linux/Documentation/filesystems/proc.rst
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   1.. SPDX-License-Identifier: GPL-2.0
   2
   3====================
   4The /proc Filesystem
   5====================
   6
   7=====================  =======================================  ================
   8/proc/sys              Terrehon Bowden <terrehon@pacbell.net>,  October 7 1999
   9                       Bodo Bauer <bb@ricochet.net>
  102.4.x update           Jorge Nerin <comandante@zaralinux.com>   November 14 2000
  11move /proc/sys         Shen Feng <shen@cn.fujitsu.com>          April 1 2009
  12fixes/update part 1.1  Stefani Seibold <stefani@seibold.net>    June 9 2009
  13=====================  =======================================  ================
  14
  15
  16
  17.. Table of Contents
  18
  19  0     Preface
  20  0.1   Introduction/Credits
  21  0.2   Legal Stuff
  22
  23  1     Collecting System Information
  24  1.1   Process-Specific Subdirectories
  25  1.2   Kernel data
  26  1.3   IDE devices in /proc/ide
  27  1.4   Networking info in /proc/net
  28  1.5   SCSI info
  29  1.6   Parallel port info in /proc/parport
  30  1.7   TTY info in /proc/tty
  31  1.8   Miscellaneous kernel statistics in /proc/stat
  32  1.9   Ext4 file system parameters
  33
  34  2     Modifying System Parameters
  35
  36  3     Per-Process Parameters
  37  3.1   /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj - Adjust the oom-killer
  38                                                                score
  39  3.2   /proc/<pid>/oom_score - Display current oom-killer score
  40  3.3   /proc/<pid>/io - Display the IO accounting fields
  41  3.4   /proc/<pid>/coredump_filter - Core dump filtering settings
  42  3.5   /proc/<pid>/mountinfo - Information about mounts
  43  3.6   /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
  44  3.7   /proc/<pid>/task/<tid>/children - Information about task children
  45  3.8   /proc/<pid>/fdinfo/<fd> - Information about opened file
  46  3.9   /proc/<pid>/map_files - Information about memory mapped files
  47  3.10  /proc/<pid>/timerslack_ns - Task timerslack value
  48  3.11  /proc/<pid>/patch_state - Livepatch patch operation state
  49  3.12  /proc/<pid>/arch_status - Task architecture specific information
  50
  51  4     Configuring procfs
  52  4.1   Mount options
  53
  54  5     Filesystem behavior
  55
  56Preface
  57=======
  58
  590.1 Introduction/Credits
  60------------------------
  61
  62This documentation is  part of a soon (or  so we hope) to be  released book on
  63the SuSE  Linux distribution. As  there is  no complete documentation  for the
  64/proc file system and we've used  many freely available sources to write these
  65chapters, it  seems only fair  to give the work  back to the  Linux community.
  66This work is  based on the 2.2.*  kernel version and the  upcoming 2.4.*. I'm
  67afraid it's still far from complete, but we  hope it will be useful. As far as
  68we know, it is the first 'all-in-one' document about the /proc file system. It
  69is focused  on the Intel  x86 hardware,  so if you  are looking for  PPC, ARM,
  70SPARC, AXP, etc., features, you probably  won't find what you are looking for.
  71It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
  72additions and patches  are welcome and will  be added to this  document if you
  73mail them to Bodo.
  74
  75We'd like  to  thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
  76other people for help compiling this documentation. We'd also like to extend a
  77special thank  you to Andi Kleen for documentation, which we relied on heavily
  78to create  this  document,  as well as the additional information he provided.
  79Thanks to  everybody  else  who contributed source or docs to the Linux kernel
  80and helped create a great piece of software... :)
  81
  82If you  have  any comments, corrections or additions, please don't hesitate to
  83contact Bodo  Bauer  at  bb@ricochet.net.  We'll  be happy to add them to this
  84document.
  85
  86The   latest   version    of   this   document   is    available   online   at
  87http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html
  88
  89If  the above  direction does  not works  for you,  you could  try the  kernel
  90mailing  list  at  linux-kernel@vger.kernel.org  and/or try  to  reach  me  at
  91comandante@zaralinux.com.
  92
  930.2 Legal Stuff
  94---------------
  95
  96We don't  guarantee  the  correctness  of this document, and if you come to us
  97complaining about  how  you  screwed  up  your  system  because  of  incorrect
  98documentation, we won't feel responsible...
  99
 100Chapter 1: Collecting System Information
 101========================================
 102
 103In This Chapter
 104---------------
 105* Investigating  the  properties  of  the  pseudo  file  system  /proc and its
 106  ability to provide information on the running Linux system
 107* Examining /proc's structure
 108* Uncovering  various  information  about the kernel and the processes running
 109  on the system
 110
 111------------------------------------------------------------------------------
 112
 113The proc  file  system acts as an interface to internal data structures in the
 114kernel. It  can  be  used to obtain information about the system and to change
 115certain kernel parameters at runtime (sysctl).
 116
 117First, we'll  take  a  look  at the read-only parts of /proc. In Chapter 2, we
 118show you how you can use /proc/sys to change settings.
 119
 1201.1 Process-Specific Subdirectories
 121-----------------------------------
 122
 123The directory  /proc  contains  (among other things) one subdirectory for each
 124process running on the system, which is named after the process ID (PID).
 125
 126The link  'self'  points to  the process reading the file system. Each process
 127subdirectory has the entries listed in Table 1-1.
 128
 129Note that an open file descriptor to /proc/<pid> or to any of its
 130contained files or subdirectories does not prevent <pid> being reused
 131for some other process in the event that <pid> exits. Operations on
 132open /proc/<pid> file descriptors corresponding to dead processes
 133never act on any new process that the kernel may, through chance, have
 134also assigned the process ID <pid>. Instead, operations on these FDs
 135usually fail with ESRCH.
 136
 137.. table:: Table 1-1: Process specific entries in /proc
 138
 139 =============  ===============================================================
 140 File           Content
 141 =============  ===============================================================
 142 clear_refs     Clears page referenced bits shown in smaps output
 143 cmdline        Command line arguments
 144 cpu            Current and last cpu in which it was executed   (2.4)(smp)
 145 cwd            Link to the current working directory
 146 environ        Values of environment variables
 147 exe            Link to the executable of this process
 148 fd             Directory, which contains all file descriptors
 149 maps           Memory maps to executables and library files    (2.4)
 150 mem            Memory held by this process
 151 root           Link to the root directory of this process
 152 stat           Process status
 153 statm          Process memory status information
 154 status         Process status in human readable form
 155 wchan          Present with CONFIG_KALLSYMS=y: it shows the kernel function
 156                symbol the task is blocked in - or "0" if not blocked.
 157 pagemap        Page table
 158 stack          Report full stack trace, enable via CONFIG_STACKTRACE
 159 smaps          An extension based on maps, showing the memory consumption of
 160                each mapping and flags associated with it
 161 smaps_rollup   Accumulated smaps stats for all mappings of the process.  This
 162                can be derived from smaps, but is faster and more convenient
 163 numa_maps      An extension based on maps, showing the memory locality and
 164                binding policy as well as mem usage (in pages) of each mapping.
 165 =============  ===============================================================
 166
 167For example, to get the status information of a process, all you have to do is
 168read the file /proc/PID/status::
 169
 170  >cat /proc/self/status
 171  Name:   cat
 172  State:  R (running)
 173  Tgid:   5452
 174  Pid:    5452
 175  PPid:   743
 176  TracerPid:      0                                             (2.4)
 177  Uid:    501     501     501     501
 178  Gid:    100     100     100     100
 179  FDSize: 256
 180  Groups: 100 14 16
 181  VmPeak:     5004 kB
 182  VmSize:     5004 kB
 183  VmLck:         0 kB
 184  VmHWM:       476 kB
 185  VmRSS:       476 kB
 186  RssAnon:             352 kB
 187  RssFile:             120 kB
 188  RssShmem:              4 kB
 189  VmData:      156 kB
 190  VmStk:        88 kB
 191  VmExe:        68 kB
 192  VmLib:      1412 kB
 193  VmPTE:        20 kb
 194  VmSwap:        0 kB
 195  HugetlbPages:          0 kB
 196  CoreDumping:    0
 197  THP_enabled:    1
 198  Threads:        1
 199  SigQ:   0/28578
 200  SigPnd: 0000000000000000
 201  ShdPnd: 0000000000000000
 202  SigBlk: 0000000000000000
 203  SigIgn: 0000000000000000
 204  SigCgt: 0000000000000000
 205  CapInh: 00000000fffffeff
 206  CapPrm: 0000000000000000
 207  CapEff: 0000000000000000
 208  CapBnd: ffffffffffffffff
 209  CapAmb: 0000000000000000
 210  NoNewPrivs:     0
 211  Seccomp:        0
 212  Speculation_Store_Bypass:       thread vulnerable
 213  SpeculationIndirectBranch:      conditional enabled
 214  voluntary_ctxt_switches:        0
 215  nonvoluntary_ctxt_switches:     1
 216
 217This shows you nearly the same information you would get if you viewed it with
 218the ps  command.  In  fact,  ps  uses  the  proc  file  system  to  obtain its
 219information.  But you get a more detailed  view of the  process by reading the
 220file /proc/PID/status. It fields are described in table 1-2.
 221
 222The  statm  file  contains  more  detailed  information about the process
 223memory usage. Its seven fields are explained in Table 1-3.  The stat file
 224contains detailed information about the process itself.  Its fields are
 225explained in Table 1-4.
 226
 227(for SMP CONFIG users)
 228
 229For making accounting scalable, RSS related information are handled in an
 230asynchronous manner and the value may not be very precise. To see a precise
 231snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
 232It's slow but very precise.
