Category Archives: How-to’s

Tutorials and step-by-step instructions.

Reinstall GRUB When Your System Isn’t Bootable

Background
From time to time, I have encountered a system where due to some conditions the GRUB installation has become corrupted.  It is a fairly simple matter to reinstall GRUB, and sometimes this can quickly salvage a broken installation.

This is not meant to be a comprehensive guide, but is a compilation of information I found online ([1], [2]) that was useful to me in repairing a few problematic GRUB loaders.  Please feel free to contribute in the comments section if you have something to add.

Setting Up The Environment
The first thing you will want to do is locate a live CD as close to the version of Linux you have installed as possible.  Boot into the Live CD.

You need to set up a functional chroot.  For the purposes of this guide, I will assume /dev/sda1 is your partition on your installation.  We will make a chroot in /mnt/chroot/.

Next, you need to bind the directories that GRUB needs to access.

Finally, chroot to your environment.

Reinstalling GRUB Automatically
You can try a simple reinstall of GRUB automatically first, see if any insightful errors are produced.

Failing that, try the following which will rescan the BIOS drives and update information in the GRUB configuration.

Reinstalling GRUB Manually
If the automatic reinstall does not work for you, try reinstalling via the GRUB shell.

How To Easily Create A DVD From Just About Any Video Format (Linux CLI)

Background
Encoding DVDs seems to be a task which is often overcomplicated.  If you have a video file you would like to convert into a DVD, it turns out it is very easy to do it from the Linux command line.

I was looking for a quick way to encode video to DVD, and I found this fantastic post by vmiimu on the ffmpeg forum. His post was fantastic and gave me the basis to create this guide, so props to vmiimu!  I thought the post was a bit crowded and might be difficult for some people to follow, so I have distilled its essence into this post.

This guide will allow you to convert a wide variety of common video formats into a video DVD.  The scope of this guide is to encode 1 video to 1 DVD with no menu.   The source file can be much larger than a DVD, it will be reduced in size automatically.

Prerequisites
For this guide, you will need the following programs \ commands available.  You may need to install the package from your distribution’s package library.

  • ffmpeg (usually available as a package called ‘ffmpeg‘).
  • dvdauthor (usually available as the package ‘dvdauthor‘)
  • genisoimage (usually available as the package ‘genisoimage‘)
  • growisofs (usually available in the package ‘dvd+rw-tools‘)

Installing these programs is beyond the scope of this guide.  You are assumed to already have them installed.

Hint: If you are using a Red Hat based distro, you may need EPEL and NUX Desktop.

Filenames & Paths Used In This Guide
For ease of understanding, I will be using the following filenames in this guide.  Please substitute your own filenames as you choose.
source.mkv – The original source video file you want to burn to DVD.  This is the only file you must supply, the rest will be created.
temp.mpg – The mpeg encoded video file which will be actually burned to DVD.
dvdmovie – The directory which will store your DVD files during encoding (AUDIO_TS, VIDEO_TS)
dvd.iso – The final .ISO image which you will burn to your DVD.
/dev/dvd – The device path for your DVD burner.


The Process:
Convert the source video to an MPEG video file <4.7GB.
(This may take a long time, and is the most CPU intensive part of the process.)

For videos with 4:3 aspect ratio, use this command:

For videos with 16:9 (widescreen) aspect ratio, use this command:

Assemble a DVD file structure.

Generate an ISO image file.

Burn the ISO to a DVD disk.
Now would be a good time to insert your blank DVD.

That’s It!
Hopefully that went smoothly for you.  Please feel free to post in the comments section if you have any questions or suggestions for improvement of this guide.

Installing Munin Node on XenServer 6.5

I recently was working with XenServer 6.5 and I wanted to install a Munin Node for graphing system vitals.

Getting Yum working properly to do the install required a bit of Googling, so I wanted to document these commands in case this is helpful to anyone else.

First, you’ll need to install the EPEL repository:

Then, you’ll need to install munin-node using both base and epel repositories.

If you are monitoring with a remote Munin server, don’t forget to add an allow rule in /etc/munin/munin-node.conf, using your favorite text editor.

You can put it somewhere by this line:

Do not fear the regex, that rule allows connections from “127.0.0.1”.  Just replace the digits and leave the other characters alone, and you can use this regex to allow any IPv4 address easily.

Now, we want to go ahead and add the Munin Node to the system startup, and start the process.

