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2 T H E /proc F I L E S Y S T E M
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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
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9 Version 1.3 Kernel version 2.2.12
10 Kernel version 2.4.0-test11-pre4
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17 0.1 Introduction/Credits
20 1 Collecting System Information
21 1.1 Process-Specific Subdirectories
23 1.3 IDE devices in /proc/ide
24 1.4 Networking info in /proc/net
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
41 2.11 /proc/sys/fs/mqueue - POSIX message queues filesystem
42 2.12 /proc/<pid>/oom_adj - Adjust the oom-killer score
43 2.13 /proc/<pid>/oom_score - Display current oom-killer score
44 2.14 /proc/<pid>/io - Display the IO accounting fields
46 ------------------------------------------------------------------------------
48 ------------------------------------------------------------------------------
50 0.1 Introduction/Credits
51 ------------------------
53 This documentation is part of a soon (or so we hope) to be released book on
54 the SuSE Linux distribution. As there is no complete documentation for the
55 /proc file system and we've used many freely available sources to write these
56 chapters, it seems only fair to give the work back to the Linux community.
57 This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm
58 afraid it's still far from complete, but we hope it will be useful. As far as
59 we know, it is the first 'all-in-one' document about the /proc file system. It
60 is focused on the Intel x86 hardware, so if you are looking for PPC, ARM,
61 SPARC, AXP, etc., features, you probably won't find what you are looking for.
62 It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
63 additions and patches are welcome and will be added to this document if you
66 We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
67 other people for help compiling this documentation. We'd also like to extend a
68 special thank you to Andi Kleen for documentation, which we relied on heavily
69 to create this document, as well as the additional information he provided.
70 Thanks to everybody else who contributed source or docs to the Linux kernel
71 and helped create a great piece of software... :)
73 If you have any comments, corrections or additions, please don't hesitate to
74 contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this
77 The latest version of this document is available online at
78 http://skaro.nightcrawler.com/~bb/Docs/Proc as HTML version.
80 If the above direction does not works for you, ypu could try the kernel
81 mailing list at linux-kernel@vger.kernel.org and/or try to reach me at
82 comandante@zaralinux.com.
87 We don't guarantee the correctness of this document, and if you come to us
88 complaining about how you screwed up your system because of incorrect
89 documentation, we won't feel responsible...
91 ------------------------------------------------------------------------------
92 CHAPTER 1: COLLECTING SYSTEM INFORMATION
93 ------------------------------------------------------------------------------
95 ------------------------------------------------------------------------------
97 ------------------------------------------------------------------------------
98 * Investigating the properties of the pseudo file system /proc and its
99 ability to provide information on the running Linux system
100 * Examining /proc's structure
101 * Uncovering various information about the kernel and the processes running
103 ------------------------------------------------------------------------------
106 The proc file system acts as an interface to internal data structures in the
107 kernel. It can be used to obtain information about the system and to change
108 certain kernel parameters at runtime (sysctl).
110 First, we'll take a look at the read-only parts of /proc. In Chapter 2, we
111 show you how you can use /proc/sys to change settings.
113 1.1 Process-Specific Subdirectories
114 -----------------------------------
116 The directory /proc contains (among other things) one subdirectory for each
117 process running on the system, which is named after the process ID (PID).
119 The link self points to the process reading the file system. Each process
120 subdirectory has the entries listed in Table 1-1.
123 Table 1-1: Process specific entries in /proc
124 ..............................................................................
126 clear_refs Clears page referenced bits shown in smaps output
127 cmdline Command line arguments
128 cpu Current and last cpu in which it was executed (2.4)(smp)
129 cwd Link to the current working directory
130 environ Values of environment variables
131 exe Link to the executable of this process
132 fd Directory, which contains all file descriptors
133 maps Memory maps to executables and library files (2.4)
134 mem Memory held by this process
135 root Link to the root directory of this process
137 statm Process memory status information
138 status Process status in human readable form
139 wchan If CONFIG_KALLSYMS is set, a pre-decoded wchan
140 smaps Extension based on maps, the rss size for each mapped file
141 ..............................................................................
143 For example, to get the status information of a process, all you have to do is
144 read the file /proc/PID/status:
146 >cat /proc/self/status
162 SigPnd: 0000000000000000
163 SigBlk: 0000000000000000
164 SigIgn: 0000000000000000
165 SigCgt: 0000000000000000
166 CapInh: 00000000fffffeff
167 CapPrm: 0000000000000000
168 CapEff: 0000000000000000
171 This shows you nearly the same information you would get if you viewed it with
172 the ps command. In fact, ps uses the proc file system to obtain its
173 information. The statm file contains more detailed information about the
174 process memory usage. Its seven fields are explained in Table 1-2.
177 Table 1-2: Contents of the statm files (as of 2.6.8-rc3)
178 ..............................................................................
180 size total program size (pages) (same as VmSize in status)
181 resident size of memory portions (pages) (same as VmRSS in status)
182 shared number of pages that are shared (i.e. backed by a file)
183 trs number of pages that are 'code' (not including libs; broken,
184 includes data segment)
185 lrs number of pages of library (always 0 on 2.6)
186 drs number of pages of data/stack (including libs; broken,
187 includes library text)
188 dt number of dirty pages (always 0 on 2.6)
189 ..............................................................................
194 Similar to the process entries, the kernel data files give information about
195 the running kernel. The files used to obtain this information are contained in
196 /proc and are listed in Table 1-3. Not all of these will be present in your
197 system. It depends on the kernel configuration and the loaded modules, which
198 files are there, and which are missing.
200 Table 1-3: Kernel info in /proc
201 ..............................................................................
203 apm Advanced power management info
204 buddyinfo Kernel memory allocator information (see text) (2.5)
205 bus Directory containing bus specific information
206 cmdline Kernel command line
207 cpuinfo Info about the CPU
208 devices Available devices (block and character)
209 dma Used DMS channels
210 filesystems Supported filesystems
211 driver Various drivers grouped here, currently rtc (2.4)
212 execdomains Execdomains, related to security (2.4)
213 fb Frame Buffer devices (2.4)
214 fs File system parameters, currently nfs/exports (2.4)
215 ide Directory containing info about the IDE subsystem
216 interrupts Interrupt usage
217 iomem Memory map (2.4)
218 ioports I/O port usage
219 irq Masks for irq to cpu affinity (2.4)(smp?)
220 isapnp ISA PnP (Plug&Play) Info (2.4)
221 kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
223 ksyms Kernel symbol table
224 loadavg Load average of last 1, 5 & 15 minutes
228 modules List of loaded modules
229 mounts Mounted filesystems
230 net Networking info (see text)
231 partitions Table of partitions known to the system
232 pci Depreciated info of PCI bus (new way -> /proc/bus/pci/,
233 decoupled by lspci (2.4)
235 scsi SCSI info (see text)
236 slabinfo Slab pool info
237 stat Overall statistics
238 swaps Swap space utilization
240 sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4)
241 tty Info of tty drivers
243 version Kernel version
244 video bttv info of video resources (2.4)
245 ..............................................................................
247 You can, for example, check which interrupts are currently in use and what
248 they are used for by looking in the file /proc/interrupts:
250 > cat /proc/interrupts
252 0: 8728810 XT-PIC timer
253 1: 895 XT-PIC keyboard
255 3: 531695 XT-PIC aha152x
256 4: 2014133 XT-PIC serial
257 5: 44401 XT-PIC pcnet_cs
260 12: 182918 XT-PIC PS/2 Mouse
262 14: 1232265 XT-PIC ide0
266 In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
267 output of a SMP machine):
269 > cat /proc/interrupts
272 0: 1243498 1214548 IO-APIC-edge timer
273 1: 8949 8958 IO-APIC-edge keyboard
274 2: 0 0 XT-PIC cascade
275 5: 11286 10161 IO-APIC-edge soundblaster
276 8: 1 0 IO-APIC-edge rtc
277 9: 27422 27407 IO-APIC-edge 3c503
278 12: 113645 113873 IO-APIC-edge PS/2 Mouse
280 14: 22491 24012 IO-APIC-edge ide0
281 15: 2183 2415 IO-APIC-edge ide1
282 17: 30564 30414 IO-APIC-level eth0
283 18: 177 164 IO-APIC-level bttv
288 NMI is incremented in this case because every timer interrupt generates a NMI
289 (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
291 LOC is the local interrupt counter of the internal APIC of every CPU.
293 ERR is incremented in the case of errors in the IO-APIC bus (the bus that
294 connects the CPUs in a SMP system. This means that an error has been detected,
295 the IO-APIC automatically retry the transmission, so it should not be a big
296 problem, but you should read the SMP-FAQ.
