Linux – Page 21

Configure Multiple Users for Shadowsocks-libev

July 14, 2019 - by mahmood

For example, Cloud and Tifa, two AVALANCHE members, are planning to deploy shadowsocks-libev services on the same VPS to bypass the firewall of Shinra Inc. In this case, they could simply create cloud.json and tifa.json configurations with different ports, passwords and encryption methods in /etc/shadowsocks-libev directory. Then enable and start the systemd services using the following commands:

sudo systemctl enable shadowsocks-libev-server@cloud.service --now
sudo systemctl enable shadowsocks-libev-server@tifa.service --now

The status of shadowsocks-libev instances could be checked with the following commands:

sudo systemctl status shadowsocks-libev-server@cloud.service
sudo systemctl status shadowsocks-libev-server@tifa.service

You can start shadowsocks-libev instances with the following commands:

sudo systemctl start shadowsocks-libev-server@cloud.service
sudo systemctl start shadowsocks-libev-server@tifa.service

References
https://blog.zzhou612.com/2019/02/15/configure-multiple-users-for-shadowsocks-libev/

Check if a command succeeded on Bash

July 14, 2019 - by mahmood

The return value is stored in $?. 0 indicates success, others indicates error.

some_command
if [ $? -eq 0 ]; then
    echo OK
else
    echo FAIL

some_command
retval=$?
do_something $retval
if [ $retval -ne 0 ]; then
    echo "Return code was not zero but $retval"
fi

References
https://askubuntu.com/questions/29370/how-to-check-if-a-command-succeeded

Apache reverse proxy configuration for socket.io

July 13, 2019 - by mahmood

sudo a2enmod proxy_http
sudo a2enmod proxy_fcgi
sudo a2enmod proxy_wstunnel

# VirtualHost ms.example.net
<VirtualHost *:80>
  ServerName ms.example.net
  ProxyRequests Off
  ProxyPreserveHost On
  RemoteIPHeader X-Forwarded-For
  <Proxy *>
    Order deny,allow
    Allow from all
  </Proxy>
  RewriteEngine On
  RewriteCond %{REQUEST_URI} ^/socket.io          [NC]
  RewriteCond %{QUERY_STRING} transport=websocket [NC]
  RewriteRule /(.*) ws://localhost:14102/$1        [P,L]

  ProxyPass /socket.io http://localhost:14102/socket.io
  ProxyPassReverse /socket.io http://localhost:14102/socket.io
</VirtualHost>

<VirtualHost *:443>
  ServerName ms.example.net
  ProxyRequests Off
  ProxyPreserveHost On
  RemoteIPHeader X-Forwarded-For
  RewriteEngine on
  <Proxy *>
    Order deny,allow
    Allow from all
  </Proxy>
  SSLEngine On
  SSLCertificateFile /etc/letsencrypt/live/example.net/fullchain.pem
  SSLCertificateKeyFile /etc/letsencrypt/live/example.net/privkey.pem
  
  RewriteEngine On
  RewriteCond %{REQUEST_URI} ^/socket.io          [NC]
  RewriteCond %{QUERY_STRING} transport=websocket [NC]
  RewriteRule /(.*) ws://localhost:14102/$1        [P,L]
  ProxyPass /socket.io http://localhost:14102/socket.io
  ProxyPassReverse /socket.io http://localhost:14102/socket.io
  
</VirtualHost>

Use a secure URL for your initial connection, i.e. instead of “http://” use “https://”. If the WebSocket transport is chosen, then Socket.IO should automatically use “wss://” (SSL) for the WebSocket connection too.

var socket = io.connect('https://localhost', {secure: true});

References
http://xpo6.com/socket-io-via-apache-reverse-proxy/
https://stackoverflow.com/questions/36472920/apache-proxy-configuration-for-socket-io-project-not-in-root
https://gist.github.com/iacchus/954e0787d6893c5ab8e1
https://stackoverflow.com/questions/6599470/node-js-socket-io-with-ssl

Install HAProxy on Ubuntu 18.04

July 13, 2019 - by mahmood

apt-get install software-properties-common
add-apt-repository ppa:vbernat/haproxy-2.0

apt-get update
apt-get install haproxy=2.0.\*

References
https://haproxy.debian.net/

Change the output color of echo using ANSI escape codes in Linux

July 13, 2019 - by mahmood

Black        0;30     Dark Gray     1;30
Red          0;31     Light Red     1;31
Green        0;32     Light Green   1;32
Brown/Orange 0;33     Yellow        1;33
Blue         0;34     Light Blue    1;34
Purple       0;35     Light Purple  1;35
Cyan         0;36     Light Cyan    1;36
Light Gray   0;37     White         1;37

