------------------------------------------------------------------------------ T H E /proc F I L E S Y S T E M ------------------------------------------------------------------------------ /proc/sys Terrehon Bowden October 7 1999 Bodo Bauer ------------------------------------------------------------------------------ Version 1.2 Kernel version 2.2.12 ------------------------------------------------------------------------------ Table of Contents ----------------- 0 Preface 0.1 Introduction/Credits 0.2 Legal Stuff 1 Collecting System Information 1.1 Process-Specific Subdirectories 1.2 Kernel data 1.3 IDE devices in /proc/ide 1.4 Networking info in /proc/net 1.5 SCSI info 1.6 Parallel port info in /proc/parport 1.7 TTY info in /proc/tty 2 Modifying System Parameters 2.1 /proc/sys/fs - File system data 2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats 2.3 /proc/sys/kernel - general kernel parameters 2.4 /proc/sys/vm - The virtual memory subsystem 2.5 /proc/sys/dev - Device specific parameters 2.6 /proc/sys/sunrpc - Remote procedure calls 2.7 /proc/sys/net - Networking stuff 2.8 /proc/sys/net/ipv4 - IPV4 settings 2.9 Appletalk 2.10 IPX ------------------------------------------------------------------------------ Preface ------------------------------------------------------------------------------ 0.1 Introduction/Credits ------------------------ This documentation is part of a soon (or so we hope) to be released book on the SuSE Linux distribution. As there is no complete documentation for the /proc file system and we've used many freely available sources to write these chapters, it seems only fair to give the work back to the Linux community. This work is based on the 2.2.* kernel version. I'm afraid it's still far from complete, but we hope it will be useful. As far as we know, it is the first 'all-in-one' document about the /proc file system. It is focused on the Intel x86 hardware, so if you are looking for PPC, ARM, SPARC, APX, etc., features, you probably won't find what you are looking for. It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But additions and patches are welcome and will be added to this document if you mail them to Bodo. We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of other people for help compiling this documentation. We'd also like to extend a special thank you to Andi Kleen for documentation, which we relied on heavily to create this document, as well as the additional information he provided. Thanks to everybody else who contributed source or docs to the Linux kernel and helped create a great piece of software... :) If you have any comments, corrections or additions, please don't hesitate to contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this document. The latest version of this document is available online at http://skaro.nightcrawler.com/~bb/Docs/Proc as HTML version. 0.2 Legal Stuff --------------- We don't guarantee the correctness of this document, and if you come to us complaining about how you screwed up your system because of incorrect documentation, we won't feel responsible... ------------------------------------------------------------------------------ CHAPTER 1: COLLECTING SYSTEM INFORMATION ------------------------------------------------------------------------------ ------------------------------------------------------------------------------ In This Chapter ------------------------------------------------------------------------------ * Investigating the properties of the pseudo file system /proc and its ability to provide information on the running Linux system * Examining /proc's structure * Uncovering various information about the kernel and the processes running on the system ------------------------------------------------------------------------------ The proc file system acts as an interface to internal data structures in the kernel. It can be used to obtain information about the system and to change certain kernel parameters at runtime. First, we'll take a look at the read-only parts of /proc. In Chapter 2, we show you how you can use /proc/sys to change settings. 1.1 Process-Specific Subdirectories ----------------------------------- The directory /proc contains (among other things) one subdirectory for each process running on the system, which is named after the process ID (PID). The link self points to the process reading the file system. Each process subdirectory has the entries listed in Table 1-1. Table 1-1: Process specific entries in /proc .............................................................................. File Content cmdline Command line arguments 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 .............................................................................. For example, to get the status information of a process, all you have to do is read the file /proc/PID/status: >cat /proc/self/status Name: cat State: R (running) Pid: 5452 PPid: 