您的位置:首页 > 运维架构 > Linux

【转】刚发现一个linux在线文档库。很好很强大。

2015-01-20 09:54 751 查看
原文网址:http://blog.csdn.net/longxibendi/article/details/6048231

1.网址: http://www.mjmwired.net

2.比如查看这个 proc.txt ,就在这里能找到。

http://www.mjmwired.net/kernel/Documentation/filesystems/proc.txt

内核参数解释全在这里了。不过,也可以下载内核完源代码,从/usr/src/linux/Documentation/proc.txt查看

下载内核从http://www.kernel.org/pub/linux/kernel/v2.6/

解压完后从这里打开:

linux-2.6.28/Documentation/filesystems/proc.txt

3.此外,在filesystems下还有很多文档,比如ext4.txt,很详细,很全面,很有用。

4.这里提供一个2.6.28的完整proc.txt文档

注意linux系统管理技术手册 第二版 说的是 proc.txt 在 /usr/src/linux/Documentation/proc.txt ,具体问题,具体分析吧。

[c-sharp] view plaincopy

------------------------------------------------------------------------------

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

2.15 /proc/<pid>/coredump_filter - Core dump filtering settings

2.16 /proc/<pid>/mountinfo - Information about mounts

2.17 /proc/sys/fs/epoll - Configuration options for the epoll interface

------------------------------------------------------------------------------

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. The stat

file contains details information about the process itself. Its fields are

explained in Table 1-3.

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)

..............................................................................

Table 1-3: Contents of the stat files (as of 2.6.22-rc3)

..............................................................................

Field Content

pid process id

tcomm filename of the executable

state state (R is running, S is sleeping, D is sleeping in an

uninterruptible wait, Z is zombie, T is traced or stopped)

ppid process id of the parent process

pgrp pgrp of the process

sid session id

tty_nr tty the process uses

tty_pgrp pgrp of the tty

flags task flags

min_flt number of minor faults

cmin_flt number of minor faults with child's

maj_flt number of major faults

cmaj_flt number of major faults with child's

utime user mode jiffies

stime kernel mode jiffies

cutime user mode jiffies with child's

cstime kernel mode jiffies with child's

priority priority level

nice nice level

num_threads number of threads

it_real_value (obsolete, always 0)

start_time time the process started after system boot

vsize virtual memory size

rss resident set memory size

rsslim current limit in bytes on the rss

start_code address above which program text can run

end_code address below which program text can run

start_stack address of the start of the stack

esp current value of ESP

eip current value of EIP

pending bitmap of pending signals (obsolete)

blocked bitmap of blocked signals (obsolete)

sigign bitmap of ignored signals (obsolete)

sigcatch bitmap of catched signals (obsolete)

wchan address where process went to sleep

0 (place holder)

0 (place holder)

exit_signal signal to send to parent thread on exit

task_cpu which CPU the task is scheduled on

rt_priority realtime priority

policy scheduling policy (man sched_setscheduler)

blkio_ticks time spent waiting for block IO

..............................................................................

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 1-4. 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 1-4: 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 Deprecated 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)

vmallocinfo Show vmalloced areas

..............................................................................

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 2.6.2* /proc/interrupts was expanded again. This time the goal was for

/proc/interrupts to display every IRQ vector in use by the system, not

just those considered 'most important'. The new vectors are:

THR -- interrupt raised when a machine check threshold counter

(typically counting ECC corrected errors of memory or cache) exceeds

a configurable threshold. Only available on some systems.

TRM -- a thermal event interrupt occurs when a temperature threshold

has been exceeded for the CPU. This interrupt may also be generated

when the temperature drops back to normal.

SPU -- a spurious interrupt is some interrupt that was raised then lowered

by some IO device before it could be fully processed by the APIC. Hence

the APIC sees the interrupt but does not know what device it came from.

For this case the APIC will generate the interrupt with a IRQ vector

of 0xff. This might also be generated by chipset bugs.

