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mount disk image created with dd using ubuntu

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If you’ve cloned a whole drive using dd and you need to access one of the partitions on it here are some steps to follow in order to gain access:

Find the partition start sectors using fdisk -b512 -l. Note that you’re explicitly setting the sector size to 512 bytes and you’ll need to change your command to match your own image file.

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fdisk -b512 -l backup_sata.img

You should get output similar to this (note I’ve truncated it to only show the appropriate output):

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Device         Boot     Start       End   Sectors   Size Id Type
backup_sata.img1 *         2048    206847    204800   100M  7 HPFS/NTFS/exFAT
backup_sata.img2         206848 237185023 236978176   113G  7 HPFS/NTFS/exFAT
backup_sata.img3      237185024 588070911 350885888 167.3G  f W95 Ext'd (LBA)
backup_sata.img4      588070912 625137663  37066752  17.7G 27 Hidden NTFS WinRE
backup_sata.img5      237187072 588070911 350883840 167.3G  7 HPFS/NTFS/exFAT

Normally sector are 512 bytes, so you can calculate the offset you need in the next command with:

start * 512 = offset

So if you want to mount backup_sata.img5 (partition 5 of the backup image) you’d run 237187072×512=121439780864:

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mount -o ro,loop,offset=121439780864 backup_sata.img /backup_sata

Remember to have created /backup_sata or whatever directory you’re mounting to first!

Linux Mint Docker “Error loading docker apparmor profile”

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I’ve recently been experimenting with Docker containers, but found there’s an error with installing it on Linux Mint:

Docker Error on Linux Mint
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2015/07/30 14:00:53 WARNING: Your kernel does not support cgroup swap limit.
Error loading docker apparmor profile: exec: "/sbin/apparmor_parser": stat /sbin/apparmor_parser: no such file or directory ()

It’s quite easy to solve, you just have to install app-armour:

Install apparmor
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sudo apt-get install apparmor

Then start the docker demon from the terminal to make sure it’s loading okay:

Start docker deamon
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sudo docker -d

You should see something similar to the following:

Docker starting
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2015/07/30 14:07:14 docker daemon: 1.0.1 990021a; execdriver: native; graphdriver:
[67068605] +job serveapi(unix:///var/run/docker.sock)
[67068605] +job initserver()
[67068605.initserver()] Creating server
2015/07/30 14:07:14 Listening for HTTP on unix (/var/run/docker.sock)
[67068605] +job init_networkdriver()
[67068605] -job init_networkdriver() = OK (0)
2015/07/30 14:07:14 WARNING: Your kernel does not support cgroup swap limit.
2015/07/30 14:07:14 Local (127.0.0.1) DNS resolver found in resolv.conf and containers can't use it. Using default external servers : [8.8.8.8 8.8.4.4]
Loading containers: : done.
[67068605.initserver()] Creating pidfile
[67068605.initserver()] Setting up signal traps
[67068605] -job initserver() = OK (0)
[67068605] +job acceptconnections()
[67068605] -job acceptconnections() = OK (0)

 

Once it loads this far, you can use ctrl + c to exit and start the service. If you have any further errors you’ll need to investigate further. Then start the service using:

Start docker service
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sudo service docker.io start

Setting up a Buildroot Environment on Ubuntu or Mint

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I’ve got a project that requires really fast boot times, so I’ve been looking into buildroot, which is a tool for building embedded Linux systems. When I started playing with the tutotials I noticed that I was getting errors with the make menuconfig command:

make menuconfig error
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make menuconfig
 
...
 
/development/rpi_buildroot/buildroot/output/build/buildroot-config/conf.o
*** Unable to find the ncurses libraries or the
*** required header files.
*** 'make menuconfig' requires the ncurses libraries.
***
*** Install ncurses (ncurses-devel) and try again.
***

In order to use buildroot on Ubuntu or Linux Mint the following packages need to be installed:

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sudo apt-get install build-essential ncurses-base ncurses-bin libncurses5-dev dialog

After which you should be able to run make menuconfig without errors.

 

Solving Debian 8 Jessie resolv.conf update issues

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With Debian Jessie, resolv.conf, which stores the name servers for the computer to use when looking up DNS requests, seems to automatically reset every so often. This results in the DNS lookup time for each request sent through the proxy to take longer if the name servers listed are not accurate or fast. For example, my resolv.conf file contained the following by default:

/etc/resolve.conf
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nameserver 192.168.0.1

The IP address listed is that of the router, which for some reason was taking an age to actually respond to requests. Originally I tried to edit this file by hand but it kept clearing itself back to default. This seems to be a particular issue in Debian Jessie.

To resolve the problem, I installed resolvconf, which is a program which has been designed to update the systems information about name servers.

install resolvconf
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apt-get install resolvconf

Once installed it’s easy enough to add the new name servers to the configuration file. I chose Google’s as a test, since they’re likely to be fast.

edit resolvconf head file
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nano /etc/resolvconf/resolv.conf.d/head

In the file I added the two IP v4 name servers for google so that it looked like this:

/etc/resolvconf/resolv.conf.d/head
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# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
#     DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 8.8.8.8
nameserver 8.8.4.4

Now that is in there, and of course you can change the name servers as you see fit, it’s just a case of running the update to resolvconf

update resolvconf
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resolvconf -u

Now your /etc/resolv.conf file should have your two lines prepended to it. Since the file works in top down priority your new requests will be sent to 8.8.8.8 by default. After implementing this Squid increased in speed significantly.

 

You may also be interested in reading alternative solutions on this particular thread at unix.stackexchagne.com.

 

 

Recommended starter hosting providers for 2014

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These are my recommended hosting providers of 2014, all of whom offer Linux machines running Ubuntu or Debian:
Linode offer a wide range of VPS solutions in multiple locations. They have a good community behind them with some great tutorials. Their control panel makes things easy to manage too. There are pay-more additions like load balancers so if you think you’re going to grow your sites quickly or get lots of traffic it’s worth going with them as a more mature hosting provider.

Digital Ocean have been making a big name for themselves in the past year. Their machines are much faster than a traditional VPS as they’re an SSD only hosting provider, so no old spinning disks to slow things down. They have a wide range of tutorials and Q&A sections on their site which are growing rapidly. The web interface is easy to use, but I’m not too keen on the spin-up process yet as they insist on providing you a password via email.

Bytemark offer a cloud platform similar to both Linode and Digital Ocean. They’re a smaller team based in the UK and the platform is still maturing, but Bytemark are always my first port of call for hosting services. They sponsor many open source events and projects, and even offer hosting to the Debian project.