 233
 234.. table:: Table 1-2: Contents of the status files (as of 4.19)
 235
 236 ==========================  ===================================================
 237 Field                       Content
 238 ==========================  ===================================================
 239 Name                        filename of the executable
 240 Umask                       file mode creation mask
 241 State                       state (R is running, S is sleeping, D is sleeping
 242                             in an uninterruptible wait, Z is zombie,
 243                             T is traced or stopped)
 244 Tgid                        thread group ID
 245 Ngid                        NUMA group ID (0 if none)
 246 Pid                         process id
 247 PPid                        process id of the parent process
 248 TracerPid                   PID of process tracing this process (0 if not)
 249 Uid                         Real, effective, saved set, and  file system UIDs
 250 Gid                         Real, effective, saved set, and  file system GIDs
 251 FDSize                      number of file descriptor slots currently allocated
 252 Groups                      supplementary group list
 253 NStgid                      descendant namespace thread group ID hierarchy
 254 NSpid                       descendant namespace process ID hierarchy
 255 NSpgid                      descendant namespace process group ID hierarchy
 256 NSsid                       descendant namespace session ID hierarchy
 257 VmPeak                      peak virtual memory size
 258 VmSize                      total program size
 259 VmLck                       locked memory size
 260 VmPin                       pinned memory size
 261 VmHWM                       peak resident set size ("high water mark")
 262 VmRSS                       size of memory portions. It contains the three
 263                             following parts
 264                             (VmRSS = RssAnon + RssFile + RssShmem)
 265 RssAnon                     size of resident anonymous memory
 266 RssFile                     size of resident file mappings
 267 RssShmem                    size of resident shmem memory (includes SysV shm,
 268                             mapping of tmpfs and shared anonymous mappings)
 269 VmData                      size of private data segments
 270 VmStk                       size of stack segments
 271 VmExe                       size of text segment
 272 VmLib                       size of shared library code
 273 VmPTE                       size of page table entries
 274 VmSwap                      amount of swap used by anonymous private data
 275                             (shmem swap usage is not included)
 276 HugetlbPages                size of hugetlb memory portions
 277 CoreDumping                 process's memory is currently being dumped
 278                             (killing the process may lead to a corrupted core)
 279 THP_enabled                 process is allowed to use THP (returns 0 when
 280                             PR_SET_THP_DISABLE is set on the process
 281 Threads                     number of threads
 282 SigQ                        number of signals queued/max. number for queue
 283 SigPnd                      bitmap of pending signals for the thread
 284 ShdPnd                      bitmap of shared pending signals for the process
 285 SigBlk                      bitmap of blocked signals
 286 SigIgn                      bitmap of ignored signals
 287 SigCgt                      bitmap of caught signals
 288 CapInh                      bitmap of inheritable capabilities
 289 CapPrm                      bitmap of permitted capabilities
 290 CapEff                      bitmap of effective capabilities
 291 CapBnd                      bitmap of capabilities bounding set
 292 CapAmb                      bitmap of ambient capabilities
 293 NoNewPrivs                  no_new_privs, like prctl(PR_GET_NO_NEW_PRIV, ...)
 294 Seccomp                     seccomp mode, like prctl(PR_GET_SECCOMP, ...)
 295 Speculation_Store_Bypass    speculative store bypass mitigation status
 296 SpeculationIndirectBranch   indirect branch speculation mode
 297 Cpus_allowed                mask of CPUs on which this process may run
 298 Cpus_allowed_list           Same as previous, but in "list format"
 299 Mems_allowed                mask of memory nodes allowed to this process
 300 Mems_allowed_list           Same as previous, but in "list format"
 301 voluntary_ctxt_switches     number of voluntary context switches
 302 nonvoluntary_ctxt_switches  number of non voluntary context switches
 303 ==========================  ===================================================
 304
 305
 306.. table:: Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
 307
 308 ======== ===============================       ==============================
 309 Field    Content
 310 ======== ===============================       ==============================
 311 size     total program size (pages)            (same as VmSize in status)
 312 resident size of memory portions (pages)       (same as VmRSS in status)
 313 shared   number of pages that are shared       (i.e. backed by a file, same
 314                                                as RssFile+RssShmem in status)
 315 trs      number of pages that are 'code'       (not including libs; broken,
 316                                                includes data segment)
 317 lrs      number of pages of library            (always 0 on 2.6)
 318 drs      number of pages of data/stack         (including libs; broken,
 319                                                includes library text)
 320 dt       number of dirty pages                 (always 0 on 2.6)
 321 ======== ===============================       ==============================
 322
 323
 324.. table:: Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
 325
 326  ============= ===============================================================
 327  Field         Content
 328  ============= ===============================================================
 329  pid           process id
 330  tcomm         filename of the executable
 331  state         state (R is running, S is sleeping, D is sleeping in an
 332                uninterruptible wait, Z is zombie, T is traced or stopped)
 333  ppid          process id of the parent process
 334  pgrp          pgrp of the process
 335  sid           session id
 336  tty_nr        tty the process uses
 337  tty_pgrp      pgrp of the tty
 338  flags         task flags
 339  min_flt       number of minor faults
 340  cmin_flt      number of minor faults with child's
 341  maj_flt       number of major faults
 342  cmaj_flt      number of major faults with child's
 343  utime         user mode jiffies
 344  stime         kernel mode jiffies
 345  cutime        user mode jiffies with child's
 346  cstime        kernel mode jiffies with child's
 347  priority      priority level
 348  nice          nice level
 349  num_threads   number of threads
 350  it_real_value (obsolete, always 0)
 351  start_time    time the process started after system boot
 352  vsize         virtual memory size
 353  rss           resident set memory size
 354  rsslim        current limit in bytes on the rss
 355  start_code    address above which program text can run
 356  end_code      address below which program text can run
 357  start_stack   address of the start of the main process stack
 358  esp           current value of ESP
 359  eip           current value of EIP
 360  pending       bitmap of pending signals
 361  blocked       bitmap of blocked signals
 362  sigign        bitmap of ignored signals
 363  sigcatch      bitmap of caught signals
 364  0             (place holder, used to be the wchan address,
 365                use /proc/PID/wchan instead)
 366  0             (place holder)
 367  0             (place holder)
 368  exit_signal   signal to send to parent thread on exit
 369  task_cpu      which CPU the task is scheduled on
 370  rt_priority   realtime priority
 371  policy        scheduling policy (man sched_setscheduler)
 372  blkio_ticks   time spent waiting for block IO
 373  gtime         guest time of the task in jiffies
 374  cgtime        guest time of the task children in jiffies
 375  start_data    address above which program data+bss is placed
 376  end_data      address below which program data+bss is placed
 377  start_brk     address above which program heap can be expanded with brk()
 378  arg_start     address above which program command line is placed
 379  arg_end       address below which program command line is placed
 380  env_start     address above which program environment is placed
 381  env_end       address below which program environment is placed
 382  exit_code     the thread's exit_code in the form reported by the waitpid
 383                system call
 384  ============= ===============================================================
 385
 386The /proc/PID/maps file contains the currently mapped memory regions and
 387their access permissions.
 388
 389The format is::
 390
 391    address           perms offset  dev   inode      pathname
 392
 393    08048000-08049000 r-xp 00000000 03:00 8312       /opt/test
 394    08049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
 395    0804a000-0806b000 rw-p 00000000 00:00 0          [heap]
 396    a7cb1000-a7cb2000 ---p 00000000 00:00 0
 397    a7cb2000-a7eb2000 rw-p 00000000 00:00 0
 398    a7eb2000-a7eb3000 ---p 00000000 00:00 0
 399    a7eb3000-a7ed5000 rw-p 00000000 00:00 0
 400    a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/libc.so.6
 401    a8008000-a800a000 r--p 00133000 03:00 4222       /lib/libc.so.6
 402    a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/libc.so.6
 403    a800b000-a800e000 rw-p 00000000 00:00 0
 404    a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/libpthread.so.0
 405    a8022000-a8023000 r--p 00013000 03:00 14462      /lib/libpthread.so.0
 406    a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/libpthread.so.0
 407    a8024000-a8027000 rw-p 00000000 00:00 0
 408    a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/ld-linux.so.2
 409    a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/ld-linux.so.2
 410    a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/ld-linux.so.2
 411    aff35000-aff4a000 rw-p 00000000 00:00 0          [stack]
 412    ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
 413
 414where "address" is the address space in the process that it occupies, "perms"
 415is a set of permissions::
 416
 417 r = read
 418 w = write
 419 x = execute
 420 s = shared
 421 p = private (copy on write)
 422
 423"offset" is the offset into the mapping, "dev" is the device (major:minor), and
 424"inode" is the inode  on that device.  0 indicates that  no inode is associated
 425with the memory region, as the case would be with BSS (uninitialized data).
 426The "pathname" shows the name associated file for this mapping.  If the mapping
 427is not associated with a file:
 428
 429 =============              ====================================
 430 [heap]                     the heap of the program
 431 [stack]                    the stack of the main process
 432 [vdso]                     the "virtual dynamic shared object",
 433                            the kernel system call handler
 434 [anon:<name>]              an anonymous mapping that has been
 435                            named by userspace
 436 =============              ====================================
 437
 438 or if empty, the mapping is anonymous.
 439
 440The /proc/PID/smaps is an extension based on maps, showing the memory
 441consumption for each of the process's mappings. For each mapping (aka Virtual
 442Memory Area, or VMA) there is a series of lines such as the following::
 443
 444    08048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
 445
 446    Size:               1084 kB
 447    KernelPageSize:        4 kB
 448    MMUPageSize:           4 kB
 449    Rss:                 892 kB
 450    Pss:                 374 kB
 451    Shared_Clean:        892 kB
 452    Shared_Dirty:          0 kB
 453    Private_Clean:         0 kB
 454    Private_Dirty:         0 kB
 455    Referenced:          892 kB
 456    Anonymous:             0 kB
 457    LazyFree:              0 kB
 458    AnonHugePages:         0 kB
 459    ShmemPmdMapped:        0 kB
 460    Shared_Hugetlb:        0 kB
 461    Private_Hugetlb:       0 kB
 462    Swap:                  0 kB
 463    SwapPss:               0 kB
 464    KernelPageSize:        4 kB
 465    MMUPageSize:           4 kB
 466    Locked:                0 kB
 467    THPeligible:           0
 468    VmFlags: rd ex mr mw me dw
 469
 470The first of these lines shows the same information as is displayed for the
 471mapping in /proc/PID/maps.  Following lines show the size of the mapping
 472(size); the size of each page allocated when backing a VMA (KernelPageSize),
 473which is usually the same as the size in the page table entries; the page size
 474used by the MMU when backing a VMA (in most cases, the same as KernelPageSize);
 475the amount of the mapping that is currently resident in RAM (RSS); the
 476process' proportional share of this mapping (PSS); and the number of clean and
 477dirty shared and private pages in the mapping.
 478
 479The "proportional set size" (PSS) of a process is the count of pages it has
 480in memory, where each page is divided by the number of processes sharing it.
 481So if a process has 1000 pages all to itself, and 1000 shared with one other
 482process, its PSS will be 1500.
 483
 484Note that even a page which is part of a MAP_SHARED mapping, but has only
 485a single pte mapped, i.e.  is currently used by only one process, is accounted
 486as private and not as shared.
 487
 488"Referenced" indicates the amount of memory currently marked as referenced or
 489accessed.
 490
 491"Anonymous" shows the amount of memory that does not belong to any file.  Even
 492a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
 493and a page is modified, the file page is replaced by a private anonymous copy.
 494
 495"LazyFree" shows the amount of memory which is marked by madvise(MADV_FREE).
 496The memory isn't freed immediately with madvise(). It's freed in memory
 497pressure if the memory is clean. Please note that the printed value might
 498be lower than the real value due to optimizations used in the current
 499implementation. If this is not desirable please file a bug report.
 500
 501"AnonHugePages" shows the ammount of memory backed by transparent hugepage.
 502
 503"ShmemPmdMapped" shows the ammount of shared (shmem/tmpfs) memory backed by
 504huge pages.
 505
 506"Shared_Hugetlb" and "Private_Hugetlb" show the ammounts of memory backed by
 507hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical
 508reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field.
 509
 510"Swap" shows how much would-be-anonymous memory is also used, but out on swap.
 511
 512For shmem mappings, "Swap" includes also the size of the mapped (and not
 513replaced by copy-on-write) part of the underlying shmem object out on swap.
 514"SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
 515does not take into account swapped out page of underlying shmem objects.
 516"Locked" indicates whether the mapping is locked in memory or not.
 517"THPeligible" indicates whether the mapping is eligible for allocating THP
 518pages - 1 if true, 0 otherwise. It just shows the current status.