298 In this context it could be interesting to note the new irq directory in 2.4.
299 It could be used to set IRQ to CPU affinity, this means that you can "hook" an
300 IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
301 irq subdir is one subdir for each IRQ, and one file; prof_cpu_mask
305 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask
306 1 11 13 15 17 19 3 5 7 9
310 The contents of the prof_cpu_mask file and each smp_affinity file for each IRQ
311 is the same by default:
313 > cat /proc/irq/0/smp_affinity
316 It's a bitmask, in which you can specify which CPUs can handle the IRQ, you can
319 > echo 1 > /proc/irq/prof_cpu_mask
321 This means that only the first CPU will handle the IRQ, but you can also echo 5
322 which means that only the first and fourth CPU can handle the IRQ.
324 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
325 between all the CPUs which are allowed to handle it. As usual the kernel has
326 more info than you and does a better job than you, so the defaults are the
327 best choice for almost everyone.
329 There are three more important subdirectories in /proc: net, scsi, and sys.
330 The general rule is that the contents, or even the existence of these
331 directories, depend on your kernel configuration. If SCSI is not enabled, the
332 directory scsi may not exist. The same is true with the net, which is there
333 only when networking support is present in the running kernel.
335 The slabinfo file gives information about memory usage at the slab level.
336 Linux uses slab pools for memory management above page level in version 2.2.
337 Commonly used objects have their own slab pool (such as network buffers,
338 directory cache, and so on).
340 ..............................................................................
342 > cat /proc/buddyinfo
344 Node 0, zone DMA 0 4 5 4 4 3 ...
345 Node 0, zone Normal 1 0 0 1 101 8 ...
346 Node 0, zone HighMem 2 0 0 1 1 0 ...
348 Memory fragmentation is a problem under some workloads, and buddyinfo is a
349 useful tool for helping diagnose these problems. Buddyinfo will give you a
350 clue as to how big an area you can safely allocate, or why a previous
353 Each column represents the number of pages of a certain order which are
354 available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
355 ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
356 available in ZONE_NORMAL, etc...
358 ..............................................................................
362 Provides information about distribution and utilization of memory. This
363 varies by architecture and compile options. The following is from a
364 16GB PIII, which has highmem enabled. You may not have all of these fields.
369 MemTotal: 16344972 kB
376 HighTotal: 15597528 kB
377 HighFree: 13629632 kB
386 CommitLimit: 7669796 kB
387 Committed_AS: 100056 kB
389 VmallocTotal: 112216 kB
391 VmallocChunk: 111088 kB
393 MemTotal: Total usable ram (i.e. physical ram minus a few reserved
394 bits and the kernel binary code)
395 MemFree: The sum of LowFree+HighFree
396 Buffers: Relatively temporary storage for raw disk blocks
397 shouldn't get tremendously large (20MB or so)
398 Cached: in-memory cache for files read from the disk (the
399 pagecache). Doesn't include SwapCached
400 SwapCached: Memory that once was swapped out, is swapped back in but
401 still also is in the swapfile (if memory is needed it
402 doesn't need to be swapped out AGAIN because it is already
403 in the swapfile. This saves I/O)
404 Active: Memory that has been used more recently and usually not
405 reclaimed unless absolutely necessary.
406 Inactive: Memory which has been less recently used. It is more
407 eligible to be reclaimed for other purposes
409 HighFree: Highmem is all memory above ~860MB of physical memory
410 Highmem areas are for use by userspace programs, or
411 for the pagecache. The kernel must use tricks to access
412 this memory, making it slower to access than lowmem.
414 LowFree: Lowmem is memory which can be used for everything that
415 highmem can be used for, but it is also available for the
416 kernel's use for its own data structures. Among many
417 other things, it is where everything from the Slab is
418 allocated. Bad things happen when you're out of lowmem.
419 SwapTotal: total amount of swap space available
420 SwapFree: Memory which has been evicted from RAM, and is temporarily
422 Dirty: Memory which is waiting to get written back to the disk
423 Writeback: Memory which is actively being written back to the disk
424 Mapped: files which have been mmaped, such as libraries
425 Slab: in-kernel data structures cache
426 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
427 this is the total amount of memory currently available to
428 be allocated on the system. This limit is only adhered to
429 if strict overcommit accounting is enabled (mode 2 in
430 'vm.overcommit_memory').
431 The CommitLimit is calculated with the following formula:
432 CommitLimit = ('vm.overcommit_ratio' * Physical RAM) + Swap
433 For example, on a system with 1G of physical RAM and 7G
434 of swap with a `vm.overcommit_ratio` of 30 it would
435 yield a CommitLimit of 7.3G.
436 For more details, see the memory overcommit documentation
437 in vm/overcommit-accounting.
438 Committed_AS: The amount of memory presently allocated on the system.
439 The committed memory is a sum of all of the memory which
440 has been allocated by processes, even if it has not been
441 "used" by them as of yet. A process which malloc()'s 1G
442 of memory, but only touches 300M of it will only show up
443 as using 300M of memory even if it has the address space
444 allocated for the entire 1G. This 1G is memory which has
445 been "committed" to by the VM and can be used at any time
446 by the allocating application. With strict overcommit
447 enabled on the system (mode 2 in 'vm.overcommit_memory'),
448 allocations which would exceed the CommitLimit (detailed
449 above) will not be permitted. This is useful if one needs
450 to guarantee that processes will not fail due to lack of
451 memory once that memory has been successfully allocated.
452 PageTables: amount of memory dedicated to the lowest level of page
454 VmallocTotal: total size of vmalloc memory area
455 VmallocUsed: amount of vmalloc area which is used
456 VmallocChunk: largest contigious block of vmalloc area which is free
459 1.3 IDE devices in /proc/ide
460 ----------------------------
462 The subdirectory /proc/ide contains information about all IDE devices of which
463 the kernel is aware. There is one subdirectory for each IDE controller, the
464 file drivers and a link for each IDE device, pointing to the device directory
465 in the controller specific subtree.
467 The file drivers contains general information about the drivers used for the
470 > cat /proc/ide/drivers
471 ide-cdrom version 4.53
472 ide-disk version 1.08
474 More detailed information can be found in the controller specific
475 subdirectories. These are named ide0, ide1 and so on. Each of these
476 directories contains the files shown in table 1-4.
479 Table 1-4: IDE controller info in /proc/ide/ide?
480 ..............................................................................
482 channel IDE channel (0 or 1)
483 config Configuration (only for PCI/IDE bridge)
485 model Type/Chipset of IDE controller
486 ..............................................................................
488 Each device connected to a controller has a separate subdirectory in the
489 controllers directory. The files listed in table 1-5 are contained in these
493 Table 1-5: IDE device information
494 ..............................................................................
497 capacity Capacity of the medium (in 512Byte blocks)
498 driver driver and version
499 geometry physical and logical geometry
500 identify device identify block
502 model device identifier
503 settings device setup
504 smart_thresholds IDE disk management thresholds
505 smart_values IDE disk management values
506 ..............................................................................
