Stefan Helander

Ubuntu 12.04 hangs in different stages of the boot sequence

/0 Comments/in /by

A server I am maintaining stopped during boot on the "Stopping userspace bootsplash" or "Configuring network interfaces". If Ctrl-Alt-Del was pressed the machine rebooted so it was not completely stuck. I tried booting in rescue mode and checked the /etc/network/interfaces syntax but no problem visible there.

The solution was quite simple. Boot in rescue mode and select package repair. After repairing my packages the machine was rebooted, then fsck was ran automatically (which took quite a while). After that the machine booted normally.

 

Stefan Helander

Install Ubuntu 14.04 on Samsung Ultrabook Ativ Book 9

/5 Comments/in /by

To install Ubuntu 14.04 on a Samung Ultrabook Ativ Book 9, this is how to do it.

I decided to keep the factory installed Windows 8.1 beside my Ubuntu install using dual boot. Thanks to enrish for the basic info. I found out there is no need to shrink the Windows 8.1 partition as long there is space enough for Ubuntu. The Ubuntu installation will do this for you. Before you do anything – make sure you have a backup as usual. If you decide not to keep the Windows 8.1 install, do keep the recovery partitions. No need to install any screen drivers, Ubuntu worked out of the box.

  1. In WIndows, run the Samsung Update Utility and update everything including BIOS/firmware.
  2. In Window Control Panel go to Power options and click on Choose what the power button does. Click on Change settings that are currently unavailable then scroll down and deselect Turn on fast startup (source http://askubuntu.com/questions/221835/installing-ubuntu-on-a-pre-installed-windows-8-64-bit-system-uefi-supported). Restart your system.
  3. When booting, press F2 to enter the setup.
  4. In the Boot section, disable Fastboot
  5. Insert the USB flash drive with Ubuntu ISO (prepared with create startup disk on another computer). 
  6. Configure boot device order, setting the flash drive to be the first option.
  7. Save and reboot. Now the system should be booting on the flash drive.
  8. Select to Install Ubuntu. During installation Ubuntu will recognize that you have Windows 8.1 installed and you have the option to install Ubuntu beside the Windows 8.1. The Ubuntu install will shrink the Windows 8.1 partition to make room for Ubuntu. By dragging the vertical bar you can decide how large the partitions for Windows vs Ubuntu should be. Continue installing Ubuntu as usual.
  9. After installing Ubuntu, unplug the flashdrive and when booting, press F2 and enable Fastboot again.

 

Stefan Helander

Disable 802.11n on Compaq 6910p with iwl4965 in Ubuntu

/1 Comment/in , , /by

I’ve found out that the 802.11n high speed wifi / wlan mode (300 Mbps theoretically) tends to cause more harm than good, i.e. the performance in many, especially crowded, wifi environments will be really poor and it is a better option to turn it off.

My Compaq 6910p laptop comes with an Intel Wireless WiFi Link 4965AGN chipset. The 802.11n mode can be disabled making it fall back to only use 802.11a/b/g modes casuing the connection to be much more stable and often the overall bandwidth will be better.

To check if your chipset is running with 802.11n enabled, enter the command:

sudo iwconfig wlan0

The output will look something like this:

wlan0     IEEE 802.11abgn  ESSID:"XXXXXX"
          Mode:Managed  Frequency:2.462 GHz  Access Point: 00:0C:F6:82:90:28
          Bit Rate=14.4 Mb/s   Tx-Power=15 dBm
          Retry  long limit:7   RTS thr:off   Fragment thr:off
          Encryption key:off
          Power Management:off
          Link Quality=51/70  Signal level=-59 dBm
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:66  Invalid misc:36   Missed beacon:0

If the first line says 802.11abgn your chipset has 802.11n activated.

To disable 802.11n mode do the following:

sudo modprobe -r iwl4965
sudo modprobe iwl4965 11n_disable=1

This will disable 802.11n until next reboot. Now check again with sudo iwconfig wlan0 and the output should display the first line without the “n” after 802.11, like this:

wlan0     IEEE 802.11abg  ESSID:”XXXXXX”
          Mode:Managed  Frequency:2.462 GHz  Access Point: 00:0C:F6:82:90:28
          Bit Rate=54 Mb/s   Tx-Power=15 dBm
          Retry  long limit:7   RTS thr:off   Fragment thr:off
          Encryption key:off
          Power Management:off
          Link Quality=46/70  Signal level=-64 dBm
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:7  Invalid misc:485   Missed beacon:0

If you want to make this change permanent, i.e. always disable 802.11n, do the following:

sudo echo "options iwl4965 11n_disable=1" >> /etc/modprobe.d/iwl4965.conf

After rebooting, verify using sudo iwconfig wlan0 that 802.11n is not enabled.

 

Stefan Helander

Fix the Heartbleed Bug on Ubuntu

/0 Comments/in /by

OpenSSL on Ubuntu can be vulnerable to the Heartbleed Bug. Not all versions of OpenSSL are affected though. 

OpenSSL version 1.0.1 to 1.0.1f are vulnerable.
OpenSSL version 1.0.1g are not vulnerable.
OpenSSL branches 1.0.0 and 0.9.8 are not vulnerable.

To fix this issue on Ubuntu systems: 

Check your OpenSSL version to see if it is vulnerable to the bug:

openssl version

If it says 1.0.1 check the build date:

openssl version -b

If it says anything before Apr 7 2014 you need to update OpenSSL. Proceed as follows:

sudo apt-get update
sudo apt-get install openssl
sudo apt-get install libssl1.0.0

Now verify that you are running the updated OpenSSL libraries:

openssl version
openssl version -b

The build date should now come out Apr 7 2014 or later.

