ia64/linux-2.6.18-xen.hg

view Documentation/filesystems/proc.txt @ 524:7f8b544237bf

netfront: Allow netfront in domain 0.

This is useful if your physical network device is in a utility domain.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
author Keir Fraser <keir.fraser@citrix.com>
date Tue Apr 15 15:18:58 2008 +0100 (2008-04-15)
parents 831230e53067
children
line source
1 ------------------------------------------------------------------------------
2 T H E /proc F I L E S Y S T E M
3 ------------------------------------------------------------------------------
4 /proc/sys Terrehon Bowden <terrehon@pacbell.net> October 7 1999
5 Bodo Bauer <bb@ricochet.net>
7 2.4.x update Jorge Nerin <comandante@zaralinux.com> November 14 2000
8 ------------------------------------------------------------------------------
9 Version 1.3 Kernel version 2.2.12
10 Kernel version 2.4.0-test11-pre4
11 ------------------------------------------------------------------------------
13 Table of Contents
14 -----------------
16 0 Preface
17 0.1 Introduction/Credits
18 0.2 Legal Stuff
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
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
43 ------------------------------------------------------------------------------
44 Preface
45 ------------------------------------------------------------------------------
47 0.1 Introduction/Credits
48 ------------------------
50 This documentation is part of a soon (or so we hope) to be released book on
51 the 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
53 chapters, it seems only fair to give the work back to the Linux community.
54 This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm
55 afraid it's still far from complete, but we hope it will be useful. As far as
56 we know, it is the first 'all-in-one' document about the /proc file system. It
57 is focused on the Intel x86 hardware, so if you are looking for PPC, ARM,
58 SPARC, AXP, etc., features, you probably won't find what you are looking for.
59 It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
60 additions and patches are welcome and will be added to this document if you
61 mail them to Bodo.
63 We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
64 other people for help compiling this documentation. We'd also like to extend a
65 special thank you to Andi Kleen for documentation, which we relied on heavily
66 to create this document, as well as the additional information he provided.
67 Thanks to everybody else who contributed source or docs to the Linux kernel
68 and helped create a great piece of software... :)
70 If you have any comments, corrections or additions, please don't hesitate to
71 contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this
72 document.
74 The latest version of this document is available online at
75 http://skaro.nightcrawler.com/~bb/Docs/Proc as HTML version.
77 If the above direction does not works for you, ypu could try the kernel
78 mailing list at linux-kernel@vger.kernel.org and/or try to reach me at
79 comandante@zaralinux.com.
81 0.2 Legal Stuff
82 ---------------
84 We don't guarantee the correctness of this document, and if you come to us
85 complaining about how you screwed up your system because of incorrect
86 documentation, we won't feel responsible...
88 ------------------------------------------------------------------------------
89 CHAPTER 1: COLLECTING SYSTEM INFORMATION
90 ------------------------------------------------------------------------------
92 ------------------------------------------------------------------------------
93 In 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 ------------------------------------------------------------------------------
103 The proc file system acts as an interface to internal data structures in the
104 kernel. It can be used to obtain information about the system and to change
105 certain kernel parameters at runtime (sysctl).
107 First, we'll take a look at the read-only parts of /proc. In Chapter 2, we
108 show you how you can use /proc/sys to change settings.
110 1.1 Process-Specific Subdirectories
111 -----------------------------------
113 The directory /proc contains (among other things) one subdirectory for each
114 process running on the system, which is named after the process ID (PID).
116 The link self points to the process reading the file system. Each process
117 subdirectory has the entries listed in Table 1-1.
120 Table 1-1: Process specific entries in /proc
121 ..............................................................................
122 File Content
123 cmdline Command line arguments
124 cpu Current and last cpu in which 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 smaps Extension based on maps, presenting the rss size for each mapped file
137 ..............................................................................
139 For example, to get the status information of a process, all you have to do is
140 read the file /proc/PID/status:
142 >cat /proc/self/status
143 Name: cat
144 State: R (running)
145 Pid: 5452
146 PPid: 743
147 TracerPid: 0 (2.4)
148 Uid: 501 501 501 501
149 Gid: 100 100 100 100
150 Groups: 100 14 16
151 VmSize: 1112 kB
152 VmLck: 0 kB
153 VmRSS: 348 kB
154 VmData: 24 kB
155 VmStk: 12 kB
156 VmExe: 8 kB
157 VmLib: 1044 kB
158 SigPnd: 0000000000000000
159 SigBlk: 0000000000000000
160 SigIgn: 0000000000000000
161 SigCgt: 0000000000000000
162 CapInh: 00000000fffffeff
163 CapPrm: 0000000000000000
164 CapEff: 0000000000000000
167 This shows you nearly the same information you would get if you viewed it with
168 the ps command. In fact, ps uses the proc file system to obtain its
169 information. The statm file contains more detailed information about the
170 process memory usage. Its seven fields are explained in Table 1-2.
173 Table 1-2: Contents of the statm files (as of 2.6.8-rc3)
174 ..............................................................................
175 Field Content
176 size total program size (pages) (same as VmSize in status)
177 resident size of memory portions (pages) (same as VmRSS in status)
178 shared number of pages that are shared (i.e. backed by a file)
179 trs number of pages that are 'code' (not including libs; broken,
180 includes data segment)
181 lrs number of pages of library (always 0 on 2.6)
182 drs number of pages of data/stack (including libs; broken,
183 includes library text)
184 dt number of dirty pages (always 0 on 2.6)
185 ..............................................................................
187 1.2 Kernel data
188 ---------------
190 Similar to the process entries, the kernel data files give information about
191 the running kernel. The files used to obtain this information are contained in
192 /proc and are listed in Table 1-3. Not all of these will be present in your
193 system. It depends on the kernel configuration and the loaded modules, which
194 files are there, and which are missing.
196 Table 1-3: Kernel info in /proc
197 ..............................................................................
198 File Content
199 apm Advanced power management info
200 buddyinfo Kernel memory allocator information (see text) (2.5)
201 bus Directory containing bus specific information
202 cmdline Kernel command line
203 cpuinfo Info about the CPU
204 devices Available devices (block and character)
205 dma Used DMS channels
206 filesystems Supported filesystems
207 driver Various drivers grouped here, currently rtc (2.4)
208 execdomains Execdomains, related to security (2.4)
209 fb Frame Buffer devices (2.4)
210 fs File system parameters, currently nfs/exports (2.4)
211 ide Directory containing info about the IDE subsystem
212 interrupts Interrupt usage
213 iomem Memory map (2.4)
214 ioports I/O port usage
215 irq Masks for irq to cpu affinity (2.4)(smp?)
216 isapnp ISA PnP (Plug&Play) Info (2.4)
217 kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
218 kmsg Kernel messages
219 ksyms Kernel symbol table
220 loadavg Load average of last 1, 5 & 15 minutes
221 locks Kernel locks
222 meminfo Memory info
223 misc Miscellaneous
224 modules List of loaded modules
225 mounts Mounted filesystems
226 net Networking info (see text)
227 partitions Table of partitions known to the system
228 pci Depreciated info of PCI bus (new way -> /proc/bus/pci/,
229 decoupled by lspci (2.4)
230 rtc Real time clock
231 scsi SCSI info (see text)
232 slabinfo Slab pool info
233 stat Overall statistics
234 swaps Swap space utilization
235 sys See chapter 2
236 sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4)
237 tty Info of tty drivers
238 uptime System uptime
239 version Kernel version
240 video bttv info of video resources (2.4)
241 ..............................................................................