508 The most interesting file is settings. This file contains a nice overview of
509 the drive parameters:
511 # cat /proc/ide/ide0/hda/settings
512 name value min max mode
513 ---- ----- --- --- ----
514 bios_cyl 526 0 65535 rw
515 bios_head 255 0 255 rw
517 breada_readahead 4 0 127 rw
519 file_readahead 72 0 2097151 rw
521 keepsettings 0 0 1 rw
522 max_kb_per_request 122 1 127 rw
526 pio_mode write-only 0 255 w
532 1.4 Networking info in /proc/net
533 --------------------------------
535 The subdirectory /proc/net follows the usual pattern. Table 1-6 shows the
536 additional values you get for IP version 6 if you configure the kernel to
537 support this. Table 1-7 lists the files and their meaning.
540 Table 1-6: IPv6 info in /proc/net
541 ..............................................................................
543 udp6 UDP sockets (IPv6)
544 tcp6 TCP sockets (IPv6)
545 raw6 Raw device statistics (IPv6)
546 igmp6 IP multicast addresses, which this host joined (IPv6)
547 if_inet6 List of IPv6 interface addresses
548 ipv6_route Kernel routing table for IPv6
549 rt6_stats Global IPv6 routing tables statistics
550 sockstat6 Socket statistics (IPv6)
551 snmp6 Snmp data (IPv6)
552 ..............................................................................
555 Table 1-7: Network info in /proc/net
556 ..............................................................................
559 dev network devices with statistics
560 dev_mcast the Layer2 multicast groups a device is listening too
561 (interface index, label, number of references, number of bound
563 dev_stat network device status
564 ip_fwchains Firewall chain linkage
565 ip_fwnames Firewall chain names
566 ip_masq Directory containing the masquerading tables
567 ip_masquerade Major masquerading table
568 netstat Network statistics
569 raw raw device statistics
570 route Kernel routing table
571 rpc Directory containing rpc info
572 rt_cache Routing cache
574 sockstat Socket statistics
576 tr_rif Token ring RIF routing table
578 unix UNIX domain sockets
579 wireless Wireless interface data (Wavelan etc)
580 igmp IP multicast addresses, which this host joined
581 psched Global packet scheduler parameters.
582 netlink List of PF_NETLINK sockets
583 ip_mr_vifs List of multicast virtual interfaces
584 ip_mr_cache List of multicast routing cache
585 ..............................................................................
587 You can use this information to see which network devices are available in
588 your system and how much traffic was routed over those devices:
592 face |bytes packets errs drop fifo frame compressed multicast|[...
593 lo: 908188 5596 0 0 0 0 0 0 [...
594 ppp0:15475140 20721 410 0 0 410 0 0 [...
595 eth0: 614530 7085 0 0 0 0 0 1 [...
598 ...] bytes packets errs drop fifo colls carrier compressed
599 ...] 908188 5596 0 0 0 0 0 0
600 ...] 1375103 17405 0 0 0 0 0 0
601 ...] 1703981 5535 0 0 0 3 0 0
603 In addition, each Channel Bond interface has it's own directory. For
604 example, the bond0 device will have a directory called /proc/net/bond0/.
605 It will contain information that is specific to that bond, such as the
606 current slaves of the bond, the link status of the slaves, and how
607 many times the slaves link has failed.
612 If you have a SCSI host adapter in your system, you'll find a subdirectory
613 named after the driver for this adapter in /proc/scsi. You'll also see a list
614 of all recognized SCSI devices in /proc/scsi:
618 Host: scsi0 Channel: 00 Id: 00 Lun: 00
619 Vendor: IBM Model: DGHS09U Rev: 03E0
620 Type: Direct-Access ANSI SCSI revision: 03
621 Host: scsi0 Channel: 00 Id: 06 Lun: 00
622 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04
623 Type: CD-ROM ANSI SCSI revision: 02
626 The directory named after the driver has one file for each adapter found in
627 the system. These files contain information about the controller, including
628 the used IRQ and the IO address range. The amount of information shown is
629 dependent on the adapter you use. The example shows the output for an Adaptec
630 AHA-2940 SCSI adapter:
632 > cat /proc/scsi/aic7xxx/0
634 Adaptec AIC7xxx driver version: 5.1.19/3.2.4
636 TCQ Enabled By Default : Disabled
637 AIC7XXX_PROC_STATS : Disabled
638 AIC7XXX_RESET_DELAY : 5
639 Adapter Configuration:
640 SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
641 Ultra Wide Controller
642 PCI MMAPed I/O Base: 0xeb001000
643 Adapter SEEPROM Config: SEEPROM found and used.
644 Adaptec SCSI BIOS: Enabled
646 SCBs: Active 0, Max Active 2,
647 Allocated 15, HW 16, Page 255
649 BIOS Control Word: 0x18b6
650 Adapter Control Word: 0x005b
651 Extended Translation: Enabled
652 Disconnect Enable Flags: 0xffff
653 Ultra Enable Flags: 0x0001
654 Tag Queue Enable Flags: 0x0000
655 Ordered Queue Tag Flags: 0x0000
656 Default Tag Queue Depth: 8
657 Tagged Queue By Device array for aic7xxx host instance 0:
658 {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
659 Actual queue depth per device for aic7xxx host instance 0:
660 {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
663 Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
664 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
665 Total transfers 160151 (74577 reads and 85574 writes)
667 Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
668 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
669 Total transfers 0 (0 reads and 0 writes)
672 1.6 Parallel port info in /proc/parport
673 ---------------------------------------
675 The directory /proc/parport contains information about the parallel ports of
676 your system. It has one subdirectory for each port, named after the port
679 These directories contain the four files shown in Table 1-8.
682 Table 1-8: Files in /proc/parport
683 ..............................................................................
685 autoprobe Any IEEE-1284 device ID information that has been acquired.
686 devices list of the device drivers using that port. A + will appear by the
687 name of the device currently using the port (it might not appear
689 hardware Parallel port's base address, IRQ line and DMA channel.
690 irq IRQ that parport is using for that port. This is in a separate
691 file to allow you to alter it by writing a new value in (IRQ
693 ..............................................................................
695 1.7 TTY info in /proc/tty
696 -------------------------
698 Information about the available and actually used tty's can be found in the
699 directory /proc/tty.You'll find entries for drivers and line disciplines in
700 this directory, as shown in Table 1-9.
703 Table 1-9: Files in /proc/tty
704 ..............................................................................
706 drivers list of drivers and their usage
707 ldiscs registered line disciplines
708 driver/serial usage statistic and status of single tty lines
709 ..............................................................................
711 To see which tty's are currently in use, you can simply look into the file
714 > cat /proc/tty/drivers
715 pty_slave /dev/pts 136 0-255 pty:slave
716 pty_master /dev/ptm 128 0-255 pty:master
717 pty_slave /dev/ttyp 3 0-255 pty:slave
718 pty_master /dev/pty 2 0-255 pty:master
719 serial /dev/cua 5 64-67 serial:callout
720 serial /dev/ttyS 4 64-67 serial
721 /dev/tty0 /dev/tty0 4 0 system:vtmaster
722 /dev/ptmx /dev/ptmx 5 2 system
723 /dev/console /dev/console 5 1 system:console
724 /dev/tty /dev/tty 5 0 system:/dev/tty
725 unknown /dev/tty 4 1-63 console
728 1.8 Miscellaneous kernel statistics in /proc/stat
729 -------------------------------------------------
731 Various pieces of information about kernel activity are available in the
732 /proc/stat file. All of the numbers reported in this file are aggregates
733 since the system first booted. For a quick look, simply cat the file:
736 cpu 2255 34 2290 22625563 6290 127 456
737 cpu0 1132 34 1441 11311718 3675 127 438
738 cpu1 1123 0 849 11313845 2614 0 18
739 intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
746 The very first "cpu" line aggregates the numbers in all of the other "cpuN"
747 lines. These numbers identify the amount of time the CPU has spent performing
748 different kinds of work. Time units are in USER_HZ (typically hundredths of a
749 second). The meanings of the columns are as follows, from left to right:
751 - user: normal processes executing in user mode
752 - nice: niced processes executing in user mode
753 - system: processes executing in kernel mode
754 - idle: twiddling thumbs
755 - iowait: waiting for I/O to complete
756 - irq: servicing interrupts
757 - softirq: servicing softirqs
759 The "intr" line gives counts of interrupts serviced since boot time, for each
760 of the possible system interrupts. The first column is the total of all
761 interrupts serviced; each subsequent column is the total for that particular
764 The "ctxt" line gives the total number of context switches across all CPUs.
766 The "btime" line gives the time at which the system booted, in seconds since
769 The "processes" line gives the number of processes and threads created, which
770 includes (but is not limited to) those created by calls to the fork() and
771 clone() system calls.
