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Items by Apostolos P. Tsompanopoulos

Καβάλα, 29.11.2011
08:51
Think like a virus!
» The light of the LAMP

Not related to L.A.M.P. technologies, but a useful quote to remember if you are a net admin:

As a network administrator, you have to think like a virus.
How can I get into a network?
Which points are the most vulnerable?
Once in, what's the easiest path to destruction?
From the "Windows sources" magazine, July 1997 issue, page 158, "NT admin> Stop network attacks" by David Chernicoff Visit The Light of the LAMP blog for more...

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Καβάλα, 31.07.2011
19:09
Re-enabling Google FriendConnect gadgets
» The light of the LAMP

In case you see blank boxes in your Firefox, instead of Google FriendConnect (GFC) gadgets, you can try searching the configuration window of the HTTPS Everywhere add-on. For me, it was the GoogleServices option, which I had to deactivate in order to re-enable the GFC gadgets.

[HTTPS] Everywhere Preferences window

It took me some time and several deactivations and reactivations of my add-ons while trying to find the culprit and I found it. Visit The Light of the LAMP blog for more...

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Καβάλα, 27.07.2011
20:26
Show all my active WordPress plugins
» The light of the LAMP

Recently, I needed to get a list of every plugin that I've activated on all of my WordPress local-hosted blogs.
So, instead of going to every blog's dashboard and noting down the list of every active plugin, I decided to write a quick (and dirty, i.e. not optimized) script.

<?php // initialize variables [you have to change them to their proper values] $dbhost = "localhost"; $dbuser = "dbuser"; $dbpass = "dbpassword"; // connect to MySQL and get all database names $db = mysql_connect( $dbhost, $dbuser, $dbpass) or die( "MySQL connection problem: " . mysql_error()); mysql_set_charset( "utf8"); mysql_select_db( "information_schema", $db) or die( mysql_error()); $sql = "SELECT SCHEMA_NAME FROM SCHEMATA"; $u0 = mysql_query( $sql, $db) or die( mysql_error()); $alldb = array(); while ($u1 = mysql_fetch_row( $u0)) { $alldb[] = $u1[ 0]; } // select each database found and check for active plugins foreach( $alldb as $adb) { $conn = mysql_select_db( $adb, $db); // get *_options table name $sql = "SHOW TABLES FROM $adb LIKE '%_options'"; $u0 = mysql_query( $sql, $db); // or continue; while ($u1 = mysql_fetch_row( $u0)) { if ($opt = $u1[0]) { // get active plugins list $sql = "SELECT * FROM $opt WHERE option_name='active_plugins'"; $u00 = mysql_query( $sql, $db); if ($u01 = mysql_fetch_array( $u00)) { $apj = $u01[ 'option_value']; if ($apj) { $ap = unserialize( $apj); foreach( $ap as $apv) echo "Database: $adb >>> $apv\n"; } } } } } mysql_close( $db); ?>
The output of this script is a list of all active plugins, one for each line, so it can be used in a shell script, for example one can find out how many of them are active:

php show_all_active_plugins.php | wc -l
or find out which blogs are using a certain plugin:

php show_all_active_plugins.php | grep akismet

Disclaimer: as usual, this script works for my setup and, for this reason, I'm sharing it here for everyone interested. I hope it will work for anyone else who tries it, but I cannot guarantee it for every possible situation. Visit The Light of the LAMP blog for more...

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Καβάλα, 05.07.2011
15:49
CRON error: grandchild failed with exit status 1 [Solution]
» The light of the LAMP

Just after I upgraded my Ubuntu to 10.10 version, I noticed some cron-related error messages in my /var/log/syslog file, like these:

Jul 5 13:40:01 agriope2 CRON[971]: (CRON) error (grandchild #974 failed with exit status 1) Jul 5 13:50:01 agriope2 CRON[7775]: (CRON) error (grandchild #7778 failed with exit status 1) Jul 5 14:00:01 agriope2 CRON[14520]: (CRON) error (grandchild #14526 failed with exit status 1) Jul 5 14:00:01 agriope2 CRON[14521]: (CRON) error (grandchild #14531 failed with exit status 1)

At first, I thought they were generated by one of my scripts, which runs via cron every 10 minutes and I wondered what happened during upgrade that caused its exit status to turn to 1 instead of 0. Unfortunately, I didn't had the time to delve deeper back then and I ignored it, since everything seemed to work as expected.

