TOMOYO Linux Cross Reference
Linux/Documentation/filesystems/proc.rst

   .. SPDX-License-Identifier: GPL-2.0
   
   ====================
   The /proc Filesystem
   ====================
   
   =====================  =======================================  ================
   /proc/sys              Terrehon Bowden <terrehon@pacbell.net>,  October 7 1999
                          Bodo Bauer <bb@ricochet.net>
  2.4.x update           Jorge Nerin <comandante@zaralinux.com>   November 14 2000
  move /proc/sys         Shen Feng <shen@cn.fujitsu.com>          April 1 2009
  fixes/update part 1.1  Stefani Seibold <stefani@seibold.net>    June 9 2009
  =====================  =======================================  ================
  
  
  
  .. Table of Contents
  
    0     Preface
    0.1   Introduction/Credits
    0.2   Legal Stuff
  
    1     Collecting System Information
    1.1   Process-Specific Subdirectories
    1.2   Kernel data
    1.3   IDE devices in /proc/ide
    1.4   Networking info in /proc/net
    1.5   SCSI info
    1.6   Parallel port info in /proc/parport
    1.7   TTY info in /proc/tty
    1.8   Miscellaneous kernel statistics in /proc/stat
    1.9   Ext4 file system parameters
  
    2     Modifying System Parameters
  
    3     Per-Process Parameters
    3.1   /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj - Adjust the oom-killer
                                                                  score
    3.2   /proc/<pid>/oom_score - Display current oom-killer score
    3.3   /proc/<pid>/io - Display the IO accounting fields
    3.4   /proc/<pid>/coredump_filter - Core dump filtering settings
    3.5   /proc/<pid>/mountinfo - Information about mounts
    3.6   /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
    3.7   /proc/<pid>/task/<tid>/children - Information about task children
    3.8   /proc/<pid>/fdinfo/<fd> - Information about opened file
    3.9   /proc/<pid>/map_files - Information about memory mapped files
    3.10  /proc/<pid>/timerslack_ns - Task timerslack value
    3.11  /proc/<pid>/patch_state - Livepatch patch operation state
    3.12  /proc/<pid>/arch_status - Task architecture specific information
    3.13  /proc/<pid>/fd - List of symlinks to open files
  
    4     Configuring procfs
    4.1   Mount options
  
    5     Filesystem behavior
  
  Preface
  =======
  
  0.1 Introduction/Credits
  ------------------------
  
  This documentation is  part of a soon (or  so we hope) to be  released book on
  the SuSE  Linux distribution. As  there is  no complete documentation  for the
  /proc file system and we've used  many freely available sources to write these
  chapters, it  seems only fair  to give the work  back to the  Linux community.
  This work is  based on the 2.2.*  kernel version and the  upcoming 2.4.*. I'm
  afraid it's still far from complete, but we  hope it will be useful. As far as
  we know, it is the first 'all-in-one' document about the /proc file system. It
  is focused  on the Intel  x86 hardware,  so if you  are looking for  PPC, ARM,
  SPARC, AXP, etc., features, you probably  won't find what you are looking for.
  It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
  additions and patches  are welcome and will  be added to this  document if you
  mail them to Bodo.
  
  We'd like  to  thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
  other people for help compiling this documentation. We'd also like to extend a
  special thank  you to Andi Kleen for documentation, which we relied on heavily
  to create  this  document,  as well as the additional information he provided.
  Thanks to  everybody  else  who contributed source or docs to the Linux kernel
  and helped create a great piece of software... :)
  
  If you  have  any comments, corrections or additions, please don't hesitate to
  contact Bodo  Bauer  at  bb@ricochet.net.  We'll  be happy to add them to this
  document.
  
  The   latest   version    of   this   document   is    available   online   at
  https://www.kernel.org/doc/html/latest/filesystems/proc.html
  
  If  the above  direction does  not works  for you,  you could  try the  kernel
  mailing  list  at  linux-kernel@vger.kernel.org  and/or try  to  reach  me  at
  comandante@zaralinux.com.
  
  0.2 Legal Stuff
  ---------------
  
  We don't  guarantee  the  correctness  of this document, and if you come to us
  complaining about  how  you  screwed  up  your  system  because  of  incorrect
  documentation, we won't feel responsible...
 
 Chapter 1: Collecting System Information
 ========================================
 
 In This Chapter
 ---------------
 * Investigating  the  properties  of  the  pseudo  file  system  /proc and its
   ability to provide information on the running Linux system
 * Examining /proc's structure
 * Uncovering  various  information  about the kernel and the processes running
   on the system
 
 ------------------------------------------------------------------------------
 
 The proc  file  system acts as an interface to internal data structures in the
 kernel. It  can  be  used to obtain information about the system and to change
 certain kernel parameters at runtime (sysctl).
 
 First, we'll  take  a  look  at the read-only parts of /proc. In Chapter 2, we
 show you how you can use /proc/sys to change settings.
 
 1.1 Process-Specific Subdirectories
 -----------------------------------
 
 The directory  /proc  contains  (among other things) one subdirectory for each
 process running on the system, which is named after the process ID (PID).
 
 The link  'self'  points to  the process reading the file system. Each process
 subdirectory has the entries listed in Table 1-1.
 
 Note that an open file descriptor to /proc/<pid> or to any of its
 contained files or subdirectories does not prevent <pid> being reused
 for some other process in the event that <pid> exits. Operations on
 open /proc/<pid> file descriptors corresponding to dead processes
 never act on any new process that the kernel may, through chance, have
 also assigned the process ID <pid>. Instead, operations on these FDs
 usually fail with ESRCH.
 
 .. table:: Table 1-1: Process specific entries in /proc
 
  =============  ===============================================================
  File           Content
  =============  ===============================================================
  clear_refs     Clears page referenced bits shown in smaps output
  cmdline        Command line arguments
  cpu            Current and last cpu in which it was executed   (2.4)(smp)
  cwd            Link to the current working directory
  environ        Values of environment variables
  exe            Link to the executable of this process
  fd             Directory, which contains all file descriptors
  maps           Memory maps to executables and library files    (2.4)
  mem            Memory held by this process
  root           Link to the root directory of this process
  stat           Process status
  statm          Process memory status information
  status         Process status in human readable form
  wchan          Present with CONFIG_KALLSYMS=y: it shows the kernel function
                 symbol the task is blocked in - or "0" if not blocked.
  pagemap        Page table
  stack          Report full stack trace, enable via CONFIG_STACKTRACE
  smaps          An extension based on maps, showing the memory consumption of
                 each mapping and flags associated with it
  smaps_rollup   Accumulated smaps stats for all mappings of the process.  This
                 can be derived from smaps, but is faster and more convenient
  numa_maps      An extension based on maps, showing the memory locality and
                 binding policy as well as mem usage (in pages) of each mapping.
  =============  ===============================================================
 
 For example, to get the status information of a process, all you have to do is
 read the file /proc/PID/status::
 
   >cat /proc/self/status
   Name:   cat
   State:  R (running)
   Tgid:   5452
   Pid:    5452
   PPid:   743
   TracerPid:      0                                             (2.4)
   Uid:    501     501     501     501
   Gid:    100     100     100     100
   FDSize: 256
   Groups: 100 14 16
   Kthread:    0
   VmPeak:     5004 kB
   VmSize:     5004 kB
   VmLck:         0 kB
   VmHWM:       476 kB
   VmRSS:       476 kB
   RssAnon:             352 kB
   RssFile:             120 kB
   RssShmem:              4 kB
   VmData:      156 kB
   VmStk:        88 kB
   VmExe:        68 kB
   VmLib:      1412 kB
   VmPTE:        20 kb
   VmSwap:        0 kB
   HugetlbPages:          0 kB
   CoreDumping:    0
   THP_enabled:    1
   Threads:        1
   SigQ:   0/28578
   SigPnd: 0000000000000000
   ShdPnd: 0000000000000000
   SigBlk: 0000000000000000
   SigIgn: 0000000000000000
   SigCgt: 0000000000000000
   CapInh: 00000000fffffeff
   CapPrm: 0000000000000000
   CapEff: 0000000000000000
   CapBnd: ffffffffffffffff
   CapAmb: 0000000000000000
   NoNewPrivs:     0
   Seccomp:        0
   Speculation_Store_Bypass:       thread vulnerable
   SpeculationIndirectBranch:      conditional enabled
   voluntary_ctxt_switches:        0
   nonvoluntary_ctxt_switches:     1
 
 This shows you nearly the same information you would get if you viewed it with
 the ps  command.  In  fact,  ps  uses  the  proc  file  system  to  obtain its
 information.  But you get a more detailed  view of the  process by reading the
 file /proc/PID/status. It fields are described in table 1-2.
 
 The  statm  file  contains  more  detailed  information about the process
 memory usage. Its seven fields are explained in Table 1-3.  The stat file
 contains detailed information about the process itself.  Its fields are
 explained in Table 1-4.
 
 (for SMP CONFIG users)
 
 For making accounting scalable, RSS related information are handled in an
 asynchronous manner and the value may not be very precise. To see a precise
 snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
 It's slow but very precise.
 
 .. table:: Table 1-2: Contents of the status fields (as of 4.19)
 
  ==========================  ===================================================
  Field                       Content
  ==========================  ===================================================
  Name                        filename of the executable
  Umask                       file mode creation mask
  State                       state (R is running, S is sleeping, D is sleeping
                              in an uninterruptible wait, Z is zombie,
                              T is traced or stopped)
  Tgid                        thread group ID
  Ngid                        NUMA group ID (0 if none)
  Pid                         process id
  PPid                        process id of the parent process
  TracerPid                   PID of process tracing this process (0 if not, or
                              the tracer is outside of the current pid namespace)
  Uid                         Real, effective, saved set, and  file system UIDs
  Gid                         Real, effective, saved set, and  file system GIDs
  FDSize                      number of file descriptor slots currently allocated
  Groups                      supplementary group list
  NStgid                      descendant namespace thread group ID hierarchy
  NSpid                       descendant namespace process ID hierarchy
  NSpgid                      descendant namespace process group ID hierarchy
  NSsid                       descendant namespace session ID hierarchy
  Kthread                     kernel thread flag, 1 is yes, 0 is no
  VmPeak                      peak virtual memory size
  VmSize                      total program size
  VmLck                       locked memory size
  VmPin                       pinned memory size
  VmHWM                       peak resident set size ("high water mark")
  VmRSS                       size of memory portions. It contains the three
                              following parts
                              (VmRSS = RssAnon + RssFile + RssShmem)
  RssAnon                     size of resident anonymous memory
  RssFile                     size of resident file mappings
  RssShmem                    size of resident shmem memory (includes SysV shm,
                              mapping of tmpfs and shared anonymous mappings)
  VmData                      size of private data segments
  VmStk                       size of stack segments
  VmExe                       size of text segment
  VmLib                       size of shared library code
  VmPTE                       size of page table entries
  VmSwap                      amount of swap used by anonymous private data
                              (shmem swap usage is not included)
  HugetlbPages                size of hugetlb memory portions
  CoreDumping                 process's memory is currently being dumped
                              (killing the process may lead to a corrupted core)
  THP_enabled                 process is allowed to use THP (returns 0 when
                              PR_SET_THP_DISABLE is set on the process
  Threads                     number of threads
  SigQ                        number of signals queued/max. number for queue
  SigPnd                      bitmap of pending signals for the thread
  ShdPnd                      bitmap of shared pending signals for the process
  SigBlk                      bitmap of blocked signals
  SigIgn                      bitmap of ignored signals
  SigCgt                      bitmap of caught signals
  CapInh                      bitmap of inheritable capabilities
  CapPrm                      bitmap of permitted capabilities
  CapEff                      bitmap of effective capabilities
  CapBnd                      bitmap of capabilities bounding set
  CapAmb                      bitmap of ambient capabilities
  NoNewPrivs                  no_new_privs, like prctl(PR_GET_NO_NEW_PRIV, ...)
  Seccomp                     seccomp mode, like prctl(PR_GET_SECCOMP, ...)
  Speculation_Store_Bypass    speculative store bypass mitigation status
  SpeculationIndirectBranch   indirect branch speculation mode
  Cpus_allowed                mask of CPUs on which this process may run
  Cpus_allowed_list           Same as previous, but in "list format"
  Mems_allowed                mask of memory nodes allowed to this process
  Mems_allowed_list           Same as previous, but in "list format"
  voluntary_ctxt_switches     number of voluntary context switches
  nonvoluntary_ctxt_switches  number of non voluntary context switches
  ==========================  ===================================================
 
