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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
45 2.15 /proc/<pid>/coredump_filter - Core dump filtering settings
47 ------------------------------------------------------------------------------
49 ------------------------------------------------------------------------------
51 0.1 Introduction/Credits
52 ------------------------
54 This documentation is part of a soon (or so we hope) to be released book on
55 the SuSE Linux distribution. As there is no complete documentation for the
56 /proc file system and we've used many freely available sources to write these
57 chapters, it seems only fair to give the work back to the Linux community.
58 This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm
59 afraid it's still far from complete, but we hope it will be useful. As far as
60 we know, it is the first 'all-in-one' document about the /proc file system. It
61 is focused on the Intel x86 hardware, so if you are looking for PPC, ARM,
62 SPARC, AXP, etc., features, you probably won't find what you are looking for.
63 It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But
64 additions and patches are welcome and will be added to this document if you
67 We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of
68 other people for help compiling this documentation. We'd also like to extend a
69 special thank you to Andi Kleen for documentation, which we relied on heavily
70 to create this document, as well as the additional information he provided.
71 Thanks to everybody else who contributed source or docs to the Linux kernel
72 and helped create a great piece of software... :)
74 If you have any comments, corrections or additions, please don't hesitate to
75 contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this
78 The latest version of this document is available online at
79 http://skaro.nightcrawler.com/~bb/Docs/Proc as HTML version.
81 If the above direction does not works for you, ypu could try the kernel
82 mailing list at linux-kernel@vger.kernel.org and/or try to reach me at
83 comandante@zaralinux.com.
88 We don't guarantee the correctness of this document, and if you come to us
89 complaining about how you screwed up your system because of incorrect
90 documentation, we won't feel responsible...
92 ------------------------------------------------------------------------------
93 CHAPTER 1: COLLECTING SYSTEM INFORMATION
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96 ------------------------------------------------------------------------------
98 ------------------------------------------------------------------------------
99 * Investigating the properties of the pseudo file system /proc and its
100 ability to provide information on the running Linux system
101 * Examining /proc's structure
102 * Uncovering various information about the kernel and the processes running
104 ------------------------------------------------------------------------------
107 The proc file system acts as an interface to internal data structures in the
108 kernel. It can be used to obtain information about the system and to change
109 certain kernel parameters at runtime (sysctl).
111 First, we'll take a look at the read-only parts of /proc. In Chapter 2, we
112 show you how you can use /proc/sys to change settings.
114 1.1 Process-Specific Subdirectories
115 -----------------------------------
117 The directory /proc contains (among other things) one subdirectory for each
118 process running on the system, which is named after the process ID (PID).
120 The link self points to the process reading the file system. Each process
121 subdirectory has the entries listed in Table 1-1.
124 Table 1-1: Process specific entries in /proc
125 ..............................................................................
127 clear_refs Clears page referenced bits shown in smaps output
128 cmdline Command line arguments
129 cpu Current and last cpu in which it was executed (2.4)(smp)
130 cwd Link to the current working directory
131 environ Values of environment variables
132 exe Link to the executable of this process
133 fd Directory, which contains all file descriptors
134 maps Memory maps to executables and library files (2.4)
135 mem Memory held by this process
136 root Link to the root directory of this process
138 statm Process memory status information
139 status Process status in human readable form
140 wchan If CONFIG_KALLSYMS is set, a pre-decoded wchan
141 smaps Extension based on maps, the rss size for each mapped file
142 ..............................................................................
144 For example, to get the status information of a process, all you have to do is
145 read the file /proc/PID/status:
147 >cat /proc/self/status
163 SigPnd: 0000000000000000
164 SigBlk: 0000000000000000
165 SigIgn: 0000000000000000
166 SigCgt: 0000000000000000
167 CapInh: 00000000fffffeff
168 CapPrm: 0000000000000000
169 CapEff: 0000000000000000
172 This shows you nearly the same information you would get if you viewed it with
173 the ps command. In fact, ps uses the proc file system to obtain its
174 information. The statm file contains more detailed information about the
175 process memory usage. Its seven fields are explained in Table 1-2. The stat
176 file contains details information about the process itself. Its fields are
177 explained in Table 1-3.
180 Table 1-2: Contents of the statm files (as of 2.6.8-rc3)
181 ..............................................................................
183 size total program size (pages) (same as VmSize in status)
184 resident size of memory portions (pages) (same as VmRSS in status)
185 shared number of pages that are shared (i.e. backed by a file)
186 trs number of pages that are 'code' (not including libs; broken,
187 includes data segment)
188 lrs number of pages of library (always 0 on 2.6)
189 drs number of pages of data/stack (including libs; broken,
190 includes library text)
191 dt number of dirty pages (always 0 on 2.6)
192 ..............................................................................
195 Table 1-3: Contents of the stat files (as of 2.6.22-rc3)
196 ..............................................................................
199 tcomm filename of the executable
200 state state (R is running, S is sleeping, D is sleeping in an
201 uninterruptible wait, Z is zombie, T is traced or stopped)
202 ppid process id of the parent process
203 pgrp pgrp of the process
205 tty_nr tty the process uses
206 tty_pgrp pgrp of the tty
208 min_flt number of minor faults
209 cmin_flt number of minor faults with child's
210 maj_flt number of major faults
211 cmaj_flt number of major faults with child's
212 utime user mode jiffies
213 stime kernel mode jiffies
214 cutime user mode jiffies with child's
215 cstime kernel mode jiffies with child's
216 priority priority level
218 num_threads number of threads
219 start_time time the process started after system boot
220 vsize virtual memory size
221 rss resident set memory size
222 rsslim current limit in bytes on the rss
223 start_code address above which program text can run
224 end_code address below which program text can run
225 start_stack address of the start of the stack
226 esp current value of ESP
227 eip current value of EIP
228 pending bitmap of pending signals (obsolete)
229 blocked bitmap of blocked signals (obsolete)
230 sigign bitmap of ignored signals (obsolete)
231 sigcatch bitmap of catched signals (obsolete)
232 wchan address where process went to sleep
235 exit_signal signal to send to parent thread on exit
236 task_cpu which CPU the task is scheduled on
237 rt_priority realtime priority
238 policy scheduling policy (man sched_setscheduler)
239 blkio_ticks time spent waiting for block IO
240 ..............................................................................
246 Similar to the process entries, the kernel data files give information about
247 the running kernel. The files used to obtain this information are contained in
248 /proc and are listed in Table 1-4. Not all of these will be present in your
249 system. It depends on the kernel configuration and the loaded modules, which
250 files are there, and which are missing.
252 Table 1-4: Kernel info in /proc
253 ..............................................................................
255 apm Advanced power management info
256 buddyinfo Kernel memory allocator information (see text) (2.5)
257 bus Directory containing bus specific information
258 cmdline Kernel command line
259 cpuinfo Info about the CPU
260 devices Available devices (block and character)
261 dma Used DMS channels
262 filesystems Supported filesystems
263 driver Various drivers grouped here, currently rtc (2.4)
264 execdomains Execdomains, related to security (2.4)
265 fb Frame Buffer devices (2.4)
266 fs File system parameters, currently nfs/exports (2.4)
267 ide Directory containing info about the IDE subsystem
268 interrupts Interrupt usage
269 iomem Memory map (2.4)
270 ioports I/O port usage
271 irq Masks for irq to cpu affinity (2.4)(smp?)
272 isapnp ISA PnP (Plug&Play) Info (2.4)
273 kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
275 ksyms Kernel symbol table
276 loadavg Load average of last 1, 5 & 15 minutes
280 modules List of loaded modules
281 mounts Mounted filesystems
282 net Networking info (see text)
283 partitions Table of partitions known to the system
284 pci Deprecated info of PCI bus (new way -> /proc/bus/pci/,
285 decoupled by lspci (2.4)
287 scsi SCSI info (see text)
288 slabinfo Slab pool info
289 stat Overall statistics
290 swaps Swap space utilization
292 sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4)
293 tty Info of tty drivers
295 version Kernel version
296 video bttv info of video resources (2.4)
297 ..............................................................................