Until today, when (after one more successful system upgrade in the meantime) I decided to examine it further.
Given that nothing has changed into my script, I thought that it would be a good idea to search into /etc/cron* directories and there I found that there was the script /etc/cron.d/update-motd, which was scheduled to run every 10 minutes and tried to run /usr/sbin/update-motd. The problem is that /usr/sbin/update-motd was not present any more at its whereabouts, probably because "the functionality formerly provided by update-motd package is now integrated into pam_motd, in libpam-modules" (as the description of update-motd package says).

So, I moved /etc/cron.d/update-motd to another location, just in case I will need it again some time in the future.

Update [2011/12/25]:
In case you are running fetchmail from cron, you 'll have messages like the above whenever you have no new mail. For this situation, the solution is already in the man page of fetchmail:

If you do not want "no mail" to be an error condition (for instance, for cron jobs), use a POSIX-compliant shell and add

|| [ $? -eq 1 ]
to the end of the fetchmail command line, note that this leaves 0 untouched, maps 1 to 0, and maps all other codes to 1. See also item #C8 in the FAQ.
Visit The Light of the LAMP blog for more...

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Καβάλα, 31.01.2010
15:10
System upgrade to Ubuntu 9.10
» The light of the LAMP

I know that I'm some months late on upgrading, but for a production system I prefer to let things cool down a little before attempting the system upgrade. However, even with this methodology, there may be still some problems after finishing, and I have found two of them today, after upgrading to karmic koala version of Ubuntu (9.10 for number-centric fans).

The first one was a problem with mysql-client, which remained in 5.0 version for some reason. I was able to resolve this issue by manually installing version 5.1:

aptitude install mysql-client-5.1

The second problem had to do with updating vnstat's database ('vnstat -u'). After testing various ideas, I came up with no other solution than deleting the previous databases and recreating new ones with the following commands:

rm /var/lib/vnstat/eth* /var/lib/vnstat/.eth*
vnstat -u -i eth0
vnstat -u -i eth1

I hope that there will be no other surprises (until the next upgrade of course) Visit The Light of the LAMP blog for more...

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Καβάλα, 02.09.2009
03:24
send mail to correct local host
» The light of the LAMP

After upgrading my previous server with a new one, I run a lot of migration scripts and update procedures to make sure that everything transferred OK and worked as expected. However, a little thing kept bugging me until today.

Usually, when you want to send an email message to a local user, you either send it to user@localhost or just to user and the mail service makes sure that the local hostname is added after the '@' (if there is nothing there of course). But the problem for me was that messages to local users relayed through my external mailgate after the upgrade.

The /etc/hosts and the configuration files of postfix were already filled with the correct hostnames and I could not find anything until I tried to search all the files in /etc hierarchy for the old hostname.

To my surprise, I found that the old hostname was still in /etc/mailname which, according to its man page, is a plain ASCII configuration file, which on a Debian system contains the visible mail name of the system.

I don't know if the upgrade kept it intact or it was the restoration of /etc data files that caused this discrepancy. The good thing is that I found it easily by searching with grep. Visit The Light of the LAMP blog for more...

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Καβάλα, 31.08.2009
14:26
Change photo extensions by content
» The light of the LAMP
Recently I had an interesting problem. I had a lot of files in a directory, all photos, with their filenames messed up, especially their extensions. So, in order to clear them and keep only the good ones, I had first to rename them in a more consistent manner (the JPEG photos ending with .jpeg, the PNGs with .png and so on).

I guess there is probably a plethora of appropriate tools, but I had no time to search in the chaotic internet, so I wrote a small PHP script (with a little help from the shell: command 'file') and run it from the command line.

The script just parses the output of the file command and renames each file accordingly.

I'm putting this here, just in case it will be useful to someone else also:
```
#!/usr/bin/php
<?php

$res = array();
exec( "file *", $res);

foreach( $res as $f) {
 list( $fn, $ft) = split( ':', $f);
 if (strpos( $ft, "JPEG") !== false) {
  rename( $fn, $fn .".jpeg");
 } else if (strpos( $ft, "PNG") !== false) {
  rename( $fn, $fn .".png");
 } else
  echo "cannot rename $fn\n";
}
?>
```
I'm actually testing only for JPEG & PNG files since I know that I have only these two types.
Don't forget to make this file executable if you want to run it from the command line. Visit The Light of the LAMP blog for more...