RES, CAL, TLB -- rescheduling, call and TLB flush interrupts are

sent from one CPU to another per the needs of the OS. Typically,

their statistics are used by kernel developers and interested users to

determine the occurance of interrupt of the given type.

The above IRQ vectors are displayed only when relevent. For example,

the threshold vector does not exist on x86_64 platforms. Others are

suppressed when the system is a uniprocessor. As of this writing, only

i386 and x86_64 platforms support the new IRQ vector displays.

Of some interest is the introduction of the /proc/irq directory to 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 two files; default_smp_affinity and

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 default_smp_affinity

> ls /proc/irq/0/

smp_affinity

smp_affinity is a bitmask, in which you can specify which CPUs can handle the

IRQ, you can set it by doing:

> echo 1 > /proc/irq/10/smp_affinity

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 contents of each smp_affinity file is the same by default:

> cat /proc/irq/0/smp_affinity

ffffffff

The default_smp_affinity mask applies to all non-active IRQs, which are the

IRQs which have not yet been allocated/activated, and hence which lack a

/proc/irq/[0-9]* directory.

prof_cpu_mask specifies which CPUs are to be profiled by the system wide

profiler. Default value is ffffffff (all cpus).

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

AnonPages: 861800 kB

Mapped: 280372 kB

Slab: 284364 kB

SReclaimable: 159856 kB

SUnreclaim: 124508 kB

PageTables: 24448 kB

NFS_Unstable: 0 kB

Bounce: 0 kB

WritebackTmp: 0 kB

CommitLimit: 7669796 kB

Committed_AS: 100056 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

AnonPages: Non-file backed pages mapped into userspace page tables

Mapped: files which have been mmaped, such as libraries

Slab: in-kernel data structures cache

SReclaimable: Part of Slab, that might be reclaimed, such as caches

SUnreclaim: Part of Slab, that cannot be reclaimed on memory pressure

PageTables: amount of memory dedicated to the lowest level of page

tables.

NFS_Unstable: NFS pages sent to the server, but not yet committed to stable

storage

Bounce: Memory used for block device "bounce buffers"

WritebackTmp: Memory used by FUSE for temporary writeback buffers

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.

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

..............................................................................

vmallocinfo:

Provides information about vmalloced/vmaped areas. One line per area,

containing the virtual address range of the area, size in bytes,

caller information of the creator, and optional information depending

on the kind of area :

pages=nr number of pages

phys=addr if a physical address was specified

ioremap I/O mapping (ioremap() and friends)

vmalloc vmalloc() area

vmap vmap()ed pages

user VM_USERMAP area

vpages buffer for pages pointers was vmalloced (huge area)

N<node>=nr (Only on NUMA kernels)

Number of pages allocated on memory node <node>

> cat /proc/vmallocinfo

0xffffc20000000000-0xffffc20000201000 2101248 alloc_large_system_hash+0x204 ...

/0x2c0 pages=512 vmalloc N0=128 N1=128 N2=128 N3=128

0xffffc20000201000-0xffffc20000302000 1052672 alloc_large_system_hash+0x204 ...

/0x2c0 pages=256 vmalloc N0=64 N1=64 N2=64 N3=64

0xffffc20000302000-0xffffc20000304000 8192 acpi_tb_verify_table+0x21/0x4f...

phys=7fee8000 ioremap

0xffffc20000304000-0xffffc20000307000 12288 acpi_tb_verify_table+0x21/0x4f...

phys=7fee7000 ioremap

0xffffc2000031d000-0xffffc2000031f000 8192 init_vdso_vars+0x112/0x210

0xffffc2000031f000-0xffffc2000032b000 49152 cramfs_uncompress_init+0x2e ...

