2                       T H E  /proc   F I L E S Y S T E M
   4/proc/sys         Terrehon Bowden <>        October 7 1999
   5                  Bodo Bauer <>
   72.4.x update      Jorge Nerin <>      November 14 2000
   8move /proc/sys    Shen Feng <>                 April 1 2009
  10Version 1.3                                              Kernel version 2.2.12
  11                                              Kernel version 2.4.0-test11-pre4
  13fixes/update part 1.1  Stefani Seibold <>       June 9 2009
  15Table of Contents
  18  0     Preface
  19  0.1   Introduction/Credits
  20  0.2   Legal Stuff
  22  1     Collecting System Information
  23  1.1   Process-Specific Subdirectories
  24  1.2   Kernel data
  25  1.3   IDE devices in /proc/ide
  26  1.4   Networking info in /proc/net
  27  1.5   SCSI info
  28  1.6   Parallel port info in /proc/parport
  29  1.7   TTY info in /proc/tty
  30  1.8   Miscellaneous kernel statistics in /proc/stat
  31  1.9 Ext4 file system parameters
  33  2     Modifying System Parameters
  35  3     Per-Process Parameters
  36  3.1   /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj - Adjust the oom-killer
  37                                                                score
  38  3.2   /proc/<pid>/oom_score - Display current oom-killer score
  39  3.3   /proc/<pid>/io - Display the IO accounting fields
  40  3.4   /proc/<pid>/coredump_filter - Core dump filtering settings
  41  3.5   /proc/<pid>/mountinfo - Information about mounts
  42  3.6   /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
  43  3.7   /proc/<pid>/task/<tid>/children - Information about task children
  45  4     Configuring procfs
  46  4.1   Mount options
  520.1 Introduction/Credits
  55This documentation is  part of a soon (or  so we hope) to be  released book on
  56the SuSE  Linux distribution. As  there is  no complete documentation  for the
  57/proc file system and we've used  many freely available sources to write these
  58chapters, it  seems only fair  to give the work  back to the  Linux community.
  59This work is  based on the 2.2.*  kernel version and the  upcoming 2.4.*. I'm
  60afraid it's still far from complete, but we  hope it will be useful. As far as
  61we know, it is the first 'all-in-one' document about the /proc file system. It
  62is focused  on the Intel  x86 hardware,  so if you  are looking for  PPC, ARM,
  63SPARC, AXP, etc., features, you probably  won't find what you are looking for.
  64It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
  65additions and patches  are welcome and will  be added to this  document if you
  66mail them to Bodo.
  68We'd like  to  thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
  69other people for help compiling this documentation. We'd also like to extend a
  70special thank  you to Andi Kleen for documentation, which we relied on heavily
  71to create  this  document,  as well as the additional information he provided.
  72Thanks to  everybody  else  who contributed source or docs to the Linux kernel
  73and helped create a great piece of software... :)
  75If you  have  any comments, corrections or additions, please don't hesitate to
  76contact Bodo  Bauer  at  We'll  be happy to add them to this
  79The   latest   version    of   this   document   is    available   online   at
  82If  the above  direction does  not works  for you,  you could  try the  kernel
  83mailing  list  at  and/or try  to  reach  me  at
  860.2 Legal Stuff
  89We don't  guarantee  the  correctness  of this document, and if you come to us
  90complaining about  how  you  screwed  up  your  system  because  of  incorrect
  91documentation, we won't feel responsible...
  98In This Chapter
 100* Investigating  the  properties  of  the  pseudo  file  system  /proc and its
 101  ability to provide information on the running Linux system
 102* Examining /proc's structure
 103* Uncovering  various  information  about the kernel and the processes running
 104  on the system
 108The proc  file  system acts as an interface to internal data structures in the
 109kernel. It  can  be  used to obtain information about the system and to change
 110certain kernel parameters at runtime (sysctl).
 112First, we'll  take  a  look  at the read-only parts of /proc. In Chapter 2, we
 113show you how you can use /proc/sys to change settings.
 1151.1 Process-Specific Subdirectories
 118The directory  /proc  contains  (among other things) one subdirectory for each
 119process running on the system, which is named after the process ID (PID).
 121The link  self  points  to  the  process reading the file system. Each process
 122subdirectory has the entries listed in Table 1-1.
 125Table 1-1: Process specific entries in /proc
 127 File           Content
 128 clear_refs     Clears page referenced bits shown in smaps output
 129 cmdline        Command line arguments
 130 cpu            Current and last cpu in which it was executed   (2.4)(smp)
 131 cwd            Link to the current working directory
 132 environ        Values of environment variables
 133 exe            Link to the executable of this process
 134 fd             Directory, which contains all file descriptors
 135 maps           Memory maps to executables and library files    (2.4)
 136 mem            Memory held by this process
 137 root           Link to the root directory of this process
 138 stat           Process status
 139 statm          Process memory status information
 140 status         Process status in human readable form
 141 wchan          If CONFIG_KALLSYMS is set, a pre-decoded wchan
 142 pagemap        Page table
 143 stack          Report full stack trace, enable via CONFIG_STACKTRACE
 144 smaps          a extension based on maps, showing the memory consumption of
 145                each mapping
 148For example, to get the status information of a process, all you have to do is
 149read the file /proc/PID/status:
 151  >cat /proc/self/status
 152  Name:   cat
 153  State:  R (running)
 154  Tgid:   5452
 155  Pid:    5452
 156  PPid:   743
 157  TracerPid:      0                                             (2.4)
 158  Uid:    501     501     501     501
 159  Gid:    100     100     100     100
 160  FDSize: 256
 161  Groups: 100 14 16
 162  VmPeak:     5004 kB
 163  VmSize:     5004 kB
 164  VmLck:         0 kB
 165  VmHWM:       476 kB
 166  VmRSS:       476 kB
 167  VmData:      156 kB
 168  VmStk:        88 kB
 169  VmExe:        68 kB
 170  VmLib:      1412 kB
 171  VmPTE:        20 kb
 172  VmSwap:        0 kB
 173  Threads:        1
 174  SigQ:   0/28578
 175  SigPnd: 0000000000000000
 176  ShdPnd: 0000000000000000
 177  SigBlk: 0000000000000000
 178  SigIgn: 0000000000000000
 179  SigCgt: 0000000000000000
 180  CapInh: 00000000fffffeff
 181  CapPrm: 0000000000000000
 182  CapEff: 0000000000000000
 183  CapBnd: ffffffffffffffff
 184  voluntary_ctxt_switches:        0
 185  nonvoluntary_ctxt_switches:     1
 187This shows you nearly the same information you would get if you viewed it with
 188the ps  command.  In  fact,  ps  uses  the  proc  file  system  to  obtain its
 189information.  But you get a more detailed  view of the  process by reading the
 190file /proc/PID/status. It fields are described in table 1-2.
 192The  statm  file  contains  more  detailed  information about the process
 193memory usage. Its seven fields are explained in Table 1-3.  The stat file
 194contains details information about the process itself.  Its fields are
 195explained in Table 1-4.
 197(for SMP CONFIG users)
 198For making accounting scalable, RSS related information are handled in
 199asynchronous manner and the vaule may not be very precise. To see a precise
 200snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
 201It's slow but very precise.
