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
51  4	Configuring procfs
52  4.1	Mount options
53
54  5	Filesystem behavior
55
56Preface
57=======
58
590.1 Introduction/Credits
60------------------------
61
62This documentation is  part of a soon (or  so we hope) to be  released book on
63the SuSE  Linux distribution. As  there is  no complete documentation  for the
64/proc file system and we've used  many freely available sources to write these
65chapters, it  seems only fair  to give the work  back to the  Linux community.
66This work is  based on the 2.2.*  kernel version and the  upcoming 2.4.*. I'm
67afraid it's still far from complete, but we  hope it will be useful. As far as
68we know, it is the first 'all-in-one' document about the /proc file system. It
69is focused  on the Intel  x86 hardware,  so if you  are looking for  PPC, ARM,
70SPARC, AXP, etc., features, you probably  won't find what you are looking for.
71It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
72additions and patches  are welcome and will  be added to this  document if you
73mail them to Bodo.
74
75We'd like  to  thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
76other people for help compiling this documentation. We'd also like to extend a
77special thank  you to Andi Kleen for documentation, which we relied on heavily
78to create  this  document,  as well as the additional information he provided.
79Thanks to  everybody  else  who contributed source or docs to the Linux kernel
80and helped create a great piece of software... :)
81
82If you  have  any comments, corrections or additions, please don't hesitate to
83contact Bodo  Bauer  at  bb@ricochet.net.  We'll  be happy to add them to this
84document.
85
86The   latest   version    of   this   document   is    available   online   at
87http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html
88
89If  the above  direction does  not works  for you,  you could  try the  kernel
90mailing  list  at  linux-kernel@vger.kernel.org  and/or try  to  reach  me  at
91comandante@zaralinux.com.
92
930.2 Legal Stuff
94---------------
95
96We don't  guarantee  the  correctness  of this document, and if you come to us
97complaining about  how  you  screwed  up  your  system  because  of  incorrect
98documentation, we won't feel responsible...
99
100Chapter 1: Collecting System Information
101========================================
102
103In This Chapter
104---------------
105* Investigating  the  properties  of  the  pseudo  file  system  /proc and its
106  ability to provide information on the running Linux system
107* Examining /proc's structure
108* Uncovering  various  information  about the kernel and the processes running
109  on the system
110
111------------------------------------------------------------------------------
112
113The proc  file  system acts as an interface to internal data structures in the
114kernel. It  can  be  used to obtain information about the system and to change
115certain kernel parameters at runtime (sysctl).
116
117First, we'll  take  a  look  at the read-only parts of /proc. In Chapter 2, we
118show you how you can use /proc/sys to change settings.
119
1201.1 Process-Specific Subdirectories
121-----------------------------------
122
123The directory  /proc  contains  (among other things) one subdirectory for each
124process running on the system, which is named after the process ID (PID).
125
126The link  'self'  points to  the process reading the file system. Each process
127subdirectory has the entries listed in Table 1-1.
128
129Note that an open file descriptor to /proc/<pid> or to any of its
130contained files or subdirectories does not prevent <pid> being reused
131for some other process in the event that <pid> exits. Operations on
132open /proc/<pid> file descriptors corresponding to dead processes
133never act on any new process that the kernel may, through chance, have
134also assigned the process ID <pid>. Instead, operations on these FDs
135usually fail with ESRCH.
136
137.. table:: Table 1-1: Process specific entries in /proc
138
139 =============  ===============================================================
140 File		Content
141 =============  ===============================================================
142 clear_refs	Clears page referenced bits shown in smaps output
143 cmdline	Command line arguments
144 cpu		Current and last cpu in which it was executed	(2.4)(smp)
145 cwd		Link to the current working directory
146 environ	Values of environment variables
147 exe		Link to the executable of this process
148 fd		Directory, which contains all file descriptors
149 maps		Memory maps to executables and library files	(2.4)
150 mem		Memory held by this process
151 root		Link to the root directory of this process
152 stat		Process status
153 statm		Process memory status information
154 status		Process status in human readable form
155 wchan		Present with CONFIG_KALLSYMS=y: it shows the kernel function
156		symbol the task is blocked in - or "0" if not blocked.
157 pagemap	Page table
158 stack		Report full stack trace, enable via CONFIG_STACKTRACE
159 smaps		An extension based on maps, showing the memory consumption of
160		each mapping and flags associated with it
161 smaps_rollup	Accumulated smaps stats for all mappings of the process.  This
162		can be derived from smaps, but is faster and more convenient
163 numa_maps	An extension based on maps, showing the memory locality and
164		binding policy as well as mem usage (in pages) of each mapping.
165 =============  ===============================================================
166
167For example, to get the status information of a process, all you have to do is
168read the file /proc/PID/status::
169
170  >cat /proc/self/status
171  Name:   cat
172  State:  R (running)
173  Tgid:   5452
174  Pid:    5452
175  PPid:   743
176  TracerPid:      0						(2.4)
177  Uid:    501     501     501     501
178  Gid:    100     100     100     100
179  FDSize: 256
180  Groups: 100 14 16
181  VmPeak:     5004 kB
182  VmSize:     5004 kB
183  VmLck:         0 kB
184  VmHWM:       476 kB
185  VmRSS:       476 kB
186  RssAnon:             352 kB
187  RssFile:             120 kB
188  RssShmem:              4 kB
189  VmData:      156 kB
190  VmStk:        88 kB
191  VmExe:        68 kB
192  VmLib:      1412 kB
193  VmPTE:        20 kb
194  VmSwap:        0 kB
195  HugetlbPages:          0 kB
196  CoreDumping:    0
197  THP_enabled:	  1
198  Threads:        1
199  SigQ:   0/28578
200  SigPnd: 0000000000000000
201  ShdPnd: 0000000000000000
202  SigBlk: 0000000000000000
203  SigIgn: 0000000000000000
204  SigCgt: 0000000000000000
205  CapInh: 00000000fffffeff
206  CapPrm: 0000000000000000
207  CapEff: 0000000000000000
208  CapBnd: ffffffffffffffff
209  CapAmb: 0000000000000000
210  NoNewPrivs:     0
211  Seccomp:        0
212  Speculation_Store_Bypass:       thread vulnerable
213  SpeculationIndirectBranch:      conditional enabled
214  voluntary_ctxt_switches:        0
215  nonvoluntary_ctxt_switches:     1
216
217This shows you nearly the same information you would get if you viewed it with
218the ps  command.  In  fact,  ps  uses  the  proc  file  system  to  obtain its
219information.  But you get a more detailed  view of the  process by reading the
220file /proc/PID/status. It fields are described in table 1-2.
221
222The  statm  file  contains  more  detailed  information about the process
223memory usage. Its seven fields are explained in Table 1-3.  The stat file
224contains detailed information about the process itself.  Its fields are
225explained in Table 1-4.
226
227(for SMP CONFIG users)
228
229For making accounting scalable, RSS related information are handled in an
230asynchronous manner and the value may not be very precise. To see a precise
231snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
232It's slow but very precise.
233
234.. table:: Table 1-2: Contents of the status files (as of 4.19)
235
236 ==========================  ===================================================
237 Field                       Content
238 ==========================  ===================================================
239 Name                        filename of the executable
240 Umask                       file mode creation mask
241 State                       state (R is running, S is sleeping, D is sleeping
242                             in an uninterruptible wait, Z is zombie,
243			     T is traced or stopped)
244 Tgid                        thread group ID
245 Ngid                        NUMA group ID (0 if none)
246 Pid                         process id
247 PPid                        process id of the parent process
248 TracerPid                   PID of process tracing this process (0 if not)
249 Uid                         Real, effective, saved set, and  file system UIDs
250 Gid                         Real, effective, saved set, and  file system GIDs
251 FDSize                      number of file descriptor slots currently allocated
252 Groups                      supplementary group list
253 NStgid                      descendant namespace thread group ID hierarchy
254 NSpid                       descendant namespace process ID hierarchy
255 NSpgid                      descendant namespace process group ID hierarchy
256 NSsid                       descendant namespace session ID hierarchy
257 VmPeak                      peak virtual memory size
258 VmSize                      total program size
259 VmLck                       locked memory size
260 VmPin                       pinned memory size
261 VmHWM                       peak resident set size ("high water mark")
262 VmRSS                       size of memory portions. It contains the three
263                             following parts
264                             (VmRSS = RssAnon + RssFile + RssShmem)
265 RssAnon                     size of resident anonymous memory
266 RssFile                     size of resident file mappings
267 RssShmem                    size of resident shmem memory (includes SysV shm,
268                             mapping of tmpfs and shared anonymous mappings)
269 VmData                      size of private data segments
270 VmStk                       size of stack segments
271 VmExe                       size of text segment
272 VmLib                       size of shared library code
273 VmPTE                       size of page table entries
274 VmSwap                      amount of swap used by anonymous private data
275                             (shmem swap usage is not included)
276 HugetlbPages                size of hugetlb memory portions
277 CoreDumping                 process's memory is currently being dumped
278                             (killing the process may lead to a corrupted core)