243 You can, for example, check which interrupts are currently in use and what
244 they are used for by looking in the file /proc/interrupts:
246 > cat /proc/interrupts
247 CPU0
248 0: 8728810 XT-PIC timer
249 1: 895 XT-PIC keyboard
250 2: 0 XT-PIC cascade
251 3: 531695 XT-PIC aha152x
252 4: 2014133 XT-PIC serial
253 5: 44401 XT-PIC pcnet_cs
254 8: 2 XT-PIC rtc
255 11: 8 XT-PIC i82365
256 12: 182918 XT-PIC PS/2 Mouse
257 13: 1 XT-PIC fpu
258 14: 1232265 XT-PIC ide0
259 15: 7 XT-PIC ide1
260 NMI: 0
262 In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
263 output of a SMP machine):
265 > cat /proc/interrupts
267 CPU0 CPU1
268 0: 1243498 1214548 IO-APIC-edge timer
269 1: 8949 8958 IO-APIC-edge keyboard
270 2: 0 0 XT-PIC cascade
271 5: 11286 10161 IO-APIC-edge soundblaster
272 8: 1 0 IO-APIC-edge rtc
273 9: 27422 27407 IO-APIC-edge 3c503
274 12: 113645 113873 IO-APIC-edge PS/2 Mouse
275 13: 0 0 XT-PIC fpu
276 14: 22491 24012 IO-APIC-edge ide0
277 15: 2183 2415 IO-APIC-edge ide1
278 17: 30564 30414 IO-APIC-level eth0
279 18: 177 164 IO-APIC-level bttv
280 NMI: 2457961 2457959
281 LOC: 2457882 2457881
282 ERR: 2155
284 NMI is incremented in this case because every timer interrupt generates a NMI
285 (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
287 LOC is the local interrupt counter of the internal APIC of every CPU.
289 ERR is incremented in the case of errors in the IO-APIC bus (the bus that
290 connects the CPUs in a SMP system. This means that an error has been detected,
291 the IO-APIC automatically retry the transmission, so it should not be a big
292 problem, but you should read the SMP-FAQ.
294 In this context it could be interesting to note the new irq directory in 2.4.
295 It could be used to set IRQ to CPU affinity, this means that you can "hook" an
296 IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
297 irq subdir is one subdir for each IRQ, and one file; prof_cpu_mask
299 For example
300 > ls /proc/irq/
301 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask
302 1 11 13 15 17 19 3 5 7 9
303 > ls /proc/irq/0/
304 smp_affinity
306 The contents of the prof_cpu_mask file and each smp_affinity file for each IRQ
307 is the same by default:
309 > cat /proc/irq/0/smp_affinity
310 ffffffff
312 It's a bitmask, in which you can specify which CPUs can handle the IRQ, you can
313 set it by doing:
315 > echo 1 > /proc/irq/prof_cpu_mask
317 This means that only the first CPU will handle the IRQ, but you can also echo 5
318 which means that only the first and fourth CPU can handle the IRQ.
320 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
321 between all the CPUs which are allowed to handle it. As usual the kernel has
322 more info than you and does a better job than you, so the defaults are the
323 best choice for almost everyone.
325 There are three more important subdirectories in /proc: net, scsi, and sys.
326 The general rule is that the contents, or even the existence of these
327 directories, depend on your kernel configuration. If SCSI is not enabled, the
328 directory scsi may not exist. The same is true with the net, which is there
329 only when networking support is present in the running kernel.
331 The slabinfo file gives information about memory usage at the slab level.
332 Linux uses slab pools for memory management above page level in version 2.2.
333 Commonly used objects have their own slab pool (such as network buffers,
334 directory cache, and so on).
336 ..............................................................................
338 > cat /proc/buddyinfo
340 Node 0, zone DMA 0 4 5 4 4 3 ...
341 Node 0, zone Normal 1 0 0 1 101 8 ...
342 Node 0, zone HighMem 2 0 0 1 1 0 ...
344 Memory fragmentation is a problem under some workloads, and buddyinfo is a
345 useful tool for helping diagnose these problems. Buddyinfo will give you a
346 clue as to how big an area you can safely allocate, or why a previous
347 allocation failed.
349 Each column represents the number of pages of a certain order which are
350 available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
351 ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
352 available in ZONE_NORMAL, etc...
354 ..............................................................................
356 meminfo:
358 Provides information about distribution and utilization of memory. This
359 varies by architecture and compile options. The following is from a
360 16GB PIII, which has highmem enabled. You may not have all of these fields.
362 > cat /proc/meminfo
365 MemTotal: 16344972 kB
366 MemFree: 13634064 kB
367 Buffers: 3656 kB
368 Cached: 1195708 kB
369 SwapCached: 0 kB
370 Active: 891636 kB
371 Inactive: 1077224 kB
372 HighTotal: 15597528 kB
373 HighFree: 13629632 kB
374 LowTotal: 747444 kB
375 LowFree: 4432 kB
376 SwapTotal: 0 kB
377 SwapFree: 0 kB
378 Dirty: 968 kB
379 Writeback: 0 kB
380 Mapped: 280372 kB
381 Slab: 684068 kB
382 CommitLimit: 7669796 kB
383 Committed_AS: 100056 kB
384 PageTables: 24448 kB
385 VmallocTotal: 112216 kB
386 VmallocUsed: 428 kB
387 VmallocChunk: 111088 kB
389 MemTotal: Total usable ram (i.e. physical ram minus a few reserved
390 bits and the kernel binary code)
391 MemFree: The sum of LowFree+HighFree
392 Buffers: Relatively temporary storage for raw disk blocks
393 shouldn't get tremendously large (20MB or so)
394 Cached: in-memory cache for files read from the disk (the
395 pagecache). Doesn't include SwapCached
396 SwapCached: Memory that once was swapped out, is swapped back in but
397 still also is in the swapfile (if memory is needed it
398 doesn't need to be swapped out AGAIN because it is already
399 in the swapfile. This saves I/O)
400 Active: Memory that has been used more recently and usually not
401 reclaimed unless absolutely necessary.
402 Inactive: Memory which has been less recently used. It is more
403 eligible to be reclaimed for other purposes
404 HighTotal:
405 HighFree: Highmem is all memory above ~860MB of physical memory
406 Highmem areas are for use by userspace programs, or
407 for the pagecache. The kernel must use tricks to access
408 this memory, making it slower to access than lowmem.
409 LowTotal:
410 LowFree: Lowmem is memory which can be used for everything that
411 highmem can be used for, but it is also availble for the
412 kernel's use for its own data structures. Among many
413 other things, it is where everything from the Slab is
414 allocated. Bad things happen when you're out of lowmem.
415 SwapTotal: total amount of swap space available
416 SwapFree: Memory which has been evicted from RAM, and is temporarily
417 on the disk
418 Dirty: Memory which is waiting to get written back to the disk
419 Writeback: Memory which is actively being written back to the disk
420 Mapped: files which have been mmaped, such as libraries
421 Slab: in-kernel data structures cache
422 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
423 this is the total amount of memory currently available to
424 be allocated on the system. This limit is only adhered to
425 if strict overcommit accounting is enabled (mode 2 in
426 'vm.overcommit_memory').
427 The CommitLimit is calculated with the following formula:
428 CommitLimit = ('vm.overcommit_ratio' * Physical RAM) + Swap
429 For example, on a system with 1G of physical RAM and 7G
430 of swap with a `vm.overcommit_ratio` of 30 it would
431 yield a CommitLimit of 7.3G.
432 For more details, see the memory overcommit documentation
433 in vm/overcommit-accounting.
434 Committed_AS: The amount of memory presently allocated on the system.
435 The committed memory is a sum of all of the memory which
436 has been allocated by processes, even if it has not been
437 "used" by them as of yet. A process which malloc()'s 1G
438 of memory, but only touches 300M of it will only show up
439 as using 300M of memory even if it has the address space
440 allocated for the entire 1G. This 1G is memory which has
441 been "committed" to by the VM and can be used at any time
442 by the allocating application. With strict overcommit
443 enabled on the system (mode 2 in 'vm.overcommit_memory'),
444 allocations which would exceed the CommitLimit (detailed
445 above) will not be permitted. This is useful if one needs
446 to guarantee that processes will not fail due to lack of
447 memory once that memory has been successfully allocated.
448 PageTables: amount of memory dedicated to the lowest level of page
449 tables.
450 VmallocTotal: total size of vmalloc memory area
451 VmallocUsed: amount of vmalloc area which is used
452 VmallocChunk: largest contigious block of vmalloc area which is free
455 1.3 IDE devices in /proc/ide
456 ----------------------------
458 The subdirectory /proc/ide contains information about all IDE devices of which
459 the kernel is aware. There is one subdirectory for each IDE controller, the
460 file drivers and a link for each IDE device, pointing to the device directory
461 in the controller specific subtree.
463 The file drivers contains general information about the drivers used for the
464 IDE devices:
466 > cat /proc/ide/drivers
467 ide-cdrom version 4.53
468 ide-disk version 1.08
470 More detailed information can be found in the controller specific
471 subdirectories. These are named ide0, ide1 and so on. Each of these
472 directories contains the files shown in table 1-4.
475 Table 1-4: IDE controller info in /proc/ide/ide?
476 ..............................................................................
477 File Content
478 channel IDE channel (0 or 1)
479 config Configuration (only for PCI/IDE bridge)
480 mate Mate name
481 model Type/Chipset of IDE controller
482 ..............................................................................
484 Each device connected to a controller has a separate subdirectory in the
485 controllers directory. The files listed in table 1-5 are contained in these
486 directories.
