proc.txt
上传用户：jlfgdled
上传日期：2013-04-10
资源大小：33168k
文件大小：70k
- ------------------------------------------------------------------------------
- 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
- 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
- ------------------------------------------------------------------------------
- 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, APX, 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
- ..............................................................................
- 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
- ..............................................................................
- File Content
- size total program size
- resident size of memory portions
- shared number of pages that are shared
- trs number of pages that are 'code'
- drs number of pages of data/stack
- lrs number of pages of library
- dt number of dirty pages
- ..............................................................................
- 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
- 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 lookups.
- 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).
- 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
- ------------------------------------------------------------------------------
- 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
- 4096. 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.
- The three values in file-nr denote the number of allocated file handles, the
- number of used file handles, and the maximum number of file handles. When the
- allocated file handles come close to the maximum, but the number of actually
- used ones is far behind, you've encountered a peak in your usage of file
- handles and you don't need to increase the maximum.
- 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.
- 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::xcaxfexbaxbe::/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_level 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.
- 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. In addition, one of the files
- (bdflush) has some influence on disk usage.
- bdflush
- -------
- This file controls the operation of the bdflush kernel daemon. It currently
- contains nine integer values, six of which are actually used by the kernel.
- They are listed in table 2-2.
- Table 2-2: Parameters in /proc/sys/vm/bdflush
- ..............................................................................
- Value Meaning
- nfract Percentage of buffer cache dirty to activate bdflush
- ndirty Maximum number of dirty blocks to write out per wake-cycle
- nrefill Number of clean buffers to try to obtain each time we call refill
- nref_dirt buffer threshold for activating bdflush when trying to refill
- buffers.
- dummy Unused
- age_buffer Time for normal buffer to age before we flush it
- age_super Time for superblock to age before we flush it
- dummy Unused
- dummy Unused
- ..............................................................................
- nfract
- ------
- This parameter governs the maximum number of dirty buffers in the buffer
- cache. Dirty means that the contents of the buffer still have to be written to
- disk (as opposed to a clean buffer, which can just be forgotten about).
- Setting this to a higher value means that Linux can delay disk writes for a
- long time, but it also means that it will have to do a lot of I/O at once when
- memory becomes short. A lower value will spread out disk I/O more evenly.
- ndirty
- ------
- Ndirty gives the maximum number of dirty buffers that bdflush can write to the
- disk at one time. A high value will mean delayed, bursty I/O, while a small
- value can lead to memory shortage when bdflush isn't woken up often enough.
- nrefill
- -------
- This is the number of buffers that bdflush will add to the list of free
- buffers when refill_freelist() is called. It is necessary to allocate free
- buffers beforehand, since the buffers are often different sizes than the
- memory pages and some bookkeeping needs to be done beforehand. The higher the
- number, the more memory will be wasted and the less often refill_freelist()
- will need to run.
- nref_dirt
- ---------
- When refill_freelist() comes across more than nref_dirt dirty buffers, it will
- wake up bdflush.
- age_buffer and age_super
- ------------------------
- Finally, the age_buffer and age_super parameters govern the maximum time Linux
- waits before writing out a dirty buffer to disk. The value is expressed in
- jiffies (clockticks), the number of jiffies per second is 100. Age_buffer is
- the maximum age for data blocks, while age_super is for filesystems meta data.
- buffermem
- ---------
- The three values in this file control how much memory should be used for
- buffer memory. The percentage is calculated as a percentage of total system
- memory.
- The values are:
- min_percent
- -----------
- This is the minimum percentage of memory that should be spent on buffer
- memory.
- borrow_percent
- --------------
- When Linux is short on memory, and the buffer cache uses more than it has been
- allotted, the memory management (MM) subsystem will prune the buffer cache
- more heavily than other memory to compensate.
- max_percent
- -----------
- This is the maximum amount of memory that can be used for buffer memory.
- freepages
- ---------
- This file contains three values: min, low and high:
- min
- ---
- When the number of free pages in the system reaches this number, only the
- kernel can allocate more memory.
- low
- ---
- If the number of free pages falls below this point, the kernel starts swapping
- aggressively.
- high
- ----
- The kernel tries to keep up to this amount of memory free; if memory falls
- below this point, the kernel starts gently swapping in the hopes that it never
- has to do really aggressive swapping.
- kswapd
- ------
- Kswapd is the kernel swap out daemon. That is, kswapd is that piece of the
- kernel that frees memory when it gets fragmented or full. Since every system
- is different, you'll probably want some control over this piece of the system.
