Figure 1.1: Files and directories in /proc/sys
The /proc Filesystem
Version 1.1
January 27, 1999
| Terrehon Bowden | Bodo Bauer |
<[email protected]> | <[email protected]> |
This documentation is part of a soon to be released book published by IDG Books on the SuSE Linux distribution. As there is no complete documentation for the /proc file system and we've used many freely available sources to write this chapter, it seems only fair to give the work back to the Linux community. This work is based on the 2.1.132 and 2.2.0-pre-kernel versions. I'm afraid it's still far from complete, but we hope it will be useful. As far as we know, it is the first 'all-in-one� document about the /proc file system. It is focused on the Intel x86 hardware, so if you are looking for PPC, ARM, SPARC, APX, etc., features, you probably won't find what you are looking for. It also only covers IPv4 networking, not IPv6 nor other protocols - sorry.
We'd like to thank Alan Cox, Rik van Riel, and Alexey Kuznetsov. We'd also like to extend a special thank you to Andi Kleen for documentation, which we relied on heavily to create this document, as well as the additional information he provided. Thanks to everybody else who contributed source or docs to the Linux kernel and helped create a great piece of software... :)
If you have any comments, corrections or additions, please don't
hesitate to contact Bodo Bauer at [email protected]. We'll be happy to
add them to this document.
The latest version of this document is available online at
http://www.suse.com/~bb/Docs/proc.html
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...
The proc file system acts as an interface to internal data structures
in the kernel. It can be used to obtain information about the system
and to change certain kernel parameters at runtime. It contains
(among other things) one subdirectory for each process running on the
system which is named after the process id (PID) of the process. The
link self points to the process reading the file system.
Each process subdirectory has the in table 1.1 listed entries.
| cmdline | Command line arguments |
| environ | Values of environment variables |
| fd | Directory, which contains all file descriptors |
| mem | Memory held by this process |
| stat | Process status |
| status | Process status in human readable form |
| cwd | Link to the current working directory |
| exe | Link to the executable of this process |
| maps | Memory maps |
| root | Link to the root directory of this process |
| statm | Process memory status information |
For example, to get the status information of a process, all you have
to do is read the file /proc/PID/status:
> cat /proc/self/status
Name: cat
State: R (running)
Pid: 5633
PPid: 5609
Uid: 501 501 501 501
Gid: 100 100 100 100
Groups: 100 16
VmSize: 804 kB
VmLck: 0 kB
VmRSS: 344 kB
VmData: 68 kB
VmStk: 20 kB
VmExe: 12 kB
VmLib: 660 kB
SigPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000000000
SigCgt: 0000000000000000
CapInh: 00000000fffffeff
CapPrm: 0000000000000000
CapEff: 0000000000000000
This shows you almost the same information as you would get if you
viewed it with the ps command. In fact, ps uses the proc
file system to obtain its information.
The statm file contains more detailed information about the
process memory usage. It co
The proc file system acts as an interface to internal data structures
in the kernel. It can be used to obtain information about the system
and to change certain kernel parameters at runtime. It contains
(among other things) one subdirectory for each process running on the
system which is named after the process id (PID) of the process. The
link self points to the process reading the file system.
Each process subdirectory has the in table 1.1 listed entries.
| cmdline | Command line arguments |
| environ | Values of environment variables |
| fd | Directory, which contains all file descriptors |
| mem | Memory held by this process |
| stat | Process status |
| status | Process status in human readable form |
| cwd | Link to the current working directory |
| exe | Link to the executable of this process |
| maps | Memory maps |
| root | Link to the root directory of this process |
| statm | Process memory status information |
For example, to get the status information of a process, all you have
to do is read the file /proc/PID/status:
> cat /proc/self/status
Name: cat
State: R (running)
Pid: 5633
PPid: 5609
Uid: 501 501 501 501
Gid: 100 100 100 100
Groups: 100 16
VmSize: 804 kB
VmLck: 0 kB
VmRSS: 344 kB
VmData: 68 kB
VmStk: 20 kB
VmExe: 12 kB
VmLib: 660 kB
SigPnd: 0000000000000000
SigBlk: 0000000000000000
SigIgn: 0000000000000000
SigCgt: 0000000000000000
CapInh: 00000000fffffeff
CapPrm: 0000000000000000
CapEff: 0000000000000000
This shows you almost the same information as you would get if you
viewed it with the ps command. In fact, ps uses the proc
file system to obtain its information.
