Matteo Mattei

Hello, my name is Matteo Mattei and this is my personal website. I am computer engineer with a long experience in Linux system administration and web software development.

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How to execute commands with specific user privilege in C and Python under Linux

If you have root access but you need to run some applications/scripts with some other user credentials you can do it with

su - username -c "command to execute"

But if you need to do it within a C/C++ program you need to write something like this:

This is how to compile and execute the above code:

[root@barracuda ~]# gcc mysu.c -o mysu
[root@barracuda ~]# id
uid=0(root) gid=0(root) gruppi=0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel),19(log)
[root@barracuda ~]# ./mysu matteo /bin/bash
[matteo@barracuda /root]$ id
uid=1000(matteo) gid=100(users) groups=100(users),3(sys),10(wheel),14(uucp),91(video),92(audio),93(optical),95(storage),96(scanner),97(camera),98(power),108(vboxusers)

The same result could be obtained also in Python with a very little effort:

How to really erase an Hard Drive

Since a REALLY secure Hard Disk erase procedure does not exist, the only way to clean every private data from a storage device is to use a powerful tool. Today we experimented the secure data cleaning on a 2.5” HD with an hammer. Yes, you have understood, an HAMMER!!! What’s more powerful than an hammer?!

This is the result of our experiment:

Broken HD

Any further feedback is really appreciated!

Shrink Ext4 partition on VMware player

VMWARE Few days ago I spent some times trying to shrink my Ubuntu 11.04 appliance with root partition formatted with EXT4 filesystem.

The main problem is that the current VMware tools (8.4.6, build-385536) does not support the ext4 shrink. If you run sudo vmware-toolbox, your root partition is formatted in ext4 and you try to execute the shrink, an error message like the following could appear.


Anyway there is a trick to streamline the final vmdk size. Run this command within a shell into the guest system:

sudo dd if=/dev/zero of=/zero.raw bs=20480
rm -f /zero.raw

Then, shutdown the virtual image and download the vdiskmanager tool from VMware website.

Now run the vmware-vdiskmanager with the -k parameter:

vmware-diskmanager -k /path/to/image.vmdk

This operation will take a while, but at the end you will get a considerable smaller vmdk image file.

How to implement MAC_X919 algorithm in Python

Today with my friend Nicola, we were looking in Internet for the implementation of the X9.19 algorithm in Python. Unfortunately we didn’t find it anywhere, so we made it ourself:

How to clone MySQL database schema in PHP


For my client I needed to create a PHP script that can export a full MySQL database schema in another database. This script also need to keep and set constraints.

You only need to configure $DB_SRC_* and $DB_DST_* variables to fit your environment.

Here below you can find the code I created for this purpose:

Update 2016-10-14: The code below has been rewritten using PHP mysqli driver (thanks to Richard Maurer).

Virtual users on vsftpd

VSFTPD logo I am usually to configure vsftp on web servers to allow FTP access based on domains. Few days ago my client asked me to create multiple FTP users for a single domain every one with a different root folder into that domain.

This is my usual configuration of my /etc/vsftpd.conf

ftpd_banner=Welcome to my private FTP service.

and this is my /etc/pam.d/vsftpd

auth required pwdfile /etc/ftpd.passwd
account required

The first time I have created the file /etc/ftpd.passwd in this way:

htpasswd -c -d -b /etc/ftpd.passwd <password>

For the next users simply avoid the “-c” parameter:

htpasswd -d -b /etc/ftpd.passwd <password>

With this simple configuration all users have these credentials:

  • host:
  • username:
  • password: password
  • port: 21
  • Root folder: /var/www/domain1/

Now the point is: how can we create multiple users for a single domain each one with a different root folder? The answer is pretty simple, follow me!

Create the folder /var/www/users and add the following line at the end of /etc/vsftpd.conf


Inside the folder /var/www/users create a file for each virtual user (for example the user containing a line with the root directory for that user:

echo "local_root=/var/www/" > /var/www/users/

Now add the new user/password in /etc/ftpd.passwd as usual:

htpasswd -d -b /etc/ftpd.passwd <password>

Restart vsftpd server and test your new configuration!