xref: /linux/Documentation/filesystems/proc.rst (revision fcb3ad4366b9c810cbb9da34c076a9a52d8aa1e0)
1.. SPDX-License-Identifier: GPL-2.0
2
3====================
4The /proc Filesystem
5====================
6
7=====================  =======================================  ================
8/proc/sys              Terrehon Bowden <terrehon@pacbell.net>,  October 7 1999
9                       Bodo Bauer <bb@ricochet.net>
102.4.x update	       Jorge Nerin <comandante@zaralinux.com>   November 14 2000
11move /proc/sys	       Shen Feng <shen@cn.fujitsu.com>	        April 1 2009
12fixes/update part 1.1  Stefani Seibold <stefani@seibold.net>    June 9 2009
13=====================  =======================================  ================
14
15
16
17.. Table of Contents
18
19  0     Preface
20  0.1	Introduction/Credits
21  0.2	Legal Stuff
22
23  1	Collecting System Information
24  1.1	Process-Specific Subdirectories
25  1.2	Kernel data
26  1.3	IDE devices in /proc/ide
27  1.4	Networking info in /proc/net
28  1.5	SCSI info
29  1.6	Parallel port info in /proc/parport
30  1.7	TTY info in /proc/tty
31  1.8	Miscellaneous kernel statistics in /proc/stat
32  1.9	Ext4 file system parameters
33
34  2	Modifying System Parameters
35
36  3	Per-Process Parameters
37  3.1	/proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj - Adjust the oom-killer
38								score
39  3.2	/proc/<pid>/oom_score - Display current oom-killer score
40  3.3	/proc/<pid>/io - Display the IO accounting fields
41  3.4	/proc/<pid>/coredump_filter - Core dump filtering settings
42  3.5	/proc/<pid>/mountinfo - Information about mounts
43  3.6	/proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
44  3.7   /proc/<pid>/task/<tid>/children - Information about task children
45  3.8   /proc/<pid>/fdinfo/<fd> - Information about opened file
46  3.9   /proc/<pid>/map_files - Information about memory mapped files
47  3.10  /proc/<pid>/timerslack_ns - Task timerslack value
48  3.11	/proc/<pid>/patch_state - Livepatch patch operation state
49  3.12	/proc/<pid>/arch_status - Task architecture specific information
50  3.13  /proc/<pid>/fd - List of symlinks to open files
51
52  4	Configuring procfs
53  4.1	Mount options
54
55  5	Filesystem behavior
56
57Preface
58=======
59
600.1 Introduction/Credits
61------------------------
62
63This documentation is  part of a soon (or  so we hope) to be  released book on
64the SuSE  Linux distribution. As  there is  no complete documentation  for the
65/proc file system and we've used  many freely available sources to write these
66chapters, it  seems only fair  to give the work  back to the  Linux community.
67This work is  based on the 2.2.*  kernel version and the  upcoming 2.4.*. I'm
68afraid it's still far from complete, but we  hope it will be useful. As far as
69we know, it is the first 'all-in-one' document about the /proc file system. It
70is focused  on the Intel  x86 hardware,  so if you  are looking for  PPC, ARM,
71SPARC, AXP, etc., features, you probably  won't find what you are looking for.
72It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
73additions and patches  are welcome and will  be added to this  document if you
74mail them to Bodo.
75
76We'd like  to  thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
77other people for help compiling this documentation. We'd also like to extend a
78special thank  you to Andi Kleen for documentation, which we relied on heavily
79to create  this  document,  as well as the additional information he provided.
80Thanks to  everybody  else  who contributed source or docs to the Linux kernel
81and helped create a great piece of software... :)
82
83If you  have  any comments, corrections or additions, please don't hesitate to
84contact Bodo  Bauer  at  bb@ricochet.net.  We'll  be happy to add them to this
85document.
86
87The   latest   version    of   this   document   is    available   online   at
88https://www.kernel.org/doc/html/latest/filesystems/proc.html
89
90If  the above  direction does  not works  for you,  you could  try the  kernel
91mailing  list  at  linux-kernel@vger.kernel.org  and/or try  to  reach  me  at
92comandante@zaralinux.com.
93
940.2 Legal Stuff
95---------------
96
97We don't  guarantee  the  correctness  of this document, and if you come to us
98complaining about  how  you  screwed  up  your  system  because  of  incorrect
99documentation, we won't feel responsible...
100
101Chapter 1: Collecting System Information
102========================================
103
104In This Chapter
105---------------
106* Investigating  the  properties  of  the  pseudo  file  system  /proc and its
107  ability to provide information on the running Linux system
108* Examining /proc's structure
109* Uncovering  various  information  about the kernel and the processes running
110  on the system
111
112------------------------------------------------------------------------------
113
114The proc  file  system acts as an interface to internal data structures in the
115kernel. It  can  be  used to obtain information about the system and to change
116certain kernel parameters at runtime (sysctl).
117
118First, we'll  take  a  look  at the read-only parts of /proc. In Chapter 2, we
119show you how you can use /proc/sys to change settings.
120
1211.1 Process-Specific Subdirectories
122-----------------------------------
123
124The directory  /proc  contains  (among other things) one subdirectory for each
125process running on the system, which is named after the process ID (PID).
126
127The link  'self'  points to  the process reading the file system. Each process
128subdirectory has the entries listed in Table 1-1.
129
130Note that an open file descriptor to /proc/<pid> or to any of its
131contained files or subdirectories does not prevent <pid> being reused
132for some other process in the event that <pid> exits. Operations on
133open /proc/<pid> file descriptors corresponding to dead processes
134never act on any new process that the kernel may, through chance, have
135also assigned the process ID <pid>. Instead, operations on these FDs
136usually fail with ESRCH.
137
138.. table:: Table 1-1: Process specific entries in /proc
139
140 =============  ===============================================================
141 File		Content
142 =============  ===============================================================
143 clear_refs	Clears page referenced bits shown in smaps output
144 cmdline	Command line arguments
145 cpu		Current and last cpu in which it was executed	(2.4)(smp)
146 cwd		Link to the current working directory
147 environ	Values of environment variables
148 exe		Link to the executable of this process
149 fd		Directory, which contains all file descriptors
150 maps		Memory maps to executables and library files	(2.4)
151 mem		Memory held by this process
152 root		Link to the root directory of this process
153 stat		Process status
154 statm		Process memory status information
155 status		Process status in human readable form
156 wchan		Present with CONFIG_KALLSYMS=y: it shows the kernel function
157		symbol the task is blocked in - or "0" if not blocked.
158 pagemap	Page table
159 stack		Report full stack trace, enable via CONFIG_STACKTRACE
160 smaps		An extension based on maps, showing the memory consumption of
161		each mapping and flags associated with it
162 smaps_rollup	Accumulated smaps stats for all mappings of the process.  This
163		can be derived from smaps, but is faster and more convenient
164 numa_maps	An extension based on maps, showing the memory locality and
165		binding policy as well as mem usage (in pages) of each mapping.
166 =============  ===============================================================
167
168For example, to get the status information of a process, all you have to do is
169read the file /proc/PID/status::
170
171  >cat /proc/self/status
172  Name:   cat
173  State:  R (running)
174  Tgid:   5452
175  Pid:    5452
176  PPid:   743
177  TracerPid:      0						(2.4)
178  Uid:    501     501     501     501
179  Gid:    100     100     100     100
180  FDSize: 256
181  Groups: 100 14 16
182  Kthread:    0
183  VmPeak:     5004 kB
184  VmSize:     5004 kB
185  VmLck:         0 kB
186  VmHWM:       476 kB
187  VmRSS:       476 kB
188  RssAnon:             352 kB
189  RssFile:             120 kB
190  RssShmem:              4 kB
191  VmData:      156 kB
192  VmStk:        88 kB
193  VmExe:        68 kB
194  VmLib:      1412 kB
195  VmPTE:        20 kb
196  VmSwap:        0 kB
197  HugetlbPages:          0 kB
198  CoreDumping:    0
199  THP_enabled:	  1
200  Threads:        1
201  SigQ:   0/28578
202  SigPnd: 0000000000000000
203  ShdPnd: 0000000000000000
204  SigBlk: 0000000000000000
205  SigIgn: 0000000000000000
206  SigCgt: 0000000000000000
207  CapInh: 00000000fffffeff
208  CapPrm: 0000000000000000
209  CapEff: 0000000000000000
210  CapBnd: ffffffffffffffff
211  CapAmb: 0000000000000000
212  NoNewPrivs:     0
213  Seccomp:        0
214  Speculation_Store_Bypass:       thread vulnerable
215  SpeculationIndirectBranch:      conditional enabled
216  voluntary_ctxt_switches:        0
217  nonvoluntary_ctxt_switches:     1
218
219This shows you nearly the same information you would get if you viewed it with
220the ps  command.  In  fact,  ps  uses  the  proc  file  system  to  obtain its
221information.  But you get a more detailed  view of the  process by reading the
222file /proc/PID/status. It fields are described in table 1-2.
223
224The  statm  file  contains  more  detailed  information about the process
225memory usage. Its seven fields are explained in Table 1-3.  The stat file
226contains detailed information about the process itself.  Its fields are
227explained in Table 1-4.
228
229(for SMP CONFIG users)
230
231For making accounting scalable, RSS related information are handled in an
232asynchronous manner and the value may not be very precise. To see a precise
233snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
234It's slow but very precise.
235
236.. table:: Table 1-2: Contents of the status fields (as of 4.19)
237
238 ==========================  ===================================================
239 Field                       Content
240 ==========================  ===================================================
241 Name                        filename of the executable
242 Umask                       file mode creation mask
243 State                       state (R is running, S is sleeping, D is sleeping
244                             in an uninterruptible wait, Z is zombie,
245			     T is traced or stopped)
246 Tgid                        thread group ID
247 Ngid                        NUMA group ID (0 if none)
248 Pid                         process id
249 PPid                        process id of the parent process
250 TracerPid                   PID of process tracing this process (0 if not, or
251                             the tracer is outside of the current pid namespace)
252 Uid                         Real, effective, saved set, and  file system UIDs
253 Gid                         Real, effective, saved set, and  file system GIDs
254 FDSize                      number of file descriptor slots currently allocated
255 Groups                      supplementary group list
256 NStgid                      descendant namespace thread group ID hierarchy
257 NSpid                       descendant namespace process ID hierarchy
258 NSpgid                      descendant namespace process group ID hierarchy
259 NSsid                       descendant namespace session ID hierarchy
260 Kthread                     kernel thread flag, 1 is yes, 0 is no
261 VmPeak                      peak virtual memory size
262 VmSize                      total program size
263 VmLck                       locked memory size
264 VmPin                       pinned memory size
265 VmHWM                       peak resident set size ("high water mark")
266 VmRSS                       size of memory portions. It contains the three
267                             following parts
268                             (VmRSS = RssAnon + RssFile + RssShmem)
269 RssAnon                     size of resident anonymous memory
270 RssFile                     size of resident file mappings
271 RssShmem                    size of resident shmem memory (includes SysV shm,
272                             mapping of tmpfs and shared anonymous mappings)
273 VmData                      size of private data segments
274 VmStk                       size of stack segments
275 VmExe                       size of text segment
276 VmLib                       size of shared library code
277 VmPTE                       size of page table entries
278 VmSwap                      amount of swap used by anonymous private data
279                             (shmem swap usage is not included)
280 HugetlbPages                size of hugetlb memory portions
281 CoreDumping                 process's memory is currently being dumped
282                             (killing the process may lead to a corrupted core)
