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diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt new file mode 100644 index 000000000000..cbe85c17176b --- /dev/null +++ b/Documentation/filesystems/proc.txt @@ -0,0 +1,1940 @@ +------------------------------------------------------------------------------ + T H E /proc F I L E S Y S T E M +------------------------------------------------------------------------------ +/proc/sys Terrehon Bowden <terrehon@pacbell.net> October 7 1999 + Bodo Bauer <bb@ricochet.net> + +2.4.x update Jorge Nerin <comandante@zaralinux.com> November 14 2000 +------------------------------------------------------------------------------ +Version 1.3 Kernel version 2.2.12 + Kernel version 2.4.0-test11-pre4 +------------------------------------------------------------------------------ + +Table of Contents +----------------- + + 0 Preface + 0.1 Introduction/Credits + 0.2 Legal Stuff + + 1 Collecting System Information + 1.1 Process-Specific Subdirectories + 1.2 Kernel data + 1.3 IDE devices in /proc/ide + 1.4 Networking info in /proc/net + 1.5 SCSI info + 1.6 Parallel port info in /proc/parport + 1.7 TTY info in /proc/tty + 1.8 Miscellaneous kernel statistics in /proc/stat + + 2 Modifying System Parameters + 2.1 /proc/sys/fs - File system data + 2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats + 2.3 /proc/sys/kernel - general kernel parameters + 2.4 /proc/sys/vm - The virtual memory subsystem + 2.5 /proc/sys/dev - Device specific parameters + 2.6 /proc/sys/sunrpc - Remote procedure calls + 2.7 /proc/sys/net - Networking stuff + 2.8 /proc/sys/net/ipv4 - IPV4 settings + 2.9 Appletalk + 2.10 IPX + 2.11 /proc/sys/fs/mqueue - POSIX message queues filesystem + +------------------------------------------------------------------------------ +Preface +------------------------------------------------------------------------------ + +0.1 Introduction/Credits +------------------------ + +This documentation is part of a soon (or so we hope) to be released book on +the SuSE Linux distribution. As there is no complete documentation for the +/proc file system and we've used many freely available sources to write these +chapters, it seems only fair to give the work back to the Linux community. +This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm +afraid it's still far from complete, but we hope it will be useful. As far as +we know, it is the first 'all-in-one' document about the /proc file system. It +is focused on the Intel x86 hardware, so if you are looking for PPC, ARM, +SPARC, AXP, etc., features, you probably won't find what you are looking for. +It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But +additions and patches are welcome and will be added to this document if you +mail them to Bodo. + +We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of +other people for help compiling this documentation. We'd also like to extend a +special thank you to Andi Kleen for documentation, which we relied on heavily +to create this document, as well as the additional information he provided. +Thanks to everybody else who contributed source or docs to the Linux kernel +and helped create a great piece of software... :) + +If you have any comments, corrections or additions, please don't hesitate to +contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this +document. + +The latest version of this document is available online at +http://skaro.nightcrawler.com/~bb/Docs/Proc as HTML version. + +If the above direction does not works for you, ypu could try the kernel +mailing list at linux-kernel@vger.kernel.org and/or try to reach me at +comandante@zaralinux.com. + +0.2 Legal Stuff +--------------- + +We don't guarantee the correctness of this document, and if you come to us +complaining about how you screwed up your system because of incorrect +documentation, we won't feel responsible... + +------------------------------------------------------------------------------ +CHAPTER 1: COLLECTING SYSTEM INFORMATION +------------------------------------------------------------------------------ + +------------------------------------------------------------------------------ +In This Chapter +------------------------------------------------------------------------------ +* Investigating the properties of the pseudo file system /proc and its + ability to provide information on the running Linux system +* Examining /proc's structure +* Uncovering various information about the kernel and the processes running + on the system +------------------------------------------------------------------------------ + + +The proc file system acts as an interface to internal data structures in the +kernel. It can be used to obtain information about the system and to change +certain kernel parameters at runtime (sysctl). + +First, we'll take a look at the read-only parts of /proc. In Chapter 2, we +show you how you can use /proc/sys to change settings. + +1.1 Process-Specific Subdirectories +----------------------------------- + +The directory /proc contains (among other things) one subdirectory for each +process running on the system, which is named after the process ID (PID). + +The link self points to the process reading the file system. Each process +subdirectory has the entries listed in Table 1-1. + + +Table 1-1: Process specific entries in /proc +.............................................................................. + File Content + cmdline Command line arguments + cpu Current and last cpu in wich it was executed (2.4)(smp) + cwd Link to the current working directory + environ Values of environment variables + exe Link to the executable of this process + fd Directory, which contains all file descriptors + maps Memory maps to executables and library files (2.4) + mem Memory held by this process + root Link to the root directory of this process + stat Process status + statm Process memory status information + status Process status in human readable form + wchan If CONFIG_KALLSYMS is set, a pre-decoded wchan +.............................................................................. + +For example, to get the status information of a process, all you have to do is +read the file /proc/PID/status: + + >cat /proc/self/status + Name: cat + State: R (running) + Pid: 5452 + PPid: 743 + TracerPid: 0 (2.4) + Uid: 501 501 501 501 + Gid: 100 100 100 100 + Groups: 100 14 16 + VmSize: 1112 kB + VmLck: 0 kB + VmRSS: 348 kB + VmData: 24 kB + VmStk: 12 kB + VmExe: 8 kB + VmLib: 1044 kB + SigPnd: 0000000000000000 + SigBlk: 0000000000000000 + SigIgn: 0000000000000000 + SigCgt: 0000000000000000 + CapInh: 00000000fffffeff + CapPrm: 0000000000000000 + CapEff: 0000000000000000 + + +This shows you nearly the same information you would get if you viewed it with +the ps command. In fact, ps uses the proc file system to obtain its +information. The statm file contains more detailed information about the +process memory usage. Its seven fields are explained in Table 1-2. + + +Table 1-2: Contents of the statm files (as of 2.6.8-rc3) +.............................................................................. + Field Content + size total program size (pages) (same as VmSize in status) + resident size of memory portions (pages) (same as VmRSS in status) + shared number of pages that are shared (i.e. backed by a file) + trs number of pages that are 'code' (not including libs; broken, + includes data segment) + lrs number of pages of library (always 0 on 2.6) + drs number of pages of data/stack (including libs; broken, + includes library text) + dt number of dirty pages (always 0 on 2.6) +.............................................................................. + +1.2 Kernel data +--------------- + +Similar to the process entries, the kernel data files give information about +the running kernel. The files used to obtain this information are contained in +/proc and are listed in Table 1-3. Not all of these will be present in your +system. It depends on the kernel configuration and the loaded modules, which +files are there, and which are missing. + +Table 1-3: Kernel info in /proc +.............................................................................. + File Content + apm Advanced power management info + buddyinfo Kernel memory allocator information (see text) (2.5) + bus Directory containing bus specific information + cmdline Kernel command line + cpuinfo Info about the CPU + devices Available devices (block and character) + dma Used DMS channels + filesystems Supported filesystems + driver Various drivers grouped here, currently rtc (2.4) + execdomains Execdomains, related to security (2.4) + fb Frame Buffer devices (2.4) + fs File system parameters, currently nfs/exports (2.4) + ide Directory containing info about the IDE subsystem + interrupts Interrupt usage + iomem Memory map (2.4) + ioports I/O port usage + irq Masks for irq to cpu affinity (2.4)(smp?) + isapnp ISA PnP (Plug&Play) Info (2.4) + kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4)) + kmsg Kernel messages + ksyms Kernel symbol table + loadavg Load average of last 1, 5 & 15 minutes + locks Kernel locks + meminfo Memory info + misc Miscellaneous + modules List of loaded modules + mounts Mounted filesystems + net Networking info (see text) + partitions Table of partitions known to the system + pci Depreciated info of PCI bus (new way -> /proc/bus/pci/, + decoupled by lspci (2.4) + rtc Real time clock + scsi SCSI info (see text) + slabinfo Slab pool info + stat Overall statistics + swaps Swap space utilization + sys See chapter 2 + sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4) + tty Info of tty drivers + uptime System uptime + version Kernel version + video bttv info of video resources (2.4) +.............................................................................. + +You can, for example, check which interrupts are currently in use and what +they are used for by looking in the file /proc/interrupts: + + > cat /proc/interrupts + CPU0 + 0: 8728810 XT-PIC timer + 1: 895 XT-PIC keyboard + 2: 0 XT-PIC cascade + 3: 531695 XT-PIC aha152x + 4: 2014133 XT-PIC serial + 5: 44401 XT-PIC pcnet_cs + 8: 2 XT-PIC rtc + 11: 8 XT-PIC i82365 + 12: 182918 XT-PIC PS/2 Mouse + 13: 1 XT-PIC fpu + 14: 1232265 XT-PIC ide0 + 15: 7 XT-PIC ide1 + NMI: 0 + +In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the +output of a SMP machine): + + > cat /proc/interrupts + + CPU0 CPU1 + 0: 1243498 1214548 IO-APIC-edge timer + 1: 8949 8958 IO-APIC-edge keyboard + 2: 0 0 XT-PIC cascade + 5: 11286 10161 IO-APIC-edge soundblaster + 8: 1 0 IO-APIC-edge rtc + 9: 27422 27407 IO-APIC-edge 3c503 + 12: 113645 113873 IO-APIC-edge PS/2 Mouse + 13: 0 0 XT-PIC fpu + 14: 22491 24012 IO-APIC-edge ide0 + 15: 2183 2415 IO-APIC-edge ide1 + 17: 30564 30414 IO-APIC-level eth0 + 18: 177 164 IO-APIC-level bttv + NMI: 2457961 2457959 + LOC: 2457882 2457881 + ERR: 2155 + +NMI is incremented in this case because every timer interrupt generates a NMI +(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups. + +LOC is the local interrupt counter of the internal APIC of every CPU. + +ERR is incremented in the case of errors in the IO-APIC bus (the bus that +connects the CPUs in a SMP system. This means that an error has been detected, +the IO-APIC automatically retry the transmission, so it should not be a big +problem, but you should read the SMP-FAQ. + +In this context it could be interesting to note the new irq directory in 2.4. +It could be used to set IRQ to CPU affinity, this means that you can "hook" an +IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the +irq subdir is one subdir for each IRQ, and one file; prof_cpu_mask + +For example + > ls /proc/irq/ + 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask + 1 11 13 15 17 19 3 5 7 9 + > ls /proc/irq/0/ + smp_affinity + +The contents of the prof_cpu_mask file and each smp_affinity file for each IRQ +is the same by default: + + > cat /proc/irq/0/smp_affinity + ffffffff + +It's a bitmask, in wich you can specify wich CPUs can handle the IRQ, you can +set it by doing: + + > echo 1 > /proc/irq/prof_cpu_mask + +This means that only the first CPU will handle the IRQ, but you can also echo 5 +wich means that only the first and fourth CPU can handle the IRQ. + +The way IRQs are routed is handled by the IO-APIC, and it's Round Robin +between all the CPUs which are allowed to handle it. As usual the kernel has +more info than you and does a better job than you, so the defaults are the +best choice for almost everyone. + +There are three more important subdirectories in /proc: net, scsi, and sys. +The general rule is that the contents, or even the existence of these +directories, depend on your kernel configuration. If SCSI is not enabled, the +directory scsi may not exist. The same is true with the net, which is there +only when networking support is present in the running kernel. + +The slabinfo file gives information about memory usage at the slab level. +Linux uses slab pools for memory management above page level in version 2.2. +Commonly used objects have their own slab pool (such as network buffers, +directory cache, and so on). + +.............................................................................. + +> cat /proc/buddyinfo + +Node 0, zone DMA 0 4 5 4 4 3 ... +Node 0, zone Normal 1 0 0 1 101 8 ... +Node 0, zone HighMem 2 0 0 1 1 0 ... + +Memory fragmentation is a problem under some workloads, and buddyinfo is a +useful tool for helping diagnose these problems. Buddyinfo will give you a +clue as to how big an area you can safely allocate, or why a previous +allocation failed. + +Each column represents the number of pages of a certain order which are +available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in +ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE +available in ZONE_NORMAL, etc... + +.............................................................................. + +meminfo: + +Provides information about distribution and utilization of memory. This +varies by architecture and compile options. The following is from a +16GB PIII, which has highmem enabled. You may not have all of these fields. + +> cat /proc/meminfo + + +MemTotal: 16344972 kB +MemFree: 13634064 kB +Buffers: 3656 kB +Cached: 1195708 kB +SwapCached: 0 kB +Active: 891636 kB +Inactive: 1077224 kB +HighTotal: 15597528 kB +HighFree: 13629632 kB +LowTotal: 747444 kB +LowFree: 4432 kB +SwapTotal: 0 kB +SwapFree: 0 kB +Dirty: 968 kB +Writeback: 0 kB +Mapped: 280372 kB +Slab: 684068 kB +CommitLimit: 7669796 kB +Committed_AS: 100056 kB +PageTables: 24448 kB +VmallocTotal: 112216 kB +VmallocUsed: 428 kB +VmallocChunk: 111088 kB + + MemTotal: Total usable ram (i.e. physical ram minus a few reserved + bits and the kernel binary code) + MemFree: The sum of LowFree+HighFree + Buffers: Relatively temporary storage for raw disk blocks + shouldn't get tremendously large (20MB or so) + Cached: in-memory cache for files read from the disk (the + pagecache). Doesn't include SwapCached + SwapCached: Memory that once was swapped out, is swapped back in but + still also is in the swapfile (if memory is needed it + doesn't need to be swapped out AGAIN because it is already + in the swapfile. This saves I/O) + Active: Memory that has been used more recently and usually not + reclaimed unless absolutely necessary. + Inactive: Memory which has been less recently used. It is more + eligible to be reclaimed for other purposes + HighTotal: + HighFree: Highmem is all memory above ~860MB of physical memory + Highmem areas are for use by userspace programs, or + for the pagecache. The kernel must use tricks to access + this memory, making it slower to access than lowmem. + LowTotal: + LowFree: Lowmem is memory which can be used for everything that + highmem can be used for, but it is also availble for the + kernel's use for its own data structures. Among many + other things, it is where everything from the Slab is + allocated. Bad things happen when you're out of lowmem. + SwapTotal: total amount of swap space available + SwapFree: Memory which has been evicted from RAM, and is temporarily + on the disk + Dirty: Memory which is waiting to get written back to the disk + Writeback: Memory which is actively being written back to the disk + Mapped: files which have been mmaped, such as libraries + Slab: in-kernel data structures cache + CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'), + this is the total amount of memory currently available to + be allocated on the system. This limit is only adhered to + if strict overcommit accounting is enabled (mode 2 in + 'vm.overcommit_memory'). + The CommitLimit is calculated with the following formula: + CommitLimit = ('vm.overcommit_ratio' * Physical RAM) + Swap + For example, on a system with 1G of physical RAM and 7G + of swap with a `vm.overcommit_ratio` of 30 it would + yield a CommitLimit of 7.3G. + For more details, see the memory overcommit documentation + in vm/overcommit-accounting. +Committed_AS: The amount of memory presently allocated on the system. + The committed memory is a sum of all of the memory which + has been allocated by processes, even if it has not been + "used" by them as of yet. A process which malloc()'s 1G + of memory, but only touches 300M of it will only show up + as using 300M of memory even if it has the address space + allocated for the entire 1G. This 1G is memory which has + been "committed" to by the VM and can be used at any time + by the allocating application. With strict overcommit + enabled on the system (mode 2 in 'vm.overcommit_memory'), + allocations which would exceed the CommitLimit (detailed + above) will not be permitted. This is useful if one needs + to guarantee that processes will not fail due to lack of + memory once that memory has been successfully allocated. + PageTables: amount of memory dedicated to the