MacLochlainns Weblog

I neglected to show how to install and configure the Java SDK on my earlier post without relying on including the $JAVA_HOME in the $PATH. This post shows how to install the Java and Java SDK on Alma Linux without layering it with the $JAVA_HOME environment variable.

You install the Java runtime and development kit with the following command:

sudo dnf install -y java-17-openjdk java-17-openjdk-devel

Then, you need to add it to the $PATH environment variable with the following syntax in your .bashrc file or environment file of your choice.

export set PATH=$PATH:/usr/lib/jvm/java-17-openjdk-17.0.8.0.7-2.el9.x86_64/bin/

After you source the new $PATH environment value, you can then write a file like this Hello.java file to test it.

// Define the Java program.
public class HelloWorld {
  public static void main(String[] args) {
    System.out.println("Hello World!");
  }
}

You compile the Hello.java file with this syntax:

javac Hello.java

Then, you run the compiled program with the following syntax:

java Hello

It’ll print:

Hello World!

These are the instructions for installing AlmaLinux 9 on MacOS Intel with VMware. It’s broken into three parts: Configuration, Installation, and Setup.

You should download the current or desired older version of AlmaLinux from the website. It’s a good idea to install it in a source directory or folder.

You need to launch VMware, click the File menu option and then the New menu option before you can configure, install, and setup AlmaLinux. It will show you the following dialog.

Use the Finder to drag the AlmaLinux-9-latest-x86_64-dvd.iso file on to the Install from disc or image to begin the configuration process.

Configuration

1. The first thing you need to do is configure the VMware container. You click on the wrench icon in the menu bar that lets you edit the hardware settings for this virtual machine. This opens the general settings dialog.

2. The General System Settings dialog lets you will configure the isolation properties for “drag and drop” and “copy and paste”, and define the network adapter.

3. Click on the Isolation menu option from the General System Settings dialog, and enable “Drag adn Drop” and “Copy and Paste” checkboxes. Then, return to the General System Settings dialog/li>

4. Click on the Network Adapter menu option from the General System Settings dialog, and click the “Autodetect” checkbox. Then, return to the General System Settings dialog.

Installation

1. The first the install asks you to do is type an I for install or T for test. Generally, you can skip the test if this is a copied file rather than DVD.

2. Click the Tab key to configure the target installation or Enter key to skip the automatic boot delay.

3. Choose the installation language and click the Continue button.

4. The Installation Summary dialog lets you fix anything with a warning message orange triangle. Fix the Root Password first by clicking on the text.

5. Enter the Root Password twice, click the Lock root account checkbox to unselect it, and click the Allow root SSH login with password checkbox to enable it.

6. Click the Done button to complete setting the root password.

7. After fixing the root password, click on the Installation Destination item to change the default partition.

8. Click the Done button to accept the initial size of the VM partition.

9. Click the Software Selection element to add software components to the default installation.

10. Click the checkboxes for the following additional software:
    • Debugging Tools
    • Performance Tools
    • Remote Desktop Clients
    • Remote Management for Linux
    • Legacy UNIX Compatibility
    • Console Internet Tools
    • Development Tools
    • .NET Development
    • Graphical Administration Tools
    • System Tools

    Click the Done button to accept the added software elements.

11. Click the Begin Installation button to begin the installation of AlmaLinux.

12. The Installing Progress dialog will show a progress bar for several minutes.

13. The Installing Progress dialog eventually completes, and you click the Reboot System button to complete the installation.

Setup

1. The Welcome to AlmaLinux page begins the set up of the operating systems.

2. Click the Slide to disable location services.

3. After clicking the Slide location services are disabled.

4. The Online Account dialog lets you connect your email, online calendar, contacts, documents, and photos. You click the Skip button to avoid setting up any of the online accounts.

5. The About You dialog lets you enter user account with sudoer privileges.

6. The About You dialog enters a title case user’s name and a lowercase user’s name.

7. The Password dialog lets you enter a case sensitive password.

8. The Password dialog displays the entry of the passwords as dots.

9. The Setup Complete dialog leaves you to click the Start Using AlmaLinux button to complete the setup.

10. The blank image page displays until you click on it.

11. The Welcome to AlmaLinux dialog invites you to take a tour or decline it. Click the No Thanks button to decline the tour.