 203Table 1-2: Contents of the status files (as of 2.6.30-rc7)
 205 Field                       Content
 206 Name                        filename of the executable
 207 State                       state (R is running, S is sleeping, D is sleeping
 208                             in an uninterruptible wait, Z is zombie,
 209                             T is traced or stopped)
 210 Tgid                        thread group ID
 211 Pid                         process id
 212 PPid                        process id of the parent process
 213 TracerPid                   PID of process tracing this process (0 if not)
 214 Uid                         Real, effective, saved set, and  file system UIDs
 215 Gid                         Real, effective, saved set, and  file system GIDs
 216 FDSize                      number of file descriptor slots currently allocated
 217 Groups                      supplementary group list
 218 VmPeak                      peak virtual memory size
 219 VmSize                      total program size
 220 VmLck                       locked memory size
 221 VmHWM                       peak resident set size ("high water mark")
 222 VmRSS                       size of memory portions
 223 VmData                      size of data, stack, and text segments
 224 VmStk                       size of data, stack, and text segments
 225 VmExe                       size of text segment
 226 VmLib                       size of shared library code
 227 VmPTE                       size of page table entries
 228 VmSwap                      size of swap usage (the number of referred swapents)
 229 Threads                     number of threads
 230 SigQ                        number of signals queued/max. number for queue
 231 SigPnd                      bitmap of pending signals for the thread
 232 ShdPnd                      bitmap of shared pending signals for the process
 233 SigBlk                      bitmap of blocked signals
 234 SigIgn                      bitmap of ignored signals
 235 SigCgt                      bitmap of catched signals
 236 CapInh                      bitmap of inheritable capabilities
 237 CapPrm                      bitmap of permitted capabilities
 238 CapEff                      bitmap of effective capabilities
 239 CapBnd                      bitmap of capabilities bounding set
 240 Cpus_allowed                mask of CPUs on which this process may run
 241 Cpus_allowed_list           Same as previous, but in "list format"
 242 Mems_allowed                mask of memory nodes allowed to this process
 243 Mems_allowed_list           Same as previous, but in "list format"
 244 voluntary_ctxt_switches     number of voluntary context switches
 245 nonvoluntary_ctxt_switches  number of non voluntary context switches
 248Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
 250 Field    Content
 251 size     total program size (pages)            (same as VmSize in status)
 252 resident size of memory portions (pages)       (same as VmRSS in status)
 253 shared   number of pages that are shared       (i.e. backed by a file)
 254 trs      number of pages that are 'code'       (not including libs; broken,
 255                                                        includes data segment)
 256 lrs      number of pages of library            (always 0 on 2.6)
 257 drs      number of pages of data/stack         (including libs; broken,
 258                                                        includes library text)
 259 dt       number of dirty pages                 (always 0 on 2.6)
 263Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
 265 Field          Content
 266  pid           process id
 267  tcomm         filename of the executable
 268  state         state (R is running, S is sleeping, D is sleeping in an
 269                uninterruptible wait, Z is zombie, T is traced or stopped)
 270  ppid          process id of the parent process
 271  pgrp          pgrp of the process
 272  sid           session id
 273  tty_nr        tty the process uses
 274  tty_pgrp      pgrp of the tty
 275  flags         task flags
 276  min_flt       number of minor faults
 277  cmin_flt      number of minor faults with child's
 278  maj_flt       number of major faults
 279  cmaj_flt      number of major faults with child's
 280  utime         user mode jiffies
 281  stime         kernel mode jiffies
 282  cutime        user mode jiffies with child's
 283  cstime        kernel mode jiffies with child's
 284  priority      priority level
 285  nice          nice level
 286  num_threads   number of threads
 287  it_real_value (obsolete, always 0)
 288  start_time    time the process started after system boot
 289  vsize         virtual memory size
 290  rss           resident set memory size
 291  rsslim        current limit in bytes on the rss
 292  start_code    address above which program text can run
 293  end_code      address below which program text can run
 294  start_stack   address of the start of the main process stack
 295  esp           current value of ESP
 296  eip           current value of EIP
 297  pending       bitmap of pending signals
 298  blocked       bitmap of blocked signals
 299  sigign        bitmap of ignored signals
 300  sigcatch      bitmap of catched signals
 301  wchan         address where process went to sleep
 302  0             (place holder)
 303  0             (place holder)
 304  exit_signal   signal to send to parent thread on exit
 305  task_cpu      which CPU the task is scheduled on
 306  rt_priority   realtime priority
 307  policy        scheduling policy (man sched_setscheduler)
 308  blkio_ticks   time spent waiting for block IO
 309  gtime         guest time of the task in jiffies
 310  cgtime        guest time of the task children in jiffies
 311  start_data    address above which program data+bss is placed
 312  end_data      address below which program data+bss is placed
 313  start_brk     address above which program heap can be expanded with brk()
 314  arg_start     address above which program command line is placed
 315  arg_end       address below which program command line is placed
 316  env_start     address above which program environment is placed
 317  env_end       address below which program environment is placed
 318  exit_code     the thread's exit_code in the form reported by the waitpid system call
 321The /proc/PID/maps file containing the currently mapped memory regions and
 322their access permissions.
 324The format is:
 326address           perms offset  dev   inode      pathname
 32808048000-08049000 r-xp 00000000 03:00 8312       /opt/test
 32908049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
 3300804a000-0806b000 rw-p 00000000 00:00 0          [heap]
 331a7cb1000-a7cb2000 ---p 00000000 00:00 0
 332a7cb2000-a7eb2000 rw-p 00000000 00:00 0
 333a7eb2000-a7eb3000 ---p 00000000 00:00 0
 334a7eb3000-a7ed5000 rw-p 00000000 00:00 0          [stack:1001]
 335a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/
 336a8008000-a800a000 r--p 00133000 03:00 4222       /lib/
 337a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/
 338a800b000-a800e000 rw-p 00000000 00:00 0
 339a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/
 340a8022000-a8023000 r--p 00013000 03:00 14462      /lib/
 341a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/
 342a8024000-a8027000 rw-p 00000000 00:00 0
 343a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/
 344a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/
 345a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/
 346aff35000-aff4a000 rw-p 00000000 00:00 0          [stack]
 347ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
 349where "address" is the address space in the process that it occupies, "perms"
 350is a set of permissions:
 352 r = read
 353 w = write
 354 x = execute
 355 s = shared
 356 p = private (copy on write)
 358"offset" is the offset into the mapping, "dev" is the device (major:minor), and
 359"inode" is the inode  on that device.  0 indicates that  no inode is associated
 360with the memory region, as the case would be with BSS (uninitialized data).
 361The "pathname" shows the name associated file for this mapping.  If the mapping
 362is not associated with a file:
 364 [heap]                   = the heap of the program
 365 [stack]                  = the stack of the main process
 366 [stack:1001]             = the stack of the thread with tid 1001
 367 [vdso]                   = the "virtual dynamic shared object",
 368                            the kernel system call handler
 370 or if empty, the mapping is anonymous.
 372The /proc/PID/task/TID/maps is a view of the virtual memory from the viewpoint
 373of the individual tasks of a process. In this file you will see a mapping marked
 374as [stack] if that task sees it as a stack. This is a key difference from the
 375content of /proc/PID/maps, where you will see all mappings that are being used
 376as stack by all of those tasks. Hence, for the example above, the task-level
 377map, i.e. /proc/PID/task/TID/maps for thread 1001 will look like this:
 37908048000-08049000 r-xp 00000000 03:00 8312       /opt/test
 38008049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
 3810804a000-0806b000 rw-p 00000000 00:00 0          [heap]
 382a7cb1000-a7cb2000 ---p 00000000 00:00 0
 383a7cb2000-a7eb2000 rw-p 00000000 00:00 0
 384a7eb2000-a7eb3000 ---p 00000000 00:00 0
 385a7eb3000-a7ed5000 rw-p 00000000 00:00 0          [stack]
 386a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/
 387a8008000-a800a000 r--p 00133000 03:00 4222       /lib/
 388a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/
 389a800b000-a800e000 rw-p 00000000 00:00 0
 390a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/
 391a8022000-a8023000 r--p 00013000 03:00 14462      /lib/
 392a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/
 393a8024000-a8027000 rw-p 00000000 00:00 0
 394a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/
 395a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/
 396a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/
 397aff35000-aff4a000 rw-p 00000000 00:00 0
 398ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
 400The /proc/PID/smaps is an extension based on maps, showing the memory
 401consumption for each of the process's mappings. For each of mappings there
 402is a series of lines such as the following:
 40408048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
 405Size:               1084 kB
 406Rss:                 892 kB
 407Pss:                 374 kB
 408Shared_Clean:        892 kB
 409Shared_Dirty:          0 kB
 410Private_Clean:         0 kB
 411Private_Dirty:         0 kB
 412Referenced:          892 kB
 413Anonymous:             0 kB
 414Swap:                  0 kB
 415KernelPageSize:        4 kB
 416MMUPageSize:           4 kB
 417Locked:              374 kB
 419The first of these lines shows the same information as is displayed for the
 420mapping in /proc/PID/maps.  The remaining lines show the size of the mapping
 421(size), the amount of the mapping that is currently resident in RAM (RSS), the
 422process' proportional share of this mapping (PSS), the number of clean and
 423dirty private pages in the mapping.  Note that even a page which is part of a
 424MAP_SHARED mapping, but has only a single pte mapped, i.e.  is currently used
 425by only one process, is accounted as private and not as shared.  "Referenced"
 426indicates the amount of memory currently marked as referenced or accessed.
