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proc.txt
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------------------------------------------------------------------------------
T H E /proc F I L E S Y S T E M
------------------------------------------------------------------------------
/proc/sys Terrehon Bowden <[email protected]> October 7 1999
Bodo Bauer <[email protected]>
2.4.x update Jorge Nerin <[email protected]> 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
------------------------------------------------------------------------------
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 [email protected]. 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 [email protected] and/or try to reach me at
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
cmdline Command line arguments
cpu Current and last cpu in wich 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
..............................................................................
For example, to get the status information of a process, all you have to do is
read the file /proc/PID/status:
>cat /proc/self/status
Name: cat
State: R (running)
Pid: 5452
PPid: 743
TracerPid: 0 (2.4)
Uid: 501 501 501 501
Gid: 100 100 100 100
Groups: 100 14 16
VmSize: 1112 kB
VmLck: 0 kB
VmRSS: 348 kB
VmData: 24 kB
VmStk: 12 kB
VmExe: 8 kB
VmLib: 1044 kB
SigPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000000000
SigCgt: 0000000000000000
CapInh: 00000000fffffeff
CapPrm: 0000000000000000
CapEff: 0000000000000000
This shows you nearly the same information you would get if you viewed it with
the ps command. In fact, ps uses the proc file system to obtain its
information. The statm file contains more detailed information about the
process memory usage. Its seven fields are explained in Table 1-2.
Table 1-2: Contents of the statm files (as of 2.6.8-rc3)
..............................................................................
Field Content
size total program size (pages) (same as VmSize in status)
resident size of memory portions (pages) (same as VmRSS in status)
shared number of pages that are shared (i.e. backed by a file)
trs number of pages that are 'code' (not including libs; broken,
includes data segment)
lrs number of pages of library (always 0 on 2.6)
drs number of pages of data/stack (including libs; broken,
includes library text)
dt number of dirty pages (always 0 on 2.6)
..............................................................................
1.2 Kernel data
---------------
Similar to the process entries, the kernel data files give information about
the running kernel. The files used to obtain this information are contained in
/proc and are listed in Table 1-3. Not all of these will be present in your
system. It depends on the kernel configuration and the loaded modules, which
files are there, and which are missing.
Table 1-3: Kernel info in /proc
..............................................................................
File Content
apm Advanced power management info
buddyinfo Kernel memory allocator information (see text) (2.5)
bus Directory containing bus specific information
cmdline Kernel command line
cpuinfo Info about the CPU
devices Available devices (block and character)
dma Used DMS channels
filesystems Supported filesystems
driver Various drivers grouped here, currently rtc (2.4)
execdomains Execdomains, related to security (2.4)
fb Frame Buffer devices (2.4)
fs File system parameters, currently nfs/exports (2.4)
ide Directory containing info about the IDE subsystem
interrupts Interrupt usage
iomem Memory map (2.4)
ioports I/O port usage
irq Masks for irq to cpu affinity (2.4)(smp?)
isapnp ISA PnP (Plug&Play) Info (2.4)
kcore Kernel core image (can be ELF or A.OUT(deprecated in 2.4))
kmsg Kernel messages
ksyms Kernel symbol table
loadavg Load average of last 1, 5 & 15 minutes
locks Kernel locks
meminfo Memory info
misc Miscellaneous
modules List of loaded modules
mounts Mounted filesystems
net Networking info (see text)
partitions Table of partitions known to the system
pci Depreciated info of PCI bus (new way -> /proc/bus/pci/,
decoupled by lspci (2.4)
rtc Real time clock
scsi SCSI info (see text)
slabinfo Slab pool info
stat Overall statistics
swaps Swap space utilization
sys See chapter 2
sysvipc Info of SysVIPC Resources (msg, sem, shm) (2.4)
tty Info of tty drivers
uptime System uptime
version Kernel version
video bttv info of video resources (2.4)
..............................................................................
