KNOW-HOW
Ask Klaus!
ASK
KLAUS!
Klaus Knopper is the creator of
Knoppix and co-founder of the
LinuxTag expo. He currently
works as a teacher, programmer, and consultant. If you have
a configuration problem, or if
you just want to learn more
about how Linux works, send
your questions to:
klaus@linux-magazine.com
No Connection
Thank you for the comments in
the September 2006 Linux Magazine regarding my IBM R50e
laptop. I have now written a C++program that solves about 90% of the Sudoku problems I give it, but I am still unable to connect reliably to the Internet.
I have sent and received about half a
dozen e-mails using Evolution, the default under Ubuntu, but I usually get a
message that says “unable to connect to
pop.tiscali.co.uk” and asks again for the
password, which I give it. The transmission eventually says “completed.” On receipt it says “unable to connect to pop.
tiscali.co.uk” and “Error while fetching
mail,” but it has received the message,
after asking twice for the pop password.
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ISSUE 72 NOVEMBER 2006
Firefox will only get the Ubuntu help
from Linux on the laptop, not from the
web. And Firefox times out if I enter
http://www.google.co.uk.
I can ping (all from the laptop) to my
desktop Windows or Linux, (time1-2
ms); www.google.co.uk (time 49-52 ms);
www.linux-magazine.com (time 46-48
ms).
iwconfig gives:
eth0 IEEE 802.11g U
ESSID:"TI-AR7WD"
Bit Rate=54Mb/s U
Tx-Power=20dBm
plus 5 more lines that look reasonable.
So I guess things are nearly correct,
but the system just doesn’t work!
This sounds like a problem with
firewall settings, or else a generic routing problem. After the
Internet connection is established,
please check the following settings:
ifconfig eth0
This should show the general IP settings
of your WLAN device (since you used
iwconfig eth0 above). The card
should have a valid IPV4 address, and eventually also
an IPV6 address. More
about that one later.
route -n
This should show how
packets are directed
over the network. There
should be an entry for
W W W. L I N U X - M A G A Z I N E . C O M
0.0.0.0 showing the default gateway
used for traffic to and from the Internet.
cat /etc/resolv.conf
This file should contain the entry
nameserver numerical-ip-address for resolving network names. If such an entry
is missing, you can connect only to ipnumbers, not to hostnames.
iptables -L
This command shows your packet filter/
firewall settings. If no rules are set, there
are usually three entries (INPUT, OUTPUT, FORWARD) with “policy accept.” If
a lot of other rules are shown, you have
some work and research ahead that’s beyond the scope of a quick answer…
cat /proc/sys/net/ipv4/U
ip_dynaddr
If you are using on-demand connect
(i.e., your computer automatically connects to the Internet when you contact
an address, rather than connecting
through a manual dial-up link), ip_dynaddr is supposed to take care
of translating the initial
(possibly unset) IP
address of the first
packet sent from
your computer.
If this file contains a 0, the
first sent
packet is discarded, and you
get a “connection
refused” message,
Ask Klaus!
KNOW-HOW
but only for the very first attempt during
this session. When this happens during
a DNS query, you get a “host unknown”
message (which should be close to the
error message shown in the web
browser). The next connection attempt
will probably succeed, unless the dialon-demand setting closes the connection
very quickly when no data is transferred
for a while. If you type:
echo 1 > U
/proc/sys/net/ipv4/ip_dynaddr
as root, you enable ip translation for
the first packet, and you will get a valid
connection or a DNS reply also for the
first packet sent. This setting is not reboot-proof; you will have to add it to
your boot scripts in case it is missing.
There may be a GUI in your distribution
for enabling ip_dynaddr on boot.
In theory, there may also be some
hooks for SElinux that prevent certain
parts of the network configuration from
working, but since you “sometimes” get
a connection, this is not very likely.
Windows-free and Sound
Card
I am installing Suse 10 on a machine that previously had Windows and has been formatted
(under Windows). The installer recommends shrinking the Windows partition
to a smaller size and then adding Linux.
How do I convince the installer that I
want a completely Windows-free clean
Linux-only install?
Also, for my professional audio recording needs, I am looking for a laptop
with a sound card that has four channels
(analog) in and out. I need the software
to run this sound card, and I need tools
for audio editing and mixing down to
two tracks. I don’t need any of the other
myriad programs you get with a Linux
distro, such as the OpenOffice Suite or
an e-mail/Internet application. This laptop will be a dedicated hard disc recorder only. I’m not asking you to design
it for me, but can you point me in the direction of a company that can set this
machine up to my requirements and sell
it to me?
If a Linux installer does not offer
you the option to only install
Linux and wipe out everything
Figure 1: The AGNULA project supports professional audio and video for Linux.
else, it is a bug. But you can surely circumvent this bug by manually partitioning the hard disk and deleting all partitions. Try to get hold of a root commandline in the booted Linux installation CD
or DVD (usually there is one on the second installer console, Ctrl-Alt-F2), and
use cfdisk /dev/hda or fdisk /dev/hda, or
the same for /dev/sda, depending on
your hard disk type.
You can also use a Knoppix live CD for
partitioning, if the installer CD does not
allow you to do this. Delete all partitions, quit the partitioning program with
“save changes,” and reboot (some controllers only recognize partitioning
changes after reboot, really!). Now, the
installer should not even give you the
choice of installing Linux as a “second”
operating system; it should be the only
option, and no “resize” is necessary.
