Increasing ssh timeout

sudo vi /etc/ssh/sshd_config

Make sure it has following two properties at the end.

ClientAliveInterval 120
ClientAliveCountMax 720

Restart ssh daemon.

sudo service ssh restart

The first one configures the server to send null packets to clients every 120 seconds and the second one configures the server to close the connection if the client has been inactive for 720 intervals that are 720*120 = 86400 seconds = 24 hours

Data Wipe On EBS Volumes - Part II

Securely erasing/Data wiping EBS volumes :

When you delete a file using the default commands of the operating system (for example “rm” in Linux/BSD/MacOS/UNIX or “del” in DOS or emptying the recycle bin in WINDOWS) the operating system does NOT delete the file, the contents of the file remains on your hard disk. So we need to explicitly delete or wipe the contents of the disk. Data wiping is the process of logically removing data from a read/write medium so that it can no longer be read.

Methods in Linux :

I will discuss some of the available data wiping methods in Linux system.

1. shred



shred is a command line utility, which overwrites data in a file or a whole device with random bits, making it nearly impossible to recover.

# shred -n 1 -vz /dev/xvdf

Make sure it is the correct device, picking the wrong device will wipe it.

This will overwrite 1 time ( -n ) by showing progress ( -v ) and adding final overwrite with zeros to hide shredding (-z ).
( Use -n more than 5 times for secure wipe, default is 25 times )
ubuntu@ip-xxxxxxxxx:~$ sudo shred -n 1 -vz /dev/xvdf shred: /dev/xvdf: pass 1/2 (random)... shred: /dev/xvdf: pass 1/2 (random)...454MiB/8.0GiB 5% shred: /dev/xvdf: pass 1/2 (random)...759MiB/8.0GiB 9% shred: /dev/xvdf: pass 1/2 (random)...1.0GiB/8.0GiB 12% shred: /dev/xvdf: pass 1/2 (random)...1.3GiB/8.0GiB 16% shred: /dev/xvdf: pass 1/2 (random)...1.6GiB/8.0GiB 20% shred: /dev/xvdf: pass 1/2 (random)...1.9GiB/8.0GiB 24% shred: /dev/xvdf: pass 1/2 (random)...2.2GiB/8.0GiB 27% shred: /dev/xvdf: pass 1/2 (random)...2.5GiB/8.0GiB 31% shred: /dev/xvdf: pass 1/2 (random)...2.8GiB/8.0GiB 35% shred: /dev/xvdf: pass 1/2 (random)...3.1GiB/8.0GiB 39% shred: /dev/xvdf: pass 1/2 (random)...3.4GiB/8.0GiB 42% shred: /dev/xvdf: pass 1/2 (random)...3.7GiB/8.0GiB 46% shred: /dev/xvdf: pass 1/2 (random)...4.0GiB/8.0GiB 50% shred: /dev/xvdf: pass 1/2 (random)...4.3GiB/8.0GiB 53% shred: /dev/xvdf: pass 1/2 (random)...4.6GiB/8.0GiB 57% shred: /dev/xvdf: pass 1/2 (random)...4.9GiB/8.0GiB 61% shred: /dev/xvdf: pass 1/2 (random)...5.2GiB/8.0GiB 65% shred: /dev/xvdf: pass 1/2 (random)...5.5GiB/8.0GiB 68% shred: /dev/xvdf: pass 1/2 (random)...5.8GiB/8.0GiB 72% shred: /dev/xvdf: pass 1/2 (random)...6.1GiB/8.0GiB 76% shred: /dev/xvdf: pass 1/2 (random)...6.4GiB/8.0GiB 80% shred: /dev/xvdf: pass 1/2 (random)...6.6GiB/8.0GiB 83% shred: /dev/xvdf: pass 1/2 (random)...6.9GiB/8.0GiB 87% shred: /dev/xvdf: pass 1/2 (random)...7.2GiB/8.0GiB 91% shred: /dev/xvdf: pass 1/2 (random)...7.5GiB/8.0GiB 94% shred: /dev/xvdf: pass 1/2 (random)...7.8GiB/8.0GiB 98% shred: /dev/xvdf: pass 1/2 (random)...8.0GiB/8.0GiB 100% shred: /dev/xvdf: pass 2/2 (000000)... shred: /dev/xvdf: pass 2/2 (000000)...375MiB/8.0GiB 4% shred: /dev/xvdf: pass 2/2 (000000)...681MiB/8.0GiB 8% shred: /dev/xvdf: pass 2/2 (000000)...985MiB/8.0GiB 12% shred: /dev/xvdf: pass 2/2 (000000)...1.2GiB/8.0GiB 15% shred: /dev/xvdf: pass 2/2 (000000)...1.5GiB/8.0GiB 19% shred: /dev/xvdf: pass 2/2 (000000)...1.8GiB/8.0GiB 23% shred: /dev/xvdf: pass 2/2 (000000)...2.1GiB/8.0GiB 26% shred: /dev/xvdf: pass 2/2 (000000)...2.4GiB/8.0GiB 30% shred: /dev/xvdf: pass 2/2 (000000)...2.7GiB/8.0GiB 34% shred: /dev/xvdf: pass 2/2 (000000)...3.0GiB/8.0GiB 38% shred: /dev/xvdf: pass 2/2 (000000)...3.3GiB/8.0GiB 41% shred: /dev/xvdf: pass 2/2 (000000)...3.6GiB/8.0GiB 45% shred: /dev/xvdf: pass 2/2 (000000)...3.9GiB/8.0GiB 49% shred: /dev/xvdf: pass 2/2 (000000)...4.2GiB/8.0GiB 53% shred: /dev/xvdf: pass 2/2 (000000)...4.5GiB/8.0GiB 56% shred: /dev/xvdf: pass 2/2 (000000)...4.8GiB/8.0GiB 60% shred: /dev/xvdf: pass 2/2 (000000)...5.1GiB/8.0GiB 64% shred: /dev/xvdf: pass 2/2 (000000)...5.4GiB/8.0GiB 67% shred: /dev/xvdf: pass 2/2 (000000)...5.7GiB/8.0GiB 71% shred: /dev/xvdf: pass 2/2 (000000)...6.0GiB/8.0GiB 75% shred: /dev/xvdf: pass 2/2 (000000)...6.3GiB/8.0GiB 79% shred: /dev/xvdf: pass 2/2 (000000)...6.6GiB/8.0GiB 82% shred: /dev/xvdf: pass 2/2 (000000)...6.9GiB/8.0GiB 86% shred: /dev/xvdf: pass 2/2 (000000)...7.2GiB/8.0GiB 90% shred: /dev/xvdf: pass 2/2 (000000)...7.5GiB/8.0GiB 93% shred: /dev/xvdf: pass 2/2 (000000)...7.8GiB/8.0GiB 97% shred: /dev/xvdf: pass 2/2 (000000)...8.0GiB/8.0GiB 100% This will clear the filesystem.

ubuntu@ip-xxxxxx:~$ sudo file -s /dev/xvdf
/dev/xvdf: data

You need to create the file system on the device to make it available for use again.

for example format device with ext4,
sudo mkfs -t ext4 /dev/xvdf

you can also use /dev/urandom as the source of random data:

ubuntu@ip-xxxxxx:~$ sudo shred -v --random-source=/dev/urandom -n1 /dev/DISK/TO/DELETE

2. using dd command .

sudo dd if=/dev/zero of=/dev/DISK/TO/DELETE bs=1M
or
sudo dd if=/dev/urandom of=/dev/DISK/TO/DELETE bs=4096

This will overwrite the whole disk with zeros and is considerably faster than generating gigabytes of random data. Like all the other tools this won't take care of blocks that were mapped out for whatever reason (write errors, reserved, etc.), but it's highly unlikely any tool will recover anything from those blocks.