299 You can, for example, check which interrupts are currently in use and what
300 they are used for by looking in the file /proc/interrupts:
302 > cat /proc/interrupts
304 0: 8728810 XT-PIC timer
305 1: 895 XT-PIC keyboard
307 3: 531695 XT-PIC aha152x
308 4: 2014133 XT-PIC serial
309 5: 44401 XT-PIC pcnet_cs
312 12: 182918 XT-PIC PS/2 Mouse
314 14: 1232265 XT-PIC ide0
318 In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
319 output of a SMP machine):
321 > cat /proc/interrupts
324 0: 1243498 1214548 IO-APIC-edge timer
325 1: 8949 8958 IO-APIC-edge keyboard
326 2: 0 0 XT-PIC cascade
327 5: 11286 10161 IO-APIC-edge soundblaster
328 8: 1 0 IO-APIC-edge rtc
329 9: 27422 27407 IO-APIC-edge 3c503
330 12: 113645 113873 IO-APIC-edge PS/2 Mouse
332 14: 22491 24012 IO-APIC-edge ide0
333 15: 2183 2415 IO-APIC-edge ide1
334 17: 30564 30414 IO-APIC-level eth0
335 18: 177 164 IO-APIC-level bttv
340 NMI is incremented in this case because every timer interrupt generates a NMI
341 (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
343 LOC is the local interrupt counter of the internal APIC of every CPU.
345 ERR is incremented in the case of errors in the IO-APIC bus (the bus that
346 connects the CPUs in a SMP system. This means that an error has been detected,
347 the IO-APIC automatically retry the transmission, so it should not be a big
348 problem, but you should read the SMP-FAQ.
350 In 2.6.2* /proc/interrupts was expanded again. This time the goal was for
351 /proc/interrupts to display every IRQ vector in use by the system, not
352 just those considered 'most important'. The new vectors are:
354 THR -- interrupt raised when a machine check threshold counter
355 (typically counting ECC corrected errors of memory or cache) exceeds
356 a configurable threshold. Only available on some systems.
358 TRM -- a thermal event interrupt occurs when a temperature threshold
359 has been exceeded for the CPU. This interrupt may also be generated
360 when the temperature drops back to normal.
362 SPU -- a spurious interrupt is some interrupt that was raised then lowered
363 by some IO device before it could be fully processed by the APIC. Hence
364 the APIC sees the interrupt but does not know what device it came from.
365 For this case the APIC will generate the interrupt with a IRQ vector
366 of 0xff. This might also be generated by chipset bugs.
368 RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are
369 sent from one CPU to another per the needs of the OS. Typically,
370 their statistics are used by kernel developers and interested users to
371 determine the occurance of interrupt of the given type.
373 The above IRQ vectors are displayed only when relevent. For example,
374 the threshold vector does not exist on x86_64 platforms. Others are
375 suppressed when the system is a uniprocessor. As of this writing, only
376 i386 and x86_64 platforms support the new IRQ vector displays.
378 Of some interest is the introduction of the /proc/irq directory to 2.4.
379 It could be used to set IRQ to CPU affinity, this means that you can "hook" an
380 IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
381 irq subdir is one subdir for each IRQ, and one file; prof_cpu_mask
385 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask
386 1 11 13 15 17 19 3 5 7 9
390 The contents of the prof_cpu_mask file and each smp_affinity file for each IRQ
391 is the same by default:
393 > cat /proc/irq/0/smp_affinity
396 It's a bitmask, in which you can specify which CPUs can handle the IRQ, you can
399 > echo 1 > /proc/irq/prof_cpu_mask
401 This means that only the first CPU will handle the IRQ, but you can also echo 5
402 which means that only the first and fourth CPU can handle the IRQ.
404 The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
405 between all the CPUs which are allowed to handle it. As usual the kernel has
406 more info than you and does a better job than you, so the defaults are the
407 best choice for almost everyone.
409 There are three more important subdirectories in /proc: net, scsi, and sys.
410 The general rule is that the contents, or even the existence of these
411 directories, depend on your kernel configuration. If SCSI is not enabled, the
412 directory scsi may not exist. The same is true with the net, which is there
413 only when networking support is present in the running kernel.
415 The slabinfo file gives information about memory usage at the slab level.
416 Linux uses slab pools for memory management above page level in version 2.2.
417 Commonly used objects have their own slab pool (such as network buffers,
418 directory cache, and so on).
420 ..............................................................................
422 > cat /proc/buddyinfo
424 Node 0, zone DMA 0 4 5 4 4 3 ...
425 Node 0, zone Normal 1 0 0 1 101 8 ...
426 Node 0, zone HighMem 2 0 0 1 1 0 ...
428 Memory fragmentation is a problem under some workloads, and buddyinfo is a
429 useful tool for helping diagnose these problems. Buddyinfo will give you a
430 clue as to how big an area you can safely allocate, or why a previous
433 Each column represents the number of pages of a certain order which are
434 available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
435 ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
436 available in ZONE_NORMAL, etc...
438 ..............................................................................
442 Provides information about distribution and utilization of memory. This
443 varies by architecture and compile options. The following is from a
444 16GB PIII, which has highmem enabled. You may not have all of these fields.
449 MemTotal: 16344972 kB
456 HighTotal: 15597528 kB
457 HighFree: 13629632 kB
466 CommitLimit: 7669796 kB
467 Committed_AS: 100056 kB
469 VmallocTotal: 112216 kB
471 VmallocChunk: 111088 kB
473 MemTotal: Total usable ram (i.e. physical ram minus a few reserved
474 bits and the kernel binary code)
475 MemFree: The sum of LowFree+HighFree
476 Buffers: Relatively temporary storage for raw disk blocks
477 shouldn't get tremendously large (20MB or so)
478 Cached: in-memory cache for files read from the disk (the
479 pagecache). Doesn't include SwapCached
480 SwapCached: Memory that once was swapped out, is swapped back in but
481 still also is in the swapfile (if memory is needed it
482 doesn't need to be swapped out AGAIN because it is already
483 in the swapfile. This saves I/O)
484 Active: Memory that has been used more recently and usually not
485 reclaimed unless absolutely necessary.
486 Inactive: Memory which has been less recently used. It is more
487 eligible to be reclaimed for other purposes
489 HighFree: Highmem is all memory above ~860MB of physical memory
490 Highmem areas are for use by userspace programs, or
491 for the pagecache. The kernel must use tricks to access
492 this memory, making it slower to access than lowmem.
494 LowFree: Lowmem is memory which can be used for everything that
495 highmem can be used for, but it is also available for the
496 kernel's use for its own data structures. Among many
497 other things, it is where everything from the Slab is
498 allocated. Bad things happen when you're out of lowmem.
499 SwapTotal: total amount of swap space available
500 SwapFree: Memory which has been evicted from RAM, and is temporarily
502 Dirty: Memory which is waiting to get written back to the disk
503 Writeback: Memory which is actively being written back to the disk
504 Mapped: files which have been mmaped, such as libraries
505 Slab: in-kernel data structures cache
506 CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
507 this is the total amount of memory currently available to
508 be allocated on the system. This limit is only adhered to
509 if strict overcommit accounting is enabled (mode 2 in
510 'vm.overcommit_memory').
511 The CommitLimit is calculated with the following formula:
512 CommitLimit = ('vm.overcommit_ratio' * Physical RAM) + Swap
513 For example, on a system with 1G of physical RAM and 7G
514 of swap with a `vm.overcommit_ratio` of 30 it would
515 yield a CommitLimit of 7.3G.
516 For more details, see the memory overcommit documentation
517 in vm/overcommit-accounting.
518 Committed_AS: The amount of memory presently allocated on the system.
519 The committed memory is a sum of all of the memory which
520 has been allocated by processes, even if it has not been
521 "used" by them as of yet. A process which malloc()'s 1G
522 of memory, but only touches 300M of it will only show up
523 as using 300M of memory even if it has the address space
524 allocated for the entire 1G. This 1G is memory which has
525 been "committed" to by the VM and can be used at any time
526 by the allocating application. With strict overcommit
527 enabled on the system (mode 2 in 'vm.overcommit_memory'),
528 allocations which would exceed the CommitLimit (detailed
529 above) will not be permitted. This is useful if one needs
530 to guarantee that processes will not fail due to lack of
531 memory once that memory has been successfully allocated.
532 PageTables: amount of memory dedicated to the lowest level of page
534 VmallocTotal: total size of vmalloc memory area
535 VmallocUsed: amount of vmalloc area which is used
536 VmallocChunk: largest contigious block of vmalloc area which is free
539 1.3 IDE devices in /proc/ide
540 ----------------------------
542 The subdirectory /proc/ide contains information about all IDE devices of which
543 the kernel is aware. There is one subdirectory for each IDE controller, the
544 file drivers and a link for each IDE device, pointing to the device directory
545 in the controller specific subtree.
547 The file drivers contains general information about the drivers used for the
550 > cat /proc/ide/drivers
551 ide-cdrom version 4.53
552 ide-disk version 1.08
554 More detailed information can be found in the controller specific
555 subdirectories. These are named ide0, ide1 and so on. Each of these
556 directories contains the files shown in table 1-5.
