Posts Tagged ‘Debian’

Another option you can employ is xkill. This is preinstalled in Ubuntu, but you can install it via the Terminal (which you can open with CTRL + ALT + T) if necessary. When called, xkill will enable you to close any desktop app. Install it with the following command:

sudo apt-get install xorg-xkill

Once this is done, run xkill by simply typing


Your mouse pointer will then display a cross (or a skull), and all you need to do is left-click on the offending application.

If it’s not possible to close your unresponsive app with any of these desktop-focused methods, the solution might be the command line…


Send Email when IP Address Changes

Posted: 6 Μαρτίου 2018 in linux
Ετικέτες: , , , ,

1. Setup Gmail and sSMTP

This time we are using sSMTP because it’s easy, and Gmail because it’s free.

I would prefer to create a new Gmail account specific only for this purpose. Use your creativity to create long and obfuscated password, e.g. with mkpasswd -m sha-512 yOuRp4ssW0rD you can get a long string which is should be very nice for password.

Next, install sSMTP and its mail “client”:

sudoapt-get install ssmtp mailutils

Then edit the config file at /etc/ssmtp/ssmtp.conf:

sSMTP is not a daemon, so don’t worry about starting the service or such.

Next, test your setup:

echo"test message"| mail -s "testing ssmtp"

2. The Script

#Script to report public IP address change
#By: Soultidis D. Christos

curl > /home/username/emailscript/erxeteip.txt

oldip=`cat /home/username/emailscript/oldip.txt`
erxeteip=`cat /home/username/emailscript/erxeteip.txt`

if [[ $erxeteip = $oldip ]]

    #echo $oldip > /home/username/emailscript/oldip.txt
    echo "Kamia allagi"

    echo $erxeteip > /home/username/emailscript/newip.txt
echo $erxeteip > /home/username/emailscript/oldip.txt

    cat /home/username/emailscript/newip.txt | mailx -s "Dynamic Public IP Address"


This time we use Bash, because you might not realize that you’re already fluent with Bash.

Save this anywhere in your home folder. I personally have my own /home/username/emailscript/


3. Cron
To make this run periodically, add the script as a cron job. More detail on cron you can STFG (Search The Fine Google).

crontab -e

Then add this to run the script every 30 minutes

#*/30 * * * * /home/username/emailscript/ >/dev/null 2>&1

ΥΓ. θα πρέπει να δημιουργήσω το oldip.txt


Cron daemon is not running. I really screwed up with this some months ago.


pgrep cron 

If you see no number, then cron is not running. sudo /etc/init.d/cron start can be used to start cron.

EDIT: Rather than invoking init scripts through /etc/init.d, use the service utility, e.g.

sudo service cron start

Debian Linux Install OpenSSH SSHD Server

Posted: 24 Ιανουαρίου 2013 in linux
Ετικέτες: , , ,


How do I install OpenSSH sshd server under Debian GNU/Linux operating systems?

You need to use the apt-get or aptitude command to install OpenSSH server under Debian Linux. Open a terminal and type the following command to update package database as root user:
# apt-get update

Task: Install OpenSSH server Under Debian Linux

Type the following command:
# apt-get install openssh-server
Sample outputs:

Reading package lists... Done
Building dependency tree
Reading state information... Done
Suggested packages:
  ssh-askpass rssh molly-guard ufw
The following NEW packages will be installed:
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 318 kB of archives.
After this operation, 717 kB of additional disk space will be used.
Get:1 squeeze/main openssh-server amd64 1:5.5p1-6+squeeze1 [318 kB]
Fetched 318 kB in 3s (89.0 kB/s)
Preconfiguring packages ...
Selecting previously deselected package openssh-server.
(Reading database ... 153448 files and directories currently installed.)
Unpacking openssh-server (from .../openssh-server_1%3a5.5p1-6+squeeze1_amd64.deb) ...
Processing triggers for man-db ...
Setting up openssh-server (1:5.5p1-6+squeeze1) ...
Creating SSH2 RSA key; this may take some time ...
Creating SSH2 DSA key; this may take some time ...
Restarting OpenBSD Secure Shell server: sshd.

By default openssh will run on the TCP port 22. You can verify the same with the following command:
# netstat -tulpn | grep :22
Sample outputs:

tcp        0      0    *               LISTEN      3946/sshd
tcp6       0      0 :::22                   :::*                    LISTEN      3946/sshd

You can connect to the Openssh server, type:
$ ssh user@localhost
$ ssh user@sever-ip-here

How Do I Start / Stop / Restart OpenSSH Server Under Debian Linux?

Type the following commands as root user:
# service ssh stop
# service ssh start
# service ssh restart
# service ssh status

# /etc/init.d/ssh stop
# /etc/init.d/ssh start
# /etc/init.d/ssh restart
# /etc/init.d/ssh status

Sample session:

Fig.01: OpenSSH under Debian LinuxClick to enlarge the image

How Do I Open Port 22 At The Firewall Level?

Edit your firewall script and append the following rule to restrict access to

/sbin/iptables -A INPUT -s -m state --state NEW -p tcp --dport 22 -j ACCEPT

Save and close the file. OR, you can type the command as follows and save it to your firewall config file:

# /sbin/iptables -A INPUT -s -m state --state NEW -p tcp --dport 22 -j ACCEPT
# iptables-save > /path/to/your.firewall.conf

How Do I Configure and Secure OpenSSH Server under Debian Linux?

You need to edit the /etc/ssh/sshd_config file using the text editor such as vi, run:
# vi /etc/ssh/sshd_config
See this article which explains config option to tweak in order to improve OpenSSH server security.

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