 519
 520"VmFlags" field deserves a separate description. This member represents the
 521kernel flags associated with the particular virtual memory area in two letter
 522encoded manner. The codes are the following:
 523
 524    ==    =======================================
 525    rd    readable
 526    wr    writeable
 527    ex    executable
 528    sh    shared
 529    mr    may read
 530    mw    may write
 531    me    may execute
 532    ms    may share
 533    gd    stack segment growns down
 534    pf    pure PFN range
 535    dw    disabled write to the mapped file
 536    lo    pages are locked in memory
 537    io    memory mapped I/O area
 538    sr    sequential read advise provided
 539    rr    random read advise provided
 540    dc    do not copy area on fork
 541    de    do not expand area on remapping
 542    ac    area is accountable
 543    nr    swap space is not reserved for the area
 544    ht    area uses huge tlb pages
 545    sf    synchronous page fault
 546    ar    architecture specific flag
 547    wf    wipe on fork
 548    dd    do not include area into core dump
 549    sd    soft dirty flag
 550    mm    mixed map area
 551    hg    huge page advise flag
 552    nh    no huge page advise flag
 553    mg    mergable advise flag
 554    bt    arm64 BTI guarded page
 555    mt    arm64 MTE allocation tags are enabled
 556    um    userfaultfd missing tracking
 557    uw    userfaultfd wr-protect tracking
 558    ==    =======================================
 559
 560Note that there is no guarantee that every flag and associated mnemonic will
 561be present in all further kernel releases. Things get changed, the flags may
 562be vanished or the reverse -- new added. Interpretation of their meaning
 563might change in future as well. So each consumer of these flags has to
 564follow each specific kernel version for the exact semantic.
 565
 566This file is only present if the CONFIG_MMU kernel configuration option is
 567enabled.
 568
 569Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy (consistent
 570output can be achieved only in the single read call).
 571
 572This typically manifests when doing partial reads of these files while the
 573memory map is being modified.  Despite the races, we do provide the following
 574guarantees:
 575
 5761) The mapped addresses never go backwards, which implies no two
 577   regions will ever overlap.
 5782) If there is something at a given vaddr during the entirety of the
 579   life of the smaps/maps walk, there will be some output for it.
 580
 581The /proc/PID/smaps_rollup file includes the same fields as /proc/PID/smaps,
 582but their values are the sums of the corresponding values for all mappings of
 583the process.  Additionally, it contains these fields:
 584
 585- Pss_Anon
 586- Pss_File
 587- Pss_Shmem
 588
 589They represent the proportional shares of anonymous, file, and shmem pages, as
 590described for smaps above.  These fields are omitted in smaps since each
 591mapping identifies the type (anon, file, or shmem) of all pages it contains.
 592Thus all information in smaps_rollup can be derived from smaps, but at a
 593significantly higher cost.
 594
 595The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
 596bits on both physical and virtual pages associated with a process, and the
 597soft-dirty bit on pte (see Documentation/admin-guide/mm/soft-dirty.rst
 598for details).
 599To clear the bits for all the pages associated with the process::
 600
 601    > echo 1 > /proc/PID/clear_refs
 602
 603To clear the bits for the anonymous pages associated with the process::
 604
 605    > echo 2 > /proc/PID/clear_refs
 606
 607To clear the bits for the file mapped pages associated with the process::
 608
 609    > echo 3 > /proc/PID/clear_refs
 610
 611To clear the soft-dirty bit::
 612
 613    > echo 4 > /proc/PID/clear_refs
 614
 615To reset the peak resident set size ("high water mark") to the process's
 616current value::
 617
 618    > echo 5 > /proc/PID/clear_refs
 619
 620Any other value written to /proc/PID/clear_refs will have no effect.
 621
 622The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
 623using /proc/kpageflags and number of times a page is mapped using
 624/proc/kpagecount. For detailed explanation, see
 625Documentation/admin-guide/mm/pagemap.rst.
 626
 627The /proc/pid/numa_maps is an extension based on maps, showing the memory
 628locality and binding policy, as well as the memory usage (in pages) of
 629each mapping. The output follows a general format where mapping details get
 630summarized separated by blank spaces, one mapping per each file line::
 631
 632    address   policy    mapping details
 633
 634    00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
 635    00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
 636    3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
 637    320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
 638    3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
 639    3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
 640    3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
 641    320698b000 default file=/lib64/libc-2.12.so
 642    3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4
 643    3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
 644    3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
 645    7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
 646    7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
 647    7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
 648    7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
 649    7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4
 650
 651Where:
 652
 653"address" is the starting address for the mapping;
 654
 655"policy" reports the NUMA memory policy set for the mapping (see Documentation/admin-guide/mm/numa_memory_policy.rst);
 656
 657"mapping details" summarizes mapping data such as mapping type, page usage counters,
 658node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
 659size, in KB, that is backing the mapping up.
 660
 6611.2 Kernel data
 662---------------
 663
 664Similar to  the  process entries, the kernel data files give information about
 665the running kernel. The files used to obtain this information are contained in
 666/proc and  are  listed  in Table 1-5. Not all of these will be present in your
 667system. It  depends  on the kernel configuration and the loaded modules, which
 668files are there, and which are missing.
 669
 670.. table:: Table 1-5: Kernel info in /proc
 671
 672 ============ ===============================================================
 673 File         Content
 674 ============ ===============================================================
 675 apm          Advanced power management info
 676 buddyinfo    Kernel memory allocator information (see text)    (2.5)
 677 bus          Directory containing bus specific information
 678 cmdline      Kernel command line
 679 cpuinfo      Info about the CPU
 680 devices      Available devices (block and character)
 681 dma          Used DMS channels
 682 filesystems  Supported filesystems
 683 driver       Various drivers grouped here, currently rtc       (2.4)
 684 execdomains  Execdomains, related to security                  (2.4)
 685 fb           Frame Buffer devices                              (2.4)
 686 fs           File system parameters, currently nfs/exports     (2.4)
 687 ide          Directory containing info about the IDE subsystem
 688 interrupts   Interrupt usage
 689 iomem        Memory map                                        (2.4)
 690 ioports      I/O port usage
 691 irq          Masks for irq to cpu affinity                     (2.4)(smp?)
 692 isapnp       ISA PnP (Plug&Play) Info                          (2.4)
 693 kcore        Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
 694 kmsg         Kernel messages
 695 ksyms        Kernel symbol table
 696 loadavg      Load average of last 1, 5 & 15 minutes;
 697                number of processes currently runnable (running or on ready queue);
 698                total number of processes in system;
 699                last pid created.
 700                All fields are separated by one space except "number of
 701                processes currently runnable" and "total number of processes
 702                in system", which are separated by a slash ('/'). Example:
 703                0.61 0.61 0.55 3/828 22084
 704 locks        Kernel locks
 705 meminfo      Memory info
 706 misc         Miscellaneous
 707 modules      List of loaded modules
 708 mounts       Mounted filesystems
 709 net          Networking info (see text)
 710 pagetypeinfo Additional page allocator information (see text)  (2.5)
 711 partitions   Table of partitions known to the system
 712 pci          Deprecated info of PCI bus (new way -> /proc/bus/pci/,
 713              decoupled by lspci                                (2.4)
 714 rtc          Real time clock
 715 scsi         SCSI info (see text)
 716 slabinfo     Slab pool info
 717 softirqs     softirq usage
 718 stat         Overall statistics
 719 swaps        Swap space utilization
 720 sys          See chapter 2
 721 sysvipc      Info of SysVIPC Resources (msg, sem, shm)         (2.4)
 722 tty          Info of tty drivers
 723 uptime       Wall clock since boot, combined idle time of all cpus
 724 version      Kernel version
 725 video        bttv info of video resources                      (2.4)
 726 vmallocinfo  Show vmalloced areas
 727 ============ ===============================================================
 728
 729You can,  for  example,  check  which interrupts are currently in use and what
 730they are used for by looking in the file /proc/interrupts::
 731
 732  > cat /proc/interrupts
 733             CPU0
 734    0:    8728810          XT-PIC  timer
 735    1:        895          XT-PIC  keyboard
 736    2:          0          XT-PIC  cascade
 737    3:     531695          XT-PIC  aha152x
 738    4:    2014133          XT-PIC  serial
 739    5:      44401          XT-PIC  pcnet_cs
 740    8:          2          XT-PIC  rtc
 741   11:          8          XT-PIC  i82365
 742   12:     182918          XT-PIC  PS/2 Mouse
 743   13:          1          XT-PIC  fpu
 744   14:    1232265          XT-PIC  ide0
 745   15:          7          XT-PIC  ide1
 746  NMI:          0
 747
 748In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
 749output of a SMP machine)::
 750
 751  > cat /proc/interrupts
 752
 753             CPU0       CPU1
 754    0:    1243498    1214548    IO-APIC-edge  timer
 755    1:       8949       8958    IO-APIC-edge  keyboard
 756    2:          0          0          XT-PIC  cascade
 757    5:      11286      10161    IO-APIC-edge  soundblaster
 758    8:          1          0    IO-APIC-edge  rtc
 759    9:      27422      27407    IO-APIC-edge  3c503
 760   12:     113645     113873    IO-APIC-edge  PS/2 Mouse
 761   13:          0          0          XT-PIC  fpu
 762   14:      22491      24012    IO-APIC-edge  ide0
 763   15:       2183       2415    IO-APIC-edge  ide1
 764   17:      30564      30414   IO-APIC-level  eth0
 765   18:        177        164   IO-APIC-level  bttv
 766  NMI:    2457961    2457959
 767  LOC:    2457882    2457881
 768  ERR:       2155
 769
 770NMI is incremented in this case because every timer interrupt generates a NMI
 771(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
 772
 773LOC is the local interrupt counter of the internal APIC of every CPU.
 774
 775ERR is incremented in the case of errors in the IO-APIC bus (the bus that
 776connects the CPUs in a SMP system. This means that an error has been detected,
 777the IO-APIC automatically retry the transmission, so it should not be a big
 778problem, but you should read the SMP-FAQ.
 779
 780In 2.6.2* /proc/interrupts was expanded again.  This time the goal was for
 781/proc/interrupts to display every IRQ vector in use by the system, not
 782just those considered 'most important'.  The new vectors are:
 783
 784THR
 785  interrupt raised when a machine check threshold counter
 786  (typically counting ECC corrected errors of memory or cache) exceeds
 787  a configurable threshold.  Only available on some systems.
 788
 789TRM
 790  a thermal event interrupt occurs when a temperature threshold
 791  has been exceeded for the CPU.  This interrupt may also be generated
 792  when the temperature drops back to normal.
 793
 794SPU
 795  a spurious interrupt is some interrupt that was raised then lowered
 796  by some IO device before it could be fully processed by the APIC.  Hence
 797  the APIC sees the interrupt but does not know what device it came from.
 798  For this case the APIC will generate the interrupt with a IRQ vector
 799  of 0xff. This might also be generated by chipset bugs.
 800
 801RES, CAL, TLB
 802  rescheduling, call and TLB flush interrupts are
 803  sent from one CPU to another per the needs of the OS.  Typically,
 804  their statistics are used by kernel developers and interested users to
 805  determine the occurrence of interrupts of the given type.
 806
 807The above IRQ vectors are displayed only when relevant.  For example,
 808the threshold vector does not exist on x86_64 platforms.  Others are
 809suppressed when the system is a uniprocessor.  As of this writing, only
 810i386 and x86_64 platforms support the new IRQ vector displays.
 811
 812Of some interest is the introduction of the /proc/irq directory to 2.4.