279 THP_enabled		     process is allowed to use THP (returns 0 when
280			     PR_SET_THP_DISABLE is set on the process
281 Threads                     number of threads
282 SigQ                        number of signals queued/max. number for queue
283 SigPnd                      bitmap of pending signals for the thread
284 ShdPnd                      bitmap of shared pending signals for the process
285 SigBlk                      bitmap of blocked signals
286 SigIgn                      bitmap of ignored signals
287 SigCgt                      bitmap of caught signals
288 CapInh                      bitmap of inheritable capabilities
289 CapPrm                      bitmap of permitted capabilities
290 CapEff                      bitmap of effective capabilities
291 CapBnd                      bitmap of capabilities bounding set
292 CapAmb                      bitmap of ambient capabilities
293 NoNewPrivs                  no_new_privs, like prctl(PR_GET_NO_NEW_PRIV, ...)
294 Seccomp                     seccomp mode, like prctl(PR_GET_SECCOMP, ...)
295 Speculation_Store_Bypass    speculative store bypass mitigation status
296 SpeculationIndirectBranch   indirect branch speculation mode
297 Cpus_allowed                mask of CPUs on which this process may run
298 Cpus_allowed_list           Same as previous, but in "list format"
299 Mems_allowed                mask of memory nodes allowed to this process
300 Mems_allowed_list           Same as previous, but in "list format"
301 voluntary_ctxt_switches     number of voluntary context switches
302 nonvoluntary_ctxt_switches  number of non voluntary context switches
303 ==========================  ===================================================
304
305
306.. table:: Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
307
308 ======== ===============================	==============================
309 Field    Content
310 ======== ===============================	==============================
311 size     total program size (pages)		(same as VmSize in status)
312 resident size of memory portions (pages)	(same as VmRSS in status)
313 shared   number of pages that are shared	(i.e. backed by a file, same
314						as RssFile+RssShmem in status)
315 trs      number of pages that are 'code'	(not including libs; broken,
316						includes data segment)
317 lrs      number of pages of library		(always 0 on 2.6)
318 drs      number of pages of data/stack		(including libs; broken,
319						includes library text)
320 dt       number of dirty pages			(always 0 on 2.6)
321 ======== ===============================	==============================
322
323
324.. table:: Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
325
326  ============= ===============================================================
327  Field         Content
328  ============= ===============================================================
329  pid           process id
330  tcomm         filename of the executable
331  state         state (R is running, S is sleeping, D is sleeping in an
332                uninterruptible wait, Z is zombie, T is traced or stopped)
333  ppid          process id of the parent process
334  pgrp          pgrp of the process
335  sid           session id
336  tty_nr        tty the process uses
337  tty_pgrp      pgrp of the tty
338  flags         task flags
339  min_flt       number of minor faults
340  cmin_flt      number of minor faults with child's
341  maj_flt       number of major faults
342  cmaj_flt      number of major faults with child's
343  utime         user mode jiffies
344  stime         kernel mode jiffies
345  cutime        user mode jiffies with child's
346  cstime        kernel mode jiffies with child's
347  priority      priority level
348  nice          nice level
349  num_threads   number of threads
350  it_real_value	(obsolete, always 0)
351  start_time    time the process started after system boot
352  vsize         virtual memory size
353  rss           resident set memory size
354  rsslim        current limit in bytes on the rss
355  start_code    address above which program text can run
356  end_code      address below which program text can run
357  start_stack   address of the start of the main process stack
358  esp           current value of ESP
359  eip           current value of EIP
360  pending       bitmap of pending signals
361  blocked       bitmap of blocked signals
362  sigign        bitmap of ignored signals
363  sigcatch      bitmap of caught signals
364  0		(place holder, used to be the wchan address,
365		use /proc/PID/wchan instead)
366  0             (place holder)
367  0             (place holder)
368  exit_signal   signal to send to parent thread on exit
369  task_cpu      which CPU the task is scheduled on
370  rt_priority   realtime priority
371  policy        scheduling policy (man sched_setscheduler)
372  blkio_ticks   time spent waiting for block IO
373  gtime         guest time of the task in jiffies
374  cgtime        guest time of the task children in jiffies
375  start_data    address above which program data+bss is placed
376  end_data      address below which program data+bss is placed
377  start_brk     address above which program heap can be expanded with brk()
378  arg_start     address above which program command line is placed
379  arg_end       address below which program command line is placed
380  env_start     address above which program environment is placed
381  env_end       address below which program environment is placed
382  exit_code     the thread's exit_code in the form reported by the waitpid
383		system call
384  ============= ===============================================================
385
386The /proc/PID/maps file contains the currently mapped memory regions and
387their access permissions.
388
389The format is::
390
391    address           perms offset  dev   inode      pathname
392
393    08048000-08049000 r-xp 00000000 03:00 8312       /opt/test
394    08049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
395    0804a000-0806b000 rw-p 00000000 00:00 0          [heap]
396    a7cb1000-a7cb2000 ---p 00000000 00:00 0
397    a7cb2000-a7eb2000 rw-p 00000000 00:00 0
398    a7eb2000-a7eb3000 ---p 00000000 00:00 0
399    a7eb3000-a7ed5000 rw-p 00000000 00:00 0
400    a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/libc.so.6
401    a8008000-a800a000 r--p 00133000 03:00 4222       /lib/libc.so.6
402    a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/libc.so.6
403    a800b000-a800e000 rw-p 00000000 00:00 0
404    a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/libpthread.so.0
405    a8022000-a8023000 r--p 00013000 03:00 14462      /lib/libpthread.so.0
406    a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/libpthread.so.0
407    a8024000-a8027000 rw-p 00000000 00:00 0
408    a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/ld-linux.so.2
409    a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/ld-linux.so.2
410    a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/ld-linux.so.2
411    aff35000-aff4a000 rw-p 00000000 00:00 0          [stack]
412    ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
413
414where "address" is the address space in the process that it occupies, "perms"
415is a set of permissions::
416
417 r = read
418 w = write
419 x = execute
420 s = shared
421 p = private (copy on write)
422
423"offset" is the offset into the mapping, "dev" is the device (major:minor), and
424"inode" is the inode  on that device.  0 indicates that  no inode is associated
425with the memory region, as the case would be with BSS (uninitialized data).
426The "pathname" shows the name associated file for this mapping.  If the mapping
427is not associated with a file:
428
429 =======                    ====================================
430 [heap]                     the heap of the program
431 [stack]                    the stack of the main process
432 [vdso]                     the "virtual dynamic shared object",
433                            the kernel system call handler
434 =======                    ====================================
435
436 or if empty, the mapping is anonymous.
437
438The /proc/PID/smaps is an extension based on maps, showing the memory
439consumption for each of the process's mappings. For each mapping (aka Virtual
440Memory Area, or VMA) there is a series of lines such as the following::
441
442    08048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
443
444    Size:               1084 kB
445    KernelPageSize:        4 kB
446    MMUPageSize:           4 kB
447    Rss:                 892 kB
448    Pss:                 374 kB
449    Shared_Clean:        892 kB
450    Shared_Dirty:          0 kB
451    Private_Clean:         0 kB
452    Private_Dirty:         0 kB
453    Referenced:          892 kB
454    Anonymous:             0 kB
455    LazyFree:              0 kB
456    AnonHugePages:         0 kB
457    ShmemPmdMapped:        0 kB
458    Shared_Hugetlb:        0 kB
459    Private_Hugetlb:       0 kB
460    Swap:                  0 kB
461    SwapPss:               0 kB
462    KernelPageSize:        4 kB
463    MMUPageSize:           4 kB
464    Locked:                0 kB
465    THPeligible:           0
466    VmFlags: rd ex mr mw me dw
467
468The first of these lines shows the same information as is displayed for the
469mapping in /proc/PID/maps.  Following lines show the size of the mapping
470(size); the size of each page allocated when backing a VMA (KernelPageSize),
471which is usually the same as the size in the page table entries; the page size
472used by the MMU when backing a VMA (in most cases, the same as KernelPageSize);
473the amount of the mapping that is currently resident in RAM (RSS); the
474process' proportional share of this mapping (PSS); and the number of clean and
475dirty shared and private pages in the mapping.
476
477The "proportional set size" (PSS) of a process is the count of pages it has
478in memory, where each page is divided by the number of processes sharing it.
479So if a process has 1000 pages all to itself, and 1000 shared with one other
480process, its PSS will be 1500.
481
482Note that even a page which is part of a MAP_SHARED mapping, but has only
483a single pte mapped, i.e.  is currently used by only one process, is accounted
484as private and not as shared.
485
486"Referenced" indicates the amount of memory currently marked as referenced or
487accessed.
488
489"Anonymous" shows the amount of memory that does not belong to any file.  Even
490a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
491and a page is modified, the file page is replaced by a private anonymous copy.
492
493"LazyFree" shows the amount of memory which is marked by madvise(MADV_FREE).
494The memory isn't freed immediately with madvise(). It's freed in memory
495pressure if the memory is clean. Please note that the printed value might
496be lower than the real value due to optimizations used in the current
497implementation. If this is not desirable please file a bug report.
498
499"AnonHugePages" shows the ammount of memory backed by transparent hugepage.
500
501"ShmemPmdMapped" shows the ammount of shared (shmem/tmpfs) memory backed by
502huge pages.
503
504"Shared_Hugetlb" and "Private_Hugetlb" show the ammounts of memory backed by
505hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical
506reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field.
507
508"Swap" shows how much would-be-anonymous memory is also used, but out on swap.
509
510For shmem mappings, "Swap" includes also the size of the mapped (and not
511replaced by copy-on-write) part of the underlying shmem object out on swap.
512"SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
513does not take into account swapped out page of underlying shmem objects.
514"Locked" indicates whether the mapping is locked in memory or not.
515"THPeligible" indicates whether the mapping is eligible for allocating THP
516pages - 1 if true, 0 otherwise. It just shows the current status.
517
518"VmFlags" field deserves a separate description. This member represents the
519kernel flags associated with the particular virtual memory area in two letter
520encoded manner. The codes are the following:
521
522    ==    =======================================
523    rd    readable
524    wr    writeable
525    ex    executable
526    sh    shared
527    mr    may read
528    mw    may write
529    me    may execute
530    ms    may share
531    gd    stack segment growns down
532    pf    pure PFN range
533    dw    disabled write to the mapped file
534    lo    pages are locked in memory
535    io    memory mapped I/O area
536    sr    sequential read advise provided
537    rr    random read advise provided
538    dc    do not copy area on fork
539    de    do not expand area on remapping
540    ac    area is accountable
541    nr    swap space is not reserved for the area
542    ht    area uses huge tlb pages
543    ar    architecture specific flag
544    dd    do not include area into core dump
545    sd    soft dirty flag
546    mm    mixed map area
547    hg    huge page advise flag
548    nh    no huge page advise flag
549    mg    mergable advise flag
550    bt    arm64 BTI guarded page
551    mt    arm64 MTE allocation tags are enabled
552    ==    =======================================
553
554Note that there is no guarantee that every flag and associated mnemonic will
555be present in all further kernel releases. Things get changed, the flags may
556be vanished or the reverse -- new added. Interpretation of their meaning
557might change in future as well. So each consumer of these flags has to
558follow each specific kernel version for the exact semantic.
559
560This file is only present if the CONFIG_MMU kernel configuration option is
561enabled.
562
563Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy (consistent
564output can be achieved only in the single read call).
565
566This typically manifests when doing partial reads of these files while the
567memory map is being modified.  Despite the races, we do provide the following
568guarantees:
569
5701) The mapped addresses never go backwards, which implies no two
571   regions will ever overlap.
5722) If there is something at a given vaddr during the entirety of the
573   life of the smaps/maps walk, there will be some output for it.
574
575The /proc/PID/smaps_rollup file includes the same fields as /proc/PID/smaps,
576but their values are the sums of the corresponding values for all mappings of
577the process.  Additionally, it contains these fields:
578
579- Pss_Anon
580- Pss_File
581- Pss_Shmem
582
583They represent the proportional shares of anonymous, file, and shmem pages, as
584described for smaps above.  These fields are omitted in smaps since each
585mapping identifies the type (anon, file, or shmem) of all pages it contains.
