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Linus Torvalds1da177e2005-04-16 15:20:36 -07001------------------------------------------------------------------------------
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>
6
72.4.x update Jorge Nerin <comandante@zaralinux.com> November 14 2000
8------------------------------------------------------------------------------
9Version 1.3 Kernel version 2.2.12
10 Kernel version 2.4.0-test11-pre4
11------------------------------------------------------------------------------
12
13Table of Contents
14-----------------
15
16 0 Preface
17 0.1 Introduction/Credits
18 0.2 Legal Stuff
19
20 1 Collecting System Information
21 1.1 Process-Specific Subdirectories
22 1.2 Kernel data
23 1.3 IDE devices in /proc/ide
24 1.4 Networking info in /proc/net
25 1.5 SCSI info
26 1.6 Parallel port info in /proc/parport
27 1.7 TTY info in /proc/tty
28 1.8 Miscellaneous kernel statistics in /proc/stat
29
30 2 Modifying System Parameters
31 2.1 /proc/sys/fs - File system data
32 2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats
33 2.3 /proc/sys/kernel - general kernel parameters
34 2.4 /proc/sys/vm - The virtual memory subsystem
35 2.5 /proc/sys/dev - Device specific parameters
36 2.6 /proc/sys/sunrpc - Remote procedure calls
37 2.7 /proc/sys/net - Networking stuff
38 2.8 /proc/sys/net/ipv4 - IPV4 settings
39 2.9 Appletalk
40 2.10 IPX
41 2.11 /proc/sys/fs/mqueue - POSIX message queues filesystem
Jan-Frode Myklebustd7ff0db2006-09-29 01:59:45 -070042 2.12 /proc/<pid>/oom_adj - Adjust the oom-killer score
43 2.13 /proc/<pid>/oom_score - Display current oom-killer score
Roland Kletzingf9c99462007-03-05 00:30:54 -080044 2.14 /proc/<pid>/io - Display the IO accounting fields
Linus Torvalds1da177e2005-04-16 15:20:36 -070045
46------------------------------------------------------------------------------
47Preface
48------------------------------------------------------------------------------
49
500.1 Introduction/Credits
51------------------------
52
53This documentation is part of a soon (or so we hope) to be released book on
54the SuSE Linux distribution. As there is no complete documentation for the
55/proc file system and we've used many freely available sources to write these
56chapters, it seems only fair to give the work back to the Linux community.
57This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm
58afraid it's still far from complete, but we hope it will be useful. As far as
59we know, it is the first 'all-in-one' document about the /proc file system. It
60is focused on the Intel x86 hardware, so if you are looking for PPC, ARM,
61SPARC, AXP, etc., features, you probably won't find what you are looking for.
62It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
63additions and patches are welcome and will be added to this document if you
64mail them to Bodo.
65
66We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
67other people for help compiling this documentation. We'd also like to extend a
68special thank you to Andi Kleen for documentation, which we relied on heavily
69to create this document, as well as the additional information he provided.
70Thanks to everybody else who contributed source or docs to the Linux kernel
71and helped create a great piece of software... :)
72
73If you have any comments, corrections or additions, please don't hesitate to
74contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this
75document.
76
77The latest version of this document is available online at
78http://skaro.nightcrawler.com/~bb/Docs/Proc as HTML version.
79
80If the above direction does not works for you, ypu could try the kernel
81mailing list at linux-kernel@vger.kernel.org and/or try to reach me at
82comandante@zaralinux.com.
83
840.2 Legal Stuff
85---------------
86
87We don't guarantee the correctness of this document, and if you come to us
88complaining about how you screwed up your system because of incorrect
89documentation, we won't feel responsible...
90
91------------------------------------------------------------------------------
92CHAPTER 1: COLLECTING SYSTEM INFORMATION
93------------------------------------------------------------------------------
94
95------------------------------------------------------------------------------
96In This Chapter
97------------------------------------------------------------------------------
98* Investigating the properties of the pseudo file system /proc and its
99 ability to provide information on the running Linux system
100* Examining /proc's structure
101* Uncovering various information about the kernel and the processes running
102 on the system
103------------------------------------------------------------------------------
104
105
106The proc file system acts as an interface to internal data structures in the
107kernel. It can be used to obtain information about the system and to change
108certain kernel parameters at runtime (sysctl).
109
110First, we'll take a look at the read-only parts of /proc. In Chapter 2, we
111show you how you can use /proc/sys to change settings.
112
1131.1 Process-Specific Subdirectories
114-----------------------------------
115
116The directory /proc contains (among other things) one subdirectory for each
117process running on the system, which is named after the process ID (PID).
118
119The link self points to the process reading the file system. Each process
120subdirectory has the entries listed in Table 1-1.
121
122
123Table 1-1: Process specific entries in /proc
124..............................................................................
David Rientjesb813e932007-05-06 14:49:24 -0700125 File Content
126 clear_refs Clears page referenced bits shown in smaps output
127 cmdline Command line arguments
128 cpu Current and last cpu in which it was executed (2.4)(smp)
129 cwd Link to the current working directory
130 environ Values of environment variables
131 exe Link to the executable of this process
132 fd Directory, which contains all file descriptors
133 maps Memory maps to executables and library files (2.4)
134 mem Memory held by this process
135 root Link to the root directory of this process
136 stat Process status
137 statm Process memory status information
138 status Process status in human readable form
139 wchan If CONFIG_KALLSYMS is set, a pre-decoded wchan
140 smaps Extension based on maps, the rss size for each mapped file
Linus Torvalds1da177e2005-04-16 15:20:36 -0700141..............................................................................
142
143For example, to get the status information of a process, all you have to do is
144read the file /proc/PID/status:
145
146 >cat /proc/self/status
147 Name: cat
148 State: R (running)
149 Pid: 5452
150 PPid: 743
151 TracerPid: 0 (2.4)
152 Uid: 501 501 501 501
153 Gid: 100 100 100 100
154 Groups: 100 14 16
155 VmSize: 1112 kB
156 VmLck: 0 kB
157 VmRSS: 348 kB
158 VmData: 24 kB
159 VmStk: 12 kB
160 VmExe: 8 kB
161 VmLib: 1044 kB
162 SigPnd: 0000000000000000
163 SigBlk: 0000000000000000
164 SigIgn: 0000000000000000
165 SigCgt: 0000000000000000
166 CapInh: 00000000fffffeff
167 CapPrm: 0000000000000000
168 CapEff: 0000000000000000
169
170
171This shows you nearly the same information you would get if you viewed it with
172the ps command. In fact, ps uses the proc file system to obtain its
173information. The statm file contains more detailed information about the
174process memory usage. Its seven fields are explained in Table 1-2.
175
176
177Table 1-2: Contents of the statm files (as of 2.6.8-rc3)
178..............................................................................
179 Field Content
180 size total program size (pages) (same as VmSize in status)
181 resident size of memory portions (pages) (same as VmRSS in status)
182 shared number of pages that are shared (i.e. backed by a file)
183 trs number of pages that are 'code' (not including libs; broken,
184 includes data segment)
185 lrs number of pages of library (always 0 on 2.6)
186 drs number of pages of data/stack (including libs; broken,
187 includes library text)
188 dt number of dirty pages (always 0 on 2.6)
189..............................................................................
190
1911.2 Kernel data
192---------------
193
194Similar to the process entries, the kernel data files give information about
195the running kernel. The files used to obtain this information are contained in
196/proc and are listed in Table 1-3. Not all of these will be present in your
197system. It depends on the kernel configuration and the loaded modules, which
198files are there, and which are missing.
199
200Table 1-3: Kernel info in /proc
201..............................................................................
202 File Content
203 apm Advanced power management info
204 buddyinfo Kernel memory allocator information (see text) (2.5)
205 bus Directory containing bus specific information
206 cmdline Kernel command line
207 cpuinfo Info about the CPU
208 devices Available devices (block and character)
209 dma Used DMS channels
210 filesystems Supported filesystems
211 driver Various drivers grouped here, currently rtc (2.4)
212 execdomains Execdomains, related to security (2.4)
213 fb Frame Buffer devices (2.4)
214 fs File system parameters, currently nfs/exports (2.4)
215 ide Directory containing info about the IDE subsystem
216 interrupts Interrupt usage
217 iomem Memory map (2.4)
218 ioports I/O port usage
219 irq Masks for irq to cpu affinity (2.4)(smp?)
220 isapnp ISA PnP (Plug&Play) Info (2.4)
221 kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
222 kmsg Kernel messages
223 ksyms Kernel symbol table
224 loadavg Load average of last 1, 5 & 15 minutes
225 locks Kernel locks
226 meminfo Memory info
227 misc Miscellaneous
228 modules List of loaded modules
229 mounts Mounted filesystems
230 net Networking info (see text)
231 partitions Table of partitions known to the system
Randy Dunlap8b607562007-05-09 07:19:14 +0200232 pci Deprecated info of PCI bus (new way -> /proc/bus/pci/,
Linus Torvalds1da177e2005-04-16 15:20:36 -0700233 decoupled by lspci (2.4)
234 rtc Real time clock
235 scsi SCSI info (see text)
236 slabinfo Slab pool info
237 stat Overall statistics
238 swaps Swap space utilization
239 sys See chapter 2
240 sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4)
241 tty Info of tty drivers
242 uptime System uptime
243 version Kernel version
244 video bttv info of video resources (2.4)
245..............................................................................
