Archive for the ‘Linux’ Category
Node.js Routing
I liked the example used to explore basic routing in Chapter 2 of the Web Development with Node & Express book. I embellished the Node.js router example and static pages just a bit. The routing example requires you create a public subdirectory where you deploy the code and put the about.html, home.html, and 404.html files in the public subdirectory. Then, you must put a logo.png file in a tmp subdirectory inside of the public directory. The book assumes you know how to build these pages, which seems reasonable but just in case, here are the files I used to test the book’s example.
The about.html page:
<html> <head> <title>About Page</title> </head> <body> <p>A small sample Node.js routing example.</p> <p><img width="25" src="/img/logo.png" /> <sup><i>MEAN Stack Development</i></sup></p> </body> </html> |
The home.html page:
<html> <head> <title>Home Page</title> </head> <body> <p style="font-size:110%">Star Trek: The Original Series - Season 1</p> <p><img width="300" src="/img/StarTrekOriginal1.png" /></p> <p><img width="25" src="/img/logo.png" /> <sup><i>MEAN Stack Development</i></sup></p> </body> </html> |
The 404.html page:
<html> <head> <title>404 Error Message</title> </head> <body> <p>A 404 Error Message Page.</p> <p><img width="25" src="/img/logo.png" /> <sup><i>MEAN Stack Development</i></sup></p> </body> </html> |
The routing example sets the path to lowercase, which is important when you type the URL to verify physical files. For example, you need to use the routing startrekoriginal1.png string value in the URL. It will fail if you use the mixed case actual file name of the StarTrekOriginal1.png file. That’s because the routing maps the lowercase string to the physical file.
While the /public directory is the home directory of the virtual map as a rule, you can’t use it in the URL (as explained in next Chapter 3). Also, the router uses /img as a virtual directory which maps to the physical /tmp subdirectory. When you want to validate a physical image file you need to know these two rules. They explain why the following URL lets you verify a physical image file found in the /public/tmp directory.
localhost:3000/img/StarTrekOriginal1.png |
you will trigger the 404 Error page. Here’s the Node.js routing code:
/* Construct a web server. */ const http = require('http') const fs = require('fs') const port = process.env.PORT || 3000 /* Function uses the fs package to read files. */ function serveStaticFile(res, path, contentType, responseCode = 200) { fs.readFile(__dirname + path, (err, data) => { if (err) { res.writeHead(500, { 'Content-Type': 'text/plain' }) return res.end('500 - Internal Error') } res.writeHead(responseCode, { 'Content-Type': contentType }) res.end(data) }) } /* Create the Node.js server. */ const server = http.createServer((req, res) => { // Normalize URL by removing query string, optional // trailing slash, and making it lowercase. const path= req.url.replace(/\/?(?:\?.*)?$/,'').toLowerCase() switch(path) { case '': serveStaticFile(res, '/public/home.html', 'text/html' ) break case '/about': serveStaticFile(res, '/public/about.html', 'text/html' ) break case '/img/startrekoriginal1.png': serveStaticFile(res, '/public/tmp/StarTrekOriginal1.png', 'image/png' ) break case '/img/logo.png': serveStaticFile(res, '/public/tmp/logo.png', 'image/png' ) break default: serveStaticFile(res, '/public/404.html', 'text/html', 404 ) break } }) server.listen(port, () => console.log(`server started on port ${port}; ` + 'press Ctrl-C to terminate...')) |
Assuming you name the Node.js routing example helloworld3.js, you would start the router with the following command:
node helloworld3.js |
It should start the router. Enter the following URL:
http://localhost:3000 |
You should see a page rendered like the following:
As always, I hope this helps those trying to use this technology.
Node.js Fedora Install
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.
- Create a Distinguished Name (
DN) file. Thecsr.pemfile is theDNfile. You need it to create a self-signed certificate: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
- Use the DN file to create your secure certificate. The following
opensslcommand creates the certificate file by using your private keykey.pemandDNcsr.pemfiles.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
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 $NODE_PATH environment variable as follows:
export NODE_PATH=/usr/local/lib/node_modules |
This will enable the JavaScript to work without error and without a specific user installation. Assuming you name either of these programs as helloworldsecure.js, you run them with the following command:
node helloworldsecure.js |
You can terminate the program with a Ctrl+c or if use the kill -15 pid command if you started it as a background process. You can find the process ID (pid) with the jobs command.
