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
  490.1 Introduction/Credits
  52This documentation is  part of a soon (or  so we hope) to be  released book on
  53the SuSE  Linux distribution. As  there is  no complete documentation  for the
  54/proc file system and we've used  many freely available sources to write these
  55chapters, it  seems only fair  to give the work  back to the  Linux community.
  56This work is  based on the 2.2.*  kernel version and the  upcoming 2.4.*. I'm
  57afraid it's still far from complete, but we  hope it will be useful. As far as
  58we know, it is the first 'all-in-one' document about the /proc file system. It
  59is focused  on the Intel  x86 hardware,  so if you  are looking for  PPC, ARM,
  60SPARC, AXP, etc., features, you probably  won't find what you are looking for.
  61It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
  62additions and patches  are welcome and will  be added to this  document if you
  63mail them to Bodo.
  65We'd like  to  thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
  66other people for help compiling this documentation. We'd also like to extend a
  67special thank  you to Andi Kleen for documentation, which we relied on heavily
  68to create  this  document,  as well as the additional information he provided.
  69Thanks to  everybody  else  who contributed source or docs to the Linux kernel
  70and helped create a great piece of software... :)
  72If you  have  any comments, corrections or additions, please don't hesitate to
  73contact Bodo  Bauer  at  We'll  be happy to add them to this
  76The   latest   version    of   this   document   is    available   online   at
  79If  the above  direction does  not works  for you,  you could  try the  kernel
  80mailing  list  at  and/or try  to  reach  me  at
  830.2 Legal Stuff
  86We don't  guarantee  the  correctness  of this document, and if you come to us
  87complaining about  how  you  screwed  up  your  system  because  of  incorrect
  88documentation, we won't feel responsible...
  95In This Chapter
  97* Investigating  the  properties  of  the  pseudo  file  system  /proc and its
  98  ability to provide information on the running Linux system
  99* Examining /proc's structure
 100* Uncovering  various  information  about the kernel and the processes running
 101  on the system
 105The proc  file  system acts as an interface to internal data structures in the
 106kernel. It  can  be  used to obtain information about the system and to change
 107certain kernel parameters at runtime (sysctl).
 109First, we'll  take  a  look  at the read-only parts of /proc. In Chapter 2, we
 110show you how you can use /proc/sys to change settings.
 1121.1 Process-Specific Subdirectories
 115The directory  /proc  contains  (among other things) one subdirectory for each
 116process running on the system, which is named after the process ID (PID).
 118The link  self  points  to  the  process reading the file system. Each process
 119subdirectory has the entries listed in Table 1-1.
 122Table 1-1: Process specific entries in /proc
 124 File           Content
 125 clear_refs     Clears page referenced bits shown in smaps output
 126 cmdline        Command line arguments
 127 cpu            Current and last cpu in which it was executed   (2.4)(smp)
 128 cwd            Link to the current working directory
 129 environ        Values of environment variables
 130 exe            Link to the executable of this process
 131 fd             Directory, which contains all file descriptors
 132 maps           Memory maps to executables and library files    (2.4)
 133 mem            Memory held by this process
 134 root           Link to the root directory of this process
 135 stat           Process status
 136 statm          Process memory status information
 137 status         Process status in human readable form
 138 wchan          If CONFIG_KALLSYMS is set, a pre-decoded wchan
 139 pagemap        Page table
 140 stack          Report full stack trace, enable via CONFIG_STACKTRACE
 141 smaps          a extension based on maps, showing the memory consumption of
 142                each mapping
 145For example, to get the status information of a process, all you have to do is
 146read the file /proc/PID/status:
 148  >cat /proc/self/status
 149  Name:   cat
 150  State:  R (running)
 151  Tgid:   5452
 152  Pid:    5452
 153  PPid:   743
 154  TracerPid:      0                                             (2.4)
 155  Uid:    501     501     501     501
 156  Gid:    100     100     100     100
 157  FDSize: 256
 158  Groups: 100 14 16
 159  VmPeak:     5004 kB
 160  VmSize:     5004 kB
 161  VmLck:         0 kB
 162  VmHWM:       476 kB
 163  VmRSS:       476 kB
 164  VmData:      156 kB
 165  VmStk:        88 kB
 166  VmExe:        68 kB
 167  VmLib:      1412 kB
 168  VmPTE:        20 kb
 169  VmSwap:        0 kB
 170  Threads:        1
 171  SigQ:   0/28578
 172  SigPnd: 0000000000000000
 173  ShdPnd: 0000000000000000
 174  SigBlk: 0000000000000000
 175  SigIgn: 0000000000000000
 176  SigCgt: 0000000000000000
 177  CapInh: 00000000fffffeff
 178  CapPrm: 0000000000000000
 179  CapEff: 0000000000000000
 180  CapBnd: ffffffffffffffff
 181  voluntary_ctxt_switches:        0
 182  nonvoluntary_ctxt_switches:     1
 184This shows you nearly the same information you would get if you viewed it with
 185the ps  command.  In  fact,  ps  uses  the  proc  file  system  to  obtain its
 186information.  But you get a more detailed  view of the  process by reading the
 187file /proc/PID/status. It fields are described in table 1-2.
 189The  statm  file  contains  more  detailed  information about the process
 190memory usage. Its seven fields are explained in Table 1-3.  The stat file
 191contains details information about the process itself.  Its fields are
 192explained in Table 1-4.
 194(for SMP CONFIG users)
 195For making accounting scalable, RSS related information are handled in
 196asynchronous manner and the vaule may not be very precise. To see a precise
 197snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
 198It's slow but very precise.
