Recently, I needed to recover a DSL password that only persisted in an old  router (Draytek Vigor 2500/We). Since the web interface only shows the username, I tried the backup feature that dumps the entire configuration to a file that you can download. Unfortunately, this data comes in an encrypted form… which makes an excellent exercise for a student of computer science. Continue reading →

Ubuntu 10.04 (Lucid Lynx) features new panel applets called “indicator applets”. If you want to get rid of some of them, they can be removed by removing the corresponding package(s) using your favourite tool (Synaptic, aptitude, apt-get, …):

• indicator-me provides the menu with your avatar and your availability status
• indicator-messages provides the menu for email/Evolution, social networks/Gwibber etc.
• indicator-session provides the menu with the shutdown/logout button (if uninstalled, this functionality will be provided by the “System” menu)
• indicator-sound provides the sound/audio settings menu

For more information, have a look at the Launchpad page and the Ubuntu Wiki page for the indicator applets.

What to do if you want to use mysqldump in a shared hosting environment without being able to access the shell (SSH…)? Use a Perl CGI script:

#!/usr/bin/perl -w

use strict;
use CGI::Carp qw(fatalsToBrowser);

print "Content-type: text/plain\nContent-disposition: attachment; filename=\"db_backup.sql\"\n\n";
print qx(mysqldump -uUSERNAME -pPASSWORD DATABASE 2>&1);

Replace USERNAME, PASSWORD and DATABASE with the configuration data for your database and drop the script into your cgi-bin directory. Don’t forget to make it executable (chmod +x) and apply some form of access restrictions! Here’s an Apache .htaccess file which serves well for this purpose: Continue reading →

Linux is quite good at scheduling the CPU time of running programs: Even when a process is running which constantly uses up all processor power, it is still possible to use another (interactive) program nearly as fast as on an idle system. But if a process is doing heavy I/O operations (i.e. backup software), the response times of interactive programs can be heavily increased.

A possible solution for this problem is the command line tool ionice which can be used to control the I/O scheduler. For example, if a backup tool is to be run, running

ionice -c3 COMMAND

will execute COMMAND with the scheduling class “idle” (will only run when no other process needs I/O).

Have a look at the man page for more information.

If you need to configure a backup of a MySQL database server, you shouldn’t simply copy it’s database files from /var/lib/mysql since they might be inconsistent (due to simultaneous changes). mysqldump is a safe choice for this task. I wrote a simple script for Debian that uses the pre-configured “debian-sys-maint” account and compresses the output:

#!/bin/bash

BACKUP_FILENAME=/var/backups/mysql/mysql.dump
mysqldump --defaults-extra-file=/etc/mysql/debian.cnf --all-databases --lock-all-tables --result-file=$BACKUP_FILENAME
gzip $BACKUP_FILENAME

Please take care that you need to create the output directory (/var/backups/mysql in the above example) first!

If you need more than one revision of the backup, you might want to use “date” to format the filename. Since I run a normal (rdiff-)backup of a big part of the server afterwards, I don’t need this.

This blog runs on a virtual server offered by Strato. They use Virtuozzo for virtualization which has a drawback: If you use top, free or other tools to show the current memory usage, not only your “slice” of the machine but more (all?) of the memory is measured. This doesn’t help much if you try to find out how much of it your own processes use, which is important as you can use only a certain part of the machine’s memory.

I could not find a better way to circumvent this but to sum up the numbers of every single process, listed by ps. Here’s a little shell script that does the job:

#!/bin/bash
echo -ne "Allocated virtual memory: "
ps auxh | sed 's/ \+/ /g' | cut -d' ' -f 5 | \
php -r '$c=0; while($line=fgets(STDIN)) $c+=intval($line); echo "$c";'
echo " kB"

echo -ne "Used physical memory: "
ps auxh | sed 's/ \+/ /g' | cut -d' ' -f 6 | \
php -r '$c=0; while($line=fgets(STDIN)) $c+=intval($line); echo "$c";'
echo " kB"

You need to have the command line version of PHP 5 installed to run this script. The corresponding Debian package is called php5-cli.