You can, for example, check which interrupts are currently in use and what
they are used for by looking in the file /proc/interrupts:
> cat /proc/interrupts
CPU0
0: 8728810 XT-PIC timer
1: 895 XT-PIC keyboard
2: 0 XT-PIC cascade
3: 531695 XT-PIC aha152x
4: 2014133 XT-PIC serial
5: 44401 XT-PIC pcnet_cs
8: 2 XT-PIC rtc
11: 8 XT-PIC i82365
12: 182918 XT-PIC PS/2 Mouse
13: 1 XT-PIC fpu
14: 1232265 XT-PIC ide0
15: 7 XT-PIC ide1
NMI: 0
In 2.4.* a couple of lines where added to this file LOC & ERR (this time is the
output of a SMP machine):
> cat /proc/interrupts
CPU0 CPU1
0: 1243498 1214548 IO-APIC-edge timer
1: 8949 8958 IO-APIC-edge keyboard
2: 0 0 XT-PIC cascade
5: 11286 10161 IO-APIC-edge soundblaster
8: 1 0 IO-APIC-edge rtc
9: 27422 27407 IO-APIC-edge 3c503
12: 113645 113873 IO-APIC-edge PS/2 Mouse
13: 0 0 XT-PIC fpu
14: 22491 24012 IO-APIC-edge ide0
15: 2183 2415 IO-APIC-edge ide1
17: 30564 30414 IO-APIC-level eth0
18: 177 164 IO-APIC-level bttv
NMI: 2457961 2457959
LOC: 2457882 2457881
ERR: 2155
NMI is incremented in this case because every timer interrupt generates a NMI
(Non Maskable Interrupt) which is used by the NMI Watchdog to detect lockups.
LOC is the local interrupt counter of the internal APIC of every CPU.
ERR is incremented in the case of errors in the IO-APIC bus (the bus that
connects the CPUs in a SMP system. This means that an error has been detected,
the IO-APIC automatically retry the transmission, so it should not be a big
problem, but you should read the SMP-FAQ.
In this context it could be interesting to note the new irq directory in 2.4.
It could be used to set IRQ to CPU affinity, this means that you can "hook" an
IRQ to only one CPU, or to exclude a CPU of handling IRQs. The contents of the
irq subdir is one subdir for each IRQ, and one file; prof_cpu_mask
For example
> ls /proc/irq/
0 10 12 14 16 18 2 4 6 8 prof_cpu_mask
1 11 13 15 17 19 3 5 7 9
> ls /proc/irq/0/
smp_affinity
The contents of the prof_cpu_mask file and each smp_affinity file for each IRQ
is the same by default:
> cat /proc/irq/0/smp_affinity
ffffffff
It's a bitmask, in wich you can specify wich CPUs can handle the IRQ, you can
set it by doing:
> echo 1 > /proc/irq/prof_cpu_mask
This means that only the first CPU will handle the IRQ, but you can also echo 5
wich means that only the first and fourth CPU can handle the IRQ.
The way IRQs are routed is handled by the IO-APIC, and it's Round Robin
between all the CPUs which are allowed to handle it. As usual the kernel has
more info than you and does a better job than you, so the defaults are the
best choice for almost everyone.
There are three more important subdirectories in /proc: net, scsi, and sys.
The general rule is that the contents, or even the existence of these
directories, depend on your kernel configuration. If SCSI is not enabled, the
directory scsi may not exist. The same is true with the net, which is there
only when networking support is present in the running kernel.
The slabinfo file gives information about memory usage at the slab level.
Linux uses slab pools for memory management above page level in version 2.2.
Commonly used objects have their own slab pool (such as network buffers,
directory cache, and so on).
..............................................................................
> cat /proc/buddyinfo
Node 0, zone DMA 0 4 5 4 4 3 ...
Node 0, zone Normal 1 0 0 1 101 8 ...
Node 0, zone HighMem 2 0 0 1 1 0 ...