246
247You can, for example, check which interrupts are currently in use and what
248they are used for by looking in the file /proc/interrupts:
249
250 > cat /proc/interrupts
251 CPU0
252 0: 8728810 XT-PIC timer
253 1: 895 XT-PIC keyboard
254 2: 0 XT-PIC cascade
255 3: 531695 XT-PIC aha152x
256 4: 2014133 XT-PIC serial
257 5: 44401 XT-PIC pcnet_cs
258 8: 2 XT-PIC rtc
259 11: 8 XT-PIC i82365
260 12: 182918 XT-PIC PS/2 Mouse
261 13: 1 XT-PIC fpu
262 14: 1232265 XT-PIC ide0
263 15: 7 XT-PIC ide1
264 NMI: 0
265
266In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
267output of a SMP machine):
268
269 > cat /proc/interrupts
270
271 CPU0 CPU1
272 0: 1243498 1214548 IO-APIC-edge timer
273 1: 8949 8958 IO-APIC-edge keyboard
274 2: 0 0 XT-PIC cascade
275 5: 11286 10161 IO-APIC-edge soundblaster
276 8: 1 0 IO-APIC-edge rtc
277 9: 27422 27407 IO-APIC-edge 3c503
278 12: 113645 113873 IO-APIC-edge PS/2 Mouse
279 13: 0 0 XT-PIC fpu
280 14: 22491 24012 IO-APIC-edge ide0
281 15: 2183 2415 IO-APIC-edge ide1
282 17: 30564 30414 IO-APIC-level eth0
283 18: 177 164 IO-APIC-level bttv
284 NMI: 2457961 2457959
285 LOC: 2457882 2457881
286 ERR: 2155
287
288NMI is incremented in this case because every timer interrupt generates a NMI
289(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
290
291LOC is the local interrupt counter of the internal APIC of every CPU.
292
293ERR is incremented in the case of errors in the IO-APIC bus (the bus that
294connects the CPUs in a SMP system. This means that an error has been detected,
295the IO-APIC automatically retry the transmission, so it should not be a big
296problem, but you should read the SMP-FAQ.
297
298In this context it could be interesting to note the new irq directory in 2.4.
299It could be used to set IRQ to CPU affinity, this means that you can "hook" an
300IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
301irq subdir is one subdir for each IRQ, and one file; prof_cpu_mask
302
303For example
304 > ls /proc/irq/
305 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask
306 1 11 13 15 17 19 3 5 7 9
307 > ls /proc/irq/0/
308 smp_affinity
309
310The contents of the prof_cpu_mask file and each smp_affinity file for each IRQ
311is the same by default:
312
313 > cat /proc/irq/0/smp_affinity
314 ffffffff
315
Uwe Zeisbergerc30fe7f2006-03-24 18:23:14 +0100316It's a bitmask, in which you can specify which CPUs can handle the IRQ, you can
Linus Torvalds1da177e2005-04-16 15:20:36 -0700317set it by doing:
318
319 > echo 1 > /proc/irq/prof_cpu_mask
320
321This means that only the first CPU will handle the IRQ, but you can also echo 5
Uwe Zeisbergerc30fe7f2006-03-24 18:23:14 +0100322which means that only the first and fourth CPU can handle the IRQ.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700323
324The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
325between all the CPUs which are allowed to handle it. As usual the kernel has
326more info than you and does a better job than you, so the defaults are the
327best choice for almost everyone.
328
329There are three more important subdirectories in /proc: net, scsi, and sys.
330The general rule is that the contents, or even the existence of these
331directories, depend on your kernel configuration. If SCSI is not enabled, the
332directory scsi may not exist. The same is true with the net, which is there
333only when networking support is present in the running kernel.
334
335The slabinfo file gives information about memory usage at the slab level.
336Linux uses slab pools for memory management above page level in version 2.2.
337Commonly used objects have their own slab pool (such as network buffers,
338directory cache, and so on).
339
340..............................................................................
341
342> cat /proc/buddyinfo
343
344Node 0, zone DMA 0 4 5 4 4 3 ...
345Node 0, zone Normal 1 0 0 1 101 8 ...
346Node 0, zone HighMem 2 0 0 1 1 0 ...
347
348Memory fragmentation is a problem under some workloads, and buddyinfo is a
349useful tool for helping diagnose these problems. Buddyinfo will give you a
350clue as to how big an area you can safely allocate, or why a previous
351allocation failed.
352
353Each column represents the number of pages of a certain order which are
354available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
355ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
356available in ZONE_NORMAL, etc...
357
358..............................................................................
359
360meminfo:
361
362Provides information about distribution and utilization of memory. This
363varies by architecture and compile options. The following is from a
36416GB PIII, which has highmem enabled. You may not have all of these fields.
365
366> cat /proc/meminfo
367
368
369MemTotal: 16344972 kB
370MemFree: 13634064 kB
371Buffers: 3656 kB
372Cached: 1195708 kB
373SwapCached: 0 kB
374Active: 891636 kB
375Inactive: 1077224 kB
376HighTotal: 15597528 kB
377HighFree: 13629632 kB
378LowTotal: 747444 kB
379LowFree: 4432 kB
380SwapTotal: 0 kB
381SwapFree: 0 kB
382Dirty: 968 kB
383Writeback: 0 kB
384Mapped: 280372 kB
385Slab: 684068 kB
386CommitLimit: 7669796 kB
387Committed_AS: 100056 kB
388PageTables: 24448 kB
389VmallocTotal: 112216 kB
390VmallocUsed: 428 kB
391VmallocChunk: 111088 kB
392
393 MemTotal: Total usable ram (i.e. physical ram minus a few reserved
394 bits and the kernel binary code)
395 MemFree: The sum of LowFree+HighFree
396 Buffers: Relatively temporary storage for raw disk blocks
397 shouldn't get tremendously large (20MB or so)
398 Cached: in-memory cache for files read from the disk (the
399 pagecache). Doesn't include SwapCached
400 SwapCached: Memory that once was swapped out, is swapped back in but
401 still also is in the swapfile (if memory is needed it
402 doesn't need to be swapped out AGAIN because it is already
403 in the swapfile. This saves I/O)
404 Active: Memory that has been used more recently and usually not
405 reclaimed unless absolutely necessary.
406 Inactive: Memory which has been less recently used. It is more
407 eligible to be reclaimed for other purposes
408 HighTotal:
409 HighFree: Highmem is all memory above ~860MB of physical memory
410 Highmem areas are for use by userspace programs, or
411 for the pagecache. The kernel must use tricks to access
412 this memory, making it slower to access than lowmem.
413 LowTotal:
414 LowFree: Lowmem is memory which can be used for everything that
Matt LaPlante3f6dee92006-10-03 22:45:33 +0200415 highmem can be used for, but it is also available for the
Linus Torvalds1da177e2005-04-16 15:20:36 -0700416 kernel's use for its own data structures. Among many
417 other things, it is where everything from the Slab is
418 allocated. Bad things happen when you're out of lowmem.
419 SwapTotal: total amount of swap space available
420 SwapFree: Memory which has been evicted from RAM, and is temporarily
421 on the disk
422 Dirty: Memory which is waiting to get written back to the disk
423 Writeback: Memory which is actively being written back to the disk
424 Mapped: files which have been mmaped, such as libraries
Adrian Bunke82443c2006-01-10 00:20:30 +0100425 Slab: in-kernel data structures cache
Linus Torvalds1da177e2005-04-16 15:20:36 -0700426 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
427 this is the total amount of memory currently available to
428 be allocated on the system. This limit is only adhered to
429 if strict overcommit accounting is enabled (mode 2 in
430 'vm.overcommit_memory').
431 The CommitLimit is calculated with the following formula:
432 CommitLimit = ('vm.overcommit_ratio' * Physical RAM) + Swap
433 For example, on a system with 1G of physical RAM and 7G
434 of swap with a `vm.overcommit_ratio` of 30 it would
435 yield a CommitLimit of 7.3G.
436 For more details, see the memory overcommit documentation
437 in vm/overcommit-accounting.
438Committed_AS: The amount of memory presently allocated on the system.
439 The committed memory is a sum of all of the memory which
440 has been allocated by processes, even if it has not been
441 "used" by them as of yet. A process which malloc()'s 1G
442 of memory, but only touches 300M of it will only show up
443 as using 300M of memory even if it has the address space
444 allocated for the entire 1G. This 1G is memory which has
445 been "committed" to by the VM and can be used at any time
446 by the allocating application. With strict overcommit
447 enabled on the system (mode 2 in 'vm.overcommit_memory'),
448 allocations which would exceed the CommitLimit (detailed
449 above) will not be permitted. This is useful if one needs
450 to guarantee that processes will not fail due to lack of
451 memory once that memory has been successfully allocated.
452 PageTables: amount of memory dedicated to the lowest level of page
453 tables.
454VmallocTotal: total size of vmalloc memory area
455 VmallocUsed: amount of vmalloc area which is used
456VmallocChunk: largest contigious block of vmalloc area which is free
457
458
4591.3 IDE devices in /proc/ide
460----------------------------
461
462The subdirectory /proc/ide contains information about all IDE devices of which
463the kernel is aware. There is one subdirectory for each IDE controller, the
464file drivers and a link for each IDE device, pointing to the device directory
465in the controller specific subtree.
466
467The file drivers contains general information about the drivers used for the
468IDE devices:
469
470 > cat /proc/ide/drivers
471 ide-cdrom version 4.53
472 ide-disk version 1.08
473
474More detailed information can be found in the controller specific
475subdirectories. These are named ide0, ide1 and so on. Each of these
476directories contains the files shown in table 1-4.
477
478
479Table 1-4: IDE controller info in /proc/ide/ide?
480..............................................................................
481 File Content
482 channel IDE channel (0 or 1)
483 config Configuration (only for PCI/IDE bridge)
484 mate Mate name
485 model Type/Chipset of IDE controller
486..............................................................................
