Linux Tips

I believe that it is my responsibility to transfer the knowledge I gathered through the years of my experience with Linux

Zipping a folder, including sub-folders and hidden files

zip -r yourzipfile.zip folder/* .*

To find a string in some files in some folder (in my case finding the string 'pane-toggle' in the folder web1)

grep --color -r -i -n -w 'pane-toggler' web1/

Options explanation:

• --color : nice colorful output ;)

• -r : recursive... process the directory and subdirectories

• -i : ignore case of letter... not like DOS/windows. I linux, grep will follow you instruction. So if you want to find 'Red' and 'red', use -i 

• -n : shows the line number in the file where the string exists

• -w : will find only matches of whole word, i.e. if you are looking for 'pencil' not pencils', use -w

Mysql Purge Binary Logs

mysql> PURGE BINARY LOGS BEFORE '2009-05-01 00:00:00';

How to get size of a MySQL database

• Size in GB

SELECT table_schema "DB Name",

        ROUND(SUM(data_length + index_length) / 1024 / (1024*1024), 1) "DB Size in GB" 

FROM information_schema.tables 

GROUP BY table_schema; 

• Size in MB

SELECT table_schema "DB Name",

        ROUND(SUM(data_length + index_length) / 1024 / 1024, 1) "DB Size in GB" 

FROM information_schema.tables 

GROUP BY table_schema;

Resize filesystem partition size without loosing data using command line, using fdisk tool

• Important notes:

  • Always backup your important data before performing this act (skip this if you are just playing around linux)

  • Examples provided here maybe different in your case, so be careful

• Steps:

  • Get the Hard disk name using the command df -h /

    • Example: (Harddisk /dev/sda)

~$ df -h /

Filesystem      Size  Used Avail Use% Mounted on

/dev/sda2       9.8G  7.4G  2.0G  80% /

~$

• • Get the Partition name using the command lsblk 

    • Example: (Partition sda2 or 2)

~$ lsblk

NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT

loop0    7:0    0 99.4M  1 loop /snap/core/11316

loop1    7:1    0 99.4M  1 loop /snap/core/11187

sda      8:0    0   20G  0 disk 

├─sda1   8:1    0    1M  0 part 

└─sda2   8:2    0   10G  0 part /

sr0     11:0    1 1024M  0 rom

~$

• • (STOP! Is the data on the hard disk important? Make sure you have a backup of it)

  • Run the command sudo fdisk /dev/sda

  • If you get an error "GPT PMBR size mismatch (41943039 != 62914559) will be corrected by w(rite)."

    • Fdisk used to not work at all on gpt partitioned drives, it just reported that drive was gpt partitioned. Better to use parted, gparted or gdisk. Gdisk has been the command line tool for gpt drives.

    • Post these:

      • sudo parted -l

        • or

      • sudo parted /dev/sda unit s print

        • or

      • sudo gdisk -l /dev/sda

    • Example:

~$sudo fdisk /dev/sda

Welcome to fdisk (util-linux 2.31.1).

Changes will remain in memory only, until you decide to write them.

Be careful before using the write command.

Command (m for help): p # print the partition table

Disk /dev/sda: 20 GiB, 21474836480 bytes, 41943040 sectors

Units: sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disklabel type: gpt

Disk identifier: ########-####-####-####-#############

Device     Start      End  Sectors Size Type

/dev/sda1   2048     4095     2048   1M BIOS boot

/dev/sda2   4096 20969471 20965376  10G Linux filesystem

Command (m for help): d # delete a partition

Partition number (1,2, default 2): 2 # partition number

Partition 2 has been deleted.

Command (m for help): n # add a new partition

Partition number (2-128, default 2): 2 # partition number 

First sector (4096-41943006, default 4096): # Make sure you same number of Start 

Last sector, +sectors or +size{K,M,G,T,P} (4096-41943006, default 41943006): # Use the default value to use the MAX available size for extending

Created a new partition 2 of type 'Linux filesystem' and of size 20 GiB.

Partition #2 contains a ext4 signature.

Do you want to remove the signature? [Y]es/[N]o: N # Don't remove the old signature, else you will loose your data!

Command (m for help): w # write table to disk and exit (If you have any doubts, type q now!)

The partition table has been altered.