Memory fragmentation is a problem under some workloads, and buddyinfo is a
useful tool for helping diagnose these problems. Buddyinfo will give you a
clue as to how big an area you can safely allocate, or why a previous
allocation failed.
Each column represents the number of pages of a certain order which are
available. In this case, there are 0 chunks of 2^0*PAGE_SIZE available in
ZONE_DMA, 4 chunks of 2^1*PAGE_SIZE in ZONE_DMA, 101 chunks of 2^4*PAGE_SIZE
available in ZONE_NORMAL, etc...
..............................................................................
meminfo:
Provides information about distribution and utilization of memory. This
varies by architecture and compile options. The following is from a
16GB PIII, which has highmem enabled. You may not have all of these fields.
> cat /proc/meminfo
MemTotal: 16344972 kB
MemFree: 13634064 kB
Buffers: 3656 kB
Cached: 1195708 kB
SwapCached: 0 kB
Active: 891636 kB
Inactive: 1077224 kB
HighTotal: 15597528 kB
HighFree: 13629632 kB
LowTotal: 747444 kB
LowFree: 4432 kB
SwapTotal: 0 kB
SwapFree: 0 kB
Dirty: 968 kB
Writeback: 0 kB
Mapped: 280372 kB
Slab: 684068 kB
CommitLimit: 7669796 kB
Committed_AS: 100056 kB
PageTables: 24448 kB
VmallocTotal: 112216 kB
VmallocUsed: 428 kB
VmallocChunk: 111088 kB
MemTotal: Total usable ram (i.e. physical ram minus a few reserved
bits and the kernel binary code)
MemFree: The sum of LowFree+HighFree
Buffers: Relatively temporary storage for raw disk blocks
shouldn't get tremendously large (20MB or so)
Cached: in-memory cache for files read from the disk (the
pagecache). Doesn't include SwapCached
SwapCached: Memory that once was swapped out, is swapped back in but
still also is in the swapfile (if memory is needed it
doesn't need to be swapped out AGAIN because it is already
in the swapfile. This saves I/O)
Active: Memory that has been used more recently and usually not
reclaimed unless absolutely necessary.
Inactive: Memory which has been less recently used. It is more
eligible to be reclaimed for other purposes
HighTotal:
HighFree: Highmem is all memory above ~860MB of physical memory
Highmem areas are for use by userspace programs, or
for the pagecache. The kernel must use tricks to access
this memory, making it slower to access than lowmem.
LowTotal:
LowFree: Lowmem is memory which can be used for everything that
highmem can be used for, but it is also availble for the
kernel's use for its own data structures. Among many
other things, it is where everything from the Slab is
allocated. Bad things happen when you're out of lowmem.
SwapTotal: total amount of swap space available
SwapFree: Memory which has been evicted from RAM, and is temporarily
on the disk
Dirty: Memory which is waiting to get written back to the disk
Writeback: Memory which is actively being written back to the disk
Mapped: files which have been mmaped, such as libraries
Slab: in-kernel data structures cache
CommitLimit: Based on the overcommit ratio ('vm.overcommit_ratio'),
this is the total amount of memory currently available to
be allocated on the system. This limit is only adhered to
if strict overcommit accounting is enabled (mode 2 in
'vm.overcommit_memory').
The CommitLimit is calculated with the following formula:
CommitLimit = ('vm.overcommit_ratio' * Physical RAM) + Swap
For example, on a system with 1G of physical RAM and 7G
of swap with a `vm.overcommit_ratio` of 30 it would
yield a CommitLimit of 7.3G.
For more details, see the memory overcommit documentation
in vm/overcommit-accounting.
Committed_AS: The amount of memory presently allocated on the system.
