MacLochlainns Weblog

Michael McLaughlin's Technical Blog

Site Admin

Archive for the ‘Ubuntu’ Category

Ubuntu, Perl & MySQL

without comments

Configuring Perl to work with MySQL is straight forward. While Perl is installed generally, you may need to install the libdbd-mysql-perl library.

You install it as a sudoer user with this syntax:

sudo apt install -y libdbd-mysql-perl

You can find the Perl version with the following version.pl program:

1
2
3
4
#!/usr/bin/perl -w
 
# Print the version.
print "Perl ".$]."\n";

The first line lets you call the program without prefacing the program name with perl. The first line invokes a subshell of perl by default. You just need to ensure the file has read and execute privileges to run by using the

chmod 755 version.pl

You call it with this:

./version.pl

It prints:

Perl 5.034000

The following static_query.pl Perl program uses the Perl DBI library to query and return a data set based on a static query.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
#!/usr/bin/perl -w
 
# Use the DBI library.
use DBI;
use strict;
use warnings;
 
# Create a connection.
my $dbh = DBI->connect("DBI:mysql:database=studentdb;host=localhost:3306"
                      ,"student","student",{'RaiseError' => 1});
 
# Create SQL statement.
my $sql = "SELECT i.item_title
           ,      ra.rating
           ,      cl.common_lookup_meaning
           FROM   item i INNER JOIN common_lookup cl
           ON     i.item_type = cl.common_lookup_id INNER JOIN rating_agency ra
           ON     i.item_rating_id = ra.rating_agency_id
           WHERE  i.item_title LIKE 'Harry%'
           AND    cl.common_lookup_type = 'BLU-RAY'";
 
# Prepare SQL statement.
my $sth = $dbh->prepare($sql);
 
# Execute statement and read result set.
$sth->execute() or die $DBI::errstr;
 
# Read through returned rows, assign elements explicitly to match SELECT-list.
while (my @row = $sth->fetchrow_array()) {
  my $item_title = $row[0];
  my $rating = $row[1];
  my $lookup_meaning = $row[2];
  print "$item_title, $rating, $lookup_meaning\n";
}
 
# Close resources.
$sth->finish();

It returns the following rows from the sample database:

Harry Potter and the Sorcerer's Stone, PG, Blu-ray
Harry Potter and the Chamber of Secrets, PG, Blu-ray
Harry Potter and the Prisoner of Azkaban, PG, Blu-ray
Harry Potter and the Goblet of Fire, PG-13, Blu-ray

The following dynamic_query.pl Perl program uses the Perl DBI library to prepare a query, bind a local variable into the query, and return a data set based on a dynamic query.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
#!/usr/bin/perl -w
 
# Use the DBI library.
use DBI;
use strict;
use warnings;
 
# Mimic a function parameter by using a local variable.
my $item_title_in = 'Star';
 
# Create a connection.
my $dbh = DBI->connect("DBI:mysql:database=studentdb;host=localhost:3306"
                      ,"student","student",{'RaiseError' => 1});
 
# Create SQL statement.
my $sql = "SELECT i.item_title
           ,      ra.rating
           ,      cl.common_lookup_meaning
           FROM   item i INNER JOIN common_lookup cl
           ON     i.item_type = cl.common_lookup_id INNER JOIN rating_agency ra
           ON     i.item_rating_id = ra.rating_agency_id
           WHERE  i.item_title LIKE CONCAT(?,'%')
           AND    cl.common_lookup_type = 'BLU-RAY'";
 
# Prepare SQL statement.
my $sth = $dbh->prepare($sql);
 
# Bind a variable to first parameter in the query string.
$sth->bind_param(1, $item_title_in);
 
# Execute statement and read result set.
$sth->execute() or die $DBI::errstr;
 
# Read through returned rows, assign elements explicitly to match SELECT-list.
while (my @row = $sth->fetchrow_array()) {
  my $item_title = $row[0];
  my $rating = $row[1];
  my $lookup_meaning = $row[2];
  print "$item_title, $rating, $lookup_meaning\n";
}
 
# Close resources.
$sth->finish();

It returns the following rows from the sample database:

Star Wars II, PG, Blu-ray

You can replace lines 34 through 40 with the following to read any number of columns into a comma-delimited row return:

34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
# Read through returned rows, assign elements explicitly to match SELECT-list.
while (my @row = $sth->fetchrow_array()) {
 
  # Read through a dynamic column list for column separated display.
  my $result = '';
  foreach(@row) {
    if (length($result) == 0) {
      $result = $_; }
    else {
      $result .= ", " . $_; }
  } 
 
  # Print comma-separted values by row.
  print $result . "\n"
}

It returns the following rows from the sample database:

Star Wars II, PG, Blu-ray

As always, I hope this helps the reader solve a problem.

