Compacting VirtualBox Disk Images - Linux Guests

1. Start the Linux virtual machine;
2. Clean the free space on the disk of the Linux virtual machine;

   dd if=/dev/zero of=zerofillfile bs=1M

   • if= specifies the input file;
   • /dev/zero indicates a bit-stream of zeros
   • of= specifies the output file
   • zerofillfile name of the file containing the bit-stream of zeros
   • bs= indicates the block size
   • 1M indicates that the block size will be 1 megabyte

   rm zerofillfile

3. Shutdown the Linux virtual machine;
4. Use the VirtualBox VBoxManage utility to compact the Linux guest image.

Ref: Compacting VirtualBox Disk Images - Linux Guests

Grant permission for virtualbox shared folder

The regular way of getting access to the files now, is to allow VirtualBox to automount the shared folder (which will make it show up under /media/sf_directory_name) and then to add your regular user to the vboxsf group (as root #).

usermod -aG vboxsf <youruser>

Build an OpenVPN server on android device

Preparation

1. An android device, in this case, Sony xperia Z is used
2. Root permission required
3. Linux Deploy for deploy image via chroot/proot
4. OpenVPN

Step

1. Root android device for superuser permission

2. Install Linux Deploy from play store or custom apk.

• Install Linux Deploy

3. Install linux

• Click download icon to select which image to deploy

• Select which distribution and suite to use
• Set user name & password
• Allow init system
• Enable SSH server

• Deploy distribution

• After installation completed, start linux

4. Connect to android via SSH

5. Install OpenVPN

• Install required packages

• Create certification folder and edit vars configuration

• Edit vars as blow

• Build ca, server and client certification

• Copy required certification to the path of openvpn
• Clone configuration file from sample config
• Edit server.conf

• Edit server.conf as blow, modify what your need

• Modify networking config sysctl.conf

• Modify content to allow transfer traffic from vpn

• Make changes work

• Edit firewall rules

• Add following content to allow route from vpn subnet to wireless

• Edit firewall configuration

• Allow forward policy

• Add firewall rule for vpn and ssh
• Make changes work. (In this case, there was some error but I ignore that)

• Start openvpn
• Validate result

6. Use vpn client to connect android device

My Conky config

About Conky: Conky is a free, light-weight system monitor for X, that displays any kind of information on your desktop.

Preview:

Convert pfx file to certificate file and private key file

Use openssl

jQuery Validation Engine default options

Compact virtualbox hdd size

Remove file not in list

Difference source code programmably from svn

Invoke Gson#toJson() on anonymous class

Create a anonymous object and try to serialize instance via gson. The code is below

Result of execution. null result when serialize a anonymous instance