 427"Anonymous" shows the amount of memory that does not belong to any file.  Even
 428a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
 429and a page is modified, the file page is replaced by a private anonymous copy.
 430"Swap" shows how much would-be-anonymous memory is also used, but out on
 433This file is only present if the CONFIG_MMU kernel configuration option is
 436The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
 437bits on both physical and virtual pages associated with a process.
 438To clear the bits for all the pages associated with the process
 439    > echo 1 > /proc/PID/clear_refs
 441To clear the bits for the anonymous pages associated with the process
 442    > echo 2 > /proc/PID/clear_refs
 444To clear the bits for the file mapped pages associated with the process
 445    > echo 3 > /proc/PID/clear_refs
 446Any other value written to /proc/PID/clear_refs will have no effect.
 448The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
 449using /proc/kpageflags and number of times a page is mapped using
 450/proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt.
 4521.2 Kernel data
 455Similar to  the  process entries, the kernel data files give information about
 456the running kernel. The files used to obtain this information are contained in
 457/proc and  are  listed  in Table 1-5. Not all of these will be present in your
 458system. It  depends  on the kernel configuration and the loaded modules, which
 459files are there, and which are missing.
 461Table 1-5: Kernel info in /proc
 463 File        Content                                           
 464 apm         Advanced power management info                    
 465 buddyinfo   Kernel memory allocator information (see text)     (2.5)
 466 bus         Directory containing bus specific information     
 467 cmdline     Kernel command line                               
 468 cpuinfo     Info about the CPU                                
 469 devices     Available devices (block and character)           
 470 dma         Used DMS channels                                 
 471 filesystems Supported filesystems                             
 472 driver      Various drivers grouped here, currently rtc (2.4)
 473 execdomains Execdomains, related to security                   (2.4)
 474 fb          Frame Buffer devices                               (2.4)
 475 fs          File system parameters, currently nfs/exports      (2.4)
 476 ide         Directory containing info about the IDE subsystem 
 477 interrupts  Interrupt usage                                   
 478 iomem       Memory map                                         (2.4)
 479 ioports     I/O port usage                                    
 480 irq         Masks for irq to cpu affinity                      (2.4)(smp?)
 481 isapnp      ISA PnP (Plug&Play) Info                           (2.4)
 482 kcore       Kernel core image (can be ELF or A.OUT(deprecated in 2.4))   
 483 kmsg        Kernel messages                                   
 484 ksyms       Kernel symbol table                               
 485 loadavg     Load average of last 1, 5 & 15 minutes                
 486 locks       Kernel locks                                      
 487 meminfo     Memory info                                       
 488 misc        Miscellaneous                                     
 489 modules     List of loaded modules                            
 490 mounts      Mounted filesystems                               
 491 net         Networking info (see text)                        
 492 pagetypeinfo Additional page allocator information (see text)  (2.5)
 493 partitions  Table of partitions known to the system           
 494 pci         Deprecated info of PCI bus (new way -> /proc/bus/pci/,
 495             decoupled by lspci                                 (2.4)
 496 rtc         Real time clock                                   
 497 scsi        SCSI info (see text)                              
 498 slabinfo    Slab pool info                                    
 499 softirqs    softirq usage
 500 stat        Overall statistics                                
 501 swaps       Swap space utilization                            
 502 sys         See chapter 2                                     
 503 sysvipc     Info of SysVIPC Resources (msg, sem, shm)          (2.4)
 504 tty         Info of tty drivers
 505 uptime      System uptime                                     
 506 version     Kernel version                                    
 507 video       bttv info of video resources                       (2.4)
 508 vmallocinfo Show vmalloced areas
 511You can,  for  example,  check  which interrupts are currently in use and what
 512they are used for by looking in the file /proc/interrupts:
 514  > cat /proc/interrupts 
 515             CPU0        
 516    0:    8728810          XT-PIC  timer 
 517    1:        895          XT-PIC  keyboard 
 518    2:          0          XT-PIC  cascade 
 519    3:     531695          XT-PIC  aha152x 
 520    4:    2014133          XT-PIC  serial 
 521    5:      44401          XT-PIC  pcnet_cs 
 522    8:          2          XT-PIC  rtc 
 523   11:          8          XT-PIC  i82365 
 524   12:     182918          XT-PIC  PS/2 Mouse 
 525   13:          1          XT-PIC  fpu 
 526   14:    1232265          XT-PIC  ide0 
 527   15:          7          XT-PIC  ide1 
 528  NMI:          0 
 530In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
 531output of a SMP machine):
 533  > cat /proc/interrupts 
 535             CPU0       CPU1       
 536    0:    1243498    1214548    IO-APIC-edge  timer
 537    1:       8949       8958    IO-APIC-edge  keyboard
 538    2:          0          0          XT-PIC  cascade
 539    5:      11286      10161    IO-APIC-edge  soundblaster
 540    8:          1          0    IO-APIC-edge  rtc
 541    9:      27422      27407    IO-APIC-edge  3c503
 542   12:     113645     113873    IO-APIC-edge  PS/2 Mouse
 543   13:          0          0          XT-PIC  fpu
 544   14:      22491      24012    IO-APIC-edge  ide0
 545   15:       2183       2415    IO-APIC-edge  ide1
 546   17:      30564      30414   IO-APIC-level  eth0
 547   18:        177        164   IO-APIC-level  bttv
 548  NMI:    2457961    2457959 
 549  LOC:    2457882    2457881 
 550  ERR:       2155
 552NMI is incremented in this case because every timer interrupt generates a NMI
 553(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
 555LOC is the local interrupt counter of the internal APIC of every CPU.
 557ERR is incremented in the case of errors in the IO-APIC bus (the bus that
 558connects the CPUs in a SMP system. This means that an error has been detected,
 559the IO-APIC automatically retry the transmission, so it should not be a big
 560problem, but you should read the SMP-FAQ.
 562In 2.6.2* /proc/interrupts was expanded again.  This time the goal was for
 563/proc/interrupts to display every IRQ vector in use by the system, not
 564just those considered 'most important'.  The new vectors are:
 566  THR -- interrupt raised when a machine check threshold counter
 567  (typically counting ECC corrected errors of memory or cache) exceeds
 568  a configurable threshold.  Only available on some systems.
 570  TRM -- a thermal event interrupt occurs when a temperature threshold
 571  has been exceeded for the CPU.  This interrupt may also be generated
 572  when the temperature drops back to normal.
 574  SPU -- a spurious interrupt is some interrupt that was raised then lowered
 575  by some IO device before it could be fully processed by the APIC.  Hence
 576  the APIC sees the interrupt but does not know what device it came from.
 577  For this case the APIC will generate the interrupt with a IRQ vector
 578  of 0xff. This might also be generated by chipset bugs.
 580  RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
 581  sent from one CPU to another per the needs of the OS.  Typically,
 582  their statistics are used by kernel developers and interested users to
 583  determine the occurrence of interrupts of the given type.
 585The above IRQ vectors are displayed only when relevant.  For example,
 586the threshold vector does not exist on x86_64 platforms.  Others are
 587suppressed when the system is a uniprocessor.  As of this writing, only
 588i386 and x86_64 platforms support the new IRQ vector displays.