489 Table 1-5: IDE device information
490 ..............................................................................
491 File Content
492 cache The cache
493 capacity Capacity of the medium (in 512Byte blocks)
494 driver driver and version
495 geometry physical and logical geometry
496 identify device identify block
497 media media type
498 model device identifier
499 settings device setup
500 smart_thresholds IDE disk management thresholds
501 smart_values IDE disk management values
502 ..............................................................................
504 The most interesting file is settings. This file contains a nice overview of
505 the drive parameters:
507 # cat /proc/ide/ide0/hda/settings
508 name value min max mode
509 ---- ----- --- --- ----
510 bios_cyl 526 0 65535 rw
511 bios_head 255 0 255 rw
512 bios_sect 63 0 63 rw
513 breada_readahead 4 0 127 rw
514 bswap 0 0 1 r
515 file_readahead 72 0 2097151 rw
516 io_32bit 0 0 3 rw
517 keepsettings 0 0 1 rw
518 max_kb_per_request 122 1 127 rw
519 multcount 0 0 8 rw
520 nice1 1 0 1 rw
521 nowerr 0 0 1 rw
522 pio_mode write-only 0 255 w
523 slow 0 0 1 rw
524 unmaskirq 0 0 1 rw
525 using_dma 0 0 1 rw
528 1.4 Networking info in /proc/net
529 --------------------------------
531 The subdirectory /proc/net follows the usual pattern. Table 1-6 shows the
532 additional values you get for IP version 6 if you configure the kernel to
533 support this. Table 1-7 lists the files and their meaning.
536 Table 1-6: IPv6 info in /proc/net
537 ..............................................................................
538 File Content
539 udp6 UDP sockets (IPv6)
540 tcp6 TCP sockets (IPv6)
541 raw6 Raw device statistics (IPv6)
542 igmp6 IP multicast addresses, which this host joined (IPv6)
543 if_inet6 List of IPv6 interface addresses
544 ipv6_route Kernel routing table for IPv6
545 rt6_stats Global IPv6 routing tables statistics
546 sockstat6 Socket statistics (IPv6)
547 snmp6 Snmp data (IPv6)
548 ..............................................................................
551 Table 1-7: Network info in /proc/net
552 ..............................................................................
553 File Content
554 arp Kernel ARP table
555 dev network devices with statistics
556 dev_mcast the Layer2 multicast groups a device is listening too
557 (interface index, label, number of references, number of bound
558 addresses).
559 dev_stat network device status
560 ip_fwchains Firewall chain linkage
561 ip_fwnames Firewall chain names
562 ip_masq Directory containing the masquerading tables
563 ip_masquerade Major masquerading table
564 netstat Network statistics
565 raw raw device statistics
566 route Kernel routing table
567 rpc Directory containing rpc info
568 rt_cache Routing cache
569 snmp SNMP data
570 sockstat Socket statistics
571 tcp TCP sockets
572 tr_rif Token ring RIF routing table
573 udp UDP sockets
574 unix UNIX domain sockets
575 wireless Wireless interface data (Wavelan etc)
576 igmp IP multicast addresses, which this host joined
577 psched Global packet scheduler parameters.
578 netlink List of PF_NETLINK sockets
579 ip_mr_vifs List of multicast virtual interfaces
580 ip_mr_cache List of multicast routing cache
581 ..............................................................................
583 You can use this information to see which network devices are available in
584 your system and how much traffic was routed over those devices:
586 > cat /proc/net/dev
587 Inter-|Receive |[...
588 face |bytes packets errs drop fifo frame compressed multicast|[...
589 lo: 908188 5596 0 0 0 0 0 0 [...
590 ppp0:15475140 20721 410 0 0 410 0 0 [...
591 eth0: 614530 7085 0 0 0 0 0 1 [...
593 ...] Transmit
594 ...] bytes packets errs drop fifo colls carrier compressed
595 ...] 908188 5596 0 0 0 0 0 0
596 ...] 1375103 17405 0 0 0 0 0 0
597 ...] 1703981 5535 0 0 0 3 0 0
599 In addition, each Channel Bond interface has it's own directory. For
600 example, the bond0 device will have a directory called /proc/net/bond0/.
601 It will contain information that is specific to that bond, such as the
602 current slaves of the bond, the link status of the slaves, and how
603 many times the slaves link has failed.
605 1.5 SCSI info
606 -------------
608 If you have a SCSI host adapter in your system, you'll find a subdirectory
609 named after the driver for this adapter in /proc/scsi. You'll also see a list
610 of all recognized SCSI devices in /proc/scsi:
612 >cat /proc/scsi/scsi
613 Attached devices:
614 Host: scsi0 Channel: 00 Id: 00 Lun: 00
615 Vendor: IBM Model: DGHS09U Rev: 03E0
616 Type: Direct-Access ANSI SCSI revision: 03
617 Host: scsi0 Channel: 00 Id: 06 Lun: 00
618 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04
619 Type: CD-ROM ANSI SCSI revision: 02
622 The directory named after the driver has one file for each adapter found in
623 the system. These files contain information about the controller, including
624 the used IRQ and the IO address range. The amount of information shown is
625 dependent on the adapter you use. The example shows the output for an Adaptec
626 AHA-2940 SCSI adapter:
628 > cat /proc/scsi/aic7xxx/0
630 Adaptec AIC7xxx driver version: 5.1.19/3.2.4
631 Compile Options:
632 TCQ Enabled By Default : Disabled
633 AIC7XXX_PROC_STATS : Disabled
634 AIC7XXX_RESET_DELAY : 5
635 Adapter Configuration:
636 SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
637 Ultra Wide Controller
638 PCI MMAPed I/O Base: 0xeb001000
639 Adapter SEEPROM Config: SEEPROM found and used.
640 Adaptec SCSI BIOS: Enabled
641 IRQ: 10
642 SCBs: Active 0, Max Active 2,
643 Allocated 15, HW 16, Page 255
644 Interrupts: 160328
645 BIOS Control Word: 0x18b6
646 Adapter Control Word: 0x005b
647 Extended Translation: Enabled
648 Disconnect Enable Flags: 0xffff
649 Ultra Enable Flags: 0x0001
650 Tag Queue Enable Flags: 0x0000
651 Ordered Queue Tag Flags: 0x0000
652 Default Tag Queue Depth: 8
653 Tagged Queue By Device array for aic7xxx host instance 0:
654 {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
655 Actual queue depth per device for aic7xxx host instance 0:
656 {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
657 Statistics:
658 (scsi0:0:0:0)
659 Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
660 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
661 Total transfers 160151 (74577 reads and 85574 writes)
662 (scsi0:0:6:0)
663 Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
664 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
665 Total transfers 0 (0 reads and 0 writes)
668 1.6 Parallel port info in /proc/parport
669 ---------------------------------------
671 The directory /proc/parport contains information about the parallel ports of
672 your system. It has one subdirectory for each port, named after the port
673 number (0,1,2,...).
675 These directories contain the four files shown in Table 1-8.
678 Table 1-8: Files in /proc/parport
679 ..............................................................................
680 File Content
681 autoprobe Any IEEE-1284 device ID information that has been acquired.
682 devices list of the device drivers using that port. A + will appear by the
683 name of the device currently using the port (it might not appear
684 against any).
685 hardware Parallel port's base address, IRQ line and DMA channel.
686 irq IRQ that parport is using for that port. This is in a separate
687 file to allow you to alter it by writing a new value in (IRQ
688 number or none).
689 ..............................................................................
691 1.7 TTY info in /proc/tty
692 -------------------------
694 Information about the available and actually used tty's can be found in the
695 directory /proc/tty.You'll find entries for drivers and line disciplines in
696 this directory, as shown in Table 1-9.
699 Table 1-9: Files in /proc/tty
700 ..............................................................................
701 File Content
702 drivers list of drivers and their usage
703 ldiscs registered line disciplines
704 driver/serial usage statistic and status of single tty lines
705 ..............................................................................