/0x80 pages=11 vmalloc N0=3 N1=3 N2=2 N3=3

0xffffc2000033a000-0xffffc2000033d000 12288 sys_swapon+0x640/0xac0 ...

pages=2 vmalloc N1=2

0xffffc20000347000-0xffffc2000034c000 20480 xt_alloc_table_info+0xfe ...

/0x130 [x_tables] pages=4 vmalloc N0=4

0xffffffffa0000000-0xffffffffa000f000 61440 sys_init_module+0xc27/0x1d00 ...

pages=14 vmalloc N2=14

0xffffffffa000f000-0xffffffffa0014000 20480 sys_init_module+0xc27/0x1d00 ...

pages=4 vmalloc N1=4

0xffffffffa0014000-0xffffffffa0017000 12288 sys_init_module+0xc27/0x1d00 ...

pages=2 vmalloc N1=2

0xffffffffa0017000-0xffffffffa0022000 45056 sys_init_module+0xc27/0x1d00 ...

pages=10 vmalloc N0=10

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 1-5.

Table 1-5: 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 1-6 are contained in these

directories.

Table 1-6: 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 0

cpu0 1132 34 1441 11311718 3675 127 438 0

cpu1 1123 0 849 11313845 2614 0 18 0

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

- steal: involuntary wait

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.

1.9 Ext4 file system parameters

------------------------------

Information about mounted ext4 file systems can be found in

/proc/fs/ext4. Each mounted filesystem will have a directory in

/proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or

/proc/fs/ext4/dm-0). The files in each per-device directory are shown

in Table 1-10, below.

Table 1-10: Files in /proc/fs/ext4/<devname>

..............................................................................

File Content

mb_groups details of multiblock allocator buddy cache of free blocks

mb_history multiblock allocation history

stats controls whether the multiblock allocator should start

collecting statistics, which are shown during the unmount

group_prealloc the multiblock allocator will round up allocation

requests to a multiple of this tuning parameter if the

stripe size is not set in the ext4 superblock

max_to_scan The maximum number of extents the multiblock allocator

will search to find the best extent

min_to_scan The minimum number of extents the multiblock allocator

will search to find the best extent

order2_req Tuning parameter which controls the minimum size for

requests (as a power of 2) where the buddy cache is

used

stream_req Files which have fewer blocks than this tunable

parameter will have their blocks allocated out of a

block group specific preallocation pool, so that small

files are packed closely together. Each large file

will have its blocks allocated out of its own unique

preallocation pool.

inode_readahead Tuning parameter which controls the maximum number of

inode table blocks that ext4's inode table readahead

algorithm will pre-read into the buffer cache

..............................................................................

------------------------------------------------------------------------------

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_open

-------

Denotes the maximum number of file-handles a process can

allocate. Default value is 1024*1024 (1048576) which should be

enough for most machines. Actual limit depends on RLIMIT_NOFILE

resource limit.

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.

panic_on_unrecovered_nmi

------------------------

The default Linux behaviour on an NMI of either memory or unknown is to continue

operation. For many environments such as scientific computing it is preferable

that the box is taken out and the error dealt with than an uncorrected

parity/ECC error get propogated.

A small number of systems do generate NMI's for bizarre random reasons such as

power management so the default is off. That sysctl works like the existing

panic controls already in that directory.

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.

msgmni

------

Maximum number of message queue ids on the system.

This value scales to the amount of lowmem. It is automatically recomputed

upon memory add/remove or ipc namespace creation/removal.

When a value is written into this file, msgmni's value becomes fixed, i.e. it

is not recomputed anymore when one of the above events occurs.

Use auto_msgmni to change this behavior.

auto_msgmni

-----------

Enables/Disables automatic recomputing of msgmni upon memory add/remove or

upon ipc namespace creation/removal (see the msgmni description above).

Echoing "1" into this file enables msgmni automatic recomputing.

Echoing "0" turns it off.

auto_msgmni default value is 1.

