List volumes
sudo docker volume ls -qf dangling=true

Delete unnecessary volumes
sudo docker volume rm $(sudo docker volume ls -qf dangling=true)

Kill all Docker containers
sudo docker kill $(sudo docker ps -q)

The following commands mount a large-scale SSD volume (/dev/xvdb) onto /mnt.
sudo mkfs.ext4 /dev/xvdb
echo "/dev/xvdb /mnt auto noatime 0 0" | sudo tee -a /etc/fstab
sudo mount /mnt

Security Group
It is enough to open the port 22 at Security Group on EC2
SSH TCP 22 0.0.0.0/32

JMeter Server Configuration
cd apache-jmeter-3.0/bin
vi ./jmeter.properties

Find and modify the following two lines
server_port=10991 # Server-side port from JMeter client: JMeter Client -> JMeter Server
server.rmi.localport=40001 # Server port to access to Client via RMI: JMeter Server -> JMeter Client

Create the following script and run:
vi color.sh
chmod +x color.sh
./color.sh

The bash script:
#!/bin/bash

export txtrst='\x1b[00m' # Reset

echo
for i in {0..255} ; do
printf "\x1b[00;${i}m ${i}${txtrst}"
done
echo

echo
for i in {0..255} ; do
printf "\x1b[38;05;%03dm 38;05;%03d " ${i} ${i}
if [ $(( ${i} % 8 )) -eq 7 ] ; then
echo
fi
done
echo

To adjust timezone on your Linux to Pacific Standard Time (PST/PDT), type the following on command line.
sudo mv /etc/localtime /etc/localtime.org; sudo ln -s /usr/share/zoneinfo/America/Los_Angeles /etc/localtime

To adjust timezone on your Linux to Japanese Standard Time (JST), type the following on command line.
sudo mv /etc/localtime /etc/localtime.org; sudo ln -s /usr/share/zoneinfo/Asia/Tokyo /etc/localtime

How can we express the data structure of "Array of Array" in Perl? Usually we create a generic array in Perl like this: @array = ('aaa', 'bbb', 'ccc'). Please take a look at the sample code shown below.
Note that a vaiable $songs starts with '$'. Also note that parenthesis is [...], not (...), even it is inside the parenthesis. This is to express a "reference" of "Array of Array". Take a look at "foreach" for accessing the reference variable.
　
#!/usr/bin/perl

Download and install a Bootstrap theme. Modify the following at
vi bootstrap/templates/menu/system/form-element.func.php

　
/**
* Overrides theme_form_element().
*/
function bootstrap_form_element(&$variables) {
$element = &$variables['element'];
$name = !empty($element['#name']) ? $element['#name'] : FALSE;
$type = !empty($element['#type']) ? $element['#type'] : FALSE;
$checkbox = $type && $type === 'checkbox';
$radio = $type && $type === 'radio';

li:before {
position: absolute;
top: 0;
left: 0;
font-family: 'FontAwesome'; /* Specify FontAwesome */
content: '\f07b'; /* This is a folder icon */
color: #fab100; /* Yellow */
}

https://pixie.works/tips/node/6

Install openssl
==================
sudo apt-get install openssl

Create a select key
==================

e.g. server.key
# Do not use 2048 byte key - It does not work on modern browsers.
sudo openssl genrsa -out server.key 4096 # e.g. no password

Alternative: with a password (e.g. server.key)
# Do not use 2048 byte key - It does not work on modern browsers.
sudo openssl genrsa -des3 -out server.key 4096

Create a public key
==================