Blog Linux Linux Proc File System | Linux Proc File System |
|
 |
|
| Written by Administrator | |
| Feb 16, 2002 at 05:21 PM | |
T H E /proc F I L E S Y S T E MInteresting reference on the "proc" filesystem in Linux. Gives definintions and what kinds of statistics can be gathered from the files under /proc.
-----------------------------------------------------------------------
T H E /proc F I L E S Y S T E M ----------------------------------------------------------------------- /proc/sys Terrehon Bowden January 27 1999 Bodo Bauer ----------------------------------------------------------------------- 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 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::xcaxfexbaxbe::/usr/local/java/bin/javawrapper:' > register echo ':HTML:E::html::/usr/local/java/bin/appletviewer:' > register echo ':Applet:M:: 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 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 =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 (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 ip_always_defrag Replaces the former Kernel-Configuration option: CONFIG_IP_ALWAYS_DEFRAG All incoming fragments (parts of IP packets that arose when some host between origin and destination decided that the packets were too large and cut them into pieces) will be reassembled (defragmented) before being processed, even if they are about to be forwarded. Only say Y here if running either a firewall that is the sole link to your network or a transparent proxy; never ever say Y here for a normal router or host. This is automagically enabled when enabling masquerading. 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 'no' 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. |
|
| Last Updated ( Oct 01, 2007 at 02:52 PM ) |
| <Previous | Next> |
|---|