| ------------------------------------------------------------------------------ |
| T H E /proc F I L E S Y S T E M |
| ------------------------------------------------------------------------------ |
| /proc/sys Terrehon Bowden <terrehon@pacbell.net> October 7 1999 |
| Bodo Bauer <bb@ricochet.net> |
| |
| 2.4.x update Jorge Nerin <comandante@zaralinux.com> November 14 2000 |
| ------------------------------------------------------------------------------ |
| Version 1.3 Kernel version 2.2.12 |
| Kernel version 2.4.0-test11-pre4 |
| ------------------------------------------------------------------------------ |
| |
| Table of Contents |
| ----------------- |
| |
| 0 Preface |
| 0.1 Introduction/Credits |
| 0.2 Legal Stuff |
| |
| 1 Collecting System Information |
| 1.1 Process-Specific Subdirectories |
| 1.2 Kernel data |
| 1.3 IDE devices in /proc/ide |
| 1.4 Networking info in /proc/net |
| 1.5 SCSI info |
| 1.6 Parallel port info in /proc/parport |
| 1.7 TTY info in /proc/tty |
| 1.8 Miscellaneous kernel statistics in /proc/stat |
| |
| 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 |
| 2.11 /proc/sys/fs/mqueue - POSIX message queues filesystem |
| 2.12 /proc/<pid>/oom_adj - Adjust the oom-killer score |
| 2.13 /proc/<pid>/oom_score - Display current oom-killer score |
| 2.14 /proc/<pid>/io - Display the IO accounting fields |
| |
| ------------------------------------------------------------------------------ |
| Preface |
| ------------------------------------------------------------------------------ |
| |
| 0.1 Introduction/Credits |
| ------------------------ |
| |
| This documentation is part of a soon (or so we hope) to be released book on |
| the SuSE Linux distribution. As there is no complete documentation for the |
| /proc file system and we've used many freely available sources to write these |
| chapters, it seems only fair to give the work back to the Linux community. |
| This work is based on the 2.2.* kernel version and the upcoming 2.4.*. I'm |
| afraid it's still far from complete, but we hope it will be useful. As far as |
| we know, it is the first 'all-in-one' document about the /proc file system. It |
| is focused on the Intel x86 hardware, so if you are looking for PPC, ARM, |
| SPARC, AXP, etc., features, you probably won't find what you are looking for. |
| It also only covers IPv4 networking, not IPv6 nor other protocols - sorry. But |
| additions and patches are welcome and will be added to this document if you |
| mail them to Bodo. |
| |
| We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov and a lot of |
| other people for help compiling this documentation. We'd also like to extend a |
| special thank you to Andi Kleen for documentation, which we relied on heavily |
| to create this document, as well as the additional information he provided. |
| Thanks to everybody else who contributed source or docs to the Linux kernel |
| and helped create a great piece of software... :) |
| |
| If you have any comments, corrections or additions, please don't hesitate to |
| contact Bodo Bauer at bb@ricochet.net. We'll be happy to add them to this |
| document. |
| |
| The latest version of this document is available online at |
| http://skaro.nightcrawler.com/~bb/Docs/Proc as HTML version. |
| |
| If the above direction does not works for you, ypu could try the kernel |
| mailing list at linux-kernel@vger.kernel.org and/or try to reach me at |
| comandante@zaralinux.com. |
| |
| 0.2 Legal Stuff |
| --------------- |
| |
| We don't guarantee the correctness of this document, and if you come to us |
| complaining about how you screwed up your system because of incorrect |
| documentation, we won't feel responsible... |
| |
| ------------------------------------------------------------------------------ |
| CHAPTER 1: COLLECTING SYSTEM INFORMATION |
| ------------------------------------------------------------------------------ |
| |
| ------------------------------------------------------------------------------ |
| In This Chapter |
| ------------------------------------------------------------------------------ |
| * Investigating the properties of the pseudo file system /proc and its |
| ability to provide information on the running Linux system |
| * Examining /proc's structure |
| * Uncovering various information about the kernel and the processes running |
| on the system |
| ------------------------------------------------------------------------------ |
| |
| |
| The proc file system acts as an interface to internal data structures in the |
| kernel. It can be used to obtain information about the system and to change |
| certain kernel parameters at runtime (sysctl). |
| |
| First, we'll take a look at the read-only parts of /proc. In Chapter 2, we |
| show you how you can use /proc/sys to change settings. |
| |
| 1.1 Process-Specific Subdirectories |
| ----------------------------------- |
| |
| The directory /proc contains (among other things) one subdirectory for each |
| process running on the system, which is named after the process ID (PID). |
| |
| The link self points to the process reading the file system. Each process |
| subdirectory has the entries listed in Table 1-1. |
| |
| |
| Table 1-1: Process specific entries in /proc |
| .............................................................................. |
| File Content |
| clear_refs Clears page referenced bits shown in smaps output |
| cmdline Command line arguments |
| cpu Current and last cpu in which it was executed (2.4)(smp) |
| cwd Link to the current working directory |
| environ Values of environment variables |
| exe Link to the executable of this process |
| fd Directory, which contains all file descriptors |
| maps Memory maps to executables and library files (2.4) |
| mem Memory held by this process |
| root Link to the root directory of this process |
| stat Process status |
| statm Process memory status information |
| status Process status in human readable form |
| wchan If CONFIG_KALLSYMS is set, a pre-decoded wchan |
| smaps Extension based on maps, the rss size for each mapped file |
| .............................................................................. |
| |
| For example, to get the status information of a process, all you have to do is |
| read the file /proc/PID/status: |
| |
| >cat /proc/self/status |
| Name: cat |
| State: R (running) |
| Pid: 5452 |
| PPid: 743 |
| TracerPid: 0 (2.4) |
| Uid: 501 501 501 501 |
| Gid: 100 100 100 100 |
| Groups: 100 14 16 |
| VmSize: 1112 kB |
| VmLck: 0 kB |
| VmRSS: 348 kB |
| VmData: 24 kB |
| VmStk: 12 kB |
| VmExe: 8 kB |
| VmLib: 1044 kB |
| SigPnd: 0000000000000000 |
| SigBlk: 0000000000000000 |
| SigIgn: 0000000000000000 |
| SigCgt: 0000000000000000 |
| CapInh: 00000000fffffeff |
| CapPrm: 0000000000000000 |
| CapEff: 0000000000000000 |
| |
| |
| This shows you nearly the same information you would get if you viewed it with |
| the ps command. In fact, ps uses the proc file system to obtain its |
| information. The statm file contains more detailed information about the |
| process memory usage. Its seven fields are explained in Table 1-2. |
| |
| |
| Table 1-2: Contents of the statm files (as of 2.6.8-rc3) |
| .............................................................................. |
| Field Content |
| size total program size (pages) (same as VmSize in status) |
| resident size of memory portions (pages) (same as VmRSS in status) |
| shared number of pages that are shared (i.e. backed by a file) |
| trs number of pages that are 'code' (not including libs; broken, |
| includes data segment) |
| lrs number of pages of library (always 0 on 2.6) |
| drs number of pages of data/stack (including libs; broken, |
| includes library text) |
| dt number of dirty pages (always 0 on 2.6) |
| .............................................................................. |
| |
| 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 |
| buddyinfo Kernel memory allocator information (see text) (2.5) |
| bus Directory containing bus specific information |
| cmdline Kernel command line |
| cpuinfo Info about the CPU |
| devices Available devices (block and character) |
| dma Used DMS channels |
| filesystems Supported filesystems |
| driver Various drivers grouped here, currently rtc (2.4) |
| execdomains Execdomains, related to security (2.4) |
| fb Frame Buffer devices (2.4) |
| fs File system parameters, currently nfs/exports (2.4) |
| ide Directory containing info about the IDE subsystem |
| interrupts Interrupt usage |
| iomem Memory map (2.4) |
| ioports I/O port usage |
| irq Masks for irq to cpu affinity (2.4)(smp?) |
| isapnp ISA PnP (Plug&Play) Info (2.4) |
| kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4)) |
| kmsg Kernel messages |
| ksyms Kernel symbol table |
| loadavg Load average of last 1, 5 & 15 minutes |
| locks Kernel locks |
| meminfo Memory info |
| misc Miscellaneous |
| modules List of loaded modules |
| mounts Mounted filesystems |
| net Networking info (see text) |
| partitions Table of partitions known to the system |
| pci Depreciated info of PCI bus (new way -> /proc/bus/pci/, |
| decoupled by lspci (2.4) |
