Connecting USB GSM / 3G / 4G Dongles to Raspberry Pi 4 (Huawei E303, usb-modeswitch, and Gammu)

USB cellular modems (such as the ubiquitous Huawei E303, E173, and E3372) enable Raspberry Pi 4 projects to send SMS notifications, handle emergency alerts, and provide cellular backup connectivity. However, modern USB modems initially boot into a virtual CD-ROM storage mode (ZeroCD) to deliver Windows drivers, requiring usb-modeswitch to toggle them into serial modem mode.

Hardware: Raspberry Pi 4 • Huawei E303 USB Dongle • usb-modeswitch • Gammu SMS Gateway

1. Installing usb-modeswitch and Gammu

sudo apt-get update
sudo apt-get install usb-modeswitch usb-modeswitch-data gammu minicom -y

2. Switching from Mass Storage to Modem Mode

Check lsusb to identify your device vendor and product ID:

# Example: ID 12d1:1f01 (Mass Storage Mode)
lsusb | grep Huawei

# Mode-switch into serial modem mode (12d1:1001 or 12d1:14db):
sudo usb_modeswitch -v 12d1 -p 1f01 -M '55534243123456780000000000000011062000000100000000000000000000'

Confirm the modem serial nodes are created under /dev/ttyUSB0, /dev/ttyUSB1, and /dev/ttyUSB2.

3. Sending a Test SMS via Gammu

Configure ~/.gammurc:

[gammu]
port = /dev/ttyUSB0
connection = at115200

Send an automated test message:

echo "Alert: Raspberry Pi online!" | gammu sendsms TEXT +1234567890

How to Install and Configure Munin Monitoring with Nginx and CGI on CentOS 8

Setting up Munin on CentOS 8 via EPEL 8 provides turnkey server performance graphs. This guide walks through configuring systemd timer units, fastcgi spawners for dynamic graph generation, and integrating the dashboard into an Nginx virtual host.

Packages: munin • munin-node • munin-cgi • spawn-fcgi

1. Installing Packages from EPEL 8

dnf install epel-release -y
dnf install munin munin-cgi munin-node spawn-fcgi nginx -y

2. Enabling Node and Systemd Services

systemctl enable --now munin-node
systemctl enable --now munin-cgi-graph.socket
systemctl enable --now munin-cgi-html.socket

3. Nginx Server Block (/etc/nginx/conf.d/munin.conf)

server {
    listen 80;
    server_name munin.example.com;

    location / {
        root /var/www/html/munin;
        index index.html;
    }

    location ^~ /munin-cgi/munin-cgi-graph/ {
        fastcgi_split_path_info ^(/munin-cgi/munin-cgi-graph)(.*);
        fastcgi_param PATH_INFO $fastcgi_path_info;
        fastcgi_pass unix:/run/munin/fcgi-graph.sock;
        include fastcgi_params;
    }
}

How to Deploy BigBlueButton Web Conferencing on CentOS 8 with Docker

BigBlueButton (BBB) is the leading open-source virtual classroom and web conferencing system. While upstream BBB exclusively provides automated installer scripts for Ubuntu LTS, organizations standardized on Enterprise Linux (CentOS 8 / RHEL 8) can deploy BigBlueButton components cleanly using Docker containers.

Stack: CentOS 8 • Docker CE • BigBlueButton Docker Compose • Nginx TLS Reverse Proxy

1. Installing Docker CE on CentOS 8

dnf config-manager --add-repo https://download.docker.com/linux/centos/docker-ce.repo
dnf install docker-ce docker-ce-cli containerd.io -y
systemctl enable --now docker

2. Deploying BigBlueButton via Docker Compose

git clone https://github.com/bigbluebutton/docker.git bbb-docker
cd bbb-docker
cp .env.example .env

# Configure your FQDN and Let's Encrypt email in .env
./scripts/generate-api-secrets.sh
docker-compose up -d

How to Install and Configure Icecast 2 Streaming Audio Server on CentOS 8

Icecast is a high-performance, open-source streaming media audio server capable of broadcasting MP3, Ogg Vorbis, and Opus audio streams. Because prebuilt Icecast packages were initially omitted from CentOS 8 and EPEL 8 repositories, compiling from source with Vorbis and Theora audio support is required.

