Answer:

With the powerful ImageMagick program, we can easily handle common graphics tasks using command only.

For example, to combine multiple images into a single image, we need just one command:

# convert file1.jpg file2.jpg file3.jpg +append -quality 90 'output.jpg'

The above command (file1.jpg file2.jpg file3.jpg) into the file output.jpg with quality set to 90.

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Answer:

To show the current Postfix queue, you can try the command "postqueue"

# postqueue -p

-Queue ID- --Size-- ----Arrival Time---- -Sender/Recipient-------
BD7E2BF973      972 Sat Aug 27 08:57:54  no-reply@example.com
(connect to alt4.gmail-smtp-in.l.google.com[209.85.143.27]:25: Connection timed out)
                                         johndoe@gmail.com

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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:

To install Google Chrome in Ubuntu, the simplest way is to us PPA

E.g.

1. Add the key and URL

# wget -q -O - https://dl-ssl.google.com/linux/linux_signing_key.pub | sudo apt-key add -
# sudo sh -c 'echo "deb http://dl.google.com/linux/chrome/deb/ stable main" >> /etc/apt/sources.list.d/google.list'

2. Install it

# sudo apt-get update
# sudo apt-get install google-chrome-stable

Done.

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Answer:

You can try the command below in order to download all the files/sub-directories under the directory "dir"

# wget -r ftp://user:password@example.com/dir/*

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Answer:

To rename an IP address using DHCP in Ubuntu, try enter the commands below:

1. Release the current IP

# sudo dhclient -r

2. Renew a new IP

# sudo dhclient

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Answer:

In the last article, you already know how to get the Facebook access token. In this post, I will tell you how to create testing accounts for your app's testing.

# curl -F 'access_token=ACCESS_TOKEN' 'https://graph.facebook.com/APP_ID/accounts/test-users?installed=true&permissions=read_stream'

You can manipulate the permissions as needed.

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Answer:

Assume you have your created a Facebook application, and you have the two things: App ID & App Secret.

You can get the access token by a simple curl command.

# curl -F type=client_cred -F client_id=APP_ID -F client_secret=APP_SECRET https://graph.facebook.com/oauth/access_token

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