283 THP_enabled		     process is allowed to use THP (returns 0 when
284			     PR_SET_THP_DISABLE is set on the process
285 Threads                     number of threads
286 SigQ                        number of signals queued/max. number for queue
287 SigPnd                      bitmap of pending signals for the thread
288 ShdPnd                      bitmap of shared pending signals for the process
289 SigBlk                      bitmap of blocked signals
290 SigIgn                      bitmap of ignored signals
291 SigCgt                      bitmap of caught signals
292 CapInh                      bitmap of inheritable capabilities
293 CapPrm                      bitmap of permitted capabilities
294 CapEff                      bitmap of effective capabilities
295 CapBnd                      bitmap of capabilities bounding set
296 CapAmb                      bitmap of ambient capabilities
297 NoNewPrivs                  no_new_privs, like prctl(PR_GET_NO_NEW_PRIV, ...)
298 Seccomp                     seccomp mode, like prctl(PR_GET_SECCOMP, ...)
299 Speculation_Store_Bypass    speculative store bypass mitigation status
300 SpeculationIndirectBranch   indirect branch speculation mode
301 Cpus_allowed                mask of CPUs on which this process may run
302 Cpus_allowed_list           Same as previous, but in "list format"
303 Mems_allowed                mask of memory nodes allowed to this process
304 Mems_allowed_list           Same as previous, but in "list format"
305 voluntary_ctxt_switches     number of voluntary context switches
306 nonvoluntary_ctxt_switches  number of non voluntary context switches
307 ==========================  ===================================================
308
309
310.. table:: Table 1-3: Contents of the statm fields (as of 2.6.8-rc3)
311
312 ======== ===============================	==============================
313 Field    Content
314 ======== ===============================	==============================
315 size     total program size (pages)		(same as VmSize in status)
316 resident size of memory portions (pages)	(same as VmRSS in status)
317 shared   number of pages that are shared	(i.e. backed by a file, same
318						as RssFile+RssShmem in status)
319 trs      number of pages that are 'code'	(not including libs; broken,
320						includes data segment)
321 lrs      number of pages of library		(always 0 on 2.6)
322 drs      number of pages of data/stack		(including libs; broken,
323						includes library text)
324 dt       number of dirty pages			(always 0 on 2.6)
325 ======== ===============================	==============================
326
327
328.. table:: Table 1-4: Contents of the stat fields (as of 2.6.30-rc7)
329
330  ============= ===============================================================
331  Field         Content
332  ============= ===============================================================
333  pid           process id
334  tcomm         filename of the executable
335  state         state (R is running, S is sleeping, D is sleeping in an
336                uninterruptible wait, Z is zombie, T is traced or stopped)
337  ppid          process id of the parent process
338  pgrp          pgrp of the process
339  sid           session id
340  tty_nr        tty the process uses
341  tty_pgrp      pgrp of the tty
342  flags         task flags
343  min_flt       number of minor faults
344  cmin_flt      number of minor faults with child's
345  maj_flt       number of major faults
346  cmaj_flt      number of major faults with child's
347  utime         user mode jiffies
348  stime         kernel mode jiffies
349  cutime        user mode jiffies with child's
350  cstime        kernel mode jiffies with child's
351  priority      priority level
352  nice          nice level
353  num_threads   number of threads
354  it_real_value	(obsolete, always 0)
355  start_time    time the process started after system boot
356  vsize         virtual memory size
357  rss           resident set memory size
358  rsslim        current limit in bytes on the rss
359  start_code    address above which program text can run
360  end_code      address below which program text can run
361  start_stack   address of the start of the main process stack
362  esp           current value of ESP
363  eip           current value of EIP
364  pending       bitmap of pending signals
365  blocked       bitmap of blocked signals
366  sigign        bitmap of ignored signals
367  sigcatch      bitmap of caught signals
368  0		(place holder, used to be the wchan address,
369		use /proc/PID/wchan instead)
370  0             (place holder)
371  0             (place holder)
372  exit_signal   signal to send to parent thread on exit
373  task_cpu      which CPU the task is scheduled on
374  rt_priority   realtime priority
375  policy        scheduling policy (man sched_setscheduler)
376  blkio_ticks   time spent waiting for block IO
377  gtime         guest time of the task in jiffies
378  cgtime        guest time of the task children in jiffies
379  start_data    address above which program data+bss is placed
380  end_data      address below which program data+bss is placed
381  start_brk     address above which program heap can be expanded with brk()
382  arg_start     address above which program command line is placed
383  arg_end       address below which program command line is placed
384  env_start     address above which program environment is placed
385  env_end       address below which program environment is placed
386  exit_code     the thread's exit_code in the form reported by the waitpid
387		system call
388  ============= ===============================================================
389
390The /proc/PID/maps file contains the currently mapped memory regions and
391their access permissions.
392
393The format is::
394
395    address           perms offset  dev   inode      pathname
396
397    08048000-08049000 r-xp 00000000 03:00 8312       /opt/test
398    08049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
399    0804a000-0806b000 rw-p 00000000 00:00 0          [heap]
400    a7cb1000-a7cb2000 ---p 00000000 00:00 0
401    a7cb2000-a7eb2000 rw-p 00000000 00:00 0
402    a7eb2000-a7eb3000 ---p 00000000 00:00 0
403    a7eb3000-a7ed5000 rw-p 00000000 00:00 0
404    a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/libc.so.6
405    a8008000-a800a000 r--p 00133000 03:00 4222       /lib/libc.so.6
406    a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/libc.so.6
407    a800b000-a800e000 rw-p 00000000 00:00 0
408    a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/libpthread.so.0
409    a8022000-a8023000 r--p 00013000 03:00 14462      /lib/libpthread.so.0
410    a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/libpthread.so.0
411    a8024000-a8027000 rw-p 00000000 00:00 0
412    a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/ld-linux.so.2
413    a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/ld-linux.so.2
414    a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/ld-linux.so.2
415    aff35000-aff4a000 rw-p 00000000 00:00 0          [stack]
416    ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
417
418where "address" is the address space in the process that it occupies, "perms"
419is a set of permissions::
420
421 r = read
422 w = write
423 x = execute
424 s = shared
425 p = private (copy on write)
426
427"offset" is the offset into the mapping, "dev" is the device (major:minor), and
428"inode" is the inode  on that device.  0 indicates that  no inode is associated
429with the memory region, as the case would be with BSS (uninitialized data).
430The "pathname" shows the name associated file for this mapping.  If the mapping
431is not associated with a file:
432
433 ===================        ===========================================
434 [heap]                     the heap of the program
435 [stack]                    the stack of the main process
436 [vdso]                     the "virtual dynamic shared object",
437                            the kernel system call handler
438 [anon:<name>]              a private anonymous mapping that has been
439                            named by userspace
440 [anon_shmem:<name>]        an anonymous shared memory mapping that has
441                            been named by userspace
442 ===================        ===========================================
443
444 or if empty, the mapping is anonymous.
445
446Starting with 6.11 kernel, /proc/PID/maps provides an alternative
447ioctl()-based API that gives ability to flexibly and efficiently query and
448filter individual VMAs. This interface is binary and is meant for more
449efficient and easy programmatic use. `struct procmap_query`, defined in
450linux/fs.h UAPI header, serves as an input/output argument to the
451`PROCMAP_QUERY` ioctl() command. See comments in linus/fs.h UAPI header for
452details on query semantics, supported flags, data returned, and general API
453usage information.
454
455The /proc/PID/smaps is an extension based on maps, showing the memory
456consumption for each of the process's mappings. For each mapping (aka Virtual
457Memory Area, or VMA) there is a series of lines such as the following::
458
459    08048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
460
461    Size:               1084 kB
462    KernelPageSize:        4 kB
463    MMUPageSize:           4 kB
464    Rss:                 892 kB
465    Pss:                 374 kB
466    Pss_Dirty:             0 kB
467    Shared_Clean:        892 kB
468    Shared_Dirty:          0 kB
469    Private_Clean:         0 kB
470    Private_Dirty:         0 kB
471    Referenced:          892 kB
472    Anonymous:             0 kB
473    KSM:                   0 kB
474    LazyFree:              0 kB
475    AnonHugePages:         0 kB
476    ShmemPmdMapped:        0 kB
477    Shared_Hugetlb:        0 kB
478    Private_Hugetlb:       0 kB
479    Swap:                  0 kB
480    SwapPss:               0 kB
481    KernelPageSize:        4 kB
482    MMUPageSize:           4 kB
483    Locked:                0 kB
484    THPeligible:           0
485    VmFlags: rd ex mr mw me dw
486
487The first of these lines shows the same information as is displayed for the
488mapping in /proc/PID/maps.  Following lines show the size of the mapping
489(size); the size of each page allocated when backing a VMA (KernelPageSize),
490which is usually the same as the size in the page table entries; the page size
491used by the MMU when backing a VMA (in most cases, the same as KernelPageSize);
492the amount of the mapping that is currently resident in RAM (RSS); the
493process' proportional share of this mapping (PSS); and the number of clean and
494dirty shared and private pages in the mapping.
495
496The "proportional set size" (PSS) of a process is the count of pages it has
497in memory, where each page is divided by the number of processes sharing it.
498So if a process has 1000 pages all to itself, and 1000 shared with one other
499process, its PSS will be 1500.  "Pss_Dirty" is the portion of PSS which
500consists of dirty pages.  ("Pss_Clean" is not included, but it can be
501calculated by subtracting "Pss_Dirty" from "Pss".)
502
503Note that even a page which is part of a MAP_SHARED mapping, but has only
504a single pte mapped, i.e.  is currently used by only one process, is accounted
505as private and not as shared.
506
507"Referenced" indicates the amount of memory currently marked as referenced or
508accessed.
509
510"Anonymous" shows the amount of memory that does not belong to any file.  Even
511a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
512and a page is modified, the file page is replaced by a private anonymous copy.
513
514"KSM" reports how many of the pages are KSM pages. Note that KSM-placed zeropages
515are not included, only actual KSM pages.
516
517"LazyFree" shows the amount of memory which is marked by madvise(MADV_FREE).
518The memory isn't freed immediately with madvise(). It's freed in memory
519pressure if the memory is clean. Please note that the printed value might
520be lower than the real value due to optimizations used in the current
521implementation. If this is not desirable please file a bug report.
522
523"AnonHugePages" shows the amount of memory backed by transparent hugepage.
524
525"ShmemPmdMapped" shows the amount of shared (shmem/tmpfs) memory backed by
526huge pages.
527
528"Shared_Hugetlb" and "Private_Hugetlb" show the amounts of memory backed by
529hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical
530reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field.
531
532"Swap" shows how much would-be-anonymous memory is also used, but out on swap.
533
534For shmem mappings, "Swap" includes also the size of the mapped (and not
535replaced by copy-on-write) part of the underlying shmem object out on swap.
536"SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
537does not take into account swapped out page of underlying shmem objects.
538"Locked" indicates whether the mapping is locked in memory or not.
539
540"THPeligible" indicates whether the mapping is eligible for allocating
541naturally aligned THP pages of any currently enabled size. 1 if true, 0
542otherwise.