 
 .. table:: Table 1-3: Contents of the statm fields (as of 2.6.8-rc3)
 
  ======== ===============================       ==============================
  Field    Content
  ======== ===============================       ==============================
  size     total program size (pages)            (same as VmSize in status)
  resident size of memory portions (pages)       (same as VmRSS in status)
  shared   number of pages that are shared       (i.e. backed by a file, same
                                                 as RssFile+RssShmem in status)
  trs      number of pages that are 'code'       (not including libs; broken,
                                                 includes data segment)
  lrs      number of pages of library            (always 0 on 2.6)
  drs      number of pages of data/stack         (including libs; broken,
                                                 includes library text)
  dt       number of dirty pages                 (always 0 on 2.6)
  ======== ===============================       ==============================
 
 
 .. table:: Table 1-4: Contents of the stat fields (as of 2.6.30-rc7)
 
   ============= ===============================================================
   Field         Content
   ============= ===============================================================
   pid           process id
   tcomm         filename of the executable
   state         state (R is running, S is sleeping, D is sleeping in an
                 uninterruptible wait, Z is zombie, T is traced or stopped)
   ppid          process id of the parent process
   pgrp          pgrp of the process
   sid           session id
   tty_nr        tty the process uses
   tty_pgrp      pgrp of the tty
   flags         task flags
   min_flt       number of minor faults
   cmin_flt      number of minor faults with child's
   maj_flt       number of major faults
   cmaj_flt      number of major faults with child's
   utime         user mode jiffies
   stime         kernel mode jiffies
   cutime        user mode jiffies with child's
   cstime        kernel mode jiffies with child's
   priority      priority level
   nice          nice level
   num_threads   number of threads
   it_real_value (obsolete, always 0)
   start_time    time the process started after system boot
   vsize         virtual memory size
   rss           resident set memory size
   rsslim        current limit in bytes on the rss
   start_code    address above which program text can run
   end_code      address below which program text can run
   start_stack   address of the start of the main process stack
   esp           current value of ESP
   eip           current value of EIP
   pending       bitmap of pending signals
   blocked       bitmap of blocked signals
   sigign        bitmap of ignored signals
   sigcatch      bitmap of caught signals
   0             (place holder, used to be the wchan address,
                 use /proc/PID/wchan instead)
   0             (place holder)
   0             (place holder)
   exit_signal   signal to send to parent thread on exit
   task_cpu      which CPU the task is scheduled on
   rt_priority   realtime priority
   policy        scheduling policy (man sched_setscheduler)
   blkio_ticks   time spent waiting for block IO
   gtime         guest time of the task in jiffies
   cgtime        guest time of the task children in jiffies
   start_data    address above which program data+bss is placed
   end_data      address below which program data+bss is placed
   start_brk     address above which program heap can be expanded with brk()
   arg_start     address above which program command line is placed
   arg_end       address below which program command line is placed
   env_start     address above which program environment is placed
   env_end       address below which program environment is placed
   exit_code     the thread's exit_code in the form reported by the waitpid
                 system call
   ============= ===============================================================
 
 The /proc/PID/maps file contains the currently mapped memory regions and
 their access permissions.
 
 The format is::
 
     address           perms offset  dev   inode      pathname
 
     08048000-08049000 r-xp 00000000 03:00 8312       /opt/test
     08049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
     0804a000-0806b000 rw-p 00000000 00:00 0          [heap]
     a7cb1000-a7cb2000 ---p 00000000 00:00 0
     a7cb2000-a7eb2000 rw-p 00000000 00:00 0
     a7eb2000-a7eb3000 ---p 00000000 00:00 0
     a7eb3000-a7ed5000 rw-p 00000000 00:00 0
     a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/libc.so.6
     a8008000-a800a000 r--p 00133000 03:00 4222       /lib/libc.so.6
     a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/libc.so.6
     a800b000-a800e000 rw-p 00000000 00:00 0
     a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/libpthread.so.0
     a8022000-a8023000 r--p 00013000 03:00 14462      /lib/libpthread.so.0
     a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/libpthread.so.0
     a8024000-a8027000 rw-p 00000000 00:00 0
     a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/ld-linux.so.2
     a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/ld-linux.so.2
     a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/ld-linux.so.2
     aff35000-aff4a000 rw-p 00000000 00:00 0          [stack]
     ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
 
 where "address" is the address space in the process that it occupies, "perms"
 is a set of permissions::
 
  r = read
  w = write
  x = execute
  s = shared
  p = private (copy on write)
 
 "offset" is the offset into the mapping, "dev" is the device (major:minor), and
 "inode" is the inode  on that device.  0 indicates that  no inode is associated
 with the memory region, as the case would be with BSS (uninitialized data).
 The "pathname" shows the name associated file for this mapping.  If the mapping
 is not associated with a file:
 
  ===================        ===========================================
  [heap]                     the heap of the program
  [stack]                    the stack of the main process
  [vdso]                     the "virtual dynamic shared object",
                             the kernel system call handler
  [anon:<name>]              a private anonymous mapping that has been
                             named by userspace
  [anon_shmem:<name>]        an anonymous shared memory mapping that has
                             been named by userspace
  ===================        ===========================================
 
  or if empty, the mapping is anonymous.
 
 Starting with 6.11 kernel, /proc/PID/maps provides an alternative
 ioctl()-based API that gives ability to flexibly and efficiently query and
 filter individual VMAs. This interface is binary and is meant for more
 efficient and easy programmatic use. `struct procmap_query`, defined in
 linux/fs.h UAPI header, serves as an input/output argument to the
 `PROCMAP_QUERY` ioctl() command. See comments in linus/fs.h UAPI header for
 details on query semantics, supported flags, data returned, and general API
 usage information.
 
 The /proc/PID/smaps is an extension based on maps, showing the memory
 consumption for each of the process's mappings. For each mapping (aka Virtual
 Memory Area, or VMA) there is a series of lines such as the following::
 
     08048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
 
     Size:               1084 kB
     KernelPageSize:        4 kB
     MMUPageSize:           4 kB
     Rss:                 892 kB
     Pss:                 374 kB
     Pss_Dirty:             0 kB
     Shared_Clean:        892 kB
     Shared_Dirty:          0 kB
     Private_Clean:         0 kB
     Private_Dirty:         0 kB
     Referenced:          892 kB
     Anonymous:             0 kB
     KSM:                   0 kB
     LazyFree:              0 kB
     AnonHugePages:         0 kB
     ShmemPmdMapped:        0 kB
     Shared_Hugetlb:        0 kB
     Private_Hugetlb:       0 kB
     Swap:                  0 kB
     SwapPss:               0 kB
     KernelPageSize:        4 kB
     MMUPageSize:           4 kB
     Locked:                0 kB
     THPeligible:           0
     VmFlags: rd ex mr mw me dw
 
 The first of these lines shows the same information as is displayed for the
 mapping in /proc/PID/maps.  Following lines show the size of the mapping
 (size); the size of each page allocated when backing a VMA (KernelPageSize),
 which is usually the same as the size in the page table entries; the page size
 used by the MMU when backing a VMA (in most cases, the same as KernelPageSize);
 the amount of the mapping that is currently resident in RAM (RSS); the
 process' proportional share of this mapping (PSS); and the number of clean and
 dirty shared and private pages in the mapping.
 
 The "proportional set size" (PSS) of a process is the count of pages it has
 in memory, where each page is divided by the number of processes sharing it.
 So if a process has 1000 pages all to itself, and 1000 shared with one other
 process, its PSS will be 1500.  "Pss_Dirty" is the portion of PSS which
 consists of dirty pages.  ("Pss_Clean" is not included, but it can be
 calculated by subtracting "Pss_Dirty" from "Pss".)
 
 Note that even a page which is part of a MAP_SHARED mapping, but has only
 a single pte mapped, i.e.  is currently used by only one process, is accounted
 as private and not as shared.
 
 "Referenced" indicates the amount of memory currently marked as referenced or
 accessed.
 
 "Anonymous" shows the amount of memory that does not belong to any file.  Even
 a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
 and a page is modified, the file page is replaced by a private anonymous copy.
 
 "KSM" reports how many of the pages are KSM pages. Note that KSM-placed zeropages
 are not included, only actual KSM pages.
 
 "LazyFree" shows the amount of memory which is marked by madvise(MADV_FREE).
 The memory isn't freed immediately with madvise(). It's freed in memory
 pressure if the memory is clean. Please note that the printed value might
 be lower than the real value due to optimizations used in the current
 implementation. If this is not desirable please file a bug report.
 
 "AnonHugePages" shows the amount of memory backed by transparent hugepage.
 
 "ShmemPmdMapped" shows the amount of shared (shmem/tmpfs) memory backed by
 huge pages.
 
 "Shared_Hugetlb" and "Private_Hugetlb" show the amounts of memory backed by
 hugetlbfs page which is *not* counted in "RSS" or "PSS" field for historical
 reasons. And these are not included in {Shared,Private}_{Clean,Dirty} field.
 
 "Swap" shows how much would-be-anonymous memory is also used, but out on swap.
 
 For shmem mappings, "Swap" includes also the size of the mapped (and not
 replaced by copy-on-write) part of the underlying shmem object out on swap.
 "SwapPss" shows proportional swap share of this mapping. Unlike "Swap", this
 does not take into account swapped out page of underlying shmem objects.
 "Locked" indicates whether the mapping is locked in memory or not.
 
 "THPeligible" indicates whether the mapping is eligible for allocating
 naturally aligned THP pages of any currently enabled size. 1 if true, 0
 otherwise.
 
