pos:	0
2064	flags:	04002
2065	mnt_id:	9
2066	ino:	63107
2067	size:   32768
2068	count:  2
2069	exp_name:  system-heap
2070
2071where 'size' is the size of the DMA buffer in bytes. 'count' is the file count of
2072the DMA buffer file. 'exp_name' is the name of the DMA buffer exporter.
2073
20743.9	/proc/<pid>/map_files - Information about memory mapped files
2075---------------------------------------------------------------------
2076This directory contains symbolic links which represent memory mapped files
2077the process is maintaining.  Example output::
2078
2079     | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
2080     | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
2081     | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
2082     | ...
2083     | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
2084     | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
2085
2086The name of a link represents the virtual memory bounds of a mapping, i.e.
2087vm_area_struct::vm_start-vm_area_struct::vm_end.
2088
2089The main purpose of the map_files is to retrieve a set of memory mapped
2090files in a fast way instead of parsing /proc/<pid>/maps or
2091/proc/<pid>/smaps, both of which contain many more records.  At the same
2092time one can open(2) mappings from the listings of two processes and
2093comparing their inode numbers to figure out which anonymous memory areas
2094are actually shared.
2095
20963.10	/proc/<pid>/timerslack_ns - Task timerslack value
2097---------------------------------------------------------
2098This file provides the value of the task's timerslack value in nanoseconds.
2099This value specifies an amount of time that normal timers may be deferred
2100in order to coalesce timers and avoid unnecessary wakeups.
2101
2102This allows a task's interactivity vs power consumption tradeoff to be
2103adjusted.
2104
2105Writing 0 to the file will set the task's timerslack to the default value.
2106
2107Valid values are from 0 - ULLONG_MAX
2108
2109An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
2110permissions on the task specified to change its timerslack_ns value.
2111
21123.11	/proc/<pid>/patch_state - Livepatch patch operation state
2113-----------------------------------------------------------------
2114When CONFIG_LIVEPATCH is enabled, this file displays the value of the
2115patch state for the task.
2116
2117A value of '-1' indicates that no patch is in transition.
2118
2119A value of '0' indicates that a patch is in transition and the task is
2120unpatched.  If the patch is being enabled, then the task hasn't been
2121patched yet.  If the patch is being disabled, then the task has already
2122been unpatched.
2123
2124A value of '1' indicates that a patch is in transition and the task is
2125patched.  If the patch is being enabled, then the task has already been
2126patched.  If the patch is being disabled, then the task hasn't been
2127unpatched yet.
2128
21293.12 /proc/<pid>/arch_status - task architecture specific status
2130-------------------------------------------------------------------
2131When CONFIG_PROC_PID_ARCH_STATUS is enabled, this file displays the
2132architecture specific status of the task.
2133
2134Example
2135~~~~~~~
2136
2137::
2138
2139 $ cat /proc/6753/arch_status
2140 AVX512_elapsed_ms:      8
2141
2142Description
2143~~~~~~~~~~~
2144
2145x86 specific entries
2146~~~~~~~~~~~~~~~~~~~~~
2147
2148AVX512_elapsed_ms
2149^^^^^^^^^^^^^^^^^^
2150
2151  If AVX512 is supported on the machine, this entry shows the milliseconds
2152  elapsed since the last time AVX512 usage was recorded. The recording
2153  happens on a best effort basis when a task is scheduled out. This means
2154  that the value depends on two factors:
2155
2156    1) The time which the task spent on the CPU without being scheduled
2157       out. With CPU isolation and a single runnable task this can take
2158       several seconds.
2159
2160    2) The time since the task was scheduled out last. Depending on the
2161       reason for being scheduled out (time slice exhausted, syscall ...)
2162       this can be arbitrary long time.
2163
2164  As a consequence the value cannot be considered precise and authoritative
2165  information. The application which uses this information has to be aware
2166  of the overall scenario on the system in order to determine whether a
2167  task is a real AVX512 user or not. Precise information can be obtained
2168  with performance counters.
2169
2170  A special value of '-1' indicates that no AVX512 usage was recorded, thus
2171  the task is unlikely an AVX512 user, but depends on the workload and the
2172  scheduling scenario, it also could be a false negative mentioned above.