743 Uid: 501 501 501 501 Gid: 100 100 100 100 Groups: 100 14 16 VmSize: 1112 kB VmLck: 0 kB VmRSS: 348 kB VmData: 24 kB VmStk: 12 kB VmExe: 8 kB VmLib: 1044 kB SigPnd: 0000000000000000 SigBlk: 0000000000000000 SigIgn: 0000000000000000 SigCgt: 0000000000000000 CapInh: 00000000fffffeff CapPrm: 0000000000000000 CapEff: 0000000000000000 This shows you nearly the same information you would get if you viewed it with the ps command. In fact, ps uses the proc file system to obtain its information. The statm file contains more detailed information about the process memory usage. Its seven fields are explained in Table 1-2. Table 1-2: Contents of the statm files .............................................................................. File Content size total program size resident size of memory portions shared number of pages that are shared trs number of pages that are 'code' drs number of pages of data/stack lrs number of pages of library dt number of dirty pages .............................................................................. 1.2 Kernel data --------------- Similar to the process entries, the kernel data files give information about the running kernel. The files used to obtain this information are contained in /proc and are listed in Table 1-3. Not all of these will be present in your system. It depends on the kernel configuration and the loaded modules, which files are there, and which are missing. Table 1-3: Kernel info in /proc .............................................................................. File Content apm Advanced power management info bus Directory containing bus specific information cmdline Kernel command line cpuinfo Info about the CPU devices Available devices (block and character) dma Used DMS channels filesystems Supported filesystems ide Directory containing info about the IDE subsystem interrupts Interrupt usage ioports I/O port usage kcore Kernel core image (can be ELF or A.OUT) 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 net Networking info (see text) partitions Table of partitions known to the system rtc Real time clock scsi SCSI info (see text) slabinfo Slab pool info stat Overall statistics swaps Swap space utilization sys See chapter 2 uptime System uptime version Kernel version .............................................................................. 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 are three more important subdirectories in /proc: net, scsi, and sys. The general rule is that the contents, or even the existence of these directories, depend on your kernel configuration. If SCSI is not enabled, the directory scsi may not exist. The same is true with the net, which is there only when networking support is present in the running kernel. The slabinfo file gives information about memory usage at the slab level. Linux uses slab pools for memory management above page level in version 2.2. Commonly used objects have their own slab pool (such as network buffers, directory cache, and so on). 1.3 IDE devices in /proc/ide ---------------------------- The subdirectory /proc/ide contains information about all IDE devices of which the kernel is aware. There is one subdirectory for each IDE controller, the file drivers and a link for each IDE device, pointing to the device directory in the controller specific subtree. The file drivers contains general information about the drivers used for the IDE devices: > cat /proc/ide/drivers ide-cdrom version 4.53 ide-disk version 1.08 More detailed information can be found in the controller specific subdirectories. These are named ide0, ide1 and so on. Each of these directories contains the files shown in table 1-4. Table 1-4: IDE controller info in /proc/ide/ide? .............................................................................. File Content channel IDE channel (0 or 1) config Configuration (only for PCI/IDE bridge) mate Mate name model Type/Chipset of IDE controller .............................................................................. Each device connected to a controller has a separate subdirectory in the controllers directory. The files listed in table 1-5 are contained in these directories. Table 1-5: IDE device information .............................................................................. File Content cache The cache capacity Capacity of the medium (in 512Byte blocks) driver driver and version geometry physical and logical geometry identify device identify block media media type model device identifier settings device setup smart_thresholds IDE disk management thresholds smart_values IDE disk management values .............................................................................. The most interesting file is settings. This file contains a nice overview of the drive parameters: # cat /proc/ide/ide0/hda/settings name value min max mode ---- ----- --- --- ---- bios_cyl 526 0 65535 rw bios_head 255 0 255 rw