Technical Notes by Afzal


Server Setup Repository	https://github.com/afzalex/serversetup.git
About Repository	https://github.com/afzalex/about.git

Configurations

EC2 user-data to add web server with web page on 80 port number

#!/usr/bin/env bash
su ec2-user
sudo yum install httpd -y
sudo service httpd start

cat <<EOF | tee /tmp/index.html
<html>
    <head>
        <title> In the Pale Moonlight</title>
        <style>
            html, body { background: #000; padding: 0; margin: 0; }
            img { display: block; margin: 0px auto; }
        </style>
    </head>
    <body>
        <img src='https://c.tenor.com/ITctI_ZpHIoAAAAM/brain-linux.gif' height='100%' />
    </body>
</html>
EOF

sudo mv /tmp/index.html /var/www/html/index.html

Enable docker remote API

sudo vim /lib/systemd/system/docker.service

now search following line

ExecStart=/usr/bin/dockerd -H fd:// --containerd=/run/containerd/containerd.sock

and modify it to add -H tcp://0.0.0.0:2375

ExecStart=/usr/bin/dockerd -H fd:// -H tcp://0.0.0.0:2375 --containerd=/run/containerd/containerd.sock

now reload docker daemon

sudo systemctl daemon-reload
sudo systemctl restart docker

Configuring VIM according to our needs

Edit or Create ~/.vimrc

set number
set tabstop=4
set softtabstop=4
set shiftwidth=4
set noexpandtab
set colorcolumn=110
set autoindent
highlight ColorColumn ctermbg=darkgray

Automate git password authentiation

On Windows :

git config --global credential.helper wincred

OR to persist password for specific time period

git config --global credential.helper 'cache --timeout=3600'

On Linux :
```
git config credential.helper store
```

Adding alias to view commit tree of git in CUI (shell/console)

Add following line in git config file i.e. ~/.gitconfig

[alias]
    flog = log --graph --abbrev-commit --decorate --format=format:'%C(bold blue)%h%C(reset) - %C(bold green)(%ar)%C(reset) %C(white)%s%C(reset) %C(dim white)- %an%C(reset)%C(bold yellow)%d%C(reset)' --all

Now formatted tree could be seen with following command

git flog

OR

Now formatted tree could be seen with following command

curl https://www.afzalex.com/scripts/install-flog.sh | /bin/bash

Setting up rsync to backup data

Create a file /etc/rsyncd.conf

motd file = /etc/rsyncd.motd
log file = /var/log/rsyncd.log
pid file = /var/run/rsyncd.pid
lock file = /var/run/rsync.lock

/home/afzal/tempo/
	path = /home/afzal/tempo/
	comment = Temporary rsync location 
	uid = nobody
	gid = nobody
	read only = no
	list = yes
	auth users = afzal
	secrets file = /etc/rsyncd.scrt

Now enable rsync using systemctl

systemctl enable rsync.service

Add command in crontab to execute every day at 1:00 PM

crontab -e

Enter below code opened window

00 13 * * * rsync --verbose --stats --compress --recursive --times --perms --links --exclude=Downloads/ /home/afzal/ /var/backups/afzal/`date +"\%a"`  >> /var/log/backup.log

Above command will sync /home/afzal into /var/backups/afzal/Mon where "Mon" value could be "Tue", "Wed", ..., "Sun" and output will be logged in /var/log/backup.log

Mind giving required previleges to files and directories used in this process

Setting static ip in local network

Check network devices attached

ifconfig

Note configuration of device you want to set for static ip Edit /etc/network/interfaces

Making VirtualBox IP permanent

Edit /etc/network/interfaces

auto eth1 # this refers to the Host-only network interface
iface eth1 inet static
address 192.168.56.10 # Arbitrary IP address
netmask 255.255.255.0

Setting linux to bootup with multicores

Edit /etc/init.d/rc and replace following line

CONCURRENCY=none

with this

CONCURRENCY=shell

Speeding up ubuntu boot speed

Reduce the default grub boot time

sudo vim /etc/default/grub
GRUB_TIMEOUT=2

sudo update-grub

If apt-daily.service taking time to boot

sudo systemctl edit apt-daily.timer
# apt-daily timer configuration override
[Timer]
OnBootSec=15min
OnUnitActiveSec=1d
AccuracySec=1h
RandomizedDelaySec=30min