The committed memory is a sum of all of the memory which
has been allocated by processes, even if it has not been
"used" by them as of yet. A process which malloc()'s 1G
of memory, but only touches 300M of it will only show up
as using 300M of memory even if it has the address space
allocated for the entire 1G. This 1G is memory which has
been "committed" to by the VM and can be used at any time
by the allocating application. With strict overcommit
enabled on the system (mode 2 in 'vm.overcommit_memory'),
allocations which would exceed the CommitLimit (detailed
above) will not be permitted. This is useful if one needs
to guarantee that processes will not fail due to lack of
memory once that memory has been successfully allocated.
PageTables: amount of memory dedicated to the lowest level of page
tables.
VmallocTotal: total size of vmalloc memory area
VmallocUsed: amount of vmalloc area which is used
VmallocChunk: largest contigious block of vmalloc area which is free
1.3 IDE devices in /proc/ide
----------------------------
The subdirectory /proc/ide contains information about all IDE devices of which
the kernel is aware. There is one subdirectory for each IDE controller, the
file drivers and a link for each IDE device, pointing to the device directory
in the controller specific subtree.
The file drivers contains general information about the drivers used for the
IDE devices:
> cat /proc/ide/drivers
ide-cdrom version 4.53
ide-disk version 1.08
More detailed information can be found in the controller specific
subdirectories. These are named ide0, ide1 and so on. Each of these
directories contains the files shown in table 1-4.
Table 1-4: IDE controller info in /proc/ide/ide?
..............................................................................
File Content
channel IDE channel (0 or 1)
config Configuration (only for PCI/IDE bridge)
mate Mate name
model Type/Chipset of IDE controller
..............................................................................
Each device connected to a controller has a separate subdirectory in the
controllers directory. The files listed in table 1-5 are contained in these
directories.
Table 1-5: IDE device information
..............................................................................
File Content
cache The cache
capacity Capacity of the medium (in 512Byte blocks)
driver driver and version
geometry physical and logical geometry
identify device identify block
media media type
model device identifier
settings device setup
smart_thresholds IDE disk management thresholds
smart_values IDE disk management values
..............................................................................
The most interesting file is settings. This file contains a nice overview of
the drive parameters:
# cat /proc/ide/ide0/hda/settings
name value min max mode
---- ----- --- --- ----
bios_cyl 526 0 65535 rw
bios_head 255 0 255 rw
bios_sect 63 0 63 rw
breada_readahead 4 0 127 rw
bswap 0 0 1 r
file_readahead 72 0 2097151 rw
io_32bit 0 0 3 rw
keepsettings 0 0 1 rw
max_kb_per_request 122 1 127 rw
multcount 0 0 8 rw
nice1 1 0 1 rw
nowerr 0 0 1 rw
pio_mode write-only 0 255 w
slow 0 0 1 rw
unmaskirq 0 0 1 rw
using_dma 0 0 1 rw
1.4 Networking info in /proc/net
--------------------------------
The subdirectory /proc/net follows the usual pattern. Table 1-6 shows the
additional values you get for IP version 6 if you configure the kernel to
support this. Table 1-7 lists the files and their meaning.
Table 1-6: IPv6 info in /proc/net
..............................................................................
File Content
udp6 UDP sockets (IPv6)
tcp6 TCP sockets (IPv6)
raw6 Raw device statistics (IPv6)
igmp6 IP multicast addresses, which this host joined (IPv6)
if_inet6 List of IPv6 interface addresses
ipv6_route Kernel routing table for IPv6
rt6_stats Global IPv6 routing tables statistics
sockstat6 Socket statistics (IPv6)
snmp6 Snmp data (IPv6)
..............................................................................
Table 1-7: Network info in /proc/net
..............................................................................
