Category: Ubuntu Server

Kernel does not support a non-PAE CPU install KVM guest on Ubuntu 13.10 – Fix

james 7 Comments

I just started to install an Ubuntu 13.10 KVM guest – however the build process failed. The command that I was using was:

vmbuilder kvm ubuntu -v --suite=saucy --libvirt=qemu:///system --arch=amd64  --cpus=1 --mem=2048 --swapsize=2048 --rootsize=220040 --flavour=virtual --hostname=mydomain --ip=1.2.3.4 --mask=1.2.3.4 --net=1.2.3.4 --bcast=1.2.3.4 --gw=1.2.3.4 --dns='8.8.8.8 8.8.4.4' --bridge=br0 --mirror=http://archive.ubuntu.com/ubuntu --components='main,universe' --addpkg=openssh-server --addpkg=acpid --addpkg=acpi-support --user=myuser --pass=mypassword --dest=/mnt/kvm/server/

However, I got this error message:

....
This kernel does not support a non-PAE CPU.
dpkg: error processing /var/cache/apt/archives/linux-image-3.8.0-32-generic_3.8.0-32.47_amd64.deb (--unpack):
 subprocess new pre-installation script returned error exit status 1
Examining /etc/kernel/postrm.d .
run-parts: executing /etc/kernel/postrm.d/initramfs-tools 3.8.0-32-generic /boot/vmlinuz-3.8.0-32-generic
run-parts: executing /etc/kernel/postrm.d/zz-update-grub 3.8.0-32-generic /boot/vmlinuz-3.8.0-32-generic
Errors were encountered while processing:
 /var/cache/apt/archives/linux-image-3.8.0-32-generic_3.8.0-32.47_amd64.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)

Basically, you just need ensure the the linux-image-generic package (i.e. a kernel which supports non-PAE CPU’s) is installed by setting the addpkg flag like so:

--addpkg=linux-image-generic

I hope this helps someone.

How to send Apache error.log to debugchannel

james Leave a comment

DebugChannel.com is a great new service / downloadable server to help debug your web application. The key things are that it speeds up debugging because all your debug output can be clearly formatted and shown in the same place. So you can get debug information from php scripts or even apache error logs. This post shows you how to send your Apache error logs or even Apache access lots to a debugchannel server.

Step 1 – Download the debugchannel tail client called dctail. This small python script is a wrapper for the the Linux tail command to watch files and send them up a debugchannel server.

wget https://github.com/debugchannel/debugchannel-tail-client/archive/master.zip

Step 2 – Extract the download and run the installer script which will install the command in /usr/bin/local/dctail and also create a service script in /etc/init.d/. This allows you to run dctail as a service on Ubuntu.

unzip master.zip

You need to run the installer script as root.

sudo ./install.sh

Step 3 – Setup the configuration files. The installer script creates a configuration files in /etc/debugchannel/dctail.conf . This is a json files. The key things to specify are the debugchannel server and which files you want to watch. To watch an Apache error.log you might need want a configuration file like this:

{
    "address": "https://debugchannel.com",
    "apiKey": "someApiKey",
    "files": { "/var/log/apache/error.log":"apachelogs" }
}

Note: we are sending the /var/log/apache/error.log -> https://debugchannel.com/apachelogs

Step 4 – Start running dctail as root (because it need permissions to read the Apache error.logs. You can either run it once using:

sudo dctail

Or (in Ubuntu) as a service

sudo service dctail start

I hope this helps someone.

How to forward all root emails to your external email address Ubuntu?

james 1 Comment

If the root user is getting mail on your server (for example from cron scripts) then it can really helpful to forward it to an external email address. There are two ways of doing this:

1) The easiest and quickest way is to make a file in the folder called /root/.forward and place your email address in it. Note – this will work for any user.

2) Alternatively you can edit the /etc/aliases and add the following line:

root: me@myemail.com

Then run:

newaliases

Then restart postfix (assuming this is you mta).

service postfix restart

Either way you can then test your configuration but sending an email:

echo test | mail -s "test message" root

p.s. You can install the mail command for this test using apt-get install mailutils 🙂

How to batch rename files in Ubuntu

james 1 Comment

You can batch rename files in Ubuntu using the “rename” command. It should be installed by default – so no need to apt-get install.

The command is quite simple:

rename s/"SEARCH"/"REPLACE"/g *

For example renaming:

google_marker_green.png
google_marker_blue.png
etc…

To:

map_marker_green.png
map_market_blue.png
etc…

rename s/"google"/"map"/g *

Hope this helps someone.