Tasks

Check disk or usb or mounted device performance

To check which device is mounted use findmnt
Then use hdparm to check performance

findmnt
hdparm -Tt /dev/mmcblk0p2

Above command should be run with sudo user

Other way to check performance is to use fio

sudo apt-get install fio
mkdir fiotest
fio --name=write_throughput --directory=fiotest --numjobs=8 --size=10M --time_based --runtime=60s --ramp_time=2s --ioengine=libaio --direct=1 --verify=0 --bs=1M --iodepth=64 --rw=write --group_reporting=1

https://cloud.google.com/compute/docs/disks/benchmarking-pd-performance

Check temperature

cat /sys/class/thermal/thermal_zone*/type

The output shows the CPU temperature in the five-digit format. Here, 49000 means 49C.

Change default format of docker ls or docker ps

mkdir -p ~/.docker
cat <<EOF > ~/.docker/config.json
{
	"psFormat": "table {{.ID}}\t{{.Names}}\t{{.Image}}\t{{.Status}}\t{{printf \"%.60s\" .Ports}}"
}
EOF

Install important libraries

apt-get update
apt-get install -y iputils-ping

Run debian command via docker

docker run -v "$PWD:/root" -w/root --rm -it --entrypoint bash debian:stable-slim

Install important libraries

apt-get update
apt-get install -y iputils-ping

View CSV file in terminal

To use below solution, nodejs is required.

npm i -g tty-table
cat data.csv | tty-table

Replace part of text file with content from another file

Consider following textual file test_bash_file.sh

#!/bin/bash
echo "Hello World"

#MANAGED_BLOCK_START
#Please don't modify this text, it is managed by replacement script
echo "This is the content to be replaced"
#MANAGED_BLOCK_END

echo "above content should be managed via replacement script"

And another textual file test_scriptlet.dat whose content is to be substituted in test_bash_file.sh

#Please don't modify this text, it is managed by replacement script
echo "Replaced Text"
echo "This is the content from replacement script"

Run following command to replace part of text file test_bash_file.sh with test_scriptlet.dat

awk '
    BEGIN       {p=1}
    /^#MANAGED_BLOCK_START/   {print;system("cat  test_scriptlet.dat");p=0}
    /^#MANAGED_BLOCK_END/     {p=1}
    p' test_bash_file.sh

To replace text and substitute environment variables in replaced text

awk '
    BEGIN       {p=1}
    /^#MANAGED_BLOCK_START/   {print;system("cat  test_scriptlet.dat  | envsubst");p=0}
    /^#MANAGED_BLOCK_END/     {p=1}
    p' test_bash_file.sh

Merge audio from different video to other video file

ffmpeg -i video.mp4 -i audio.wav -c:v copy -c:a aac -map 0:v:0 -map 1:a:0 output.mp4

with video re-encoding

ffmpeg -i video.mp4 -i audio.wav -c:v libx264 -c:a aac -map 0:v:0 -map 1:a:0 output.mp4

Reduce video size

Audio
- Audio quantity : 1
- Codec : MP3
- Bitrate : 160 (Or 256 or 320 if music is main element)
Codec and Container
- Codec : H.264
- Container : MP4

Video resolution

2160p (3840×2160)
1440p (2560×1440)
1080p (1920×1080)
720p (1280×720)
480p (854×480)
360p (640×360)
240p (426×240)

Bitrate

TYPE	Bitrate: 24-30fps	Bitrage: 48-60fps
2160p(4k)	35-45 Mbps	53-68 Mbps
1440p(2k)	16 Mbps	24 Mbps
1080p	8 Mbps	12 Mbps
720p	5 Mbps	7.5 Mbps
480p	2.5 Mbps	4 Mbps
360p	1 Mbps	1.5 Mbps

ffmpeg -i <inputfile> -acodec mp3 -vcodec h264 -b:a <audio_bitrate> -vf scale=<resolution_width>:<resolution_height> <outputfile_mp4>
ffmpeg -i input.mov -acodec mp3 -vcodec h264 -b:a 160k -vf scale=1280:720 output.mp4