| rtc Real time clock |
| scsi SCSI info (see text) |
| slabinfo Slab pool info |
| stat Overall statistics |
| swaps Swap space utilization |
| sys See chapter 2 |
| sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4) |
| tty Info of tty drivers |
| uptime System uptime |
| version Kernel version |
| video bttv info of video resources (2.4) |
| .............................................................................. |
| |
| You can, for example, check which interrupts are currently in use and what |
| they are used for by looking in the file /proc/interrupts: |
| |
| > cat /proc/interrupts |
| CPU0 |
| 0: 8728810 XT-PIC timer |
| 1: 895 XT-PIC keyboard |
| 2: 0 XT-PIC cascade |
| 3: 531695 XT-PIC aha152x |
| 4: 2014133 XT-PIC serial |
| 5: 44401 XT-PIC pcnet_cs |
| 8: 2 XT-PIC rtc |
| 11: 8 XT-PIC i82365 |
| 12: 182918 XT-PIC PS/2 Mouse |
| 13: 1 XT-PIC fpu |
| 14: 1232265 XT-PIC ide0 |
| 15: 7 XT-PIC ide1 |
| NMI: 0 |
| |
| In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the |
| output of a SMP machine): |
| |
| > cat /proc/interrupts |
| |
| CPU0 CPU1 |
| 0: 1243498 1214548 IO-APIC-edge timer |
| 1: 8949 8958 IO-APIC-edge keyboard |
| 2: 0 0 XT-PIC cascade |
| 5: 11286 10161 IO-APIC-edge soundblaster |
| 8: 1 0 IO-APIC-edge rtc |
| 9: 27422 27407 IO-APIC-edge 3c503 |
| 12: 113645 113873 IO-APIC-edge PS/2 Mouse |
| 13: 0 0 XT-PIC fpu |
| 14: 22491 24012 IO-APIC-edge ide0 |
| 15: 2183 2415 IO-APIC-edge ide1 |
| 17: 30564 30414 IO-APIC-level eth0 |
| 18: 177 164 IO-APIC-level bttv |
| NMI: 2457961 2457959 |
| LOC: 2457882 2457881 |
| ERR: 2155 |
| |
| NMI is incremented in this case because every timer interrupt generates a NMI |
| (Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups. |
| |
| LOC is the local interrupt counter of the internal APIC of every CPU. |
| |
| ERR is incremented in the case of errors in the IO-APIC bus (the bus that |
| connects the CPUs in a SMP system. This means that an error has been detected, |
| the IO-APIC automatically retry the transmission, so it should not be a big |
| problem, but you should read the SMP-FAQ. |
| |
| In this context it could be interesting to note the new irq directory in 2.4. |
| It could be used to set IRQ to CPU affinity, this means that you can "hook" an |
| IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the |
| irq subdir is one subdir for each IRQ, and one file; prof_cpu_mask |
| |
| For example |
| > ls /proc/irq/ |
| 0 10 12 14 16 18 2 4 6 8 prof_cpu_mask |
| 1 11 13 15 17 19 3 5 7 9 |
| > ls /proc/irq/0/ |
| smp_affinity |
| |
| The contents of the prof_cpu_mask file and each smp_affinity file for each IRQ |
| is the same by default: |
| |
| > cat /proc/irq/0/smp_affinity |
| ffffffff |
| |
| It's a bitmask, in which you can specify which CPUs can handle the IRQ, you can |
| set it by doing: |
| |
| > echo 1 > /proc/irq/prof_cpu_mask |
| |
| This means that only the first CPU will handle the IRQ, but you can also echo 5 |
| which means that only the first and fourth CPU can handle the IRQ. |
| |
| The way IRQs are routed is handled by the IO-APIC, and it's Round Robin |
| between all the CPUs which are allowed to handle it. As usual the kernel has |
| more info than you and does a better job than you, so the defaults are the |
| best choice for almost everyone. |
| |
| There are three more important subdirectories in /proc: net, scsi, and sys. |
| The general rule is that the contents, or even the existence of these |
| directories, depend on your kernel configuration. If SCSI is not enabled, the |
| directory scsi may not exist. The same is true with the net, which is there |
| only when networking support is present in the running kernel. |
| |
| The slabinfo file gives information about memory usage at the slab level. |
| Linux uses slab pools for memory management above page level in version 2.2. |
| Commonly used objects have their own slab pool (such as network buffers, |
| directory cache, and so on). |
| |
| .............................................................................. |
| |
| > cat /proc/buddyinfo |
| |
| Node 0, zone DMA 0 4 5 4 4 3 ... |
| Node 0, zone Normal 1 0 0 1 101 8 ... |
| Node 0, zone HighMem 2 0 0 1 1 0 ... |
| |
| Memory fragmentation is a problem under some workloads, and buddyinfo is a |
| useful tool for helping diagnose these problems. Buddyinfo will give you a |
| clue as to how big an area you can safely allocate, or why a previous |
| allocation failed. |
| |
| Each column represents the number of pages of a certain order which are |
| available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in |
| ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE |
| available in ZONE_NORMAL, etc... |
| |
| .............................................................................. |
| |
| meminfo: |
| |
| Provides information about distribution and utilization of memory. This |
| varies by architecture and compile options. The following is from a |
| 16GB PIII, which has highmem enabled. You may not have all of these fields. |
| |
| > cat /proc/meminfo |
| |
| |
| MemTotal: 16344972 kB |
| MemFree: 13634064 kB |
| Buffers: 3656 kB |
| Cached: 1195708 kB |
| SwapCached: 0 kB |
| Active: 891636 kB |
| Inactive: 1077224 kB |
| HighTotal: 15597528 kB |
| HighFree: 13629632 kB |
| LowTotal: 747444 kB |
| LowFree: 4432 kB |
| SwapTotal: 0 kB |
| SwapFree: 0 kB |
| Dirty: 968 kB |
| Writeback: 0 kB |
| Mapped: 280372 kB |
| Slab: 684068 kB |
| CommitLimit: 7669796 kB |
| Committed_AS: 100056 kB |
| PageTables: 24448 kB |
| VmallocTotal: 112216 kB |
| VmallocUsed: 428 kB |
| VmallocChunk: 111088 kB |
| |
| MemTotal: Total usable ram (i.e. physical ram minus a few reserved |
| bits and the kernel binary code) |
| MemFree: The sum of LowFree+HighFree |
| Buffers: Relatively temporary storage for raw disk blocks |
| shouldn't get tremendously large (20MB or so) |
| Cached: in-memory cache for files read from the disk (the |
| pagecache). Doesn't include SwapCached |
| SwapCached: Memory that once was swapped out, is swapped back in but |
| still also is in the swapfile (if memory is needed it |
| doesn't need to be swapped out AGAIN because it is already |
| in the swapfile. This saves I/O) |
| Active: Memory that has been used more recently and usually not |
| reclaimed unless absolutely necessary. |
| Inactive: Memory which has been less recently used. It is more |
| eligible to be reclaimed for other purposes |
| HighTotal: |
| HighFree: Highmem is all memory above ~860MB of physical memory |
| Highmem areas are for use by userspace programs, or |
| for the pagecache. The kernel must use tricks to access |
| this memory, making it slower to access than lowmem. |
| LowTotal: |
| LowFree: Lowmem is memory which can be used for everything that |
| highmem can be used for, but it is also available for the |
| kernel's use for its own data structures. Among many |
| other things, it is where everything from the Slab is |
| allocated. Bad things happen when you're out of lowmem. |
| SwapTotal: total amount of swap space available |
| SwapFree: Memory which has been evicted from RAM, and is temporarily |
| on the disk |
| Dirty: Memory which is waiting to get written back to the disk |
| Writeback: Memory which is actively being written back to the disk |
| Mapped: files which have been mmaped, such as libraries |
| Slab: in-kernel data structures cache |
| CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'), |
| this is the total amount of memory currently available to |
| be allocated on the system. This limit is only adhered to |
| if strict overcommit accounting is enabled (mode 2 in |
| 'vm.overcommit_memory'). |
| The CommitLimit is calculated with the following formula: |
| CommitLimit = ('vm.overcommit_ratio' * Physical RAM) + Swap |
| For example, on a system with 1G of physical RAM and 7G |
| of swap with a `vm.overcommit_ratio` of 30 it would |
| yield a CommitLimit of 7.3G. |
| For more details, see the memory overcommit documentation |
| in vm/overcommit-accounting. |
| Committed_AS: The amount of memory presently allocated on the system. |
| The committed memory is a sum of all of the memory which |
| has been allocated by processes, even if it has not been |
| "used" by them as of yet. A process which malloc()'s 1G |
| of memory, but only touches 300M of it will only show up |
| as using 300M of memory even if it has the address space |
| allocated for the entire 1G. This 1G is memory which has |
| been "committed" to by the VM and can be used at any time |
| by the allocating application. With strict overcommit |
| enabled on the system (mode 2 in 'vm.overcommit_memory'), |
| allocations which would exceed the CommitLimit (detailed |
| above) will not be permitted. This is useful if one needs |
| to guarantee that processes will not fail due to lack of |
| memory once that memory has been successfully allocated. |
| PageTables: amount of memory dedicated to the lowest level of page |
| tables. |
| VmallocTotal: total size of vmalloc memory area |
| VmallocUsed: amount of vmalloc area which is used |
| VmallocChunk: largest contigious block of vmalloc area which is free |
