TechniTip.Net

Status of a Software RAID under Linux

You might want to check the rebuild status of your Linux software RAID e.g. after a disc failure or a hard server crash. As you know this might take several hours, depending on the disc size.

In my case mdadm is used to configure the software RAID and mdadm –detail /dev/md1 can be used to show the rebuild status:

[root@hxxxxxxx ~]# mdadm --detail /dev/md1
/dev/md1:
Version : 00.90
Creation Time : Thu Nov  9 18:57:15 2006
Raid Level : raid1
Array Size : 159726144 (152.33 GiB 163.56 GB)
Used Dev Size : 159726144 (152.33 GiB 163.56 GB)
Raid Devices : 2
Total Devices : 2
Preferred Minor : 1
Persistence : Superblock is persistent

Update Time : Sun Feb 14 19:45:21 2010
State : active, resyncing
Active Devices : 2
Working Devices : 2
Failed Devices : 0
Spare Devices : 0

Rebuild Status : 31% complete

UUID : be29700c:083d0c62:67a9c130:e044323b
Events : 0.3626065

Number   Major   Minor   RaidDevice State
0       8        3        0      active sync   /dev/sda3
1       8       19        1      active sync   /dev/sdb3

In my case 31% of the rebuilt process are finished. We still have to wait a little bit..

Links

• The Software-RAID HOWTO: Detecting, querying and testing
• The Software-RAID HOTWO

Bash Prompt too long?

People often using Putty, xterm or any other Linux test based console will probably now this annoying issue:

• Changing into a deeper directory structure will create an incredible long bash prompt

For me it was quite annoying to have the prompt sometimes wider than the terminal window. In Debian standard configuration this is the case. So I decided to shorten the prompt.

I kept my prompt very simple, the only thing you have to do is to add the following lines to your ~/.bashrc

export PS1="[\u@\h \W]\\$ "
export PS2="> "

Make sure to add it at the end of your .bashrc file in your home directory. Otherwise it may be overwritten by other prompt definitions in your .bashrc.

Before

harry@h1096660:/usr/local/include/ffmpeg$

After

[harry@h1096660 ffmpeg]$

Better

Further links and examples

• Bash Prompt HOWTO
• Bash Prompts

Linuxcaffe in Toronto

Received from a friend while he was on a holiday trip in Toronto. A Linuxcaffe pretty cool I think. Nowadays Linux seems to be everywhere! Thank you Bogi for this nice shot.

Linux under Windows with andLinux

Nowadays there are several virtualization products like VMWare and Virtual PC available. Searching the Internet I came across coLinux and andLinux. This free and open source tools allow you to run Linux natively on your Windows PC.

coLinux is the base – a port of the Linux kernel which allows you to run Linux cooperatively on your Windows PC. andLinux is a complete Ubuntu Linux system which uses coLinux, Xming as X server and PulseAudio as sound server.

I’ve tried andLinux on my Windows XP notebook, installation was easy. Quite nice if you also want to have Linux running on your PC without purchasing other products. You can start Linux applications and they appear like a regular Windows application on your desktop.

andLinux offers some more features:

• Access from Linux applications to Windows filesystem
• Quick start of Linux applications from Quicklaunch bar
• Easy start of applications from KDE Start menu

See also:

• German andLinux website: andlinux.de

Definitely a try worth!

How To Change Time Zone in Linux

On modern Linux systems the time zone can be changed using the command:

dpkg-reconfigure tzdata

Now you will be prompted to choose your desired time zone.

How the time zone can be change manually can be found here:

• http://www.wikihow.com/Change-the-Timezone-in-Linux
• http://www.linuxsa.org.au/tips/time.html

PuTTY SSH Login Without Password Prompt

Annoyed of typing login passwords?

Your desktop is running with Windows and you often need to connect remote servers using SSH then you will already know PuTTY. You will also know that it’s getting frustrating to enter the passoword every time. There is a simple way to login to remote machines using RSA/DAS keys.

What is needed?

First of all you will need to download the PuTTY.exe. And to generate the keys on your Windows desktop you’ll need to download  PuTTYgen.exe as well.

