----------------------------------------------------------------------- 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 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::