 "VmFlags" field deserves a separate description. This member represents the
 kernel flags associated with the particular virtual memory area in two letter
 encoded manner. The codes are the following:
 
     ==    =======================================
     rd    readable
     wr    writeable
     ex    executable
     sh    shared
     mr    may read
     mw    may write
     me    may execute
     ms    may share
     gd    stack segment growns down
     pf    pure PFN range
     dw    disabled write to the mapped file
     lo    pages are locked in memory
     io    memory mapped I/O area
     sr    sequential read advise provided
     rr    random read advise provided
     dc    do not copy area on fork
     de    do not expand area on remapping
     ac    area is accountable
     nr    swap space is not reserved for the area
     ht    area uses huge tlb pages
     sf    synchronous page fault
     ar    architecture specific flag
     wf    wipe on fork
     dd    do not include area into core dump
     sd    soft dirty flag
     mm    mixed map area
     hg    huge page advise flag
     nh    no huge page advise flag
     mg    mergeable advise flag
     bt    arm64 BTI guarded page
     mt    arm64 MTE allocation tags are enabled
     um    userfaultfd missing tracking
     uw    userfaultfd wr-protect tracking
     ss    shadow stack page
     sl    sealed
     ==    =======================================
 
 Note that there is no guarantee that every flag and associated mnemonic will
 be present in all further kernel releases. Things get changed, the flags may
 be vanished or the reverse -- new added. Interpretation of their meaning
 might change in future as well. So each consumer of these flags has to
 follow each specific kernel version for the exact semantic.
 
 This file is only present if the CONFIG_MMU kernel configuration option is
 enabled.
 
 Note: reading /proc/PID/maps or /proc/PID/smaps is inherently racy (consistent
 output can be achieved only in the single read call).
 
 This typically manifests when doing partial reads of these files while the
 memory map is being modified.  Despite the races, we do provide the following
 guarantees:
 
 1) The mapped addresses never go backwards, which implies no two
    regions will ever overlap.
 2) If there is something at a given vaddr during the entirety of the
    life of the smaps/maps walk, there will be some output for it.
 
 The /proc/PID/smaps_rollup file includes the same fields as /proc/PID/smaps,
 but their values are the sums of the corresponding values for all mappings of
 the process.  Additionally, it contains these fields:
 
 - Pss_Anon
 - Pss_File
 - Pss_Shmem
 
 They represent the proportional shares of anonymous, file, and shmem pages, as
 described for smaps above.  These fields are omitted in smaps since each
 mapping identifies the type (anon, file, or shmem) of all pages it contains.
 Thus all information in smaps_rollup can be derived from smaps, but at a
 significantly higher cost.
 
 The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
 bits on both physical and virtual pages associated with a process, and the
 soft-dirty bit on pte (see Documentation/admin-guide/mm/soft-dirty.rst
 for details).
 To clear the bits for all the pages associated with the process::
 
     > echo 1 > /proc/PID/clear_refs
 
 To clear the bits for the anonymous pages associated with the process::
 
     > echo 2 > /proc/PID/clear_refs
 
 To clear the bits for the file mapped pages associated with the process::
 
     > echo 3 > /proc/PID/clear_refs
 
 To clear the soft-dirty bit::
 
     > echo 4 > /proc/PID/clear_refs
 
 To reset the peak resident set size ("high water mark") to the process's
 current value::
 
     > echo 5 > /proc/PID/clear_refs
 
 Any other value written to /proc/PID/clear_refs will have no effect.
 
 The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
 using /proc/kpageflags and number of times a page is mapped using
 /proc/kpagecount. For detailed explanation, see
 Documentation/admin-guide/mm/pagemap.rst.
 
 The /proc/pid/numa_maps is an extension based on maps, showing the memory
 locality and binding policy, as well as the memory usage (in pages) of
 each mapping. The output follows a general format where mapping details get
 summarized separated by blank spaces, one mapping per each file line::
 
     address   policy    mapping details
 
     00400000 default file=/usr/local/bin/app mapped=1 active=0 N3=1 kernelpagesize_kB=4
     00600000 default file=/usr/local/bin/app anon=1 dirty=1 N3=1 kernelpagesize_kB=4
     3206000000 default file=/lib64/ld-2.12.so mapped=26 mapmax=6 N0=24 N3=2 kernelpagesize_kB=4
     320621f000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
     3206220000 default file=/lib64/ld-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
     3206221000 default anon=1 dirty=1 N3=1 kernelpagesize_kB=4
     3206800000 default file=/lib64/libc-2.12.so mapped=59 mapmax=21 active=55 N0=41 N3=18 kernelpagesize_kB=4
     320698b000 default file=/lib64/libc-2.12.so
     3206b8a000 default file=/lib64/libc-2.12.so anon=2 dirty=2 N3=2 kernelpagesize_kB=4
     3206b8e000 default file=/lib64/libc-2.12.so anon=1 dirty=1 N3=1 kernelpagesize_kB=4
     3206b8f000 default anon=3 dirty=3 active=1 N3=3 kernelpagesize_kB=4
     7f4dc10a2000 default anon=3 dirty=3 N3=3 kernelpagesize_kB=4
     7f4dc10b4000 default anon=2 dirty=2 active=1 N3=2 kernelpagesize_kB=4
     7f4dc1200000 default file=/anon_hugepage\040(deleted) huge anon=1 dirty=1 N3=1 kernelpagesize_kB=2048
     7fff335f0000 default stack anon=3 dirty=3 N3=3 kernelpagesize_kB=4
     7fff3369d000 default mapped=1 mapmax=35 active=0 N3=1 kernelpagesize_kB=4
 
 Where:
 
 "address" is the starting address for the mapping;
 
 "policy" reports the NUMA memory policy set for the mapping (see Documentation/admin-guide/mm/numa_memory_policy.rst);
 
 "mapping details" summarizes mapping data such as mapping type, page usage counters,
 node locality page counters (N0 == node0, N1 == node1, ...) and the kernel page
 size, in KB, that is backing the mapping up.
 
 1.2 Kernel data
 ---------------
 
 Similar to  the  process entries, the kernel data files give information about
 the running kernel. The files used to obtain this information are contained in
 /proc and  are  listed  in Table 1-5. Not all of these will be present in your
 system. It  depends  on the kernel configuration and the loaded modules, which
 files are there, and which are missing.
 
 .. table:: Table 1-5: Kernel info in /proc
 
  ============ ===============================================================
  File         Content
  ============ ===============================================================
  allocinfo    Memory allocations profiling information
  apm          Advanced power management info
  bootconfig   Kernel command line obtained from boot config,
               and, if there were kernel parameters from the
               boot loader, a "# Parameters from bootloader:"
               line followed by a line containing those
               parameters prefixed by "# ".                      (5.5)
  buddyinfo    Kernel memory allocator information (see text)    (2.5)
  bus          Directory containing bus specific information
  cmdline      Kernel command line, both from bootloader and embedded
               in the kernel image
  cpuinfo      Info about the CPU
  devices      Available devices (block and character)
  dma          Used DMS channels
  filesystems  Supported filesystems
  driver       Various drivers grouped here, currently rtc       (2.4)
  execdomains  Execdomains, related to security                  (2.4)
  fb           Frame Buffer devices                              (2.4)
  fs           File system parameters, currently nfs/exports     (2.4)
  ide          Directory containing info about the IDE subsystem
  interrupts   Interrupt usage
  iomem        Memory map                                        (2.4)
  ioports      I/O port usage
  irq          Masks for irq to cpu affinity                     (2.4)(smp?)
  isapnp       ISA PnP (Plug&Play) Info                          (2.4)
  kcore        Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
  kmsg         Kernel messages
  ksyms        Kernel symbol table
  loadavg      Load average of last 1, 5 & 15 minutes;
                 number of processes currently runnable (running or on ready queue);
                 total number of processes in system;
                 last pid created.
                 All fields are separated by one space except "number of
                 processes currently runnable" and "total number of processes
                 in system", which are separated by a slash ('/'). Example:
                 0.61 0.61 0.55 3/828 22084
  locks        Kernel locks
  meminfo      Memory info
  misc         Miscellaneous
  modules      List of loaded modules
  mounts       Mounted filesystems
  net          Networking info (see text)
  pagetypeinfo Additional page allocator information (see text)  (2.5)
  partitions   Table of partitions known to the system
  pci          Deprecated info of PCI bus (new way -> /proc/bus/pci/,
               decoupled by lspci                                (2.4)
  rtc          Real time clock
  scsi         SCSI info (see text)
  slabinfo     Slab pool info
  softirqs     softirq usage
  stat         Overall statistics
  swaps        Swap space utilization
  sys          See chapter 2
  sysvipc      Info of SysVIPC Resources (msg, sem, shm)         (2.4)
  tty          Info of tty drivers
  uptime       Wall clock since boot, combined idle time of all cpus
  version      Kernel version
  video        bttv info of video resources                      (2.4)
  vmallocinfo  Show vmalloced areas
  ============ ===============================================================
 
 You can,  for  example,  check  which interrupts are currently in use and what
 they are used for by looking in the file /proc/interrupts::
 
   > cat /proc/interrupts
              CPU0
     0:    8728810          XT-PIC  timer
     1:        895          XT-PIC  keyboard
     2:          0          XT-PIC  cascade
     3:     531695          XT-PIC  aha152x
     4:    2014133          XT-PIC  serial
     5:      44401          XT-PIC  pcnet_cs
     8:          2          XT-PIC  rtc
    11:          8          XT-PIC  i82365
    12:     182918          XT-PIC  PS/2 Mouse
    13:          1          XT-PIC  fpu
    14:    1232265          XT-PIC  ide0
    15:          7          XT-PIC  ide1
   NMI:          0
 
 In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
 output of a SMP machine)::
 
   > cat /proc/interrupts
 
              CPU0       CPU1
     0:    1243498    1214548    IO-APIC-edge  timer
     1:       8949       8958    IO-APIC-edge  keyboard
     2:          0          0          XT-PIC  cascade
     5:      11286      10161    IO-APIC-edge  soundblaster
     8:          1          0    IO-APIC-edge  rtc
     9:      27422      27407    IO-APIC-edge  3c503
    12:     113645     113873    IO-APIC-edge  PS/2 Mouse
    13:          0          0          XT-PIC  fpu
    14:      22491      24012    IO-APIC-edge  ide0
    15:       2183       2415    IO-APIC-edge  ide1
    17:      30564      30414   IO-APIC-level  eth0
    18:        177        164   IO-APIC-level  bttv
   NMI:    2457961    2457959
   LOC:    2457882    2457881
   ERR:       2155
 
 NMI is incremented in this case because every timer interrupt generates a NMI
 (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
 
 LOC is the local interrupt counter of the internal APIC of every CPU.
 
 ERR is incremented in the case of errors in the IO-APIC bus (the bus that
 connects the CPUs in a SMP system. This means that an error has been detected,
 the IO-APIC automatically retry the transmission, so it should not be a big
 problem, but you should read the SMP-FAQ.
 
 In 2.6.2* /proc/interrupts was expanded again.  This time the goal was for
 /proc/interrupts to display every IRQ vector in use by the system, not
 just those considered 'most important'.  The new vectors are:
 
 THR
   interrupt raised when a machine check threshold counter
   (typically counting ECC corrected errors of memory or cache) exceeds
   a configurable threshold.  Only available on some systems.
 
 TRM
   a thermal event interrupt occurs when a temperature threshold
   has been exceeded for the CPU.  This interrupt may also be generated
   when the temperature drops back to normal.
 
 SPU
   a spurious interrupt is some interrupt that was raised then lowered
   by some IO device before it could be fully processed by the APIC.  Hence
   the APIC sees the interrupt but does not know what device it came from.
   For this case the APIC will generate the interrupt with a IRQ vector
   of 0xff. This might also be generated by chipset bugs.
 
 RES, CAL, TLB
   rescheduling, call and TLB flush interrupts are
   sent from one CPU to another per the needs of the OS.  Typically,
   their statistics are used by kernel developers and interested users to
   determine the occurrence of interrupts of the given type.
 