Don’t forget to allow incoming port 4949 TCP in your firewall if you are using a remote server to monitor the connections.  Munin shouldn’t talk to unauthorized IPs, but it wouldn’t hurt to only allow connections from the Munin server on that port.  That will not be covered in the scope of this guide, as I don’t know what firewall solution you are using.

Of course, the last step is to add the node in your /etc/munin/munin.conf on your monitoring server.  That config would look something like this, where 123.45.67.89 is your Xen server.

From here, I assume you know the drill with Munin, the server should appear on your HTML pages in 5-10 minutes.  If you’re impatient, you can nudge the cron job that does this by running this:

Have fun!  As always, please feel free to post any questions you have in the comments section, and I will do my best to assist.

Digital Signage with a Raspberry Pi and Google Slides

I have been looking at an easier way to Digital Signage and I just got my first Raspberry Pi.  I figured the low and High def inputs would allow me to strap a rPi on the back of a TV and provide rich content.

I am looking for a opensource, free/very low cost solution that is easy to manage and simple for the people updating it.  I foresee about 10 devices in my future.

I did a lot of reading and found that there are plenty of projects out there already that enable digital signage for the rPi.  I found this site and started down the list.

I tried a few applications and liked Screenly the best.  It is simple, performs well, and overall just works.  See their online demo for their interface. They provide their own rPi image or allow installation onto raspbian if you want to further customize it.  SSH is available on the Screenly image out of the box.  Screenly allows web pages, images, and videos (MP4) to be streamed to the rPi which gives me plenty of flexibility to mix and match what I like.  They have 2 versions; a centrally managed model or a free, per device management model.

My immediate thoughts were to convert our ancient overused powerpoint into something more rich, but to get users to buy into this solution I would first convert them over to Google Slides which would provide an easy to use, collaborative, updating presentation to all devices without actually touching any of the devices.

I created a simple Google Slide presentation with four or five slides and random comments on it.  I followed these instructions to make it automatically full-screen and play right in the browser.  I took that link and threw it right into Screenly-OSE and viola!

Caveats…

  • Google sets a single time for all slides…  Therefore you cannot make one slide longer than the others (as far as I can tell).  Transitions can be set differently though.
    • You could leverage second presentation and set the delay longer, or use the Screenly interface to get more specific in necessary.
  • One issue I ran into was that if you have Google loop the presentation rather than Screenly, the content never updates.  Obviously this defeats the purpose of using Google Slides in the first place.  Let Google finish the presentation and let Screenly reload the presentation and it will be fairly straightforward.
    • Related to the above post, then timing becomes an issue.  Some simple math should work to fix that though.
      • 5 seconds a slide (as per when publishing within Google) plus 3 seconds for transition time (as set in presentation) times 5 (number of slides) should come out to be about 40 seconds.  Tweak as needed.

Things to investigate:

It appears the database being used is simply for the ‘Playlist’.  I would imagine that the application would refresh the playlist frequently.  That being said, would placing the /home folder in a shared NFS location make management easier?  This could also lessen the wear and tear of the SDcard.  If all clients pointed back to this NFS share, would this update all of the clients or would this require a reboot/restart on the clients to apply any updates?  I do not know how the software is triggered or written… So more experiments to come when I get more Pi’s!

Configuration of OVH IP Failover on VMs

Background
I have had a server with OVH for the past several years, and one of the things that took me many months of research, as well as trial and error, to get right was my IP address configuration for virtual machines.  The documentation available from OVH has been consistently lacking these past few years on how to properly configure it.

Debian \ Ubuntu systems will add to the complications, because they do not agree with the necessary configuration.  If you try to add it traditionally, just by editing /etc/network/interfaces, you will most likely end up with no default gateway when you’re all said and done, and your connection still won’t work.

For the first few months I was with OVH, I was launching my networking through a shell script in a cron job, because configuring it with /etc/network/interfaces just didn’t seem possible.

 

What You Need For This Guide \ Assumptions About Your Setup
1. A dedicated server on the OVH network.  This guide has been tested in the Roubaix datacenter  and the Gravelines datacenter, but OVH uses the same schema in Montreal as far as I know.
2. A virtualization platform installed, and a virtual switch bridged with your network interface.  I have been using VMWare, and a vSwitch bridged with my eth0 interface.  This guide should be applicable to any virtualization suite (Xen, OpenVZ, etc) as long as your networking is bridged.
3. A Debian \ Ubuntu VM.  You can apply the knowledge gained from this guide to other operating systems (eg. CentOS) but the configuration will be different as the files are located in different places and are parsed differently.
4. A purchased IP range.  You can purchase IP addresses from OVH in your Manager Panel.

