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+
+-----------------------------------------------------------------------
+
+                T H E  /proc   F I L E S Y S T E M
+
+-----------------------------------------------------------------------
+/proc/sys      Terrehon Bowden <terrehon@wpi.com>       January 27 1999
+               Bodo Bauer <bb@ricochet.net>                
+-----------------------------------------------------------------------
+Version 1.1                                         Kernel version 2.2
+-----------------------------------------------------------------------
+Contents
+
+1   Introduction/Credits
+
+1.1  Legal Issues
+
+2   The /proc file system
+
+2.1  Process specific subdirectories
+2.2  Kernel data
+2.3  IDE devices in /proc/ide
+2.4  Networking info in /proc/net
+2.5  SCSI info
+2.6  Parallel port info in /proc/parport
+2.7  TTY info in /proc/tty
+
+3   Reading and modifying kernel parameters
+
+3.1  /proc/sys/debug and /proc/sys/proc
+3.2  /proc/fs - File system data
+3.3  /proc/fs/binfmt_misc - Miscellaneous binary formats
+3.4  /proc/sys/kernel - General kernel parameters
+3.5  /proc/sys/vm - The virtual memory subsystem
+3.6  /proc/sys/dev - Device specific parameters
+3.7  /proc/sys/sunrpc - Remote procedure calls
+3.8  /proc/sys/net - Networking stuff
+3.9  /proc/sys/net/ipv4 - IPV4 settings=20
+3.10 Appletalk
+3.11 IPX
+
+-----------------------------------------------------------------------
+
+1   Introduction/Credits
+
+This documentation is part of a soon to be released book published by
+IDG Books 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 this chapter, it seems only fair to give
+the work back to the Linux community. This work is based on the
+2.1.132 and 2.2.0-pre-kernel versions. 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.
+
+We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov.  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://www.suse.com/~bb/Docs/proc.html in HTML, ASCII, and as 
+Postscript file. 
+
+1.1  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...
+
+-----------------------------------------------------------------------
+
+2   The /proc file 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.  It contains
+(among other things) one subdirectory for each process running on the
+system which is named after the process id (PID) of the process. The
+link self points to the process reading the file system.
+
+2.1  Process specific subdirectories
+
+Each process subdirectory has the in table 1.1 listed entries.
+
+      _________________________________________________
+      cmdline Command line arguments
+      environ Values of environment variables
+      fd    Directory, which contains all file descriptors
+      mem   Memory held by this process
+      stat   Process status
+      status  Process status in human readable form
+      cwd   Link to the current working directory
+      exe   Link to the executable of this process
+      maps   Memory maps
+      root   Link to the root directory of this process
+      statm  Process memory status information
+     _________________________________________________
+      Table 1.1: Process specific entries in /proc
+
+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:    5633
+PPid:   5609
+Uid:    501     501     501     501
+Gid:    100     100     100     100
+Groups: 100 16 
+VmSize:      804 kB
+VmLck:         0 kB
+VmRSS:       344 kB
+VmData:       68 kB
+VmStk:        20 kB
+VmExe:        12 kB
+VmLib:       660 kB
+SigPnd: 0000000000000000
+SigBlk: 0000000000000000
+SigIgn: 0000000000000000
+SigCgt: 0000000000000000
+CapInh: 00000000fffffeff
+CapPrm: 0000000000000000
+CapEff: 0000000000000000
+
+This shows you almost the same information as 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. It contains seven values with the following meanings:
+
+size       total program size
+resident   size of in memory portions
+shared     number of the 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
+
+The ratio text/data/library is approximate only by heuristics.
+
+2.2  Kernel data
+
+Similar to the process entries, these are files which give information
+about the running kernel. The files used to obtain this information
+are contained in /proc and are listed in table 1.2. 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.
+
+      ________________________________________________
+      apm           Advanced power management info
+      cmdline       Kernel command line
+      cpuinfo       Info about the CPU
+      devices       Available devices (block and character)
+      dma           Used DMS channels
+      filesystems   Supported filesystems
+      interrupts    Interrupt usage
+      ioports       I/O port usage
+      kcore         Kernel core image
+      kmsg          Kernel messages
+      ksyms         Kernel symbol table
+      loadavg       Load average
+      locks         Kernel locks
+      meminfo       Memory info
+      misc          Miscellaneous
+      modules       List of loaded modules
+      mounts        Mounted filesystems
+      partitions    Table of partitions known to the system
+      rtc           Real time clock
+      slabinfo      Slab pool info
+      stat          Overall statistics
+      swaps         Swap space utilization
+      uptime        System uptime
+      version       Kernel version
+      ________________________________________________
+           Table 1.2: Kernel info in /proc
+
+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
+
+There three more important subdirectories in /proc: net, scsi and
+sys. The general rule is that the contents, or even the existence of
+these directories, depends on your kernel configuration. If SCSI is
+not enabled, the directory scsi may not exist. The same is true with
+the net, which is only there when networking support is present in the
+running kernel.