 The above IRQ vectors are displayed only when relevant.  For example,
 the threshold vector does not exist on x86_64 platforms.  Others are
 suppressed when the system is a uniprocessor.  As of this writing, only
 i386 and x86_64 platforms support the new IRQ vector displays.
 
 Of some interest is the introduction of the /proc/irq directory to 2.4.
 It could be used to set IRQ to CPU affinity. This means that you can "hook" an
 IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
 irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
 prof_cpu_mask.
 
 For example::
 
   > ls /proc/irq/
   0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
   1  11  13  15  17  19  3  5  7  9  default_smp_affinity
   > ls /proc/irq/0/
   smp_affinity
 
 smp_affinity is a bitmask, in which you can specify which CPUs can handle the
 IRQ. You can set it by doing::
 
   > echo 1 > /proc/irq/10/smp_affinity
 
 This means that only the first CPU will handle the IRQ, but you can also echo
 5 which means that only the first and third CPU can handle the IRQ.
 
 The contents of each smp_affinity file is the same by default::
 
   > cat /proc/irq/0/smp_affinity
   ffffffff
 
 There is an alternate interface, smp_affinity_list which allows specifying
 a CPU range instead of a bitmask::
 
   > cat /proc/irq/0/smp_affinity_list
   1024-1031
 
 The default_smp_affinity mask applies to all non-active IRQs, which are the
 IRQs which have not yet been allocated/activated, and hence which lack a
 /proc/irq/[0-9]* directory.
 
 The node file on an SMP system shows the node to which the device using the IRQ
 reports itself as being attached. This hardware locality information does not
 include information about any possible driver locality preference.
 
 prof_cpu_mask specifies which CPUs are to be profiled by the system wide
 profiler. Default value is ffffffff (all CPUs if there are only 32 of them).
 
 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
 between all the CPUs which are allowed to handle it. As usual the kernel has
 more info than you and does a better job than you, so the defaults are the
 best choice for almost everyone.  [Note this applies only to those IO-APIC's
 that support "Round Robin" interrupt distribution.]
 
 There are  three  more  important subdirectories in /proc: net, scsi, and sys.
 The general  rule  is  that  the  contents,  or  even  the  existence of these
 directories, depend  on your kernel configuration. If SCSI is not enabled, the
 directory scsi  may  not  exist. The same is true with the net, which is there
 only when networking support is present in the running kernel.
 
 The slabinfo  file  gives  information  about  memory usage at the slab level.
 Linux uses  slab  pools for memory management above page level in version 2.2.
 Commonly used  objects  have  their  own  slab  pool (such as network buffers,
 directory cache, and so on).
 
 ::
 
     > cat /proc/buddyinfo
 
     Node 0, zone      DMA      0      4      5      4      4      3 ...
     Node 0, zone   Normal      1      0      0      1    101      8 ...
     Node 0, zone  HighMem      2      0      0      1      1      0 ...
 
 External fragmentation is a problem under some workloads, and buddyinfo is a
 useful tool for helping diagnose these problems.  Buddyinfo will give you a
 clue as to how big an area you can safely allocate, or why a previous
 allocation failed.
 
 Each column represents the number of pages of a certain order which are
 available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
 ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
 available in ZONE_NORMAL, etc...
 
 More information relevant to external fragmentation can be found in
 pagetypeinfo::
 
     > cat /proc/pagetypeinfo
     Page block order: 9
     Pages per block:  512
 
     Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
     Node    0, zone      DMA, type    Unmovable      0      0      0      1      1      1      1      1      1      1      0
     Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0
     Node    0, zone      DMA, type      Movable      1      1      2      1      2      1      1      0      1      0      2
     Node    0, zone      DMA, type      Reserve      0      0      0      0      0      0      0      0      0      1      0
     Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
     Node    0, zone    DMA32, type    Unmovable    103     54     77      1      1      1     11      8      7      1      9
     Node    0, zone    DMA32, type  Reclaimable      0      0      2      1      0      0      0      0      1      0      0
     Node    0, zone    DMA32, type      Movable    169    152    113     91     77     54     39     13      6      1    452
     Node    0, zone    DMA32, type      Reserve      1      2      2      2      2      0      1      1      1      1      0
     Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
 
     Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate
     Node 0, zone      DMA            2            0            5            1            0
     Node 0, zone    DMA32           41            6          967            2            0
 
 Fragmentation avoidance in the kernel works by grouping pages of different
 migrate types into the same contiguous regions of memory called page blocks.
 A page block is typically the size of the default hugepage size, e.g. 2MB on
 X86-64. By keeping pages grouped based on their ability to move, the kernel
 can reclaim pages within a page block to satisfy a high-order allocation.
 
 The pagetypinfo begins with information on the size of a page block. It
 then gives the same type of information as buddyinfo except broken down
 by migrate-type and finishes with details on how many page blocks of each
 type exist.
 
 If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
 from libhugetlbfs https://github.com/libhugetlbfs/libhugetlbfs/), one can
 make an estimate of the likely number of huge pages that can be allocated
 at a given point in time. All the "Movable" blocks should be allocatable
 unless memory has been mlock()'d. Some of the Reclaimable blocks should
 also be allocatable although a lot of filesystem metadata may have to be
 reclaimed to achieve this.
 
 
 allocinfo
 ~~~~~~~~~
 
 Provides information about memory allocations at all locations in the code
 base. Each allocation in the code is identified by its source file, line
 number, module (if originates from a loadable module) and the function calling
 the allocation. The number of bytes allocated and number of calls at each
 location are reported. The first line indicates the version of the file, the
 second line is the header listing fields in the file.
 
 Example output.
 
 ::
 
     > tail -n +3 /proc/allocinfo | sort -rn
    127664128    31168 mm/page_ext.c:270 func:alloc_page_ext
     56373248     4737 mm/slub.c:2259 func:alloc_slab_page
     14880768     3633 mm/readahead.c:247 func:page_cache_ra_unbounded
     14417920     3520 mm/mm_init.c:2530 func:alloc_large_system_hash
     13377536      234 block/blk-mq.c:3421 func:blk_mq_alloc_rqs
     11718656     2861 mm/filemap.c:1919 func:__filemap_get_folio
      9192960     2800 kernel/fork.c:307 func:alloc_thread_stack_node
      4206592        4 net/netfilter/nf_conntrack_core.c:2567 func:nf_ct_alloc_hashtable
      4136960     1010 drivers/staging/ctagmod/ctagmod.c:20 [ctagmod] func:ctagmod_start
      3940352      962 mm/memory.c:4214 func:alloc_anon_folio
      2894464    22613 fs/kernfs/dir.c:615 func:__kernfs_new_node
      ...
 
 
 meminfo
 ~~~~~~~
 
 Provides information about distribution and utilization of memory.  This
 varies by architecture and compile options.  Some of the counters reported
 here overlap.  The memory reported by the non overlapping counters may not
 add up to the overall memory usage and the difference for some workloads
 can be substantial.  In many cases there are other means to find out
 additional memory using subsystem specific interfaces, for instance
 /proc/net/sockstat for TCP memory allocations.
 
 Example output. You may not have all of these fields.
 
 ::
 
     > cat /proc/meminfo
 
     MemTotal:       32858820 kB
     MemFree:        21001236 kB
     MemAvailable:   27214312 kB
     Buffers:          581092 kB
     Cached:          5587612 kB
     SwapCached:            0 kB
     Active:          3237152 kB
     Inactive:        7586256 kB
     Active(anon):      94064 kB
     Inactive(anon):  4570616 kB
     Active(file):    3143088 kB
     Inactive(file):  3015640 kB
     Unevictable:           0 kB
     Mlocked:               0 kB
     SwapTotal:             0 kB
     SwapFree:              0 kB
     Zswap:              1904 kB
     Zswapped:           7792 kB
     Dirty:                12 kB
     Writeback:             0 kB
     AnonPages:       4654780 kB
     Mapped:           266244 kB
     Shmem:              9976 kB
     KReclaimable:     517708 kB
     Slab:             660044 kB
     SReclaimable:     517708 kB
     SUnreclaim:       142336 kB
     KernelStack:       11168 kB
     PageTables:        20540 kB
     SecPageTables:         0 kB
     NFS_Unstable:          0 kB
     Bounce:                0 kB
     WritebackTmp:          0 kB
     CommitLimit:    16429408 kB
     Committed_AS:    7715148 kB
     VmallocTotal:   34359738367 kB
     VmallocUsed:       40444 kB
     VmallocChunk:          0 kB
     Percpu:            29312 kB
     EarlyMemtestBad:       0 kB
     HardwareCorrupted:     0 kB
     AnonHugePages:   4149248 kB
     ShmemHugePages:        0 kB
     ShmemPmdMapped:        0 kB
     FileHugePages:         0 kB
     FilePmdMapped:         0 kB
     CmaTotal:              0 kB
     CmaFree:               0 kB
     HugePages_Total:       0
     HugePages_Free:        0
     HugePages_Rsvd:        0
     HugePages_Surp:        0
     Hugepagesize:       2048 kB
     Hugetlb:               0 kB
     DirectMap4k:      401152 kB
     DirectMap2M:    10008576 kB
     DirectMap1G:    24117248 kB
 
 MemTotal
               Total usable RAM (i.e. physical RAM minus a few reserved
               bits and the kernel binary code)
 MemFree
               Total free RAM. On highmem systems, the sum of LowFree+HighFree
 MemAvailable
               An estimate of how much memory is available for starting new
               applications, without swapping. Calculated from MemFree,
               SReclaimable, the size of the file LRU lists, and the low
               watermarks in each zone.
               The estimate takes into account that the system needs some
               page cache to function well, and that not all reclaimable
               slab will be reclaimable, due to items being in use. The
               impact of those factors will vary from system to system.
 Buffers
               Relatively temporary storage for raw disk blocks
               shouldn't get tremendously large (20MB or so)
 Cached
               In-memory cache for files read from the disk (the
               pagecache) as well as tmpfs & shmem.
               Doesn't include SwapCached.
 SwapCached
               Memory that once was swapped out, is swapped back in but
               still also is in the swapfile (if memory is needed it
               doesn't need to be swapped out AGAIN because it is already
               in the swapfile. This saves I/O)
 Active
               Memory that has been used more recently and usually not
               reclaimed unless absolutely necessary.
 Inactive
               Memory which has been less recently used.  It is more
               eligible to be reclaimed for other purposes
 Unevictable
               Memory allocated for userspace which cannot be reclaimed, such
               as mlocked pages, ramfs backing pages, secret memfd pages etc.
 Mlocked
               Memory locked with mlock().
 HighTotal, HighFree
               Highmem is all memory above ~860MB of physical memory.
               Highmem areas are for use by userspace programs, or
               for the pagecache.  The kernel must use tricks to access
               this memory, making it slower to access than lowmem.
 LowTotal, LowFree
               Lowmem is memory which can be used for everything that
               highmem can be used for, but it is also available for the
               kernel's use for its own data structures.  Among many
               other things, it is where everything from the Slab is
               allocated.  Bad things happen when you're out of lowmem.
 SwapTotal
               total amount of swap space available
 SwapFree
               Memory which has been evicted from RAM, and is temporarily
               on the disk
 Zswap
               Memory consumed by the zswap backend (compressed size)
 Zswapped
               Amount of anonymous memory stored in zswap (original size)
 Dirty
               Memory which is waiting to get written back to the disk
 Writeback
               Memory which is actively being written back to the disk
 AnonPages
               Non-file backed pages mapped into userspace page tables
 Mapped
               files which have been mmapped, such as libraries
 Shmem
               Total memory used by shared memory (shmem) and tmpfs
 KReclaimable
               Kernel allocations that the kernel will attempt to reclaim
               under memory pressure. Includes SReclaimable (below), and other
               direct allocations with a shrinker.
 Slab
               in-kernel data structures cache
 SReclaimable
               Part of Slab, that might be reclaimed, such as caches
 SUnreclaim
               Part of Slab, that cannot be reclaimed on memory pressure
 KernelStack
               Memory consumed by the kernel stacks of all tasks
 PageTables
               Memory consumed by userspace page tables
 SecPageTables
               Memory consumed by secondary page tables, this currently includes
               KVM mmu and IOMMU allocations on x86 and arm64.
 NFS_Unstable
               Always zero. Previous counted pages which had been written to
               the server, but has not been committed to stable storage.
 Bounce
               Memory used for block device "bounce buffers"
 WritebackTmp
               Memory used by FUSE for temporary writeback buffers
 CommitLimit
               Based on the overcommit ratio ('vm.overcommit_ratio'),
               this is the total amount of  memory currently available to
               be allocated on the system. This limit is only adhered to
               if strict overcommit accounting is enabled (mode 2 in
               'vm.overcommit_memory').
 