 590Of some interest is the introduction of the /proc/irq directory to 2.4.
 591It could be used to set IRQ to CPU affinity, this means that you can "hook" an
 592IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
 593irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
 596For example 
 597  > ls /proc/irq/
 598  0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
 599  1  11  13  15  17  19  3  5  7  9  default_smp_affinity
 600  > ls /proc/irq/0/
 601  smp_affinity
 603smp_affinity is a bitmask, in which you can specify which CPUs can handle the
 604IRQ, you can set it by doing:
 606  > echo 1 > /proc/irq/10/smp_affinity
 608This means that only the first CPU will handle the IRQ, but you can also echo
 6095 which means that only the first and fourth CPU can handle the IRQ.
 611The contents of each smp_affinity file is the same by default:
 613  > cat /proc/irq/0/smp_affinity
 614  ffffffff
 616There is an alternate interface, smp_affinity_list which allows specifying
 617a cpu range instead of a bitmask:
 619  > cat /proc/irq/0/smp_affinity_list
 620  1024-1031
 622The default_smp_affinity mask applies to all non-active IRQs, which are the
 623IRQs which have not yet been allocated/activated, and hence which lack a
 624/proc/irq/[0-9]* directory.
 626The node file on an SMP system shows the node to which the device using the IRQ
 627reports itself as being attached. This hardware locality information does not
 628include information about any possible driver locality preference.
 630prof_cpu_mask specifies which CPUs are to be profiled by the system wide
 631profiler. Default value is ffffffff (all cpus if there are only 32 of them).
 633The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
 634between all the CPUs which are allowed to handle it. As usual the kernel has
 635more info than you and does a better job than you, so the defaults are the
 636best choice for almost everyone.  [Note this applies only to those IO-APIC's
 637that support "Round Robin" interrupt distribution.]
 639There are  three  more  important subdirectories in /proc: net, scsi, and sys.
 640The general  rule  is  that  the  contents,  or  even  the  existence of these
 641directories, depend  on your kernel configuration. If SCSI is not enabled, the
 642directory scsi  may  not  exist. The same is true with the net, which is there
 643only when networking support is present in the running kernel.
 645The slabinfo  file  gives  information  about  memory usage at the slab level.
 646Linux uses  slab  pools for memory management above page level in version 2.2.
 647Commonly used  objects  have  their  own  slab  pool (such as network buffers,
 648directory cache, and so on).
 652> cat /proc/buddyinfo
 654Node 0, zone      DMA      0      4      5      4      4      3 ...
 655Node 0, zone   Normal      1      0      0      1    101      8 ...
 656Node 0, zone  HighMem      2      0      0      1      1      0 ...
 658External fragmentation is a problem under some workloads, and buddyinfo is a
 659useful tool for helping diagnose these problems.  Buddyinfo will give you a 
 660clue as to how big an area you can safely allocate, or why a previous
 661allocation failed.
 663Each column represents the number of pages of a certain order which are 
 664available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in 
 665ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE 
 666available in ZONE_NORMAL, etc... 
 668More information relevant to external fragmentation can be found in
 671> cat /proc/pagetypeinfo
 672Page block order: 9
 673Pages per block:  512
 675Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
 676Node    0, zone      DMA, type    Unmovable      0      0      0      1      1      1      1      1      1      1      0
 677Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0
 678Node    0, zone      DMA, type      Movable      1      1      2      1      2      1      1      0      1      0      2
 679Node    0, zone      DMA, type      Reserve      0      0      0      0      0      0      0      0      0      1      0
 680Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
 681Node    0, zone    DMA32, type    Unmovable    103     54     77      1      1      1     11      8      7      1      9
 682Node    0, zone    DMA32, type  Reclaimable      0      0      2      1      0      0      0      0      1      0      0
 683Node    0, zone    DMA32, type      Movable    169    152    113     91     77     54     39     13      6      1    452
 684Node    0, zone    DMA32, type      Reserve      1      2      2      2      2      0      1      1      1      1      0
 685Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
 687Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate
 688Node 0, zone      DMA            2            0            5            1            0
 689Node 0, zone    DMA32           41            6          967            2            0
 691Fragmentation avoidance in the kernel works by grouping pages of different
 692migrate types into the same contiguous regions of memory called page blocks.
 693A page block is typically the size of the default hugepage size e.g. 2MB on
 694X86-64. By keeping pages grouped based on their ability to move, the kernel
 695can reclaim pages within a page block to satisfy a high-order allocation.
 697The pagetypinfo begins with information on the size of a page block. It
 698then gives the same type of information as buddyinfo except broken down
 699by migrate-type and finishes with details on how many page blocks of each
 700type exist.
 702If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
 703from libhugetlbfs, one can
 704make an estimate of the likely number of huge pages that can be allocated
 705at a given point in time. All the "Movable" blocks should be allocatable
 706unless memory has been mlock()'d. Some of the Reclaimable blocks should
 707also be allocatable although a lot of filesystem metadata may have to be
 708reclaimed to achieve this.
 714Provides information about distribution and utilization of memory.  This
 715varies by architecture and compile options.  The following is from a
 71616GB PIII, which has highmem enabled.  You may not have all of these fields.
 718> cat /proc/meminfo
 720The "Locked" indicates whether the mapping is locked in memory or not.
 723MemTotal:     16344972 kB
 724MemFree:      13634064 kB
 725Buffers:          3656 kB
 726Cached:        1195708 kB
 727SwapCached:          0 kB
 728Active:         891636 kB
 729Inactive:      1077224 kB
 730HighTotal:    15597528 kB
 731HighFree:     13629632 kB
 732LowTotal:       747444 kB
 733LowFree:          4432 kB
 734SwapTotal:           0 kB
 735SwapFree:            0 kB
 736Dirty:             968 kB
 737Writeback:           0 kB
 738AnonPages:      861800 kB
 739Mapped:         280372 kB
 740Slab:           284364 kB
 741SReclaimable:   159856 kB
 742SUnreclaim:     124508 kB
 743PageTables:      24448 kB
 744NFS_Unstable:        0 kB
 745Bounce:              0 kB
 746WritebackTmp:        0 kB
 747CommitLimit:   7669796 kB
 748Committed_AS:   100056 kB
 749VmallocTotal:   112216 kB
 750VmallocUsed:       428 kB
 751VmallocChunk:   111088 kB
 752AnonHugePages:   49152 kB
 754    MemTotal: Total usable ram (i.e. physical ram minus a few reserved
 755              bits and the kernel binary code)
 756     MemFree: The sum of LowFree+HighFree
 757     Buffers: Relatively temporary storage for raw disk blocks
 758              shouldn't get tremendously large (20MB or so)
 759      Cached: in-memory cache for files read from the disk (the
 760              pagecache).  Doesn't include SwapCached
 761  SwapCached: Memory that once was swapped out, is swapped back in but
 762              still also is in the swapfile (if memory is needed it
 763              doesn't need to be swapped out AGAIN because it is already
 764              in the swapfile. This saves I/O)
 765      Active: Memory that has been used more recently and usually not
 766              reclaimed unless absolutely necessary.
 767    Inactive: Memory which has been less recently used.  It is more
 768              eligible to be reclaimed for other purposes
 769   HighTotal:
 770    HighFree: Highmem is all memory above ~860MB of physical memory
 771              Highmem areas are for use by userspace programs, or
 772              for the pagecache.  The kernel must use tricks to access
 773              this memory, making it slower to access than lowmem.
 774    LowTotal:
 775     LowFree: Lowmem is memory which can be used for everything that
 776              highmem can be used for, but it is also available for the
 777              kernel's use for its own data structures.  Among many
 778              other things, it is where everything from the Slab is
 779              allocated.  Bad things happen when you're out of lowmem.
