1 ------------------------------------------------------------------------------
2 T H E /proc F I L E S Y S T E M
3 ------------------------------------------------------------------------------
4 /proc/sys Terrehon Bowden <terrehon@pacbell.net> October 7 1999
5 Bodo Bauer <bb@ricochet.net>
7 2.4.x update Jorge Nerin <comandante@zaralinux.com> November 14 2000
8 move /proc/sys Shen Feng <shen@cn.fujitsu.com> April 1 2009
9 ------------------------------------------------------------------------------
10 Version 1.3 Kernel version 2.2.12
11 Kernel version 2.4.0-test11-pre4
12 ------------------------------------------------------------------------------
13 fixes/update part 1.1 Stefani Seibold <stefani@seibold.net> June 9 2009
19 0.1 Introduction/Credits
22 1 Collecting System Information
23 1.1 Process-Specific Subdirectories
25 1.3 IDE devices in /proc/ide
26 1.4 Networking info in /proc/net
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
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
45 ------------------------------------------------------------------------------
47 ------------------------------------------------------------------------------
49 0.1 Introduction/Credits
50 ------------------------
52 This documentation is part of a soon (or so we hope) to be released book on
53 the 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
55 chapters, it seems only fair to give the work back to the Linux community.
56 This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm
57 afraid it's still far from complete, but we hope it will be useful. As far as
58 we know, it is the first 'all-in-one' document about the /proc file system. It
59 is focused on the Intel x86 hardware, so if you are looking for PPC, ARM,
60 SPARC, AXP, etc., features, you probably won't find what you are looking for.
61 It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
62 additions and patches are welcome and will be added to this document if you
65 We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
66 other people for help compiling this documentation. We'd also like to extend a
67 special thank you to Andi Kleen for documentation, which we relied on heavily
68 to create this document, as well as the additional information he provided.
69 Thanks to everybody else who contributed source or docs to the Linux kernel
70 and helped create a great piece of software... :)
72 If you have any comments, corrections or additions, please don't hesitate to
73 contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this
76 The latest version of this document is available online at
77 http://tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html
79 If the above direction does not works for you, you could try the kernel
80 mailing list at linux-kernel@vger.kernel.org and/or try to reach me at
81 comandante@zaralinux.com.
86 We don't guarantee the correctness of this document, and if you come to us
87 complaining about how you screwed up your system because of incorrect
88 documentation, we won't feel responsible...
90 ------------------------------------------------------------------------------
91 CHAPTER 1: COLLECTING SYSTEM INFORMATION
92 ------------------------------------------------------------------------------
94 ------------------------------------------------------------------------------
96 ------------------------------------------------------------------------------
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
102 ------------------------------------------------------------------------------
105 The proc file system acts as an interface to internal data structures in the
106 kernel. It can be used to obtain information about the system and to change
107 certain kernel parameters at runtime (sysctl).
109 First, we'll take a look at the read-only parts of /proc. In Chapter 2, we
110 show you how you can use /proc/sys to change settings.
112 1.1 Process-Specific Subdirectories
113 -----------------------------------
115 The directory /proc contains (among other things) one subdirectory for each
116 process running on the system, which is named after the process ID (PID).
118 The link self points to the process reading the file system. Each process
119 subdirectory has the entries listed in Table 1-1.
122 Table 1-1: Process specific entries in /proc
123 ..............................................................................
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
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
140 stack Report full stack trace, enable via CONFIG_STACKTRACE
141 smaps a extension based on maps, showing the memory consumption of
143 ..............................................................................
145 For example, to get the status information of a process, all you have to do is
146 read the file /proc/PID/status:
148 >cat /proc/self/status
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
184 This shows you nearly the same information you would get if you viewed it with
185 the ps command. In fact, ps uses the proc file system to obtain its
186 information. But you get a more detailed view of the process by reading the
187 file /proc/PID/status. It fields are described in table 1-2.
189 The statm file contains more detailed information about the process
190 memory usage. Its seven fields are explained in Table 1-3. The stat file
191 contains details information about the process itself. Its fields are
192 explained in Table 1-4.
194 (for SMP CONFIG users)
195 For making accounting scalable, RSS related information are handled in
196 asynchronous manner and the vaule may not be very precise. To see a precise
197 snapshot of a moment, you can see /proc/<pid>/smaps file and scan page table.