lowest level of page + tables. +VmallocTotal: total size of vmalloc memory area + VmallocUsed: amount of vmalloc area which is used +VmallocChunk: largest contigious block of vmalloc area which is free + + +1.3 IDE devices in /proc/ide +---------------------------- + +The subdirectory /proc/ide contains information about all IDE devices of which +the kernel is aware. There is one subdirectory for each IDE controller, the +file drivers and a link for each IDE device, pointing to the device directory +in the controller specific subtree. + +The file drivers contains general information about the drivers used for the +IDE devices: + + > cat /proc/ide/drivers + ide-cdrom version 4.53 + ide-disk version 1.08 + +More detailed information can be found in the controller specific +subdirectories. These are named ide0, ide1 and so on. Each of these +directories contains the files shown in table 1-4. + + +Table 1-4: IDE controller info in /proc/ide/ide? +.............................................................................. + File Content + channel IDE channel (0 or 1) + config Configuration (only for PCI/IDE bridge) + mate Mate name + model Type/Chipset of IDE controller +.............................................................................. + +Each device connected to a controller has a separate subdirectory in the +controllers directory. The files listed in table 1-5 are contained in these +directories. + + +Table 1-5: IDE device information +.............................................................................. + File Content + cache The cache + capacity Capacity of the medium (in 512Byte blocks) + driver driver and version + geometry physical and logical geometry + identify device identify block + media media type + model device identifier + settings device setup + smart_thresholds IDE disk management thresholds + smart_values IDE disk management values +.............................................................................. + +The most interesting file is settings. This file contains a nice overview of +the drive parameters: + + # cat /proc/ide/ide0/hda/settings + name value min max mode + ---- ----- --- --- ---- + bios_cyl 526 0 65535 rw + bios_head 255 0 255 rw + bios_sect 63 0 63 rw + breada_readahead 4 0 127 rw + bswap 0 0 1 r + file_readahead 72 0 2097151 rw + io_32bit 0 0 3 rw + keepsettings 0 0 1 rw + max_kb_per_request 122 1 127 rw + multcount 0 0 8 rw + nice1 1 0 1 rw + nowerr 0 0 1 rw + pio_mode write-only 0 255 w + slow 0 0 1 rw + unmaskirq 0 0 1 rw + using_dma 0 0 1 rw + + +1.4 Networking info in /proc/net +-------------------------------- + +The subdirectory /proc/net follows the usual pattern. Table 1-6 shows the +additional values you get for IP version 6 if you configure the kernel to +support this. Table 1-7 lists the files and their meaning. + + +Table 1-6: IPv6 info in /proc/net +.............................................................................. + File Content + udp6 UDP sockets (IPv6) + tcp6 TCP sockets (IPv6) + raw6 Raw device statistics (IPv6) + igmp6 IP multicast addresses, which this host joined (IPv6) + if_inet6 List of IPv6 interface addresses + ipv6_route Kernel routing table for IPv6 + rt6_stats Global IPv6 routing tables statistics + sockstat6 Socket statistics (IPv6) + snmp6 Snmp data (IPv6) +.............................................................................. + + +Table 1-7: Network info in /proc/net +.............................................................................. + File Content + arp Kernel ARP table + dev network devices with statistics + dev_mcast the Layer2 multicast groups a device is listening too + (interface index, label, number of references, number of bound + addresses). + dev_stat network device status + ip_fwchains Firewall chain linkage + ip_fwnames Firewall chain names + ip_masq Directory containing the masquerading tables + ip_masquerade Major masquerading table + netstat Network statistics + raw raw device statistics + route Kernel routing table + rpc Directory containing rpc info + rt_cache Routing cache + snmp SNMP data + sockstat Socket statistics + tcp TCP sockets + tr_rif Token ring RIF routing table + udp UDP sockets + unix UNIX domain sockets + wireless Wireless interface data (Wavelan etc) + igmp IP multicast addresses, which this host joined + psched Global packet scheduler parameters. + netlink List of PF_NETLINK sockets + ip_mr_vifs List of multicast virtual interfaces + ip_mr_cache List of multicast routing cache +.............................................................................. + +You can use this information to see which network devices are available in +your system and how much traffic was routed over those devices: + + > cat /proc/net/dev + Inter-|Receive |[... + face |bytes packets errs drop fifo frame compressed multicast|[... + lo: 908188 5596 0 0 0 0 0 0 [... + ppp0:15475140 20721 410 0 0 410 0 0 [... + eth0: 614530 7085 0 0 0 0 0 1 [... + + ...] Transmit + ...] bytes packets errs drop fifo colls carrier compressed + ...] 908188 5596 0 0 0 0 0 0 + ...] 1375103 17405 0 0 0 0 0 0 + ...] 1703981 5535 0 0 0 3 0 0 + +In addition, each Channel Bond interface has it's own directory. For +example, the bond0 device will have a directory called /proc/net/bond0/. +It will contain information that is specific to that bond, such as the +current slaves of the bond, the link status of the slaves, and how +many times the slaves link has failed. + +1.5 SCSI info +------------- + +If you have a SCSI host adapter in your system, you'll find a subdirectory +named after the driver for this adapter in /proc/scsi. You'll also see a list +of all recognized SCSI devices in /proc/scsi: + + >cat /proc/scsi/scsi + Attached devices: + Host: scsi0 Channel: 00 Id: 00 Lun: 00 + Vendor: IBM Model: DGHS09U Rev: 03E0 + Type: Direct-Access ANSI SCSI revision: 03 + Host: scsi0 Channel: 00 Id: 06 Lun: 00 + Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04 + Type: CD-ROM ANSI SCSI revision: 02 + + +The directory named after the driver has one file for each adapter found in +the system. These files contain information about the controller, including +the used IRQ and the IO address range. The amount of information shown is +dependent on the adapter you use. The example shows the output for an Adaptec +AHA-2940 SCSI adapter: + + > cat /proc/scsi/aic7xxx/0 + + Adaptec AIC7xxx driver version: 5.1.19/3.2.4 + Compile Options: + TCQ Enabled By Default : Disabled + AIC7XXX_PROC_STATS : Disabled + AIC7XXX_RESET_DELAY : 5 + Adapter Configuration: + SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter + Ultra Wide Controller + PCI MMAPed I/O Base: 0xeb001000 + Adapter SEEPROM Config: SEEPROM found and used. + Adaptec SCSI BIOS: Enabled + IRQ: 10 + SCBs: Active 0, Max Active 2, + Allocated 15, HW 16, Page 255 + Interrupts: 160328 + BIOS Control Word: 0x18b6 + Adapter Control Word: 0x005b + Extended Translation: Enabled + Disconnect Enable Flags: 0xffff + Ultra Enable Flags: 0x0001 + Tag Queue Enable Flags: 0x0000 + Ordered Queue Tag Flags: 0x0000 + Default Tag Queue Depth: 8 + Tagged Queue By Device array for aic7xxx host instance 0: + {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} + Actual queue depth per device for aic7xxx host instance 0: + {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} + Statistics: + (scsi0:0:0:0) + Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 + Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) + Total transfers 160151 (74577 reads and 85574 writes) + (scsi0:0:6:0) + Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 + Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) + Total transfers 0 (0 reads and 0 writes) + + +1.6 Parallel port info in /proc/parport +--------------------------------------- + +The directory /proc/parport contains information about the parallel ports of +your system. It has one subdirectory for each port, named after the port +number (0,1,2,...). + +These directories contain the four files shown in Table 1-8. + + +Table 1-8: Files in /proc/parport +.............................................................................. + File Content + autoprobe Any IEEE-1284 device ID information that has been acquired. + devices list of the device drivers using that port. A + will appear by the + name of the device currently using the port (it might not appear + against any). + hardware Parallel port's base address, IRQ line and DMA channel. + irq IRQ that parport is using for that port. This is in a separate + file to allow you to alter it by writing a new value in (IRQ + number or none). +.............................................................................. + +1.7 TTY info in /proc/tty +------------------------- + +Information about the available and actually used tty's can be found in the +directory /proc/tty.You'll find entries for drivers and line disciplines in +this directory, as shown in Table 