707 To see which tty's are currently in use, you can simply look into the file
708 /proc/tty/drivers:
710 > cat /proc/tty/drivers
711 pty_slave /dev/pts 136 0-255 pty:slave
712 pty_master /dev/ptm 128 0-255 pty:master
713 pty_slave /dev/ttyp 3 0-255 pty:slave
714 pty_master /dev/pty 2 0-255 pty:master
715 serial /dev/cua 5 64-67 serial:callout
716 serial /dev/ttyS 4 64-67 serial
717 /dev/tty0 /dev/tty0 4 0 system:vtmaster
718 /dev/ptmx /dev/ptmx 5 2 system
719 /dev/console /dev/console 5 1 system:console
720 /dev/tty /dev/tty 5 0 system:/dev/tty
721 unknown /dev/tty 4 1-63 console
724 1.8 Miscellaneous kernel statistics in /proc/stat
725 -------------------------------------------------
727 Various pieces of information about kernel activity are available in the
728 /proc/stat file. All of the numbers reported in this file are aggregates
729 since the system first booted. For a quick look, simply cat the file:
731 > cat /proc/stat
732 cpu 2255 34 2290 22625563 6290 127 456
733 cpu0 1132 34 1441 11311718 3675 127 438
734 cpu1 1123 0 849 11313845 2614 0 18
735 intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
736 ctxt 1990473
737 btime 1062191376
738 processes 2915
739 procs_running 1
740 procs_blocked 0
742 The very first "cpu" line aggregates the numbers in all of the other "cpuN"
743 lines. These numbers identify the amount of time the CPU has spent performing
744 different kinds of work. Time units are in USER_HZ (typically hundredths of a
745 second). The meanings of the columns are as follows, from left to right:
747 - user: normal processes executing in user mode
748 - nice: niced processes executing in user mode
749 - system: processes executing in kernel mode
750 - idle: twiddling thumbs
751 - iowait: waiting for I/O to complete
752 - irq: servicing interrupts
753 - softirq: servicing softirqs
755 The "intr" line gives counts of interrupts serviced since boot time, for each
756 of the possible system interrupts. The first column is the total of all
757 interrupts serviced; each subsequent column is the total for that particular
758 interrupt.
760 The "ctxt" line gives the total number of context switches across all CPUs.
762 The "btime" line gives the time at which the system booted, in seconds since
763 the Unix epoch.
765 The "processes" line gives the number of processes and threads created, which
766 includes (but is not limited to) those created by calls to the fork() and
767 clone() system calls.
769 The "procs_running" line gives the number of processes currently running on
770 CPUs.
772 The "procs_blocked" line gives the number of processes currently blocked,
773 waiting for I/O to complete.
776 ------------------------------------------------------------------------------
777 Summary
778 ------------------------------------------------------------------------------
779 The /proc file system serves information about the running system. It not only
780 allows access to process data but also allows you to request the kernel status
781 by reading files in the hierarchy.
783 The directory structure of /proc reflects the types of information and makes
784 it easy, if not obvious, where to look for specific data.
785 ------------------------------------------------------------------------------
787 ------------------------------------------------------------------------------
788 CHAPTER 2: MODIFYING SYSTEM PARAMETERS
789 ------------------------------------------------------------------------------
791 ------------------------------------------------------------------------------
792 In This Chapter
793 ------------------------------------------------------------------------------
794 * Modifying kernel parameters by writing into files found in /proc/sys
795 * Exploring the files which modify certain parameters
796 * Review of the /proc/sys file tree
797 ------------------------------------------------------------------------------
800 A very interesting part of /proc is the directory /proc/sys. This is not only
801 a source of information, it also allows you to change parameters within the
802 kernel. Be very careful when attempting this. You can optimize your system,
803 but you can also cause it to crash. Never alter kernel parameters on a
804 production system. Set up a development machine and test to make sure that
805 everything works the way you want it to. You may have no alternative but to
806 reboot the machine once an error has been made.
808 To change a value, simply echo the new value into the file. An example is
809 given below in the section on the file system data. You need to be root to do
810 this. You can create your own boot script to perform this every time your
811 system boots.
813 The files in /proc/sys can be used to fine tune and monitor miscellaneous and
814 general things in the operation of the Linux kernel. Since some of the files
815 can inadvertently disrupt your system, it is advisable to read both
816 documentation and source before actually making adjustments. In any case, be
817 very careful when writing to any of these files. The entries in /proc may
818 change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
819 review the kernel documentation in the directory /usr/src/linux/Documentation.
820 This chapter is heavily based on the documentation included in the pre 2.2
821 kernels, and became part of it in version 2.2.1 of the Linux kernel.
823 2.1 /proc/sys/fs - File system data
824 -----------------------------------
826 This subdirectory contains specific file system, file handle, inode, dentry
827 and quota information.
829 Currently, these files are in /proc/sys/fs:
831 dentry-state
832 ------------
834 Status of the directory cache. Since directory entries are dynamically
835 allocated and deallocated, this file indicates the current status. It holds
836 six values, in which the last two are not used and are always zero. The others
837 are listed in table 2-1.
840 Table 2-1: Status files of the directory cache
841 ..............................................................................
842 File Content
843 nr_dentry Almost always zero
844 nr_unused Number of unused cache entries
845 age_limit
846 in seconds after the entry may be reclaimed, when memory is short
847 want_pages internally
848 ..............................................................................
850 dquot-nr and dquot-max
851 ----------------------
853 The file dquot-max shows the maximum number of cached disk quota entries.
855 The file dquot-nr shows the number of allocated disk quota entries and the
856 number of free disk quota entries.
858 If the number of available cached disk quotas is very low and you have a large
859 number of simultaneous system users, you might want to raise the limit.
861 file-nr and file-max
862 --------------------
864 The kernel allocates file handles dynamically, but doesn't free them again at
865 this time.
867 The value in file-max denotes the maximum number of file handles that the
868 Linux kernel will allocate. When you get a lot of error messages about running
869 out of file handles, you might want to raise this limit. The default value is
870 10% of RAM in kilobytes. To change it, just write the new number into the
871 file:
873 # cat /proc/sys/fs/file-max
874 4096
875 # echo 8192 > /proc/sys/fs/file-max
876 # cat /proc/sys/fs/file-max
877 8192
880 This method of revision is useful for all customizable parameters of the
881 kernel - simply echo the new value to the corresponding file.
883 Historically, the three values in file-nr denoted the number of allocated file
884 handles, the number of allocated but unused file handles, and the maximum
885 number of file handles. Linux 2.6 always reports 0 as the number of free file
886 handles -- this is not an error, it just means that the number of allocated
887 file handles exactly matches the number of used file handles.
889 Attempts to allocate more file descriptors than file-max are reported with
890 printk, look for "VFS: file-max limit <number> reached".
892 inode-state and inode-nr
893 ------------------------
895 The file inode-nr contains the first two items from inode-state, so we'll skip
896 to that file...
898 inode-state contains two actual numbers and five dummy values. The numbers
899 are nr_inodes and nr_free_inodes (in order of appearance).
901 nr_inodes
902 ~~~~~~~~~
904 Denotes the number of inodes the system has allocated. This number will
905 grow and shrink dynamically.
907 nr_free_inodes
908 --------------
910 Represents the number of free inodes. Ie. The number of inuse inodes is
911 (nr_inodes - nr_free_inodes).
913 aio-nr and aio-max-nr
914 ---------------------
916 aio-nr is the running total of the number of events specified on the
917 io_setup system call for all currently active aio contexts. If aio-nr
918 reaches aio-max-nr then io_setup will fail with EAGAIN. Note that
919 raising aio-max-nr does not result in the pre-allocation or re-sizing
920 of any kernel data structures.
922 2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats
923 -----------------------------------------------------------
925 Besides these files, there is the subdirectory /proc/sys/fs/binfmt_misc. This
926 handles the kernel support for miscellaneous binary formats.
928 Binfmt_misc provides the ability to register additional binary formats to the
929 Kernel without compiling an additional module/kernel. Therefore, binfmt_misc
930 needs to know magic numbers at the beginning or the filename extension of the
931 binary.
933 It works by maintaining a linked list of structs that contain a description of
934 a binary format, including a magic with size (or the filename extension),
935 offset and mask, and the interpreter name. On request it invokes the given
936 interpreter with the original program as argument, as binfmt_java and
937 binfmt_em86 and binfmt_mz do. Since binfmt_misc does not define any default
938 binary-formats, you have to register an additional binary-format.
940 There are two general files in binfmt_misc and one file per registered format.
941 The two general files are register and status.
943 Registering a new binary format
944 -------------------------------
946 To register a new binary format you have to issue the command
948 echo :name:type:offset:magic:mask:interpreter: > /proc/sys/fs/binfmt_misc/register
952 with appropriate name (the name for the /proc-dir entry), offset (defaults to
953 0, if omitted), magic, mask (which can be omitted, defaults to all 0xff) and
954 last but not least, the interpreter that is to be invoked (for example and
955 testing /bin/echo). Type can be M for usual magic matching or E for filename
956 extension matching (give extension in place of magic).