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 the dirtyable system memory (free pages + mapped

pages + file cache, not including locked pages and HugePages), the number of

pages at which the pdflush background writeback daemon will start writing out

dirty data.

dirty_ratio

-----------------

Contains, as a percentage of the dirtyable system memory (free pages + mapped

pages + file cache, not including locked pages and HugePages), 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.

highmem_is_dirtyable

--------------------

Only present if CONFIG_HIGHMEM is set.

This defaults to 0 (false), meaning that the ratios set above are calculated

as a percentage of lowmem only. This protects against excessive scanning

in page reclaim, swapping and general VM distress.

Setting this to 1 can be useful on 32 bit machines where you want to make

random changes within an MMAPed file that is larger than your available

lowmem without causing large quantities of random IO. Is is safe if the

behavior of all programs running on the machine is known and memory will

not be otherwise stressed.

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.

lowmem_reserve_ratio

---------------------

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 `lowmem_reserve_ratio' tunable determines how aggressive the kernel is

in defending these lower zones.

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 change the lowmem_reserve_ratio setting.

The lowmem_reserve_ratio is an array. You can see them by reading this file.

-

% cat /proc/sys/vm/lowmem_reserve_ratio

256 256 32

-

Note: # of this elements is one fewer than number of zones. Because the highest

zone's value is not necessary for following calculation.

But, these values are not used directly. The kernel calculates # of protection

pages for each zones from them. These are shown as array of protection pages

in /proc/zoneinfo like followings. (This is an example of x86-64 box).

Each zone has an array of protection pages like this.

-

Node 0, zone DMA

pages free 1355

min 3

low 3

high 4

:

:

numa_other 0

protection: (0, 2004, 2004, 2004)

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

pagesets

cpu: 0 pcp: 0

:

-

These protections are added to score to judge whether this zone should be used

for page allocation or should be reclaimed.

In this example, if normal pages (index=2) are required to this DMA zone and

pages_high is used for watermark, the kernel judges this zone should not be

used because pages_free(1355) is smaller than watermark + protection[2]

(4 + 2004 = 2008). If this protection value is 0, this zone would be used for

normal page requirement. If requirement is DMA zone(index=0), protection[0]

(=0) is used.

zone[i]'s protection[j] is calculated by following expression.

(i < j):

zone[i]->protection[j]

= (total sums of present_pages from zone[i+1] to zone[j] on the node)

/ lowmem_reserve_ratio[i];

(i = j):

(should not be protected. = 0;

(i > j):

(not necessary, but looks 0)

The default values of lowmem_reserve_ratio[i] are

256 (if zone[i] means DMA or DMA32 zone)

32 (others).

As above expression, they are reciprocal number of ratio.

256 means 1/256. # of protection pages becomes about "0.39%" of total present

pages of higher zones on the node.

If you would like to protect more pages, smaller values are effective.

The minimum value is 1 (1/1 -> 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.

hugepages_treat_as_movable

--------------------------

This parameter is only useful when kernelcore= is specified at boot time to

create ZONE_MOVABLE for pages that may be reclaimed or migrated. Huge pages

are not movable so are not normally allocated from ZONE_MOVABLE. A non-zero

value written to hugepages_treat_as_movable allows huge pages to be allocated

from ZONE_MOVABLE.

Once enabled, the ZONE_MOVABLE is treated as an area of memory the huge

pages pool can easily grow or shrink within. Assuming that applications are

not running that mlock() a lot of memory, it is likely the huge pages pool

can grow to the size of ZONE_MOVABLE by repeatedly entering the desired value

into nr_hugepages and triggering page reclaim.

laptop_mode

-----------

laptop_mode is a knob that controls "laptop mode". All the things that are

controlled by this knob are discussed in Documentation/laptops/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/laptops/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.

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.