198 It's slow but very precise.
200 Table 1-2: Contents of the status files (as of 2.6.30-rc7)
201 ..............................................................................
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)
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
243 ..............................................................................
245 Table 1-3: Contents of the statm files (as of 2.6.8-rc3)
246 ..............................................................................
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)
257 ..............................................................................
260 Table 1-4: Contents of the stat files (as of 2.6.30-rc7)
261 ..............................................................................
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
270 tty_nr tty the process uses
271 tty_pgrp pgrp of the tty
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
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
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
308 ..............................................................................
310 The /proc/PID/maps file containing the currently mapped memory regions and
311 their access permissions.
315 address perms offset dev inode pathname
317 08048000-08049000 r-xp 00000000 03:00 8312 /opt/test
318 08049000-0804a000 rw-p 00001000 03:00 8312 /opt/test
319 0804a000-0806b000 rw-p 00000000 00:00 0 [heap]
320 a7cb1000-a7cb2000 ---p 00000000 00:00 0
321 a7cb2000-a7eb2000 rw-p 00000000 00:00 0
322 a7eb2000-a7eb3000 ---p 00000000 00:00 0
323 a7eb3000-a7ed5000 rw-p 00000000 00:00 0
324 a7ed5000-a8008000 r-xp 00000000 03:00 4222 /lib/libc.so.6
325 a8008000-a800a000 r--p 00133000 03:00 4222 /lib/libc.so.6
326 a800a000-a800b000 rw-p 00135000 03:00 4222 /lib/libc.so.6
327 a800b000-a800e000 rw-p 00000000 00:00 0
328 a800e000-a8022000 r-xp 00000000 03:00 14462 /lib/libpthread.so.0
329 a8022000-a8023000 r--p 00013000 03:00 14462 /lib/libpthread.so.0
330 a8023000-a8024000 rw-p 00014000 03:00 14462 /lib/libpthread.so.0
331 a8024000-a8027000 rw-p 00000000 00:00 0
332 a8027000-a8043000 r-xp 00000000 03:00 8317 /lib/ld-linux.so.2
333 a8043000-a8044000 r--p 0001b000 03:00 8317 /lib/ld-linux.so.2
334 a8044000-a8045000 rw-p 0001c000 03:00 8317 /lib/ld-linux.so.2
335 aff35000-aff4a000 rw-p 00000000 00:00 0 [stack]
336 ffffe000-fffff000 r-xp 00000000 00:00 0 [vdso]
338 where "address" is the address space in the process that it occupies, "perms"
339 is a set of permissions:
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
349 with the memory region, as the case would be with BSS (uninitialized data).
350 The "pathname" shows the name associated file for this mapping. If the mapping
351 is 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.
361 The /proc/PID/smaps is an extension based on maps, showing the memory
362 consumption for each of the process's mappings. For each of mappings there
363 is a series of lines such as the following:
365 08048000-080bc000 r-xp 00000000 03:02 13130 /bin/bash
380 The first of these lines shows the same information as is displayed for the
381 mapping 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
383 process' proportional share of this mapping (PSS), the number of clean and
384 dirty private pages in the mapping. Note that even a page which is part of a
385 MAP_SHARED mapping, but has only a single pte mapped, i.e. is currently used
386 by only one process, is accounted as private and not as shared. "Referenced"
387 indicates 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
389 a mapping associated with a file may contain anonymous pages: when MAP_PRIVATE
390 and 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
394 This file is only present if the CONFIG_MMU kernel configuration option is
397 The /proc/PID/clear_refs is used to reset the PG_Referenced and ACCESSED/YOUNG
398 bits on both physical and virtual pages associated with a process.
399 To clear the bits for all the pages associated with the process
400 > echo 1 > /proc/PID/clear_refs
402 To clear the bits for the anonymous pages associated with the process
403 > echo 2 > /proc/PID/clear_refs
405 To clear the bits for the file mapped pages associated with the process
406 > echo 3 > /proc/PID/clear_refs
407 Any other value written to /proc/PID/clear_refs will have no effect.
409 The /proc/pid/pagemap gives the PFN, which can be used to find the pageflags
410 using /proc/kpageflags and number of times a page is mapped using
411 /proc/kpagecount. For detailed explanation, see Documentation/vm/pagemap.txt.
416 Similar to the process entries, the kernel data files give information about
417 the 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
419 system. It depends on the kernel configuration and the loaded modules, which
420 files are there, and which are missing.