586Thus all information in smaps_rollup can be derived from smaps, but at a
587significantly higher cost.
588
589The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
590bits on both physical and virtual pages associated with a process, and the
591soft-dirty bit on pte (see Documentation/admin-guide/mm/soft-dirty.rst
592for details).
593To clear the bits for all the pages associated with the process::
594
595    > echo 1 > /proc/PID/clear_refs
596
597To clear the bits for the anonymous pages associated with the process::
598
599    > echo 2 > /proc/PID/clear_refs
600
601To clear the bits for the file mapped pages associated with the process::
602
603    > echo 3 > /proc/PID/clear_refs
604
605To clear the soft-dirty bit::
606
607    > echo 4 > /proc/PID/clear_refs
608
609To reset the peak resident set size ("high water mark") to the process's
610current value::
611
612    > echo 5 > /proc/PID/clear_refs
613
614Any other value written to /proc/PID/clear_refs will have no effect.
615
616The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
617using /proc/kpageflags and number of times a page is mapped using
618/proc/kpagecount. For detailed explanation, see
619Documentation/admin-guide/mm/pagemap.rst.
620
621The /proc/pid/numa_maps is an extension based on maps, showing the memory
622locality and binding policy, as well as the memory usage (in pages) of
623each mapping. The output follows a general format where mapping details get
624summarized separated by blank spaces, one mapping per each file line::
625
626    address   policy    mapping details
627
628    00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
629    00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
630    3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
631    320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
632    3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
633    3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
634    3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
635    320698b000 default file=/lib64/libc-2.12.so
636    3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4
637    3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
638    3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
639    7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
640    7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
641    7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
642    7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
643    7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4
644
645Where:
646
647"address" is the starting address for the mapping;
648
649"policy" reports the NUMA memory policy set for the mapping (see Documentation/admin-guide/mm/numa_memory_policy.rst);
650
651"mapping details" summarizes mapping data such as mapping type, page usage counters,
652node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
653size, in KB, that is backing the mapping up.
654
6551.2 Kernel data
656---------------
657
658Similar to  the  process entries, the kernel data files give information about
659the running kernel. The files used to obtain this information are contained in
660/proc and  are  listed  in Table 1-5. Not all of these will be present in your
661system. It  depends  on the kernel configuration and the loaded modules, which
662files are there, and which are missing.
663
664.. table:: Table 1-5: Kernel info in /proc
665
666 ============ ===============================================================
667 File         Content
668 ============ ===============================================================
669 apm          Advanced power management info
670 buddyinfo    Kernel memory allocator information (see text)	(2.5)
671 bus          Directory containing bus specific information
672 cmdline      Kernel command line
673 cpuinfo      Info about the CPU
674 devices      Available devices (block and character)
675 dma          Used DMS channels
676 filesystems  Supported filesystems
677 driver       Various drivers grouped here, currently rtc	(2.4)
678 execdomains  Execdomains, related to security			(2.4)
679 fb 	      Frame Buffer devices				(2.4)
680 fs 	      File system parameters, currently nfs/exports	(2.4)
681 ide          Directory containing info about the IDE subsystem
682 interrupts   Interrupt usage
683 iomem 	      Memory map					(2.4)
684 ioports      I/O port usage
685 irq 	      Masks for irq to cpu affinity			(2.4)(smp?)
686 isapnp       ISA PnP (Plug&Play) Info				(2.4)
687 kcore        Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
688 kmsg         Kernel messages
689 ksyms        Kernel symbol table
690 loadavg      Load average of last 1, 5 & 15 minutes;
691                number of processes currently runnable (running or on ready queue);
692                total number of processes in system;
693                last pid created.
694                All fields are separated by one space except "number of
695                processes currently runnable" and "total number of processes
696                in system", which are separated by a slash ('/'). Example:
697                0.61 0.61 0.55 3/828 22084
698 locks        Kernel locks
699 meminfo      Memory info
700 misc         Miscellaneous
701 modules      List of loaded modules
702 mounts       Mounted filesystems
703 net          Networking info (see text)
704 pagetypeinfo Additional page allocator information (see text)  (2.5)
705 partitions   Table of partitions known to the system
706 pci 	      Deprecated info of PCI bus (new way -> /proc/bus/pci/,
707              decoupled by lspci				(2.4)
708 rtc          Real time clock
709 scsi         SCSI info (see text)
710 slabinfo     Slab pool info
711 softirqs     softirq usage
712 stat         Overall statistics
713 swaps        Swap space utilization
714 sys          See chapter 2
715 sysvipc      Info of SysVIPC Resources (msg, sem, shm)		(2.4)
716 tty 	      Info of tty drivers
717 uptime       Wall clock since boot, combined idle time of all cpus
718 version      Kernel version
719 video 	      bttv info of video resources			(2.4)
720 vmallocinfo  Show vmalloced areas
721 ============ ===============================================================
722
723You can,  for  example,  check  which interrupts are currently in use and what
724they are used for by looking in the file /proc/interrupts::
725
726  > cat /proc/interrupts
727             CPU0
728    0:    8728810          XT-PIC  timer
729    1:        895          XT-PIC  keyboard
730    2:          0          XT-PIC  cascade
731    3:     531695          XT-PIC  aha152x
732    4:    2014133          XT-PIC  serial
733    5:      44401          XT-PIC  pcnet_cs
734    8:          2          XT-PIC  rtc
735   11:          8          XT-PIC  i82365
736   12:     182918          XT-PIC  PS/2 Mouse
737   13:          1          XT-PIC  fpu
738   14:    1232265          XT-PIC  ide0
739   15:          7          XT-PIC  ide1
740  NMI:          0
741
742In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
743output of a SMP machine)::
744
745  > cat /proc/interrupts
746
747             CPU0       CPU1
748    0:    1243498    1214548    IO-APIC-edge  timer
749    1:       8949       8958    IO-APIC-edge  keyboard
750    2:          0          0          XT-PIC  cascade
751    5:      11286      10161    IO-APIC-edge  soundblaster
752    8:          1          0    IO-APIC-edge  rtc
753    9:      27422      27407    IO-APIC-edge  3c503
754   12:     113645     113873    IO-APIC-edge  PS/2 Mouse
755   13:          0          0          XT-PIC  fpu
756   14:      22491      24012    IO-APIC-edge  ide0
757   15:       2183       2415    IO-APIC-edge  ide1
758   17:      30564      30414   IO-APIC-level  eth0
759   18:        177        164   IO-APIC-level  bttv
760  NMI:    2457961    2457959
761  LOC:    2457882    2457881
762  ERR:       2155
763
764NMI is incremented in this case because every timer interrupt generates a NMI
765(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
766
767LOC is the local interrupt counter of the internal APIC of every CPU.
768
769ERR is incremented in the case of errors in the IO-APIC bus (the bus that
770connects the CPUs in a SMP system. This means that an error has been detected,
771the IO-APIC automatically retry the transmission, so it should not be a big
772problem, but you should read the SMP-FAQ.
773
774In 2.6.2* /proc/interrupts was expanded again.  This time the goal was for
775/proc/interrupts to display every IRQ vector in use by the system, not
776just those considered 'most important'.  The new vectors are:
777
778THR
779  interrupt raised when a machine check threshold counter
780  (typically counting ECC corrected errors of memory or cache) exceeds
781  a configurable threshold.  Only available on some systems.
782
783TRM
784  a thermal event interrupt occurs when a temperature threshold
785  has been exceeded for the CPU.  This interrupt may also be generated
786  when the temperature drops back to normal.
787
788SPU
789  a spurious interrupt is some interrupt that was raised then lowered
790  by some IO device before it could be fully processed by the APIC.  Hence
791  the APIC sees the interrupt but does not know what device it came from.
792  For this case the APIC will generate the interrupt with a IRQ vector
793  of 0xff. This might also be generated by chipset bugs.
794
795RES, CAL, TLB
796  rescheduling, call and TLB flush interrupts are
797  sent from one CPU to another per the needs of the OS.  Typically,
798  their statistics are used by kernel developers and interested users to
799  determine the occurrence of interrupts of the given type.
800
801The above IRQ vectors are displayed only when relevant.  For example,
802the threshold vector does not exist on x86_64 platforms.  Others are
803suppressed when the system is a uniprocessor.  As of this writing, only
804i386 and x86_64 platforms support the new IRQ vector displays.
805
806Of some interest is the introduction of the /proc/irq directory to 2.4.
807It could be used to set IRQ to CPU affinity. This means that you can "hook" an
808IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
809irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
810prof_cpu_mask.
811
812For example::
813
814  > ls /proc/irq/
815  0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
816  1  11  13  15  17  19  3  5  7  9  default_smp_affinity
817  > ls /proc/irq/0/
818  smp_affinity
819
820smp_affinity is a bitmask, in which you can specify which CPUs can handle the
821IRQ. You can set it by doing::
822
823  > echo 1 > /proc/irq/10/smp_affinity
824
825This means that only the first CPU will handle the IRQ, but you can also echo
8265 which means that only the first and third CPU can handle the IRQ.
827
828The contents of each smp_affinity file is the same by default::
829
830  > cat /proc/irq/0/smp_affinity
831  ffffffff
832
833There is an alternate interface, smp_affinity_list which allows specifying
834a CPU range instead of a bitmask::
835
836  > cat /proc/irq/0/smp_affinity_list
837  1024-1031
838
839The default_smp_affinity mask applies to all non-active IRQs, which are the
840IRQs which have not yet been allocated/activated, and hence which lack a
841/proc/irq/[0-9]* directory.
842
843The node file on an SMP system shows the node to which the device using the IRQ
844reports itself as being attached. This hardware locality information does not
845include information about any possible driver locality preference.
846
847prof_cpu_mask specifies which CPUs are to be profiled by the system wide
848profiler. Default value is ffffffff (all CPUs if there are only 32 of them).
849
850The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
851between all the CPUs which are allowed to handle it. As usual the kernel has
852more info than you and does a better job than you, so the defaults are the
853best choice for almost everyone.  [Note this applies only to those IO-APIC's
854that support "Round Robin" interrupt distribution.]
855
856There are  three  more  important subdirectories in /proc: net, scsi, and sys.
857The general  rule  is  that  the  contents,  or  even  the  existence of these
858directories, depend  on your kernel configuration. If SCSI is not enabled, the
859directory scsi  may  not  exist. The same is true with the net, which is there
860only when networking support is present in the running kernel.
861
862The slabinfo  file  gives  information  about  memory usage at the slab level.
863Linux uses  slab  pools for memory management above page level in version 2.2.