Written by maclochlainn

January 8th, 2024 at 10:37 pm

Oracle 23c Free SQL*Plus

without comments

It’s always frustrated me when using the sqlplus command-line interface (CLI) that you can’t just “up arrow” to through the history. At least, that’s the default case unless you wrap the sqlplus executable.

I like to do my development work as close to the database as possible. The delay from SQL Developer to the database or VSCode to the database is just too long. Therefore, I like the native sqlplus to be as efficient as possible. This post shows you how to install the rlwarp utility to wrap sqlplus and create a sandboxed student user for a local development account inside the Oracle 23c Free container. You should note that the Docker or Podman Container is using Oracle Unbreakable Linux 8 as it’s native OS.

You can connect to your Docker version of Oracle Database 23c Free with the following command:

docker exec -it -u root oracle23c bash

You can’t just use dnf to install rlwrap and get it to magically install all the dependencies. That would be too easy, eh?

Attempting to do so will lock your base OS and eventually force you to kill with prejudice the hung dnf process (at least it forced me to do so). You need to determine the rlwrap dependencies and then install them first. In that process, I noticed that the which utility program wasn’t installed in the container.

Naturally, I installed the which utility first with this command:

dnf install -y which

The rlwrap dependencies are: glibc, ncurses, perl, readline, python, and git. Only the perl, python, and git are missing from the list of formal dependencies but there’s another dependency the epel-release package.

If you want to verify whether a package is installed, you can use the rpm command like this:

rpm -qa | grep package_name

I installed the perl programming environment (a big install) with this command:

dnf install -y perl

I installed the python3 with this command:

dnf install -y python3

I installed the git module with this command:

dnf install -y git

I installed the epel-release container with this command:

dnf install -y epel-release

After installing all of these, you’re now ready to install the core rlwrap utility program. Like the other installations, you use:

dnf install -y rlwrap

At this point, you need to create a sandboxed user account for the Docker instance because as a developer using the root user for simple tasks is a bad idea. While you could do this with a Docker command, the Oracle 23c Free edition raised a lock on the /etc/group file when I tried it. Naturally, that’s not a problem because you can connect as the root user with this syntax:

docker exec -it -u root oracle23c bash

As the root user, create a student account as a developer account in the Oracle 23c Free container:

useradd -u 501 -g dba -G users -d /home/student -s /bin/bash/ -c "Student" -n student

You’ll be unable to leverage the tnsnames.ora file unless you alter the prior command to replace dba with oinstall or add the following command:

usermod -a -G oinstall student

Exit the Oracle 23c Free container as the root user and reconnect as the student user with this syntax:

docker exec -it --user student oracle23c bash

While you’re connected as the root user, you should create an upload directory as a subdirectory of the $ORACLE_BASE directory. The $ORACLE_BASE directory in the Oracle Database 23c Free Docker image is the /opt/oracle directory.

You should use the following syntax to create the upload directory and change its permission to that of the Oracle Database 23c Free installation (for a future blog post on developing external table deployment on the Docker image):

mkdir /opt/oracle
chown -R oracle:install /opt/oracle/upload

You also can add the following student function to the Ubuntu student user’s .bashrc file. It means all you need to type to connect to the Oracle Database 23c Free Docker instance is “student“. I like shortcuts like this one, which let you leverage one-line Python commands.

student () 
{
    # Discover the fully qualified program name. 
    path=`which docker 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} = "docker" ]]; then
        python -c "import subprocess; subprocess.run(['docker exec -it --user student oracle23c bash'], shell=True)" 
    else
        echo "Docker is unavailable: Install the docker package."
    fi
}

Open a Ubuntu Terminal shell and type a student function name to connect to the Docker Oracle Database 23c Free instance where you can now test things like external tables with the SQL*Plus command line without installing it on the Ubuntu local operating system.

student@student-virtual-machine:~$ student
[student@d28375f0c43f ~]$ sqlplus c##student/student@free
 
SQL*Plus: Release 23.0.0.0.0 - Production on Wed Jan 3 02:14:22 2024
Version 23.3.0.23.09
 
Copyright (c) 1982, 2023, Oracle.  All rights reserved.
 