               The CommitLimit is calculated with the following formula::
 
                 CommitLimit = ([total RAM pages] - [total huge TLB pages]) *
                                overcommit_ratio / 100 + [total swap pages]
 
               For example, on a system with 1G of physical RAM and 7G
               of swap with a `vm.overcommit_ratio` of 30 it would
               yield a CommitLimit of 7.3G.
 
               For more details, see the memory overcommit documentation
               in mm/overcommit-accounting.
 Committed_AS
               The amount of memory presently allocated on the system.
               The committed memory is a sum of all of the memory which
               has been allocated by processes, even if it has not been
               "used" by them as of yet. A process which malloc()'s 1G
               of memory, but only touches 300M of it will show up as
               using 1G. This 1G is memory which has been "committed" to
               by the VM and can be used at any time by the allocating
               application. With strict overcommit enabled on the system
               (mode 2 in 'vm.overcommit_memory'), allocations which would
               exceed the CommitLimit (detailed above) will not be permitted.
               This is useful if one needs to guarantee that processes will
               not fail due to lack of memory once that memory has been
               successfully allocated.
 VmallocTotal
               total size of vmalloc virtual address space
 VmallocUsed
               amount of vmalloc area which is used
 VmallocChunk
               largest contiguous block of vmalloc area which is free
 Percpu
               Memory allocated to the percpu allocator used to back percpu
               allocations. This stat excludes the cost of metadata.
 EarlyMemtestBad
               The amount of RAM/memory in kB, that was identified as corrupted
               by early memtest. If memtest was not run, this field will not
               be displayed at all. Size is never rounded down to 0 kB.
               That means if 0 kB is reported, you can safely assume
               there was at least one pass of memtest and none of the passes
               found a single faulty byte of RAM.
 HardwareCorrupted
               The amount of RAM/memory in KB, the kernel identifies as
               corrupted.
 AnonHugePages
               Non-file backed huge pages mapped into userspace page tables
 ShmemHugePages
               Memory used by shared memory (shmem) and tmpfs allocated
               with huge pages
 ShmemPmdMapped
               Shared memory mapped into userspace with huge pages
 FileHugePages
               Memory used for filesystem data (page cache) allocated
               with huge pages
 FilePmdMapped
               Page cache mapped into userspace with huge pages
 CmaTotal
               Memory reserved for the Contiguous Memory Allocator (CMA)
 CmaFree
               Free remaining memory in the CMA reserves
 HugePages_Total, HugePages_Free, HugePages_Rsvd, HugePages_Surp, Hugepagesize, Hugetlb
               See Documentation/admin-guide/mm/hugetlbpage.rst.
 DirectMap4k, DirectMap2M, DirectMap1G
               Breakdown of page table sizes used in the kernel's
               identity mapping of RAM
 
 vmallocinfo
 ~~~~~~~~~~~
 
 Provides information about vmalloced/vmaped areas. One line per area,
 containing the virtual address range of the area, size in bytes,
 caller information of the creator, and optional information depending
 on the kind of area:
 
  ==========  ===================================================
  pages=nr    number of pages
  phys=addr   if a physical address was specified
  ioremap     I/O mapping (ioremap() and friends)
  vmalloc     vmalloc() area
  vmap        vmap()ed pages
  user        VM_USERMAP area
  vpages      buffer for pages pointers was vmalloced (huge area)
  N<node>=nr  (Only on NUMA kernels)
              Number of pages allocated on memory node <node>
  ==========  ===================================================
 
 ::
 
     > cat /proc/vmallocinfo
     0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
     /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
     0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
     /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
     0xffffc20000302000-0xffffc20000304000    8192 acpi_tb_verify_table+0x21/0x4f...
     phys=7fee8000 ioremap
     0xffffc20000304000-0xffffc20000307000   12288 acpi_tb_verify_table+0x21/0x4f...
     phys=7fee7000 ioremap
     0xffffc2000031d000-0xffffc2000031f000    8192 init_vdso_vars+0x112/0x210
     0xffffc2000031f000-0xffffc2000032b000   49152 cramfs_uncompress_init+0x2e ...
     /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
     0xffffc2000033a000-0xffffc2000033d000   12288 sys_swapon+0x640/0xac0      ...
     pages=2 vmalloc N1=2
     0xffffc20000347000-0xffffc2000034c000   20480 xt_alloc_table_info+0xfe ...
     /0x130 [x_tables] pages=4 vmalloc N0=4
     0xffffffffa0000000-0xffffffffa000f000   61440 sys_init_module+0xc27/0x1d00 ...
     pages=14 vmalloc N2=14
     0xffffffffa000f000-0xffffffffa0014000   20480 sys_init_module+0xc27/0x1d00 ...
     pages=4 vmalloc N1=4
     0xffffffffa0014000-0xffffffffa0017000   12288 sys_init_module+0xc27/0x1d00 ...
     pages=2 vmalloc N1=2
     0xffffffffa0017000-0xffffffffa0022000   45056 sys_init_module+0xc27/0x1d00 ...
     pages=10 vmalloc N0=10
 
 
 softirqs
 ~~~~~~~~
 
 Provides counts of softirq handlers serviced since boot time, for each CPU.
 
 ::
 
     > cat /proc/softirqs
                   CPU0       CPU1       CPU2       CPU3
         HI:          0          0          0          0
     TIMER:       27166      27120      27097      27034
     NET_TX:          0          0          0         17
     NET_RX:         42          0          0         39
     BLOCK:           0          0        107       1121
     TASKLET:         0          0          0        290
     SCHED:       27035      26983      26971      26746
     HRTIMER:         0          0          0          0
         RCU:      1678       1769       2178       2250
 
 1.3 Networking info in /proc/net
 --------------------------------
 
 The subdirectory  /proc/net  follows  the  usual  pattern. Table 1-8 shows the
 additional values  you  get  for  IP  version 6 if you configure the kernel to
 support this. Table 1-9 lists the files and their meaning.
 
 
 .. table:: Table 1-8: IPv6 info in /proc/net
 
  ========== =====================================================
  File       Content
  ========== =====================================================
  udp6       UDP sockets (IPv6)
  tcp6       TCP sockets (IPv6)
  raw6       Raw device statistics (IPv6)
  igmp6      IP multicast addresses, which this host joined (IPv6)
  if_inet6   List of IPv6 interface addresses
  ipv6_route Kernel routing table for IPv6
  rt6_stats  Global IPv6 routing tables statistics
  sockstat6  Socket statistics (IPv6)
  snmp6      Snmp data (IPv6)
  ========== =====================================================
 
 .. table:: Table 1-9: Network info in /proc/net
 
  ============= ================================================================
  File          Content
  ============= ================================================================
  arp           Kernel  ARP table
  dev           network devices with statistics
  dev_mcast     the Layer2 multicast groups a device is listening too
                (interface index, label, number of references, number of bound
                addresses).
  dev_stat      network device status
  ip_fwchains   Firewall chain linkage
  ip_fwnames    Firewall chain names
  ip_masq       Directory containing the masquerading tables
  ip_masquerade Major masquerading table
  netstat       Network statistics
  raw           raw device statistics
  route         Kernel routing table
  rpc           Directory containing rpc info
  rt_cache      Routing cache
  snmp          SNMP data
  sockstat      Socket statistics
  softnet_stat  Per-CPU incoming packets queues statistics of online CPUs
  tcp           TCP  sockets
  udp           UDP sockets
  unix          UNIX domain sockets
  wireless      Wireless interface data (Wavelan etc)
  igmp          IP multicast addresses, which this host joined
  psched        Global packet scheduler parameters.
  netlink       List of PF_NETLINK sockets
  ip_mr_vifs    List of multicast virtual interfaces
  ip_mr_cache   List of multicast routing cache
  ============= ================================================================
 
 You can  use  this  information  to see which network devices are available in
 your system and how much traffic was routed over those devices::
 
   > cat /proc/net/dev
   Inter-|Receive                                                   |[...
    face |bytes    packets errs drop fifo frame compressed multicast|[...
       lo:  908188   5596     0    0    0     0          0         0 [...
     ppp0:15475140  20721   410    0    0   410          0         0 [...
     eth0:  614530   7085     0    0    0     0          0         1 [...
 
   ...] Transmit
   ...] bytes    packets errs drop fifo colls carrier compressed
   ...]  908188     5596    0    0    0     0       0          0
   ...] 1375103    17405    0    0    0     0       0          0
   ...] 1703981     5535    0    0    0     3       0          0
 
 In addition, each Channel Bond interface has its own directory.  For
 example, the bond0 device will have a directory called /proc/net/bond0/.
 It will contain information that is specific to that bond, such as the
 current slaves of the bond, the link status of the slaves, and how
 many times the slaves link has failed.
 