1-9. + + +Table 1-9: Files in /proc/tty +.............................................................................. + File Content + drivers list of drivers and their usage + ldiscs registered line disciplines + driver/serial usage statistic and status of single tty lines +.............................................................................. + +To see which tty's are currently in use, you can simply look into the file +/proc/tty/drivers: + + > cat /proc/tty/drivers + pty_slave /dev/pts 136 0-255 pty:slave + pty_master /dev/ptm 128 0-255 pty:master + pty_slave /dev/ttyp 3 0-255 pty:slave + pty_master /dev/pty 2 0-255 pty:master + serial /dev/cua 5 64-67 serial:callout + serial /dev/ttyS 4 64-67 serial + /dev/tty0 /dev/tty0 4 0 system:vtmaster + /dev/ptmx /dev/ptmx 5 2 system + /dev/console /dev/console 5 1 system:console + /dev/tty /dev/tty 5 0 system:/dev/tty + unknown /dev/tty 4 1-63 console + + +1.8 Miscellaneous kernel statistics in /proc/stat +------------------------------------------------- + +Various pieces of information about kernel activity are available in the +/proc/stat file. All of the numbers reported in this file are aggregates +since the system first booted. For a quick look, simply cat the file: + + > cat /proc/stat + cpu 2255 34 2290 22625563 6290 127 456 + cpu0 1132 34 1441 11311718 3675 127 438 + cpu1 1123 0 849 11313845 2614 0 18 + intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...] + ctxt 1990473 + btime 1062191376 + processes 2915 + procs_running 1 + procs_blocked 0 + +The very first "cpu" line aggregates the numbers in all of the other "cpuN" +lines. These numbers identify the amount of time the CPU has spent performing +different kinds of work. Time units are in USER_HZ (typically hundredths of a +second). The meanings of the columns are as follows, from left to right: + +- user: normal processes executing in user mode +- nice: niced processes executing in user mode +- system: processes executing in kernel mode +- idle: twiddling thumbs +- iowait: waiting for I/O to complete +- irq: servicing interrupts +- softirq: servicing softirqs + +The "intr" line gives counts of interrupts serviced since boot time, for each +of the possible system interrupts. The first column is the total of all +interrupts serviced; each subsequent column is the total for that particular +interrupt. + +The "ctxt" line gives the total number of context switches across all CPUs. + +The "btime" line gives the time at which the system booted, in seconds since +the Unix epoch. + +The "processes" line gives the number of processes and threads created, which +includes (but is not limited to) those created by calls to the fork() and +clone() system calls. + +The "procs_running" line gives the number of processes currently running on +CPUs. + +The "procs_blocked" line gives the number of processes currently blocked, +waiting for I/O to complete. + + +------------------------------------------------------------------------------ +Summary +------------------------------------------------------------------------------ +The /proc file system serves information about the running system. It not only +allows access to process data but also allows you to request the kernel status +by reading files in the hierarchy. + +The directory structure of /proc reflects the types of information and makes +it easy, if not obvious, where to look for specific data. +------------------------------------------------------------------------------ + +------------------------------------------------------------------------------ +CHAPTER 2: MODIFYING SYSTEM PARAMETERS +------------------------------------------------------------------------------ + +------------------------------------------------------------------------------ +In This Chapter +------------------------------------------------------------------------------ +* Modifying kernel parameters by writing into files found in /proc/sys +* Exploring the files which modify certain parameters +* Review of the /proc/sys file tree +------------------------------------------------------------------------------ + + +A very interesting part of /proc is the directory /proc/sys. This is not only +a source of information, it also allows you to change parameters within the +kernel. Be very careful when attempting this. You can optimize your system, +but you can also cause it to crash. Never alter kernel parameters on a +production system. Set up a development machine and test to make sure that +everything works the way you want it to. You may have no alternative but to +reboot the machine once an error has been made. + +To change a value, simply echo the new value into the file. An example is +given below in the section on the file system data. You need to be root to do +this. You can create your own boot script to perform this every time your +system boots. + +The files in /proc/sys can be used to fine tune and monitor miscellaneous and +general things in the operation of the Linux kernel. Since some of the files +can inadvertently disrupt your system, it is advisable to read both +documentation and source before actually making adjustments. In any case, be +very careful when writing to any of these files. The entries in /proc may +change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt +review the kernel documentation in the directory /usr/src/linux/Documentation. +This chapter is heavily based on the documentation included in the pre 2.2 +kernels, and became part of it in version 2.2.1 of the Linux kernel. + +2.1 /proc/sys/fs - File system data +----------------------------------- + +This subdirectory contains specific file system, file handle, inode, dentry +and quota information. + +Currently, these files are in /proc/sys/fs: + +dentry-state +------------ + +Status of the directory cache. Since directory entries are dynamically +allocated and deallocated, this file indicates the current status. It holds +six values, in which the last two are not used and are always zero. The others +are listed in table 2-1. + + +Table 2-1: Status files of the directory cache +.............................................................................. + File Content + nr_dentry Almost always zero + nr_unused Number of unused cache entries + age_limit + in seconds after the entry may be reclaimed, when memory is short + want_pages internally +.............................................................................. + +dquot-nr and dquot-max +---------------------- + +The file dquot-max shows the maximum number of cached disk quota entries. + +The file dquot-nr shows the number of allocated disk quota entries and the +number of free disk quota entries. + +If the number of available cached disk quotas is very low and you have a large +number of simultaneous system users, you might want to raise the limit. + +file-nr and file-max +-------------------- + +The kernel allocates file handles dynamically, but doesn't free them again at +this time. + +The value in file-max denotes the maximum number of file handles that the +Linux kernel will allocate. When you get a lot of error messages about running +out of file handles, you might want to raise this limit. The default value is +10% of RAM in kilobytes. To change it, just write the new number into the +file: + + # cat /proc/sys/fs/file-max + 4096 + # echo 8192 > /proc/sys/fs/file-max + # cat /proc/sys/fs/file-max + 8192 + + +This method of revision is useful for all customizable parameters of the +kernel - simply echo the new value to the corresponding file. + +Historically, the three values in file-nr denoted the number of allocated file +handles, the number of allocated but unused file handles, and the maximum +number of file handles. Linux 2.6 always reports 0 as the number of free file +handles -- this is not an error, it just means that the number of allocated +file handles exactly matches the number of used file handles. + +Attempts to allocate more file descriptors than file-max are reported with +printk, look for "VFS: file-max limit <number> reached". + +inode-state and inode-nr +------------------------ + +The file inode-nr contains the first two items from inode-state, so we'll skip +to that file... + +inode-state contains two actual numbers and five dummy values. The numbers +are nr_inodes and nr_free_inodes (in order of appearance). + +nr_inodes +~~~~~~~~~ + +Denotes the number of inodes the system has allocated. This number will +grow and shrink dynamically. + +nr_free_inodes +-------------- + +Represents the number of free inodes. Ie. The number of inuse inodes is +(nr_inodes - nr_free_inodes). + +super-nr and super-max +---------------------- + +Again, super block structures are allocated by the kernel, but not freed. The +file super-max contains the maximum number of super block handlers, where +super-nr shows the number of currently allocated ones. + +Every mounted file system needs a super block, so if