Last Successful login time: Wed Jan 03 2024 01:56:44 +00:00
 
Connected to:
Oracle Database 23c Free Release 23.0.0.0.0 - Develop, Learn, and Run for Free
Version 23.3.0.23.09
 
SQL>

Then, I added this sqlplus function to the /home/student/.bashrc file, which is owned by the student user. However, I also added the instruction to change to the student user’s home directory because the Oracle 23c Free container will connect you to the /home/oracle directory by default. I also added the default long list (ll) alias to the .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
}
 
# Change to the user's home directory.
cd ${HOME}
 
# Create a long list alias:
alias ll='ls -l --color=auto'

After you’ve configured your student user, you can configure the oracle user account to work like a regular server. Exit the Docker Oracle Database 23c Free as the student user, then connect as the root user with this command:

docker exec -it -u root oracle23c bash

As the root user you can become the oracle user with the following command:

su - oracle

Now, add the following .bashrc shell in the /home/oracle directory:

# The oracle user's .bashrc
 
# Source global definitions
if [ -f /etc/bashrc ]; then
	. /etc/bashrc
fi
 
# User specific environment
if ! [[ "$PATH" =~ "$HOME/.local/bin:$HOME/bin:" ]]
then
    PATH="$HOME/.local/bin:$HOME/bin:$PATH"
fi
export PATH
 
# Uncomment the following line if you don't like systemctl's auto-paging feature:
# export SYSTEMD_PAGER=
 
# User specific aliases and functions
export ORACLE_SID=FREE
export ORACLE_BASE=/opt/oracle
export ORACLE_HOME=/opt/oracle/product/23c/dbhomeFree
export PATH=$PATH:/$ORACLE_HOME/bin
 
# Change to the user's home directory.
cd ${HOME}
 
# Create a long list alias:
alias ll='ls -l --color=auto'
 
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
}

You need to manually source the .bashrc for the oracle user because it’s not an externally available user. Use this syntax to connect as the internal user:

sqlplus / as sysdba

It’ll display:

SQL*Plus: RELEASE 23.0.0.0.0 - Production ON Wed Jan 3 07:08:11 2024
Version 23.3.0.23.09
 
Copyright (c) 1982, 2023, Oracle.  ALL rights reserved.
 
 
Connected TO:
Oracle DATABASE 23c Free RELEASE 23.0.0.0.0 - Develop, Learn, AND Run FOR Free
Version 23.3.0.23.09
 
SQL>

After all this, I can now click the “up arrow” to edit any of the sqlplus command history. If you like to work inside sqlplus natively, this should help you.

Written by maclochlainn

December 20th, 2023 at 11:11 pm

Ubuntu DaaS VM

without comments

Completed the build of my new Ubuntu Virtual Machine (VM) with Oracle 23c installed in a Docker instance, and MySQL and PostgreSQL installed locally. The VM image also provides a LAMP stack with Apache2, PHP 8.1 with MySQLi and PDO modules. Since the original post, I’ve added a number of items to support our program courses and the Data Science degrees.

There are lots of tricks and techniques in the blog associated with creating the build. I took the background photograph of Chapel Bridge early on Sunday morning August 30, 1987 in Lucerne Switzerland (with a Canon A1 and ASA 64 slide film that subsequently digitized well).

Next step: roll it out into an AWS image for the students to use for their courses.

Related blog posts:

As always, I hope the post and information helps others.

Written by maclochlainn

December 13th, 2023 at 1:15 am

Apache2 on Ubuntu

without comments

It’s always interesting when I build new instances. Ubuntu 22.0.4 was no different but I ran into an issue with installing Apache2 and eventually loading the mysqli module.

The Apache2 error was an issue with an unsupported module or hidden prerequisite. The MySQLi required an Apache reload after installation. Contrary to some erroneous posts the mysqli driver is supported on PHP 8.1.

Apache2 installation starts first and the mysqli module reload and verification script follows. On Ubuntu, you install Apache2 if you’re unaware of the hidden pre-requisite, otherwise install the pre-requisite first and avoid the error.

This is the command to install the apache2 module:

sudo apt-get install -y apache2

It generated the following error message:

apache2: Syntax error on line 146 of /etc/apache2/apache2.conf: Syntax error on line 1 of /etc/apache2/mods-enabled/wsgi.load: Cannot load /usr/lib/apache2/modules/mod_wsgi.so into server: /usr/lib/apache2/modules/mod_wsgi.so: cannot open shared object file: No such file or directory
Action 'start' failed.
The Apache error log may have more information.