| |
| |
| 1.3 IDE devices in /proc/ide |
| ---------------------------- |
| |
| The subdirectory /proc/ide contains information about all IDE devices of which |
| the kernel is aware. There is one subdirectory for each IDE controller, the |
| file drivers and a link for each IDE device, pointing to the device directory |
| in the controller specific subtree. |
| |
| The file drivers contains general information about the drivers used for the |
| IDE devices: |
| |
| > cat /proc/ide/drivers |
| ide-cdrom version 4.53 |
| ide-disk version 1.08 |
| |
| More detailed information can be found in the controller specific |
| subdirectories. These are named ide0, ide1 and so on. Each of these |
| directories contains the files shown in table 1-4. |
| |
| |
| Table 1-4: IDE controller info in /proc/ide/ide? |
| .............................................................................. |
| File Content |
| channel IDE channel (0 or 1) |
| config Configuration (only for PCI/IDE bridge) |
| mate Mate name |
| model Type/Chipset of IDE controller |
| .............................................................................. |
| |
| Each device connected to a controller has a separate subdirectory in the |
| controllers directory. The files listed in table 1-5 are contained in these |
| directories. |
| |
| |
| Table 1-5: IDE device information |
| .............................................................................. |
| File Content |
| cache The cache |
| capacity Capacity of the medium (in 512Byte blocks) |
| driver driver and version |
| geometry physical and logical geometry |
| identify device identify block |
| media media type |
| model device identifier |
| settings device setup |
| smart_thresholds IDE disk management thresholds |
| smart_values IDE disk management values |
| .............................................................................. |
| |
| The most interesting file is settings. This file contains a nice overview of |
| the drive parameters: |
| |
| # cat /proc/ide/ide0/hda/settings |
| name value min max mode |
| ---- ----- --- --- ---- |
| bios_cyl 526 0 65535 rw |
| bios_head 255 0 255 rw |
| bios_sect 63 0 63 rw |
| breada_readahead 4 0 127 rw |
| bswap 0 0 1 r |
| file_readahead 72 0 2097151 rw |
| io_32bit 0 0 3 rw |
| keepsettings 0 0 1 rw |
| max_kb_per_request 122 1 127 rw |
| multcount 0 0 8 rw |
| nice1 1 0 1 rw |
| nowerr 0 0 1 rw |
| pio_mode write-only 0 255 w |
| slow 0 0 1 rw |
| unmaskirq 0 0 1 rw |
| using_dma 0 0 1 rw |
| |
| |
| 1.4 Networking info in /proc/net |
| -------------------------------- |
| |
| The subdirectory /proc/net follows the usual pattern. Table 1-6 shows the |
| additional values you get for IP version 6 if you configure the kernel to |
| support this. Table 1-7 lists the files and their meaning. |
| |
| |
| Table 1-6: IPv6 info in /proc/net |
| .............................................................................. |
| File Content |
| udp6 UDP sockets (IPv6) |
| tcp6 TCP sockets (IPv6) |
| raw6 Raw device statistics (IPv6) |
| igmp6 IP multicast addresses, which this host joined (IPv6) |
| if_inet6 List of IPv6 interface addresses |
| ipv6_route Kernel routing table for IPv6 |
| rt6_stats Global IPv6 routing tables statistics |
| sockstat6 Socket statistics (IPv6) |
| snmp6 Snmp data (IPv6) |
| .............................................................................. |
| |
| |
| Table 1-7: Network info in /proc/net |
| .............................................................................. |
| File Content |
| arp Kernel ARP table |
| dev network devices with statistics |
| dev_mcast the Layer2 multicast groups a device is listening too |
| (interface index, label, number of references, number of bound |
| addresses). |
| dev_stat network device status |
| ip_fwchains Firewall chain linkage |
| ip_fwnames Firewall chain names |
| ip_masq Directory containing the masquerading tables |
| ip_masquerade Major masquerading table |
| netstat Network statistics |
| raw raw device statistics |
| route Kernel routing table |
| rpc Directory containing rpc info |
| rt_cache Routing cache |
| snmp SNMP data |
| sockstat Socket statistics |
| tcp TCP sockets |
| tr_rif Token ring RIF routing table |
| udp UDP sockets |
| unix UNIX domain sockets |
| wireless Wireless interface data (Wavelan etc) |
| igmp IP multicast addresses, which this host joined |
| psched Global packet scheduler parameters. |
| netlink List of PF_NETLINK sockets |
| ip_mr_vifs List of multicast virtual interfaces |
| ip_mr_cache List of multicast routing cache |
| .............................................................................. |
| |
| You can use this information to see which network devices are available in |
| your system and how much traffic was routed over those devices: |
| |
| > cat /proc/net/dev |
| Inter-|Receive |[... |
| face |bytes packets errs drop fifo frame compressed multicast|[... |
| lo: 908188 5596 0 0 0 0 0 0 [... |
| ppp0:15475140 20721 410 0 0 410 0 0 [... |
| eth0: 614530 7085 0 0 0 0 0 1 [... |
| |
| ...] Transmit |
| ...] bytes packets errs drop fifo colls carrier compressed |
| ...] 908188 5596 0 0 0 0 0 0 |
| ...] 1375103 17405 0 0 0 0 0 0 |
| ...] 1703981 5535 0 0 0 3 0 0 |
| |
| In addition, each Channel Bond interface has it's own directory. For |
| example, the bond0 device will have a directory called /proc/net/bond0/. |
| It will contain information that is specific to that bond, such as the |
| current slaves of the bond, the link status of the slaves, and how |
| many times the slaves link has failed. |
| |
| 1.5 SCSI info |
| ------------- |
| |
| If you have a SCSI host adapter in your system, you'll find a subdirectory |
| named after the driver for this adapter in /proc/scsi. You'll also see a list |
| of all recognized SCSI devices in /proc/scsi: |
| |
| >cat /proc/scsi/scsi |
| Attached devices: |
| Host: scsi0 Channel: 00 Id: 00 Lun: 00 |
| Vendor: IBM Model: DGHS09U Rev: 03E0 |
| Type: Direct-Access ANSI SCSI revision: 03 |
| Host: scsi0 Channel: 00 Id: 06 Lun: 00 |
| Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04 |
| Type: CD-ROM ANSI SCSI revision: 02 |
| |
| |
| The directory named after the driver has one file for each adapter found in |
| the system. These files contain information about the controller, including |
| the used IRQ and the IO address range. The amount of information shown is |
| dependent on the adapter you use. The example shows the output for an Adaptec |
| AHA-2940 SCSI adapter: |
| |
| > cat /proc/scsi/aic7xxx/0 |
| |
| Adaptec AIC7xxx driver version: 5.1.19/3.2.4 |
| Compile Options: |
| TCQ Enabled By Default : Disabled |
| AIC7XXX_PROC_STATS : Disabled |
| AIC7XXX_RESET_DELAY : 5 |
| Adapter Configuration: |
| SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter |
| Ultra Wide Controller |
| PCI MMAPed I/O Base: 0xeb001000 |
| Adapter SEEPROM Config: SEEPROM found and used. |
| Adaptec SCSI BIOS: Enabled |
| IRQ: 10 |
| SCBs: Active 0, Max Active 2, |
| Allocated 15, HW 16, Page 255 |
| Interrupts: 160328 |
| BIOS Control Word: 0x18b6 |
| Adapter Control Word: 0x005b |
| Extended Translation: Enabled |
| Disconnect Enable Flags: 0xffff |
| Ultra Enable Flags: 0x0001 |
| Tag Queue Enable Flags: 0x0000 |
| Ordered Queue Tag Flags: 0x0000 |
| Default Tag Queue Depth: 8 |
| Tagged Queue By Device array for aic7xxx host instance 0: |
| {255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255} |
| Actual queue depth per device for aic7xxx host instance 0: |
| {1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1} |
| Statistics: |
| (scsi0:0:0:0) |
| Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8 |
| Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0) |
| Total transfers 160151 (74577 reads and 85574 writes) |
| (scsi0:0:6:0) |
| Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15 |
| Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0) |
| Total transfers 0 (0 reads and 0 writes) |
| |
| |
| 1.6 Parallel port info in /proc/parport |
| --------------------------------------- |
| |
| The directory /proc/parport contains information about the parallel ports of |
| your system. It has one subdirectory for each port, named after the port |
| number (0,1,2,...). |
| |
| These directories contain the four files shown in Table 1-8. |
| |
| |
| Table 1-8: Files in /proc/parport |
| .............................................................................. |
| File Content |
| autoprobe Any IEEE-1284 device ID information that has been acquired. |
| devices list of the device drivers using that port. A + will appear by the |
| name of the device currently using the port (it might not appear |
| against any). |
| hardware Parallel port's base address, IRQ line and DMA channel. |
| irq IRQ that parport is using for that port. This is in a separate |
| file to allow you to alter it by writing a new value in (IRQ |
| number or none). |
| .............................................................................. |
| |
| 1.7 TTY info in /proc/tty |
| ------------------------- |
| |
| Information about the available and actually used tty's can be found in the |