The statm file contains more detailed information about the
process memory usage. It contains seven values with the following
meanings:
| size | total program size |
| resident | size of in memory portions |
| shared | number of the pages that are shared |
| trs | number of pages that are 'code' |
| drs | number of pages of data/stack |
| lrs | number of pages of library |
| dt | number of dirty pages |
The ratio text/data/library is approximate only by heuristics.
Similar to the process entries, these are files which give information
about the running kernel. The files used to obtain this information
are contained in /proc and are listed in
table 1.2. Not all of these will be present in your
system. It depends on the kernel configuration and the loaded modules,
which files are there, and which are missing.
| apm | Advanced power management info |
| cmdline | Kernel command line |
| cpuinfo | Info about the CPU |
| devices | Available devices (block and character) |
| dma | Used DMS channels |
| filesystems | Supported filesystems |
| interrupts | Interrupt usage |
| ioports | I/O port usage |
| kcore | Kernel core image |
| kmsg | Kernel messages |
| ksyms | Kernel symbol table |
| loadavg | Load average |
| locks | Kernel locks |
| meminfo | Memory info |
| misc | Miscellaneous |
| modules | List of loaded modules |
| mounts | Mounted filesystems |
| partitions | Table of partitions known to the system |
| rtc | Real time clock |
| slabinfo | Slab pool info |
| stat | Overall statistics |
| swaps | Swap space utilization |
| uptime | System uptime |
| version | Kernel version |
You can, for example, check which interrupts are currently in use and
what they are used for by looking in the file /proc/interrupts:
> cat /proc/interrupts
CPU0
0: 8728810 XT-PIC timer
1: 895 XT-PIC keyboard
2: 0 XT-PIC cascade
3: 531695 XT-PIC aha152x
4: 2014133 XT-PIC serial
5: 44401 XT-PIC pcnet_cs
8: 2 XT-PIC rtc
11: 8 XT-PIC i82365
12: 182918 XT-PIC PS/2 Mouse
13: 1 XT-PIC fpu
14: 1232265 XT-PIC ide0
15: 7 XT-PIC ide1
NMI: 0
There three more important subdirectories in /proc: net,
scsi and sys. The general rule is that the contents, or
even the existence of these directories, depends on your kernel
configuration. If SCSI is not enabled, the directory scsi may not
exist. The same is true with the net, which is only there when
networking support is present in the running kernel.
The slabinfo file gives information about memory usage on the slab level. Linux uses slab pools for memory management above page level in version 2.2. Commonly used objects have their own slab pool (like network buffers, directory cache, etc.).
This subdirectory contains information about all IDE devices that the kernel is aware of. There is one subdirectory for each device (i.e. hard disk) containing the following files:
| cache | The cache |
| capacity | Capacity of the medium |
| driver | driver and version |
| geometry | physical and logical geometry |
| identify | device identify block |
| media | media type |
| model | device identifier |
| settings | device setup |
| smart_thresholds | IDE disk management thresholds |
| smart_values | IDE disk management values |
This directory follows the usual pattern. Table 1.3 lists the files and their meaning.
| arp | Kernel ARP table |
| dev | network devices with statistics |
| dev_mcast | Lists the Layer2 multicast groups a device is listening 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 |
| 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) |
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
If you have a SCSI host adapter in your system, you'll find a
subdirectory named after the driver for this adapter in /proc/scsi.