2.15 /proc/<pid>/coredump_filter - Core dump filtering settings

---------------------------------------------------------------

When a process is dumped, all anonymous memory is written to a core file as

long as the size of the core file isn't limited. But sometimes we don't want

to dump some memory segments, for example, huge shared memory. Conversely,

sometimes we want to save file-backed memory segments into a core file, not

only the individual files.

/proc/<pid>/coredump_filter allows you to customize which memory segments

will be dumped when the <pid> process is dumped. coredump_filter is a bitmask

of memory types. If a bit of the bitmask is set, memory segments of the

corresponding memory type are dumped, otherwise they are not dumped.

The following 7 memory types are supported:

- (bit 0) anonymous private memory

- (bit 1) anonymous shared memory

- (bit 2) file-backed private memory

- (bit 3) file-backed shared memory

- (bit 4) ELF header pages in file-backed private memory areas (it is

effective only if the bit 2 is cleared)

- (bit 5) hugetlb private memory

- (bit 6) hugetlb shared memory

Note that MMIO pages such as frame buffer are never dumped and vDSO pages

are always dumped regardless of the bitmask status.

Note bit 0-4 doesn't effect any hugetlb memory. hugetlb memory are only

effected by bit 5-6.

Default value of coredump_filter is 0x23; this means all anonymous memory

segments and hugetlb private memory are dumped.

If you don't want to dump all shared memory segments attached to pid 1234,

write 0x21 to the process's proc file.

$ echo 0x21 > /proc/1234/coredump_filter

When a new process is created, the process inherits the bitmask status from its

parent. It is useful to set up coredump_filter before the program runs.

For example:

$ echo 0x7 > /proc/self/coredump_filter

$ ./some_program

2.16 /proc/<pid>/mountinfo - Information about mounts

--------------------------------------------------------

This file contains lines of the form:

36 35 98:0 /mnt1 /mnt2 rw,noatime master:1 - ext3 /dev/root rw,errors=continue

(1)(2)(3) (4) (5) (6) (7) (8) (9) (10) (11)

(1) mount ID: unique identifier of the mount (may be reused after umount)

(2) parent ID: ID of parent (or of self for the top of the mount tree)

(3) major:minor: value of st_dev for files on filesystem

(4) root: root of the mount within the filesystem

(5) mount point: mount point relative to the process's root

(6) mount options: per mount options

(7) optional fields: zero or more fields of the form "tag[:value]"

(8) separator: marks the end of the optional fields

(9) filesystem type: name of filesystem of the form "type[.subtype]"

(10) mount source: filesystem specific information or "none"

(11) super options: per super block options

Parsers should ignore all unrecognised optional fields. Currently the

possible optional fields are:

shared:X mount is shared in peer group X

master:X mount is slave to peer group X

propagate_from:X mount is slave and receives propagation from peer group X (*)

unbindable mount is unbindable

(*) X is the closest dominant peer group under the process's root. If

X is the immediate master of the mount, or if there's no dominant peer

group under the same root, then only the "master:X" field is present

and not the "propagate_from:X" field.

For more information on mount propagation see:

Documentation/filesystems/sharedsubtree.txt

2.17 /proc/sys/fs/epoll - Configuration options for the epoll interface

--------------------------------------------------------

This directory contains configuration options for the epoll(7) interface.

max_user_instances

------------------

This is the maximum number of epoll file descriptors that a single user can

have open at a given time. The default value is 128, and should be enough

for normal users.

max_user_watches

----------------

Every epoll file descriptor can store a number of files to be monitored

for event readiness. Each one of these monitored files constitutes a "watch".

This configuration option sets the maximum number of "watches" that are

allowed for each user.

Each "watch" costs roughly 90 bytes on a 32bit kernel, and roughly 160 bytes

on a 64bit one.

The current default value for max_user_watches is the 1/32 of the available

low memory, divided for the "watch" cost in bytes.

------------------------------------------------------------------------------
内容来自用户分享和网络整理,不保证内容的准确性,如有侵权内容,可联系管理员处理 点击这里给我发消息
标签: