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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
42
43------------------------------------------------------------------------------
44Preface
45------------------------------------------------------------------------------
46
470.1 Introduction/Credits
48------------------------
49
50This documentation is part of a soon (or so we hope) to be released book on
51the SuSE Linux distribution. As there is no complete documentation for the
52/proc file system and we've used many freely available sources to write these
53chapters, it seems only fair to give the work back to the Linux community.
54This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm
55afraid it's still far from complete, but we hope it will be useful. As far as
56we know, it is the first 'all-in-one' document about the /proc file system. It
57is focused on the Intel x86 hardware, so if you are looking for PPC, ARM,
58SPARC, AXP, etc., features, you probably won't find what you are looking for.
59It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
60additions and patches are welcome and will be added to this document if you
61mail them to Bodo.
62
63We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
64other people for help compiling this documentation. We'd also like to extend a
65special thank you to Andi Kleen for documentation, which we relied on heavily
66to create this document, as well as the additional information he provided.
67Thanks to everybody else who contributed source or docs to the Linux kernel
68and helped create a great piece of software... :)
69
70If you have any comments, corrections or additions, please don't hesitate to
71contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this
72document.
73
74The latest version of this document is available online at
75http://skaro.nightcrawler.com/~bb/Docs/Proc as HTML version.
76
77If the above direction does not works for you, ypu could try the kernel
78mailing list at linux-kernel@vger.kernel.org and/or try to reach me at
79comandante@zaralinux.com.
80
810.2 Legal Stuff
82---------------
83
84We don't guarantee the correctness of this document, and if you come to us
85complaining about how you screwed up your system because of incorrect
86documentation, we won't feel responsible...
87
88------------------------------------------------------------------------------
89CHAPTER 1: COLLECTING SYSTEM INFORMATION
90------------------------------------------------------------------------------
91
92------------------------------------------------------------------------------
93In This Chapter
94------------------------------------------------------------------------------
95* Investigating the properties of the pseudo file system /proc and its
96 ability to provide information on the running Linux system
97* Examining /proc's structure
98* Uncovering various information about the kernel and the processes running
99 on the system
100------------------------------------------------------------------------------
101
102
103The proc file system acts as an interface to internal data structures in the
104kernel. It can be used to obtain information about the system and to change
105certain kernel parameters at runtime (sysctl).
106
107First, we'll take a look at the read-only parts of /proc. In Chapter 2, we
108show you how you can use /proc/sys to change settings.
109
1101.1 Process-Specific Subdirectories
111-----------------------------------
112
113The directory /proc contains (among other things) one subdirectory for each
114process running on the system, which is named after the process ID (PID).
115
116The link self points to the process reading the file system. Each process
117subdirectory has the entries listed in Table 1-1.
118
119
120Table 1-1: Process specific entries in /proc
121..............................................................................
122 File Content
123 cmdline Command line arguments
124 cpu Current and last cpu in wich it was executed (2.4)(smp)
125 cwd Link to the current working directory
126 environ Values of environment variables
127 exe Link to the executable of this process
128 fd Directory, which contains all file descriptors
129 maps Memory maps to executables and library files (2.4)
130 mem Memory held by this process
131 root Link to the root directory of this process
132 stat Process status
133 statm Process memory status information
134 status Process status in human readable form
135 wchan If CONFIG_KALLSYMS is set, a pre-decoded wchan
136..............................................................................
137
138For example, to get the status information of a process, all you have to do is
139read the file /proc/PID/status:
140
141 >cat /proc/self/status
142 Name: cat
143 State: R (running)
144 Pid: 5452
145 PPid: 743
146 TracerPid: 0 (2.4)
147 Uid: 501 501 501 501
148 Gid: 100 100 100 100
149 Groups: 100 14 16
150 VmSize: 1112 kB
151 VmLck: 0 kB
152 VmRSS: 348 kB
153 VmData: 24 kB
154 VmStk: 12 kB
155 VmExe: 8 kB
156 VmLib: 1044 kB
157 SigPnd: 0000000000000000
158 SigBlk: 0000000000000000
159 SigIgn: 0000000000000000
160 SigCgt: 0000000000000000
161 CapInh: 00000000fffffeff
162 CapPrm: 0000000000000000
163 CapEff: 0000000000000000
164
165
166This shows you nearly the same information you would get if you viewed it with
167the ps command. In fact, ps uses the proc file system to obtain its
168information. The statm file contains more detailed information about the
169process memory usage. Its seven fields are explained in Table 1-2.
170
171
172Table 1-2: Contents of the statm files (as of 2.6.8-rc3)
173..............................................................................
174 Field Content
175 size total program size (pages) (same as VmSize in status)
176 resident size of memory portions (pages) (same as VmRSS in status)
177 shared number of pages that are shared (i.e. backed by a file)
178 trs number of pages that are 'code' (not including libs; broken,
179 includes data segment)
180 lrs number of pages of library (always 0 on 2.6)
181 drs number of pages of data/stack (including libs; broken,
182 includes library text)
183 dt number of dirty pages (always 0 on 2.6)
184..............................................................................
185
1861.2 Kernel data
187---------------
188
189Similar to the process entries, the kernel data files give information about
190the running kernel. The files used to obtain this information are contained in
191/proc and are listed in Table 1-3. Not all of these will be present in your
192system. It depends on the kernel configuration and the loaded modules, which
193files are there, and which are missing.
194
195Table 1-3: Kernel info in /proc
196..............................................................................
197 File Content
198 apm Advanced power management info
199 buddyinfo Kernel memory allocator information (see text) (2.5)
200 bus Directory containing bus specific information
201 cmdline Kernel command line
202 cpuinfo Info about the CPU
203 devices Available devices (block and character)
204 dma Used DMS channels
205 filesystems Supported filesystems
206 driver Various drivers grouped here, currently rtc (2.4)
207 execdomains Execdomains, related to security (2.4)
208 fb Frame Buffer devices (2.4)
209 fs File system parameters, currently nfs/exports (2.4)
210 ide Directory containing info about the IDE subsystem
211 interrupts Interrupt usage
212 iomem Memory map (2.4)
213 ioports I/O port usage
214 irq Masks for irq to cpu affinity (2.4)(smp?)
215 isapnp ISA PnP (Plug&Play) Info (2.4)
216 kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
217 kmsg Kernel messages
218 ksyms Kernel symbol table
219 loadavg Load average of last 1, 5 & 15 minutes
220 locks Kernel locks
221 meminfo Memory info
222 misc Miscellaneous
223 modules List of loaded modules
224 mounts Mounted filesystems
225 net Networking info (see text)
226 partitions Table of partitions known to the system
227 pci Depreciated info of PCI bus (new way -> /proc/bus/pci/,
228 decoupled by lspci (2.4)
229 rtc Real time clock
230 scsi SCSI info (see text)
231 slabinfo Slab pool info
232 stat Overall statistics
233 swaps Swap space utilization
234 sys See chapter 2
235 sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4)
236 tty Info of tty drivers
237 uptime System uptime
238 version Kernel version
239 video bttv info of video resources (2.4)
240..............................................................................
241
242You can, for example, check which interrupts are currently in use and what
243they are used for by looking in the file /proc/interrupts:
244
245 > cat /proc/interrupts
246 CPU0
247 0: 8728810 XT-PIC timer
248 1: 895 XT-PIC keyboard
249 2: 0 XT-PIC cascade
250 3: 531695 XT-PIC aha152x
251 4: 2014133 XT-PIC serial
252 5: 44401 XT-PIC pcnet_cs
253 8: 2 XT-PIC rtc
254 11: 8 XT-PIC i82365
255 12: 182918 XT-PIC PS/2 Mouse
256 13: 1 XT-PIC fpu
257 14: 1232265 XT-PIC ide0
258 15: 7 XT-PIC ide1
259 NMI: 0
260
261In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
262output of a SMP machine):
263
264 > cat /proc/interrupts
265
266 CPU0 CPU1
267 0: 1243498 1214548 IO-APIC-edge timer
268 1: 8949 8958 IO-APIC-edge keyboard
269 2: 0 0 XT-PIC cascade
270 5: 11286 10161 IO-APIC-edge soundblaster
271 8: 1 0 IO-APIC-edge rtc
272 9: 27422 27407 IO-APIC-edge 3c503
273 12: 113645 113873 IO-APIC-edge PS/2 Mouse
274 13: 0 0 XT-PIC fpu
275 14: 22491 24012 IO-APIC-edge ide0
276 15: 2183 2415 IO-APIC-edge ide1
277 17: 30564 30414 IO-APIC-level eth0
278 18: 177 164 IO-APIC-level bttv
279 NMI: 2457961 2457959
280 LOC: 2457882 2457881
281 ERR: 2155
282
283NMI is incremented in this case because every timer interrupt generates a NMI
284(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
285
286LOC is the local interrupt counter of the internal APIC of every CPU.
