I will talk on this one about an error I got when running the S3 synchronisation:

S3 command failed:
list_bucket prefix /data max-keys 200 delimiter /
With result 403 Forbidden
S3 ERROR: #
s3sync.rb:290:in `+': can't convert nil into Array (TypeError)
	from s3sync.rb:290:in `s3TreeRecurse'
	from s3sync.rb:346:in `main'
	from ./thread_generator.rb:79:in `call'
	from ./thread_generator.rb:79:in `initialize'
	from ./thread_generator.rb:76:in `new'
	from ./thread_generator.rb:76:in `initialize'
	from s3sync.rb:267:in `new'
	from s3sync.rb:267:in `main'
	from s3sync.rb:735

As you can see, this error is not very human-friendly! The only thing we know is that the S3 command failed because of the error can't convert nil into Array. It looks to me like an internal error within s3sync…

But after some investigation, it appears it is simply because the system date on the server is not correct. I cannot tell you how much time I spent on this one! 

Anyway, if you are doing automatic backups as describe on John Eberly’s blog, you need to add the following code at the top of your upload.sh script:

# update the system date
/usr/sbin/ntpdate 3.uk.pool.ntp.org 2.uk.pool.ntp.org 1.uk.pool.ntp.org 0.uk.pool.ntp.org

NB: please find below the command lines I use to install ntpdate on a Debian server:

apt-get install ntpdate
dpkg-reconfigure tzdata

I am using this tool to automatically backup the important data from Debian servers to Amazon S3. I am not going to explain here how to install s3sync as it is not the purpose of this article. However, you can read this very useful article from John Eberly’s blog: How I automated my backups to Amazon S3 using s3sync.

If you followed the steps from John Eberly’s post, you should have an upload.sh script and a crontab job which executes this script periodically.

From this point, here is what you need to do to monitor the success of the synchronisation with Zabbix:

1. Add the following code at the end of your upload.sh script:

   # print the exit code
   RETVAL=$?
   [ $RETVAL -eq 0 ] && echo "Synchronization succeed"
   [ $RETVAL -ne 0 ] && echo "Synchronization failed"
   

2. Log the output of the cron script as follow:

   30 2 * * sun /path/to/upload.sh > /var/log/s3sync.log 2>&1
   

3. On Zabbix, create a new item which will check the existence of the sentence “Synchronization failed” in the file /var/log/s3sync.log:
   
   Item key: vfs.file.regmatch[/var/log/s3sync.log,Synchronization failed]
   
   
4. Still on Zabbix, define a new trigger for the previously created item:
   
   Trigger expression: {Template_AmazonCloud_Debian:vfs.file.regmatch[/var/log/s3sync.log,Synchronization failed].last(0)}=1

With these few steps, you should now receive Zabbix alerts when a backup on S3 fails.

This tool is also coming with an Apache module allowing to redirect users depending on their location. For example, we could redirect all users from France to the French home page of a multi-language website, or we could block the traffic to users from a specific country.

To install this module on a Debian server, you simply need to run the following command:

apt-get install libapache2-mod-geoip

But, how does this module work? How does it know where the user comes from? 
It is actually quite simple: GeoIP is using a mapping file of IP address by country. On Debian, this file is stored in the folder /usr/share/GeoIP and is named GeoIP.dat.

However, the IP addresses are something which change all the time. So this file will get out-of-date very quickly. This is why MaxMind provides an updated file at the beginning of each month for free. To read the installation instructions, please click the following link: http://www.maxmind.com/app/installation

This is good and well, but who will remember or even have the time to update this file every month? And imagine if you have to do this on hundreds of servers?
The solution is to use a shell script which will download, extract and install the updated GeoIP file automatically once a month:

#!/bin/sh

# Go in the GeoIP folder
cd /usr/share/GeoIP

# Remove the previous GeoIP file (if present)
rm GeoIP.dat.gz

# Download the new GeoIP file
wget http://geolite.maxmind.com/download/geoip/database/GeoLiteCountry/GeoIP.dat.gz

# Remove the previous GeoIP backup file
rm GeoIP.dat.bak

# Backup the existing GeoIP file
mv GeoIP.dat GeoIP.dat.bak

# Extract the new GeoIP file
gunzip GeoIP.dat.gz

# Change the permission of the GeoIP file
chmod 644 GeoIP.dat

# Reload Apache
service apache2 reload

You can place this file in your root folder and set up the following crontab job:

0 0 3 * * /root/update_geoip.sh

This will execute the script automatically on the third day of every month.

This is the error message it returned:

%prompt> run-parts --report /etc/cron.daily
/etc/cron.daily/myscript:
run-parts: failed to exec /etc/cron.daily/myscript: Exec format error
run-parts: /etc/cron.daily/myscript exited with return code 1
%prompt>

Actually, the answer of this problem is quite simple!
I simply forgot the shebang on the first line of the script…

So, if you get the same error than me, make sure you have the following line at the beginning of your script:

#!/bin/sh

Anyway, why do we get a “Segmentation fault” at the end of a PHP script? And when I say ‘the end’, I mean after any other lines!