As always, I hope this is helpful to those starting out with this cool technology stack.
Recursive bash function
While teaching a class on the Linux Command-Line (CLI), the book gave an example of generating a list of random US telephone numbers into a file. The book uses the RANDOM function to generate segments of the telephone number, and then the grep command to identify malformed telephone numbers.
My students wanted me to explain why the numbers were malformed. I had to explain that the RANDOM function returns a random number between 1 and 99,999. The RANDOM function may return a 1 to 5 digit random number, which means you may get a 1-digit or 2-digit number when you request a 3-digit random number or a 1- to 3-digit number when you request a 4-digit random number.
The author’s example is:
for i in {1..10}; do echo "(${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.
Wrap Oracle SQL*Plus
One of the key problems with Oracle’s deployment is that you can not use the up-arrow key to navigate the sqlplus command-line history. Here’s little Bash shell function that you can put in your .bashrc file. It requires you to have your system administrator install the rlwrap package, which wraps the sqlplus command-line history.
You should also set the $ORACLE_HOME environment variable before you put this function in your .bashrc file.
sqlplus () { # Discover the fully qualified program name. path=`which rlwrap 2>/dev/null` file='' # Parse the program name from the path. if [ -n ${path} ]; then file=${path##/*/} fi; # Wrap when there is a file and it is rewrap. if [ -n ${file} ] && [[ ${file} = "rlwrap" ]]; then rlwrap sqlplus "${@}" else echo "Command-line history unavailable: Install the rlwrap package." $ORACLE_HOME/bin/sqlplus "${@}" fi } |
If you port this shell script to an environment where rlwrap is not installed, it simply prints the error message and advises you to install the rlwrap package.
As always, I hope this helps those looking for a solution.
MySQL 8.0.20 JDBC
In April, when I updated from MySQL 8.0.17 to MySQL 8.0.19, I found that my Java connection example failed. That’s because of a change in the JDBC driver, which I blogged about then. Starting yesterday, I began updating a base Fedora 30 configuration again to MySQL 8.0.20. I wrote a testing program for the Java JDBC file last time, and when I ran it this time it told me that I didn’t have the JDBC driver installed, or in the $CLASSPATH. My Java diagnostic script, MySQLDriver.java, returned the following error message:
Error: Could not find or load main class MySQLDriver |
The Java JDBC test program code is in the prior post. It simply loads the user, password, database, host, and port statically for my student image, which you can update for your MySQL deployment.
You can find the MySQL 8.0 Connector/J installation in Chapter 4 of the MySQL Connector/J 8.0 Developer Guide. The link to page where you can download the Connector/J driver is in Chapter 4, but to save time you can click on the following download link. You’ll find Ubuntu, Debian, SUSE Enterprise Linux Server, Red Hat Enterprise Linux/Oracle Linux, Fedora, Platform Independent, and Source Code at that download link.
I downloaded Fedora 30, 31, and 32 because eventually they get deprecated and sometimes I need the deprecated versions. Since Python 2.7 is deprecated, keeping an old Fedora 30 with both Python 2.7 and 3.7 is very attractive as a developer, keeping these Java libraries is also a potential convenience. On the Fedora 30 platform, you should download:
mysql-connector-java-8.0.20-1.fc30.noarch.rpm |
You install the RPM package with the following syntax:
rpm -ivh mysql-connector-java-8.0.20-1.fc30.noarch.rpm |
It installs a single mysql-connector-java.jar file in the /usr/share/java directory. Then, you need to export the Java Archive file like so in your .bashrc file:
# Set the Java CLASSPATH path. export CLASSPATH=/usr/share/java/mysql-connector-java.jar:. |
Now, my MySQLDriver Java program returned:
Cannot connect to database server: The server time zone value 'MDT' is unrecognized or represents more than one time zone. You must configure either the server or JDBC driver (via the 'serverTimezone' configuration property) to use a more specifc time zone value if you want to utilize time zone support. |
As qualified in the prior post, it required me to add the following line to my /etc/my.cnf configuration file, which synchronizes the database’s timezone with the operating system.
