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 [anon:<name>]              an anonymous mapping that has been
435                            named by userspace
436 =============              ====================================
437
438 or if empty, the mapping is anonymous.
439
440The /proc/PID/smaps is an extension based on maps, showing the memory
441consumption for each of the process's mappings. For each mapping (aka Virtual
442Memory Area, or VMA) there is a series of lines such as the following::
443
444    08048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
445
446    Size:               1084 kB
447    KernelPageSize:        4 kB
448    MMUPageSize:           4 kB
449    Rss:                 892 kB
450    Pss:                 374 kB
451    Pss_Dirty:             0 kB
452    Shared_Clean:        892 kB
453    Shared_Dirty:          0 kB
454    Private_Clean:         0 kB
455    Private_Dirty:         0 kB
456    Referenced:          892 kB
457    Anonymous:             0 kB
458    LazyFree:              0 kB
459    AnonHugePages:         0 kB
460    ShmemPmdMapped:        0 kB
461    Shared_Hugetlb:        0 kB
462    Private_Hugetlb:       0 kB
463    Swap:                  0 kB
464    SwapPss:               0 kB
465    KernelPageSize:        4 kB
466    MMUPageSize:           4 kB
467    Locked:                0 kB
468    THPeligible:           0
469    VmFlags: rd ex mr mw me dw
470
471The first of these lines shows the same information as is displayed for the
472mapping in /proc/PID/maps.  Following lines show the size of the mapping
473(size); the size of each page allocated when backing a VMA (KernelPageSize),
474which is usually the same as the size in the page table entries; the page size
475used by the MMU when backing a VMA (in most cases, the same as KernelPageSize);
476the amount of the mapping that is currently resident in RAM (RSS); the
477process' proportional share of this mapping (PSS); and the number of clean and
478dirty shared and private pages in the mapping.
479
480The "proportional set size" (PSS) of a process is the count of pages it has
481in memory, where each page is divided by the number of processes sharing it.
482So if a process has 1000 pages all to itself, and 1000 shared with one other
483process, its PSS will be 1500.  "Pss_Dirty" is the portion of PSS which
484consists of dirty pages.  ("Pss_Clean" is not included, but it can be
485calculated by subtracting "Pss_Dirty" from "Pss".)
486
487Note that even a page which is part of a MAP_SHARED mapping, but has only
488a single pte mapped, i.e.  is currently used by only one process, is accounted
489as private and not as shared.
490
491"Referenced" indicates the amount of memory currently marked as referenced or
492accessed.
493
494"Anonymous" shows the amount of memory that does not belong to any file.  Even
495a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
496and a page is modified, the file page is replaced by a private anonymous copy.
497
498"LazyFree" shows the amount of memory which is marked by madvise(MADV_FREE).
499The memory isn't freed immediately with madvise(). It's freed in memory
500pressure if the memory is clean. Please note that the printed value might
501be lower than the real value due to optimizations used in the current
502implementation. If this is not desirable please file a bug report.
503
504"AnonHugePages" shows the ammount of memory backed by transparent hugepage.
505
506"ShmemPmdMapped" shows the ammount of shared (shmem/tmpfs) memory backed by
507huge pages.
508
509"Shared_Hugetlb" and "Private_Hugetlb" show the ammounts of memory backed by
510hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical
511reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field.
512
513"Swap" shows how much would-be-anonymous memory is also used, but out on swap.
514
515For shmem mappings, "Swap" includes also the size of the mapped (and not
516replaced by copy-on-write) part of the underlying shmem object out on swap.
517"SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
518does not take into account swapped out page of underlying shmem objects.
519"Locked" indicates whether the mapping is locked in memory or not.
520
521"THPeligible" indicates whether the mapping is eligible for allocating THP
522pages as well as the THP is PMD mappable or not - 1 if true, 0 otherwise.
523It just shows the current status.
524
525"VmFlags" field deserves a separate description. This member represents the
526kernel flags associated with the particular virtual memory area in two letter
527encoded manner. The codes are the following:
528
529    ==    =======================================
530    rd    readable
531    wr    writeable
532    ex    executable
533    sh    shared
534    mr    may read
535    mw    may write
536    me    may execute
537    ms    may share
538    gd    stack segment growns down
539    pf    pure PFN range
540    dw    disabled write to the mapped file
541    lo    pages are locked in memory
542    io    memory mapped I/O area
543    sr    sequential read advise provided
544    rr    random read advise provided
545    dc    do not copy area on fork
546    de    do not expand area on remapping
547    ac    area is accountable
548    nr    swap space is not reserved for the area
549    ht    area uses huge tlb pages
550    sf    synchronous page fault
551    ar    architecture specific flag
552    wf    wipe on fork
553    dd    do not include area into core dump
554    sd    soft dirty flag
555    mm    mixed map area
556    hg    huge page advise flag
557    nh    no huge page advise flag
558    mg    mergable advise flag
559    bt    arm64 BTI guarded page
560    mt    arm64 MTE allocation tags are enabled
561    um    userfaultfd missing tracking
562    uw    userfaultfd wr-protect tracking
563    ==    =======================================
564
565Note that there is no guarantee that every flag and associated mnemonic will
566be present in all further kernel releases. Things get changed, the flags may
567be vanished or the reverse -- new added. Interpretation of their meaning
568might change in future as well. So each consumer of these flags has to
569follow each specific kernel version for the exact semantic.
570
571This file is only present if the CONFIG_MMU kernel configuration option is
572enabled.
573
574Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy (consistent
575output can be achieved only in the single read call).
576
577This typically manifests when doing partial reads of these files while the
578memory map is being modified.  Despite the races, we do provide the following
579guarantees:
580
5811) The mapped addresses never go backwards, which implies no two
582   regions will ever overlap.
5832) If there is something at a given vaddr during the entirety of the
584   life of the smaps/maps walk, there will be some output for it.
585
586The /proc/PID/smaps_rollup file includes the same fields as /proc/PID/smaps,
587but their values are the sums of the corresponding values for all mappings of
588the process.  Additionally, it contains these fields:
589
590- Pss_Anon
591- Pss_File
592- Pss_Shmem
593
594They represent the proportional shares of anonymous, file, and shmem pages, as
595described for smaps above.  These fields are omitted in smaps since each
596mapping identifies the type (anon, file, or shmem) of all pages it contains.
597Thus all information in smaps_rollup can be derived from smaps, but at a
598significantly higher cost.
599
600The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
601bits on both physical and virtual pages associated with a process, and the
602soft-dirty bit on pte (see Documentation/admin-guide/mm/soft-dirty.rst
603for details).
604To clear the bits for all the pages associated with the process::
605
606    > echo 1 > /proc/PID/clear_refs
607
608To clear the bits for the anonymous pages associated with the process::
609
610    > echo 2 > /proc/PID/clear_refs
611
612To clear the bits for the file mapped pages associated with the process::
613
614    > echo 3 > /proc/PID/clear_refs
615
616To clear the soft-dirty bit::
617
618    > echo 4 > /proc/PID/clear_refs
619
620To reset the peak resident set size ("high water mark") to the process's
621current value::
622
623    > echo 5 > /proc/PID/clear_refs
624
625Any other value written to /proc/PID/clear_refs will have no effect.
626
627The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
628using /proc/kpageflags and number of times a page is mapped using
629/proc/kpagecount. For detailed explanation, see
630Documentation/admin-guide/mm/pagemap.rst.
631
632The /proc/pid/numa_maps is an extension based on maps, showing the memory
633locality and binding policy, as well as the memory usage (in pages) of
634each mapping. The output follows a general format where mapping details get
635summarized separated by blank spaces, one mapping per each file line::
636
637    address   policy    mapping details
638
639    00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
640    00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
641    3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
642    320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
643    3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
644    3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
645    3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
646    320698b000 default file=/lib64/libc-2.12.so
647    3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4
648    3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
649    3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
650    7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
651    7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
652    7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
653    7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
654    7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4
655
656Where:
657
658"address" is the starting address for the mapping;
659
660"policy" reports the NUMA memory policy set for the mapping (see Documentation/admin-guide/mm/numa_memory_policy.rst);
661
662"mapping details" summarizes mapping data such as mapping type, page usage counters,
663node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
664size, in KB, that is backing the mapping up.
665
6661.2 Kernel data
667---------------
668
669Similar to  the  process entries, the kernel data files give information about
670the running kernel. The files used to obtain this information are contained in
671/proc and  are  listed  in Table 1-5. Not all of these will be present in your
672system. It  depends  on the kernel configuration and the loaded modules, which
673files are there, and which are missing.
674
675.. table:: Table 1-5: Kernel info in /proc
676
677 ============ ===============================================================
678 File         Content
679 ============ ===============================================================
680 apm          Advanced power management info
681 buddyinfo    Kernel memory allocator information (see text)	(2.5)
682 bus          Directory containing bus specific information
683 cmdline      Kernel command line
684 cpuinfo      Info about the CPU
685 devices      Available devices (block and character)
686 dma          Used DMS channels
687 filesystems  Supported filesystems
688 driver       Various drivers grouped here, currently rtc	(2.4)
689 execdomains  Execdomains, related to security			(2.4)
690 fb 	      Frame Buffer devices				(2.4)
691 fs 	      File system parameters, currently nfs/exports	(2.4)
692 ide          Directory containing info about the IDE subsystem
693 interrupts   Interrupt usage
694 iomem 	      Memory map					(2.4)
695 ioports      I/O port usage
696 irq 	      Masks for irq to cpu affinity			(2.4)(smp?)
697 isapnp       ISA PnP (Plug&Play) Info				(2.4)
698 kcore        Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
699 kmsg         Kernel messages
700 ksyms        Kernel symbol table
701 loadavg      Load average of last 1, 5 & 15 minutes;
702                number of processes currently runnable (running or on ready queue);
703                total number of processes in system;
704                last pid created.
705                All fields are separated by one space except "number of
706                processes currently runnable" and "total number of processes
707                in system", which are separated by a slash ('/'). Example:
708                0.61 0.61 0.55 3/828 22084
709 locks        Kernel locks
710 meminfo      Memory info
711 misc         Miscellaneous
712 modules      List of loaded modules
713 mounts       Mounted filesystems
714 net          Networking info (see text)
715 pagetypeinfo Additional page allocator information (see text)  (2.5)
716 partitions   Table of partitions known to the system
717 pci 	      Deprecated info of PCI bus (new way -> /proc/bus/pci/,
718              decoupled by lspci				(2.4)
719 rtc          Real time clock
720 scsi         SCSI info (see text)
721 slabinfo     Slab pool info
722 softirqs     softirq usage
723 stat         Overall statistics
724 swaps        Swap space utilization
725 sys          See chapter 2
726 sysvipc      Info of SysVIPC Resources (msg, sem, shm)		(2.4)
727 tty 	      Info of tty drivers
728 uptime       Wall clock since boot, combined idle time of all cpus
729 version      Kernel version
730 video 	      bttv info of video resources			(2.4)
731 vmallocinfo  Show vmalloced areas
732 ============ ===============================================================
733
734You can,  for  example,  check  which interrupts are currently in use and what
735they are used for by looking in the file /proc/interrupts::
736
737  > cat /proc/interrupts
738             CPU0
739    0:    8728810          XT-PIC  timer
740    1:        895          XT-PIC  keyboard
741    2:          0          XT-PIC  cascade
742    3:     531695          XT-PIC  aha152x
743    4:    2014133          XT-PIC  serial
744    5:      44401          XT-PIC  pcnet_cs
745    8:          2          XT-PIC  rtc
746   11:          8          XT-PIC  i82365
747   12:     182918          XT-PIC  PS/2 Mouse
748   13:          1          XT-PIC  fpu
749   14:    1232265          XT-PIC  ide0
750   15:          7          XT-PIC  ide1
751  NMI:          0
752
753In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
754output of a SMP machine)::
755
756  > cat /proc/interrupts
757
758             CPU0       CPU1
759    0:    1243498    1214548    IO-APIC-edge  timer
760    1:       8949       8958    IO-APIC-edge  keyboard
761    2:          0          0          XT-PIC  cascade
762    5:      11286      10161    IO-APIC-edge  soundblaster
763    8:          1          0    IO-APIC-edge  rtc
764    9:      27422      27407    IO-APIC-edge  3c503
765   12:     113645     113873    IO-APIC-edge  PS/2 Mouse
766   13:          0          0          XT-PIC  fpu
767   14:      22491      24012    IO-APIC-edge  ide0
768   15:       2183       2415    IO-APIC-edge  ide1
769   17:      30564      30414   IO-APIC-level  eth0
770   18:        177        164   IO-APIC-level  bttv
771  NMI:    2457961    2457959
772  LOC:    2457882    2457881
773  ERR:       2155
774
775NMI is incremented in this case because every timer interrupt generates a NMI
776(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
777
778LOC is the local interrupt counter of the internal APIC of every CPU.
779
780ERR is incremented in the case of errors in the IO-APIC bus (the bus that
781connects the CPUs in a SMP system. This means that an error has been detected,
782the IO-APIC automatically retry the transmission, so it should not be a big
783problem, but you should read the SMP-FAQ.
784
785In 2.6.2* /proc/interrupts was expanded again.  This time the goal was for
786/proc/interrupts to display every IRQ vector in use by the system, not
787just those considered 'most important'.  The new vectors are:
788
789THR
790  interrupt raised when a machine check threshold counter
791  (typically counting ECC corrected errors of memory or cache) exceeds
792  a configurable threshold.  Only available on some systems.
793
794TRM
795  a thermal event interrupt occurs when a temperature threshold
796  has been exceeded for the CPU.  This interrupt may also be generated
797  when the temperature drops back to normal.
798
799SPU
800  a spurious interrupt is some interrupt that was raised then lowered
801  by some IO device before it could be fully processed by the APIC.  Hence
802  the APIC sees the interrupt but does not know what device it came from.
803  For this case the APIC will generate the interrupt with a IRQ vector
804  of 0xff. This might also be generated by chipset bugs.
805
806RES, CAL, TLB
807  rescheduling, call and TLB flush interrupts are
808  sent from one CPU to another per the needs of the OS.  Typically,
809  their statistics are used by kernel developers and interested users to
810  determine the occurrence of interrupts of the given type.
811
812The above IRQ vectors are displayed only when relevant.  For example,
813the threshold vector does not exist on x86_64 platforms.  Others are
814suppressed when the system is a uniprocessor.  As of this writing, only
815i386 and x86_64 platforms support the new IRQ vector displays.
816
817Of some interest is the introduction of the /proc/irq directory to 2.4.
818It could be used to set IRQ to CPU affinity. This means that you can "hook" an
819IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
820irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
821prof_cpu_mask.
822
823For example::
824
825  > ls /proc/irq/
826  0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
827  1  11  13  15  17  19  3  5  7  9  default_smp_affinity
828  > ls /proc/irq/0/
829  smp_affinity
830
831smp_affinity is a bitmask, in which you can specify which CPUs can handle the
832IRQ. You can set it by doing::
833
834  > echo 1 > /proc/irq/10/smp_affinity
835
836This means that only the first CPU will handle the IRQ, but you can also echo
8375 which means that only the first and third CPU can handle the IRQ.
838
839The contents of each smp_affinity file is the same by default::
840
841  > cat /proc/irq/0/smp_affinity
842  ffffffff
843
844There is an alternate interface, smp_affinity_list which allows specifying
845a CPU range instead of a bitmask::
846
847  > cat /proc/irq/0/smp_affinity_list
848  1024-1031
849
850The default_smp_affinity mask applies to all non-active IRQs, which are the
851IRQs which have not yet been allocated/activated, and hence which lack a
852/proc/irq/[0-9]* directory.
853
854The node file on an SMP system shows the node to which the device using the IRQ
855reports itself as being attached. This hardware locality information does not
856include information about any possible driver locality preference.
857
858prof_cpu_mask specifies which CPUs are to be profiled by the system wide
859profiler. Default value is ffffffff (all CPUs if there are only 32 of them).
860
861The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
862between all the CPUs which are allowed to handle it. As usual the kernel has
863more info than you and does a better job than you, so the defaults are the
864best choice for almost everyone.  [Note this applies only to those IO-APIC's
865that support "Round Robin" interrupt distribution.]
866
867There are  three  more  important subdirectories in /proc: net, scsi, and sys.
868The general  rule  is  that  the  contents,  or  even  the  existence of these
869directories, depend  on your kernel configuration. If SCSI is not enabled, the
870directory scsi  may  not  exist. The same is true with the net, which is there
871only when networking support is present in the running kernel.
872
873The slabinfo  file  gives  information  about  memory usage at the slab level.
874Linux uses  slab  pools for memory management above page level in version 2.2.
875Commonly used  objects  have  their  own  slab  pool (such as network buffers,
876directory cache, and so on).
877
878::
879
880    > cat /proc/buddyinfo
881
882    Node 0, zone      DMA      0      4      5      4      4      3 ...
883    Node 0, zone   Normal      1      0      0      1    101      8 ...
884    Node 0, zone  HighMem      2      0      0      1      1      0 ...
885
886External fragmentation is a problem under some workloads, and buddyinfo is a
887useful tool for helping diagnose these problems.  Buddyinfo will give you a
888clue as to how big an area you can safely allocate, or why a previous
889allocation failed.
890
891Each column represents the number of pages of a certain order which are
892available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
893ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
894available in ZONE_NORMAL, etc...