864Commonly used  objects  have  their  own  slab  pool (such as network buffers,
865directory cache, and so on).
866
867::
868
869    > cat /proc/buddyinfo
870
871    Node 0, zone      DMA      0      4      5      4      4      3 ...
872    Node 0, zone   Normal      1      0      0      1    101      8 ...
873    Node 0, zone  HighMem      2      0      0      1      1      0 ...
874
875External fragmentation is a problem under some workloads, and buddyinfo is a
876useful tool for helping diagnose these problems.  Buddyinfo will give you a
877clue as to how big an area you can safely allocate, or why a previous
878allocation failed.
879
880Each column represents the number of pages of a certain order which are
881available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
882ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
883available in ZONE_NORMAL, etc...
884
885More information relevant to external fragmentation can be found in
886pagetypeinfo::
887
888    > cat /proc/pagetypeinfo
889    Page block order: 9
890    Pages per block:  512
891
892    Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
893    Node    0, zone      DMA, type    Unmovable      0      0      0      1      1      1      1      1      1      1      0
894    Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0
895    Node    0, zone      DMA, type      Movable      1      1      2      1      2      1      1      0      1      0      2
896    Node    0, zone      DMA, type      Reserve      0      0      0      0      0      0      0      0      0      1      0
897    Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
898    Node    0, zone    DMA32, type    Unmovable    103     54     77      1      1      1     11      8      7      1      9
899    Node    0, zone    DMA32, type  Reclaimable      0      0      2      1      0      0      0      0      1      0      0
900    Node    0, zone    DMA32, type      Movable    169    152    113     91     77     54     39     13      6      1    452
901    Node    0, zone    DMA32, type      Reserve      1      2      2      2      2      0      1      1      1      1      0
902    Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
903
904    Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate
905    Node 0, zone      DMA            2            0            5            1            0
906    Node 0, zone    DMA32           41            6          967            2            0
907
908Fragmentation avoidance in the kernel works by grouping pages of different
909migrate types into the same contiguous regions of memory called page blocks.
910A page block is typically the size of the default hugepage size, e.g. 2MB on
911X86-64. By keeping pages grouped based on their ability to move, the kernel
912can reclaim pages within a page block to satisfy a high-order allocation.
913
914The pagetypinfo begins with information on the size of a page block. It
915then gives the same type of information as buddyinfo except broken down
916by migrate-type and finishes with details on how many page blocks of each
917type exist.
918
919If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
920from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can
921make an estimate of the likely number of huge pages that can be allocated
922at a given point in time. All the "Movable" blocks should be allocatable
923unless memory has been mlock()'d. Some of the Reclaimable blocks should
924also be allocatable although a lot of filesystem metadata may have to be
925reclaimed to achieve this.
926
927
928meminfo
929~~~~~~~
930
931Provides information about distribution and utilization of memory.  This
932varies by architecture and compile options.  The following is from a
93316GB PIII, which has highmem enabled.  You may not have all of these fields.
934
935::
936
937    > cat /proc/meminfo
938
939    MemTotal:     16344972 kB
940    MemFree:      13634064 kB
941    MemAvailable: 14836172 kB
942    Buffers:          3656 kB
943    Cached:        1195708 kB
944    SwapCached:          0 kB
945    Active:         891636 kB
946    Inactive:      1077224 kB
947    HighTotal:    15597528 kB
948    HighFree:     13629632 kB
949    LowTotal:       747444 kB
950    LowFree:          4432 kB
951    SwapTotal:           0 kB
952    SwapFree:            0 kB
953    Dirty:             968 kB
954    Writeback:           0 kB
955    AnonPages:      861800 kB
956    Mapped:         280372 kB
957    Shmem:             644 kB
958    KReclaimable:   168048 kB
959    Slab:           284364 kB
960    SReclaimable:   159856 kB
961    SUnreclaim:     124508 kB
962    PageTables:      24448 kB
963    NFS_Unstable:        0 kB
964    Bounce:              0 kB
965    WritebackTmp:        0 kB
966    CommitLimit:   7669796 kB
967    Committed_AS:   100056 kB
968    VmallocTotal:   112216 kB
969    VmallocUsed:       428 kB
970    VmallocChunk:   111088 kB
971    Percpu:          62080 kB
972    HardwareCorrupted:   0 kB
973    AnonHugePages:   49152 kB
974    ShmemHugePages:      0 kB
975    ShmemPmdMapped:      0 kB
976
977MemTotal
978              Total usable RAM (i.e. physical RAM minus a few reserved
979              bits and the kernel binary code)
980MemFree
981              The sum of LowFree+HighFree
982MemAvailable
983              An estimate of how much memory is available for starting new
984              applications, without swapping. Calculated from MemFree,
985              SReclaimable, the size of the file LRU lists, and the low
986              watermarks in each zone.
987              The estimate takes into account that the system needs some
988              page cache to function well, and that not all reclaimable
989              slab will be reclaimable, due to items being in use. The
990              impact of those factors will vary from system to system.
991Buffers
992              Relatively temporary storage for raw disk blocks
993              shouldn't get tremendously large (20MB or so)
994Cached
995              in-memory cache for files read from the disk (the
996              pagecache).  Doesn't include SwapCached
997SwapCached
998              Memory that once was swapped out, is swapped back in but
999              still also is in the swapfile (if memory is needed it
1000              doesn't need to be swapped out AGAIN because it is already
1001              in the swapfile. This saves I/O)
1002Active
1003              Memory that has been used more recently and usually not
1004              reclaimed unless absolutely necessary.
1005Inactive
1006              Memory which has been less recently used.  It is more
1007              eligible to be reclaimed for other purposes
1008HighTotal, HighFree
1009              Highmem is all memory above ~860MB of physical memory.
1010              Highmem areas are for use by userspace programs, or
1011              for the pagecache.  The kernel must use tricks to access
1012              this memory, making it slower to access than lowmem.
1013LowTotal, LowFree
1014              Lowmem is memory which can be used for everything that
1015              highmem can be used for, but it is also available for the
1016              kernel's use for its own data structures.  Among many
1017              other things, it is where everything from the Slab is
1018              allocated.  Bad things happen when you're out of lowmem.
1019SwapTotal
1020              total amount of swap space available
1021SwapFree
1022              Memory which has been evicted from RAM, and is temporarily
1023              on the disk
1024Dirty
1025              Memory which is waiting to get written back to the disk
1026Writeback
1027              Memory which is actively being written back to the disk
1028AnonPages
1029              Non-file backed pages mapped into userspace page tables
1030HardwareCorrupted
1031              The amount of RAM/memory in KB, the kernel identifies as
1032	      corrupted.
1033AnonHugePages
1034              Non-file backed huge pages mapped into userspace page tables
1035Mapped
1036              files which have been mmaped, such as libraries
1037Shmem
1038              Total memory used by shared memory (shmem) and tmpfs
1039ShmemHugePages
1040              Memory used by shared memory (shmem) and tmpfs allocated
1041              with huge pages
1042ShmemPmdMapped
1043              Shared memory mapped into userspace with huge pages
1044KReclaimable
1045              Kernel allocations that the kernel will attempt to reclaim
1046              under memory pressure. Includes SReclaimable (below), and other
1047              direct allocations with a shrinker.
1048Slab
1049              in-kernel data structures cache
1050SReclaimable
1051              Part of Slab, that might be reclaimed, such as caches
1052SUnreclaim
1053              Part of Slab, that cannot be reclaimed on memory pressure
1054PageTables
1055              amount of memory dedicated to the lowest level of page
1056              tables.
1057NFS_Unstable
1058              Always zero. Previous counted pages which had been written to
1059              the server, but has not been committed to stable storage.
1060Bounce
1061              Memory used for block device "bounce buffers"
1062WritebackTmp
1063              Memory used by FUSE for temporary writeback buffers
1064CommitLimit
1065              Based on the overcommit ratio ('vm.overcommit_ratio'),
1066              this is the total amount of  memory currently available to
1067              be allocated on the system. This limit is only adhered to
1068              if strict overcommit accounting is enabled (mode 2 in
1069              'vm.overcommit_memory').
1070
1071              The CommitLimit is calculated with the following formula::
1072
1073                CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
1074                               overcommit_ratio / 100 + [total swap pages]
1075
1076              For example, on a system with 1G of physical RAM and 7G
1077              of swap with a `vm.overcommit_ratio` of 30 it would
1078              yield a CommitLimit of 7.3G.
1079
1080              For more details, see the memory overcommit documentation
1081              in vm/overcommit-accounting.
1082Committed_AS
1083              The amount of memory presently allocated on the system.
1084              The committed memory is a sum of all of the memory which
1085              has been allocated by processes, even if it has not been
1086              "used" by them as of yet. A process which malloc()'s 1G
1087              of memory, but only touches 300M of it will show up as
1088	      using 1G. This 1G is memory which has been "committed" to
1089              by the VM and can be used at any time by the allocating
1090              application. With strict overcommit enabled on the system
1091              (mode 2 in 'vm.overcommit_memory'), allocations which would
1092              exceed the CommitLimit (detailed above) will not be permitted.
1093              This is useful if one needs to guarantee that processes will
1094              not fail due to lack of memory once that memory has been
1095              successfully allocated.
1096VmallocTotal
1097              total size of vmalloc memory area
1098VmallocUsed
1099              amount of vmalloc area which is used
1100VmallocChunk
1101              largest contiguous block of vmalloc area which is free
1102Percpu
1103              Memory allocated to the percpu allocator used to back percpu
1104              allocations. This stat excludes the cost of metadata.
1105
1106vmallocinfo
1107~~~~~~~~~~~
1108
1109Provides information about vmalloced/vmaped areas. One line per area,
1110containing the virtual address range of the area, size in bytes,
1111caller information of the creator, and optional information depending
1112on the kind of area:
1113
1114 ==========  ===================================================
1115 pages=nr    number of pages
1116 phys=addr   if a physical address was specified
1117 ioremap     I/O mapping (ioremap() and friends)
1118 vmalloc     vmalloc() area
1119 vmap        vmap()ed pages
1120 user        VM_USERMAP area
1121 vpages      buffer for pages pointers was vmalloced (huge area)
1122 N<node>=nr  (Only on NUMA kernels)
1123             Number of pages allocated on memory node <node>
1124 ==========  ===================================================
1125
1126::
1127
1128    > cat /proc/vmallocinfo
1129    0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
1130    /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
1131    0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
1132    /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
1133    0xffffc20000302000-0xffffc20000304000    8192 acpi_tb_verify_table+0x21/0x4f...