422 Table 1-5: Kernel info in /proc
423 ..............................................................................
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))
445 ksyms Kernel symbol table
446 loadavg Load average of last 1, 5 & 15 minutes
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)
458 scsi SCSI info (see text)
459 slabinfo Slab pool info
460 softirqs softirq usage
461 stat Overall statistics
462 swaps Swap space utilization
464 sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4)
465 tty Info of tty drivers
467 version Kernel version
468 video bttv info of video resources (2.4)
469 vmallocinfo Show vmalloced areas
470 ..............................................................................
472 You can, for example, check which interrupts are currently in use and what
473 they are used for by looking in the file /proc/interrupts:
475 > cat /proc/interrupts
477 0: 8728810 XT-PIC timer
478 1: 895 XT-PIC keyboard
480 3: 531695 XT-PIC aha152x
481 4: 2014133 XT-PIC serial
482 5: 44401 XT-PIC pcnet_cs
485 12: 182918 XT-PIC PS/2 Mouse
487 14: 1232265 XT-PIC ide0
491 In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
492 output of a SMP machine):
494 > cat /proc/interrupts
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
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
513 NMI 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.
516 LOC is the local interrupt counter of the internal APIC of every CPU.
518 ERR is incremented in the case of errors in the IO-APIC bus (the bus that
519 connects the CPUs in a SMP system. This means that an error has been detected,
520 the IO-APIC automatically retry the transmission, so it should not be a big
521 problem, but you should read the SMP-FAQ.
523 In 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
525 just 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.
546 The above IRQ vectors are displayed only when relevant. For example,
547 the threshold vector does not exist on x86_64 platforms. Others are
548 suppressed when the system is a uniprocessor. As of this writing, only
549 i386 and x86_64 platforms support the new IRQ vector displays.
551 Of some interest is the introduction of the /proc/irq directory to 2.4.
552 It could be used to set IRQ to CPU affinity, this means that you can "hook" an
553 IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
554 irq subdir is one subdir for each IRQ, and two files; default_smp_affinity and
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
564 smp_affinity is a bitmask, in which you can specify which CPUs can handle the
565 IRQ, you can set it by doing:
567 > echo 1 > /proc/irq/10/smp_affinity
569 This means that only the first CPU will handle the IRQ, but you can also echo
570 5 which means that only the first and fourth CPU can handle the IRQ.
572 The contents of each smp_affinity file is the same by default:
574 > cat /proc/irq/0/smp_affinity
577 The default_smp_affinity mask applies to all non-active IRQs, which are the
578 IRQs which have not yet been allocated/activated, and hence which lack a
579 /proc/irq/[0-9]* directory.
581 The node file on an SMP system shows the node to which the device using the IRQ
582 reports itself as being attached. This hardware locality information does not
583 include information about any possible driver locality preference.
585 prof_cpu_mask specifies which CPUs are to be profiled by the system wide
586 profiler. Default value is ffffffff (all cpus).
588 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
589 between all the CPUs which are allowed to handle it. As usual the kernel has
590 more info than you and does a better job than you, so the defaults are the
591 best choice for almost everyone.
593 There are three more important subdirectories in /proc: net, scsi, and sys.
594 The general rule is that the contents, or even the existence of these
595 directories, depend on your kernel configuration. If SCSI is not enabled, the
596 directory scsi may not exist. The same is true with the net, which is there
597 only when networking support is present in the running kernel.
599 The slabinfo file gives information about memory usage at the slab level.
600 Linux uses slab pools for memory management above page level in version 2.2.
601 Commonly used objects have their own slab pool (such as network buffers,
602 directory cache, and so on).
604 ..............................................................................
606 > cat /proc/buddyinfo
608 Node 0, zone DMA 0 4 5 4 4 3 ...
609 Node 0, zone Normal 1 0 0 1 101 8 ...
610 Node 0, zone HighMem 2 0 0 1 1 0 ...
612 External fragmentation is a problem under some workloads, and buddyinfo is a
613 useful tool for helping diagnose these problems. Buddyinfo will give you a
614 clue as to how big an area you can safely allocate, or why a previous
617 Each column represents the number of pages of a certain order which are
618 available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
619 ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
620 available in ZONE_NORMAL, etc...