Creating ssl certificate / certificate authority / self sign certificate

Generate private rsa key
```
openssl genrsa -aes256 -out server.key 1024
                ^optional     ^keyName   ^keySize
```
p1 - prompted password if aes256 (or other encryption) is used [p1] -> server.key
Generate a CSR (Certificate Signing Request)
```
openssl req -new -key server.key -out server.csr
                         ^keyName        ^csrFile
```
Information will be asked about certificate. Common Name should match hostname e.g. for http://www.google.com value should be www.google.com p2 - Challenge Password [server.key, p2] -> server.csr

Remove Passphrase from Key (if rsa key is encrypted)

cp server.key server.key.org
openssl rsa -in server.key.org -out server.key

Generating a Self-Signed Certificate

openssl x509 -req -days 365 -in server.csr -signkey server.key -out server.crt

[server.csr, server.key] -> server.crt

Converting certificate into PKCS12

openssl pkcs12 -export -in server.crt -inkey server.key -out server.p12 -name default -CAfile server.crt -caname root
^aliasName

p3 - pkcs12 password [server.crt, server.key, p3] -> server.p12

Import pkcs12 into keystore

keytool -importkeystore -deststorepass <paswd> -destkeypass <paswd> -destkeystore server.jks -srckeystore server.p12 -srcstoretype PKCS12 -srcstorepass <csr paswd> -alias default
                                          ^p4                  ^p5                                                                                         ^p2

[server.p12, p2] -> server.jks

Verification of keys

Verify a Private Key : sh openssl rsa -check -in server.key

Verify a Private Key Matches a Certificate and CSR : sh openssl rsa -noout -modulus -in server.key | openssl md5 openssl x509 -noout -modulus -in server.crt | openssl md5 openssl req -noout -modulus -in server.csr | openssl md5 If the output of each command is identical there is an extremely high probability that the private key, certificate, and CSR are related.

Setup gmail to allow other applications to send mail on your behalf

Visit following links (self explanatory)

https://myaccount.google.com/lesssecureapps https://accounts.google.com/b/0/DisplayUnlockCaptcha

Port used to connect with ssl : 465 Port used to connect with tls : 587

Check which port is used by which application

netstat -plntu

Install a .deb file from terminal

sudo dpkg -i <PATH_TO_DEB_FILE>
sudo apt-get -f install

Making notify-send work in shell. (To make notify-send work in cron i.e. crontab and ssh)

eval "export $(egrep -z DBUS_SESSION_BUS_ADDRESS /proc/$(pgrep -u $LOGNAME gnome-session)/environ)";
notify-send "TITLE" "YOUR_MESSAGE"

Disable notify-send

mv /usr/share/dbus-1/services/org.freedesktop.Notifications.service /usr/share/dbus-1/services/org.freedesktop.Notifications.service.disabled`

Adding git with ssh protocol on windows

Open git-bash

ssh-keygen
vim ~/.bashrc

Enter following lines in editor

eval `ssh-agent`
ssh-add

Restart git-bash

rm ~/.bashrc

Close git-bash RSA public key of ssh is present in .ssh directory inside %userprofile%

Convert openssh private key to pem format

ssh-keygen -p -N "" -m pem -f /path/to/key

Analyze which service taken how much time during startup or bootup

systemd-analyze blame

Linux Sending mail from command line

MSMTP (SMTP client) : >(Documentation could be found at http://msmtp.sourceforge.net/doc/msmtp.html)

```sh
sudo apt-get install msmtp
vim ~/.msmtprc
```
Now in opened editor set default values for all following accounts.
```vi
# Set default values for all following accounts.
defaults
auth           on
tls            on
tls_trust_file /etc/ssl/certs/ca-certificates.crt
logfile        ~/.msmtp.log

# Gmail
account        gmail
host           smtp.gmail.com
port           587
from           [email protected]
user           username
password       plain-text-password

# A freemail service
account        freemail
host           smtp.freemail.example
from           [email protected]
...

# Set a default account
account default : gmail
```

Linux fetching mail from command line

fetchmail (remote-mail retrieval and forwarding utility intended to be used over on-demand TCP/IP) ... PENDING ...