 780   SwapTotal: total amount of swap space available
 781    SwapFree: Memory which has been evicted from RAM, and is temporarily
 782              on the disk
 783       Dirty: Memory which is waiting to get written back to the disk
 784   Writeback: Memory which is actively being written back to the disk
 785   AnonPages: Non-file backed pages mapped into userspace page tables
 786AnonHugePages: Non-file backed huge pages mapped into userspace page tables
 787      Mapped: files which have been mmaped, such as libraries
 788        Slab: in-kernel data structures cache
 789SReclaimable: Part of Slab, that might be reclaimed, such as caches
 790  SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
 791  PageTables: amount of memory dedicated to the lowest level of page
 792              tables.
 793NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
 794              storage
 795      Bounce: Memory used for block device "bounce buffers"
 796WritebackTmp: Memory used by FUSE for temporary writeback buffers
 797 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
 798              this is the total amount of  memory currently available to
 799              be allocated on the system. This limit is only adhered to
 800              if strict overcommit accounting is enabled (mode 2 in
 801              'vm.overcommit_memory').
 802              The CommitLimit is calculated with the following formula:
 803              CommitLimit = ('vm.overcommit_ratio' * Physical RAM) + Swap
 804              For example, on a system with 1G of physical RAM and 7G
 805              of swap with a `vm.overcommit_ratio` of 30 it would
 806              yield a CommitLimit of 7.3G.
 807              For more details, see the memory overcommit documentation
 808              in vm/overcommit-accounting.
 809Committed_AS: The amount of memory presently allocated on the system.
 810              The committed memory is a sum of all of the memory which
 811              has been allocated by processes, even if it has not been
 812              "used" by them as of yet. A process which malloc()'s 1G
 813              of memory, but only touches 300M of it will only show up
 814              as using 300M of memory even if it has the address space
 815              allocated for the entire 1G. This 1G is memory which has
 816              been "committed" to by the VM and can be used at any time
 817              by the allocating application. With strict overcommit
 818              enabled on the system (mode 2 in 'vm.overcommit_memory'),
 819              allocations which would exceed the CommitLimit (detailed
 820              above) will not be permitted. This is useful if one needs
 821              to guarantee that processes will not fail due to lack of
 822              memory once that memory has been successfully allocated.
 823VmallocTotal: total size of vmalloc memory area
 824 VmallocUsed: amount of vmalloc area which is used
 825VmallocChunk: largest contiguous block of vmalloc area which is free
 831Provides information about vmalloced/vmaped areas. One line per area,
 832containing the virtual address range of the area, size in bytes,
 833caller information of the creator, and optional information depending
 834on the kind of area :
 836 pages=nr    number of pages
 837 phys=addr   if a physical address was specified
 838 ioremap     I/O mapping (ioremap() and friends)
 839 vmalloc     vmalloc() area
 840 vmap        vmap()ed pages
 841 user        VM_USERMAP area
 842 vpages      buffer for pages pointers was vmalloced (huge area)
 843 N<node>=nr  (Only on NUMA kernels)
 844             Number of pages allocated on memory node <node>
 846> cat /proc/vmallocinfo
 8470xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
 848  /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
 8490xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
 850  /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
 8510xffffc20000302000-0xffffc20000304000    8192 acpi_tb_verify_table+0x21/0x4f...
 852  phys=7fee8000 ioremap
 8530xffffc20000304000-0xffffc20000307000   12288 acpi_tb_verify_table+0x21/0x4f...
 854  phys=7fee7000 ioremap
 8550xffffc2000031d000-0xffffc2000031f000    8192 init_vdso_vars+0x112/0x210
 8560xffffc2000031f000-0xffffc2000032b000   49152 cramfs_uncompress_init+0x2e ...
 857  /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
 8580xffffc2000033a000-0xffffc2000033d000   12288 sys_swapon+0x640/0xac0      ...
 859  pages=2 vmalloc N1=2
 8600xffffc20000347000-0xffffc2000034c000   20480 xt_alloc_table_info+0xfe ...
 861  /0x130 [x_tables] pages=4 vmalloc N0=4
 8620xffffffffa0000000-0xffffffffa000f000   61440 sys_init_module+0xc27/0x1d00 ...
 863   pages=14 vmalloc N2=14
 8640xffffffffa000f000-0xffffffffa0014000   20480 sys_init_module+0xc27/0x1d00 ...
 865   pages=4 vmalloc N1=4
 8660xffffffffa0014000-0xffffffffa0017000   12288 sys_init_module+0xc27/0x1d00 ...
 867   pages=2 vmalloc N1=2
 8680xffffffffa0017000-0xffffffffa0022000   45056 sys_init_module+0xc27/0x1d00 ...
 869   pages=10 vmalloc N0=10
 875Provides counts of softirq handlers serviced since boot time, for each cpu.
 877> cat /proc/softirqs
 878                CPU0       CPU1       CPU2       CPU3
 879      HI:          0          0          0          0
 880   TIMER:      27166      27120      27097      27034
 881  NET_TX:          0          0          0         17
 882  NET_RX:         42          0          0         39
 883   BLOCK:          0          0        107       1121
 884 TASKLET:          0          0          0        290
 885   SCHED:      27035      26983      26971      26746
 886 HRTIMER:          0          0          0          0
 887     RCU:       1678       1769       2178       2250
 8901.3 IDE devices in /proc/ide
 893The subdirectory /proc/ide contains information about all IDE devices of which
 894the kernel  is  aware.  There is one subdirectory for each IDE controller, the
 895file drivers  and a link for each IDE device, pointing to the device directory
 896in the controller specific subtree.
 898The file  drivers  contains general information about the drivers used for the
 899IDE devices:
 901  > cat /proc/ide/drivers
 902  ide-cdrom version 4.53
 903  ide-disk version 1.08
 905More detailed  information  can  be  found  in  the  controller  specific
 906subdirectories. These  are  named  ide0,  ide1  and  so  on.  Each  of  these
 907directories contains the files shown in table 1-6.
 910Table 1-6: IDE controller info in  /proc/ide/ide?
 912 File    Content                                 
 913 channel IDE channel (0 or 1)                    
 914 config  Configuration (only for PCI/IDE bridge) 
 915 mate    Mate name                               
 916 model   Type/Chipset of IDE controller          
 919Each device  connected  to  a  controller  has  a separate subdirectory in the
 920controllers directory.  The  files  listed in table 1-7 are contained in these
 924Table 1-7: IDE device information
 926 File             Content                                    
 927 cache            The cache                                  
 928 capacity         Capacity of the medium (in 512Byte blocks) 
 929 driver           driver and version                         
 930 geometry         physical and logical geometry              
 931 identify         device identify block                      
 932 media            media type                                 
 933 model            device identifier                          
 934 settings         device setup                               
 935 smart_thresholds IDE disk management thresholds             
 936 smart_values     IDE disk management values                 
 939The most  interesting  file is settings. This file contains a nice overview of
 940the drive parameters:
 942  # cat /proc/ide/ide0/hda/settings 
 943  name                    value           min             max             mode 
 944  ----                    -----           ---             ---             ---- 
 945  bios_cyl                526             0               65535           rw 
 946  bios_head               255             0               255             rw 
 947  bios_sect               63              0               63              rw 
 948  breada_readahead        4               0               127             rw 
 949  bswap                   0               0               1               r 
 950  file_readahead          72              0               2097151         rw 
 951  io_32bit                0               0               3               rw 
 952  keepsettings            0               0               1               rw 
 953  max_kb_per_request      122             1               127             rw 
 954  multcount               0               0               8               rw 
 955  nice1                   1               0               1               rw 
 956  nowerr                  0               0               1               rw 
 957  pio_mode                write-only      0               255             w 
 958  slow                    0               0               1               rw 
 959  unmaskirq               0               0               1               rw 
 960  using_dma               0               0               1               rw 
 9631.4 Networking info in /proc/net
 966The subdirectory  /proc/net  follows  the  usual  pattern. Table 1-8 shows the
 967additional values  you  get  for  IP  version 6 if you configure the kernel to
 968support this. Table 1-9 lists the files and their meaning.