 813It could be used to set IRQ to CPU affinity. This means that you can "hook" an
 814IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
 815irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
 816prof_cpu_mask.
 817
 818For example::
 819
 820  > ls /proc/irq/
 821  0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
 822  1  11  13  15  17  19  3  5  7  9  default_smp_affinity
 823  > ls /proc/irq/0/
 824  smp_affinity
 825
 826smp_affinity is a bitmask, in which you can specify which CPUs can handle the
 827IRQ. You can set it by doing::
 828
 829  > echo 1 > /proc/irq/10/smp_affinity
 830
 831This means that only the first CPU will handle the IRQ, but you can also echo
 8325 which means that only the first and third CPU can handle the IRQ.
 833
 834The contents of each smp_affinity file is the same by default::
 835
 836  > cat /proc/irq/0/smp_affinity
 837  ffffffff
 838
 839There is an alternate interface, smp_affinity_list which allows specifying
 840a CPU range instead of a bitmask::
 841
 842  > cat /proc/irq/0/smp_affinity_list
 843  1024-1031
 844
 845The default_smp_affinity mask applies to all non-active IRQs, which are the
 846IRQs which have not yet been allocated/activated, and hence which lack a
 847/proc/irq/[0-9]* directory.
 848
 849The node file on an SMP system shows the node to which the device using the IRQ
 850reports itself as being attached. This hardware locality information does not
 851include information about any possible driver locality preference.
 852
 853prof_cpu_mask specifies which CPUs are to be profiled by the system wide
 854profiler. Default value is ffffffff (all CPUs if there are only 32 of them).
 855
 856The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
 857between all the CPUs which are allowed to handle it. As usual the kernel has
 858more info than you and does a better job than you, so the defaults are the
 859best choice for almost everyone.  [Note this applies only to those IO-APIC's
 860that support "Round Robin" interrupt distribution.]
 861
 862There are  three  more  important subdirectories in /proc: net, scsi, and sys.
 863The general  rule  is  that  the  contents,  or  even  the  existence of these
 864directories, depend  on your kernel configuration. If SCSI is not enabled, the
 865directory scsi  may  not  exist. The same is true with the net, which is there
 866only when networking support is present in the running kernel.
 867
 868The slabinfo  file  gives  information  about  memory usage at the slab level.
 869Linux uses  slab  pools for memory management above page level in version 2.2.
 870Commonly used  objects  have  their  own  slab  pool (such as network buffers,
 871directory cache, and so on).
 872
 873::
 874
 875    > cat /proc/buddyinfo
 876
 877    Node 0, zone      DMA      0      4      5      4      4      3 ...
 878    Node 0, zone   Normal      1      0      0      1    101      8 ...
 879    Node 0, zone  HighMem      2      0      0      1      1      0 ...
 880
 881External fragmentation is a problem under some workloads, and buddyinfo is a
 882useful tool for helping diagnose these problems.  Buddyinfo will give you a
 883clue as to how big an area you can safely allocate, or why a previous
 884allocation failed.
 885
 886Each column represents the number of pages of a certain order which are
 887available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
 888ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
 889available in ZONE_NORMAL, etc...
 890
 891More information relevant to external fragmentation can be found in
 892pagetypeinfo::
 893
 894    > cat /proc/pagetypeinfo
 895    Page block order: 9
 896    Pages per block:  512
 897
 898    Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
 899    Node    0, zone      DMA, type    Unmovable      0      0      0      1      1      1      1      1      1      1      0
 900    Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0
 901    Node    0, zone      DMA, type      Movable      1      1      2      1      2      1      1      0      1      0      2
 902    Node    0, zone      DMA, type      Reserve      0      0      0      0      0      0      0      0      0      1      0
 903    Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
 904    Node    0, zone    DMA32, type    Unmovable    103     54     77      1      1      1     11      8      7      1      9
 905    Node    0, zone    DMA32, type  Reclaimable      0      0      2      1      0      0      0      0      1      0      0
 906    Node    0, zone    DMA32, type      Movable    169    152    113     91     77     54     39     13      6      1    452
 907    Node    0, zone    DMA32, type      Reserve      1      2      2      2      2      0      1      1      1      1      0
 908    Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
 909
 910    Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate
 911    Node 0, zone      DMA            2            0            5            1            0
 912    Node 0, zone    DMA32           41            6          967            2            0
 913
 914Fragmentation avoidance in the kernel works by grouping pages of different
 915migrate types into the same contiguous regions of memory called page blocks.
 916A page block is typically the size of the default hugepage size, e.g. 2MB on
 917X86-64. By keeping pages grouped based on their ability to move, the kernel
 918can reclaim pages within a page block to satisfy a high-order allocation.
 919
 920The pagetypinfo begins with information on the size of a page block. It
 921then gives the same type of information as buddyinfo except broken down
 922by migrate-type and finishes with details on how many page blocks of each
 923type exist.
 924
 925If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
 926from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can
 927make an estimate of the likely number of huge pages that can be allocated
 928at a given point in time. All the "Movable" blocks should be allocatable
 929unless memory has been mlock()'d. Some of the Reclaimable blocks should
 930also be allocatable although a lot of filesystem metadata may have to be
 931reclaimed to achieve this.
 932
 933
 934meminfo
 935~~~~~~~
 936
 937Provides information about distribution and utilization of memory.  This
 938varies by architecture and compile options.  Some of the counters reported
 939here overlap.  The memory reported by the non overlapping counters may not
 940add up to the overall memory usage and the difference for some workloads
 941can be substantial.  In many cases there are other means to find out
 942additional memory using subsystem specific interfaces, for instance
 943/proc/net/sockstat for TCP memory allocations.
 944
 945The following is from a 16GB PIII, which has highmem enabled.
 946You may not have all of these fields.
 947
 948::
 949
 950    > cat /proc/meminfo
 951
 952    MemTotal:     16344972 kB
 953    MemFree:      13634064 kB
 954    MemAvailable: 14836172 kB
 955    Buffers:          3656 kB
 956    Cached:        1195708 kB
 957    SwapCached:          0 kB
 958    Active:         891636 kB
 959    Inactive:      1077224 kB
 960    HighTotal:    15597528 kB
 961    HighFree:     13629632 kB
 962    LowTotal:       747444 kB
 963    LowFree:          4432 kB
 964    SwapTotal:           0 kB
 965    SwapFree:            0 kB
 966    Dirty:             968 kB
 967    Writeback:           0 kB
 968    AnonPages:      861800 kB
 969    Mapped:         280372 kB
 970    Shmem:             644 kB
 971    KReclaimable:   168048 kB
 972    Slab:           284364 kB
 973    SReclaimable:   159856 kB
 974    SUnreclaim:     124508 kB
 975    PageTables:      24448 kB
 976    NFS_Unstable:        0 kB
 977    Bounce:              0 kB
 978    WritebackTmp:        0 kB
 979    CommitLimit:   7669796 kB
 980    Committed_AS:   100056 kB
 981    VmallocTotal:   112216 kB
 982    VmallocUsed:       428 kB
 983    VmallocChunk:   111088 kB
 984    Percpu:          62080 kB
 985    HardwareCorrupted:   0 kB
 986    AnonHugePages:   49152 kB
 987    ShmemHugePages:      0 kB
 988    ShmemPmdMapped:      0 kB
 989
 990MemTotal
 991              Total usable RAM (i.e. physical RAM minus a few reserved
 992              bits and the kernel binary code)
 993MemFree
 994              The sum of LowFree+HighFree
 995MemAvailable
 996              An estimate of how much memory is available for starting new
 997              applications, without swapping. Calculated from MemFree,
 998              SReclaimable, the size of the file LRU lists, and the low
 999              watermarks in each zone.
1000              The estimate takes into account that the system needs some
1001              page cache to function well, and that not all reclaimable
1002              slab will be reclaimable, due to items being in use. The
1003              impact of those factors will vary from system to system.
1004Buffers
1005              Relatively temporary storage for raw disk blocks
1006              shouldn't get tremendously large (20MB or so)
1007Cached
1008              in-memory cache for files read from the disk (the
1009              pagecache).  Doesn't include SwapCached
1010SwapCached
1011              Memory that once was swapped out, is swapped back in but
1012              still also is in the swapfile (if memory is needed it
1013              doesn't need to be swapped out AGAIN because it is already
1014              in the swapfile. This saves I/O)
1015Active
1016              Memory that has been used more recently and usually not
1017              reclaimed unless absolutely necessary.
1018Inactive
1019              Memory which has been less recently used.  It is more
1020              eligible to be reclaimed for other purposes
1021HighTotal, HighFree
1022              Highmem is all memory above ~860MB of physical memory.
1023              Highmem areas are for use by userspace programs, or
1024              for the pagecache.  The kernel must use tricks to access
1025              this memory, making it slower to access than lowmem.
1026LowTotal, LowFree
1027              Lowmem is memory which can be used for everything that
1028              highmem can be used for, but it is also available for the
1029              kernel's use for its own data structures.  Among many
1030              other things, it is where everything from the Slab is
1031              allocated.  Bad things happen when you're out of lowmem.
1032SwapTotal
1033              total amount of swap space available
1034SwapFree
1035              Memory which has been evicted from RAM, and is temporarily
1036              on the disk
1037Dirty
1038              Memory which is waiting to get written back to the disk
1039Writeback
1040              Memory which is actively being written back to the disk
1041AnonPages
1042              Non-file backed pages mapped into userspace page tables
1043HardwareCorrupted
1044              The amount of RAM/memory in KB, the kernel identifies as
1045              corrupted.
1046AnonHugePages
1047              Non-file backed huge pages mapped into userspace page tables
1048Mapped
1049              files which have been mmaped, such as libraries
1050Shmem
1051              Total memory used by shared memory (shmem) and tmpfs
1052ShmemHugePages
1053              Memory used by shared memory (shmem) and tmpfs allocated
1054              with huge pages
1055ShmemPmdMapped
1056              Shared memory mapped into userspace with huge pages
1057KReclaimable
1058              Kernel allocations that the kernel will attempt to reclaim
1059              under memory pressure. Includes SReclaimable (below), and other
1060              direct allocations with a shrinker.
1061Slab
1062              in-kernel data structures cache
1063SReclaimable
1064              Part of Slab, that might be reclaimed, such as caches
1065SUnreclaim
1066              Part of Slab, that cannot be reclaimed on memory pressure
1067PageTables
1068              amount of memory dedicated to the lowest level of page
1069              tables.
1070NFS_Unstable
1071              Always zero. Previous counted pages which had been written to
1072              the server, but has not been committed to stable storage.
1073Bounce
1074              Memory used for block device "bounce buffers"
1075WritebackTmp
1076              Memory used by FUSE for temporary writeback buffers
1077CommitLimit
1078              Based on the overcommit ratio ('vm.overcommit_ratio'),
1079              this is the total amount of  memory currently available to
1080              be allocated on the system. This limit is only adhered to
1081              if strict overcommit accounting is enabled (mode 2 in
1082              'vm.overcommit_memory').
1083
1084              The CommitLimit is calculated with the following formula::
1085
1086                CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
1087                               overcommit_ratio / 100 + [total swap pages]
1088
1089              For example, on a system with 1G of physical RAM and 7G
1090              of swap with a `vm.overcommit_ratio` of 30 it would
1091              yield a CommitLimit of 7.3G.
