Kernel Crashing after upgrading to Fedora 23

After upgrading to from fedora 22 to fedora 23, I was unable to boot into linux due to a kernel crash. I was able to load up the previous kernel from 22 to get back to desktop.

I thought it might be a bad grub config so I ran this to rebuild grub
grub2-mkconfig -o /boot/grub2/grub.cfg

This produced a lot of errors such as:
ERROR: pdc: reading /dev/sdb[Input/output error]

It looks like the initramfs could be corrupt.

Solution:
sudo dracut --regenerate-all --force
sudo grub2-mkconfig -o /boot/grub2/grub.cfg

No errors were produced at this time.

Getting the fontNames from Swift with XCode 7.01

func fontForDisplay(atIndexPath indexPath: NSIndexPath) -> UIFont? {
    if indexPath.section == 0 {
        let familyName = familyNames[indexPath.row]
        let fontName = UIFont.fontNamesForFamilyName(familyName).first as String
        return UIFont(name: fontName, size: cellPointSize)
    } else {
        return nil
    }
}

The above snippet of code is from
Beginning iPhone Development with Swift Exploring the iOS SDK
I'm trying this on el capitan and xcode 7.01, which now uses swift 2.0

The first issue is that xcode will warn you that 'String?' is not convertible to 'String'
Adding a ! to force cast and will allow the code to run. (append it to either first! or String!)

The next issue is that this is thrown: EXC_BAD_EXCEPTION
Looking at the trace, we can see

familyName = (String) "Bangla Sangam MN"
fontName = (String!) nil

So it appears that we're trying to get the first element of an empty array. I ended up with this solution:

    let fontArray: String? = UIFont.fontNamesForFamilyName(familyName).first
    let fontName = (fontArray != nil) ? fontArray! : ""

Let me know if there is a more idiomatic way of doing this with Swift 2.0

golang: Do you need a singleton? Where are my private/public class modifiers?

Intro: Singletons can be useful, but as mentioned in other people's posts they are an anti pattern and can make testing and debugging difficult. A post on stack overflow had this short nonspecific message "Just put your variables and functions at the package level." http://stackoverflow.com/questions/1823286/singleton-in-go I took this as a hint that with a little more knowledge of how go packages work, I could get a single instance of an object and have it abstracted so that modification would be difficult, if not impossible.

Let's start with three files.

src/logger/logger.go
src/chat_server/main.go
src/chat_server/sub/sub.go

logger.go

package logger

import (
     "fmt"
)

type logger struct {
    Timestamp int
}

type Togger struct {
    Timestamp int
}

var log = logger{Timestamp: 12345}
var Tog = Togger{Timestamp: 12345}

func (l *logger)writeInfoFile(s string) {
    fmt.Println(s)
}

func (l *logger)writeErrorFile(s string) {
    fmt.Println(s)
}

func Debug(s string) {
    log.writeInfoFile(s)
    fmt.Println(&log.Timestamp)
}

There is a logger object named log with a single timestamp field. The other thing to note is that the functions, variables and structs (golang's version of a class) can have an upper or lower case first letter.

"if something starts with a capital letter that means other packages (and programs) are able to see it" - http://www.golang-book.com/11/index.htm

For those us who are used to having public and private keywords in our OO language, this capital letter convention is how go restricts access. This means that Togger, Tog, and Debug() can be referred to once logger is imported in another file. While log, loger and write*() can not. This takes a little closer to our goal because we should be able to instantiate an instance of logger, and only allow specific functions to act on it.

main.go

package main

import (
    "logger"
    "chat_server/sub"
    "fmt"
)

func main() {
    logger.Debug("one")
    logger.Debug("two")
   
    sub.CheckingAddress()
   
    isPublic := logger.Togger{Timestamp: 555}
   
    fmt.Println(isPublic.Timestamp)
    fmt.Println(logger.Tog.Timestamp)
   
    // These will cause an error
//    fmt.Println(logger.log.Timestamp)
//    isPublic := logger.logger{Timestamp: 333}
}   

Here are some examples of how this works. Debug is a function that can be accessed after the import. It can refer to var log as it's within the same package. Trying to access logger.log directly is not allowed, while the analagous struct value logger.Tog can be called. Any attempt to init a new 'logger' object also fails.

There is one more quick check that I wanted to verify and that is to confirm the log object continues to be the only instance no matter where it is imported.

sub.go

package sub

import (
    "logger"
)

func CheckingAddress() {
   
    logger.Debug("In SUB")
   
}

Way back in logger.go I print out the memory address of the Timestamp field.

fmt.Println(&log.Timestamp)

After running main, the output is:

one
0x547068
two
0x547068
In SUB
0x547068
555
12345

We get the same address so it's good.