487
488Each device connected to a controller has a separate subdirectory in the
489controllers directory. The files listed in table 1-5 are contained in these
490directories.
491
492
493Table 1-5: IDE device information
494..............................................................................
495 File Content
496 cache The cache
497 capacity Capacity of the medium (in 512Byte blocks)
498 driver driver and version
499 geometry physical and logical geometry
500 identify device identify block
501 media media type
502 model device identifier
503 settings device setup
504 smart_thresholds IDE disk management thresholds
505 smart_values IDE disk management values
506..............................................................................
507
508The most interesting file is settings. This file contains a nice overview of
509the drive parameters:
510
511 # cat /proc/ide/ide0/hda/settings
512 name value min max mode
513 ---- ----- --- --- ----
514 bios_cyl 526 0 65535 rw
515 bios_head 255 0 255 rw
516 bios_sect 63 0 63 rw
517 breada_readahead 4 0 127 rw
518 bswap 0 0 1 r
519 file_readahead 72 0 2097151 rw
520 io_32bit 0 0 3 rw
521 keepsettings 0 0 1 rw
522 max_kb_per_request 122 1 127 rw
523 multcount 0 0 8 rw
524 nice1 1 0 1 rw
525 nowerr 0 0 1 rw
526 pio_mode write-only 0 255 w
527 slow 0 0 1 rw
528 unmaskirq 0 0 1 rw
529 using_dma 0 0 1 rw
530
531
5321.4 Networking info in /proc/net
533--------------------------------
534
535The subdirectory /proc/net follows the usual pattern. Table 1-6 shows the
536additional values you get for IP version 6 if you configure the kernel to
537support this. Table 1-7 lists the files and their meaning.
538
539
540Table 1-6: IPv6 info in /proc/net
541..............................................................................
542 File Content
543 udp6 UDP sockets (IPv6)
544 tcp6 TCP sockets (IPv6)
545 raw6 Raw device statistics (IPv6)
546 igmp6 IP multicast addresses, which this host joined (IPv6)
547 if_inet6 List of IPv6 interface addresses
548 ipv6_route Kernel routing table for IPv6
549 rt6_stats Global IPv6 routing tables statistics
550 sockstat6 Socket statistics (IPv6)
551 snmp6 Snmp data (IPv6)
552..............................................................................
553
554
555Table 1-7: Network info in /proc/net
556..............................................................................
557 File Content
558 arp Kernel ARP table
559 dev network devices with statistics
560 dev_mcast the Layer2 multicast groups a device is listening too
561 (interface index, label, number of references, number of bound
562 addresses).
563 dev_stat network device status
564 ip_fwchains Firewall chain linkage
565 ip_fwnames Firewall chain names
566 ip_masq Directory containing the masquerading tables
567 ip_masquerade Major masquerading table
568 netstat Network statistics
569 raw raw device statistics
570 route Kernel routing table
571 rpc Directory containing rpc info
572 rt_cache Routing cache
573 snmp SNMP data
574 sockstat Socket statistics
575 tcp TCP sockets
576 tr_rif Token ring RIF routing table
577 udp UDP sockets
578 unix UNIX domain sockets
579 wireless Wireless interface data (Wavelan etc)
580 igmp IP multicast addresses, which this host joined
581 psched Global packet scheduler parameters.
582 netlink List of PF_NETLINK sockets
583 ip_mr_vifs List of multicast virtual interfaces
584 ip_mr_cache List of multicast routing cache
585..............................................................................
586
587You can use this information to see which network devices are available in
588your system and how much traffic was routed over those devices:
589
590 > cat /proc/net/dev
591 Inter-|Receive |[...
592 face |bytes packets errs drop fifo frame compressed multicast|[...
593 lo: 908188 5596 0 0 0 0 0 0 [...
594 ppp0:15475140 20721 410 0 0 410 0 0 [...
595 eth0: 614530 7085 0 0 0 0 0 1 [...
596
597 ...] Transmit
598 ...] bytes packets errs drop fifo colls carrier compressed
599 ...] 908188 5596 0 0 0 0 0 0
600 ...] 1375103 17405 0 0 0 0 0 0
601 ...] 1703981 5535 0 0 0 3 0 0
602
603In addition, each Channel Bond interface has it's own directory. For
604example, the bond0 device will have a directory called /proc/net/bond0/.
605It will contain information that is specific to that bond, such as the
606current slaves of the bond, the link status of the slaves, and how
607many times the slaves link has failed.
608
6091.5 SCSI info
610-------------
611
612If you have a SCSI host adapter in your system, you'll find a subdirectory
613named after the driver for this adapter in /proc/scsi. You'll also see a list
614of all recognized SCSI devices in /proc/scsi:
615
616 >cat /proc/scsi/scsi
617 Attached devices:
618 Host: scsi0 Channel: 00 Id: 00 Lun: 00
619 Vendor: IBM Model: DGHS09U Rev: 03E0
620 Type: Direct-Access ANSI SCSI revision: 03
621 Host: scsi0 Channel: 00 Id: 06 Lun: 00
622 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04
623 Type: CD-ROM ANSI SCSI revision: 02
624
625
626The directory named after the driver has one file for each adapter found in
627the system. These files contain information about the controller, including
628the used IRQ and the IO address range. The amount of information shown is
629dependent on the adapter you use. The example shows the output for an Adaptec
630AHA-2940 SCSI adapter:
631
632 > cat /proc/scsi/aic7xxx/0
633
634 Adaptec AIC7xxx driver version: 5.1.19/3.2.4
635 Compile Options:
636 TCQ Enabled By Default : Disabled
637 AIC7XXX_PROC_STATS : Disabled
638 AIC7XXX_RESET_DELAY : 5
639 Adapter Configuration:
640 SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
641 Ultra Wide Controller
642 PCI MMAPed I/O Base: 0xeb001000
643 Adapter SEEPROM Config: SEEPROM found and used.
644 Adaptec SCSI BIOS: Enabled
645 IRQ: 10
646 SCBs: Active 0, Max Active 2,
647 Allocated 15, HW 16, Page 255
648 Interrupts: 160328
649 BIOS Control Word: 0x18b6
650 Adapter Control Word: 0x005b
651 Extended Translation: Enabled
652 Disconnect Enable Flags: 0xffff
653 Ultra Enable Flags: 0x0001
654 Tag Queue Enable Flags: 0x0000
655 Ordered Queue Tag Flags: 0x0000
656 Default Tag Queue Depth: 8
657 Tagged Queue By Device array for aic7xxx host instance 0:
658 {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
659 Actual queue depth per device for aic7xxx host instance 0:
660 {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
661 Statistics:
662 (scsi0:0:0:0)
663 Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
664 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
665 Total transfers 160151 (74577 reads and 85574 writes)
666 (scsi0:0:6:0)
667 Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
668 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
669 Total transfers 0 (0 reads and 0 writes)
670
671
6721.6 Parallel port info in /proc/parport
673---------------------------------------
674
675The directory /proc/parport contains information about the parallel ports of
676your system. It has one subdirectory for each port, named after the port
677number (0,1,2,...).
678
679These directories contain the four files shown in Table 1-8.
680
681
682Table 1-8: Files in /proc/parport
683..............................................................................
684 File Content
685 autoprobe Any IEEE-1284 device ID information that has been acquired.
686 devices list of the device drivers using that port. A + will appear by the
687 name of the device currently using the port (it might not appear
688 against any).
689 hardware Parallel port's base address, IRQ line and DMA channel.
690 irq IRQ that parport is using for that port. This is in a separate
691 file to allow you to alter it by writing a new value in (IRQ
692 number or none).
693..............................................................................
694
6951.7 TTY info in /proc/tty
696-------------------------
697
698Information about the available and actually used tty's can be found in the
699directory /proc/tty.You'll find entries for drivers and line disciplines in
700this directory, as shown in Table 1-9.
701
702
703Table 1-9: Files in /proc/tty
704..............................................................................
705 File Content
706 drivers list of drivers and their usage
707 ldiscs registered line disciplines
708 driver/serial usage statistic and status of single tty lines
709..............................................................................
710
711To see which tty's are currently in use, you can simply look into the file
712/proc/tty/drivers:
713
714 > cat /proc/tty/drivers
715 pty_slave /dev/pts 136 0-255 pty:slave
716 pty_master /dev/ptm 128 0-255 pty:master
717 pty_slave /dev/ttyp 3 0-255 pty:slave
718 pty_master /dev/pty 2 0-255 pty:master
719 serial /dev/cua 5 64-67 serial:callout
720 serial /dev/ttyS 4 64-67 serial
721 /dev/tty0 /dev/tty0 4 0 system:vtmaster
722 /dev/ptmx /dev/ptmx 5 2 system
723 /dev/console /dev/console 5 1 system:console
724 /dev/tty /dev/tty 5 0 system:/dev/tty
725 unknown /dev/tty 4 1-63 console
726
727
7281.8 Miscellaneous kernel statistics in /proc/stat
729-------------------------------------------------
730
731Various pieces of information about kernel activity are available in the
732/proc/stat file. All of the numbers reported in this file are aggregates
733since the system first booted. For a quick look, simply cat the file:
734
735 > cat /proc/stat
736 cpu 2255 34 2290 22625563 6290 127 456
737 cpu0 1132 34 1441 11311718 3675 127 438
738 cpu1 1123 0 849 11313845 2614 0 18
739 intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
740 ctxt 1990473
741 btime 1062191376
742 processes 2915
743 procs_running 1
744 procs_blocked 0
745
746The very first "cpu" line aggregates the numbers in all of the other "cpuN"
747lines. These numbers identify the amount of time the CPU has spent performing
748different kinds of work. Time units are in USER_HZ (typically hundredths of a
749second). The meanings of the columns are as follows, from left to right:
750
751- user: normal processes executing in user mode
752- nice: niced processes executing in user mode
753- system: processes executing in kernel mode
754- idle: twiddling thumbs
755- iowait: waiting for I/O to complete
756- irq: servicing interrupts
757- softirq: servicing softirqs
758
759The "intr" line gives counts of interrupts serviced since boot time, for each
760of the possible system interrupts. The first column is the total of all
761interrupts serviced; each subsequent column is the total for that particular
762interrupt.