287
288ERR is incremented in the case of errors in the IO-APIC bus (the bus that
289connects the CPUs in a SMP system. This means that an error has been detected,
290the IO-APIC automatically retry the transmission, so it should not be a big
291problem, but you should read the SMP-FAQ.
292
293In this context it could be interesting to note the new irq directory in 2.4.
294It could be used to set IRQ to CPU affinity, this means that you can "hook" an
295IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
296irq subdir is one subdir for each IRQ, and one file; prof_cpu_mask
297
298For example
299 > ls /proc/irq/
300 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask
301 1 11 13 15 17 19 3 5 7 9
302 > ls /proc/irq/0/
303 smp_affinity
304
305The contents of the prof_cpu_mask file and each smp_affinity file for each IRQ
306is the same by default:
307
308 > cat /proc/irq/0/smp_affinity
309 ffffffff
310
311It's a bitmask, in wich you can specify wich CPUs can handle the IRQ, you can
312set it by doing:
313
314 > echo 1 > /proc/irq/prof_cpu_mask
315
316This means that only the first CPU will handle the IRQ, but you can also echo 5
317wich means that only the first and fourth CPU can handle the IRQ.
318
319The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
320between all the CPUs which are allowed to handle it. As usual the kernel has
321more info than you and does a better job than you, so the defaults are the
322best choice for almost everyone.
323
324There are three more important subdirectories in /proc: net, scsi, and sys.
325The general rule is that the contents, or even the existence of these
326directories, depend on your kernel configuration. If SCSI is not enabled, the
327directory scsi may not exist. The same is true with the net, which is there
328only when networking support is present in the running kernel.
329
330The slabinfo file gives information about memory usage at the slab level.
331Linux uses slab pools for memory management above page level in version 2.2.
332Commonly used objects have their own slab pool (such as network buffers,
333directory cache, and so on).
334
335..............................................................................
336
337> cat /proc/buddyinfo
338
339Node 0, zone DMA 0 4 5 4 4 3 ...
340Node 0, zone Normal 1 0 0 1 101 8 ...
341Node 0, zone HighMem 2 0 0 1 1 0 ...
342
343Memory fragmentation is a problem under some workloads, and buddyinfo is a
344useful tool for helping diagnose these problems. Buddyinfo will give you a
345clue as to how big an area you can safely allocate, or why a previous
346allocation failed.
347
348Each column represents the number of pages of a certain order which are
349available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
350ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
351available in ZONE_NORMAL, etc...
352
353..............................................................................
354
355meminfo:
356
357Provides information about distribution and utilization of memory. This
358varies by architecture and compile options. The following is from a
35916GB PIII, which has highmem enabled. You may not have all of these fields.
360
361> cat /proc/meminfo
362
363
364MemTotal: 16344972 kB
365MemFree: 13634064 kB
366Buffers: 3656 kB
367Cached: 1195708 kB
368SwapCached: 0 kB
369Active: 891636 kB
370Inactive: 1077224 kB
371HighTotal: 15597528 kB
372HighFree: 13629632 kB
373LowTotal: 747444 kB
374LowFree: 4432 kB
375SwapTotal: 0 kB
376SwapFree: 0 kB
377Dirty: 968 kB
378Writeback: 0 kB
379Mapped: 280372 kB
380Slab: 684068 kB
381CommitLimit: 7669796 kB
382Committed_AS: 100056 kB
383PageTables: 24448 kB
384VmallocTotal: 112216 kB
385VmallocUsed: 428 kB
386VmallocChunk: 111088 kB
387
388 MemTotal: Total usable ram (i.e. physical ram minus a few reserved
389 bits and the kernel binary code)
390 MemFree: The sum of LowFree+HighFree
391 Buffers: Relatively temporary storage for raw disk blocks
392 shouldn't get tremendously large (20MB or so)
393 Cached: in-memory cache for files read from the disk (the
394 pagecache). Doesn't include SwapCached
395 SwapCached: Memory that once was swapped out, is swapped back in but
396 still also is in the swapfile (if memory is needed it
397 doesn't need to be swapped out AGAIN because it is already
398 in the swapfile. This saves I/O)
399 Active: Memory that has been used more recently and usually not
400 reclaimed unless absolutely necessary.
401 Inactive: Memory which has been less recently used. It is more
402 eligible to be reclaimed for other purposes
403 HighTotal:
404 HighFree: Highmem is all memory above ~860MB of physical memory
405 Highmem areas are for use by userspace programs, or
406 for the pagecache. The kernel must use tricks to access
407 this memory, making it slower to access than lowmem.
408 LowTotal:
409 LowFree: Lowmem is memory which can be used for everything that
410 highmem can be used for, but it is also availble for the
411 kernel's use for its own data structures. Among many
412 other things, it is where everything from the Slab is
413 allocated. Bad things happen when you're out of lowmem.
414 SwapTotal: total amount of swap space available
415 SwapFree: Memory which has been evicted from RAM, and is temporarily
416 on the disk
417 Dirty: Memory which is waiting to get written back to the disk
418 Writeback: Memory which is actively being written back to the disk
419 Mapped: files which have been mmaped, such as libraries
420 Slab: in-kernel data structures cache
421 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
422 this is the total amount of memory currently available to
423 be allocated on the system. This limit is only adhered to
424 if strict overcommit accounting is enabled (mode 2 in
425 'vm.overcommit_memory').
426 The CommitLimit is calculated with the following formula:
427 CommitLimit = ('vm.overcommit_ratio' * Physical RAM) + Swap
428 For example, on a system with 1G of physical RAM and 7G
429 of swap with a `vm.overcommit_ratio` of 30 it would
430 yield a CommitLimit of 7.3G.
431 For more details, see the memory overcommit documentation
432 in vm/overcommit-accounting.
433Committed_AS: The amount of memory presently allocated on the system.
434 The committed memory is a sum of all of the memory which
435 has been allocated by processes, even if it has not been
436 "used" by them as of yet. A process which malloc()'s 1G
437 of memory, but only touches 300M of it will only show up
438 as using 300M of memory even if it has the address space
439 allocated for the entire 1G. This 1G is memory which has
440 been "committed" to by the VM and can be used at any time
441 by the allocating application. With strict overcommit
442 enabled on the system (mode 2 in 'vm.overcommit_memory'),
443 allocations which would exceed the CommitLimit (detailed
444 above) will not be permitted. This is useful if one needs
445 to guarantee that processes will not fail due to lack of
446 memory once that memory has been successfully allocated.
447 PageTables: amount of memory dedicated to the lowest level of page
448 tables.
449VmallocTotal: total size of vmalloc memory area
450 VmallocUsed: amount of vmalloc area which is used
451VmallocChunk: largest contigious block of vmalloc area which is free
452
453
4541.3 IDE devices in /proc/ide
455----------------------------
456
457The subdirectory /proc/ide contains information about all IDE devices of which
458the kernel is aware. There is one subdirectory for each IDE controller, the
459file drivers and a link for each IDE device, pointing to the device directory
460in the controller specific subtree.
461
462The file drivers contains general information about the drivers used for the
463IDE devices:
464
465 > cat /proc/ide/drivers
466 ide-cdrom version 4.53
467 ide-disk version 1.08
468
469More detailed information can be found in the controller specific
470subdirectories. These are named ide0, ide1 and so on. Each of these
471directories contains the files shown in table 1-4.
472
473
474Table 1-4: IDE controller info in /proc/ide/ide?
475..............................................................................
476 File Content
477 channel IDE channel (0 or 1)
478 config Configuration (only for PCI/IDE bridge)
479 mate Mate name
480 model Type/Chipset of IDE controller
481..............................................................................
482
483Each device connected to a controller has a separate subdirectory in the
484controllers directory. The files listed in table 1-5 are contained in these
485directories.
486
487
488Table 1-5: IDE device information
489..............................................................................