 1.4 SCSI info
 -------------
 
 If you have a SCSI or ATA host adapter in your system, you'll find a
 subdirectory named after the driver for this adapter in /proc/scsi.
 You'll also see a list of all recognized SCSI devices in /proc/scsi::
 
   >cat /proc/scsi/scsi
   Attached devices:
   Host: scsi0 Channel: 00 Id: 00 Lun: 00
     Vendor: IBM      Model: DGHS09U          Rev: 03E0
     Type:   Direct-Access                    ANSI SCSI revision: 03
   Host: scsi0 Channel: 00 Id: 06 Lun: 00
     Vendor: PIONEER  Model: CD-ROM DR-U06S   Rev: 1.04
     Type:   CD-ROM                           ANSI SCSI revision: 02
 
 
 The directory  named  after  the driver has one file for each adapter found in
 the system.  These  files  contain information about the controller, including
 the used  IRQ  and  the  IO  address range. The amount of information shown is
 dependent on  the adapter you use. The example shows the output for an Adaptec
 AHA-2940 SCSI adapter::
 
   > cat /proc/scsi/aic7xxx/0
 
   Adaptec AIC7xxx driver version: 5.1.19/3.2.4
   Compile Options:
     TCQ Enabled By Default : Disabled
     AIC7XXX_PROC_STATS     : Disabled
     AIC7XXX_RESET_DELAY    : 5
   Adapter Configuration:
              SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
                              Ultra Wide Controller
       PCI MMAPed I/O Base: 0xeb001000
    Adapter SEEPROM Config: SEEPROM found and used.
         Adaptec SCSI BIOS: Enabled
                       IRQ: 10
                      SCBs: Active 0, Max Active 2,
                            Allocated 15, HW 16, Page 255
                Interrupts: 160328
         BIOS Control Word: 0x18b6
      Adapter Control Word: 0x005b
      Extended Translation: Enabled
   Disconnect Enable Flags: 0xffff
        Ultra Enable Flags: 0x0001
    Tag Queue Enable Flags: 0x0000
   Ordered Queue Tag Flags: 0x0000
   Default Tag Queue Depth: 8
       Tagged Queue By Device array for aic7xxx host instance 0:
         {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
       Actual queue depth per device for aic7xxx host instance 0:
         {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
   Statistics:
   (scsi0:0:0:0)
     Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
     Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
     Total transfers 160151 (74577 reads and 85574 writes)
   (scsi0:0:6:0)
     Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
     Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
     Total transfers 0 (0 reads and 0 writes)
 
 
 1.5 Parallel port info in /proc/parport
 ---------------------------------------
 
 The directory  /proc/parport  contains information about the parallel ports of
 your system.  It  has  one  subdirectory  for  each port, named after the port
 number (0,1,2,...).
 
 These directories contain the four files shown in Table 1-10.
 
 
 .. table:: Table 1-10: Files in /proc/parport
 
  ========= ====================================================================
  File      Content
  ========= ====================================================================
  autoprobe Any IEEE-1284 device ID information that has been acquired.
  devices   list of the device drivers using that port. A + will appear by the
            name of the device currently using the port (it might not appear
            against any).
  hardware  Parallel port's base address, IRQ line and DMA channel.
  irq       IRQ that parport is using for that port. This is in a separate
            file to allow you to alter it by writing a new value in (IRQ
            number or none).
  ========= ====================================================================
 
 1.6 TTY info in /proc/tty
 -------------------------
 
 Information about  the  available  and actually used tty's can be found in the
 directory /proc/tty. You'll find  entries  for drivers and line disciplines in
 this directory, as shown in Table 1-11.
 
 
 .. table:: Table 1-11: Files in /proc/tty
 
  ============= ==============================================
  File          Content
  ============= ==============================================
  drivers       list of drivers and their usage
  ldiscs        registered line disciplines
  driver/serial usage statistic and status of single tty lines
  ============= ==============================================
 
 To see  which  tty's  are  currently in use, you can simply look into the file
 /proc/tty/drivers::
 
   > cat /proc/tty/drivers
   pty_slave            /dev/pts      136   0-255 pty:slave
   pty_master           /dev/ptm      128   0-255 pty:master
   pty_slave            /dev/ttyp       3   0-255 pty:slave
   pty_master           /dev/pty        2   0-255 pty:master
   serial               /dev/cua        5   64-67 serial:callout
   serial               /dev/ttyS       4   64-67 serial
   /dev/tty0            /dev/tty0       4       0 system:vtmaster
   /dev/ptmx            /dev/ptmx       5       2 system
   /dev/console         /dev/console    5       1 system:console
   /dev/tty             /dev/tty        5       0 system:/dev/tty
   unknown              /dev/tty        4    1-63 console
 
 
 1.7 Miscellaneous kernel statistics in /proc/stat
 -------------------------------------------------
 
 Various pieces   of  information about  kernel activity  are  available in the
 /proc/stat file.  All  of  the numbers reported  in  this file are  aggregates
 since the system first booted.  For a quick look, simply cat the file::
 
   > cat /proc/stat
   cpu  237902850 368826709 106375398 1873517540 1135548 0 14507935 0 0 0
   cpu0 60045249 91891769 26331539 468411416 495718 0 5739640 0 0 0
   cpu1 59746288 91759249 26609887 468860630 312281 0 4384817 0 0 0
   cpu2 59489247 92985423 26904446 467808813 171668 0 2268998 0 0 0
   cpu3 58622065 92190267 26529524 468436680 155879 0 2114478 0 0 0
   intr 8688370575 8 3373 0 0 0 0 0 0 1 40791 0 0 353317 0 0 0 0 224789828 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 190974333 41958554 123983334 43 0 224593 0 0 0 <more 0's deleted>
   ctxt 22848221062
   btime 1605316999
   processes 746787147
   procs_running 2
   procs_blocked 0
   softirq 12121874454 100099120 3938138295 127375644 2795979 187870761 0 173808342 3072582055 52608 224184354
 
 The very first  "cpu" line aggregates the  numbers in all  of the other "cpuN"
 lines.  These numbers identify the amount of time the CPU has spent performing
 different kinds of work.  Time units are in USER_HZ (typically hundredths of a
 second).  The meanings of the columns are as follows, from left to right:
 
 - user: normal processes executing in user mode
 - nice: niced processes executing in user mode
 - system: processes executing in kernel mode
 - idle: twiddling thumbs
 - iowait: In a word, iowait stands for waiting for I/O to complete. But there
   are several problems:
 
   1. CPU will not wait for I/O to complete, iowait is the time that a task is
      waiting for I/O to complete. When CPU goes into idle state for
      outstanding task I/O, another task will be scheduled on this CPU.
   2. In a multi-core CPU, the task waiting for I/O to complete is not running
      on any CPU, so the iowait of each CPU is difficult to calculate.
   3. The value of iowait field in /proc/stat will decrease in certain
      conditions.
 
   So, the iowait is not reliable by reading from /proc/stat.
 - irq: servicing interrupts
 - softirq: servicing softirqs
 - steal: involuntary wait
 - guest: running a normal guest
 - guest_nice: running a niced guest
 
 The "intr" line gives counts of interrupts  serviced since boot time, for each
 of the  possible system interrupts.   The first  column  is the  total of  all
 interrupts serviced  including  unnumbered  architecture specific  interrupts;
 each  subsequent column is the  total for that particular numbered interrupt.
 Unnumbered interrupts are not shown, only summed into the total.
 
 The "ctxt" line gives the total number of context switches across all CPUs.
 
 The "btime" line gives  the time at which the  system booted, in seconds since
 the Unix epoch.
 
 The "processes" line gives the number  of processes and threads created, which
 includes (but  is not limited  to) those  created by  calls to the  fork() and
 clone() system calls.
 
 The "procs_running" line gives the total number of threads that are
 running or ready to run (i.e., the total number of runnable threads).
 
 The   "procs_blocked" line gives  the  number of  processes currently blocked,
 waiting for I/O to complete.
 
 The "softirq" line gives counts of softirqs serviced since boot time, for each
 of the possible system softirqs. The first column is the total of all
 softirqs serviced; each subsequent column is the total for that particular
 softirq.
 
 
 1.8 Ext4 file system parameters
 -------------------------------
 
 Information about mounted ext4 file systems can be found in
 /proc/fs/ext4.  Each mounted filesystem will have a directory in
 /proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
 /proc/fs/ext4/sda9 or /proc/fs/ext4/dm-0).   The files in each per-device
 directory are shown in Table 1-12, below.
 
 .. table:: Table 1-12: Files in /proc/fs/ext4/<devname>
 
  ==============  ==========================================================
  File            Content
  mb_groups       details of multiblock allocator buddy cache of free blocks
  ==============  ==========================================================
 
 1.9 /proc/consoles
 -------------------
 Shows registered system console lines.
 
 To see which character device lines are currently used for the system console
 /dev/console, you may simply look into the file /proc/consoles::
 
   > cat /proc/consoles
   tty0                 -WU (ECp)       4:7
   ttyS0                -W- (Ep)        4:64
 
 The columns are:
 
 +--------------------+-------------------------------------------------------+
 | device             | name of the device                                    |
 +====================+=======================================================+
 | operations         | * R = can do read operations                          |
 |                    | * W = can do write operations                         |
 |                    | * U = can do unblank                                  |
 +--------------------+-------------------------------------------------------+
 | flags              | * E = it is enabled                                   |
 |                    | * C = it is preferred console                         |
 |                    | * B = it is primary boot console                      |
 |                    | * p = it is used for printk buffer                    |
 |                    | * b = it is not a TTY but a Braille device            |
 |                    | * a = it is safe to use when cpu is offline           |
 +--------------------+-------------------------------------------------------+
 | major:minor        | major and minor number of the device separated by a   |
 |                    | colon                                                 |
 +--------------------+-------------------------------------------------------+
 
 Summary
 -------
 
 The /proc file system serves information about the running system. It not only
 allows access to process data but also allows you to request the kernel status
 by reading files in the hierarchy.
 
 The directory  structure  of /proc reflects the types of information and makes
 it easy, if not obvious, where to look for specific data.
 
 Chapter 2: Modifying System Parameters
 ======================================
 
 In This Chapter
 ---------------
 
 * Modifying kernel parameters by writing into files found in /proc/sys
 * Exploring the files which modify certain parameters
 * Review of the /proc/sys file tree
 
 ------------------------------------------------------------------------------
 
 A very  interesting part of /proc is the directory /proc/sys. This is not only
 a source  of  information,  it also allows you to change parameters within the
 kernel. Be  very  careful  when attempting this. You can optimize your system,
 but you  can  also  cause  it  to  crash.  Never  alter kernel parameters on a
 production system.  Set  up  a  development machine and test to make sure that
 everything works  the  way  you want it to. You may have no alternative but to
 reboot the machine once an error has been made.
 
 To change  a  value,  simply  echo  the new value into the file.
 You need to be root to do this. You  can  create  your  own  boot script
 to perform this every time your system boots.
 
 The files  in /proc/sys can be used to fine tune and monitor miscellaneous and
 general things  in  the operation of the Linux kernel. Since some of the files
 can inadvertently  disrupt  your  system,  it  is  advisable  to  read  both
 documentation and  source  before actually making adjustments. In any case, be
 very careful  when  writing  to  any  of these files. The entries in /proc may
 change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
 review the kernel documentation in the directory linux/Documentation.
 This chapter  is  heavily  based  on the documentation included in the pre 2.2
 kernels, and became part of it in version 2.2.1 of the Linux kernel.
 
 Please see: Documentation/admin-guide/sysctl/ directory for descriptions of
 these entries.
 
 Summary
 -------
 
 Certain aspects  of  kernel  behavior  can be modified at runtime, without the
 need to  recompile  the kernel, or even to reboot the system. The files in the
 /proc/sys tree  can  not only be read, but also modified. You can use the echo
 command to write value into these files, thereby changing the default settings
 of the kernel.
 
 
 Chapter 3: Per-process Parameters
 =================================
 
 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
 --------------------------------------------------------------------------------
 
 These files can be used to adjust the badness heuristic used to select which
 process gets killed in out of memory (oom) conditions.
 
 The badness heuristic assigns a value to each candidate task ranging from 0
 (never kill) to 1000 (always kill) to determine which process is targeted.  The
 units are roughly a proportion along that range of allowed memory the process
 may allocate from based on an estimation of its current memory and swap use.
 For example, if a task is using all allowed memory, its badness score will be
 1000.  If it is using half of its allowed memory, its score will be 500.
 