# Synchronize the MySQL clock with the computer system clock. default-time-zone='+00:00' |
You need to restart the MySQL Daemon to apply the change, like:
sudo systemctl restart mysqld.service |
Then, running my MySQL Driver connection test program worked like a charm. It returns the following:
Database connection established MySQLDriver Version [8.0.20] Database connection terminated |
As always, I hope this helps those looking for a quick solution.
MySQL 8.0.20 Update
After I updated a Fedora 30 instance, I could no longer connect to the MySQL database. An attempt to connect raised the following error:
Error: Can't connect to local MySQL server through socket '/var/lib/mysql/mysql.sock' (2) |
My guess was correct, the mysqld.service got removed during the update (a synonym for upgrade). So, I ran the following command as a sudoer user:
sudo systemctl enable mysqld.service |
It creates the following symbolic link:
Created symlink /etc/systemd/system/multi-user.target.wants/mysqld.service → /usr/lib/systemd/system/mysqld.service. |
That would start the MySQL Daemon (mysqld) on the next restart of the OS. However, I didn’t want to restart to have access to the service. I simply started it with the following command:
sudo systemctl start mysqld.service |
Then, I could connect to the MySQL database. As always, I hope this helps those looking for a solution.
Fedora Exlixir Install
Having played around with Erlang some twelve years ago, I felt it was time to experiment with the Elixir programming language. The install on Fedora was straightforward with Dandified YUM. Naturally, you need to be the root user or a user found in the sudoer‘s list:
sudo dnf install -y elixir |
Display detailed console log →
The installation said to add it to the $PATH variable but on Fedora 30, a symbolic link of elixir is installed in the /usr/bin directory that points to /usr/share/elixir/1.9.0/bin/elixir shell script. Next, a version check, like this:
elixir --version |
it returned
Erlang/OTP 21 [erts-10.3.5.11] [source] [64-bit] [smp:1:1] [ds:1:1:10] [async-threads:1] [hipe] Elixir 1.9.0 (compiled with Erlang/OTP 21) |
Next, I created a little elixir test program, naturally after I glanced through the documentation for a Hello World program, like this hello.exs file:
IO.puts "Hello, Elixir World!" |
Then, I ran it as stand alone file with only read and write, read, and read privileges:
elixir hello.exs |
It returns:
Hello, Elixir World! |
Next, I tried to read the file from the file system in the iex interactive shell. I thought the example on the website was odd because it gave the impression that you were to call iex recursively but I discovered that’s not the case. You can only run it from the OS shell, and the file must have read, write, execute privileges for whomever calls it. Then, this syntax works from the Linux CLI interfaace:
iex -S hello.exs |
Then, you exit the shell by issuing a ^Z (CTRL+Z). If you try ^C, you’ll need to follow that with ^D, which I found in some notes. The ^Z is the normal kill signal for the current process, which appears the proper way to exit the iex interactive shell. Overall, the interactive shell is virtually useless except to validate small syntax examples.
MySQL Linux to Windows
My students want to transfer their course setup MySQL files from the Linux VM that I provide to Microsoft Windows 10. This post explains how because I found a couple small errors in the Google’d posts they would most likely see.
The first step is required because when I didn’t assign a name or domain to the the Fedora VM, which allows it to run as localhost on any student machine. In tandem, I didn’t assign a static IP address but opted for dynamic IP assignment. That means, the first step to securely copy the files requires you to find the assigned IP address. You can do that with the following Linux command:
ifconfig -a | grep 'inet[[:blank:]]' | head -1 | cut -c 14-30 |
It would return something like:
192.168.147.198 |
After you have discovered the IP address, you need to download PuTTy from their web site because includes the pscp (PuTTy Secure Copy) utility. I recommend you click on the MSI (Microsoft Installer Package) file, and install it on your Windows machine. As a rule, you should accept the default location, which is C:\Program Files\PuTTy.
While you could alter your system-level %PATH% environment variable after you install the software, I recommend you only include it in the %PATH% within the scope of a Command (cmd) shell. Navigate to your Windows Start and enter cmd in the search field. It should launch the Command Prompt terminal, which is a terminal emulator.