958 Check or reset the status of the binary format handler
959 ------------------------------------------------------
961 If you do a cat on the file /proc/sys/fs/binfmt_misc/status, you will get the
962 current status (enabled/disabled) of binfmt_misc. Change the status by echoing
963 0 (disables) or 1 (enables) or -1 (caution: this clears all previously
964 registered binary formats) to status. For example echo 0 > status to disable
965 binfmt_misc (temporarily).
967 Status of a single handler
968 --------------------------
970 Each registered handler has an entry in /proc/sys/fs/binfmt_misc. These files
971 perform the same function as status, but their scope is limited to the actual
972 binary format. By cating this file, you also receive all related information
973 about the interpreter/magic of the binfmt.
975 Example usage of binfmt_misc (emulate binfmt_java)
976 --------------------------------------------------
978 cd /proc/sys/fs/binfmt_misc
979 echo ':Java:M::\xca\xfe\xba\xbe::/usr/local/java/bin/javawrapper:' > register
980 echo ':HTML:E::html::/usr/local/java/bin/appletviewer:' > register
981 echo ':Applet:M::<!--applet::/usr/local/java/bin/appletviewer:' > register
982 echo ':DEXE:M::\x0eDEX::/usr/bin/dosexec:' > register
985 These four lines add support for Java executables and Java applets (like
986 binfmt_java, additionally recognizing the .html extension with no need to put
987 <!--applet> to every applet file). You have to install the JDK and the
988 shell-script /usr/local/java/bin/javawrapper too. It works around the
989 brokenness of the Java filename handling. To add a Java binary, just create a
990 link to the class-file somewhere in the path.
992 2.3 /proc/sys/kernel - general kernel parameters
993 ------------------------------------------------
995 This directory reflects general kernel behaviors. As I've said before, the
996 contents depend on your configuration. Here you'll find the most important
997 files, along with descriptions of what they mean and how to use them.
999 acct
1000 ----
1002 The file contains three values; highwater, lowwater, and frequency.
1004 It exists only when BSD-style process accounting is enabled. These values
1005 control its behavior. If the free space on the file system where the log lives
1006 goes below lowwater percentage, accounting suspends. If it goes above
1007 highwater percentage, accounting resumes. Frequency determines how often you
1008 check the amount of free space (value is in seconds). Default settings are: 4,
1009 2, and 30. That is, suspend accounting if there is less than 2 percent free;
1010 resume it if we have a value of 3 or more percent; consider information about
1011 the amount of free space valid for 30 seconds
1013 ctrl-alt-del
1014 ------------
1016 When the value in this file is 0, ctrl-alt-del is trapped and sent to the init
1017 program to handle a graceful restart. However, when the value is greater that
1018 zero, Linux's reaction to this key combination will be an immediate reboot,
1019 without syncing its dirty buffers.
1021 [NOTE]
1022 When a program (like dosemu) has the keyboard in raw mode, the
1023 ctrl-alt-del is intercepted by the program before it ever reaches the
1024 kernel tty layer, and it is up to the program to decide what to do with
1025 it.
1027 domainname and hostname
1028 -----------------------
1030 These files can be controlled to set the NIS domainname and hostname of your
1031 box. For the classic darkstar.frop.org a simple:
1033 # echo "darkstar" > /proc/sys/kernel/hostname
1034 # echo "frop.org" > /proc/sys/kernel/domainname
1037 would suffice to set your hostname and NIS domainname.
1039 osrelease, ostype and version
1040 -----------------------------
1042 The names make it pretty obvious what these fields contain:
1044 > cat /proc/sys/kernel/osrelease
1045 2.2.12
1047 > cat /proc/sys/kernel/ostype
1048 Linux
1050 > cat /proc/sys/kernel/version
1051 #4 Fri Oct 1 12:41:14 PDT 1999
1054 The files osrelease and ostype should be clear enough. Version needs a little
1055 more clarification. The #4 means that this is the 4th kernel built from this
1056 source base and the date after it indicates the time the kernel was built. The
1057 only way to tune these values is to rebuild the kernel.
1059 panic
1060 -----
1062 The value in this file represents the number of seconds the kernel waits
1063 before rebooting on a panic. When you use the software watchdog, the
1064 recommended setting is 60. If set to 0, the auto reboot after a kernel panic
1065 is disabled, which is the default setting.
1067 printk
1068 ------
1070 The four values in printk denote
1071 * console_loglevel,
1072 * default_message_loglevel,
1073 * minimum_console_loglevel and
1074 * default_console_loglevel
1075 respectively.
1077 These values influence printk() behavior when printing or logging error
1078 messages, which come from inside the kernel. See syslog(2) for more
1079 information on the different log levels.
1081 console_loglevel
1082 ----------------
1084 Messages with a higher priority than this will be printed to the console.
1086 default_message_level
1087 ---------------------
1089 Messages without an explicit priority will be printed with this priority.
1091 minimum_console_loglevel
1092 ------------------------
1094 Minimum (highest) value to which the console_loglevel can be set.
1096 default_console_loglevel
1097 ------------------------
1099 Default value for console_loglevel.
1101 sg-big-buff
1102 -----------
1104 This file shows the size of the generic SCSI (sg) buffer. At this point, you
1105 can't tune it yet, but you can change it at compile time by editing
1106 include/scsi/sg.h and changing the value of SG_BIG_BUFF.
1108 If you use a scanner with SANE (Scanner Access Now Easy) you might want to set
1109 this to a higher value. Refer to the SANE documentation on this issue.
1111 modprobe
1112 --------
1114 The location where the modprobe binary is located. The kernel uses this
1115 program to load modules on demand.
1117 unknown_nmi_panic
1118 -----------------
1120 The value in this file affects behavior of handling NMI. When the value is
1121 non-zero, unknown NMI is trapped and then panic occurs. At that time, kernel
1122 debugging information is displayed on console.
1124 NMI switch that most IA32 servers have fires unknown NMI up, for example.
1125 If a system hangs up, try pressing the NMI switch.
1127 [NOTE]
1128 This function and oprofile share a NMI callback. Therefore this function
1129 cannot be enabled when oprofile is activated.
1130 And NMI watchdog will be disabled when the value in this file is set to
1131 non-zero.
1134 2.4 /proc/sys/vm - The virtual memory subsystem
1135 -----------------------------------------------
1137 The files in this directory can be used to tune the operation of the virtual
1138 memory (VM) subsystem of the Linux kernel.
1140 vfs_cache_pressure
1141 ------------------
1143 Controls the tendency of the kernel to reclaim the memory which is used for
1144 caching of directory and inode objects.
1146 At the default value of vfs_cache_pressure=100 the kernel will attempt to
1147 reclaim dentries and inodes at a "fair" rate with respect to pagecache and
1148 swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer
1149 to retain dentry and inode caches. Increasing vfs_cache_pressure beyond 100
1150 causes the kernel to prefer to reclaim dentries and inodes.
1152 dirty_background_ratio
1153 ----------------------
1155 Contains, as a percentage of total system memory, the number of pages at which
1156 the pdflush background writeback daemon will start writing out dirty data.
1158 dirty_ratio
1159 -----------------
1161 Contains, as a percentage of total system memory, the number of pages at which
1162 a process which is generating disk writes will itself start writing out dirty
1163 data.
1165 dirty_writeback_centisecs
1166 -------------------------
1168 The pdflush writeback daemons will periodically wake up and write `old' data
1169 out to disk. This tunable expresses the interval between those wakeups, in
1170 100'ths of a second.
1172 Setting this to zero disables periodic writeback altogether.
1174 dirty_expire_centisecs
1175 ----------------------
1177 This tunable is used to define when dirty data is old enough to be eligible
1178 for writeout by the pdflush daemons. It is expressed in 100'ths of a second.
1179 Data which has been dirty in-memory for longer than this interval will be
1180 written out next time a pdflush daemon wakes up.
1182 legacy_va_layout
1183 ----------------
1185 If non-zero, this sysctl disables the new 32-bit mmap mmap layout - the kernel
1186 will use the legacy (2.4) layout for all processes.
1188 lower_zone_protection
1189 ---------------------
1191 For some specialised workloads on highmem machines it is dangerous for
1192 the kernel to allow process memory to be allocated from the "lowmem"
1193 zone. This is because that memory could then be pinned via the mlock()
1194 system call, or by unavailability of swapspace.
1196 And on large highmem machines this lack of reclaimable lowmem memory
1197 can be fatal.