559 Table 1-5: IDE controller info in /proc/ide/ide?
560 ..............................................................................
562 channel IDE channel (0 or 1)
563 config Configuration (only for PCI/IDE bridge)
565 model Type/Chipset of IDE controller
566 ..............................................................................
568 Each device connected to a controller has a separate subdirectory in the
569 controllers directory. The files listed in table 1-6 are contained in these
573 Table 1-6: IDE device information
574 ..............................................................................
577 capacity Capacity of the medium (in 512Byte blocks)
578 driver driver and version
579 geometry physical and logical geometry
580 identify device identify block
582 model device identifier
583 settings device setup
584 smart_thresholds IDE disk management thresholds
585 smart_values IDE disk management values
586 ..............................................................................
588 The most interesting file is settings. This file contains a nice overview of
589 the drive parameters:
591 # cat /proc/ide/ide0/hda/settings
592 name value min max mode
593 ---- ----- --- --- ----
594 bios_cyl 526 0 65535 rw
595 bios_head 255 0 255 rw
597 breada_readahead 4 0 127 rw
599 file_readahead 72 0 2097151 rw
601 keepsettings 0 0 1 rw
602 max_kb_per_request 122 1 127 rw
606 pio_mode write-only 0 255 w
612 1.4 Networking info in /proc/net
613 --------------------------------
615 The subdirectory /proc/net follows the usual pattern. Table 1-6 shows the
616 additional values you get for IP version 6 if you configure the kernel to
617 support this. Table 1-7 lists the files and their meaning.
620 Table 1-6: IPv6 info in /proc/net
621 ..............................................................................
623 udp6 UDP sockets (IPv6)
624 tcp6 TCP sockets (IPv6)
625 raw6 Raw device statistics (IPv6)
626 igmp6 IP multicast addresses, which this host joined (IPv6)
627 if_inet6 List of IPv6 interface addresses
628 ipv6_route Kernel routing table for IPv6
629 rt6_stats Global IPv6 routing tables statistics
630 sockstat6 Socket statistics (IPv6)
631 snmp6 Snmp data (IPv6)
632 ..............................................................................
635 Table 1-7: Network info in /proc/net
636 ..............................................................................
639 dev network devices with statistics
640 dev_mcast the Layer2 multicast groups a device is listening too
641 (interface index, label, number of references, number of bound
643 dev_stat network device status
644 ip_fwchains Firewall chain linkage
645 ip_fwnames Firewall chain names
646 ip_masq Directory containing the masquerading tables
647 ip_masquerade Major masquerading table
648 netstat Network statistics
649 raw raw device statistics
650 route Kernel routing table
651 rpc Directory containing rpc info
652 rt_cache Routing cache
654 sockstat Socket statistics
656 tr_rif Token ring RIF routing table
658 unix UNIX domain sockets
659 wireless Wireless interface data (Wavelan etc)
660 igmp IP multicast addresses, which this host joined
661 psched Global packet scheduler parameters.
662 netlink List of PF_NETLINK sockets
663 ip_mr_vifs List of multicast virtual interfaces
664 ip_mr_cache List of multicast routing cache
665 ..............................................................................
667 You can use this information to see which network devices are available in
668 your system and how much traffic was routed over those devices:
672 face |bytes packets errs drop fifo frame compressed multicast|[...
673 lo: 908188 5596 0 0 0 0 0 0 [...
674 ppp0:15475140 20721 410 0 0 410 0 0 [...
675 eth0: 614530 7085 0 0 0 0 0 1 [...
678 ...] bytes packets errs drop fifo colls carrier compressed
679 ...] 908188 5596 0 0 0 0 0 0
680 ...] 1375103 17405 0 0 0 0 0 0
681 ...] 1703981 5535 0 0 0 3 0 0
683 In addition, each Channel Bond interface has it's own directory. For
684 example, the bond0 device will have a directory called /proc/net/bond0/.
685 It will contain information that is specific to that bond, such as the
686 current slaves of the bond, the link status of the slaves, and how
687 many times the slaves link has failed.
692 If you have a SCSI host adapter in your system, you'll find a subdirectory
693 named after the driver for this adapter in /proc/scsi. You'll also see a list
694 of all recognized SCSI devices in /proc/scsi:
698 Host: scsi0 Channel: 00 Id: 00 Lun: 00
699 Vendor: IBM Model: DGHS09U Rev: 03E0
700 Type: Direct-Access ANSI SCSI revision: 03
701 Host: scsi0 Channel: 00 Id: 06 Lun: 00
702 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04
703 Type: CD-ROM ANSI SCSI revision: 02
706 The directory named after the driver has one file for each adapter found in
707 the system. These files contain information about the controller, including
708 the used IRQ and the IO address range. The amount of information shown is
709 dependent on the adapter you use. The example shows the output for an Adaptec
710 AHA-2940 SCSI adapter:
712 > cat /proc/scsi/aic7xxx/0
714 Adaptec AIC7xxx driver version: 5.1.19/3.2.4
716 TCQ Enabled By Default : Disabled
717 AIC7XXX_PROC_STATS : Disabled
718 AIC7XXX_RESET_DELAY : 5
719 Adapter Configuration:
720 SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
721 Ultra Wide Controller
722 PCI MMAPed I/O Base: 0xeb001000
723 Adapter SEEPROM Config: SEEPROM found and used.
724 Adaptec SCSI BIOS: Enabled
726 SCBs: Active 0, Max Active 2,
727 Allocated 15, HW 16, Page 255
729 BIOS Control Word: 0x18b6
730 Adapter Control Word: 0x005b
731 Extended Translation: Enabled
732 Disconnect Enable Flags: 0xffff
733 Ultra Enable Flags: 0x0001
734 Tag Queue Enable Flags: 0x0000
735 Ordered Queue Tag Flags: 0x0000
736 Default Tag Queue Depth: 8
737 Tagged Queue By Device array for aic7xxx host instance 0:
738 {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
739 Actual queue depth per device for aic7xxx host instance 0:
740 {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
743 Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
744 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
745 Total transfers 160151 (74577 reads and 85574 writes)
747 Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
748 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
749 Total transfers 0 (0 reads and 0 writes)
752 1.6 Parallel port info in /proc/parport
753 ---------------------------------------
755 The directory /proc/parport contains information about the parallel ports of
756 your system. It has one subdirectory for each port, named after the port
759 These directories contain the four files shown in Table 1-8.
762 Table 1-8: Files in /proc/parport
763 ..............................................................................
765 autoprobe Any IEEE-1284 device ID information that has been acquired.
766 devices list of the device drivers using that port. A + will appear by the
767 name of the device currently using the port (it might not appear
769 hardware Parallel port's base address, IRQ line and DMA channel.
770 irq IRQ that parport is using for that port. This is in a separate
771 file to allow you to alter it by writing a new value in (IRQ
773 ..............................................................................
775 1.7 TTY info in /proc/tty
776 -------------------------
778 Information about the available and actually used tty's can be found in the
779 directory /proc/tty.You'll find entries for drivers and line disciplines in
780 this directory, as shown in Table 1-9.
783 Table 1-9: Files in /proc/tty
784 ..............................................................................
786 drivers list of drivers and their usage
787 ldiscs registered line disciplines
788 driver/serial usage statistic and status of single tty lines
789 ..............................................................................
791 To see which tty's are currently in use, you can simply look into the file
794 > cat /proc/tty/drivers
795 pty_slave /dev/pts 136 0-255 pty:slave
796 pty_master /dev/ptm 128 0-255 pty:master
797 pty_slave /dev/ttyp 3 0-255 pty:slave
798 pty_master /dev/pty 2 0-255 pty:master
799 serial /dev/cua 5 64-67 serial:callout
800 serial /dev/ttyS 4 64-67 serial
801 /dev/tty0 /dev/tty0 4 0 system:vtmaster
802 /dev/ptmx /dev/ptmx 5 2 system
803 /dev/console /dev/console 5 1 system:console
804 /dev/tty /dev/tty 5 0 system:/dev/tty
805 unknown /dev/tty 4 1-63 console
808 1.8 Miscellaneous kernel statistics in /proc/stat
809 -------------------------------------------------
811 Various pieces of information about kernel activity are available in the
812 /proc/stat file. All of the numbers reported in this file are aggregates
813 since the system first booted. For a quick look, simply cat the file:
816 cpu 2255 34 2290 22625563 6290 127 456
817 cpu0 1132 34 1441 11311718 3675 127 438
818 cpu1 1123 0 849 11313845 2614 0 18
819 intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
826 The very first "cpu" line aggregates the numbers in all of the other "cpuN"
827 lines. These numbers identify the amount of time the CPU has spent performing
828 different kinds of work. Time units are in USER_HZ (typically hundredths of a
829 second). The meanings of the columns are as follows, from left to right:
831 - user: normal processes executing in user mode
832 - nice: niced processes executing in user mode
833 - system: processes executing in kernel mode
834 - idle: twiddling thumbs
835 - iowait: waiting for I/O to complete
836 - irq: servicing interrupts
837 - softirq: servicing softirqs
839 The "intr" line gives counts of interrupts serviced since boot time, for each
840 of the possible system interrupts. The first column is the total of all
841 interrupts serviced; each subsequent column is the total for that particular
844 The "ctxt" line gives the total number of context switches across all CPUs.
846 The "btime" line gives the time at which the system booted, in seconds since
849 The "processes" line gives the number of processes and threads created, which
850 includes (but is not limited to) those created by calls to the fork() and
851 clone() system calls.