 200Table 1-2: Contents of the status files (as of 2.6.30-rc7)
 202 Field                       Content
 203 Name                        filename of the executable
 204 State                       state (R is running, S is sleeping, D is sleeping
 205                             in an uninterruptible wait, Z is zombie,
 206                             T is traced or stopped)
 207 Tgid                        thread group ID
 208 Pid                         process id
 209 PPid                        process id of the parent process
 210 TracerPid                   PID of process tracing this process (0 if not)
 211 Uid                         Real, effective, saved set, and  file system UIDs
 212 Gid                         Real, effective, saved set, and  file system GIDs
 213 FDSize                      number of file descriptor slots currently allocated
 214 Groups                      supplementary group list
 215 VmPeak                      peak virtual memory size
 216 VmSize                      total program size
 217 VmLck                       locked memory size
 218 VmHWM                       peak resident set size ("high water mark")
 219 VmRSS                       size of memory portions
 220 VmData                      size of data, stack, and text segments
 221 VmStk                       size of data, stack, and text segments
 222 VmExe                       size of text segment
 223 VmLib                       size of shared library code
 224 VmPTE                       size of page table entries
 225 VmSwap                      size of swap usage (the number of referred swapents)
 226 Threads                     number of threads
 227 SigQ                        number of signals queued/max. number for queue
 228 SigPnd                      bitmap of pending signals for the thread
 229 ShdPnd                      bitmap of shared pending signals for the process
 230 SigBlk                      bitmap of blocked signals
 231 SigIgn                      bitmap of ignored signals
 232 SigCgt                      bitmap of catched signals
 233 CapInh                      bitmap of inheritable capabilities
 234 CapPrm                      bitmap of permitted capabilities
 235 CapEff                      bitmap of effective capabilities
 236 CapBnd                      bitmap of capabilities bounding set
 237 Cpus_allowed                mask of CPUs on which this process may run
 238 Cpus_allowed_list           Same as previous, but in "list format"
 239 Mems_allowed                mask of memory nodes allowed to this process
 240 Mems_allowed_list           Same as previous, but in "list format"
 241 voluntary_ctxt_switches     number of voluntary context switches
 242 nonvoluntary_ctxt_switches  number of non voluntary context switches
 245Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
 247 Field    Content
 248 size     total program size (pages)            (same as VmSize in status)
 249 resident size of memory portions (pages)       (same as VmRSS in status)
 250 shared   number of pages that are shared       (i.e. backed by a file)
 251 trs      number of pages that are 'code'       (not including libs; broken,
 252                                                        includes data segment)
 253 lrs      number of pages of library            (always 0 on 2.6)
 254 drs      number of pages of data/stack         (including libs; broken,
 255                                                        includes library text)
 256 dt       number of dirty pages                 (always 0 on 2.6)
 260Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
 262 Field          Content
 263  pid           process id
 264  tcomm         filename of the executable
 265  state         state (R is running, S is sleeping, D is sleeping in an
 266                uninterruptible wait, Z is zombie, T is traced or stopped)
 267  ppid          process id of the parent process
 268  pgrp          pgrp of the process
 269  sid           session id
 270  tty_nr        tty the process uses
 271  tty_pgrp      pgrp of the tty
 272  flags         task flags
 273  min_flt       number of minor faults
 274  cmin_flt      number of minor faults with child's
 275  maj_flt       number of major faults
 276  cmaj_flt      number of major faults with child's
 277  utime         user mode jiffies
 278  stime         kernel mode jiffies
 279  cutime        user mode jiffies with child's
 280  cstime        kernel mode jiffies with child's
 281  priority      priority level
 282  nice          nice level
 283  num_threads   number of threads
 284  it_real_value (obsolete, always 0)
 285  start_time    time the process started after system boot
 286  vsize         virtual memory size
 287  rss           resident set memory size
 288  rsslim        current limit in bytes on the rss
 289  start_code    address above which program text can run
 290  end_code      address below which program text can run
 291  start_stack   address of the start of the stack
 292  esp           current value of ESP
 293  eip           current value of EIP
 294  pending       bitmap of pending signals
 295  blocked       bitmap of blocked signals
 296  sigign        bitmap of ignored signals
 297  sigcatch      bitmap of catched signals
 298  wchan         address where process went to sleep
 299  0             (place holder)
 300  0             (place holder)
 301  exit_signal   signal to send to parent thread on exit
 302  task_cpu      which CPU the task is scheduled on
 303  rt_priority   realtime priority
 304  policy        scheduling policy (man sched_setscheduler)
 305  blkio_ticks   time spent waiting for block IO
 306  gtime         guest time of the task in jiffies
 307  cgtime        guest time of the task children in jiffies
 310The /proc/PID/maps file containing the currently mapped memory regions and
 311their access permissions.
 313The format is:
 315address           perms offset  dev   inode      pathname
 31708048000-08049000 r-xp 00000000 03:00 8312       /opt/test
 31808049000-0804a000 rw-p 00001000 03:00 8312       /opt/test
 3190804a000-0806b000 rw-p 00000000 00:00 0          [heap]
 320a7cb1000-a7cb2000 ---p 00000000 00:00 0
 321a7cb2000-a7eb2000 rw-p 00000000 00:00 0
 322a7eb2000-a7eb3000 ---p 00000000 00:00 0
 323a7eb3000-a7ed5000 rw-p 00000000 00:00 0
 324a7ed5000-a8008000 r-xp 00000000 03:00 4222       /lib/
 325a8008000-a800a000 r--p 00133000 03:00 4222       /lib/
 326a800a000-a800b000 rw-p 00135000 03:00 4222       /lib/
 327a800b000-a800e000 rw-p 00000000 00:00 0
 328a800e000-a8022000 r-xp 00000000 03:00 14462      /lib/
 329a8022000-a8023000 r--p 00013000 03:00 14462      /lib/
 330a8023000-a8024000 rw-p 00014000 03:00 14462      /lib/
 331a8024000-a8027000 rw-p 00000000 00:00 0
 332a8027000-a8043000 r-xp 00000000 03:00 8317       /lib/
 333a8043000-a8044000 r--p 0001b000 03:00 8317       /lib/
 334a8044000-a8045000 rw-p 0001c000 03:00 8317       /lib/
 335aff35000-aff4a000 rw-p 00000000 00:00 0          [stack]
 336ffffe000-fffff000 r-xp 00000000 00:00 0          [vdso]
 338where "address" is the address space in the process that it occupies, "perms"
 339is a set of permissions:
 341 r = read
 342 w = write
 343 x = execute
 344 s = shared
 345 p = private (copy on write)
 347"offset" is the offset into the mapping, "dev" is the device (major:minor), and
 348"inode" is the inode  on that device.  0 indicates that  no inode is associated
 349with the memory region, as the case would be with BSS (uninitialized data).
 350The "pathname" shows the name associated file for this mapping.  If the mapping
 351is not associated with a file:
 353 [heap]                   = the heap of the program
 354 [stack]                  = the stack of the main process
 355 [vdso]                   = the "virtual dynamic shared object",
 356                            the kernel system call handler
 358 or if empty, the mapping is anonymous.
 361The /proc/PID/smaps is an extension based on maps, showing the memory
 362consumption for each of the process's mappings. For each of mappings there
 363is a series of lines such as the following:
 36508048000-080bc000 r-xp 00000000 03:02 13130      /bin/bash
 366Size:               1084 kB
 367Rss:                 892 kB
 368Pss:                 374 kB
 369Shared_Clean:        892 kB
 370Shared_Dirty:          0 kB
 371Private_Clean:         0 kB
 372Private_Dirty:         0 kB
 373Referenced:          892 kB
 374Anonymous:             0 kB
 375Swap:                  0 kB
 376KernelPageSize:        4 kB
 377MMUPageSize:           4 kB
 378Locked:              374 kB
 380The first of these lines shows the same information as is displayed for the
 381mapping in /proc/PID/maps.  The remaining lines show the size of the mapping
 382(size), the amount of the mapping that is currently resident in RAM (RSS), the
 383process' proportional share of this mapping (PSS), the number of clean and
 384dirty private pages in the mapping.  Note that even a page which is part of a
 385MAP_SHARED mapping, but has only a single pte mapped, i.e.  is currently used
 386by only one process, is accounted as private and not as shared.  "Referenced"
 387indicates the amount of memory currently marked as referenced or accessed.
 388"Anonymous" shows the amount of memory that does not belong to any file.  Even
 389a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
 390and a page is modified, the file page is replaced by a private anonymous copy.
 391"Swap" shows how much would-be-anonymous memory is also used, but out on
 394This file is only present if the CONFIG_MMU kernel configuration option is
 397The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
 398bits on both physical and virtual pages associated with a process.
 399To clear the bits for all the pages associated with the process
 400    > echo 1 > /proc/PID/clear_refs
 402To clear the bits for the anonymous pages associated with the process
 403    > echo 2 > /proc/PID/clear_refs
 405To clear the bits for the file mapped pages associated with the process
 406    > echo 3 > /proc/PID/clear_refs
 407Any other value written to /proc/PID/clear_refs will have no effect.
 409The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
 410using /proc/kpageflags and number of times a page is mapped using
 411/proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt.
