Linux Ask!

Linux Ask! is a Q & A web site specific for Linux related questions. Questions are collected, answered and audited by experienced Linux users.

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.

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.

..

How to get the MD5 checksum of a file under Mac OSX

Answer:

To get the MD5 checksum of a file under Mac OSX, like the md5sum command in Linux, you can use:

# md5 my-file.zip

How to uncompress a WAR file using command

Answer:

To un-compress a Java Web Archives file (*.war), you can use the command

# jar xvf my-app.war

Import private key into Mac's KeyChain

Answer:

To import a private key e.g. key.p12 into your login keychain, use the command:

# security import key.p12 -k ~/Library/Keychains/login.keychain