Now you need to regenerate your SSL certificates as they might been compromised. A guide can be found here: https://www.digitalocean.com/community/articles/how-to-create-a-ssl-certificate-on-apache-for-ubuntu-12-04
 

 

Stefan Helander

Remmina on Ubuntu 12.04 problem to connect to Windows 7 with RDP ‘Unable to connect to RDP server’

/0 Comments/in /by

Suddenly I couldn’t connect to my Windows 7 machine by RDP using Remmina on Ubuntu 12.04. It had worked before and suddenly stopped working. The error message displayed was ‘Unable to connect to RDP server’. Other RDP connections worked fine.

For some reason the problem was solved by editing the file ~/.freerdp/known_hosts and deleting the line with the server having the problem. When connecting again I was asked to accept the certificate and now the RDP connection worked again.

 

Stefan Helander

Err 310 ERR_TOO_MANY_REDIRECTS in Chrome and Firefox using Apache’s mod_rewrite

/0 Comments/in , /by

I used Apache’s mod_rewrite in order to direct a couple of domains pointing to the same website using the 301 moved permanently (to avoid duplicate content), i.e. something like this in .htaccess: 

RewriteEngine On
RewriteCond %{HTTP_HOST} !^example\.com$
RewriteRule ^(.*)$ http://example.com/$1 [R=301,L]

I randomly got the error message 310 ERR_TOO_MANY_REDIRECTS when trying the different domains in both Chrome and Firefox (other browsers seemd to work). I had decided my site should be reached without "www", so http://www.example.com was redirected to http://example.com also. 

After a while of head scratching I found a couple of forgotten DNS entries. Two of them where outdated. My domain setup for example.com in DNS looked like this (sample IP-addresses): 

example.com zone:

@  IN  A  192.168.100.1
@  IN  A  192.168.100.2
@  IN  A  192.168.100.3

www  IN  A  192.168.100.1

But only 192.168.100.1 was valid and had a running web server on it.

I guess what happens is when Chrome/Firefox tries to talk to 192.168.100.2 or .3 and get no response, they add "www" in front of the domain name, i.e. http://www.example.com. Now it got a response from the webserver saying 301 redirect to http://example.com. Now trying to talk to example.com on 192.168.100.2 or .3 no response, adding "www" and there we have our loop.

Fixing the DNS entries (removed the invalid 192.168.100.2 and .3) fixed the problem. A bit odd and hard to find, and most of all stupid to have the outdated records still in the zone. 

 

Stefan Helander

Remove or add www to URL using Apache mod_rewrite

/0 Comments/in , /by

To avoid a website being considered as "duplicate content" by Google (i.e. the same website appearing under different URLs) it is a good idea to make sure the website doesnt appear as both http://www.example.com and http://example.com. This can be achieved by using the mod_rewrite in Apache using the .htaccess file.

To remove "www" from the URL, i.e. the website’s URL should be http://example.com, your .htaccess should look like this: 

RewriteEngine On
RewriteCond %{HTTP_HOST} !^example\.com$
RewriteRule ^(.*)$ http://example.com/$1 [R=301,L]

If you instead want to make sure "www" is added, i.e. the website’s URL should be http://www.example.com, your .htaccess should look like this: 

RewriteEngine On
RewriteCond %{HTTP_HOST} !^www\.example\.com$
RewriteRule ^(.*)$ http://www.example.com/$1 [R=301,L]

 

Stefan Helander

postfix only listens on localhost (127.0.0.1)

/0 Comments/in /by

On a newly installed VPS (Parallells Virtuozzo) running Ubuntu 12.04 LTS I also installed postfix as my MTA. However, it turned out that it only listened on localhost. I checked that "inet_interfaces = all" in main.cf and that my /etc/hosts was up to date with my server’s hostname. The reason was that the machine had sendmail preinstalled and running.

A netstat -an gives: 

tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN

To the solution to this is: 

sudo /etc/init.d/sendmail stop
sudo update-rc.d -f sendmail remove
sudo /etc/init.d/postfix restart

Now netstat -anp show that postfix listens to all interfaces: 

tcp 0 0 0.0.0.0:25 0.0.0.0:* LISTEN 691/master

 

Stefan Helander

Avoiding a SSH client connection to timeout

/0 Comments/in /by

If you’re behind a firewall you sometimes run into a problem where the SSH client connection times out after a period of time (typically when going out for lunch leaving your SSH sessions logged in). The easiest way to solve this is by changing the configuration of the SSH client (it can also be fixed through the server config but since the problem often relates to the firewall protecting the client it is a better solution to fix this in the client). 

Just edit the file ./ssh/config and add the lines: 

Host *
ServerAliveInterval 30

The above assumes the firewall drops inactive connections at an interval > 30 seconds. 

 

Stefan Helander

How to make a floppy file image and mounting it in Linux

/0 Comments/in /by

To make a file image of a floppy disk in Linux (like Ubuntu), you need (of course) a computer with a floppy drive (/dev/fd0). Insert the floppy you want to copy to an image file and issue the command:

$ sudo dd bs=512 count=2880 if=/dev/fd0 of=floppy.img 

Block size (bs) and count above is for a 1,44 MB 3.5" floppy disk.

The image file can be copied back to another floppy disk with the command: 

$ sudo dd bs=512 count=2880 if=floppy.img of=/dev/fd0

The image file can also be mounted directly from the image file without the need of a physical floppy disk: 

$ sudo mkdir /media/fd
$ sudo mount -o loop floppy.img /media/fd/

I use the above method to move the content from a number of floppy disks to my hard drives. Computers today are rarely seen with a floppy drive and I wanted to secure the content before it is too late 🙂