| directory /proc/tty.You'll find entries for drivers and line disciplines in |
| this directory, as shown in Table 1-9. |
| |
| |
| Table 1-9: Files in /proc/tty |
| .............................................................................. |
| File Content |
| drivers list of drivers and their usage |
| ldiscs registered line disciplines |
| driver/serial usage statistic and status of single tty lines |
| .............................................................................. |
| |
| To see which tty's are currently in use, you can simply look into the file |
| /proc/tty/drivers: |
| |
| > cat /proc/tty/drivers |
| pty_slave /dev/pts 136 0-255 pty:slave |
| pty_master /dev/ptm 128 0-255 pty:master |
| pty_slave /dev/ttyp 3 0-255 pty:slave |
| pty_master /dev/pty 2 0-255 pty:master |
| serial /dev/cua 5 64-67 serial:callout |
| serial /dev/ttyS 4 64-67 serial |
| /dev/tty0 /dev/tty0 4 0 system:vtmaster |
| /dev/ptmx /dev/ptmx 5 2 system |
| /dev/console /dev/console 5 1 system:console |
| /dev/tty /dev/tty 5 0 system:/dev/tty |
| unknown /dev/tty 4 1-63 console |
| |
| |
| 1.8 Miscellaneous kernel statistics in /proc/stat |
| ------------------------------------------------- |
| |
| Various pieces of information about kernel activity are available in the |
| /proc/stat file. All of the numbers reported in this file are aggregates |
| since the system first booted. For a quick look, simply cat the file: |
| |
| > cat /proc/stat |
| cpu 2255 34 2290 22625563 6290 127 456 |
| cpu0 1132 34 1441 11311718 3675 127 438 |
| cpu1 1123 0 849 11313845 2614 0 18 |
| intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...] |
| ctxt 1990473 |
| btime 1062191376 |
| processes 2915 |
| procs_running 1 |
| procs_blocked 0 |
| |
| The very first "cpu" line aggregates the numbers in all of the other "cpuN" |
| lines. These numbers identify the amount of time the CPU has spent performing |
| different kinds of work. Time units are in USER_HZ (typically hundredths of a |
| second). The meanings of the columns are as follows, from left to right: |
| |
| - user: normal processes executing in user mode |
| - nice: niced processes executing in user mode |
| - system: processes executing in kernel mode |
| - idle: twiddling thumbs |
| - iowait: waiting for I/O to complete |
| - irq: servicing interrupts |
| - softirq: servicing softirqs |
| |
| The "intr" line gives counts of interrupts serviced since boot time, for each |
| of the possible system interrupts. The first column is the total of all |
| interrupts serviced; each subsequent column is the total for that particular |
| interrupt. |
| |
| The "ctxt" line gives the total number of context switches across all CPUs. |
| |
| The "btime" line gives the time at which the system booted, in seconds since |
| the Unix epoch. |
| |
| The "processes" line gives the number of processes and threads created, which |
| includes (but is not limited to) those created by calls to the fork() and |
| clone() system calls. |
| |
| The "procs_running" line gives the number of processes currently running on |
| CPUs. |
| |
| The "procs_blocked" line gives the number of processes currently blocked, |
| waiting for I/O to complete. |
| |
| |
| ------------------------------------------------------------------------------ |
| 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 |
| 10% of RAM in kilobytes. 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. |
| |
| Historically, the three values in file-nr denoted the number of allocated file |
| handles, the number of allocated but unused file handles, and the maximum |
| number of file handles. Linux 2.6 always reports 0 as the number of free file |
| handles -- this is not an error, it just means that the number of allocated |
| file handles exactly matches the number of used file handles. |
| |
| Attempts to allocate more file descriptors than file-max are reported with |
| printk, look for "VFS: file-max limit <number> reached". |
| |
| inode-state and inode-nr |
| ------------------------ |
| |
| The file inode-nr contains the first two items from inode-state, so we'll skip |
| to that file... |
| |
| inode-state contains two actual numbers and five dummy values. The numbers |
| are nr_inodes and nr_free_inodes (in order of appearance). |
| |
| nr_inodes |
| ~~~~~~~~~ |
| |
| Denotes the number of inodes the system has allocated. This number will |
| grow and shrink dynamically. |
| |
| nr_free_inodes |
| -------------- |
| |
| Represents the number of free inodes. Ie. The number of inuse inodes is |
| (nr_inodes - nr_free_inodes). |
| |
| aio-nr and aio-max-nr |
| --------------------- |
| |
| aio-nr is the running total of the number of events specified on the |
| io_setup system call for all currently active aio contexts. If aio-nr |
| reaches aio-max-nr then io_setup will fail with EAGAIN. Note that |
| raising aio-max-nr does not result in the pre-allocation or re-sizing |
| of any kernel data structures. |
| |
| 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::<!--applet::/usr/local/java/bin/appletviewer:' > register |
| echo ':DEXE:M::\x0eDEX::/usr/bin/dosexec:' > register |
| |
| |
| These four lines add support for Java executables and Java applets (like |
| binfmt_java, additionally recognizing the .html extension with no need to put |
| <!--applet> to every applet file). You have to install the JDK and the |
| shell-script /usr/local/java/bin/javawrapper too. It works around the |
| brokenness of the Java filename handling. To add a Java binary, just create a |
| link to the class-file somewhere in the path. |
| |
| 2.3 /proc/sys/kernel - general kernel parameters |
| ------------------------------------------------ |
| |
| This directory reflects general kernel behaviors. As I've said before, the |
| contents depend on your configuration. Here you'll find the most important |
| files, along with descriptions of what they mean and how to use them. |
| |
| acct |
| ---- |
| |
| The file contains three values; highwater, lowwater, and frequency. |
| |
| It exists only when BSD-style process accounting is enabled. These values |
| control its behavior. If the free space on the file system where the log lives |
| goes below lowwater percentage, accounting suspends. If it goes above |
| highwater percentage, accounting resumes. Frequency determines how often you |
| check the amount of free space (value is in seconds). Default settings are: 4, |
| 2, and 30. That is, suspend accounting if there is less than 2 percent free; |
| resume it if we have a value of 3 or more percent; consider information about |
| the amount of free space valid for 30 seconds |
| |
| ctrl-alt-del |
| ------------ |
| |
| When the value in this file is 0, ctrl-alt-del is trapped and sent to the init |
| program to handle a graceful restart. However, when the value is greater that |
| zero, Linux's reaction to this key combination will be an immediate reboot, |
| without syncing its dirty buffers. |
| |
| [NOTE] |
| When a program (like dosemu) has the keyboard in raw mode, the |
| ctrl-alt-del is intercepted by the program before it ever reaches the |
| kernel tty layer, and it is up to the program to decide what to do with |
| it. |
| |
| domainname and hostname |
| ----------------------- |
| |
| These files can be controlled to set the NIS domainname and hostname of your |
| box. For the classic darkstar.frop.org a simple: |
| |
| # echo "darkstar" > /proc/sys/kernel/hostname |
| # echo "frop.org" > /proc/sys/kernel/domainname |
| |
| |
| would suffice to set your hostname and NIS domainname. |
| |
| osrelease, ostype and version |
| ----------------------------- |
| |
| The names make it pretty obvious what these fields contain: |
| |
| > cat /proc/sys/kernel/osrelease |
| 2.2.12 |
| |
| > cat /proc/sys/kernel/ostype |
| Linux |
| |
| > cat /proc/sys/kernel/version |
| #4 Fri Oct 1 12:41:14 PDT 1999 |
| |
| |
| The files osrelease and ostype should be clear enough. Version needs a little |
| more clarification. The #4 means that this is the 4th kernel built from this |
| source base and the date after it indicates the time the kernel was built. The |
| only way to tune these values is to rebuild the kernel. |
| |
| panic |
| ----- |
| |
| The value in this file represents the number of seconds the kernel waits |
| before rebooting on a panic. When you use the software watchdog, the |
| recommended setting is 60. If set to 0, the auto reboot after a kernel panic |
| is disabled, which is the default setting. |
| |
| printk |
| ------ |
| |
| The four values in printk denote |
| * console_loglevel, |
| * default_message_loglevel, |
| * minimum_console_loglevel and |
| * default_console_loglevel |
| respectively. |
| |
| These values influence printk() behavior when printing or logging error |
| messages, which come from inside the kernel. See syslog(2) for more |
| information on the different log levels. |
| |
| console_loglevel |
| ---------------- |
| |
| Messages with a higher priority than this will be printed to the console. |
| |
| default_message_level |
| --------------------- |
| |