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Καβάλα, 29.03.2009
02:11
3D: Desktop Describing Day
» The light of the LAMP

Our desktops are (like) our offices, right?
Well, not for me friends!

Although my 3D (i.e. real life) office is rather messy (at least for other people, not for me of course), my computer desktop is rather simple.

I work usually with my laptop, as most people do these days, and, since I'm rather a CLI person, I like it 'naked'. I'm using XFCE as my window manager with 2 virtual desktops (featuring a dark, mostly black, photo from my favorite tv-show as a background picture and only 4 icons which I rarely open) and its tray sitting on the lower right corner with a bottom-up direction.

This tray contains (bottom -> up): battery readings, time/date, gwibber, RSIBreak, the sound applet and the open applications bar.

I have only two windows open all the time: xfce4-terminal (with at least 3 open tabs) and Firefox (with 2+ open tabs). Of course, when needed, I may open OpenOffice.org or some other windows, but usually I work with just these two.

Don't worry about underusing my laptop; it's actually a full LAMP server, working 24/7 and serving 4 web sites (for now).

You may find this arrangement rather minimalistic, but I find it very work-oriented and I prefer it from a more complicated one.

So, what is your desktop like? Visit The Light of the LAMP blog for more...

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Καβάλα, 23.10.2008
09:43
Sample data and how to produce them
» The light of the LAMP

Sometimes a programmer needs to test/debug one application by feeding it with data, random or not. In a situation like this, there are some utilities one can use to produce as many data as she needs.

Let's start with a simple example of feeding our test application (we will call it "test_data") with zeroes, say 100 bytes with a value of zero.

head --bytes=100 /dev/zero | ./test_data

The above command has two parts; the first one (before the '|' delimiter), 'head', reads /dev/zero device, which provides us with zero-valued bytes as a stream, up to a count of 100 bytes and sends them to the second one, 'test_data', as input. If we wanted more, say 100 KBytes, we would replace the parameter of 'bytes' argument with "100k", as follows:

head --bytes=100k /dev/zero | ./test_data

Now, let's say we want random data. It's as simple as replacing '/dev/zero' device with '/dev/random':

head --bytes=100k /dev/random | ./test_data

With the above command combination, we produce 100 KBytes of random data as input to our test_data application.

And what if we wanted some specific data, like "testing with sample data", repeated 40 times?

yes "testing with sample data" | head -40 | ./test_data

The 'yes' command just outputs its input continuously; 'head' keeps only the first 40 lines; 'test_data' works with these 40 lines of the sample string.

Programming life can be very simple (and entertaining) some times! Visit The Light of the LAMP blog for more...

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Καβάλα, 18.06.2008
12:22
Firefox 3 download day
» The light of the LAMP

Today is the day Firefox 3 has launched and the day it tries to break a world record of the most downloads and installations of a software package in a day.

So, if you like Firefox, why don't you help?

Visit The Light of the LAMP blog for more...

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Καβάλα, 13.06.2008
09:02
Backup files before editing
» The light of the LAMP

It's a fact that many text editors (or word processors) have the ability to keep a backup copy of every file you edit, just to assure you that you can always restore the previous version of the file. This is usually implemented by creating a copy of the file with a file extension of .bak or by appending a "~" character at the end of the current file extension, like .c~

Although being a useful option for a programmer (or a writer), it lacks the capability of keeping more backup copies, like a CVS (Concurrent Versions System) where the author can go back in time and find the text file as is was e.g. a month ago (very handy if you want to restore something you have deleted just before one week).

In order to avoid the complexity of a CVS, yet having the option to "travel" back in time, I wrote a small shell script, which I'm running just before my editing sessions. The script looks like this:

#!/bin/bash
datetime=`date +%Y%m%d_%H%M`
bdir=".backup"

mkdir $bdir 2> /dev/null

for a in $*; do
cp -av $a $bdir/$datetime.$a
done
gzip -9 $bdir/$datetime.*

All it does is to keep a compressed copy of every file you want to edit in a directory named ".backup", hence I named it "backup2.backup" and I run it as:

backup2.backup *.php *.html

It doesn't check many things, but I'm using it for some time now. Feel free to enhance it as you like it.