1092
1093              For more details, see the memory overcommit documentation
1094              in vm/overcommit-accounting.
1095Committed_AS
1096              The amount of memory presently allocated on the system.
1097              The committed memory is a sum of all of the memory which
1098              has been allocated by processes, even if it has not been
1099              "used" by them as of yet. A process which malloc()'s 1G
1100              of memory, but only touches 300M of it will show up as
1101              using 1G. This 1G is memory which has been "committed" to
1102              by the VM and can be used at any time by the allocating
1103              application. With strict overcommit enabled on the system
1104              (mode 2 in 'vm.overcommit_memory'), allocations which would
1105              exceed the CommitLimit (detailed above) will not be permitted.
1106              This is useful if one needs to guarantee that processes will
1107              not fail due to lack of memory once that memory has been
1108              successfully allocated.
1109VmallocTotal
1110              total size of vmalloc memory area
1111VmallocUsed
1112              amount of vmalloc area which is used
1113VmallocChunk
1114              largest contiguous block of vmalloc area which is free
1115Percpu
1116              Memory allocated to the percpu allocator used to back percpu
1117              allocations. This stat excludes the cost of metadata.
1118
1119vmallocinfo
1120~~~~~~~~~~~
1121
1122Provides information about vmalloced/vmaped areas. One line per area,
1123containing the virtual address range of the area, size in bytes,
1124caller information of the creator, and optional information depending
1125on the kind of area:
1126
1127 ==========  ===================================================
1128 pages=nr    number of pages
1129 phys=addr   if a physical address was specified
1130 ioremap     I/O mapping (ioremap() and friends)
1131 vmalloc     vmalloc() area
1132 vmap        vmap()ed pages
1133 user        VM_USERMAP area
1134 vpages      buffer for pages pointers was vmalloced (huge area)
1135 N<node>=nr  (Only on NUMA kernels)
1136             Number of pages allocated on memory node <node>
1137 ==========  ===================================================
1138
1139::
1140
1141    > cat /proc/vmallocinfo
1142    0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
1143    /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
1144    0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
1145    /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
1146    0xffffc20000302000-0xffffc20000304000    8192 acpi_tb_verify_table+0x21/0x4f...
1147    phys=7fee8000 ioremap
1148    0xffffc20000304000-0xffffc20000307000   12288 acpi_tb_verify_table+0x21/0x4f...
1149    phys=7fee7000 ioremap
1150    0xffffc2000031d000-0xffffc2000031f000    8192 init_vdso_vars+0x112/0x210
1151    0xffffc2000031f000-0xffffc2000032b000   49152 cramfs_uncompress_init+0x2e ...
1152    /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
1153    0xffffc2000033a000-0xffffc2000033d000   12288 sys_swapon+0x640/0xac0      ...
1154    pages=2 vmalloc N1=2
1155    0xffffc20000347000-0xffffc2000034c000   20480 xt_alloc_table_info+0xfe ...
1156    /0x130 [x_tables] pages=4 vmalloc N0=4
1157    0xffffffffa0000000-0xffffffffa000f000   61440 sys_init_module+0xc27/0x1d00 ...
1158    pages=14 vmalloc N2=14
1159    0xffffffffa000f000-0xffffffffa0014000   20480 sys_init_module+0xc27/0x1d00 ...
1160    pages=4 vmalloc N1=4
1161    0xffffffffa0014000-0xffffffffa0017000   12288 sys_init_module+0xc27/0x1d00 ...
1162    pages=2 vmalloc N1=2
1163    0xffffffffa0017000-0xffffffffa0022000   45056 sys_init_module+0xc27/0x1d00 ...
1164    pages=10 vmalloc N0=10
1165
1166
1167softirqs
1168~~~~~~~~
1169
1170Provides counts of softirq handlers serviced since boot time, for each CPU.
1171
1172::
1173
1174    > cat /proc/softirqs
1175                  CPU0       CPU1       CPU2       CPU3
1176        HI:          0          0          0          0
1177    TIMER:       27166      27120      27097      27034
1178    NET_TX:          0          0          0         17
1179    NET_RX:         42          0          0         39
1180    BLOCK:           0          0        107       1121
1181    TASKLET:         0          0          0        290
1182    SCHED:       27035      26983      26971      26746
1183    HRTIMER:         0          0          0          0
1184        RCU:      1678       1769       2178       2250
1185
1186
11871.3 IDE devices in /proc/ide
1188----------------------------
1189
1190The subdirectory /proc/ide contains information about all IDE devices of which
1191the kernel  is  aware.  There is one subdirectory for each IDE controller, the
1192file drivers  and a link for each IDE device, pointing to the device directory
1193in the controller specific subtree.
1194
1195The file 'drivers' contains general information about the drivers used for the
1196IDE devices::
1197
1198  > cat /proc/ide/drivers
1199  ide-cdrom version 4.53
1200  ide-disk version 1.08
1201
1202More detailed  information  can  be  found  in  the  controller  specific
1203subdirectories. These  are  named  ide0,  ide1  and  so  on.  Each  of  these
1204directories contains the files shown in table 1-6.
1205
1206
1207.. table:: Table 1-6: IDE controller info in  /proc/ide/ide?
1208
1209 ======= =======================================
1210 File    Content
1211 ======= =======================================
1212 channel IDE channel (0 or 1)
1213 config  Configuration (only for PCI/IDE bridge)
1214 mate    Mate name
1215 model   Type/Chipset of IDE controller
1216 ======= =======================================
1217
1218Each device  connected  to  a  controller  has  a separate subdirectory in the
1219controllers directory.  The  files  listed in table 1-7 are contained in these
1220directories.
1221
1222
1223.. table:: Table 1-7: IDE device information
1224
1225 ================ ==========================================
1226 File             Content
1227 ================ ==========================================
1228 cache            The cache
1229 capacity         Capacity of the medium (in 512Byte blocks)
1230 driver           driver and version
1231 geometry         physical and logical geometry
1232 identify         device identify block
1233 media            media type
1234 model            device identifier
1235 settings         device setup
1236 smart_thresholds IDE disk management thresholds
1237 smart_values     IDE disk management values
1238 ================ ==========================================
1239
1240The most  interesting  file is ``settings``. This file contains a nice
1241overview of the drive parameters::
1242
1243  # cat /proc/ide/ide0/hda/settings
1244  name                    value           min             max             mode
1245  ----                    -----           ---             ---             ----
1246  bios_cyl                526             0               65535           rw
1247  bios_head               255             0               255             rw
1248  bios_sect               63              0               63              rw
1249  breada_readahead        4               0               127             rw
1250  bswap                   0               0               1               r
1251  file_readahead          72              0               2097151         rw
1252  io_32bit                0               0               3               rw
1253  keepsettings            0               0               1               rw
1254  max_kb_per_request      122             1               127             rw
1255  multcount               0               0               8               rw
1256  nice1                   1               0               1               rw
1257  nowerr                  0               0               1               rw
1258  pio_mode                write-only      0               255             w
1259  slow                    0               0               1               rw
1260  unmaskirq               0               0               1               rw
1261  using_dma               0               0               1               rw
1262
1263
12641.4 Networking info in /proc/net
1265--------------------------------
1266
1267The subdirectory  /proc/net  follows  the  usual  pattern. Table 1-8 shows the
1268additional values  you  get  for  IP  version 6 if you configure the kernel to
1269support this. Table 1-9 lists the files and their meaning.
1270
1271
1272.. table:: Table 1-8: IPv6 info in /proc/net
1273
1274 ========== =====================================================
1275 File       Content
1276 ========== =====================================================
1277 udp6       UDP sockets (IPv6)
1278 tcp6       TCP sockets (IPv6)
1279 raw6       Raw device statistics (IPv6)
1280 igmp6      IP multicast addresses, which this host joined (IPv6)
1281 if_inet6   List of IPv6 interface addresses
1282 ipv6_route Kernel routing table for IPv6
1283 rt6_stats  Global IPv6 routing tables statistics
1284 sockstat6  Socket statistics (IPv6)
1285 snmp6      Snmp data (IPv6)
1286 ========== =====================================================
1287
1288.. table:: Table 1-9: Network info in /proc/net
1289
1290 ============= ================================================================
1291 File          Content
1292 ============= ================================================================
1293 arp           Kernel  ARP table
1294 dev           network devices with statistics
1295 dev_mcast     the Layer2 multicast groups a device is listening too
1296               (interface index, label, number of references, number of bound
1297               addresses).
1298 dev_stat      network device status
1299 ip_fwchains   Firewall chain linkage
1300 ip_fwnames    Firewall chain names
1301 ip_masq       Directory containing the masquerading tables
1302 ip_masquerade Major masquerading table
1303 netstat       Network statistics
1304 raw           raw device statistics
1305 route         Kernel routing table
1306 rpc           Directory containing rpc info
1307 rt_cache      Routing cache
1308 snmp          SNMP data
1309 sockstat      Socket statistics
1310 tcp           TCP  sockets
1311 udp           UDP sockets
1312 unix          UNIX domain sockets
1313 wireless      Wireless interface data (Wavelan etc)
1314 igmp          IP multicast addresses, which this host joined
1315 psched        Global packet scheduler parameters.
1316 netlink       List of PF_NETLINK sockets
1317 ip_mr_vifs    List of multicast virtual interfaces
1318 ip_mr_cache   List of multicast routing cache
1319 ============= ================================================================
1320
1321You can  use  this  information  to see which network devices are available in
1322your system and how much traffic was routed over those devices::
1323
1324  > cat /proc/net/dev
1325  Inter-|Receive                                                   |[...
1326   face |bytes    packets errs drop fifo frame compressed multicast|[...
1327      lo:  908188   5596     0    0    0     0          0         0 [...
1328    ppp0:15475140  20721   410    0    0   410          0         0 [...
1329    eth0:  614530   7085     0    0    0     0          0         1 [...
1330
1331  ...] Transmit
1332  ...] bytes    packets errs drop fifo colls carrier compressed
1333  ...]  908188     5596    0    0    0     0       0          0
1334  ...] 1375103    17405    0    0    0     0       0          0
1335  ...] 1703981     5535    0    0    0     3       0          0
1336
1337In addition, each Channel Bond interface has its own directory.  For
1338example, the bond0 device will have a directory called /proc/net/bond0/.
1339It will contain information that is specific to that bond, such as the
1340current slaves of the bond, the link status of the slaves, and how
1341many times the slaves link has failed.