| Messages without an explicit priority will be printed with this priority. |
| |
| minimum_console_loglevel |
| ------------------------ |
| |
| Minimum (highest) value to which the console_loglevel can be set. |
| |
| default_console_loglevel |
| ------------------------ |
| |
| Default value for console_loglevel. |
| |
| sg-big-buff |
| ----------- |
| |
| This file shows the size of the generic SCSI (sg) buffer. At this point, you |
| can't tune it yet, but you can change it at compile time by editing |
| include/scsi/sg.h and changing the value of SG_BIG_BUFF. |
| |
| If you use a scanner with SANE (Scanner Access Now Easy) you might want to set |
| this to a higher value. Refer to the SANE documentation on this issue. |
| |
| modprobe |
| -------- |
| |
| The location where the modprobe binary is located. The kernel uses this |
| program to load modules on demand. |
| |
| unknown_nmi_panic |
| ----------------- |
| |
| The value in this file affects behavior of handling NMI. When the value is |
| non-zero, unknown NMI is trapped and then panic occurs. At that time, kernel |
| debugging information is displayed on console. |
| |
| NMI switch that most IA32 servers have fires unknown NMI up, for example. |
| If a system hangs up, try pressing the NMI switch. |
| |
| nmi_watchdog |
| ------------ |
| |
| Enables/Disables the NMI watchdog on x86 systems. When the value is non-zero |
| the NMI watchdog is enabled and will continuously test all online cpus to |
| determine whether or not they are still functioning properly. |
| |
| Because the NMI watchdog shares registers with oprofile, by disabling the NMI |
| watchdog, oprofile may have more registers to utilize. |
| |
| |
| 2.4 /proc/sys/vm - The virtual memory subsystem |
| ----------------------------------------------- |
| |
| The files in this directory can be used to tune the operation of the virtual |
| memory (VM) subsystem of the Linux kernel. |
| |
| vfs_cache_pressure |
| ------------------ |
| |
| Controls the tendency of the kernel to reclaim the memory which is used for |
| caching of directory and inode objects. |
| |
| At the default value of vfs_cache_pressure=100 the kernel will attempt to |
| reclaim dentries and inodes at a "fair" rate with respect to pagecache and |
| swapcache reclaim. Decreasing vfs_cache_pressure causes the kernel to prefer |
| to retain dentry and inode caches. Increasing vfs_cache_pressure beyond 100 |
| causes the kernel to prefer to reclaim dentries and inodes. |
| |
| dirty_background_ratio |
| ---------------------- |
| |
| Contains, as a percentage of total system memory, the number of pages at which |
| the pdflush background writeback daemon will start writing out dirty data. |
| |
| dirty_ratio |
| ----------------- |
| |
| Contains, as a percentage of total system memory, the number of pages at which |
| a process which is generating disk writes will itself start writing out dirty |
| data. |
| |
| dirty_writeback_centisecs |
| ------------------------- |
| |
| The pdflush writeback daemons will periodically wake up and write `old' data |
| out to disk. This tunable expresses the interval between those wakeups, in |
| 100'ths of a second. |
| |
| Setting this to zero disables periodic writeback altogether. |
| |
| dirty_expire_centisecs |
| ---------------------- |
| |
| This tunable is used to define when dirty data is old enough to be eligible |
| for writeout by the pdflush daemons. It is expressed in 100'ths of a second. |
| Data which has been dirty in-memory for longer than this interval will be |
| written out next time a pdflush daemon wakes up. |
| |
| legacy_va_layout |
| ---------------- |
| |
| If non-zero, this sysctl disables the new 32-bit mmap mmap layout - the kernel |
| will use the legacy (2.4) layout for all processes. |
| |
| lower_zone_protection |
| --------------------- |
| |
| For some specialised workloads on highmem machines it is dangerous for |
| the kernel to allow process memory to be allocated from the "lowmem" |
| zone. This is because that memory could then be pinned via the mlock() |
| system call, or by unavailability of swapspace. |
| |
| And on large highmem machines this lack of reclaimable lowmem memory |
| can be fatal. |
| |
| So the Linux page allocator has a mechanism which prevents allocations |
| which _could_ use highmem from using too much lowmem. This means that |
| a certain amount of lowmem is defended from the possibility of being |
| captured into pinned user memory. |
| |
| (The same argument applies to the old 16 megabyte ISA DMA region. This |
| mechanism will also defend that region from allocations which could use |
| highmem or lowmem). |
| |
| The `lower_zone_protection' tunable determines how aggressive the kernel is |
| in defending these lower zones. The default value is zero - no |
| protection at all. |
| |
| If you have a machine which uses highmem or ISA DMA and your |
| applications are using mlock(), or if you are running with no swap then |
| you probably should increase the lower_zone_protection setting. |
| |
| The units of this tunable are fairly vague. It is approximately equal |
| to "megabytes," so setting lower_zone_protection=100 will protect around 100 |
| megabytes of the lowmem zone from user allocations. It will also make |
| those 100 megabytes unavailable for use by applications and by |
| pagecache, so there is a cost. |
| |
| The effects of this tunable may be observed by monitoring |
| /proc/meminfo:LowFree. Write a single huge file and observe the point |
| at which LowFree ceases to fall. |
| |
| A reasonable value for lower_zone_protection is 100. |
| |
| page-cluster |
| ------------ |
| |
| page-cluster controls the number of pages which are written to swap in |
| a single attempt. The swap I/O size. |
| |
| It is a logarithmic value - setting it to zero means "1 page", setting |
| it to 1 means "2 pages", setting it to 2 means "4 pages", etc. |
| |
| The default value is three (eight pages at a time). There may be some |
| small benefits in tuning this to a different value if your workload is |
| swap-intensive. |
| |
| overcommit_memory |
| ----------------- |
| |
| Controls overcommit of system memory, possibly allowing processes |
| to allocate (but not use) more memory than is actually available. |
| |
| |
| 0 - Heuristic overcommit handling. Obvious overcommits of |
| address space are refused. Used for a typical system. It |
| ensures a seriously wild allocation fails while allowing |
| overcommit to reduce swap usage. root is allowed to |
| allocate slightly more memory in this mode. This is the |
| default. |
| |
| 1 - Always overcommit. Appropriate for some scientific |
| applications. |
| |
| 2 - Don't overcommit. The total address space commit |
| for the system is not permitted to exceed swap plus a |
| configurable percentage (default is 50) of physical RAM. |
| Depending on the percentage you use, in most situations |
| this means a process will not be killed while attempting |
| to use already-allocated memory but will receive errors |
| on memory allocation as appropriate. |
| |
| overcommit_ratio |
| ---------------- |
| |
| Percentage of physical memory size to include in overcommit calculations |
| (see above.) |
| |
| Memory allocation limit = swapspace + physmem * (overcommit_ratio / 100) |
| |
| swapspace = total size of all swap areas |
| physmem = size of physical memory in system |
| |
| nr_hugepages and hugetlb_shm_group |
| ---------------------------------- |
| |
| nr_hugepages configures number of hugetlb page reserved for the system. |
| |
| hugetlb_shm_group contains group id that is allowed to create SysV shared |
| memory segment using hugetlb page. |
| |
| laptop_mode |
| ----------- |
| |
| laptop_mode is a knob that controls "laptop mode". All the things that are |
| controlled by this knob are discussed in Documentation/laptop-mode.txt. |
| |
| block_dump |
| ---------- |
| |
| block_dump enables block I/O debugging when set to a nonzero value. More |
| information on block I/O debugging is in Documentation/laptop-mode.txt. |
| |
| swap_token_timeout |
| ------------------ |
| |
| This file contains valid hold time of swap out protection token. The Linux |
| VM has token based thrashing control mechanism and uses the token to prevent |
| unnecessary page faults in thrashing situation. The unit of the value is |
| second. The value would be useful to tune thrashing behavior. |
| |
| drop_caches |
| ----------- |
| |
| Writing to this will cause the kernel to drop clean caches, dentries and |
| inodes from memory, causing that memory to become free. |
| |
| To free pagecache: |
| echo 1 > /proc/sys/vm/drop_caches |
| To free dentries and inodes: |
| echo 2 > /proc/sys/vm/drop_caches |
| To free pagecache, dentries and inodes: |
| echo 3 > /proc/sys/vm/drop_caches |
| |
| As this is a non-destructive operation and dirty objects are not freeable, the |
| user should run `sync' first. |
| |
| |
| 2.5 /proc/sys/dev - Device specific parameters |
| ---------------------------------------------- |
| |
| Currently there is only support for CDROM drives, and for those, there is only |
