Fix ubuntu when the OS will not boot – kernel panic – kernel panic not syncing vfs unable to mount root fs on unknown-block 0 0 – error /boot full remove old kernels from command line

To begin, it will probably take at least 30 minutes resolve this issue…

This fix solved my problem with the “vfs unable to mount root fs” error, but of course your results may vary. As always, first backup your system or do an export of the vm so you have a copy of the system as it existed before you started screwing around with it 😉

After running apt-get update / apt-get upgrade and then a reboot, you may receive the following error: kernel panic not syncing vfs unable to mount root fs on unknown-block 0 0 on ubuntu 16.04.

In many cases this  will be due to the /boot drive becoming 100% full because many updates have been made to the kernel. By default, ubuntu will retain the old kernels and add them to the list of available kernels you can boot into in the Grub2 boot loader menu. You can confirm that your drive is full by issueing the command:

df -h

The result will likely show the following:

In order to resolve this issue and boot successfully, while you’re looking at the error during boot, (you should already be at the console), and restart the vm or computer into the Grub2 menu then choose “Advanced options for ubuntu” view where you can see a list of old kernels you can boot into. Some report you can do this booting with the Shift key held down, or in the event it’s a virtual machine, you should be able to arrow-down in the Grub start screen and choose Advanced options for ubuntu on startup:

Grub2 boot menu.

Once you go into the advanced boot menu you will likely see several kernels listed. Choose the next-oldest kernel from the top/highest version of kernels. In my case I booted into the version labeled Ubuntu, with Linux 4.4.0-57-generic (my boot menu screenshot below is clean, but you’ll likely see several kernels listed).

Cross your fingers and hope you get to your login prompt. From here I jumped on putty and connected from that client, as I prefer it over the console.

Next, login and follow the directions that I found here:

http://askubuntu.com/questions/2793/how-do-i-remove-old-kernel-versions-to-clean-up-the-boot-menu

To save you the search, here are the instructions I used to first list and then remove the old kernels:

Open terminal and check your current kernel:

uname -a

DO NOT REMOVE THIS KERNEL! Make a note of the version in notepad or something.

Next, type the command below to view/list all installed kernels on your system.

dpkg --list | grep linux-image

Find all the kernels that lower than your current kernel. When you know which kernel to remove, continue below to remove it. Run the commands below to remove the kernel you selected.

sudo apt-get purge linux-image-x.x.x.x-generic

Or:

sudo apt-get purge linux-image-extra-x.x.x-xx-generic

Finally, run the commands below to update grub2

sudo update-grub2

Reboot your system.

sudo reboot

As you can see from my terminal history, I had to remove a few:

589  uname -a
 590  dpkg --list | grep linux-image
 591  sudo apt-get purge linux-image-4.4.0-21-generic
 592  sudo apt-get purge linux-image-4.4.0-22-generic
 593  sudo apt-get purge linux-image-4.4.0-24-generic
 594  df -h
 595  sudo apt-get purge linux-image-4.4.0-24-generic
 596  sudo apt-get purge linux-image-4.4.0-28-generic
 597  sudo apt-get purge linux-image-4.4.0-31-generic
 598  sudo apt-get purge linux-image-4.4.0-34-generic
 599  sudo apt-get purge linux-image-4.4.0-36-generic
 600  sudo apt-get purge linux-image-4.4.0-38-generic
 601  df -h
 602  sudo apt-get purge linux-image-4.4.0-42-generic
 603  sudo apt-get purge linux-image-4.4.0-45-generic
 604  sudo apt-get purge linux-image-4.4.0-47-generic
 605  sudo apt-get purge linux-image-4.4.0-51-generic
 606  sudo apt-get purge linux-image-4.4.0-53-generic
 607  sudo update-grub2
 608  dpkg --list | grep linux-image
 609  df -h
 610  sudo apt-get purge linux-image-extra-4.4.0-21-generic
 611  sudo apt-get purge linux-image-extra-4.4.0-22-generic
 612  sudo apt-get purge linux-image-extra-4.4.0-24-generic
 613  sudo apt-get purge linux-image-extra-4.4.0-28-generic
 614  sudo apt-get purge linux-image-extra-4.4.0-31-generic
 615  sudo update-grub2
 616  df -h
 617  sudo reboot
 618  dpkg --list | grep linux-image
 619  uname -a
 620  sudo reboot

After the reboot, you can see my /boot partition returned to a manageable size:

I hope this post helps someone save some time and help them fix their ubuntu boot problems.