543
544"VmFlags" field deserves a separate description. This member represents the
545kernel flags associated with the particular virtual memory area in two letter
546encoded manner. The codes are the following:
547
548    ==    =======================================
549    rd    readable
550    wr    writeable
551    ex    executable
552    sh    shared
553    mr    may read
554    mw    may write
555    me    may execute
556    ms    may share
557    gd    stack segment growns down
558    pf    pure PFN range
559    dw    disabled write to the mapped file
560    lo    pages are locked in memory
561    io    memory mapped I/O area
562    sr    sequential read advise provided
563    rr    random read advise provided
564    dc    do not copy area on fork
565    de    do not expand area on remapping
566    ac    area is accountable
567    nr    swap space is not reserved for the area
568    ht    area uses huge tlb pages
569    sf    synchronous page fault
570    ar    architecture specific flag
571    wf    wipe on fork
572    dd    do not include area into core dump
573    sd    soft dirty flag
574    mm    mixed map area
575    hg    huge page advise flag
576    nh    no huge page advise flag
577    mg    mergeable advise flag
578    bt    arm64 BTI guarded page
579    mt    arm64 MTE allocation tags are enabled
580    um    userfaultfd missing tracking
581    uw    userfaultfd wr-protect tracking
582    ss    shadow/guarded control stack page
583    sl    sealed
584    ==    =======================================
585
586Note that there is no guarantee that every flag and associated mnemonic will
587be present in all further kernel releases. Things get changed, the flags may
588be vanished or the reverse -- new added. Interpretation of their meaning
589might change in future as well. So each consumer of these flags has to
590follow each specific kernel version for the exact semantic.
591
592This file is only present if the CONFIG_MMU kernel configuration option is
593enabled.
594
595Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy (consistent
596output can be achieved only in the single read call).
597
598This typically manifests when doing partial reads of these files while the
599memory map is being modified.  Despite the races, we do provide the following
600guarantees:
601
6021) The mapped addresses never go backwards, which implies no two
603   regions will ever overlap.
6042) If there is something at a given vaddr during the entirety of the
605   life of the smaps/maps walk, there will be some output for it.
606
607The /proc/PID/smaps_rollup file includes the same fields as /proc/PID/smaps,
608but their values are the sums of the corresponding values for all mappings of
609the process.  Additionally, it contains these fields:
610
611- Pss_Anon
612- Pss_File
613- Pss_Shmem
614
615They represent the proportional shares of anonymous, file, and shmem pages, as
616described for smaps above.  These fields are omitted in smaps since each
617mapping identifies the type (anon, file, or shmem) of all pages it contains.
618Thus all information in smaps_rollup can be derived from smaps, but at a
619significantly higher cost.
620
621The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
622bits on both physical and virtual pages associated with a process, and the
623soft-dirty bit on pte (see Documentation/admin-guide/mm/soft-dirty.rst
624for details).
625To clear the bits for all the pages associated with the process::
626
627    > echo 1 > /proc/PID/clear_refs
628
629To clear the bits for the anonymous pages associated with the process::
630
631    > echo 2 > /proc/PID/clear_refs
632
633To clear the bits for the file mapped pages associated with the process::
634
635    > echo 3 > /proc/PID/clear_refs
636
637To clear the soft-dirty bit::
638
639    > echo 4 > /proc/PID/clear_refs
640
641To reset the peak resident set size ("high water mark") to the process's
642current value::
643
644    > echo 5 > /proc/PID/clear_refs
645
646Any other value written to /proc/PID/clear_refs will have no effect.
647
648The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
649using /proc/kpageflags and number of times a page is mapped using
650/proc/kpagecount. For detailed explanation, see
651Documentation/admin-guide/mm/pagemap.rst.
652
653The /proc/pid/numa_maps is an extension based on maps, showing the memory
654locality and binding policy, as well as the memory usage (in pages) of
655each mapping. The output follows a general format where mapping details get
656summarized separated by blank spaces, one mapping per each file line::
657
658    address   policy    mapping details
659
660    00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
661    00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
662    3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
663    320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
664    3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
665    3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
666    3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
667    320698b000 default file=/lib64/libc-2.12.so
668    3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4
669    3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
670    3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
671    7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
672    7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
673    7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
674    7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
675    7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4
676
677Where:
678
679"address" is the starting address for the mapping;
680
681"policy" reports the NUMA memory policy set for the mapping (see Documentation/admin-guide/mm/numa_memory_policy.rst);
682
683"mapping details" summarizes mapping data such as mapping type, page usage counters,
684node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
685size, in KB, that is backing the mapping up.
686
6871.2 Kernel data
688---------------
689
690Similar to  the  process entries, the kernel data files give information about
691the running kernel. The files used to obtain this information are contained in
692/proc and  are  listed  in Table 1-5. Not all of these will be present in your
693system. It  depends  on the kernel configuration and the loaded modules, which
694files are there, and which are missing.
695
696.. table:: Table 1-5: Kernel info in /proc
697
698 ============ ===============================================================
699 File         Content
700 ============ ===============================================================
701 allocinfo    Memory allocations profiling information
702 apm          Advanced power management info
703 bootconfig   Kernel command line obtained from boot config,
704 	      and, if there were kernel parameters from the
705	      boot loader, a "# Parameters from bootloader:"
706	      line followed by a line containing those
707	      parameters prefixed by "# ".			(5.5)
708 buddyinfo    Kernel memory allocator information (see text)	(2.5)
709 bus          Directory containing bus specific information
710 cmdline      Kernel command line, both from bootloader and embedded
711              in the kernel image
712 cpuinfo      Info about the CPU
713 devices      Available devices (block and character)
714 dma          Used DMS channels
715 filesystems  Supported filesystems
716 driver       Various drivers grouped here, currently rtc	(2.4)
717 execdomains  Execdomains, related to security			(2.4)
718 fb 	      Frame Buffer devices				(2.4)
719 fs 	      File system parameters, currently nfs/exports	(2.4)
720 ide          Directory containing info about the IDE subsystem
721 interrupts   Interrupt usage
722 iomem 	      Memory map					(2.4)
723 ioports      I/O port usage
724 irq 	      Masks for irq to cpu affinity			(2.4)(smp?)
725 isapnp       ISA PnP (Plug&Play) Info				(2.4)
726 kcore        Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
727 kmsg         Kernel messages
728 ksyms        Kernel symbol table
729 loadavg      Load average of last 1, 5 & 15 minutes;
730                number of processes currently runnable (running or on ready queue);
731                total number of processes in system;
732                last pid created.
733                All fields are separated by one space except "number of
734                processes currently runnable" and "total number of processes
735                in system", which are separated by a slash ('/'). Example:
736                0.61 0.61 0.55 3/828 22084
737 locks        Kernel locks
738 meminfo      Memory info
739 misc         Miscellaneous
740 modules      List of loaded modules
741 mounts       Mounted filesystems
742 net          Networking info (see text)
743 pagetypeinfo Additional page allocator information (see text)  (2.5)
744 partitions   Table of partitions known to the system
745 pci 	      Deprecated info of PCI bus (new way -> /proc/bus/pci/,
746              decoupled by lspci				(2.4)
747 rtc          Real time clock
748 scsi         SCSI info (see text)
749 slabinfo     Slab pool info
750 softirqs     softirq usage
751 stat         Overall statistics
752 swaps        Swap space utilization
753 sys          See chapter 2
754 sysvipc      Info of SysVIPC Resources (msg, sem, shm)		(2.4)
755 tty 	      Info of tty drivers
756 uptime       Wall clock since boot, combined idle time of all cpus
757 version      Kernel version
758 video 	      bttv info of video resources			(2.4)
759 vmallocinfo  Show vmalloced areas
760 ============ ===============================================================
761
762You can,  for  example,  check  which interrupts are currently in use and what
763they are used for by looking in the file /proc/interrupts::
764
765  > cat /proc/interrupts
766             CPU0
767    0:    8728810          XT-PIC  timer
768    1:        895          XT-PIC  keyboard
769    2:          0          XT-PIC  cascade
770    3:     531695          XT-PIC  aha152x
771    4:    2014133          XT-PIC  serial
772    5:      44401          XT-PIC  pcnet_cs
773    8:          2          XT-PIC  rtc
774   11:          8          XT-PIC  i82365
775   12:     182918          XT-PIC  PS/2 Mouse
776   13:          1          XT-PIC  fpu
777   14:    1232265          XT-PIC  ide0
778   15:          7          XT-PIC  ide1
779  NMI:          0
780
781In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
782output of a SMP machine)::
783
784  > cat /proc/interrupts
785
786             CPU0       CPU1
787    0:    1243498    1214548    IO-APIC-edge  timer
788    1:       8949       8958    IO-APIC-edge  keyboard
789    2:          0          0          XT-PIC  cascade
790    5:      11286      10161    IO-APIC-edge  soundblaster
791    8:          1          0    IO-APIC-edge  rtc
792    9:      27422      27407    IO-APIC-edge  3c503
793   12:     113645     113873    IO-APIC-edge  PS/2 Mouse
794   13:          0          0          XT-PIC  fpu
795   14:      22491      24012    IO-APIC-edge  ide0
796   15:       2183       2415    IO-APIC-edge  ide1
797   17:      30564      30414   IO-APIC-level  eth0
798   18:        177        164   IO-APIC-level  bttv
799  NMI:    2457961    2457959
800  LOC:    2457882    2457881
801  ERR:       2155
802
803NMI is incremented in this case because every timer interrupt generates a NMI
804(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
805
806LOC is the local interrupt counter of the internal APIC of every CPU.
807
808ERR is incremented in the case of errors in the IO-APIC bus (the bus that
809connects the CPUs in a SMP system. This means that an error has been detected,
810the IO-APIC automatically retry the transmission, so it should not be a big
811problem, but you should read the SMP-FAQ.
812
813In 2.6.2* /proc/interrupts was expanded again.  This time the goal was for
814/proc/interrupts to display every IRQ vector in use by the system, not
815just those considered 'most important'.  The new vectors are:
816
817THR
818  interrupt raised when a machine check threshold counter
819  (typically counting ECC corrected errors of memory or cache) exceeds
820  a configurable threshold.  Only available on some systems.
821
822TRM
823  a thermal event interrupt occurs when a temperature threshold
824  has been exceeded for the CPU.  This interrupt may also be generated
825  when the temperature drops back to normal.
826
827SPU
828  a spurious interrupt is some interrupt that was raised then lowered
829  by some IO device before it could be fully processed by the APIC.  Hence
830  the APIC sees the interrupt but does not know what device it came from.
831  For this case the APIC will generate the interrupt with a IRQ vector
832  of 0xff. This might also be generated by chipset bugs.
833
834RES, CAL, TLB
835  rescheduling, call and TLB flush interrupts are
836  sent from one CPU to another per the needs of the OS.  Typically,
837  their statistics are used by kernel developers and interested users to
838  determine the occurrence of interrupts of the given type.
839
840The above IRQ vectors are displayed only when relevant.  For example,
841the threshold vector does not exist on x86_64 platforms.  Others are
842suppressed when the system is a uniprocessor.  As of this writing, only
843i386 and x86_64 platforms support the new IRQ vector displays.
844
845Of some interest is the introduction of the /proc/irq directory to 2.4.
846It could be used to set IRQ to CPU affinity. This means that you can "hook" an
847IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
848irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
849prof_cpu_mask.
850
851For example::
852
853  > ls /proc/irq/
854  0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
855  1  11  13  15  17  19  3  5  7  9  default_smp_affinity
856  > ls /proc/irq/0/
857  smp_affinity
858
859smp_affinity is a bitmask, in which you can specify which CPUs can handle the
860IRQ. You can set it by doing::
861
862  > echo 1 > /proc/irq/10/smp_affinity
863
864This means that only the first CPU will handle the IRQ, but you can also echo
8655 which means that only the first and third CPU can handle the IRQ.
866
867The contents of each smp_affinity file is the same by default::
868
869  > cat /proc/irq/0/smp_affinity
870  ffffffff
871
872There is an alternate interface, smp_affinity_list which allows specifying
873a CPU range instead of a bitmask::
874
875  > cat /proc/irq/0/smp_affinity_list
876  1024-1031
877
878The default_smp_affinity mask applies to all non-active IRQs, which are the
879IRQs which have not yet been allocated/activated, and hence which lack a
880/proc/irq/[0-9]* directory.