RED='\033[0;31m'
NC='\033[0m' # No Color

echo -e "I ${RED}love${NC} Stack Overflow"

References
https://stackoverflow.com/questions/5947742/how-to-change-the-output-color-of-echo-in-linux
https://misc.flogisoft.com/bash/tip_colors_and_formatting

Change the output color of echo using tput in Linux

July 13, 2019 - by mahmood

tput setaf 1; echo "this is red text"

The count of colors available to tput is given by tput colors

To see the basic 8 colors (as used by setf in urxvt terminal and setaf in xterm terminal):

Color       #define       Value       RGB
black     COLOR_BLACK       0     0, 0, 0
red       COLOR_RED         1     max,0,0
green     COLOR_GREEN       2     0,max,0
yellow    COLOR_YELLOW      3     max,max,0
blue      COLOR_BLUE        4     0,0,max
magenta   COLOR_MAGENTA     5     max,0,max
cyan      COLOR_CYAN        6     0,max,max
white     COLOR_WHITE       7     max,max,max

To print all 256 colors in the terminal, try the following one-liner:

for c in {0..255}; do tput setaf $c; tput setaf $c | cat -v; echo =$c; done

References
https://stackoverflow.com/questions/5947742/how-to-change-the-output-color-of-echo-in-linux
https://unix.stackexchange.com/questions/269077/tput-setaf-color-table-how-to-determine-color-codes

Obtaining Let’s Encrypt Certificate valid for sub domains

July 12, 2019 - by mahmood

sudo certbot --apache -d example.com -d www.example.com

References
https://www.digitalocean.com/community/tutorials/how-to-secure-apache-with-let-s-encrypt-on-ubuntu-18-04

Functions in Bash

July 12, 2019 - by mahmood

#!/bin/bash
# Basic function
print_something () {
echo Hello I am a function
}
print_something
print_something

Passing Arguments

#!/bin/bash
# Passing arguments to a function
print_something () {
echo Hello $1
}
print_something Mars
print_something Jupiter

Return Values

#!/bin/bash
# Setting a return status for a function
print_something () {
echo Hello $1
return 5
}
print_something Mars
print_something Jupiter
echo The previous function has a return value of $?

Passing Arguments

#!/bin/bash
# Passing arguments to a function
print_something () {
echo Hello $1
}
print_something Mars
print_something Jupiter

Return Values

#!/bin/bash
# Setting a return status for a function
print_something () {
echo Hello $1
return 5
}
print_something Mars
print_something Jupiter
echo The previous function has a return value of $?

the variable $? contains the return status of the previously run command or function.

References
https://ryanstutorials.net/bash-scripting-tutorial/bash-functions.php

Use ‘pushd’ and ‘popd’ for Filesystem Navigation in Linux

July 12, 2019 - by mahmood

pushd dir1
# bash commands ...
popd

References
https://unix.stackexchange.com/questions/77077/how-do-i-use-pushd-and-popd-commands
https://www.tecmint.com/pushd-and-popd-linux-filesystem-navigation/

If Statements in Bash

July 12, 2019 - by mahmood

Basic If Statements

#!/bin/bash
# Basic if statement
if [ $1 -gt 100 ]
then
echo Hey that\'s a large number.
pwd
fi
date

If Else

#!/bin/bash
# else example
if [ $# -eq 1 ]
then
nl $1
else
nl /dev/stdin
fi

If Elif Else

#!/bin/bash
# elif statements
if [ $1 -ge 18 ]
then
echo You may go to the party.
elif [ $2 == 'yes' ]
then
echo You may go to the party but be back before midnight.
else
echo You may not go to the party.
fi

Boolean Operations

#!/bin/bash
# and example
if [ -r $1 ] && [ -s $1 ]
then
echo This file is useful.
fi

#!/bin/bash
# or example
if [ $USER == 'bob' ] || [ $USER == 'andy' ]
then
ls -alh
else
ls
fi

Multiple logical operators, ((A || B) && C)

use double brackets

if [[ ($A -eq 0 || $B -ne 0) && $C -eq 0 ]]; then …

References
https://ryanstutorials.net/bash-scripting-tutorial/bash-if-statements.php
https://unix.stackexchange.com/questions/290146/multiple-logical-operators-a-b-c-and-syntax-error-near-unexpected-t