Accessing android phone via ssh using termux

The ability to access your phone remotely is very useful. I frequently used this technique to copy files to and from my phone and checking my battery status while the phone is charging without actually holding the phone.

First and foremost, we have to install termux. You can install it from google playstore by clicking here. 

Once installed, fire up termux, and install openssh:

$ pkg install openssh

Then, create a password for the default user. The default user is u0_a274.

$ passwd

Then, launch an sshd daemon using below command to start openssh server in the phone, on port 1234 (the port can be any number above 1000).

$ sshd -p 1234

Check your ip address. using below command.

$ ip address 

Let's say our phone's ip address is 192.168.0.179. Make sure your desktop/laptop is connected to the same network as the phone's wifi connection. Fire up a terminal, and ssh to the ip address.

$ ssh u0_a274@192.168.0.179 -p 1234 

Congratulations, you are now connected to your phone, via ssh.

 

Enabling passwordless ssh for Synology DSM version 6

Synology DSM 6.0 does not allow, let alone passwordless ssh by default. In order to enable that, so that we can have automated backup to Synology NAS, below are the steps:

1. Enable User Home in User → Advanced

 

2. Enable SSH in "Terminal & SNMP" → Terminal

3. (Recommended) Create a user, and add the user into administrator group by going to User → Create. As an example, I created a user called dbbackup.

4. Change permission of the user's home directory to 755. You can do this by ssh'ing into synology as admin, and run below command

$ ssh administrator@synology-ip

$ sudo chmod 775 /var/services/homes/dbbackup 

$ exit 

5. Ssh into synology as your new user. Edit below lines in /etc/ssh/sshd_config, and save the file.

$ ssh dbbackup@synology-ip

$ sudo vi /etc/ssh/sshd_config

...

PubkeyAuthentication yes

AuthorizedKeysFile .ssh/authorized_keys

ChallengeResponseAuthentication no

...

6. Restart sshd service

$ sudo synoservicectl --restart sshd

7. Exit from synology shell, and create a pair of ssh key in client machine, and press enter for all the questions

$ ssh-keygen

8. Transfer the public key into synology

$ ssh-copy-id dbbackup@synology-ip

9. Test you ssh connection to synology. You should be able to ssh without password into synology.

$ ssh dbbackup@synology-ip 

Sharing linux directory with windows through remote desktop protocol

Rdesktop is a remote desktop protocol client for linux, to connect to windows machine through remote desktop protocol. Using the usual windows remote desktop client, user can easily drag and drop files between remote and local machines, but not with the rdesktop application.

To overcome this issue, rdesktop comes with an option to share the local linux directory, to the remote windows, so that the windows can access the local linux directory once rdesktop is connected. 

To do that, just specify -r while connecting using rdesktop

$ rdesktop -u administrator -r disk:download=/home/mine/Download mywindows:3389

The above command will share /home/mine/Download to mywindows machine, shown as download, just like below:

 

I can now open the download folder, and it will show me the Download folder in my linux machine (I call it workmachine).

If you do not have rdesktop command, you can easily install it in ubuntu using 

$ sudo apt install rdesktop -y

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.