Category Archives: linux

CEntos 6.7 Migrating from mysql-server/mysql-community-server into latest MariaDB

Ok, first you should install yum-replace plugin if you haven’t already have it.

Get MariaDB packages repo from MariaDB repos builder here
MariaDB repo builder
You’ll get some repo config text that you can save to /etc/yum.repos.d/MariaDb.repo like these:

Do update your repo chache

If you’re installing mysql-server from CentOS 6.7 default repo, you should do this:

If you’re installing mysql server from webtatic repo (mysql55w-server), you should do this:

If you’re installing from MySQL Community repository, do this:

Just answer with ‘Y’ if the yum replace command show you some conflicts.
Next, just install all MariaDB related packages:

Start MariaDB:

Confirm that you’re using MariaDB:

Don’t worry, if you have successfully installing MariaDB over MySQL:

  1. your web app that use MySQL will not broken, no need to change anything
  2. your data will stay intact (no data loss)
  3. use MySQL commands as usual (such as: mysql -u root -p)
  4. the MariaDB config is still in /etc/my.cnf

In short, business as usual!

Save bandwidth, block image hot linking

Image hot-linking is (simply put): other site is showing your image that still on your server. This can cause problem for bandwidth limited website, they steal your bandwidth! Also, this doesn’t make visitor from that notorious site to come to your site.¬† More visitor for them, more bandwidth lost for you. We will handle this issue using htaccess.

Remember that to use .htaccess fully (including this tips), you have to activate Apache mod_rewrite.

In our case, we will allow only few sites that directly show/link our image. Other sites that have no permission will show an error/no leech image. This is the full .htaccess code:

 

The explanation:

  • (line 1) Activate rule only if mod_rewrite is activated
  • (line 4) we don’t allow Facebook bot to steal our image. Comment (#) this line if you want to allow Facebook to grab image from your site (this is used by Facebook to create thumbnail image whenever FB users posting your website¬† URL)
  • (line 6-9) allow only few sites to direct link/hot link our image: ahowto.net, mp32u.net, google.com and bing.com
  • (line 10) don’t apply the rule for “no leech” image that will be served to bandwidth leecher/stealer. Don’t forget this line, or you’ll get forever loop that eventually stress your webserver.
  • (line 11) Serve the leecher with our error/no leech image. I suggest you to use more informative image, such as image that contain messages “visit my site to view the image”
example no_leech image

just an example that might annoy bandwidth stealer

Special case for Wordpress

Yes, I know that there are few “anti-leech/anti-hot-linkplugins out there, but make sure they have the correct htaccess code placement. Make sure the placement is before main wordpress htaccess default code. So, your wordpress blog htaccess code would be like this:

 

[debian] apt command to search which packages that provide certain file/library

Suppose you want to compile an application that need some library file such as libcurl.so but you don’t know the exact packages name. Sure, you can guess by using apt-cache search but the result might not be pleasant. (apt-cache search result when combined with file name will –usally– return empty result).
Here, I’ll show you other alternative to apt-cache search to search packages name who provide certain files/libraries.

  • Install apt-file package:

 

  • before using apt-file, you should update the database first (you need internet connection to do this):

  • wait until all package databases from repository downloaded. Now you can use it:

that command will search which packages from repository that provide libcurl.so file. Use –package-only to only package name, without this option, the result will also include file name and directory name inside packages (which –in my opinion– quite distracting). Oh, almost forgot, apt-file can be used by non-root users.
man apt-file for more complete usage!

[debian] apt-get install specific version of package

When you’re adding additional repositories beside the default in your /etc/apt/sources.list, Debian will provide more than one version of package where available. You can use “apt-cache policy package-name” to check the package’s available version. For example, you want to check available ffmpeg version on your repositories, you can use this command:

If you add additional repositories other than default, you may have several version of ffmpeg. This one is the output example on my server (I add debian-multimedia and backports repository beside the default):

Those lines above show you which ffmpeg version is already installed and which one is available on other repository.
Suppose you want to install ffmpeg version 5:0.7.11-0.1 from debian-multimedia repository, you can use this command:

Notice that I put “=” and the version number [omitting the last number (0)] after the package name. That apt-get command will install ffmpeg from debian-multimedia and removing the one from backports that already installed.
When a package have some configuration file (such as Apache with it’s apache2.conf), apt-get will ask you whether to keep your current configuration or use the new version (overwrite the old one).

find file based on its content

On my last post I’ve mentioned tool called Agent Ransack for Windows that has ability to search file based on it’s content (and other criteria such as modification time). On Linux, there’s no need to install additional package/application. There is already a command line tool that will do the trick, i.e. grep.

For example, you want to find all php files in the current folder and its subfolder that contain word “stat

Parameters explanation:
–color=auto : this will made the word ‘stat‘ highlighted
-i : ignore pattern case (case in-sensitive — the pattern is ‘stat’)
-nH : show filename and the line number

grep example output

example output

If you want to add file modification time as the other criterion, you must combine find and grep command.
For example, you want to search all php files in the current folder and its subfolder that contain word ‘stat‘ and the file was last modified within less than one day a go:

Please refer to find man pages for more option about file modification/access/creation time options.