 971Table 1-8: IPv6 info in /proc/net
 973 File       Content                                               
 974 udp6       UDP sockets (IPv6)                                    
 975 tcp6       TCP sockets (IPv6)                                    
 976 raw6       Raw device statistics (IPv6)                          
 977 igmp6      IP multicast addresses, which this host joined (IPv6) 
 978 if_inet6   List of IPv6 interface addresses                      
 979 ipv6_route Kernel routing table for IPv6                         
 980 rt6_stats  Global IPv6 routing tables statistics                 
 981 sockstat6  Socket statistics (IPv6)                              
 982 snmp6      Snmp data (IPv6)                                      
 986Table 1-9: Network info in /proc/net
 988 File          Content                                                         
 989 arp           Kernel  ARP table                                               
 990 dev           network devices with statistics                                 
 991 dev_mcast     the Layer2 multicast groups a device is listening too
 992               (interface index, label, number of references, number of bound
 993               addresses). 
 994 dev_stat      network device status                                           
 995 ip_fwchains   Firewall chain linkage                                          
 996 ip_fwnames    Firewall chain names                                            
 997 ip_masq       Directory containing the masquerading tables                    
 998 ip_masquerade Major masquerading table                                        
 999 netstat       Network statistics                                              
1000 raw           raw device statistics                                           
1001 route         Kernel routing table                                            
1002 rpc           Directory containing rpc info                                   
1003 rt_cache      Routing cache                                                   
1004 snmp          SNMP data                                                       
1005 sockstat      Socket statistics                                               
1006 tcp           TCP  sockets                                                    
1007 udp           UDP sockets                                                     
1008 unix          UNIX domain sockets                                             
1009 wireless      Wireless interface data (Wavelan etc)                           
1010 igmp          IP multicast addresses, which this host joined                  
1011 psched        Global packet scheduler parameters.                             
1012 netlink       List of PF_NETLINK sockets                                      
1013 ip_mr_vifs    List of multicast virtual interfaces                            
1014 ip_mr_cache   List of multicast routing cache                                 
1017You can  use  this  information  to see which network devices are available in
1018your system and how much traffic was routed over those devices:
1020  > cat /proc/net/dev 
1021  Inter-|Receive                                                   |[... 
1022   face |bytes    packets errs drop fifo frame compressed multicast|[... 
1023      lo:  908188   5596     0    0    0     0          0         0 [...         
1024    ppp0:15475140  20721   410    0    0   410          0         0 [...  
1025    eth0:  614530   7085     0    0    0     0          0         1 [... 
1027  ...] Transmit 
1028  ...] bytes    packets errs drop fifo colls carrier compressed 
1029  ...]  908188     5596    0    0    0     0       0          0 
1030  ...] 1375103    17405    0    0    0     0       0          0 
1031  ...] 1703981     5535    0    0    0     3       0          0 
1033In addition, each Channel Bond interface has its own directory.  For
1034example, the bond0 device will have a directory called /proc/net/bond0/.
1035It will contain information that is specific to that bond, such as the
1036current slaves of the bond, the link status of the slaves, and how
1037many times the slaves link has failed.
10391.5 SCSI info
1042If you  have  a  SCSI  host adapter in your system, you'll find a subdirectory
1043named after  the driver for this adapter in /proc/scsi. You'll also see a list
1044of all recognized SCSI devices in /proc/scsi:
1046  >cat /proc/scsi/scsi 
1047  Attached devices: 
1048  Host: scsi0 Channel: 00 Id: 00 Lun: 00 
1049    Vendor: IBM      Model: DGHS09U          Rev: 03E0 
1050    Type:   Direct-Access                    ANSI SCSI revision: 03 
1051  Host: scsi0 Channel: 00 Id: 06 Lun: 00 
1052    Vendor: PIONEER  Model: CD-ROM DR-U06S   Rev: 1.04 
1053    Type:   CD-ROM                           ANSI SCSI revision: 02 
1056The directory  named  after  the driver has one file for each adapter found in
1057the system.  These  files  contain information about the controller, including
1058the used  IRQ  and  the  IO  address range. The amount of information shown is
1059dependent on  the adapter you use. The example shows the output for an Adaptec
1060AHA-2940 SCSI adapter:
1062  > cat /proc/scsi/aic7xxx/0 
1064  Adaptec AIC7xxx driver version: 5.1.19/3.2.4 
1065  Compile Options: 
1066    TCQ Enabled By Default : Disabled 
1067    AIC7XXX_PROC_STATS     : Disabled 
1068    AIC7XXX_RESET_DELAY    : 5 
1069  Adapter Configuration: 
1070             SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter 
1071                             Ultra Wide Controller 
1072      PCI MMAPed I/O Base: 0xeb001000 
1073   Adapter SEEPROM Config: SEEPROM found and used. 
1074        Adaptec SCSI BIOS: Enabled 
1075                      IRQ: 10 
1076                     SCBs: Active 0, Max Active 2, 
1077                           Allocated 15, HW 16, Page 255 
1078               Interrupts: 160328 
1079        BIOS Control Word: 0x18b6 
1080     Adapter Control Word: 0x005b 
1081     Extended Translation: Enabled 
1082  Disconnect Enable Flags: 0xffff 
1083       Ultra Enable Flags: 0x0001 
1084   Tag Queue Enable Flags: 0x0000 
1085  Ordered Queue Tag Flags: 0x0000 
1086  Default Tag Queue Depth: 8 
1087      Tagged Queue By Device array for aic7xxx host instance 0: 
1088        {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} 
1089      Actual queue depth per device for aic7xxx host instance 0: 
1090        {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} 
1091  Statistics: 
1092  (scsi0:0:0:0) 
1093    Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 
1094    Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) 
1095    Total transfers 160151 (74577 reads and 85574 writes) 
1096  (scsi0:0:6:0) 
1097    Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 
1098    Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) 
1099    Total transfers 0 (0 reads and 0 writes) 
11021.6 Parallel port info in /proc/parport
1105The directory  /proc/parport  contains information about the parallel ports of
1106your system.  It  has  one  subdirectory  for  each port, named after the port
1107number (0,1,2,...).
1109These directories contain the four files shown in Table 1-10.
1112Table 1-10: Files in /proc/parport
1114 File      Content                                                             
1115 autoprobe Any IEEE-1284 device ID information that has been acquired.         
1116 devices   list of the device drivers using that port. A + will appear by the
1117           name of the device currently using the port (it might not appear
1118           against any). 
1119 hardware  Parallel port's base address, IRQ line and DMA channel.             
1120 irq       IRQ that parport is using for that port. This is in a separate
1121           file to allow you to alter it by writing a new value in (IRQ
1122           number or none). 
11251.7 TTY info in /proc/tty
1128Information about  the  available  and actually used tty's can be found in the
1129directory /proc/tty.You'll  find  entries  for drivers and line disciplines in
1130this directory, as shown in Table 1-11.