File Content
arp Kernel ARP table
dev network devices with statistics
dev_mcast the Layer2 multicast groups a device is listening too
(interface index, label, number of references, number of bound
addresses).
dev_stat network device status
ip_fwchains Firewall chain linkage
ip_fwnames Firewall chain names
ip_masq Directory containing the masquerading tables
ip_masquerade Major masquerading table
netstat Network statistics
raw raw device statistics
route Kernel routing table
rpc Directory containing rpc info
rt_cache Routing cache
snmp SNMP data
sockstat Socket statistics
tcp TCP sockets
tr_rif Token ring RIF routing table
udp UDP sockets
unix UNIX domain sockets
wireless Wireless interface data (Wavelan etc)
igmp IP multicast addresses, which this host joined
psched Global packet scheduler parameters.
netlink List of PF_NETLINK sockets
ip_mr_vifs List of multicast virtual interfaces
ip_mr_cache List of multicast routing cache
..............................................................................
You can use this information to see which network devices are available in
your system and how much traffic was routed over those devices:
> cat /proc/net/dev
Inter-|Receive |[...
face |bytes packets errs drop fifo frame compressed multicast|[...
lo: 908188 5596 0 0 0 0 0 0 [...
ppp0:15475140 20721 410 0 0 410 0 0 [...
eth0: 614530 7085 0 0 0 0 0 1 [...
...] Transmit
...] bytes packets errs drop fifo colls carrier compressed
...] 908188 5596 0 0 0 0 0 0
...] 1375103 17405 0 0 0 0 0 0
...] 1703981 5535 0 0 0 3 0 0
In addition, each Channel Bond interface has it's own directory. For
example, the bond0 device will have a directory called /proc/net/bond0/.
It will contain information that is specific to that bond, such as the
current slaves of the bond, the link status of the slaves, and how
many times the slaves link has failed.
1.5 SCSI info
-------------
If you have a SCSI host adapter in your system, you'll find a subdirectory
named after the driver for this adapter in /proc/scsi. You'll also see a list
of all recognized SCSI devices in /proc/scsi:
>cat /proc/scsi/scsi
Attached devices:
Host: scsi0 Channel: 00 Id: 00 Lun: 00
Vendor: IBM Model: DGHS09U Rev: 03E0
Type: Direct-Access ANSI SCSI revision: 03
Host: scsi0 Channel: 00 Id: 06 Lun: 00
Vendor: PIONEER Model: CD-ROM DR-U06S Rev: 1.04
Type: CD-ROM ANSI SCSI revision: 02
The directory named after the driver has one file for each adapter found in
the system. These files contain information about the controller, including
the used IRQ and the IO address range. The amount of information shown is
dependent on the adapter you use. The example shows the output for an Adaptec
AHA-2940 SCSI adapter:
> cat /proc/scsi/aic7xxx/0
Adaptec AIC7xxx driver version: 5.1.19/3.2.4
Compile Options:
TCQ Enabled By Default : Disabled
AIC7XXX_PROC_STATS : Disabled
AIC7XXX_RESET_DELAY : 5
Adapter Configuration:
SCSI Adapter: Adaptec AHA-294X Ultra SCSI host adapter
Ultra Wide Controller
PCI MMAPed I/O Base: 0xeb001000
Adapter SEEPROM Config: SEEPROM found and used.
Adaptec SCSI BIOS: Enabled
IRQ: 10
SCBs: Active 0, Max Active 2,
Allocated 15, HW 16, Page 255
Interrupts: 160328
BIOS Control Word: 0x18b6
Adapter Control Word: 0x005b
Extended Translation: Enabled
Disconnect Enable Flags: 0xffff
Ultra Enable Flags: 0x0001
Tag Queue Enable Flags: 0x0000
Ordered Queue Tag Flags: 0x0000
Default Tag Queue Depth: 8
Tagged Queue By Device array for aic7xxx host instance 0:
{255,255,255,255,255,255,255,255,255,255,255,255,255,255,255,255}
Actual queue depth per device for aic7xxx host instance 0:
{1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1}
Statistics:
(scsi0:0:0:0)
Device using Wide/Sync transfers at 40.0 MByte/sec, offset 8
Transinfo settings: current(12/8/1/0), goal(12/8/1/0), user(12/15/1/0)
Total transfers 160151 (74577 reads and 85574 writes)
(scsi0:0:6:0)
Device using Narrow/Sync transfers at 5.0 MByte/sec, offset 15
Transinfo settings: current(50/15/0/0), goal(50/15/0/0), user(50/15/0/0)
Total transfers 0 (0 reads and 0 writes)
1.6 Parallel port info in /proc/parport
---------------------------------------
The directory /proc/parport contains information about the parallel ports of
your system. It has one subdirectory for each port, named after the port
number (0,1,2,...).