Adding ssh client in linux

sudo apt-get install openssh-server

Create a file ~/.ssh/authorized_keys if not exist

touch ~/.ssh/authorized_keys

Append your public key in this file

cat rsa_public_key.pub >> ~/.ssh/authorized_keys

Now you can access this linux from windows by following command

ssh -i rsa_private_key username@ipaddress

You can use ssh-keygen to create public private rsa key pair

Forcefully disconnect an ssh client

find process id of ssh for client

sudo netstat -tnpa | grep ssh

kill process

kill -9 <pid>

Logging ssh session `Important`

Download log-session script

wget http://www.jms1.net/log-session

Find out where the sftp-server binary is located

grep sftp /etc/ssh/sshd_config

Edit log-session file and replace following content

SFTP_SERVER=<location_of_sftp_server>
SFTP_SERVER=/usr/lib/openssh/sftp-server

Make log-session file executable

chmod 755 log-session

Edit ~/.ssh/authorized_keys and append following

command="<location_of_log_session>"
command="/usr/local/sbin/log-session" ssh-dss AAAAB3Nz...

Securing your password with public key encryption

Securing your password (or anything for the secure transmission of information between parties) with public key encryption Install gnupg

sudo apt-get install gnupg

Create key pair (give desired inputs and wait until key is created)

gpg --gen-key

To encrypt

<CMD TO O/P> | gpg -e -r <RECIPIENT>

To decrypt

<CMD TO O/P> | gpg -d

To get list of keys

gpg -k

To get public key ... PENDING ...

Downloading entire site with wget

wget \
 --recursive \
 --no-clobber \
 --page-requisites \
 --html-extension \
 --convert-links \
 --restrict-file-names=windows \
 --domains website.org \
 --no-parent \
     www.website.org/tutorials/html/

Persist iptables configuration

install iptables-persistent

sudo apt-get install iptables-persistent

save iptables configuration with iptables-persistent

sudo iptables-persistent save

Setting iptables to redirect port (could be used to set wildfly to get request from 80 port)

sudo iptables -A PREROUTING -t nat -p tcp --dport 80 -j REDIRECT --to-port 8080

Setting iptables to redirect port on local machine

sudo iptables -t nat -I OUTPUT -p tcp -o lo --dport 80 -j REDIRECT --to-ports 8080

Get linux distribution information

lsb_release -a
cat /etc/*-release
uname -a
cat /proc/version

Compress, zip, extract files directory etc

tar -cvzf <filename_with_.tar.gz_extension> <directory_or_file>
tar -xvzf <filename_with_.tar.gz_extension> 
tar -cvzf - <file1> <file2> ... <filen>

Continue last transaction of package manager like apt-get or yum

yum-complete-transaction [--cleanup-only] 
yum history redo last

View image from command line

Using caca to view image with characters : sh sudo apt-get install caca-utils cacaview <any_image_.jpg>

Using fbi which will use framebuffer : sh sudo apt-get install fbi fbi <any_image_.jpg>

Creating desktop launcher for an application

vim /home/$HOME/.local/share/applications/<application_name>.desktop

[Desktop Entry]
Version=1.0
Name=<Application Name>
Comment=<e.g. Java IDE>
Type=Application
Categories=<e.g. Development;IDE;>
Exec=<application location e.g. /home/${USERNAME}/applications/eclipse/eclipse>
Terminal=false
StartupNotify=true
Icon=<icon location e.g. /home/${USERNAME}/applications/eclipse/icon.xpm>
Name[en_US]=<Application Name e.g. Eclipse>