bios_sect 63 0 63 rw breada_readahead 4 0 127 rw bswap 0 0 1 r file_readahead 72 0 2097151 rw io_32bit 0 0 3 rw keepsettings 0 0 1 rw max_kb_per_request 122 1 127 rw multcount 0 0 8 rw nice1 1 0 1 rw nowerr 0 0 1 rw pio_mode write-only 0 255 w slow 0 0 1 rw unmaskirq 0 0 1 rw using_dma 0 0 1 rw 1.4 Networking info in /proc/net -------------------------------- The subdirectory /proc/net follows the usual pattern. Table 1-6 shows the additional values you get for IP version 6 if you configure the kernel to support this. Table 1-7 lists the files and their meaning. Table 1-6: IPv6 info in /proc/net .............................................................................. File Content udp6 UDP sockets (IPv6) tcp6 TCP sockets (IPv6) raw6 Raw device statistics (IPv6) igmp6 IP multicast addresses, which this host joined (IPv6) if_inet6 List of IPv6 interface addresses ipv6_route Kernel routing table for IPv6 rt6_stats Global IPv6 routing tables statistics sockstat6 Socket statistics (IPv6) snmp6 Snmp data (IPv6) .............................................................................. Table 1-7: Network info in /proc/net .............................................................................. File Content arp Kernel ARP table dev network devices with statistics dev_mcast the Layer2 multicast groups a device is listening too (interface index, label, number of references, number of bound addresses). dev_stat network device status ip_fwchains Firewall chain linkage ip_fwnames Firewall chain names ip_masq Directory containing the masquerading tables ip_masquerade Major masquerading table netstat Network statistics raw raw device statistics route Kernel routing table rpc Directory containing rpc info rt_cache Routing cache snmp SNMP data sockstat Socket statistics tcp TCP sockets tr_rif Token ring RIF routing table udp UDP sockets unix UNIX domain sockets wireless Wireless interface data (Wavelan etc) igmp IP multicast addresses, which this host joined psched Global packet scheduler parameters. netlink List of PF_NETLINK sockets ip_mr_vifs List of multicast virtual interfaces ip_mr_cache List of multicast routing cache .............................................................................. You can use this information to see which network devices are available in your system and how much traffic was routed over those devices: > cat /proc/net/dev Inter-|Receive |[... face |bytes packets errs drop fifo frame compressed multicast|[... lo: 908188 5596 0 0 0 0 0 0 [... ppp0:15475140 20721 410 0 0 410 0 0 [... eth0: 614530 7085 0 0 0 0 0 1 [... ...] Transmit ...] bytes packets errs drop fifo colls carrier compressed ...] 908188 5596 0 0 0 0 0 0 ...] 1375103 17405 0 0 0 0 0 0 ...] 1703981 5535 0 0 0 3 0 0 1.5 SCSI info ------------- If you have a SCSI host adapter in your system, you'll find a subdirectory named after the driver for this adapter in /proc/scsi. You'll also see a list of all recognized SCSI devices in /proc/scsi: >cat /proc/scsi/scsi Attached devices: Host: scsi0 Channel: 00 Id: 00 Lun: 00 Vendor: IBM Model: DGHS09U Rev: 03E0 Type: Direct-Access ANSI SCSI revision: 03 Host: scsi0 Channel: 00 Id: 06 Lun: 00 Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04 Type: CD-ROM ANSI SCSI revision: 02 The directory named after the driver has one file for each adapter found in the system. These files contain information about the controller, including the used IRQ and the IO address range. The amount of information shown is dependent on the adapter you use. The example shows the output for an Adaptec AHA-2940 SCSI adapter: > cat /proc/scsi/aic7xxx/0 Adaptec AIC7xxx driver version: 5.1.19/3.2.4 Compile Options: TCQ Enabled By Default : Disabled AIC7XXX_PROC_STATS : Disabled AIC7XXX_RESET_DELAY : 5 Adapter Configuration: SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter Ultra Wide Controller PCI MMAPed I/O Base: 0xeb001000 Adapter SEEPROM Config: SEEPROM found and used. Adaptec SCSI BIOS: Enabled IRQ: 10 SCBs: Active 0, Max Active 2, Allocated 15, HW 16, Page 255 Interrupts: 160328 BIOS Control Word: 0x18b6 Adapter Control Word: 0x005b Extended Translation: Enabled Disconnect Enable Flags: 0xffff Ultra Enable Flags: 0x0001 Tag Queue Enable Flags: 0x0000 Ordered Queue Tag Flags: 0x0000 Default Tag Queue Depth: 8 Tagged Queue By Device array for aic7xxx host instance 0: {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} Actual queue depth per device for aic7xxx host instance 0: {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} Statistics: (scsi0:0:0:0) Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) Total transfers 160151 (74577 reads and 85574 writes) (scsi0:0:6:0) Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) Total transfers 0 (0 reads and 0 writes) 1.6 Parallel port info in /proc/parport --------------------------------------- The directory /proc/parport contains information about the parallel ports of your system. It