These directories contain the four files shown in Table 1-8.
Table 1-8: Files in /proc/parport
..............................................................................
File Content
autoprobe Any IEEE-1284 device ID information that has been acquired.
devices list of the device drivers using that port. A + will appear by the
name of the device currently using the port (it might not appear
against any).
hardware Parallel port's base address, IRQ line and DMA channel.
irq IRQ that parport is using for that port. This is in a separate
file to allow you to alter it by writing a new value in (IRQ
number or none).
..............................................................................
1.7 TTY info in /proc/tty
-------------------------
Information about the available and actually used tty's can be found in the
directory /proc/tty.You'll find entries for drivers and line disciplines in
this directory, as shown in Table 1-9.
Table 1-9: Files in /proc/tty
..............................................................................
File Content
drivers list of drivers and their usage
ldiscs registered line disciplines
driver/serial usage statistic and status of single tty lines
..............................................................................
To see which tty's are currently in use, you can simply look into the file
/proc/tty/drivers:
> cat /proc/tty/drivers
pty_slave /dev/pts 136 0-255 pty:slave
pty_master /dev/ptm 128 0-255 pty:master
pty_slave /dev/ttyp 3 0-255 pty:slave
pty_master /dev/pty 2 0-255 pty:master
serial /dev/cua 5 64-67 serial:callout
serial /dev/ttyS 4 64-67 serial
/dev/tty0 /dev/tty0 4 0 system:vtmaster
/dev/ptmx /dev/ptmx 5 2 system
/dev/console /dev/console 5 1 system:console
/dev/tty /dev/tty 5 0 system:/dev/tty
unknown /dev/tty 4 1-63 console
1.8 Miscellaneous kernel statistics in /proc/stat
-------------------------------------------------
Various pieces of information about kernel activity are available in the
/proc/stat file. All of the numbers reported in this file are aggregates
since the system first booted. For a quick look, simply cat the file:
> cat /proc/stat
cpu 2255 34 2290 22625563 6290 127 456
cpu0 1132 34 1441 11311718 3675 127 438
cpu1 1123 0 849 11313845 2614 0 18
intr 114930548 113199788 3 0 5 263 0 4 [... lots more numbers ...]
ctxt 1990473
btime 1062191376
processes 2915
procs_running 1
procs_blocked 0
The very first "cpu" line aggregates the numbers in all of the other "cpuN"
lines. These numbers identify the amount of time the CPU has spent performing
different kinds of work. Time units are in USER_HZ (typically hundredths of a
second). The meanings of the columns are as follows, from left to right:
- user: normal processes executing in user mode
- nice: niced processes executing in user mode
- system: processes executing in kernel mode
- idle: twiddling thumbs
- iowait: waiting for I/O to complete
- irq: servicing interrupts
- softirq: servicing softirqs
The "intr" line gives counts of interrupts serviced since boot time, for each
of the possible system interrupts. The first column is the total of all
interrupts serviced; each subsequent column is the total for that particular
interrupt.
The "ctxt" line gives the total number of context switches across all CPUs.
The "btime" line gives the time at which the system booted, in seconds since
the Unix epoch.
The "processes" line gives the number of processes and threads created, which
includes (but is not limited to) those created by calls to the fork() and
clone() system calls.
The "procs_running" line gives the number of processes currently running on
CPUs.