881
882The node file on an SMP system shows the node to which the device using the IRQ
883reports itself as being attached. This hardware locality information does not
884include information about any possible driver locality preference.
885
886prof_cpu_mask specifies which CPUs are to be profiled by the system wide
887profiler. Default value is ffffffff (all CPUs if there are only 32 of them).
888
889The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
890between all the CPUs which are allowed to handle it. As usual the kernel has
891more info than you and does a better job than you, so the defaults are the
892best choice for almost everyone.  [Note this applies only to those IO-APIC's
893that support "Round Robin" interrupt distribution.]
894
895There are  three  more  important subdirectories in /proc: net, scsi, and sys.
896The general  rule  is  that  the  contents,  or  even  the  existence of these
897directories, depend  on your kernel configuration. If SCSI is not enabled, the
898directory scsi  may  not  exist. The same is true with the net, which is there
899only when networking support is present in the running kernel.
900
901The slabinfo  file  gives  information  about  memory usage at the slab level.
902Linux uses  slab  pools for memory management above page level in version 2.2.
903Commonly used  objects  have  their  own  slab  pool (such as network buffers,
904directory cache, and so on).
905
906::
907
908    > cat /proc/buddyinfo
909
910    Node 0, zone      DMA      0      4      5      4      4      3 ...
911    Node 0, zone   Normal      1      0      0      1    101      8 ...
912    Node 0, zone  HighMem      2      0      0      1      1      0 ...
913
914External fragmentation is a problem under some workloads, and buddyinfo is a
915useful tool for helping diagnose these problems.  Buddyinfo will give you a
916clue as to how big an area you can safely allocate, or why a previous
917allocation failed.
918
919Each column represents the number of pages of a certain order which are
920available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
921ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
922available in ZONE_NORMAL, etc...
923
924More information relevant to external fragmentation can be found in
925pagetypeinfo::
926
927    > cat /proc/pagetypeinfo
928    Page block order: 9
929    Pages per block:  512
930
931    Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
932    Node    0, zone      DMA, type    Unmovable      0      0      0      1      1      1      1      1      1      1      0
933    Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0
934    Node    0, zone      DMA, type      Movable      1      1      2      1      2      1      1      0      1      0      2
935    Node    0, zone      DMA, type      Reserve      0      0      0      0      0      0      0      0      0      1      0
936    Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
937    Node    0, zone    DMA32, type    Unmovable    103     54     77      1      1      1     11      8      7      1      9
938    Node    0, zone    DMA32, type  Reclaimable      0      0      2      1      0      0      0      0      1      0      0
939    Node    0, zone    DMA32, type      Movable    169    152    113     91     77     54     39     13      6      1    452
940    Node    0, zone    DMA32, type      Reserve      1      2      2      2      2      0      1      1      1      1      0
941    Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
942
943    Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate
944    Node 0, zone      DMA            2            0            5            1            0
945    Node 0, zone    DMA32           41            6          967            2            0
946
947Fragmentation avoidance in the kernel works by grouping pages of different
948migrate types into the same contiguous regions of memory called page blocks.
949A page block is typically the size of the default hugepage size, e.g. 2MB on
950X86-64. By keeping pages grouped based on their ability to move, the kernel
951can reclaim pages within a page block to satisfy a high-order allocation.
952
953The pagetypinfo begins with information on the size of a page block. It
954then gives the same type of information as buddyinfo except broken down
955by migrate-type and finishes with details on how many page blocks of each
956type exist.
957
958If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
959from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can
960make an estimate of the likely number of huge pages that can be allocated
961at a given point in time. All the "Movable" blocks should be allocatable
962unless memory has been mlock()'d. Some of the Reclaimable blocks should
963also be allocatable although a lot of filesystem metadata may have to be
964reclaimed to achieve this.
965
966
967allocinfo
968~~~~~~~~~
969
970Provides information about memory allocations at all locations in the code
971base. Each allocation in the code is identified by its source file, line
972number, module (if originates from a loadable module) and the function calling
973the allocation. The number of bytes allocated and number of calls at each
974location are reported. The first line indicates the version of the file, the
975second line is the header listing fields in the file.
976
977Example output.
978
979::
980
981    > tail -n +3 /proc/allocinfo | sort -rn
982   127664128    31168 mm/page_ext.c:270 func:alloc_page_ext
983    56373248     4737 mm/slub.c:2259 func:alloc_slab_page
984    14880768     3633 mm/readahead.c:247 func:page_cache_ra_unbounded
985    14417920     3520 mm/mm_init.c:2530 func:alloc_large_system_hash
986    13377536      234 block/blk-mq.c:3421 func:blk_mq_alloc_rqs
987    11718656     2861 mm/filemap.c:1919 func:__filemap_get_folio
988     9192960     2800 kernel/fork.c:307 func:alloc_thread_stack_node
989     4206592        4 net/netfilter/nf_conntrack_core.c:2567 func:nf_ct_alloc_hashtable
990     4136960     1010 drivers/staging/ctagmod/ctagmod.c:20 [ctagmod] func:ctagmod_start
991     3940352      962 mm/memory.c:4214 func:alloc_anon_folio
992     2894464    22613 fs/kernfs/dir.c:615 func:__kernfs_new_node
993     ...
994
995
996meminfo
997~~~~~~~
998
999Provides information about distribution and utilization of memory.  This
1000varies by architecture and compile options.  Some of the counters reported
1001here overlap.  The memory reported by the non overlapping counters may not
1002add up to the overall memory usage and the difference for some workloads
1003can be substantial.  In many cases there are other means to find out
1004additional memory using subsystem specific interfaces, for instance
1005/proc/net/sockstat for TCP memory allocations.
1006
1007Example output. You may not have all of these fields.
1008
1009::
1010
1011    > cat /proc/meminfo
1012
1013    MemTotal:       32858820 kB
1014    MemFree:        21001236 kB
1015    MemAvailable:   27214312 kB
1016    Buffers:          581092 kB
1017    Cached:          5587612 kB
1018    SwapCached:            0 kB
1019    Active:          3237152 kB
1020    Inactive:        7586256 kB
1021    Active(anon):      94064 kB
1022    Inactive(anon):  4570616 kB
1023    Active(file):    3143088 kB
1024    Inactive(file):  3015640 kB
1025    Unevictable:           0 kB
1026    Mlocked:               0 kB
1027    SwapTotal:             0 kB
1028    SwapFree:              0 kB
1029    Zswap:              1904 kB
1030    Zswapped:           7792 kB
1031    Dirty:                12 kB
1032    Writeback:             0 kB
1033    AnonPages:       4654780 kB
1034    Mapped:           266244 kB
1035    Shmem:              9976 kB
1036    KReclaimable:     517708 kB
1037    Slab:             660044 kB
1038    SReclaimable:     517708 kB
1039    SUnreclaim:       142336 kB
1040    KernelStack:       11168 kB
1041    PageTables:        20540 kB
1042    SecPageTables:         0 kB
1043    NFS_Unstable:          0 kB
1044    Bounce:                0 kB
1045    WritebackTmp:          0 kB
1046    CommitLimit:    16429408 kB
1047    Committed_AS:    7715148 kB
1048    VmallocTotal:   34359738367 kB
1049    VmallocUsed:       40444 kB
1050    VmallocChunk:          0 kB
1051    Percpu:            29312 kB
1052    EarlyMemtestBad:       0 kB
1053    HardwareCorrupted:     0 kB
1054    AnonHugePages:   4149248 kB
1055    ShmemHugePages:        0 kB
1056    ShmemPmdMapped:        0 kB
1057    FileHugePages:         0 kB
1058    FilePmdMapped:         0 kB
1059    CmaTotal:              0 kB
1060    CmaFree:               0 kB
1061    HugePages_Total:       0
1062    HugePages_Free:        0
1063    HugePages_Rsvd:        0
1064    HugePages_Surp:        0
1065    Hugepagesize:       2048 kB
1066    Hugetlb:               0 kB
1067    DirectMap4k:      401152 kB
1068    DirectMap2M:    10008576 kB
1069    DirectMap1G:    24117248 kB
1070
1071MemTotal
1072              Total usable RAM (i.e. physical RAM minus a few reserved
1073              bits and the kernel binary code)
1074MemFree
1075              Total free RAM. On highmem systems, the sum of LowFree+HighFree
1076MemAvailable
1077              An estimate of how much memory is available for starting new
1078              applications, without swapping. Calculated from MemFree,
1079              SReclaimable, the size of the file LRU lists, and the low
1080              watermarks in each zone.
1081              The estimate takes into account that the system needs some
1082              page cache to function well, and that not all reclaimable
1083              slab will be reclaimable, due to items being in use. The
1084              impact of those factors will vary from system to system.
1085Buffers
1086              Relatively temporary storage for raw disk blocks
1087              shouldn't get tremendously large (20MB or so)
1088Cached
1089              In-memory cache for files read from the disk (the
1090              pagecache) as well as tmpfs & shmem.
1091              Doesn't include SwapCached.
1092SwapCached
1093              Memory that once was swapped out, is swapped back in but
1094              still also is in the swapfile (if memory is needed it
1095              doesn't need to be swapped out AGAIN because it is already
1096              in the swapfile. This saves I/O)
1097Active
1098              Memory that has been used more recently and usually not
1099              reclaimed unless absolutely necessary.
1100Inactive
1101              Memory which has been less recently used.  It is more
1102              eligible to be reclaimed for other purposes
1103Unevictable
1104              Memory allocated for userspace which cannot be reclaimed, such
1105              as mlocked pages, ramfs backing pages, secret memfd pages etc.
1106Mlocked
1107              Memory locked with mlock().
1108HighTotal, HighFree
1109              Highmem is all memory above ~860MB of physical memory.
1110              Highmem areas are for use by userspace programs, or
1111              for the pagecache.  The kernel must use tricks to access
1112              this memory, making it slower to access than lowmem.
1113LowTotal, LowFree
1114              Lowmem is memory which can be used for everything that
1115              highmem can be used for, but it is also available for the
1116              kernel's use for its own data structures.  Among many
1117              other things, it is where everything from the Slab is
1118              allocated.  Bad things happen when you're out of lowmem.
1119SwapTotal
1120              total amount of swap space available
1121SwapFree
1122              Memory which has been evicted from RAM, and is temporarily
1123              on the disk
1124Zswap
1125              Memory consumed by the zswap backend (compressed size)
1126Zswapped
1127              Amount of anonymous memory stored in zswap (original size)
1128Dirty
1129              Memory which is waiting to get written back to the disk
1130Writeback
1131              Memory which is actively being written back to the disk
1132AnonPages
1133              Non-file backed pages mapped into userspace page tables
1134Mapped
1135              files which have been mmapped, such as libraries
1136Shmem
1137              Total memory used by shared memory (shmem) and tmpfs
1138KReclaimable
1139              Kernel allocations that the kernel will attempt to reclaim
1140              under memory pressure. Includes SReclaimable (below), and other
1141              direct allocations with a shrinker.
1142Slab
1143              in-kernel data structures cache
1144SReclaimable
1145              Part of Slab, that might be reclaimed, such as caches
1146SUnreclaim
1147              Part of Slab, that cannot be reclaimed on memory pressure
1148KernelStack
1149              Memory consumed by the kernel stacks of all tasks
1150PageTables
1151              Memory consumed by userspace page tables
1152SecPageTables
1153              Memory consumed by secondary page tables, this currently includes
1154              KVM mmu and IOMMU allocations on x86 and arm64.
1155NFS_Unstable
1156              Always zero. Previous counted pages which had been written to
1157              the server, but has not been committed to stable storage.