763
764The "ctxt" line gives the total number of context switches across all CPUs.
765
766The "btime" line gives the time at which the system booted, in seconds since
767the Unix epoch.
768
769The "processes" line gives the number of processes and threads created, which
770includes (but is not limited to) those created by calls to the fork() and
771clone() system calls.
772
773The "procs_running" line gives the number of processes currently running on
774CPUs.
775
776The "procs_blocked" line gives the number of processes currently blocked,
777waiting for I/O to complete.
778
779
780------------------------------------------------------------------------------
781Summary
782------------------------------------------------------------------------------
783The /proc file system serves information about the running system. It not only
784allows access to process data but also allows you to request the kernel status
785by reading files in the hierarchy.
786
787The directory structure of /proc reflects the types of information and makes
788it easy, if not obvious, where to look for specific data.
789------------------------------------------------------------------------------
790
791------------------------------------------------------------------------------
792CHAPTER 2: MODIFYING SYSTEM PARAMETERS
793------------------------------------------------------------------------------
794
795------------------------------------------------------------------------------
796In This Chapter
797------------------------------------------------------------------------------
798* Modifying kernel parameters by writing into files found in /proc/sys
799* Exploring the files which modify certain parameters
800* Review of the /proc/sys file tree
801------------------------------------------------------------------------------
802
803
804A very interesting part of /proc is the directory /proc/sys. This is not only
805a source of information, it also allows you to change parameters within the
806kernel. Be very careful when attempting this. You can optimize your system,
807but you can also cause it to crash. Never alter kernel parameters on a
808production system. Set up a development machine and test to make sure that
809everything works the way you want it to. You may have no alternative but to
810reboot the machine once an error has been made.
811
812To change a value, simply echo the new value into the file. An example is
813given below in the section on the file system data. You need to be root to do
814this. You can create your own boot script to perform this every time your
815system boots.
816
817The files in /proc/sys can be used to fine tune and monitor miscellaneous and
818general things in the operation of the Linux kernel. Since some of the files
819can inadvertently disrupt your system, it is advisable to read both
820documentation and source before actually making adjustments. In any case, be
821very careful when writing to any of these files. The entries in /proc may
822change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
823review the kernel documentation in the directory /usr/src/linux/Documentation.
824This chapter is heavily based on the documentation included in the pre 2.2
825kernels, and became part of it in version 2.2.1 of the Linux kernel.
826
8272.1 /proc/sys/fs - File system data
828-----------------------------------
829
830This subdirectory contains specific file system, file handle, inode, dentry
831and quota information.
832
833Currently, these files are in /proc/sys/fs:
834
835dentry-state
836------------
837
838Status of the directory cache. Since directory entries are dynamically
839allocated and deallocated, this file indicates the current status. It holds
840six values, in which the last two are not used and are always zero. The others
841are listed in table 2-1.
842
843
844Table 2-1: Status files of the directory cache
845..............................................................................
846 File Content
847 nr_dentry Almost always zero
848 nr_unused Number of unused cache entries
849 age_limit
850 in seconds after the entry may be reclaimed, when memory is short
851 want_pages internally
852..............................................................................
853
854dquot-nr and dquot-max
855----------------------
856
857The file dquot-max shows the maximum number of cached disk quota entries.
858
859The file dquot-nr shows the number of allocated disk quota entries and the
860number of free disk quota entries.
861
862If the number of available cached disk quotas is very low and you have a large
863number of simultaneous system users, you might want to raise the limit.
864
865file-nr and file-max
866--------------------
867
868The kernel allocates file handles dynamically, but doesn't free them again at
869this time.
870
871The value in file-max denotes the maximum number of file handles that the
872Linux kernel will allocate. When you get a lot of error messages about running
873out of file handles, you might want to raise this limit. The default value is
87410% of RAM in kilobytes. To change it, just write the new number into the
875file:
876
877 # cat /proc/sys/fs/file-max
878 4096
879 # echo 8192 > /proc/sys/fs/file-max
880 # cat /proc/sys/fs/file-max
881 8192
882
883
884This method of revision is useful for all customizable parameters of the
885kernel - simply echo the new value to the corresponding file.
886
887Historically, the three values in file-nr denoted the number of allocated file
888handles, the number of allocated but unused file handles, and the maximum
889number of file handles. Linux 2.6 always reports 0 as the number of free file
890handles -- this is not an error, it just means that the number of allocated
891file handles exactly matches the number of used file handles.
892
893Attempts to allocate more file descriptors than file-max are reported with
894printk, look for "VFS: file-max limit <number> reached".
895
896inode-state and inode-nr
897------------------------
898
899The file inode-nr contains the first two items from inode-state, so we'll skip
900to that file...
901
902inode-state contains two actual numbers and five dummy values. The numbers
903are nr_inodes and nr_free_inodes (in order of appearance).
904
905nr_inodes
906~~~~~~~~~
907
908Denotes the number of inodes the system has allocated. This number will
909grow and shrink dynamically.
910
911nr_free_inodes
912--------------
913
914Represents the number of free inodes. Ie. The number of inuse inodes is
915(nr_inodes - nr_free_inodes).
916
Linus Torvalds1da177e2005-04-16 15:20:36 -0700917aio-nr and aio-max-nr
918---------------------
919
920aio-nr is the running total of the number of events specified on the
921io_setup system call for all currently active aio contexts. If aio-nr
922reaches aio-max-nr then io_setup will fail with EAGAIN. Note that
923raising aio-max-nr does not result in the pre-allocation or re-sizing
924of any kernel data structures.
925
9262.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats
927-----------------------------------------------------------
928
929Besides these files, there is the subdirectory /proc/sys/fs/binfmt_misc. This
930handles the kernel support for miscellaneous binary formats.
931
932Binfmt_misc provides the ability to register additional binary formats to the
933Kernel without compiling an additional module/kernel. Therefore, binfmt_misc
934needs to know magic numbers at the beginning or the filename extension of the
935binary.
936
937It works by maintaining a linked list of structs that contain a description of
938a binary format, including a magic with size (or the filename extension),
939offset and mask, and the interpreter name. On request it invokes the given
940interpreter with the original program as argument, as binfmt_java and
941binfmt_em86 and binfmt_mz do. Since binfmt_misc does not define any default
942binary-formats, you have to register an additional binary-format.
943
944There are two general files in binfmt_misc and one file per registered format.
945The two general files are register and status.
946
947Registering a new binary format
948-------------------------------
949
950To register a new binary format you have to issue the command
951
952 echo :name:type:offset:magic:mask:interpreter: > /proc/sys/fs/binfmt_misc/register
953
954
955
956with appropriate name (the name for the /proc-dir entry), offset (defaults to
9570, if omitted), magic, mask (which can be omitted, defaults to all 0xff) and
958last but not least, the interpreter that is to be invoked (for example and
959testing /bin/echo). Type can be M for usual magic matching or E for filename
960extension matching (give extension in place of magic).
961
962Check or reset the status of the binary format handler
963------------------------------------------------------
964
965If you do a cat on the file /proc/sys/fs/binfmt_misc/status, you will get the
966current status (enabled/disabled) of binfmt_misc. Change the status by echoing
9670 (disables) or 1 (enables) or -1 (caution: this clears all previously
968registered binary formats) to status. For example echo 0 > status to disable
969binfmt_misc (temporarily).
970
971Status of a single handler
972--------------------------
973
974Each registered handler has an entry in /proc/sys/fs/binfmt_misc. These files
975perform the same function as status, but their scope is limited to the actual
976binary format. By cating this file, you also receive all related information
977about the interpreter/magic of the binfmt.
978
979Example usage of binfmt_misc (emulate binfmt_java)
980--------------------------------------------------
981
982 cd /proc/sys/fs/binfmt_misc
983 echo ':Java:M::\xca\xfe\xba\xbe::/usr/local/java/bin/javawrapper:' > register
984 echo ':HTML:E::html::/usr/local/java/bin/appletviewer:' > register
985 echo ':Applet:M::<!--applet::/usr/local/java/bin/appletviewer:' > register
986 echo ':DEXE:M::\x0eDEX::/usr/bin/dosexec:' > register
987
988
989These four lines add support for Java executables and Java applets (like
990binfmt_java, additionally recognizing the .html extension with no need to put
991<!--applet> to every applet file). You have to install the JDK and the
992shell-script /usr/local/java/bin/javawrapper too. It works around the
993brokenness of the Java filename handling. To add a Java binary, just create a
994link to the class-file somewhere in the path.
995
9962.3 /proc/sys/kernel - general kernel parameters
997------------------------------------------------
998
999This directory reflects general kernel behaviors. As I've said before, the
1000contents depend on your configuration. Here you'll find the most important
1001files, along with descriptions of what they mean and how to use them.
1002
1003acct
1004----
1005
1006The file contains three values; highwater, lowwater, and frequency.