In the terminal editor, type the following case sensitive command to add the PuTTy directory to your path (yes, it’s case sensitive):
SET PATH=%PATH%;%ProgramFiles%\PuTTy |
Now, you can securely copy the files and directory structure from Linux to Windows with the following command (where you replace the traditional server name with the dynamically assigned IP address). You should also be in the target directory where you want the files and directories copied:
C:\Data\cit225>pscp -r student@192.168.147.198:/home/student/Data/cit225/mysql . |
After entering the password for the student on the Linux VM, you should see the following copy over:
Raiders2.png | 99 kB | 99.5 kB/s | ETA: 00:00:00 | 100% LordOfTheRings3.png | 119 kB | 119.8 kB/s | ETA: 00:00:00 | 100% HarryPotter4.png | 103 kB | 103.9 kB/s | ETA: 00:00:00 | 100% Raiders1.png | 92 kB | 92.4 kB/s | ETA: 00:00:00 | 100% Raiders3.png | 123 kB | 123.9 kB/s | ETA: 00:00:00 | 100% LordOfTheRings2.png | 111 kB | 111.7 kB/s | ETA: 00:00:00 | 100% LordOfTheRings1.png | 103 kB | 104.0 kB/s | ETA: 00:00:00 | 100% HarryPotter2.png | 118 kB | 118.7 kB/s | ETA: 00:00:00 | 100% HarryPotter7.png | 150 kB | 150.2 kB/s | ETA: 00:00:00 | 100% HarryPotter3.png | 106 kB | 106.1 kB/s | ETA: 00:00:00 | 100% HarryPotter5.png | 82 kB | 82.5 kB/s | ETA: 00:00:00 | 100% HarryPotter6.png | 129 kB | 129.9 kB/s | ETA: 00:00:00 | 100% HarryPotter1.png | 118 kB | 118.8 kB/s | ETA: 00:00:00 | 100% HarryPotter8.png | 150 kB | 150.9 kB/s | ETA: 00:00:00 | 100% HarryPotter8.txt | 8 kB | 8.5 kB/s | ETA: 00:00:00 | 100% HarryPotter3.txt | 5 kB | 5.8 kB/s | ETA: 00:00:00 | 100% HarryPotter5.txt | 7 kB | 7.9 kB/s | ETA: 00:00:00 | 100% HarryPotter1.txt | 6 kB | 6.6 kB/s | ETA: 00:00:00 | 100% HarryPotter2.txt | 7 kB | 7.8 kB/s | ETA: 00:00:00 | 100% Raiders3.txt | 5 kB | 5.6 kB/s | ETA: 00:00:00 | 100% HarryPotter4.txt | 7 kB | 7.5 kB/s | ETA: 00:00:00 | 100% HarryPotter7.txt | 5 kB | 5.4 kB/s | ETA: 00:00:00 | 100% HarryPotter6.txt | 7 kB | 7.4 kB/s | ETA: 00:00:00 | 100% LOTRFellowship.txt | 4 kB | 5.0 kB/s | ETA: 00:00:00 | 100% apply_store_base.sql | 1 kB | 1.6 kB/s | ETA: 00:00:00 | 100% query_membership.sql | 0 kB | 0.3 kB/s | ETA: 00:00:00 | 100% apply_mysql_lab1.sql | 1 kB | 1.9 kB/s | ETA: 00:00:00 | 100% configure_mysql_web.sql | 37 kB | 37.1 kB/s | ETA: 00:00:00 | 100% seed_mysql_store_ri2.sql | 58 kB | 58.5 kB/s | ETA: 00:00:00 | 100% cleanup_mysql_store.sql | 5 kB | 5.4 kB/s | ETA: 00:00:00 | 100% create_mysql_store_ri2.sq | 21 kB | 21.1 kB/s | ETA: 00:00:00 | 100% |
My students will need to repeat this step to transfer all of the sample PHP files that demonstrate web application patterns. They also need to inspect individual files to ensure any path referencing commands are manually converted to their new Windows equivalent.
They can move the physical files as the root superuser with the following pscp command provide you haven’t stored the files somewhere other than the default location:
C:\Data\temp>pscp -r root@192.168.147.198:/var/lib/mysql . |
As always, I hope this helps those trying to sort things out.