490 File Content
491 cache The cache
492 capacity Capacity of the medium (in 512Byte blocks)
493 driver driver and version
494 geometry physical and logical geometry
495 identify device identify block
496 media media type
497 model device identifier
498 settings device setup
499 smart_thresholds IDE disk management thresholds
500 smart_values IDE disk management values
501..............................................................................
502
503The most interesting file is settings. This file contains a nice overview of
504the drive parameters:
505
506 # cat /proc/ide/ide0/hda/settings
507 name value min max mode
508 ---- ----- --- --- ----
509 bios_cyl 526 0 65535 rw
510 bios_head 255 0 255 rw
511 bios_sect 63 0 63 rw
512 breada_readahead 4 0 127 rw
513 bswap 0 0 1 r
514 file_readahead 72 0 2097151 rw
515 io_32bit 0 0 3 rw
516 keepsettings 0 0 1 rw
517 max_kb_per_request 122 1 127 rw
518 multcount 0 0 8 rw
519 nice1 1 0 1 rw
520 nowerr 0 0 1 rw
521 pio_mode write-only 0 255 w
522 slow 0 0 1 rw
523 unmaskirq 0 0 1 rw
524 using_dma 0 0 1 rw
525
526
5271.4 Networking info in /proc/net
528--------------------------------
529
530The subdirectory /proc/net follows the usual pattern. Table 1-6 shows the
531additional values you get for IP version 6 if you configure the kernel to
532support this. Table 1-7 lists the files and their meaning.
533
534
535Table 1-6: IPv6 info in /proc/net
536..............................................................................
537 File Content
538 udp6 UDP sockets (IPv6)
539 tcp6 TCP sockets (IPv6)
540 raw6 Raw device statistics (IPv6)
541 igmp6 IP multicast addresses, which this host joined (IPv6)
542 if_inet6 List of IPv6 interface addresses
543 ipv6_route Kernel routing table for IPv6
544 rt6_stats Global IPv6 routing tables statistics
545 sockstat6 Socket statistics (IPv6)
546 snmp6 Snmp data (IPv6)
547..............................................................................
548
549
550Table 1-7: Network info in /proc/net
551..............................................................................
552 File Content
553 arp Kernel ARP table
554 dev network devices with statistics
555 dev_mcast the Layer2 multicast groups a device is listening too
556 (interface index, label, number of references, number of bound
557 addresses).
558 dev_stat network device status
559 ip_fwchains Firewall chain linkage
560 ip_fwnames Firewall chain names
561 ip_masq Directory containing the masquerading tables
562 ip_masquerade Major masquerading table
563 netstat Network statistics
564 raw raw device statistics
565 route Kernel routing table
566 rpc Directory containing rpc info
567 rt_cache Routing cache
568 snmp SNMP data
569 sockstat Socket statistics
570 tcp TCP sockets
571 tr_rif Token ring RIF routing table
572 udp UDP sockets
573 unix UNIX domain sockets
574 wireless Wireless interface data (Wavelan etc)
575 igmp IP multicast addresses, which this host joined
576 psched Global packet scheduler parameters.
577 netlink List of PF_NETLINK sockets
578 ip_mr_vifs List of multicast virtual interfaces
579 ip_mr_cache List of multicast routing cache
580..............................................................................
581
582You can use this information to see which network devices are available in
583your system and how much traffic was routed over those devices:
584
585 > cat /proc/net/dev
586 Inter-|Receive |[...
587 face |bytes packets errs drop fifo frame compressed multicast|[...
588 lo: 908188 5596 0 0 0 0 0 0 [...
589 ppp0:15475140 20721 410 0 0 410 0 0 [...
590 eth0: 614530 7085 0 0 0 0 0 1 [...
591
592 ...] Transmit
593 ...] bytes packets errs drop fifo colls carrier compressed
594 ...] 908188 5596 0 0 0 0 0 0
595 ...] 1375103 17405 0 0 0 0 0 0
596 ...] 1703981 5535 0 0 0 3 0 0
597
598In addition, each Channel Bond interface has it's own directory. For
599example, the bond0 device will have a directory called /proc/net/bond0/.
600It will contain information that is specific to that bond, such as the
601current slaves of the bond, the link status of the slaves, and how
602many times the slaves link has failed.
603
6041.5 SCSI info
605-------------
606
607If you have a SCSI host adapter in your system, you'll find a subdirectory
608named after the driver for this adapter in /proc/scsi. You'll also see a list
609of all recognized SCSI devices in /proc/scsi:
610
611 >cat /proc/scsi/scsi
612 Attached devices:
613 Host: scsi0 Channel: 00 Id: 00 Lun: 00
614 Vendor: IBM Model: DGHS09U Rev: 03E0
615 Type: Direct-Access ANSI SCSI revision: 03
616 Host: scsi0 Channel: 00 Id: 06 Lun: 00
617 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04
618 Type: CD-ROM ANSI SCSI revision: 02
619
620
621The directory named after the driver has one file for each adapter found in
622the system. These files contain information about the controller, including
623the used IRQ and the IO address range. The amount of information shown is
624dependent on the adapter you use. The example shows the output for an Adaptec
625AHA-2940 SCSI adapter:
626
627 > cat /proc/scsi/aic7xxx/0
628
629 Adaptec AIC7xxx driver version: 5.1.19/3.2.4
630 Compile Options:
631 TCQ Enabled By Default : Disabled
632 AIC7XXX_PROC_STATS : Disabled
633 AIC7XXX_RESET_DELAY : 5
634 Adapter Configuration:
635 SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
636 Ultra Wide Controller
637 PCI MMAPed I/O Base: 0xeb001000
638 Adapter SEEPROM Config: SEEPROM found and used.
639 Adaptec SCSI BIOS: Enabled
640 IRQ: 10
641 SCBs: Active 0, Max Active 2,
642 Allocated 15, HW 16, Page 255
643 Interrupts: 160328
644 BIOS Control Word: 0x18b6
645 Adapter Control Word: 0x005b
646 Extended Translation: Enabled
647 Disconnect Enable Flags: 0xffff
648 Ultra Enable Flags: 0x0001
649 Tag Queue Enable Flags: 0x0000
650 Ordered Queue Tag Flags: 0x0000
651 Default Tag Queue Depth: 8
652 Tagged Queue By Device array for aic7xxx host instance 0:
653 {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
654 Actual queue depth per device for aic7xxx host instance 0:
655 {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
656 Statistics:
657 (scsi0:0:0:0)
658 Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
659 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
660 Total transfers 160151 (74577 reads and 85574 writes)
661 (scsi0:0:6:0)
662 Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
663 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
664 Total transfers 0 (0 reads and 0 writes)
665
666
6671.6 Parallel port info in /proc/parport
668---------------------------------------
669
670The directory /proc/parport contains information about the parallel ports of
671your system. It has one subdirectory for each port, named after the port
672number (0,1,2,...).
673
674These directories contain the four files shown in Table 1-8.
675
676
677Table 1-8: Files in /proc/parport
678..............................................................................
679 File Content
680 autoprobe Any IEEE-1284 device ID information that has been acquired.
681 devices list of the device drivers using that port. A + will appear by the
682 name of the device currently using the port (it might not appear
683 against any).
684 hardware Parallel port's base address, IRQ line and DMA channel.
685 irq IRQ that parport is using for that port. This is in a separate
686 file to allow you to alter it by writing a new value in (IRQ
687 number or none).
688..............................................................................
689
6901.7 TTY info in /proc/tty
691-------------------------
692
693Information about the available and actually used tty's can be found in the
694directory /proc/tty.You'll find entries for drivers and line disciplines in
695this directory, as shown in Table 1-9.
696
697
698Table 1-9: Files in /proc/tty
699..............................................................................
700 File Content
701 drivers list of drivers and their usage
702 ldiscs registered line disciplines
703 driver/serial usage statistic and status of single tty lines
704..............................................................................