773 The "procs_running" line gives the number of processes currently running on
776 The "procs_blocked" line gives the number of processes currently blocked,
777 waiting for I/O to complete.
780 ------------------------------------------------------------------------------
782 ------------------------------------------------------------------------------
783 The /proc file system serves information about the running system. It not only
784 allows access to process data but also allows you to request the kernel status
785 by reading files in the hierarchy.
787 The directory structure of /proc reflects the types of information and makes
788 it easy, if not obvious, where to look for specific data.
789 ------------------------------------------------------------------------------
791 ------------------------------------------------------------------------------
792 CHAPTER 2: MODIFYING SYSTEM PARAMETERS
793 ------------------------------------------------------------------------------
795 ------------------------------------------------------------------------------
797 ------------------------------------------------------------------------------
798 * Modifying kernel parameters by writing into files found in /proc/sys
799 * Exploring the files which modify certain parameters
800 * Review of the /proc/sys file tree
801 ------------------------------------------------------------------------------
804 A very interesting part of /proc is the directory /proc/sys. This is not only
805 a source of information, it also allows you to change parameters within the
806 kernel. Be very careful when attempting this. You can optimize your system,
807 but you can also cause it to crash. Never alter kernel parameters on a
808 production system. Set up a development machine and test to make sure that
809 everything works the way you want it to. You may have no alternative but to
810 reboot the machine once an error has been made.
812 To change a value, simply echo the new value into the file. An example is
813 given below in the section on the file system data. You need to be root to do
814 this. You can create your own boot script to perform this every time your
817 The files in /proc/sys can be used to fine tune and monitor miscellaneous and
818 general things in the operation of the Linux kernel. Since some of the files
819 can inadvertently disrupt your system, it is advisable to read both
820 documentation and source before actually making adjustments. In any case, be
821 very careful when writing to any of these files. The entries in /proc may
822 change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
823 review the kernel documentation in the directory /usr/src/linux/Documentation.
824 This chapter is heavily based on the documentation included in the pre 2.2
825 kernels, and became part of it in version 2.2.1 of the Linux kernel.
827 2.1 /proc/sys/fs - File system data
828 -----------------------------------
830 This subdirectory contains specific file system, file handle, inode, dentry
831 and quota information.
833 Currently, these files are in /proc/sys/fs:
838 Status of the directory cache. Since directory entries are dynamically
839 allocated and deallocated, this file indicates the current status. It holds
840 six values, in which the last two are not used and are always zero. The others
841 are listed in table 2-1.
844 Table 2-1: Status files of the directory cache
845 ..............................................................................
847 nr_dentry Almost always zero
848 nr_unused Number of unused cache entries
850 in seconds after the entry may be reclaimed, when memory is short
851 want_pages internally
852 ..............................................................................
854 dquot-nr and dquot-max
855 ----------------------
857 The file dquot-max shows the maximum number of cached disk quota entries.
859 The file dquot-nr shows the number of allocated disk quota entries and the
860 number of free disk quota entries.
862 If the number of available cached disk quotas is very low and you have a large
863 number of simultaneous system users, you might want to raise the limit.
868 The kernel allocates file handles dynamically, but doesn't free them again at
871 The value in file-max denotes the maximum number of file handles that the
872 Linux kernel will allocate. When you get a lot of error messages about running
873 out of file handles, you might want to raise this limit. The default value is
874 10% of RAM in kilobytes. To change it, just write the new number into the
877 # cat /proc/sys/fs/file-max
879 # echo 8192 > /proc/sys/fs/file-max
880 # cat /proc/sys/fs/file-max
884 This method of revision is useful for all customizable parameters of the
885 kernel - simply echo the new value to the corresponding file.
887 Historically, the three values in file-nr denoted the number of allocated file
888 handles, the number of allocated but unused file handles, and the maximum
889 number of file handles. Linux 2.6 always reports 0 as the number of free file
890 handles -- this is not an error, it just means that the number of allocated
891 file handles exactly matches the number of used file handles.
893 Attempts to allocate more file descriptors than file-max are reported with
894 printk, look for "VFS: file-max limit <number> reached".
896 inode-state and inode-nr
897 ------------------------
899 The file inode-nr contains the first two items from inode-state, so we'll skip
902 inode-state contains two actual numbers and five dummy values. The numbers
903 are nr_inodes and nr_free_inodes (in order of appearance).
908 Denotes the number of inodes the system has allocated. This number will
909 grow and shrink dynamically.
914 Represents the number of free inodes. Ie. The number of inuse inodes is
915 (nr_inodes - nr_free_inodes).
917 aio-nr and aio-max-nr
918 ---------------------
920 aio-nr is the running total of the number of events specified on the
921 io_setup system call for all currently active aio contexts. If aio-nr
922 reaches aio-max-nr then io_setup will fail with EAGAIN. Note that
923 raising aio-max-nr does not result in the pre-allocation or re-sizing
924 of any kernel data structures.
926 2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats
927 -----------------------------------------------------------
929 Besides these files, there is the subdirectory /proc/sys/fs/binfmt_misc. This
930 handles the kernel support for miscellaneous binary formats.
932 Binfmt_misc provides the ability to register additional binary formats to the
933 Kernel without compiling an additional module/kernel. Therefore, binfmt_misc
934 needs to know magic numbers at the beginning or the filename extension of the
937 It works by maintaining a linked list of structs that contain a description of
938 a binary format, including a magic with size (or the filename extension),
939 offset and mask, and the interpreter name. On request it invokes the given
940 interpreter with the original program as argument, as binfmt_java and
941 binfmt_em86 and binfmt_mz do. Since binfmt_misc does not define any default
942 binary-formats, you have to register an additional binary-format.
944 There are two general files in binfmt_misc and one file per registered format.
945 The two general files are register and status.
947 Registering a new binary format
948 -------------------------------
950 To register a new binary format you have to issue the command
952 echo :name:type:offset:magic:mask:interpreter: > /proc/sys/fs/binfmt_misc/register
956 with appropriate name (the name for the /proc-dir entry), offset (defaults to
957 0, if omitted), magic, mask (which can be omitted, defaults to all 0xff) and
958 last but not least, the interpreter that is to be invoked (for example and
959 testing /bin/echo). Type can be M for usual magic matching or E for filename
960 extension matching (give extension in place of magic).
962 Check or reset the status of the binary format handler
963 ------------------------------------------------------
965 If you do a cat on the file /proc/sys/fs/binfmt_misc/status, you will get the
966 current status (enabled/disabled) of binfmt_misc. Change the status by echoing
967 0 (disables) or 1 (enables) or -1 (caution: this clears all previously
968 registered binary formats) to status. For example echo 0 > status to disable
969 binfmt_misc (temporarily).
971 Status of a single handler
972 --------------------------
974 Each registered handler has an entry in /proc/sys/fs/binfmt_misc. These files
975 perform the same function as status, but their scope is limited to the actual
976 binary format. By cating this file, you also receive all related information
977 about the interpreter/magic of the binfmt.
979 Example usage of binfmt_misc (emulate binfmt_java)
980 --------------------------------------------------
982 cd /proc/sys/fs/binfmt_misc
983 echo ':Java:M::\xca\xfe\xba\xbe::/usr/local/java/bin/javawrapper:' > register
984 echo ':HTML:E::html::/usr/local/java/bin/appletviewer:' > register
985 echo ':Applet:M::<!--applet::/usr/local/java/bin/appletviewer:' > register
986 echo ':DEXE:M::\x0eDEX::/usr/bin/dosexec:' > register
989 These four lines add support for Java executables and Java applets (like
990 binfmt_java, additionally recognizing the .html extension with no need to put
991 <!--applet> to every applet file). You have to install the JDK and the
992 shell-script /usr/local/java/bin/javawrapper too. It works around the
993 brokenness of the Java filename handling. To add a Java binary, just create a
994 link to the class-file somewhere in the path.