Key Generation

Start PuTTYgen.exe after download and press the Generate button. Now follow the instruction and move the mouse cursor over the desired area. I’ve used the default parameter [x] SSH-2 RSA with a key length of 1024 bits.

I leave the Key passphrase empty because I don’t want to enter any passwords during login.

To have the key later available for other servers use the “Save public key” and “Save private key” button. My private key is saved as haifisch.ppk and my public key as haifisch. By the way, haifisch is German and means shark.

Now mark the generated public key, copy it to the clip board and paste it into ~/.ssh/authorized_keys file on the remote server of the user you want to login as.

PuTTY Configuration

Keys have been generated and stored on the remote server, therefore PuTTYgen can be closed now and the PuTTY.exe is needed now.

In PuTTY under the item “Session” enter the host name of the remote server and connection type SSH. Next choose “Connection/Data” and enter the remote user name. Also the previously defined private key is needed, it is given in “Connection/SSH/Auth” using the “Browse” button. In my case it’s haifisch.ppk.

When all settings are done go back to “Session”, enter a name for this session and press “Save”.

That’s it. Try it by double clicking on the saved session.

Login via Desktop Icon

If you want to have a desktop icon which opens putty and logs into a remote server generate a file e.g. www.myserver.com.bat with the content:

start C:\temp\putty\putty.exe -load "Session Name in PuTTY"

Now generate a link to this batch file on your desktop and login in by double clicking.

Debian “Lenny” 5.0 Released

Finally after 2 years running Debian “Etech” 4.0 the new version Debian 5.0 codename “Lenny” has been released. The new release is dedicated to Thiemo Seufer, a Debian Developer who dies on December 26th, 2008 in a tragic car accident. Read more information about “Lenny” on the Debian homepage.

As you know only the early bird catches the worm, I immediately decided to update one server to Lenny. Sure, sometimes the worm isn’t delicious but if you are dealing with IT stuff you will know this kind of bad tasting worms already.

Okay the good news are: The worm wasn’t bad tasting in this case. Find my upgrade report below.

Upgrade Procedure

First I started with:

apt-get update

And received the error message:

There are no public key available for the following key IDs: 4D270D06F42584E6

Which means we need to get a new public key:

gpg --recv-key --keyserver wwwkeys.eu.pgp.net 4D270D06F42584E6
gpg --export 4D270D06F42584E6 | apt-key add -

or optionally with (not tested):

apt-get install debian-archive-keyring

Fine, next apt-get update was done again and several packages have been updated. It was prompted if a new /etc/mysql/my.cnf should be installed or my old one should be kept. I decided to keep my old one.

Afterwards I upgraded the distribution with apt-get dist-upgrade and many packages have been downloaded and installed.

For several config files it is again prompted if the old one should be kept or overwritten. I decided to backup to old configuration files and overwrite them with the new ones from the current distribution. I wanted to make sure that I don’t run into conflicts. Using this way the upgrade is performed very quick.

In the next step I adapted all my changes from backuped config files into the new ones. In my case mainly the Apache2 and MySQL configurations.

Apache2

After doing this Apache2 started with the message “NameVirtualHost *:80 has no VirtualHosts” and no one of my virtual hosts was recognized. I resolved this issue by changing the file /etc/apache2/sites-enabled/000-default and /etc/apache2/ports.conf. Within both files I’ve changed declarations “*:80″ to “*”:

/etc/apache2/sites-enabled/000-default

<VirtualHost *>

/etc/apache2/ports.conf

NameVirtualHost *

Note that all your virtual host configurations also have to be defined with “<VirtualHost * >”.