You'll also see a list of all recognized SCSI devices in /proc/scsi:
>cat /proc/scsi/scsi
Attached devices:
Host: scsi0 Channel: 00 Id: 00 Lun: 00
Vendor: QUANTUM Model: XP34550W Rev: LXY4
Type: Direct-Access ANSI SCSI revision: 02
Host: scsi0 Channel: 00 Id: 01 Lun: 00
Vendor: SEAGATE Model: ST34501W Rev: 0018
Type: Direct-Access ANSI SCSI revision: 02
Host: scsi0 Channel: 00 Id: 02 Lun: 00
Vendor: SEAGATE Model: ST34501W Rev: 0017
Type: Direct-Access ANSI SCSI revision: 02
Host: scsi0 Channel: 00 Id: 04 Lun: 00
Vendor: ARCHIVE Model: Python 04106-XXX Rev: 703b
Type: Sequential-Access ANSI SCSI revision: 02
The directory named after the driver has one file for each adapter found in the system. These files contain information about the controller, including the used IRQ and the IO address range:
>cat /proc/scsi/ncr53c8xx/0
General information:
Chip NCR53C875, device id 0xf, revision id 0x4
IO port address 0xec00, IRQ number 11
Synchronous period factor 12, max commands per lun 4
The directory /proc/parport contains information about the
parallel ports of your system. It has one subdirectory for each port,
named after the port number (0,1,2,...).
This directory contains four files:
| autoprobe | Autoprobe results of this port |
| devices | Connected device modules |
| hardware | Hardware info (port type, io-port, DMA, IRQ, ...) |
| irq | Used interrupt, if any |
Information about the available and the actually used tty's can be
found in /proc/tty. You'll find entries for drivers and line
disciplines in this directory, as shown in the table below:
| drivers | list of drivers and their usage |
| ldiscs | registered line disciplines |
| driver/serial | usage statistic and status of single tty lines |
To see which tty's are currently in use, you can simply look into the
file
/proc/tty/drivers:
>cat /proc/tty/drivers
pty_slave /dev/pts 136 0-255 pty:slave
pty_master /dev/ptm 128 0-255 pty:master
pty_slave /dev/ttyp 3 0-255 pty:slave
pty_master /dev/pty 2 0-255 pty:master
serial /dev/cua 5 64-67 serial:callout
serial /dev/ttyS 4 64-67 serial
/dev/tty0 /dev/tty0 4 0 system:vtmaster
/dev/ptmx /dev/ptmx 5 2 system
/dev/console /dev/console 5 1 system:console
/dev/tty /dev/tty 5 0 system:/dev/tty
unknown /dev/tty 4 1-63 console
A very interesting part of /proc is the directory
/proc/sys. This not only provides information, it also allows
you to change parameters within the kernel. Be very careful when
trying this. You can optimize your system, but you also can crash
it. Never play around with kernel parameters on a production
system. Set up a development machine and test to make sure that
everything works the way you want it to. You may have no alternative
but to reboot the machine once an error has been made.
To change a value, simply echo the new value into the file. An example is given below in the section on the file system data. You need to be root to do this. You can create your own boot script to get this done every time your system boots.
Figure 1.1: Files and directories in /proc/sys
Figure 1.1 shows a snapshot of /proc/sys on a
SuSE system running kernel version 2.1.131. Please note, that this
figure shows actual files, not only directories like the figures we've
seen so far. As the contents of /proc change dynamically, this
picture may look different on your system. It also missed the subtree
/proc/sys/net/ipv4 which is shown in figure 1.2 and
discussed in section 1.3.8.
The files in /proc/sys can be used to tune and monitor
miscellaneous and general things in the operation of the Linux kernel.