has one subdirectory for each port, named after the port number (0,1,2,...). These directories contain the four files shown in Table 1-8. Table 1-8: Files in /proc/parport .............................................................................. File Content autoprobe Any IEEE-1284 device ID information that has been acquired. devices list of the device drivers using that port. A + will appear by the name of the device currently using the port (it might not appear against any). hardware Parallel port's base address, IRQ line and DMA channel. irq IRQ that parport is using for that port. This is in a separate file to allow you to alter it by writing a new value in (IRQ number or none). .............................................................................. 1.7 TTY info in /proc/tty ------------------------- Information about the available and actually used tty's can be found in the directory /proc/tty.You'll find entries for drivers and line disciplines in this directory, as shown in Table 1-9. Table 1-9: Files in /proc/tty .............................................................................. File Content drivers list of drivers and their usage ldiscs registered line disciplines driver/serial usage statistic and status of single tty lines .............................................................................. To see which tty's are currently in use, you can simply look into the file /proc/tty/drivers: > cat /proc/tty/drivers pty_slave /dev/pts 136 0-255 pty:slave pty_master /dev/ptm 128 0-255 pty:master pty_slave /dev/ttyp 3 0-255 pty:slave pty_master /dev/pty 2 0-255 pty:master serial /dev/cua 5 64-67 serial:callout serial /dev/ttyS 4 64-67 serial /dev/tty0 /dev/tty0 4 0 system:vtmaster /dev/ptmx /dev/ptmx 5 2 system /dev/console /dev/console 5 1 system:console /dev/tty /dev/tty 5 0 system:/dev/tty unknown /dev/tty 4 1-63 console ------------------------------------------------------------------------------ Summary ------------------------------------------------------------------------------ The /proc file system serves information about the running system. It not only allows access to process data but also allows you to request the kernel status by reading files in the hierarchy. The directory structure of /proc reflects the types of information and makes it easy, if not obvious, where to look for specific data. ------------------------------------------------------------------------------ ------------------------------------------------------------------------------ CHAPTER 2: MODIFYING SYSTEM PARAMETERS ------------------------------------------------------------------------------ ------------------------------------------------------------------------------ In This Chapter ------------------------------------------------------------------------------ * Modifying kernel parameters by writing into files found in /proc/sys * Exploring the files which modify certain parameters * Review of the /proc/sys file tree ------------------------------------------------------------------------------ A very interesting part of /proc is the directory /proc/sys. This is not only a source of information, it also allows you to change parameters within the kernel. Be very careful when attempting this. You can optimize your system, but you can also cause it to crash. Never alter kernel parameters on a production system. Set up a development machine and test to make sure that everything works the way you want it to. You may have no alternative but to reboot the machine once an error has been made. To change a value, simply echo the new value into the file. An example is given below in the section on the file system data. You need to be root to do this. You can create your own boot script to perform this every time your system boots. The files in /proc/sys can be used to fine tune and monitor miscellaneous and general things in the operation of the Linux kernel. Since some of the files can inadvertently disrupt your system, it is advisable to read both documentation and source before actually making adjustments. In any case, be very careful when writing to any of these files. The entries in /proc may change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt review the kernel documentation in the directory /usr/src/linux/Documentation. This chapter is heavily based on the documentation included in the pre 2.2 kernels, and became part of it in version 2.2.1 of the Linux kernel. 