 4131.2 Kernel data
 416Similar to  the  process entries, the kernel data files give information about
 417the running kernel. The files used to obtain this information are contained in
 418/proc and  are  listed  in Table 1-5. Not all of these will be present in your
 419system. It  depends  on the kernel configuration and the loaded modules, which
 420files are there, and which are missing.
 422Table 1-5: Kernel info in /proc
 424 File        Content                                           
 425 apm         Advanced power management info                    
 426 buddyinfo   Kernel memory allocator information (see text)     (2.5)
 427 bus         Directory containing bus specific information     
 428 cmdline     Kernel command line                               
 429 cpuinfo     Info about the CPU                                
 430 devices     Available devices (block and character)           
 431 dma         Used DMS channels                                 
 432 filesystems Supported filesystems                             
 433 driver      Various drivers grouped here, currently rtc (2.4)
 434 execdomains Execdomains, related to security                   (2.4)
 435 fb          Frame Buffer devices                               (2.4)
 436 fs          File system parameters, currently nfs/exports      (2.4)
 437 ide         Directory containing info about the IDE subsystem 
 438 interrupts  Interrupt usage                                   
 439 iomem       Memory map                                         (2.4)
 440 ioports     I/O port usage                                    
 441 irq         Masks for irq to cpu affinity                      (2.4)(smp?)
 442 isapnp      ISA PnP (Plug&Play) Info                           (2.4)
 443 kcore       Kernel core image (can be ELF or A.OUT(deprecated in 2.4))   
 444 kmsg        Kernel messages                                   
 445 ksyms       Kernel symbol table                               
 446 loadavg     Load average of last 1, 5 & 15 minutes                
 447 locks       Kernel locks                                      
 448 meminfo     Memory info                                       
 449 misc        Miscellaneous                                     
 450 modules     List of loaded modules                            
 451 mounts      Mounted filesystems                               
 452 net         Networking info (see text)                        
 453 pagetypeinfo Additional page allocator information (see text)  (2.5)
 454 partitions  Table of partitions known to the system           
 455 pci         Deprecated info of PCI bus (new way -> /proc/bus/pci/,
 456             decoupled by lspci                                 (2.4)
 457 rtc         Real time clock                                   
 458 scsi        SCSI info (see text)                              
 459 slabinfo    Slab pool info                                    
 460 softirqs    softirq usage
 461 stat        Overall statistics                                
 462 swaps       Swap space utilization                            
 463 sys         See chapter 2                                     
 464 sysvipc     Info of SysVIPC Resources (msg, sem, shm)          (2.4)
 465 tty         Info of tty drivers
 466 uptime      System uptime                                     
 467 version     Kernel version                                    
 468 video       bttv info of video resources                       (2.4)
 469 vmallocinfo Show vmalloced areas
 472You can,  for  example,  check  which interrupts are currently in use and what
 473they are used for by looking in the file /proc/interrupts:
 475  > cat /proc/interrupts 
 476             CPU0        
 477    0:    8728810          XT-PIC  timer 
 478    1:        895          XT-PIC  keyboard 
 479    2:          0          XT-PIC  cascade 
 480    3:     531695          XT-PIC  aha152x 
 481    4:    2014133          XT-PIC  serial 
 482    5:      44401          XT-PIC  pcnet_cs 
 483    8:          2          XT-PIC  rtc 
 484   11:          8          XT-PIC  i82365 
 485   12:     182918          XT-PIC  PS/2 Mouse 
 486   13:          1          XT-PIC  fpu 
 487   14:    1232265          XT-PIC  ide0 
 488   15:          7          XT-PIC  ide1 
 489  NMI:          0 
 491In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
 492output of a SMP machine):
 494  > cat /proc/interrupts 
 496             CPU0       CPU1       
 497    0:    1243498    1214548    IO-APIC-edge  timer
 498    1:       8949       8958    IO-APIC-edge  keyboard
 499    2:          0          0          XT-PIC  cascade
 500    5:      11286      10161    IO-APIC-edge  soundblaster
 501    8:          1          0    IO-APIC-edge  rtc
 502    9:      27422      27407    IO-APIC-edge  3c503
 503   12:     113645     113873    IO-APIC-edge  PS/2 Mouse
 504   13:          0          0          XT-PIC  fpu
 505   14:      22491      24012    IO-APIC-edge  ide0
 506   15:       2183       2415    IO-APIC-edge  ide1
 507   17:      30564      30414   IO-APIC-level  eth0
 508   18:        177        164   IO-APIC-level  bttv
 509  NMI:    2457961    2457959 
 510  LOC:    2457882    2457881 
 511  ERR:       2155
 513NMI is incremented in this case because every timer interrupt generates a NMI
 514(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
 516LOC is the local interrupt counter of the internal APIC of every CPU.
 518ERR is incremented in the case of errors in the IO-APIC bus (the bus that
 519connects the CPUs in a SMP system. This means that an error has been detected,
 520the IO-APIC automatically retry the transmission, so it should not be a big
 521problem, but you should read the SMP-FAQ.
 523In 2.6.2* /proc/interrupts was expanded again.  This time the goal was for
 524/proc/interrupts to display every IRQ vector in use by the system, not
 525just those considered 'most important'.  The new vectors are:
 527  THR -- interrupt raised when a machine check threshold counter
 528  (typically counting ECC corrected errors of memory or cache) exceeds
 529  a configurable threshold.  Only available on some systems.
 531  TRM -- a thermal event interrupt occurs when a temperature threshold
 532  has been exceeded for the CPU.  This interrupt may also be generated
 533  when the temperature drops back to normal.
 535  SPU -- a spurious interrupt is some interrupt that was raised then lowered
 536  by some IO device before it could be fully processed by the APIC.  Hence
 537  the APIC sees the interrupt but does not know what device it came from.
 538  For this case the APIC will generate the interrupt with a IRQ vector
 539  of 0xff. This might also be generated by chipset bugs.
 541  RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
 542  sent from one CPU to another per the needs of the OS.  Typically,
 543  their statistics are used by kernel developers and interested users to
 544  determine the occurrence of interrupts of the given type.
 546The above IRQ vectors are displayed only when relevant.  For example,
 547the threshold vector does not exist on x86_64 platforms.  Others are
 548suppressed when the system is a uniprocessor.  As of this writing, only
 549i386 and x86_64 platforms support the new IRQ vector displays.
 551Of some interest is the introduction of the /proc/irq directory to 2.4.
 552It could be used to set IRQ to CPU affinity, this means that you can "hook" an
 553IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
 554irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
 557For example 
 558  > ls /proc/irq/
 559  0  10  12  14  16  18  2  4  6  8  prof_cpu_mask
 560  1  11  13  15  17  19  3  5  7  9  default_smp_affinity
 561  > ls /proc/irq/0/
 562  smp_affinity
 564smp_affinity is a bitmask, in which you can specify which CPUs can handle the
 565IRQ, you can set it by doing:
 567  > echo 1 > /proc/irq/10/smp_affinity
 569This means that only the first CPU will handle the IRQ, but you can also echo
 5705 which means that only the first and fourth CPU can handle the IRQ.
 572The contents of each smp_affinity file is the same by default:
 574  > cat /proc/irq/0/smp_affinity
 575  ffffffff
 577The default_smp_affinity mask applies to all non-active IRQs, which are the
 578IRQs which have not yet been allocated/activated, and hence which lack a
 579/proc/irq/[0-9]* directory.
 581The node file on an SMP system shows the node to which the device using the IRQ
 582reports itself as being attached. This hardware locality information does not
 583include information about any possible driver locality preference.
