Technotes

Technical Notes by Afzal | https://afzalex.com

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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 ```bash 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

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 \t\t\t\t"
}
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

Creating ssl certificate / certificate authority / self sign certificate

  1. 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

  2. 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

  3. Remove Passphrase from Key (if rsa key is encrypted) 
     cp server.key server.key.org
 openssl rsa -in server.key.org -out server.key
  4. 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

  5. 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

  6. Import pkcs12 into keystore
  7. 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
openssl rsa -check -in server.key
Verify a Private Key Matches a Certificate and CSR
 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)

sudo apt-get install msmtp
vim ~/.msmtprc

Now in opened editor set default values for all following accounts.

# 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           username@gmail.com
user           username
password       plain-text-password

# A freemail service
account        freemail
host           smtp.freemail.example
from           joe_smith@freemail.example
...

# 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
sudo apt-get install caca-utils
cacaview <any_image_.jpg>
Using fbi which will use framebuffer
  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

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

Installing LAMPP

  1. Install apache web server 
    sudo apt-get install apache2

    /etc/apache2/apache2.conf contains configurations /etc/apache2/ports.conf contains ports configuration

  2. Install PHP 
     sudo apt-get install php5 libapache2-mod-php5

    directory for lookup is /var/www/html

  3. Install mysql 
    sudo apt-get install mysql-server

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

    #phpMyAdmin Configuration
Include /etc/phpmyadmin/apache.conf
  4. In Ubuntu also need to run following commands to make mcrypt recognized in phpmyadmin/install mcrypt right way 
    php5enmod mcrypt

Installing LEMP

  1. 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)

    1. Add index.php to the index line.
    2. Change the server_name from local host to your domain name or IP address (replace the example.com in the configuration)
    3. 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;
					
     }
 }
  2. 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
  3. 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
  4. Create info.php 
     sudo nano /usr/share/nginx/html/info.php

     <?php
 phpinfo();
 ?>

    restart nginx

     sudo service nginx restart

Installing Composer in Linux

  1. Download the installer to the current directory
  2. 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’); }”
  3. Run the installer php composer-setup.php
  4. Remove the installer php -r “unlink(‘composer-setup.php’);”
  5. To install composer Globally move the downloaded file to /usr/local/bin/composer mv composer.phar /usr/local/bin/composer

Installing Laravel

On Windows
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

<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)

  1. 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*

  2. 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

  1. 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
apt-get policy nodejs
apt-get madison nodejs

Check boot performance | boot services time analysis
systemd-analyze blame

Check systemctl service dependency tree
systemctl list-dependencies --reverse snapd.socket

Getting list of installed packages
dpkg --get-selections | grep -v deinstall

Copying files from one machine to other
scp /file_in_current_system root@target_machine /path_of_destination

Getting information of current distribution
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
pygmentize -l xml
sudo apt-get install python-pygments
sudo apt-get install python-image

Formatter for xml
sudo apt-get install libxml2-utils			
xmllint

Get info of ip addresses in network (computer name, logged in user etc..)
sudo apt-get install nbtscan		
nbtscan 192.168.1.0/24

Network scanner. (find hosts systems and open ports on systems.)
sudo apt-get install nmap
nmap <ip-address>

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
amixer -D pulse sset Master 5%+
alsamixer


If amixer is not found, install it using below command

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
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



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 = "afzalex.store@gmail.com"  # Enter your address
receiver_email = "afzalex.testing@gmail.com"  # 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);

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