Speed-up your virtual machine created with VMware Player

20 Mar 2012

Matteo Mattei

vmware logo

If your virtual machine created with VMware Player becomes very slow and takes a long time to complete some operations it’s time to improve its performance! Close your VM, and open the *.vmx file with a text editor. Then add at the end of the file the following lines:

mainMem.useNamedFile = "FALSE"
sched.mem.pshare.enable = "FALSE"
MemTrimRate = 0
MemAllowAutoScaleDown = "FALSE"
prefvmx.useRecommendedLockedMemSize = "TRUE"
prefvmx.minVmMemPct = "100"

Make sure to not duplicate the keywords (in case you already have some lines set) otherwise the VM will not start. The above lines totally reserve the memory requested by the VM to the guest system and avoid to continuously ask to the host (and so to the swap file) for new memory chunks.

Try yourself and give me a feedback!

PHP Fatal error with PhpMyAdmin and APC

26 Nov 2011

Matteo Mattei

linux mysql php apc tricks

If you are running PhpMyAdmin and APC, it can happens that you get some errors like these:

PHP Fatal error:  Call to undefined function PMA_log_user() in /usr/share/webapps/phpMyAdmin/libraries/common.inc.php on line 914
PHP Fatal error:  Call to undefined function PMA_select_language() in /usr/share/webapps/phpMyAdmin/libraries/auth/cookie.auth.lib.php on line 220
PHP Fatal error:  Call to undefined function pma_generate_common_url() in /usr/share/webapps/phpMyAdmin/libraries/header_meta_style.inc.php on line 48
PHP Fatal error:  Call to undefined function PMA_DBI_connect() in /srv/http/librolandia.it/test/phpmyadmin/libraries/common.inc.php on line 916
PHP Fatal error:  Class 'PMA_Error_Handler' not found in /path/to/phpMyAdmin/libraries/common.inc.php on line 58
PHP Fatal error:  Call to undefined function PMA_getenv() in /path/to/phpMyAdmin/libraries/common.inc.php on line 143

If this is the case, you need to make some little changes to disable apc in your phpmyadmin virtual host:

Alias /phpmyadmin "/usr/share/webapps/phpMyAdmin"
<Directory "/usr/share/webapps/phpMyAdmin">
      AllowOverride All
      Options FollowSymlinks
      Order allow,deny
      Allow from all
      php_admin_value open_basedir "/srv/:/tmp/:/usr/share/webapps/:/etc/webapps:/usr/share/pear/"
      php_admin_value apc.enabled 0
</Directory>

And also modify your apc filter in php.ini under the APC section:

[APC]
apc.filter="-/usr/share/webapps/phpMyAdmin/.*"

Now restart Apache and you phpMyAdmin should work regularly.

Extract u-boot multi-file image in Python

25 Oct 2011

Matteo Mattei

embedded linux python

This simple piece of code shows how to extract/decompress a u-boot multi-file image created with mkimage using Python. The image format is very simple:

64 bytes of image header.
4 bytes for the size of first image.
4 bytes for the size of second image.
...
4 bytes of zeros for termination.
image1.
image2.
...

You need to remember also that each image is padded to 4 bytes.

PySide Signals and Slots with QThread example

28 Aug 2011

Matteo Mattei

python pyside qt thread

In these days I started studying PySide. After some days spent in reading lot of stuff, I thought that a real example could be useful for who intends to start learning PySide as well. In this example I can show you how you can implement a custom signal (MySignal) together with the usage of threads with QThread.

The following code creates a window with two buttons: the first starts and stop a thread (MyThread) that runs a batch that prints a point in the stdout every seconds continuously. The second button lets you only start another thread (MyLongThread) that prints an asterisk in the stdout every second for 10 seconds.

This example uses the api version 2 (introduced with PyQt 4.5) to connect signals to slots.

For more information you can look at:

QThread documentation: http://doc.qt.nokia.com/latest/qthread.html
PySide signals and slots: http://developer.qt.nokia.com/wiki/Signals_and_Slots_in_PySide
PyQt api 2 on PySide: http://www.pyside.org/docs/pseps/psep-0101.html

Export MySQL table in CSV format using PHP

30 Jul 2011

Matteo Mattei

linux mysql php backup dump

The following PHP code is intended to be used to export a MySQL table in CSV format in order to be used with MS Excel.

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

27 Jul 2011

Matteo Mattei

c/c++ linux python

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:

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