 The amount of "allowed" memory depends on the context in which the oom killer
 was called.  If it is due to the memory assigned to the allocating task's cpuset
 being exhausted, the allowed memory represents the set of mems assigned to that
 cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
 memory represents the set of mempolicy nodes.  If it is due to a memory
 limit (or swap limit) being reached, the allowed memory is that configured
 limit.  Finally, if it is due to the entire system being out of memory, the
 allowed memory represents all allocatable resources.
 
 The value of /proc/<pid>/oom_score_adj is added to the badness score before it
 is used to determine which task to kill.  Acceptable values range from -1000
 (OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
 polarize the preference for oom killing either by always preferring a certain
 task or completely disabling it.  The lowest possible value, -1000, is
 equivalent to disabling oom killing entirely for that task since it will always
 report a badness score of 0.
 
 Consequently, it is very simple for userspace to define the amount of memory to
 consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
 example, is roughly equivalent to allowing the remainder of tasks sharing the
 same system, cpuset, mempolicy, or memory controller resources to use at least
 50% more memory.  A value of -500, on the other hand, would be roughly
 equivalent to discounting 50% of the task's allowed memory from being considered
 as scoring against the task.
 
 For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
 be used to tune the badness score.  Its acceptable values range from -16
 (OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
 (OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
 scaled linearly with /proc/<pid>/oom_score_adj.
 
 The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
 value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
 requires CAP_SYS_RESOURCE.
 
 
 3.2 /proc/<pid>/oom_score - Display current oom-killer score
 -------------------------------------------------------------
 
 This file can be used to check the current score used by the oom-killer for
 any given <pid>. Use it together with /proc/<pid>/oom_score_adj to tune which
 process should be killed in an out-of-memory situation.
 
 Please note that the exported value includes oom_score_adj so it is
 effectively in range [0,2000].
 
 
 3.3  /proc/<pid>/io - Display the IO accounting fields
 -------------------------------------------------------
 
 This file contains IO statistics for each running process.
 
 Example
 ~~~~~~~
 
 ::
 
     test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
     [1] 3828
 
     test:/tmp # cat /proc/3828/io
     rchar: 323934931
     wchar: 323929600
     syscr: 632687
     syscw: 632675
     read_bytes: 0
     write_bytes: 323932160
     cancelled_write_bytes: 0
 
 
 Description
 ~~~~~~~~~~~
 
 rchar
 ^^^^^
 
 I/O counter: chars read
 The number of bytes which this task has caused to be read from storage. This
 is simply the sum of bytes which this process passed to read() and pread().
 It includes things like tty IO and it is unaffected by whether or not actual
 physical disk IO was required (the read might have been satisfied from
 pagecache).
 
 
 wchar
 ^^^^^
 
 I/O counter: chars written
 The number of bytes which this task has caused, or shall cause to be written
 to disk. Similar caveats apply here as with rchar.
 
 
 syscr
 ^^^^^
 
 I/O counter: read syscalls
 Attempt to count the number of read I/O operations, i.e. syscalls like read()
 and pread().
 
 
 syscw
 ^^^^^
 
 I/O counter: write syscalls
 Attempt to count the number of write I/O operations, i.e. syscalls like
 write() and pwrite().
 
 
 read_bytes
 ^^^^^^^^^^
 
 I/O counter: bytes read
 Attempt to count the number of bytes which this process really did cause to
 be fetched from the storage layer. Done at the submit_bio() level, so it is
 accurate for block-backed filesystems. <please add status regarding NFS and
 CIFS at a later time>
 
 
 write_bytes
 ^^^^^^^^^^^
 
 I/O counter: bytes written
 Attempt to count the number of bytes which this process caused to be sent to
 the storage layer. This is done at page-dirtying time.
 
 
 cancelled_write_bytes
 ^^^^^^^^^^^^^^^^^^^^^
 
 The big inaccuracy here is truncate. If a process writes 1MB to a file and
 then deletes the file, it will in fact perform no writeout. But it will have
 been accounted as having caused 1MB of write.
 In other words: The number of bytes which this process caused to not happen,
 by truncating pagecache. A task can cause "negative" IO too. If this task
 truncates some dirty pagecache, some IO which another task has been accounted
 for (in its write_bytes) will not be happening. We _could_ just subtract that
 from the truncating task's write_bytes, but there is information loss in doing
 that.
 
 
 .. Note::
 
    At its current implementation state, this is a bit racy on 32-bit machines:
    if process A reads process B's /proc/pid/io while process B is updating one
    of those 64-bit counters, process A could see an intermediate result.
 
 
 More information about this can be found within the taskstats documentation in
 Documentation/accounting.
 
 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
 ---------------------------------------------------------------
 When a process is dumped, all anonymous memory is written to a core file as
 long as the size of the core file isn't limited. But sometimes we don't want
 to dump some memory segments, for example, huge shared memory or DAX.
 Conversely, sometimes we want to save file-backed memory segments into a core
 file, not only the individual files.
 
 /proc/<pid>/coredump_filter allows you to customize which memory segments
 will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
 of memory types. If a bit of the bitmask is set, memory segments of the
 corresponding memory type are dumped, otherwise they are not dumped.
 
 The following 9 memory types are supported:
 
   - (bit 0) anonymous private memory
   - (bit 1) anonymous shared memory
   - (bit 2) file-backed private memory
   - (bit 3) file-backed shared memory
   - (bit 4) ELF header pages in file-backed private memory areas (it is
     effective only if the bit 2 is cleared)
   - (bit 5) hugetlb private memory
   - (bit 6) hugetlb shared memory
   - (bit 7) DAX private memory
   - (bit 8) DAX shared memory
 
   Note that MMIO pages such as frame buffer are never dumped and vDSO pages
   are always dumped regardless of the bitmask status.
 
   Note that bits 0-4 don't affect hugetlb or DAX memory. hugetlb memory is
   only affected by bit 5-6, and DAX is only affected by bits 7-8.
 
 The default value of coredump_filter is 0x33; this means all anonymous memory
 segments, ELF header pages and hugetlb private memory are dumped.
 
 If you don't want to dump all shared memory segments attached to pid 1234,
 write 0x31 to the process's proc file::
 
   $ echo 0x31 > /proc/1234/coredump_filter
 
 When a new process is created, the process inherits the bitmask status from its
 parent. It is useful to set up coredump_filter before the program runs.
 For example::
 
   $ echo 0x7 > /proc/self/coredump_filter
   $ ./some_program
 
 3.5     /proc/<pid>/mountinfo - Information about mounts
 --------------------------------------------------------
 
 This file contains lines of the form::
 
     36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
     (1)(2)(3)   (4)   (5)      (6)     (n…m) (m+1)(m+2) (m+3)         (m+4)
 
     (1)   mount ID:        unique identifier of the mount (may be reused after umount)
     (2)   parent ID:       ID of parent (or of self for the top of the mount tree)
     (3)   major:minor:     value of st_dev for files on filesystem
     (4)   root:            root of the mount within the filesystem
     (5)   mount point:     mount point relative to the process's root
     (6)   mount options:   per mount options
     (n…m) optional fields: zero or more fields of the form "tag[:value]"
     (m+1) separator:       marks the end of the optional fields
     (m+2) filesystem type: name of filesystem of the form "type[.subtype]"
     (m+3) mount source:    filesystem specific information or "none"
     (m+4) super options:   per super block options
 
 Parsers should ignore all unrecognised optional fields.  Currently the
 possible optional fields are:
 
 ================  ==============================================================
 shared:X          mount is shared in peer group X
 master:X          mount is slave to peer group X
 propagate_from:X  mount is slave and receives propagation from peer group X [#]_
 unbindable        mount is unbindable
 ================  ==============================================================
 
 .. [#] X is the closest dominant peer group under the process's root.  If
        X is the immediate master of the mount, or if there's no dominant peer
        group under the same root, then only the "master:X" field is present
        and not the "propagate_from:X" field.
 
 For more information on mount propagation see:
 
   Documentation/filesystems/sharedsubtree.rst
 
 
 3.6     /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
 --------------------------------------------------------
 These files provide a method to access a task's comm value. It also allows for
 a task to set its own or one of its thread siblings comm value. The comm value
 is limited in size compared to the cmdline value, so writing anything longer
 then the kernel's TASK_COMM_LEN (currently 16 chars, including the NUL
 terminator) will result in a truncated comm value.
 
 
 3.7     /proc/<pid>/task/<tid>/children - Information about task children
 -------------------------------------------------------------------------
 This file provides a fast way to retrieve first level children pids
 of a task pointed by <pid>/<tid> pair. The format is a space separated
 stream of pids.
 
 Note the "first level" here -- if a child has its own children they will
 not be listed here; one needs to read /proc/<children-pid>/task/<tid>/children
 to obtain the descendants.
 
 Since this interface is intended to be fast and cheap it doesn't
 guarantee to provide precise results and some children might be
 skipped, especially if they've exited right after we printed their
 pids, so one needs to either stop or freeze processes being inspected
 if precise results are needed.
 
 
 3.8     /proc/<pid>/fdinfo/<fd> - Information about opened file
 ---------------------------------------------------------------
 This file provides information associated with an opened file. The regular
 files have at least four fields -- 'pos', 'flags', 'mnt_id' and 'ino'.
 The 'pos' represents the current offset of the opened file in decimal
 form [see lseek(2) for details], 'flags' denotes the octal O_xxx mask the
 file has been created with [see open(2) for details] and 'mnt_id' represents
 mount ID of the file system containing the opened file [see 3.5
 /proc/<pid>/mountinfo for details]. 'ino' represents the inode number of
 the file.
 
 A typical output is::
 
         pos:    0
         flags:  0100002
         mnt_id: 19
         ino:    63107
 
 All locks associated with a file descriptor are shown in its fdinfo too::
 
     lock:       1: FLOCK  ADVISORY  WRITE 359 00:13:11691 0 EOF
 
 The files such as eventfd, fsnotify, signalfd, epoll among the regular pos/flags
 pair provide additional information particular to the objects they represent.
 
 Eventfd files
 ~~~~~~~~~~~~~
 
 ::
 
         pos:    0
         flags:  04002
         mnt_id: 9
         ino:    63107
         eventfd-count:  5a
 
 where 'eventfd-count' is hex value of a counter.
 
 Signalfd files
 ~~~~~~~~~~~~~~
 
 ::
 
         pos:    0
         flags:  04002
         mnt_id: 9
         ino:    63107
         sigmask:        0000000000000200
 
 where 'sigmask' is hex value of the signal mask associated
 with a file.
 
 Epoll files
 ~~~~~~~~~~~
 
 ::
 
         pos:    0
         flags:  02
         mnt_id: 9
         ino:    63107
         tfd:        5 events:       1d data: ffffffffffffffff pos:0 ino:61af sdev:7
 
 where 'tfd' is a target file descriptor number in decimal form,
 'events' is events mask being watched and the 'data' is data
 associated with a target [see epoll(7) for more details].
 
 The 'pos' is current offset of the target file in decimal form
 [see lseek(2)], 'ino' and 'sdev' are inode and device numbers
 where target file resides, all in hex format.
 
 Fsnotify files
 ~~~~~~~~~~~~~~
 For inotify files the format is the following::
 
         pos:    0
         flags:  02000000
         mnt_id: 9
         ino:    63107
         inotify wd:3 ino:9e7e sdev:800013 mask:800afce ignored_mask:0 fhandle-bytes:8 fhandle-type:1 f_handle:7e9e0000640d1b6d
 
 where 'wd' is a watch descriptor in decimal form, i.e. a target file
 descriptor number, 'ino' and 'sdev' are inode and device where the
 target file resides and the 'mask' is the mask of events, all in hex
 form [see inotify(7) for more details].
 
