Archive for the ‘Linux & Unix’ Category

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  [email protected]
(Host or domain name not found. Name service error for name=otherdomain.com type=MX: Host not found, try again)
[email protected]

-- 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 == "[email protected]" && $9 == "")
print $1 }
' | tr -d '*!' | postsuper -d -

replace "[email protected]" with the sender email address.

Remove emails by recipient

mailq | tail +2 | awk 'BEGIN { RS = "" }
# $7=sender, $8=recipient1, $9=recipient2
{ if ($8 == "[email protected]" && $9 == "")
print $1 }
' | tr -d '*!' | postsuper -d -

replace [email protected] 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

How to enable active corners aka Exposé in Ubuntu 9.10 with Ubuntu Tweak

Wednesday, November 25, 2009 posted by andreea

If you always wanted the Exposé effect on your Ubuntu Desktop, here you go!  Active corners, known from Mac as Exposé, allow you e.g. to see all your open windows at once just by one mouse move into the corner of the desktop. Very useful if you are a multi-tasking god or goddess!

First open you terminal and copy & paste:

sudo apt-key adv --recv-keys --keyserver keyserver.ubuntu.com FE85409EEAB40ECCB65740816AF0E1940624A220

Log in with your admin password and continue:

sudo gedit /etc/apt/sources.list

Then add the following lines at the end of the file:

deb http://ppa.launchpad.net/tualatrix/ppa/ubuntu karmic main
deb-src http://ppa.launchpad.net/tualatrix/ppa/ubuntu karmic main

The source of Ubuntu tweak will be added to your repository. Updates for Ubuntu-Tweak will be installed automatically in future. Install Ubuntu-Tweak:

sudo apt-get update
sudo apt-get install ubuntu-tweak

Before using Ubuntu-Tweak, make sure you enabled visual effects for your desktop. Go to System/Preferences/Appearance an check under Visual Effects "Normal".
visualeffects

Check your system tools for Ubuntu-Tweak, open it and go to Desktop, then to Compiz Fusion as you can see here:
tweak tweak2 tweak3

Now you can enable a function for every corner, as you like. That's it.

How to reset the administrator password in ISPConfig 3

Friday, November 6, 2009 posted by Till

If you lost your ISPConfig 3 administrator password, you can reset it with the following SQL query.

UPDATE sys_user SET passwort = md5('admin') WHERE username = 'admin';

The SQL query sets the password to "admin" for the user "admin", it has to be executed in the ISPConfig mysql database, e.g. with phpmyadmin. If you dont have phpmyadmin installed, then the query can be executed with the mysql commandline utility as well:

Login to the mysql database.

mysql -u root -p

and enter the password of the mysql root user. To switch to the ISPConfig database, run this command:

use dbispconfig;

Now execute the SQL command:

UPDATE sys_user SET passwort = md5('admin') WHERE username = 'admin';

and close the mysql shell:

quit;

How to open winmail.dat files on Ubuntu and Debian Linux

Friday, November 6, 2009 posted by Till

The winmail.dat file is a container file format used by Microsoft Outlook to send attachments in richtext formatted emails. To open winmail.dat on Linux, use the tnef utility.

Installation

sudo apt-get install tnef

Usage

Open a shell window, navigate to the directory where the winmail.dat file is saved,  then execute the command:

tnef winmail.dat

to extract all files that are stored in the winmail.dat into the current directory.

How to enable port 465 (smtps) in postfix mailserver

Wednesday, October 28, 2009 posted by Till

More and more internet access providers are closing port 25 to reduce spam except for connections to their own mailservers. If you run your own mailserver and have problems to connect to it on port 25, you can enable port 465 (smtps) in postfix as a workaround. Edit the /etc/postfix/master.cf file:

vi /etc/postfix/master.cf

and remove the # in front of the smtps line. Example for Debain 5, change the line:

#smtps     inet  n       -       -       -       -       smtpd

to:

smtps     inet  n       -       -       -       -       smtpd

and restart postfix:

/etc/init.d/postfix restart

How to prevent a Linux system user from loggin into the system

Friday, October 23, 2009 posted by Till

If a linux system user is able to login on the shell or with SSH depends on its shell setting in /etc/passwd. If you want to prevent that a certain user is able to login, then set the shell either to /bin/false or /sbin/nologin.

Example for Debian and Ubuntu Linux for the user with the username "otheruser":

usermod -s /bin/false otheruser

For Redhat, Fedora or CentOS use /sbin/nologin:

usermod -s /sbin/nologin otheruser

Warning: Do not set the shell for the root user to /bin/false or /sbin/nologin!