1133Table 1-11: Files in /proc/tty
1135 File          Content                                        
1136 drivers       list of drivers and their usage                
1137 ldiscs        registered line disciplines                    
1138 driver/serial usage statistic and status of single tty lines 
1141To see  which  tty's  are  currently in use, you can simply look into the file
1144  > cat /proc/tty/drivers 
1145  pty_slave            /dev/pts      136   0-255 pty:slave 
1146  pty_master           /dev/ptm      128   0-255 pty:master 
1147  pty_slave            /dev/ttyp       3   0-255 pty:slave 
1148  pty_master           /dev/pty        2   0-255 pty:master 
1149  serial               /dev/cua        5   64-67 serial:callout 
1150  serial               /dev/ttyS       4   64-67 serial 
1151  /dev/tty0            /dev/tty0       4       0 system:vtmaster 
1152  /dev/ptmx            /dev/ptmx       5       2 system 
1153  /dev/console         /dev/console    5       1 system:console 
1154  /dev/tty             /dev/tty        5       0 system:/dev/tty 
1155  unknown              /dev/tty        4    1-63 console 
11581.8 Miscellaneous kernel statistics in /proc/stat
1161Various pieces   of  information about  kernel activity  are  available in the
1162/proc/stat file.  All  of  the numbers reported  in  this file are  aggregates
1163since the system first booted.  For a quick look, simply cat the file:
1165  > cat /proc/stat
1166  cpu  2255 34 2290 22625563 6290 127 456 0 0
1167  cpu0 1132 34 1441 11311718 3675 127 438 0 0
1168  cpu1 1123 0 849 11313845 2614 0 18 0 0
1169  intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1170  ctxt 1990473
1171  btime 1062191376
1172  processes 2915
1173  procs_running 1
1174  procs_blocked 0
1175  softirq 183433 0 21755 12 39 1137 231 21459 2263
1177The very first  "cpu" line aggregates the  numbers in all  of the other "cpuN"
1178lines.  These numbers identify the amount of time the CPU has spent performing
1179different kinds of work.  Time units are in USER_HZ (typically hundredths of a
1180second).  The meanings of the columns are as follows, from left to right:
1182- user: normal processes executing in user mode
1183- nice: niced processes executing in user mode
1184- system: processes executing in kernel mode
1185- idle: twiddling thumbs
1186- iowait: waiting for I/O to complete
1187- irq: servicing interrupts
1188- softirq: servicing softirqs
1189- steal: involuntary wait
1190- guest: running a normal guest
1191- guest_nice: running a niced guest
1193The "intr" line gives counts of interrupts  serviced since boot time, for each
1194of the  possible system interrupts.   The first  column  is the  total of  all
1195interrupts serviced; each  subsequent column is the  total for that particular
1198The "ctxt" line gives the total number of context switches across all CPUs.
1200The "btime" line gives  the time at which the  system booted, in seconds since
1201the Unix epoch.
1203The "processes" line gives the number  of processes and threads created, which
1204includes (but  is not limited  to) those  created by  calls to the  fork() and
1205clone() system calls.
1207The "procs_running" line gives the total number of threads that are
1208running or ready to run (i.e., the total number of runnable threads).
1210The   "procs_blocked" line gives  the  number of  processes currently blocked,
1211waiting for I/O to complete.
1213The "softirq" line gives counts of softirqs serviced since boot time, for each
1214of the possible system softirqs. The first column is the total of all
1215softirqs serviced; each subsequent column is the total for that particular
12191.9 Ext4 file system parameters
1222Information about mounted ext4 file systems can be found in
1223/proc/fs/ext4.  Each mounted filesystem will have a directory in
1224/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1225/proc/fs/ext4/dm-0).   The files in each per-device directory are shown
1226in Table 1-12, below.
1228Table 1-12: Files in /proc/fs/ext4/<devname>
1230 File            Content                                        
1231 mb_groups       details of multiblock allocator buddy cache of free blocks
12342.0 /proc/consoles
1236Shows registered system console lines.
1238To see which character device lines are currently used for the system console
1239/dev/console, you may simply look into the file /proc/consoles:
1241  > cat /proc/consoles
1242  tty0                 -WU (ECp)       4:7
1243  ttyS0                -W- (Ep)        4:64
1245The columns are:
1247  device               name of the device
1248  operations           R = can do read operations
1249                       W = can do write operations
1250                       U = can do unblank
1251  flags                E = it is enabled
1252                       C = it is preferred console
1253                       B = it is primary boot console
1254                       p = it is used for printk buffer
1255                       b = it is not a TTY but a Braille device
1256                       a = it is safe to use when cpu is offline
1257  major:minor          major and minor number of the device separated by a colon
1262The /proc file system serves information about the running system. It not only
1263allows access to process data but also allows you to request the kernel status
1264by reading files in the hierarchy.
1266The directory  structure  of /proc reflects the types of information and makes
1267it easy, if not obvious, where to look for specific data.
1275In This Chapter
1277* Modifying kernel parameters by writing into files found in /proc/sys
1278* Exploring the files which modify certain parameters
1279* Review of the /proc/sys file tree
1283A very  interesting part of /proc is the directory /proc/sys. This is not only
1284a source  of  information,  it also allows you to change parameters within the
1285kernel. Be  very  careful  when attempting this. You can optimize your system,
1286but you  can  also  cause  it  to  crash.  Never  alter kernel parameters on a
1287production system.  Set  up  a  development machine and test to make sure that
1288everything works  the  way  you want it to. You may have no alternative but to
1289reboot the machine once an error has been made.
1291To change  a  value,  simply  echo  the new value into the file. An example is
1292given below  in the section on the file system data. You need to be root to do
1293this. You  can  create  your  own  boot script to perform this every time your
1294system boots.
1296The files  in /proc/sys can be used to fine tune and monitor miscellaneous and
1297general things  in  the operation of the Linux kernel. Since some of the files
1298can inadvertently  disrupt  your  system,  it  is  advisable  to  read  both
1299documentation and  source  before actually making adjustments. In any case, be
1300very careful  when  writing  to  any  of these files. The entries in /proc may
1301change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1302review the kernel documentation in the directory /usr/src/linux/Documentation.
1303This chapter  is  heavily  based  on the documentation included in the pre 2.2
1304kernels, and became part of it in version 2.2.1 of the Linux kernel.
1306Please see: Documentation/sysctl/ directory for descriptions of these
1312Certain aspects  of  kernel  behavior  can be modified at runtime, without the
1313need to  recompile  the kernel, or even to reboot the system. The files in the
1314/proc/sys tree  can  not only be read, but also modified. You can use the echo
1315command to write value into these files, thereby changing the default settings
1316of the kernel.
13233.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1326These file can be used to adjust the badness heuristic used to select which
1327process gets killed in out of memory conditions.
1329The badness heuristic assigns a value to each candidate task ranging from 0
1330(never kill) to 1000 (always kill) to determine which process is targeted.  The
1331units are roughly a proportion along that range of allowed memory the process
1332may allocate from based on an estimation of its current memory and swap use.
1333For example, if a task is using all allowed memory, its badness score will be
13341000.  If it is using half of its allowed memory, its score will be 500.
1336There is an additional factor included in the badness score: root
1337processes are given 3% extra memory over other tasks.
1339The amount of "allowed" memory depends on the context in which the oom killer
1340was called.  If it is due to the memory assigned to the allocating task's cpuset
1341being exhausted, the allowed memory represents the set of mems assigned to that
1342cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
1343memory represents the set of mempolicy nodes.  If it is due to a memory
1344limit (or swap limit) being reached, the allowed memory is that configured
1345limit.  Finally, if it is due to the entire system being out of memory, the
1346allowed memory represents all allocatable resources.
1348The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1349is used to determine which task to kill.  Acceptable values range from -1000
1350(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
1351polarize the preference for oom killing either by always preferring a certain
1352task or completely disabling it.  The lowest possible value, -1000, is
1353equivalent to disabling oom killing entirely for that task since it will always
1354report a badness score of 0.
1356Consequently, it is very simple for userspace to define the amount of memory to
1357consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
1358example, is roughly equivalent to allowing the remainder of tasks sharing the
1359same system, cpuset, mempolicy, or memory controller resources to use at least
136050% more memory.  A value of -500, on the other hand, would be roughly
1361equivalent to discounting 50% of the task's allowed memory from being considered
1362as scoring against the task.
1364For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1365be used to tune the badness score.  Its acceptable values range from -16
1366(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1367(OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
1368scaled linearly with /proc/<pid>/oom_score_adj.
1370Writing to /proc/<pid>/oom_score_adj or /proc/<pid>/oom_adj will change the
1371other with its scaled value.
1373The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1374value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1375requires CAP_SYS_RESOURCE.
1377NOTICE: /proc/<pid>/oom_adj is deprecated and will be removed, please see
1380Caveat: when a parent task is selected, the oom killer will sacrifice any first
1381generation children with separate address spaces instead, if possible.  This
1382avoids servers and important system daemons from being killed and loses the
1383minimal amount of work.