12. After declining the tour, it displays the core AlmaLinux screen.

13. Rebooting the system is necessary to complete the installation. Click on the circle icon on the right to begin the process to restart or shutdown the operating system. Click on the Power Off / Log Out dropdown to continue.

14. Click the Restart… menu option to restart the operating system.

15. Click the Restart… menu option to confirm the restart of the operating system.

16. Click the Student icon to get prompted for a password.

17. Enter the Student password to connect to the AlmaLinux operating system.

18. This displays the standard working interface for the AlmaLinux operating system.

I’m always updating VMs, and I was gratified to notice that there’s a Fedora arm64 ISO. If you’re interested in it, you can download the Live Workstation from here or the Fedora Server from here.

Unfortunately, I only have macOS running on i7 and i9 Intel Processors. It would be great to hear back how it goes for somebody one of the new Apple M1 chip.

I typically install the workstation version because it meets my needs to run MySQL and other native Linux development tools. However, the server version is also available. Fedora is a wonderful option, as a small footprint for testing things on my MacBookPro.

My students working in Linux would have a series of labs to negotiate and I’d have them log the activities of their Oracle SQL scripts. Many of them would suffer quite a bit because they didn’t know how to find the errors in the log files.

I wrote this SQL function for them to put in their .bashrc files. It searches all the .txt files for errors and organizes them by log file, line number, and descriptive error message.

errors () 
{ 
  label="File Name:Line Number:Error Code";
  list=`ls ./*.$1 | wc -l`;
  if [[ ${list} -eq 1 ]]; then
    echo ${label};
    echo "----------------------------------------";
    filename=`ls *.txt`;
    echo ${filename}:`find . -type f | grep -in *.txt -e ora\- -e pls\- -e sp2\-`;
  else
    if [[ ${list} -gt 1 ]]; then
      echo ${label};
      echo "----------------------------------------";
      find . -type f | grep --color=auto -in *.txt -e ora\- -e pls\- -e sp2\-;
    fi;
  fi
}

I hope it helps others now too.

Interesting problems seem to plague me from time to time. The current problem isn’t yet solved but I’m working on it. After a sleep cycle, IPV6 networking isn’t starting.

ERR_INTERNET_DISCONNECTED

In the broken Fedora 30 VM, I checked the status with the nmcli tool:

sudo nmcli general status

It returned:

STATE   CONNECTIVITY  WIFI-HW  WIFI     WWAN-HW  WWAN    
asleep  none          enabled  enabled  enabled  enabled

The STATE should return connected and connectivity return full. Unfortunately, that’s not the case.

There was little surprise that the next check:

sudo nmcli device

Returned the following:

DEVICE      TYPE      STATE      CONNECTION 
virbr0      bridge    unmanaged  --         
ens33       ethernet  unmanaged  --         
lo          loopback  unmanaged  --         
virbr0-nic  tun       unmanaged  --

In a working instance, it should return:

DEVICE      TYPE      STATE      CONNECTION 
ens33       ethernet  connected  ens33      
virbr0      bridge    connected  virbr0     
lo          loopback  unmanaged  --         
virbr0-nic  tun       unmanaged  --

I’m currently troubleshooting what failed by leveraging an article on How to Configure Network Connection Using ‘nmcli’ Tool and the Gnome nmcli documentation. Naturally, when I get it fixed, I’ll finish this article.

If you’ve worked with the Oracle database a while, you probably noticed that some utilities write to stdout for both standard output and what should be standard error (stderr). One of those commands is the tnsping utility.

