Removed opened port in ufw
Answer:
If you have opened a port using the ufw command in Ubuntu, but now you want to delete it, you can..
# sudo ufw delete allow 8080/tcp
And then do a reload
# # sudo ufw reload
That's all.
Jan 202012
How to perform a reverse DNS lookup in Linux
Answer:
To perform a reverse DNS lookup for a domain in Linux, you can use the dig command, e.g.
# dig -x 8.8.8.8
; <<>> DiG 9.7.0-P1 <<>> -x 8.8.8.8
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 59808
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 0
;; QUESTION SECTION:
;8.8.8.8.in-addr.arpa. IN PTR
;; ANSWER SECTION:
8.8.8.8.in-addr.arpa. 86328 IN PTR google-public-dns-a.google.com.
..
Erase old downloaded packages from apt-get's cache
Answer:
The erase old downloaded packages from apt-get's cache, which are stored under the location: /var/cache/apt/archives
Try:
# sudo apt-get autoclean
Disable a service in Ubuntu using upstart
Answer:
In newer version of Ubuntu such as 10.04, some services are managed by upstart and you cannot disable them by using the old method.
For example, to disable the OpenSSH server, you need to edit the file /etc/init/ssh.conf, comment out the following lines:
# start on filesystem
# stop on runlevel [!2345]
Then this service will not start when you reboot your machine next time. All the upstart configurations files are under this folder and feel free to try it out.
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