you plan to mount lots of +file systems, you may want to increase these numbers. + +aio-nr and aio-max-nr +--------------------- + +aio-nr is the running total of the number of events specified on the +io_setup system call for all currently active aio contexts. If aio-nr +reaches aio-max-nr then io_setup will fail with EAGAIN. Note that +raising aio-max-nr does not result in the pre-allocation or re-sizing +of any kernel data structures. + +2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats +----------------------------------------------------------- + +Besides these files, there is the subdirectory /proc/sys/fs/binfmt_misc. This +handles the kernel support for miscellaneous binary formats. + +Binfmt_misc provides the ability to register additional binary formats to the +Kernel without compiling an additional module/kernel. Therefore, binfmt_misc +needs to know magic numbers at the beginning or the filename extension of the +binary. + +It works by maintaining a linked list of structs that contain a description of +a binary format, including a magic with size (or the filename extension), +offset and mask, and the interpreter name. On request it invokes the given +interpreter with the original program as argument, as binfmt_java and +binfmt_em86 and binfmt_mz do. Since binfmt_misc does not define any default +binary-formats, you have to register an additional binary-format. + +There are two general files in binfmt_misc and one file per registered format. +The two general files are register and status. + +Registering a new binary format +------------------------------- + +To register a new binary format you have to issue the command + + echo :name:type:offset:magic:mask:interpreter: > /proc/sys/fs/binfmt_misc/register + + + +with appropriate name (the name for the /proc-dir entry), offset (defaults to +0, if omitted), magic, mask (which can be omitted, defaults to all 0xff) and +last but not least, the interpreter that is to be invoked (for example and +testing /bin/echo). Type can be M for usual magic matching or E for filename +extension matching (give extension in place of magic). + +Check or reset the status of the binary format handler +------------------------------------------------------ + +If you do a cat on the file /proc/sys/fs/binfmt_misc/status, you will get the +current status (enabled/disabled) of binfmt_misc. Change the status by echoing +0 (disables) or 1 (enables) or -1 (caution: this clears all previously +registered binary formats) to status. For example echo 0 > status to disable +binfmt_misc (temporarily). + +Status of a single handler +-------------------------- + +Each registered handler has an entry in /proc/sys/fs/binfmt_misc. These files +perform the same function as status, but their scope is limited to the actual +binary format. By cating this file, you also receive all related information +about the interpreter/magic of the binfmt. + +Example usage of binfmt_misc (emulate binfmt_java) +-------------------------------------------------- + + cd /proc/sys/fs/binfmt_misc + echo ':Java:M::\xca\xfe\xba\xbe::/usr/local/java/bin/javawrapper:' > register + echo ':HTML:E::html::/usr/local/java/bin/appletviewer:' > register + echo ':Applet:M::<!--applet::/usr/local/java/bin/appletviewer:' > register + echo ':DEXE:M::\x0eDEX::/usr/bin/dosexec:' > register + + +These four lines add support for Java executables and Java applets (like +binfmt_java, additionally recognizing the .html extension with no need to put +<!--applet> to every applet file). You have to install the JDK and the +shell-script /usr/local/java/bin/javawrapper too. It works around the +brokenness of the Java filename handling. To add a Java binary, just create a +link to the class-file somewhere in the path. + +2.3 /proc/sys/kernel - general kernel parameters +------------------------------------------------ + +This directory reflects general kernel behaviors. As I've said before, the +contents depend on your configuration. Here you'll find the most important +files, along with descriptions of what they mean and how to use them. + +acct +---- + +The file contains three values; highwater, lowwater, and frequency. + +It exists only when BSD-style process accounting is enabled. These values +control its behavior. If the free space on the file system where the log lives +goes below lowwater percentage, accounting suspends. If it goes above +highwater percentage, accounting resumes. Frequency determines how often you +check the amount of free space (value is in seconds). Default settings are: 4, +2, and 30. That is, suspend accounting if there is less than 2 percent free; +resume it if we have a value of 3 or more percent; consider information about +the amount of free space valid for 30 seconds + +ctrl-alt-del +------------ + +When the value in this file is 0, ctrl-alt-del is trapped and sent to the init +program to handle a graceful restart. However, when the value is greater that +zero, Linux's reaction to this key combination will be an immediate reboot, +without syncing its dirty buffers. + +[NOTE] + When a program (like dosemu) has the keyboard in raw mode, the + ctrl-alt-del is intercepted by the program before it ever reaches the + kernel tty layer, and it is up to the program to decide what to do with + it. + +domainname and hostname +----------------------- + +These files can be controlled to set the NIS domainname and hostname of your +box. For the classic darkstar.frop.org a simple: + + # echo "darkstar" > /proc/sys/kernel/hostname + # echo "frop.org" > /proc/sys/kernel/domainname + + +would suffice to set your hostname and NIS domainname. + +osrelease, ostype and version +----------------------------- + +The names make it pretty obvious what these fields contain: + + > cat /proc/sys/kernel/osrelease + 2.2.12 + + > cat /proc/sys/kernel/ostype + Linux + + > cat /proc/sys/kernel/version + #4 Fri Oct 1 12:41:14 PDT 1999 + + +The files osrelease and ostype should be clear enough. Version needs a little +more clarification. The #4 means that this is the 4th kernel built from this +source base and the date after it indicates the time the kernel was built. The +only way to tune these values is to rebuild the kernel. + +panic +----- + +The value in this file represents the number of seconds the kernel waits +before rebooting on a panic. When you use the software watchdog, the +recommended setting is 60. If set to 0, the auto reboot after a kernel panic +is disabled, which is the default setting. + +printk +------ + +The four values in printk denote +* console_loglevel, +* default_message_loglevel, +* minimum_console_loglevel and +* default_console_loglevel +respectively. + +These values influence printk() behavior when printing or logging error +messages, which come from inside the kernel. See syslog(2) for more +information on the different log levels. + +console_loglevel +---------------- + +Messages with a higher priority than this will be printed to the console. + +default_message_level +--------------------- + +Messages without an explicit priority will be printed with this priority. + +minimum_console_loglevel +------------------------ + +Minimum (highest) value to which the console_loglevel can be set. + +default_console_loglevel +------------------------ + +Default value for console_loglevel. + +sg-big-buff +----------- + +This file shows the size of the generic SCSI (sg) buffer. At this point, you +can't tune it yet, but you can change it at compile time by editing +include/scsi/sg.h and changing the value of SG_BIG_BUFF. + +If you use a scanner with SANE (Scanner Access Now Easy) you might want to set +this to a higher value. Refer to the SANE documentation on this issue. + +modprobe +-------- + +The location where the modprobe binary is located. The kernel uses this +program to load modules on demand. + +unknown_nmi_panic +----------------- + +The value in this file affects behavior of handling NMI. When the value is +non-zero, unknown NMI is trapped and then panic occurs. At that time, kernel +debugging information is displayed on console. + +NMI switch that most IA32 servers have fires unknown NMI up, for example. +If a system hangs up, try pressing the NMI switch. + +[NOTE] + This function and oprofile share a NMI callback. Therefore this function + cannot be enabled when oprofile is activated. + And NMI watchdog will be disabled when the value in this file is set to + non-zero. + + +2.4 /proc/sys/vm - The virtual memory subsystem +----------------------------------------------- + +The files in this directory can be used to tune the operation of the virtual +memory (VM) subsystem of the Linux kernel. + +vfs_cache_pressure +------------------ + +Controls the tendency of the kernel to reclaim the memory which is used for +caching of directory and inode objects. + +At the default value of vfs_cache_pressure=100 the kernel will attempt to +reclaim dentries and inodes at a "fair" rate with