996 2.3 /proc/sys/kernel - general kernel parameters
997 ------------------------------------------------
999 This directory reflects general kernel behaviors. As I've said before, the
1000 contents depend on your configuration. Here you'll find the most important
1001 files, along with descriptions of what they mean and how to use them.
1006 The file contains three values; highwater, lowwater, and frequency.
1008 It exists only when BSD-style process accounting is enabled. These values
1009 control its behavior. If the free space on the file system where the log lives
1010 goes below lowwater percentage, accounting suspends. If it goes above
1011 highwater percentage, accounting resumes. Frequency determines how often you
1012 check the amount of free space (value is in seconds). Default settings are: 4,
1013 2, and 30. That is, suspend accounting if there is less than 2 percent free;
1014 resume it if we have a value of 3 or more percent; consider information about
1015 the amount of free space valid for 30 seconds
1020 When the value in this file is 0, ctrl-alt-del is trapped and sent to the init
1021 program to handle a graceful restart. However, when the value is greater that
1022 zero, Linux's reaction to this key combination will be an immediate reboot,
1023 without syncing its dirty buffers.
1026 When a program (like dosemu) has the keyboard in raw mode, the
1027 ctrl-alt-del is intercepted by the program before it ever reaches the
1028 kernel tty layer, and it is up to the program to decide what to do with
1031 domainname and hostname
1032 -----------------------
1034 These files can be controlled to set the NIS domainname and hostname of your
1035 box. For the classic darkstar.frop.org a simple:
1037 # echo "darkstar" > /proc/sys/kernel/hostname
1038 # echo "frop.org" > /proc/sys/kernel/domainname
1041 would suffice to set your hostname and NIS domainname.
1043 osrelease, ostype and version
1044 -----------------------------
1046 The names make it pretty obvious what these fields contain:
1048 > cat /proc/sys/kernel/osrelease
1051 > cat /proc/sys/kernel/ostype
1054 > cat /proc/sys/kernel/version
1055 #4 Fri Oct 1 12:41:14 PDT 1999
1058 The files osrelease and ostype should be clear enough. Version needs a little
1059 more clarification. The #4 means that this is the 4th kernel built from this
1060 source base and the date after it indicates the time the kernel was built. The
1061 only way to tune these values is to rebuild the kernel.
1066 The value in this file represents the number of seconds the kernel waits
1067 before rebooting on a panic. When you use the software watchdog, the
1068 recommended setting is 60. If set to 0, the auto reboot after a kernel panic
1069 is disabled, which is the default setting.
1074 The four values in printk denote
1076 * default_message_loglevel,
1077 * minimum_console_loglevel and
1078 * default_console_loglevel
1081 These values influence printk() behavior when printing or logging error
1082 messages, which come from inside the kernel. See syslog(2) for more
1083 information on the different log levels.
1088 Messages with a higher priority than this will be printed to the console.
1090 default_message_level
1091 ---------------------
1093 Messages without an explicit priority will be printed with this priority.
1095 minimum_console_loglevel
1096 ------------------------
1098 Minimum (highest) value to which the console_loglevel can be set.
1100 default_console_loglevel
1101 ------------------------
1103 Default value for console_loglevel.
1108 This file shows the size of the generic SCSI (sg) buffer. At this point, you
1109 can't tune it yet, but you can change it at compile time by editing
1110 include/scsi/sg.h and changing the value of SG_BIG_BUFF.
1112 If you use a scanner with SANE (Scanner Access Now Easy) you might want to set
1113 this to a higher value. Refer to the SANE documentation on this issue.
1118 The location where the modprobe binary is located. The kernel uses this
1119 program to load modules on demand.
1124 The value in this file affects behavior of handling NMI. When the value is
1125 non-zero, unknown NMI is trapped and then panic occurs. At that time, kernel
1126 debugging information is displayed on console.
1128 NMI switch that most IA32 servers have fires unknown NMI up, for example.
1129 If a system hangs up, try pressing the NMI switch.
1134 Enables/Disables the NMI watchdog on x86 systems. When the value is non-zero
1135 the NMI watchdog is enabled and will continuously test all online cpus to
1136 determine whether or not they are still functioning properly.
1138 Because the NMI watchdog shares registers with oprofile, by disabling the NMI
1139 watchdog, oprofile may have more registers to utilize.
1144 Enables/Disables the protection of the per-process proc entries "maps" and
1145 "smaps". When enabled, the contents of these files are visible only to
1146 readers that are allowed to ptrace() the given process.
1149 2.4 /proc/sys/vm - The virtual memory subsystem
1150 -----------------------------------------------
1152 The files in this directory can be used to tune the operation of the virtual
1153 memory (VM) subsystem of the Linux kernel.
1158 Controls the tendency of the kernel to reclaim the memory which is used for
1159 caching of directory and inode objects.
1161 At the default value of vfs_cache_pressure=100 the kernel will attempt to
1162 reclaim dentries and inodes at a "fair" rate with respect to pagecache and
1163 swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer
1164 to retain dentry and inode caches. Increasing vfs_cache_pressure beyond 100
1165 causes the kernel to prefer to reclaim dentries and inodes.
1167 dirty_background_ratio
1168 ----------------------
1170 Contains, as a percentage of total system memory, the number of pages at which
1171 the pdflush background writeback daemon will start writing out dirty data.
1176 Contains, as a percentage of total system memory, the number of pages at which
1177 a process which is generating disk writes will itself start writing out dirty
1180 dirty_writeback_centisecs
1181 -------------------------
1183 The pdflush writeback daemons will periodically wake up and write `old' data
1184 out to disk. This tunable expresses the interval between those wakeups, in
1185 100'ths of a second.
1187 Setting this to zero disables periodic writeback altogether.
1189 dirty_expire_centisecs
1190 ----------------------
1192 This tunable is used to define when dirty data is old enough to be eligible
1193 for writeout by the pdflush daemons. It is expressed in 100'ths of a second.
1194 Data which has been dirty in-memory for longer than this interval will be
1195 written out next time a pdflush daemon wakes up.
1200 If non-zero, this sysctl disables the new 32-bit mmap mmap layout - the kernel
1201 will use the legacy (2.4) layout for all processes.
1203 lower_zone_protection
1204 ---------------------
1206 For some specialised workloads on highmem machines it is dangerous for
1207 the kernel to allow process memory to be allocated from the "lowmem"
1208 zone. This is because that memory could then be pinned via the mlock()
1209 system call, or by unavailability of swapspace.
1211 And on large highmem machines this lack of reclaimable lowmem memory
1214 So the Linux page allocator has a mechanism which prevents allocations
1215 which _could_ use highmem from using too much lowmem. This means that
1216 a certain amount of lowmem is defended from the possibility of being
1217 captured into pinned user memory.
1219 (The same argument applies to the old 16 megabyte ISA DMA region. This
1220 mechanism will also defend that region from allocations which could use
1223 The `lower_zone_protection' tunable determines how aggressive the kernel is
1224 in defending these lower zones. The default value is zero - no
1227 If you have a machine which uses highmem or ISA DMA and your
1228 applications are using mlock(), or if you are running with no swap then
1229 you probably should increase the lower_zone_protection setting.
1231 The units of this tunable are fairly vague. It is approximately equal
1232 to "megabytes," so setting lower_zone_protection=100 will protect around 100
1233 megabytes of the lowmem zone from user allocations. It will also make
1234 those 100 megabytes unavailable for use by applications and by
1235 pagecache, so there is a cost.