 585prof_cpu_mask specifies which CPUs are to be profiled by the system wide
 586profiler. Default value is ffffffff (all cpus).
 588The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
 589between all the CPUs which are allowed to handle it. As usual the kernel has
 590more info than you and does a better job than you, so the defaults are the
 591best choice for almost everyone.
 593There are  three  more  important subdirectories in /proc: net, scsi, and sys.
 594The general  rule  is  that  the  contents,  or  even  the  existence of these
 595directories, depend  on your kernel configuration. If SCSI is not enabled, the
 596directory scsi  may  not  exist. The same is true with the net, which is there
 597only when networking support is present in the running kernel.
 599The slabinfo  file  gives  information  about  memory usage at the slab level.
 600Linux uses  slab  pools for memory management above page level in version 2.2.
 601Commonly used  objects  have  their  own  slab  pool (such as network buffers,
 602directory cache, and so on).
 606> cat /proc/buddyinfo
 608Node 0, zone      DMA      0      4      5      4      4      3 ...
 609Node 0, zone   Normal      1      0      0      1    101      8 ...
 610Node 0, zone  HighMem      2      0      0      1      1      0 ...
 612External fragmentation is a problem under some workloads, and buddyinfo is a
 613useful tool for helping diagnose these problems.  Buddyinfo will give you a 
 614clue as to how big an area you can safely allocate, or why a previous
 615allocation failed.
 617Each column represents the number of pages of a certain order which are 
 618available.  In this case, there are 0 chunks of 2^0*PAGE_SIZE available in 
 619ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE 
 620available in ZONE_NORMAL, etc... 
 622More information relevant to external fragmentation can be found in
 625> cat /proc/pagetypeinfo
 626Page block order: 9
 627Pages per block:  512
 629Free pages count per migrate type at order       0      1      2      3      4      5      6      7      8      9     10
 630Node    0, zone      DMA, type    Unmovable      0      0      0      1      1      1      1      1      1      1      0
 631Node    0, zone      DMA, type  Reclaimable      0      0      0      0      0      0      0      0      0      0      0
 632Node    0, zone      DMA, type      Movable      1      1      2      1      2      1      1      0      1      0      2
 633Node    0, zone      DMA, type      Reserve      0      0      0      0      0      0      0      0      0      1      0
 634Node    0, zone      DMA, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
 635Node    0, zone    DMA32, type    Unmovable    103     54     77      1      1      1     11      8      7      1      9
 636Node    0, zone    DMA32, type  Reclaimable      0      0      2      1      0      0      0      0      1      0      0
 637Node    0, zone    DMA32, type      Movable    169    152    113     91     77     54     39     13      6      1    452
 638Node    0, zone    DMA32, type      Reserve      1      2      2      2      2      0      1      1      1      1      0
 639Node    0, zone    DMA32, type      Isolate      0      0      0      0      0      0      0      0      0      0      0
 641Number of blocks type     Unmovable  Reclaimable      Movable      Reserve      Isolate
 642Node 0, zone      DMA            2            0            5            1            0
 643Node 0, zone    DMA32           41            6          967            2            0
 645Fragmentation avoidance in the kernel works by grouping pages of different
 646migrate types into the same contiguous regions of memory called page blocks.
 647A page block is typically the size of the default hugepage size e.g. 2MB on
 648X86-64. By keeping pages grouped based on their ability to move, the kernel
 649can reclaim pages within a page block to satisfy a high-order allocation.
 651The pagetypinfo begins with information on the size of a page block. It
 652then gives the same type of information as buddyinfo except broken down
 653by migrate-type and finishes with details on how many page blocks of each
 654type exist.
 656If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
 657from libhugetlbfs, one can
 658make an estimate of the likely number of huge pages that can be allocated
 659at a given point in time. All the "Movable" blocks should be allocatable
 660unless memory has been mlock()'d. Some of the Reclaimable blocks should
 661also be allocatable although a lot of filesystem metadata may have to be
 662reclaimed to achieve this.
 668Provides information about distribution and utilization of memory.  This
 669varies by architecture and compile options.  The following is from a
 67016GB PIII, which has highmem enabled.  You may not have all of these fields.
 672> cat /proc/meminfo
 674The "Locked" indicates whether the mapping is locked in memory or not.
 677MemTotal:     16344972 kB
 678MemFree:      13634064 kB
 679Buffers:          3656 kB
 680Cached:        1195708 kB
 681SwapCached:          0 kB
 682Active:         891636 kB
 683Inactive:      1077224 kB
 684HighTotal:    15597528 kB
 685HighFree:     13629632 kB
 686LowTotal:       747444 kB
 687LowFree:          4432 kB
 688SwapTotal:           0 kB
 689SwapFree:            0 kB
 690Dirty:             968 kB
 691Writeback:           0 kB
 692AnonPages:      861800 kB
 693Mapped:         280372 kB
 694Slab:           284364 kB
 695SReclaimable:   159856 kB
 696SUnreclaim:     124508 kB
 697PageTables:      24448 kB
 698NFS_Unstable:        0 kB
 699Bounce:              0 kB
 700WritebackTmp:        0 kB
 701CommitLimit:   7669796 kB
 702Committed_AS:   100056 kB
 703VmallocTotal:   112216 kB
 704VmallocUsed:       428 kB
 705VmallocChunk:   111088 kB
 707    MemTotal: Total usable ram (i.e. physical ram minus a few reserved
 708              bits and the kernel binary code)
 709     MemFree: The sum of LowFree+HighFree
 710     Buffers: Relatively temporary storage for raw disk blocks
 711              shouldn't get tremendously large (20MB or so)
 712      Cached: in-memory cache for files read from the disk (the
 713              pagecache).  Doesn't include SwapCached
 714  SwapCached: Memory that once was swapped out, is swapped back in but
 715              still also is in the swapfile (if memory is needed it
 716              doesn't need to be swapped out AGAIN because it is already
 717              in the swapfile. This saves I/O)
 718      Active: Memory that has been used more recently and usually not
 719              reclaimed unless absolutely necessary.
 720    Inactive: Memory which has been less recently used.  It is more
 721              eligible to be reclaimed for other purposes
 722   HighTotal:
 723    HighFree: Highmem is all memory above ~860MB of physical memory
 724              Highmem areas are for use by userspace programs, or
 725              for the pagecache.  The kernel must use tricks to access
 726              this memory, making it slower to access than lowmem.
 727    LowTotal:
 728     LowFree: Lowmem is memory which can be used for everything that
 729              highmem can be used for, but it is also available for the
 730              kernel's use for its own data structures.  Among many
 731              other things, it is where everything from the Slab is
 732              allocated.  Bad things happen when you're out of lowmem.
 733   SwapTotal: total amount of swap space available
 734    SwapFree: Memory which has been evicted from RAM, and is temporarily
 735              on the disk
 736       Dirty: Memory which is waiting to get written back to the disk
 737   Writeback: Memory which is actively being written back to the disk
 738   AnonPages: Non-file backed pages mapped into userspace page tables
 739      Mapped: files which have been mmaped, such as libraries
 740        Slab: in-kernel data structures cache
 741SReclaimable: Part of Slab, that might be reclaimed, such as caches
 742  SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure
 743  PageTables: amount of memory dedicated to the lowest level of page
 744              tables.