1342
13431.5 SCSI info
1344-------------
1345
1346If you  have  a  SCSI  host adapter in your system, you'll find a subdirectory
1347named after  the driver for this adapter in /proc/scsi. You'll also see a list
1348of all recognized SCSI devices in /proc/scsi::
1349
1350  >cat /proc/scsi/scsi
1351  Attached devices:
1352  Host: scsi0 Channel: 00 Id: 00 Lun: 00
1353    Vendor: IBM      Model: DGHS09U          Rev: 03E0
1354    Type:   Direct-Access                    ANSI SCSI revision: 03
1355  Host: scsi0 Channel: 00 Id: 06 Lun: 00
1356    Vendor: PIONEER  Model: CD-ROM DR-U06S   Rev: 1.04
1357    Type:   CD-ROM                           ANSI SCSI revision: 02
1358
1359
1360The directory  named  after  the driver has one file for each adapter found in
1361the system.  These  files  contain information about the controller, including
1362the used  IRQ  and  the  IO  address range. The amount of information shown is
1363dependent on  the adapter you use. The example shows the output for an Adaptec
1364AHA-2940 SCSI adapter::
1365
1366  > cat /proc/scsi/aic7xxx/0
1367
1368  Adaptec AIC7xxx driver version: 5.1.19/3.2.4
1369  Compile Options:
1370    TCQ Enabled By Default : Disabled
1371    AIC7XXX_PROC_STATS     : Disabled
1372    AIC7XXX_RESET_DELAY    : 5
1373  Adapter Configuration:
1374             SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
1375                             Ultra Wide Controller
1376      PCI MMAPed I/O Base: 0xeb001000
1377   Adapter SEEPROM Config: SEEPROM found and used.
1378        Adaptec SCSI BIOS: Enabled
1379                      IRQ: 10
1380                     SCBs: Active 0, Max Active 2,
1381                           Allocated 15, HW 16, Page 255
1382               Interrupts: 160328
1383        BIOS Control Word: 0x18b6
1384     Adapter Control Word: 0x005b
1385     Extended Translation: Enabled
1386  Disconnect Enable Flags: 0xffff
1387       Ultra Enable Flags: 0x0001
1388   Tag Queue Enable Flags: 0x0000
1389  Ordered Queue Tag Flags: 0x0000
1390  Default Tag Queue Depth: 8
1391      Tagged Queue By Device array for aic7xxx host instance 0:
1392        {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
1393      Actual queue depth per device for aic7xxx host instance 0:
1394        {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
1395  Statistics:
1396  (scsi0:0:0:0)
1397    Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
1398    Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
1399    Total transfers 160151 (74577 reads and 85574 writes)
1400  (scsi0:0:6:0)
1401    Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
1402    Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
1403    Total transfers 0 (0 reads and 0 writes)
1404
1405
14061.6 Parallel port info in /proc/parport
1407---------------------------------------
1408
1409The directory  /proc/parport  contains information about the parallel ports of
1410your system.  It  has  one  subdirectory  for  each port, named after the port
1411number (0,1,2,...).
1412
1413These directories contain the four files shown in Table 1-10.
1414
1415
1416.. table:: Table 1-10: Files in /proc/parport
1417
1418 ========= ====================================================================
1419 File      Content
1420 ========= ====================================================================
1421 autoprobe Any IEEE-1284 device ID information that has been acquired.
1422 devices   list of the device drivers using that port. A + will appear by the
1423           name of the device currently using the port (it might not appear
1424           against any).
1425 hardware  Parallel port's base address, IRQ line and DMA channel.
1426 irq       IRQ that parport is using for that port. This is in a separate
1427           file to allow you to alter it by writing a new value in (IRQ
1428           number or none).
1429 ========= ====================================================================
1430
14311.7 TTY info in /proc/tty
1432-------------------------
1433
1434Information about  the  available  and actually used tty's can be found in the
1435directory /proc/tty. You'll find  entries  for drivers and line disciplines in
1436this directory, as shown in Table 1-11.
1437
1438
1439.. table:: Table 1-11: Files in /proc/tty
1440
1441 ============= ==============================================
1442 File          Content
1443 ============= ==============================================
1444 drivers       list of drivers and their usage
1445 ldiscs        registered line disciplines
1446 driver/serial usage statistic and status of single tty lines
1447 ============= ==============================================
1448
1449To see  which  tty's  are  currently in use, you can simply look into the file
1450/proc/tty/drivers::
1451
1452  > cat /proc/tty/drivers
1453  pty_slave            /dev/pts      136   0-255 pty:slave
1454  pty_master           /dev/ptm      128   0-255 pty:master
1455  pty_slave            /dev/ttyp       3   0-255 pty:slave
1456  pty_master           /dev/pty        2   0-255 pty:master
1457  serial               /dev/cua        5   64-67 serial:callout
1458  serial               /dev/ttyS       4   64-67 serial
1459  /dev/tty0            /dev/tty0       4       0 system:vtmaster
1460  /dev/ptmx            /dev/ptmx       5       2 system
1461  /dev/console         /dev/console    5       1 system:console
1462  /dev/tty             /dev/tty        5       0 system:/dev/tty
1463  unknown              /dev/tty        4    1-63 console
1464
1465
14661.8 Miscellaneous kernel statistics in /proc/stat
1467-------------------------------------------------
1468
1469Various pieces   of  information about  kernel activity  are  available in the
1470/proc/stat file.  All  of  the numbers reported  in  this file are  aggregates
1471since the system first booted.  For a quick look, simply cat the file::
1472
1473  > cat /proc/stat
1474  cpu  2255 34 2290 22625563 6290 127 456 0 0 0
1475  cpu0 1132 34 1441 11311718 3675 127 438 0 0 0
1476  cpu1 1123 0 849 11313845 2614 0 18 0 0 0
1477  intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1478  ctxt 1990473
1479  btime 1062191376
1480  processes 2915
1481  procs_running 1
1482  procs_blocked 0
1483  softirq 183433 0 21755 12 39 1137 231 21459 2263
1484
1485The very first  "cpu" line aggregates the  numbers in all  of the other "cpuN"
1486lines.  These numbers identify the amount of time the CPU has spent performing
1487different kinds of work.  Time units are in USER_HZ (typically hundredths of a
1488second).  The meanings of the columns are as follows, from left to right:
1489
1490- user: normal processes executing in user mode
1491- nice: niced processes executing in user mode
1492- system: processes executing in kernel mode
1493- idle: twiddling thumbs
1494- iowait: In a word, iowait stands for waiting for I/O to complete. But there
1495  are several problems:
1496
1497  1. CPU will not wait for I/O to complete, iowait is the time that a task is
1498     waiting for I/O to complete. When CPU goes into idle state for
1499     outstanding task I/O, another task will be scheduled on this CPU.
1500  2. In a multi-core CPU, the task waiting for I/O to complete is not running
1501     on any CPU, so the iowait of each CPU is difficult to calculate.
1502  3. The value of iowait field in /proc/stat will decrease in certain
1503     conditions.
1504
1505  So, the iowait is not reliable by reading from /proc/stat.
1506- irq: servicing interrupts
1507- softirq: servicing softirqs
1508- steal: involuntary wait
1509- guest: running a normal guest
1510- guest_nice: running a niced guest
1511
1512The "intr" line gives counts of interrupts  serviced since boot time, for each
1513of the  possible system interrupts.   The first  column  is the  total of  all
1514interrupts serviced  including  unnumbered  architecture specific  interrupts;
1515each  subsequent column is the  total for that particular numbered interrupt.
1516Unnumbered interrupts are not shown, only summed into the total.
1517
1518The "ctxt" line gives the total number of context switches across all CPUs.
1519
1520The "btime" line gives  the time at which the  system booted, in seconds since
1521the Unix epoch.
1522
1523The "processes" line gives the number  of processes and threads created, which
1524includes (but  is not limited  to) those  created by  calls to the  fork() and
1525clone() system calls.
1526
1527The "procs_running" line gives the total number of threads that are
1528running or ready to run (i.e., the total number of runnable threads).
1529
1530The   "procs_blocked" line gives  the  number of  processes currently blocked,
1531waiting for I/O to complete.
1532
1533The "softirq" line gives counts of softirqs serviced since boot time, for each
1534of the possible system softirqs. The first column is the total of all
1535softirqs serviced; each subsequent column is the total for that particular
1536softirq.
1537
1538
15391.9 Ext4 file system parameters
1540-------------------------------
1541
1542Information about mounted ext4 file systems can be found in
1543/proc/fs/ext4.  Each mounted filesystem will have a directory in
1544/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1545/proc/fs/ext4/dm-0).   The files in each per-device directory are shown
1546in Table 1-12, below.
1547
1548.. table:: Table 1-12: Files in /proc/fs/ext4/<devname>
1549
1550 ==============  ==========================================================
1551 File            Content
1552 mb_groups       details of multiblock allocator buddy cache of free blocks
1553 ==============  ==========================================================
1554
15551.10 /proc/consoles
1556-------------------
1557Shows registered system console lines.
1558
1559To see which character device lines are currently used for the system console
1560/dev/console, you may simply look into the file /proc/consoles::
1561
1562  > cat /proc/consoles
1563  tty0                 -WU (ECp)       4:7
1564  ttyS0                -W- (Ep)        4:64
1565
1566The columns are:
1567
1568+--------------------+-------------------------------------------------------+
1569| device             | name of the device                                    |
1570+====================+=======================================================+
1571| operations         | * R = can do read operations                          |
1572|                    | * W = can do write operations                         |
1573|                    | * U = can do unblank                                  |
1574+--------------------+-------------------------------------------------------+
1575| flags              | * E = it is enabled                                   |
1576|                    | * C = it is preferred console                         |
1577|                    | * B = it is primary boot console                      |
1578|                    | * p = it is used for printk buffer                    |
1579|                    | * b = it is not a TTY but a Braille device            |
1580|                    | * a = it is safe to use when cpu is offline           |
1581+--------------------+-------------------------------------------------------+
1582| major:minor        | major and minor number of the device separated by a   |
1583|                    | colon                                                 |
1584+--------------------+-------------------------------------------------------+
1585
1586Summary
1587-------
1588
1589The /proc file system serves information about the running system. It not only
1590allows access to process data but also allows you to request the kernel status
1591by reading files in the hierarchy.
1592
1593The directory  structure  of /proc reflects the types of information and makes
1594it easy, if not obvious, where to look for specific data.
1595
1596Chapter 2: Modifying System Parameters
1597======================================
1598
1599In This Chapter
1600---------------
1601
1602* Modifying kernel parameters by writing into files found in /proc/sys
1603* Exploring the files which modify certain parameters
1604* Review of the /proc/sys file tree
1605
1606------------------------------------------------------------------------------
1607
1608A very  interesting part of /proc is the directory /proc/sys. This is not only
1609a source  of  information,  it also allows you to change parameters within the
1610kernel. Be  very  careful  when attempting this. You can optimize your system,
1611but you  can  also  cause  it  to  crash.  Never  alter kernel parameters on a
1612production system.  Set  up  a  development machine and test to make sure that
1613everything works  the  way  you want it to. You may have no alternative but to
1614reboot the machine once an error has been made.
1615
1616To change  a  value,  simply  echo  the new value into the file.
1617You need to be root to do this. You  can  create  your  own  boot script
1618to perform this every time your system boots.
1619
1620The files  in /proc/sys can be used to fine tune and monitor miscellaneous and
1621general things  in  the operation of the Linux kernel. Since some of the files
1622can inadvertently  disrupt  your  system,  it  is  advisable  to  read  both
1623documentation and  source  before actually making adjustments. In any case, be
1624very careful  when  writing  to  any  of these files. The entries in /proc may
1625change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1626review the kernel documentation in the directory /usr/src/linux/Documentation.
1627This chapter  is  heavily  based  on the documentation included in the pre 2.2
1628kernels, and became part of it in version 2.2.1 of the Linux kernel.
1629
1630Please see: Documentation/admin-guide/sysctl/ directory for descriptions of these
1631entries.
1632
1633Summary
1634-------
1635
1636Certain aspects  of  kernel  behavior  can be modified at runtime, without the
1637need to  recompile  the kernel, or even to reboot the system. The files in the
1638/proc/sys tree  can  not only be read, but also modified. You can use the echo
1639command to write value into these files, thereby changing the default settings
1640of the kernel.