This will clear the filesystem.

ubuntu@ip-xxxxxx:~$ sudo file -s /dev/xvdf
/dev/xvdf: data

You need to create the file system on the device to make it available for use again.

for example format device with ext4,
sudo mkfs -t ext4 /dev/xvdf

However, these above-discussed tools are not DoD compliant. Government or Defense organizations request for Department of Defense (DoD) compliant disk wipe program to remove files securely.

3. DOD Wiping

What is DoD ?

DoD 5220.22-M is a software-based data sanitization method used in various file shredder and data destruction programs to overwrite existing information on a hard drive or other storage devices. Erasing a hard drive using the DoD 5220.22-M data sanitization method will prevent all software based file recovery methods from lifting information from the drive and should also prevent most if not all hardware based recovery methods.

DoD 5220.22-M Wipe Method

The DoD 5220.22-M data sanitization method is usually implemented in the following way:

Pass 1: Writes a zero and verifies the write
Pass 2: Writes a one and verifies the write
Pass 3: Writes a random character and verifies the write

Scrub :

Most widely used DoD wiping software in Linux is the scrub, which writes patterns on special files (i.e. raw disk devices) or regular files to make retrieving the data more difficult. Scrub implements user-selectable pattern algorithms that are compliant with DoD 5520.22-M or NNSA NAP-14.x.

The dod scrub sequence is compliant with the DoD 5220.22-M procedure for sanitizing removable and non-removable rigid disks which require overwriting all addressable locations with a character, its complement, then a random character, and verify.

$ sudo apt-get install scrub

Once installed, wipe data using dod method like below.

$ sudo scrub -p dod /dev/xvdf
scrub: using DoD 5220.22-M patterns scrub: please verify that device size below is correct! scrub: scrubbing /dev/xvdf 8589934592 bytes (~8192MB) scrub: random |................................................| scrub: 0x00 |................................................| scrub: 0xff |................................................| scrub: verify |................................................|

LUKS ENCRYPTION

sudo apt-get install cryptsetup
sudo fallocate -l 64G /root/fordocker
sudo cryptsetup -y luksFormat /root/fordocker
sudo file /root/fordocker
sudo cryptsetup luksOpen /root/test2 volume1
sudo mkfs.ext4 -j /dev/mapper/volume1
sudo mkdir /var/lib/docker
sudo mount /dev/mapper/volume1 /var/lib/docker
df -h


LUKS is a on-disk format for encrypted volumes. It puts metadata in front of the actual encrypted data. The metadata stores the encryption algorithm, key length, block chaining method etc. Therefore one does not need to memorize those parameters which make LUKS suitable for use on e.g. USB memory sticks. Additionally LUKS uses a master key that is encrypted using the passphrase hash. That way it's possible to change the passphrase and one can use multiple passphrases. cryptsetup is able to handle LUKS volumes.

Luks is an encryption layer on a block device, it operates on a particular block device, and exposes a new block device which is the decrypted version. Access to this device will trigger transparent encryption/decryption while it's in use.

LUKs stores a bunch of metadata at the start of the device.

It has slots for multiple passphrases. Each slot has a 256-bit salt that is shown in the clear along with an encrypted message. When entering a passphrase LUKS combines it with each of the salts, in turn, hashing the result and tries to use the result as keys to decrypt an encrypted message in each slot. This message consists of some known text and a copy of the master key. If it works for any one of the slots because of the known text matches, the master key is now known and you can decrypt the entire container. The master key must remain unencrypted in RAM while the container is in use.

Knowing the master key allows you access to all the data in the container, but doesn't reveal the passwords in the password slots so one user cannot see the passwords of other users. The system is not designed for users to be able to see the master key while in operation, and this key can't be changed without re-encrypting. The use of password slots, however, means that passwords can be changed without re-encrypting the entire container, and allows for use of multiple passwords.