Syncing disks.

~$

• • Run the command sudo resize2fs /dev/sda2

    • Example:

~$ sudo resize2fs /dev/sda2

resize2fs 1.44.1 (24-Mar-2018)

Filesystem at /dev/sda2 is mounted on /; on-line resizing required

old_desc_blocks = 2, new_desc_blocks = 3

The filesystem on /dev/sda2 is now 5242363 (4k) blocks long.

~$

Fixed EXIM Error : all hosts for 'domain.tld' have been failing for a long time (and retry time not reached)

In most situations this error It occurs when database "Exim Retry" It is corrupt. So the problem is The server that is trying to send the message.

resolving error consists Exim delete Retry Database si restartEXIM service area server.

Perform the following server command line to delete database Exim Relay:

cd /var/spool/exim/db

rm -f retry retry.lockfile

rm -f wait-remote_smtp wait-remote_smtp.lockfile

After executing these commands, the files will be deleted: retry, retry.lockfile, wait-remote_smtp and wait-remote_smtp.lockfile, restartyou have the "exim" service.

service exim restart

To execute these commands you must have access to the server console (or SSH access) and sufficient permissions.

How do I run a single command at startup using systemd?

You can see a list of all services using the command below:

systemctl list-units --type=service

For now, you can start creating a unit file here and then finally when it is done move it to /etc/systemd/system the directory. Creating a unit file with the name of your service:

$ touch <service name>.service

File content:

[Unit]

Description=<service description>

After=network.target

[Service]

Type=simple

ExecStart=<command>

WorkingDirectory=<path>

Restart=always

RestartSec=5

StandardOutput=syslog

StandardError=syslog

SyslogIdentifier=%n

[Install]

WantedBy=multi-user.target

Load/enable/start as service:

$ sudo systemctl daemon-reload

$ sudo systemctl enable <service name>.service

$ sudo systemctl start <service name>.service

How to Install Webmin on Ubuntu 24.04 (step by step)

• Deploy a Ubuntu 24.04 server instance on your server

• Create a new subdomain DNS record pointing to your server IP address. For example, webmin.example.com

• Access the server using SSH as a non-root user with sudo privileges

sudo curl -o setup-repos.sh https://raw.githubusercontent.com/webmin/webmin/master/setup-repos.sh; sudo bash setup-repos.sh

sudo bash setup-repos.sh

sudo apt install --install-recommends webmin -y

sudo systemctl status webmin

sudo ufw allow 80/tcp

sudo apt install certbot -y

sudo certbot certonly --standalone -d webmin.example.com -m webmin@example.com --agree-tos

sudo cat /etc/letsencrypt/live/webmin.example.com/fullchain.pem /etc/letsencrypt/live/webmin.example.com/privkey.pem > webmin.pem

sudo mv webmin.pem /etc/webmin/

sudo nano /etc/webmin/miniserv.conf

keyfile=/etc/webmin/webmin.pem

sudo systemctl restart webmin

sudo ufw allow 10000

sudo nano /etc/webmin/miniserv.conf

sudo ufw reload

sudo ufw reload

https://webmin.example.com:10000

source: https://docs.vultr.com/how-to-install-webmin-on-ubuntu-24-04

Creating a LAMP container on PROXMOX - use it SMTP testing tool

• Create a CT from the ubuntu CT Templates.

• Start and Login to the CT 

• Run this line:

apt update && apt install apache2 php php-mysql php-curl php-cli php-xml php-mbstring php-zip php-gd php-bcmath mysql-server -y

Run it in the folder /var/www/html

composer require phpmailer/phpmailer

• Create index.php and paste the code below in it

<?php

use PHPMailer\PHPMailer\PHPMailer;

use PHPMailer\PHPMailer\Exception;

require 'vendor/autoload.php';

$message = '';

if ($_SERVER['REQUEST_METHOD'] === 'POST') {

    $smtp_host = $_POST['smtp_host'] ?? '';

    $smtp_port = $_POST['smtp_port'] ?? '';

    $smtp_user = $_POST['smtp_user'] ?? '';

    $smtp_pass = $_POST['smtp_pass'] ?? '';

    $smtp_secure = $_POST['smtp_secure'] ?? '';

    $from_email = $_POST['from_email'] ?? '';