1199 So the Linux page allocator has a mechanism which prevents allocations
1200 which _could_ use highmem from using too much lowmem. This means that
1201 a certain amount of lowmem is defended from the possibility of being
1202 captured into pinned user memory.
1204 (The same argument applies to the old 16 megabyte ISA DMA region. This
1205 mechanism will also defend that region from allocations which could use
1206 highmem or lowmem).
1208 The `lower_zone_protection' tunable determines how aggressive the kernel is
1209 in defending these lower zones. The default value is zero - no
1210 protection at all.
1212 If you have a machine which uses highmem or ISA DMA and your
1213 applications are using mlock(), or if you are running with no swap then
1214 you probably should increase the lower_zone_protection setting.
1216 The units of this tunable are fairly vague. It is approximately equal
1217 to "megabytes". So setting lower_zone_protection=100 will protect around 100
1218 megabytes of the lowmem zone from user allocations. It will also make
1219 those 100 megabytes unavaliable for use by applications and by
1220 pagecache, so there is a cost.
1222 The effects of this tunable may be observed by monitoring
1223 /proc/meminfo:LowFree. Write a single huge file and observe the point
1224 at which LowFree ceases to fall.
1226 A reasonable value for lower_zone_protection is 100.
1228 page-cluster
1229 ------------
1231 page-cluster controls the number of pages which are written to swap in
1232 a single attempt. The swap I/O size.
1234 It is a logarithmic value - setting it to zero means "1 page", setting
1235 it to 1 means "2 pages", setting it to 2 means "4 pages", etc.
1237 The default value is three (eight pages at a time). There may be some
1238 small benefits in tuning this to a different value if your workload is
1239 swap-intensive.
1241 overcommit_memory
1242 -----------------
1244 Controls overcommit of system memory, possibly allowing processes
1245 to allocate (but not use) more memory than is actually available.
1248 0 - Heuristic overcommit handling. Obvious overcommits of
1249 address space are refused. Used for a typical system. It
1250 ensures a seriously wild allocation fails while allowing
1251 overcommit to reduce swap usage. root is allowed to
1252 allocate slighly more memory in this mode. This is the
1253 default.
1255 1 - Always overcommit. Appropriate for some scientific
1256 applications.
1258 2 - Don't overcommit. The total address space commit
1259 for the system is not permitted to exceed swap plus a
1260 configurable percentage (default is 50) of physical RAM.
1261 Depending on the percentage you use, in most situations
1262 this means a process will not be killed while attempting
1263 to use already-allocated memory but will receive errors
1264 on memory allocation as appropriate.
1266 overcommit_ratio
1267 ----------------
1269 Percentage of physical memory size to include in overcommit calculations
1270 (see above.)
1272 Memory allocation limit = swapspace + physmem * (overcommit_ratio / 100)
1274 swapspace = total size of all swap areas
1275 physmem = size of physical memory in system
1277 nr_hugepages and hugetlb_shm_group
1278 ----------------------------------
1280 nr_hugepages configures number of hugetlb page reserved for the system.
1282 hugetlb_shm_group contains group id that is allowed to create SysV shared
1283 memory segment using hugetlb page.
1285 laptop_mode
1286 -----------
1288 laptop_mode is a knob that controls "laptop mode". All the things that are
1289 controlled by this knob are discussed in Documentation/laptop-mode.txt.
1291 block_dump
1292 ----------
1294 block_dump enables block I/O debugging when set to a nonzero value. More
1295 information on block I/O debugging is in Documentation/laptop-mode.txt.
1297 swap_token_timeout
1298 ------------------
1300 This file contains valid hold time of swap out protection token. The Linux
1301 VM has token based thrashing control mechanism and uses the token to prevent
1302 unnecessary page faults in thrashing situation. The unit of the value is
1303 second. The value would be useful to tune thrashing behavior.
1305 drop_caches
1306 -----------
1308 Writing to this will cause the kernel to drop clean caches, dentries and
1309 inodes from memory, causing that memory to become free.
1311 To free pagecache:
1312 echo 1 > /proc/sys/vm/drop_caches
1313 To free dentries and inodes:
1314 echo 2 > /proc/sys/vm/drop_caches
1315 To free pagecache, dentries and inodes:
1316 echo 3 > /proc/sys/vm/drop_caches
1318 As this is a non-destructive operation and dirty objects are not freeable, the
1319 user should run `sync' first.
1322 2.5 /proc/sys/dev - Device specific parameters
1323 ----------------------------------------------
1325 Currently there is only support for CDROM drives, and for those, there is only
1326 one read-only file containing information about the CD-ROM drives attached to
1327 the system:
1329 >cat /proc/sys/dev/cdrom/info
1330 CD-ROM information, Id: cdrom.c 2.55 1999/04/25
1332 drive name: sr0 hdb
1333 drive speed: 32 40
1334 drive # of slots: 1 0
1335 Can close tray: 1 1
1336 Can open tray: 1 1
1337 Can lock tray: 1 1
1338 Can change speed: 1 1
1339 Can select disk: 0 1
1340 Can read multisession: 1 1
1341 Can read MCN: 1 1
1342 Reports media changed: 1 1
1343 Can play audio: 1 1
1346 You see two drives, sr0 and hdb, along with a list of their features.
1348 2.6 /proc/sys/sunrpc - Remote procedure calls
1349 ---------------------------------------------
1351 This directory contains four files, which enable or disable debugging for the
1352 RPC functions NFS, NFS-daemon, RPC and NLM. The default values are 0. They can
1353 be set to one to turn debugging on. (The default value is 0 for each)
1355 2.7 /proc/sys/net - Networking stuff
1356 ------------------------------------
1358 The interface to the networking parts of the kernel is located in
1359 /proc/sys/net. Table 2-3 shows all possible subdirectories. You may see only
1360 some of them, depending on your kernel's configuration.
1363 Table 2-3: Subdirectories in /proc/sys/net
1364 ..............................................................................
1365 Directory Content Directory Content
1366 core General parameter appletalk Appletalk protocol
1367 unix Unix domain sockets netrom NET/ROM
1368 802 E802 protocol ax25 AX25
1369 ethernet Ethernet protocol rose X.25 PLP layer
1370 ipv4 IP version 4 x25 X.25 protocol
1371 ipx IPX token-ring IBM token ring
1372 bridge Bridging decnet DEC net
1373 ipv6 IP version 6
1374 ..............................................................................
1376 We will concentrate on IP networking here. Since AX15, X.25, and DEC Net are
1377 only minor players in the Linux world, we'll skip them in this chapter. You'll
1378 find some short info on Appletalk and IPX further on in this chapter. Review
1379 the online documentation and the kernel source to get a detailed view of the
1380 parameters for those protocols. In this section we'll discuss the
1381 subdirectories printed in bold letters in the table above. As default values
1382 are suitable for most needs, there is no need to change these values.
1384 /proc/sys/net/core - Network core options
1385 -----------------------------------------
1387 rmem_default
1388 ------------
1390 The default setting of the socket receive buffer in bytes.
1392 rmem_max
1393 --------
1395 The maximum receive socket buffer size in bytes.
1397 wmem_default
1398 ------------
1400 The default setting (in bytes) of the socket send buffer.
1402 wmem_max
1403 --------
1405 The maximum send socket buffer size in bytes.
1407 message_burst and message_cost
1408 ------------------------------
1410 These parameters are used to limit the warning messages written to the kernel
1411 log from the networking code. They enforce a rate limit to make a
1412 denial-of-service attack impossible. A higher message_cost factor, results in
1413 fewer messages that will be written. Message_burst controls when messages will
1414 be dropped. The default settings limit warning messages to one every five
1415 seconds.
1417 netdev_max_backlog
1418 ------------------
1420 Maximum number of packets, queued on the INPUT side, when the interface
1421 receives packets faster than kernel can process them.
1423 optmem_max
1424 ----------
1426 Maximum ancillary buffer size allowed per socket. Ancillary data is a sequence
1427 of struct cmsghdr structures with appended data.
1429 /proc/sys/net/unix - Parameters for Unix domain sockets
1430 -------------------------------------------------------
1432 There are only two files in this subdirectory. They control the delays for
1433 deleting and destroying socket descriptors.
1435 2.8 /proc/sys/net/ipv4 - IPV4 settings
1436 --------------------------------------
1438 IP version 4 is still the most used protocol in Unix networking. It will be
1439 replaced by IP version 6 in the next couple of years, but for the moment it's
1440 the de facto standard for the internet and is used in most networking
1441 environments around the world. Because of the importance of this protocol,
1442 we'll have a deeper look into the subtree controlling the behavior of the IPv4
1443 subsystem of the Linux kernel.
