Answer:

To move to the end of a line in VIM, type

$

You can also type "A" to append at end of the line.

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Answer:

To move to the end of a file in VIM, type

G

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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.

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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.

..

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Answer:

It is easy to use du command to estimate disk usage, however, sometimes you want to ignore some files during the calculation.

To do so, try

# du -h --exclude='*.bak'

The above command will exclude all the file end with the extension .bak during the disk space calculation.

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Answer:

You can simulate a HTTP form post, with a file being uploaded to a remote server using the curl command.

curl -F 'photo=@/upload/image.jpg' http://example.com/upload.php

Assume the name of the form element of your upload is called "photo"

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Answer:

A simple way to debug and verify your Postfix configurations is the use the sendmail command with the -bv flag.

Example:

# sendmail -bv username@example.com

No email will be sent using the above command, it just report after verifying each recipient address. This is very useful for testing the Postfix configurations.

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Answer:

You can use the following command to create an empty png file, using the ImageMagick.

# convert -size 100x100 xc:none empty.png

an empty png of size 100x100 will be created.

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Answer:

If you have a remote file and you can have a quick edit, if you use the following command:

# ssh -t john@remote-server vim /data/test.txt

You will be prompted to login if you don't have proper ssh key in the remote server, and after finishing editing the file, you will quit the ssh session automatically.

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Answer:

To add a new directory into the PATH environment variable, you can use the following command.

# export PATH=$PATH:/opt/myprogram/bin

If you want to have this path being set automatically, then follow this article.

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