| one read-only file containing information about the CD-ROM drives attached to |
| the system: |
| |
| >cat /proc/sys/dev/cdrom/info |
| CD-ROM information, Id: cdrom.c 2.55 1999/04/25 |
| |
| drive name: sr0 hdb |
| drive speed: 32 40 |
| drive # of slots: 1 0 |
| Can close tray: 1 1 |
| Can open tray: 1 1 |
| Can lock tray: 1 1 |
| Can change speed: 1 1 |
| Can select disk: 0 1 |
| Can read multisession: 1 1 |
| Can read MCN: 1 1 |
| Reports media changed: 1 1 |
| Can play audio: 1 1 |
| |
| |
| You see two drives, sr0 and hdb, along with a list of their features. |
| |
| 2.6 /proc/sys/sunrpc - Remote procedure calls |
| --------------------------------------------- |
| |
| This directory contains four files, which enable or disable debugging for the |
| RPC functions NFS, NFS-daemon, RPC and NLM. The default values are 0. They can |
| be set to one to turn debugging on. (The default value is 0 for each) |
| |
| 2.7 /proc/sys/net - Networking stuff |
| ------------------------------------ |
| |
| The interface to the networking parts of the kernel is located in |
| /proc/sys/net. Table 2-3 shows all possible subdirectories. You may see only |
| some of them, depending on your kernel's configuration. |
| |
| |
| Table 2-3: Subdirectories in /proc/sys/net |
| .............................................................................. |
| Directory Content Directory Content |
| core General parameter appletalk Appletalk protocol |
| unix Unix domain sockets netrom NET/ROM |
| 802 E802 protocol ax25 AX25 |
| ethernet Ethernet protocol rose X.25 PLP layer |
| ipv4 IP version 4 x25 X.25 protocol |
| ipx IPX token-ring IBM token ring |
| bridge Bridging decnet DEC net |
| ipv6 IP version 6 |
| .............................................................................. |
| |
| We will concentrate on IP networking here. Since AX15, X.25, and DEC Net are |
| only minor players in the Linux world, we'll skip them in this chapter. You'll |
| find some short info on Appletalk and IPX further on in this chapter. Review |
| the online documentation and the kernel source to get a detailed view of the |
| parameters for those protocols. In this section we'll discuss the |
| subdirectories printed in bold letters in the table above. As default values |
| are suitable for most needs, there is no need to change these values. |
| |
| /proc/sys/net/core - Network core options |
| ----------------------------------------- |
| |
| rmem_default |
| ------------ |
| |
| The default setting of the socket receive buffer in bytes. |
| |
| rmem_max |
| -------- |
| |
| The maximum receive socket buffer size in bytes. |
| |
| wmem_default |
| ------------ |
| |
| The default setting (in bytes) of the socket send buffer. |
| |
| wmem_max |
| -------- |
| |
| The maximum send socket buffer size in bytes. |
| |
| message_burst and message_cost |
| ------------------------------ |
| |
| These parameters are used to limit the warning messages written to the kernel |
| log from the networking code. They enforce a rate limit to make a |
| denial-of-service attack impossible. A higher message_cost factor, results in |
| fewer messages that will be written. Message_burst controls when messages will |
| be dropped. The default settings limit warning messages to one every five |
| seconds. |
| |
| warnings |
| -------- |
| |
| This controls console messages from the networking stack that can occur because |
| of problems on the network like duplicate address or bad checksums. Normally, |
| this should be enabled, but if the problem persists the messages can be |
| disabled. |
| |
| |
| netdev_max_backlog |
| ------------------ |
| |
| Maximum number of packets, queued on the INPUT side, when the interface |
| receives packets faster than kernel can process them. |
| |
| optmem_max |
| ---------- |
| |
| Maximum ancillary buffer size allowed per socket. Ancillary data is a sequence |
| of struct cmsghdr structures with appended data. |
| |
| /proc/sys/net/unix - Parameters for Unix domain sockets |
| ------------------------------------------------------- |
| |
| There are only two files in this subdirectory. They control the delays for |
| deleting and destroying socket descriptors. |
| |
| 2.8 /proc/sys/net/ipv4 - IPV4 settings |
| -------------------------------------- |
| |
| IP version 4 is still the most used protocol in Unix networking. It will be |
| replaced by IP version 6 in the next couple of years, but for the moment it's |
| the de facto standard for the internet and is used in most networking |
| environments around the world. Because of the importance of this protocol, |
| we'll have a deeper look into the subtree controlling the behavior of the IPv4 |
| subsystem of the Linux kernel. |
| |
| Let's start with the entries in /proc/sys/net/ipv4. |
| |
| ICMP settings |
| ------------- |
| |
| icmp_echo_ignore_all and icmp_echo_ignore_broadcasts |
| ---------------------------------------------------- |
| |
| Turn on (1) or off (0), if the kernel should ignore all ICMP ECHO requests, or |
| just those to broadcast and multicast addresses. |
| |
| Please note that if you accept ICMP echo requests with a broadcast/multi\-cast |
| destination address your network may be used as an exploder for denial of |
| service packet flooding attacks to other hosts. |
| |
| icmp_destunreach_rate, icmp_echoreply_rate, icmp_paramprob_rate and icmp_timeexeed_rate |
| --------------------------------------------------------------------------------------- |
| |
| Sets limits for sending ICMP packets to specific targets. A value of zero |
| disables all limiting. Any positive value sets the maximum package rate in |
| hundredth of a second (on Intel systems). |
| |
| IP settings |
| ----------- |
| |
| ip_autoconfig |
| ------------- |
| |
| This file contains the number one if the host received its IP configuration by |
| RARP, BOOTP, DHCP or a similar mechanism. Otherwise it is zero. |
| |
| ip_default_ttl |
| -------------- |
| |
| TTL (Time To Live) for IPv4 interfaces. This is simply the maximum number of |
| hops a packet may travel. |
| |
| ip_dynaddr |
| ---------- |
| |
| Enable dynamic socket address rewriting on interface address change. This is |
| useful for dialup interface with changing IP addresses. |
| |
| ip_forward |
| ---------- |
| |
| Enable or disable forwarding of IP packages between interfaces. Changing this |
| value resets all other parameters to their default values. They differ if the |
| kernel is configured as host or router. |
| |
| ip_local_port_range |
| ------------------- |
| |
| Range of ports used by TCP and UDP to choose the local port. Contains two |
| numbers, the first number is the lowest port, the second number the highest |
| local port. Default is 1024-4999. Should be changed to 32768-61000 for |
| high-usage systems. |
| |
| ip_no_pmtu_disc |
| --------------- |
| |
| Global switch to turn path MTU discovery off. It can also be set on a per |
| socket basis by the applications or on a per route basis. |
| |
| ip_masq_debug |
| ------------- |
| |
| Enable/disable debugging of IP masquerading. |
| |
| IP fragmentation settings |
| ------------------------- |
| |
| ipfrag_high_trash and ipfrag_low_trash |
| -------------------------------------- |
| |
| Maximum memory used to reassemble IP fragments. When ipfrag_high_thresh bytes |
| of memory is allocated for this purpose, the fragment handler will toss |
| packets until ipfrag_low_thresh is reached. |
| |
| ipfrag_time |
| ----------- |
| |
| Time in seconds to keep an IP fragment in memory. |
| |
| TCP settings |
| ------------ |
| |
| tcp_ecn |
| ------- |
| |
| This file controls the use of the ECN bit in the IPv4 headers. This is a new |
| feature about Explicit Congestion Notification, but some routers and firewalls |
| block traffic that has this bit set, so it could be necessary to echo 0 to |
| /proc/sys/net/ipv4/tcp_ecn if you want to talk to these sites. For more info |
| you could read RFC2481. |
| |
| tcp_retrans_collapse |
| -------------------- |
| |
| Bug-to-bug compatibility with some broken printers. On retransmit, try to send |
| larger packets to work around bugs in certain TCP stacks. Can be turned off by |
| setting it to zero. |
| |
| tcp_keepalive_probes |
| -------------------- |
| |
| Number of keep alive probes TCP sends out, until it decides that the |
| connection is broken. |
| |
| tcp_keepalive_time |
| ------------------ |
| |
| How often TCP sends out keep alive messages, when keep alive is enabled. The |
| default is 2 hours. |
| |
| tcp_syn_retries |
| --------------- |
| |
| Number of times initial SYNs for a TCP connection attempt will be |
| retransmitted. Should not be higher than 255. This is only the timeout for |
| outgoing connections, for incoming connections the number of retransmits is |
| defined by tcp_retries1. |
| |
| tcp_sack |
| -------- |
| |
| Enable select acknowledgments after RFC2018. |
| |
| tcp_timestamps |
| -------------- |
| |
| Enable timestamps as defined in RFC1323. |
| |
| tcp_stdurg |
| ---------- |
| |
| Enable the strict RFC793 interpretation of the TCP urgent pointer field. The |