Environment: CentOS 8 / RHEL 8 • Icecast 2.4.x • Ogg / Vorbis / Theora Codecs

1. Install Build Tools and Codec Dependencies

yum groupinstall "Development Tools" -y
yum install curl-devel libtheora-devel libvorbis-devel libxslt-devel speex-devel libshout-devel -y

2. Download and Build Icecast

cd /usr/src
wget http://downloads.xiph.org/releases/icecast/icecast-2.4.4.tar.gz
tar -zxf icecast-2.4.4.tar.gz
cd icecast-2.4.4

./configure --prefix=/usr --sysconfdir=/etc --localstatedir=/var
make && make install

3. Create Service User and Start Daemon

useradd -r -s /sbin/nologin icecast
chown -R icecast:icecast /var/log/icecast

# Launch Icecast as a background daemon
icecast -b -c /etc/icecast.xml

How to Rebuild Apache httpd to Change suexec AP_DOC_ROOT from /var/www to /home (CentOS & RHEL)

Standard RPM packages of Apache httpd in CentOS and RHEL compile suexec with a hardcoded document root of /var/www (--with-suexec-docroot=/var/www). However, web control panels like Virtualmin host customer accounts under /home. When suexec executes a user script under /home, it aborts with "command not in docroot". Here is how to rebuild the official upstream httpd SRPM with AP_DOC_ROOT set to /home.

Compilation Flag: --with-suexec-docroot=/home

Rebuilding the RPM

# 1. Install build tools and dependencies
yum install rpm-build redhat-rpm-config gcc make -y
yum-builddep httpd -y

# 2. Download and unpack httpd SRPM
mkdir -p ~/rpmbuild/{BUILD,RPMS,SOURCES,SPECS,SRPMS}
cd ~/rpmbuild/SRPMS
yumdownloader --source httpd
rpm -ivh httpd-*.src.rpm

# 3. Edit SPECS/httpd.spec and modify suexec docroot
cd ~/rpmbuild/SPECS
sed -i 's|--with-suexec-docroot=/var/www|--with-suexec-docroot=/home|g' httpd.spec

# 4. Rebuild binary RPM
rpmbuild -bb httpd.spec

# 5. Install the custom suexec binary
rpm -Uvh --force ~/rpmbuild/RPMS/x86_64/httpd-*.rpm

Confirm the new docroot:

suexec -V | grep AP_DOC_ROOT

[Solved] Fixing Apache suexec and mod_fcgid: Error Reading Data from FastCGI Server

When running PHP applications under Apache using mod_fcgid combined with suexec privilege separation, web requests may suddenly abort with HTTP 500 Internal Server Errors and the following message in Apache error logs:

Error Message: End of script output before headers: php.fcgi • mod_fcgid: error reading data from FastCGI server

Root Cause

suexec enforces strict security checks on the FastCGI wrapper script and user directory:

1. The wrapper script and parent directories must be owned exclusively by the virtual server user and group—not root or apache.
2. File permissions cannot be group-writeable (chmod 755 is required, 775 or 777 causes instant suexec rejection).
3. The target script must reside strictly inside the compiled suexec document root (e.g. /home/user/public_html).

Resolution Steps

Inspect /var/log/httpd/suexec.log to reveal the exact permission violation, and enforce correct ownership:

# Fix permissions and ownership
chown -R user:user /home/user/fcgi-bin /home/user/public_html
chmod 755 /home/user/fcgi-bin/php.fcgi
chmod 755 /home/user/public_html

How to Install Virtualmin with Multiple PHP and MySQL Versions on CentOS 8

Deploying a production web hosting stack on CentOS 8 with Virtualmin requires modern multi-PHP support (allowing legacy applications to run PHP 5.6 or 7.2 while modern apps run PHP 7.4 or 8.0) and reliable database server management via Remi repositories.

Stack: CentOS 8 • Virtualmin 6.x • Remi Software Collections (SCL) • MySQL 8.0 • Multi-PHP

1. Fix Perl UTF-8 Locale Warnings

cat << 'EOF' > /etc/environment
LANGUAGE=en_US.utf8
LC_ALL=en_US.utf-8
LANG=en_US.utf8
LC_TYPE=en_US.utf8
EOF

2. Enable EPEL and Remi Repositories

dnf install epel-release -y
dnf install https://rpms.remirepo.net/enterprise/remi-release-8.rpm -y
dnf module reset php -y
dnf module enable php:remi-7.4 -y

3. Installing Parallel PHP Versions

dnf install php56-php-fpm php72-php-fpm php74-php-fpm php80-php-fpm -y

4. Install Virtualmin

wget http://software.virtualmin.com/gpl/scripts/install.sh
sh install.sh