SQL Developer Error
It’s been a couple releases trying to fix the following error thrown by SQL Developer on Fedora 30 and shown as the following dialog:
When you click the Detail button it shows the following error stack:
java.lang.NoClassDefFoundError: javafx/embed/swing/JFXPanel at oracle.dbtools.raptor.javafx.ui.JFXPanelFactory.createJFXPanelImpl(JFXPanelFactory.java:58) at oracle.dbtools.raptor.javafx.ui.JFXPanelFactory.createJFXPanel(JFXPanelFactory.java:34) at oracle.dbtools.raptor.startpage.StartPageViewer.createGUIComponent(StartPageViewer.java:179) at oracle.dbtools.raptor.startpage.StartPageViewer.getEditorContent(StartPageViewer.java:136) at oracle.ide.editor.AsynchronousEditor$2.run(AsynchronousEditor.java:345) at oracle.ide.editor.AsynchronousEditor$5.run(AsynchronousEditor.java:555) at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1443) at org.netbeans.modules.openide.util.GlobalLookup.execute(GlobalLookup.java:68) at org.openide.util.lookup.Lookups.executeWith(Lookups.java:303) at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2058) Caused by: java.lang.ClassNotFoundException: javafx.embed.swing.JFXPanel cannot be found by oracle.sqldeveloper_19.2.0 at org.eclipse.osgi.internal.loader.BundleLoader.findClassInternal(BundleLoader.java:501) at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:421) at org.eclipse.osgi.internal.loader.BundleLoader.findClass(BundleLoader.java:412) at org.eclipse.osgi.internal.baseadaptor.DefaultClassLoader.loadClass(DefaultClassLoader.java:107) at org.netbeans.modules.netbinox.NetbinoxLoader.loadClass(NetbinoxLoader.java:81) at java.lang.ClassLoader.loadClass(ClassLoader.java:352) ... 10 more |
I thought applying the Open Java FX package might fix the problem. I installed the package like the following:
yum install -y openjfx |
The installation log:
Last metadata expiration check: 4:03:29 ago on Tue 21 Apr 2020 06:42:26 PM MDT. Dependencies resolved. ============================================================================================= Package Architecture Version Repository Size ============================================================================================= Installing: openjfx x86_64 8.0.202-8.b07.fc30 updates 8.8 M Transaction Summary ============================================================================================= Install 1 Package Total download size: 8.8 M Installed size: 11 M Downloading Packages: openjfx-8.0.202-8.b07.fc30.x86_64.rpm 2.5 MB/s | 8.8 MB 00:03 --------------------------------------------------------------------------------------------- Total 2.1 MB/s | 8.8 MB 00:04 Running transaction check Transaction check succeeded. Running transaction test Transaction test succeeded. Running transaction Preparing : 1/1 Installing : openjfx-8.0.202-8.b07.fc30.x86_64 1/1 Running scriptlet: openjfx-8.0.202-8.b07.fc30.x86_64 1/1 Verifying : openjfx-8.0.202-8.b07.fc30.x86_64 1/1 Installed: openjfx-8.0.202-8.b07.fc30.x86_64 Complete! |
After installing the software, I determined the new JAR files. Then, I added them to my $CLASSPATH environment variable, like:
export CLASSPATH=/usr/share/java/mysql-connector-java.jar:/usr/lib/jvm/openjfx/rt/lib/ext/fxrt.jar:/usr/lib/jvm/openjfx/rt/lib/jfxswt.jar:. |
While it appears to load faster with these JAR files, it still raises the same Dialog error. I simply have to continue to look for a complete fix.
Fedora 30 pgAdmin4 Install
Last September, the pgAdmin4 installation stymied me. I wasn’t sure what was I had done wrong in the installation but I was on a deadline to release my Fedora 30 Linux virtualization. That meant I had to move on and leave it for later. Today, I’m building the new image and returned to the task.
I installed pgadmin4 with the following command:
dnf -y install pgadmin4 |
The pgadmin4 configuration instructions can be found for several Linux versions at Josphat Mutai’s Computing for Geeks web page. On Fedora 30, you need to do the following:
- Install, start, and enable Apache as the
httpdservice unless you already have done that. - Copy the
/etc/httpd/conf.d/pgadmin4.conf.samplefile to/etc/httpd/conf.d/pgadmin4.conf, which is a new file. - Restart the
httpdservice to incorporate thepgadmin4configuration file.