respect to pagecache and +swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer +to retain dentry and inode caches. Increasing vfs_cache_pressure beyond 100 +causes the kernel to prefer to reclaim dentries and inodes. + +dirty_background_ratio +---------------------- + +Contains, as a percentage of total system memory, the number of pages at which +the pdflush background writeback daemon will start writing out dirty data. + +dirty_ratio +----------------- + +Contains, as a percentage of total system memory, the number of pages at which +a process which is generating disk writes will itself start writing out dirty +data. + +dirty_writeback_centisecs +------------------------- + +The pdflush writeback daemons will periodically wake up and write `old' data +out to disk. This tunable expresses the interval between those wakeups, in +100'ths of a second. + +Setting this to zero disables periodic writeback altogether. + +dirty_expire_centisecs +---------------------- + +This tunable is used to define when dirty data is old enough to be eligible +for writeout by the pdflush daemons. It is expressed in 100'ths of a second. +Data which has been dirty in-memory for longer than this interval will be +written out next time a pdflush daemon wakes up. + +legacy_va_layout +---------------- + +If non-zero, this sysctl disables the new 32-bit mmap mmap layout - the kernel +will use the legacy (2.4) layout for all processes. + +lower_zone_protection +--------------------- + +For some specialised workloads on highmem machines it is dangerous for +the kernel to allow process memory to be allocated from the "lowmem" +zone. This is because that memory could then be pinned via the mlock() +system call, or by unavailability of swapspace. + +And on large highmem machines this lack of reclaimable lowmem memory +can be fatal. + +So the Linux page allocator has a mechanism which prevents allocations +which _could_ use highmem from using too much lowmem. This means that +a certain amount of lowmem is defended from the possibility of being +captured into pinned user memory. + +(The same argument applies to the old 16 megabyte ISA DMA region. This +mechanism will also defend that region from allocations which could use +highmem or lowmem). + +The `lower_zone_protection' tunable determines how aggressive the kernel is +in defending these lower zones. The default value is zero - no +protection at all. + +If you have a machine which uses highmem or ISA DMA and your +applications are using mlock(), or if you are running with no swap then +you probably should increase the lower_zone_protection setting. + +The units of this tunable are fairly vague. It is approximately equal +to "megabytes". So setting lower_zone_protection=100 will protect around 100 +megabytes of the lowmem zone from user allocations. It will also make +those 100 megabytes unavaliable for use by applications and by +pagecache, so there is a cost. + +The effects of this tunable may be observed by monitoring +/proc/meminfo:LowFree. Write a single huge file and observe the point +at which LowFree ceases to fall. + +A reasonable value for lower_zone_protection is 100. + +page-cluster +------------ + +page-cluster controls the number of pages which are written to swap in +a single attempt. The swap I/O size. + +It is a logarithmic value - setting it to zero means "1 page", setting +it to 1 means "2 pages", setting it to 2 means "4 pages", etc. + +The default value is three (eight pages at a time). There may be some +small benefits in tuning this to a different value if your workload is +swap-intensive. + +overcommit_memory +----------------- + +This file contains one value. The following algorithm is used to decide if +there's enough memory: if the value of overcommit_memory is positive, then +there's always enough memory. This is a useful feature, since programs often +malloc() huge amounts of memory 'just in case', while they only use a small +part of it. Leaving this value at 0 will lead to the failure of such a huge +malloc(), when in fact the system has enough memory for the program to run. + +On the other hand, enabling this feature can cause you to run out of memory +and thrash the system to death, so large and/or important servers will want to +set this value to 0. + +nr_hugepages and hugetlb_shm_group +---------------------------------- + +nr_hugepages configures number of hugetlb page reserved for the system. + +hugetlb_shm_group contains group id that is allowed to create SysV shared +memory segment using hugetlb page. + +laptop_mode +----------- + +laptop_mode is a knob that controls "laptop mode". All the things that are +controlled by this knob are discussed in Documentation/laptop-mode.txt. + +block_dump +---------- + +block_dump enables block I/O debugging when set to a nonzero value. More +information on block I/O debugging is in Documentation/laptop-mode.txt. + +swap_token_timeout +------------------ + +This file contains valid hold time of swap out protection token. The Linux +VM has token based thrashing control mechanism and uses the token to prevent +unnecessary page faults in thrashing situation. The unit of the value is +second. The value would be useful to tune thrashing behavior. + +2.5 /proc/sys/dev - Device specific parameters +---------------------------------------------- + +Currently there is only support for CDROM drives, and for those, there is only +one read-only file containing information about the CD-ROM drives attached to +the system: + + >cat /proc/sys/dev/cdrom/info + CD-ROM information, Id: cdrom.c 2.55 1999/04/25 + + drive name: sr0 hdb + drive speed: 32 40 + drive # of slots: 1 0 + Can close tray: 1 1 + Can open tray: 1 1 + Can lock tray: 1 1 + Can change speed: 1 1 + Can select disk: 0 1 + Can read multisession: 1 1 + Can read MCN: 1 1 + Reports media changed: 1 1 + Can play audio: 1 1 + + +You see two drives, sr0 and hdb, along with a list of their features. + +2.6 /proc/sys/sunrpc - Remote procedure calls +--------------------------------------------- + +This directory contains four files, which enable or disable debugging for the +RPC functions NFS, NFS-daemon, RPC and NLM. The default values are 0. They can +be set to one to turn debugging on. (The default value is 0 for each) + +2.7 /proc/sys/net - Networking stuff +------------------------------------ + +The interface to the networking parts of the kernel is located in +/proc/sys/net. Table 2-3 shows all possible subdirectories. You may see only +some of them, depending on your kernel's configuration. + + +Table 2-3: Subdirectories in /proc/sys/net +.............................................................................. + Directory Content Directory Content + core General parameter appletalk Appletalk protocol + unix Unix domain sockets netrom NET/ROM + 802 E802 protocol ax25 AX25 + ethernet Ethernet protocol rose X.25 PLP layer + ipv4 IP version 4 x25 X.25 protocol + ipx IPX token-ring IBM token ring + bridge Bridging decnet DEC net + ipv6 IP version 6 +.............................................................................. + +We will concentrate on IP networking here. Since AX15, X.25, and DEC Net are +only minor players in the Linux world, we'll skip them in this chapter. You'll +find some short info on Appletalk and IPX further on in this chapter. Review +the online documentation and the kernel source to get a detailed view of the +parameters for those protocols. In this section we'll discuss the +subdirectories printed in bold letters in the table above. As default values +are suitable for most needs, there is no need to change these values. + +/proc/sys/net/core - Network core options +----------------------------------------- + +rmem_default +------------ + +The default setting of the socket receive buffer in bytes. + +rmem_max +-------- + +The maximum receive socket buffer size in bytes. + +wmem_default +------------ + +The default setting (in bytes) of the socket send buffer. + +wmem_max +-------- + +The maximum send socket buffer size in bytes. + +message_burst and message_cost +------------------------------ + +These parameters are used to limit the warning messages written to the kernel +log from the networking code. They enforce a rate limit to make a +denial-of-service attack impossible. A higher message_cost factor, results in +fewer messages that will be written. Message_burst controls when messages will +be dropped. The default settings limit warning messages to one every five +seconds. + +netdev_max_backlog +------------------ + +Maximum number of packets, queued on the INPUT side, when the interface +receives packets faster than kernel can process them. + +optmem_max +---------- + +Maximum ancillary buffer size allowed per socket. Ancillary data is a sequence +of struct cmsghdr structures with appended data. + +/proc/sys/net/unix - Parameters for Unix domain sockets +------------------------------------------------------- + +There