895
896More information relevant to external fragmentation can be found in
897pagetypeinfo::
898
899    > cat /proc/pagetypeinfo
900    Page block order: 9
901    Pages per block:  512
902
903    Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
904    Node    0, zone      DMA, type    Unmovable      0      0      0      1      1      1      1      1      1      1      0
905    Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0
906    Node    0, zone      DMA, type      Movable      1      1      2      1      2      1      1      0      1      0      2
907    Node    0, zone      DMA, type      Reserve      0      0      0      0      0      0      0      0      0      1      0
908    Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
909    Node    0, zone    DMA32, type    Unmovable    103     54     77      1      1      1     11      8      7      1      9
910    Node    0, zone    DMA32, type  Reclaimable      0      0      2      1      0      0      0      0      1      0      0
911    Node    0, zone    DMA32, type      Movable    169    152    113     91     77     54     39     13      6      1    452
912    Node    0, zone    DMA32, type      Reserve      1      2      2      2      2      0      1      1      1      1      0
913    Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
914
915    Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate
916    Node 0, zone      DMA            2            0            5            1            0
917    Node 0, zone    DMA32           41            6          967            2            0
918
919Fragmentation avoidance in the kernel works by grouping pages of different
920migrate types into the same contiguous regions of memory called page blocks.
921A page block is typically the size of the default hugepage size, e.g. 2MB on
922X86-64. By keeping pages grouped based on their ability to move, the kernel
923can reclaim pages within a page block to satisfy a high-order allocation.
924
925The pagetypinfo begins with information on the size of a page block. It
926then gives the same type of information as buddyinfo except broken down
927by migrate-type and finishes with details on how many page blocks of each
928type exist.
929
930If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
931from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can
932make an estimate of the likely number of huge pages that can be allocated
933at a given point in time. All the "Movable" blocks should be allocatable
934unless memory has been mlock()'d. Some of the Reclaimable blocks should
935also be allocatable although a lot of filesystem metadata may have to be
936reclaimed to achieve this.
937
938
939meminfo
940~~~~~~~
941
942Provides information about distribution and utilization of memory.  This
943varies by architecture and compile options.  Some of the counters reported
944here overlap.  The memory reported by the non overlapping counters may not
945add up to the overall memory usage and the difference for some workloads
946can be substantial.  In many cases there are other means to find out
947additional memory using subsystem specific interfaces, for instance
948/proc/net/sockstat for TCP memory allocations.
949
950Example output. You may not have all of these fields.
951
952::
953
954    > cat /proc/meminfo
955
956    MemTotal:       32858820 kB
957    MemFree:        21001236 kB
958    MemAvailable:   27214312 kB
959    Buffers:          581092 kB
960    Cached:          5587612 kB
961    SwapCached:            0 kB
962    Active:          3237152 kB
963    Inactive:        7586256 kB
964    Active(anon):      94064 kB
965    Inactive(anon):  4570616 kB
966    Active(file):    3143088 kB
967    Inactive(file):  3015640 kB
968    Unevictable:           0 kB
969    Mlocked:               0 kB
970    SwapTotal:             0 kB
971    SwapFree:              0 kB
972    Zswap:              1904 kB
973    Zswapped:           7792 kB
974    Dirty:                12 kB
975    Writeback:             0 kB
976    AnonPages:       4654780 kB
977    Mapped:           266244 kB
978    Shmem:              9976 kB
979    KReclaimable:     517708 kB
980    Slab:             660044 kB
981    SReclaimable:     517708 kB
982    SUnreclaim:       142336 kB
983    KernelStack:       11168 kB
984    PageTables:        20540 kB
985    NFS_Unstable:          0 kB
986    Bounce:                0 kB
987    WritebackTmp:          0 kB
988    CommitLimit:    16429408 kB
989    Committed_AS:    7715148 kB
990    VmallocTotal:   34359738367 kB
991    VmallocUsed:       40444 kB
992    VmallocChunk:          0 kB
993    Percpu:            29312 kB
994    HardwareCorrupted:     0 kB
995    AnonHugePages:   4149248 kB
996    ShmemHugePages:        0 kB
997    ShmemPmdMapped:        0 kB
998    FileHugePages:         0 kB
999    FilePmdMapped:         0 kB
1000    CmaTotal:              0 kB
1001    CmaFree:               0 kB
1002    HugePages_Total:       0
1003    HugePages_Free:        0
1004    HugePages_Rsvd:        0
1005    HugePages_Surp:        0
1006    Hugepagesize:       2048 kB
1007    Hugetlb:               0 kB
1008    DirectMap4k:      401152 kB
1009    DirectMap2M:    10008576 kB
1010    DirectMap1G:    24117248 kB
1011
1012MemTotal
1013              Total usable RAM (i.e. physical RAM minus a few reserved
1014              bits and the kernel binary code)
1015MemFree
1016              Total free RAM. On highmem systems, the sum of LowFree+HighFree
1017MemAvailable
1018              An estimate of how much memory is available for starting new
1019              applications, without swapping. Calculated from MemFree,
1020              SReclaimable, the size of the file LRU lists, and the low
1021              watermarks in each zone.
1022              The estimate takes into account that the system needs some
1023              page cache to function well, and that not all reclaimable
1024              slab will be reclaimable, due to items being in use. The
1025              impact of those factors will vary from system to system.
1026Buffers
1027              Relatively temporary storage for raw disk blocks
1028              shouldn't get tremendously large (20MB or so)
1029Cached
1030              In-memory cache for files read from the disk (the
1031              pagecache) as well as tmpfs & shmem.
1032              Doesn't include SwapCached.
1033SwapCached
1034              Memory that once was swapped out, is swapped back in but
1035              still also is in the swapfile (if memory is needed it
1036              doesn't need to be swapped out AGAIN because it is already
1037              in the swapfile. This saves I/O)
1038Active
1039              Memory that has been used more recently and usually not
1040              reclaimed unless absolutely necessary.
1041Inactive
1042              Memory which has been less recently used.  It is more
1043              eligible to be reclaimed for other purposes
1044Unevictable
1045              Memory allocated for userspace which cannot be reclaimed, such
1046              as mlocked pages, ramfs backing pages, secret memfd pages etc.
1047Mlocked
1048              Memory locked with mlock().
1049HighTotal, HighFree
1050              Highmem is all memory above ~860MB of physical memory.
1051              Highmem areas are for use by userspace programs, or
1052              for the pagecache.  The kernel must use tricks to access
1053              this memory, making it slower to access than lowmem.
1054LowTotal, LowFree
1055              Lowmem is memory which can be used for everything that
1056              highmem can be used for, but it is also available for the
1057              kernel's use for its own data structures.  Among many
1058              other things, it is where everything from the Slab is
1059              allocated.  Bad things happen when you're out of lowmem.
1060SwapTotal
1061              total amount of swap space available
1062SwapFree
1063              Memory which has been evicted from RAM, and is temporarily
1064              on the disk
1065Zswap
1066              Memory consumed by the zswap backend (compressed size)
1067Zswapped
1068              Amount of anonymous memory stored in zswap (original size)
1069Dirty
1070              Memory which is waiting to get written back to the disk
1071Writeback
1072              Memory which is actively being written back to the disk
1073AnonPages
1074              Non-file backed pages mapped into userspace page tables
1075Mapped
1076              files which have been mmaped, such as libraries
1077Shmem
1078              Total memory used by shared memory (shmem) and tmpfs
1079KReclaimable
1080              Kernel allocations that the kernel will attempt to reclaim
1081              under memory pressure. Includes SReclaimable (below), and other
1082              direct allocations with a shrinker.
1083Slab
1084              in-kernel data structures cache
1085SReclaimable
1086              Part of Slab, that might be reclaimed, such as caches
1087SUnreclaim
1088              Part of Slab, that cannot be reclaimed on memory pressure
1089KernelStack
1090              Memory consumed by the kernel stacks of all tasks
1091PageTables
1092              Memory consumed by userspace page tables
1093NFS_Unstable
1094              Always zero. Previous counted pages which had been written to
1095              the server, but has not been committed to stable storage.
1096Bounce
1097              Memory used for block device "bounce buffers"
1098WritebackTmp
1099              Memory used by FUSE for temporary writeback buffers
1100CommitLimit
1101              Based on the overcommit ratio ('vm.overcommit_ratio'),
1102              this is the total amount of  memory currently available to
1103              be allocated on the system. This limit is only adhered to
1104              if strict overcommit accounting is enabled (mode 2 in
1105              'vm.overcommit_memory').
1106
1107              The CommitLimit is calculated with the following formula::
1108
1109                CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
1110                               overcommit_ratio / 100 + [total swap pages]
1111
1112              For example, on a system with 1G of physical RAM and 7G
1113              of swap with a `vm.overcommit_ratio` of 30 it would
1114              yield a CommitLimit of 7.3G.