 

Gather Your Information \ Initial Setup On OVH Side
1. Your dedicated server’s Main IP will be needed for this guide.   Say, for example, your main IP is 123.4.5.67.
2. Your dedicated server’s Gateway IP will be needed for this guide.  On the OVH network, this is the first three octets of your main IP, ending in 254.  For 123.4.5.67, the gateway is 123.4.5.254.
3. A Fail Over IP Range registered with OVH.  You can register any size IP block, and you can pick any IP from the block.  Say for example, you bought 5.6.77.8/29.  All of the Fail Over IPs are usable at OVH, so you have available all 8 IPs from 5.6.77.8 to 5.6.77.15 for use for your VMs.  You can purchase an IP block from your Manager Panel.
4. A Registered VM MAC Address associated on OVH’s routers.  Without this step, your connection will not work.  You can register VM MACs in your Manager Panel.

 

How To Register A VM MAC Address
In the new OVH Manager panel, you can register a VM MAC address by going to the “Manage IPs” page, clicking the gear icon next to the IP(s) you want to assign to the VM, and clicking “Add A Virtual MAC”.  You can choose an existing MAC address if you are assigning more than 1 IP, otherwise OVH will assign a new MAC address to you, and you will edit your VM preferences so your network interface has this MAC address.  Make sure you select the MAC address type “VMWare” if you are using a VMWare server, as this will generate MAC addresses which VMWare will accept.  You can use type “OVH” for any other virtualization platform.  The “name of virtual machine” field is just for your notes, and can be anything.

 

Operating System Installation
Install Debian \ Ubuntu to the VM, from a full install media.  Do not plan on doing a network install, as this guide does not cover how to make the OVH networking functional during installation; only after installation.  Skip the step for setting up networking during the installer, leave it unconfigured.

 

Setting Up /etc/network/interfaces
Now that you have your operating system installed, you are ready to configure your /etc/network/interfaces file.  This guide assumes that eth0 is your Internet interface. I will use IP addresses from the example above under “Gather Your Information”.  Do not use these addresses, substitute your own IP addresses.

A few things to note, for anyone asking any technical questions about what I just did above:

  • You should choose 1 IP address from your IP block.  If you want to add more, see the further instructions below.  This IP is the Main IP of your VM.
  • Regardless of the size of your block, you will treat the IP address as a /32 with a netmask 255.255.255.255.
  • Because you are using a /32, the network\broadcast IP is your IP.
  • Your default gateway should be the same as your dedicated server’s default gateway.  DO NOT try to use what should logically be the gateway IP for your IP block, and DO NOT try to set your dedicated server itself as the gateway.  The IP block is irrelevant, the gateway is always the dedicated server’s gateway IP.
  • The routes have to be added this way, because the configuration is not valid.  The gateway should not be reachable from this network range, because it’s a /32.  However, the gateway will be reachable anyway, and adding the routes this way should work.

 

DNS Resolution
You will also need to edit your /etc/resolv.conf to put a DNS name server in there, otherwise your server will be able to ping other IPs, but it will not be able to resolve DNS.  You can just put a line in there, like this line which uses the public OpenDNS resolver:

 

Want To Add More IPs?
Sometimes it is desirable to have more than one IP address on your server.  You can easily add additional IPs from any IP block as an alias IP.  You don’t need to configure any additional gateways, because the gateway is always your dedicated server gateway.  You can purchase as many IP blocks as you want, and assign them all this way, it doesn’t matter if they are totally different IP ranges.  In the example below, I will add 2 additional IPs from the IP range I used as an example, 5.6.77.8/29.

 

Having Problems?
If you are having any problems, please review these items:

  • First, reboot the VM to ensure that all of the networking changes you made are fully applied.
  • Can you ping your default gateway?  If not, did your route persist?  Run “route -n” and see if the route is there.  If it isn’t there, try adding it manually by running the commands in the post-up in /etc/network/interfaces.  See if you get any errors.
  • Did you configure DNS?  Try pinging just an IP address, (eg. ping 4.2.2.1) and see if you get any response.
  • Did you remember to register a MAC address, and did you change the MAC address for the VM?  Run “ifconfig eth0” and make sure the MAC address shown matches what’s registered in your OVH Manager Panel.

 

Need Further Assistance?
As always, feel free to leave a comment below if you need any assistance.  I will be happy to help!