Deep Dive: Analyzing the Issabel PBX and Asterisk Netinstall Architecture

When deploying open-source Unified Communications and VoIP PBX platforms like Issabel PBX (the open-source continuation of Elastix), understanding how the automated installation script provisions your operating system is critical for enterprise security and stability.

Rather than running installer scripts blindly, conducting a structural teardown allows sysadmins to verify package sources, review firewall modifications, and understand underlying database initializations.

In this guide, I will analyze the official Issabel PBX netinstall.sh architecture, exploring how it builds Yum package manifests, initializes MariaDB, manages Asterisk runtime environments, configures amportal, and renders interactive ncurses terminal dialogs.

Prerequisites

To explore this architecture, you need a CentOS 7 virtual machine and familiarity with Bash scripting, systemd service management, and Asterisk PBX directory structures.

---

Step 1: Structuring the Yum Package Manifests

The core of the Issabel netinstall script relies on dynamically generating two large package manifest files (inst1.txt and inst2.txt) in /tmp.

The first manifest installs foundational OS utilities, Python libraries, Perl modules, and database engines. The second manifest installs specific Asterisk versions (asterisk11, asterisk13, or asterisk16), Dahdi hardware drivers, and Issabel framework modules.

# Snippet of dynamic manifest generation function
function generate_files
{
cat > /tmp/inst1.txt << "EOF"
acl
apr
audit
basesystem
bash
bind-libs-lite
chrony
curl
epel-release
firewalld
httpd
mariadb-server
openssh-server
php
postfix
python
sudo
systemd
yum
EOF

cat > /tmp/inst2.txt << "EOF"
asterisk$ASTVER
asterisk$ASTVER-devel
asterisk-codec-g729
asterisk-perl
asterisk-sounds-en-gsm
dahdi-linux
issabel-system
issabel-framework
issabel-pbx
issabel-security
issabel-reports
EOF
}

---

Step 2: Repository Provisioning and Commercial Addons

Once the package manifests are constructed, the script injects official Issabel repositories into /etc/yum.repos.d/. This configures base, updates, extras, and commercial addon mirrors.

# /etc/yum.repos.d/Issabel.repo
[issabel-base]
name=Base RPM Repository for Issabel
mirrorlist=http://mirror.issabel.org/?release=4&arch=$basearch&repo=base
gpgcheck=0
enabled=1
gpgkey=http://repo.issabel.org/issabel/RPM-GPG-KEY-Issabel

[issabel-extras]
name=Extras RPM Repository for Issabel
mirrorlist=http://mirror.issabel.org/?release=4&arch=$basearch&repo=extras
gpgcheck=1
enabled=1
gpgkey=http://repo.issabel.org/issabel/RPM-GPG-KEY-Issabel

Interactive Addons Selection

The script uses dialog to render interactive checklists allowing administrators to toggle optional modules like Sangoma Wanpipe drivers or Community Realtime Block Lists (PacketBL) to defend against automated SIP brute-force attacks.

function additional_packages
{
  ADDPKGS=""
  OPTS=$(dialog --backtitle "$BACKTITLE" --no-tags \
        --checklist "Choose additional package(s) to install:" 0 0 0 \
        1 "Issabel Network Licensed modules" on \
        2 "Community Realtime Block List" on \
        3 "Sangoma wanpipe drivers" off \
        3>&1 1>&2 2>&3)
}

---

Step 3: OS Environment and User Group Settings

Before installing Asterisk packages, the script ensures that the system environment is properly configured. It creates a dedicated asterisk user and group to prevent the PBX from running under root privileges.

function settings
{
  # Disable SELinux during base installation
  setenforce 0
  sed -i 's/\(^SELINUX=\).*/\SELINUX=disabled/' /etc/selinux/config

  # Create unprivileged Asterisk group and user
  /usr/sbin/groupadd -f -r asterisk
  if ! grep -q asterisk: /etc/passwd ; then
      /usr/sbin/useradd -r -g asterisk -c "Asterisk PBX" -s /bin/bash -d /var/lib/asterisk asterisk
  fi
}

---

Step 4: Executing Mass Package Installation (Yum Gauge)

To provide visual feedback during mass RPM installation, the script implements a custom yum_gauge function. It iterates through the space-separated package lists from /tmp/inst1.txt and /tmp/inst2.txt, calculating percentage progress and piping output directly into an ncurses progress bar.

function yum_gauge
{
  PACKAGES=$1
  TITLE=$2
  YUMCMD=$3
  dialog --backtitle "$BACKTITLE" --title "$TITLE" --gauge "Installing..." 10 75 < <(
   n=$(echo $PACKAGES | wc -w); 
   i=0
   for p in $PACKAGES
   do
      PCT=$(( 100*(++i)/n ))
cat <<EOF
XXX
$PCT
Installing "$p"...
XXX
EOF
    rpm --quiet -q $p
    if [ $? -ne 0 ] || [ "$YUMCMD" = "update" ]; then
       yum $BETAREPO --nogpg -y $YUMCMD $p &>/dev/null
    fi
  done
)
}

---

Step 5: Post-Installation Initialization and Database Setup

After all packages are installed, the script enters its post-installation phase. It enables MariaDB, configures root database credentials, backs up existing iptables rules, opens HTTPS port 443, and patches Asterisk configurations.

function post_install
{
  # Enable and start MariaDB
  systemctl enable mariadb.service
  systemctl start mariadb
  
  # Set temporary database credentials
  mysql -e "SET PASSWORD FOR 'root'@'localhost' = PASSWORD('Randompassword')"
  
  # Backup iptables and configure firewalld
  cp -a /etc/sysconfig/iptables /etc/sysconfig/iptables.org-issabel-$(/bin/date "+%Y-%m-%d-%H-%M-%S")
  systemctl enable httpd
  systemctl disable firewalld && systemctl stop firewalld
  
  # Patch Asterisk modules configuration
  echo "noload => cdr_mysql.so" >> /mnt/sysimage/etc/asterisk/modules_additional.conf
  mkdir -p /var/log/asterisk/cdr-csv
  mv /etc/asterisk/extensions_custom.conf.sample /etc/asterisk/extensions_custom.conf
  
  # Enforce proper ownership across Asterisk directories
  /usr/sbin/amportal chown
}

---

Step 6: Final Cleanup and Administrative Passwords

In the final phase, the script invokes issabel-admin-passwords --init to prompt the sysadmin for secure web UI and FreePBX administrative passwords, cleans up temporary /tmp manifests, and initiates a system reboot.

function cleanup
{
  rm -f /tmp/inst1.txt
  rm -f /tmp/inst2.txt
  /usr/sbin/amportal chown
}

References

• Issabel Open Source PBX Project
• Asterisk PBX Documentation