Installations

Installation scripts to setup environment

alpine setup environment

<<<<<<<<<<<<<<<<<<<<<<<<

Adding new php version in wamp server

create new folder [path-to-wamp]/bin/php/php.#.#.# and copy files here
copy following files from older php
1. php.ini
2. phpForApache.ini
3. wampserver.conf
Take snapshots of wamp>PHP>PHP Settings and wamp>PHP>PHP Extendsion
Open wamp>PHP>php.ini and save it as a backup
Restart wamp , Change wamp>PHP>Version>latest_version
Use a diff tool to get differences between old php.ini and new one to satisfy all extensions

Installing LAMPP

Install apache web server
```
sudo apt-get install apache2
```
/etc/apache2/apache2.conf contains configurations /etc/apache2/ports.conf contains ports configuration
Install PHP
```
sudo apt-get install php5 libapache2-mod-php5
```
directory for lookup is /var/www/html

Install mysql

sudo apt-get install mysql-server

add following lines in /etc/apache2/apache2.conf

#phpMyAdmin Configuration
Include /etc/phpmyadmin/apache.conf

In Ubuntu also need to run following commands to make mcrypt recognized in phpmyadmin/install mcrypt right way
```
php5enmod mcrypt
```

Installing LEMP

Install nginx

sudo apt-get install nginx

Edit /etc/nginx/sites-available/default (If /usr/share/nginx/www does not exist, it's probably called html. Make sure you update your configuration appropriately)

Add index.php to the index line.
Change the server_name from local host to your domain name or IP address (replace the example.com in the configuration)

Change the correct lines in “location ~ .php$ {“ section

server {
	listen   80;

	root /usr/share/nginx/www;
	index index.php index.html index.htm;

	server_name example.com;

	location / {
			try_files $uri $uri/ /index.html;
	}

	error_page 404 /404.html;

	error_page 500 502 503 504 /50x.html;
	location = /50x.html {
		  root /usr/share/nginx/www;
	}
	
	# pass the PHP scripts to FastCGI server listening on the php-fpm socket
	location ~ \.php$ {
			try_files $uri =404;
			fastcgi_pass unix:/var/run/php5-fpm.sock;
			fastcgi_index index.php;
			fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
			include fastcgi_params;
			
	}
}

Install mysql with php-mysql

sudo apt-get install mysql-server php5-mysql

Activate mysql

sudo mysql_install_db

setup script

sudo /usr/bin/mysql_secure_installation

Install PHP
```
sudo apt-get install php5-fpm
```
Configure php Edit php.ini file vim /etc/php5/fpm/php.ini
```
cgi.fix_pathinfo=0
```
Edit /etc/php5/fpm/pool.d/www.conf Find the line, listen = 127.0.0.1:9000, and change the 127.0.0.1:9000 to /var/run/php5-fpm.sock.
```
listen = /var/run/php5-fpm.sock
```
Restart php-fpm
```
sudo service php5-fpm restart
```

Create info.php

sudo nano /usr/share/nginx/html/info.php

<?php
phpinfo();
?>

restart nginx

sudo service nginx restart

Installing Composer in Linux

Download the installer to the current directory
Verify the installer SHA-384 either by below command or cross checking at https://composer.github.io/pubkeys.html php -r "if (hash('SHA384', file_get_contents('composer-setup.php')) === 'fd26ce67e3b237fffd5e5544b45b0d92c41a4afe3e3f778e942e43ce6be197b9cdc7c251dcde6e2a52297ea269370680') { echo 'Installer verified'; } else { echo 'Installer corrupt'; unlink('composer-setup.php'); }"
Run the installer php composer-setup.php
Remove the installer php -r "unlink('composer-setup.php');"
To install composer Globally move the downloaded file to /usr/local/bin/composer mv composer.phar /usr/local/bin/composer

Installing Laravel

On Windows : sh composer global require "laravel/installer" On Linux using local composer.phar : sh php composer.phar global require "laravel/installer"

Plugin to add laravel framework in netbeans https://github.com/nbphpcouncil/nb-laravel-plugin/releases

Installing java manually

Download .tar.gz file (preferred to be downloaded from oracle's site)

wget  --no-cookies --no-check-certificate --header "Cookie: gpw_e24=http%3A%2F%2Fwww.oracle.com%2F; oraclelicense=accept-securebackup-cookie" <url>

