Keep Your Linux SSH Session From Disconnecting

Global Configuration

Add the following line to the /etc/ssh/ssh_config file:

ServerAliveInterval 60

The number is the amount of seconds before the server with send the no-op code.

Current User Configuration

Add the following lines to the ~/.ssh/config file (create if it doesn’t exist)

Host *hostname.com
   ServerAliveInterval 60

Ref: http://www.howtogeek.com/howto/linux/keep-your-linux-ssh-session-from-disconnecting/

 

GSON Null Object Support

The default behaviour that is implemented in Gson is that null object fields are ignored.  This allows for a more compact output format; however, the client must define a default value for these fields as the JSON format is converted back into its Java.

Here’s how you would configure a Gson instance to output null:
Gson gson = new GsonBuilder().serializeNulls().create();

NOTE: when serializing nulls with Gson, it will add a JsonNull element to the JsonElement structure.  Therefore, this object can be used in custom serialization/deserialization.

Here’s an example:

public class Foo {
  private final String s;
  private final int i;

  public Foo() {
    this(null, 5);
  }

  public Foo(String s, int i) {
    this.s = s;
    this.i = i;
  }
}

Gson gson = new GsonBuilder().serializeNulls().create();
Foo foo = new Foo();
String json = gson.toJson(foo);
System.out.println(json);

json = gson.toJson(null);
System.out.println(json);

======== OUTPUT ========
{"s":null,"i":5}
null

Ref: https://sites.google.com/site/gson/gson-user-guide#TOC-Null-Object-Support

Hadoop save “parquet” error OutOfMemoryError: PermGen space

This may be caused by many reasons, the following is solution for  the one that I faced

1. Set max perm size

   -Xms256m -Xmx1024m -XX:PermSize=512m -XX:MaxPermSize=512m

   You should modify the value as long as suitable for your situation

2. Using higher jdk version
   In this case I update my jdk version to 8

 

Linux Increase “Open Files Limit”

If you are getting error “Too many open files (24)” then your application/command/script is hitting max open file limit allowed by linux. You need to increase open file limit as below:

Increase limit

Per-User Limit

Open file: /etc/security/limits.conf

Paste following towards end:

*         hard    nofile      500000
*         soft    nofile      500000
root      hard    nofile      500000
root      soft    nofile      500000

 

500000 is fair number. I am not sure what is max limit but 999999 (Six-9) worked for me once as far as I remember.

Once you save file, you may need to logout and login again.

Verify New Limits

Use following command to see max limit of file descriptors:

cat /proc/sys/fs/file-max

Ref: https://rtcamp.com/tutorials/linux/increase-open-files-limit/

How to run nodejs app as background service (daemon)

There are 2 ways to make your node js app run as background service:

1. Using nohup
   Just type the following from your terminal:

   $ nohup node [yourapp.js] &

2. Using forever
   Install forever by typing the following command:

   $ npm install forever

   Usage

   Using forever from command line

   $ forever start server.js

   Using an instance of Forever from Nodejs
   

   var forever = require('forever');
   
     var child = new (forever.Forever)('your-filename.js', {
       max: 3,
       silent: true,
       args: []
     });
   
     child.on('exit', this.callback);
     child.start();

Ref: http://stackoverflow.com/questions/4903570/how-does-one-start-a-node-js-server-as-a-daemon-process

Laravel fix error “Call to undefined method Illuminate\Foundation\Application::getCachedCompilePath”

When you run command:

composer update

You may get error:

You should remove vendor/compiler.php

rm vendor/compiler.php

then re-run:

composer update

How to upgrade PHP version 5.3.x to 5.4.x or 5.5.x on CentOS

Step1. Add EPEL and Remi repositories onto your system:

On CentOS 6.x 32-bit

wget http://dl.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm
wget http://rpms.famillecollet.com/enterprise/remi-release-6.rpm
rpm -Uvh remi-release-6*.rpm epel-release-6*.rpm

On CentOS 6.x x86_64 (64-bit)

wget http://dl.fedoraproject.org/pub/epel/6/x86_64/epel-release-6-8.noarch.rpm
wget http://rpms.famillecollet.com/enterprise/remi-release-6.rpm
rpm -Uvh remi-release-6*.rpm epel-release-6*.rpm

Step 2 – Now enable your newly added Remi repo. Open the /etc/yum.repos.d/remi.reporepository file using a text editor of your choice

vi /etc/yum.repos.d/remi.repo

Step 3 – Edit enabled=0 line to enabled=1:

4.a – Update to PHP 5.4, in [remi] section:

4.b – Update to PHP 5.5, in [remi-php55] section:

Step 4 – Now update yum

yum update -y

Step 5 – Done. Now you can check using this command:

php -v

Now you can test your PHP script on your browser and hope everything still runs smoothly.

Source from: http://www.servermom.org/upgrade-php-53-54-55-centos/1534/