13863.2 /proc/<pid>/oom_score - Display current oom-killer score
1389This file can be used to check the current score used by the oom-killer is for
1390any given <pid>. Use it together with /proc/<pid>/oom_adj to tune which
1391process should be killed in an out-of-memory situation.
13943.3  /proc/<pid>/io - Display the IO accounting fields
1397This file contains IO statistics for each running process
1402test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1403[1] 3828
1405test:/tmp # cat /proc/3828/io
1406rchar: 323934931
1407wchar: 323929600
1408syscr: 632687
1409syscw: 632675
1410read_bytes: 0
1411write_bytes: 323932160
1412cancelled_write_bytes: 0
1421I/O counter: chars read
1422The number of bytes which this task has caused to be read from storage. This
1423is simply the sum of bytes which this process passed to read() and pread().
1424It includes things like tty IO and it is unaffected by whether or not actual
1425physical disk IO was required (the read might have been satisfied from
1432I/O counter: chars written
1433The number of bytes which this task has caused, or shall cause to be written
1434to disk. Similar caveats apply here as with rchar.
1440I/O counter: read syscalls
1441Attempt to count the number of read I/O operations, i.e. syscalls like read()
1442and pread().
1448I/O counter: write syscalls
1449Attempt to count the number of write I/O operations, i.e. syscalls like
1450write() and pwrite().
1456I/O counter: bytes read
1457Attempt to count the number of bytes which this process really did cause to
1458be fetched from the storage layer. Done at the submit_bio() level, so it is
1459accurate for block-backed filesystems. <please add status regarding NFS and
1460CIFS at a later time>
1466I/O counter: bytes written
1467Attempt to count the number of bytes which this process caused to be sent to
1468the storage layer. This is done at page-dirtying time.
1474The big inaccuracy here is truncate. If a process writes 1MB to a file and
1475then deletes the file, it will in fact perform no writeout. But it will have
1476been accounted as having caused 1MB of write.
1477In other words: The number of bytes which this process caused to not happen,
1478by truncating pagecache. A task can cause "negative" IO too. If this task
1479truncates some dirty pagecache, some IO which another task has been accounted
1480for (in its write_bytes) will not be happening. We _could_ just subtract that
1481from the truncating task's write_bytes, but there is information loss in doing
1488At its current implementation state, this is a bit racy on 32-bit machines: if
1489process A reads process B's /proc/pid/io while process B is updating one of
1490those 64-bit counters, process A could see an intermediate result.
1493More information about this can be found within the taskstats documentation in
14963.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1498When a process is dumped, all anonymous memory is written to a core file as
1499long as the size of the core file isn't limited. But sometimes we don't want
1500to dump some memory segments, for example, huge shared memory. Conversely,
1501sometimes we want to save file-backed memory segments into a core file, not
1502only the individual files.
1504/proc/<pid>/coredump_filter allows you to customize which memory segments
1505will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1506of memory types. If a bit of the bitmask is set, memory segments of the
1507corresponding memory type are dumped, otherwise they are not dumped.
1509The following 7 memory types are supported:
1510  - (bit 0) anonymous private memory
1511  - (bit 1) anonymous shared memory
1512  - (bit 2) file-backed private memory
1513  - (bit 3) file-backed shared memory
1514  - (bit 4) ELF header pages in file-backed private memory areas (it is
1515            effective only if the bit 2 is cleared)
1516  - (bit 5) hugetlb private memory
1517  - (bit 6) hugetlb shared memory
1519  Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1520  are always dumped regardless of the bitmask status.
1522  Note bit 0-4 doesn't effect any hugetlb memory. hugetlb memory are only
1523  effected by bit 5-6.
1525Default value of coredump_filter is 0x23; this means all anonymous memory
1526segments and hugetlb private memory are dumped.
1528If you don't want to dump all shared memory segments attached to pid 1234,
1529write 0x21 to the process's proc file.
1531  $ echo 0x21 > /proc/1234/coredump_filter
1533When a new process is created, the process inherits the bitmask status from its
1534parent. It is useful to set up coredump_filter before the program runs.
1535For example:
1537  $ echo 0x7 > /proc/self/coredump_filter
1538  $ ./some_program
15403.5     /proc/<pid>/mountinfo - Information about mounts
1543This file contains lines of the form:
154536 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1546(1)(2)(3)   (4)   (5)      (6)      (7)   (8) (9)   (10)         (11)
1548(1) mount ID:  unique identifier of the mount (may be reused after umount)
1549(2) parent ID:  ID of parent (or of self for the top of the mount tree)
1550(3) major:minor:  value of st_dev for files on filesystem
1551(4) root:  root of the mount within the filesystem
1552(5) mount point:  mount point relative to the process's root
1553(6) mount options:  per mount options
1554(7) optional fields:  zero or more fields of the form "tag[:value]"
1555(8) separator:  marks the end of the optional fields
1556(9) filesystem type:  name of filesystem of the form "type[.subtype]"
1557(10) mount source:  filesystem specific information or "none"
1558(11) super options:  per super block options
1560Parsers should ignore all unrecognised optional fields.  Currently the
1561possible optional fields are:
1563shared:X  mount is shared in peer group X
1564master:X  mount is slave to peer group X
1565propagate_from:X  mount is slave and receives propagation from peer group X (*)
1566unbindable  mount is unbindable
1568(*) X is the closest dominant peer group under the process's root.  If
1569X is the immediate master of the mount, or if there's no dominant peer
1570group under the same root, then only the "master:X" field is present
1571and not the "propagate_from:X" field.
1573For more information on mount propagation see:
1575  Documentation/filesystems/sharedsubtree.txt
15783.6     /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
1580These files provide a method to access a tasks comm value. It also allows for
1581a task to set its own or one of its thread siblings comm value. The comm value
1582is limited in size compared to the cmdline value, so writing anything longer
1583then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1584comm value.
15873.7     /proc/<pid>/task/<tid>/children - Information about task children
1589This file provides a fast way to retrieve first level children pids
1590of a task pointed by <pid>/<tid> pair. The format is a space separated
1591stream of pids.
1593Note the "first level" here -- if a child has own children they will
1594not be listed here, one needs to read /proc/<children-pid>/task/<tid>/children
1595to obtain the descendants.
1597Since this interface is intended to be fast and cheap it doesn't
1598guarantee to provide precise results and some children might be
1599skipped, especially if they've exited right after we printed their
1600pids, so one need to either stop or freeze processes being inspected
1601if precise results are needed.
1605Configuring procfs
16084.1     Mount options
1611The following mount options are supported:
1613        hidepid=        Set /proc/<pid>/ access mode.
1614        gid=            Set the group authorized to learn processes information.
1616hidepid=0 means classic mode - everybody may access all /proc/<pid>/ directories
1619hidepid=1 means users may not access any /proc/<pid>/ directories but their
1620own.  Sensitive files like cmdline, sched*, status are now protected against
1621other users.  This makes it impossible to learn whether any user runs
1622specific program (given the program doesn't reveal itself by its behaviour).
1623As an additional bonus, as /proc/<pid>/cmdline is unaccessible for other users,
1624poorly written programs passing sensitive information via program arguments are
1625now protected against local eavesdroppers.
1627hidepid=2 means hidepid=1 plus all /proc/<pid>/ will be fully invisible to other
1628users.  It doesn't mean that it hides a fact whether a process with a specific
1629pid value exists (it can be learned by other means, e.g. by "kill -0 $PID"),
1630but it hides process' uid and gid, which may be learned by stat()'ing
1631/proc/<pid>/ otherwise.  It greatly complicates an intruder's task of gathering
1632information about running processes, whether some daemon runs with elevated
1633privileges, whether other user runs some sensitive program, whether other users
1634run any program at all, etc.
1636gid= defines a group authorized to learn processes information otherwise
1637prohibited by hidepid=.  If you use some daemon like identd which needs to learn
1638information about processes information, just add identd to this group.
1639 kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.