Trim Whitespace From Your Image

$ convert -trim img.png

Create A New Image From Text

Note: You can combine this with the ‘trim’ tip above by passing the -trim argument.

$ convert -background white -fill black -pointsize 72 label:"Sean Fox" output.png

Output:

List Fonts ImageMagick Can Use

$ identify -list font

The Problem

The line endings in the following file are not consistent. Do you want to normalize the line endings?

This probably means some of the developers have been editing our source code using a text-editor (instead of Visual Studio) and they had their line endings set to “Unix” or “Mac” instead of “Dos/Windows”. This isn’t a big deal, though it is annoying.

Vim: Convert All Files to Dos/Windows Line Endings

Since I don’t know which files have this problem, I decided to just normalize all the line endings. There are various ways to do this, but I chose to use vim since the documentation on this topic is excellent.

To convert from any mixture of CRLF endings and LF-only endings, to CRLF endings:

:set ffs=dos
:args **\*.cs
:argdo w

We’re basically asking vim to assume Dos/Windows line endings, having it open all *.cs files (C# code files), then having it write the line-ending changes.

Downsides

This does change every single file that was found, regardless of the original line endings. It’s best to do this as one commit in source control to avoid any confusion.

Alternatives

You can also use unix2dos to do this conversion or any scripting language (python, perl, powershell).

Some people also let their source control handle their line endings. Git can enforce these line endings by updating them for you if you prefer. However, at my office, we choose not to let our source control alter our code in any way; we prefer to do that ourselves.

Now get back to coding!

Using ssh-keygen

The ssh-keygen command allows you to regenerate a public key using the -y flag. Using the -t flag you can tell it whether the key is rsa or dsa.

Is my key RSA or DSA?

Chances are it doesn’t matter; ssh-keygen will try to guess based on the input key. However, if you don’t know your key encryption, it’s probably rsa since that’s the default. The filename will also typically tell you, since it’s usually either id_rsa or id_dsa. And even beyond that, if you look at the text in the file, it should be present there as well.

Regenerating a Public Key

Here’s an example:

# ssh-keygen -y
Enter file in which the key is (/home/username/.ssh/id_rsa):
ssh-rsa AAAAB3NzaC1yc2EAAAABIwAAAQEAr3T65FaSononqBjGEZXMg8x0U3ZjYvZxAUZQA7H27VtPgrn9FhsP8Jn+sp0zOi2nFjDsbXWM5L6OPVg1N0OHpiNcg7I
lrc83GiqVGg2AWeHWWolnOwXIsrfwybVcS6ZSCGbGKVWWL5VB/mt/zzF5WD6bhU+TZXYLq8fZC4sa0sapqVccubKw2YbjA53n0wKxrYLfOjP1k56EfkHzm4n7fmlyFi
3kaCvPo31yaMD3zIVJnl/4wMntnnxqFkG7mEtQ29ngkc5ocgRvSbNNvD9IFNvL/9BqlUtiOUcV790cdoLyd0o1mFV8sGPY3zsL6l3lTkjYDmSXTTnxavjHEudC5w==

BAM! There’s your public key!

Is this safe?

Yes, regenerating your key is completely safe and there’s no reason why you wouldn’t want to do this. Public keys are public, just as their name implies. You can give your public key to anyone.

The private key is the one you should keep to yourself and safe-guard. You should be the only one with your private key, and there’s no reason you should not be able to get a copy of your own public key.

–

Now save that public key somewhere safe so you don’t have to generate it every time!

Happy authenticating!

Well, as it turns out, your PHP installation must be configured to support SSH before this option will show up in your WordPress dashboard. In this article I’ll explain how to set this up using just a few simple commands or a plugin.

Option 1: Install libssh2 and use the built-in WordPress SSH/SFTP Support

The upside of following this guide instead of installing the plugin is you’ll be installing libssh2, which means you’re enabling SSH/SFTP support across all PHP applications. You’re also be enabling and using the built-in WordPress support for SSH/SFTP, which is updated and supported with each new release. I personally followed this method, so I can also confirm that it works first-hand. The downside to this guide, of course, is that it takes a bit longer.