622 More information relevant to external fragmentation can be found in
625 > cat /proc/pagetypeinfo
629 Free pages count per migrate type at order 0 1 2 3 4 5 6 7 8 9 10
630 Node 0, zone DMA, type Unmovable 0 0 0 1 1 1 1 1 1 1 0
631 Node 0, zone DMA, type Reclaimable 0 0 0 0 0 0 0 0 0 0 0
632 Node 0, zone DMA, type Movable 1 1 2 1 2 1 1 0 1 0 2
633 Node 0, zone DMA, type Reserve 0 0 0 0 0 0 0 0 0 1 0
634 Node 0, zone DMA, type Isolate 0 0 0 0 0 0 0 0 0 0 0
635 Node 0, zone DMA32, type Unmovable 103 54 77 1 1 1 11 8 7 1 9
636 Node 0, zone DMA32, type Reclaimable 0 0 2 1 0 0 0 0 1 0 0
637 Node 0, zone DMA32, type Movable 169 152 113 91 77 54 39 13 6 1 452
638 Node 0, zone DMA32, type Reserve 1 2 2 2 2 0 1 1 1 1 0
639 Node 0, zone DMA32, type Isolate 0 0 0 0 0 0 0 0 0 0 0
641 Number of blocks type Unmovable Reclaimable Movable Reserve Isolate
642 Node 0, zone DMA 2 0 5 1 0
643 Node 0, zone DMA32 41 6 967 2 0
645 Fragmentation avoidance in the kernel works by grouping pages of different
646 migrate types into the same contiguous regions of memory called page blocks.
647 A page block is typically the size of the default hugepage size e.g. 2MB on
648 X86-64. By keeping pages grouped based on their ability to move, the kernel
649 can reclaim pages within a page block to satisfy a high-order allocation.
651 The pagetypinfo begins with information on the size of a page block. It
652 then gives the same type of information as buddyinfo except broken down
653 by migrate-type and finishes with details on how many page blocks of each
656 If min_free_kbytes has been tuned correctly (recommendations made by hugeadm
657 from libhugetlbfs http://sourceforge.net/projects/libhugetlbfs/), one can
658 make an estimate of the likely number of huge pages that can be allocated
659 at a given point in time. All the "Movable" blocks should be allocatable
660 unless memory has been mlock()'d. Some of the Reclaimable blocks should
661 also be allocatable although a lot of filesystem metadata may have to be
662 reclaimed to achieve this.
664 ..............................................................................
668 Provides information about distribution and utilization of memory. This
669 varies by architecture and compile options. The following is from a
670 16GB PIII, which has highmem enabled. You may not have all of these fields.
674 The "Locked" indicates whether the mapping is locked in memory or not.
677 MemTotal: 16344972 kB
684 HighTotal: 15597528 kB
685 HighFree: 13629632 kB
695 SReclaimable: 159856 kB
696 SUnreclaim: 124508 kB
701 CommitLimit: 7669796 kB
702 Committed_AS: 100056 kB
703 VmallocTotal: 112216 kB
705 VmallocChunk: 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
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.
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
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
741 SReclaimable: 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
745 NFS_Unstable: NFS pages sent to the server, but not yet committed to stable
747 Bounce: Memory used for block device "bounce buffers"
748 WritebackTmp: 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.
761 Committed_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.
775 VmallocTotal: total size of vmalloc memory area
776 VmallocUsed: amount of vmalloc area which is used
777 VmallocChunk: largest contiguous block of vmalloc area which is free
779 ..............................................................................
783 Provides information about vmalloced/vmaped areas. One line per area,
784 containing the virtual address range of the area, size in bytes,
785 caller information of the creator, and optional information depending
786 on 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
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
799 0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...
800 /0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128
801 0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...
802 /0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64
803 0xffffc20000302000-0xffffc20000304000 8192 acpi_tb_verify_table+0x21/0x4f...
804 phys=7fee8000 ioremap
805 0xffffc20000304000-0xffffc20000307000 12288 acpi_tb_verify_table+0x21/0x4f...
806 phys=7fee7000 ioremap
807 0xffffc2000031d000-0xffffc2000031f000 8192 init_vdso_vars+0x112/0x210
808 0xffffc2000031f000-0xffffc2000032b000 49152 cramfs_uncompress_init+0x2e ...
809 /0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3
810 0xffffc2000033a000-0xffffc2000033d000 12288 sys_swapon+0x640/0xac0 ...