853 The "procs_running" line gives the number of processes currently running on
856 The "procs_blocked" line gives the number of processes currently blocked,
857 waiting for I/O to complete.
860 ------------------------------------------------------------------------------
862 ------------------------------------------------------------------------------
863 The /proc file system serves information about the running system. It not only
864 allows access to process data but also allows you to request the kernel status
865 by reading files in the hierarchy.
867 The directory structure of /proc reflects the types of information and makes
868 it easy, if not obvious, where to look for specific data.
869 ------------------------------------------------------------------------------
871 ------------------------------------------------------------------------------
872 CHAPTER 2: MODIFYING SYSTEM PARAMETERS
873 ------------------------------------------------------------------------------
875 ------------------------------------------------------------------------------
877 ------------------------------------------------------------------------------
878 * Modifying kernel parameters by writing into files found in /proc/sys
879 * Exploring the files which modify certain parameters
880 * Review of the /proc/sys file tree
881 ------------------------------------------------------------------------------
884 A very interesting part of /proc is the directory /proc/sys. This is not only
885 a source of information, it also allows you to change parameters within the
886 kernel. Be very careful when attempting this. You can optimize your system,
887 but you can also cause it to crash. Never alter kernel parameters on a
888 production system. Set up a development machine and test to make sure that
889 everything works the way you want it to. You may have no alternative but to
890 reboot the machine once an error has been made.
892 To change a value, simply echo the new value into the file. An example is
893 given below in the section on the file system data. You need to be root to do
894 this. You can create your own boot script to perform this every time your
897 The files in /proc/sys can be used to fine tune and monitor miscellaneous and
898 general things in the operation of the Linux kernel. Since some of the files
899 can inadvertently disrupt your system, it is advisable to read both
900 documentation and source before actually making adjustments. In any case, be
901 very careful when writing to any of these files. The entries in /proc may
902 change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
903 review the kernel documentation in the directory /usr/src/linux/Documentation.
904 This chapter is heavily based on the documentation included in the pre 2.2
905 kernels, and became part of it in version 2.2.1 of the Linux kernel.
907 2.1 /proc/sys/fs - File system data
908 -----------------------------------
910 This subdirectory contains specific file system, file handle, inode, dentry
911 and quota information.
913 Currently, these files are in /proc/sys/fs:
918 Status of the directory cache. Since directory entries are dynamically
919 allocated and deallocated, this file indicates the current status. It holds
920 six values, in which the last two are not used and are always zero. The others
921 are listed in table 2-1.
924 Table 2-1: Status files of the directory cache
925 ..............................................................................
927 nr_dentry Almost always zero
928 nr_unused Number of unused cache entries
930 in seconds after the entry may be reclaimed, when memory is short
931 want_pages internally
932 ..............................................................................
934 dquot-nr and dquot-max
935 ----------------------
937 The file dquot-max shows the maximum number of cached disk quota entries.
939 The file dquot-nr shows the number of allocated disk quota entries and the
940 number of free disk quota entries.
942 If the number of available cached disk quotas is very low and you have a large
943 number of simultaneous system users, you might want to raise the limit.
948 The kernel allocates file handles dynamically, but doesn't free them again at
951 The value in file-max denotes the maximum number of file handles that the
952 Linux kernel will allocate. When you get a lot of error messages about running
953 out of file handles, you might want to raise this limit. The default value is
954 10% of RAM in kilobytes. To change it, just write the new number into the
957 # cat /proc/sys/fs/file-max
959 # echo 8192 > /proc/sys/fs/file-max
960 # cat /proc/sys/fs/file-max
964 This method of revision is useful for all customizable parameters of the
965 kernel - simply echo the new value to the corresponding file.
967 Historically, the three values in file-nr denoted the number of allocated file
968 handles, the number of allocated but unused file handles, and the maximum
969 number of file handles. Linux 2.6 always reports 0 as the number of free file
970 handles -- this is not an error, it just means that the number of allocated
971 file handles exactly matches the number of used file handles.
973 Attempts to allocate more file descriptors than file-max are reported with
974 printk, look for "VFS: file-max limit <number> reached".
976 inode-state and inode-nr
977 ------------------------
979 The file inode-nr contains the first two items from inode-state, so we'll skip
982 inode-state contains two actual numbers and five dummy values. The numbers
983 are nr_inodes and nr_free_inodes (in order of appearance).
988 Denotes the number of inodes the system has allocated. This number will
989 grow and shrink dynamically.
994 Represents the number of free inodes. Ie. The number of inuse inodes is
995 (nr_inodes - nr_free_inodes).
997 aio-nr and aio-max-nr
998 ---------------------
1000 aio-nr is the running total of the number of events specified on the
1001 io_setup system call for all currently active aio contexts. If aio-nr
1002 reaches aio-max-nr then io_setup will fail with EAGAIN. Note that
1003 raising aio-max-nr does not result in the pre-allocation or re-sizing
1004 of any kernel data structures.
1006 2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats
1007 -----------------------------------------------------------
1009 Besides these files, there is the subdirectory /proc/sys/fs/binfmt_misc. This
1010 handles the kernel support for miscellaneous binary formats.
1012 Binfmt_misc provides the ability to register additional binary formats to the
1013 Kernel without compiling an additional module/kernel. Therefore, binfmt_misc
1014 needs to know magic numbers at the beginning or the filename extension of the
1017 It works by maintaining a linked list of structs that contain a description of
1018 a binary format, including a magic with size (or the filename extension),
1019 offset and mask, and the interpreter name. On request it invokes the given
1020 interpreter with the original program as argument, as binfmt_java and
1021 binfmt_em86 and binfmt_mz do. Since binfmt_misc does not define any default
1022 binary-formats, you have to register an additional binary-format.
1024 There are two general files in binfmt_misc and one file per registered format.
1025 The two general files are register and status.
1027 Registering a new binary format
1028 -------------------------------
1030 To register a new binary format you have to issue the command
1032 echo :name:type:offset:magic:mask:interpreter: > /proc/sys/fs/binfmt_misc/register
1036 with appropriate name (the name for the /proc-dir entry), offset (defaults to
1037 0, if omitted), magic, mask (which can be omitted, defaults to all 0xff) and
1038 last but not least, the interpreter that is to be invoked (for example and
1039 testing /bin/echo). Type can be M for usual magic matching or E for filename
1040 extension matching (give extension in place of magic).
1042 Check or reset the status of the binary format handler
1043 ------------------------------------------------------
1045 If you do a cat on the file /proc/sys/fs/binfmt_misc/status, you will get the
1046 current status (enabled/disabled) of binfmt_misc. Change the status by echoing
1047 0 (disables) or 1 (enables) or -1 (caution: this clears all previously
1048 registered binary formats) to status. For example echo 0 > status to disable
1049 binfmt_misc (temporarily).
1051 Status of a single handler
1052 --------------------------
1054 Each registered handler has an entry in /proc/sys/fs/binfmt_misc. These files
1055 perform the same function as status, but their scope is limited to the actual
1056 binary format. By cating this file, you also receive all related information
1057 about the interpreter/magic of the binfmt.
1059 Example usage of binfmt_misc (emulate binfmt_java)
1060 --------------------------------------------------
1062 cd /proc/sys/fs/binfmt_misc
1063 echo ':Java:M::\xca\xfe\xba\xbe::/usr/local/java/bin/javawrapper:' > register
1064 echo ':HTML:E::html::/usr/local/java/bin/appletviewer:' > register
1065 echo ':Applet:M::<!--applet::/usr/local/java/bin/appletviewer:' > register
1066 echo ':DEXE:M::\x0eDEX::/usr/bin/dosexec:' > register
1069 These four lines add support for Java executables and Java applets (like
1070 binfmt_java, additionally recognizing the .html extension with no need to put
1071 <!--applet> to every applet file). You have to install the JDK and the
1072 shell-script /usr/local/java/bin/javawrapper too. It works around the
1073 brokenness of the Java filename handling. To add a Java binary, just create a
1074 link to the class-file somewhere in the path.