Step 1: See if it’s enabled already

Chances are SSH/SFTP is not enabled already, but it doesn’t hurt to check. If SSH is not enabled, your WordPress connection info page should look like this when you go to install updates:

Notice the distinct lack of an SSH/SFTP option. If this is what your page looks like, continue with the instructions below!

Step 2: Install all the development tools you’ll need

We’ll be installing the PHP package for libssh2, which will be compiled from source; this requires some development tools. Run these commands to install the tools you need:

$ sudo yum groupinstall "Development Tools"
$ sudo yum install kernel-devel kernel-headers

Step 3: Install libssh2

You’ll need libssh2 and some php development tools, so make sure those are installed by running the following command:

$ sudo yum install php-devel php-pear libssh2 libssh2-devel

Step 4: Use PECL to install SSH2 for PHP

PECL is the PHP Extension Community Library and we can use it to install SSH for PHP, like so:

$ sudo pecl install -f ssh2

After running this command, you’ll notice that it stops at a line and waits for input from you. It will look like this:

..
........done: 22,740 bytes
5 source files, building
running: phpize
Configuring for:
PHP Api Version:         20041225
Zend Module Api No:      20060613
Zend Extension Api No:   220060519
libssh2 prefix? [autodetect] :

There’s no need to enter a specific prefix; just press the [enter] key to move forward and it will autodetect the prefix.

Step 5: Configure PHP to load the SSH2 extension

Now that the SSH2 extension has been installed, you just have to tell PHP to load it. Configure PHP to load the extension by running the following commands:

$ sudo touch /etc/php.d/ssh2.ini
$ echo 'extension=ssh2.so' | sudo tee -a /etc/php.d/ssh2.ini

Step 6: Restart Apache

You’re almost done! Just restart the web server to have your changes take effect:

$ sudo /etc/init.d/httpd restart

Step 7: Verify the extension is loaded

Finally, check to see if the extension has been loaded by running php -m to see the installed PHP modules:

$ php -m | grep ssh2
ssh2

If you don’t see the ssh2 output from the above command, then something went wrong! Try following the steps again carefully to see what you might have missed.

Finish Line

You’re all done! You can now use SFTP to install and update plugins in WordPress. If you did everything correctly, your WordPress connection info page should now look like this:

* Thanks to Jacob for the original guide to installing libssh2 for PHP under CentOS.

Option 2: Install a Plugin for WordPress

Update: User ‘diamondback’ pointed out that there’s also a WordPress plugin for this. I haven’t used it myself, but it utilizes phpseclib, which is an implementation of SSH/SFTP entirely in PHP.

The upside to using a plugin is WordPress plugins are incredibly easy to install and uninstall. Additionally, the plugin developer could incorporate features that the standard WordPress installation does not have. The downside to using this plugin is this enables SSH/SFTP in WordPress only! It will not enable it in any other PHP applications. On top of that, you now have to rely on the author to update his plugin for new versions of WordPress instead of relying on the built-in WordPress support, which you get with the libssh2 installation.

Step 1: Install the plugin

Just install the SSH SFTP Updater Support plugin. You’re done!

Disclaimer: I haven’t used this plugin and do not endorse it in any way.

Enjoy your SSH/SFTP support! Happy blogging!

Installing build tools in Debian/Ubuntu

In Debian/Ubuntu, you can install the typical build tools by installing the package build-essentials, which is just a pseudo-package that downloads all the popular development packages:

# apt-get install build-essentials

Installing build tools in CentOS

Since I prefer CentOS as my server platform, I also occasionally need to install packages using yum.

To install the common build tools using yum in CentOS you’ll want to install the group package “Development Tools”, which is similar to build-essentials in Debian/Ubuntu flavors of linux. You’ll probably also want to install kernel-devel and kernel-headers if they’re not already installed:

# yum groupinstall "Development Tools"
# yum install kernel-devel kernel-headers

This should give you a copy of make, gcc, gdb, and all those other tools you were looking for.

Happy hacking!

Why?

xargs takes a file list as input and performs some arbitrary operation on it. This is obviously useful for scripting and bulk file operations. Why use xargs? Well, quite frankly, it’s faster than using find -exec because it splits the file list into sublists and calls the command once for every sublist instead of calling the command once for every file. Also, because it uses sublists you never run into problems when trying to run commands with very large argument lists (it is actually possible to run a command and have bash reply that the maximum line length is exceeded). Below is example usage.