 745NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
 746              storage
 747      Bounce: Memory used for block device "bounce buffers"
 748WritebackTmp: Memory used by FUSE for temporary writeback buffers
 749 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
 750              this is the total amount of  memory currently available to
 751              be allocated on the system. This limit is only adhered to
 752              if strict overcommit accounting is enabled (mode 2 in
 753              'vm.overcommit_memory').
 754              The CommitLimit is calculated with the following formula:
 755              CommitLimit = ('vm.overcommit_ratio' * Physical RAM) + Swap
 756              For example, on a system with 1G of physical RAM and 7G
 757              of swap with a `vm.overcommit_ratio` of 30 it would
 758              yield a CommitLimit of 7.3G.
 759              For more details, see the memory overcommit documentation
 760              in vm/overcommit-accounting.
 761Committed_AS: The amount of memory presently allocated on the system.
 762              The committed memory is a sum of all of the memory which
 763              has been allocated by processes, even if it has not been
 764              "used" by them as of yet. A process which malloc()'s 1G
 765              of memory, but only touches 300M of it will only show up
 766              as using 300M of memory even if it has the address space
 767              allocated for the entire 1G. This 1G is memory which has
 768              been "committed" to by the VM and can be used at any time
 769              by the allocating application. With strict overcommit
 770              enabled on the system (mode 2 in 'vm.overcommit_memory'),
 771              allocations which would exceed the CommitLimit (detailed
 772              above) will not be permitted. This is useful if one needs
 773              to guarantee that processes will not fail due to lack of
 774              memory once that memory has been successfully allocated.
 775VmallocTotal: total size of vmalloc memory area
 776 VmallocUsed: amount of vmalloc area which is used
 777VmallocChunk: largest contiguous block of vmalloc area which is free
 783Provides information about vmalloced/vmaped areas. One line per area,
 784containing the virtual address range of the area, size in bytes,
 785caller information of the creator, and optional information depending
 786on the kind of area :
 788 pages=nr    number of pages
 789 phys=addr   if a physical address was specified
 790 ioremap     I/O mapping (ioremap() and friends)
 791 vmalloc     vmalloc() area
 792 vmap        vmap()ed pages
 793 user        VM_USERMAP area
 794 vpages      buffer for pages pointers was vmalloced (huge area)
 795 N<node>=nr  (Only on NUMA kernels)
 796             Number of pages allocated on memory node <node>
 798> cat /proc/vmallocinfo
 7990xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
 800  /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
 8010xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
 802  /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
 8030xffffc20000302000-0xffffc20000304000    8192 acpi_tb_verify_table+0x21/0x4f...
 804  phys=7fee8000 ioremap
 8050xffffc20000304000-0xffffc20000307000   12288 acpi_tb_verify_table+0x21/0x4f...
 806  phys=7fee7000 ioremap
 8070xffffc2000031d000-0xffffc2000031f000    8192 init_vdso_vars+0x112/0x210
 8080xffffc2000031f000-0xffffc2000032b000   49152 cramfs_uncompress_init+0x2e ...
 809  /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
 8100xffffc2000033a000-0xffffc2000033d000   12288 sys_swapon+0x640/0xac0      ...
 811  pages=2 vmalloc N1=2
 8120xffffc20000347000-0xffffc2000034c000   20480 xt_alloc_table_info+0xfe ...
 813  /0x130 [x_tables] pages=4 vmalloc N0=4
 8140xffffffffa0000000-0xffffffffa000f000   61440 sys_init_module+0xc27/0x1d00 ...
 815   pages=14 vmalloc N2=14
 8160xffffffffa000f000-0xffffffffa0014000   20480 sys_init_module+0xc27/0x1d00 ...
 817   pages=4 vmalloc N1=4
 8180xffffffffa0014000-0xffffffffa0017000   12288 sys_init_module+0xc27/0x1d00 ...
 819   pages=2 vmalloc N1=2
 8200xffffffffa0017000-0xffffffffa0022000   45056 sys_init_module+0xc27/0x1d00 ...
 821   pages=10 vmalloc N0=10
 827Provides counts of softirq handlers serviced since boot time, for each cpu.
 829> cat /proc/softirqs
 830                CPU0       CPU1       CPU2       CPU3
 831      HI:          0          0          0          0
 832   TIMER:      27166      27120      27097      27034
 833  NET_TX:          0          0          0         17
 834  NET_RX:         42          0          0         39
 835   BLOCK:          0          0        107       1121
 836 TASKLET:          0          0          0        290
 837   SCHED:      27035      26983      26971      26746
 838 HRTIMER:          0          0          0          0
 839     RCU:       1678       1769       2178       2250
 8421.3 IDE devices in /proc/ide
 845The subdirectory /proc/ide contains information about all IDE devices of which
 846the kernel  is  aware.  There is one subdirectory for each IDE controller, the
 847file drivers  and a link for each IDE device, pointing to the device directory
 848in the controller specific subtree.
 850The file  drivers  contains general information about the drivers used for the
 851IDE devices:
 853  > cat /proc/ide/drivers
 854  ide-cdrom version 4.53
 855  ide-disk version 1.08
 857More detailed  information  can  be  found  in  the  controller  specific
 858subdirectories. These  are  named  ide0,  ide1  and  so  on.  Each  of  these
 859directories contains the files shown in table 1-6.
 862Table 1-6: IDE controller info in  /proc/ide/ide?
 864 File    Content                                 
 865 channel IDE channel (0 or 1)                    
 866 config  Configuration (only for PCI/IDE bridge) 
 867 mate    Mate name                               
 868 model   Type/Chipset of IDE controller          
 871Each device  connected  to  a  controller  has  a separate subdirectory in the
 872controllers directory.  The  files  listed in table 1-7 are contained in these
 876Table 1-7: IDE device information
 878 File             Content                                    
 879 cache            The cache                                  
 880 capacity         Capacity of the medium (in 512Byte blocks) 
 881 driver           driver and version                         
 882 geometry         physical and logical geometry              
 883 identify         device identify block                      
 884 media            media type                                 
 885 model            device identifier                          
 886 settings         device setup                               
 887 smart_thresholds IDE disk management thresholds             
 888 smart_values     IDE disk management values                 
 891The most  interesting  file is settings. This file contains a nice overview of
 892the drive parameters:
 894  # cat /proc/ide/ide0/hda/settings 
 895  name                    value           min             max             mode 
 896  ----                    -----           ---             ---             ---- 
 897  bios_cyl                526             0               65535           rw 
 898  bios_head               255             0               255             rw 
 899  bios_sect               63              0               63              rw 
 900  breada_readahead        4               0               127             rw 
 901  bswap                   0               0               1               r 
 902  file_readahead          72              0               2097151         rw 
 903  io_32bit                0               0               3               rw 
 904  keepsettings            0               0               1               rw 
 905  max_kb_per_request      122             1               127             rw 
 906  multcount               0               0               8               rw 
 907  nice1                   1               0               1               rw 
 908  nowerr                  0               0               1               rw 
 909  pio_mode                write-only      0               255             w 
 910  slow                    0               0               1               rw 
 911  unmaskirq               0               0               1               rw 
 912  using_dma               0               0               1               rw 
 9151.4 Networking info in /proc/net
 918The subdirectory  /proc/net  follows  the  usual  pattern. Table 1-8 shows the
 919additional values  you  get  for  IP  version 6 if you configure the kernel to
 920support this. Table 1-9 lists the files and their meaning.