705
706To see which tty's are currently in use, you can simply look into the file
707/proc/tty/drivers:
708
709 > cat /proc/tty/drivers
710 pty_slave /dev/pts 136 0-255 pty:slave
711 pty_master /dev/ptm 128 0-255 pty:master
712 pty_slave /dev/ttyp 3 0-255 pty:slave
713 pty_master /dev/pty 2 0-255 pty:master
714 serial /dev/cua 5 64-67 serial:callout
715 serial /dev/ttyS 4 64-67 serial
716 /dev/tty0 /dev/tty0 4 0 system:vtmaster
717 /dev/ptmx /dev/ptmx 5 2 system
718 /dev/console /dev/console 5 1 system:console
719 /dev/tty /dev/tty 5 0 system:/dev/tty
720 unknown /dev/tty 4 1-63 console
721
722
7231.8 Miscellaneous kernel statistics in /proc/stat
724-------------------------------------------------
725
726Various pieces of information about kernel activity are available in the
727/proc/stat file. All of the numbers reported in this file are aggregates
728since the system first booted. For a quick look, simply cat the file:
729
730 > cat /proc/stat
731 cpu 2255 34 2290 22625563 6290 127 456
732 cpu0 1132 34 1441 11311718 3675 127 438
733 cpu1 1123 0 849 11313845 2614 0 18
734 intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
735 ctxt 1990473
736 btime 1062191376
737 processes 2915
738 procs_running 1
739 procs_blocked 0
740
741The very first "cpu" line aggregates the numbers in all of the other "cpuN"
742lines. These numbers identify the amount of time the CPU has spent performing
743different kinds of work. Time units are in USER_HZ (typically hundredths of a
744second). The meanings of the columns are as follows, from left to right:
745
746- user: normal processes executing in user mode
747- nice: niced processes executing in user mode
748- system: processes executing in kernel mode
749- idle: twiddling thumbs
750- iowait: waiting for I/O to complete
751- irq: servicing interrupts
752- softirq: servicing softirqs
753
754The "intr" line gives counts of interrupts serviced since boot time, for each
755of the possible system interrupts. The first column is the total of all
756interrupts serviced; each subsequent column is the total for that particular
757interrupt.
758
759The "ctxt" line gives the total number of context switches across all CPUs.
760
761The "btime" line gives the time at which the system booted, in seconds since
762the Unix epoch.
763
764The "processes" line gives the number of processes and threads created, which
765includes (but is not limited to) those created by calls to the fork() and
766clone() system calls.
767
768The "procs_running" line gives the number of processes currently running on
769CPUs.
770
771The "procs_blocked" line gives the number of processes currently blocked,
772waiting for I/O to complete.
773
774
775------------------------------------------------------------------------------
776Summary
777------------------------------------------------------------------------------
778The /proc file system serves information about the running system. It not only
779allows access to process data but also allows you to request the kernel status
780by reading files in the hierarchy.
781
782The directory structure of /proc reflects the types of information and makes
783it easy, if not obvious, where to look for specific data.
784------------------------------------------------------------------------------
785
786------------------------------------------------------------------------------
787CHAPTER 2: MODIFYING SYSTEM PARAMETERS
788------------------------------------------------------------------------------
789
790------------------------------------------------------------------------------
791In This Chapter
792------------------------------------------------------------------------------
793* Modifying kernel parameters by writing into files found in /proc/sys
794* Exploring the files which modify certain parameters
795* Review of the /proc/sys file tree
796------------------------------------------------------------------------------
797
798
799A very interesting part of /proc is the directory /proc/sys. This is not only
800a source of information, it also allows you to change parameters within the
801kernel. Be very careful when attempting this. You can optimize your system,
802but you can also cause it to crash. Never alter kernel parameters on a
803production system. Set up a development machine and test to make sure that
804everything works the way you want it to. You may have no alternative but to
805reboot the machine once an error has been made.
806
807To change a value, simply echo the new value into the file. An example is
808given below in the section on the file system data. You need to be root to do
809this. You can create your own boot script to perform this every time your
810system boots.
811
812The files in /proc/sys can be used to fine tune and monitor miscellaneous and
813general things in the operation of the Linux kernel. Since some of the files
814can inadvertently disrupt your system, it is advisable to read both
815documentation and source before actually making adjustments. In any case, be
816very careful when writing to any of these files. The entries in /proc may
817change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
818review the kernel documentation in the directory /usr/src/linux/Documentation.
819This chapter is heavily based on the documentation included in the pre 2.2
820kernels, and became part of it in version 2.2.1 of the Linux kernel.
821
8222.1 /proc/sys/fs - File system data
823-----------------------------------
824
825This subdirectory contains specific file system, file handle, inode, dentry
826and quota information.
827
828Currently, these files are in /proc/sys/fs:
829
830dentry-state
831------------
832
833Status of the directory cache. Since directory entries are dynamically
834allocated and deallocated, this file indicates the current status. It holds
835six values, in which the last two are not used and are always zero. The others
836are listed in table 2-1.
837
838
839Table 2-1: Status files of the directory cache
840..............................................................................
841 File Content
842 nr_dentry Almost always zero
843 nr_unused Number of unused cache entries
844 age_limit
845 in seconds after the entry may be reclaimed, when memory is short
846 want_pages internally
847..............................................................................
848
849dquot-nr and dquot-max
850----------------------
851
852The file dquot-max shows the maximum number of cached disk quota entries.
853
854The file dquot-nr shows the number of allocated disk quota entries and the
855number of free disk quota entries.
856
857If the number of available cached disk quotas is very low and you have a large
858number of simultaneous system users, you might want to raise the limit.
859
860file-nr and file-max
861--------------------
862
863The kernel allocates file handles dynamically, but doesn't free them again at
864this time.
865
866The value in file-max denotes the maximum number of file handles that the
867Linux kernel will allocate. When you get a lot of error messages about running
868out of file handles, you might want to raise this limit. The default value is
86910% of RAM in kilobytes. To change it, just write the new number into the
870file:
871
872 # cat /proc/sys/fs/file-max
873 4096
874 # echo 8192 > /proc/sys/fs/file-max
875 # cat /proc/sys/fs/file-max
876 8192
877
878
879This method of revision is useful for all customizable parameters of the
880kernel - simply echo the new value to the corresponding file.
881
882Historically, the three values in file-nr denoted the number of allocated file
883handles, the number of allocated but unused file handles, and the maximum
884number of file handles. Linux 2.6 always reports 0 as the number of free file
885handles -- this is not an error, it just means that the number of allocated
886file handles exactly matches the number of used file handles.
887
888Attempts to allocate more file descriptors than file-max are reported with
889printk, look for "VFS: file-max limit <number> reached".
890
891inode-state and inode-nr
892------------------------
893
894The file inode-nr contains the first two items from inode-state, so we'll skip
895to that file...
896
897inode-state contains two actual numbers and five dummy values. The numbers
898are nr_inodes and nr_free_inodes (in order of appearance).
899
900nr_inodes
901~~~~~~~~~
902
903Denotes the number of inodes the system has allocated. This number will
904grow and shrink dynamically.
905
906nr_free_inodes
907--------------
908
909Represents the number of free inodes. Ie. The number of inuse inodes is
910(nr_inodes - nr_free_inodes).
911
912super-nr and super-max
913----------------------
914
915Again, super block structures are allocated by the kernel, but not freed. The
916file super-max contains the maximum number of super block handlers, where
917super-nr shows the number of currently allocated ones.
918
919Every mounted file system needs a super block, so if you plan to mount lots of
920file systems, you may want to increase these numbers.
921
922aio-nr and aio-max-nr
923---------------------
924
925aio-nr is the running total of the number of events specified on the
926io_setup system call for all currently active aio contexts. If aio-nr
927reaches aio-max-nr then io_setup will fail with EAGAIN. Note that
928raising aio-max-nr does not result in the pre-allocation or re-sizing
929of any kernel data structures.
930
9312.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats
932-----------------------------------------------------------
933
934Besides these files, there is the subdirectory /proc/sys/fs/binfmt_misc. This
935handles the kernel support for miscellaneous binary formats.
936
937Binfmt_misc provides the ability to register additional binary formats to the
938Kernel without compiling an additional module/kernel. Therefore, binfmt_misc
939needs to know magic numbers at the beginning or the filename extension of the
940binary.
941
942It works by maintaining a linked list of structs that contain a description of
943a binary format, including a magic with size (or the filename extension),
944offset and mask, and the interpreter name. On request it invokes the given
945interpreter with the original program as argument, as binfmt_java and
946binfmt_em86 and binfmt_mz do. Since binfmt_misc does not define any default
947binary-formats, you have to register an additional binary-format.
948
949There are two general files in binfmt_misc and one file per registered format.
950The two general files are register and status.