The "procs_blocked" line gives the number of processes currently blocked,
waiting for I/O to complete.
------------------------------------------------------------------------------
Summary
------------------------------------------------------------------------------
The /proc file system serves information about the running system. It not only
allows access to process data but also allows you to request the kernel status
by reading files in the hierarchy.
The directory structure of /proc reflects the types of information and makes
it easy, if not obvious, where to look for specific data.
------------------------------------------------------------------------------
------------------------------------------------------------------------------
CHAPTER 2: MODIFYING SYSTEM PARAMETERS
------------------------------------------------------------------------------
------------------------------------------------------------------------------
In This Chapter
------------------------------------------------------------------------------
* Modifying kernel parameters by writing into files found in /proc/sys
* Exploring the files which modify certain parameters
* Review of the /proc/sys file tree
------------------------------------------------------------------------------
A very interesting part of /proc is the directory /proc/sys. This is not only
a source of information, it also allows you to change parameters within the
kernel. Be very careful when attempting this. You can optimize your system,
but you can also cause it to crash. Never alter kernel parameters on a
production system. Set up a development machine and test to make sure that
everything works the way you want it to. You may have no alternative but to
reboot the machine once an error has been made.
To change a value, simply echo the new value into the file. An example is
given below in the section on the file system data. You need to be root to do
this. You can create your own boot script to perform this every time your
system boots.
The files in /proc/sys can be used to fine tune and monitor miscellaneous and
general things in the operation of the Linux kernel. Since some of the files
can inadvertently disrupt your system, it is advisable to read both
documentation and source before actually making adjustments. In any case, be
very careful when writing to any of these files. The entries in /proc may
change slightly between the 2.1.* and the 2.2 kernel, so if there is any doubt
review the kernel documentation in the directory /usr/src/linux/Documentation.
This chapter is heavily based on the documentation included in the pre 2.2
kernels, and became part of it in version 2.2.1 of the Linux kernel.
2.1 /proc/sys/fs - File system data
-----------------------------------
This subdirectory contains specific file system, file handle, inode, dentry
and quota information.
Currently, these files are in /proc/sys/fs:
dentry-state
------------
Status of the directory cache. Since directory entries are dynamically
allocated and deallocated, this file indicates the current status. It holds
six values, in which the last two are not used and are always zero. The others
are listed in table 2-1.
Table 2-1: Status files of the directory cache
..............................................................................
File Content
nr_dentry Almost always zero
nr_unused Number of unused cache entries
age_limit
in seconds after the entry may be reclaimed, when memory is short
want_pages internally
..............................................................................
dquot-nr and dquot-max
----------------------
The file dquot-max shows the maximum number of cached disk quota entries.
The file dquot-nr shows the number of allocated disk quota entries and the
number of free disk quota entries.
If the number of available cached disk quotas is very low and you have a large
number of simultaneous system users, you might want to raise the limit.
file-nr and file-max
--------------------
The kernel allocates file handles dynamically, but doesn't free them again at
this time.
The value in file-max denotes the maximum number of file handles that the
Linux kernel will allocate. When you get a lot of error messages about running
out of file handles, you might want to raise this limit. The default value is
10% of RAM in kilobytes. To change it, just write the new number into the
file:
# cat /proc/sys/fs/file-max
4096
# echo 8192 > /proc/sys/fs/file-max
# cat /proc/sys/fs/file-max
8192
This method of revision is useful for all customizable parameters of the
kernel - simply echo the new value to the corresponding file.
Historically, the three values in file-nr denoted the number of allocated file
handles, the number of allocated but unused file handles, and the maximum
number of file handles. Linux 2.6 always reports 0 as the number of free file
handles -- this is not an error, it just means that the number of allocated
file handles exactly matches the number of used file handles.