Since some of the files can inadvertently disrupt your system, it is
advisable to read both documentation and source before actually making
adjustments. In any case, be very careful when writing to any of these
files. The entries in /proc may change slightly between the
2.1.* and the 2.2 kernel, so review the kernel documentation if there
is any doubt. You'll find the documentation in the directory
/usr/src/linux/Documentation/sys. This chapter is heavily based
on the documentation included in the pre 2.2 kernels. Thanks to Rick
van Riel for providing this information.
These two subdirectories are empty.
This subdirectory contains specific file system, file handle, inode, dentry and quota information.
Currently, these files are in /proc/sys/fs:
| nr_dentry | Seems to be zero all the time |
| nr_unused | Number of unused cache entries |
| age_limit | Age in seconds after the entry may be |
| reclaimed, when memory is short | |
| want_pages | internal |
dquot-max shows the maximum number of cached disk quota
entries.
The file dquot-nr shows the number of allocated disk quota
entries and the number of free disk quota entries.
If the number of free cached disk quotas is very low and you have a large number of simultaneous system users, you might want to raise the limit.
The value in file-max denotes the maximum number of file handles
that the Linux kernel will allocate. When you get a lot of error
messages about running out of file handles, you might want to raise
this limit. The default value is 4096. To change it, just write the
new number into the file:
# cat /proc/sys/fs/file-max
4096
# echo 8192 > /proc/sys/fs/file-max
# cat /proc/sys/fs/file-max
8192
This method of revision is useful for all customizable parameters of the kernel - simply echo the new value to the corresponding file.
The three values in file-nr denote the number of allocated file
handles, the number of used file handles, and the maximum number of
file handles. When the allocated file handles come close to the
maximum, but the number of actually used ones is far behind, you've
encountered a peak in your usage of file handles and you don't need
to increase the maximum.
However, there is still a per process limit of open files, which
unfortunatly can't be changed that easily. It is set to 1024 by
default. To change this you have to edit the files limits.h and
fs.h in the directory /usr/src/linux/include/linux. Change the
definition of NR_OPEN and recompile the kernel.
The value in inode-max denotes the maximum number of inode
handlers. This value should be 3 to 4 times larger than the value
in file-max, since stdin, stdout, and network sockets also need an
inode struct to handle them. If you regularly run out of inodes,
you should increase this value.
The file inode-nr contains the first two items from inode-state, so
we'll skip to that file...
inode-state contains three actual numbers and four dummy values. The
actual numbers are (in order of appearance) nr_inodes, nr_free_inodes,
and preshrink.
inode-max because Linux allocates them one
pageful at a time.
preshrink is nonzero
when the nr_inodes > inode-max and the system needs to prune the
inode list instead of allocating more.
super-max contains the maximum number of
super block handlers, where super-nr shows the number of
currently allocated ones.
Every mounted file system needs a super block, so if you plan to mount lots of file systems, you may want to increase these numbers.
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.
echo :name:type:offset:magic:mask:interpreter: > \
/proc/sys/fs/binfmt_misc/register
with appropriate name (the name for the /proc-dir entry),
offset (defaults to 0, if omitted), magic and
mask (which can be omitted, defaults to all 0xff) and
last but not least, the interpreter that is to be invoked (for
example and testing '/bin/echo'). Type can be M for
usual magic matching or E for filename extension matching (give
extension in place of magic).
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).
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.
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.
This directory reflects general kernel behaviors. As I've said before, the contents are depend on your configuration. I'll list the most important files, along with descriptions of what they mean and how to use them.
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%, accounting
suspends. If it goes above highwater%, 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 left 2% free;
resume it if we have a value 3%; consider information about the
amount of free space valid for 30 seconds
init(1) program to handle a graceful
restart. However, when the value is 0, 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.
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.