How to setup an Amazon AWS VPC, What is a VPC, and Subnets, Part 1 of 3

Amazon Web Services (AWS) provides the capacity to create a Virtual Private Cloud (VPC), which is a virtual network dedicated to your AWS account. In the first part of this three-part series, I will show you how to create a VPC with the corresponding subnets.

Read the rest of the articles Here

AWS VPC – Overview, setup, subnets

Modern PHP development environment – Setup of Ansible, pycharm, sourcetree and workflow with bitbucket

When getting started with development with a cloud repository such as git, it may be a little daunting to decide how to get started. With some help from an associate, I put together a short simple guide to setup a development environment on OS X. I hope this information provides someone with a good start to development with bitbucket, version control, and PHP Development in conjunction with a cloud repository.

Bitbucket is similar to git, but allows free repos. We prefer to use bitbucket for a repository of code so that we can manage changes to our ubuntu servers and files. Bitbucket is the “Book of Truth” and will be the keeper of all files and things that are good. Ansible runs on a dedicated management ubuntu server and pushes out changes (playbooks) to either a single, a few, or all of our linux servers. Either way, with pull/push of data from our code repository, we can control what is deployed on our systems, an use our repo as our backup. If a server dies, we can setup a new system, and pull in the good data.

Setup

First, you need a bitbucket account and sign-on. Once signed on to https://bitbucket.org/brooksinstitute/ You should be able to create your first repo. You might want to create your own private repo for notes, configs etc. As mentioned earlier, bitbucket is where we keep our known-good source code, and changes to this should only be done from your own computer’s copy of the repo, and only changed with commits – more on this later.

sourcetree

Next on your local machine, download sourcetree https://www.sourcetreeapp.com/

Once downloaded and installed, tell sourcetree where your repos live at bitbucket (simple username/password login).

Next, SourceTree will ask you which remote repository you want to clone to your local machine. You want to clone the remote repos on bitbucket so that you can make changes to your local versions before you commit them back to bitbucket. If you work with a group of developers you will probably want someone to review your files before you commit. You should also “checkout” local copies within pycharm, if someone else will also be working on your local files.

pycharm

Now it’s time to install and configure pycharm Community Edition https://www.jetbrains.com/pycharm/ . Pycharm is a Development Environment (IDE) that provides code completion, nice pretty colors and integrates with VCS/Git to do versioning control of your local (cloned) repo. In Pycharm, you want to go to the File → Open menu, browse your local machine, and choose the root folder of the cloned repo of your choice. This will get you to the point where you can begin to edit files.

ansible

Ansible http://www.ansible.com/ is a management utility that helps you easily manage systems and deploy apps. Here is some introductory documentation http://docs.ansible.com/ansible/intro_getting_started.html. Ansible usually runs on a dedicated Admin server, and this is the server that issues commands or “playbooks”. Although your Admin server contains the ansible playbook files, we only want to make changes to the files linked to the bitbucket repo before we pull them into the Admin server and then execute the commands.

 

Vagrant

Vagrant https://www.vagrantup.com/ provides easy to configure, reproducible, and portable work environments built on top of industry-standard technology and controlled by a single consistent workflow to help maximize productivity. First download, install, and run VirtualBox https://www.virtualbox.org/wiki/Downloads , then open a terminal, and startup a vagrant “box” with the following:

   $ vagrant init hashicorp/precise32
   $ vagrant up

Vagrant will download and install the ‘precise32’ “box”. And now, in virtualbox you will see the new virtual machine. Then next from the command line you can issue the command ‘vagrant ssh’ which will open a shell to your new precise32 vm. You can use this vm to test your configurations and playbooks against before you roll them out to your production servers.

Workflow

When you’ve changed something in your local (cloned) repo, and you want to have that become the “truth” on bitbucket, do the following:

  1. Open the file from your local repo in pycharm (double-click on the file icon in the menu tree)
  2. Edit the file
  3. When done editing, right-click on the file → Git → Commit file
  4. Now you want to push this edited file up to bitbucket. Review the code, make comments and then push.

 

Ubuntu Linux Server setup guide – Setup ssh, keygen, brew, and ssh-copy-id on Mac OS X

 

 

iTerm on OS X
ssh config file in iTerm on OS X

What follows is a ubuntu/linux server setup guide that can be used to configure, 1. A new linux server and 2. setup an OS X workstation to easily connect to your linux servers with preshared keys.