812 0xffffc20000347000-0xffffc2000034c000 20480 xt_alloc_table_info+0xfe ...
813 /0x130 [x_tables] pages=4 vmalloc N0=4
814 0xffffffffa0000000-0xffffffffa000f000 61440 sys_init_module+0xc27/0x1d00 ...
815 pages=14 vmalloc N2=14
816 0xffffffffa000f000-0xffffffffa0014000 20480 sys_init_module+0xc27/0x1d00 ...
818 0xffffffffa0014000-0xffffffffa0017000 12288 sys_init_module+0xc27/0x1d00 ...
820 0xffffffffa0017000-0xffffffffa0022000 45056 sys_init_module+0xc27/0x1d00 ...
821 pages=10 vmalloc N0=10
823 ..............................................................................
827 Provides counts of softirq handlers serviced since boot time, for each cpu.
832 TIMER: 27166 27120 27097 27034
837 SCHED: 27035 26983 26971 26746
839 RCU: 1678 1769 2178 2250
842 1.3 IDE devices in /proc/ide
843 ----------------------------
845 The subdirectory /proc/ide contains information about all IDE devices of which
846 the kernel is aware. There is one subdirectory for each IDE controller, the
847 file drivers and a link for each IDE device, pointing to the device directory
848 in the controller specific subtree.
850 The file drivers contains general information about the drivers used for the
853 > cat /proc/ide/drivers
854 ide-cdrom version 4.53
855 ide-disk version 1.08
857 More detailed information can be found in the controller specific
858 subdirectories. These are named ide0, ide1 and so on. Each of these
859 directories contains the files shown in table 1-6.
862 Table 1-6: IDE controller info in /proc/ide/ide?
863 ..............................................................................
865 channel IDE channel (0 or 1)
866 config Configuration (only for PCI/IDE bridge)
868 model Type/Chipset of IDE controller
869 ..............................................................................
871 Each device connected to a controller has a separate subdirectory in the
872 controllers directory. The files listed in table 1-7 are contained in these
876 Table 1-7: IDE device information
877 ..............................................................................
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
885 model device identifier
886 settings device setup
887 smart_thresholds IDE disk management thresholds
888 smart_values IDE disk management values
889 ..............................................................................
891 The most interesting file is settings. This file contains a nice overview of
892 the 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
900 breada_readahead 4 0 127 rw
902 file_readahead 72 0 2097151 rw
904 keepsettings 0 0 1 rw
905 max_kb_per_request 122 1 127 rw
909 pio_mode write-only 0 255 w
915 1.4 Networking info in /proc/net
916 --------------------------------
918 The subdirectory /proc/net follows the usual pattern. Table 1-8 shows the
919 additional values you get for IP version 6 if you configure the kernel to
920 support this. Table 1-9 lists the files and their meaning.
923 Table 1-8: IPv6 info in /proc/net
924 ..............................................................................
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)
935 ..............................................................................
938 Table 1-9: Network info in /proc/net
939 ..............................................................................
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
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
957 sockstat Socket statistics
959 tr_rif Token ring RIF routing table
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
968 ..............................................................................
970 You can use this information to see which network devices are available in
971 your system and how much traffic was routed over those devices:
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 [...
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
986 In addition, each Channel Bond interface has its own directory. For
987 example, the bond0 device will have a directory called /proc/net/bond0/.
988 It will contain information that is specific to that bond, such as the
989 current slaves of the bond, the link status of the slaves, and how
990 many times the slaves link has failed.
995 If you have a SCSI host adapter in your system, you'll find a subdirectory
996 named after the driver for this adapter in /proc/scsi. You'll also see a list
997 of all recognized SCSI devices in /proc/scsi:
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
1009 The directory named after the driver has one file for each adapter found in
1010 the system. These files contain information about the controller, including
1011 the used IRQ and the IO address range. The amount of information shown is
1012 dependent on the adapter you use. The example shows the output for an Adaptec
1013 AHA-2940 SCSI adapter:
1015 > cat /proc/scsi/aic7xxx/0
1017 Adaptec AIC7xxx driver version: 5.1.19/3.2.4
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
1029 SCBs: Active 0, Max Active 2,
1030 Allocated 15, HW 16, Page 255
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}
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)
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)
1055 1.6 Parallel port info in /proc/parport
1056 ---------------------------------------
1058 The directory /proc/parport contains information about the parallel ports of
1059 your system. It has one subdirectory for each port, named after the port
1062 These directories contain the four files shown in Table 1-10.
1065 Table 1-10: Files in /proc/parport
1066 ..............................................................................
