If you stare at the list of running processes on your server for long enough, you are bound to come across the user called “nobody”. Before you call a security expert and prepare to fight off a hacker, relax. While the username “nobody” may seem suspicious, it is actually supposed to be there.
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Therefore, do not fear “nobody” and do not take any steps to hinder the user’s ability to run some of your critical applications, like the web server. What nobody does is nobody’s business.

There, you’ve been told!

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3. What’s my IP? Check your IP address from the command line.

Your .htaccess file might look like this:

order deny,allow
deny from all

# allow from example.dyndns.org
allow from 8.8.4.4

And your sed code to update the allowed IP address might look like this:

sed -i -r "/# allow from example.dyndns.org/I{\
n; s/([0-9]{1,3}.){3}[0-9]{1,3}/8.8.8.8/\
}" .htaccess

Let’s look at it piece by piece.

• /# allow from example.dyndns.org/I will search the file for this string. The I flag at the end makes the search case insensitive.
• n; will tell sed to continue processing on the next line.
• s/([0-9]{1,3}\.){3}[0-9]{1,3}/8.8.8.8/ will regex search for an IP and replace the match with your updated IP (in this case 8.8.8.8).
• .htaccess is of course the input file to process.

Note that in .htaccess files, comments must be on a line of their own. End of line or inline comments are not permitted. In cases where you do not need to replace a part of the next line but rather all of it, our replacement becomes s/.*/8.8.8.8/

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1. Securing WordPress Dashboard using .htaccess behind CloudFlare (or any other CDN)
2. What’s my IP? Check your IP address from the command line.
3. Handy command line currency converter.

I’ve recently purchased an Epson Stylus Photo PX830FWD which doesn’t seem to want to stop impressing me. Following the death of my last desktop PC, I needed a way to be able to scan again since there’s no way I’d ever be able to use my SCSI scanner. Wireless was the way to go as our lives are surrounded by laptops, tablets and smartphones not to mention the whole internet. Yes, this is a Google Cloud Print enabled printer which means I can print to it from my Android devices, or from Chrome, etc… wherever I am in the world. Epson have their own cloud print service if you prefer, but I haven’t tested it yet.

I was very happy to learn that I can use this device wirelessly from my Fedora machines as well since booting Windows just to scan wirelessly was not something that I was looking forward to have to do. If you do use Windows, the Scan-to-PC feature is pretty cool. It means that you can scan a bunch of documents at the scanner without touching a PC. I stuck Windows inside a VirtualBox guest, mounted a folder on my Synology NAS and scan to that directly. This way my scans are immediately accessible on my local network, remotely via scp/sshfs and even via the NAS’ web interface.

I haven’t tested the fax capabilities yet, but over and above manual mode there is a Print-to-Fax driver under Windows with it’s own address book. And if you ever run out of ruled or graph paper, stick a blank A4 sheet in it, press a button and hey presto. Stick in an SD card with pictures and it will even use a photo as a background. The 32GB Transcend Class 10 SDHC which I bought for my Canon EOS 550D Rebel T2i worked no problem with the printer.

I no longer have a need to print on CDs or DVDs myself, but it has it’s own built-in tray which sounds like a Transformer transforming as it moves around the internal parts of the printer during eject/insert. All in all, an excellent piece of kit which I would recommend any day. Now I need a good shredder (minimum DIN/Level 3). Any recommendations?

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As always with Linux, there’s a plethora of ways to do what I am doing below, so this is just an example for your reference:

function check_mounted () {
    local result=`df | grep $1`
    echo $((${#result} > 0 ? 1 : 0))
}

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$ pwd
/media/usbdisk/bin

$ readlink -f ./../mnt/.Skype
/media/usbdisk/mnt/.Skype

When you use readlink in a script and assign a resulting path to a variable, you should add the n flag (-fn) to suppress the trailing newline.

As you might have noticed, I needed to use this in a script to launch Skype but specify that I want to use the data files on my usb key as opposed to the default ~/.Skype location. This however was not working with relative paths and Skype would crash with something like:

$ FatalAssert(*out_ptr != ‘.’ && !strstr(out_ptr, “../”) && !strstr(out_ptr, “..\\”))
FatalAssert(*out_ptr != ‘.’ && !strstr(out_ptr, “../”) && !strstr(out_ptr, “..\\”))

The moment I pass a real path to Skype’s –dbpath parameter, everything works as expected.

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3. How to install KDE on Fedora Core 13 and onwards.

This is very bad:

find / -delete -type f -name 'Thumbs.db' -mtime +7

This is good:

find / -type f -name 'Thumbs.db' -mtime +7 -delete

The order of the -delete flag is very important. In the first case find will delete everything it finds (totally ignoring the subsequent criteria), whereas the second case will delete what is matched.