Line 146 in the /etc/apache2/apache2.conf file contains the instruction to load modules. The error says it can’t find the mod_wsgi.so library, which was originally part of the deprecated Python 2.7 release.

IncludeOptional mods-enabled/*.load

The first step I pursued was finding the missing library, which appeared to be in the libapache2-mod-wsgi package. However, it became clear there is no installation candidate for that module, which supported Python 3.x. A little more research led me to find the appropriate library version for Python 3, which is found in the libapache2-mod-wsgi-py3 package.

I installed the libapache2-mod-wsgi-py3 package with the following syntax:

sudo apt-get install -y libapache2-mod-wsgi-py3

After applying it, I was able to start Apache2. Then, typing in localhost returns the Apache2 index.htm page, like:

After creating the following file in the default directory:

<?php
  phpinfo();
?>

Typing in localhost/infophp returns the Apache2 info.php page, like:

After the basics for PHP, the next step is the mysqli module for the MySQL database. This can be done in two steps on Ubuntu.

  1. Install the MySQLi software with the following syntax on Ubuntu:

    sudo apt-get install -y php8.1-mysql

    If you forget and use the old php-mysqli, it will redirect to the new PHP 8.1 MySQL module.

  2. You need to reload the Apache configuration with the following syntax:

    sudo systemctl reload apache2

Now, you can use the following PHP program to verify that the mysqli and pdo drivers are installed:

<html>
<header>
<title>Module Verification</title>
</header>
<body>
<?php
  if (!function_exists('mysqli_init') && !extension_loaded('mysqli')) {
    print 'mysqli not installed.'; }
  else {
    print 'mysqli installed.'; }
  if (!function_exists('pdo_init') && !extension_loaded('pdo')) {
    print '<p>pdo not installed.</p>'; }
  else {
    print '<p>pdo installed.</p>'; }
?>
</script>
</body>
</html>

If everything is correct, it should return the following in a browser when you query it from localhost/the-file-name and the file is in the /var/www/html directory:

mysqli installed.
 
pdo installed.

This means you can now write PHP applications, like the following example for my students:

I also have some demonstration programs that upload PNG files. As usual, I forgot about that while building the Ubuntu installation with MySQL 8, PHP 8.1 and Apache2. Fortunately, I solved it back in the day when moving from PHP 5.7 to 7.1 and here are the equivalent steps for Ubuntu:

I installed the libapache2-mod-wsgi-py3 package with the following syntax:

sudo apt-get install -y php-gd

Then, I restarted the Apache2 server to incorporate the php-gd library in my PHP module with this syntax:

sudo systemctl restart apache2.service

Retesting the PHP form to upload and render a PNG image file with this code (note that the only thing you can display is the html header and converted image, as shown on lines 64 and 65):

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
<?php
  /*  ConvertBlobToImage.php
   *  by Michael McLaughlin
   *
   *  This script queries an image from a BLOB column and
   *  converts it to a PNG image.
   *
   *  ALERT:
   *
   *  The header must be inside the PHP script tag because nothing
   *  can be rendered before the header() function call that signals
   *  this is a PNG file.
   */
 
    // Database credentials must be set manually because an include_once() function
    // call puts something ahead of the header, which causes a failure when rendering
    // an image.
 
    // Include the credential library.
    include_once("MySQLCredentials.inc");
 
  // Return successful attempt to connect to the database.
  if (!$c = @mysqli_connect(HOSTNAME,USERNAME,PASSWORD,DATABASE)) {
 
    // Print user message.
    print "Sorry! The connection to the database failed. Please try again later.";
 
    // Assign the OCI error and format double and single quotes.
    print mysqli_error();
 
    // Kill the resource.
    die();
  }
  else {
 
    // Declare input variables.
    $id = (isset($_GET['id'])) ? (int) $_GET['id'] : 1023;
 
    // Initialize a statement in the scope of the connection.
    $stmt = mysqli_stmt_init($c);
 
    // Declare a SQL SELECT statement returning a MediumBLOB.
    $sql = "SELECT item_blob FROM item WHERE item_id = ?";
 
    // Prepare statement and link it to a connection.
    if (mysqli_stmt_prepare($stmt,$sql)) {
      mysqli_stmt_bind_param($stmt,"i",$id);
 
      // Execute the PL/SQL statement.
      if (mysqli_stmt_execute($stmt)) {
 
        // Bind result to local variable.
	      mysqli_stmt_bind_result($stmt, $image);
 
        // Read result.
        mysqli_stmt_fetch($stmt);
      }
    } 
 
    // Disconnect from database.
    mysqli_close($c);
 
    // Print the header first.
    header('Content-type: image/png');
    imagepng(imagecreatefromstring($image));
  }
?>

The call to the ConvertMySQLBlobToImage.php is handled in an image tag, as shown:

<img src="ConvertMySQLBlobToImage.php?id='.$id.'">

Rendering a web page, like:

As always, I hope this explains something worthwhile.