1134    phys=7fee8000 ioremap
1135    0xffffc20000304000-0xffffc20000307000   12288 acpi_tb_verify_table+0x21/0x4f...
1136    phys=7fee7000 ioremap
1137    0xffffc2000031d000-0xffffc2000031f000    8192 init_vdso_vars+0x112/0x210
1138    0xffffc2000031f000-0xffffc2000032b000   49152 cramfs_uncompress_init+0x2e ...
1139    /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
1140    0xffffc2000033a000-0xffffc2000033d000   12288 sys_swapon+0x640/0xac0      ...
1141    pages=2 vmalloc N1=2
1142    0xffffc20000347000-0xffffc2000034c000   20480 xt_alloc_table_info+0xfe ...
1143    /0x130 [x_tables] pages=4 vmalloc N0=4
1144    0xffffffffa0000000-0xffffffffa000f000   61440 sys_init_module+0xc27/0x1d00 ...
1145    pages=14 vmalloc N2=14
1146    0xffffffffa000f000-0xffffffffa0014000   20480 sys_init_module+0xc27/0x1d00 ...
1147    pages=4 vmalloc N1=4
1148    0xffffffffa0014000-0xffffffffa0017000   12288 sys_init_module+0xc27/0x1d00 ...
1149    pages=2 vmalloc N1=2
1150    0xffffffffa0017000-0xffffffffa0022000   45056 sys_init_module+0xc27/0x1d00 ...
1151    pages=10 vmalloc N0=10
1152
1153
1154softirqs
1155~~~~~~~~
1156
1157Provides counts of softirq handlers serviced since boot time, for each CPU.
1158
1159::
1160
1161    > cat /proc/softirqs
1162		  CPU0       CPU1       CPU2       CPU3
1163	HI:          0          0          0          0
1164    TIMER:       27166      27120      27097      27034
1165    NET_TX:          0          0          0         17
1166    NET_RX:         42          0          0         39
1167    BLOCK:           0          0        107       1121
1168    TASKLET:         0          0          0        290
1169    SCHED:       27035      26983      26971      26746
1170    HRTIMER:         0          0          0          0
1171	RCU:      1678       1769       2178       2250
1172
1173
11741.3 IDE devices in /proc/ide
1175----------------------------
1176
1177The subdirectory /proc/ide contains information about all IDE devices of which
1178the kernel  is  aware.  There is one subdirectory for each IDE controller, the
1179file drivers  and a link for each IDE device, pointing to the device directory
1180in the controller specific subtree.
1181
1182The file 'drivers' contains general information about the drivers used for the
1183IDE devices::
1184
1185  > cat /proc/ide/drivers
1186  ide-cdrom version 4.53
1187  ide-disk version 1.08
1188
1189More detailed  information  can  be  found  in  the  controller  specific
1190subdirectories. These  are  named  ide0,  ide1  and  so  on.  Each  of  these
1191directories contains the files shown in table 1-6.
1192
1193
1194.. table:: Table 1-6: IDE controller info in  /proc/ide/ide?
1195
1196 ======= =======================================
1197 File    Content
1198 ======= =======================================
1199 channel IDE channel (0 or 1)
1200 config  Configuration (only for PCI/IDE bridge)
1201 mate    Mate name
1202 model   Type/Chipset of IDE controller
1203 ======= =======================================
1204
1205Each device  connected  to  a  controller  has  a separate subdirectory in the
1206controllers directory.  The  files  listed in table 1-7 are contained in these
1207directories.
1208
1209
1210.. table:: Table 1-7: IDE device information
1211
1212 ================ ==========================================
1213 File             Content
1214 ================ ==========================================
1215 cache            The cache
1216 capacity         Capacity of the medium (in 512Byte blocks)
1217 driver           driver and version
1218 geometry         physical and logical geometry
1219 identify         device identify block
1220 media            media type
1221 model            device identifier
1222 settings         device setup
1223 smart_thresholds IDE disk management thresholds
1224 smart_values     IDE disk management values
1225 ================ ==========================================
1226
1227The most  interesting  file is ``settings``. This file contains a nice
1228overview of the drive parameters::
1229
1230  # cat /proc/ide/ide0/hda/settings
1231  name                    value           min             max             mode
1232  ----                    -----           ---             ---             ----
1233  bios_cyl                526             0               65535           rw
1234  bios_head               255             0               255             rw
1235  bios_sect               63              0               63              rw
1236  breada_readahead        4               0               127             rw
1237  bswap                   0               0               1               r
1238  file_readahead          72              0               2097151         rw
1239  io_32bit                0               0               3               rw
1240  keepsettings            0               0               1               rw
1241  max_kb_per_request      122             1               127             rw
1242  multcount               0               0               8               rw
1243  nice1                   1               0               1               rw
1244  nowerr                  0               0               1               rw
1245  pio_mode                write-only      0               255             w
1246  slow                    0               0               1               rw
1247  unmaskirq               0               0               1               rw
1248  using_dma               0               0               1               rw
1249
1250
12511.4 Networking info in /proc/net
1252--------------------------------
1253
1254The subdirectory  /proc/net  follows  the  usual  pattern. Table 1-8 shows the
1255additional values  you  get  for  IP  version 6 if you configure the kernel to
1256support this. Table 1-9 lists the files and their meaning.
1257
1258
1259.. table:: Table 1-8: IPv6 info in /proc/net
1260
1261 ========== =====================================================
1262 File       Content
1263 ========== =====================================================
1264 udp6       UDP sockets (IPv6)
1265 tcp6       TCP sockets (IPv6)
1266 raw6       Raw device statistics (IPv6)
1267 igmp6      IP multicast addresses, which this host joined (IPv6)
1268 if_inet6   List of IPv6 interface addresses
1269 ipv6_route Kernel routing table for IPv6
1270 rt6_stats  Global IPv6 routing tables statistics
1271 sockstat6  Socket statistics (IPv6)
1272 snmp6      Snmp data (IPv6)
1273 ========== =====================================================
1274
1275.. table:: Table 1-9: Network info in /proc/net
1276
1277 ============= ================================================================
1278 File          Content
1279 ============= ================================================================
1280 arp           Kernel  ARP table
1281 dev           network devices with statistics
1282 dev_mcast     the Layer2 multicast groups a device is listening too
1283               (interface index, label, number of references, number of bound
1284               addresses).
1285 dev_stat      network device status
1286 ip_fwchains   Firewall chain linkage
1287 ip_fwnames    Firewall chain names
1288 ip_masq       Directory containing the masquerading tables
1289 ip_masquerade Major masquerading table
1290 netstat       Network statistics
1291 raw           raw device statistics
1292 route         Kernel routing table
1293 rpc           Directory containing rpc info
1294 rt_cache      Routing cache
1295 snmp          SNMP data
1296 sockstat      Socket statistics
1297 tcp           TCP  sockets
1298 udp           UDP sockets
1299 unix          UNIX domain sockets
1300 wireless      Wireless interface data (Wavelan etc)
1301 igmp          IP multicast addresses, which this host joined
1302 psched        Global packet scheduler parameters.
1303 netlink       List of PF_NETLINK sockets
1304 ip_mr_vifs    List of multicast virtual interfaces
1305 ip_mr_cache   List of multicast routing cache
1306 ============= ================================================================
1307
1308You can  use  this  information  to see which network devices are available in
1309your system and how much traffic was routed over those devices::
1310
1311  > cat /proc/net/dev
1312  Inter-|Receive                                                   |[...
1313   face |bytes    packets errs drop fifo frame compressed multicast|[...
1314      lo:  908188   5596     0    0    0     0          0         0 [...
1315    ppp0:15475140  20721   410    0    0   410          0         0 [...
1316    eth0:  614530   7085     0    0    0     0          0         1 [...
1317
1318  ...] Transmit
1319  ...] bytes    packets errs drop fifo colls carrier compressed
1320  ...]  908188     5596    0    0    0     0       0          0
1321  ...] 1375103    17405    0    0    0     0       0          0
1322  ...] 1703981     5535    0    0    0     3       0          0
1323
1324In addition, each Channel Bond interface has its own directory.  For
1325example, the bond0 device will have a directory called /proc/net/bond0/.
1326It will contain information that is specific to that bond, such as the
1327current slaves of the bond, the link status of the slaves, and how
1328many times the slaves link has failed.
1329
13301.5 SCSI info
1331-------------
1332
1333If you  have  a  SCSI  host adapter in your system, you'll find a subdirectory
1334named after  the driver for this adapter in /proc/scsi. You'll also see a list
1335of all recognized SCSI devices in /proc/scsi::
1336
1337  >cat /proc/scsi/scsi
1338  Attached devices:
1339  Host: scsi0 Channel: 00 Id: 00 Lun: 00
1340    Vendor: IBM      Model: DGHS09U          Rev: 03E0
1341    Type:   Direct-Access                    ANSI SCSI revision: 03
1342  Host: scsi0 Channel: 00 Id: 06 Lun: 00
1343    Vendor: PIONEER  Model: CD-ROM DR-U06S   Rev: 1.04
1344    Type:   CD-ROM                           ANSI SCSI revision: 02
1345
1346
1347The directory  named  after  the driver has one file for each adapter found in
1348the system.  These  files  contain information about the controller, including
1349the used  IRQ  and  the  IO  address range. The amount of information shown is
1350dependent on  the adapter you use. The example shows the output for an Adaptec
1351AHA-2940 SCSI adapter::
1352
1353  > cat /proc/scsi/aic7xxx/0
1354
1355  Adaptec AIC7xxx driver version: 5.1.19/3.2.4
1356  Compile Options:
1357    TCQ Enabled By Default : Disabled
1358    AIC7XXX_PROC_STATS     : Disabled
1359    AIC7XXX_RESET_DELAY    : 5
1360  Adapter Configuration:
1361             SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
1362                             Ultra Wide Controller
1363      PCI MMAPed I/O Base: 0xeb001000
1364   Adapter SEEPROM Config: SEEPROM found and used.
1365        Adaptec SCSI BIOS: Enabled
1366                      IRQ: 10
1367                     SCBs: Active 0, Max Active 2,
1368                           Allocated 15, HW 16, Page 255
1369               Interrupts: 160328
1370        BIOS Control Word: 0x18b6
1371     Adapter Control Word: 0x005b
1372     Extended Translation: Enabled
1373  Disconnect Enable Flags: 0xffff
1374       Ultra Enable Flags: 0x0001
1375   Tag Queue Enable Flags: 0x0000
1376  Ordered Queue Tag Flags: 0x0000
1377  Default Tag Queue Depth: 8
1378      Tagged Queue By Device array for aic7xxx host instance 0:
1379        {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
1380      Actual queue depth per device for aic7xxx host instance 0:
1381        {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
1382  Statistics:
1383  (scsi0:0:0:0)
1384    Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
1385    Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
1386    Total transfers 160151 (74577 reads and 85574 writes)
1387  (scsi0:0:6:0)
1388    Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
1389    Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
1390    Total transfers 0 (0 reads and 0 writes)
1391
1392
13931.6 Parallel port info in /proc/parport
1394---------------------------------------
1395
1396The directory  /proc/parport  contains information about the parallel ports of
1397your system.  It  has  one  subdirectory  for  each port, named after the port
1398number (0,1,2,...).