In other words, the order of the find flags/parameters/actions are very important. If you are in doubt, or even if you are not, you should always have a backup in case something goes wrong.

CentOS help for -delete flag:

Delete files; true if removal succeeded. If the removal failed, an error message is issued. Use of this action automatically turns on the ’-depth’ option.

Fedora help for -delete flag:

Delete files; true if removal succeeded. If the removal failed, an error message is issued. If -delete fails, find’s exit status will be nonzero (when it eventually exits). Use of -delete automatically turns on the `-depth’ option.

Warnings: Don’t forget that the find command line is evaluated as an expression, so putting -delete first will make find try to delete everything below the starting points you specified. When testing a find command line that you later intend to use with -delete, you should explicitly specify -depth in order to avoid later surprises. Because -delete implies -depth, you cannot usefully use -prune and -delete together.

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Since FC13, the group name has changed to the not-so-obvious KDE Software Compilation.

sudo yum groupinstall “KDE Software Compilation” (with the quotes) and you’re off!

I’m installing KDE in a fresh install of FC16 as I’m writing this, because like Leonid, one of the things which annoy me about GNOME 3 is the inability to see a Skype icon with notifications of incoming chats without having to move your mouse to bottom right corner all the time. We are using Skype as an example here, there are of course other icons which one might miss, such as the Dropbox icon for example to know if any synchronisation is in progress.

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In all cases, there are 2 areas that can be locked down from 2 separate .htaccess files. These are:

• /wordpress/.htaccess to secure the wp-login.php file (used to log in).
• /wordpress/wp-admin/.htaccess to secure everything under the wp-admin directory.

I want to allow only a few IP addresses to be able to access these areas. This is how it’s done without a cloud:

# add the following lines to /wordpress/.htaccess
<Files wp-login.php>
    order deny,allow
    deny from all
    allow from 93.75.252.219
    allow from 110.170.50.32
</Files>

# add the following lines to /wordpress/wp-admin/.htaccess
order deny,allow
deny from all
allow from 93.75.252.219
allow from 110.170.50.32

Access to the login and admin areas of your website are now restricted to only the IPs you allow. If however, you are using a service like CloudFlare, the above will not work because apache can’t see your (the visitor’s) IP address. Let’s fix this:

# add the following lines to /wordpress/.htaccess
<Files wp-login.php>
    SetEnvIf X-FORWARDED-FOR 93.75.252.219 allowedip
    SetEnvIf X-FORWARDED-FOR 110.170.50.32 allowedip
    order deny,allow
    deny from all
    allow from allowedip
</Files>

# add the following lines to /wordpress/wp-admin/.htaccess
SetEnvIf X-FORWARDED-FOR 93.75.252.219 allowedip
SetEnvIf X-FORWARDED-FOR 110.170.50.32 allowedip
order deny,allow
deny from all
allow from allowedip

Apache is now reading your IP address and setting the allowedip environment variable which is then whitelisted on the last line.

Note that you should *not* rely on this security measure alone since an IP address you have whitelisted can and may be spoofed. Always monitor your access logs and combine this with other security methods (such as basic authentication for example) to further increase security.

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In this file you can define multiple ssh connections that you frequent and this becomes even more useful if you have many hosts/accounts to connect to.

Consider the following:

ssh user1@example.com -p2222

Sure, it’s easy to remember, but what if you have many hosts, each with different ports?

Whilst reminding me about the config file however, he complained that you can’t define 2 different users for the same system. This isn’t true, and this is how it’s done:

Host user1
HostName ssh.example.com
User user1
Port 2222

Host user2
HostName ssh.example.com
User user2
Port 2222

That’s all! Now, when using ssh, you can just type “ssh ” and the first few characters of a Host and then hit tab to get a list of all available accounts. The autocompletion comes from the “Host” definition. Inside any Host profile, you can basically use any other parameter documented in `man ssh_config`. Definition for Host as follows:

Host Restricts the following declarations (up to the next Host keyword) to be only for those hosts that match one of the patterns given after the keyword.  If more than one pattern is provided, they should be separated by whitespace.  A single ‘*’ as a pattern can be used to provide global defaults for all hosts.  The host is the hostname argument given on the command line (i.e. the name is not converted to a canonicalized host name before matching).

Edit: As pointed out by Leonid, you will need `yum install bash-completion` or its equivalent for host autocompletion to work.

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Today I tried a few more combinations and finally got it working, most probably because I have chosen “TwinView” in the configuration, rather than “Separate X screen”. I also specified each screen’s resolution and refresh rates instead of leaving everything on “Auto”. Further settings include:

• Screen 0: Absolute Position +0+0
• Screen 0: Make this the primary display for the X screen
• Screen 1: Position +1920+0 (where 1920 is the width of the laptop display)

My setup is perfect again.

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2. Installing Fedora Core 12 (FC12 “Constantine”) on old hardware.