+
+The slabinfo file gives information about memory usage on 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 (like
+network buffers, directory cache, etc.).
+
+2.3  IDE devices in /proc/ide
+
+This subdirectory contains information about all IDE devices that the
+kernel is aware of.  There is one subdirectory for each device
+(i.e. hard disk) containing the following files:
+
+       cache             The cache
+       capacity          Capacity of the medium
+       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
+
+2.4  Networking info in /proc/net
+
+This directory follows the usual pattern. Table 1.3 lists the files
+and their meaning.
+
+     ____________________________________________________
+     arp             Kernel ARP table
+     dev             network devices with statistics
+     dev_mcast       Lists the Layer2 multicast groups a
+                     device is listening to (interface index,
+                     label, number of references, number of
+                     bound addresses).
+     dev_stat        network device status
+     ip_fwchains     Firewall chain linkage
+     ip_fwnames      Firewall chains
+     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.
+     udp6            UDP sockets (IPv6)
+     tcp6            TCP sockets (IPv6)
+     raw6            Raw device statistics (IPv6)
+     igmp6	     IP multicast addresses, which this host joineed (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 1.3: Network info in /proc/net
+
+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
+
+2.5  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: QUANTUM  Model: XP34550W         Rev: LXY4
+  Type:   Direct-Access                    ANSI SCSI revision: 02
+Host: scsi0 Channel: 00 Id: 01 Lun: 00
+  Vendor: SEAGATE  Model: ST34501W         Rev: 0018
+  Type:   Direct-Access                    ANSI SCSI revision: 02
+Host: scsi0 Channel: 00 Id: 02 Lun: 00
+  Vendor: SEAGATE  Model: ST34501W         Rev: 0017
+  Type:   Direct-Access                    ANSI SCSI revision: 02
+Host: scsi0 Channel: 00 Id: 04 Lun: 00
+  Vendor: ARCHIVE  Model: Python 04106-XXX Rev: 703b
+  Type:   Sequential-Access                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:
+
+>cat /proc/scsi/ncr53c8xx/0
+General information:
+ Chip NCR53C875, device id 0xf, revision id 0x4
+ IO port address 0xec00, IRQ number 11
+ Synchronous period factor 12, max commands per lun 4
+
+2.6  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,...).
+
+This directory contains four files:
+
+    autoprobe   Autoprobe results of this port
+    devices     Connected device modules
+    hardware    Hardware info (port type, io-port, DMA, IRQ, etc.)
+    irq         Used interrupt, if any
+
+2.7  TTY info in /proc/tty
+
+Information about the available and the actually used tty's can be
+found in /proc/tty. You'll find entries for drivers and line
+disciplines in this directory, as shown in the table below:
+
+     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
+
+-----------------------------------------------------------------------
+
+3   Reading and modifying kernel parameters
+
+A very interesting part of /proc is the directory /proc/sys. This not
+only provides information, it also allows you to change parameters
+within the kernel. Be very careful when trying this. You can optimize
+your system, but you also can crash it. Never play around with 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 get this done
+every time your system boots. 
+
+The files in /proc/sys can be used to 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 review the kernel documentation if there is any
+doubt. You'll find the documentation in the directory
+/usr/src/linux/Documentation/sys. This chapter is heavily based on the
+documentation included in the pre 2.2 kernels. Thanks to Rick van Riel
+for providing this information.
+
+3.1  /proc/sys/debug and /proc/sys/proc
+
+These two subdirectories are empty.
+
+3.2  /proc/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 gives information
+   about the current status. It holds six values, in which the last
+   two are not used and are always zero. The other four mean:
+
+       nr_dentry   Seems to be zero all the time
+       nr_unused   Number of unused cache entries
+       age_limit   Age in seconds after the entry may be
+                   reclaimed, when memory is short
+       want_pages  internal
+
+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 free 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 as yet
+   doesn't free them again.
+
+   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.
+
+   However, there is still a per process limit of open files, which
+   unfortunatly can't be changed that easily. It is set to 1024 by
+   default. To change this you have to edit the files limits.h and
+   fs.h in the directory /usr/src/linux/include/linux. Change the
+   definition of NR_OPEN and recompile the kernel.
+
+inode-state, inode-nr and inode-max
+   As with file handles, the kernel allocates the inode structures
+   dynamically, but can't free them yet.
+
+   The value in inode-max denotes the maximum number of inode
+   handlers. This value should be 3 to 4 times larger than the value
+   in file-max, since stdin, stdout, and network sockets also need an
+   inode struct to handle them. If you regularly run out of inodes,
+   you should increase this value.