Visit The Light of the LAMP blog for more...

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Καβάλα, 23.04.2008
16:57
Formatting human readable numbers with PHP
» The light of the LAMP

One of my former colleagues, Athanassios Bakalidis, in his latest blog post "Java: Formatting a Number Using a Custom Format", has written about number formatting in Java language. This post made me think about the ways we 're using to print numbers from PHP to HTML output.

When we 're dealing with integers, usually it's sufficient to add a

style="text-align: right;"
to right-align the numbers in a column.

Floating point numbers, on the other hand, may require the use of number_format() function to properly format them, for example to have the same number of decimals (added to the obvious round(), floor() and ceil() functions).

But, what if I wanted to sort an array having two arithmetic columns?
Then, I'd use the sprintf() function to zero-pad numeric values, like this (certain sections are omitted):

$u0 = mysql_query( $sql, $db) or die( mysql_error()); $aa = array(); while ($u1 = mysql_fetch_row( $u0)) { $id = $u1[0]; $c1 = $u1[1]; $aa[$id] = number_format($u1[2]/$c1,4) .":". sprintf("%06d", $c1); } arsort( $aa); reset( $aa); while (list($k, $v) = each($aa)) { list( $v1, $c1) = explode( ":", $v); $c1 = intval( $c1); $v1 = round( $v1, 2); [......] }

With this technique, one can sort numeric values properly as numbers (although by internally converting them to strings). Visit The Light of the LAMP blog for more...

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Καβάλα, 22.03.2008
12:15
Twit from PHP with cURL
» The light of the LAMP
There are cases you need to update a special Twitter feed to inform your visitors about something that has happened to your site. Then, this PHP function might be very useful if you add it in your functions arsenal:
```
/* inform twitter about something */
function twit( $msg = "")
{
 $username = "twitter-username";
 $password = "twitter-password";
 $ch = curl_init();
 curl_setopt( $ch, CURLOPT_URL, "http://twitter.com/statuses/update.xml");
 curl_setopt( $ch, CURLOPT_RETURNTRANSFER, TRUE); // change to FALSE for not reporting XML output
 curl_setopt( $ch, CURLOPT_POST, 1);
 curl_setopt( $ch, CURLOPT_POSTFIELDS, "status=" . urlencode( $msg));
 curl_setopt( $ch, CURLOPT_USERPWD, "$username:$password");
 ob_start();
 $response = curl_exec( $ch);
 ob_end_clean();
 curl_close( $ch);
 return $response;
}
```
As you can see, it only takes a string argument; the message you want to send. It returns also a string, which is either a true/false value or an XML-formatted response, depending on the value of CURLOPT_RETURNTRANSFER.
In order to use this function, you need to have installed the cURL extension of PHP. You can check if it's installed quickly with the following command:
```
$ php -i | grep -i curl
```
If cURL is installed, you can expect an output like this:
```
additional .ini files parsed => /etc/php5/cli/conf.d/curl.ini,
curl
cURL support => enabled
cURL Information => libcurl/7.16.4 OpenSSL/0.9.8e zlib/1.2.3.3 libidn/1.0
```
If not, the package you need to install is php5-curl.
Visit The Light of the LAMP blog for more...

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Καβάλα, 09.03.2008
12:18
Some KDE tips
» The light of the LAMP
It's a beautiful Sunday morning and, in case you 're working with KDE Desktop Environment, here are some tips on using it more productively. Some of them are very old, but still useful.
- Let's say you 're programming or writing a script and you don't remember the syntax of a command. Bring up the command line (press Alt-F2), enter a hash (#) mark followed by the command name. The man page, in hyperlinked text, will open in Konqueror.
- You can maximize windows in three different ways:
  - Click on maximize with the left mouse button to open to full screen.
  - Click on maximize with the middle mouse button to maximize only vertically.
  - For horizontal only, use the right mouse button.
- Clicking on the title of a window with middle mouse button, pushes it behind the other windows, while it retains its focus. For example, when you 're editing a file, you can check the contents of another window while, in parallel, you can continue editing.
- You can change the desktop wallpaper by dragging an image from a Konqueror window to the desktop and selecting "Set As Wallpaper".
Visit The Light of the LAMP blog for more...

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Items by Apostolos P. Tsompanopoulos