  • Build the server on Hyperv, then setup your initial account during the Ubuntu LTS 14.04.2 setup.
  • Log in as the initial user and add accounts as necessary:
    • “sudo su -“ – this does a sudo and copies root path and all environmental variables
    • useradd -m -s /bin/bash jcoltrin
    • passwd jcoltrin
    • vi /etc/sudoers
      • (end of file) add line: jcoltrin ALL=NOPASSWD: ALL
    • su jcoltrin – make sure you can su.
    • sudo su – this sequence has allowed you to sudo without having to type in your password.
    • Just a note: modifying /etc/group – putting users in here is the wrong way of adding sudoers – no granular control – users here will be required to enter their password when doing sudo.
  • ctrl+l clears screen
  • Add static IP address and dns-nameservers to /etc/network/interfaces
    • Get the name of your network interface with command:
    • ifconfig -a

      In my case, the network interface name is ens33. So to make my ens33 interface a static interface, I configure the /etc/network/interface with the text editor vi. The first interface is lo, which is the loopback interface. The line ‘auto ens33’ is necessary because it is used to start the interface when the system boots.

    • 
      source /etc/network/interfaces.d/*
      
      # The loopback network interface
      auto lo
      iface lo inet loopback
      
      # The primary network interface
      auto ens33
      iface ens33 inet static
              address 10.0.10.151
              netmask 255.255.255.0
              gateway 10.0.10.254
              dns-nameservers 8.8.8.8 8.8.4.4

       

  • apt-get:
    • apt-get update – checks online for updates
    • apt-get upgrade – installs updates and security patches
    • apt-get dist-upgrade – note: make sure /boot dir is not more than 80% full. If it’s full it may have old kernel upgrades so google ubuntu clean old kernels.
    • reboot
Setup ssh, keygen, brew, and ssh-copy-id on Mac OS X

Now we need to establish a secure and easy connection from our mac to the new server. On our Mac issue the commands:

  • Install iTerm on your Mac. Configure to your liking, but it’s a good idea to set, in the Terminal settings, the scroll-back limit to either 99,999 or unlimited. Now in our new iTerminal, issue the command: ssh-keygen – this generates both public and private keys in our .ssh directory in our home directory.
    • Install HomeBrew on your Mac in order to get unix tools installed on your mac:
      • Make sure your account on your Mac is an administrator by going into System Preferences → Users and Groups → (unlock) → Select Account → checkmark Allow user to administer this computer.
      • First install XCode, then open a terminal again and paste in the command for installing homebrew from http://brew.sh
      • Install homebrew as it prompts, and run brew doctor so that we know we’re ready to install homebrew
      • brew install nmap ssh-copy-id wget htop ccze – this installs the linux tools we want on our mac
  • ssh-copy-id jcoltrin@serverIPaddress (password) – this copies our public key into the server we connected to. Now we can log into the servers from our mac terminal without having to type in the password.
    • Also on the mac we want to make it easy to ssh into, for example, server.domain.com.
    • vi .ssh/config
    • Line 1: host server
    • Line 2: hostname server.domain.com
    • Line 3: User jcoltrin
    • Line 4: KeepAlive yes
    • ctrl+wq!
    • The result should look like the following:

jcmbp:.ssh jcoltrin$ cat config

Host	    server
    Hostname server.domain.com
    User jcoltrin
    KeepAlive yes
    ServerAliveInterval 15

Host    myAmazonAWS1
    Hostname jasoncoltrin.com
    user ubuntu
    IdentityFile ~/.ssh/jasoncoltrin_keypair1.pem
    KeepAlive yes  
    ServerAliveInterval 15
  • ssh server – now we are able to issue this command and get in immediately without having to enter a password and also we can run sudo commands without having to enter our password again. As you can see in the config file above, we can also copy our .pem files into our .ssh directory and have config point to them so that we can easily ssh into our amazon AWS servers as well.
  • If we will be running websites, we now want to install virtualmin. Go to http://www.virtualmin.com/download.html#gpl and follow instructions here for downloading install.sh
Adding a new remote Administrative User’s ssh keys to a Linux Server

useradd -m -s /bin/bash newadmin1
mkdir ~newadmin1/.ssh
echo ssh-dss ****key data***..xxblahblahACBAM……kpucyrGw== newadmin1@remotedomain.com » ~newadmin1/.ssh/authorized_keys
chown -R newadmin1:newadmin1 ~newadmin1/.ssh
chmod 700 ~newadmin1/.ssh
chmod 600 ~newadmin1/.ssh/authorized_keys

vi /etc/sudoers

newadmin1 ALL=NOPASSWD: ALL

While this guide is not meant to be a comprehensive step-by-step guide, it should provide you with enough to setup an OS X workstation with pre-shared keys, and copy those keys to your new server. Working with iTerm and pre-shared keys, I think, is vastly superior to Putty on Windows. I hope this guide helps a few admins become more efficient and versatile working on OS X and linux.