+
+   The file inode-nr contains the first two items from inode-state, so
+   we'll skip to that file...
+
+   inode-state contains three actual numbers and four dummy values. The 
+   actual numbers are (in order of appearance) nr_inodes, nr_free_inodes,
+   and preshrink.
+
+   nr_inodes 
+     Denotes the number of inodes the system has allocated. This can
+     be slightly more than inode-max because Linux allocates them one
+     pageful at a time.
+
+   nr_free_inodes 
+     Represents the number of free inodes and pre shrink is nonzero
+     when the nr_inodes > inode-max and the system needs to prune the
+     inode list instead of allocating more.
+
+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.
+
+3.3  /proc/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
+
+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 and 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).
+
+To 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 three 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.
+
+3.4  /proc/sys/kernel - general kernel parameters
+
+This directory reflects general kernel behaviors. As I've said before,
+the contents are depend on your configuration. I'll list 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%, accounting suspends. If
+   it goes above highwater%, 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 left <= 2% free; resume it if we have a value
+   >=3%; 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(1) program to handle a graceful restart. However, when
+   the value is > 0, 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
+   2.1.131
+   >cat /proc/sys/kernel/ostype
+   Linux
+   >cat /proc/sys/kernel/version
+   #8 Mon Jan 25 19:45:02 PST 1999
+ 
+   The files osrelease and ostype should be clear enough. Version
+   needs a little more clarification however. The #8 means that this
+   is the 8th kernel built from this source base and the date behind
+   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, this 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. Look into 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.
+
+3.5  /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 a little influence on disk usage.
+
+bdflush
+   This file controls the operation of the bdflush kernel daemon. It
+   currently contains 9 integer values, 6 of which are actually used
+   by the kernel:
+
+    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   Dirty buffer threshold for activating bdflush
+                when trying to refill buffers.
+    dummy       unused
+    age_buffer  Time for normal buffer to age before you flush it
+    age_super   Time for superblock to age before you 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 high 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 low 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 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 mangement (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 gets below this point, the kernel
+     starts swapping aggressively.
+
+   high
+     The kernel tries to keep up to this amount of memory free; if
+     memory comes below this point, the kernel gently starts 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 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
+   aquire the kernel memory lock.
+
+   For large systems, the settings are probably fine. For normal
+   systems they won't hurt a bit. For small systems (<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:
+
+    o If the page was used since the last time we scanned, its age
+      is increased by sc_page_advance (default 3) up to a
+      maximum of sc_max_page_age (default 20).
+
+    o Else (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 next four 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
+           -------------------- * resident set size
+              1024   =20
+
+   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, this is done so 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 might want to either
+   increase sc_bufferout_weight, or decrease the value of
+   sc_pageout_weight.
+
+3.6  /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
+
+drive name:           sr0  hdc
+drive speed:           0    6
+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 hdc, and their lists of features.
+
+3.7  /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)
+
+3.8  /proc/sys/net - Networking stuff
+
+The interface to the networking parts of the kernel is located in
+/proc/sys/net. The table below shows all possible subdirectories. You
+may see only some of them, depending on the configuration of your
+kernel:
+
++-------------------------------------------------------------+
+| 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. As 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 to Appletalk and IPX further down
+in section 3.10 and 3.11. Please look in 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. The higher the
+   message_cost factor is, the less messages 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
+   Maximal number of packets, queued on 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.
+
+3.9  /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 itself.
+
+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/multicast 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 hundredths of a second (on Intel systems).
+
+IP settings
+
+ip_autoconfig
+   This file contains one, if the host got 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. A
+   change of 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_retrans_collapse
+   Bug-to-bug compatibility with some broken printers. On retransmit
+   try to send bigger 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 prevent against 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
+   How many seconds to wait for 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
+   How many keepalive probes are sent per slow timer run. Shouldn't 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, where
+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 'np' for hosts.
+
+bootp_relay
+   Accept packets with source address 0.b.c.d destined not to this
+   host as local ones. It is supposed that BOOTP relay daemon will
+   catch and forward such packets.
+
+   The default is 'no', as this feature is not implemented yet
+   (kernel version 2.2.0-pre?).
+
+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
+   Do (1) or don't (0) do proxy ARP.
+
+rp_filter
+   Integer value deciding if 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 evidently prevents 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 if or if not 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 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 - how many packets
+   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. 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 (useful when an IP address
+   migrates to another machine). When ucast_solicit is > 0 it first
+   tries to send an ARP packet directly to the known host, when that
+   fails and mcast_solicit is > 0, an ARP request is broadcasted.
+
+3.10  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 AARP 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 expiries 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 ad- dress (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 via.
+
+3.11  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 transmit and receive. 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.

FUNET's LINUX-ADM group, linux-adm@nic.funet.fi
TCL-scripts by Sam Shen (who was at: slshen@lbl.gov)