APT

To receive the updates for “Lenny” edit the file /etc/apt/sources.conf and change the line:

deb http://security.debian.org/ etch/updates main contrib non-free

to

deb http://security.debian.org/ lenny/updates main contrib non-free

Grub

One special thing on my server here (Strato root server) is the Grub configuration. The server is configured with SATA RAID 1, therefore partitions are mounted on /dev/md0 and /dev/md1. After every kernel update I manually change the /boot/grub/menu.lst file. Here I copy the two parts for the latest running kernel and simply adjust the kernel versions:

title           Debian GNU/Linux, kernel (2.6.26-1-686)
root            (hd0,0)
kernel          /vmlinuz-2.6.26-1-686 root=/dev/md1 ro console=tty0 console=ttyS                   0,57600
initrd          /initrd.img-2.6.26-1-686
savedefault
boot

title           Debian GNU/Linux, kernel (2.6.26-1-686, recovery mode)
root            (hd0,0)
kernel          /vmlinuz-2.6.26-1-686 root=/dev/md1 ro console=tty0 console=ttyS                   0,57600 single
initrd          /initrd.img-2.6.26-1-686
savedefault
boot

Finally reboot and your issue will show “Debian GNU/Linux 5.0″.

Make VIM Nice Looking

Linux users usually know the text editor called “vi”. For beginners it’s tough to use and the look and feel is not very nice. “vim” which means vi-improved brings many improvements. To make vim more nice looking I’ve put my settings for your .vimrc together. I personally like the following settings:

• Syntax highlighting
• Different color scheme
• Disable indenting when copy and pasting a text from clip board
• Replace tabs with blanks
• Use 2 spaces as tabs instead of 4 spaces
• Improve the search
• Display cursor position

Open the .vimrc in your home directory and add the following settings:

" enable syntax highlightning
syntax enable

" set a different color scheme
colorscheme desert

" avoid identing when pasting a text
set paste

" enable auto indent
set autoindent

" expand tabs to spaces
set expandtab

" set the tab stop to 2 spaces and soft tab stop to 2 spaces
set tabstop=2 sts=2
set shiftwidth=2

" immediately search and display the typed search pattern
set incsearch

" highlighting of search matches
set hlsearch

" show cursor position
set ruler

Much better now! Try the search (e.g. ESC /high) and you will recognize that the search pattern will be immediately highlighted when you enter it.

Note: If you want to replace all tabs within an existing file you can now use the vi command “:retab” and all tabs will be removed according the settings done in your .vimrc.

And finally the result:

Network Bandwidth Performance Measurement with Iperf

Another easy to use tool for measuring the network bandwidth is Iperf. On Debian it can be installed using:

apt-get install iperf

Optionally the source or the Windows binary is available from sourceforge.net/projects/iperf

Building and installing from source is done using a few commands:

tar xvfz iperf-2.0.4.tar.gz
cd iperf-2.0.4
./configure
make
make install

Once installed iperf the server is started on machine 1:

machine1:~# iperf -s
------------------------------------------------------------
Server listening on TCP port 5001
TCP window size: 85.3 KByte (default)
------------------------------------------------------------

Next the client is started on machine 2:

machine2:~# iperf -c machine1.mydomain.de
------------------------------------------------------------
Client connecting to machine1.mydomain.de, TCP port 5001
TCP window size: 16.0 KByte (default)
------------------------------------------------------------
[  3] local xx.xx.xx.xx port 45325 connected with yy.yy.yy.yyport 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  96.6 MBytes  80.9 Mbits/sec

Tested on two servers connected with 100 MBit/s located at two different providers in Germany we get a result of 80.9 MBits/sec.

This result is slightly higher compared to the result from our measurement done with NETIO in the article Network Throughput Measurement. So we start the test again with addtional parameters:

machine2:~# iperf -c machine1.mydomain.de -w 512k -l 512k
------------------------------------------------------------
Client connecting to machine1.mydomain.de, TCP port 5001
TCP window size:   256 KByte (WARNING: requested   512 KByte)
------------------------------------------------------------
[  3] local xx.xx.xx.xx port 40987 connected with yy.yy.yy.yyport 5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-10.0 sec  72.0 MBytes  60.3 Mbits/sec

Now using modified read/write buffer size and TCP windows size we get almost the same result as in our test with netio.

Definitely a tool which can be recommended to check your network throughput!

FTP/SFTP with Resume

File transfers with resume are also possible for secure SFTP connections with WinSCP. A nice free SFTP, FTP and SCP client for Windows. At the WinSCP homepage more information regarding resume can be found.

For secure file transfers SFTP protocol allows resume. WinSCP definitly a nice and free tool!

See also: FTP with resume