1399
1400These directories contain the four files shown in Table 1-10.
1401
1402
1403.. table:: Table 1-10: Files in /proc/parport
1404
1405 ========= ====================================================================
1406 File      Content
1407 ========= ====================================================================
1408 autoprobe Any IEEE-1284 device ID information that has been acquired.
1409 devices   list of the device drivers using that port. A + will appear by the
1410           name of the device currently using the port (it might not appear
1411           against any).
1412 hardware  Parallel port's base address, IRQ line and DMA channel.
1413 irq       IRQ that parport is using for that port. This is in a separate
1414           file to allow you to alter it by writing a new value in (IRQ
1415           number or none).
1416 ========= ====================================================================
1417
14181.7 TTY info in /proc/tty
1419-------------------------
1420
1421Information about  the  available  and actually used tty's can be found in the
1422directory /proc/tty. You'll find  entries  for drivers and line disciplines in
1423this directory, as shown in Table 1-11.
1424
1425
1426.. table:: Table 1-11: Files in /proc/tty
1427
1428 ============= ==============================================
1429 File          Content
1430 ============= ==============================================
1431 drivers       list of drivers and their usage
1432 ldiscs        registered line disciplines
1433 driver/serial usage statistic and status of single tty lines
1434 ============= ==============================================
1435
1436To see  which  tty's  are  currently in use, you can simply look into the file
1437/proc/tty/drivers::
1438
1439  > cat /proc/tty/drivers
1440  pty_slave            /dev/pts      136   0-255 pty:slave
1441  pty_master           /dev/ptm      128   0-255 pty:master
1442  pty_slave            /dev/ttyp       3   0-255 pty:slave
1443  pty_master           /dev/pty        2   0-255 pty:master
1444  serial               /dev/cua        5   64-67 serial:callout
1445  serial               /dev/ttyS       4   64-67 serial
1446  /dev/tty0            /dev/tty0       4       0 system:vtmaster
1447  /dev/ptmx            /dev/ptmx       5       2 system
1448  /dev/console         /dev/console    5       1 system:console
1449  /dev/tty             /dev/tty        5       0 system:/dev/tty
1450  unknown              /dev/tty        4    1-63 console
1451
1452
14531.8 Miscellaneous kernel statistics in /proc/stat
1454-------------------------------------------------
1455
1456Various pieces   of  information about  kernel activity  are  available in the
1457/proc/stat file.  All  of  the numbers reported  in  this file are  aggregates
1458since the system first booted.  For a quick look, simply cat the file::
1459
1460  > cat /proc/stat
1461  cpu  2255 34 2290 22625563 6290 127 456 0 0 0
1462  cpu0 1132 34 1441 11311718 3675 127 438 0 0 0
1463  cpu1 1123 0 849 11313845 2614 0 18 0 0 0
1464  intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1465  ctxt 1990473
1466  btime 1062191376
1467  processes 2915
1468  procs_running 1
1469  procs_blocked 0
1470  softirq 183433 0 21755 12 39 1137 231 21459 2263
1471
1472The very first  "cpu" line aggregates the  numbers in all  of the other "cpuN"
1473lines.  These numbers identify the amount of time the CPU has spent performing
1474different kinds of work.  Time units are in USER_HZ (typically hundredths of a
1475second).  The meanings of the columns are as follows, from left to right:
1476
1477- user: normal processes executing in user mode
1478- nice: niced processes executing in user mode
1479- system: processes executing in kernel mode
1480- idle: twiddling thumbs
1481- iowait: In a word, iowait stands for waiting for I/O to complete. But there
1482  are several problems:
1483
1484  1. CPU will not wait for I/O to complete, iowait is the time that a task is
1485     waiting for I/O to complete. When CPU goes into idle state for
1486     outstanding task I/O, another task will be scheduled on this CPU.
1487  2. In a multi-core CPU, the task waiting for I/O to complete is not running
1488     on any CPU, so the iowait of each CPU is difficult to calculate.
1489  3. The value of iowait field in /proc/stat will decrease in certain
1490     conditions.
1491
1492  So, the iowait is not reliable by reading from /proc/stat.
1493- irq: servicing interrupts
1494- softirq: servicing softirqs
1495- steal: involuntary wait
1496- guest: running a normal guest
1497- guest_nice: running a niced guest
1498
1499The "intr" line gives counts of interrupts  serviced since boot time, for each
1500of the  possible system interrupts.   The first  column  is the  total of  all
1501interrupts serviced  including  unnumbered  architecture specific  interrupts;
1502each  subsequent column is the  total for that particular numbered interrupt.
1503Unnumbered interrupts are not shown, only summed into the total.
1504
1505The "ctxt" line gives the total number of context switches across all CPUs.
1506
1507The "btime" line gives  the time at which the  system booted, in seconds since
1508the Unix epoch.
1509
1510The "processes" line gives the number  of processes and threads created, which
1511includes (but  is not limited  to) those  created by  calls to the  fork() and
1512clone() system calls.
1513
1514The "procs_running" line gives the total number of threads that are
1515running or ready to run (i.e., the total number of runnable threads).
1516
1517The   "procs_blocked" line gives  the  number of  processes currently blocked,
1518waiting for I/O to complete.
1519
1520The "softirq" line gives counts of softirqs serviced since boot time, for each
1521of the possible system softirqs. The first column is the total of all
1522softirqs serviced; each subsequent column is the total for that particular
1523softirq.
1524
1525
15261.9 Ext4 file system parameters
1527-------------------------------
1528
1529Information about mounted ext4 file systems can be found in
1530/proc/fs/ext4.  Each mounted filesystem will have a directory in
1531/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1532/proc/fs/ext4/dm-0).   The files in each per-device directory are shown
1533in Table 1-12, below.
1534
1535.. table:: Table 1-12: Files in /proc/fs/ext4/<devname>
1536
1537 ==============  ==========================================================
1538 File            Content
1539 mb_groups       details of multiblock allocator buddy cache of free blocks
1540 ==============  ==========================================================
1541
15421.10 /proc/consoles
1543-------------------
1544Shows registered system console lines.
1545
1546To see which character device lines are currently used for the system console
1547/dev/console, you may simply look into the file /proc/consoles::
1548
1549  > cat /proc/consoles
1550  tty0                 -WU (ECp)       4:7
1551  ttyS0                -W- (Ep)        4:64
1552
1553The columns are:
1554
1555+--------------------+-------------------------------------------------------+
1556| device             | name of the device                                    |
1557+====================+=======================================================+
1558| operations         | * R = can do read operations                          |
1559|                    | * W = can do write operations                         |
1560|                    | * U = can do unblank                                  |
1561+--------------------+-------------------------------------------------------+
1562| flags              | * E = it is enabled                                   |
1563|                    | * C = it is preferred console                         |
1564|                    | * B = it is primary boot console                      |
1565|                    | * p = it is used for printk buffer                    |
1566|                    | * b = it is not a TTY but a Braille device            |
1567|                    | * a = it is safe to use when cpu is offline           |
1568+--------------------+-------------------------------------------------------+
1569| major:minor        | major and minor number of the device separated by a   |
1570|                    | colon                                                 |
1571+--------------------+-------------------------------------------------------+
1572
1573Summary
1574-------
1575
1576The /proc file system serves information about the running system. It not only
1577allows access to process data but also allows you to request the kernel status
1578by reading files in the hierarchy.
1579
1580The directory  structure  of /proc reflects the types of information and makes
1581it easy, if not obvious, where to look for specific data.
1582
1583Chapter 2: Modifying System Parameters
1584======================================
1585
1586In This Chapter
1587---------------
1588
1589* Modifying kernel parameters by writing into files found in /proc/sys
1590* Exploring the files which modify certain parameters
1591* Review of the /proc/sys file tree
1592
1593------------------------------------------------------------------------------
1594
1595A very  interesting part of /proc is the directory /proc/sys. This is not only
1596a source  of  information,  it also allows you to change parameters within the
1597kernel. Be  very  careful  when attempting this. You can optimize your system,
1598but you  can  also  cause  it  to  crash.  Never  alter kernel parameters on a
1599production system.  Set  up  a  development machine and test to make sure that
1600everything works  the  way  you want it to. You may have no alternative but to
1601reboot the machine once an error has been made.
1602
1603To change  a  value,  simply  echo  the new value into the file.
1604You need to be root to do this. You  can  create  your  own  boot script
1605to perform this every time your system boots.
1606
1607The files  in /proc/sys can be used to fine tune and monitor miscellaneous and
1608general things  in  the operation of the Linux kernel. Since some of the files
1609can inadvertently  disrupt  your  system,  it  is  advisable  to  read  both
1610documentation and  source  before actually making adjustments. In any case, be
1611very careful  when  writing  to  any  of these files. The entries in /proc may
1612change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1613review the kernel documentation in the directory /usr/src/linux/Documentation.
1614This chapter  is  heavily  based  on the documentation included in the pre 2.2
1615kernels, and became part of it in version 2.2.1 of the Linux kernel.
1616
1617Please see: Documentation/admin-guide/sysctl/ directory for descriptions of these
1618entries.
1619
1620Summary
1621-------
1622
1623Certain aspects  of  kernel  behavior  can be modified at runtime, without the
1624need to  recompile  the kernel, or even to reboot the system. The files in the
1625/proc/sys tree  can  not only be read, but also modified. You can use the echo
1626command to write value into these files, thereby changing the default settings
1627of the kernel.
1628
1629
1630Chapter 3: Per-process Parameters
1631=================================
1632
16333.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1634--------------------------------------------------------------------------------
1635
1636These files can be used to adjust the badness heuristic used to select which
1637process gets killed in out of memory (oom) conditions.
1638
1639The badness heuristic assigns a value to each candidate task ranging from 0
1640(never kill) to 1000 (always kill) to determine which process is targeted.  The
1641units are roughly a proportion along that range of allowed memory the process
1642may allocate from based on an estimation of its current memory and swap use.
