https://support.cpanel.net/hc/en-us/articles/33990336418583-How-to-install-composer-on-cPanel-version-130-and-higher

cloudlinux_cpanel_install_php_composer.sh

#!/usr/bin/env bash
set -euo pipefail

# Function to print error and exit
die() {
  echo "ERROR: $*" >&2
  exit 1
}

# Check if running as root
if [[ $EUID -ne 0 ]]; then
  die "This script must be run as root"
fi

# (Optional) check that php CLI exists
if ! command -v php &> /dev/null; then
  die "php CLI not found. Please install or enable php CLI."
fi

# 1. Check allow_url_fopen is enabled in the default PHP version

# 2. Download composer installer
echo "Downloading Composer installer..."
php -r "copy('https://getcomposer.org/installer', 'composer-setup.php');"

# 3. Download the signature for verification
echo "Downloading installer signature..."
php -r "copy('https://composer.github.io/installer.sig', 'composer.sig');"

# 4. Verify the installer
echo "Verifying installer..."
php -r "if (hash_file('sha384', 'composer-setup.php') === trim(file_get_contents('composer.sig'))) { echo 'Installer verified' . PHP_EOL; } else { echo 'Installer corrupt' . PHP_EOL; unlink('composer-setup.php'); exit(1); }"

# 5. Run installer
echo "Running installer..."
php composer-setup.php

# 6. Move the resulting phar to a system‐wide location
echo "Installing composer to /usr/local/bin/composer ..."
mv -v composer.phar /usr/local/bin/composer

# 7. Clean up installer files
echo "Cleaning up..."
php -r "unlink('composer-setup.php'); unlink('composer.sig');"

echo "Composer has been installed successfully."

# Extra: for CloudLinux servers with CageFS, add composer to CageFS map
if command -v cagefsctl &> /dev/null; then
  echo "Detected cagefsctl — assuming CloudLinux with CageFS. Configuring composer in CageFS..."
  # create composer.cfg
  cat <<EOF > /etc/cagefs/conf.d/composer.cfg
[composer]
comment=Composer https://getcomposer.org/
paths=/usr/local/bin/composer
EOF
  # rebuild cagefs
  echo "Rebuilding CageFS..."
  cagefsctl --force-update

  echo "CageFS configuration updated."
fi

echo "Done."