Category Archives: Ubuntu

Using “apitrace” with an OpenGL application

The basic commands for using apitrace with an OpenGL application are:

apitrace trace --api=gl MyApp
qapitrace MyApp.trace
apitrace dump --blobs MyApp.trace 

The last command generates blobs that can be inspected with the following command, for example:

tail -c $((12*10)) ~/repos/MyApp/build/blob_call2325.bin | xxd -g1

Or by writing a simple C++ program that converts them into CVS format:


Backing up and restoring all the PHP MySQL websites on a Linux server

All the following commands assumes we saved MySQL root password into MROOTPASS variable:

export MROOTPASS=<mysql root password>

The most straight forward method to backup all the MySQL databases and all the website files (PHP scripts, images, etc..) stored in the /home directory is the following:

mysqldump --all-databases -u root -p$MROOTPASS | gzip > all-databases-$(date '+%Y-%m-%d_%H-%M-%S').sql.gz
tar -cvzf home.tar.gz /home

If we backup some individual database (probably not as root) and change its user while restoring it, it might make a sense to remove DEFINER from the output script:

sed -e 's/DEFINER=[^*]*\*/\*/'

The following commands restore all the websites from the archives:

gunzip -c all-databases-2017-05-23_15-31-00.sql.gz | mysql -u root -p$MROOTPASS
cd /
sudo tar -xvzf home.tar.gz

After migration from MySQL version  14.14 Distrib 5.5.54 to 14.14 Distrib 5.7.18 (I do not know what is the difference between them) I got the following error: “ERROR 1805 (HY000) at line 1: Column count of mysql.user is wrong. Expected 45, found 42. The table is probably corrupted” while trying to drop some user, and fixed it by running:

mysql_upgrade -u root -p$MROOTPASS
service mysql restart

How to rename multiple files in Linux

The following bash script renames all the files matching src_name.* with dst_name.*:

unset $1
cp $src_name.* ~/temp/
cd ~/temp/
rename "s/$src_name\.([a-z]+)/$dst_name\.\$1/" *
cd -
mv ~/temp/$dst_name.* .

If you have some files like src1.h and src1.cpp, you can save this script into file, for example, and then rename those files with src2.h and src2.cpp using the following command: src1 src2

The script requires ~/temp directory to exist and be writable.

What packages QAudioDecoder may require on Ubuntu and CentOS?

If QAudioDecoder does not decode mp3, reporting a format error (GStreamer; Unable to start decoding process), the following package can help:
On Ubuntu:

apt-get install gstreamer0.10-fluendo-mp3

On CentOS:

yum -y install
yum install gstreamer{,1}-plugins-ugly


How to convert mp3 to wav in Ubuntu

Install sox tool with mp3 support:

apt-get install sox
apt-get install libsox-fmt-mp3
sox file.mp3 file.wav

Basically that is all, but if you need to check resulting wav file parameters like channels, sample rate, precision, duration, bit rate, etc…, use soxi command:

Detecting memory leaks of C++ application in Ubuntu

First, I tried Valgrind tool using the following command:

valgrind --tool=memcheck --leak-check=yes ./app

With some large QT application started for some short period I got the following output:

==7090== HEAP SUMMARY:
==7090==     in use at exit: 5,623,365 bytes in 36,268 blocks
==7090==   total heap usage: 32,454,680 allocs, 32,418,412 frees, 12,822,939,874 bytes allocated
==7090== LEAK SUMMARY:
==7090== definitely lost: 20,163 bytes in 74 blocks
==7090== indirectly lost: 60,053 bytes in 1,273 blocks
==7090== possibly lost: 396,167 bytes in 2,169 blocks
==7090== still reachable: 4,834,822 bytes in 31,576 blocks
==7090== suppressed: 0 bytes in 0 blocks
==7090== Reachable blocks (those to which a pointer was found) are not shown.
==7090== To see them, rerun with: –leak-check=full –show-leak-kinds=all
==7090== For counts of detected and suppressed errors, rerun with: -v
==7090== Use –track-origins=yes to see where uninitialised values come from
==7090== ERROR SUMMARY: 20905 errors from 1583 contexts (suppressed: 15 from 2)


Compiling GDAL on Ubuntu Linux with SQLite and MySQL support

Fist install MySQL client libraries and check their location:

apt-get install libmysqlclient-dev
find / -name '*libmysqlclient*'

Then install SQLite:

sudo apt-get install sqlite3 libsqlite3-dev

Extract GDAL sources and configure supported modules (MySQL and SQLite are not compiled by default, so we need to specify them explicitly):

cd gdal-2.1.1/
./configure --with-sqlite3 --with-mysql

this will output “MySQL support: yes” and “SQLite support: yes” along with other information.


How to find files by permission on Ubuntu

Today I accidentally changed permissions of all the files in some folder /usr/lib/git-core with the following command:

chmod o-rx *

At first I thought that I have broken my system, but in few minutes I remembered that I have the same distribution on some other machine, I listed the same folder on this machine and used the following commands to restore original permissions:

chmod o+rx *
find -maxdepth 1 -type f -perm 645 -exec chmod o-x {} \;

645 means the files that initially were -rw-r–r— and became -rw-r–r-x. This two commands saved me a lot of time. After that I even count the number of files with all permission combinations:

find -maxdepth 1 -type f -perm 644 | wc -l
find -maxdepth 1 -type f -perm 755 | wc -l
find -maxdepth 1 -type f -perm -o=x | wc -l

Installing Git on Ubuntu 12.04 and enabling HTTP access with Nginx

Git is a good alternative for developers who need a version control supported on both Windows and Linux platforms. Below I provided basic steps for installing Git on Ubuntu 12.04 and enabling HTTP access to the repositories with Nginx web server.

Installing required packages

First, we need to install Nginx and Git packages:

apt-get install nginx git

by default Nginx processes will run as www-data, (check “user” keyword in /etc/nginx/nginx.conf configuration file). Git installation has not created any user yet.


Installing Jabber Messaging Service on Ubuntu 12.04

Ejabberd (Jabber daemon written in Erlang programming language) can be easily installed on Ubuntu 12.04 Server (Precise Pangolin) with the following command:

apt-get install ejabberd

The only steps needed to make Ejabberd work after the installation are to specify admin user and hostname in /etc/ejabberd/ejabberd.cfg file:

%% Options which are set by Debconf and managed by ucf

%% Admin user
{acl, admin, {user, "admin", ""}}.

%% Hostname
{hosts, [""]}.