 923Table 1-8: IPv6 info in /proc/net
 925 File       Content                                               
 926 udp6       UDP sockets (IPv6)                                    
 927 tcp6       TCP sockets (IPv6)                                    
 928 raw6       Raw device statistics (IPv6)                          
 929 igmp6      IP multicast addresses, which this host joined (IPv6) 
 930 if_inet6   List of IPv6 interface addresses                      
 931 ipv6_route Kernel routing table for IPv6                         
 932 rt6_stats  Global IPv6 routing tables statistics                 
 933 sockstat6  Socket statistics (IPv6)                              
 934 snmp6      Snmp data (IPv6)                                      
 938Table 1-9: Network info in /proc/net
 940 File          Content                                                         
 941 arp           Kernel  ARP table                                               
 942 dev           network devices with statistics                                 
 943 dev_mcast     the Layer2 multicast groups a device is listening too
 944               (interface index, label, number of references, number of bound
 945               addresses). 
 946 dev_stat      network device status                                           
 947 ip_fwchains   Firewall chain linkage                                          
 948 ip_fwnames    Firewall chain names                                            
 949 ip_masq       Directory containing the masquerading tables                    
 950 ip_masquerade Major masquerading table                                        
 951 netstat       Network statistics                                              
 952 raw           raw device statistics                                           
 953 route         Kernel routing table                                            
 954 rpc           Directory containing rpc info                                   
 955 rt_cache      Routing cache                                                   
 956 snmp          SNMP data                                                       
 957 sockstat      Socket statistics                                               
 958 tcp           TCP  sockets                                                    
 959 tr_rif        Token ring RIF routing table                                    
 960 udp           UDP sockets                                                     
 961 unix          UNIX domain sockets                                             
 962 wireless      Wireless interface data (Wavelan etc)                           
 963 igmp          IP multicast addresses, which this host joined                  
 964 psched        Global packet scheduler parameters.                             
 965 netlink       List of PF_NETLINK sockets                                      
 966 ip_mr_vifs    List of multicast virtual interfaces                            
 967 ip_mr_cache   List of multicast routing cache                                 
 970You can  use  this  information  to see which network devices are available in
 971your system and how much traffic was routed over those devices:
 973  > cat /proc/net/dev 
 974  Inter-|Receive                                                   |[... 
 975   face |bytes    packets errs drop fifo frame compressed multicast|[... 
 976      lo:  908188   5596     0    0    0     0          0         0 [...         
 977    ppp0:15475140  20721   410    0    0   410          0         0 [...  
 978    eth0:  614530   7085     0    0    0     0          0         1 [... 
 980  ...] Transmit 
 981  ...] bytes    packets errs drop fifo colls carrier compressed 
 982  ...]  908188     5596    0    0    0     0       0          0 
 983  ...] 1375103    17405    0    0    0     0       0          0 
 984  ...] 1703981     5535    0    0    0     3       0          0 
 986In addition, each Channel Bond interface has its own directory.  For
 987example, the bond0 device will have a directory called /proc/net/bond0/.
 988It will contain information that is specific to that bond, such as the
 989current slaves of the bond, the link status of the slaves, and how
 990many times the slaves link has failed.
 9921.5 SCSI info
 995If you  have  a  SCSI  host adapter in your system, you'll find a subdirectory
 996named after  the driver for this adapter in /proc/scsi. You'll also see a list
 997of all recognized SCSI devices in /proc/scsi:
 999  >cat /proc/scsi/scsi 
1000  Attached devices: 
1001  Host: scsi0 Channel: 00 Id: 00 Lun: 00 
1002    Vendor: IBM      Model: DGHS09U          Rev: 03E0 
1003    Type:   Direct-Access                    ANSI SCSI revision: 03 
1004  Host: scsi0 Channel: 00 Id: 06 Lun: 00 
1005    Vendor: PIONEER  Model: CD-ROM DR-U06S   Rev: 1.04 
1006    Type:   CD-ROM                           ANSI SCSI revision: 02 
1009The directory  named  after  the driver has one file for each adapter found in
1010the system.  These  files  contain information about the controller, including
1011the used  IRQ  and  the  IO  address range. The amount of information shown is
1012dependent on  the adapter you use. The example shows the output for an Adaptec
1013AHA-2940 SCSI adapter:
1015  > cat /proc/scsi/aic7xxx/0 
1017  Adaptec AIC7xxx driver version: 5.1.19/3.2.4 
1018  Compile Options: 
1019    TCQ Enabled By Default : Disabled 
1020    AIC7XXX_PROC_STATS     : Disabled 
1021    AIC7XXX_RESET_DELAY    : 5 
1022  Adapter Configuration: 
1023             SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter 
1024                             Ultra Wide Controller 
1025      PCI MMAPed I/O Base: 0xeb001000 
1026   Adapter SEEPROM Config: SEEPROM found and used. 
1027        Adaptec SCSI BIOS: Enabled 
1028                      IRQ: 10 
1029                     SCBs: Active 0, Max Active 2, 
1030                           Allocated 15, HW 16, Page 255 
1031               Interrupts: 160328 
1032        BIOS Control Word: 0x18b6 
1033     Adapter Control Word: 0x005b 
1034     Extended Translation: Enabled 
1035  Disconnect Enable Flags: 0xffff 
1036       Ultra Enable Flags: 0x0001 
1037   Tag Queue Enable Flags: 0x0000 
1038  Ordered Queue Tag Flags: 0x0000 
1039  Default Tag Queue Depth: 8 
1040      Tagged Queue By Device array for aic7xxx host instance 0: 
1041        {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} 
1042      Actual queue depth per device for aic7xxx host instance 0: 
1043        {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} 
1044  Statistics: 
1045  (scsi0:0:0:0) 
1046    Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 
1047    Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) 
1048    Total transfers 160151 (74577 reads and 85574 writes) 
1049  (scsi0:0:6:0) 
1050    Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 
1051    Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) 
1052    Total transfers 0 (0 reads and 0 writes) 
10551.6 Parallel port info in /proc/parport
1058The directory  /proc/parport  contains information about the parallel ports of
1059your system.  It  has  one  subdirectory  for  each port, named after the port
1060number (0,1,2,...).
1062These directories contain the four files shown in Table 1-10.
1065Table 1-10: Files in /proc/parport
1067 File      Content                                                             
1068 autoprobe Any IEEE-1284 device ID information that has been acquired.         
1069 devices   list of the device drivers using that port. A + will appear by the
1070           name of the device currently using the port (it might not appear
1071           against any). 
1072 hardware  Parallel port's base address, IRQ line and DMA channel.             
1073 irq       IRQ that parport is using for that port. This is in a separate
1074           file to allow you to alter it by writing a new value in (IRQ
1075           number or none). 
10781.7 TTY info in /proc/tty
1081Information about  the  available  and actually used tty's can be found in the
1082directory /proc/tty.You'll  find  entries  for drivers and line disciplines in
1083this directory, as shown in Table 1-11.