Extract .tar.gz file in /opt directory

tar -zxvf jdk-*u**-linux-****.tar.gz

Create symbolic link in order to simplify java updates in future

ln -s /opt/jdk1.8.0_144 /opt/java

Tell system where java and ts executables are intalled.

update-alternatives --install /usr/bin/java java /opt/java/bin/java 100
update-alternatives --config java

Create necessary environment variables

sudo vim /etc/profile.d/java.sh

if ! echo ${PATH} | grep -q /opt/java/bin ; then
	export PATH=/opt/java/bin:${PATH}
fi      
if ! echo ${PATH} | grep -q /opt/java/jre/bin ; then
   export PATH=/opt/java/jre/bin:${PATH}
fi      
export JAVA_HOME=/opt/java
export JRE_HOME=/opt/java/jre
export CLASSPATH=.:/opt/java/lib/tools.jar:/opt/java/jre/lib/rt.jar

sudo chmod 755 /etc/profile.d/java.sh

Uninstall a package properly on Ubuntu

sudo apt-get purge git; 
sudo apt-get autoremove;

now delete related files if exist in your home directory

rm ~/.gitconfig

Installing postgresql debugger

Edit postgresql.conf file present in c:\program files\postgresql\9.3\data directory Un-comment or add this line:

shared_preload_libraries = '$libdir/plugin_debugger.dll'

Restart PostgreSQL server In the required database run following command

create extension pldbgapi;

Maven download / install sources and javadocs

Download sources

mvn dependency:sources

Download docs

mvn dependency:resolve -Dclassifier=javadoc

Download sources of specific package

mvn dependency:sources -DincludeArtifactIds=guava

Add plugin in pom.xml

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <artifactId>maven-eclipse-plugin</artifactId>
    <configuration>
        <downloadSources>true</downloadSources>
        <downloadJavadocs>true</downloadJavadocs>
    </configuration>
</plugin>

Maven run a particular class

Directly from command line : mvn exec:java -Dexec.mainClass="com.example.Main" mvn exec:java -Dexec.mainClass="com.example.Main" -Dexec.args="arg0 arg1" Using plugin : pom <plugin> <groupId>org.codehaus.mojo</groupId> <artifactId>exec-maven-plugin</artifactId> <version>1.2.1</version> <executions> <execution> <goals> <goal>java</goal> </goals> </execution> </executions> <configuration> <mainClass>com.example.Main</mainClass> <arguments> <argument>foo</argument> <argument>bar</argument> </arguments> </configuration> </plugin>

Mongodb on Ubuntu-16.0

Reference taken from https://www.howtoforge.com/tutorial/install-mongodb-on-ubuntu-16.04 Importing key

sudo apt-key adv --keyserver hkp://keyserver.ubuntu.com:80 --recv EA312927

Create source list file MongoDB

echo "deb http://repo.mongodb.org/apt/ubuntu "$(lsb_release -sc)"/mongodb-org/3.2 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-3.2.list
sudo apt-get install mongodb-org

Create a new mongodb systemd service file in the '/lib/systemd/system' directory.

cd /lib/systemd/system/
vim mongod.service

Now update the systemd service with command below:

systemctl daemon-reload

Start mongodb and add it as service to be started at boot time:

systemctl start mongod
systemctl enable mongod

Further to add mongodb in php

composer require mongodb/mongodb

Generic runnable/executable file/application as service in ubuntu

Edit /etc/systemd/system/prometheus.service

[Unit]
Description=Prometheus Service
After=network.target

[Service]
Type=simple
ExecStart=/usr/local/bin/prometheus/prometheus --config.file=/usr/local/bin/prometheus/prometheus.yml

[Install]
WantedBy=multi-user.target

sudo service prometheus start

Setup

Disabling lightdm (or other service)

Method 1
```
echo manual | sudo tee etc/init.d/lightdm.override
```
i.e. create .override file to disable it (override it) This method is not working after 14.0
Method 2 edit /etc/default/grub replace GRUB_CMDLINE_LINUX_DEFAULT="quiet splash" with GRUB_CMDLINE_LINUX_DEFAULT="text"
```
sudo update-grub
```