1076 2.3 /proc/sys/kernel - general kernel parameters
1077 ------------------------------------------------
1079 This directory reflects general kernel behaviors. As I've said before, the
1080 contents depend on your configuration. Here you'll find the most important
1081 files, along with descriptions of what they mean and how to use them.
1086 The file contains three values; highwater, lowwater, and frequency.
1088 It exists only when BSD-style process accounting is enabled. These values
1089 control its behavior. If the free space on the file system where the log lives
1090 goes below lowwater percentage, accounting suspends. If it goes above
1091 highwater percentage, accounting resumes. Frequency determines how often you
1092 check the amount of free space (value is in seconds). Default settings are: 4,
1093 2, and 30. That is, suspend accounting if there is less than 2 percent free;
1094 resume it if we have a value of 3 or more percent; consider information about
1095 the amount of free space valid for 30 seconds
1100 The file contains a single value denoting the limit on the argv array size
1101 for execve (in KiB). This limit is only applied when system call auditing for
1102 execve is enabled, otherwise the value is ignored.
1107 When the value in this file is 0, ctrl-alt-del is trapped and sent to the init
1108 program to handle a graceful restart. However, when the value is greater that
1109 zero, Linux's reaction to this key combination will be an immediate reboot,
1110 without syncing its dirty buffers.
1113 When a program (like dosemu) has the keyboard in raw mode, the
1114 ctrl-alt-del is intercepted by the program before it ever reaches the
1115 kernel tty layer, and it is up to the program to decide what to do with
1118 domainname and hostname
1119 -----------------------
1121 These files can be controlled to set the NIS domainname and hostname of your
1122 box. For the classic darkstar.frop.org a simple:
1124 # echo "darkstar" > /proc/sys/kernel/hostname
1125 # echo "frop.org" > /proc/sys/kernel/domainname
1128 would suffice to set your hostname and NIS domainname.
1130 osrelease, ostype and version
1131 -----------------------------
1133 The names make it pretty obvious what these fields contain:
1135 > cat /proc/sys/kernel/osrelease
1138 > cat /proc/sys/kernel/ostype
1141 > cat /proc/sys/kernel/version
1142 #4 Fri Oct 1 12:41:14 PDT 1999
1145 The files osrelease and ostype should be clear enough. Version needs a little
1146 more clarification. The #4 means that this is the 4th kernel built from this
1147 source base and the date after it indicates the time the kernel was built. The
1148 only way to tune these values is to rebuild the kernel.
1153 The value in this file represents the number of seconds the kernel waits
1154 before rebooting on a panic. When you use the software watchdog, the
1155 recommended setting is 60. If set to 0, the auto reboot after a kernel panic
1156 is disabled, which is the default setting.
1161 The four values in printk denote
1163 * default_message_loglevel,
1164 * minimum_console_loglevel and
1165 * default_console_loglevel
1168 These values influence printk() behavior when printing or logging error
1169 messages, which come from inside the kernel. See syslog(2) for more
1170 information on the different log levels.
1175 Messages with a higher priority than this will be printed to the console.
1177 default_message_level
1178 ---------------------
1180 Messages without an explicit priority will be printed with this priority.
1182 minimum_console_loglevel
1183 ------------------------
1185 Minimum (highest) value to which the console_loglevel can be set.
1187 default_console_loglevel
1188 ------------------------
1190 Default value for console_loglevel.
1195 This file shows the size of the generic SCSI (sg) buffer. At this point, you
1196 can't tune it yet, but you can change it at compile time by editing
1197 include/scsi/sg.h and changing the value of SG_BIG_BUFF.
1199 If you use a scanner with SANE (Scanner Access Now Easy) you might want to set
1200 this to a higher value. Refer to the SANE documentation on this issue.
1205 The location where the modprobe binary is located. The kernel uses this
1206 program to load modules on demand.
1211 The value in this file affects behavior of handling NMI. When the value is
1212 non-zero, unknown NMI is trapped and then panic occurs. At that time, kernel
1213 debugging information is displayed on console.
1215 NMI switch that most IA32 servers have fires unknown NMI up, for example.
1216 If a system hangs up, try pressing the NMI switch.
1221 Enables/Disables the NMI watchdog on x86 systems. When the value is non-zero
1222 the NMI watchdog is enabled and will continuously test all online cpus to
1223 determine whether or not they are still functioning properly.
1225 Because the NMI watchdog shares registers with oprofile, by disabling the NMI
1226 watchdog, oprofile may have more registers to utilize.
1231 Enables/Disables the protection of the per-process proc entries "maps" and
1232 "smaps". When enabled, the contents of these files are visible only to
1233 readers that are allowed to ptrace() the given process.
1236 2.4 /proc/sys/vm - The virtual memory subsystem
1237 -----------------------------------------------
1239 The files in this directory can be used to tune the operation of the virtual
1240 memory (VM) subsystem of the Linux kernel.
1245 Controls the tendency of the kernel to reclaim the memory which is used for
1246 caching of directory and inode objects.
1248 At the default value of vfs_cache_pressure=100 the kernel will attempt to
1249 reclaim dentries and inodes at a "fair" rate with respect to pagecache and
1250 swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer
1251 to retain dentry and inode caches. Increasing vfs_cache_pressure beyond 100
1252 causes the kernel to prefer to reclaim dentries and inodes.
1254 dirty_background_ratio
1255 ----------------------
1257 Contains, as a percentage of total system memory, the number of pages at which
1258 the pdflush background writeback daemon will start writing out dirty data.
1263 Contains, as a percentage of total system memory, the number of pages at which
1264 a process which is generating disk writes will itself start writing out dirty
1267 dirty_writeback_centisecs
1268 -------------------------
1270 The pdflush writeback daemons will periodically wake up and write `old' data
1271 out to disk. This tunable expresses the interval between those wakeups, in
1272 100'ths of a second.
1274 Setting this to zero disables periodic writeback altogether.
1276 dirty_expire_centisecs
1277 ----------------------
1279 This tunable is used to define when dirty data is old enough to be eligible
1280 for writeout by the pdflush daemons. It is expressed in 100'ths of a second.
1281 Data which has been dirty in-memory for longer than this interval will be
1282 written out next time a pdflush daemon wakes up.
1287 If non-zero, this sysctl disables the new 32-bit mmap mmap layout - the kernel
1288 will use the legacy (2.4) layout for all processes.
1290 lower_zone_protection
1291 ---------------------
1293 For some specialised workloads on highmem machines it is dangerous for
1294 the kernel to allow process memory to be allocated from the "lowmem"
1295 zone. This is because that memory could then be pinned via the mlock()
1296 system call, or by unavailability of swapspace.
1298 And on large highmem machines this lack of reclaimable lowmem memory
1301 So the Linux page allocator has a mechanism which prevents allocations
1302 which _could_ use highmem from using too much lowmem. This means that
1303 a certain amount of lowmem is defended from the possibility of being
1304 captured into pinned user memory.
1306 (The same argument applies to the old 16 megabyte ISA DMA region. This
1307 mechanism will also defend that region from allocations which could use
1310 The `lower_zone_protection' tunable determines how aggressive the kernel is
1311 in defending these lower zones. The default value is zero - no
1314 If you have a machine which uses highmem or ISA DMA and your
1315 applications are using mlock(), or if you are running with no swap then
1316 you probably should increase the lower_zone_protection setting.
1318 The units of this tunable are fairly vague. It is approximately equal
1319 to "megabytes," so setting lower_zone_protection=100 will protect around 100
1320 megabytes of the lowmem zone from user allocations. It will also make
1321 those 100 megabytes unavailable for use by applications and by
1322 pagecache, so there is a cost.
1324 The effects of this tunable may be observed by monitoring
1325 /proc/meminfo:LowFree. Write a single huge file and observe the point
1326 at which LowFree ceases to fall.
1328 A reasonable value for lower_zone_protection is 100.
1333 page-cluster controls the number of pages which are written to swap in
1334 a single attempt. The swap I/O size.
1336 It is a logarithmic value - setting it to zero means "1 page", setting
1337 it to 1 means "2 pages", setting it to 2 means "4 pages", etc.