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
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
1076 ..............................................................................
1078 1.7 TTY info in /proc/tty
1079 -------------------------
1081 Information about the available and actually used tty's can be found in the
1082 directory /proc/tty.You'll find entries for drivers and line disciplines in
1083 this directory, as shown in Table 1-11.
1086 Table 1-11: Files in /proc/tty
1087 ..............................................................................
1089 drivers list of drivers and their usage
1090 ldiscs registered line disciplines
1091 driver/serial usage statistic and status of single tty lines
1092 ..............................................................................
1094 To 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
1111 1.8 Miscellaneous kernel statistics in /proc/stat
1112 -------------------------------------------------
1114 Various pieces of information about kernel activity are available in the
1115 /proc/stat file. All of the numbers reported in this file are aggregates
1116 since the system first booted. For a quick look, simply cat the file:
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 ...]
1128 softirq 183433 0 21755 12 39 1137 231 21459 2263
1130 The very first "cpu" line aggregates the numbers in all of the other "cpuN"
1131 lines. These numbers identify the amount of time the CPU has spent performing
1132 different kinds of work. Time units are in USER_HZ (typically hundredths of a
1133 second). 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
1146 The "intr" line gives counts of interrupts serviced since boot time, for each
1147 of the possible system interrupts. The first column is the total of all
1148 interrupts serviced; each subsequent column is the total for that particular
1151 The "ctxt" line gives the total number of context switches across all CPUs.
1153 The "btime" line gives the time at which the system booted, in seconds since
1156 The "processes" line gives the number of processes and threads created, which
1157 includes (but is not limited to) those created by calls to the fork() and
1158 clone() system calls.
1160 The "procs_running" line gives the total number of threads that are
1161 running or ready to run (i.e., the total number of runnable threads).
1163 The "procs_blocked" line gives the number of processes currently blocked,
1164 waiting for I/O to complete.
1166 The "softirq" line gives counts of softirqs serviced since boot time, for each
1167 of the possible system softirqs. The first column is the total of all
1168 softirqs serviced; each subsequent column is the total for that particular
1172 1.9 Ext4 file system parameters
1173 ------------------------------
1175 Information 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
1179 in Table 1-12, below.
1181 Table 1-12: Files in /proc/fs/ext4/<devname>
1182 ..............................................................................
1184 mb_groups details of multiblock allocator buddy cache of free blocks
1185 ..............................................................................
1189 Shows registered system console lines.
1191 To 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
1200 device name of the device
1201 operations R = can do read operations
1202 W = can do write operations
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
1212 ------------------------------------------------------------------------------
1214 ------------------------------------------------------------------------------
1215 The /proc file system serves information about the running system. It not only
1216 allows access to process data but also allows you to request the kernel status
1217 by reading files in the hierarchy.
1219 The directory structure of /proc reflects the types of information and makes
1220 it easy, if not obvious, where to look for specific data.
1221 ------------------------------------------------------------------------------
1223 ------------------------------------------------------------------------------
1224 CHAPTER 2: MODIFYING SYSTEM PARAMETERS
1225 ------------------------------------------------------------------------------
1227 ------------------------------------------------------------------------------
1229 ------------------------------------------------------------------------------
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
1233 ------------------------------------------------------------------------------
1236 A very interesting part of /proc is the directory /proc/sys. This is not only
1237 a source of information, it also allows you to change parameters within the
1238 kernel. Be very careful when attempting this. You can optimize your system,
1239 but you can also cause it to crash. Never alter kernel parameters on a
1240 production system. Set up a development machine and test to make sure that
1241 everything works the way you want it to. You may have no alternative but to
1242 reboot the machine once an error has been made.
1244 To change a value, simply echo the new value into the file. An example is
1245 given below in the section on the file system data. You need to be root to do
1246 this. You can create your own boot script to perform this every time your
1249 The files in /proc/sys can be used to fine tune and monitor miscellaneous and
1250 general things in the operation of the Linux kernel. Since some of the files
1251 can inadvertently disrupt your system, it is advisable to read both
1252 documentation and source before actually making adjustments. In any case, be
1253 very careful when writing to any of these files. The entries in /proc may
1254 change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
1255 review the kernel documentation in the directory /usr/src/linux/Documentation.