After that, my instructions vary from the original web page because they didn’t work. You actually need to create four directories as the sudo or root user:
/var/lib/pgadmin4/var/lib/pgadmin4/sessions/var/lib/pgadmin4/storage/var/log/pgadmin4
You can make both directories with a single mkdir command, like:
mkdir -p /var/lib/pgadmin4 /var/lib/pgadmin4/sessions /var/lib/pgadmin4/storage /var/log/pgadmin4 |
As the root or sudo user, change the ownership of these two directories to the apache user with the following syntax:
chown -R apache:apache /var/lib/pgadmin4 /var/lib/pgadmin4/sessions /var/lib/pgadmin4/storage /var/log/pgadmin4 |
You add the following four statements to the config_distro.py file in the /usr/lib/python3.7/site-packages/pgadmin4-web directory as the root or sudo user:
LOG_FILE = '/var/log/pgadmin4/pgadmin4.log' SQLITE_PATH = '/var/lib/pgadmin4/pgadmin4.db' SESSION_DB_PATH = '/var/lib/pgadmin4/sessions' STORAGE_DIR = '/var/lib/pgadmin4/storage' |
You need to setup the pgadmin user with the following python3 command:
python3 /usr/lib/python3.7/site-packages/pgadmin4-web/setup.py |
Enter the following values, a real email address and a password twice:
NOTE: Configuring authentication for SERVER mode. Enter the email address and password to use for the initial pgAdmin user account: Email address: admin@example.com Password: your_password Retype password: your_password pgAdmin 4 - Application Initialisation ====================================== |
Before you move on, you should check ownership of the pgadmin4 directories in the /var/lib and /var/log directories and their files by long listing them as follows:
- Check the
/var/libdirectory:ll /var/lib/pgadmin4
It should display:
total 148 -rw-r--r--. 1 root root 1296 Apr 11 12:12 my-httpd.pp -rw-r--r--. 1 root root 332 Apr 11 12:12 my-httpd.te -rw-------. 1 apache apache 131072 Apr 11 12:16 pgadmin4.db drwx------. 2 apache apache 4096 Apr 11 12:15 sessions drwxr-xr-x. 2 apache apache 4096 Apr 10 17:33 storage
- Check the
/var/logdirectory:ll /var/log/pgadmin4
It should display:
total 4 -rw-r--r--. 1 apache apache 1174 Apr 11 12:15 pgadmin4.log
Assuming you have an enabled firewall, you need to issue the following two commands as the root or sudo user:
firewall-cmd --permanent --add-service=http firewall-cmd --reload |
You invoke pgAdmin4 from within a browser window with the following URL for a stand alone workstation (for a workstation on a DNS network you would enter pgadmin.domain.domain_type in lieu of localhost):
pgadmin/localhost/pgadmin4 |
You most likely will encounter an Internal Server Error, the recommended fix is reputed to be:
ausearch -c 'httpd' --raw | audit2allow -M my-httpd semodule -i my-httpd.pp |
After completing the installation, you should be able to run pgadmin4, by typing in the following URL into a web browser:
http://localhost/pgadmin4 |
You should see the pgAmin4 web page if everything works. If it fails to launch, you should check the Apache error log. The error_log file is found in the /var/log/httpd directory. This is a type of error you may get if the ownership privileges aren’t assigned to the apache user and apache group.