The names make it pretty obvious what these fields contain:
>cat /proc/sys/kernel/osrelease
2.2.0-final
>cat /proc/sys/kernel/ostype
Linux
>cat /proc/sys/kernel/version
#8 Mon Jan 25 19:45:02 PST 1999
The files osrelease and ostype should be clear
enough. Version needs a little more clarification
however. The #8 means that this is the 8th kernel built from
this source base and the date behind it indicates the time the
kernel was built. The only way to tune these values is to rebuild
the kernel.
printk denote
console_loglevel,
default_message_loglevel,
minimum_console_level and
default_console_loglevel
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 can be set.
console_loglevel.
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. Look into the SANE documentation on this issue.
The files in this directory can be used to tune the operation of the virtual memory (VM) subsystem of the Linux kernel. In addition, one of the files (bdflush) has a little influence on disk usage.
| nfract | Percentage of buffer cache dirty to |
| activate bdflush | |
| ndirty | Maximum number of dirty blocks to |
| write out per wake-cycle | |
| nrefill | Number of clean buffers to try to obtain |
| each time we call refill | |
| nref_dirt | Dirty buffer threshold for activating bdflush |
| when trying to refill buffers. | |
| dummy | unused |
| age_buffer | Time for normal buffer to age before we flush it |
| age_super | Time for superblock to age before we flush it |
| dummy | unused |
| dummy | unused |
refill_freelist() is called. It is
necessary to allocate free buffers beforehand, since the
buffers are often different sizes than the memory pages
and some bookkeeping needs to be done beforehand. The
higher the number, the more memory will be wasted and the
less often refill_freelist() will need to run.
refill_freelist() comes across more
than nref_dirt dirty buffers, it will wake up bdflush.
age_buffer and age_super parameters govern the
maximum time Linux waits before writing out a dirty buffer
to disk. The value is expressed in jiffies (clockticks), the
number of jiffies per second is 100. Age_buffer is the
maximum age for data blocks, while age_super is for
filesystems meta data.
The values are:
min, low and high:
The file contains three numbers:
mm/vmscan.c), so it isn't as big as it looks.
When you need to increase the bandwidth to/from swap, you'll want to increase this number.
swap_cluster is the number of pages kswapd writes in
one turn. You�ll want this value to be large so that kswapd does
its I/O in large chunks and the disk doesn�t have to seek as
often., but you don�t want it to be too large since that would
flood the request queue.
overcommit_memory is positive, then there's always enough
memory. This is a useful feature, since programs often
malloc() huge amounts of memory 'just in case', while they
only use a small part of it. Leaving this value at 0 will lead to
the failure of such a huge malloc(), when in fact the system has
enough memory for the program to run.
On the other hand, enabling this feature can cause you to run out of memory and thrash the system to death, so large and/or important servers will want to set this value to 0.
buffermem, only this file
controls the amount of memory allowed for memory mapping and
generic caching of files.
You don't want the minimum level to be too low, otherwise your system might thrash when memory is tight or fragmentation is high.
On a low-memory, single CPU system, you can safely set these values to 0 so you don't waste memory. It is used on SMP systems so that the system can perform fast pagetable allocations without having to aquire the kernel memory lock.
For large systems, the settings are probably fine. For normal systems they won't hurt a bit. For small systems (<16MB ram) it might be advantageous to set both values to 0.
The first four variables
sc_max_page_age,
sc_page_advance,
sc_page_decline and
sc_page_initial_age
When a page is swapped in, it starts at sc_page_initial_age
(default 3) and when the page is scanned by kswapd, its age is
adjusted according to the following scheme:
sc_page_advance (default 3). Where the maximum
value is given by sc_max_page_age (default 20).
sc_page_decline (default 1).
When a page reaches age 0, it's ready to be swapped out.
The next four variables sc_age_cluster_fract,
sc_age_cluster_min, sc_pageout_weight and
sc_bufferout_weight, can be used to control kswapd's
aggressiveness in swapping out pages.
Sc_age_cluster_fract is used to calculate how many pages
from a process are to be scanned by kswapd. The formula used is
So if you want kswapd to scan the whole process,
sc_age_cluster_fract needs to have a value of 1024. The minimum
number of pages kswapd will scan is represented by
sc_age_cluster_min, this is done so kswapd will also scan small
processes.