1007
1008It exists only when BSD-style process accounting is enabled. These values
1009control its behavior. If the free space on the file system where the log lives
1010goes below lowwater percentage, accounting suspends. If it goes above
1011highwater percentage, accounting resumes. Frequency determines how often you
1012check the amount of free space (value is in seconds). Default settings are: 4,
10132, and 30. That is, suspend accounting if there is less than 2 percent free;
1014resume it if we have a value of 3 or more percent; consider information about
1015the amount of free space valid for 30 seconds
1016
1017ctrl-alt-del
1018------------
1019
1020When the value in this file is 0, ctrl-alt-del is trapped and sent to the init
1021program to handle a graceful restart. However, when the value is greater that
1022zero, Linux's reaction to this key combination will be an immediate reboot,
1023without syncing its dirty buffers.
1024
1025[NOTE]
1026 When a program (like dosemu) has the keyboard in raw mode, the
1027 ctrl-alt-del is intercepted by the program before it ever reaches the
1028 kernel tty layer, and it is up to the program to decide what to do with
1029 it.
1030
1031domainname and hostname
1032-----------------------
1033
1034These files can be controlled to set the NIS domainname and hostname of your
1035box. For the classic darkstar.frop.org a simple:
1036
1037 # echo "darkstar" > /proc/sys/kernel/hostname
1038 # echo "frop.org" > /proc/sys/kernel/domainname
1039
1040
1041would suffice to set your hostname and NIS domainname.
1042
1043osrelease, ostype and version
1044-----------------------------
1045
1046The names make it pretty obvious what these fields contain:
1047
1048 > cat /proc/sys/kernel/osrelease
1049 2.2.12
1050
1051 > cat /proc/sys/kernel/ostype
1052 Linux
1053
1054 > cat /proc/sys/kernel/version
1055 #4 Fri Oct 1 12:41:14 PDT 1999
1056
1057
1058The files osrelease and ostype should be clear enough. Version needs a little
1059more clarification. The #4 means that this is the 4th kernel built from this
1060source base and the date after it indicates the time the kernel was built. The
1061only way to tune these values is to rebuild the kernel.
1062
1063panic
1064-----
1065
1066The value in this file represents the number of seconds the kernel waits
1067before rebooting on a panic. When you use the software watchdog, the
1068recommended setting is 60. If set to 0, the auto reboot after a kernel panic
1069is disabled, which is the default setting.
1070
1071printk
1072------
1073
1074The four values in printk denote
1075* console_loglevel,
1076* default_message_loglevel,
1077* minimum_console_loglevel and
1078* default_console_loglevel
1079respectively.
1080
1081These values influence printk() behavior when printing or logging error
1082messages, which come from inside the kernel. See syslog(2) for more
1083information on the different log levels.
1084
1085console_loglevel
1086----------------
1087
1088Messages with a higher priority than this will be printed to the console.
1089
1090default_message_level
1091---------------------
1092
1093Messages without an explicit priority will be printed with this priority.
1094
1095minimum_console_loglevel
1096------------------------
1097
1098Minimum (highest) value to which the console_loglevel can be set.
1099
1100default_console_loglevel
1101------------------------
1102
1103Default value for console_loglevel.
1104
1105sg-big-buff
1106-----------
1107
1108This file shows the size of the generic SCSI (sg) buffer. At this point, you
1109can't tune it yet, but you can change it at compile time by editing
1110include/scsi/sg.h and changing the value of SG_BIG_BUFF.
1111
1112If you use a scanner with SANE (Scanner Access Now Easy) you might want to set
1113this to a higher value. Refer to the SANE documentation on this issue.
1114
1115modprobe
1116--------
1117
1118The location where the modprobe binary is located. The kernel uses this
1119program to load modules on demand.
1120
1121unknown_nmi_panic
1122-----------------
1123
1124The value in this file affects behavior of handling NMI. When the value is
1125non-zero, unknown NMI is trapped and then panic occurs. At that time, kernel
1126debugging information is displayed on console.
1127
1128NMI switch that most IA32 servers have fires unknown NMI up, for example.
1129If a system hangs up, try pressing the NMI switch.
1130
Don Zickuse33e89a2006-09-26 10:52:27 +02001131nmi_watchdog
1132------------
1133
1134Enables/Disables the NMI watchdog on x86 systems. When the value is non-zero
1135the NMI watchdog is enabled and will continuously test all online cpus to
1136determine whether or not they are still functioning properly.
1137
1138Because the NMI watchdog shares registers with oprofile, by disabling the NMI
1139watchdog, oprofile may have more registers to utilize.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001140
Kees Cook5096add2007-05-08 00:26:04 -07001141maps_protect
1142------------
1143
1144Enables/Disables the protection of the per-process proc entries "maps" and
1145"smaps". When enabled, the contents of these files are visible only to
1146readers that are allowed to ptrace() the given process.
1147
Linus Torvalds1da177e2005-04-16 15:20:36 -07001148
11492.4 /proc/sys/vm - The virtual memory subsystem
1150-----------------------------------------------
1151
1152The files in this directory can be used to tune the operation of the virtual
1153memory (VM) subsystem of the Linux kernel.
1154
1155vfs_cache_pressure
1156------------------
1157
1158Controls the tendency of the kernel to reclaim the memory which is used for
1159caching of directory and inode objects.
1160
1161At the default value of vfs_cache_pressure=100 the kernel will attempt to
1162reclaim dentries and inodes at a "fair" rate with respect to pagecache and
1163swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer
1164to retain dentry and inode caches. Increasing vfs_cache_pressure beyond 100
1165causes the kernel to prefer to reclaim dentries and inodes.
1166
1167dirty_background_ratio
1168----------------------
1169
1170Contains, as a percentage of total system memory, the number of pages at which
1171the pdflush background writeback daemon will start writing out dirty data.
1172
1173dirty_ratio
1174-----------------
1175
1176Contains, as a percentage of total system memory, the number of pages at which
1177a process which is generating disk writes will itself start writing out dirty
1178data.
1179
1180dirty_writeback_centisecs
1181-------------------------
1182
1183The pdflush writeback daemons will periodically wake up and write `old' data
1184out to disk. This tunable expresses the interval between those wakeups, in
1185100'ths of a second.
1186
1187Setting this to zero disables periodic writeback altogether.
1188
1189dirty_expire_centisecs
1190----------------------
1191
1192This tunable is used to define when dirty data is old enough to be eligible
1193for writeout by the pdflush daemons. It is expressed in 100'ths of a second.
1194Data which has been dirty in-memory for longer than this interval will be
1195written out next time a pdflush daemon wakes up.
1196
1197legacy_va_layout
1198----------------
1199
1200If non-zero, this sysctl disables the new 32-bit mmap mmap layout - the kernel
1201will use the legacy (2.4) layout for all processes.
1202
1203lower_zone_protection
1204---------------------
1205
1206For some specialised workloads on highmem machines it is dangerous for
1207the kernel to allow process memory to be allocated from the "lowmem"
1208zone. This is because that memory could then be pinned via the mlock()
1209system call, or by unavailability of swapspace.
1210
1211And on large highmem machines this lack of reclaimable lowmem memory
1212can be fatal.
1213
1214So the Linux page allocator has a mechanism which prevents allocations
1215which _could_ use highmem from using too much lowmem. This means that
1216a certain amount of lowmem is defended from the possibility of being
1217captured into pinned user memory.
1218
1219(The same argument applies to the old 16 megabyte ISA DMA region. This
1220mechanism will also defend that region from allocations which could use
1221highmem or lowmem).
1222
1223The `lower_zone_protection' tunable determines how aggressive the kernel is
1224in defending these lower zones. The default value is zero - no
1225protection at all.
1226
1227If you have a machine which uses highmem or ISA DMA and your
1228applications are using mlock(), or if you are running with no swap then
1229you probably should increase the lower_zone_protection setting.
1230
1231The units of this tunable are fairly vague. It is approximately equal
Matt LaPlante4ae0edc2006-11-30 04:58:40 +01001232to "megabytes," so setting lower_zone_protection=100 will protect around 100
Linus Torvalds1da177e2005-04-16 15:20:36 -07001233megabytes of the lowmem zone from user allocations. It will also make
Matt LaPlante4ae0edc2006-11-30 04:58:40 +01001234those 100 megabytes unavailable for use by applications and by
Linus Torvalds1da177e2005-04-16 15:20:36 -07001235pagecache, so there is a cost.
1236
1237The effects of this tunable may be observed by monitoring
1238/proc/meminfo:LowFree. Write a single huge file and observe the point
1239at which LowFree ceases to fall.
1240
1241A reasonable value for lower_zone_protection is 100.
1242
1243page-cluster
1244------------
1245
1246page-cluster controls the number of pages which are written to swap in
1247a single attempt. The swap I/O size.
1248
1249It is a logarithmic value - setting it to zero means "1 page", setting
1250it to 1 means "2 pages", setting it to 2 means "4 pages", etc.
1251
1252The default value is three (eight pages at a time). There may be some
1253small benefits in tuning this to a different value if your workload is
1254swap-intensive.
1255
1256overcommit_memory
1257-----------------
1258
Chuck Ebbertaf97c722005-09-09 13:10:15 -07001259Controls overcommit of system memory, possibly allowing processes
1260to allocate (but not use) more memory than is actually available.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001261
Chuck Ebbertaf97c722005-09-09 13:10:15 -07001262
12630 - Heuristic overcommit handling. Obvious overcommits of
1264 address space are refused. Used for a typical system. It
1265 ensures a seriously wild allocation fails while allowing
1266 overcommit to reduce swap usage. root is allowed to
Matt LaPlante53cb4722006-10-03 22:55:17 +02001267 allocate slightly more memory in this mode. This is the
Chuck Ebbertaf97c722005-09-09 13:10:15 -07001268 default.
