Archive for the ‘Linux & Unix’ Category

Test the phising filter of your web browser

Wednesday, January 13, 2010 posted by Till

If you like to test if the phising filter of your webbrowser works, open the following URL of the mozilla test page in the browser:

You should get a result page that looks similar to this one if you use the Mozilla Firefox browser:

Make the gnome desktop in Ubuntu 9.10 to look like Windows XP

Thursday, January 7, 2010 posted by Till

The following steps describe the Installation of the XPGnome theme for Ubuntu Linux. Run the following commands in the Ubuntu Shell window to make Ubuntu look like Windows XP:

cd /tmp
wget http://ubuntu.online02.com/files/XP_Gnome.tar.gz
cd XP_Gnome
./InstallXpGnome.sh

Screenshots:

http://ubuntu.online02.com/node/14

Since january 1 2010, spamassassin is falsely marking non spam emails as spam due to an error in the regular expression of the FH_DATE_PAST_20XX rule.

Description of the bug:

https://secure.grepular.com/blog/index.php/2010/01/01/spamassassin-2010-bug/

To fix this, run the following command on the shell as root user:

sa-update

If you use the software ISPConfig 2 on your server, run this command:

/home/admispconfig/ispconfig/tools/spamassassin/usr/bin/sa-update

How to renew the SSL certificate for dovecot on CentOS

Wednesday, December 23, 2009 posted by Till

Make a backup of the old key and certificate file

mv /etc/ssl/certs/dovecot.pem /etc/ssl/certs/dovecot.pem.old
mv /etc/ssl/private/dovecot.key /etc/ssl/private/dovecot.key.old

Create the new SSL certificate

openssl genrsa -out /etc/ssl/private/dovecot.key 1024
openssl req -new -x509 -key /etc/ssl/private/dovecot.key -out /etc/ssl/certs/dovecot.pem -days 730

Restart Dovecot:

/etc/init.d/dovecot restart

Optimize MySQL performance with mysqltuner

Tuesday, December 22, 2009 posted by Till

The following tutorial describes the steps to optimize the performance of a MySQL database with the mysqltuner script.

Login to your server on the shell, then execute the following commands:

Download the mysqltuner script:

cd /usr/local/bin
wget http://mysqltuner.pl/mysqltuner.pl
chmod +x mysqltuner.pl

Run mysqltuner

/usr/local/bin/mysqltuner.pl

Then enter root as username and the mysql root password.

You will get a output similar to this:

root@v221:/usr/local/bin# /usr/local/bin/mysqltuner.pl

>>  MySQLTuner 1.0.1 - Major Hayden <major@mhtx.net>
>>  Bug reports, feature requests, and downloads at http://mysqltuner.com/
>>  Run with '--help' for additional options and output filtering
Please enter your MySQL administrative login: root
Please enter your MySQL administrative password:

-------- General Statistics --------------------------------------------------
[--] Skipped version check for MySQLTuner script
[OK] Currently running supported MySQL version 5.0.51a-24+lenny2
[!!] Switch to 64-bit OS - MySQL cannot currently use all of your RAM

-------- Storage Engine Statistics -------------------------------------------
[--] Status: +Archive -BDB -Federated +InnoDB -ISAM -NDBCluster
[--] Data in MyISAM tables: 26M (Tables: 215)
[!!] InnoDB is enabled but isn't being used
[!!] Total fragmented tables: 33

-------- Performance Metrics -------------------------------------------------
[--] Up for: 96d 23h 3m 41s (10M q [1.239 qps], 686K conn, TX: 701M, RX: 1B)
[--] Reads / Writes: 44% / 56%
[--] Total buffers: 58.0M global + 2.6M per thread (100 max threads)
[OK] Maximum possible memory usage: 320.5M (12% of installed RAM)
[OK] Slow queries: 0% (20/10M)
[OK] Highest usage of available connections: 33% (33/100)
[OK] Key buffer size / total MyISAM indexes: 16.0M/8.5M
[OK] Key buffer hit rate: 99.9% (57M cached / 30K reads)
[OK] Query cache efficiency: 78.6% (5M cached / 6M selects)
[!!] Query cache prunes per day: 483
[OK] Sorts requiring temporary tables: 0% (0 temp sorts / 408K sorts)
[!!] Temporary tables created on disk: 36% (269K on disk / 745K total)
[OK] Thread cache hit rate: 99% (427 created / 686K connections)
[!!] Table cache hit rate: 2% (64 open / 3K opened)
[OK] Open file limit used: 11% (120/1K)
[OK] Table locks acquired immediately: 99% (3M immediate / 3M locks)

-------- Recommendations -----------------------------------------------------
General recommendations:
Add skip-innodb to MySQL configuration to disable InnoDB
Run OPTIMIZE TABLE to defragment tables for better performance
Enable the slow query log to troubleshoot bad queries
When making adjustments, make tmp_table_size/max_heap_table_size equal
Reduce your SELECT DISTINCT queries without LIMIT clauses
Increase table_cache gradually to avoid file descriptor limits
Variables to adjust:
query_cache_size (> 16M)
tmp_table_size (> 32M)
max_heap_table_size (> 16M)
table_cache (> 64)

The script recommends to adjust or add the following variables in the mysql my.cnf file. The location of my.cnf is normally /etc/my.cnf or /etc/mysql/my.cnf depending on the Linux distribution that is installed on your server.