Written by maclochlainn

December 10th, 2023 at 11:25 pm

pgAdmin4 on Ubuntu

without comments

Installing pgAdmin4 is qualified by the pgAdmin4 (APT) web page, which relies on the curl utility. Ubuntu doesn’t install curl by default, so you need to install it before you can download and install pgAdmin4:

  1. Download and install curl utility

    sudo apt-get install -y curl

  2. Download and install the public key for the repository (if not done previously):

    sudo curl -fsS https://www.pgadmin.org/static/packages_pgadmin_org.pub | sudo gpg --dearmor -o /usr/share/keyrings/packages-pgadmin-org.gpg

    It may find an existing key and require you to confirm its replacement:

    File '/usr/share/keyrings/packages-pgadmin-org.gpg' exists. Overwrite? (y/N) y
  3. Create the repository configuration file:

    sudo sh -c 'echo "deb [signed-by=/usr/share/keyrings/packages-pgadmin-org.gpg] https://ftp.postgresql.org/pub/pgadmin/pgadmin4/apt/$(lsb_release -cs) pgadmin4 main" > /etc/apt/sources.list.d/pgadmin4.list && apt update'

  4. Install the pgadmin4 Desktop:

    sudo apt install pgadmin4-desktop

  5. You can launch your pgadmin4 program file or by clicking the pgAdmin4 icon in the other applications menu:

  6. It takes a couple moments to launch the pgadmin4 desktop. The initial screen will look like:

  7. After pgadmin4 launches, you’re prompted for a master password. Enter the password and click the OK button to proceed or simply let it sit for a couple minutes to avoid entering a password.

  8. After entering the password or skipping its entry you arrive at the base dialog, as shown.

  9. Click the Add New Server link, which prompts you to register your database. Enter videodb in the Name field and click the Connection tab to the right of the General tab.

  10. In the Connection dialog, enter the following values:

    • Host name/address: localhost
    • Port: 5432
    • Maintenance database: postgres
    • Username: student
    • Password: student

    Enter a name for your database. In this example, videodb is the Server Name. Click the Save button to proceed.

  11. Having completed the configuration, you now see the home page.

This completes the instructions for installing, configuring, and using PostgreSQL on AlmaLinux. As always, I hope it helps those looking for instructions.

Written by maclochlainn

December 7th, 2023 at 10:36 pm

Posted in Linux,Ubuntu

Python3 on PostgreSQL

without comments

The necessary Python 3 driver for connections to the PostgreSQL database is python3-psycopg2, as qualified by this earlier post with full test examples for Red Hat distributions. You can install it on Ubuntu with the following command:

sudo apt-get install -y python3-psycopg2

As always, I hope this helps those looking for a solution. Also, remember the referenced post above provides Linux distribution neutral full solutions.

Written by maclochlainn

December 3rd, 2023 at 11:00 pm

SQL Developer on Ubuntu

without comments

The following steps show how to install and configure SQL Developer on Ubuntu 22.0.4 to work with Oracle Database 23c Free in a Docker container. The first steps are installing the Java Runtime Environment and Java Development Kit, and then downloading, installing and configuring SQL Developer. These are the required steps:

  1. Install the Java Runtime Environment:

    sudo apt install default-jre

    The log file for this is:

  2. Install the Java Runtime Environment:

    sudo apt install -y default-idk

    The log file for this is:

  3. Download SQL Developer from here; and then install SQL Developer to the /opt directory on your Ubuntu local instance:

    Use the following command to unzip the SQL Developer files to the /opt directory:

    sudo unzip ~/Downloads/sqldeveloper-23.1.0.097.1607-no-jre.zip
  4. Create the following /usr/local/bin/sqldeveloper symbolic link:

    sudo ln -s /opt/sqldeveloper/sqldeveloper.sh /usr/local/bin/sqldeveloper
  5. Edit the /opt/sqldeveloper/sqldeveloper.sh file by replacing the following line:

    cd "`dirname $0`"/sqldeveloper/bin && bash sqldeveloper $*

    with this version:

    /opt/sqldeveloper/sqldeveloper/bin/sqldeveloper $*
  6. Now, you can launch SQL Developer from any location on your local Ubuntu operating system, like:

    sqldeveloper
  7. You can now connect as the system user through SQL Developer to the Oracle Database 23c Free Docker instance with the following connection information:

  8. You can also create a Desktop shortcut by creating the sqldeveloper.desktop file in the /usr/share/applications directory. The SQL Developer icon is provided in the sqldeveloper base directory.

