Linux Ask! is a Q & A web site specific for Linux related questions. Questions are collected, answered and audited by experienced Linux users.
Allow a remote IP for incoming connection in UFW (Uncomplicated firewall)
Answer:
To allow a remote IP for incoming connection in Ubuntu's UFW (Uncomplicated firewall), you can use the following command:
# sudo ufw allow from x.x.x.x
Of course you need to reload the firewall.
# sudo ufw reload
Send ARP REQUEST to a neighbour host in Linux
Answer:
The arping command allow you to Ping destination on device interface by ARP packets, using source address source.
E.g.
# arping -U 192.168.1.5
The above command send an Unsolicited ARP request to update neighbours' ARP caches.
What is the difference between ip address 0.0.0.0 and 127.0.0.1?
Answer:
Sometimes when using the netstat command, which print out something like
# netstat -ntpl
(No info could be read for "-p": geteuid()=1001 but you should be root.)
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:25 0.0.0.0:* LISTEN -
...
What is the real meaning of 0.0.0.0?
In fact, this special IP means "all the IP addresses on the local machine". So if you have seen a service listening on 0.0.0.0, it means you can connect to the service using any IP addresses of the machine.
Simple file encryption with OpenSSL
Answer:
You have a single file (input.txt), and you want to encrypt it with a password, it is easy with OpenSSL.
# openssl aes-128-cbc -salt -in input.txt-out input.aes
Enter the password twice.
When you want to decrypt it, use the command.
# openssl aes-128-cbc -d -salt -in input.aes -out output.txt
How to transfer your identity.pub to the remote machine’s authorized_keys?
Answer:
While you can ssh into the remote machine and edit the authorized_keys file, it is easier with the following command.
# ssh-copy-id -i identity-rsa-dsa.pub user@remote-server