| default is to use the BSD compatible interpretation of the urgent pointer |
| pointing to the first byte after the urgent data. The RFC793 interpretation is |
| to have it point to the last byte of urgent data. Enabling this option may |
| lead to interoperability problems. Disabled by default. |
| |
| tcp_syncookies |
| -------------- |
| |
| Only valid when the kernel was compiled with CONFIG_SYNCOOKIES. Send out |
| syncookies when the syn backlog queue of a socket overflows. This is to ward |
| off the common 'syn flood attack'. Disabled by default. |
| |
| Note that the concept of a socket backlog is abandoned. This means the peer |
| may not receive reliable error messages from an over loaded server with |
| syncookies enabled. |
| |
| tcp_window_scaling |
| ------------------ |
| |
| Enable window scaling as defined in RFC1323. |
| |
| tcp_fin_timeout |
| --------------- |
| |
| The length of time in seconds it takes to receive a final FIN before the |
| socket is always closed. This is strictly a violation of the TCP |
| specification, but required to prevent denial-of-service attacks. |
| |
| tcp_max_ka_probes |
| ----------------- |
| |
| Indicates how many keep alive probes are sent per slow timer run. Should not |
| be set too high to prevent bursts. |
| |
| tcp_max_syn_backlog |
| ------------------- |
| |
| Length of the per socket backlog queue. Since Linux 2.2 the backlog specified |
| in listen(2) only specifies the length of the backlog queue of already |
| established sockets. When more connection requests arrive Linux starts to drop |
| packets. When syncookies are enabled the packets are still answered and the |
| maximum queue is effectively ignored. |
| |
| tcp_retries1 |
| ------------ |
| |
| Defines how often an answer to a TCP connection request is retransmitted |
| before giving up. |
| |
| tcp_retries2 |
| ------------ |
| |
| Defines how often a TCP packet is retransmitted before giving up. |
| |
| Interface specific settings |
| --------------------------- |
| |
| In the directory /proc/sys/net/ipv4/conf you'll find one subdirectory for each |
| interface the system knows about and one directory calls all. Changes in the |
| all subdirectory affect all interfaces, whereas changes in the other |
| subdirectories affect only one interface. All directories have the same |
| entries: |
| |
| accept_redirects |
| ---------------- |
| |
| This switch decides if the kernel accepts ICMP redirect messages or not. The |
| default is 'yes' if the kernel is configured for a regular host and 'no' for a |
| router configuration. |
| |
| accept_source_route |
| ------------------- |
| |
| Should source routed packages be accepted or declined. The default is |
| dependent on the kernel configuration. It's 'yes' for routers and 'no' for |
| hosts. |
| |
| bootp_relay |
| ~~~~~~~~~~~ |
| |
| Accept packets with source address 0.b.c.d with destinations not to this host |
| as local ones. It is supposed that a BOOTP relay daemon will catch and forward |
| such packets. |
| |
| The default is 0, since this feature is not implemented yet (kernel version |
| 2.2.12). |
| |
| forwarding |
| ---------- |
| |
| Enable or disable IP forwarding on this interface. |
| |
| log_martians |
| ------------ |
| |
| Log packets with source addresses with no known route to kernel log. |
| |
| mc_forwarding |
| ------------- |
| |
| Do multicast routing. The kernel needs to be compiled with CONFIG_MROUTE and a |
| multicast routing daemon is required. |
| |
| proxy_arp |
| --------- |
| |
| Does (1) or does not (0) perform proxy ARP. |
| |
| rp_filter |
| --------- |
| |
| Integer value determines if a source validation should be made. 1 means yes, 0 |
| means no. Disabled by default, but local/broadcast address spoofing is always |
| on. |
| |
| If you set this to 1 on a router that is the only connection for a network to |
| the net, it will prevent spoofing attacks against your internal networks |
| (external addresses can still be spoofed), without the need for additional |
| firewall rules. |
| |
| secure_redirects |
| ---------------- |
| |
| Accept ICMP redirect messages only for gateways, listed in default gateway |
| list. Enabled by default. |
| |
| shared_media |
| ------------ |
| |
| If it is not set the kernel does not assume that different subnets on this |
| device can communicate directly. Default setting is 'yes'. |
| |
| send_redirects |
| -------------- |
| |
| Determines whether to send ICMP redirects to other hosts. |
| |
| Routing settings |
| ---------------- |
| |
| The directory /proc/sys/net/ipv4/route contains several file to control |
| routing issues. |
| |
| error_burst and error_cost |
| -------------------------- |
| |
| These parameters are used to limit how many ICMP destination unreachable to |
| send from the host in question. ICMP destination unreachable messages are |
| sent when we cannot reach the next hop while trying to transmit a packet. |
| It will also print some error messages to kernel logs if someone is ignoring |
| our ICMP redirects. The higher the error_cost factor is, the fewer |
| destination unreachable and error messages will be let through. Error_burst |
| controls when destination unreachable messages and error messages will be |
| dropped. The default settings limit warning messages to five every second. |
| |
| flush |
| ----- |
| |
| Writing to this file results in a flush of the routing cache. |
| |
| gc_elasticity, gc_interval, gc_min_interval_ms, gc_timeout, gc_thresh |
| --------------------------------------------------------------------- |
| |
| Values to control the frequency and behavior of the garbage collection |
| algorithm for the routing cache. gc_min_interval is deprecated and replaced |
| by gc_min_interval_ms. |
| |
| |
| max_size |
| -------- |
| |
| Maximum size of the routing cache. Old entries will be purged once the cache |
| reached has this size. |
| |
| max_delay, min_delay |
| -------------------- |
| |
| Delays for flushing the routing cache. |
| |
| redirect_load, redirect_number |
| ------------------------------ |
| |
| Factors which determine if more ICPM redirects should be sent to a specific |
| host. No redirects will be sent once the load limit or the maximum number of |
| redirects has been reached. |
| |
| redirect_silence |
| ---------------- |
| |
| Timeout for redirects. After this period redirects will be sent again, even if |
| this has been stopped, because the load or number limit has been reached. |
| |
| Network Neighbor handling |
| ------------------------- |
| |
| Settings about how to handle connections with direct neighbors (nodes attached |
| to the same link) can be found in the directory /proc/sys/net/ipv4/neigh. |
| |
| As we saw it in the conf directory, there is a default subdirectory which |
| holds the default values, and one directory for each interface. The contents |
| of the directories are identical, with the single exception that the default |
| settings contain additional options to set garbage collection parameters. |
| |
| In the interface directories you'll find the following entries: |
| |
| base_reachable_time, base_reachable_time_ms |
| ------------------------------------------- |
| |
| A base value used for computing the random reachable time value as specified |
| in RFC2461. |
| |
| Expression of base_reachable_time, which is deprecated, is in seconds. |
| Expression of base_reachable_time_ms is in milliseconds. |
| |
| retrans_time, retrans_time_ms |
| ----------------------------- |
| |
| The time between retransmitted Neighbor Solicitation messages. |
| Used for address resolution and to determine if a neighbor is |
| unreachable. |
| |
| Expression of retrans_time, which is deprecated, is in 1/100 seconds (for |
| IPv4) or in jiffies (for IPv6). |
| Expression of retrans_time_ms is in milliseconds. |
| |
| unres_qlen |
| ---------- |
| |
| Maximum queue length for a pending arp request - the number of packets which |
| are accepted from other layers while the ARP address is still resolved. |
| |
| anycast_delay |
| ------------- |
| |
| Maximum for random delay of answers to neighbor solicitation messages in |
| jiffies (1/100 sec). Not yet implemented (Linux does not have anycast support |
| yet). |
| |
| ucast_solicit |
| ------------- |
| |
| Maximum number of retries for unicast solicitation. |
| |
| mcast_solicit |
| ------------- |
| |
| Maximum number of retries for multicast solicitation. |
| |
| delay_first_probe_time |
| ---------------------- |
| |
| Delay for the first time probe if the neighbor is reachable. (see |
| gc_stale_time) |
| |
| locktime |
| -------- |
| |
| An ARP/neighbor entry is only replaced with a new one if the old is at least |
| locktime old. This prevents ARP cache thrashing. |
| |
| proxy_delay |
| ----------- |
| |
| Maximum time (real time is random [0..proxytime]) before answering to an ARP |
| request for which we have an proxy ARP entry. In some cases, this is used to |
| prevent network flooding. |
| |
| proxy_qlen |
| ---------- |
| |
| Maximum queue length of the delayed proxy arp timer. (see proxy_delay). |
| |
| app_solicit |
| ---------- |
| |