1237 The effects of this tunable may be observed by monitoring
1238 /proc/meminfo:LowFree. Write a single huge file and observe the point
1239 at which LowFree ceases to fall.
1241 A reasonable value for lower_zone_protection is 100.
1246 page-cluster controls the number of pages which are written to swap in
1247 a single attempt. The swap I/O size.
1249 It is a logarithmic value - setting it to zero means "1 page", setting
1250 it to 1 means "2 pages", setting it to 2 means "4 pages", etc.
1252 The default value is three (eight pages at a time). There may be some
1253 small benefits in tuning this to a different value if your workload is
1259 Controls overcommit of system memory, possibly allowing processes
1260 to allocate (but not use) more memory than is actually available.
1263 0 - Heuristic overcommit handling. Obvious overcommits of
1264 address space are refused. Used for a typical system. It
1265 ensures a seriously wild allocation fails while allowing
1266 overcommit to reduce swap usage. root is allowed to
1267 allocate slightly more memory in this mode. This is the
1270 1 - Always overcommit. Appropriate for some scientific
1273 2 - Don't overcommit. The total address space commit
1274 for the system is not permitted to exceed swap plus a
1275 configurable percentage (default is 50) of physical RAM.
1276 Depending on the percentage you use, in most situations
1277 this means a process will not be killed while attempting
1278 to use already-allocated memory but will receive errors
1279 on memory allocation as appropriate.
1284 Percentage of physical memory size to include in overcommit calculations
1287 Memory allocation limit = swapspace + physmem * (overcommit_ratio / 100)
1289 swapspace = total size of all swap areas
1290 physmem = size of physical memory in system
1292 nr_hugepages and hugetlb_shm_group
1293 ----------------------------------
1295 nr_hugepages configures number of hugetlb page reserved for the system.
1297 hugetlb_shm_group contains group id that is allowed to create SysV shared
1298 memory segment using hugetlb page.
1303 laptop_mode is a knob that controls "laptop mode". All the things that are
1304 controlled by this knob are discussed in Documentation/laptop-mode.txt.
1309 block_dump enables block I/O debugging when set to a nonzero value. More
1310 information on block I/O debugging is in Documentation/laptop-mode.txt.
1315 This file contains valid hold time of swap out protection token. The Linux
1316 VM has token based thrashing control mechanism and uses the token to prevent
1317 unnecessary page faults in thrashing situation. The unit of the value is
1318 second. The value would be useful to tune thrashing behavior.
1323 Writing to this will cause the kernel to drop clean caches, dentries and
1324 inodes from memory, causing that memory to become free.
1327 echo 1 > /proc/sys/vm/drop_caches
1328 To free dentries and inodes:
1329 echo 2 > /proc/sys/vm/drop_caches
1330 To free pagecache, dentries and inodes:
1331 echo 3 > /proc/sys/vm/drop_caches
1333 As this is a non-destructive operation and dirty objects are not freeable, the
1334 user should run `sync' first.
1337 2.5 /proc/sys/dev - Device specific parameters
1338 ----------------------------------------------
1340 Currently there is only support for CDROM drives, and for those, there is only
1341 one read-only file containing information about the CD-ROM drives attached to
1344 >cat /proc/sys/dev/cdrom/info
1345 CD-ROM information, Id: cdrom.c 2.55 1999/04/25
1349 drive # of slots: 1 0
1353 Can change speed: 1 1
1354 Can select disk: 0 1
1355 Can read multisession: 1 1
1357 Reports media changed: 1 1
1361 You see two drives, sr0 and hdb, along with a list of their features.
1363 2.6 /proc/sys/sunrpc - Remote procedure calls
1364 ---------------------------------------------
1366 This directory contains four files, which enable or disable debugging for the
1367 RPC functions NFS, NFS-daemon, RPC and NLM. The default values are 0. They can
1368 be set to one to turn debugging on. (The default value is 0 for each)
1370 2.7 /proc/sys/net - Networking stuff
1371 ------------------------------------
1373 The interface to the networking parts of the kernel is located in
1374 /proc/sys/net. Table 2-3 shows all possible subdirectories. You may see only
1375 some of them, depending on your kernel's configuration.
1378 Table 2-3: Subdirectories in /proc/sys/net
1379 ..............................................................................
1380 Directory Content Directory Content
1381 core General parameter appletalk Appletalk protocol
1382 unix Unix domain sockets netrom NET/ROM
1383 802 E802 protocol ax25 AX25
1384 ethernet Ethernet protocol rose X.25 PLP layer
1385 ipv4 IP version 4 x25 X.25 protocol
1386 ipx IPX token-ring IBM token ring
1387 bridge Bridging decnet DEC net
1389 ..............................................................................
1391 We will concentrate on IP networking here. Since AX15, X.25, and DEC Net are
1392 only minor players in the Linux world, we'll skip them in this chapter. You'll
1393 find some short info on Appletalk and IPX further on in this chapter. Review
1394 the online documentation and the kernel source to get a detailed view of the
1395 parameters for those protocols. In this section we'll discuss the
1396 subdirectories printed in bold letters in the table above. As default values
1397 are suitable for most needs, there is no need to change these values.
1399 /proc/sys/net/core - Network core options
1400 -----------------------------------------
1405 The default setting of the socket receive buffer in bytes.
1410 The maximum receive socket buffer size in bytes.
1415 The default setting (in bytes) of the socket send buffer.
1420 The maximum send socket buffer size in bytes.
1422 message_burst and message_cost
1423 ------------------------------
1425 These parameters are used to limit the warning messages written to the kernel
1426 log from the networking code. They enforce a rate limit to make a
1427 denial-of-service attack impossible. A higher message_cost factor, results in
1428 fewer messages that will be written. Message_burst controls when messages will
1429 be dropped. The default settings limit warning messages to one every five
1435 This controls console messages from the networking stack that can occur because
1436 of problems on the network like duplicate address or bad checksums. Normally,
1437 this should be enabled, but if the problem persists the messages can be
1444 Maximum number of packets, queued on the INPUT side, when the interface
1445 receives packets faster than kernel can process them.
1450 Maximum ancillary buffer size allowed per socket. Ancillary data is a sequence
1451 of struct cmsghdr structures with appended data.
1453 /proc/sys/net/unix - Parameters for Unix domain sockets
1454 -------------------------------------------------------
1456 There are only two files in this subdirectory. They control the delays for
1457 deleting and destroying socket descriptors.
1459 2.8 /proc/sys/net/ipv4 - IPV4 settings
1460 --------------------------------------
1462 IP version 4 is still the most used protocol in Unix networking. It will be
1463 replaced by IP version 6 in the next couple of years, but for the moment it's
1464 the de facto standard for the internet and is used in most networking
1465 environments around the world. Because of the importance of this protocol,
1466 we'll have a deeper look into the subtree controlling the behavior of the IPv4
1467 subsystem of the Linux kernel.
1469 Let's start with the entries in /proc/sys/net/ipv4.
1474 icmp_echo_ignore_all and icmp_echo_ignore_broadcasts
1475 ----------------------------------------------------
1477 Turn on (1) or off (0), if the kernel should ignore all ICMP ECHO requests, or
1478 just those to broadcast and multicast addresses.
1480 Please note that if you accept ICMP echo requests with a broadcast/multi\-cast
1481 destination address your network may be used as an exploder for denial of
1482 service packet flooding attacks to other hosts.
1484 icmp_destunreach_rate, icmp_echoreply_rate, icmp_paramprob_rate and icmp_timeexeed_rate
1485 ---------------------------------------------------------------------------------------
1487 Sets limits for sending ICMP packets to specific targets. A value of zero
1488 disables all limiting. Any positive value sets the maximum package rate in
1489 hundredth of a second (on Intel systems).
1497 This file contains the number one if the host received its IP configuration by
1498 RARP, BOOTP, DHCP or a similar mechanism. Otherwise it is zero.
1503 TTL (Time To Live) for IPv4 interfaces. This is simply the maximum number of
1504 hops a packet may travel.