1115
1116              For more details, see the memory overcommit documentation
1117              in mm/overcommit-accounting.
1118Committed_AS
1119              The amount of memory presently allocated on the system.
1120              The committed memory is a sum of all of the memory which
1121              has been allocated by processes, even if it has not been
1122              "used" by them as of yet. A process which malloc()'s 1G
1123              of memory, but only touches 300M of it will show up as
1124              using 1G. This 1G is memory which has been "committed" to
1125              by the VM and can be used at any time by the allocating
1126              application. With strict overcommit enabled on the system
1127              (mode 2 in 'vm.overcommit_memory'), allocations which would
1128              exceed the CommitLimit (detailed above) will not be permitted.
1129              This is useful if one needs to guarantee that processes will
1130              not fail due to lack of memory once that memory has been
1131              successfully allocated.
1132VmallocTotal
1133              total size of vmalloc virtual address space
1134VmallocUsed
1135              amount of vmalloc area which is used
1136VmallocChunk
1137              largest contiguous block of vmalloc area which is free
1138Percpu
1139              Memory allocated to the percpu allocator used to back percpu
1140              allocations. This stat excludes the cost of metadata.
1141HardwareCorrupted
1142              The amount of RAM/memory in KB, the kernel identifies as
1143              corrupted.
1144AnonHugePages
1145              Non-file backed huge pages mapped into userspace page tables
1146ShmemHugePages
1147              Memory used by shared memory (shmem) and tmpfs allocated
1148              with huge pages
1149ShmemPmdMapped
1150              Shared memory mapped into userspace with huge pages
1151FileHugePages
1152              Memory used for filesystem data (page cache) allocated
1153              with huge pages
1154FilePmdMapped
1155              Page cache mapped into userspace with huge pages
1156CmaTotal
1157              Memory reserved for the Contiguous Memory Allocator (CMA)
1158CmaFree
1159              Free remaining memory in the CMA reserves
1160HugePages_Total, HugePages_Free, HugePages_Rsvd, HugePages_Surp, Hugepagesize, Hugetlb
1161              See Documentation/admin-guide/mm/hugetlbpage.rst.
1162DirectMap4k, DirectMap2M, DirectMap1G
1163              Breakdown of page table sizes used in the kernel's
1164              identity mapping of RAM
1165
1166vmallocinfo
1167~~~~~~~~~~~
1168
1169Provides information about vmalloced/vmaped areas. One line per area,
1170containing the virtual address range of the area, size in bytes,
1171caller information of the creator, and optional information depending
1172on the kind of area:
1173
1174 ==========  ===================================================
1175 pages=nr    number of pages
1176 phys=addr   if a physical address was specified
1177 ioremap     I/O mapping (ioremap() and friends)
1178 vmalloc     vmalloc() area
1179 vmap        vmap()ed pages
1180 user        VM_USERMAP area
1181 vpages      buffer for pages pointers was vmalloced (huge area)
1182 N<node>=nr  (Only on NUMA kernels)
1183             Number of pages allocated on memory node <node>
1184 ==========  ===================================================
1185
1186::
1187
1188    > cat /proc/vmallocinfo
1189    0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
1190    /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
1191    0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
1192    /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
1193    0xffffc20000302000-0xffffc20000304000    8192 acpi_tb_verify_table+0x21/0x4f...
1194    phys=7fee8000 ioremap
1195    0xffffc20000304000-0xffffc20000307000   12288 acpi_tb_verify_table+0x21/0x4f...
1196    phys=7fee7000 ioremap
1197    0xffffc2000031d000-0xffffc2000031f000    8192 init_vdso_vars+0x112/0x210
1198    0xffffc2000031f000-0xffffc2000032b000   49152 cramfs_uncompress_init+0x2e ...
1199    /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
1200    0xffffc2000033a000-0xffffc2000033d000   12288 sys_swapon+0x640/0xac0      ...
1201    pages=2 vmalloc N1=2
1202    0xffffc20000347000-0xffffc2000034c000   20480 xt_alloc_table_info+0xfe ...
1203    /0x130 [x_tables] pages=4 vmalloc N0=4
1204    0xffffffffa0000000-0xffffffffa000f000   61440 sys_init_module+0xc27/0x1d00 ...
1205    pages=14 vmalloc N2=14
1206    0xffffffffa000f000-0xffffffffa0014000   20480 sys_init_module+0xc27/0x1d00 ...
1207    pages=4 vmalloc N1=4
1208    0xffffffffa0014000-0xffffffffa0017000   12288 sys_init_module+0xc27/0x1d00 ...
1209    pages=2 vmalloc N1=2
1210    0xffffffffa0017000-0xffffffffa0022000   45056 sys_init_module+0xc27/0x1d00 ...
1211    pages=10 vmalloc N0=10
1212
1213
1214softirqs
1215~~~~~~~~
1216
1217Provides counts of softirq handlers serviced since boot time, for each CPU.
1218
1219::
1220
1221    > cat /proc/softirqs
1222		  CPU0       CPU1       CPU2       CPU3
1223	HI:          0          0          0          0
1224    TIMER:       27166      27120      27097      27034
1225    NET_TX:          0          0          0         17
1226    NET_RX:         42          0          0         39
1227    BLOCK:           0          0        107       1121
1228    TASKLET:         0          0          0        290
1229    SCHED:       27035      26983      26971      26746
1230    HRTIMER:         0          0          0          0
1231	RCU:      1678       1769       2178       2250
1232
12331.3 Networking info in /proc/net
1234--------------------------------
1235
1236The subdirectory  /proc/net  follows  the  usual  pattern. Table 1-8 shows the
1237additional values  you  get  for  IP  version 6 if you configure the kernel to
1238support this. Table 1-9 lists the files and their meaning.
1239
1240
1241.. table:: Table 1-8: IPv6 info in /proc/net
1242
1243 ========== =====================================================
1244 File       Content
1245 ========== =====================================================
1246 udp6       UDP sockets (IPv6)
1247 tcp6       TCP sockets (IPv6)
1248 raw6       Raw device statistics (IPv6)
1249 igmp6      IP multicast addresses, which this host joined (IPv6)
1250 if_inet6   List of IPv6 interface addresses
1251 ipv6_route Kernel routing table for IPv6
1252 rt6_stats  Global IPv6 routing tables statistics
1253 sockstat6  Socket statistics (IPv6)
1254 snmp6      Snmp data (IPv6)
1255 ========== =====================================================
1256
1257.. table:: Table 1-9: Network info in /proc/net
1258
1259 ============= ================================================================
1260 File          Content
1261 ============= ================================================================
1262 arp           Kernel  ARP table
1263 dev           network devices with statistics
1264 dev_mcast     the Layer2 multicast groups a device is listening too
1265               (interface index, label, number of references, number of bound
1266               addresses).
1267 dev_stat      network device status
1268 ip_fwchains   Firewall chain linkage
1269 ip_fwnames    Firewall chain names
1270 ip_masq       Directory containing the masquerading tables
1271 ip_masquerade Major masquerading table
1272 netstat       Network statistics
1273 raw           raw device statistics
1274 route         Kernel routing table
1275 rpc           Directory containing rpc info
1276 rt_cache      Routing cache
1277 snmp          SNMP data
1278 sockstat      Socket statistics
1279 tcp           TCP  sockets
1280 udp           UDP sockets
1281 unix          UNIX domain sockets
1282 wireless      Wireless interface data (Wavelan etc)
1283 igmp          IP multicast addresses, which this host joined
1284 psched        Global packet scheduler parameters.
1285 netlink       List of PF_NETLINK sockets
1286 ip_mr_vifs    List of multicast virtual interfaces
1287 ip_mr_cache   List of multicast routing cache
1288 ============= ================================================================
1289
1290You can  use  this  information  to see which network devices are available in
1291your system and how much traffic was routed over those devices::
1292
1293  > cat /proc/net/dev
1294  Inter-|Receive                                                   |[...
1295   face |bytes    packets errs drop fifo frame compressed multicast|[...
1296      lo:  908188   5596     0    0    0     0          0         0 [...
1297    ppp0:15475140  20721   410    0    0   410          0         0 [...
1298    eth0:  614530   7085     0    0    0     0          0         1 [...
1299
1300  ...] Transmit
1301  ...] bytes    packets errs drop fifo colls carrier compressed
1302  ...]  908188     5596    0    0    0     0       0          0
1303  ...] 1375103    17405    0    0    0     0       0          0
1304  ...] 1703981     5535    0    0    0     3       0          0
1305
1306In addition, each Channel Bond interface has its own directory.  For
1307example, the bond0 device will have a directory called /proc/net/bond0/.