1269
12701 - Always overcommit. Appropriate for some scientific
1271 applications.
1272
12732 - Don't overcommit. The total address space commit
1274 for the system is not permitted to exceed swap plus a
1275 configurable percentage (default is 50) of physical RAM.
1276 Depending on the percentage you use, in most situations
1277 this means a process will not be killed while attempting
1278 to use already-allocated memory but will receive errors
1279 on memory allocation as appropriate.
1280
1281overcommit_ratio
1282----------------
1283
1284Percentage of physical memory size to include in overcommit calculations
1285(see above.)
1286
1287Memory allocation limit = swapspace + physmem * (overcommit_ratio / 100)
1288
1289 swapspace = total size of all swap areas
1290 physmem = size of physical memory in system
Linus Torvalds1da177e2005-04-16 15:20:36 -07001291
1292nr_hugepages and hugetlb_shm_group
1293----------------------------------
1294
1295nr_hugepages configures number of hugetlb page reserved for the system.
1296
1297hugetlb_shm_group contains group id that is allowed to create SysV shared
1298memory segment using hugetlb page.
1299
1300laptop_mode
1301-----------
1302
1303laptop_mode is a knob that controls "laptop mode". All the things that are
1304controlled by this knob are discussed in Documentation/laptop-mode.txt.
1305
1306block_dump
1307----------
1308
1309block_dump enables block I/O debugging when set to a nonzero value. More
1310information on block I/O debugging is in Documentation/laptop-mode.txt.
1311
1312swap_token_timeout
1313------------------
1314
1315This file contains valid hold time of swap out protection token. The Linux
1316VM has token based thrashing control mechanism and uses the token to prevent
1317unnecessary page faults in thrashing situation. The unit of the value is
1318second. The value would be useful to tune thrashing behavior.
1319
Andrew Morton9d0243b2006-01-08 01:00:39 -08001320drop_caches
1321-----------
1322
1323Writing to this will cause the kernel to drop clean caches, dentries and
1324inodes from memory, causing that memory to become free.
1325
1326To free pagecache:
1327 echo 1 > /proc/sys/vm/drop_caches
1328To free dentries and inodes:
1329 echo 2 > /proc/sys/vm/drop_caches
1330To free pagecache, dentries and inodes:
1331 echo 3 > /proc/sys/vm/drop_caches
1332
1333As this is a non-destructive operation and dirty objects are not freeable, the
1334user should run `sync' first.
1335
1336
Linus Torvalds1da177e2005-04-16 15:20:36 -070013372.5 /proc/sys/dev - Device specific parameters
1338----------------------------------------------
1339
1340Currently there is only support for CDROM drives, and for those, there is only
1341one read-only file containing information about the CD-ROM drives attached to
1342the system:
1343
1344 >cat /proc/sys/dev/cdrom/info
1345 CD-ROM information, Id: cdrom.c 2.55 1999/04/25
1346
1347 drive name: sr0 hdb
1348 drive speed: 32 40
1349 drive # of slots: 1 0
1350 Can close tray: 1 1
1351 Can open tray: 1 1
1352 Can lock tray: 1 1
1353 Can change speed: 1 1
1354 Can select disk: 0 1
1355 Can read multisession: 1 1
1356 Can read MCN: 1 1
1357 Reports media changed: 1 1
1358 Can play audio: 1 1
1359
1360
1361You see two drives, sr0 and hdb, along with a list of their features.
1362
13632.6 /proc/sys/sunrpc - Remote procedure calls
1364---------------------------------------------
1365
1366This directory contains four files, which enable or disable debugging for the
1367RPC functions NFS, NFS-daemon, RPC and NLM. The default values are 0. They can
1368be set to one to turn debugging on. (The default value is 0 for each)
1369
13702.7 /proc/sys/net - Networking stuff
1371------------------------------------
1372
1373The interface to the networking parts of the kernel is located in
1374/proc/sys/net. Table 2-3 shows all possible subdirectories. You may see only
1375some of them, depending on your kernel's configuration.
1376
1377
1378Table 2-3: Subdirectories in /proc/sys/net
1379..............................................................................
1380 Directory Content Directory Content
1381 core General parameter appletalk Appletalk protocol
1382 unix Unix domain sockets netrom NET/ROM
1383 802 E802 protocol ax25 AX25
1384 ethernet Ethernet protocol rose X.25 PLP layer
1385 ipv4 IP version 4 x25 X.25 protocol
1386 ipx IPX token-ring IBM token ring
1387 bridge Bridging decnet DEC net
1388 ipv6 IP version 6
1389..............................................................................
1390
1391We will concentrate on IP networking here. Since AX15, X.25, and DEC Net are
1392only minor players in the Linux world, we'll skip them in this chapter. You'll
1393find some short info on Appletalk and IPX further on in this chapter. Review
1394the online documentation and the kernel source to get a detailed view of the
1395parameters for those protocols. In this section we'll discuss the
1396subdirectories printed in bold letters in the table above. As default values
1397are suitable for most needs, there is no need to change these values.
1398
1399/proc/sys/net/core - Network core options
1400-----------------------------------------
1401
1402rmem_default
1403------------
1404
1405The default setting of the socket receive buffer in bytes.
1406
1407rmem_max
1408--------
1409
1410The maximum receive socket buffer size in bytes.
1411
1412wmem_default
1413------------
1414
1415The default setting (in bytes) of the socket send buffer.
1416
1417wmem_max
1418--------
1419
1420The maximum send socket buffer size in bytes.
1421
1422message_burst and message_cost
1423------------------------------
1424
1425These parameters are used to limit the warning messages written to the kernel
1426log from the networking code. They enforce a rate limit to make a
1427denial-of-service attack impossible. A higher message_cost factor, results in
1428fewer messages that will be written. Message_burst controls when messages will
1429be dropped. The default settings limit warning messages to one every five
1430seconds.
1431
Stephen Hemmingera2a316f2007-03-08 20:41:08 -08001432warnings
1433--------
1434
1435This controls console messages from the networking stack that can occur because
1436of problems on the network like duplicate address or bad checksums. Normally,
1437this should be enabled, but if the problem persists the messages can be
1438disabled.
1439
1440
Linus Torvalds1da177e2005-04-16 15:20:36 -07001441netdev_max_backlog
1442------------------
1443
1444Maximum number of packets, queued on the INPUT side, when the interface
1445receives packets faster than kernel can process them.
1446
1447optmem_max
1448----------
1449
1450Maximum ancillary buffer size allowed per socket. Ancillary data is a sequence
1451of struct cmsghdr structures with appended data.
1452
1453/proc/sys/net/unix - Parameters for Unix domain sockets
1454-------------------------------------------------------
1455
1456There are only two files in this subdirectory. They control the delays for
1457deleting and destroying socket descriptors.
1458
14592.8 /proc/sys/net/ipv4 - IPV4 settings
1460--------------------------------------
1461
1462IP version 4 is still the most used protocol in Unix networking. It will be
1463replaced by IP version 6 in the next couple of years, but for the moment it's
1464the de facto standard for the internet and is used in most networking
1465environments around the world. Because of the importance of this protocol,
1466we'll have a deeper look into the subtree controlling the behavior of the IPv4
1467subsystem of the Linux kernel.
1468
1469Let's start with the entries in /proc/sys/net/ipv4.
1470
1471ICMP settings
1472-------------
1473
1474icmp_echo_ignore_all and icmp_echo_ignore_broadcasts
1475----------------------------------------------------
1476
1477Turn on (1) or off (0), if the kernel should ignore all ICMP ECHO requests, or
1478just those to broadcast and multicast addresses.
1479
1480Please note that if you accept ICMP echo requests with a broadcast/multi\-cast
1481destination address your network may be used as an exploder for denial of
1482service packet flooding attacks to other hosts.
1483
1484icmp_destunreach_rate, icmp_echoreply_rate, icmp_paramprob_rate and icmp_timeexeed_rate
1485---------------------------------------------------------------------------------------
1486
1487Sets limits for sending ICMP packets to specific targets. A value of zero
1488disables all limiting. Any positive value sets the maximum package rate in
1489hundredth of a second (on Intel systems).
1490
1491IP settings
1492-----------
1493
1494ip_autoconfig
1495-------------
1496
1497This file contains the number one if the host received its IP configuration by
1498RARP, BOOTP, DHCP or a similar mechanism. Otherwise it is zero.
1499
1500ip_default_ttl
1501--------------
1502
1503TTL (Time To Live) for IPv4 interfaces. This is simply the maximum number of
1504hops a packet may travel.
1505
1506ip_dynaddr
1507----------
1508
1509Enable dynamic socket address rewriting on interface address change. This is
1510useful for dialup interface with changing IP addresses.
1511
1512ip_forward
1513----------
1514
1515Enable or disable forwarding of IP packages between interfaces. Changing this
1516value resets all other parameters to their default values. They differ if the
1517kernel is configured as host or router.
1518
1519ip_local_port_range
1520-------------------
1521
1522Range of ports used by TCP and UDP to choose the local port. Contains two
1523numbers, the first number is the lowest port, the second number the highest
1524local port. Default is 1024-4999. Should be changed to 32768-61000 for
1525high-usage systems.
1526
1527ip_no_pmtu_disc
1528---------------
1529
1530Global switch to turn path MTU discovery off. It can also be set on a per
1531socket basis by the applications or on a per route basis.
1532
1533ip_masq_debug
1534-------------
1535
1536Enable/disable debugging of IP masquerading.