As for your sound recording needs,
you may want to have a look at the AGNULA project, http://www.agnula.org/,
and specifically the Audio/Video-focused, Debian-basd DeMuDi distribution, http://demudi.agnula.org/, which
should cover the software side and
maybe also contain hints about which
hardware is perfect for this task.
I’m not a notebook hardware expert.
In fact, I am not even sure if there are
notebooks with professional audio quality. Even high-end notebooks tend to be
equipped with noisy fans and hard
disks, as well as wiring that is so tight
W W W. L I N U X - M A G A Z I N E . C O M
that you get line noise on analog audio
input because of insufficient electric
shielding. Onboard soundcards are also
usually not of perfect audio quality. But I
may be wrong about this.
So I would just recommend asking a
linux-focused notebook vendor like
http://www.xtops.de/ who can tell you
which hardware is fastest and most compatible, and let them build a system for
you, equipped with the right kernel
modules and software especially optimized for what you plan to do. Open
Source business is all about customizing
and support.
See also http://www.linux-laptops.org/
for information about notebooks and
Linux compatibility.
No Upload
I use openSuse 10.0. I can transfer files over the Internet using
ftp, but I can’t seem to upload
files to websites using http. The file
transfer stalls at 162,816 bytes regardless
of the size of the file or the destination. I
have also had this problem when I am
attaching files to yahoo.mail and google.
mail, as well as when I am using Kontact.
I have a dual boot machine and the
files transfer just fine using MS Windows. I suspect there must be a Linux
configuration file somewhere that needs
to be modified. Can you help me find
what I need to do to fix this?
ISSUE 72 NOVEMBER 2006
55
KNOW-HOW
Ask Klaus!
File upload size is not an operating system limit (at least, not in
the dimensions used for webforms or attachments; you may have
problems if you try to attach a full DVD).
An http upload most likely uses one of
the following methods:
• HTTP PUT – a protocol option that is
not supported by too many web servers. Most admins use webDAV nowadays to directly modify files on a web
server. But this is probably not what
you want in this case.
• HTTP POST – an option that sends a
file, MIME-encoded, to a script or program running on the web server. The
script on the receiving side decides
what to do with this data. This is the
technique webmail forms use.
The file size limit for uploads is most
likely a browser (client) limit or a web
server limit. In PHP, which many servers
use as a scripting language for handling
“attachments,” there are some system
variables that control upload size:
; Whether to allow U
HTTP file uploads.
file_uploads = On
; Maximum allowed size U
for uploaded files.
upload_max_filesize = 2M
; Maximum size of POST U
data that PHP will accept.
post_max_size = 8M
You cannot upload more data than these
variables allow. But this, again, is a limit
on the server side. There are tricks for
circumventing these server-side limits,
by using compressed data formats, by
using different file encodings, or by
sending chunks of files and letting a
server-side script reassemble them. The
solution depends on your browser settings. Check for a limit set for POST operations or maximum size of transferred
files in your browser. If you use Firefox
on Windows, and file transfer for large
files works fine, it should also succeed
with Firefox on Linux, if you use the
same settings.
There is still the possibility nothing
is wrong with your setup, but the upload
script of your provider is broken, or it
limits file uploads to certain browsers or
client operating systems. In this case,
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ISSUE 72 NOVEMBER 2006
Figure 2: Setting the browser identification in Konqueror.
you could try to trick that broken server
script by setting your browser identity
(the “user-agent” id that your browser
sends to the server) to a setting similar
to what you use in Windows. You'll find
a menu for this in Konqueror. In Firefox,
try the User Agent Switcher plugin.
IPV6
The Internet protocol v6 is a new network address and routing technology.
It’s already implemented in Linux and
most network-capable programs, but, in
most cases, it is not really in use today.
Yet, IPV6 configuration CAN have an impact on your general IP connectivity,
even if you are quite sure you only use a
plain IPV4 network.
Even if your system does not have an
IPV6 address (yet), some programs may
still try to do IPV6 routing by default in
order to reach hosts on the Internet.
While this should – in theory – not be a
problem (Linux and all components in
the modern KDE, as well as the Gnome
desktop, are IPV6-aware), it could lead
to an initial timeout when the system
tries to connect to the nameserver or default gateway by IPV6. In KDE, you can
disable IPV6 by adding the following:
KDE_NO_IPV6=TRUE
to /etc/environment and restarting KDE.
Rumors have it that KDE network access
W W W. L I N U X - M A G A Z I N E . C O M
will “tremendously speed up” with this
setting, but I cannot verify this personally. Another way to disable IPV6 completely, without restarting KDE, is:
ip -6 addr flush eth0
This removes IPV6 addresses (and
aliases) from your network interface, in
your case, the WLAN device. This may
or may not improve IPV4 connectivity.
A final hint: Maybe the problem is
really on your provider’s side. Perhaps
there are too many connections to POP3
at certain times, and the POP3 server actively disconnects clients. Other operating systems and client programs sometimes have a silent “auto-retry” feature,
although most Linux mail clients only
reconnect as a response to a user action.
You could circumvent this dropped
connection problem by choosing POP3S,
the encrypted version of POP3, by
checking Use SSL as a configuration option and using port 995 instead of 110 for
your mail client. Since this also protects
your passwords and private email from
being transferred in plaintext, it is generally a good idea even without the possible connectivity improvements. ■
Send your Linux questions to
klaus@linux-magazine.com.