1509 Enable dynamic socket address rewriting on interface address change. This is
1510 useful for dialup interface with changing IP addresses.
1515 Enable or disable forwarding of IP packages between interfaces. Changing this
1516 value resets all other parameters to their default values. They differ if the
1517 kernel is configured as host or router.
1522 Range of ports used by TCP and UDP to choose the local port. Contains two
1523 numbers, the first number is the lowest port, the second number the highest
1524 local port. Default is 1024-4999. Should be changed to 32768-61000 for
1530 Global switch to turn path MTU discovery off. It can also be set on a per
1531 socket basis by the applications or on a per route basis.
1536 Enable/disable debugging of IP masquerading.
1538 IP fragmentation settings
1539 -------------------------
1541 ipfrag_high_trash and ipfrag_low_trash
1542 --------------------------------------
1544 Maximum memory used to reassemble IP fragments. When ipfrag_high_thresh bytes
1545 of memory is allocated for this purpose, the fragment handler will toss
1546 packets until ipfrag_low_thresh is reached.
1551 Time in seconds to keep an IP fragment in memory.
1559 This file controls the use of the ECN bit in the IPv4 headers. This is a new
1560 feature about Explicit Congestion Notification, but some routers and firewalls
1561 block traffic that has this bit set, so it could be necessary to echo 0 to
1562 /proc/sys/net/ipv4/tcp_ecn if you want to talk to these sites. For more info
1563 you could read RFC2481.
1565 tcp_retrans_collapse
1566 --------------------
1568 Bug-to-bug compatibility with some broken printers. On retransmit, try to send
1569 larger packets to work around bugs in certain TCP stacks. Can be turned off by
1572 tcp_keepalive_probes
1573 --------------------
1575 Number of keep alive probes TCP sends out, until it decides that the
1576 connection is broken.
1581 How often TCP sends out keep alive messages, when keep alive is enabled. The
1587 Number of times initial SYNs for a TCP connection attempt will be
1588 retransmitted. Should not be higher than 255. This is only the timeout for
1589 outgoing connections, for incoming connections the number of retransmits is
1590 defined by tcp_retries1.
1595 Enable select acknowledgments after RFC2018.
1600 Enable timestamps as defined in RFC1323.
1605 Enable the strict RFC793 interpretation of the TCP urgent pointer field. The
1606 default is to use the BSD compatible interpretation of the urgent pointer
1607 pointing to the first byte after the urgent data. The RFC793 interpretation is
1608 to have it point to the last byte of urgent data. Enabling this option may
1609 lead to interoperability problems. Disabled by default.
1614 Only valid when the kernel was compiled with CONFIG_SYNCOOKIES. Send out
1615 syncookies when the syn backlog queue of a socket overflows. This is to ward
1616 off the common 'syn flood attack'. Disabled by default.
1618 Note that the concept of a socket backlog is abandoned. This means the peer
1619 may not receive reliable error messages from an over loaded server with
1625 Enable window scaling as defined in RFC1323.
1630 The length of time in seconds it takes to receive a final FIN before the
1631 socket is always closed. This is strictly a violation of the TCP
1632 specification, but required to prevent denial-of-service attacks.
1637 Indicates how many keep alive probes are sent per slow timer run. Should not
1638 be set too high to prevent bursts.
1643 Length of the per socket backlog queue. Since Linux 2.2 the backlog specified
1644 in listen(2) only specifies the length of the backlog queue of already
1645 established sockets. When more connection requests arrive Linux starts to drop
1646 packets. When syncookies are enabled the packets are still answered and the
1647 maximum queue is effectively ignored.
1652 Defines how often an answer to a TCP connection request is retransmitted
1658 Defines how often a TCP packet is retransmitted before giving up.
1660 Interface specific settings
1661 ---------------------------
1663 In the directory /proc/sys/net/ipv4/conf you'll find one subdirectory for each
1664 interface the system knows about and one directory calls all. Changes in the
1665 all subdirectory affect all interfaces, whereas changes in the other
1666 subdirectories affect only one interface. All directories have the same
1672 This switch decides if the kernel accepts ICMP redirect messages or not. The
1673 default is 'yes' if the kernel is configured for a regular host and 'no' for a
1674 router configuration.
1679 Should source routed packages be accepted or declined. The default is
1680 dependent on the kernel configuration. It's 'yes' for routers and 'no' for
1686 Accept packets with source address 0.b.c.d with destinations not to this host
1687 as local ones. It is supposed that a BOOTP relay daemon will catch and forward
1690 The default is 0, since this feature is not implemented yet (kernel version
1696 Enable or disable IP forwarding on this interface.
1701 Log packets with source addresses with no known route to kernel log.
1706 Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE and a
1707 multicast routing daemon is required.
1712 Does (1) or does not (0) perform proxy ARP.
1717 Integer value determines if a source validation should be made. 1 means yes, 0
1718 means no. Disabled by default, but local/broadcast address spoofing is always
1721 If you set this to 1 on a router that is the only connection for a network to
1722 the net, it will prevent spoofing attacks against your internal networks
1723 (external addresses can still be spoofed), without the need for additional
1729 Accept ICMP redirect messages only for gateways, listed in default gateway
1730 list. Enabled by default.
1735 If it is not set the kernel does not assume that different subnets on this
1736 device can communicate directly. Default setting is 'yes'.
1741 Determines whether to send ICMP redirects to other hosts.
1746 The directory /proc/sys/net/ipv4/route contains several file to control
1749 error_burst and error_cost
1750 --------------------------
1752 These parameters are used to limit how many ICMP destination unreachable to
1753 send from the host in question. ICMP destination unreachable messages are
1754 sent when we cannot reach the next hop while trying to transmit a packet.
1755 It will also print some error messages to kernel logs if someone is ignoring
1756 our ICMP redirects. The higher the error_cost factor is, the fewer
1757 destination unreachable and error messages will be let through. Error_burst
1758 controls when destination unreachable messages and error messages will be
1759 dropped. The default settings limit warning messages to five every second.
1764 Writing to this file results in a flush of the routing cache.
1766 gc_elasticity, gc_interval, gc_min_interval_ms, gc_timeout, gc_thresh
1767 ---------------------------------------------------------------------
1769 Values to control the frequency and behavior of the garbage collection
1770 algorithm for the routing cache. gc_min_interval is deprecated and replaced
1771 by gc_min_interval_ms.
1777 Maximum size of the routing cache. Old entries will be purged once the cache
1778 reached has this size.
1780 max_delay, min_delay
1781 --------------------
1783 Delays for flushing the routing cache.
1785 redirect_load, redirect_number
1786 ------------------------------
1788 Factors which determine if more ICPM redirects should be sent to a specific
1789 host. No redirects will be sent once the load limit or the maximum number of
1790 redirects has been reached.
1795 Timeout for redirects. After this period redirects will be sent again, even if
1796 this has been stopped, because the load or number limit has been reached.
1798 Network Neighbor handling
1799 -------------------------
1801 Settings about how to handle connections with direct neighbors (nodes attached
1802 to the same link) can be found in the directory /proc/sys/net/ipv4/neigh.
1804 As we saw it in the conf directory, there is a default subdirectory which
1805 holds the default values, and one directory for each interface. The contents
1806 of the directories are identical, with the single exception that the default
1807 settings contain additional options to set garbage collection parameters.
1809 In the interface directories you'll find the following entries:
1811 base_reachable_time, base_reachable_time_ms
1812 -------------------------------------------
1814 A base value used for computing the random reachable time value as specified
1817 Expression of base_reachable_time, which is deprecated, is in seconds.
1818 Expression of base_reachable_time_ms is in milliseconds.
1820 retrans_time, retrans_time_ms
1821 -----------------------------
1823 The time between retransmitted Neighbor Solicitation messages.
1824 Used for address resolution and to determine if a neighbor is
1827 Expression of retrans_time, which is deprecated, is in 1/100 seconds (for
1828 IPv4) or in jiffies (for IPv6).
1829 Expression of retrans_time_ms is in milliseconds.
1834 Maximum queue length for a pending arp request - the number of packets which
1835 are accepted from other layers while the ARP address is still resolved.