Example: fixing permissions

Using xargs we can easily correct permissions recursively. For instance, let’s improve our web security by locking down write privileges on our directories and files to only the owner:

find . -type d -print0 | xargs -0 -I {} chmod 755 {}
find . -type f -print0 | xargs -0 -I {} chmod 644 {}

Here’s what’s happening:

• we use find and -type d to locate all directories under the current directory
• we use -print0 so find will print the directories and separate the directory names by null characters instead of newlines; delimiting this way improves xargs ability to handle special characters in file names
• then we pipe this list to xargs and use -0 to tell xargs the list is null-character delimited
• we also use -I {} to tell xargs to replace any occurrence of {} with each filename as it runs the following command
• ultimately the command chmod 755 {} tells xargs to chmod 755 each directory

Of course we then do the same by running chmod 644 on all files under the current directory.

Efficiency

Using xargs this way is faster than running these equivalent find commands:

find . -type d -exec chmod 755 '{}' \;
find . -type f -exec chmod 644 '{}' \;

Using find this way will run chmod individually for each directory and file, which is less efficient. The general rule of thumb is to always opt for xargs.

You can use xargs for several other things, but this example is my most frequent use-case. Happy hacking!

During the installation Yii uses a ‘Requirement Checker’ webpage that verifies you have the correct PHP version and the necessary plugins. If you’re like me, you like to see all your boxes turn green just to be sure you can get the full functionality out of your apps and frameworks instead of having to debug stuff like this later and going down a rabbit hole.

Install All The Packages

To make the best use of Yii (and several other things), you’ll need these packages: GD, mcrypt, MySQL, PDO, PEAR, APC, Memcache, PgSQL, SOAP, and XML. To get proper packages for these extensions on CentOS 5, I recommend adding the IUS Community Repository. Here’s a one-liner you can run with sudo or as root after you’ve set up that repo:

yum install php53u php53u-cli php53u-common php53u-devel php53u-gd php53u-mcrypt php53u-mysql php53u-pdo \
php53u-pear php53u-pecl-apc.x86_64 php53u-pecl-memcache.x86_64 php53u-pgsql.x86_64 php53u-soap.x86_64 php53u-xml.x86_64

Have fun with Yii!

Pre-installation

First close Firefox! It’s safer to perform these instructions with all browsers closed.

Next, remove any existing Flash installations or files:

# apt-get -y purge flashplugin-nonfree flashplugin-installer gnash gnash-common mozilla-plugin-gnash swfdec-mozilla
# rm -f /usr/lib/firefox/plugins/libflashplayer.so
# rm -f /usr/lib/mozilla/plugins/libflashplayer.so
# rm -f /usr/lib/mozilla/plugins/flashplugin-alternative.so
# rm -f /usr/lib/mozilla/plugins/npwrapper*flash*so
# rm -f ~/.mozilla/plugins/*flash*so

Installation

Now download Flash.

Finally, extract and install the Flash player plugin you just downloaded:

# tar xvfz install_flash_player_10_linux.tar.gz
# mkdir -p ~/.mozilla/plugins
# mv -f libflashplayer.so ~/.mozilla/plugins/

Start up Firefox and you should have a working Flash installation! You can visit Adobe’s website to be sure it’s installed correctly.

Have fun using Nessus and enjoying the rest of the internet.

Wget

Surprise! Wget supports FTP and can download recursively! You could download the full contents of an FTP server like this:

wget -r 'ftp://user:pass@host'

Or just grab a single directory like this:

wget -r 'ftp://user:pass@host/dir'

Cool, huh?

# as -o example32bit.o example32bit.s
example32bit.s: Assembler messages:
example32bit.s:10: Error: suffix or operands invalid for `pop'

To fix this problem you need to pass the compiler or assembler a flag telling it you want to compile the software as 32-bit and not 64-bit.

The fix for C: Compiling with the -m32 flag

If you’re using gcc to compile a C program, pass in -m32. There’s a complete example here on my blog.

The fix for assembly: Compiling with the –32 flag

If you’re using as to compile an assembly program, pass in –32. Then when you link with ld pass in -m elf_i386. There’s a complete example here on my blog.

Happy hacking!