1256 This chapter is heavily based on the documentation included in the pre 2.2
1257 kernels, and became part of it in version 2.2.1 of the Linux kernel.
1259 Please see: Documentation/sysctls/ directory for descriptions of these
1262 ------------------------------------------------------------------------------
1264 ------------------------------------------------------------------------------
1265 Certain aspects of kernel behavior can be modified at runtime, without the
1266 need 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
1268 command to write value into these files, thereby changing the default settings
1270 ------------------------------------------------------------------------------
1272 ------------------------------------------------------------------------------
1273 CHAPTER 3: PER-PROCESS PARAMETERS
1274 ------------------------------------------------------------------------------
1276 3.1 /proc/<pid>/oom_adj & /proc/<pid>/oom_score_adj- Adjust the oom-killer score
1277 --------------------------------------------------------------------------------
1279 These file can be used to adjust the badness heuristic used to select which
1280 process gets killed in out of memory conditions.
1282 The 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
1284 units are roughly a proportion along that range of allowed memory the process
1285 may allocate from based on an estimation of its current memory and swap use.
1286 For example, if a task is using all allowed memory, its badness score will be
1287 1000. If it is using half of its allowed memory, its score will be 500.
1289 There is an additional factor included in the badness score: root
1290 processes are given 3% extra memory over other tasks.
1292 The amount of "allowed" memory depends on the context in which the oom killer
1293 was called. If it is due to the memory assigned to the allocating task's cpuset
1294 being exhausted, the allowed memory represents the set of mems assigned to that
1295 cpuset. If it is due to a mempolicy's node(s) being exhausted, the allowed
1296 memory represents the set of mempolicy nodes. If it is due to a memory
1297 limit (or swap limit) being reached, the allowed memory is that configured
1298 limit. Finally, if it is due to the entire system being out of memory, the
1299 allowed memory represents all allocatable resources.
1301 The value of /proc/<pid>/oom_score_adj is added to the badness score before it
1302 is 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
1304 polarize the preference for oom killing either by always preferring a certain
1305 task or completely disabling it. The lowest possible value, -1000, is
1306 equivalent to disabling oom killing entirely for that task since it will always
1307 report a badness score of 0.
1309 Consequently, it is very simple for userspace to define the amount of memory to
1310 consider for each task. Setting a /proc/<pid>/oom_score_adj value of +500, for
1311 example, is roughly equivalent to allowing the remainder of tasks sharing the
1312 same system, cpuset, mempolicy, or memory controller resources to use at least
1313 50% more memory. A value of -500, on the other hand, would be roughly
1314 equivalent to discounting 50% of the task's allowed memory from being considered
1315 as scoring against the task.
1317 For backwards compatibility with previous kernels, /proc/<pid>/oom_adj may also
1318 be 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
1321 scaled linearly with /proc/<pid>/oom_score_adj.
1323 Writing to /proc/<pid>/oom_score_adj or /proc/<pid>/oom_adj will change the
1324 other with its scaled value.
1326 The value of /proc/<pid>/oom_score_adj may be reduced no lower than the last
1327 value set by a CAP_SYS_RESOURCE process. To reduce the value any lower
1328 requires CAP_SYS_RESOURCE.
1330 NOTICE: /proc/<pid>/oom_adj is deprecated and will be removed, please see
1331 Documentation/feature-removal-schedule.txt.
1333 Caveat: when a parent task is selected, the oom killer will sacrifice any first
1334 generation children with separate address spaces instead, if possible. This
1335 avoids servers and important system daemons from being killed and loses the
1336 minimal amount of work.
1339 3.2 /proc/<pid>/oom_score - Display current oom-killer score
1340 -------------------------------------------------------------
1342 This file can be used to check the current score used by the oom-killer is for
1343 any given <pid>. Use it together with /proc/<pid>/oom_adj to tune which
1344 process should be killed in an out-of-memory situation.
1347 3.3 /proc/<pid>/io - Display the IO accounting fields
1348 -------------------------------------------------------
1350 This file contains IO statistics for each running process
1355 test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
1358 test:/tmp # cat /proc/3828/io
1364 write_bytes: 323932160
1365 cancelled_write_bytes: 0
1374 I/O counter: chars read
1375 The number of bytes which this task has caused to be read from storage. This
1376 is simply the sum of bytes which this process passed to read() and pread().