The values of sc_pageout_weight and sc_bufferout_weight are used
to control how many tries kswapd will make in order to swap out
one page/buffer. These values can be used to fine-tune the ratio
between user pages and buffer/cache memory. When you find that
your Linux system is swapping out too many process pages in order
to satisfy buffer memory demands, you might want to either
increase sc_bufferout_weight, or decrease the value of
sc_pageout_weight.
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
drive name: sr0 hdc
drive speed: 0 6
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 hdc, and their lists of
features.
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)
The interface to the networking parts of the kernel is located in
/proc/sys/net. The table below shows all possible subdirectories. You
may see only some of them, depending on the configuration of your
kernel:
| 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. As 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 to Appletalk and IPX further down in section 1.3.10 and 1.3.11. Please look in 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.
message_cost factor is, the less messages will be
written. Message_burst controls when messages will be dropped. The
default settings limit warning messages to one every five seconds.
There are only two files in this subdirectory. They control the delays for deleting and destroying socket descriptors.
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 te subtree controlling the behavior of the IPv4 subsystem of the Linux kernel.
Figure 1.2: The IPv4 subtree of /proc/sys/net
Figure 1.2 shows the relevant fils for the IPv4 settings. As some directories have the same entries, they are shown only once.
Let's start with the entries in /proc/sys/net/ipv4 itself.
ICMP settings
Please note that if you accept ICMP echo requests with a broadcast/multicast destination address your network may be used as an exploder for denial of service packet flooding attacks to other hosts.
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 hundredths of a second (on Intel systems).
IP settings
IP fragmentation settings
ipfrag_high_thresh bytes of memory is allocated for this purpose,
the fragment handler will toss packets until ipfrag_low_thresh is
reached.
TCP settings
tcp_retries1.
CONFIG_SYNCOOKIES. Send out syncookies when the syn backlog queue
of a socket overflows. This is to prevent against 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.
FIN before the socket is
always closed. This is strictly a violation of the TCP
specification, but required to prevent denial-of-service attacks.
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.
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, where changes in the other subdirectories affect only one
interface.
All directories have the same entries:
'yes', if the kernel is configured for a
regular host; and 'no' for a router configuration.
'yes' for
routers and 'no' for hosts.
0.b.c.d destined not to this
host as local ones. It is supposed that BOOTP relay daemon will
catch and forward such packets.
The default is 'no', as this feature is not implemented yet
(kernel version 2.2.0-pre?).
CONFIG_MROUTE and a multicast routing daemon is required.
If you set this to 1 on a router that is the only connection for a network to the net , it evidently prevents spoofing attacks against your internal networks (external addresses can still be spoofed), without the need for additional firewall rules.
'yes'.
Routing settings
The directory /proc/sys/net/ipv4/route contains several file to
control routing issues.
error_cost factor is, the fewer messages will be
written. Error_burst controls when messages will be dropped. The
default settings limit warning messages to one every five seconds.
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:
gc_stale_time)
proxy\_delay).
ucast_solicit is > 0 it first
tries to send an ARP packet directly to the known host, when that
fails and mcast_solicit is > 0, an ARP request is broadcasted.
The /proc/sys/net/appletalk directory holds the Appletalk
configuration data when Appletalk is loaded. The configurable
parameters are:
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 via.
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 transmit and receive. 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.
The /proc Filesystem
This document was generated using the LaTeX2HTML translator Version 96.1-h (September 30, 1996) Copyright © 1993, 1994, 1995, 1996, Nikos Drakos, Computer Based Learning Unit, University of Leeds.
The command line arguments were:
latex2html -no_navigation -split 0 Kerneldoc.tex -.
The translation was initiated by Bodo Bauer on Sat Jan 30 20:43:27 PST 1999