1158Bounce
1159              Memory used for block device "bounce buffers"
1160WritebackTmp
1161              Memory used by FUSE for temporary writeback buffers
1162CommitLimit
1163              Based on the overcommit ratio ('vm.overcommit_ratio'),
1164              this is the total amount of  memory currently available to
1165              be allocated on the system. This limit is only adhered to
1166              if strict overcommit accounting is enabled (mode 2 in
1167              'vm.overcommit_memory').
1168
1169              The CommitLimit is calculated with the following formula::
1170
1171                CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
1172                               overcommit_ratio / 100 + [total swap pages]
1173
1174              For example, on a system with 1G of physical RAM and 7G
1175              of swap with a `vm.overcommit_ratio` of 30 it would
1176              yield a CommitLimit of 7.3G.
1177
1178              For more details, see the memory overcommit documentation
1179              in mm/overcommit-accounting.
1180Committed_AS
1181              The amount of memory presently allocated on the system.
1182              The committed memory is a sum of all of the memory which
1183              has been allocated by processes, even if it has not been
1184              "used" by them as of yet. A process which malloc()'s 1G
1185              of memory, but only touches 300M of it will show up as
1186              using 1G. This 1G is memory which has been "committed" to
1187              by the VM and can be used at any time by the allocating
1188              application. With strict overcommit enabled on the system
1189              (mode 2 in 'vm.overcommit_memory'), allocations which would
1190              exceed the CommitLimit (detailed above) will not be permitted.
1191              This is useful if one needs to guarantee that processes will
1192              not fail due to lack of memory once that memory has been
1193              successfully allocated.
1194VmallocTotal
1195              total size of vmalloc virtual address space
1196VmallocUsed
1197              amount of vmalloc area which is used
1198VmallocChunk
1199              largest contiguous block of vmalloc area which is free
1200Percpu
1201              Memory allocated to the percpu allocator used to back percpu
1202              allocations. This stat excludes the cost of metadata.
1203EarlyMemtestBad
1204              The amount of RAM/memory in kB, that was identified as corrupted
1205              by early memtest. If memtest was not run, this field will not
1206              be displayed at all. Size is never rounded down to 0 kB.
1207              That means if 0 kB is reported, you can safely assume
1208              there was at least one pass of memtest and none of the passes
1209              found a single faulty byte of RAM.
1210HardwareCorrupted
1211              The amount of RAM/memory in KB, the kernel identifies as
1212              corrupted.
1213AnonHugePages
1214              Non-file backed huge pages mapped into userspace page tables
1215ShmemHugePages
1216              Memory used by shared memory (shmem) and tmpfs allocated
1217              with huge pages
1218ShmemPmdMapped
1219              Shared memory mapped into userspace with huge pages
1220FileHugePages
1221              Memory used for filesystem data (page cache) allocated
1222              with huge pages
1223FilePmdMapped
1224              Page cache mapped into userspace with huge pages
1225CmaTotal
1226              Memory reserved for the Contiguous Memory Allocator (CMA)
1227CmaFree
1228              Free remaining memory in the CMA reserves
1229HugePages_Total, HugePages_Free, HugePages_Rsvd, HugePages_Surp, Hugepagesize, Hugetlb
1230              See Documentation/admin-guide/mm/hugetlbpage.rst.
1231DirectMap4k, DirectMap2M, DirectMap1G
1232              Breakdown of page table sizes used in the kernel's
1233              identity mapping of RAM
1234
1235vmallocinfo
1236~~~~~~~~~~~
1237
1238Provides information about vmalloced/vmaped areas. One line per area,
1239containing the virtual address range of the area, size in bytes,
1240caller information of the creator, and optional information depending
1241on the kind of area:
1242
1243 ==========  ===================================================
1244 pages=nr    number of pages
1245 phys=addr   if a physical address was specified
1246 ioremap     I/O mapping (ioremap() and friends)
1247 vmalloc     vmalloc() area
1248 vmap        vmap()ed pages
1249 user        VM_USERMAP area
1250 vpages      buffer for pages pointers was vmalloced (huge area)
1251 N<node>=nr  (Only on NUMA kernels)
1252             Number of pages allocated on memory node <node>
1253 ==========  ===================================================
1254
1255::
1256
1257    > cat /proc/vmallocinfo
1258    0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
1259    /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
1260    0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
1261    /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
1262    0xffffc20000302000-0xffffc20000304000    8192 acpi_tb_verify_table+0x21/0x4f...
1263    phys=7fee8000 ioremap
1264    0xffffc20000304000-0xffffc20000307000   12288 acpi_tb_verify_table+0x21/0x4f...
1265    phys=7fee7000 ioremap
1266    0xffffc2000031d000-0xffffc2000031f000    8192 init_vdso_vars+0x112/0x210
1267    0xffffc2000031f000-0xffffc2000032b000   49152 cramfs_uncompress_init+0x2e ...
1268    /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
1269    0xffffc2000033a000-0xffffc2000033d000   12288 sys_swapon+0x640/0xac0      ...
1270    pages=2 vmalloc N1=2
1271    0xffffc20000347000-0xffffc2000034c000   20480 xt_alloc_table_info+0xfe ...
1272    /0x130 [x_tables] pages=4 vmalloc N0=4
1273    0xffffffffa0000000-0xffffffffa000f000   61440 sys_init_module+0xc27/0x1d00 ...
1274    pages=14 vmalloc N2=14
1275    0xffffffffa000f000-0xffffffffa0014000   20480 sys_init_module+0xc27/0x1d00 ...
1276    pages=4 vmalloc N1=4
1277    0xffffffffa0014000-0xffffffffa0017000   12288 sys_init_module+0xc27/0x1d00 ...
1278    pages=2 vmalloc N1=2
1279    0xffffffffa0017000-0xffffffffa0022000   45056 sys_init_module+0xc27/0x1d00 ...
1280    pages=10 vmalloc N0=10
1281
1282
1283softirqs
1284~~~~~~~~
1285
1286Provides counts of softirq handlers serviced since boot time, for each CPU.
1287
1288::
1289
1290    > cat /proc/softirqs
1291		  CPU0       CPU1       CPU2       CPU3
1292	HI:          0          0          0          0
1293    TIMER:       27166      27120      27097      27034
1294    NET_TX:          0          0          0         17
1295    NET_RX:         42          0          0         39
1296    BLOCK:           0          0        107       1121
1297    TASKLET:         0          0          0        290
1298    SCHED:       27035      26983      26971      26746
1299    HRTIMER:         0          0          0          0
1300	RCU:      1678       1769       2178       2250
1301
13021.3 Networking info in /proc/net
1303--------------------------------
1304
1305The subdirectory  /proc/net  follows  the  usual  pattern. Table 1-8 shows the
1306additional values  you  get  for  IP  version 6 if you configure the kernel to
1307support this. Table 1-9 lists the files and their meaning.
1308
1309
1310.. table:: Table 1-8: IPv6 info in /proc/net
1311
1312 ========== =====================================================
1313 File       Content
1314 ========== =====================================================
1315 udp6       UDP sockets (IPv6)
1316 tcp6       TCP sockets (IPv6)
1317 raw6       Raw device statistics (IPv6)
1318 igmp6      IP multicast addresses, which this host joined (IPv6)
1319 if_inet6   List of IPv6 interface addresses
1320 ipv6_route Kernel routing table for IPv6
1321 rt6_stats  Global IPv6 routing tables statistics
1322 sockstat6  Socket statistics (IPv6)
1323 snmp6      Snmp data (IPv6)
1324 ========== =====================================================
1325
1326.. table:: Table 1-9: Network info in /proc/net
1327
1328 ============= ================================================================
1329 File          Content
1330 ============= ================================================================
1331 arp           Kernel  ARP table
1332 dev           network devices with statistics
1333 dev_mcast     the Layer2 multicast groups a device is listening too
1334               (interface index, label, number of references, number of bound
1335               addresses).
1336 dev_stat      network device status
1337 ip_fwchains   Firewall chain linkage
1338 ip_fwnames    Firewall chain names
1339 ip_masq       Directory containing the masquerading tables
1340 ip_masquerade Major masquerading table
1341 netstat       Network statistics
1342 raw           raw device statistics
1343 route         Kernel routing table
1344 rpc           Directory containing rpc info
1345 rt_cache      Routing cache
1346 snmp          SNMP data
1347 sockstat      Socket statistics
1348 softnet_stat  Per-CPU incoming packets queues statistics of online CPUs
1349 tcp           TCP  sockets
1350 udp           UDP sockets
1351 unix          UNIX domain sockets
1352 wireless      Wireless interface data (Wavelan etc)
1353 igmp          IP multicast addresses, which this host joined
1354 psched        Global packet scheduler parameters.
1355 netlink       List of PF_NETLINK sockets
1356 ip_mr_vifs    List of multicast virtual interfaces
1357 ip_mr_cache   List of multicast routing cache
1358 ============= ================================================================
1359
1360You can  use  this  information  to see which network devices are available in
1361your system and how much traffic was routed over those devices::
1362
1363  > cat /proc/net/dev
1364  Inter-|Receive                                                   |[...
1365   face |bytes    packets errs drop fifo frame compressed multicast|[...
1366      lo:  908188   5596     0    0    0     0          0         0 [...
1367    ppp0:15475140  20721   410    0    0   410          0         0 [...
1368    eth0:  614530   7085     0    0    0     0          0         1 [...
1369
1370  ...] Transmit
1371  ...] bytes    packets errs drop fifo colls carrier compressed
1372  ...]  908188     5596    0    0    0     0       0          0
1373  ...] 1375103    17405    0    0    0     0       0          0
1374  ...] 1703981     5535    0    0    0     3       0          0
1375
1376In addition, each Channel Bond interface has its own directory.  For
1377example, the bond0 device will have a directory called /proc/net/bond0/.
1378It will contain information that is specific to that bond, such as the
1379current slaves of the bond, the link status of the slaves, and how
1380many times the slaves link has failed.
1381
13821.4 SCSI info
1383-------------
1384
1385If you have a SCSI or ATA host adapter in your system, you'll find a
1386subdirectory named after the driver for this adapter in /proc/scsi.