951
952Registering a new binary format
953-------------------------------
954
955To register a new binary format you have to issue the command
956
957 echo :name:type:offset:magic:mask:interpreter: > /proc/sys/fs/binfmt_misc/register
958
959
960
961with appropriate name (the name for the /proc-dir entry), offset (defaults to
9620, if omitted), magic, mask (which can be omitted, defaults to all 0xff) and
963last but not least, the interpreter that is to be invoked (for example and
964testing /bin/echo). Type can be M for usual magic matching or E for filename
965extension matching (give extension in place of magic).
966
967Check or reset the status of the binary format handler
968------------------------------------------------------
969
970If you do a cat on the file /proc/sys/fs/binfmt_misc/status, you will get the
971current status (enabled/disabled) of binfmt_misc. Change the status by echoing
9720 (disables) or 1 (enables) or -1 (caution: this clears all previously
973registered binary formats) to status. For example echo 0 > status to disable
974binfmt_misc (temporarily).
975
976Status of a single handler
977--------------------------
978
979Each registered handler has an entry in /proc/sys/fs/binfmt_misc. These files
980perform the same function as status, but their scope is limited to the actual
981binary format. By cating this file, you also receive all related information
982about the interpreter/magic of the binfmt.
983
984Example usage of binfmt_misc (emulate binfmt_java)
985--------------------------------------------------
986
987 cd /proc/sys/fs/binfmt_misc
988 echo ':Java:M::\xca\xfe\xba\xbe::/usr/local/java/bin/javawrapper:' > register
989 echo ':HTML:E::html::/usr/local/java/bin/appletviewer:' > register
990 echo ':Applet:M::<!--applet::/usr/local/java/bin/appletviewer:' > register
991 echo ':DEXE:M::\x0eDEX::/usr/bin/dosexec:' > register
992
993
994These four lines add support for Java executables and Java applets (like
995binfmt_java, additionally recognizing the .html extension with no need to put
996<!--applet> to every applet file). You have to install the JDK and the
997shell-script /usr/local/java/bin/javawrapper too. It works around the
998brokenness of the Java filename handling. To add a Java binary, just create a
999link to the class-file somewhere in the path.
1000
10012.3 /proc/sys/kernel - general kernel parameters
1002------------------------------------------------
1003
1004This directory reflects general kernel behaviors. As I've said before, the
1005contents depend on your configuration. Here you'll find the most important
1006files, along with descriptions of what they mean and how to use them.
1007
1008acct
1009----
1010
1011The file contains three values; highwater, lowwater, and frequency.
1012
1013It exists only when BSD-style process accounting is enabled. These values
1014control its behavior. If the free space on the file system where the log lives
1015goes below lowwater percentage, accounting suspends. If it goes above
1016highwater percentage, accounting resumes. Frequency determines how often you
1017check the amount of free space (value is in seconds). Default settings are: 4,
10182, and 30. That is, suspend accounting if there is less than 2 percent free;
1019resume it if we have a value of 3 or more percent; consider information about
1020the amount of free space valid for 30 seconds
1021
1022ctrl-alt-del
1023------------
1024
1025When the value in this file is 0, ctrl-alt-del is trapped and sent to the init
1026program to handle a graceful restart. However, when the value is greater that
1027zero, Linux's reaction to this key combination will be an immediate reboot,
1028without syncing its dirty buffers.
1029
1030[NOTE]
1031 When a program (like dosemu) has the keyboard in raw mode, the
1032 ctrl-alt-del is intercepted by the program before it ever reaches the
1033 kernel tty layer, and it is up to the program to decide what to do with
1034 it.
1035
1036domainname and hostname
1037-----------------------
1038
1039These files can be controlled to set the NIS domainname and hostname of your
1040box. For the classic darkstar.frop.org a simple:
1041
1042 # echo "darkstar" > /proc/sys/kernel/hostname
1043 # echo "frop.org" > /proc/sys/kernel/domainname
1044
1045
1046would suffice to set your hostname and NIS domainname.
1047
1048osrelease, ostype and version
1049-----------------------------
1050
1051The names make it pretty obvious what these fields contain:
1052
1053 > cat /proc/sys/kernel/osrelease
1054 2.2.12
1055
1056 > cat /proc/sys/kernel/ostype
1057 Linux
1058
1059 > cat /proc/sys/kernel/version
1060 #4 Fri Oct 1 12:41:14 PDT 1999
1061
1062
1063The files osrelease and ostype should be clear enough. Version needs a little
1064more clarification. The #4 means that this is the 4th kernel built from this
1065source base and the date after it indicates the time the kernel was built. The
1066only way to tune these values is to rebuild the kernel.
1067
1068panic
1069-----
1070
1071The value in this file represents the number of seconds the kernel waits
1072before rebooting on a panic. When you use the software watchdog, the
1073recommended setting is 60. If set to 0, the auto reboot after a kernel panic
1074is disabled, which is the default setting.
1075
1076printk
1077------
1078
1079The four values in printk denote
1080* console_loglevel,
1081* default_message_loglevel,
1082* minimum_console_loglevel and
1083* default_console_loglevel
1084respectively.
1085
1086These values influence printk() behavior when printing or logging error
1087messages, which come from inside the kernel. See syslog(2) for more
1088information on the different log levels.
1089
1090console_loglevel
1091----------------
1092
1093Messages with a higher priority than this will be printed to the console.
1094
1095default_message_level
1096---------------------
1097
1098Messages without an explicit priority will be printed with this priority.
1099
1100minimum_console_loglevel
1101------------------------
1102
1103Minimum (highest) value to which the console_loglevel can be set.
1104
1105default_console_loglevel
1106------------------------
1107
1108Default value for console_loglevel.
1109
1110sg-big-buff
1111-----------
1112
1113This file shows the size of the generic SCSI (sg) buffer. At this point, you
1114can't tune it yet, but you can change it at compile time by editing
1115include/scsi/sg.h and changing the value of SG_BIG_BUFF.
1116
1117If you use a scanner with SANE (Scanner Access Now Easy) you might want to set
1118this to a higher value. Refer to the SANE documentation on this issue.
1119
1120modprobe
1121--------
1122
1123The location where the modprobe binary is located. The kernel uses this
1124program to load modules on demand.
1125
1126unknown_nmi_panic
1127-----------------
1128
1129The value in this file affects behavior of handling NMI. When the value is
1130non-zero, unknown NMI is trapped and then panic occurs. At that time, kernel
1131debugging information is displayed on console.
1132
1133NMI switch that most IA32 servers have fires unknown NMI up, for example.
1134If a system hangs up, try pressing the NMI switch.
1135
1136[NOTE]
1137 This function and oprofile share a NMI callback. Therefore this function
1138 cannot be enabled when oprofile is activated.
1139 And NMI watchdog will be disabled when the value in this file is set to
1140 non-zero.
1141
1142
11432.4 /proc/sys/vm - The virtual memory subsystem
1144-----------------------------------------------
1145
1146The files in this directory can be used to tune the operation of the virtual
1147memory (VM) subsystem of the Linux kernel.
1148
1149vfs_cache_pressure
1150------------------
1151
1152Controls the tendency of the kernel to reclaim the memory which is used for
1153caching of directory and inode objects.
1154
1155At the default value of vfs_cache_pressure=100 the kernel will attempt to
1156reclaim dentries and inodes at a "fair" rate with respect to pagecache and
1157swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer
1158to retain dentry and inode caches. Increasing vfs_cache_pressure beyond 100
1159causes the kernel to prefer to reclaim dentries and inodes.
1160
1161dirty_background_ratio
1162----------------------
1163
1164Contains, as a percentage of total system memory, the number of pages at which
1165the pdflush background writeback daemon will start writing out dirty data.
1166
1167dirty_ratio
1168-----------------
1169
1170Contains, as a percentage of total system memory, the number of pages at which
1171a process which is generating disk writes will itself start writing out dirty
1172data.
1173
1174dirty_writeback_centisecs
1175-------------------------
1176
1177The pdflush writeback daemons will periodically wake up and write `old' data
1178out to disk. This tunable expresses the interval between those wakeups, in
1179100'ths of a second.
1180
1181Setting this to zero disables periodic writeback altogether.
1182
1183dirty_expire_centisecs
1184----------------------
1185
1186This tunable is used to define when dirty data is old enough to be eligible
1187for writeout by the pdflush daemons. It is expressed in 100'ths of a second.
1188Data which has been dirty in-memory for longer than this interval will be
1189written out next time a pdflush daemon wakes up.
1190
1191legacy_va_layout
1192----------------
1193
1194If non-zero, this sysctl disables the new 32-bit mmap mmap layout - the kernel
1195will use the legacy (2.4) layout for all processes.