You can wrap the tnsping command to send the TNS-03505 error to stdout with the following code. I put Bash functions like these in a library.sh script, which I can source when automating tasks.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16

#!/usr/bin/bash
 
tnsping()
{
  if [ ! -z ${1} ]; then
    # Set default return value.
    stdout=`$ORACLE_HOME/bin/tnsping ${1} | tail -1`
 
    # Check stdout to return 0 for success and 1 for failure.
    if [[ `echo ${stdout} | cut -c1-9` = 'TNS-03505' ]]; then
      python -c 'import os, sys; arg = sys.argv[1]; os.write(2,arg + "\n")' "${stdout}"
    else
      echo "${1}"
    fi
  fi
}

You should notice that the script uses a Python call to redirect the error message to standard out (stdout) but you can redirect in Bash shell with the following:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16

#!/usr/bin/bash
 
tnsping()
{
  if [ ! -z ${1} ]; then
    # Set default return value.
    stdout=`$ORACLE_HOME/bin/tnsping ${1} | tail -1`
 
    # Check stdout to return 0 for success and 1 for failure.
    if [[ `echo ${stdout} | cut -c1-9` = 'TNS-03505' ]]; then
      echo ${stdout} 1>&2
    else
      echo "${1}"
    fi
  fi
}

Interactively, we can now test a non-existent service name like wrong with this syntax:

tnsping wrong

It’ll print the standard error to console, like:

TNS-03505: Failed to resolve name

or, you can suppress standard error (stderr) by redirecting it to the traditional black hole, like:

tnsping wrong 2>/dev/null

After redirecting standard error (stderr), you simply receive nothing back. That lets you evaluate in another script whether or not the utility raises an error.

In an automating Bash shell script, you use the source command to put the Bash function in scope, like this:

source library.sh

As always, I hope this helps those looking for a solution.

I want to add the MEAN (MongoDB, Express.js, Angular.js, and Node.js) stack to my backend server development course. This post documents the installation and configuration of components on Fedora 30.

The first step requires installing the Node package. The Node package also contains the Node package manager (npm). You install the Node packages as the root user or as a sudoer user with the following command.

yum install -y npm

It should produce the following installation log:

Last metadata expiration check: 1:10:42 ago on Wed 08 Jul 2020 06:57:52 PM MDT.
Dependencies resolved.
================================================================================================================================
 Package                         Architecture          Version                                     Repository              Size
================================================================================================================================
Installing:
 npm                             x86_64                1:6.13.4-1.10.19.0.1.fc30                   updates                3.8 M
Installing dependencies:
 nodejs                          x86_64                1:10.19.0-1.fc30                            updates                 88 k
 nodejs-libs                     x86_64                1:10.19.0-1.fc30                            updates                9.1 M
Installing weak dependencies:
 nodejs-full-i18n                x86_64                1:10.19.0-1.fc30                            updates                7.3 M
 
Transaction Summary
================================================================================================================================
Install  4 Packages
 
Total download size: 20 M
Installed size: 91 M
Downloading Packages:
(1/4): nodejs-10.19.0-1.fc30.x86_64.rpm                                                         173 kB/s |  88 kB     00:00    
(2/4): nodejs-full-i18n-10.19.0-1.fc30.x86_64.rpm                                               2.8 MB/s | 7.3 MB     00:02    
(3/4): nodejs-libs-10.19.0-1.fc30.x86_64.rpm                                                    2.7 MB/s | 9.1 MB     00:03    
(4/4): npm-6.13.4-1.10.19.0.1.fc30.x86_64.rpm                                                   1.3 MB/s | 3.8 MB     00:02    
--------------------------------------------------------------------------------------------------------------------------------
Total                                                                                           4.9 MB/s |  20 MB     00:04     
Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transaction
  Running scriptlet: npm-1:6.13.4-1.10.19.0.1.fc30.x86_64                                                                   1/1 
  Preparing        :                                                                                                        1/1 
  Installing       : nodejs-libs-1:10.19.0-1.fc30.x86_64                                                                    1/4 
  Installing       : nodejs-full-i18n-1:10.19.0-1.fc30.x86_64                                                               2/4 
  Installing       : npm-1:6.13.4-1.10.19.0.1.fc30.x86_64                                                                   3/4 
  Installing       : nodejs-1:10.19.0-1.fc30.x86_64                                                                         4/4 
  Running scriptlet: nodejs-1:10.19.0-1.fc30.x86_64                                                                         4/4 
  Verifying        : nodejs-1:10.19.0-1.fc30.x86_64                                                                         1/4 
  Verifying        : nodejs-full-i18n-1:10.19.0-1.fc30.x86_64                                                               2/4 
  Verifying        : nodejs-libs-1:10.19.0-1.fc30.x86_64                                                                    3/4 
  Verifying        : npm-1:6.13.4-1.10.19.0.1.fc30.x86_64                                                                   4/4 
 