1086Table 1-11: Files in /proc/tty
1088 File          Content                                        
1089 drivers       list of drivers and their usage                
1090 ldiscs        registered line disciplines                    
1091 driver/serial usage statistic and status of single tty lines 
1094To see  which  tty's  are  currently in use, you can simply look into the file
1097  > cat /proc/tty/drivers 
1098  pty_slave            /dev/pts      136   0-255 pty:slave 
1099  pty_master           /dev/ptm      128   0-255 pty:master 
1100  pty_slave            /dev/ttyp       3   0-255 pty:slave 
1101  pty_master           /dev/pty        2   0-255 pty:master 
1102  serial               /dev/cua        5   64-67 serial:callout 
1103  serial               /dev/ttyS       4   64-67 serial 
1104  /dev/tty0            /dev/tty0       4       0 system:vtmaster 
1105  /dev/ptmx            /dev/ptmx       5       2 system 
1106  /dev/console         /dev/console    5       1 system:console 
1107  /dev/tty             /dev/tty        5       0 system:/dev/tty 
1108  unknown              /dev/tty        4    1-63 console 
11111.8 Miscellaneous kernel statistics in /proc/stat
1114Various pieces   of  information about  kernel activity  are  available in the
1115/proc/stat file.  All  of  the numbers reported  in  this file are  aggregates
1116since the system first booted.  For a quick look, simply cat the file:
1118  > cat /proc/stat
1119  cpu  2255 34 2290 22625563 6290 127 456 0 0
1120  cpu0 1132 34 1441 11311718 3675 127 438 0 0
1121  cpu1 1123 0 849 11313845 2614 0 18 0 0
1122  intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
1123  ctxt 1990473
1124  btime 1062191376
1125  processes 2915
1126  procs_running 1
1127  procs_blocked 0
1128  softirq 183433 0 21755 12 39 1137 231 21459 2263
1130The very first  "cpu" line aggregates the  numbers in all  of the other "cpuN"
1131lines.  These numbers identify the amount of time the CPU has spent performing
1132different kinds of work.  Time units are in USER_HZ (typically hundredths of a
1133second).  The meanings of the columns are as follows, from left to right:
1135- user: normal processes executing in user mode
1136- nice: niced processes executing in user mode
1137- system: processes executing in kernel mode
1138- idle: twiddling thumbs
1139- iowait: waiting for I/O to complete
1140- irq: servicing interrupts
1141- softirq: servicing softirqs
1142- steal: involuntary wait
1143- guest: running a normal guest
1144- guest_nice: running a niced guest
1146The "intr" line gives counts of interrupts  serviced since boot time, for each
1147of the  possible system interrupts.   The first  column  is the  total of  all
1148interrupts serviced; each  subsequent column is the  total for that particular
1151The "ctxt" line gives the total number of context switches across all CPUs.
1153The "btime" line gives  the time at which the  system booted, in seconds since
1154the Unix epoch.
1156The "processes" line gives the number  of processes and threads created, which
1157includes (but  is not limited  to) those  created by  calls to the  fork() and
1158clone() system calls.
1160The "procs_running" line gives the total number of threads that are
1161running or ready to run (i.e., the total number of runnable threads).
1163The   "procs_blocked" line gives  the  number of  processes currently blocked,
1164waiting for I/O to complete.
1166The "softirq" line gives counts of softirqs serviced since boot time, for each
1167of the possible system softirqs. The first column is the total of all
1168softirqs serviced; each subsequent column is the total for that particular
11721.9 Ext4 file system parameters
1175Information about mounted ext4 file systems can be found in
1176/proc/fs/ext4.  Each mounted filesystem will have a directory in
1177/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
1178/proc/fs/ext4/dm-0).   The files in each per-device directory are shown
1179in Table 1-12, below.
1181Table 1-12: Files in /proc/fs/ext4/<devname>
1183 File            Content                                        
1184 mb_groups       details of multiblock allocator buddy cache of free blocks
11872.0 /proc/consoles
1189Shows registered system console lines.
1191To see which character device lines are currently used for the system console
1192/dev/console, you may simply look into the file /proc/consoles:
1194  > cat /proc/consoles
1195  tty0                 -WU (ECp)       4:7
1196  ttyS0                -W- (Ep)        4:64
1198The columns are:
1200  device               name of the device
1201  operations           R = can do read operations
1202                       W = can do write operations
1203                       U = can do unblank
1204  flags                E = it is enabled
1205                       C = it is preferred console
1206                       B = it is primary boot console
1207                       p = it is used for printk buffer
1208                       b = it is not a TTY but a Braille device
1209                       a = it is safe to use when cpu is offline
1210  major:minor          major and minor number of the device separated by a colon
1215The /proc file system serves information about the running system. It not only
1216allows access to process data but also allows you to request the kernel status
1217by reading files in the hierarchy.
1219The directory  structure  of /proc reflects the types of information and makes
1220it easy, if not obvious, where to look for specific data.
1228In This Chapter
1230* Modifying kernel parameters by writing into files found in /proc/sys
1231* Exploring the files which modify certain parameters
1232* Review of the /proc/sys file tree
1236A very  interesting part of /proc is the directory /proc/sys. This is not only
1237a source  of  information,  it also allows you to change parameters within the
1238kernel. Be  very  careful  when attempting this. You can optimize your system,
1239but you  can  also  cause  it  to  crash.  Never  alter kernel parameters on a
1240production system.  Set  up  a  development machine and test to make sure that
1241everything works  the  way  you want it to. You may have no alternative but to
1242reboot the machine once an error has been made.
1244To change  a  value,  simply  echo  the new value into the file. An example is
1245given below  in the section on the file system data. You need to be root to do
1246this. You  can  create  your  own  boot script to perform this every time your
1247system boots.
1249The files  in /proc/sys can be used to fine tune and monitor miscellaneous and
1250general things  in  the operation of the Linux kernel. Since some of the files
1251can inadvertently  disrupt  your  system,  it  is  advisable  to  read  both
1252documentation and  source  before actually making adjustments. In any case, be
1253very careful  when  writing  to  any  of these files. The entries in /proc may
1254change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1255review the kernel documentation in the directory /usr/src/linux/Documentation.
1256This chapter  is  heavily  based  on the documentation included in the pre 2.2
1257kernels, and became part of it in version 2.2.1 of the Linux kernel.
1259Please see: Documentation/sysctls/ directory for descriptions of these
1265Certain aspects  of  kernel  behavior  can be modified at runtime, without the
1266need to  recompile  the kernel, or even to reboot the system. The files in the
1267/proc/sys tree  can  not only be read, but also modified. You can use the echo
1268command to write value into these files, thereby changing the default settings
1269of the kernel.
12763.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1279These file can be used to adjust the badness heuristic used to select which
1280process gets killed in out of memory conditions.
1282The badness heuristic assigns a value to each candidate task ranging from 0
1283(never kill) to 1000 (always kill) to determine which process is targeted.  The
1284units are roughly a proportion along that range of allowed memory the process
1285may allocate from based on an estimation of its current memory and swap use.
1286For example, if a task is using all allowed memory, its badness score will be
12871000.  If it is using half of its allowed memory, its score will be 500.
1289There is an additional factor included in the badness score: root
1290processes are given 3% extra memory over other tasks.
1292The amount of "allowed" memory depends on the context in which the oom killer
1293was called.  If it is due to the memory assigned to the allocating task's cpuset
1294being exhausted, the allowed memory represents the set of mems assigned to that
1295cpuset.  If it is due to a mempolicy's node(s) being exhausted, the allowed
1296memory represents the set of mempolicy nodes.  If it is due to a memory
1297limit (or swap limit) being reached, the allowed memory is that configured
1298limit.  Finally, if it is due to the entire system being out of memory, the
1299allowed memory represents all allocatable resources.
1301The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1302is used to determine which task to kill.  Acceptable values range from -1000
1303(OOM_SCORE_ADJ_MIN) to +1000 (OOM_SCORE_ADJ_MAX).  This allows userspace to
1304polarize the preference for oom killing either by always preferring a certain
1305task or completely disabling it.  The lowest possible value, -1000, is
1306equivalent to disabling oom killing entirely for that task since it will always
1307report a badness score of 0.