1641
1642
1643Chapter 3: Per-process Parameters
1644=================================
1645
16463.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1647--------------------------------------------------------------------------------
1648
1649These files can be used to adjust the badness heuristic used to select which
1650process gets killed in out of memory (oom) conditions.
1651
1652The badness heuristic assigns a value to each candidate task ranging from 0
1653(never kill) to 1000 (always kill) to determine which process is targeted.  The
1654units are roughly a proportion along that range of allowed memory the process
1655may allocate from based on an estimation of its current memory and swap use.
1656For example, if a task is using all allowed memory, its badness score will be
16571000.  If it is using half of its allowed memory, its score will be 500.
1658
1659The amount of "allowed" memory depends on the context in which the oom killer
1660was called.  If it is due to the memory assigned to the allocating task's cpuset
1661being exhausted, the allowed memory represents the set of mems assigned to that
1662cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
1663memory represents the set of mempolicy nodes.  If it is due to a memory
1664limit (or swap limit) being reached, the allowed memory is that configured
1665limit.  Finally, if it is due to the entire system being out of memory, the
1666allowed memory represents all allocatable resources.
1667
1668The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1669is used to determine which task to kill.  Acceptable values range from -1000
1670(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
1671polarize the preference for oom killing either by always preferring a certain
1672task or completely disabling it.  The lowest possible value, -1000, is
1673equivalent to disabling oom killing entirely for that task since it will always
1674report a badness score of 0.
1675
1676Consequently, it is very simple for userspace to define the amount of memory to
1677consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
1678example, is roughly equivalent to allowing the remainder of tasks sharing the
1679same system, cpuset, mempolicy, or memory controller resources to use at least
168050% more memory.  A value of -500, on the other hand, would be roughly
1681equivalent to discounting 50% of the task's allowed memory from being considered
1682as scoring against the task.
1683
1684For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1685be used to tune the badness score.  Its acceptable values range from -16
1686(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1687(OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
1688scaled linearly with /proc/<pid>/oom_score_adj.
1689
1690The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1691value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1692requires CAP_SYS_RESOURCE.
1693
1694
16953.2 /proc/<pid>/oom_score - Display current oom-killer score
1696-------------------------------------------------------------
1697
1698This file can be used to check the current score used by the oom-killer for
1699any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
1700process should be killed in an out-of-memory situation.
1701
1702Please note that the exported value includes oom_score_adj so it is
1703effectively in range [0,2000].
1704
1705
17063.3  /proc/<pid>/io - Display the IO accounting fields
1707-------------------------------------------------------
1708
1709This file contains IO statistics for each running process.
1710
1711Example
1712~~~~~~~
1713
1714::
1715
1716    test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1717    [1] 3828
1718
1719    test:/tmp # cat /proc/3828/io
1720    rchar: 323934931
1721    wchar: 323929600
1722    syscr: 632687
1723    syscw: 632675
1724    read_bytes: 0
1725    write_bytes: 323932160
1726    cancelled_write_bytes: 0
1727
1728
1729Description
1730~~~~~~~~~~~
1731
1732rchar
1733^^^^^
1734
1735I/O counter: chars read
1736The number of bytes which this task has caused to be read from storage. This
1737is simply the sum of bytes which this process passed to read() and pread().
1738It includes things like tty IO and it is unaffected by whether or not actual
1739physical disk IO was required (the read might have been satisfied from
1740pagecache).
1741
1742
1743wchar
1744^^^^^
1745
1746I/O counter: chars written
1747The number of bytes which this task has caused, or shall cause to be written
1748to disk. Similar caveats apply here as with rchar.
1749
1750
1751syscr
1752^^^^^
1753
1754I/O counter: read syscalls
1755Attempt to count the number of read I/O operations, i.e. syscalls like read()
1756and pread().
1757
1758
1759syscw
1760^^^^^
1761
1762I/O counter: write syscalls
1763Attempt to count the number of write I/O operations, i.e. syscalls like
1764write() and pwrite().
1765
1766
1767read_bytes
1768^^^^^^^^^^
1769
1770I/O counter: bytes read
1771Attempt to count the number of bytes which this process really did cause to
1772be fetched from the storage layer. Done at the submit_bio() level, so it is
1773accurate for block-backed filesystems. <please add status regarding NFS and
1774CIFS at a later time>
1775
1776
1777write_bytes
1778^^^^^^^^^^^
1779
1780I/O counter: bytes written
1781Attempt to count the number of bytes which this process caused to be sent to
1782the storage layer. This is done at page-dirtying time.
1783
1784
1785cancelled_write_bytes
1786^^^^^^^^^^^^^^^^^^^^^
1787
1788The big inaccuracy here is truncate. If a process writes 1MB to a file and
1789then deletes the file, it will in fact perform no writeout. But it will have
1790been accounted as having caused 1MB of write.
1791In other words: The number of bytes which this process caused to not happen,
1792by truncating pagecache. A task can cause "negative" IO too. If this task
1793truncates some dirty pagecache, some IO which another task has been accounted
1794for (in its write_bytes) will not be happening. We _could_ just subtract that
1795from the truncating task's write_bytes, but there is information loss in doing
1796that.
1797
1798
1799.. Note::
1800
1801   At its current implementation state, this is a bit racy on 32-bit machines:
1802   if process A reads process B's /proc/pid/io while process B is updating one
1803   of those 64-bit counters, process A could see an intermediate result.
1804
1805
1806More information about this can be found within the taskstats documentation in
1807Documentation/accounting.
1808
18093.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1810---------------------------------------------------------------
1811When a process is dumped, all anonymous memory is written to a core file as
1812long as the size of the core file isn't limited. But sometimes we don't want
1813to dump some memory segments, for example, huge shared memory or DAX.
1814Conversely, sometimes we want to save file-backed memory segments into a core
1815file, not only the individual files.
1816
1817/proc/<pid>/coredump_filter allows you to customize which memory segments
1818will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1819of memory types. If a bit of the bitmask is set, memory segments of the
1820corresponding memory type are dumped, otherwise they are not dumped.
1821
1822The following 9 memory types are supported:
1823
1824  - (bit 0) anonymous private memory
1825  - (bit 1) anonymous shared memory
1826  - (bit 2) file-backed private memory
1827  - (bit 3) file-backed shared memory
1828  - (bit 4) ELF header pages in file-backed private memory areas (it is
1829    effective only if the bit 2 is cleared)
1830  - (bit 5) hugetlb private memory
1831  - (bit 6) hugetlb shared memory
1832  - (bit 7) DAX private memory
1833  - (bit 8) DAX shared memory
1834
1835  Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1836  are always dumped regardless of the bitmask status.
1837
1838  Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
1839  only affected by bit 5-6, and DAX is only affected by bits 7-8.
1840
1841The default value of coredump_filter is 0x33; this means all anonymous memory
1842segments, ELF header pages and hugetlb private memory are dumped.
1843
1844If you don't want to dump all shared memory segments attached to pid 1234,
1845write 0x31 to the process's proc file::
1846
1847  $ echo 0x31 > /proc/1234/coredump_filter
1848
1849When a new process is created, the process inherits the bitmask status from its
1850parent. It is useful to set up coredump_filter before the program runs.
1851For example::
1852
1853  $ echo 0x7 > /proc/self/coredump_filter
1854  $ ./some_program
1855
18563.5     /proc/<pid>/mountinfo - Information about mounts
1857--------------------------------------------------------
1858
1859This file contains lines of the form::
1860
1861    36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1862    (1)(2)(3)   (4)   (5)      (6)     (n…m) (m+1)(m+2) (m+3)         (m+4)
1863
1864    (1)   mount ID:        unique identifier of the mount (may be reused after umount)
1865    (2)   parent ID:       ID of parent (or of self for the top of the mount tree)
1866    (3)   major:minor:     value of st_dev for files on filesystem
1867    (4)   root:            root of the mount within the filesystem
1868    (5)   mount point:     mount point relative to the process's root
1869    (6)   mount options:   per mount options
1870    (n…m) optional fields: zero or more fields of the form "tag[:value]"
1871    (m+1) separator:       marks the end of the optional fields
1872    (m+2) filesystem type: name of filesystem of the form "type[.subtype]"
1873    (m+3) mount source:    filesystem specific information or "none"
1874    (m+4) super options:   per super block options
1875
1876Parsers should ignore all unrecognised optional fields.  Currently the
1877possible optional fields are:
1878
1879================  ==============================================================
1880shared:X          mount is shared in peer group X
1881master:X          mount is slave to peer group X
1882propagate_from:X  mount is slave and receives propagation from peer group X [#]_
1883unbindable        mount is unbindable
1884================  ==============================================================
1885
1886.. [#] X is the closest dominant peer group under the process's root.  If
1887       X is the immediate master of the mount, or if there's no dominant peer
1888       group under the same root, then only the "master:X" field is present
1889       and not the "propagate_from:X" field.
1890
1891For more information on mount propagation see:
1892
1893  Documentation/filesystems/sharedsubtree.rst
1894
1895
18963.6     /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
1897--------------------------------------------------------
1898These files provide a method to access a task's comm value. It also allows for
1899a task to set its own or one of its thread siblings comm value. The comm value
1900is limited in size compared to the cmdline value, so writing anything longer
1901then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1902comm value.
1903
1904
19053.7     /proc/<pid>/task/<tid>/children - Information about task children
1906-------------------------------------------------------------------------
1907This file provides a fast way to retrieve first level children pids
1908of a task pointed by <pid>/<tid> pair. The format is a space separated
1909stream of pids.
1910
1911Note the "first level" here -- if a child has its own children they will
1912not be listed here; one needs to read /proc/<children-pid>/task/<tid>/children
1913to obtain the descendants.
1914
1915Since this interface is intended to be fast and cheap it doesn't
1916guarantee to provide precise results and some children might be
1917skipped, especially if they've exited right after we printed their
1918pids, so one needs to either stop or freeze processes being inspected
1919if precise results are needed.
1920
1921
19223.8     /proc/<pid>/fdinfo/<fd> - Information about opened file
1923---------------------------------------------------------------
1924This file provides information associated with an opened file. The regular
1925files have at least four fields -- 'pos', 'flags', 'mnt_id' and 'ino'.
1926The 'pos' represents the current offset of the opened file in decimal
1927form [see lseek(2) for details], 'flags' denotes the octal O_xxx mask the
1928file has been created with [see open(2) for details] and 'mnt_id' represents
1929mount ID of the file system containing the opened file [see 3.5
1930/proc/<pid>/mountinfo for details]. 'ino' represents the inode number of
1931the file.
1932
1933A typical output is::
1934
1935        pos:    0
1936        flags:  0100002
1937        mnt_id: 19
1938        ino:    63107
1939
1940All locks associated with a file descriptor are shown in its fdinfo too::
1941
1942    lock:       1: FLOCK  ADVISORY  WRITE 359 00:13:11691 0 EOF
1943
1944The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
1945pair provide additional information particular to the objects they represent.
1946
1947Eventfd files
1948~~~~~~~~~~~~~
1949
1950::
1951
1952        pos:    0
1953        flags:  04002
1954        mnt_id: 9
1955        ino:    63107
1956        eventfd-count:  5a
1957
1958where 'eventfd-count' is hex value of a counter.