1537
1538IP fragmentation settings
1539-------------------------
1540
1541ipfrag_high_trash and ipfrag_low_trash
1542--------------------------------------
1543
1544Maximum memory used to reassemble IP fragments. When ipfrag_high_thresh bytes
1545of memory is allocated for this purpose, the fragment handler will toss
1546packets until ipfrag_low_thresh is reached.
1547
1548ipfrag_time
1549-----------
1550
1551Time in seconds to keep an IP fragment in memory.
1552
1553TCP settings
1554------------
1555
1556tcp_ecn
1557-------
1558
Matt LaPlantefa00e7e2006-11-30 04:55:36 +01001559This file controls the use of the ECN bit in the IPv4 headers. This is a new
Linus Torvalds1da177e2005-04-16 15:20:36 -07001560feature about Explicit Congestion Notification, but some routers and firewalls
Matt LaPlantefa00e7e2006-11-30 04:55:36 +01001561block traffic that has this bit set, so it could be necessary to echo 0 to
1562/proc/sys/net/ipv4/tcp_ecn if you want to talk to these sites. For more info
Linus Torvalds1da177e2005-04-16 15:20:36 -07001563you could read RFC2481.
1564
1565tcp_retrans_collapse
1566--------------------
1567
1568Bug-to-bug compatibility with some broken printers. On retransmit, try to send
1569larger packets to work around bugs in certain TCP stacks. Can be turned off by
1570setting it to zero.
1571
1572tcp_keepalive_probes
1573--------------------
1574
1575Number of keep alive probes TCP sends out, until it decides that the
1576connection is broken.
1577
1578tcp_keepalive_time
1579------------------
1580
1581How often TCP sends out keep alive messages, when keep alive is enabled. The
1582default is 2 hours.
1583
1584tcp_syn_retries
1585---------------
1586
1587Number of times initial SYNs for a TCP connection attempt will be
1588retransmitted. Should not be higher than 255. This is only the timeout for
1589outgoing connections, for incoming connections the number of retransmits is
1590defined by tcp_retries1.
1591
1592tcp_sack
1593--------
1594
1595Enable select acknowledgments after RFC2018.
1596
1597tcp_timestamps
1598--------------
1599
1600Enable timestamps as defined in RFC1323.
1601
1602tcp_stdurg
1603----------
1604
1605Enable the strict RFC793 interpretation of the TCP urgent pointer field. The
1606default is to use the BSD compatible interpretation of the urgent pointer
1607pointing to the first byte after the urgent data. The RFC793 interpretation is
1608to have it point to the last byte of urgent data. Enabling this option may
Matt LaPlante2fe0ae72006-10-03 22:50:39 +02001609lead to interoperability problems. Disabled by default.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001610
1611tcp_syncookies
1612--------------
1613
1614Only valid when the kernel was compiled with CONFIG_SYNCOOKIES. Send out
1615syncookies when the syn backlog queue of a socket overflows. This is to ward
1616off the common 'syn flood attack'. Disabled by default.
1617
1618Note that the concept of a socket backlog is abandoned. This means the peer
1619may not receive reliable error messages from an over loaded server with
1620syncookies enabled.
1621
1622tcp_window_scaling
1623------------------
1624
1625Enable window scaling as defined in RFC1323.
1626
1627tcp_fin_timeout
1628---------------
1629
1630The length of time in seconds it takes to receive a final FIN before the
1631socket is always closed. This is strictly a violation of the TCP
1632specification, but required to prevent denial-of-service attacks.
1633
1634tcp_max_ka_probes
1635-----------------
1636
1637Indicates how many keep alive probes are sent per slow timer run. Should not
1638be set too high to prevent bursts.
1639
1640tcp_max_syn_backlog
1641-------------------
1642
1643Length of the per socket backlog queue. Since Linux 2.2 the backlog specified
1644in listen(2) only specifies the length of the backlog queue of already
1645established sockets. When more connection requests arrive Linux starts to drop
1646packets. When syncookies are enabled the packets are still answered and the
1647maximum queue is effectively ignored.
1648
1649tcp_retries1
1650------------
1651
1652Defines how often an answer to a TCP connection request is retransmitted
1653before giving up.
1654
1655tcp_retries2
1656------------
1657
1658Defines how often a TCP packet is retransmitted before giving up.
1659
1660Interface specific settings
1661---------------------------
1662
1663In the directory /proc/sys/net/ipv4/conf you'll find one subdirectory for each
1664interface the system knows about and one directory calls all. Changes in the
1665all subdirectory affect all interfaces, whereas changes in the other
1666subdirectories affect only one interface. All directories have the same
1667entries:
1668
1669accept_redirects
1670----------------
1671
1672This switch decides if the kernel accepts ICMP redirect messages or not. The
1673default is 'yes' if the kernel is configured for a regular host and 'no' for a
1674router configuration.
1675
1676accept_source_route
1677-------------------
1678
1679Should source routed packages be accepted or declined. The default is
1680dependent on the kernel configuration. It's 'yes' for routers and 'no' for
1681hosts.
1682
1683bootp_relay
1684~~~~~~~~~~~
1685
1686Accept packets with source address 0.b.c.d with destinations not to this host
1687as local ones. It is supposed that a BOOTP relay daemon will catch and forward
1688such packets.
1689
1690The default is 0, since this feature is not implemented yet (kernel version
16912.2.12).
1692
1693forwarding
1694----------
1695
1696Enable or disable IP forwarding on this interface.
1697
1698log_martians
1699------------
1700
1701Log packets with source addresses with no known route to kernel log.
1702
1703mc_forwarding
1704-------------
1705
1706Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE and a
1707multicast routing daemon is required.
1708
1709proxy_arp
1710---------
1711
1712Does (1) or does not (0) perform proxy ARP.
1713
1714rp_filter
1715---------
1716
1717Integer value determines if a source validation should be made. 1 means yes, 0
1718means no. Disabled by default, but local/broadcast address spoofing is always
1719on.
1720
1721If you set this to 1 on a router that is the only connection for a network to
1722the net, it will prevent spoofing attacks against your internal networks
1723(external addresses can still be spoofed), without the need for additional
1724firewall rules.
1725
1726secure_redirects
1727----------------
1728
1729Accept ICMP redirect messages only for gateways, listed in default gateway
1730list. Enabled by default.
1731
1732shared_media
1733------------
1734
1735If it is not set the kernel does not assume that different subnets on this
1736device can communicate directly. Default setting is 'yes'.
1737
1738send_redirects
1739--------------
1740
1741Determines whether to send ICMP redirects to other hosts.
1742
1743Routing settings
1744----------------
1745
1746The directory /proc/sys/net/ipv4/route contains several file to control
1747routing issues.
1748
1749error_burst and error_cost
1750--------------------------
1751
1752These parameters are used to limit how many ICMP destination unreachable to
1753send from the host in question. ICMP destination unreachable messages are
Matt LaPlante84eb8d02006-10-03 22:53:09 +02001754sent when we cannot reach the next hop while trying to transmit a packet.
Linus Torvalds1da177e2005-04-16 15:20:36 -07001755It will also print some error messages to kernel logs if someone is ignoring
1756our ICMP redirects. The higher the error_cost factor is, the fewer
1757destination unreachable and error messages will be let through. Error_burst
1758controls when destination unreachable messages and error messages will be
1759dropped. The default settings limit warning messages to five every second.
1760
1761flush
1762-----
1763
1764Writing to this file results in a flush of the routing cache.
1765
1766gc_elasticity, gc_interval, gc_min_interval_ms, gc_timeout, gc_thresh
1767---------------------------------------------------------------------
1768
1769Values to control the frequency and behavior of the garbage collection
1770algorithm for the routing cache. gc_min_interval is deprecated and replaced
1771by gc_min_interval_ms.
1772
1773
1774max_size
1775--------
1776
1777Maximum size of the routing cache. Old entries will be purged once the cache
1778reached has this size.
1779
1780max_delay, min_delay
1781--------------------
1782
1783Delays for flushing the routing cache.
1784
1785redirect_load, redirect_number
1786------------------------------
1787
1788Factors which determine if more ICPM redirects should be sent to a specific
1789host. No redirects will be sent once the load limit or the maximum number of
1790redirects has been reached.
1791
1792redirect_silence
1793----------------
1794
1795Timeout for redirects. After this period redirects will be sent again, even if
1796this has been stopped, because the load or number limit has been reached.
1797
1798Network Neighbor handling
1799-------------------------
1800
1801Settings about how to handle connections with direct neighbors (nodes attached
1802to the same link) can be found in the directory /proc/sys/net/ipv4/neigh.
1803
1804As we saw it in the conf directory, there is a default subdirectory which
1805holds the default values, and one directory for each interface. The contents
1806of the directories are identical, with the single exception that the default
1807settings contain additional options to set garbage collection parameters.
1808
1809In the interface directories you'll find the following entries:
1810
1811base_reachable_time, base_reachable_time_ms
1812-------------------------------------------
1813
1814A base value used for computing the random reachable time value as specified
1815in RFC2461.
1816
1817Expression of base_reachable_time, which is deprecated, is in seconds.
1818Expression of base_reachable_time_ms is in milliseconds.
1819
1820retrans_time, retrans_time_ms
1821-----------------------------
1822
1823The time between retransmitted Neighbor Solicitation messages.
1824Used for address resolution and to determine if a neighbor is
1825unreachable.
1826
1827Expression of retrans_time, which is deprecated, is in 1/100 seconds (for
1828IPv4) or in jiffies (for IPv6).
1829Expression of retrans_time_ms is in milliseconds.
1830
1831unres_qlen
1832----------
1833
1834Maximum queue length for a pending arp request - the number of packets which
1835are accepted from other layers while the ARP address is still resolved.