Disable ssh login without password

Edit /etc/ssh/sshd_config and change following settings

ChallengeResponseAuthentication no
PasswordAuthentication no
UsePAM no

sudo /etc/init.d/ssh reload

Setting git to login wihout password + using ssh in git

Create ssh-key

ssh-keygen

Copy your .pub file in remote git application from where you want to connect Add your private key using ssh-agent into your system (if you don't want to provide key every time)

ssh-add ~/.ssh/id_rsa

Useful commands

List all apt-get packages versions or list current version of package : sh apt-get policy nodejs apt-get madison nodejs

Check boot performance | boot services time analysis : ```sh systemd-analyze blame ```
Check systemctl service dependency tree : ```sh systemctl list-dependencies --reverse snapd.socket ```
Getting list of installed packages : ```sh dpkg --get-selections | grep -v deinstall ```
Copying files from one machine to other : ```sh scp /file_in_current_system root@target_machine /path_of_destination ```
Getting information of current distribution : ```sh uname -r cat /etc/*-release lsb_release -a cat /proc/version ```
Download content : curl
Download file : wget
json formatter with stream : jq
Generic syntax highlighter : ```sh pygmentize -l xml sudo apt-get install python-pygments sudo apt-get install python-image ```
Formatter for xml : ```sh sudo apt-get install libxml2-utils xmllint ```
Get info of ip addresses in network (computer name, logged in user etc..) : ```sh sudo apt-get install nbtscan nbtscan 192.168.1.0/24 ```
Network scanner. (find hosts systems and open ports on systems.) : ```sh sudo apt-get install nmap nmap ```
Arbitrary TCP and UDP connections and listens : nc
To record voice : avconv -f pulse -i default file.wav
To edit sam file : chntpw
To get mouse coordinates, open windows etc : xdotool
Controlling audio devices : ```sh amixer -D pulse sset Master 5%+ alsamixer ```
If amixer is not found, install it using below command ```sh sudo apt-get install alsa-utils ```
Control menubar time format or modify anyway : gsettings set com.canonical.indicator.datetime show-seconds true
Remove/Delete file completely (permanently) : shred -zun3 -f
Reduce JPEG file size : jpegoptim
Create Conda Environment : ```sh conda create --name email-sending-env python=3.7 ```

Delete all idle connections of postgresql

SELECT
  DATE_TRUNC('second',NOW()-query_start) AS age,
  pg_terminate_backend(pid),
  *
FROM
  pg_stat_activity
WHERE NOW() - query_start > '00:10:00'
ORDER BY
  age DESC;

git autocomplete feature in Mac

curl https://raw.githubusercontent.com/git/git/master/contrib/completion/git-completion.bash > ~/.git-auto-complete.bash
source ~/.git-auto-complete.bash

Use netcat or nc to execute a command or script remotely

while true; do if [[ $(nc -lp 1234 2> /dev/null) == 'install' ]]; then ./myexec.sh; fi; done

Useful python commands for page number converter

",".join([ str(i) for i in range(1, 102) if int((i + 1) / 2) % 2 != 0])
",".join([ str(i) for i in range(1, 102) if int((i + 1) / 2) % 2 == 0])

Informations

In virtualbox guest 10.0.2.2 will be the IP of host
Accessing guest from host in virtualbox
In virtual box settings > Network > Attached to : NAT
1. In virtual box settings > Network > Attached to : NAT
2. In guest type ifconfig
In Ubuntu the packages installed are stored in /var/cache/apt/archives
Crontab could be used to schedule tasks in linux. Command to edit crontab is
```
crontab -e
```
Location to install your own sh files so that it could be used as commands /usr/local/bin/
Location to get information of ifconfig or current network or eth* or to get mac addresses is **/sys/class/net/*/address
Personal RootCA Certificate : Download