2173
21743.13 /proc/<pid>/fd - List of symlinks to open files
2175-------------------------------------------------------
2176This directory contains symbolic links which represent open files
2177the process is maintaining.  Example output::
2178
2179  lr-x------ 1 root root 64 Sep 20 17:53 0 -> /dev/null
2180  l-wx------ 1 root root 64 Sep 20 17:53 1 -> /dev/null
2181  lrwx------ 1 root root 64 Sep 20 17:53 10 -> 'socket:[12539]'
2182  lrwx------ 1 root root 64 Sep 20 17:53 11 -> 'socket:[12540]'
2183  lrwx------ 1 root root 64 Sep 20 17:53 12 -> 'socket:[12542]'
2184
2185The number of open files for the process is stored in 'size' member
2186of stat() output for /proc/<pid>/fd for fast access.
2187-------------------------------------------------------
2188
2189
2190Chapter 4: Configuring procfs
2191=============================
2192
21934.1	Mount options
2194---------------------
2195
2196The following mount options are supported:
2197
2198	=========	========================================================
2199	hidepid=	Set /proc/<pid>/ access mode.
2200	gid=		Set the group authorized to learn processes information.
2201	subset=		Show only the specified subset of procfs.
2202	=========	========================================================
2203
2204hidepid=off or hidepid=0 means classic mode - everybody may access all
2205/proc/<pid>/ directories (default).
2206
2207hidepid=noaccess or hidepid=1 means users may not access any /proc/<pid>/
2208directories but their own.  Sensitive files like cmdline, sched*, status are now
2209protected against other users.  This makes it impossible to learn whether any
2210user runs specific program (given the program doesn't reveal itself by its
2211behaviour).  As an additional bonus, as /proc/<pid>/cmdline is unaccessible for
2212other users, poorly written programs passing sensitive information via program
2213arguments are now protected against local eavesdroppers.
2214
2215hidepid=invisible or hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be
2216fully invisible to other users.  It doesn't mean that it hides a fact whether a
2217process with a specific pid value exists (it can be learned by other means, e.g.
2218by "kill -0 $PID"), but it hides process' uid and gid, which may be learned by
2219stat()'ing /proc/<pid>/ otherwise.  It greatly complicates an intruder's task of
2220gathering information about running processes, whether some daemon runs with
2221elevated privileges, whether other user runs some sensitive program, whether
2222other users run any program at all, etc.
2223
2224hidepid=ptraceable or hidepid=4 means that procfs should only contain
2225/proc/<pid>/ directories that the caller can ptrace.
2226
2227gid= defines a group authorized to learn processes information otherwise
2228prohibited by hidepid=.  If you use some daemon like identd which needs to learn
2229information about processes information, just add identd to this group.
2230
2231subset=pid hides all top level files and directories in the procfs that
2232are not related to tasks.
2233
2234Chapter 5: Filesystem behavior
2235==============================
2236
2237Originally, before the advent of pid namespace, procfs was a global file
2238system. It means that there was only one procfs instance in the system.
2239
2240When pid namespace was added, a separate procfs instance was mounted in
2241each pid namespace. So, procfs mount options are global among all
2242mountpoints within the same namespace::
2243
2244	# grep ^proc /proc/mounts
2245	proc /proc proc rw,relatime,hidepid=2 0 0
2246
2247	# strace -e mount mount -o hidepid=1 -t proc proc /tmp/proc
2248	mount("proc", "/tmp/proc", "proc", 0, "hidepid=1") = 0
2249	+++ exited with 0 +++
2250
2251	# grep ^proc /proc/mounts
2252	proc /proc proc rw,relatime,hidepid=2 0 0
2253	proc /tmp/proc proc rw,relatime,hidepid=2 0 0
2254
2255and only after remounting procfs mount options will change at all
2256mountpoints::
2257
2258	# mount -o remount,hidepid=1 -t proc proc /tmp/proc
2259
2260	# grep ^proc /proc/mounts
2261	proc /proc proc rw,relatime,hidepid=1 0 0
2262	proc /tmp/proc proc rw,relatime,hidepid=1 0 0
2263
2264This behavior is different from the behavior of other filesystems.
2265
2266The new procfs behavior is more like other filesystems. Each procfs mount
2267creates a new procfs instance. Mount options affect own procfs instance.
2268It means that it became possible to have several procfs instances
2269displaying tasks with different filtering options in one pid namespace::
2270
2271	# mount -o hidepid=invisible -t proc proc /proc
2272	# mount -o hidepid=noaccess -t proc proc /tmp/proc
2273	# grep ^proc /proc/mounts
2274	proc /proc proc rw,relatime,hidepid=invisible 0 0
2275	proc /tmp/proc proc rw,relatime,hidepid=noaccess 0 0
2276