 If the kernel was built with exportfs support, the path to the target
 file is encoded as a file handle.  The file handle is provided by three
 fields 'fhandle-bytes', 'fhandle-type' and 'f_handle', all in hex
 format.
 
 If the kernel is built without exportfs support the file handle won't be
 printed out.
 
 If there is no inotify mark attached yet the 'inotify' line will be omitted.
 
 For fanotify files the format is::
 
         pos:    0
         flags:  02
         mnt_id: 9
         ino:    63107
         fanotify flags:10 event-flags:0
         fanotify mnt_id:12 mflags:40 mask:38 ignored_mask:40000003
         fanotify ino:4f969 sdev:800013 mflags:0 mask:3b ignored_mask:40000000 fhandle-bytes:8 fhandle-type:1 f_handle:69f90400c275b5b4
 
 where fanotify 'flags' and 'event-flags' are values used in fanotify_init
 call, 'mnt_id' is the mount point identifier, 'mflags' is the value of
 flags associated with mark which are tracked separately from events
 mask. 'ino' and 'sdev' are target inode and device, 'mask' is the events
 mask and 'ignored_mask' is the mask of events which are to be ignored.
 All are in hex format. Incorporation of 'mflags', 'mask' and 'ignored_mask'
 provide information about flags and mask used in fanotify_mark
 call [see fsnotify manpage for details].
 
 While the first three lines are mandatory and always printed, the rest is
 optional and may be omitted if no marks created yet.
 
 Timerfd files
 ~~~~~~~~~~~~~
 
 ::
 
         pos:    0
         flags:  02
         mnt_id: 9
         ino:    63107
         clockid: 0
         ticks: 0
         settime flags: 01
         it_value: (0, 49406829)
         it_interval: (1, 0)
 
 where 'clockid' is the clock type and 'ticks' is the number of the timer expirations
 that have occurred [see timerfd_create(2) for details]. 'settime flags' are
 flags in octal form been used to setup the timer [see timerfd_settime(2) for
 details]. 'it_value' is remaining time until the timer expiration.
 'it_interval' is the interval for the timer. Note the timer might be set up
 with TIMER_ABSTIME option which will be shown in 'settime flags', but 'it_value'
 still exhibits timer's remaining time.
 
 DMA Buffer files
 ~~~~~~~~~~~~~~~~
 
 ::
 
         pos:    0
         flags:  04002
         mnt_id: 9
         ino:    63107
         size:   32768
         count:  2
         exp_name:  system-heap
 
 where 'size' is the size of the DMA buffer in bytes. 'count' is the file count of
 the DMA buffer file. 'exp_name' is the name of the DMA buffer exporter.
 
 3.9     /proc/<pid>/map_files - Information about memory mapped files
 ---------------------------------------------------------------------
 This directory contains symbolic links which represent memory mapped files
 the process is maintaining.  Example output::
 
      | lr-------- 1 root root 64 Jan 27 11:24 333c600000-333c620000 -> /usr/lib64/ld-2.18.so
      | lr-------- 1 root root 64 Jan 27 11:24 333c81f000-333c820000 -> /usr/lib64/ld-2.18.so
      | lr-------- 1 root root 64 Jan 27 11:24 333c820000-333c821000 -> /usr/lib64/ld-2.18.so
      | ...
      | lr-------- 1 root root 64 Jan 27 11:24 35d0421000-35d0422000 -> /usr/lib64/libselinux.so.1
      | lr-------- 1 root root 64 Jan 27 11:24 400000-41a000 -> /usr/bin/ls
 
 The name of a link represents the virtual memory bounds of a mapping, i.e.
 vm_area_struct::vm_start-vm_area_struct::vm_end.
 
 The main purpose of the map_files is to retrieve a set of memory mapped
 files in a fast way instead of parsing /proc/<pid>/maps or
 /proc/<pid>/smaps, both of which contain many more records.  At the same
 time one can open(2) mappings from the listings of two processes and
 comparing their inode numbers to figure out which anonymous memory areas
 are actually shared.
 
 3.10    /proc/<pid>/timerslack_ns - Task timerslack value
 ---------------------------------------------------------
 This file provides the value of the task's timerslack value in nanoseconds.
 This value specifies an amount of time that normal timers may be deferred
 in order to coalesce timers and avoid unnecessary wakeups.
 
 This allows a task's interactivity vs power consumption tradeoff to be
 adjusted.
 
 Writing 0 to the file will set the task's timerslack to the default value.
 
 Valid values are from 0 - ULLONG_MAX
 
 An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
 permissions on the task specified to change its timerslack_ns value.
 
 3.11    /proc/<pid>/patch_state - Livepatch patch operation state
 -----------------------------------------------------------------
 When CONFIG_LIVEPATCH is enabled, this file displays the value of the
 patch state for the task.
 
 A value of '-1' indicates that no patch is in transition.
 
 A value of '0' indicates that a patch is in transition and the task is
 unpatched.  If the patch is being enabled, then the task hasn't been
 patched yet.  If the patch is being disabled, then the task has already
 been unpatched.
 
 A value of '1' indicates that a patch is in transition and the task is
 patched.  If the patch is being enabled, then the task has already been
 patched.  If the patch is being disabled, then the task hasn't been
 unpatched yet.
 
 3.12 /proc/<pid>/arch_status - task architecture specific status
 -------------------------------------------------------------------
 When CONFIG_PROC_PID_ARCH_STATUS is enabled, this file displays the
 architecture specific status of the task.
 
 Example
 ~~~~~~~
 
 ::
 
  $ cat /proc/6753/arch_status
  AVX512_elapsed_ms:      8
 
 Description
 ~~~~~~~~~~~
 
 x86 specific entries
 ~~~~~~~~~~~~~~~~~~~~~
 
 AVX512_elapsed_ms
 ^^^^^^^^^^^^^^^^^^
 
   If AVX512 is supported on the machine, this entry shows the milliseconds
   elapsed since the last time AVX512 usage was recorded. The recording
   happens on a best effort basis when a task is scheduled out. This means
   that the value depends on two factors:
 
     1) The time which the task spent on the CPU without being scheduled
        out. With CPU isolation and a single runnable task this can take
        several seconds.
 
     2) The time since the task was scheduled out last. Depending on the
        reason for being scheduled out (time slice exhausted, syscall ...)
        this can be arbitrary long time.
 
   As a consequence the value cannot be considered precise and authoritative
   information. The application which uses this information has to be aware
   of the overall scenario on the system in order to determine whether a
   task is a real AVX512 user or not. Precise information can be obtained
   with performance counters.
 
   A special value of '-1' indicates that no AVX512 usage was recorded, thus
   the task is unlikely an AVX512 user, but depends on the workload and the
   scheduling scenario, it also could be a false negative mentioned above.
 
 3.13 /proc/<pid>/fd - List of symlinks to open files
 -------------------------------------------------------
 This directory contains symbolic links which represent open files
 the process is maintaining.  Example output::
 
   lr-x------ 1 root root 64 Sep 20 17:53 0 -> /dev/null
   l-wx------ 1 root root 64 Sep 20 17:53 1 -> /dev/null
   lrwx------ 1 root root 64 Sep 20 17:53 10 -> 'socket:[12539]'
   lrwx------ 1 root root 64 Sep 20 17:53 11 -> 'socket:[12540]'
   lrwx------ 1 root root 64 Sep 20 17:53 12 -> 'socket:[12542]'
 
 The number of open files for the process is stored in 'size' member
 of stat() output for /proc/<pid>/fd for fast access.
 -------------------------------------------------------
 
 
 Chapter 4: Configuring procfs
 =============================
 
 4.1     Mount options
 ---------------------
 
 The following mount options are supported:
 
         =========       ========================================================
         hidepid=        Set /proc/<pid>/ access mode.
         gid=            Set the group authorized to learn processes information.
         subset=         Show only the specified subset of procfs.
         =========       ========================================================
 
 hidepid=off or hidepid=0 means classic mode - everybody may access all
 /proc/<pid>/ directories (default).
 
 hidepid=noaccess or hidepid=1 means users may not access any /proc/<pid>/
 directories but their own.  Sensitive files like cmdline, sched*, status are now
 protected against other users.  This makes it impossible to learn whether any
 user runs specific program (given the program doesn't reveal itself by its
 behaviour).  As an additional bonus, as /proc/<pid>/cmdline is unaccessible for
 other users, poorly written programs passing sensitive information via program
 arguments are now protected against local eavesdroppers.
 
 hidepid=invisible or hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be
 fully invisible to other users.  It doesn't mean that it hides a fact whether a
 process with a specific pid value exists (it can be learned by other means, e.g.
 by "kill -0 $PID"), but it hides process' uid and gid, which may be learned by
 stat()'ing /proc/<pid>/ otherwise.  It greatly complicates an intruder's task of
 gathering information about running processes, whether some daemon runs with
 elevated privileges, whether other user runs some sensitive program, whether
 other users run any program at all, etc.
 
 hidepid=ptraceable or hidepid=4 means that procfs should only contain
 /proc/<pid>/ directories that the caller can ptrace.
 
 gid= defines a group authorized to learn processes information otherwise
 prohibited by hidepid=.  If you use some daemon like identd which needs to learn
 information about processes information, just add identd to this group.
 
 subset=pid hides all top level files and directories in the procfs that
 are not related to tasks.
 
 Chapter 5: Filesystem behavior
 ==============================
 
 Originally, before the advent of pid namespace, procfs was a global file
 system. It means that there was only one procfs instance in the system.
 
 When pid namespace was added, a separate procfs instance was mounted in
 each pid namespace. So, procfs mount options are global among all
 mountpoints within the same namespace::
 
         # grep ^proc /proc/mounts
         proc /proc proc rw,relatime,hidepid=2 0 0
 
         # strace -e mount mount -o hidepid=1 -t proc proc /tmp/proc
         mount("proc", "/tmp/proc", "proc", 0, "hidepid=1") = 0
         +++ exited with 0 +++
 
         # grep ^proc /proc/mounts
         proc /proc proc rw,relatime,hidepid=2 0 0
         proc /tmp/proc proc rw,relatime,hidepid=2 0 0
 
 and only after remounting procfs mount options will change at all
 mountpoints::
 
         # mount -o remount,hidepid=1 -t proc proc /tmp/proc
 
         # grep ^proc /proc/mounts
         proc /proc proc rw,relatime,hidepid=1 0 0
         proc /tmp/proc proc rw,relatime,hidepid=1 0 0
 
 This behavior is different from the behavior of other filesystems.
 
 The new procfs behavior is more like other filesystems. Each procfs mount
 creates a new procfs instance. Mount options affect own procfs instance.
 It means that it became possible to have several procfs instances
 displaying tasks with different filtering options in one pid namespace::
 
         # mount -o hidepid=invisible -t proc proc /proc
         # mount -o hidepid=noaccess -t proc proc /tmp/proc
         # grep ^proc /proc/mounts
         proc /proc proc rw,relatime,hidepid=invisible 0 0
         proc /tmp/proc proc rw,relatime,hidepid=noaccess 0 0

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