1836
1837anycast_delay
1838-------------
1839
1840Maximum for random delay of answers to neighbor solicitation messages in
1841jiffies (1/100 sec). Not yet implemented (Linux does not have anycast support
1842yet).
1843
1844ucast_solicit
1845-------------
1846
1847Maximum number of retries for unicast solicitation.
1848
1849mcast_solicit
1850-------------
1851
1852Maximum number of retries for multicast solicitation.
1853
1854delay_first_probe_time
1855----------------------
1856
1857Delay for the first time probe if the neighbor is reachable. (see
1858gc_stale_time)
1859
1860locktime
1861--------
1862
1863An ARP/neighbor entry is only replaced with a new one if the old is at least
1864locktime old. This prevents ARP cache thrashing.
1865
1866proxy_delay
1867-----------
1868
1869Maximum time (real time is random [0..proxytime]) before answering to an ARP
1870request for which we have an proxy ARP entry. In some cases, this is used to
1871prevent network flooding.
1872
1873proxy_qlen
1874----------
1875
1876Maximum queue length of the delayed proxy arp timer. (see proxy_delay).
1877
Matt LaPlante53cb4722006-10-03 22:55:17 +02001878app_solicit
Linus Torvalds1da177e2005-04-16 15:20:36 -07001879----------
1880
1881Determines the number of requests to send to the user level ARP daemon. Use 0
1882to turn off.
1883
1884gc_stale_time
1885-------------
1886
1887Determines how often to check for stale ARP entries. After an ARP entry is
1888stale it will be resolved again (which is useful when an IP address migrates
1889to another machine). When ucast_solicit is greater than 0 it first tries to
1890send an ARP packet directly to the known host When that fails and
1891mcast_solicit is greater than 0, an ARP request is broadcasted.
1892
18932.9 Appletalk
1894-------------
1895
1896The /proc/sys/net/appletalk directory holds the Appletalk configuration data
1897when Appletalk is loaded. The configurable parameters are:
1898
1899aarp-expiry-time
1900----------------
1901
1902The amount of time we keep an ARP entry before expiring it. Used to age out
1903old hosts.
1904
1905aarp-resolve-time
1906-----------------
1907
1908The amount of time we will spend trying to resolve an Appletalk address.
1909
1910aarp-retransmit-limit
1911---------------------
1912
1913The number of times we will retransmit a query before giving up.
1914
1915aarp-tick-time
1916--------------
1917
1918Controls the rate at which expires are checked.
1919
1920The directory /proc/net/appletalk holds the list of active Appletalk sockets
1921on a machine.
1922
1923The fields indicate the DDP type, the local address (in network:node format)
1924the remote address, the size of the transmit pending queue, the size of the
1925received queue (bytes waiting for applications to read) the state and the uid
1926owning the socket.
1927
1928/proc/net/atalk_iface lists all the interfaces configured for appletalk.It
1929shows the name of the interface, its Appletalk address, the network range on
1930that address (or network number for phase 1 networks), and the status of the
1931interface.
1932
1933/proc/net/atalk_route lists each known network route. It lists the target
1934(network) that the route leads to, the router (may be directly connected), the
1935route flags, and the device the route is using.
1936
19372.10 IPX
1938--------
1939
1940The IPX protocol has no tunable values in proc/sys/net.
1941
1942The IPX protocol does, however, provide proc/net/ipx. This lists each IPX
1943socket giving the local and remote addresses in Novell format (that is
1944network:node:port). In accordance with the strange Novell tradition,
1945everything but the port is in hex. Not_Connected is displayed for sockets that
1946are not tied to a specific remote address. The Tx and Rx queue sizes indicate
1947the number of bytes pending for transmission and reception. The state
1948indicates the state the socket is in and the uid is the owning uid of the
1949socket.
1950
1951The /proc/net/ipx_interface file lists all IPX interfaces. For each interface
1952it gives the network number, the node number, and indicates if the network is
1953the primary network. It also indicates which device it is bound to (or
1954Internal for internal networks) and the Frame Type if appropriate. Linux
1955supports 802.3, 802.2, 802.2 SNAP and DIX (Blue Book) ethernet framing for
1956IPX.
1957
1958The /proc/net/ipx_route table holds a list of IPX routes. For each route it
1959gives the destination network, the router node (or Directly) and the network
1960address of the router (or Connected) for internal networks.
1961
19622.11 /proc/sys/fs/mqueue - POSIX message queues filesystem
1963----------------------------------------------------------
1964
1965The "mqueue" filesystem provides the necessary kernel features to enable the
1966creation of a user space library that implements the POSIX message queues
1967API (as noted by the MSG tag in the POSIX 1003.1-2001 version of the System
1968Interfaces specification.)
1969
1970The "mqueue" filesystem contains values for determining/setting the amount of
1971resources used by the file system.
1972
1973/proc/sys/fs/mqueue/queues_max is a read/write file for setting/getting the
1974maximum number of message queues allowed on the system.
1975
1976/proc/sys/fs/mqueue/msg_max is a read/write file for setting/getting the
1977maximum number of messages in a queue value. In fact it is the limiting value
1978for another (user) limit which is set in mq_open invocation. This attribute of
1979a queue must be less or equal then msg_max.
1980
1981/proc/sys/fs/mqueue/msgsize_max is a read/write file for setting/getting the
1982maximum message size value (it is every message queue's attribute set during
1983its creation).
1984
Jan-Frode Myklebustd7ff0db2006-09-29 01:59:45 -070019852.12 /proc/<pid>/oom_adj - Adjust the oom-killer score
1986------------------------------------------------------
1987
1988This file can be used to adjust the score used to select which processes
1989should be killed in an out-of-memory situation. Giving it a high score will
1990increase the likelihood of this process being killed by the oom-killer. Valid
1991values are in the range -16 to +15, plus the special value -17, which disables
1992oom-killing altogether for this process.
1993
19942.13 /proc/<pid>/oom_score - Display current oom-killer score
1995-------------------------------------------------------------
1996
1997------------------------------------------------------------------------------
1998This file can be used to check the current score used by the oom-killer is for
1999any given <pid>. Use it together with /proc/<pid>/oom_adj to tune which
2000process should be killed in an out-of-memory situation.
Linus Torvalds1da177e2005-04-16 15:20:36 -07002001
2002------------------------------------------------------------------------------
2003Summary
2004------------------------------------------------------------------------------
2005Certain aspects of kernel behavior can be modified at runtime, without the
2006need to recompile the kernel, or even to reboot the system. The files in the
2007/proc/sys tree can not only be read, but also modified. You can use the echo
2008command to write value into these files, thereby changing the default settings
2009of the kernel.
2010------------------------------------------------------------------------------
Roland Kletzingf9c99462007-03-05 00:30:54 -08002011
20122.14 /proc/<pid>/io - Display the IO accounting fields
2013-------------------------------------------------------
2014
2015This file contains IO statistics for each running process
2016
2017Example
2018-------
2019
2020test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
2021[1] 3828
2022
2023test:/tmp # cat /proc/3828/io
2024rchar: 323934931
2025wchar: 323929600
2026syscr: 632687
2027syscw: 632675
2028read_bytes: 0
2029write_bytes: 323932160
2030cancelled_write_bytes: 0
2031
2032
2033Description
2034-----------
2035
2036rchar
2037-----
2038
2039I/O counter: chars read
2040The number of bytes which this task has caused to be read from storage. This
2041is simply the sum of bytes which this process passed to read() and pread().
2042It includes things like tty IO and it is unaffected by whether or not actual
2043physical disk IO was required (the read might have been satisfied from
2044pagecache)
2045
2046
2047wchar
2048-----
2049
2050I/O counter: chars written
2051The number of bytes which this task has caused, or shall cause to be written
2052to disk. Similar caveats apply here as with rchar.
2053
2054
2055syscr
2056-----
2057
2058I/O counter: read syscalls
2059Attempt to count the number of read I/O operations, i.e. syscalls like read()
2060and pread().
2061
2062
2063syscw
2064-----
2065
2066I/O counter: write syscalls
2067Attempt to count the number of write I/O operations, i.e. syscalls like
2068write() and pwrite().
2069
2070
2071read_bytes
2072----------
2073
2074I/O counter: bytes read
2075Attempt to count the number of bytes which this process really did cause to
2076be fetched from the storage layer. Done at the submit_bio() level, so it is
2077accurate for block-backed filesystems. <please add status regarding NFS and
2078CIFS at a later time>
2079
2080
2081write_bytes
2082-----------
2083
2084I/O counter: bytes written
2085Attempt to count the number of bytes which this process caused to be sent to
2086the storage layer. This is done at page-dirtying time.
2087
2088
2089cancelled_write_bytes
2090---------------------
2091
2092The big inaccuracy here is truncate. If a process writes 1MB to a file and
2093then deletes the file, it will in fact perform no writeout. But it will have
2094been accounted as having caused 1MB of write.
2095In other words: The number of bytes which this process caused to not happen,
2096by truncating pagecache. A task can cause "negative" IO too. If this task
2097truncates some dirty pagecache, some IO which another task has been accounted
2098for (in it's write_bytes) will not be happening. We _could_ just subtract that
2099from the truncating task's write_bytes, but there is information loss in doing
2100that.
2101
2102
2103Note
2104----
2105
2106At its current implementation state, this is a bit racy on 32-bit machines: if
2107process A reads process B's /proc/pid/io while process B is updating one of
2108those 64-bit counters, process A could see an intermediate result.
2109
2110
2111More information about this can be found within the taskstats documentation in
2112Documentation/accounting.
2113
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