1196
1197lower_zone_protection
1198---------------------
1199
1200For some specialised workloads on highmem machines it is dangerous for
1201the kernel to allow process memory to be allocated from the "lowmem"
1202zone. This is because that memory could then be pinned via the mlock()
1203system call, or by unavailability of swapspace.
1204
1205And on large highmem machines this lack of reclaimable lowmem memory
1206can be fatal.
1207
1208So the Linux page allocator has a mechanism which prevents allocations
1209which _could_ use highmem from using too much lowmem. This means that
1210a certain amount of lowmem is defended from the possibility of being
1211captured into pinned user memory.
1212
1213(The same argument applies to the old 16 megabyte ISA DMA region. This
1214mechanism will also defend that region from allocations which could use
1215highmem or lowmem).
1216
1217The `lower_zone_protection' tunable determines how aggressive the kernel is
1218in defending these lower zones. The default value is zero - no
1219protection at all.
1220
1221If you have a machine which uses highmem or ISA DMA and your
1222applications are using mlock(), or if you are running with no swap then
1223you probably should increase the lower_zone_protection setting.
1224
1225The units of this tunable are fairly vague. It is approximately equal
1226to "megabytes". So setting lower_zone_protection=100 will protect around 100
1227megabytes of the lowmem zone from user allocations. It will also make
1228those 100 megabytes unavaliable for use by applications and by
1229pagecache, so there is a cost.
1230
1231The effects of this tunable may be observed by monitoring
1232/proc/meminfo:LowFree. Write a single huge file and observe the point
1233at which LowFree ceases to fall.
1234
1235A reasonable value for lower_zone_protection is 100.
1236
1237page-cluster
1238------------
1239
1240page-cluster controls the number of pages which are written to swap in
1241a single attempt. The swap I/O size.
1242
1243It is a logarithmic value - setting it to zero means "1 page", setting
1244it to 1 means "2 pages", setting it to 2 means "4 pages", etc.
1245
1246The default value is three (eight pages at a time). There may be some
1247small benefits in tuning this to a different value if your workload is
1248swap-intensive.
1249
1250overcommit_memory
1251-----------------
1252
1253This file contains one value. The following algorithm is used to decide if
1254there's enough memory: if the value of overcommit_memory is positive, then
1255there's always enough memory. This is a useful feature, since programs often
1256malloc() huge amounts of memory 'just in case', while they only use a small
1257part of it. Leaving this value at 0 will lead to the failure of such a huge
1258malloc(), when in fact the system has enough memory for the program to run.
1259
1260On the other hand, enabling this feature can cause you to run out of memory
1261and thrash the system to death, so large and/or important servers will want to
1262set this value to 0.
1263
1264nr_hugepages and hugetlb_shm_group
1265----------------------------------
1266
1267nr_hugepages configures number of hugetlb page reserved for the system.
1268
1269hugetlb_shm_group contains group id that is allowed to create SysV shared
1270memory segment using hugetlb page.
1271
1272laptop_mode
1273-----------
1274
1275laptop_mode is a knob that controls "laptop mode". All the things that are
1276controlled by this knob are discussed in Documentation/laptop-mode.txt.
1277
1278block_dump
1279----------
1280
1281block_dump enables block I/O debugging when set to a nonzero value. More
1282information on block I/O debugging is in Documentation/laptop-mode.txt.
1283
1284swap_token_timeout
1285------------------
1286
1287This file contains valid hold time of swap out protection token. The Linux
1288VM has token based thrashing control mechanism and uses the token to prevent
1289unnecessary page faults in thrashing situation. The unit of the value is
1290second. The value would be useful to tune thrashing behavior.
1291
12922.5 /proc/sys/dev - Device specific parameters
1293----------------------------------------------
1294
1295Currently there is only support for CDROM drives, and for those, there is only
1296one read-only file containing information about the CD-ROM drives attached to
1297the system:
1298
1299 >cat /proc/sys/dev/cdrom/info
1300 CD-ROM information, Id: cdrom.c 2.55 1999/04/25
1301
1302 drive name: sr0 hdb
1303 drive speed: 32 40
1304 drive # of slots: 1 0
1305 Can close tray: 1 1
1306 Can open tray: 1 1
1307 Can lock tray: 1 1
1308 Can change speed: 1 1
1309 Can select disk: 0 1
1310 Can read multisession: 1 1
1311 Can read MCN: 1 1
1312 Reports media changed: 1 1
1313 Can play audio: 1 1
1314
1315
1316You see two drives, sr0 and hdb, along with a list of their features.
1317
13182.6 /proc/sys/sunrpc - Remote procedure calls
1319---------------------------------------------
1320
1321This directory contains four files, which enable or disable debugging for the
1322RPC functions NFS, NFS-daemon, RPC and NLM. The default values are 0. They can
1323be set to one to turn debugging on. (The default value is 0 for each)
1324
13252.7 /proc/sys/net - Networking stuff
1326------------------------------------
1327
1328The interface to the networking parts of the kernel is located in
1329/proc/sys/net. Table 2-3 shows all possible subdirectories. You may see only
1330some of them, depending on your kernel's configuration.
1331
1332
1333Table 2-3: Subdirectories in /proc/sys/net
1334..............................................................................
1335 Directory Content Directory Content
1336 core General parameter appletalk Appletalk protocol
1337 unix Unix domain sockets netrom NET/ROM
1338 802 E802 protocol ax25 AX25
1339 ethernet Ethernet protocol rose X.25 PLP layer
1340 ipv4 IP version 4 x25 X.25 protocol
1341 ipx IPX token-ring IBM token ring
1342 bridge Bridging decnet DEC net
1343 ipv6 IP version 6
1344..............................................................................
1345
1346We will concentrate on IP networking here. Since AX15, X.25, and DEC Net are
1347only minor players in the Linux world, we'll skip them in this chapter. You'll
1348find some short info on Appletalk and IPX further on in this chapter. Review
1349the online documentation and the kernel source to get a detailed view of the
1350parameters for those protocols. In this section we'll discuss the
1351subdirectories printed in bold letters in the table above. As default values
1352are suitable for most needs, there is no need to change these values.
1353
1354/proc/sys/net/core - Network core options
1355-----------------------------------------
1356
1357rmem_default
1358------------
1359
1360The default setting of the socket receive buffer in bytes.
1361
1362rmem_max
1363--------
1364
1365The maximum receive socket buffer size in bytes.
1366
1367wmem_default
1368------------
1369
1370The default setting (in bytes) of the socket send buffer.
1371
1372wmem_max
1373--------
1374
1375The maximum send socket buffer size in bytes.
1376
1377message_burst and message_cost
1378------------------------------
1379
1380These parameters are used to limit the warning messages written to the kernel
1381log from the networking code. They enforce a rate limit to make a
1382denial-of-service attack impossible. A higher message_cost factor, results in
1383fewer messages that will be written. Message_burst controls when messages will
1384be dropped. The default settings limit warning messages to one every five
1385seconds.
1386
1387netdev_max_backlog
1388------------------
1389
1390Maximum number of packets, queued on the INPUT side, when the interface
1391receives packets faster than kernel can process them.
1392
1393optmem_max
1394----------
1395
1396Maximum ancillary buffer size allowed per socket. Ancillary data is a sequence
1397of struct cmsghdr structures with appended data.
1398
1399/proc/sys/net/unix - Parameters for Unix domain sockets
1400-------------------------------------------------------
1401
1402There are only two files in this subdirectory. They control the delays for
1403deleting and destroying socket descriptors.
1404
14052.8 /proc/sys/net/ipv4 - IPV4 settings
1406--------------------------------------
1407
1408IP version 4 is still the most used protocol in Unix networking. It will be
1409replaced by IP version 6 in the next couple of years, but for the moment it's
1410the de facto standard for the internet and is used in most networking
1411environments around the world. Because of the importance of this protocol,
1412we'll have a deeper look into the subtree controlling the behavior of the IPv4
1413subsystem of the Linux kernel.
1414
1415Let's start with the entries in /proc/sys/net/ipv4.
1416
1417ICMP settings
1418-------------
1419
1420icmp_echo_ignore_all and icmp_echo_ignore_broadcasts
1421----------------------------------------------------
1422
1423Turn on (1) or off (0), if the kernel should ignore all ICMP ECHO requests, or
1424just those to broadcast and multicast addresses.