1959
1960Signalfd files
1961~~~~~~~~~~~~~~
1962
1963::
1964
1965        pos:    0
1966        flags:  04002
1967        mnt_id: 9
1968        ino:    63107
1969        sigmask:        0000000000000200
1970
1971where 'sigmask' is hex value of the signal mask associated
1972with a file.
1973
1974Epoll files
1975~~~~~~~~~~~
1976
1977::
1978
1979        pos:    0
1980        flags:  02
1981        mnt_id: 9
1982        ino:    63107
1983        tfd:        5 events:       1d data: ffffffffffffffff pos:0 ino:61af sdev:7
1984
1985where 'tfd' is a target file descriptor number in decimal form,
1986'events' is events mask being watched and the 'data' is data
1987associated with a target [see epoll(7) for more details].
1988
1989The 'pos' is current offset of the target file in decimal form
1990[see lseek(2)], 'ino' and 'sdev' are inode and device numbers
1991where target file resides, all in hex format.
1992
1993Fsnotify files
1994~~~~~~~~~~~~~~
1995For inotify files the format is the following::
1996
1997        pos:    0
1998        flags:  02000000
1999        mnt_id: 9
2000        ino:    63107
2001        inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
2002
2003where 'wd' is a watch descriptor in decimal form, i.e. a target file
2004descriptor number, 'ino' and 'sdev' are inode and device where the
2005target file resides and the 'mask' is the mask of events, all in hex
2006form [see inotify(7) for more details].
2007
2008If the kernel was built with exportfs support, the path to the target
2009file is encoded as a file handle.  The file handle is provided by three
2010fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
2011format.
2012
2013If the kernel is built without exportfs support the file handle won't be
2014printed out.
2015
2016If there is no inotify mark attached yet the 'inotify' line will be omitted.
2017
2018For fanotify files the format is::
2019
2020        pos:    0
2021        flags:  02
2022        mnt_id: 9
2023        ino:    63107
2024        fanotify flags:10 event-flags:0
2025        fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
2026        fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
2027
2028where fanotify 'flags' and 'event-flags' are values used in fanotify_init
2029call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
2030flags associated with mark which are tracked separately from events
2031mask. 'ino' and 'sdev' are target inode and device, 'mask' is the events
2032mask and 'ignored_mask' is the mask of events which are to be ignored.
2033All are in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
2034provide information about flags and mask used in fanotify_mark
2035call [see fsnotify manpage for details].
2036
2037While the first three lines are mandatory and always printed, the rest is
2038optional and may be omitted if no marks created yet.
2039
2040Timerfd files
2041~~~~~~~~~~~~~
2042
2043::
2044
2045        pos:    0
2046        flags:  02
2047        mnt_id: 9
2048        ino:    63107
2049        clockid: 0
2050        ticks: 0
2051        settime flags: 01
2052        it_value: (0, 49406829)
2053        it_interval: (1, 0)
2054
2055where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
2056that have occurred [see timerfd_create(2) for details]. 'settime flags' are
2057flags in octal form been used to setup the timer [see timerfd_settime(2) for
2058details]. 'it_value' is remaining time until the timer expiration.
2059'it_interval' is the interval for the timer. Note the timer might be set up
2060with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
2061still exhibits timer's remaining time.
2062
2063DMA Buffer files
2064~~~~~~~~~~~~~~~~
2065
2066::
2067
2068        pos:    0
2069        flags:  04002
2070        mnt_id: 9
2071        ino:    63107
2072        size:   32768
2073        count:  2
2074        exp_name:  system-heap
2075
2076where 'size' is the size of the DMA buffer in bytes. 'count' is the file count of
2077the DMA buffer file. 'exp_name' is the name of the DMA buffer exporter.
2078
20793.9     /proc/<pid>/map_files - Information about memory mapped files
2080---------------------------------------------------------------------
2081This directory contains symbolic links which represent memory mapped files
2082the process is maintaining.  Example output::
2083
2084     | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
2085     | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
2086     | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
2087     | ...
2088     | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
2089     | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
2090
2091The name of a link represents the virtual memory bounds of a mapping, i.e.
2092vm_area_struct::vm_start-vm_area_struct::vm_end.
2093
2094The main purpose of the map_files is to retrieve a set of memory mapped
2095files in a fast way instead of parsing /proc/<pid>/maps or
2096/proc/<pid>/smaps, both of which contain many more records.  At the same
2097time one can open(2) mappings from the listings of two processes and
2098comparing their inode numbers to figure out which anonymous memory areas
2099are actually shared.
2100
21013.10    /proc/<pid>/timerslack_ns - Task timerslack value
2102---------------------------------------------------------
2103This file provides the value of the task's timerslack value in nanoseconds.
2104This value specifies an amount of time that normal timers may be deferred
2105in order to coalesce timers and avoid unnecessary wakeups.
2106
2107This allows a task's interactivity vs power consumption tradeoff to be
2108adjusted.
2109
2110Writing 0 to the file will set the task's timerslack to the default value.
2111
2112Valid values are from 0 - ULLONG_MAX
2113
2114An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
2115permissions on the task specified to change its timerslack_ns value.
2116
21173.11    /proc/<pid>/patch_state - Livepatch patch operation state
2118-----------------------------------------------------------------
2119When CONFIG_LIVEPATCH is enabled, this file displays the value of the
2120patch state for the task.
2121
2122A value of '-1' indicates that no patch is in transition.
2123
2124A value of '0' indicates that a patch is in transition and the task is
2125unpatched.  If the patch is being enabled, then the task hasn't been
2126patched yet.  If the patch is being disabled, then the task has already
2127been unpatched.
2128
2129A value of '1' indicates that a patch is in transition and the task is
2130patched.  If the patch is being enabled, then the task has already been
2131patched.  If the patch is being disabled, then the task hasn't been
2132unpatched yet.
2133
21343.12 /proc/<pid>/arch_status - task architecture specific status
2135-------------------------------------------------------------------
2136When CONFIG_PROC_PID_ARCH_STATUS is enabled, this file displays the
2137architecture specific status of the task.
2138
2139Example
2140~~~~~~~
2141
2142::
2143
2144 $ cat /proc/6753/arch_status
2145 AVX512_elapsed_ms:      8
2146
2147Description
2148~~~~~~~~~~~
2149
2150x86 specific entries
2151~~~~~~~~~~~~~~~~~~~~~
2152
2153AVX512_elapsed_ms
2154^^^^^^^^^^^^^^^^^^
2155
2156  If AVX512 is supported on the machine, this entry shows the milliseconds
2157  elapsed since the last time AVX512 usage was recorded. The recording
2158  happens on a best effort basis when a task is scheduled out. This means
2159  that the value depends on two factors:
2160
2161    1) The time which the task spent on the CPU without being scheduled
2162       out. With CPU isolation and a single runnable task this can take
2163       several seconds.
2164
2165    2) The time since the task was scheduled out last. Depending on the
2166       reason for being scheduled out (time slice exhausted, syscall ...)
2167       this can be arbitrary long time.
2168
2169  As a consequence the value cannot be considered precise and authoritative
2170  information. The application which uses this information has to be aware
2171  of the overall scenario on the system in order to determine whether a
2172  task is a real AVX512 user or not. Precise information can be obtained
2173  with performance counters.
2174
2175  A special value of '-1' indicates that no AVX512 usage was recorded, thus
2176  the task is unlikely an AVX512 user, but depends on the workload and the
2177  scheduling scenario, it also could be a false negative mentioned above.
2178
2179Chapter 4: Configuring procfs
2180=============================
2181
21824.1     Mount options
2183---------------------
2184
2185The following mount options are supported:
2186
2187        =========       ========================================================
2188        hidepid=        Set /proc/<pid>/ access mode.
2189        gid=            Set the group authorized to learn processes information.
2190        subset=         Show only the specified subset of procfs.
2191        =========       ========================================================
2192
2193hidepid=off or hidepid=0 means classic mode - everybody may access all
2194/proc/<pid>/ directories (default).
2195
2196hidepid=noaccess or hidepid=1 means users may not access any /proc/<pid>/
2197directories but their own.  Sensitive files like cmdline, sched*, status are now
2198protected against other users.  This makes it impossible to learn whether any
2199user runs specific program (given the program doesn't reveal itself by its
2200behaviour).  As an additional bonus, as /proc/<pid>/cmdline is unaccessible for
2201other users, poorly written programs passing sensitive information via program
2202arguments are now protected against local eavesdroppers.
2203
2204hidepid=invisible or hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be
2205fully invisible to other users.  It doesn't mean that it hides a fact whether a
2206process with a specific pid value exists (it can be learned by other means, e.g.
2207by "kill -0 $PID"), but it hides process' uid and gid, which may be learned by
2208stat()'ing /proc/<pid>/ otherwise.  It greatly complicates an intruder's task of
2209gathering information about running processes, whether some daemon runs with
2210elevated privileges, whether other user runs some sensitive program, whether
2211other users run any program at all, etc.
2212
2213hidepid=ptraceable or hidepid=4 means that procfs should only contain
2214/proc/<pid>/ directories that the caller can ptrace.
2215
2216gid= defines a group authorized to learn processes information otherwise
2217prohibited by hidepid=.  If you use some daemon like identd which needs to learn
2218information about processes information, just add identd to this group.
2219
2220subset=pid hides all top level files and directories in the procfs that
2221are not related to tasks.
2222
2223Chapter 5: Filesystem behavior
2224==============================
2225
2226Originally, before the advent of pid namepsace, procfs was a global file
2227system. It means that there was only one procfs instance in the system.
2228
2229When pid namespace was added, a separate procfs instance was mounted in
2230each pid namespace. So, procfs mount options are global among all
2231mountpoints within the same namespace::
2232
2233        # grep ^proc /proc/mounts
2234        proc /proc proc rw,relatime,hidepid=2 0 0
2235
2236        # strace -e mount mount -o hidepid=1 -t proc proc /tmp/proc
2237        mount("proc", "/tmp/proc", "proc", 0, "hidepid=1") = 0
2238        +++ exited with 0 +++
2239
2240        # grep ^proc /proc/mounts
2241        proc /proc proc rw,relatime,hidepid=2 0 0
2242        proc /tmp/proc proc rw,relatime,hidepid=2 0 0
2243
2244and only after remounting procfs mount options will change at all
2245mountpoints::
2246
2247        # mount -o remount,hidepid=1 -t proc proc /tmp/proc
2248
2249        # grep ^proc /proc/mounts
2250        proc /proc proc rw,relatime,hidepid=1 0 0
2251        proc /tmp/proc proc rw,relatime,hidepid=1 0 0
2252
2253This behavior is different from the behavior of other filesystems.
2254
2255The new procfs behavior is more like other filesystems. Each procfs mount
2256creates a new procfs instance. Mount options affect own procfs instance.
2257It means that it became possible to have several procfs instances
2258displaying tasks with different filtering options in one pid namespace::
2259
2260        # mount -o hidepid=invisible -t proc proc /proc
2261        # mount -o hidepid=noaccess -t proc proc /tmp/proc
2262        # grep ^proc /proc/mounts
2263        proc /proc proc rw,relatime,hidepid=invisible 0 0
2264        proc /tmp/proc proc rw,relatime,hidepid=noaccess 0 0
2265