1308It will contain information that is specific to that bond, such as the
1309current slaves of the bond, the link status of the slaves, and how
1310many times the slaves link has failed.
1311
13121.4 SCSI info
1313-------------
1314
1315If you  have  a  SCSI  host adapter in your system, you'll find a subdirectory
1316named after  the driver for this adapter in /proc/scsi. You'll also see a list
1317of all recognized SCSI devices in /proc/scsi::
1318
1319  >cat /proc/scsi/scsi
1320  Attached devices:
1321  Host: scsi0 Channel: 00 Id: 00 Lun: 00
1322    Vendor: IBM      Model: DGHS09U          Rev: 03E0
1323    Type:   Direct-Access                    ANSI SCSI revision: 03
1324  Host: scsi0 Channel: 00 Id: 06 Lun: 00
1325    Vendor: PIONEER  Model: CD-ROM DR-U06S   Rev: 1.04
1326    Type:   CD-ROM                           ANSI SCSI revision: 02
1327
1328
1329The directory  named  after  the driver has one file for each adapter found in
1330the system.  These  files  contain information about the controller, including
1331the used  IRQ  and  the  IO  address range. The amount of information shown is
1332dependent on  the adapter you use. The example shows the output for an Adaptec
1333AHA-2940 SCSI adapter::
1334
1335  > cat /proc/scsi/aic7xxx/0
1336
1337  Adaptec AIC7xxx driver version: 5.1.19/3.2.4
1338  Compile Options:
1339    TCQ Enabled By Default : Disabled
1340    AIC7XXX_PROC_STATS     : Disabled
1341    AIC7XXX_RESET_DELAY    : 5
1342  Adapter Configuration:
1343             SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
1344                             Ultra Wide Controller
1345      PCI MMAPed I/O Base: 0xeb001000
1346   Adapter SEEPROM Config: SEEPROM found and used.
1347        Adaptec SCSI BIOS: Enabled
1348                      IRQ: 10
1349                     SCBs: Active 0, Max Active 2,
1350                           Allocated 15, HW 16, Page 255
1351               Interrupts: 160328
1352        BIOS Control Word: 0x18b6
1353     Adapter Control Word: 0x005b
1354     Extended Translation: Enabled
1355  Disconnect Enable Flags: 0xffff
1356       Ultra Enable Flags: 0x0001
1357   Tag Queue Enable Flags: 0x0000
1358  Ordered Queue Tag Flags: 0x0000
1359  Default Tag Queue Depth: 8
1360      Tagged Queue By Device array for aic7xxx host instance 0:
1361        {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
1362      Actual queue depth per device for aic7xxx host instance 0:
1363        {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
1364  Statistics:
1365  (scsi0:0:0:0)
1366    Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
1367    Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
1368    Total transfers 160151 (74577 reads and 85574 writes)
1369  (scsi0:0:6:0)
1370    Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
1371    Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
1372    Total transfers 0 (0 reads and 0 writes)
1373
1374
13751.5 Parallel port info in /proc/parport
1376---------------------------------------
1377
1378The directory  /proc/parport  contains information about the parallel ports of
1379your system.  It  has  one  subdirectory  for  each port, named after the port
1380number (0,1,2,...).
1381
1382These directories contain the four files shown in Table 1-10.
1383
1384
1385.. table:: Table 1-10: Files in /proc/parport
1386
1387 ========= ====================================================================
1388 File      Content
1389 ========= ====================================================================
1390 autoprobe Any IEEE-1284 device ID information that has been acquired.
1391 devices   list of the device drivers using that port. A + will appear by the
1392           name of the device currently using the port (it might not appear
1393           against any).
1394 hardware  Parallel port's base address, IRQ line and DMA channel.
1395 irq       IRQ that parport is using for that port. This is in a separate
1396           file to allow you to alter it by writing a new value in (IRQ
1397           number or none).
1398 ========= ====================================================================
1399
14001.6 TTY info in /proc/tty
1401-------------------------
1402
1403Information about  the  available  and actually used tty's can be found in the
1404directory /proc/tty. You'll find  entries  for drivers and line disciplines in
1405this directory, as shown in Table 1-11.
1406
1407
1408.. table:: Table 1-11: Files in /proc/tty
1409
1410 ============= ==============================================
1411 File          Content
1412 ============= ==============================================
1413 drivers       list of drivers and their usage
1414 ldiscs        registered line disciplines
1415 driver/serial usage statistic and status of single tty lines
1416 ============= ==============================================
1417
1418To see  which  tty's  are  currently in use, you can simply look into the file
1419/proc/tty/drivers::
1420
1421  > cat /proc/tty/drivers
1422  pty_slave            /dev/pts      136   0-255 pty:slave
1423  pty_master           /dev/ptm      128   0-255 pty:master
1424  pty_slave            /dev/ttyp       3   0-255 pty:slave
1425  pty_master           /dev/pty        2   0-255 pty:master
1426  serial               /dev/cua        5   64-67 serial:callout
1427  serial               /dev/ttyS       4   64-67 serial
1428  /dev/tty0            /dev/tty0       4       0 system:vtmaster
1429  /dev/ptmx            /dev/ptmx       5       2 system
1430  /dev/console         /dev/console    5       1 system:console
1431  /dev/tty             /dev/tty        5       0 system:/dev/tty
1432  unknown              /dev/tty        4    1-63 console
1433
1434
14351.7 Miscellaneous kernel statistics in /proc/stat
1436-------------------------------------------------
1437
1438Various pieces   of  information about  kernel activity  are  available in the
1439/proc/stat file.  All  of  the numbers reported  in  this file are  aggregates
1440since the system first booted.  For a quick look, simply cat the file::
1441
1442  > cat /proc/stat
1443  cpu  2255 34 2290 22625563 6290 127 456 0 0 0
1444  cpu0 1132 34 1441 11311718 3675 127 438 0 0 0
1445  cpu1 1123 0 849 11313845 2614 0 18 0 0 0
1446  intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1447  ctxt 1990473
1448  btime 1062191376
1449  processes 2915
1450  procs_running 1
1451  procs_blocked 0
1452  softirq 183433 0 21755 12 39 1137 231 21459 2263
1453
1454The very first  "cpu" line aggregates the  numbers in all  of the other "cpuN"
1455lines.  These numbers identify the amount of time the CPU has spent performing
1456different kinds of work.  Time units are in USER_HZ (typically hundredths of a
1457second).  The meanings of the columns are as follows, from left to right:
1458
1459- user: normal processes executing in user mode
1460- nice: niced processes executing in user mode
1461- system: processes executing in kernel mode
1462- idle: twiddling thumbs
1463- iowait: In a word, iowait stands for waiting for I/O to complete. But there
1464  are several problems:
1465
1466  1. CPU will not wait for I/O to complete, iowait is the time that a task is
1467     waiting for I/O to complete. When CPU goes into idle state for
1468     outstanding task I/O, another task will be scheduled on this CPU.
1469  2. In a multi-core CPU, the task waiting for I/O to complete is not running
1470     on any CPU, so the iowait of each CPU is difficult to calculate.
1471  3. The value of iowait field in /proc/stat will decrease in certain
1472     conditions.
1473
1474  So, the iowait is not reliable by reading from /proc/stat.
1475- irq: servicing interrupts
1476- softirq: servicing softirqs
1477- steal: involuntary wait
1478- guest: running a normal guest
1479- guest_nice: running a niced guest
1480
1481The "intr" line gives counts of interrupts  serviced since boot time, for each
1482of the  possible system interrupts.   The first  column  is the  total of  all
1483interrupts serviced  including  unnumbered  architecture specific  interrupts;
1484each  subsequent column is the  total for that particular numbered interrupt.
1485Unnumbered interrupts are not shown, only summed into the total.
1486
1487The "ctxt" line gives the total number of context switches across all CPUs.
1488
1489The "btime" line gives  the time at which the  system booted, in seconds since
1490the Unix epoch.
1491
1492The "processes" line gives the number  of processes and threads created, which
1493includes (but  is not limited  to) those  created by  calls to the  fork() and
1494clone() system calls.
1495
1496The "procs_running" line gives the total number of threads that are
1497running or ready to run (i.e., the total number of runnable threads).
1498
1499The   "procs_blocked" line gives  the  number of  processes currently blocked,
1500waiting for I/O to complete.
1501
1502The "softirq" line gives counts of softirqs serviced since boot time, for each
1503of the possible system softirqs. The first column is the total of all
1504softirqs serviced; each subsequent column is the total for that particular
1505softirq.
1506
1507
15081.8 Ext4 file system parameters
1509-------------------------------
1510
1511Information about mounted ext4 file systems can be found in
1512/proc/fs/ext4.  Each mounted filesystem will have a directory in
1513/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1514/proc/fs/ext4/dm-0).   The files in each per-device directory are shown
1515in Table 1-12, below.