Installed:
  nodejs-1:10.19.0-1.fc30.x86_64           nodejs-full-i18n-1:10.19.0-1.fc30.x86_64     nodejs-libs-1:10.19.0-1.fc30.x86_64    
  npm-1:6.13.4-1.10.19.0.1.fc30.x86_64    
 
Complete!

After installing the Node package, you should use the Node package manager (npm) to install the Node Monitor nodemon. nodemon is a popular utility that automatically lets you restart Node programs when you make changes to the source code.

While npm is installed as part of the Node package, you must use npm to install the Node Monitor. The following command installs the nodemon globally on your Fedora system. The -g flag lets you install it globally, which is important when you manage package.json files.

npm install -g nodemon

You install nodemon globally but most of your web app or project files will be installed locally. Node is a different paradigm than building an Apache or IIS web application because Node provides a framework for you to build a web server.

Here’s a quick Hello World! example that I borrowed a JavaScript helloworld.js file from an excellent Web Development with Node & Express: Leveraging the JavaScript Stack by Ethan Brown. For those who haven’t worked with JavaScript in years, semicolons are optional now.

/* Construct a web server. */
const http = require('http')
const port = process.env.PORT || 3000
 
const server = http.createServer((req, res) => {
  res.writeHead(200, { 'Content-Type': 'text/plain' })
  res.end('Hello world!')
})
 
server.listen(port, () => console.log(`server started on port ${port}); ` +
                                      'press Ctrl-C to terminate...'))

I put this in /var/www/html/node directory, which is owned by the superuser, root. You need to start the server before accessing it from a browser. You can start the program with the following syntax as a privileged user:

node /var/www/html/node/helloworld.js

Then, you can use the localhost to access it with the following URL:

http://localhost:3000

It will display the following:

Next, you need to use the Node Package Manager (npm) to install the Express.js packages. You do that with the following syntax:

npm install -g express express-generator

It should produce a console out put like the following:

npm WARN deprecated mkdirp@0.5.1: Legacy versions of mkdirp are no longer supported. Please update to mkdirp 1.x. (Note that the API surface has changed to use Promises in 1.x.)
/usr/local/bin/express -> /usr/local/lib/node_modules/express-generator/bin/express-cli.js
+ express@4.17.1
+ express-generator@4.16.1
added 60 packages from 42 contributors in 4.798s

After you install all the packages, you can inspect them with the following command. The packages are found in the /usr/local/lib/node_modules/express directory. The listing is generated from the package.json file on Fedora and Ubuntu Linux.

npm list -g

It should display something like this:

/usr/local/lib
├─┬ express@4.17.1
│ ├─┬ accepts@1.3.7
│ │ ├─┬ mime-types@2.1.27
│ │ │ └── mime-db@1.44.0
│ │ └── negotiator@0.6.2
│ ├── array-flatten@1.1.1
│ ├─┬ body-parser@1.19.0
│ │ ├── bytes@3.1.0
│ │ ├── content-type@1.0.4 deduped
│ │ ├── debug@2.6.9 deduped
│ │ ├── depd@1.1.2 deduped
│ │ ├─┬ http-errors@1.7.2
│ │ │ ├── depd@1.1.2 deduped
│ │ │ ├── inherits@2.0.3
│ │ │ ├── setprototypeof@1.1.1 deduped
│ │ │ ├── statuses@1.5.0 deduped
│ │ │ └── toidentifier@1.0.0
│ │ ├─┬ iconv-lite@0.4.24
│ │ │ └── safer-buffer@2.1.2
│ │ ├── on-finished@2.3.0 deduped
│ │ ├── qs@6.7.0 deduped
│ │ ├─┬ raw-body@2.4.0
│ │ │ ├── bytes@3.1.0 deduped
│ │ │ ├── http-errors@1.7.2 deduped
│ │ │ ├── iconv-lite@0.4.24 deduped
│ │ │ └── unpipe@1.0.0 deduped
│ │ └── type-is@1.6.18 deduped
│ ├─┬ content-disposition@0.5.3
│ │ └── safe-buffer@5.1.2 deduped
│ ├── content-type@1.0.4
│ ├── cookie@0.4.0
│ ├── cookie-signature@1.0.6
│ ├─┬ debug@2.6.9
│ │ └── ms@2.0.0
│ ├── depd@1.1.2
│ ├── encodeurl@1.0.2
│ ├── escape-html@1.0.3
│ ├── etag@1.8.1
│ ├─┬ finalhandler@1.1.2
│ │ ├── debug@2.6.9 deduped
│ │ ├── encodeurl@1.0.2 deduped
│ │ ├── escape-html@1.0.3 deduped
│ │ ├── on-finished@2.3.0 deduped
│ │ ├── parseurl@1.3.3 deduped
│ │ ├── statuses@1.5.0 deduped
│ │ └── unpipe@1.0.0
│ ├── fresh@0.5.2
│ ├── merge-descriptors@1.0.1
│ ├── methods@1.1.2
│ ├─┬ on-finished@2.3.0
│ │ └── ee-first@1.1.1
│ ├── parseurl@1.3.3
│ ├── path-to-regexp@0.1.7
│ ├─┬ proxy-addr@2.0.6
│ │ ├── forwarded@0.1.2
│ │ └── ipaddr.js@1.9.1
│ ├── qs@6.7.0
│ ├── range-parser@1.2.1
│ ├── safe-buffer@5.1.2
│ ├─┬ send@0.17.1
│ │ ├── debug@2.6.9 deduped
│ │ ├── depd@1.1.2 deduped
│ │ ├── destroy@1.0.4
│ │ ├── encodeurl@1.0.2 deduped
│ │ ├── escape-html@1.0.3 deduped
│ │ ├── etag@1.8.1 deduped
│ │ ├── fresh@0.5.2 deduped
│ │ ├── http-errors@1.7.2 deduped
│ │ ├── mime@1.6.0
│ │ ├── ms@2.1.1
│ │ ├── on-finished@2.3.0 deduped
│ │ ├── range-parser@1.2.1 deduped
│ │ └── statuses@1.5.0 deduped
│ ├─┬ serve-static@1.14.1
│ │ ├── encodeurl@1.0.2 deduped
│ │ ├── escape-html@1.0.3 deduped
│ │ ├── parseurl@1.3.3 deduped
│ │ └── send@0.17.1 deduped
│ ├── setprototypeof@1.1.1
│ ├── statuses@1.5.0
│ ├─┬ type-is@1.6.18
│ │ ├── media-typer@0.3.0
│ │ └── mime-types@2.1.27 deduped
│ ├── utils-merge@1.0.1
│ └── vary@1.1.2
└─┬ express-generator@4.16.1
  ├── commander@2.15.1
  ├── ejs@2.6.1
  ├─┬ minimatch@3.0.4
  │ └─┬ brace-expansion@1.1.11
  │   ├── balanced-match@1.0.0
  │   └── concat-map@0.0.1
  ├─┬ mkdirp@0.5.1
  │ └── minimist@0.0.8
  └── sorted-object@2.0.1

You can also create a secure node site (HTTPS) with the following additional steps. They include creating a self-signed secure public and private key. This creates the public key:

openssl genrsa -out key.pem

The openssl command will generate a private key key.pem file. It generates something like the following text message to console:

Generating RSA private key, 2048 bit long modulus (2 primes)
...........+++++
.............................................+++++
e is 65537 (0x010001)

Next, you need to generate a self-signed certificate. You do this in two steps.