1643For example, if a task is using all allowed memory, its badness score will be
16441000.  If it is using half of its allowed memory, its score will be 500.
1645
1646The amount of "allowed" memory depends on the context in which the oom killer
1647was called.  If it is due to the memory assigned to the allocating task's cpuset
1648being exhausted, the allowed memory represents the set of mems assigned to that
1649cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
1650memory represents the set of mempolicy nodes.  If it is due to a memory
1651limit (or swap limit) being reached, the allowed memory is that configured
1652limit.  Finally, if it is due to the entire system being out of memory, the
1653allowed memory represents all allocatable resources.
1654
1655The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1656is used to determine which task to kill.  Acceptable values range from -1000
1657(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
1658polarize the preference for oom killing either by always preferring a certain
1659task or completely disabling it.  The lowest possible value, -1000, is
1660equivalent to disabling oom killing entirely for that task since it will always
1661report a badness score of 0.
1662
1663Consequently, it is very simple for userspace to define the amount of memory to
1664consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
1665example, is roughly equivalent to allowing the remainder of tasks sharing the
1666same system, cpuset, mempolicy, or memory controller resources to use at least
166750% more memory.  A value of -500, on the other hand, would be roughly
1668equivalent to discounting 50% of the task's allowed memory from being considered
1669as scoring against the task.
1670
1671For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1672be used to tune the badness score.  Its acceptable values range from -16
1673(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1674(OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
1675scaled linearly with /proc/<pid>/oom_score_adj.
1676
1677The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1678value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1679requires CAP_SYS_RESOURCE.
1680
1681
16823.2 /proc/<pid>/oom_score - Display current oom-killer score
1683-------------------------------------------------------------
1684
1685This file can be used to check the current score used by the oom-killer for
1686any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1687process should be killed in an out-of-memory situation.
1688
1689Please note that the exported value includes oom_score_adj so it is
1690effectively in range [0,2000].
1691
1692
16933.3  /proc/<pid>/io - Display the IO accounting fields
1694-------------------------------------------------------
1695
1696This file contains IO statistics for each running process.
1697
1698Example
1699~~~~~~~
1700
1701::
1702
1703    test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1704    [1] 3828
1705
1706    test:/tmp # cat /proc/3828/io
1707    rchar: 323934931
1708    wchar: 323929600
1709    syscr: 632687
1710    syscw: 632675
1711    read_bytes: 0
1712    write_bytes: 323932160
1713    cancelled_write_bytes: 0
1714
1715
1716Description
1717~~~~~~~~~~~
1718
1719rchar
1720^^^^^
1721
1722I/O counter: chars read
1723The number of bytes which this task has caused to be read from storage. This
1724is simply the sum of bytes which this process passed to read() and pread().
1725It includes things like tty IO and it is unaffected by whether or not actual
1726physical disk IO was required (the read might have been satisfied from
1727pagecache).
1728
1729
1730wchar
1731^^^^^
1732
1733I/O counter: chars written
1734The number of bytes which this task has caused, or shall cause to be written
1735to disk. Similar caveats apply here as with rchar.
1736
1737
1738syscr
1739^^^^^
1740
1741I/O counter: read syscalls
1742Attempt to count the number of read I/O operations, i.e. syscalls like read()
1743and pread().
1744
1745
1746syscw
1747^^^^^
1748
1749I/O counter: write syscalls
1750Attempt to count the number of write I/O operations, i.e. syscalls like
1751write() and pwrite().
1752
1753
1754read_bytes
1755^^^^^^^^^^
1756
1757I/O counter: bytes read
1758Attempt to count the number of bytes which this process really did cause to
1759be fetched from the storage layer. Done at the submit_bio() level, so it is
1760accurate for block-backed filesystems. <please add status regarding NFS and
1761CIFS at a later time>
1762
1763
1764write_bytes
1765^^^^^^^^^^^
1766
1767I/O counter: bytes written
1768Attempt to count the number of bytes which this process caused to be sent to
1769the storage layer. This is done at page-dirtying time.
1770
1771
1772cancelled_write_bytes
1773^^^^^^^^^^^^^^^^^^^^^
1774
1775The big inaccuracy here is truncate. If a process writes 1MB to a file and
1776then deletes the file, it will in fact perform no writeout. But it will have
1777been accounted as having caused 1MB of write.
1778In other words: The number of bytes which this process caused to not happen,
1779by truncating pagecache. A task can cause "negative" IO too. If this task
1780truncates some dirty pagecache, some IO which another task has been accounted
1781for (in its write_bytes) will not be happening. We _could_ just subtract that
1782from the truncating task's write_bytes, but there is information loss in doing
1783that.
1784
1785
1786.. Note::
1787
1788   At its current implementation state, this is a bit racy on 32-bit machines:
1789   if process A reads process B's /proc/pid/io while process B is updating one
1790   of those 64-bit counters, process A could see an intermediate result.
1791
1792
1793More information about this can be found within the taskstats documentation in
1794Documentation/accounting.
1795
17963.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1797---------------------------------------------------------------
1798When a process is dumped, all anonymous memory is written to a core file as
1799long as the size of the core file isn't limited. But sometimes we don't want
1800to dump some memory segments, for example, huge shared memory or DAX.
1801Conversely, sometimes we want to save file-backed memory segments into a core
1802file, not only the individual files.
1803
1804/proc/<pid>/coredump_filter allows you to customize which memory segments
1805will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1806of memory types. If a bit of the bitmask is set, memory segments of the
1807corresponding memory type are dumped, otherwise they are not dumped.
1808
1809The following 9 memory types are supported:
1810
1811  - (bit 0) anonymous private memory
1812  - (bit 1) anonymous shared memory
1813  - (bit 2) file-backed private memory
1814  - (bit 3) file-backed shared memory
1815  - (bit 4) ELF header pages in file-backed private memory areas (it is
1816    effective only if the bit 2 is cleared)
1817  - (bit 5) hugetlb private memory
1818  - (bit 6) hugetlb shared memory
1819  - (bit 7) DAX private memory
1820  - (bit 8) DAX shared memory
1821
1822  Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1823  are always dumped regardless of the bitmask status.
1824
1825  Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
1826  only affected by bit 5-6, and DAX is only affected by bits 7-8.
1827
1828The default value of coredump_filter is 0x33; this means all anonymous memory
1829segments, ELF header pages and hugetlb private memory are dumped.
1830
1831If you don't want to dump all shared memory segments attached to pid 1234,
1832write 0x31 to the process's proc file::
1833
1834  $ echo 0x31 > /proc/1234/coredump_filter
1835
1836When a new process is created, the process inherits the bitmask status from its
1837parent. It is useful to set up coredump_filter before the program runs.
1838For example::
1839
1840  $ echo 0x7 > /proc/self/coredump_filter
1841  $ ./some_program
1842
18433.5	/proc/<pid>/mountinfo - Information about mounts
1844--------------------------------------------------------
1845
1846This file contains lines of the form::
1847
1848    36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1849    (1)(2)(3)   (4)   (5)      (6)      (7)   (8) (9)   (10)         (11)
1850
1851    (1) mount ID:  unique identifier of the mount (may be reused after umount)
1852    (2) parent ID:  ID of parent (or of self for the top of the mount tree)
1853    (3) major:minor:  value of st_dev for files on filesystem
1854    (4) root:  root of the mount within the filesystem
1855    (5) mount point:  mount point relative to the process's root
1856    (6) mount options:  per mount options
1857    (7) optional fields:  zero or more fields of the form "tag[:value]"
1858    (8) separator:  marks the end of the optional fields
1859    (9) filesystem type:  name of filesystem of the form "type[.subtype]"
1860    (10) mount source:  filesystem specific information or "none"
1861    (11) super options:  per super block options
1862
1863Parsers should ignore all unrecognised optional fields.  Currently the
1864possible optional fields are:
1865
1866================  ==============================================================
1867shared:X          mount is shared in peer group X
1868master:X          mount is slave to peer group X
1869propagate_from:X  mount is slave and receives propagation from peer group X [#]_
1870unbindable        mount is unbindable
1871================  ==============================================================
1872
1873.. [#] X is the closest dominant peer group under the process's root.  If
1874       X is the immediate master of the mount, or if there's no dominant peer
1875       group under the same root, then only the "master:X" field is present
1876       and not the "propagate_from:X" field.
1877
1878For more information on mount propagation see:
1879
1880  Documentation/filesystems/sharedsubtree.rst
1881
1882
18833.6	/proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
1884--------------------------------------------------------
1885These files provide a method to access a task's comm value. It also allows for
1886a task to set its own or one of its thread siblings comm value. The comm value
1887is limited in size compared to the cmdline value, so writing anything longer
1888then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1889comm value.
1890
1891
18923.7	/proc/<pid>/task/<tid>/children - Information about task children
1893-------------------------------------------------------------------------
1894This file provides a fast way to retrieve first level children pids
1895of a task pointed by <pid>/<tid> pair. The format is a space separated
1896stream of pids.
1897
1898Note the "first level" here -- if a child has its own children they will
1899not be listed here; one needs to read /proc/<children-pid>/task/<tid>/children
1900to obtain the descendants.
1901
1902Since this interface is intended to be fast and cheap it doesn't
1903guarantee to provide precise results and some children might be
1904skipped, especially if they've exited right after we printed their
1905pids, so one needs to either stop or freeze processes being inspected
1906if precise results are needed.
1907
1908
19093.8	/proc/<pid>/fdinfo/<fd> - Information about opened file
1910---------------------------------------------------------------
1911This file provides information associated with an opened file. The regular
1912files have at least three fields -- 'pos', 'flags' and 'mnt_id'. The 'pos'
1913represents the current offset of the opened file in decimal form [see lseek(2)
1914for details], 'flags' denotes the octal O_xxx mask the file has been
1915created with [see open(2) for details] and 'mnt_id' represents mount ID of
1916the file system containing the opened file [see 3.5 /proc/<pid>/mountinfo
1917for details].
1918
1919A typical output is::
1920
1921	pos:	0
1922	flags:	0100002
1923	mnt_id:	19
1924
1925All locks associated with a file descriptor are shown in its fdinfo too::
1926
1927    lock:       1: FLOCK  ADVISORY  WRITE 359 00:13:11691 0 EOF
1928
1929The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1930pair provide additional information particular to the objects they represent.
1931
1932Eventfd files
1933~~~~~~~~~~~~~
1934
1935::
1936
1937	pos:	0
1938	flags:	04002
1939	mnt_id:	9
1940	eventfd-count:	5a
1941
1942where 'eventfd-count' is hex value of a counter.