1516
1517.. table:: Table 1-12: Files in /proc/fs/ext4/<devname>
1518
1519 ==============  ==========================================================
1520 File            Content
1521 mb_groups       details of multiblock allocator buddy cache of free blocks
1522 ==============  ==========================================================
1523
15241.9 /proc/consoles
1525-------------------
1526Shows registered system console lines.
1527
1528To see which character device lines are currently used for the system console
1529/dev/console, you may simply look into the file /proc/consoles::
1530
1531  > cat /proc/consoles
1532  tty0                 -WU (ECp)       4:7
1533  ttyS0                -W- (Ep)        4:64
1534
1535The columns are:
1536
1537+--------------------+-------------------------------------------------------+
1538| device             | name of the device                                    |
1539+====================+=======================================================+
1540| operations         | * R = can do read operations                          |
1541|                    | * W = can do write operations                         |
1542|                    | * U = can do unblank                                  |
1543+--------------------+-------------------------------------------------------+
1544| flags              | * E = it is enabled                                   |
1545|                    | * C = it is preferred console                         |
1546|                    | * B = it is primary boot console                      |
1547|                    | * p = it is used for printk buffer                    |
1548|                    | * b = it is not a TTY but a Braille device            |
1549|                    | * a = it is safe to use when cpu is offline           |
1550+--------------------+-------------------------------------------------------+
1551| major:minor        | major and minor number of the device separated by a   |
1552|                    | colon                                                 |
1553+--------------------+-------------------------------------------------------+
1554
1555Summary
1556-------
1557
1558The /proc file system serves information about the running system. It not only
1559allows access to process data but also allows you to request the kernel status
1560by reading files in the hierarchy.
1561
1562The directory  structure  of /proc reflects the types of information and makes
1563it easy, if not obvious, where to look for specific data.
1564
1565Chapter 2: Modifying System Parameters
1566======================================
1567
1568In This Chapter
1569---------------
1570
1571* Modifying kernel parameters by writing into files found in /proc/sys
1572* Exploring the files which modify certain parameters
1573* Review of the /proc/sys file tree
1574
1575------------------------------------------------------------------------------
1576
1577A very  interesting part of /proc is the directory /proc/sys. This is not only
1578a source  of  information,  it also allows you to change parameters within the
1579kernel. Be  very  careful  when attempting this. You can optimize your system,
1580but you  can  also  cause  it  to  crash.  Never  alter kernel parameters on a
1581production system.  Set  up  a  development machine and test to make sure that
1582everything works  the  way  you want it to. You may have no alternative but to
1583reboot the machine once an error has been made.
1584
1585To change  a  value,  simply  echo  the new value into the file.
1586You need to be root to do this. You  can  create  your  own  boot script
1587to perform this every time your system boots.
1588
1589The files  in /proc/sys can be used to fine tune and monitor miscellaneous and
1590general things  in  the operation of the Linux kernel. Since some of the files
1591can inadvertently  disrupt  your  system,  it  is  advisable  to  read  both
1592documentation and  source  before actually making adjustments. In any case, be
1593very careful  when  writing  to  any  of these files. The entries in /proc may
1594change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1595review the kernel documentation in the directory /usr/src/linux/Documentation.
1596This chapter  is  heavily  based  on the documentation included in the pre 2.2
1597kernels, and became part of it in version 2.2.1 of the Linux kernel.
1598
1599Please see: Documentation/admin-guide/sysctl/ directory for descriptions of these
1600entries.
1601
1602Summary
1603-------
1604
1605Certain aspects  of  kernel  behavior  can be modified at runtime, without the
1606need to  recompile  the kernel, or even to reboot the system. The files in the
1607/proc/sys tree  can  not only be read, but also modified. You can use the echo
1608command to write value into these files, thereby changing the default settings
1609of the kernel.
1610
1611
1612Chapter 3: Per-process Parameters
1613=================================
1614
16153.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1616--------------------------------------------------------------------------------
1617
1618These files can be used to adjust the badness heuristic used to select which
1619process gets killed in out of memory (oom) conditions.
1620
1621The badness heuristic assigns a value to each candidate task ranging from 0
1622(never kill) to 1000 (always kill) to determine which process is targeted.  The
1623units are roughly a proportion along that range of allowed memory the process
1624may allocate from based on an estimation of its current memory and swap use.
1625For example, if a task is using all allowed memory, its badness score will be
16261000.  If it is using half of its allowed memory, its score will be 500.
1627
1628The amount of "allowed" memory depends on the context in which the oom killer
1629was called.  If it is due to the memory assigned to the allocating task's cpuset
1630being exhausted, the allowed memory represents the set of mems assigned to that
1631cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
1632memory represents the set of mempolicy nodes.  If it is due to a memory
1633limit (or swap limit) being reached, the allowed memory is that configured
1634limit.  Finally, if it is due to the entire system being out of memory, the
1635allowed memory represents all allocatable resources.
1636
1637The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1638is used to determine which task to kill.  Acceptable values range from -1000
1639(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
1640polarize the preference for oom killing either by always preferring a certain
1641task or completely disabling it.  The lowest possible value, -1000, is
1642equivalent to disabling oom killing entirely for that task since it will always
1643report a badness score of 0.
1644
1645Consequently, it is very simple for userspace to define the amount of memory to
1646consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
1647example, is roughly equivalent to allowing the remainder of tasks sharing the
1648same system, cpuset, mempolicy, or memory controller resources to use at least
164950% more memory.  A value of -500, on the other hand, would be roughly
1650equivalent to discounting 50% of the task's allowed memory from being considered
1651as scoring against the task.
1652
1653For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1654be used to tune the badness score.  Its acceptable values range from -16
1655(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1656(OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
1657scaled linearly with /proc/<pid>/oom_score_adj.
1658
1659The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1660value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1661requires CAP_SYS_RESOURCE.
1662
1663
16643.2 /proc/<pid>/oom_score - Display current oom-killer score
1665-------------------------------------------------------------
1666
1667This file can be used to check the current score used by the oom-killer for
1668any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1669process should be killed in an out-of-memory situation.
1670
1671Please note that the exported value includes oom_score_adj so it is
1672effectively in range [0,2000].
1673
1674
16753.3  /proc/<pid>/io - Display the IO accounting fields
1676-------------------------------------------------------
1677
1678This file contains IO statistics for each running process.
1679
1680Example
1681~~~~~~~
1682
1683::
1684
1685    test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1686    [1] 3828
1687
1688    test:/tmp # cat /proc/3828/io
1689    rchar: 323934931
1690    wchar: 323929600
1691    syscr: 632687
1692    syscw: 632675
1693    read_bytes: 0
1694    write_bytes: 323932160
1695    cancelled_write_bytes: 0
1696
1697
1698Description
1699~~~~~~~~~~~
1700
1701rchar
1702^^^^^
1703
1704I/O counter: chars read
1705The number of bytes which this task has caused to be read from storage. This
1706is simply the sum of bytes which this process passed to read() and pread().
1707It includes things like tty IO and it is unaffected by whether or not actual
1708physical disk IO was required (the read might have been satisfied from
1709pagecache).
1710
1711
1712wchar
1713^^^^^
1714
1715I/O counter: chars written
1716The number of bytes which this task has caused, or shall cause to be written
1717to disk. Similar caveats apply here as with rchar.
1718
1719
1720syscr
1721^^^^^
1722
1723I/O counter: read syscalls
1724Attempt to count the number of read I/O operations, i.e. syscalls like read()
1725and pread().
1726
1727
1728syscw
1729^^^^^
1730
1731I/O counter: write syscalls
1732Attempt to count the number of write I/O operations, i.e. syscalls like
1733write() and pwrite().
1734
1735
1736read_bytes
1737^^^^^^^^^^
1738
1739I/O counter: bytes read
1740Attempt to count the number of bytes which this process really did cause to
1741be fetched from the storage layer. Done at the submit_bio() level, so it is
1742accurate for block-backed filesystems. <please add status regarding NFS and
1743CIFS at a later time>
1744
1745
1746write_bytes
1747^^^^^^^^^^^
1748
1749I/O counter: bytes written
1750Attempt to count the number of bytes which this process caused to be sent to
1751the storage layer. This is done at page-dirtying time.
1752
1753
1754cancelled_write_bytes
1755^^^^^^^^^^^^^^^^^^^^^
1756
1757The big inaccuracy here is truncate. If a process writes 1MB to a file and
1758then deletes the file, it will in fact perform no writeout. But it will have
1759been accounted as having caused 1MB of write.
1760In other words: The number of bytes which this process caused to not happen,
1761by truncating pagecache. A task can cause "negative" IO too. If this task
1762truncates some dirty pagecache, some IO which another task has been accounted
1763for (in its write_bytes) will not be happening. We _could_ just subtract that
1764from the truncating task's write_bytes, but there is information loss in doing
1765that.