Code

To read .env file to set environment variables

environmentSetupFile=$(mktemp)
if [ -f '.env' ]; then 
    cat '.env' | while read line; do echo "export $line"; done > "${environmentSetupFile}"
    source "${environmentSetupFile}"
    rm -f "${environmentSetupFile}"
else 
    echo '>> .env not found'
    exit 1
fi

Trigger code on file change

#!/bin/sh

FILE="/root/default.conf"
COPYLOC="/etc/nginx/http.d/default.conf"

cp -f $FILE $COPYLOC
LT=`stat -c %Z $FILE`; 
while true
do 
    AT=`stat -c %Z $FILE`
    if [[ "$AT"  != "$LT" ]]; then 
        cp -f $FILE $COPYLOC
        sleep 1
        nginx -s reload
        LT=$AT
        echo `date "+%Y/%m/%d %H:%m:%S"` [reloader] Default config file reloaded
    fi
    sleep 1
done

Python code to send a simple text email

import smtplib, ssl
from getpass import getpass

port = 465  # For SSL
smtp_server = "smtp.gmail.com"
sender_email = "[email protected]"  # Enter your address
receiver_email = "[email protected]"  # Enter receiver address
password = getpass("Type your password and press enter: ")
message = """\
Subject: Hi there

This message is sent from Python.
"""

context = ssl.create_default_context()
with smtplib.SMTP_SSL(smtp_server, port, context=context) as server:
    server.login(sender_email, password)
    server.sendmail(sender_email, receiver_email, message)

Python code for page number converter

",".join([ str(i) for i in range(1, 102) if int((i + 1) / 2) % 2 != 0])
",".join([ str(i) for i in range(1, 102) if int((i + 1) / 2) % 2 == 0])

Intercept requests of XMLHttpRequest

window.fzinterceptor = {
	predicate: url => (/\/followers\/\?count=/i).test(url),
	collectorInitializer: () => []
};
fzinterceptor.collector = fzinterceptor.collectorInitializer()
fzinterceptor.renewCollector = function(newCollector) {
	const oldCollector = fzinterceptor.collector
	if (!newCollector) {
		newCollector = fzinterceptor.collectorInitializer()
	}
	fzinterceptor.collector = newCollector
	return oldCollector;
}
fzinterceptor.executor = (data, collector, url, postData) => {
    console.log(url + " : " + postData)
    console.log(data)
    return [...collector, ...data.users]
}
(function(xhr, fzinterceptor) {
    const XHR = XMLHttpRequest.prototype;
    const send = XHR.send;
    XHR.send = function(postData) {
        this.addEventListener('load', function() {
			if (fzinterceptor.predicate(this.responseURL)) {
            	const data = JSON.parse(this.responseText)
				const returned = fzinterceptor.executor(data, fzinterceptor.collector, this.responseURL, postData)
				if (returned) {
					fzinterceptor.collector = returned
				}
			}
        });
        return send.apply(this, arguments);
    };
})(XMLHttpRequest, fzinterceptor);

Edit Technotes | v2

Name		Name	Last commit message	Last commit date
Latest commit History 23 Commits
_includes		_includes
assets		assets
.ignore		.ignore
CNAME		CNAME
README.md		README.md
_config.yml		_config.yml
apple-touch-icon-114x114.png		apple-touch-icon-114x114.png
apple-touch-icon-120x120.png		apple-touch-icon-120x120.png
apple-touch-icon-144x144.png		apple-touch-icon-144x144.png
apple-touch-icon-152x152.png		apple-touch-icon-152x152.png
apple-touch-icon-57x57.png		apple-touch-icon-57x57.png
apple-touch-icon-60x60.png		apple-touch-icon-60x60.png
apple-touch-icon-72x72.png		apple-touch-icon-72x72.png
apple-touch-icon-76x76.png		apple-touch-icon-76x76.png
favicon-128.png		favicon-128.png
favicon-16x16.png		favicon-16x16.png
favicon-196x196.png		favicon-196x196.png
favicon-32x32.png		favicon-32x32.png
favicon-96x96.png		favicon-96x96.png
favicon.ico		favicon.ico
favicon.png		favicon.png
google467cf08e899fd7d0.html		google467cf08e899fd7d0.html

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