Close Linux Apps with “xkill”

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

xkill

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

Εγκατάσταση msmtp σε  GNU/Linux για να στέλνουμε  emails από το  gmail

Βήμα 1: Κάνουμε εγκατάσταση μέσω τερματικού τα απαραίτητα πακέτα.

sudo apt-get install msmtp msmtp-mta

Βήμα 2: Δημιουργούμε ένα app password στο  Google λογαριασμό μας για το  msmtp

This (Step 2.* in this tutorial) was the missing piece of the puzzle which weren’t in any of the msmtp tutorials I did through. I found out about it in one of the Postfix tutorials where it was included after many hours of trial and error. Because at first, I thought the msmtp config file where was password field had to be filled with the same password with what you log in as a person to your account.

Go to: https://myaccount.google.com and log into the email account you want to start sending the emails.

Step 2.1: Select Security from the side menu and turn 2-Step Verification ON.

Step 2.2: After that click on App passwords

Step 2.3: Next up select Other (Custom name)

Step 2.4: Fill in the name as msmtp for example

Step 2.5: Get the password for your msmtp configuration file

Save this password to some notepad temporarily so you can copy & paste it later to a configuration file because once you click DONE you cannot see the password again. At least I have not found a way to re-open this popup.

Βήμα 3: Μπαίνουμε στο msmtprc

sudo nano /etc/msmtprc

Βήμα 4: Διαμορφώστε το msmtprc αρχείο

defaults
auth           on
tls            on
tls_trust_file /etc/ssl/certs/ca-certificates.crt
logfile        ~/.msmtp.log
account        gmail
host           smtp.gmail.com
port           587
from           username@gmail.com
user           username
password       password
account default : gmail

To  username@gmail.com θα πρέπει να αλλαχτεί στο  config file με το email σας

To password με  τον κωδικό του app του google

Αλλάζουμε αν θέλουμε και το username

Βήμα 5:  Κάνουμε τεστ το email

echo "Message" | mail -s "Title" youremailaddress@gmail.com

Μετά την εντολή θα πρέπει να έχεις παραλάβει το email όπου έστειλες

Βήμα 6:  Κάνουμε εγκατάσταση το curl εάν δεν το έχουμε 

apt-get install curl

Βήμα 7:  Δημιουργούμε τα αρχεία 

1. Δημιουργούμε τα παρακάτω κενά αρχεία

erxeteip.txt  

newip.txt

oldip.txt

 

2. The Script

#!/bin/bash
 
#Script to report public IP address change
#By: Soultidis D. Christos
 

curl ipinfo.io/ip > /home/username/emailscript/erxeteip.txt


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

if [[ $erxeteip = $oldip ]]
then

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

else
    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" youremail@gmail.com

fi

 

Αποθήκευσε το script  σαν  ip.sh εκτελέσιμο και βάλτο σε έναν φάκελο μαζί με τα άλλα αρχεία

π.χ.

/home/username/emailscript/

Βήμα 8:  Cron και χρονική διάρκεια εκτέλεσης του script μας 

3. Cron
Πατάμε την παρακάτω εντολή στο τερματικό

 

crontab -e

Προσθέτουμε  αυτό ώστε να μπορεί να τρέχει το  script  ανα 5 λεπτά

*/5 * * * * /home/username/emailscript/ip.sh >/dev/null 2>&1

(Το 5 δηλώνει τα λεπτά , βάζουμε όσο θέλουμε εμείς)

Αποθήκευση

Γράφουμε στο τερματικό :

pgrep cron 

Άμα δεν βλέπουμε αριθμό ο  cron δεν τρέχει. Έτσι πατάμε  sudo /etc/init.d/cron start  για να ξεκινήσει

Τέλος

Debian Linux Install OpenSSH SSHD Server

by nixCraft

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:
  openssh-server
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 http://mirror.anl.gov/debian/ 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 0.0.0.0:22              0.0.0.0:*               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
OR
# /etc/init.d/ssh stop
# /etc/init.d/ssh start
# /etc/init.d/ssh restart
# /etc/init.d/ssh status

Sample session:

Click 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 192.168.1.0/24:

/sbin/iptables -A INPUT -s 192.168.1.0/24 -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 192.168.1.0/24 -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.

Πηγή : http://www.cyberciti.biz/faq/debian-linux-install-openssh-sshd-server/