1445 Let's start with the entries in /proc/sys/net/ipv4.
1447 ICMP settings
1448 -------------
1450 icmp_echo_ignore_all and icmp_echo_ignore_broadcasts
1451 ----------------------------------------------------
1453 Turn on (1) or off (0), if the kernel should ignore all ICMP ECHO requests, or
1454 just those to broadcast and multicast addresses.
1456 Please note that if you accept ICMP echo requests with a broadcast/multi\-cast
1457 destination address your network may be used as an exploder for denial of
1458 service packet flooding attacks to other hosts.
1460 icmp_destunreach_rate, icmp_echoreply_rate, icmp_paramprob_rate and icmp_timeexeed_rate
1461 ---------------------------------------------------------------------------------------
1463 Sets limits for sending ICMP packets to specific targets. A value of zero
1464 disables all limiting. Any positive value sets the maximum package rate in
1465 hundredth of a second (on Intel systems).
1467 IP settings
1468 -----------
1470 ip_autoconfig
1471 -------------
1473 This file contains the number one if the host received its IP configuration by
1474 RARP, BOOTP, DHCP or a similar mechanism. Otherwise it is zero.
1476 ip_default_ttl
1477 --------------
1479 TTL (Time To Live) for IPv4 interfaces. This is simply the maximum number of
1480 hops a packet may travel.
1482 ip_dynaddr
1483 ----------
1485 Enable dynamic socket address rewriting on interface address change. This is
1486 useful for dialup interface with changing IP addresses.
1488 ip_forward
1489 ----------
1491 Enable or disable forwarding of IP packages between interfaces. Changing this
1492 value resets all other parameters to their default values. They differ if the
1493 kernel is configured as host or router.
1495 ip_local_port_range
1496 -------------------
1498 Range of ports used by TCP and UDP to choose the local port. Contains two
1499 numbers, the first number is the lowest port, the second number the highest
1500 local port. Default is 1024-4999. Should be changed to 32768-61000 for
1501 high-usage systems.
1503 ip_no_pmtu_disc
1504 ---------------
1506 Global switch to turn path MTU discovery off. It can also be set on a per
1507 socket basis by the applications or on a per route basis.
1509 ip_masq_debug
1510 -------------
1512 Enable/disable debugging of IP masquerading.
1514 IP fragmentation settings
1515 -------------------------
1517 ipfrag_high_trash and ipfrag_low_trash
1518 --------------------------------------
1520 Maximum memory used to reassemble IP fragments. When ipfrag_high_thresh bytes
1521 of memory is allocated for this purpose, the fragment handler will toss
1522 packets until ipfrag_low_thresh is reached.
1524 ipfrag_time
1525 -----------
1527 Time in seconds to keep an IP fragment in memory.
1529 TCP settings
1530 ------------
1532 tcp_ecn
1533 -------
1535 This file controls the use of the ECN bit in the IPv4 headers, this is a new
1536 feature about Explicit Congestion Notification, but some routers and firewalls
1537 block trafic that has this bit set, so it could be necessary to echo 0 to
1538 /proc/sys/net/ipv4/tcp_ecn, if you want to talk to this sites. For more info
1539 you could read RFC2481.
1541 tcp_retrans_collapse
1542 --------------------
1544 Bug-to-bug compatibility with some broken printers. On retransmit, try to send
1545 larger packets to work around bugs in certain TCP stacks. Can be turned off by
1546 setting it to zero.
1548 tcp_keepalive_probes
1549 --------------------
1551 Number of keep alive probes TCP sends out, until it decides that the
1552 connection is broken.
1554 tcp_keepalive_time
1555 ------------------
1557 How often TCP sends out keep alive messages, when keep alive is enabled. The
1558 default is 2 hours.
1560 tcp_syn_retries
1561 ---------------
1563 Number of times initial SYNs for a TCP connection attempt will be
1564 retransmitted. Should not be higher than 255. This is only the timeout for
1565 outgoing connections, for incoming connections the number of retransmits is
1566 defined by tcp_retries1.
1568 tcp_sack
1569 --------
1571 Enable select acknowledgments after RFC2018.
1573 tcp_timestamps
1574 --------------
1576 Enable timestamps as defined in RFC1323.
1578 tcp_stdurg
1579 ----------
1581 Enable the strict RFC793 interpretation of the TCP urgent pointer field. The
1582 default is to use the BSD compatible interpretation of the urgent pointer
1583 pointing to the first byte after the urgent data. The RFC793 interpretation is
1584 to have it point to the last byte of urgent data. Enabling this option may
1585 lead to interoperatibility problems. Disabled by default.
1587 tcp_syncookies
1588 --------------
1590 Only valid when the kernel was compiled with CONFIG_SYNCOOKIES. Send out
1591 syncookies when the syn backlog queue of a socket overflows. This is to ward
1592 off the common 'syn flood attack'. Disabled by default.
1594 Note that the concept of a socket backlog is abandoned. This means the peer
1595 may not receive reliable error messages from an over loaded server with
1596 syncookies enabled.
1598 tcp_window_scaling
1599 ------------------
1601 Enable window scaling as defined in RFC1323.
1603 tcp_fin_timeout
1604 ---------------
1606 The length of time in seconds it takes to receive a final FIN before the
1607 socket is always closed. This is strictly a violation of the TCP
1608 specification, but required to prevent denial-of-service attacks.
1610 tcp_max_ka_probes
1611 -----------------
1613 Indicates how many keep alive probes are sent per slow timer run. Should not
1614 be set too high to prevent bursts.
1616 tcp_max_syn_backlog
1617 -------------------
1619 Length of the per socket backlog queue. Since Linux 2.2 the backlog specified
1620 in listen(2) only specifies the length of the backlog queue of already
1621 established sockets. When more connection requests arrive Linux starts to drop
1622 packets. When syncookies are enabled the packets are still answered and the
1623 maximum queue is effectively ignored.
1625 tcp_retries1
1626 ------------
1628 Defines how often an answer to a TCP connection request is retransmitted
1629 before giving up.
1631 tcp_retries2
1632 ------------
1634 Defines how often a TCP packet is retransmitted before giving up.
1636 Interface specific settings
1637 ---------------------------
1639 In the directory /proc/sys/net/ipv4/conf you'll find one subdirectory for each
1640 interface the system knows about and one directory calls all. Changes in the
1641 all subdirectory affect all interfaces, whereas changes in the other
1642 subdirectories affect only one interface. All directories have the same
1643 entries:
1645 accept_redirects
1646 ----------------
1648 This switch decides if the kernel accepts ICMP redirect messages or not. The
1649 default is 'yes' if the kernel is configured for a regular host and 'no' for a
1650 router configuration.
1652 accept_source_route
1653 -------------------
1655 Should source routed packages be accepted or declined. The default is
1656 dependent on the kernel configuration. It's 'yes' for routers and 'no' for
1657 hosts.
1659 bootp_relay
1660 ~~~~~~~~~~~
1662 Accept packets with source address 0.b.c.d with destinations not to this host
1663 as local ones. It is supposed that a BOOTP relay daemon will catch and forward
1664 such packets.
1666 The default is 0, since this feature is not implemented yet (kernel version
1667 2.2.12).
1669 forwarding
1670 ----------
1672 Enable or disable IP forwarding on this interface.
1674 log_martians
1675 ------------
1677 Log packets with source addresses with no known route to kernel log.
1679 mc_forwarding
1680 -------------
1682 Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE and a
1683 multicast routing daemon is required.
1685 proxy_arp
1686 ---------
1688 Does (1) or does not (0) perform proxy ARP.
1690 rp_filter
1691 ---------
1693 Integer value determines if a source validation should be made. 1 means yes, 0
1694 means no. Disabled by default, but local/broadcast address spoofing is always
1695 on.
1697 If you set this to 1 on a router that is the only connection for a network to
1698 the net, it will prevent spoofing attacks against your internal networks
1699 (external addresses can still be spoofed), without the need for additional
1700 firewall rules.
1702 secure_redirects
1703 ----------------
1705 Accept ICMP redirect messages only for gateways, listed in default gateway
1706 list. Enabled by default.
1708 shared_media
1709 ------------
1711 If it is not set the kernel does not assume that different subnets on this
1712 device can communicate directly. Default setting is 'yes'.
1714 send_redirects
1715 --------------
1717 Determines whether to send ICMP redirects to other hosts.
1719 Routing settings
1720 ----------------
1722 The directory /proc/sys/net/ipv4/route contains several file to control
1723 routing issues.