are only two files in this subdirectory. They control the delays for +deleting and destroying socket descriptors. + +2.8 /proc/sys/net/ipv4 - IPV4 settings +-------------------------------------- + +IP version 4 is still the most used protocol in Unix networking. It will be +replaced by IP version 6 in the next couple of years, but for the moment it's +the de facto standard for the internet and is used in most networking +environments around the world. Because of the importance of this protocol, +we'll have a deeper look into the subtree controlling the behavior of the IPv4 +subsystem of the Linux kernel. + +Let's start with the entries in /proc/sys/net/ipv4. + +ICMP settings +------------- + +icmp_echo_ignore_all and icmp_echo_ignore_broadcasts +---------------------------------------------------- + +Turn on (1) or off (0), if the kernel should ignore all ICMP ECHO requests, or +just those to broadcast and multicast addresses. + +Please note that if you accept ICMP echo requests with a broadcast/multi\-cast +destination address your network may be used as an exploder for denial of +service packet flooding attacks to other hosts. + +icmp_destunreach_rate, icmp_echoreply_rate, icmp_paramprob_rate and icmp_timeexeed_rate +--------------------------------------------------------------------------------------- + +Sets limits for sending ICMP packets to specific targets. A value of zero +disables all limiting. Any positive value sets the maximum package rate in +hundredth of a second (on Intel systems). + +IP settings +----------- + +ip_autoconfig +------------- + +This file contains the number one if the host received its IP configuration by +RARP, BOOTP, DHCP or a similar mechanism. Otherwise it is zero. + +ip_default_ttl +-------------- + +TTL (Time To Live) for IPv4 interfaces. This is simply the maximum number of +hops a packet may travel. + +ip_dynaddr +---------- + +Enable dynamic socket address rewriting on interface address change. This is +useful for dialup interface with changing IP addresses. + +ip_forward +---------- + +Enable or disable forwarding of IP packages between interfaces. Changing this +value resets all other parameters to their default values. They differ if the +kernel is configured as host or router. + +ip_local_port_range +------------------- + +Range of ports used by TCP and UDP to choose the local port. Contains two +numbers, the first number is the lowest port, the second number the highest +local port. Default is 1024-4999. Should be changed to 32768-61000 for +high-usage systems. + +ip_no_pmtu_disc +--------------- + +Global switch to turn path MTU discovery off. It can also be set on a per +socket basis by the applications or on a per route basis. + +ip_masq_debug +------------- + +Enable/disable debugging of IP masquerading. + +IP fragmentation settings +------------------------- + +ipfrag_high_trash and ipfrag_low_trash +-------------------------------------- + +Maximum memory used to reassemble IP fragments. When ipfrag_high_thresh bytes +of memory is allocated for this purpose, the fragment handler will toss +packets until ipfrag_low_thresh is reached. + +ipfrag_time +----------- + +Time in seconds to keep an IP fragment in memory. + +TCP settings +------------ + +tcp_ecn +------- + +This file controls the use of the ECN bit in the IPv4 headers, this is a new +feature about Explicit Congestion Notification, but some routers and firewalls +block trafic that has this bit set, so it could be necessary to echo 0 to +/proc/sys/net/ipv4/tcp_ecn, if you want to talk to this sites. For more info +you could read RFC2481. + +tcp_retrans_collapse +-------------------- + +Bug-to-bug compatibility with some broken printers. On retransmit, try to send +larger packets to work around bugs in certain TCP stacks. Can be turned off by +setting it to zero. + +tcp_keepalive_probes +-------------------- + +Number of keep alive probes TCP sends out, until it decides that the +connection is broken. + +tcp_keepalive_time +------------------ + +How often TCP sends out keep alive messages, when keep alive is enabled. The +default is 2 hours. + +tcp_syn_retries +--------------- + +Number of times initial SYNs for a TCP connection attempt will be +retransmitted. Should not be higher than 255. This is only the timeout for +outgoing connections, for incoming connections the number of retransmits is +defined by tcp_retries1. + +tcp_sack +-------- + +Enable select acknowledgments after RFC2018. + +tcp_timestamps +-------------- + +Enable timestamps as defined in RFC1323. + +tcp_stdurg +---------- + +Enable the strict RFC793 interpretation of the TCP urgent pointer field. The +default is to use the BSD compatible interpretation of the urgent pointer +pointing to the first byte after the urgent data. The RFC793 interpretation is +to have it point to the last byte of urgent data. Enabling this option may +lead to interoperatibility problems. Disabled by default. + +tcp_syncookies +-------------- + +Only valid when the kernel was compiled with CONFIG_SYNCOOKIES. Send out +syncookies when the syn backlog queue of a socket overflows. This is to ward +off the common 'syn flood attack'. Disabled by default. + +Note that the concept of a socket backlog is abandoned. This means the peer +may not receive reliable error messages from an over loaded server with +syncookies enabled. + +tcp_window_scaling +------------------ + +Enable window scaling as defined in RFC1323. + +tcp_fin_timeout +--------------- + +The length of time in seconds it takes to receive a final FIN before the +socket is always closed. This is strictly a violation of the TCP +specification, but required to prevent denial-of-service attacks. + +tcp_max_ka_probes +----------------- + +Indicates how many keep alive probes are sent per slow timer run. Should not +be set too high to prevent bursts. + +tcp_max_syn_backlog +------------------- + +Length of the per socket backlog queue. Since Linux 2.2 the backlog specified +in listen(2) only specifies the length of the backlog queue of already +established sockets. When more connection requests arrive Linux starts to drop +packets. When syncookies are enabled the packets are still answered and the +maximum queue is effectively ignored. + +tcp_retries1 +------------ + +Defines how often an answer to a TCP connection request is retransmitted +before giving up. + +tcp_retries2 +------------ + +Defines how often a TCP packet is retransmitted before giving up. + +Interface specific settings +--------------------------- + +In the directory /proc/sys/net/ipv4/conf you'll find one subdirectory for each +interface the system knows about and one directory calls all. Changes in the +all subdirectory affect all interfaces, whereas changes in the other +subdirectories affect only one interface. All directories have the same +entries: + +accept_redirects +---------------- + +This switch decides if the kernel accepts ICMP redirect messages or not. The +default is 'yes' if the kernel is configured for a regular host and 'no' for a +router configuration. + +accept_source_route +------------------- + +Should source routed packages be accepted or declined. The default is +dependent on the kernel configuration. It's 'yes' for routers and 'no' for +hosts. + +bootp_relay +~~~~~~~~~~~ + +Accept packets with source address 0.b.c.d with destinations not to this host +as local ones. It is supposed that a BOOTP relay daemon will catch and forward +such packets. + +The default is 0, since this feature is not implemented yet (kernel version +2.2.12). + +forwarding +---------- + +Enable or disable IP forwarding on this interface. + +log_martians +------------ + +Log packets with source addresses with no known route to kernel log. + +mc_forwarding +------------- + +Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE and a +multicast routing daemon is required. + +proxy_arp +--------- + +Does (1) or does not (0) perform proxy ARP. + +rp_filter +--------- + +Integer value determines if a source validation should be made. 1 means yes, 0 +means no. Disabled by default, but local/broadcast address spoofing is always +on. + +If you set this to 1 on a router that is the only connection for a network to +the net, it will prevent spoofing attacks against your internal networks +(external addresses can still be spoofed), without the need for additional +firewall rules. + +secure_redirects +---------------- + +Accept ICMP redirect messages only for gateways, listed in default gateway +list. Enabled by default. + +shared_media +------------ + +If it is not set the kernel does not assume that different subnets on this +device can communicate directly. Default setting is 'yes'. + +send_redirects +-------------- + +Determines whether to send ICMP redirects to other hosts. + +Routing settings +---------------- + +The directory /proc/sys/net/ipv4/route contains several file to control +routing issues. + +error_burst and