1. Create a Distinguished Name (DN) file. The csr.pem file is the DN file. You need it to create a self-signed certificate:

   openssl req -new -key key.pem -out csr.pem

   openssl req -new -key key.pem -out csr.pem

   It will prompt you for values, like the following:

   You are about to be asked to enter information that will be incorporated into your certificate request. What you are about to enter is what is called a Distinguished Name or a DN. There are quite a few fields but you can leave some blank For some fields there will be a default value, If you enter '.', the field will be left blank. ----- Country Name (2 letter code) [XX]: State or Province Name (full name) []:MiddleEarth Locality Name (eg, city) [Default City]:Rivendell Organization Name (eg, company) [Default Company Ltd]:Fellowship Organizational Unit Name (eg, section) []:Self Common Name (eg, your name or your server's hostname) []:Localhost Email Address []:bilbo@loth.org   Please enter the following 'extra' attributes to be sent with your certificate request A challenge password []:friend An optional company name []:Bilbo

   You are about to be asked to enter information that will be incorporated into your certificate request. What you are about to enter is what is called a Distinguished Name or a DN. There are quite a few fields but you can leave some blank For some fields there will be a default value, If you enter '.', the field will be left blank. ----- Country Name (2 letter code) [XX]: State or Province Name (full name) []:MiddleEarth Locality Name (eg, city) [Default City]:Rivendell Organization Name (eg, company) [Default Company Ltd]:Fellowship Organizational Unit Name (eg, section) []:Self Common Name (eg, your name or your server's hostname) []:Localhost Email Address []:bilbo@loth.org Please enter the following 'extra' attributes to be sent with your certificate request A challenge password []:friend An optional company name []:Bilbo

2. Use the DN file to create your secure certificate. The following openssl command creates the certificate file by using your private key key.pem and DN csr.pem files.

   openssl x509 -req -days 9999 -in csr.pem -signkey key.pem -out cert.pem

   openssl x509 -req -days 9999 -in csr.pem -signkey key.pem -out cert.pem

   It should generate a Secure certificate cert.pem file and return something like the following to the console.

   Signature ok subject=C = XX, ST = MiddleEarth, L = Rivendell, O = Fellowship, OU = Self, CN = Localhost, emailAddress = bilbo@loth.org Getting Private key

   Signature ok subject=C = XX, ST = MiddleEarth, L = Rivendell, O = Fellowship, OU = Self, CN = Localhost, emailAddress = bilbo@loth.org Getting Private key

You can put these private key (key.pem) and certificate (cert.pem) files in an ssl subdirectory of the directory where you put the JavaScript program. The following creates a secure server page with the following code.

/* Construct a secure web server. */ 
const https = require('https') 
const fs = require('fs') 
const port = process.env.PORT || 3000 
 
const options = { 
 key: fs.readFileSync('ssl/key.pem'), 
 cert: fs.readFileSync('ssl/cert.pem') 
} 
 
const server = https.createServer((options, res) => { 
 res.writeHead(200, { 'Content-Type': 'text/plain' }) 
 res.end('Hello world!') 
}) 
 
server.listen(port, () => console.log(`server started on port ${port}); ` + 
                                     'press Ctrl-C to terminate...'))

If you try launch your browser using the localhost instead of a DNS or file resolved network name on the designated port, it will raise the following security error:

This site can't be reached
https's server IP address could not be found.
DNS_PROBE_FINISHED_NXDOMAIN

An alternate approach to writing a secure server includes using Express.js library. The syntax changes somewhat and you include two new libraries, as shown below:

/* Construct a secure web server. */ 
const https = require('https') 
const express = require('express') 
const fs = require('fs') 
const app = express() 
const port = process.env.PORT || 3001 
 
const options = { 
 key:  fs.readFileSync('ssl/key.pem'), 
 cert: fs.readFileSync('ssl/cert.pem') 
} 
 
https.createServer(options, app).listen(port, () => { 
 console.log(`Express started in ${app.get('env')} mode ` + 
             `on port + ${port}.`) 
})