1309Consequently, it is very simple for userspace to define the amount of memory to
1310consider for each task.  Setting a /proc/<pid>/oom_score_adj value of +500, for
1311example, is roughly equivalent to allowing the remainder of tasks sharing the
1312same system, cpuset, mempolicy, or memory controller resources to use at least
131350% more memory.  A value of -500, on the other hand, would be roughly
1314equivalent to discounting 50% of the task's allowed memory from being considered
1315as scoring against the task.
1317For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1318be used to tune the badness score.  Its acceptable values range from -16
1319(OOM_ADJUST_MIN) to +15 (OOM_ADJUST_MAX) and a special value of -17
1320(OOM_DISABLE) to disable oom killing entirely for that task.  Its value is
1321scaled linearly with /proc/<pid>/oom_score_adj.
1323Writing to /proc/<pid>/oom_score_adj or /proc/<pid>/oom_adj will change the
1324other with its scaled value.
1326The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1327value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1328requires CAP_SYS_RESOURCE.
1330NOTICE: /proc/<pid>/oom_adj is deprecated and will be removed, please see
1333Caveat: when a parent task is selected, the oom killer will sacrifice any first
1334generation children with separate address spaces instead, if possible.  This
1335avoids servers and important system daemons from being killed and loses the
1336minimal amount of work.
13393.2 /proc/<pid>/oom_score - Display current oom-killer score
1342This file can be used to check the current score used by the oom-killer is for
1343any given <pid>. Use it together with /proc/<pid>/oom_adj to tune which
1344process should be killed in an out-of-memory situation.
13473.3  /proc/<pid>/io - Display the IO accounting fields
1350This file contains IO statistics for each running process
1355test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1356[1] 3828
1358test:/tmp # cat /proc/3828/io
1359rchar: 323934931
1360wchar: 323929600
1361syscr: 632687
1362syscw: 632675
1363read_bytes: 0
1364write_bytes: 323932160
1365cancelled_write_bytes: 0
1374I/O counter: chars read
1375The number of bytes which this task has caused to be read from storage. This
1376is simply the sum of bytes which this process passed to read() and pread().
1377It includes things like tty IO and it is unaffected by whether or not actual
1378physical disk IO was required (the read might have been satisfied from
1385I/O counter: chars written
1386The number of bytes which this task has caused, or shall cause to be written
1387to disk. Similar caveats apply here as with rchar.
1393I/O counter: read syscalls
1394Attempt to count the number of read I/O operations, i.e. syscalls like read()
1395and pread().
1401I/O counter: write syscalls
1402Attempt to count the number of write I/O operations, i.e. syscalls like
1403write() and pwrite().
1409I/O counter: bytes read
1410Attempt to count the number of bytes which this process really did cause to
1411be fetched from the storage layer. Done at the submit_bio() level, so it is
1412accurate for block-backed filesystems. <please add status regarding NFS and
1413CIFS at a later time>
1419I/O counter: bytes written
1420Attempt to count the number of bytes which this process caused to be sent to
1421the storage layer. This is done at page-dirtying time.
1427The big inaccuracy here is truncate. If a process writes 1MB to a file and
1428then deletes the file, it will in fact perform no writeout. But it will have
1429been accounted as having caused 1MB of write.
1430In other words: The number of bytes which this process caused to not happen,
1431by truncating pagecache. A task can cause "negative" IO too. If this task
1432truncates some dirty pagecache, some IO which another task has been accounted
1433for (in its write_bytes) will not be happening. We _could_ just subtract that
1434from the truncating task's write_bytes, but there is information loss in doing
1441At its current implementation state, this is a bit racy on 32-bit machines: if
1442process A reads process B's /proc/pid/io while process B is updating one of
1443those 64-bit counters, process A could see an intermediate result.
1446More information about this can be found within the taskstats documentation in
14493.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1451When a process is dumped, all anonymous memory is written to a core file as
1452long as the size of the core file isn't limited. But sometimes we don't want
1453to dump some memory segments, for example, huge shared memory. Conversely,
1454sometimes we want to save file-backed memory segments into a core file, not
1455only the individual files.
1457/proc/<pid>/coredump_filter allows you to customize which memory segments
1458will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1459of memory types. If a bit of the bitmask is set, memory segments of the
1460corresponding memory type are dumped, otherwise they are not dumped.
1462The following 7 memory types are supported:
1463  - (bit 0) anonymous private memory
1464  - (bit 1) anonymous shared memory
1465  - (bit 2) file-backed private memory
1466  - (bit 3) file-backed shared memory
1467  - (bit 4) ELF header pages in file-backed private memory areas (it is
1468            effective only if the bit 2 is cleared)
1469  - (bit 5) hugetlb private memory
1470  - (bit 6) hugetlb shared memory
1472  Note that MMIO pages such as frame buffer are never dumped and vDSO pages
1473  are always dumped regardless of the bitmask status.
1475  Note bit 0-4 doesn't effect any hugetlb memory. hugetlb memory are only
1476  effected by bit 5-6.
1478Default value of coredump_filter is 0x23; this means all anonymous memory
1479segments and hugetlb private memory are dumped.
1481If you don't want to dump all shared memory segments attached to pid 1234,
1482write 0x21 to the process's proc file.
1484  $ echo 0x21 > /proc/1234/coredump_filter
1486When a new process is created, the process inherits the bitmask status from its
1487parent. It is useful to set up coredump_filter before the program runs.
1488For example:
1490  $ echo 0x7 > /proc/self/coredump_filter
1491  $ ./some_program
14933.5     /proc/<pid>/mountinfo - Information about mounts
1496This file contains lines of the form:
149836 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue
1499(1)(2)(3)   (4)   (5)      (6)      (7)   (8) (9)   (10)         (11)
1501(1) mount ID:  unique identifier of the mount (may be reused after umount)
1502(2) parent ID:  ID of parent (or of self for the top of the mount tree)
1503(3) major:minor:  value of st_dev for files on filesystem
1504(4) root:  root of the mount within the filesystem
1505(5) mount point:  mount point relative to the process's root
1506(6) mount options:  per mount options
1507(7) optional fields:  zero or more fields of the form "tag[:value]"
1508(8) separator:  marks the end of the optional fields
1509(9) filesystem type:  name of filesystem of the form "type[.subtype]"
1510(10) mount source:  filesystem specific information or "none"
1511(11) super options:  per super block options
1513Parsers should ignore all unrecognised optional fields.  Currently the
1514possible optional fields are:
1516shared:X  mount is shared in peer group X
1517master:X  mount is slave to peer group X
1518propagate_from:X  mount is slave and receives propagation from peer group X (*)
1519unbindable  mount is unbindable
1521(*) X is the closest dominant peer group under the process's root.  If
1522X is the immediate master of the mount, or if there's no dominant peer
1523group under the same root, then only the "master:X" field is present
1524and not the "propagate_from:X" field.
1526For more information on mount propagation see:
1528  Documentation/filesystems/sharedsubtree.txt
15313.6     /proc/<pid>/comm  & /proc/<pid>/task/<tid>/comm
1533These files provide a method to access a tasks comm value. It also allows for
1534a task to set its own or one of its thread siblings comm value. The comm value
1535is limited in size compared to the cmdline value, so writing anything longer
1536then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
1537comm value.
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