1425
1426Please note that if you accept ICMP echo requests with a broadcast/multi\-cast
1427destination address your network may be used as an exploder for denial of
1428service packet flooding attacks to other hosts.
1429
1430icmp_destunreach_rate, icmp_echoreply_rate, icmp_paramprob_rate and icmp_timeexeed_rate
1431---------------------------------------------------------------------------------------
1432
1433Sets limits for sending ICMP packets to specific targets. A value of zero
1434disables all limiting. Any positive value sets the maximum package rate in
1435hundredth of a second (on Intel systems).
1436
1437IP settings
1438-----------
1439
1440ip_autoconfig
1441-------------
1442
1443This file contains the number one if the host received its IP configuration by
1444RARP, BOOTP, DHCP or a similar mechanism. Otherwise it is zero.
1445
1446ip_default_ttl
1447--------------
1448
1449TTL (Time To Live) for IPv4 interfaces. This is simply the maximum number of
1450hops a packet may travel.
1451
1452ip_dynaddr
1453----------
1454
1455Enable dynamic socket address rewriting on interface address change. This is
1456useful for dialup interface with changing IP addresses.
1457
1458ip_forward
1459----------
1460
1461Enable or disable forwarding of IP packages between interfaces. Changing this
1462value resets all other parameters to their default values. They differ if the
1463kernel is configured as host or router.
1464
1465ip_local_port_range
1466-------------------
1467
1468Range of ports used by TCP and UDP to choose the local port. Contains two
1469numbers, the first number is the lowest port, the second number the highest
1470local port. Default is 1024-4999. Should be changed to 32768-61000 for
1471high-usage systems.
1472
1473ip_no_pmtu_disc
1474---------------
1475
1476Global switch to turn path MTU discovery off. It can also be set on a per
1477socket basis by the applications or on a per route basis.
1478
1479ip_masq_debug
1480-------------
1481
1482Enable/disable debugging of IP masquerading.
1483
1484IP fragmentation settings
1485-------------------------
1486
1487ipfrag_high_trash and ipfrag_low_trash
1488--------------------------------------
1489
1490Maximum memory used to reassemble IP fragments. When ipfrag_high_thresh bytes
1491of memory is allocated for this purpose, the fragment handler will toss
1492packets until ipfrag_low_thresh is reached.
1493
1494ipfrag_time
1495-----------
1496
1497Time in seconds to keep an IP fragment in memory.
1498
1499TCP settings
1500------------
1501
1502tcp_ecn
1503-------
1504
1505This file controls the use of the ECN bit in the IPv4 headers, this is a new
1506feature about Explicit Congestion Notification, but some routers and firewalls
1507block trafic that has this bit set, so it could be necessary to echo 0 to
1508/proc/sys/net/ipv4/tcp_ecn, if you want to talk to this sites. For more info
1509you could read RFC2481.
1510
1511tcp_retrans_collapse
1512--------------------
1513
1514Bug-to-bug compatibility with some broken printers. On retransmit, try to send
1515larger packets to work around bugs in certain TCP stacks. Can be turned off by
1516setting it to zero.
1517
1518tcp_keepalive_probes
1519--------------------
1520
1521Number of keep alive probes TCP sends out, until it decides that the
1522connection is broken.
1523
1524tcp_keepalive_time
1525------------------
1526
1527How often TCP sends out keep alive messages, when keep alive is enabled. The
1528default is 2 hours.
1529
1530tcp_syn_retries
1531---------------
1532
1533Number of times initial SYNs for a TCP connection attempt will be
1534retransmitted. Should not be higher than 255. This is only the timeout for
1535outgoing connections, for incoming connections the number of retransmits is
1536defined by tcp_retries1.
1537
1538tcp_sack
1539--------
1540
1541Enable select acknowledgments after RFC2018.
1542
1543tcp_timestamps
1544--------------
1545
1546Enable timestamps as defined in RFC1323.
1547
1548tcp_stdurg
1549----------
1550
1551Enable the strict RFC793 interpretation of the TCP urgent pointer field. The
1552default is to use the BSD compatible interpretation of the urgent pointer
1553pointing to the first byte after the urgent data. The RFC793 interpretation is
1554to have it point to the last byte of urgent data. Enabling this option may
1555lead to interoperatibility problems. Disabled by default.
1556
1557tcp_syncookies
1558--------------
1559
1560Only valid when the kernel was compiled with CONFIG_SYNCOOKIES. Send out
1561syncookies when the syn backlog queue of a socket overflows. This is to ward
1562off the common 'syn flood attack'. Disabled by default.
1563
1564Note that the concept of a socket backlog is abandoned. This means the peer
1565may not receive reliable error messages from an over loaded server with
1566syncookies enabled.
1567
1568tcp_window_scaling
1569------------------
1570
1571Enable window scaling as defined in RFC1323.
1572
1573tcp_fin_timeout
1574---------------
1575
1576The length of time in seconds it takes to receive a final FIN before the
1577socket is always closed. This is strictly a violation of the TCP
1578specification, but required to prevent denial-of-service attacks.
1579
1580tcp_max_ka_probes
1581-----------------
1582
1583Indicates how many keep alive probes are sent per slow timer run. Should not
1584be set too high to prevent bursts.
1585
1586tcp_max_syn_backlog
1587-------------------
1588
1589Length of the per socket backlog queue. Since Linux 2.2 the backlog specified
1590in listen(2) only specifies the length of the backlog queue of already
1591established sockets. When more connection requests arrive Linux starts to drop
1592packets. When syncookies are enabled the packets are still answered and the
1593maximum queue is effectively ignored.
1594
1595tcp_retries1
1596------------
1597
1598Defines how often an answer to a TCP connection request is retransmitted
1599before giving up.
1600
1601tcp_retries2
1602------------
1603
1604Defines how often a TCP packet is retransmitted before giving up.
1605
1606Interface specific settings
1607---------------------------
1608
1609In the directory /proc/sys/net/ipv4/conf you'll find one subdirectory for each
1610interface the system knows about and one directory calls all. Changes in the
1611all subdirectory affect all interfaces, whereas changes in the other
1612subdirectories affect only one interface. All directories have the same
1613entries:
1614
1615accept_redirects
1616----------------
1617
1618This switch decides if the kernel accepts ICMP redirect messages or not. The
1619default is 'yes' if the kernel is configured for a regular host and 'no' for a
1620router configuration.
1621
1622accept_source_route
1623-------------------
1624
1625Should source routed packages be accepted or declined. The default is
1626dependent on the kernel configuration. It's 'yes' for routers and 'no' for
1627hosts.
1628
1629bootp_relay
1630~~~~~~~~~~~
1631
1632Accept packets with source address 0.b.c.d with destinations not to this host
1633as local ones. It is supposed that a BOOTP relay daemon will catch and forward
1634such packets.
1635
1636The default is 0, since this feature is not implemented yet (kernel version
16372.2.12).
1638
1639forwarding
1640----------
1641
1642Enable or disable IP forwarding on this interface.
1643
1644log_martians
1645------------
1646
1647Log packets with source addresses with no known route to kernel log.
1648
1649mc_forwarding
1650-------------
1651
1652Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE and a
1653multicast routing daemon is required.
1654
1655proxy_arp
1656---------
1657
1658Does (1) or does not (0) perform proxy ARP.
1659
1660rp_filter
1661---------
1662
1663Integer value determines if a source validation should be made. 1 means yes, 0
1664means no. Disabled by default, but local/broadcast address spoofing is always
1665on.
1666
1667If you set this to 1 on a router that is the only connection for a network to
1668the net, it will prevent spoofing attacks against your internal networks
1669(external addresses can still be spoofed), without the need for additional
1670firewall rules.
1671
1672secure_redirects
1673----------------
1674
1675Accept ICMP redirect messages only for gateways, listed in default gateway
1676list. Enabled by default.
1677
1678shared_media
1679------------
1680
1681If it is not set the kernel does not assume that different subnets on this
1682device can communicate directly. Default setting is 'yes'.
1683
1684send_redirects
1685--------------
1686
1687Determines whether to send ICMP redirects to other hosts.
1688
1689Routing settings
1690----------------
1691
1692The directory /proc/sys/net/ipv4/route contains several file to control
1693routing issues.
1694
1695error_burst and error_cost
1696--------------------------
1697
1698These parameters are used to limit how many ICMP destination unreachable to
1699send from the host in question. ICMP destination unreachable messages are
1700sent when we can not reach the next hop, while trying to transmit a packet.