This will fail with the following error message if you’re running it with a global installation unless you set the $NODE_PATH environment variable correctly. Without setting the variable you may get the following error message:

internal/modules/cjs/loader.js:638 
   throw err; 
   ^ 
 
Error: Cannot find module 'express' 
   at Function.Module._resolveFilename (internal/modules/cjs/loader.js:636:15) 
   at Function.Module._load (internal/modules/cjs/loader.js:562:25) 
   at Module.require (internal/modules/cjs/loader.js:692:17) 
   at require (internal/modules/cjs/helpers.js:25:18) 
   at Object.<anonymous> (/var/www/html/node/helloworldsecure.js:3:17) 
   at Module._compile (internal/modules/cjs/loader.js:778:30) 
   at Object.Module._extensions..js (internal/modules/cjs/loader.js:789:10) 
   at Module.load (internal/modules/cjs/loader.js:653:32) 
   at tryModuleLoad (internal/modules/cjs/loader.js:593:12) 
   at Function.Module._load (internal/modules/cjs/loader.js:585:3)

Sometimes they’ll advise you to do an individual user installation of Express.js to get past this error but that’s not necessary. You just need to set the $NODE_PATH environment variable as follows:

export NODE_PATH=/usr/local/lib/node_modules

This will enable the JavaScript to work without error and without a specific user installation. Assuming you name either of these programs as helloworldsecure.js, you run them with the following command:

node helloworldsecure.js

You can terminate the program with a Ctrl+c or if use the kill -15 pid command if you started it as a background process. You can find the process ID (pid) with the jobs command.

As always, I hope this is helpful to those starting out with this cool technology stack.

While teaching a class on the Linux Command-Line (CLI), the book gave an example of generating a list of random US telephone numbers into a file. The book uses the RANDOM function to generate segments of the telephone number, and then the grep command to identify malformed telephone numbers.

My students wanted me to explain why the numbers were malformed. I had to explain that the RANDOM function returns a random number between 1 and 99,999. The RANDOM function may return a 1 to 5 digit random number, which means you may get a 1-digit or 2-digit number when you request a 3-digit random number or a 1- to 3-digit number when you request a 4-digit random number.

The author’s example is:

for i in {1..10}; do
  echo "(${RANDOM:0:3}) ${RANDOM:0:3}-${RANDOM:0:4}" >> list.txt
done

They asked if there was a way to write a shell script that guaranteed random but well-formed US telephone numbers. I said yes, however, you need to write a recursive bash shell function and assign the result to a global variable set in the shell script.

They seemed doubtful, so I wrote it for them. Here’s the script if you’re interested in learning more about bash shell scripting. While I implemented it with an bash array, that’s optional.

#!/usr/bin/bash
 
# ============================================================
#  Name:   telephone.sh
#  Author: Michael McLaughlin
#  Date:   05-May-2020
# ------------------------------------------------------------
#  Purpose: Demonstrate how to generate random telehpone
#           numbers. The RANDOM function returns a random
#           number between 1 and 99999; and while you can
#           easily shave off a extra digit guarnteeing a
#           value above 100 is impossible without logic.
# ============================================================
 
targetLength()
{
  # Declare variable in function-level scope.
  randomString=''
 
  # Check the number of parameters to process.
  if [[ ${#} = 2 ]]; then
    # Assign value to function-level and local variables.
    randomString=${1}
    formatLength=${2}
 
    # Get the length of the telephone number as integer.
    length=`echo -n ${randomString} | wc -c`
 
    # Calculate any shortfall.
    short=$((${formatLength}-${length}))
 
    # Check if the telephone number is too short.
    if [[ ${short} > 0 ]]; then
      randomString=`echo "${randomString}${RANDOM:0:${short}}"`
    fi
  fi
 
  # Check if the combination of random numbers equals the target length
  # and assign the value to the global variable, or repeat processing
  # by making a recursive function call.
  if [[ `echo -n ${randomString} | wc -c` = ${formatLength} ]]; then
    result=${randomString}
  else
    targetLength ${randomString} ${formatLength}
  fi
}
 
# Declare global variable to support targetLength().
result=''
 
# Declare an array of strings.
declare -A telephone_parts
 
# Generate one hundred random telephone numbers.
for i in {1..100}; do
  # Create random three digit area code.
  targetLength ${RANDOM:0:3} 3
  telephone_parts[1]=${result}
 