Looking around the web, I found the following bug report: http://bugs.php.net/bug.php?id=43823
This user seems to have the same problem than me except he is using a PostgreSQL database instead of a MySQL database.

Reading through the page, it looks like the problem comes from the order in which PHP loads his extensions! They explain that PostgreSQL should be loaded before cURL. If I apply the same logic, MySQL should then be loaded before cURL too.

To do that, we need to comment out the line extension=curl.so from the file /etc/php5/cli/conf.d/curl.ini:

# configuration for php CURL module
#extension=curl.so

And add it to the file /etc/php5/cli/conf.d/mysql.ini AFTER the line extension=mysql.so:

# configuration for php MySQL module
extension=mysql.so
extension=curl.so

To be honest, I don’t really like this solution as it is a bit messy. I would prefer PHP developers to fix the root cause or at least have a way to change the order in which PHP loads the extensions.

NB: I was executing this PHP script on a Debian GNU/Linux 5.0 with Apache 2.2.9 and PHP 5.2.6.

In order to get access to the box by command line, I installed the Fonz fun_plug. I then wanted to automatically synchronise the internal time with some NTP Pool Time Servers. But, for some reason, the version of the ntpd process provided with fun_plug is completely freezing the NAS. I wasn’t able to find the root cause of it, trust me, I tried everything I could think of!
Please also note that the same process is working perfectly fine on his brother, the D-Link DNS-323. As I said, I can’t explain why…

But there is a good news! The ntpd process is actually part of the D-Link DNS-313 firmware. And it is working fine! After double-checking, this process is however NOT part of the D-Link DNS-323 firmware. Why is that? Maybe D-Link got complaints from DNS-313 users and fixed it? Who knows…

Anyway, in order to get the ntpd process to work on the D-Link DNS-313, you need to replace the content of your ntpd startup script (/ffp/start/ntpd.sh) by the one below:

#!/ffp/bin/sh

# PROVIDE: ntpd
# REQUIRE: SERVERS
# BEFORE: LOGIN

. /ffp/etc/ffp.subr

name="ntpd"
command="/usr/sbin/ntpd"
ntpd_flags="-f /ffp/etc/ntpd.conf"
required_files="/ffp/etc/ntpd.conf"
start_cmd="ntpd_start"

ntpd_start()
{
    # remove rtc and daylight cron jobs
    crontab -l | grep -vw '/usr/sbin/daylight' | grep -vw '/usr/sbin/rtc' | crontab -

    proc_start $command
}

run_rc_command "$1"

The other day, this very useful Linux tool gave me a hard time!
Indeed, one of my commands wasn’t working in cron but was working perfectly fine when written in a shell console.

The faulty command looked like this:

0 5 * * 3 /data/script.sh > /data/script_`date +%y%m%d`.log 2>&1

If I run this command in a shell console, everything works fine and I get a log file containing today’s date in its filename. However, if I set this command line in my crontab, it doesn’t work and no log file is even created!

Reading the documentation of cron, I discovered the following statement:

Percent-signs (%) in the command, unless escaped with backslash (\), will be changed into newline characters, and all data after the first % will be sent to the command as standard input.

Well, this is good to know, isn’t it?
We need to escape the percent-signs on our command line.

So in order to get our ‘faulty’ command to run in cron, it needs to look like the following:

0 5 * * 3 /data/script.sh > /data/script_`date +\%y\%m\%d`.log 2>&1

The reason of this characters problem is probably because of your locale settings.
Indeed, If you try to run the command locale from the command line and from a cron job, you may get different results such as:

LANG=en_US.UTF-8
LC_CTYPE="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_PAPER="en_US.UTF-8"
LC_NAME="en_US.UTF-8"
LC_ADDRESS="en_US.UTF-8"
LC_TELEPHONE="en_US.UTF-8"
LC_MEASUREMENT="en_US.UTF-8"
LC_IDENTIFICATION="en_US.UTF-8"
LC_ALL=

LANG=
LC_CTYPE="POSIX"
LC_NUMERIC="POSIX"
LC_TIME="POSIX"
LC_COLLATE="POSIX"
LC_MONETARY="POSIX"
LC_MESSAGES="POSIX"
LC_PAPER="POSIX"
LC_NAME="POSIX"
LC_ADDRESS="POSIX"
LC_TELEPHONE="POSIX"
LC_MEASUREMENT="POSIX"
LC_IDENTIFICATION="POSIX"
LC_ALL=

As you can see, the cron job is not using UTF-8. That must be the problem!

So the question now is how to change the locale settings for the cron job?
Some people say that you need to add the following environment variables to the crontab entry:

SHELL=/bin/bash
LANG=en_US.UTF-8
LANGUAGE=en
LC_CTYPE=en_US.UTF-8

But this actually didn’t work for me.

What you can do instead is create (if not already present) the file /etc/environment and add the following line:

LANG=en_US.UTF-8

The cron process will read this file when it starts, so you need to restart it in order to apply the change:

service cron restart

Hope this will fix your characters problem.