1725 error_burst and error_cost
1726 --------------------------
1728 These parameters are used to limit how many ICMP destination unreachable to
1729 send from the host in question. ICMP destination unreachable messages are
1730 sent when we can not reach the next hop, while trying to transmit a packet.
1731 It will also print some error messages to kernel logs if someone is ignoring
1732 our ICMP redirects. The higher the error_cost factor is, the fewer
1733 destination unreachable and error messages will be let through. Error_burst
1734 controls when destination unreachable messages and error messages will be
1735 dropped. The default settings limit warning messages to five every second.
1737 flush
1738 -----
1740 Writing to this file results in a flush of the routing cache.
1742 gc_elasticity, gc_interval, gc_min_interval_ms, gc_timeout, gc_thresh
1743 ---------------------------------------------------------------------
1745 Values to control the frequency and behavior of the garbage collection
1746 algorithm for the routing cache. gc_min_interval is deprecated and replaced
1747 by gc_min_interval_ms.
1750 max_size
1751 --------
1753 Maximum size of the routing cache. Old entries will be purged once the cache
1754 reached has this size.
1756 max_delay, min_delay
1757 --------------------
1759 Delays for flushing the routing cache.
1761 redirect_load, redirect_number
1762 ------------------------------
1764 Factors which determine if more ICPM redirects should be sent to a specific
1765 host. No redirects will be sent once the load limit or the maximum number of
1766 redirects has been reached.
1768 redirect_silence
1769 ----------------
1771 Timeout for redirects. After this period redirects will be sent again, even if
1772 this has been stopped, because the load or number limit has been reached.
1774 Network Neighbor handling
1775 -------------------------
1777 Settings about how to handle connections with direct neighbors (nodes attached
1778 to the same link) can be found in the directory /proc/sys/net/ipv4/neigh.
1780 As we saw it in the conf directory, there is a default subdirectory which
1781 holds the default values, and one directory for each interface. The contents
1782 of the directories are identical, with the single exception that the default
1783 settings contain additional options to set garbage collection parameters.
1785 In the interface directories you'll find the following entries:
1787 base_reachable_time, base_reachable_time_ms
1788 -------------------------------------------
1790 A base value used for computing the random reachable time value as specified
1791 in RFC2461.
1793 Expression of base_reachable_time, which is deprecated, is in seconds.
1794 Expression of base_reachable_time_ms is in milliseconds.
1796 retrans_time, retrans_time_ms
1797 -----------------------------
1799 The time between retransmitted Neighbor Solicitation messages.
1800 Used for address resolution and to determine if a neighbor is
1801 unreachable.
1803 Expression of retrans_time, which is deprecated, is in 1/100 seconds (for
1804 IPv4) or in jiffies (for IPv6).
1805 Expression of retrans_time_ms is in milliseconds.
1807 unres_qlen
1808 ----------
1810 Maximum queue length for a pending arp request - the number of packets which
1811 are accepted from other layers while the ARP address is still resolved.
1813 anycast_delay
1814 -------------
1816 Maximum for random delay of answers to neighbor solicitation messages in
1817 jiffies (1/100 sec). Not yet implemented (Linux does not have anycast support
1818 yet).
1820 ucast_solicit
1821 -------------
1823 Maximum number of retries for unicast solicitation.
1825 mcast_solicit
1826 -------------
1828 Maximum number of retries for multicast solicitation.
1830 delay_first_probe_time
1831 ----------------------
1833 Delay for the first time probe if the neighbor is reachable. (see
1834 gc_stale_time)
1836 locktime
1837 --------
1839 An ARP/neighbor entry is only replaced with a new one if the old is at least
1840 locktime old. This prevents ARP cache thrashing.
1842 proxy_delay
1843 -----------
1845 Maximum time (real time is random [0..proxytime]) before answering to an ARP
1846 request for which we have an proxy ARP entry. In some cases, this is used to
1847 prevent network flooding.
1849 proxy_qlen
1850 ----------
1852 Maximum queue length of the delayed proxy arp timer. (see proxy_delay).
1854 app_solcit
1855 ----------
1857 Determines the number of requests to send to the user level ARP daemon. Use 0
1858 to turn off.
1860 gc_stale_time
1861 -------------
1863 Determines how often to check for stale ARP entries. After an ARP entry is
1864 stale it will be resolved again (which is useful when an IP address migrates
1865 to another machine). When ucast_solicit is greater than 0 it first tries to
1866 send an ARP packet directly to the known host When that fails and
1867 mcast_solicit is greater than 0, an ARP request is broadcasted.
1869 2.9 Appletalk
1870 -------------
1872 The /proc/sys/net/appletalk directory holds the Appletalk configuration data
1873 when Appletalk is loaded. The configurable parameters are:
1875 aarp-expiry-time
1876 ----------------
1878 The amount of time we keep an ARP entry before expiring it. Used to age out
1879 old hosts.
1881 aarp-resolve-time
1882 -----------------
1884 The amount of time we will spend trying to resolve an Appletalk address.
1886 aarp-retransmit-limit
1887 ---------------------
1889 The number of times we will retransmit a query before giving up.
1891 aarp-tick-time
1892 --------------
1894 Controls the rate at which expires are checked.
1896 The directory /proc/net/appletalk holds the list of active Appletalk sockets
1897 on a machine.
1899 The fields indicate the DDP type, the local address (in network:node format)
1900 the remote address, the size of the transmit pending queue, the size of the
1901 received queue (bytes waiting for applications to read) the state and the uid
1902 owning the socket.
1904 /proc/net/atalk_iface lists all the interfaces configured for appletalk.It
1905 shows the name of the interface, its Appletalk address, the network range on
1906 that address (or network number for phase 1 networks), and the status of the
1907 interface.
1909 /proc/net/atalk_route lists each known network route. It lists the target
1910 (network) that the route leads to, the router (may be directly connected), the
1911 route flags, and the device the route is using.
1913 2.10 IPX
1914 --------
1916 The IPX protocol has no tunable values in proc/sys/net.
1918 The IPX protocol does, however, provide proc/net/ipx. This lists each IPX
1919 socket giving the local and remote addresses in Novell format (that is
1920 network:node:port). In accordance with the strange Novell tradition,
1921 everything but the port is in hex. Not_Connected is displayed for sockets that
1922 are not tied to a specific remote address. The Tx and Rx queue sizes indicate
1923 the number of bytes pending for transmission and reception. The state
1924 indicates the state the socket is in and the uid is the owning uid of the
1925 socket.
1927 The /proc/net/ipx_interface file lists all IPX interfaces. For each interface
1928 it gives the network number, the node number, and indicates if the network is
1929 the primary network. It also indicates which device it is bound to (or
1930 Internal for internal networks) and the Frame Type if appropriate. Linux
1931 supports 802.3, 802.2, 802.2 SNAP and DIX (Blue Book) ethernet framing for
1932 IPX.
1934 The /proc/net/ipx_route table holds a list of IPX routes. For each route it
1935 gives the destination network, the router node (or Directly) and the network
1936 address of the router (or Connected) for internal networks.
1938 2.11 /proc/sys/fs/mqueue - POSIX message queues filesystem
1939 ----------------------------------------------------------
1941 The "mqueue" filesystem provides the necessary kernel features to enable the
1942 creation of a user space library that implements the POSIX message queues
1943 API (as noted by the MSG tag in the POSIX 1003.1-2001 version of the System
1944 Interfaces specification.)
1946 The "mqueue" filesystem contains values for determining/setting the amount of
1947 resources used by the file system.
1949 /proc/sys/fs/mqueue/queues_max is a read/write file for setting/getting the
1950 maximum number of message queues allowed on the system.
1952 /proc/sys/fs/mqueue/msg_max is a read/write file for setting/getting the
1953 maximum number of messages in a queue value. In fact it is the limiting value
1954 for another (user) limit which is set in mq_open invocation. This attribute of
1955 a queue must be less or equal then msg_max.
1957 /proc/sys/fs/mqueue/msgsize_max is a read/write file for setting/getting the
1958 maximum message size value (it is every message queue's attribute set during
1959 its creation).
1962 ------------------------------------------------------------------------------
1963 Summary
1964 ------------------------------------------------------------------------------
1965 Certain aspects of kernel behavior can be modified at runtime, without the
1966 need to recompile the kernel, or even to reboot the system. The files in the
1967 /proc/sys tree can not only be read, but also modified. You can use the echo
1968 command to write value into these files, thereby changing the default settings
1969 of the kernel.
1970 ------------------------------------------------------------------------------