    $from_name = $_POST['from_name'] ?? '';

    $to_email = $_POST['to_email'] ?? '';

    $subject = $_POST['subject'] ?? '';

    $body = $_POST['body'] ?? '';

    $mail = new PHPMailer(true);

    try {

        // SMTP configuration

        $mail->isSMTP();

        $mail->Host       = $smtp_host;

        $mail->SMTPAuth   = true;

        $mail->Username   = $smtp_user;

        $mail->Password   = $smtp_pass;

        $mail->SMTPSecure = $smtp_secure ?: PHPMailer::ENCRYPTION_STARTTLS;

        $mail->Port       = (int)$smtp_port;

        // Sender & Recipient

        $mail->setFrom($from_email, $from_name);

        $mail->addAddress($to_email);

        // Email content

        $mail->isHTML(true);

        $mail->Subject = $subject;

        $mail->Body    = nl2br($body);

        $mail->AltBody = strip_tags($body);

        // Send email

        $mail->send();

        $message = '<div style="color: green;">✅ Email sent successfully!</div>';

    } catch (Exception $e) {

        $message = '<div style="color: red;">❌ Mailer Error: ' . htmlspecialchars($mail->ErrorInfo) . '</div>';

    }

}

?>

<!DOCTYPE html>

<html lang="en">

<head>

<meta charset="UTF-8">

<meta name="viewport" content="width=device-width, initial-scale=1.0">

<title>SMTP Mailer</title>

<style>

    body {

        font-family: Arial, sans-serif;

        background: #f2f5f8;

        margin: 0;

        padding: 0;

    }

    .container {

        max-width: 750px;

        margin: 50px auto;

        background: #fff;

        padding: 30px;

        border-radius: 10px;

        box-shadow: 0 4px 15px rgba(0,0,0,0.1);

    }

    h2 {

        text-align: center;

        color: #333;

        margin-bottom: 25px;

    }

    label {

        display: block;

        margin-top: 12px;

        font-weight: bold;

        color: #333;

    }

    input, textarea, select {

        width: 100%;

        padding: 10px;

        margin-top: 6px;

        border: 1px solid #ccc;

        border-radius: 6px;

        font-size: 14px;

    }

    textarea {

        resize: vertical;

    }

    button {

        width: 100%;

        margin-top: 25px;

        background: #007BFF;

        color: #fff;

        border: none;

        padding: 12px;

        border-radius: 6px;

        font-size: 16px;

        cursor: pointer;

    }

    button:hover {

        background: #0056b3;

    }

    .message {

        margin-top: 20px;

        text-align: center;

    }

</style>

</head>

<body>

<div class="container">

    <h2>Send Email via Authenticated SMTP</h2>

    <form method="POST" action="">

        <h3>SMTP Configuration</h3>

        <label>SMTP Host:</label>

        <input type="text" name="smtp_host" placeholder="smtp.example.com" required>

        <label>SMTP Port:</label>

        <input type="number" name="smtp_port" value="587" required>

        <label>SMTP Username:</label>

        <input type="text" name="smtp_user" placeholder="your_email@example.com" required>

        <label>SMTP Password:</label>

        <input type="password" name="smtp_pass" placeholder="Your SMTP password" required>

        <label>Encryption Type:</label>

        <select name="smtp_secure">

            <option value="tls" selected>TLS (Port 587)</option>

            <option value="ssl">SSL (Port 465)</option>

            <option value="">None</option>

        </select>

        <h3>Sender & Recipient</h3>

        <label>From Email:</label>

        <input type="email" name="from_email" placeholder="your_email@example.com" required>

        <label>From Name:</label>

        <input type="text" name="from_name" placeholder="Your Name" required>

        <label>To (Recipient Email):</label>

        <input type="email" name="to_email" placeholder="recipient@example.com" required>

        <h3>Message</h3>

        <label>Subject:</label>

        <input type="text" name="subject" placeholder="Subject" required>

        <label>Body:</label>

        <textarea name="body" rows="6" placeholder="Type your message..." required></textarea>

        <button type="submit">Send Email</button>

    </form>

    <div class="message"><?= $message ?></div>

</div>

</body>

</html>

• Save the file and point your browser to your CT IP

• Leave a comment below if you need more information