1339 The default value is three (eight pages at a time). There may be some
1340 small benefits in tuning this to a different value if your workload is
1346 Controls overcommit of system memory, possibly allowing processes
1347 to allocate (but not use) more memory than is actually available.
1350 0 - Heuristic overcommit handling. Obvious overcommits of
1351 address space are refused. Used for a typical system. It
1352 ensures a seriously wild allocation fails while allowing
1353 overcommit to reduce swap usage. root is allowed to
1354 allocate slightly more memory in this mode. This is the
1357 1 - Always overcommit. Appropriate for some scientific
1360 2 - Don't overcommit. The total address space commit
1361 for the system is not permitted to exceed swap plus a
1362 configurable percentage (default is 50) of physical RAM.
1363 Depending on the percentage you use, in most situations
1364 this means a process will not be killed while attempting
1365 to use already-allocated memory but will receive errors
1366 on memory allocation as appropriate.
1371 Percentage of physical memory size to include in overcommit calculations
1374 Memory allocation limit = swapspace + physmem * (overcommit_ratio / 100)
1376 swapspace = total size of all swap areas
1377 physmem = size of physical memory in system
1379 nr_hugepages and hugetlb_shm_group
1380 ----------------------------------
1382 nr_hugepages configures number of hugetlb page reserved for the system.
1384 hugetlb_shm_group contains group id that is allowed to create SysV shared
1385 memory segment using hugetlb page.
1387 hugepages_treat_as_movable
1388 --------------------------
1390 This parameter is only useful when kernelcore= is specified at boot time to
1391 create ZONE_MOVABLE for pages that may be reclaimed or migrated. Huge pages
1392 are not movable so are not normally allocated from ZONE_MOVABLE. A non-zero
1393 value written to hugepages_treat_as_movable allows huge pages to be allocated
1396 Once enabled, the ZONE_MOVABLE is treated as an area of memory the huge
1397 pages pool can easily grow or shrink within. Assuming that applications are
1398 not running that mlock() a lot of memory, it is likely the huge pages pool
1399 can grow to the size of ZONE_MOVABLE by repeatedly entering the desired value
1400 into nr_hugepages and triggering page reclaim.
1405 laptop_mode is a knob that controls "laptop mode". All the things that are
1406 controlled by this knob are discussed in Documentation/laptop-mode.txt.
1411 block_dump enables block I/O debugging when set to a nonzero value. More
1412 information on block I/O debugging is in Documentation/laptop-mode.txt.
1417 This file contains valid hold time of swap out protection token. The Linux
1418 VM has token based thrashing control mechanism and uses the token to prevent
1419 unnecessary page faults in thrashing situation. The unit of the value is
1420 second. The value would be useful to tune thrashing behavior.
1425 Writing to this will cause the kernel to drop clean caches, dentries and
1426 inodes from memory, causing that memory to become free.
1429 echo 1 > /proc/sys/vm/drop_caches
1430 To free dentries and inodes:
1431 echo 2 > /proc/sys/vm/drop_caches
1432 To free pagecache, dentries and inodes:
1433 echo 3 > /proc/sys/vm/drop_caches
1435 As this is a non-destructive operation and dirty objects are not freeable, the
1436 user should run `sync' first.
1439 2.5 /proc/sys/dev - Device specific parameters
1440 ----------------------------------------------
1442 Currently there is only support for CDROM drives, and for those, there is only
1443 one read-only file containing information about the CD-ROM drives attached to
1446 >cat /proc/sys/dev/cdrom/info
1447 CD-ROM information, Id: cdrom.c 2.55 1999/04/25
1451 drive # of slots: 1 0
1455 Can change speed: 1 1
1456 Can select disk: 0 1
1457 Can read multisession: 1 1
1459 Reports media changed: 1 1
1463 You see two drives, sr0 and hdb, along with a list of their features.
1465 2.6 /proc/sys/sunrpc - Remote procedure calls
1466 ---------------------------------------------
1468 This directory contains four files, which enable or disable debugging for the
1469 RPC functions NFS, NFS-daemon, RPC and NLM. The default values are 0. They can
1470 be set to one to turn debugging on. (The default value is 0 for each)
1472 2.7 /proc/sys/net - Networking stuff
1473 ------------------------------------
1475 The interface to the networking parts of the kernel is located in
1476 /proc/sys/net. Table 2-3 shows all possible subdirectories. You may see only
1477 some of them, depending on your kernel's configuration.
1480 Table 2-3: Subdirectories in /proc/sys/net
1481 ..............................................................................
1482 Directory Content Directory Content
1483 core General parameter appletalk Appletalk protocol
1484 unix Unix domain sockets netrom NET/ROM
1485 802 E802 protocol ax25 AX25
1486 ethernet Ethernet protocol rose X.25 PLP layer
1487 ipv4 IP version 4 x25 X.25 protocol
1488 ipx IPX token-ring IBM token ring
1489 bridge Bridging decnet DEC net
1491 ..............................................................................
1493 We will concentrate on IP networking here. Since AX15, X.25, and DEC Net are
1494 only minor players in the Linux world, we'll skip them in this chapter. You'll
1495 find some short info on Appletalk and IPX further on in this chapter. Review
1496 the online documentation and the kernel source to get a detailed view of the
1497 parameters for those protocols. In this section we'll discuss the
1498 subdirectories printed in bold letters in the table above. As default values
1499 are suitable for most needs, there is no need to change these values.
1501 /proc/sys/net/core - Network core options
1502 -----------------------------------------
1507 The default setting of the socket receive buffer in bytes.
1512 The maximum receive socket buffer size in bytes.
1517 The default setting (in bytes) of the socket send buffer.
1522 The maximum send socket buffer size in bytes.
1524 message_burst and message_cost
1525 ------------------------------
1527 These parameters are used to limit the warning messages written to the kernel
1528 log from the networking code. They enforce a rate limit to make a
1529 denial-of-service attack impossible. A higher message_cost factor, results in
1530 fewer messages that will be written. Message_burst controls when messages will
1531 be dropped. The default settings limit warning messages to one every five
1537 This controls console messages from the networking stack that can occur because
1538 of problems on the network like duplicate address or bad checksums. Normally,
1539 this should be enabled, but if the problem persists the messages can be
1546 Maximum number of packets, queued on the INPUT side, when the interface
1547 receives packets faster than kernel can process them.
1552 Maximum ancillary buffer size allowed per socket. Ancillary data is a sequence
1553 of struct cmsghdr structures with appended data.
1555 /proc/sys/net/unix - Parameters for Unix domain sockets
1556 -------------------------------------------------------
1558 There are only two files in this subdirectory. They control the delays for
1559 deleting and destroying socket descriptors.
1561 2.8 /proc/sys/net/ipv4 - IPV4 settings
1562 --------------------------------------
1564 IP version 4 is still the most used protocol in Unix networking. It will be
1565 replaced by IP version 6 in the next couple of years, but for the moment it's
1566 the de facto standard for the internet and is used in most networking
1567 environments around the world. Because of the importance of this protocol,
1568 we'll have a deeper look into the subtree controlling the behavior of the IPv4
1569 subsystem of the Linux kernel.
1571 Let's start with the entries in /proc/sys/net/ipv4.
1576 icmp_echo_ignore_all and icmp_echo_ignore_broadcasts
1577 ----------------------------------------------------
1579 Turn on (1) or off (0), if the kernel should ignore all ICMP ECHO requests, or
1580 just those to broadcast and multicast addresses.
1582 Please note that if you accept ICMP echo requests with a broadcast/multi\-cast
1583 destination address your network may be used as an exploder for denial of
1584 service packet flooding attacks to other hosts.
1586 icmp_destunreach_rate, icmp_echoreply_rate, icmp_paramprob_rate and icmp_timeexeed_rate
1587 ---------------------------------------------------------------------------------------
1589 Sets limits for sending ICMP packets to specific targets. A value of zero
1590 disables all limiting. Any positive value sets the maximum package rate in
1591 hundredth of a second (on Intel systems).
1599 This file contains the number one if the host received its IP configuration by
1600 RARP, BOOTP, DHCP or a similar mechanism. Otherwise it is zero.
1605 TTL (Time To Live) for IPv4 interfaces. This is simply the maximum number of
1606 hops a packet may travel.
1611 Enable dynamic socket address rewriting on interface address change. This is
1612 useful for dialup interface with changing IP addresses.
1617 Enable or disable forwarding of IP packages between interfaces. Changing this
1618 value resets all other parameters to their default values. They differ if the
1619 kernel is configured as host or router.