1840 Maximum for random delay of answers to neighbor solicitation messages in
1841 jiffies (1/100 sec). Not yet implemented (Linux does not have anycast support
1847 Maximum number of retries for unicast solicitation.
1852 Maximum number of retries for multicast solicitation.
1854 delay_first_probe_time
1855 ----------------------
1857 Delay for the first time probe if the neighbor is reachable. (see
1863 An ARP/neighbor entry is only replaced with a new one if the old is at least
1864 locktime old. This prevents ARP cache thrashing.
1869 Maximum time (real time is random [0..proxytime]) before answering to an ARP
1870 request for which we have an proxy ARP entry. In some cases, this is used to
1871 prevent network flooding.
1876 Maximum queue length of the delayed proxy arp timer. (see proxy_delay).
1881 Determines the number of requests to send to the user level ARP daemon. Use 0
1887 Determines how often to check for stale ARP entries. After an ARP entry is
1888 stale it will be resolved again (which is useful when an IP address migrates
1889 to another machine). When ucast_solicit is greater than 0 it first tries to
1890 send an ARP packet directly to the known host When that fails and
1891 mcast_solicit is greater than 0, an ARP request is broadcasted.
1896 The /proc/sys/net/appletalk directory holds the Appletalk configuration data
1897 when Appletalk is loaded. The configurable parameters are:
1902 The amount of time we keep an ARP entry before expiring it. Used to age out
1908 The amount of time we will spend trying to resolve an Appletalk address.
1910 aarp-retransmit-limit
1911 ---------------------
1913 The number of times we will retransmit a query before giving up.
1918 Controls the rate at which expires are checked.
1920 The directory /proc/net/appletalk holds the list of active Appletalk sockets
1923 The fields indicate the DDP type, the local address (in network:node format)
1924 the remote address, the size of the transmit pending queue, the size of the
1925 received queue (bytes waiting for applications to read) the state and the uid
1928 /proc/net/atalk_iface lists all the interfaces configured for appletalk.It
1929 shows the name of the interface, its Appletalk address, the network range on
1930 that address (or network number for phase 1 networks), and the status of the
1933 /proc/net/atalk_route lists each known network route. It lists the target
1934 (network) that the route leads to, the router (may be directly connected), the
1935 route flags, and the device the route is using.
1940 The IPX protocol has no tunable values in proc/sys/net.
1942 The IPX protocol does, however, provide proc/net/ipx. This lists each IPX
1943 socket giving the local and remote addresses in Novell format (that is
1944 network:node:port). In accordance with the strange Novell tradition,
1945 everything but the port is in hex. Not_Connected is displayed for sockets that
1946 are not tied to a specific remote address. The Tx and Rx queue sizes indicate
1947 the number of bytes pending for transmission and reception. The state
1948 indicates the state the socket is in and the uid is the owning uid of the
1951 The /proc/net/ipx_interface file lists all IPX interfaces. For each interface
1952 it gives the network number, the node number, and indicates if the network is
1953 the primary network. It also indicates which device it is bound to (or
1954 Internal for internal networks) and the Frame Type if appropriate. Linux
1955 supports 802.3, 802.2, 802.2 SNAP and DIX (Blue Book) ethernet framing for
1958 The /proc/net/ipx_route table holds a list of IPX routes. For each route it
1959 gives the destination network, the router node (or Directly) and the network
1960 address of the router (or Connected) for internal networks.
1962 2.11 /proc/sys/fs/mqueue - POSIX message queues filesystem
1963 ----------------------------------------------------------
1965 The "mqueue" filesystem provides the necessary kernel features to enable the
1966 creation of a user space library that implements the POSIX message queues
1967 API (as noted by the MSG tag in the POSIX 1003.1-2001 version of the System
1968 Interfaces specification.)
1970 The "mqueue" filesystem contains values for determining/setting the amount of
1971 resources used by the file system.
1973 /proc/sys/fs/mqueue/queues_max is a read/write file for setting/getting the
1974 maximum number of message queues allowed on the system.
1976 /proc/sys/fs/mqueue/msg_max is a read/write file for setting/getting the
1977 maximum number of messages in a queue value. In fact it is the limiting value
1978 for another (user) limit which is set in mq_open invocation. This attribute of
1979 a queue must be less or equal then msg_max.
1981 /proc/sys/fs/mqueue/msgsize_max is a read/write file for setting/getting the
1982 maximum message size value (it is every message queue's attribute set during
1985 2.12 /proc/<pid>/oom_adj - Adjust the oom-killer score
1986 ------------------------------------------------------
1988 This file can be used to adjust the score used to select which processes
1989 should be killed in an out-of-memory situation. Giving it a high score will
1990 increase the likelihood of this process being killed by the oom-killer. Valid
1991 values are in the range -16 to +15, plus the special value -17, which disables
1992 oom-killing altogether for this process.
1994 2.13 /proc/<pid>/oom_score - Display current oom-killer score
1995 -------------------------------------------------------------
1997 ------------------------------------------------------------------------------
1998 This file can be used to check the current score used by the oom-killer is for
1999 any given <pid>. Use it together with /proc/<pid>/oom_adj to tune which
2000 process should be killed in an out-of-memory situation.
2002 ------------------------------------------------------------------------------
2004 ------------------------------------------------------------------------------
2005 Certain aspects of kernel behavior can be modified at runtime, without the
2006 need to recompile the kernel, or even to reboot the system. The files in the
2007 /proc/sys tree can not only be read, but also modified. You can use the echo
2008 command to write value into these files, thereby changing the default settings
2010 ------------------------------------------------------------------------------
2012 2.14 /proc/<pid>/io - Display the IO accounting fields
2013 -------------------------------------------------------
2015 This file contains IO statistics for each running process
2020 test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
2023 test:/tmp # cat /proc/3828/io
2029 write_bytes: 323932160
2030 cancelled_write_bytes: 0
2039 I/O counter: chars read
2040 The number of bytes which this task has caused to be read from storage. This
2041 is simply the sum of bytes which this process passed to read() and pread().
2042 It includes things like tty IO and it is unaffected by whether or not actual
2043 physical disk IO was required (the read might have been satisfied from
2050 I/O counter: chars written
2051 The number of bytes which this task has caused, or shall cause to be written
2052 to disk. Similar caveats apply here as with rchar.
2058 I/O counter: read syscalls
2059 Attempt to count the number of read I/O operations, i.e. syscalls like read()
2066 I/O counter: write syscalls
2067 Attempt to count the number of write I/O operations, i.e. syscalls like
2068 write() and pwrite().
2074 I/O counter: bytes read
2075 Attempt to count the number of bytes which this process really did cause to
2076 be fetched from the storage layer. Done at the submit_bio() level, so it is
2077 accurate for block-backed filesystems. <please add status regarding NFS and
2078 CIFS at a later time>
2084 I/O counter: bytes written
2085 Attempt to count the number of bytes which this process caused to be sent to
2086 the storage layer. This is done at page-dirtying time.
2089 cancelled_write_bytes
2090 ---------------------
2092 The big inaccuracy here is truncate. If a process writes 1MB to a file and
2093 then deletes the file, it will in fact perform no writeout. But it will have
2094 been accounted as having caused 1MB of write.
2095 In other words: The number of bytes which this process caused to not happen,
2096 by truncating pagecache. A task can cause "negative" IO too. If this task
2097 truncates some dirty pagecache, some IO which another task has been accounted
2098 for (in it's write_bytes) will not be happening. We _could_ just subtract that
2099 from the truncating task's write_bytes, but there is information loss in doing
2106 At its current implementation state, this is a bit racy on 32-bit machines: if
2107 process A reads process B's /proc/pid/io while process B is updating one of
2108 those 64-bit counters, process A could see an intermediate result.
2111 More information about this can be found within the taskstats documentation in
2112 Documentation/accounting.
2114 ------------------------------------------------------------------------------
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