Some good info: https://hackertarget.com/ssh-examples-tunnels

Move in a directory

root@eve-ng:~# cd ..
root@eve-ng:~# cd /opt/unetlab/addons/qemu

View all existing file

root@eve-ng:/opt/unetlab/addons/qemu# ls
root@eve-ng:/opt/unetlab/addons/qemu# ls nextExisting_File_Name

Create a new directory

root@eve-ng:/opt/unetlab/addons/qemu# mkdir newDirName

Rename Directory

root@eve-ng:/opt/unetlab/addons/qemu# mv oldDirName NewDirName

Rename Files:

root@eve-ng:/opt/unetlab/addons/qemu# mv oldFileName newFileName

Create qcow2 file

root@eve-ng:/opt/unetlab/addons/qemu/NeededFolder# /opt/qemu/bin/qemu-img create -f qcow2 hda.qcow2 30G (use what needed)

Delete files

root@eve-ng:/opt/unetlab/addons/qemu# sudo rm myFile.txt myFile1.txt myFile2.txt
Password: ...

Delete a whole folder and its content

root@eve-ng:/opt/unetlab/addons/qemu# sudo rm -rf foldername/
Password: ...

Problem and solution

Problem when using ssh

murgescusilvia@Murgescus-MacBook-Pro ~ % ssh silvia@ip-address  

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 
@       WARNING: POSSIBLE DNS SPOOFING DETECTED!          @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 

The ECDSA host key for us01 has changed, and the key for the corresponding IP address ip-address is unchanged. 
This could either mean that DNS SPOOFING is happening or the IP address for the host and its host key have changed at the same time. 
Offending key for IP in /Users/murgescusilvia/.ssh/known_hosts:20 

@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 
@    WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED!     @
@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ 

IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY! Someone could be eavesdropping on you right now (man-in-the-middle attack)! It is also possible that a host key has just been changed. 

The fingerprint for the ECDSA key sent by the remote host is SHA256:5b11LsICh7VVaHkfY/HiLh6IThcZYjkkDD7Pt6dixJw. 

Please contact your system administrator. Add correct host key in /Users/murgescusilvia/.ssh/known_hosts to get rid of this message. Offending ECDSA key in /Users/murgescusilvia/.ssh/known_hosts:19 ECDSA host key for ip-address has changed and you have requested strict checking. 

Host key verification failed.

Solution to solve this problem:

murgescusilvia@Murgescus-MacBook-Pro ~ % ssh-keygen -R ip-address 

# Host ip-address found: line 19 /Users/murgescusilvia/.ssh/known_hosts updated. 
Original contents retained as /Users/murgescusilvia/.ssh/known_hosts.old

I will add a command every time I search and use something.