1701It will also print some error messages to kernel logs if someone is ignoring
1702our ICMP redirects. The higher the error_cost factor is, the fewer
1703destination unreachable and error messages will be let through. Error_burst
1704controls when destination unreachable messages and error messages will be
1705dropped. The default settings limit warning messages to five every second.
1706
1707flush
1708-----
1709
1710Writing to this file results in a flush of the routing cache.
1711
1712gc_elasticity, gc_interval, gc_min_interval_ms, gc_timeout, gc_thresh
1713---------------------------------------------------------------------
1714
1715Values to control the frequency and behavior of the garbage collection
1716algorithm for the routing cache. gc_min_interval is deprecated and replaced
1717by gc_min_interval_ms.
1718
1719
1720max_size
1721--------
1722
1723Maximum size of the routing cache. Old entries will be purged once the cache
1724reached has this size.
1725
1726max_delay, min_delay
1727--------------------
1728
1729Delays for flushing the routing cache.
1730
1731redirect_load, redirect_number
1732------------------------------
1733
1734Factors which determine if more ICPM redirects should be sent to a specific
1735host. No redirects will be sent once the load limit or the maximum number of
1736redirects has been reached.
1737
1738redirect_silence
1739----------------
1740
1741Timeout for redirects. After this period redirects will be sent again, even if
1742this has been stopped, because the load or number limit has been reached.
1743
1744Network Neighbor handling
1745-------------------------
1746
1747Settings about how to handle connections with direct neighbors (nodes attached
1748to the same link) can be found in the directory /proc/sys/net/ipv4/neigh.
1749
1750As we saw it in the conf directory, there is a default subdirectory which
1751holds the default values, and one directory for each interface. The contents
1752of the directories are identical, with the single exception that the default
1753settings contain additional options to set garbage collection parameters.
1754
1755In the interface directories you'll find the following entries:
1756
1757base_reachable_time, base_reachable_time_ms
1758-------------------------------------------
1759
1760A base value used for computing the random reachable time value as specified
1761in RFC2461.
1762
1763Expression of base_reachable_time, which is deprecated, is in seconds.
1764Expression of base_reachable_time_ms is in milliseconds.
1765
1766retrans_time, retrans_time_ms
1767-----------------------------
1768
1769The time between retransmitted Neighbor Solicitation messages.
1770Used for address resolution and to determine if a neighbor is
1771unreachable.
1772
1773Expression of retrans_time, which is deprecated, is in 1/100 seconds (for
1774IPv4) or in jiffies (for IPv6).
1775Expression of retrans_time_ms is in milliseconds.
1776
1777unres_qlen
1778----------
1779
1780Maximum queue length for a pending arp request - the number of packets which
1781are accepted from other layers while the ARP address is still resolved.
1782
1783anycast_delay
1784-------------
1785
1786Maximum for random delay of answers to neighbor solicitation messages in
1787jiffies (1/100 sec). Not yet implemented (Linux does not have anycast support
1788yet).
1789
1790ucast_solicit
1791-------------
1792
1793Maximum number of retries for unicast solicitation.
1794
1795mcast_solicit
1796-------------
1797
1798Maximum number of retries for multicast solicitation.
1799
1800delay_first_probe_time
1801----------------------
1802
1803Delay for the first time probe if the neighbor is reachable. (see
1804gc_stale_time)
1805
1806locktime
1807--------
1808
1809An ARP/neighbor entry is only replaced with a new one if the old is at least
1810locktime old. This prevents ARP cache thrashing.
1811
1812proxy_delay
1813-----------
1814
1815Maximum time (real time is random [0..proxytime]) before answering to an ARP
1816request for which we have an proxy ARP entry. In some cases, this is used to
1817prevent network flooding.
1818
1819proxy_qlen
1820----------
1821
1822Maximum queue length of the delayed proxy arp timer. (see proxy_delay).
1823
1824app_solcit
1825----------
1826
1827Determines the number of requests to send to the user level ARP daemon. Use 0
1828to turn off.
1829
1830gc_stale_time
1831-------------
1832
1833Determines how often to check for stale ARP entries. After an ARP entry is
1834stale it will be resolved again (which is useful when an IP address migrates
1835to another machine). When ucast_solicit is greater than 0 it first tries to
1836send an ARP packet directly to the known host When that fails and
1837mcast_solicit is greater than 0, an ARP request is broadcasted.
1838
18392.9 Appletalk
1840-------------
1841
1842The /proc/sys/net/appletalk directory holds the Appletalk configuration data
1843when Appletalk is loaded. The configurable parameters are:
1844
1845aarp-expiry-time
1846----------------
1847
1848The amount of time we keep an ARP entry before expiring it. Used to age out
1849old hosts.
1850
1851aarp-resolve-time
1852-----------------
1853
1854The amount of time we will spend trying to resolve an Appletalk address.
1855
1856aarp-retransmit-limit
1857---------------------
1858
1859The number of times we will retransmit a query before giving up.
1860
1861aarp-tick-time
1862--------------
1863
1864Controls the rate at which expires are checked.
1865
1866The directory /proc/net/appletalk holds the list of active Appletalk sockets
1867on a machine.
1868
1869The fields indicate the DDP type, the local address (in network:node format)
1870the remote address, the size of the transmit pending queue, the size of the
1871received queue (bytes waiting for applications to read) the state and the uid
1872owning the socket.
1873
1874/proc/net/atalk_iface lists all the interfaces configured for appletalk.It
1875shows the name of the interface, its Appletalk address, the network range on
1876that address (or network number for phase 1 networks), and the status of the
1877interface.
1878
1879/proc/net/atalk_route lists each known network route. It lists the target
1880(network) that the route leads to, the router (may be directly connected), the
1881route flags, and the device the route is using.
1882
18832.10 IPX
1884--------
1885
1886The IPX protocol has no tunable values in proc/sys/net.
1887
1888The IPX protocol does, however, provide proc/net/ipx. This lists each IPX
1889socket giving the local and remote addresses in Novell format (that is
1890network:node:port). In accordance with the strange Novell tradition,
1891everything but the port is in hex. Not_Connected is displayed for sockets that
1892are not tied to a specific remote address. The Tx and Rx queue sizes indicate
1893the number of bytes pending for transmission and reception. The state
1894indicates the state the socket is in and the uid is the owning uid of the
1895socket.
1896
1897The /proc/net/ipx_interface file lists all IPX interfaces. For each interface
1898it gives the network number, the node number, and indicates if the network is
1899the primary network. It also indicates which device it is bound to (or
1900Internal for internal networks) and the Frame Type if appropriate. Linux
1901supports 802.3, 802.2, 802.2 SNAP and DIX (Blue Book) ethernet framing for
1902IPX.
1903
1904The /proc/net/ipx_route table holds a list of IPX routes. For each route it
1905gives the destination network, the router node (or Directly) and the network
1906address of the router (or Connected) for internal networks.
1907
19082.11 /proc/sys/fs/mqueue - POSIX message queues filesystem
1909----------------------------------------------------------
1910
1911The "mqueue" filesystem provides the necessary kernel features to enable the
1912creation of a user space library that implements the POSIX message queues
1913API (as noted by the MSG tag in the POSIX 1003.1-2001 version of the System
1914Interfaces specification.)
1915
1916The "mqueue" filesystem contains values for determining/setting the amount of
1917resources used by the file system.
1918
1919/proc/sys/fs/mqueue/queues_max is a read/write file for setting/getting the
1920maximum number of message queues allowed on the system.
1921
1922/proc/sys/fs/mqueue/msg_max is a read/write file for setting/getting the
1923maximum number of messages in a queue value. In fact it is the limiting value
1924for another (user) limit which is set in mq_open invocation. This attribute of
1925a queue must be less or equal then msg_max.
1926
1927/proc/sys/fs/mqueue/msgsize_max is a read/write file for setting/getting the
1928maximum message size value (it is every message queue's attribute set during
1929its creation).
1930
1931
1932------------------------------------------------------------------------------
1933Summary
1934------------------------------------------------------------------------------
1935Certain aspects of kernel behavior can be modified at runtime, without the
1936need to recompile the kernel, or even to reboot the system. The files in the
1937/proc/sys tree can not only be read, but also modified. You can use the echo
1938command to write value into these files, thereby changing the default settings
1939of the kernel.
1940------------------------------------------------------------------------------