2.1 /proc/sys/fs - File system data ----------------------------------- This subdirectory contains specific file system, file handle, inode, dentry and quota information. Currently, these files are in /proc/sys/fs: dentry-state ------------ Status of the directory cache. Since directory entries are dynamically allocated and deallocated, this file indicates the current status. It holds six values, in which the last two are not used and are always zero. The others are listed in table 2-1. Table 2-1: Status files of the directory cache .............................................................................. File Content nr_dentry Almost always zero nr_unused Number of unused cache entries age_limit in seconds after the entry may be reclaimed, when memory is short want_pages internally .............................................................................. dquot-nr and dquot-max ---------------------- The file dquot-max shows the maximum number of cached disk quota entries. The file dquot-nr shows the number of allocated disk quota entries and the number of free disk quota entries. If the number of available cached disk quotas is very low and you have a large number of simultaneous system users, you might want to raise the limit. file-nr and file-max -------------------- The kernel allocates file handles dynamically, but doesn't free them again at this time. The value in file-max denotes the maximum number of file handles that the Linux kernel will allocate. When you get a lot of error messages about running out of file handles, you might want to raise this limit. The default value is 4096. To change it, just write the new number into the file: # cat /proc/sys/fs/file-max 4096 # echo 8192 > /proc/sys/fs/file-max # cat /proc/sys/fs/file-max 8192 This method of revision is useful for all customizable parameters of the kernel - simply echo the new value to the corresponding file. The three values in file-nr denote the number of allocated file handles, the number of used file handles, and the maximum number of file handles. When the allocated file handles come close to the maximum, but the number of actually used ones is far behind, you've encountered a peak in your usage of file handles and you don't need to increase the maximum. However, there is still a per process limit of open files, which unfortunately 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 kernel source tree. Finally, 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 numbers are nr_inodes, nr_free_inodes, and preshrink (in order of appearance). 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 preshrink is nonzero when nr_inodes is greater than 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. 2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats ----------------------------------------------------------- Besides these files, there is the subdirectory /proc/sys/fs/binfmt_misc. This handles the kernel support for miscellaneous binary formats. Binfmt_misc provides the ability to register additional binary formats to the Kernel without compiling an additional module/kernel. Therefore, binfmt_misc needs to know magic numbers at the beginning or the filename extension of the binary. It works by maintaining a linked list of structs that contain a description of a binary format, including a magic with size (or the filename extension), offset and mask, and the interpreter name. On request it invokes the given interpreter with the original program as argument, as binfmt_java and binfmt_em86 and binfmt_mz do. Since binfmt_misc does not define any default binary-formats, you have to register an additional binary-format. There are two general files in binfmt_misc and one file per registered format. The two general files are register and status. Registering a new binary format ------------------------------- To register a new binary format you have to issue the command echo :name:type:offset:magic:mask:interpreter: > /proc/sys/fs/binfmt_misc/register with appropriate name (the name for the /proc-dir entry), offset (defaults to 0, if omitted), magic, mask (which can be omitted, defaults to all 0xff) and last but not least, the interpreter that is to be invoked (for example and testing /bin/echo). Type can be M for usual magic matching or E for filename extension matching (give extension in place of magic). Check or reset the status of the binary format handler ------------------------------------------------------ If you do a cat on the file /proc/sys/fs/binfmt_misc/status, you will get the current status (enabled/disabled) of binfmt_misc. Change the status by echoing 0 (disables) or 1 (enables) or -1 (caution: this clears all previously registered binary formats) to status. For example echo 0 > status to disable binfmt_misc (temporarily). Status of a single handler -------------------------- Each registered handler has an entry in /proc/sys/fs/binfmt_misc. These files perform the same function as status, but their scope is limited to the actual binary format. By cating this file, you also receive all related information about the interpreter/magic of the binfmt. Example usage of binfmt_misc (emulate binfmt_java) -------------------------------------------------- cd /proc/sys/fs/binfmt_misc echo ':Java:M::\xca\xfe\xba\xbe::/usr/local/java/bin/javawrapper:' > register echo ':HTML:E::html::/usr/local/java/bin/appletviewer:' > register echo ':Applet:M::