1943
1944Signalfd files
1945~~~~~~~~~~~~~~
1946
1947::
1948
1949	pos:	0
1950	flags:	04002
1951	mnt_id:	9
1952	sigmask:	0000000000000200
1953
1954where 'sigmask' is hex value of the signal mask associated
1955with a file.
1956
1957Epoll files
1958~~~~~~~~~~~
1959
1960::
1961
1962	pos:	0
1963	flags:	02
1964	mnt_id:	9
1965	tfd:        5 events:       1d data: ffffffffffffffff pos:0 ino:61af sdev:7
1966
1967where 'tfd' is a target file descriptor number in decimal form,
1968'events' is events mask being watched and the 'data' is data
1969associated with a target [see epoll(7) for more details].
1970
1971The 'pos' is current offset of the target file in decimal form
1972[see lseek(2)], 'ino' and 'sdev' are inode and device numbers
1973where target file resides, all in hex format.
1974
1975Fsnotify files
1976~~~~~~~~~~~~~~
1977For inotify files the format is the following::
1978
1979	pos:	0
1980	flags:	02000000
1981	inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
1982
1983where 'wd' is a watch descriptor in decimal form, i.e. a target file
1984descriptor number, 'ino' and 'sdev' are inode and device where the
1985target file resides and the 'mask' is the mask of events, all in hex
1986form [see inotify(7) for more details].
1987
1988If the kernel was built with exportfs support, the path to the target
1989file is encoded as a file handle.  The file handle is provided by three
1990fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
1991format.
1992
1993If the kernel is built without exportfs support the file handle won't be
1994printed out.
1995
1996If there is no inotify mark attached yet the 'inotify' line will be omitted.
1997
1998For fanotify files the format is::
1999
2000	pos:	0
2001	flags:	02
2002	mnt_id:	9
2003	fanotify flags:10 event-flags:0
2004	fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
2005	fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
2006
2007where fanotify 'flags' and 'event-flags' are values used in fanotify_init
2008call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
2009flags associated with mark which are tracked separately from events
2010mask. 'ino' and 'sdev' are target inode and device, 'mask' is the events
2011mask and 'ignored_mask' is the mask of events which are to be ignored.
2012All are in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
2013provide information about flags and mask used in fanotify_mark
2014call [see fsnotify manpage for details].
2015
2016While the first three lines are mandatory and always printed, the rest is
2017optional and may be omitted if no marks created yet.
2018
2019Timerfd files
2020~~~~~~~~~~~~~
2021
2022::
2023
2024	pos:	0
2025	flags:	02
2026	mnt_id:	9
2027	clockid: 0
2028	ticks: 0
2029	settime flags: 01
2030	it_value: (0, 49406829)
2031	it_interval: (1, 0)
2032
2033where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
2034that have occurred [see timerfd_create(2) for details]. 'settime flags' are
2035flags in octal form been used to setup the timer [see timerfd_settime(2) for
2036details]. 'it_value' is remaining time until the timer expiration.
2037'it_interval' is the interval for the timer. Note the timer might be set up
2038with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
2039still exhibits timer's remaining time.
2040
20413.9	/proc/<pid>/map_files - Information about memory mapped files
2042---------------------------------------------------------------------
2043This directory contains symbolic links which represent memory mapped files
2044the process is maintaining.  Example output::
2045
2046     | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
2047     | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
2048     | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
2049     | ...
2050     | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
2051     | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
2052
2053The name of a link represents the virtual memory bounds of a mapping, i.e.
2054vm_area_struct::vm_start-vm_area_struct::vm_end.
2055
2056The main purpose of the map_files is to retrieve a set of memory mapped
2057files in a fast way instead of parsing /proc/<pid>/maps or
2058/proc/<pid>/smaps, both of which contain many more records.  At the same
2059time one can open(2) mappings from the listings of two processes and
2060comparing their inode numbers to figure out which anonymous memory areas
2061are actually shared.
2062
20633.10	/proc/<pid>/timerslack_ns - Task timerslack value
2064---------------------------------------------------------
2065This file provides the value of the task's timerslack value in nanoseconds.
2066This value specifies an amount of time that normal timers may be deferred
2067in order to coalesce timers and avoid unnecessary wakeups.
2068
2069This allows a task's interactivity vs power consumption tradeoff to be
2070adjusted.
2071
2072Writing 0 to the file will set the task's timerslack to the default value.
2073
2074Valid values are from 0 - ULLONG_MAX
2075
2076An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
2077permissions on the task specified to change its timerslack_ns value.
2078
20793.11	/proc/<pid>/patch_state - Livepatch patch operation state
2080-----------------------------------------------------------------
2081When CONFIG_LIVEPATCH is enabled, this file displays the value of the
2082patch state for the task.
2083
2084A value of '-1' indicates that no patch is in transition.
2085
2086A value of '0' indicates that a patch is in transition and the task is
2087unpatched.  If the patch is being enabled, then the task hasn't been
2088patched yet.  If the patch is being disabled, then the task has already
2089been unpatched.
2090
2091A value of '1' indicates that a patch is in transition and the task is
2092patched.  If the patch is being enabled, then the task has already been
2093patched.  If the patch is being disabled, then the task hasn't been
2094unpatched yet.
2095
20963.12 /proc/<pid>/arch_status - task architecture specific status
2097-------------------------------------------------------------------
2098When CONFIG_PROC_PID_ARCH_STATUS is enabled, this file displays the
2099architecture specific status of the task.
2100
2101Example
2102~~~~~~~
2103
2104::
2105
2106 $ cat /proc/6753/arch_status
2107 AVX512_elapsed_ms:      8
2108
2109Description
2110~~~~~~~~~~~
2111
2112x86 specific entries
2113~~~~~~~~~~~~~~~~~~~~~
2114
2115AVX512_elapsed_ms
2116^^^^^^^^^^^^^^^^^^
2117
2118  If AVX512 is supported on the machine, this entry shows the milliseconds
2119  elapsed since the last time AVX512 usage was recorded. The recording
2120  happens on a best effort basis when a task is scheduled out. This means
2121  that the value depends on two factors:
2122
2123    1) The time which the task spent on the CPU without being scheduled
2124       out. With CPU isolation and a single runnable task this can take
2125       several seconds.
2126
2127    2) The time since the task was scheduled out last. Depending on the
2128       reason for being scheduled out (time slice exhausted, syscall ...)
2129       this can be arbitrary long time.
2130
2131  As a consequence the value cannot be considered precise and authoritative
2132  information. The application which uses this information has to be aware
2133  of the overall scenario on the system in order to determine whether a
2134  task is a real AVX512 user or not. Precise information can be obtained
2135  with performance counters.
2136
2137  A special value of '-1' indicates that no AVX512 usage was recorded, thus
2138  the task is unlikely an AVX512 user, but depends on the workload and the
2139  scheduling scenario, it also could be a false negative mentioned above.
2140
2141Chapter 4: Configuring procfs
2142=============================
2143
21444.1	Mount options
2145---------------------
2146
2147The following mount options are supported:
2148
2149	=========	========================================================
2150	hidepid=	Set /proc/<pid>/ access mode.
2151	gid=		Set the group authorized to learn processes information.
2152	subset=		Show only the specified subset of procfs.
2153	=========	========================================================
2154
2155hidepid=off or hidepid=0 means classic mode - everybody may access all
2156/proc/<pid>/ directories (default).
2157
2158hidepid=noaccess or hidepid=1 means users may not access any /proc/<pid>/
2159directories but their own.  Sensitive files like cmdline, sched*, status are now
2160protected against other users.  This makes it impossible to learn whether any
2161user runs specific program (given the program doesn't reveal itself by its
2162behaviour).  As an additional bonus, as /proc/<pid>/cmdline is unaccessible for
2163other users, poorly written programs passing sensitive information via program
2164arguments are now protected against local eavesdroppers.
2165
2166hidepid=invisible or hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be
2167fully invisible to other users.  It doesn't mean that it hides a fact whether a
2168process with a specific pid value exists (it can be learned by other means, e.g.
2169by "kill -0 $PID"), but it hides process' uid and gid, which may be learned by
2170stat()'ing /proc/<pid>/ otherwise.  It greatly complicates an intruder's task of
2171gathering information about running processes, whether some daemon runs with
2172elevated privileges, whether other user runs some sensitive program, whether
2173other users run any program at all, etc.
2174
2175hidepid=ptraceable or hidepid=4 means that procfs should only contain
2176/proc/<pid>/ directories that the caller can ptrace.
2177
2178gid= defines a group authorized to learn processes information otherwise
2179prohibited by hidepid=.  If you use some daemon like identd which needs to learn
2180information about processes information, just add identd to this group.
2181
2182subset=pid hides all top level files and directories in the procfs that
2183are not related to tasks.
2184
2185Chapter 5: Filesystem behavior
2186==============================
2187
2188Originally, before the advent of pid namepsace, procfs was a global file
2189system. It means that there was only one procfs instance in the system.
2190
2191When pid namespace was added, a separate procfs instance was mounted in
2192each pid namespace. So, procfs mount options are global among all
2193mountpoints within the same namespace::
2194
2195	# grep ^proc /proc/mounts
2196	proc /proc proc rw,relatime,hidepid=2 0 0
2197
2198	# strace -e mount mount -o hidepid=1 -t proc proc /tmp/proc
2199	mount("proc", "/tmp/proc", "proc", 0, "hidepid=1") = 0
2200	+++ exited with 0 +++
2201
2202	# grep ^proc /proc/mounts
2203	proc /proc proc rw,relatime,hidepid=2 0 0
2204	proc /tmp/proc proc rw,relatime,hidepid=2 0 0
2205
2206and only after remounting procfs mount options will change at all
2207mountpoints::
2208
2209	# mount -o remount,hidepid=1 -t proc proc /tmp/proc
2210
2211	# grep ^proc /proc/mounts
2212	proc /proc proc rw,relatime,hidepid=1 0 0
2213	proc /tmp/proc proc rw,relatime,hidepid=1 0 0
2214
2215This behavior is different from the behavior of other filesystems.
2216
2217The new procfs behavior is more like other filesystems. Each procfs mount
2218creates a new procfs instance. Mount options affect own procfs instance.
2219It means that it became possible to have several procfs instances
2220displaying tasks with different filtering options in one pid namespace::
2221
2222	# mount -o hidepid=invisible -t proc proc /proc
2223	# mount -o hidepid=noaccess -t proc proc /tmp/proc
2224	# grep ^proc /proc/mounts
2225	proc /proc proc rw,relatime,hidepid=invisible 0 0
2226	proc /tmp/proc proc rw,relatime,hidepid=noaccess 0 0
2227