1377 It includes things like tty IO and it is unaffected by whether or not actual
1378 physical disk IO was required (the read might have been satisfied from
1385 I/O counter: chars written
1386 The number of bytes which this task has caused, or shall cause to be written
1387 to disk. Similar caveats apply here as with rchar.
1393 I/O counter: read syscalls
1394 Attempt to count the number of read I/O operations, i.e. syscalls like read()
1401 I/O counter: write syscalls
1402 Attempt to count the number of write I/O operations, i.e. syscalls like
1403 write() and pwrite().
1409 I/O counter: bytes read
1410 Attempt to count the number of bytes which this process really did cause to
1411 be fetched from the storage layer. Done at the submit_bio() level, so it is
1412 accurate for block-backed filesystems. <please add status regarding NFS and
1413 CIFS at a later time>
1419 I/O counter: bytes written
1420 Attempt to count the number of bytes which this process caused to be sent to
1421 the storage layer. This is done at page-dirtying time.
1424 cancelled_write_bytes
1425 ---------------------
1427 The big inaccuracy here is truncate. If a process writes 1MB to a file and
1428 then deletes the file, it will in fact perform no writeout. But it will have
1429 been accounted as having caused 1MB of write.
1430 In other words: The number of bytes which this process caused to not happen,
1431 by truncating pagecache. A task can cause "negative" IO too. If this task
1432 truncates some dirty pagecache, some IO which another task has been accounted
1433 for (in its write_bytes) will not be happening. We _could_ just subtract that
1434 from the truncating task's write_bytes, but there is information loss in doing
1441 At its current implementation state, this is a bit racy on 32-bit machines: if
1442 process A reads process B's /proc/pid/io while process B is updating one of
1443 those 64-bit counters, process A could see an intermediate result.
1446 More information about this can be found within the taskstats documentation in
1447 Documentation/accounting.
1449 3.4 /proc/<pid>/coredump_filter - Core dump filtering settings
1450 ---------------------------------------------------------------
1451 When a process is dumped, all anonymous memory is written to a core file as
1452 long as the size of the core file isn't limited. But sometimes we don't want
1453 to dump some memory segments, for example, huge shared memory. Conversely,
1454 sometimes we want to save file-backed memory segments into a core file, not
1455 only the individual files.
1457 /proc/<pid>/coredump_filter allows you to customize which memory segments
1458 will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
1459 of memory types. If a bit of the bitmask is set, memory segments of the
1460 corresponding memory type are dumped, otherwise they are not dumped.
1462 The 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.
1478 Default value of coredump_filter is 0x23; this means all anonymous memory
1479 segments and hugetlb private memory are dumped.
1481 If you don't want to dump all shared memory segments attached to pid 1234,
1482 write 0x21 to the process's proc file.
1484 $ echo 0x21 > /proc/1234/coredump_filter
1486 When a new process is created, the process inherits the bitmask status from its
1487 parent. It is useful to set up coredump_filter before the program runs.
1490 $ echo 0x7 > /proc/self/coredump_filter
1493 3.5 /proc/<pid>/mountinfo - Information about mounts
1494 --------------------------------------------------------
1496 This file contains lines of the form:
1498 36 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
1513 Parsers should ignore all unrecognised optional fields. Currently the
1514 possible optional fields are:
1516 shared:X mount is shared in peer group X
1517 master:X mount is slave to peer group X
1518 propagate_from:X mount is slave and receives propagation from peer group X (*)
1519 unbindable mount is unbindable
1521 (*) X is the closest dominant peer group under the process's root. If
1522 X is the immediate master of the mount, or if there's no dominant peer
1523 group under the same root, then only the "master:X" field is present
1524 and not the "propagate_from:X" field.
1526 For more information on mount propagation see:
1528 Documentation/filesystems/sharedsubtree.txt
1531 3.6 /proc/<pid>/comm & /proc/<pid>/task/<tid>/comm
1532 --------------------------------------------------------
1533 These files provide a method to access a tasks comm value. It also allows for
1534 a task to set its own or one of its thread siblings comm value. The comm value
1535 is limited in size compared to the cmdline value, so writing anything longer
1536 then the kernel's TASK_COMM_LEN (currently 16 chars) will result in a truncated
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