How to profile JVM running on a remote server docker container.

On a Ubuntu desktop install JProfiler GUI from here.

Download script and run it.
http://download-keycdn.ej-technologies.com/jprofiler/jprofiler_linux_9_2.sh

Provide key if you have , else use evaluation.

Now on the Ubuntu server where docker container is running, you need to stop containers first and modify Dockerfile to add jprofiler

wget http://download-keycdn.ej-technologies.com/jprofiler/jprofiler_linux_9_2.tar.gz && \
tar -xzf jprofiler_linux_9_1_1.tar.gz -C /usr/local

Also expose the port 8849 from container to host so that you can connect from your desktop.

If you use docker-compose.yml, map the port in the service , which you want to connect.
For example

version: "2"
services:
  some_service:
    build: .
    ports:
      - "8849:8849"
    depends_on:
      - "db"
    entrypoint:


This will download jprofiler 9.2 and unpack it in /usr/local when you run docker container next time and map the port on host server.

Once docker container is up , you can ssh to it
docker exec -it /bin/bash
And just start the jprofiler using following command.
/usr/local/jprofiler9/bin/jpenable
You will be asked for 2 options , 1) GUI connect 2. Using config.xml

Use option 1 GUI connect
Now from Desktop you can open JProfiler UI and connect to server-ip:8849
You can profile the JVM you want.

Quick Emulator ( qemu ) for Hardware Virtualization

Have you ever met a requirement where you had to install a windows on top of linux ? Here is a cool solution. QEMU is a free and open-source hosted hypervisor that performs hardware virtualization. Lets see how to install a windows server on a Ubuntu server.

This tutorial assumes that your hardware supports virtualization.
You can check by running following command on your linux terminal.
egrep -c '(vmx|svm)' /proc/cpuinfo

If output is 0 , then not supported , any value above 0 means it is supported.

1. Install qemu
apt-get install qemu-kvm

Once QEMU has been installed, it should be ready to run a guest OS from a disk image.

Now we will test with a tiny example.Download a small image of linux from here.
This is a Small Linux disk image containing a 2.6.20 Linux kernel, X11 and various utilities to test QEMU.

Now unzip archive
bzip2 -d linux-0.2.img.bz2
Note, that this command will not preserve original archive file.
To preserve the original archive, add the -k option:
bzip2 -dk linux-0.2.img.bz2
Now the image is ready.

you can issue the following command.
sudo qemu-system-x86_64 -display vnc=0.0.0.0:1 -smp cpus=2 -m 250M -machine pc-1.0,accel=kvm -net user,hostfwd=tcp::80-:80,hostfwd=tcp::3389-:3389 -net nic linux-0.2.img

This command creates a virtualization with 2 cpu , 250MB memory with VNC server running on it.
You can connect through any vnc client ( realvnc or tightvnc ) 0.0.0.0:1

Now to install a windows OS , we first need to create an empty image

sudo qemu-img create -f raw win.img 40G

This creates an image with 40GB hardisk and raw format.
Now we can install windows os by using the iso image like below.

sudo qemu-system-x86_64 -display vnc=0.0.0.0:1 -cdrom /media/windows_server_2012_r2_with_update_x64_dvd_6052708.iso -smp cpus=2 -m 16G -machine pc-1.0,accel=kvm /var/spool/win.img

Once you run the above command , a vnc server is started and you can connect from a vnc client on display 1 or 5901, depending on client and install the windows.

Enable IIS.
Enable RDP.
Shutdown VM.
Run Windows VM with IIS via:

sudo qemu-system-x86_64 -display vnc=0.0.0.0:1 -smp cpus=2 -m 16G -machine pc-1.0,accel=kvm -net user,hostfwd=tcp::80-:80,hostfwd=tcp::3389-:3389 -net nic /var/spool/win.img

This will launch the machine with 16GB ram , 40G Hardisk . You can connect from RDP and work on it.