| Determines the number of requests to send to the user level ARP daemon. Use 0 |
| to turn off. |
| |
| gc_stale_time |
| ------------- |
| |
| Determines how often to check for stale ARP entries. After an ARP entry is |
| stale it will be resolved again (which is useful when an IP address migrates |
| to another machine). When ucast_solicit is greater than 0 it first tries to |
| send an ARP packet directly to the known host When that fails and |
| mcast_solicit is greater than 0, an ARP request is broadcasted. |
| |
| 2.9 Appletalk |
| ------------- |
| |
| The /proc/sys/net/appletalk directory holds the Appletalk configuration data |
| when Appletalk is loaded. The configurable parameters are: |
| |
| aarp-expiry-time |
| ---------------- |
| |
| The amount of time we keep an ARP entry before expiring it. Used to age out |
| old hosts. |
| |
| aarp-resolve-time |
| ----------------- |
| |
| The amount of time we will spend trying to resolve an Appletalk address. |
| |
| aarp-retransmit-limit |
| --------------------- |
| |
| The number of times we will retransmit a query before giving up. |
| |
| aarp-tick-time |
| -------------- |
| |
| Controls the rate at which expires are checked. |
| |
| The directory /proc/net/appletalk holds the list of active Appletalk sockets |
| on a machine. |
| |
| The fields indicate the DDP type, the local address (in network:node format) |
| the remote address, the size of the transmit pending queue, the size of the |
| received queue (bytes waiting for applications to read) the state and the uid |
| owning the socket. |
| |
| /proc/net/atalk_iface lists all the interfaces configured for appletalk.It |
| shows the name of the interface, its Appletalk address, the network range on |
| that address (or network number for phase 1 networks), and the status of the |
| interface. |
| |
| /proc/net/atalk_route lists each known network route. It lists the target |
| (network) that the route leads to, the router (may be directly connected), the |
| route flags, and the device the route is using. |
| |
| 2.10 IPX |
| -------- |
| |
| The IPX protocol has no tunable values in proc/sys/net. |
| |
| The IPX protocol does, however, provide proc/net/ipx. This lists each IPX |
| socket giving the local and remote addresses in Novell format (that is |
| network:node:port). In accordance with the strange Novell tradition, |
| everything but the port is in hex. Not_Connected is displayed for sockets that |
| are not tied to a specific remote address. The Tx and Rx queue sizes indicate |
| the number of bytes pending for transmission and reception. The state |
| indicates the state the socket is in and the uid is the owning uid of the |
| socket. |
| |
| The /proc/net/ipx_interface file lists all IPX interfaces. For each interface |
| it gives the network number, the node number, and indicates if the network is |
| the primary network. It also indicates which device it is bound to (or |
| Internal for internal networks) and the Frame Type if appropriate. Linux |
| supports 802.3, 802.2, 802.2 SNAP and DIX (Blue Book) ethernet framing for |
| IPX. |
| |
| The /proc/net/ipx_route table holds a list of IPX routes. For each route it |
| gives the destination network, the router node (or Directly) and the network |
| address of the router (or Connected) for internal networks. |
| |
| 2.11 /proc/sys/fs/mqueue - POSIX message queues filesystem |
| ---------------------------------------------------------- |
| |
| The "mqueue" filesystem provides the necessary kernel features to enable the |
| creation of a user space library that implements the POSIX message queues |
| API (as noted by the MSG tag in the POSIX 1003.1-2001 version of the System |
| Interfaces specification.) |
| |
| The "mqueue" filesystem contains values for determining/setting the amount of |
| resources used by the file system. |
| |
| /proc/sys/fs/mqueue/queues_max is a read/write file for setting/getting the |
| maximum number of message queues allowed on the system. |
| |
| /proc/sys/fs/mqueue/msg_max is a read/write file for setting/getting the |
| maximum number of messages in a queue value. In fact it is the limiting value |
| for another (user) limit which is set in mq_open invocation. This attribute of |
| a queue must be less or equal then msg_max. |
| |
| /proc/sys/fs/mqueue/msgsize_max is a read/write file for setting/getting the |
| maximum message size value (it is every message queue's attribute set during |
| its creation). |
| |
| 2.12 /proc/<pid>/oom_adj - Adjust the oom-killer score |
| ------------------------------------------------------ |
| |
| This file can be used to adjust the score used to select which processes |
| should be killed in an out-of-memory situation. Giving it a high score will |
| increase the likelihood of this process being killed by the oom-killer. Valid |
| values are in the range -16 to +15, plus the special value -17, which disables |
| oom-killing altogether for this process. |
| |
| 2.13 /proc/<pid>/oom_score - Display current oom-killer score |
| ------------------------------------------------------------- |
| |
| ------------------------------------------------------------------------------ |
| This file can be used to check the current score used by the oom-killer is for |
| any given <pid>. Use it together with /proc/<pid>/oom_adj to tune which |
| process should be killed in an out-of-memory situation. |
| |
| ------------------------------------------------------------------------------ |
| Summary |
| ------------------------------------------------------------------------------ |
| Certain aspects of kernel behavior can be modified at runtime, without the |
| need to recompile the kernel, or even to reboot the system. The files in the |
| /proc/sys tree can not only be read, but also modified. You can use the echo |
| command to write value into these files, thereby changing the default settings |
| of the kernel. |
| ------------------------------------------------------------------------------ |
| |
| 2.14 /proc/<pid>/io - Display the IO accounting fields |
| ------------------------------------------------------- |
| |
| This file contains IO statistics for each running process |
| |
| Example |
| ------- |
| |
| test:/tmp # dd if=/dev/zero of=/tmp/test.dat & |
| [1] 3828 |
| |
| test:/tmp # cat /proc/3828/io |
| rchar: 323934931 |
| wchar: 323929600 |
| syscr: 632687 |
| syscw: 632675 |
| read_bytes: 0 |
| write_bytes: 323932160 |
| cancelled_write_bytes: 0 |
| |
| |
| Description |
| ----------- |
| |
| rchar |
| ----- |
| |
| I/O counter: chars read |
| The number of bytes which this task has caused to be read from storage. This |
| is simply the sum of bytes which this process passed to read() and pread(). |
| It includes things like tty IO and it is unaffected by whether or not actual |
| physical disk IO was required (the read might have been satisfied from |
| pagecache) |
| |
| |
| wchar |
| ----- |
| |
| I/O counter: chars written |
| The number of bytes which this task has caused, or shall cause to be written |
| to disk. Similar caveats apply here as with rchar. |
| |
| |
| syscr |
| ----- |
| |
| I/O counter: read syscalls |
| Attempt to count the number of read I/O operations, i.e. syscalls like read() |
| and pread(). |
| |
| |
| syscw |
| ----- |
| |
| I/O counter: write syscalls |
| Attempt to count the number of write I/O operations, i.e. syscalls like |
| write() and pwrite(). |
| |
| |
| read_bytes |
| ---------- |
| |
| I/O counter: bytes read |
| Attempt to count the number of bytes which this process really did cause to |
| be fetched from the storage layer. Done at the submit_bio() level, so it is |
| accurate for block-backed filesystems. <please add status regarding NFS and |
| CIFS at a later time> |
| |
| |
| write_bytes |
| ----------- |
| |
| I/O counter: bytes written |
| Attempt to count the number of bytes which this process caused to be sent to |
| the storage layer. This is done at page-dirtying time. |
| |
| |
| cancelled_write_bytes |
| --------------------- |
| |
| The big inaccuracy here is truncate. If a process writes 1MB to a file and |
| then deletes the file, it will in fact perform no writeout. But it will have |
| been accounted as having caused 1MB of write. |
| In other words: The number of bytes which this process caused to not happen, |
| by truncating pagecache. A task can cause "negative" IO too. If this task |
| truncates some dirty pagecache, some IO which another task has been accounted |
| for (in it's write_bytes) will not be happening. We _could_ just subtract that |
| from the truncating task's write_bytes, but there is information loss in doing |
| that. |
| |
| |
| Note |
| ---- |
| |
| At its current implementation state, this is a bit racy on 32-bit machines: if |
| process A reads process B's /proc/pid/io while process B is updating one of |
| those 64-bit counters, process A could see an intermediate result. |
| |
| |
| More information about this can be found within the taskstats documentation in |
| Documentation/accounting. |
| |
| ------------------------------------------------------------------------------ |