Linux Ask! is a Q & A web site specific for Linux related questions. Questions are collected, answered and audited by experienced Linux users.
Securely remove files or directories in Linux
Answer:
Normally you would remove a file by using the rm command, but what if you want to make sure the file is removed securely which prevent other people from recovering it?
Use srm, e.g.
# srm confidential.txt
Perform AES256 encryption on a string using command
Answer:
To encrypt a string using AES256, you can use the openssl tool.
# echo -n 'apple' | openssl enc -aes256 -k password -nosalt -iv 0 -a -p
key=1F3870BE274F6C49B3E31A0C6728957F0628DEF3179C824405825F85F5527096
iv =00000000000000000000000000000000
PMcE/8RE+RLRlQWT5tlLWA==
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.