Display sample log →
[Sat Apr 11 12:06:25.433570 2020] [wsgi:error] [pid 16086:tid 139914869880576] [remote ::1:39136] mod_wsgi (pid=16086): Failed to exec Python script file '/usr/lib/python3.7/site-packages/pgadmin4-web/pgAdmin4.wsgi'. [Sat Apr 11 12:06:25.433611 2020] [wsgi:error] [pid 16086:tid 139914869880576] [remote ::1:39136] mod_wsgi (pid=16086): Exception occurred processing WSGI script '/usr/lib/python3.7/site-packages/pgadmin4-web/pgAdmin4.wsgi'. [Sat Apr 11 12:06:25.433720 2020] [wsgi:error] [pid 16086:tid 139914869880576] [remote ::1:39136] Traceback (most recent call last): [Sat Apr 11 12:06:25.433741 2020] [wsgi:error] [pid 16086:tid 139914869880576] [remote ::1:39136] File "/usr/lib/python3.7/site-packages/pgadmin4-web/pgAdmin4.wsgi", line 36, in <module> [Sat Apr 11 12:06:25.433745 2020] [wsgi:error] [pid 16086:tid 139914869880576] [remote ::1:39136] from pgAdmin4 import app as application [Sat Apr 11 12:06:25.433749 2020] [wsgi:error] [pid 16086:tid 139914869880576] [remote ::1:39136] File "/usr/lib/python3.7/site-packages/pgadmin4-web/pgAdmin4.py", line 109, in <module> [Sat Apr 11 12:06:25.433752 2020] [wsgi:error] [pid 16086:tid 139914869880576] [remote ::1:39136] app = create_app() [Sat Apr 11 12:06:25.433756 2020] [wsgi:error] [pid 16086:tid 139914869880576] [remote ::1:39136] File "/usr/lib/python3.7/site-packages/pgadmin4-web/pgadmin/__init__.py", line 345, in create_app [Sat Apr 11 12:06:25.433759 2020] [wsgi:error] [pid 16086:tid 139914869880576] [remote ::1:39136] os.chmod(config.SQLITE_PATH, 0o600) [Sat Apr 11 12:06:25.433768 2020] [wsgi:error] [pid 16086:tid 139914869880576] [remote ::1:39136] PermissionError: [Errno 13] Permission denied: '/var/lib/pgadmin4/pgadmin4.db' [Sat Apr 11 12:06:28.234643 2020] [wsgi:error] [pid 16086:tid 139914945414912] [remote ::1:39138] mod_wsgi (pid=16086): Failed to exec Python script file '/usr/lib/python3.7/site-packages/pgadmin4-web/pgAdmin4.wsgi'. [Sat Apr 11 12:06:28.234694 2020] [wsgi:error] [pid 16086:tid 139914945414912] [remote ::1:39138] mod_wsgi (pid=16086): Exception occurred processing WSGI script '/usr/lib/python3.7/site-packages/pgadmin4-web/pgAdmin4.wsgi'. [Sat Apr 11 12:06:28.234781 2020] [wsgi:error] [pid 16086:tid 139914945414912] [remote ::1:39138] Traceback (most recent call last): [Sat Apr 11 12:06:28.234816 2020] [wsgi:error] [pid 16086:tid 139914945414912] [remote ::1:39138] File "/usr/lib/python3.7/site-packages/pgadmin4-web/pgAdmin4.wsgi", line 36, in <module> [Sat Apr 11 12:06:28.234820 2020] [wsgi:error] [pid 16086:tid 139914945414912] [remote ::1:39138] from pgAdmin4 import app as application [Sat Apr 11 12:06:28.234824 2020] [wsgi:error] [pid 16086:tid 139914945414912] [remote ::1:39138] File "/usr/lib/python3.7/site-packages/pgadmin4-web/pgAdmin4.py", line 109, in <module> [Sat Apr 11 12:06:28.234826 2020] [wsgi:error] [pid 16086:tid 139914945414912] [remote ::1:39138] app = create_app() [Sat Apr 11 12:06:28.234830 2020] [wsgi:error] [pid 16086:tid 139914945414912] [remote ::1:39138] File "/usr/lib/python3.7/site-packages/pgadmin4-web/pgadmin/__init__.py", line 345, in create_app [Sat Apr 11 12:06:28.234832 2020] [wsgi:error] [pid 16086:tid 139914945414912] [remote ::1:39138] os.chmod(config.SQLITE_PATH, 0o600) [Sat Apr 11 12:06:28.234841 2020] [wsgi:error] [pid 16086:tid 139914945414912] [remote ::1:39138] PermissionError: [Errno 13] Permission denied: '/var/lib/pgadmin4/pgadmin4.db' |
As always, I hope my notes are helpful to those who want to work with pgadmin4 and the PostgreSQL database.
Subscribe via RSS