1766
1767
1768.. Note::
1769
1770   At its current implementation state, this is a bit racy on 32-bit machines:
1771   if process A reads process B's /proc/pid/io while process B is updating one
1772   of those 64-bit counters, process A could see an intermediate result.
1773
1774
1775More information about this can be found within the taskstats documentation in
1776Documentation/accounting.
1777
17783.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1779---------------------------------------------------------------
1780When a process is dumped, all anonymous memory is written to a core file as
1781long as the size of the core file isn't limited. But sometimes we don't want
1782to dump some memory segments, for example, huge shared memory or DAX.
1783Conversely, sometimes we want to save file-backed memory segments into a core
1784file, not only the individual files.
1785
1786/proc/<pid>/coredump_filter allows you to customize which memory segments
1787will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1788of memory types. If a bit of the bitmask is set, memory segments of the
1789corresponding memory type are dumped, otherwise they are not dumped.
1790
1791The following 9 memory types are supported:
1792
1793  - (bit 0) anonymous private memory
1794  - (bit 1) anonymous shared memory
1795  - (bit 2) file-backed private memory
1796  - (bit 3) file-backed shared memory
1797  - (bit 4) ELF header pages in file-backed private memory areas (it is
1798    effective only if the bit 2 is cleared)
1799  - (bit 5) hugetlb private memory
1800  - (bit 6) hugetlb shared memory
1801  - (bit 7) DAX private memory
1802  - (bit 8) DAX shared memory
1803
1804  Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1805  are always dumped regardless of the bitmask status.
1806
1807  Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
1808  only affected by bit 5-6, and DAX is only affected by bits 7-8.
1809
1810The default value of coredump_filter is 0x33; this means all anonymous memory
1811segments, ELF header pages and hugetlb private memory are dumped.
1812
1813If you don't want to dump all shared memory segments attached to pid 1234,
1814write 0x31 to the process's proc file::
1815
1816  $ echo 0x31 > /proc/1234/coredump_filter
1817
1818When a new process is created, the process inherits the bitmask status from its
1819parent. It is useful to set up coredump_filter before the program runs.
1820For example::
1821
1822  $ echo 0x7 > /proc/self/coredump_filter
1823  $ ./some_program
1824
18253.5	/proc/<pid>/mountinfo - Information about mounts
1826--------------------------------------------------------
1827
1828This file contains lines of the form::
1829
1830    36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1831    (1)(2)(3)   (4)   (5)      (6)     (n…m) (m+1)(m+2) (m+3)         (m+4)
1832
1833    (1)   mount ID:        unique identifier of the mount (may be reused after umount)
1834    (2)   parent ID:       ID of parent (or of self for the top of the mount tree)
1835    (3)   major:minor:     value of st_dev for files on filesystem
1836    (4)   root:            root of the mount within the filesystem
1837    (5)   mount point:     mount point relative to the process's root
1838    (6)   mount options:   per mount options
1839    (n…m) optional fields: zero or more fields of the form "tag[:value]"
1840    (m+1) separator:       marks the end of the optional fields
1841    (m+2) filesystem type: name of filesystem of the form "type[.subtype]"
1842    (m+3) mount source:    filesystem specific information or "none"
1843    (m+4) super options:   per super block options
1844
1845Parsers should ignore all unrecognised optional fields.  Currently the
1846possible optional fields are:
1847
1848================  ==============================================================
1849shared:X          mount is shared in peer group X
1850master:X          mount is slave to peer group X
1851propagate_from:X  mount is slave and receives propagation from peer group X [#]_
1852unbindable        mount is unbindable
1853================  ==============================================================
1854
1855.. [#] X is the closest dominant peer group under the process's root.  If
1856       X is the immediate master of the mount, or if there's no dominant peer
1857       group under the same root, then only the "master:X" field is present
1858       and not the "propagate_from:X" field.
1859
1860For more information on mount propagation see:
1861
1862  Documentation/filesystems/sharedsubtree.rst
1863
1864
18653.6	/proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
1866--------------------------------------------------------
1867These files provide a method to access a task's comm value. It also allows for
1868a task to set its own or one of its thread siblings comm value. The comm value
1869is limited in size compared to the cmdline value, so writing anything longer
1870then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1871comm value.
1872
1873
18743.7	/proc/<pid>/task/<tid>/children - Information about task children
1875-------------------------------------------------------------------------
1876This file provides a fast way to retrieve first level children pids
1877of a task pointed by <pid>/<tid> pair. The format is a space separated
1878stream of pids.
1879
1880Note the "first level" here -- if a child has its own children they will
1881not be listed here; one needs to read /proc/<children-pid>/task/<tid>/children
1882to obtain the descendants.
1883
1884Since this interface is intended to be fast and cheap it doesn't
1885guarantee to provide precise results and some children might be
1886skipped, especially if they've exited right after we printed their
1887pids, so one needs to either stop or freeze processes being inspected
1888if precise results are needed.
1889
1890
18913.8	/proc/<pid>/fdinfo/<fd> - Information about opened file
1892---------------------------------------------------------------
1893This file provides information associated with an opened file. The regular
1894files have at least four fields -- 'pos', 'flags', 'mnt_id' and 'ino'.
1895The 'pos' represents the current offset of the opened file in decimal
1896form [see lseek(2) for details], 'flags' denotes the octal O_xxx mask the
1897file has been created with [see open(2) for details] and 'mnt_id' represents
1898mount ID of the file system containing the opened file [see 3.5
1899/proc/<pid>/mountinfo for details]. 'ino' represents the inode number of
1900the file.
1901
1902A typical output is::
1903
1904	pos:	0
1905	flags:	0100002
1906	mnt_id:	19
1907	ino:	63107
1908
1909All locks associated with a file descriptor are shown in its fdinfo too::
1910
1911    lock:       1: FLOCK  ADVISORY  WRITE 359 00:13:11691 0 EOF
1912
1913The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1914pair provide additional information particular to the objects they represent.
1915
1916Eventfd files
1917~~~~~~~~~~~~~
1918
1919::
1920
1921	pos:	0
1922	flags:	04002
1923	mnt_id:	9
1924	ino:	63107
1925	eventfd-count:	5a
1926
1927where 'eventfd-count' is hex value of a counter.
1928
1929Signalfd files
1930~~~~~~~~~~~~~~
1931
1932::
1933
1934	pos:	0
1935	flags:	04002
1936	mnt_id:	9
1937	ino:	63107
1938	sigmask:	0000000000000200
1939
1940where 'sigmask' is hex value of the signal mask associated
1941with a file.
1942
1943Epoll files
1944~~~~~~~~~~~
1945
1946::
1947
1948	pos:	0
1949	flags:	02
1950	mnt_id:	9
1951	ino:	63107
1952	tfd:        5 events:       1d data: ffffffffffffffff pos:0 ino:61af sdev:7
1953
1954where 'tfd' is a target file descriptor number in decimal form,
1955'events' is events mask being watched and the 'data' is data
1956associated with a target [see epoll(7) for more details].
1957
1958The 'pos' is current offset of the target file in decimal form
1959[see lseek(2)], 'ino' and 'sdev' are inode and device numbers
1960where target file resides, all in hex format.
1961
1962Fsnotify files
1963~~~~~~~~~~~~~~
1964For inotify files the format is the following::
1965
1966	pos:	0
1967	flags:	02000000
1968	mnt_id:	9
1969	ino:	63107
1970	inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
1971
1972where 'wd' is a watch descriptor in decimal form, i.e. a target file
1973descriptor number, 'ino' and 'sdev' are inode and device where the
1974target file resides and the 'mask' is the mask of events, all in hex
1975form [see inotify(7) for more details].
1976
1977If the kernel was built with exportfs support, the path to the target
1978file is encoded as a file handle.  The file handle is provided by three
1979fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
1980format.
1981
1982If the kernel is built without exportfs support the file handle won't be
1983printed out.
1984
1985If there is no inotify mark attached yet the 'inotify' line will be omitted.
1986
1987For fanotify files the format is::
1988
1989	pos:	0
1990	flags:	02
1991	mnt_id:	9
1992	ino:	63107
1993	fanotify flags:10 event-flags:0
1994	fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
1995	fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
1996
1997where fanotify 'flags' and 'event-flags' are values used in fanotify_init
1998call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
1999flags associated with mark which are tracked separately from events
2000mask. 'ino' and 'sdev' are target inode and device, 'mask' is the events
2001mask and 'ignored_mask' is the mask of events which are to be ignored.
2002All are in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
2003provide information about flags and mask used in fanotify_mark
2004call [see fsnotify manpage for details].
2005
2006While the first three lines are mandatory and always printed, the rest is
2007optional and may be omitted if no marks created yet.