  # Create random three digit prefix code.
  targetLength ${RANDOM:0:3} 3
  telephone_parts[2]=${result}
 
  # Create random four digit number code.
  targetLength ${RANDOM:0:4} 4
  telephone_parts[3]=${result}
 
  # Print the telephone numbers.
  echo "[${i}] (${telephone_parts[1]}) ${telephone_parts[2]}-${telephone_parts[3]}"
done

For reference, a recursive function call isn’t required here. It could be done more effectively with the following while loop:

targetLength()
{
  # Declare variable in function-level scope.
  randomString=''
  short=1
 
  # Check the number of parameters to process.
  if [[ ${#} = 2 ]]; then
    # Assign value to function-level and local variables.
    randomString=${1}
    formatLength=${2}
 
    # Check if the telephone number is too short.
    while [[ ${short} > 0 ]]; do
      # Get the length of the telephone number as integer.
      length=`echo -n ${randomString} | wc -c`
 
      # Calculate any shortfall.
      short=$((${formatLength}-${length}))
 
      # Assign new value to randomString.
      randomString=`echo "${randomString}${RANDOM:0:${short}}"`
    done
 
    # Assign randomString to global result variable.
    result=${randomString}
  fi
}

As always, I hope this helps those you want to learn or solve a problem.

The installation of MongoDB doesn’t do everything for you. In fact, the first time you start the mongod service, like this as the root user or sudoer user with the command:

service mongod start

A sudoer user will be prompted for their password, like

A typical MongoDB instance raises the following errors:

Redirecting to /bin/systemctl start mongod.service
[student@localhost cit425]$ mongo
MongoDB shell version v3.4.11
connecting to: mongodb://127.0.0.1:27017
MongoDB server version: 3.4.11
Server has startup warnings: 
2018-10-29T10:51:57.515-0600 I STORAGE  [initandlisten] 
2018-10-29T10:51:57.515-0600 I STORAGE  [initandlisten] ** WARNING: Using the XFS filesystem is strongly recommended with the WiredTiger storage engine
2018-10-29T10:51:57.515-0600 I STORAGE  [initandlisten] **          See http://dochub.mongodb.org/core/prodnotes-filesystem
2018-10-29T10:51:58.264-0600 I CONTROL  [initandlisten] 
2018-10-29T10:51:58.264-0600 I CONTROL  [initandlisten] ** WARNING: Access control is not enabled for the database.                                                                                               
2018-10-29T10:51:58.264-0600 I CONTROL  [initandlisten] **          Read and write access to data and configuration is unrestricted.                                                                              
2018-10-29T10:51:58.264-0600 I CONTROL  [initandlisten]                                                  
2018-10-29T10:51:58.265-0600 I CONTROL  [initandlisten]                                                  
2018-10-29T10:51:58.265-0600 I CONTROL  [initandlisten] ** WARNING: soft rlimits too low. rlimits set to 15580 processes, 64000 files. Number of processes should be at least 32000 : 0.5 times number of files.

You can fix this by following the MongoDB instructions for the Unix ulimit Settings, which will tell you to create a mongod file in the /etc/systemd/system directory. You should create this file as the root superuser. This is what you should put in the file:

[Unit]
Description=MongoDB
Documentation=man:mongo
 
[Service]
# Other directives omitted
# (file size)
LimitFSIZE=infinity
# (cpu time)
LimitCPU=infinity
# (virtual memory size)
LimitAS=infinity
# (locked-in-memory size)
LimitMEMLOCK=infinity
# (open files)
LimitNOFILE=64000
# (processes/threads)
LimitNPROC=64000

Then, you should be able to restart the mongod service without any warnings with this command:

service mongod restart

As always, I hope this helps somebody.

Just back from Oracle OpenWorld and somebody desperately wants to know how to disable the 5 minute default screen saver setting in the KDE environment. OK, you navigate to the Fedora “f” in the lower left hand corner and choose System Settings, like:

In the System Setting menu page, select Desktop Behavior:

In the Desktop Behavior dialog, select Screen Locking. Change the default to something large like 90 for 1 and half hours.

As always, I hope that solves your problem.