- The file contains three numbers:
- tries_base
- ----------
- The maximum number of pages kswapd tries to free in one round is calculated
- from this number. Usually this number will be divided by 4 or 8 (see
- mm/vmscan.c), so it isn't as big as it looks.
- When you need to increase the bandwidth to/from swap, you'll want to increase
- this number.
- tries_min
- ---------
- This is the minimum number of times kswapd tries to free a page each time it
- is called. Basically it's just there to make sure that kswapd frees some pages
- even when it's being called with minimum priority.
- swap_cluster
- ------------
- This is probably the greatest influence on system performance.
- swap_cluster is the number of pages kswapd writes in one turn. You'll want
- this value to be large so that kswapd does its I/O in large chunks and the
- disk doesn't have to seek as often, but you don't want it to be too large
- since that would flood the request queue.
- 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.
- pagecache
- ---------
- This file does exactly the same job as buffermem, only this file controls the
- amount of memory allowed for memory mapping and generic caching of files.
- You don't want the minimum level to be too low, otherwise your system might
- thrash when memory is tight or fragmentation is high.
- pagetable_cache
- ---------------
- The kernel keeps a number of page tables in a per-processor cache (this helps
- a lot on SMP systems). The cache size for each processor will be between the
- low and the high value.
- On a low-memory, single CPU system, you can safely set these values to 0 so
- you don't waste memory. It is used on SMP systems so that the system can
- perform fast pagetable allocations without having to acquire the kernel memory
- lock.
- For large systems, the settings are probably fine. For normal systems they
- won't hurt a bit. For small systems ( less than 16MB ram) it might be
- advantageous to set both values to 0.
- swapctl
- -------
- This file contains no less than 8 variables. All of these values are used by
- kswapd.
- The first four variables
- * sc_max_page_age,
- * sc_page_advance,
- * sc_page_decline and
- * sc_page_initial_age
- are used to keep track of Linux's page aging. Page aging is a bookkeeping
- method to track which pages of memory are often used, and which pages can be
- swapped out without consequences.
- When a page is swapped in, it starts at sc_page_initial_age (default 3) and
- when the page is scanned by kswapd, its age is adjusted according to the
- following scheme:
- * If the page was used since the last time we scanned, its age is increased
- by sc_page_advance (default 3). Where the maximum value is given by
- sc_max_page_age (default 20).
- * Otherwise (meaning it wasn't used) its age is decreased by sc_page_decline
- (default 1).
- When a page reaches age 0, it's ready to be swapped out.
- The variables sc_age_cluster_fract, sc_age_cluster_min, sc_pageout_weight and
- sc_bufferout_weight, can be used to control kswapd's aggressiveness in
- swapping out pages.
- Sc_age_cluster_fract is used to calculate how many pages from a process are to
- be scanned by kswapd. The formula used is
- (sc_age_cluster_fract divided by 1024) times resident set size
- So if you want kswapd to scan the whole process, sc_age_cluster_fract needs to
- have a value of 1024. The minimum number of pages kswapd will scan is
- represented by sc_age_cluster_min, which is done so that kswapd will also scan
- small processes.
- The values of sc_pageout_weight and sc_bufferout_weight are used to control
- how many tries kswapd will make in order to swap out one page/buffer. These
- values can be used to fine-tune the ratio between user pages and buffer/cache
- memory. When you find that your Linux system is swapping out too many process
- pages in order to satisfy buffer memory demands, you may want to either
- increase sc_bufferout_weight, or decrease the value of sc_pageout_weight.
- 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 the warning messages written to the kernel
- log from the routing code. The higher the error_cost factor is, the fewer
- messages will be written. Error_burst controls when messages will be dropped.
- The default settings limit warning messages to one every five seconds.
- flush
- -----
- Writing to this file results in a flush of the routing cache.
- gc_elastic, gc_interval, gc_min_interval, gc_tresh, gc_timeout
- --------------------------------------------------------------
- Values to control the frequency and behavior of the garbage collection
- algorithm for the routing cache.
- 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
- -------------------
- A base value used for computing the random reachable time value as specified
- in RFC2461.
- retrans_time
- ------------
- The time, expressed in jiffies (1/100 sec), between retransmitted Neighbor
- Solicitation messages. Used for address resolution and to determine if a
- neighbor is unreachable.
- 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.
- ------------------------------------------------------------------------------
- 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.
- ------------------------------------------------------------------------------
English