Attempts to allocate more file descriptors than file-max are reported with
printk, look for "VFS: file-max limit <number> reached".
inode-state and inode-nr
------------------------
The file inode-nr contains the first two items from inode-state, so we'll skip
to that file...
inode-state contains two actual numbers and five dummy values. The numbers
are nr_inodes and nr_free_inodes (in order of appearance).
nr_inodes
~~~~~~~~~
Denotes the number of inodes the system has allocated. This number will
grow and shrink dynamically.
nr_free_inodes
--------------
Represents the number of free inodes. Ie. The number of inuse inodes is
(nr_inodes - nr_free_inodes).
aio-nr and aio-max-nr
---------------------
aio-nr is the running total of the number of events specified on the
io_setup system call for all currently active aio contexts. If aio-nr
reaches aio-max-nr then io_setup will fail with EAGAIN. Note that
raising aio-max-nr does not result in the pre-allocation or re-sizing
of any kernel data structures.
2.2 /proc/sys/fs/binfmt_misc - Miscellaneous binary formats
-----------------------------------------------------------
Besides these files, there is the subdirectory /proc/sys/fs/binfmt_misc. This
handles the kernel support for miscellaneous binary formats.
Binfmt_misc provides the ability to register additional binary formats to the
Kernel without compiling an additional module/kernel. Therefore, binfmt_misc
needs to know magic numbers at the beginning or the filename extension of the
binary.
It works by maintaining a linked list of structs that contain a description of
a binary format, including a magic with size (or the filename extension),
offset and mask, and the interpreter name. On request it invokes the given
interpreter with the original program as argument, as binfmt_java and
binfmt_em86 and binfmt_mz do. Since binfmt_misc does not define any default
binary-formats, you have to register an additional binary-format.
There are two general files in binfmt_misc and one file per registered format.
The two general files are register and status.
Registering a new binary format
-------------------------------
To register a new binary format you have to issue the command
echo :name:type:offset:magic:mask:interpreter: > /proc/sys/fs/binfmt_misc/register
with appropriate name (the name for the /proc-dir entry), offset (defaults to
0, if omitted), magic, mask (which can be omitted, defaults to all 0xff) and
last but not least, the interpreter that is to be invoked (for example and
testing /bin/echo). Type can be M for usual magic matching or E for filename
extension matching (give extension in place of magic).
Check or reset the status of the binary format handler
------------------------------------------------------
If you do a cat on the file /proc/sys/fs/binfmt_misc/status, you will get the
current status (enabled/disabled) of binfmt_misc. Change the status by echoing
0 (disables) or 1 (enables) or -1 (caution: this clears all previously
registered binary formats) to status. For example echo 0 > status to disable
binfmt_misc (temporarily).
Status of a single handler
--------------------------
Each registered handler has an entry in /proc/sys/fs/binfmt_misc. These files
perform the same function as status, but their scope is limited to the actual
binary format. By cating this file, you also receive all related information
about the interpreter/magic of the binfmt.
Example usage of binfmt_misc (emulate binfmt_java)
--------------------------------------------------
cd /proc/sys/fs/binfmt_misc
echo ':Java:M::\xca\xfe\xba\xbe::/usr/local/java/bin/javawrapper:' > register
echo ':HTML:E::html::/usr/local/java/bin/appletviewer:' > register
echo ':Applet:M::<!--applet::/usr/local/java/bin/appletviewer:' > register
echo ':DEXE:M::\x0eDEX::/usr/bin/dosexec:' > register
These four lines add support for Java executables and Java applets (like
binfmt_java, additionally recognizing the .html extension with no need to put
<!--applet> to every applet file). You have to install the JDK and the
shell-script /usr/local/java/bin/javawrapper too. It works around the
brokenness of the Java filename handling. To add a Java binary, just create a
link to the class-file somewhere in the path.
2.3 /proc/sys/kernel - general kernel parameters
------------------------------------------------
This directory reflects general kernel behaviors. As I've said before, the
contents depend on your configuration. Here you'll find the most important
files, along with descriptions of what they mean and how to use them.
acct
----