Sunday, July 31, 2022

Test UDP Port to Linux Server

To test if a udp port is allowed to a linux server, and not blocked by any firewall, we need ngrep on the server side, and nc (netcat) on the client side.

First, install ngrep on the server
$ sudo apt install ngrep -y

And start to watch the udp 10000 traffic (for example)
$ ngrep -q "accessible" udp port 10000

In the client side, we need to install netcat-openbsd 
$ sudo apt install netcat-openbsd

We are now going to test port 10000 udp in the server, from the client (the "yes, accessible" message could be anything, as long as it contains accessible keyword)
$ echo "yes, accesible" | nc -u server-ip 10000

If the port is opened (not blocked by any firewall), you will get message like below in the server terminal
U client-ip:39062 -> server-ip:443 #1
  yes, accessible...    

If the port is blocked, you won't get any output on the server terminal

Friday, July 1, 2022

Change Docker Data Location

The default location that docker use to store all the components of docker, such as images and containers is /var/lib/docker.

In some linux installation, sometimes the / or /var directories are not that big, and we would like to have our docker save all the images and containers in another directory.

To set docker to use other directory:

1. Create the new directory (let's say we are using /data/docker )
$ sudo mkdir /data/docker

2. Stop docker daemon
$ sudo systemctl stop docker

3. Create a file called /etc/docker/daemon.json (Edit if the file is already exist)
$ sudo touch /etc/docker/daemon.json

4. Edit and put in below content into the file
        "data-root": "/data/docker"

5. Save and exit the editor

6. Start docker
$ sudo systemctl start docker

7. Verify that docker is running
$ sudo systemctl status docker