Open the my.cnf file:

vi /etc/mysql/my.cnf

and increase or set the variables in the [mysqld] section of the file. Mine looks now like this:

[mysqld]
#
# * Basic Settings
#
user            = mysql
pid-file        = /var/run/mysqld/mysqld.pid
socket          = /var/run/mysqld/mysqld.sock
port            = 3306
basedir         = /usr
datadir         = /var/lib/mysql
tmpdir          = /tmp
language        = /usr/share/mysql/english
skip-external-locking
#
# Instead of skip-networking the default is now to listen only on
# localhost which is more compatible and is not less secure.
bind-address            = 127.0.0.1
#
# * Fine Tuning
#
key_buffer              = 16M
max_allowed_packet      = 16M
thread_stack            = 128K
thread_cache_size       = 8
# This replaces the startup script and checks MyISAM tables if needed
# the first time they are touched
myisam-recover          = BACKUP
#max_connections        = 100
table_cache            = 128
#thread_concurrency     = 10
#
# * Query Cache Configuration
#
query_cache_limit       = 1M

query_cache_size        = 32M
tmp_table_sizee        = 64M
max_heap_table_sizee        = 32M

Then save the file and restart mysql. After a few hours, rerun mysqltuner and check again if the values are fine now or if the have to be increased to a higher value.

How to renew the SSL certificate for dovecot on Ubuntu Linux

Monday, December 21, 2009 posted by Till

To create new SSL certificates for the dovecot pop3 and imap server on Ubuntu, follow these steps:

Make a backup copy of the old key and certificate file

sudo cp /etc/ssl/private/dovecot.key /etc/ssl/private/dovecot.key.old
sudo cp /etc/ssl/certs/dovecot.pem /etc/ssl/certs/dovecot.pem.old

Create the new key file

openssl genrsa -out /etc/ssl/private/dovecot.key 1024

Create the new certificate file, valid for 2 years

openssl req -new -x509 -key /etc/ssl/private/dovecot.key -out /etc/ssl/certs/dovecot.pem -days 730

Then restart dovecot

/etc/init.d/dovecot restart

Postfix provides with postsuper, postqueue and mailq some  shell utilitys to manage the mailqueue.

Here are some examples for common tasks:

List all messages that are in the mailqueue

postqueue -p

The output looks like this:

root@server:/# postqueue -p
-Queue ID- --Size-- ----Arrival Time---- -Sender/Recipient-------
501CA23B43DB     2182 Thu Dec  3 14:24:39  test@yourdomain.com
(Host or domain name not found. Name service error for name=otherdomain.com type=MX: Host not found, try again)
info@otherdomain.com

-- 8 Kbytes in 1 Requests.

Delete a message by message ID

postsuper -d MessageID

replace MessageID with the ID of the message, e.g. 501CA23B43DB

root@server:/# postsuper -d 501CA23B43DB
postsuper: 501CA23B43DB: removed
postsuper: Deleted: 1 message

Remove emails by sender

mailq | tail +2 | awk 'BEGIN { RS = "" }
# $7=sender, $8=recipient1, $9=recipient2
{ if ($7 == "info@otherdomain.com" && $9 == "")
print $1 }
' | tr -d '*!' | postsuper -d -

replace "info@otherdomain.com" with the sender email address.

Remove emails by recipient

mailq | tail +2 | awk 'BEGIN { RS = "" }
# $7=sender, $8=recipient1, $9=recipient2
{ if ($8 == "you@yourdomain.com" && $9 == "")
print $1 }
' | tr -d '*!' | postsuper -d -

replace you@yourdomain.com with the recipient email address.

Remove emails by sender hostname

mailq | grep senderhostname | awk ‘{ print $1′} | postsuper -d -

replace the word "senderhostname" with the hostname of the email sender.

If your server has very high load and you want to temporarily move all message from the incoming queue to the hold queue, use the command:

postsuper -h ALL

to move the messages back to the incoming queue, use the command:

postsuper -r ALL

Instead of the word "ALL" you can also provide a specific message ID to move only one message to or from the hold queue. Message in the hold queue will not processed by postfix until they were requeued with postsuper -r.

Sometimes you need to know to which debian or ubuntu package a specific file belongs, e.g. because you deleted a system file and want to reinstall it. There is a handy utility called apt-file which searches for a filename in all debian packages.

Installation

apt-get install apt-file

Usage example

search for the file /etc/sysctl.conf

apt-file search /etc/sysctl.conf

result:

apt-file search /etc/sysctl.conf
procps: /etc/sysctl.conf
mypc:~#

Now we see that the file is part of the debian / ubuntu package with the name "procps".

How does Ubuntu’s screenshot tool Take Screenshot actually work?

Friday, November 27, 2009 posted by andreea

The easiest way to make screenshots is to use Take Screenshot. You find it under Applications/Accessoires.
First change the delaytime for the screenshot from 0 to 1 or 2 seconds. This is the time you have to mark the chosen area. You should be fine with 1 second!

Then choose your screenshot option, e.g. Grab the current window. Klick on Take Screenshot and activate the window you need.

takescreenshot

Take Screenshot closes. If all works well, a pop-up comes up to ask where to save the screenshot, which comes a s a .png.

takescreenshot2

For another screenshot you have to open the application again, so put it best in your panel.

The uncommon thing is that you have to run first Take screenshot and then choose an object, and not the other way round. That's it!

How to install a professional image editing tool (KRITA) for Ubuntu 9.10

Thursday, November 26, 2009 posted by andreea

KRITA is a free image editing tool that ist pretty versatile and helps you not only to edit images, but also to use it for more artistic work on e.g. tablet PCs. It will surely remind you of Photoshop.
The easiest way to install KRITA is to download it over the Ubuntu Software Center. Do not take the complicated way to install it manually...

First go to Applications/Ubuntu Software Center:

UbuntuSoftwareCenter1

Type in the searchfield KRITA and press Enter to mark KRITA for installation.
As KRITA appears, double click it, and then just klick on the Install button, start the installation and wait some seconds.

UbuntuSoftwareCenter2

Now KRITA should appear checked as it has beeninstalled. That's it!

UbuntuSoftwareCenter3