1624 Range of ports used by TCP and UDP to choose the local port. Contains two
1625 numbers, the first number is the lowest port, the second number the highest
1626 local port. Default is 1024-4999. Should be changed to 32768-61000 for
1632 Global switch to turn path MTU discovery off. It can also be set on a per
1633 socket basis by the applications or on a per route basis.
1638 Enable/disable debugging of IP masquerading.
1640 IP fragmentation settings
1641 -------------------------
1643 ipfrag_high_trash and ipfrag_low_trash
1644 --------------------------------------
1646 Maximum memory used to reassemble IP fragments. When ipfrag_high_thresh bytes
1647 of memory is allocated for this purpose, the fragment handler will toss
1648 packets until ipfrag_low_thresh is reached.
1653 Time in seconds to keep an IP fragment in memory.
1661 This file controls the use of the ECN bit in the IPv4 headers. This is a new
1662 feature about Explicit Congestion Notification, but some routers and firewalls
1663 block traffic that has this bit set, so it could be necessary to echo 0 to
1664 /proc/sys/net/ipv4/tcp_ecn if you want to talk to these sites. For more info
1665 you could read RFC2481.
1667 tcp_retrans_collapse
1668 --------------------
1670 Bug-to-bug compatibility with some broken printers. On retransmit, try to send
1671 larger packets to work around bugs in certain TCP stacks. Can be turned off by
1674 tcp_keepalive_probes
1675 --------------------
1677 Number of keep alive probes TCP sends out, until it decides that the
1678 connection is broken.
1683 How often TCP sends out keep alive messages, when keep alive is enabled. The
1689 Number of times initial SYNs for a TCP connection attempt will be
1690 retransmitted. Should not be higher than 255. This is only the timeout for
1691 outgoing connections, for incoming connections the number of retransmits is
1692 defined by tcp_retries1.
1697 Enable select acknowledgments after RFC2018.
1702 Enable timestamps as defined in RFC1323.
1707 Enable the strict RFC793 interpretation of the TCP urgent pointer field. The
1708 default is to use the BSD compatible interpretation of the urgent pointer
1709 pointing to the first byte after the urgent data. The RFC793 interpretation is
1710 to have it point to the last byte of urgent data. Enabling this option may
1711 lead to interoperability problems. Disabled by default.
1716 Only valid when the kernel was compiled with CONFIG_SYNCOOKIES. Send out
1717 syncookies when the syn backlog queue of a socket overflows. This is to ward
1718 off the common 'syn flood attack'. Disabled by default.
1720 Note that the concept of a socket backlog is abandoned. This means the peer
1721 may not receive reliable error messages from an over loaded server with
1727 Enable window scaling as defined in RFC1323.
1732 The length of time in seconds it takes to receive a final FIN before the
1733 socket is always closed. This is strictly a violation of the TCP
1734 specification, but required to prevent denial-of-service attacks.
1739 Indicates how many keep alive probes are sent per slow timer run. Should not
1740 be set too high to prevent bursts.
1745 Length of the per socket backlog queue. Since Linux 2.2 the backlog specified
1746 in listen(2) only specifies the length of the backlog queue of already
1747 established sockets. When more connection requests arrive Linux starts to drop
1748 packets. When syncookies are enabled the packets are still answered and the
1749 maximum queue is effectively ignored.
1754 Defines how often an answer to a TCP connection request is retransmitted
1760 Defines how often a TCP packet is retransmitted before giving up.
1762 Interface specific settings
1763 ---------------------------
1765 In the directory /proc/sys/net/ipv4/conf you'll find one subdirectory for each
1766 interface the system knows about and one directory calls all. Changes in the
1767 all subdirectory affect all interfaces, whereas changes in the other
1768 subdirectories affect only one interface. All directories have the same
1774 This switch decides if the kernel accepts ICMP redirect messages or not. The
1775 default is 'yes' if the kernel is configured for a regular host and 'no' for a
1776 router configuration.
1781 Should source routed packages be accepted or declined. The default is
1782 dependent on the kernel configuration. It's 'yes' for routers and 'no' for
1788 Accept packets with source address 0.b.c.d with destinations not to this host
1789 as local ones. It is supposed that a BOOTP relay daemon will catch and forward
1792 The default is 0, since this feature is not implemented yet (kernel version
1798 Enable or disable IP forwarding on this interface.
1803 Log packets with source addresses with no known route to kernel log.
1808 Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE and a
1809 multicast routing daemon is required.
1814 Does (1) or does not (0) perform proxy ARP.
1819 Integer value determines if a source validation should be made. 1 means yes, 0
1820 means no. Disabled by default, but local/broadcast address spoofing is always
1823 If you set this to 1 on a router that is the only connection for a network to
1824 the net, it will prevent spoofing attacks against your internal networks
1825 (external addresses can still be spoofed), without the need for additional
1831 Accept ICMP redirect messages only for gateways, listed in default gateway
1832 list. Enabled by default.
1837 If it is not set the kernel does not assume that different subnets on this
1838 device can communicate directly. Default setting is 'yes'.
1843 Determines whether to send ICMP redirects to other hosts.
1848 The directory /proc/sys/net/ipv4/route contains several file to control
1851 error_burst and error_cost
1852 --------------------------
1854 These parameters are used to limit how many ICMP destination unreachable to
1855 send from the host in question. ICMP destination unreachable messages are
1856 sent when we cannot reach the next hop while trying to transmit a packet.
1857 It will also print some error messages to kernel logs if someone is ignoring
1858 our ICMP redirects. The higher the error_cost factor is, the fewer
1859 destination unreachable and error messages will be let through. Error_burst
1860 controls when destination unreachable messages and error messages will be
1861 dropped. The default settings limit warning messages to five every second.
1866 Writing to this file results in a flush of the routing cache.
1868 gc_elasticity, gc_interval, gc_min_interval_ms, gc_timeout, gc_thresh
1869 ---------------------------------------------------------------------
1871 Values to control the frequency and behavior of the garbage collection
1872 algorithm for the routing cache. gc_min_interval is deprecated and replaced
1873 by gc_min_interval_ms.
1879 Maximum size of the routing cache. Old entries will be purged once the cache
1880 reached has this size.
1882 max_delay, min_delay
1883 --------------------
1885 Delays for flushing the routing cache.
1887 redirect_load, redirect_number
1888 ------------------------------
1890 Factors which determine if more ICPM redirects should be sent to a specific
1891 host. No redirects will be sent once the load limit or the maximum number of
1892 redirects has been reached.
1897 Timeout for redirects. After this period redirects will be sent again, even if
1898 this has been stopped, because the load or number limit has been reached.
1900 Network Neighbor handling
1901 -------------------------
1903 Settings about how to handle connections with direct neighbors (nodes attached
1904 to the same link) can be found in the directory /proc/sys/net/ipv4/neigh.
1906 As we saw it in the conf directory, there is a default subdirectory which
1907 holds the default values, and one directory for each interface. The contents
1908 of the directories are identical, with the single exception that the default
1909 settings contain additional options to set garbage collection parameters.
1911 In the interface directories you'll find the following entries:
1913 base_reachable_time, base_reachable_time_ms
1914 -------------------------------------------
1916 A base value used for computing the random reachable time value as specified
1919 Expression of base_reachable_time, which is deprecated, is in seconds.
1920 Expression of base_reachable_time_ms is in milliseconds.
1922 retrans_time, retrans_time_ms
1923 -----------------------------
1925 The time between retransmitted Neighbor Solicitation messages.
1926 Used for address resolution and to determine if a neighbor is
1929 Expression of retrans_time, which is deprecated, is in 1/100 seconds (for
1930 IPv4) or in jiffies (for IPv6).
1931 Expression of retrans_time_ms is in milliseconds.
1936 Maximum queue length for a pending arp request - the number of packets which
1937 are accepted from other layers while the ARP address is still resolved.
1942 Maximum for random delay of answers to neighbor solicitation messages in
1943 jiffies (1/100 sec). Not yet implemented (Linux does not have anycast support
1949 Maximum number of retries for unicast solicitation.
1954 Maximum number of retries for multicast solicitation.
1956 delay_first_probe_time
1957 ----------------------
1959 Delay for the first time probe if the neighbor is reachable. (see
1965 An ARP/neighbor entry is only replaced with a new one if the old is at least
1966 locktime old. This prevents ARP cache thrashing.
1971 Maximum time (real time is random [0..proxytime]) before answering to an ARP
1972 request for which we have an proxy ARP entry. In some cases, this is used to
1973 prevent network flooding.