2008
2009Timerfd files
2010~~~~~~~~~~~~~
2011
2012::
2013
2014	pos:	0
2015	flags:	02
2016	mnt_id:	9
2017	ino:	63107
2018	clockid: 0
2019	ticks: 0
2020	settime flags: 01
2021	it_value: (0, 49406829)
2022	it_interval: (1, 0)
2023
2024where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
2025that have occurred [see timerfd_create(2) for details]. 'settime flags' are
2026flags in octal form been used to setup the timer [see timerfd_settime(2) for
2027details]. 'it_value' is remaining time until the timer expiration.
2028'it_interval' is the interval for the timer. Note the timer might be set up
2029with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
2030still exhibits timer's remaining time.
2031
2032DMA Buffer files
2033~~~~~~~~~~~~~~~~
2034
2035::
2036
2037	pos:	0
2038	flags:	04002
2039	mnt_id:	9
2040	ino:	63107
2041	size:   32768
2042	count:  2
2043	exp_name:  system-heap
2044
2045where 'size' is the size of the DMA buffer in bytes. 'count' is the file count of
2046the DMA buffer file. 'exp_name' is the name of the DMA buffer exporter.
2047
20483.9	/proc/<pid>/map_files - Information about memory mapped files
2049---------------------------------------------------------------------
2050This directory contains symbolic links which represent memory mapped files
2051the process is maintaining.  Example output::
2052
2053     | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
2054     | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
2055     | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
2056     | ...
2057     | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
2058     | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
2059
2060The name of a link represents the virtual memory bounds of a mapping, i.e.
2061vm_area_struct::vm_start-vm_area_struct::vm_end.
2062
2063The main purpose of the map_files is to retrieve a set of memory mapped
2064files in a fast way instead of parsing /proc/<pid>/maps or
2065/proc/<pid>/smaps, both of which contain many more records.  At the same
2066time one can open(2) mappings from the listings of two processes and
2067comparing their inode numbers to figure out which anonymous memory areas
2068are actually shared.
2069
20703.10	/proc/<pid>/timerslack_ns - Task timerslack value
2071---------------------------------------------------------
2072This file provides the value of the task's timerslack value in nanoseconds.
2073This value specifies an amount of time that normal timers may be deferred
2074in order to coalesce timers and avoid unnecessary wakeups.
2075
2076This allows a task's interactivity vs power consumption tradeoff to be
2077adjusted.
2078
2079Writing 0 to the file will set the task's timerslack to the default value.
2080
2081Valid values are from 0 - ULLONG_MAX
2082
2083An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
2084permissions on the task specified to change its timerslack_ns value.
2085
20863.11	/proc/<pid>/patch_state - Livepatch patch operation state
2087-----------------------------------------------------------------
2088When CONFIG_LIVEPATCH is enabled, this file displays the value of the
2089patch state for the task.
2090
2091A value of '-1' indicates that no patch is in transition.
2092
2093A value of '0' indicates that a patch is in transition and the task is
2094unpatched.  If the patch is being enabled, then the task hasn't been
2095patched yet.  If the patch is being disabled, then the task has already
2096been unpatched.
2097
2098A value of '1' indicates that a patch is in transition and the task is
2099patched.  If the patch is being enabled, then the task has already been
2100patched.  If the patch is being disabled, then the task hasn't been
2101unpatched yet.
2102
21033.12 /proc/<pid>/arch_status - task architecture specific status
2104-------------------------------------------------------------------
2105When CONFIG_PROC_PID_ARCH_STATUS is enabled, this file displays the
2106architecture specific status of the task.
2107
2108Example
2109~~~~~~~
2110
2111::
2112
2113 $ cat /proc/6753/arch_status
2114 AVX512_elapsed_ms:      8
2115
2116Description
2117~~~~~~~~~~~
2118
2119x86 specific entries
2120~~~~~~~~~~~~~~~~~~~~~
2121
2122AVX512_elapsed_ms
2123^^^^^^^^^^^^^^^^^^
2124
2125  If AVX512 is supported on the machine, this entry shows the milliseconds
2126  elapsed since the last time AVX512 usage was recorded. The recording
2127  happens on a best effort basis when a task is scheduled out. This means
2128  that the value depends on two factors:
2129
2130    1) The time which the task spent on the CPU without being scheduled
2131       out. With CPU isolation and a single runnable task this can take
2132       several seconds.
2133
2134    2) The time since the task was scheduled out last. Depending on the
2135       reason for being scheduled out (time slice exhausted, syscall ...)
2136       this can be arbitrary long time.
2137
2138  As a consequence the value cannot be considered precise and authoritative
2139  information. The application which uses this information has to be aware
2140  of the overall scenario on the system in order to determine whether a
2141  task is a real AVX512 user or not. Precise information can be obtained
2142  with performance counters.
2143
2144  A special value of '-1' indicates that no AVX512 usage was recorded, thus
2145  the task is unlikely an AVX512 user, but depends on the workload and the
2146  scheduling scenario, it also could be a false negative mentioned above.
2147
2148Chapter 4: Configuring procfs
2149=============================
2150
21514.1	Mount options
2152---------------------
2153
2154The following mount options are supported:
2155
2156	=========	========================================================
2157	hidepid=	Set /proc/<pid>/ access mode.
2158	gid=		Set the group authorized to learn processes information.
2159	subset=		Show only the specified subset of procfs.
2160	=========	========================================================
2161
2162hidepid=off or hidepid=0 means classic mode - everybody may access all
2163/proc/<pid>/ directories (default).
2164
2165hidepid=noaccess or hidepid=1 means users may not access any /proc/<pid>/
2166directories but their own.  Sensitive files like cmdline, sched*, status are now
2167protected against other users.  This makes it impossible to learn whether any
2168user runs specific program (given the program doesn't reveal itself by its
2169behaviour).  As an additional bonus, as /proc/<pid>/cmdline is unaccessible for
2170other users, poorly written programs passing sensitive information via program
2171arguments are now protected against local eavesdroppers.
2172
2173hidepid=invisible or hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be
2174fully invisible to other users.  It doesn't mean that it hides a fact whether a
2175process with a specific pid value exists (it can be learned by other means, e.g.
2176by "kill -0 $PID"), but it hides process' uid and gid, which may be learned by
2177stat()'ing /proc/<pid>/ otherwise.  It greatly complicates an intruder's task of
2178gathering information about running processes, whether some daemon runs with
2179elevated privileges, whether other user runs some sensitive program, whether
2180other users run any program at all, etc.
2181
2182hidepid=ptraceable or hidepid=4 means that procfs should only contain
2183/proc/<pid>/ directories that the caller can ptrace.
2184
2185gid= defines a group authorized to learn processes information otherwise
2186prohibited by hidepid=.  If you use some daemon like identd which needs to learn
2187information about processes information, just add identd to this group.
2188
2189subset=pid hides all top level files and directories in the procfs that
2190are not related to tasks.
2191
2192Chapter 5: Filesystem behavior
2193==============================
2194
2195Originally, before the advent of pid namepsace, procfs was a global file
2196system. It means that there was only one procfs instance in the system.
2197
2198When pid namespace was added, a separate procfs instance was mounted in
2199each pid namespace. So, procfs mount options are global among all
2200mountpoints within the same namespace::
2201
2202	# grep ^proc /proc/mounts
2203	proc /proc proc rw,relatime,hidepid=2 0 0
2204
2205	# strace -e mount mount -o hidepid=1 -t proc proc /tmp/proc
2206	mount("proc", "/tmp/proc", "proc", 0, "hidepid=1") = 0
2207	+++ exited with 0 +++
2208
2209	# grep ^proc /proc/mounts
2210	proc /proc proc rw,relatime,hidepid=2 0 0
2211	proc /tmp/proc proc rw,relatime,hidepid=2 0 0
2212
2213and only after remounting procfs mount options will change at all
2214mountpoints::
2215
2216	# mount -o remount,hidepid=1 -t proc proc /tmp/proc
2217
2218	# grep ^proc /proc/mounts
2219	proc /proc proc rw,relatime,hidepid=1 0 0
2220	proc /tmp/proc proc rw,relatime,hidepid=1 0 0
2221
2222This behavior is different from the behavior of other filesystems.
2223
2224The new procfs behavior is more like other filesystems. Each procfs mount
2225creates a new procfs instance. Mount options affect own procfs instance.
2226It means that it became possible to have several procfs instances
2227displaying tasks with different filtering options in one pid namespace::
2228
2229	# mount -o hidepid=invisible -t proc proc /proc
2230	# mount -o hidepid=noaccess -t proc proc /tmp/proc
2231	# grep ^proc /proc/mounts
2232	proc /proc proc rw,relatime,hidepid=invisible 0 0
2233	proc /tmp/proc proc rw,relatime,hidepid=noaccess 0 0
2234