How to remove / purge / prune old mysql binary logs (safely)

james Leave a comment

I generally setup binary logs on a MySQL server where the data isn’t being replicated and I’m using daily mysql-dumps to backup the data. This allows me to recover the database to a specific point in time. However sometimes the binary logs can become very large if there are lots of changes occuring to the data. Then you can suddenly need to delete / purge / prune the mysql binary log files. Here is how I did it:

1 – Examine the binary logs to decide up to where you want to delete to:

ls -la /var/lib/mysql/

2 – Here the traffic to one server had suddenly increased and the server had been logging 101MB every few minutes for several days.

....
-rw-rw----  1 mysql mysql   104871967 Aug 24 00:01 BINLOG.015687
-rw-rw----  1 mysql mysql   104885618 Aug 24 00:04 BINLOG.015688
-rw-rw----  1 mysql mysql   104866713 Aug 24 00:06 BINLOG.015689
...

3 – You can either prune by date or by file. For simplicity, I pruned by file. You need to do this from the MySQL command line.
I connected to mysql and ran the following command:

PURGE BINARY LOGS TO 'BINLOG.015689';

But you could prune by date:

PURGE BINARY LOGS BEFORE '2013-08-24 00:06:00';

You can read the offical mysql documentation here.

Visual Disk Usage Analyser From the Command Line Ubuntu

james 3 Comments

When you are trying to analyse disk usage there are a limited set of command line tools on Linux. Most people use either of ‘find’ or ‘du’. However using these tools it can be a lot of work to get an overall picture and drill down into directories to find the problems. Enter ncdu (short for ncurses-based disk usage). Simply put ncdu is a fanatastic graphical disk usage analyser.

It could not be simplier to install.

sudo apt-get install ncdu

To use:

ncdu

And you get a lovely screen like the one below. You can then navigate around using the cursor keys.

ncdu-screenshot

Thanks ncdu people 🙂

How to install wildcard certificates on multiple servers

james 2 Comments

If you have a wildcard certificate (for example *.randomhacks.co.uk) you might need to install it on multiple servers which host the different subdomains.

Basically, don’t rekey the certificate for each server just copy the same keys and certificate files across all the servers. If you rekey the certificate each time then you will invalidate any certificates which used the old key.

Typically you would need to copy these files:

/etc/ssl/private/wildcard.randomhacks.key
/etc/ssl/private/wildcard.randomhacks.sf_bundle.crt
/etc/certs/wildcard.randomhacks.crt

Note: GoDaddy let you use their wildcard certificates across an unlimited number of servers. However if you are using another certificate provider you might need to check that they don’t have a limited.

How to change /etc/apt/sources.list to use local apt-cache server in a single sed command

james Leave a comment

I’ve just installed an Ubuntu apt-cache server on our local network to speed up downloading packages each time we install or upgrade an Ubuntu computer. However, changing all the /etc/apt/sources.list file for every computer in the office is a real pain. Here is a simple command using sed which does this automatically for you:

The apt-cache server in our office is 192.168.2.2 but obviously change this to suit your needs. Note: the command can be run multiple times and won’t change the result:

 sed -i '/192.168\|^#/! s/http:\/\//http:\/\/192.168.2.2:3142\//g' /etc/apt/sources.list

Hope this helps someone.

How to resize a qcow2 harddrive images

james 13 Comments

I usually make the hard drives on my virtual machines as small as possible to save disk space on the host. I do this because it is reasonably easy to resize them at a later date (especially if you using LVM). Anyhow here is a quick guide to resizing a qcow2 disk image.

1 – Shutdown the guest.. It’s important to shutdown the vm properly rather than pausing it or forcing it to a stop because you need the file system to be a perfect condition before resizing it.

virsh shutdown hostname

2 – Increase the qcow2 disk. It a simple command to increase the size of the disk. Here I am adding 5GB to an Ubuntu Server disk.

qemu-img resize ubuntu-server.qcow2 +5GB

3 – Resize the partition Now that the virtual disk has been resized you need to resize the guest’s partitions within the image. I recommend using a small live Linux distrobution such as GParted Live. First download an iso image of GParted and attach it to the virtual machine by editing the vm settings.

virsh edit hostname

Add a boot order at the top. By default there will be one node that should read:

<boot dev='hd'/>

Simply change this to:

<boot dev='cdrom'/>

Add a cdrom after the hard disk. Make sure to change the /path/to/image.iso to the ISO image you want to boot from. If you don’t set this correctly the VM will not boot.

<disk type='file' device='cdrom'/> 
<source file='/mnt/iso/gparted-live-0.16.1-1-i486.iso'/>
<target dev='hdc' bus='ide'/>
<readonly/>
</disk>

Finally, start the VM and VNC into it. I tend to use Virtual Machine Manager to connect to a VM. It works brilliantly on most Linux machines. You should then be able to use GParted to increase the size of the partition.

resizing_qcow_image_using_gparted

how_to_resize_a_qcow_file_using_gparted

4 – Start the VM backup Note: Unless you really need it – I generally edit the VM and remove the cdrom and boot order by reversing the step described above.

virsh start hostname