    You should create the following sqldeveloper.desktop file to use a Desktop shortcut:

    [Desktop Entry]
    Name=Oracle SQL Developer
    Comment=SQL Developer from Oracle
    GenericName=SQL Tool
    Exec=/usr/local/bin/sqldeveloper
    Icon=/opt/sqldeveloper/icon.png
    Type=Application
    StartupNotify=true
    Categories=Utility;Oracle;Development;SQL;

You can create a sandboxed container c##student user with the instructions from this earlier post on Oracle Database 18c, which remains the correct syntax.

As always, I hope this helps those trying to accomplish this task.

Written by maclochlainn

December 3rd, 2023 at 12:11 am

PostgreSQL User Password

without comments

Miraculous events happen on my students’ computers almost weekly. For example, one couldn’t remember their student user’s password, which I set by default. How did they change it? They don’t recall.

Assuming you have sudoer authority on a Linux operating system, you can change a PostgreSQL user’s password as follows:

  1. Assume the root user’s role with the following command:

    sudo sh
  2. As the root user, assume the postgres user’s role with the following command:

    su - postgres
  3. As the postgres user, connect to the PostgreSQL database with the following command:

    psql -U postgres
  4. Assuming the user’s name is student and you want to set the password to a trivial value like student, use the following command:

    ALTER USER student WITH ENCRYPTED PASSWORD 'student';

As always, I hope this helps somebody trying to sort out the syntax and workflow.

Written by maclochlainn

November 7th, 2023 at 9:41 pm

Parallels + Ubuntu

without comments

Installing Parallels on my iStudio (M2) was straightforward because I let it install Windows 11. Then, when I wanted to install Ubuntu it wasn’t quite that easy. You just need to understand that you click the Parallels’ Window menu option and Control Center option.

The Control Center option provides the following dialog.

Click the + symbol to create a new virtualization and you get the following dialog; and choose the Download Ubuntu with x86_64 emulation if you want to install a Docker image that’s not ported to ARM, like the Oracle Database 19c.

It’ll then explain in this dialog that is uses Apple’s Rosetta 2 technology, which means you should be able to install an Intel architecture Docker image with Oracle Database 23c.

As always, I hope this helps those trying to sort out how to leverage a new stack.

Written by maclochlainn

October 19th, 2023 at 3:41 pm

Install Docker Ubuntu

without comments

Contrary to the instructions, you should do the following as a sudoer user:

sudo apt install -y docker.io

Install all dependency packages using the following command:

sudo snap install docker

You should see the following:

docker 20.10.24 from Canonical✓ installed

You can verify the Docker install with the following command:

sudo docker --version

It should show something like this:

Docker version 24.0.5, build 24.0.5-0ubuntu1~22.04.1

You can check the pulled containers with the following command but at this point there should be no pulled containers.

sudo docker images

At this point, a docker group already exists but you need to add your user to the docker group with the following command:

sudo usermod -aG docker $USER

Using the Docker Commands:

  • To activate the logging, utilize the -f parameter.
  • To divide JSON, use Docker by default; to extract individual keys, use JQ.
  • In your Container file, there are quite a few areas where commands may be specified.
  • Posting to the volumes could be more effective while the picture is being built.
  • Docker offers a highly efficient way to create an alias for its own built-in commands. This makes it easier to set up and handle lengthy and enormous orders. These alias values are stored in the directories /.bashrc or and /.bash_aliases.
  • Docker offers further assistance to remove unused code fragments from the installation of the container.
  • Docker always favors reading statements from the container file that have not changed. Therefore, time savings may be realized by arranging what is shown in the container file in a way that ensures the elements that are susceptible to change are shown towards the end of the document and those that are most likely to undergo change are shown at the top.

As always, I hope this helps.

Written by maclochlainn

October 18th, 2023 at 10:34 pm

Posted in Linux,Ubuntu

Tagged with