1387You'll also see a list of all recognized SCSI devices in /proc/scsi::
1388
1389  >cat /proc/scsi/scsi
1390  Attached devices:
1391  Host: scsi0 Channel: 00 Id: 00 Lun: 00
1392    Vendor: IBM      Model: DGHS09U          Rev: 03E0
1393    Type:   Direct-Access                    ANSI SCSI revision: 03
1394  Host: scsi0 Channel: 00 Id: 06 Lun: 00
1395    Vendor: PIONEER  Model: CD-ROM DR-U06S   Rev: 1.04
1396    Type:   CD-ROM                           ANSI SCSI revision: 02
1397
1398
1399The directory  named  after  the driver has one file for each adapter found in
1400the system.  These  files  contain information about the controller, including
1401the used  IRQ  and  the  IO  address range. The amount of information shown is
1402dependent on  the adapter you use. The example shows the output for an Adaptec
1403AHA-2940 SCSI adapter::
1404
1405  > cat /proc/scsi/aic7xxx/0
1406
1407  Adaptec AIC7xxx driver version: 5.1.19/3.2.4
1408  Compile Options:
1409    TCQ Enabled By Default : Disabled
1410    AIC7XXX_PROC_STATS     : Disabled
1411    AIC7XXX_RESET_DELAY    : 5
1412  Adapter Configuration:
1413             SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
1414                             Ultra Wide Controller
1415      PCI MMAPed I/O Base: 0xeb001000
1416   Adapter SEEPROM Config: SEEPROM found and used.
1417        Adaptec SCSI BIOS: Enabled
1418                      IRQ: 10
1419                     SCBs: Active 0, Max Active 2,
1420                           Allocated 15, HW 16, Page 255
1421               Interrupts: 160328
1422        BIOS Control Word: 0x18b6
1423     Adapter Control Word: 0x005b
1424     Extended Translation: Enabled
1425  Disconnect Enable Flags: 0xffff
1426       Ultra Enable Flags: 0x0001
1427   Tag Queue Enable Flags: 0x0000
1428  Ordered Queue Tag Flags: 0x0000
1429  Default Tag Queue Depth: 8
1430      Tagged Queue By Device array for aic7xxx host instance 0:
1431        {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
1432      Actual queue depth per device for aic7xxx host instance 0:
1433        {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
1434  Statistics:
1435  (scsi0:0:0:0)
1436    Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
1437    Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
1438    Total transfers 160151 (74577 reads and 85574 writes)
1439  (scsi0:0:6:0)
1440    Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
1441    Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
1442    Total transfers 0 (0 reads and 0 writes)
1443
1444
14451.5 Parallel port info in /proc/parport
1446---------------------------------------
1447
1448The directory  /proc/parport  contains information about the parallel ports of
1449your system.  It  has  one  subdirectory  for  each port, named after the port
1450number (0,1,2,...).
1451
1452These directories contain the four files shown in Table 1-10.
1453
1454
1455.. table:: Table 1-10: Files in /proc/parport
1456
1457 ========= ====================================================================
1458 File      Content
1459 ========= ====================================================================
1460 autoprobe Any IEEE-1284 device ID information that has been acquired.
1461 devices   list of the device drivers using that port. A + will appear by the
1462           name of the device currently using the port (it might not appear
1463           against any).
1464 hardware  Parallel port's base address, IRQ line and DMA channel.
1465 irq       IRQ that parport is using for that port. This is in a separate
1466           file to allow you to alter it by writing a new value in (IRQ
1467           number or none).
1468 ========= ====================================================================
1469
14701.6 TTY info in /proc/tty
1471-------------------------
1472
1473Information about  the  available  and actually used tty's can be found in the
1474directory /proc/tty. You'll find  entries  for drivers and line disciplines in
1475this directory, as shown in Table 1-11.
1476
1477
1478.. table:: Table 1-11: Files in /proc/tty
1479
1480 ============= ==============================================
1481 File          Content
1482 ============= ==============================================
1483 drivers       list of drivers and their usage
1484 ldiscs        registered line disciplines
1485 driver/serial usage statistic and status of single tty lines
1486 ============= ==============================================
1487
1488To see  which  tty's  are  currently in use, you can simply look into the file
1489/proc/tty/drivers::
1490
1491  > cat /proc/tty/drivers
1492  pty_slave            /dev/pts      136   0-255 pty:slave
1493  pty_master           /dev/ptm      128   0-255 pty:master
1494  pty_slave            /dev/ttyp       3   0-255 pty:slave
1495  pty_master           /dev/pty        2   0-255 pty:master
1496  serial               /dev/cua        5   64-67 serial:callout
1497  serial               /dev/ttyS       4   64-67 serial
1498  /dev/tty0            /dev/tty0       4       0 system:vtmaster
1499  /dev/ptmx            /dev/ptmx       5       2 system
1500  /dev/console         /dev/console    5       1 system:console
1501  /dev/tty             /dev/tty        5       0 system:/dev/tty
1502  unknown              /dev/tty        4    1-63 console
1503
1504
15051.7 Miscellaneous kernel statistics in /proc/stat
1506-------------------------------------------------
1507
1508Various pieces   of  information about  kernel activity  are  available in the
1509/proc/stat file.  All  of  the numbers reported  in  this file are  aggregates
1510since the system first booted.  For a quick look, simply cat the file::
1511
1512  > cat /proc/stat
1513  cpu  237902850 368826709 106375398 1873517540 1135548 0 14507935 0 0 0
1514  cpu0 60045249 91891769 26331539 468411416 495718 0 5739640 0 0 0
1515  cpu1 59746288 91759249 26609887 468860630 312281 0 4384817 0 0 0
1516  cpu2 59489247 92985423 26904446 467808813 171668 0 2268998 0 0 0
1517  cpu3 58622065 92190267 26529524 468436680 155879 0 2114478 0 0 0
1518  intr 8688370575 8 3373 0 0 0 0 0 0 1 40791 0 0 353317 0 0 0 0 224789828 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 190974333 41958554 123983334 43 0 224593 0 0 0 <more 0's deleted>
1519  ctxt 22848221062
1520  btime 1605316999
1521  processes 746787147
1522  procs_running 2
1523  procs_blocked 0
1524  softirq 12121874454 100099120 3938138295 127375644 2795979 187870761 0 173808342 3072582055 52608 224184354
1525
1526The very first  "cpu" line aggregates the  numbers in all  of the other "cpuN"
1527lines.  These numbers identify the amount of time the CPU has spent performing
1528different kinds of work.  Time units are in USER_HZ (typically hundredths of a
1529second).  The meanings of the columns are as follows, from left to right:
1530
1531- user: normal processes executing in user mode
1532- nice: niced processes executing in user mode
1533- system: processes executing in kernel mode
1534- idle: twiddling thumbs
1535- iowait: In a word, iowait stands for waiting for I/O to complete. But there
1536  are several problems:
1537
1538  1. CPU will not wait for I/O to complete, iowait is the time that a task is
1539     waiting for I/O to complete. When CPU goes into idle state for
1540     outstanding task I/O, another task will be scheduled on this CPU.
1541  2. In a multi-core CPU, the task waiting for I/O to complete is not running
1542     on any CPU, so the iowait of each CPU is difficult to calculate.
1543  3. The value of iowait field in /proc/stat will decrease in certain
1544     conditions.
1545
1546  So, the iowait is not reliable by reading from /proc/stat.
1547- irq: servicing interrupts
1548- softirq: servicing softirqs
1549- steal: involuntary wait
1550- guest: running a normal guest
1551- guest_nice: running a niced guest
1552
1553The "intr" line gives counts of interrupts  serviced since boot time, for each
1554of the  possible system interrupts.   The first  column  is the  total of  all
1555interrupts serviced  including  unnumbered  architecture specific  interrupts;
1556each  subsequent column is the  total for that particular numbered interrupt.
1557Unnumbered interrupts are not shown, only summed into the total.
1558
1559The "ctxt" line gives the total number of context switches across all CPUs.
1560
1561The "btime" line gives  the time at which the  system booted, in seconds since
1562the Unix epoch.
1563
1564The "processes" line gives the number  of processes and threads created, which
1565includes (but  is not limited  to) those  created by  calls to the  fork() and
1566clone() system calls.
1567
1568The "procs_running" line gives the total number of threads that are
1569running or ready to run (i.e., the total number of runnable threads).
1570
1571The   "procs_blocked" line gives  the  number of  processes currently blocked,
1572waiting for I/O to complete.
1573
1574The "softirq" line gives counts of softirqs serviced since boot time, for each
1575of the possible system softirqs. The first column is the total of all
1576softirqs serviced; each subsequent column is the total for that particular
1577softirq.
1578
1579
15801.8 Ext4 file system parameters
1581-------------------------------
1582
1583Information about mounted ext4 file systems can be found in
1584/proc/fs/ext4.  Each mounted filesystem will have a directory in
1585/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1586/proc/fs/ext4/sda9 or /proc/fs/ext4/dm-0).   The files in each per-device
1587directory are shown in Table 1-12, below.
1588
1589.. table:: Table 1-12: Files in /proc/fs/ext4/<devname>
1590
1591 ==============  ==========================================================
1592 File            Content
1593 mb_groups       details of multiblock allocator buddy cache of free blocks
1594 ==============  ==========================================================
1595
15961.9 /proc/consoles
1597-------------------
1598Shows registered system console lines.
1599
1600To see which character device lines are currently used for the system console
1601/dev/console, you may simply look into the file /proc/consoles::
1602
1603  > cat /proc/consoles
1604  tty0                 -WU (ECp)       4:7
1605  ttyS0                -W- (Ep)        4:64
1606
1607The columns are:
1608
1609+--------------------+-------------------------------------------------------+
1610| device             | name of the device                                    |
1611+====================+=======================================================+
1612| operations         | * R = can do read operations                          |
1613|                    | * W = can do write operations                         |
1614|                    | * U = can do unblank                                  |
1615+--------------------+-------------------------------------------------------+
1616| flags              | * E = it is enabled                                   |
1617|                    | * C = it is preferred console                         |
1618|                    | * B = it is primary boot console                      |
1619|                    | * p = it is used for printk buffer                    |
1620|                    | * b = it is not a TTY but a Braille device            |
1621|                    | * a = it is safe to use when cpu is offline           |
1622+--------------------+-------------------------------------------------------+
1623| major:minor        | major and minor number of the device separated by a   |
1624|                    | colon                                                 |
1625+--------------------+-------------------------------------------------------+
1626
1627Summary
1628-------
1629
1630The /proc file system serves information about the running system. It not only
1631allows access to process data but also allows you to request the kernel status
1632by reading files in the hierarchy.
1633
1634The directory  structure  of /proc reflects the types of information and makes
1635it easy, if not obvious, where to look for specific data.
1636
1637Chapter 2: Modifying System Parameters
1638======================================
1639
1640In This Chapter
1641---------------
1642
1643* Modifying kernel parameters by writing into files found in /proc/sys
1644* Exploring the files which modify certain parameters
1645* Review of the /proc/sys file tree
1646
1647------------------------------------------------------------------------------
1648
1649A very  interesting part of /proc is the directory /proc/sys. This is not only
1650a source  of  information,  it also allows you to change parameters within the
1651kernel. Be  very  careful  when attempting this. You can optimize your system,
1652but you  can  also  cause  it  to  crash.  Never  alter kernel parameters on a
1653production system.  Set  up  a  development machine and test to make sure that
1654everything works  the  way  you want it to. You may have no alternative but to
1655reboot the machine once an error has been made.
1656
1657To change  a  value,  simply  echo  the new value into the file.
1658You need to be root to do this. You  can  create  your  own  boot script
1659to perform this every time your system boots.
1660
1661The files  in /proc/sys can be used to fine tune and monitor miscellaneous and
1662general things  in  the operation of the Linux kernel. Since some of the files
1663can inadvertently  disrupt  your  system,  it  is  advisable  to  read  both
1664documentation and  source  before actually making adjustments. In any case, be
1665very careful  when  writing  to  any  of these files. The entries in /proc may
1666change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1667review the kernel documentation in the directory linux/Documentation.
1668This chapter  is  heavily  based  on the documentation included in the pre 2.2
1669kernels, and became part of it in version 2.2.1 of the Linux kernel.
1670
1671Please see: Documentation/admin-guide/sysctl/ directory for descriptions of
1672these entries.
1673
1674Summary
1675-------
1676
1677Certain aspects  of  kernel  behavior  can be modified at runtime, without the
1678need to  recompile  the kernel, or even to reboot the system. The files in the
1679/proc/sys tree  can  not only be read, but also modified. You can use the echo
1680command to write value into these files, thereby changing the default settings
1681of the kernel.
1682
1683
1684Chapter 3: Per-process Parameters
1685=================================
1686
16873.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1688--------------------------------------------------------------------------------
1689
1690These files can be used to adjust the badness heuristic used to select which
1691process gets killed in out of memory (oom) conditions.