1978 Maximum queue length of the delayed proxy arp timer. (see proxy_delay).
1983 Determines the number of requests to send to the user level ARP daemon. Use 0
1989 Determines how often to check for stale ARP entries. After an ARP entry is
1990 stale it will be resolved again (which is useful when an IP address migrates
1991 to another machine). When ucast_solicit is greater than 0 it first tries to
1992 send an ARP packet directly to the known host When that fails and
1993 mcast_solicit is greater than 0, an ARP request is broadcasted.
1998 The /proc/sys/net/appletalk directory holds the Appletalk configuration data
1999 when Appletalk is loaded. The configurable parameters are:
2004 The amount of time we keep an ARP entry before expiring it. Used to age out
2010 The amount of time we will spend trying to resolve an Appletalk address.
2012 aarp-retransmit-limit
2013 ---------------------
2015 The number of times we will retransmit a query before giving up.
2020 Controls the rate at which expires are checked.
2022 The directory /proc/net/appletalk holds the list of active Appletalk sockets
2025 The fields indicate the DDP type, the local address (in network:node format)
2026 the remote address, the size of the transmit pending queue, the size of the
2027 received queue (bytes waiting for applications to read) the state and the uid
2030 /proc/net/atalk_iface lists all the interfaces configured for appletalk.It
2031 shows the name of the interface, its Appletalk address, the network range on
2032 that address (or network number for phase 1 networks), and the status of the
2035 /proc/net/atalk_route lists each known network route. It lists the target
2036 (network) that the route leads to, the router (may be directly connected), the
2037 route flags, and the device the route is using.
2042 The IPX protocol has no tunable values in proc/sys/net.
2044 The IPX protocol does, however, provide proc/net/ipx. This lists each IPX
2045 socket giving the local and remote addresses in Novell format (that is
2046 network:node:port). In accordance with the strange Novell tradition,
2047 everything but the port is in hex. Not_Connected is displayed for sockets that
2048 are not tied to a specific remote address. The Tx and Rx queue sizes indicate
2049 the number of bytes pending for transmission and reception. The state
2050 indicates the state the socket is in and the uid is the owning uid of the
2053 The /proc/net/ipx_interface file lists all IPX interfaces. For each interface
2054 it gives the network number, the node number, and indicates if the network is
2055 the primary network. It also indicates which device it is bound to (or
2056 Internal for internal networks) and the Frame Type if appropriate. Linux
2057 supports 802.3, 802.2, 802.2 SNAP and DIX (Blue Book) ethernet framing for
2060 The /proc/net/ipx_route table holds a list of IPX routes. For each route it
2061 gives the destination network, the router node (or Directly) and the network
2062 address of the router (or Connected) for internal networks.
2064 2.11 /proc/sys/fs/mqueue - POSIX message queues filesystem
2065 ----------------------------------------------------------
2067 The "mqueue" filesystem provides the necessary kernel features to enable the
2068 creation of a user space library that implements the POSIX message queues
2069 API (as noted by the MSG tag in the POSIX 1003.1-2001 version of the System
2070 Interfaces specification.)
2072 The "mqueue" filesystem contains values for determining/setting the amount of
2073 resources used by the file system.
2075 /proc/sys/fs/mqueue/queues_max is a read/write file for setting/getting the
2076 maximum number of message queues allowed on the system.
2078 /proc/sys/fs/mqueue/msg_max is a read/write file for setting/getting the
2079 maximum number of messages in a queue value. In fact it is the limiting value
2080 for another (user) limit which is set in mq_open invocation. This attribute of
2081 a queue must be less or equal then msg_max.
2083 /proc/sys/fs/mqueue/msgsize_max is a read/write file for setting/getting the
2084 maximum message size value (it is every message queue's attribute set during
2087 2.12 /proc/<pid>/oom_adj - Adjust the oom-killer score
2088 ------------------------------------------------------
2090 This file can be used to adjust the score used to select which processes
2091 should be killed in an out-of-memory situation. Giving it a high score will
2092 increase the likelihood of this process being killed by the oom-killer. Valid
2093 values are in the range -16 to +15, plus the special value -17, which disables
2094 oom-killing altogether for this process.
2096 2.13 /proc/<pid>/oom_score - Display current oom-killer score
2097 -------------------------------------------------------------
2099 ------------------------------------------------------------------------------
2100 This file can be used to check the current score used by the oom-killer is for
2101 any given <pid>. Use it together with /proc/<pid>/oom_adj to tune which
2102 process should be killed in an out-of-memory situation.
2104 ------------------------------------------------------------------------------
2106 ------------------------------------------------------------------------------
2107 Certain aspects of kernel behavior can be modified at runtime, without the
2108 need to recompile the kernel, or even to reboot the system. The files in the
2109 /proc/sys tree can not only be read, but also modified. You can use the echo
2110 command to write value into these files, thereby changing the default settings
2112 ------------------------------------------------------------------------------
2114 2.14 /proc/<pid>/io - Display the IO accounting fields
2115 -------------------------------------------------------
2117 This file contains IO statistics for each running process
2122 test:/tmp # dd if=/dev/zero of=/tmp/test.dat &
2125 test:/tmp # cat /proc/3828/io
2131 write_bytes: 323932160
2132 cancelled_write_bytes: 0
2141 I/O counter: chars read
2142 The number of bytes which this task has caused to be read from storage. This
2143 is simply the sum of bytes which this process passed to read() and pread().
2144 It includes things like tty IO and it is unaffected by whether or not actual
2145 physical disk IO was required (the read might have been satisfied from
2152 I/O counter: chars written
2153 The number of bytes which this task has caused, or shall cause to be written
2154 to disk. Similar caveats apply here as with rchar.
2160 I/O counter: read syscalls
2161 Attempt to count the number of read I/O operations, i.e. syscalls like read()
2168 I/O counter: write syscalls
2169 Attempt to count the number of write I/O operations, i.e. syscalls like
2170 write() and pwrite().
2176 I/O counter: bytes read
2177 Attempt to count the number of bytes which this process really did cause to
2178 be fetched from the storage layer. Done at the submit_bio() level, so it is
2179 accurate for block-backed filesystems. <please add status regarding NFS and
2180 CIFS at a later time>
2186 I/O counter: bytes written
2187 Attempt to count the number of bytes which this process caused to be sent to
2188 the storage layer. This is done at page-dirtying time.
2191 cancelled_write_bytes
2192 ---------------------
2194 The big inaccuracy here is truncate. If a process writes 1MB to a file and
2195 then deletes the file, it will in fact perform no writeout. But it will have
2196 been accounted as having caused 1MB of write.
2197 In other words: The number of bytes which this process caused to not happen,
2198 by truncating pagecache. A task can cause "negative" IO too. If this task
2199 truncates some dirty pagecache, some IO which another task has been accounted
2200 for (in it's write_bytes) will not be happening. We _could_ just subtract that
2201 from the truncating task's write_bytes, but there is information loss in doing
2208 At its current implementation state, this is a bit racy on 32-bit machines: if
2209 process A reads process B's /proc/pid/io while process B is updating one of
2210 those 64-bit counters, process A could see an intermediate result.
2213 More information about this can be found within the taskstats documentation in
2214 Documentation/accounting.
2216 2.15 /proc/<pid>/coredump_filter - Core dump filtering settings
2217 ---------------------------------------------------------------
2218 When a process is dumped, all anonymous memory is written to a core file as
2219 long as the size of the core file isn't limited. But sometimes we don't want
2220 to dump some memory segments, for example, huge shared memory. Conversely,
2221 sometimes we want to save file-backed memory segments into a core file, not
2222 only the individual files.
2224 /proc/<pid>/coredump_filter allows you to customize which memory segments
2225 will be dumped when the <pid> process is dumped. coredump_filter is a bitmask
2226 of memory types. If a bit of the bitmask is set, memory segments of the
2227 corresponding memory type are dumped, otherwise they are not dumped.
2229 The following 4 memory types are supported:
2230 - (bit 0) anonymous private memory
2231 - (bit 1) anonymous shared memory
2232 - (bit 2) file-backed private memory
2233 - (bit 3) file-backed shared memory
2235 Note that MMIO pages such as frame buffer are never dumped and vDSO pages
2236 are always dumped regardless of the bitmask status.
2238 Default value of coredump_filter is 0x3; this means all anonymous memory
2239 segments are dumped.
2241 If you don't want to dump all shared memory segments attached to pid 1234,
2242 write 1 to the process's proc file.
2244 $ echo 0x1 > /proc/1234/coredump_filter
2246 When a new process is created, the process inherits the bitmask status from its
2247 parent. It is useful to set up coredump_filter before the program runs.
2250 $ echo 0x7 > /proc/self/coredump_filter
2253 ------------------------------------------------------------------------------
git.openpandora.org / pandora-kernel.git / blob