error_cost +-------------------------- + +These parameters are used to limit how many ICMP destination unreachable to +send from the host in question. ICMP destination unreachable messages are +sent when we can not reach the next hop, while trying to transmit a packet. +It will also print some error messages to kernel logs if someone is ignoring +our ICMP redirects. The higher the error_cost factor is, the fewer +destination unreachable and error messages will be let through. Error_burst +controls when destination unreachable messages and error messages will be +dropped. The default settings limit warning messages to five every second. + +flush +----- + +Writing to this file results in a flush of the routing cache. + +gc_elasticity, gc_interval, gc_min_interval_ms, gc_timeout, gc_thresh +--------------------------------------------------------------------- + +Values to control the frequency and behavior of the garbage collection +algorithm for the routing cache. gc_min_interval is deprecated and replaced +by gc_min_interval_ms. + + +max_size +-------- + +Maximum size of the routing cache. Old entries will be purged once the cache +reached has this size. + +max_delay, min_delay +-------------------- + +Delays for flushing the routing cache. + +redirect_load, redirect_number +------------------------------ + +Factors which determine if more ICPM redirects should be sent to a specific +host. No redirects will be sent once the load limit or the maximum number of +redirects has been reached. + +redirect_silence +---------------- + +Timeout for redirects. After this period redirects will be sent again, even if +this has been stopped, because the load or number limit has been reached. + +Network Neighbor handling +------------------------- + +Settings about how to handle connections with direct neighbors (nodes attached +to the same link) can be found in the directory /proc/sys/net/ipv4/neigh. + +As we saw it in the conf directory, there is a default subdirectory which +holds the default values, and one directory for each interface. The contents +of the directories are identical, with the single exception that the default +settings contain additional options to set garbage collection parameters. + +In the interface directories you'll find the following entries: + +base_reachable_time, base_reachable_time_ms +------------------------------------------- + +A base value used for computing the random reachable time value as specified +in RFC2461. + +Expression of base_reachable_time, which is deprecated, is in seconds. +Expression of base_reachable_time_ms is in milliseconds. + +retrans_time, retrans_time_ms +----------------------------- + +The time between retransmitted Neighbor Solicitation messages. +Used for address resolution and to determine if a neighbor is +unreachable. + +Expression of retrans_time, which is deprecated, is in 1/100 seconds (for +IPv4) or in jiffies (for IPv6). +Expression of retrans_time_ms is in milliseconds. + +unres_qlen +---------- + +Maximum queue length for a pending arp request - the number of packets which +are accepted from other layers while the ARP address is still resolved. + +anycast_delay +------------- + +Maximum for random delay of answers to neighbor solicitation messages in +jiffies (1/100 sec). Not yet implemented (Linux does not have anycast support +yet). + +ucast_solicit +------------- + +Maximum number of retries for unicast solicitation. + +mcast_solicit +------------- + +Maximum number of retries for multicast solicitation. + +delay_first_probe_time +---------------------- + +Delay for the first time probe if the neighbor is reachable. (see +gc_stale_time) + +locktime +-------- + +An ARP/neighbor entry is only replaced with a new one if the old is at least +locktime old. This prevents ARP cache thrashing. + +proxy_delay +----------- + +Maximum time (real time is random [0..proxytime]) before answering to an ARP +request for which we have an proxy ARP entry. In some cases, this is used to +prevent network flooding. + +proxy_qlen +---------- + +Maximum queue length of the delayed proxy arp timer. (see proxy_delay). + +app_solcit +---------- + +Determines the number of requests to send to the user level ARP daemon. Use 0 +to turn off. + +gc_stale_time +------------- + +Determines how often to check for stale ARP entries. After an ARP entry is +stale it will be resolved again (which is useful when an IP address migrates +to another machine). When ucast_solicit is greater than 0 it first tries to +send an ARP packet directly to the known host When that fails and +mcast_solicit is greater than 0, an ARP request is broadcasted. + +2.9 Appletalk +------------- + +The /proc/sys/net/appletalk directory holds the Appletalk configuration data +when Appletalk is loaded. The configurable parameters are: + +aarp-expiry-time +---------------- + +The amount of time we keep an ARP entry before expiring it. Used to age out +old hosts. + +aarp-resolve-time +----------------- + +The amount of time we will spend trying to resolve an Appletalk address. + +aarp-retransmit-limit +--------------------- + +The number of times we will retransmit a query before giving up. + +aarp-tick-time +-------------- + +Controls the rate at which expires are checked. + +The directory /proc/net/appletalk holds the list of active Appletalk sockets +on a machine. + +The fields indicate the DDP type, the local address (in network:node format) +the remote address, the size of the transmit pending queue, the size of the +received queue (bytes waiting for applications to read) the state and the uid +owning the socket. + +/proc/net/atalk_iface lists all the interfaces configured for appletalk.It +shows the name of the interface, its Appletalk address, the network range on +that address (or network number for phase 1 networks), and the status of the +interface. + +/proc/net/atalk_route lists each known network route. It lists the target +(network) that the route leads to, the router (may be directly connected), the +route flags, and the device the route is using. + +2.10 IPX +-------- + +The IPX protocol has no tunable values in proc/sys/net. + +The IPX protocol does, however, provide proc/net/ipx. This lists each IPX +socket giving the local and remote addresses in Novell format (that is +network:node:port). In accordance with the strange Novell tradition, +everything but the port is in hex. Not_Connected is displayed for sockets that +are not tied to a specific remote address. The Tx and Rx queue sizes indicate +the number of bytes pending for transmission and reception. The state +indicates the state the socket is in and the uid is the owning uid of the +socket. + +The /proc/net/ipx_interface file lists all IPX interfaces. For each interface +it gives the network number, the node number, and indicates if the network is +the primary network. It also indicates which device it is bound to (or +Internal for internal networks) and the Frame Type if appropriate. Linux +supports 802.3, 802.2, 802.2 SNAP and DIX (Blue Book) ethernet framing for +IPX. + +The /proc/net/ipx_route table holds a list of IPX routes. For each route it +gives the destination network, the router node (or Directly) and the network +address of the router (or Connected) for internal networks. + +2.11 /proc/sys/fs/mqueue - POSIX message queues filesystem +---------------------------------------------------------- + +The "mqueue" filesystem provides the necessary kernel features to enable the +creation of a user space library that implements the POSIX message queues +API (as noted by the MSG tag in the POSIX 1003.1-2001 version of the System +Interfaces specification.) + +The "mqueue" filesystem contains values for determining/setting the amount of +resources used by the file system. + +/proc/sys/fs/mqueue/queues_max is a read/write file for setting/getting the +maximum number of message queues allowed on the system. + +/proc/sys/fs/mqueue/msg_max is a read/write file for setting/getting the +maximum number of messages in a queue value. In fact it is the limiting value +for another (user) limit which is set in mq_open invocation. This attribute of +a queue must be less or equal then msg_max. + +/proc/sys/fs/mqueue/msgsize_max is a read/write file for setting/getting the +maximum message size value (it is every message queue's attribute set during +its creation). + + +------------------------------------------------------------------------------ +Summary +------------------------------------------------------------------------------ +Certain aspects of kernel behavior can be modified at runtime, without the +need to recompile the kernel, or even to reboot the system. The files in the +/proc/sys tree can not only be read, but also modified. You can use the echo +command to write value into these files, thereby changing the default settings +of the kernel. +------------------------------------------------------------------------------ |