Setup an openssh-server in a docker container

This is mainly used for testing only. 

First create a Dockerfile. I am using ubuntu:20.04 image for this

$ cat >> Dockerfile <<EOF

FROM ubuntu:20.04

RUN apt update && apt install openssh-server -y

RUN useradd myuser && echo "myuser:123456" | chpasswd && echo "root:123456" | chpasswd && mkdir /run/sshd

EXPOSE 22

CMD /usr/sbin/sshd -D

EOF

Then, build the image

$ docker build -t mysshimage .

Finally, run a container based on the image, and ssh into it. Use 123456 as password.

$ docker run -dit -p 1022:22 mysshimage

$ ssh myuser@localhost -p 1022 

To be a root user, just use su - command once you are logged in as myuser.

Combining pdf files in linux

One of the tool I always use to combine pdf file, is pdftk.

To install pdftk, just run apt install

$ sudo apt update && sudo apt install pdftk -y

To combine pdf files into one:

$ pdftk file1.pdf file2.pdf file3.pdf cat output combined.pdf

where file1.pdf , file2.pdf and file3.pdf are the outputs, and the combined.pdf is the result after the combination process.

Git clone over ssh socks proxy

This is useful for a machine that needs to clone some repository from github, but does not having internet connection.

First, we must identify another machine that can access github.com, we can call this server proxy-server.

Then, establish a socks proxy from our no-internet-server

$ ssh -qN -D 1234 proxy-server

The above command will create a socks proxy at localhost port 1234

Use the git command with socks proxy. Let's say we want to clone the 30-seconds-of-code repository, run below command in a new shell

$ git -c http-proxy=socks5h://localhost:1234 clone https://github.com/30-seconds/30-seconds-of-code

Once done, press ctrl-c in the first shell, to terminate the socks proxy