1692
1693The badness heuristic assigns a value to each candidate task ranging from 0
1694(never kill) to 1000 (always kill) to determine which process is targeted.  The
1695units are roughly a proportion along that range of allowed memory the process
1696may allocate from based on an estimation of its current memory and swap use.
1697For example, if a task is using all allowed memory, its badness score will be
16981000.  If it is using half of its allowed memory, its score will be 500.
1699
1700The amount of "allowed" memory depends on the context in which the oom killer
1701was called.  If it is due to the memory assigned to the allocating task's cpuset
1702being exhausted, the allowed memory represents the set of mems assigned to that
1703cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
1704memory represents the set of mempolicy nodes.  If it is due to a memory
1705limit (or swap limit) being reached, the allowed memory is that configured
1706limit.  Finally, if it is due to the entire system being out of memory, the
1707allowed memory represents all allocatable resources.
1708
1709The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1710is used to determine which task to kill.  Acceptable values range from -1000
1711(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
1712polarize the preference for oom killing either by always preferring a certain
1713task or completely disabling it.  The lowest possible value, -1000, is
1714equivalent to disabling oom killing entirely for that task since it will always
1715report a badness score of 0.
1716
1717Consequently, it is very simple for userspace to define the amount of memory to
1718consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
1719example, is roughly equivalent to allowing the remainder of tasks sharing the
1720same system, cpuset, mempolicy, or memory controller resources to use at least
172150% more memory.  A value of -500, on the other hand, would be roughly
1722equivalent to discounting 50% of the task's allowed memory from being considered
1723as scoring against the task.
1724
1725For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1726be used to tune the badness score.  Its acceptable values range from -16
1727(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1728(OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
1729scaled linearly with /proc/<pid>/oom_score_adj.
1730
1731The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1732value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1733requires CAP_SYS_RESOURCE.
1734
1735
17363.2 /proc/<pid>/oom_score - Display current oom-killer score
1737-------------------------------------------------------------
1738
1739This file can be used to check the current score used by the oom-killer for
1740any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1741process should be killed in an out-of-memory situation.
1742
1743Please note that the exported value includes oom_score_adj so it is
1744effectively in range [0,2000].
1745
1746
17473.3  /proc/<pid>/io - Display the IO accounting fields
1748-------------------------------------------------------
1749
1750This file contains IO statistics for each running process.
1751
1752Example
1753~~~~~~~
1754
1755::
1756
1757    test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1758    [1] 3828
1759
1760    test:/tmp # cat /proc/3828/io
1761    rchar: 323934931
1762    wchar: 323929600
1763    syscr: 632687
1764    syscw: 632675
1765    read_bytes: 0
1766    write_bytes: 323932160
1767    cancelled_write_bytes: 0
1768
1769
1770Description
1771~~~~~~~~~~~
1772
1773rchar
1774^^^^^
1775
1776I/O counter: chars read
1777The number of bytes which this task has caused to be read from storage. This
1778is simply the sum of bytes which this process passed to read() and pread().
1779It includes things like tty IO and it is unaffected by whether or not actual
1780physical disk IO was required (the read might have been satisfied from
1781pagecache).
1782
1783
1784wchar
1785^^^^^
1786
1787I/O counter: chars written
1788The number of bytes which this task has caused, or shall cause to be written
1789to disk. Similar caveats apply here as with rchar.
1790
1791
1792syscr
1793^^^^^
1794
1795I/O counter: read syscalls
1796Attempt to count the number of read I/O operations, i.e. syscalls like read()
1797and pread().
1798
1799
1800syscw
1801^^^^^
1802
1803I/O counter: write syscalls
1804Attempt to count the number of write I/O operations, i.e. syscalls like
1805write() and pwrite().
1806
1807
1808read_bytes
1809^^^^^^^^^^
1810
1811I/O counter: bytes read
1812Attempt to count the number of bytes which this process really did cause to
1813be fetched from the storage layer. Done at the submit_bio() level, so it is
1814accurate for block-backed filesystems. <please add status regarding NFS and
1815CIFS at a later time>
1816
1817
1818write_bytes
1819^^^^^^^^^^^
1820
1821I/O counter: bytes written
1822Attempt to count the number of bytes which this process caused to be sent to
1823the storage layer. This is done at page-dirtying time.
1824
1825
1826cancelled_write_bytes
1827^^^^^^^^^^^^^^^^^^^^^
1828
1829The big inaccuracy here is truncate. If a process writes 1MB to a file and
1830then deletes the file, it will in fact perform no writeout. But it will have
1831been accounted as having caused 1MB of write.
1832In other words: The number of bytes which this process caused to not happen,
1833by truncating pagecache. A task can cause "negative" IO too. If this task
1834truncates some dirty pagecache, some IO which another task has been accounted
1835for (in its write_bytes) will not be happening. We _could_ just subtract that
1836from the truncating task's write_bytes, but there is information loss in doing
1837that.
1838
1839
1840.. Note::
1841
1842   At its current implementation state, this is a bit racy on 32-bit machines:
1843   if process A reads process B's /proc/pid/io while process B is updating one
1844   of those 64-bit counters, process A could see an intermediate result.
1845
1846
1847More information about this can be found within the taskstats documentation in
1848Documentation/accounting.
1849
18503.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1851---------------------------------------------------------------
1852When a process is dumped, all anonymous memory is written to a core file as
1853long as the size of the core file isn't limited. But sometimes we don't want
1854to dump some memory segments, for example, huge shared memory or DAX.
1855Conversely, sometimes we want to save file-backed memory segments into a core
1856file, not only the individual files.
1857
1858/proc/<pid>/coredump_filter allows you to customize which memory segments
1859will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1860of memory types. If a bit of the bitmask is set, memory segments of the
1861corresponding memory type are dumped, otherwise they are not dumped.
1862
1863The following 9 memory types are supported:
1864
1865  - (bit 0) anonymous private memory
1866  - (bit 1) anonymous shared memory
1867  - (bit 2) file-backed private memory
1868  - (bit 3) file-backed shared memory
1869  - (bit 4) ELF header pages in file-backed private memory areas (it is
1870    effective only if the bit 2 is cleared)
1871  - (bit 5) hugetlb private memory
1872  - (bit 6) hugetlb shared memory
1873  - (bit 7) DAX private memory
1874  - (bit 8) DAX shared memory
1875
1876  Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1877  are always dumped regardless of the bitmask status.
1878
1879  Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
1880  only affected by bit 5-6, and DAX is only affected by bits 7-8.
1881
1882The default value of coredump_filter is 0x33; this means all anonymous memory
1883segments, ELF header pages and hugetlb private memory are dumped.
1884
1885If you don't want to dump all shared memory segments attached to pid 1234,
1886write 0x31 to the process's proc file::
1887
1888  $ echo 0x31 > /proc/1234/coredump_filter
1889
1890When a new process is created, the process inherits the bitmask status from its
1891parent. It is useful to set up coredump_filter before the program runs.
1892For example::
1893
1894  $ echo 0x7 > /proc/self/coredump_filter
1895  $ ./some_program
1896
18973.5	/proc/<pid>/mountinfo - Information about mounts
1898--------------------------------------------------------
1899
1900This file contains lines of the form::
1901
1902    36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1903    (1)(2)(3)   (4)   (5)      (6)     (n…m) (m+1)(m+2) (m+3)         (m+4)
1904
1905    (1)   mount ID:        unique identifier of the mount (may be reused after umount)
1906    (2)   parent ID:       ID of parent (or of self for the top of the mount tree)
1907    (3)   major:minor:     value of st_dev for files on filesystem
1908    (4)   root:            root of the mount within the filesystem
1909    (5)   mount point:     mount point relative to the process's root
1910    (6)   mount options:   per mount options
1911    (n…m) optional fields: zero or more fields of the form "tag[:value]"
1912    (m+1) separator:       marks the end of the optional fields
1913    (m+2) filesystem type: name of filesystem of the form "type[.subtype]"
1914    (m+3) mount source:    filesystem specific information or "none"
1915    (m+4) super options:   per super block options
1916
1917Parsers should ignore all unrecognised optional fields.  Currently the
1918possible optional fields are:
1919
1920================  ==============================================================
1921shared:X          mount is shared in peer group X
1922master:X          mount is slave to peer group X
1923propagate_from:X  mount is slave and receives propagation from peer group X [#]_
1924unbindable        mount is unbindable
1925================  ==============================================================
1926
1927.. [#] X is the closest dominant peer group under the process's root.  If
1928       X is the immediate master of the mount, or if there's no dominant peer
1929       group under the same root, then only the "master:X" field is present
1930       and not the "propagate_from:X" field.
1931
1932For more information on mount propagation see:
1933
1934  Documentation/filesystems/sharedsubtree.rst
1935
1936
19373.6	/proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
1938--------------------------------------------------------
1939These files provide a method to access a task's comm value. It also allows for
1940a task to set its own or one of its thread siblings comm value. The comm value
1941is limited in size compared to the cmdline value, so writing anything longer
1942then the kernel's TASK_COMM_LEN (currently 16 chars, including the NUL
1943terminator) will result in a truncated comm value.
1944
1945
19463.7	/proc/<pid>/task/<tid>/children - Information about task children
1947-------------------------------------------------------------------------
1948This file provides a fast way to retrieve first level children pids
1949of a task pointed by <pid>/<tid> pair. The format is a space separated
1950stream of pids.
1951
1952Note the "first level" here -- if a child has its own children they will
1953not be listed here; one needs to read /proc/<children-pid>/task/<tid>/children
1954to obtain the descendants.
1955
1956Since this interface is intended to be fast and cheap it doesn't
1957guarantee to provide precise results and some children might be
1958skipped, especially if they've exited right after we printed their
1959pids, so one needs to either stop or freeze processes being inspected
1960if precise results are needed.
1961
1962
19633.8	/proc/<pid>/fdinfo/<fd> - Information about opened file
1964---------------------------------------------------------------
1965This file provides information associated with an opened file. The regular
1966files have at least four fields -- 'pos', 'flags', 'mnt_id' and 'ino'.
1967The 'pos' represents the current offset of the opened file in decimal
1968form [see lseek(2) for details], 'flags' denotes the octal O_xxx mask the
1969file has been created with [see open(2) for details] and 'mnt_id' represents
1970mount ID of the file system containing the opened file [see 3.5
1971/proc/<pid>/mountinfo for details]. 'ino' represents the inode number of
1972the file.
1973
1974A typical output is::
1975
1976	pos:	0
1977	flags:	0100002
1978	mnt_id:	19
1979	ino:	63107
1980
1981All locks associated with a file descriptor are shown in its fdinfo too::
1982
1983    lock:       1: FLOCK  ADVISORY  WRITE 359 00:13:11691 0 EOF
1984
1985The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1986pair provide additional information particular to the objects they represent.
1987
1988Eventfd files
1989~~~~~~~~~~~~~
1990
1991::
1992
1993	pos:	0
1994	flags:	04002
1995	mnt_id:	9
1996	ino:	63107
1997	eventfd-count:	5a
1998
1999where 'eventfd-count' is hex value of a counter.
2000
2001Signalfd files
2002~~~~~~~~~~~~~~
2003
2004::
2005
2006	pos:	0
2007	flags:	04002
2008	mnt_id:	9
2009	ino:	63107
2010	sigmask:	0000000000000200
2011
2012where 'sigmask' is hex value of the signal mask associated
2013with a file.