Conclusion: I was able to create a single instance of my logger struct without resorting to a singleton and learned how go packages limit access to vars and and functions.

VMware Player Free and changing boot devices.

VMWare player free doesn't include all the settings that the commercial editions offer. In order to boot an iso, you must hand edit the *.vmx file and add the following settings.

bios.bootOrder = "cdrom,hdd,floppy"
bios.hddOrder = "scsi0:0,ide1:0"

Adding the above information allowed me to install fedora 21 over my existing fedora 20.

Tip: After installation, I powered the vm off. Removed the above lines and removed the fedora iso from the vmware cd drive.

Using Chef to auto create an instance on Amazon ec2

Chef is one of the major server automation tools out there along with Puppet and Ansible. I decided to give chef a try by auto creating an ec2 instance. They're all trying to get you to buy saas packages for nodes greater than around 5. I will be using the free account offered by opscode to store my recipes.

1) Create a new chef-repo or use your current chef-repo

For testing I cloned a new chef-repo
git clone git://github.com/opscode/chef-repo.git ec2chefrepo

2) From the previous tutorial ./chef-repo copy over ./chef-repo/.chef into our new chef-repo

3) In Amazon Ec2 click on your name in the top right

I get a password old/new page. Instead go to the left side and click on Users.

Then click on your email and then the security credential tab

4) Get the Access Keys and Secret Keys

Click on Manage Access Keys
Create a new key and you will get two strings.
Note: The secret key is show and available this one time. You will need to create new access keys if the secret key is lost.

Access Key Id
AKAJG6Z4AFQ5YPQ

Secret Access Key
Mw5sHvDgJRtAVP2vkA8gL8XJkvoZijhNMf

5) With the above access keys and your ec2 .pem add these lines to ec2chefrepo/.chef/knife.rb

knife[:aws_access_key_id] = 'AKAJG6Z4AFQ5YPQ'
knife[:aws_ssh_key_id] = 'bunwichchef'
knife[:aws_secret_access_key] = 'Mw5sHvDgJRtAVP2vkA8gL8XJkvoZijhNMf' 

Note: the ssh_key_id is your key name without the pem

6) Create a gemfile to install some gems

gem install bundle
rbenv rehash
cd ~/ec2chefrepo/
vim Gemfile

source 'https://rubygems.org'
gem 'chef'
gem 'knife-ec2'

Note: I had to run this before running bundle installs
sudo yum install gcc-c++

bundle install

7) Create and Deploy An Instance

Had to run:
gem install rb-readline unf
http://aws.amazon.com/amazon-linux-ami/
To get a list of AMI Image Ids

knife ec2 server create \
  --availability-zone us-east-1b \
  --node-name bunwichchefinstance.demo \
  --flavor t1.micro \
  --image ami-ba18d2 \
  --run-list "role[memcached]" \
  --identity-file ~/.ssh/bunwichchef.pem \
  --ssh-user ec2-user 

vlc no decoder module fedora 20

Sometime after updating Fedora 19 to 20 (using fedup), VLC stopped playing some h264 videos.

An error message such as this appeared:

no suitable decoder module for fourcc `h264'. VLC probably does not support this sound or video format.

No suitable decoder module:

VLC does not support the audio or video format "h264". Unfortunately there is no way for you to fix this.

It was missing lame-libs. A sudo yum install lame-libs solved my issue.

What is more important is how I solved this:

a) vlc -vvv mediafile.mp4

b) Look for yellow or red warning/error messages. A lot of information gets outputted.

eg:
0x1666118] main libvlc warning: cannot load module `/usr/lib64/vlc/plugins/demux/libavformat_plugin.so' (libmp3lame.so.0: cannot open shared object file: No such file or directory)

c) This message states that libmp3lame.so.0 does not exist.

d) sudo repoquery --whatprovides '*/libmp3lame.so.0'

returned:
lame-libs-0:3.99.5-2.fc19.i686

Failed to load libGL.so on Fedora 20 and Android emulator

I got this warning when trying to get the android emulator working on Fedora 20.

You need to install 2 packages to get this working:

sudo yum install mesa-libGL-devel mesa-libGL-devel.i686

The libGL.so message disappeared after this. Command to search for this lib on future installs.

sudo yum whatprovides */libGL.so