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Copy or backup MySQL tables


This is a very simple and very effective procedure. Log on to your server and then log on to your database with the usual command..

mysql -u root -p

and enter your password.

Select your database using the command

USE your_database_name;

Then, use the following commands..

To copy the table and the data…

CREATE TABLE your_table_backup SELECT * FROM your_table;

To copy the table structure only, no data, use…

CREATE TABLE your_table_backup SELECT * FROM your_table LIMIT 0;


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See a file without comments..


Configuration files often come with a lot of commentary. Documentation is always good, but sometimes you just want the red meat. Here’s how to see a file without all the ‘#’ commentary.

grep ^[^#] /etc/someconfig.conf
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How to download a YouTube video


If you want to download a YouTube video, here’s how. First install the youtube-dl binary and the associated codecs…

sudo apt-get install youtube-dl ffmpeg libavcodec-extra-53

Once it installs, get your YouTube URL and simply run the command..


to download the video. There are a load of other options you can use which are all shown thus..

youtube-dl --help

Conveniently, the youtube-dl command also does on-the-fly conversion of downloaded videos to just the .mp3 version for audio playback, thus…

youtube-dl -x --audio-format mp3

Where -x means ‘eXtract’. Again, there are a load of options here.

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Display the fields in a MySQL table..


Simple command that you sometimes need. Obviously this runs from the mysql client prompt, so open a command line and type

mysql -u root -p

and then enter the root password for your mySQL database.

Then, switch to your database…

USE yourdatabasename;

An now, all you need is..

SHOW columns FROM your_table;


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Your IP Address


You appear to be coming from the ip address below..

Reset user home directory permissions


Simple. Fire these three commands…

sudo chown -R bob:admin /home/bob
sudo find /home/bob -type f -print0 | xargs -0 chmod 0600
sudo find /home/bob -type d -print0 | xargs -0 chmod 0700
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Backup and restore MySQL database quickly


Very simple. Use the following commands..

Backup to an external file.

On the *nix command line, just run..

mysqldump -u root -p database_name > /path/to/database_dump_file.sql

Punch in the password for root (in this case) and the backup is output to the file database_dump_file.sql. It’s ASCII so it can be edited if needed.

Restore from an external file..

mysql -u root -p database_name < /path/to/database_dump_file.sql

Typed the password and that's it, finished.

Need the database names quickly?

Log in to the database as ususal with the command at the *nix command line.

mysql -u root -p

And then issue the following at the prompt..

mysql> show databases;

and you get this....

| Database             |
| information_schema   |
| largedump            |
| dspam                |
| mysql                |
| performance_schema   |
| testdata             |
| testdata_1           |
| dataset_4            |
| dataset_2            |
9 rows in set (0.01 sec)
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Ban a sender from sending you mail on Postfix


This is quite handy and easy to set up.

First, open up, the principal configuration file in Postfix. I use vim, but of course you can use whatever editor you like, e.g. vi, nano etc.

sudo vim /etc/postfix/

In your, add the following lines in the configuration

smtpd_sender_restrictions =
        check_sender_access hash:/etc/postfix/sender_access

Now, create a file to store the list of banned names.

sudo touch /etc/postfix/sender_access

and now edit it to add the banned names…

sudo vim /etc/postfix/sender_access

Add the banned addresses in the following format.. REJECT REJECT REJECT REJECT REJECT

Save the file. Now, create the hashed db file for this file..

sudo postmap /etc/postfix/sender_access

Now you should have a file in the /etc/postfix directory called /etc/postfix/sender_access.db

Now all you need to do is restart postfix.

sudo service postfix restart


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What’s the command line to run Clamscan?


Here’s the command to run a complete scan but exclude the sys, proc, dev and lib directories.

sudo clamscan -r -i --exclude-dir='^/sys|^/proc|^/dev|^/lib' /
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How do I downsize a Hi-Def movie?


In Debian / Ubuntu, use avconv.

avconv -i input.mp4 -b 64k -s hd720 -strict experimental output.mp4

This command uses avconv, where..

-i input.mp4 = the input file name
-b 64k = down sample the audio channel to 64k – should be fine.
-s hd720 = reduce the video from hd1020 to the 720 format
-strict experimental = Allows mp4 output
output.mp4 = the output file.

If you haven’t got avconv installed, use

sudo apt-get install avconv

and follow instructions.

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