2014
2015Epoll files
2016~~~~~~~~~~~
2017
2018::
2019
2020	pos:	0
2021	flags:	02
2022	mnt_id:	9
2023	ino:	63107
2024	tfd:        5 events:       1d data: ffffffffffffffff pos:0 ino:61af sdev:7
2025
2026where 'tfd' is a target file descriptor number in decimal form,
2027'events' is events mask being watched and the 'data' is data
2028associated with a target [see epoll(7) for more details].
2029
2030The 'pos' is current offset of the target file in decimal form
2031[see lseek(2)], 'ino' and 'sdev' are inode and device numbers
2032where target file resides, all in hex format.
2033
2034Fsnotify files
2035~~~~~~~~~~~~~~
2036For inotify files the format is the following::
2037
2038	pos:	0
2039	flags:	02000000
2040	mnt_id:	9
2041	ino:	63107
2042	inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
2043
2044where 'wd' is a watch descriptor in decimal form, i.e. a target file
2045descriptor number, 'ino' and 'sdev' are inode and device where the
2046target file resides and the 'mask' is the mask of events, all in hex
2047form [see inotify(7) for more details].
2048
2049If the kernel was built with exportfs support, the path to the target
2050file is encoded as a file handle.  The file handle is provided by three
2051fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
2052format.
2053
2054If the kernel is built without exportfs support the file handle won't be
2055printed out.
2056
2057If there is no inotify mark attached yet the 'inotify' line will be omitted.
2058
2059For fanotify files the format is::
2060
2061	pos:	0
2062	flags:	02
2063	mnt_id:	9
2064	ino:	63107
2065	fanotify flags:10 event-flags:0
2066	fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
2067	fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
2068
2069where fanotify 'flags' and 'event-flags' are values used in fanotify_init
2070call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
2071flags associated with mark which are tracked separately from events
2072mask. 'ino' and 'sdev' are target inode and device, 'mask' is the events
2073mask and 'ignored_mask' is the mask of events which are to be ignored.
2074All are in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
2075provide information about flags and mask used in fanotify_mark
2076call [see fsnotify manpage for details].
2077
2078While the first three lines are mandatory and always printed, the rest is
2079optional and may be omitted if no marks created yet.
2080
2081Timerfd files
2082~~~~~~~~~~~~~
2083
2084::
2085
2086	pos:	0
2087	flags:	02
2088	mnt_id:	9
2089	ino:	63107
2090	clockid: 0
2091	ticks: 0
2092	settime flags: 01
2093	it_value: (0, 49406829)
2094	it_interval: (1, 0)
2095
2096where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
2097that have occurred [see timerfd_create(2) for details]. 'settime flags' are
2098flags in octal form been used to setup the timer [see timerfd_settime(2) for
2099details]. 'it_value' is remaining time until the timer expiration.
2100'it_interval' is the interval for the timer. Note the timer might be set up
2101with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
2102still exhibits timer's remaining time.
2103
2104DMA Buffer files
2105~~~~~~~~~~~~~~~~
2106
2107::
2108
2109	pos:	0
2110	flags:	04002
2111	mnt_id:	9
2112	ino:	63107
2113	size:   32768
2114	count:  2
2115	exp_name:  system-heap
2116
2117where 'size' is the size of the DMA buffer in bytes. 'count' is the file count of
2118the DMA buffer file. 'exp_name' is the name of the DMA buffer exporter.
2119
21203.9	/proc/<pid>/map_files - Information about memory mapped files
2121---------------------------------------------------------------------
2122This directory contains symbolic links which represent memory mapped files
2123the process is maintaining.  Example output::
2124
2125     | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
2126     | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
2127     | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
2128     | ...
2129     | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
2130     | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
2131
2132The name of a link represents the virtual memory bounds of a mapping, i.e.
2133vm_area_struct::vm_start-vm_area_struct::vm_end.
2134
2135The main purpose of the map_files is to retrieve a set of memory mapped
2136files in a fast way instead of parsing /proc/<pid>/maps or
2137/proc/<pid>/smaps, both of which contain many more records.  At the same
2138time one can open(2) mappings from the listings of two processes and
2139comparing their inode numbers to figure out which anonymous memory areas
2140are actually shared.
2141
21423.10	/proc/<pid>/timerslack_ns - Task timerslack value
2143---------------------------------------------------------
2144This file provides the value of the task's timerslack value in nanoseconds.
2145This value specifies an amount of time that normal timers may be deferred
2146in order to coalesce timers and avoid unnecessary wakeups.
2147
2148This allows a task's interactivity vs power consumption tradeoff to be
2149adjusted.
2150
2151Writing 0 to the file will set the task's timerslack to the default value.
2152
2153Valid values are from 0 - ULLONG_MAX
2154
2155An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
2156permissions on the task specified to change its timerslack_ns value.
2157
21583.11	/proc/<pid>/patch_state - Livepatch patch operation state
2159-----------------------------------------------------------------
2160When CONFIG_LIVEPATCH is enabled, this file displays the value of the
2161patch state for the task.
2162
2163A value of '-1' indicates that no patch is in transition.
2164
2165A value of '0' indicates that a patch is in transition and the task is
2166unpatched.  If the patch is being enabled, then the task hasn't been
2167patched yet.  If the patch is being disabled, then the task has already
2168been unpatched.
2169
2170A value of '1' indicates that a patch is in transition and the task is
2171patched.  If the patch is being enabled, then the task has already been
2172patched.  If the patch is being disabled, then the task hasn't been
2173unpatched yet.
2174
21753.12 /proc/<pid>/arch_status - task architecture specific status
2176-------------------------------------------------------------------
2177When CONFIG_PROC_PID_ARCH_STATUS is enabled, this file displays the
2178architecture specific status of the task.
2179
2180Example
2181~~~~~~~
2182
2183::
2184
2185 $ cat /proc/6753/arch_status
2186 AVX512_elapsed_ms:      8
2187
2188Description
2189~~~~~~~~~~~
2190
2191x86 specific entries
2192~~~~~~~~~~~~~~~~~~~~~
2193
2194AVX512_elapsed_ms
2195^^^^^^^^^^^^^^^^^^
2196
2197  If AVX512 is supported on the machine, this entry shows the milliseconds
2198  elapsed since the last time AVX512 usage was recorded. The recording
2199  happens on a best effort basis when a task is scheduled out. This means
2200  that the value depends on two factors:
2201
2202    1) The time which the task spent on the CPU without being scheduled
2203       out. With CPU isolation and a single runnable task this can take
2204       several seconds.
2205
2206    2) The time since the task was scheduled out last. Depending on the
2207       reason for being scheduled out (time slice exhausted, syscall ...)
2208       this can be arbitrary long time.
2209
2210  As a consequence the value cannot be considered precise and authoritative
2211  information. The application which uses this information has to be aware
2212  of the overall scenario on the system in order to determine whether a
2213  task is a real AVX512 user or not. Precise information can be obtained
2214  with performance counters.
2215
2216  A special value of '-1' indicates that no AVX512 usage was recorded, thus
2217  the task is unlikely an AVX512 user, but depends on the workload and the
2218  scheduling scenario, it also could be a false negative mentioned above.
2219
22203.13 /proc/<pid>/fd - List of symlinks to open files
2221-------------------------------------------------------
2222This directory contains symbolic links which represent open files
2223the process is maintaining.  Example output::
2224
2225  lr-x------ 1 root root 64 Sep 20 17:53 0 -> /dev/null
2226  l-wx------ 1 root root 64 Sep 20 17:53 1 -> /dev/null
2227  lrwx------ 1 root root 64 Sep 20 17:53 10 -> 'socket:[12539]'
2228  lrwx------ 1 root root 64 Sep 20 17:53 11 -> 'socket:[12540]'
2229  lrwx------ 1 root root 64 Sep 20 17:53 12 -> 'socket:[12542]'
2230
2231The number of open files for the process is stored in 'size' member
2232of stat() output for /proc/<pid>/fd for fast access.
2233-------------------------------------------------------
2234
2235
2236Chapter 4: Configuring procfs
2237=============================
2238
22394.1	Mount options
2240---------------------
2241
2242The following mount options are supported:
2243
2244	=========	========================================================
2245	hidepid=	Set /proc/<pid>/ access mode.
2246	gid=		Set the group authorized to learn processes information.
2247	subset=		Show only the specified subset of procfs.
2248	=========	========================================================
2249
2250hidepid=off or hidepid=0 means classic mode - everybody may access all
2251/proc/<pid>/ directories (default).
2252
2253hidepid=noaccess or hidepid=1 means users may not access any /proc/<pid>/
2254directories but their own.  Sensitive files like cmdline, sched*, status are now
2255protected against other users.  This makes it impossible to learn whether any
2256user runs specific program (given the program doesn't reveal itself by its
2257behaviour).  As an additional bonus, as /proc/<pid>/cmdline is unaccessible for
2258other users, poorly written programs passing sensitive information via program
2259arguments are now protected against local eavesdroppers.
2260
2261hidepid=invisible or hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be
2262fully invisible to other users.  It doesn't mean that it hides a fact whether a
2263process with a specific pid value exists (it can be learned by other means, e.g.
2264by "kill -0 $PID"), but it hides process' uid and gid, which may be learned by
2265stat()'ing /proc/<pid>/ otherwise.  It greatly complicates an intruder's task of
2266gathering information about running processes, whether some daemon runs with
2267elevated privileges, whether other user runs some sensitive program, whether
2268other users run any program at all, etc.
2269
2270hidepid=ptraceable or hidepid=4 means that procfs should only contain
2271/proc/<pid>/ directories that the caller can ptrace.
2272
2273gid= defines a group authorized to learn processes information otherwise
2274prohibited by hidepid=.  If you use some daemon like identd which needs to learn
2275information about processes information, just add identd to this group.
2276
2277subset=pid hides all top level files and directories in the procfs that
2278are not related to tasks.
2279
2280Chapter 5: Filesystem behavior
2281==============================
2282
2283Originally, before the advent of pid namespace, procfs was a global file
2284system. It means that there was only one procfs instance in the system.
2285
2286When pid namespace was added, a separate procfs instance was mounted in
2287each pid namespace. So, procfs mount options are global among all
2288mountpoints within the same namespace::
2289
2290	# grep ^proc /proc/mounts
2291	proc /proc proc rw,relatime,hidepid=2 0 0
2292
2293	# strace -e mount mount -o hidepid=1 -t proc proc /tmp/proc
2294	mount("proc", "/tmp/proc", "proc", 0, "hidepid=1") = 0
2295	+++ exited with 0 +++
2296
2297	# grep ^proc /proc/mounts
2298	proc /proc proc rw,relatime,hidepid=2 0 0
2299	proc /tmp/proc proc rw,relatime,hidepid=2 0 0
2300
2301and only after remounting procfs mount options will change at all
2302mountpoints::
2303
2304	# mount -o remount,hidepid=1 -t proc proc /tmp/proc
2305
2306	# grep ^proc /proc/mounts
2307	proc /proc proc rw,relatime,hidepid=1 0 0
2308	proc /tmp/proc proc rw,relatime,hidepid=1 0 0
2309
2310This behavior is different from the behavior of other filesystems.
2311
2312The new procfs behavior is more like other filesystems. Each procfs mount
2313creates a new procfs instance. Mount options affect own procfs instance.
2314It means that it became possible to have several procfs instances
2315displaying tasks with different filtering options in one pid namespace::
2316
2317	# mount -o hidepid=invisible -t proc proc /proc
2318	# mount -o hidepid=noaccess -t proc proc /tmp/proc
2319	# grep ^proc /proc/mounts
2320	proc /proc proc rw,relatime,hidepid=invisible 0 0
2321	proc /tmp/proc proc rw,relatime,hidepid=noaccess 0 0
2322