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Tips, Hints, and useful information

General maintainability of your packages

  • Try hard to make all files work on all platforms you support.
    • Maintaining separate scripts, config, service files, etc for each platform quickly becomes difficult
  • Put as much conditional logic in the pre/post install scripts as possible instead of trying to build it into the nfpm.yaml
  • if you need to know the packaging system I have found it useful to add a /etc/path-to-cfg/package.env that contains _INSTALLED_FROM=apk|deb|rpm which can be sourced into the pre/post install/remove scripts
  • if/when you need to ask questions during the installation process, create an install.sh || setup.sh script that asks those questions and stores the answers as env vars in /etc/path-to-cfg/package.env for use by the pre/post install/remove scripts
  • If you only need to support deb packages you can use the debconf template/config feature, but since rpm does not support this I would try to unify the way you ask questions.

Pre/Post Install/Remove/Upgrade scripts

Example Multi platform post-install script

#!/bin/sh

# Step 1, decide if we should use systemd or init/upstart
use_systemctl="True"
systemd_version=0
if ! command -V systemctl >/dev/null 2>&1; then
  use_systemctl="False"
else
    systemd_version=$(systemctl --version | head -1 | sed 's/systemd //g')
fi

cleanup() {
    # This is where you remove files that were not needed on this platform / system
    if [ "${use_systemctl}" = "False" ]; then
        rm -f /path/to/<SERVICE NAME>.service
    else
        rm -f /etc/chkconfig/<SERVICE NAME>
        rm -f /etc/init.d/<SERVICE NAME>
    fi
}

cleanInstall() {
    printf "\033[32m Post Install of an clean install\033[0m\n"
    # Step 3 (clean install), enable the service in the proper way for this platform
    if [ "${use_systemctl}" = "False" ]; then
        if command -V chkconfig >/dev/null 2>&1; then
          chkconfig --add <SERVICE NAME>
        fi

        service <SERVICE NAME> restart ||:
    else
        # rhel/centos7 cannot use ExecStartPre=+ to specify the pre start should be run as root
        # even if you want your service to run as non root.
        if [ "${systemd_version}" -lt 231 ]; then
            printf "\033[31m systemd version %s is less then 231, fixing the service file \033[0m\n" "${systemd_version}"
            sed -i "s/=+/=/g" /path/to/<SERVICE NAME>.service
        fi
        printf "\033[32m Reload the service unit from disk\033[0m\n"
        systemctl daemon-reload ||:
        printf "\033[32m Unmask the service\033[0m\n"
        systemctl unmask <SERVICE NAME> ||:
        printf "\033[32m Set the preset flag for the service unit\033[0m\n"
        systemctl preset <SERVICE NAME> ||:
        printf "\033[32m Set the enabled flag for the service unit\033[0m\n"
        systemctl enable <SERVICE NAME> ||:
        systemctl restart <SERVICE NAME> ||:
    fi
}

upgrade() {
    printf "\033[32m Post Install of an upgrade\033[0m\n"
    # Step 3(upgrade), do what you need
    ...
}

# Step 2, check if this is a clean install or an upgrade
action="$1"
if  [ "$1" = "configure" ] && [ -z "$2" ]; then
  # Alpine linux does not pass args, and deb passes $1=configure
  action="install"
elif [ "$1" = "configure" ] && [ -n "$2" ]; then
    # deb passes $1=configure $2=<current version>
    action="upgrade"
fi

case "$action" in
  "1" | "install")
    cleanInstall
    ;;
  "2" | "upgrade")
    printf "\033[32m Post Install of an upgrade\033[0m\n"
    upgrade
    ;;
  *)
    # $1 == version being installed  
    printf "\033[32m Alpine\033[0m"
    cleanInstall
    ;;
esac

# Step 4, clean up unused files, yes you get a warning when you remove the package, but that is ok. 
cleanup

Example Multi platform (RPM & Deb) post-remove script

#!/bin/sh

cleanInstall() {
    printf "\033[32m Post Install of a clean install\033[0m\n"
}

upgrade() {
    printf "\033[32m Post Install of an upgrade\033[0m\n"
}

action="$1"
if  [ "$1" = "configure" ] && [ -z "$2" ]; then
  # Alpine linux does not pass args, and deb passes $1=configure
  action="install"
elif [ "$1" = "configure" ] && [ -n "$2" ]; then
    # deb passes $1=configure $2=<current version>
    action="upgrade"
fi

case "$action" in
  "1" | "install")
    printf "\033[32m Post Install of a clean install\033[0m\n"
    cleanInstall
    ;;
  "2" | "upgrade")
    printf "\033[32m Post Install of an upgrade\033[0m\n"
    upgrade
    ;;
  *)
    # $1 == version being installed  
    printf "\033[32m Alpine\033[0m"
    cleanInstall
    ;;
esac

Deb & RPM

  • On upgrade, the scripts are being executed in the following order:
    1. pretrans of new package (only applies to RPM)
    2. preinstall of new package
    3. postinstall of new package
    4. preremove of old package
    5. postremove of old package
    6. posttrans of new package (only applies to RPM)

Systemd and upstart/init

upstart / init

  • try to just say no to supporting this, but if you must make sure you have a single script that works on all platforms you need to support.
  • as the post-install script above does.

Systemd

  • The docs you find for systemd are generally for the latest and greatest version, and it can be hard to find docs for older versions.
  • In the above post-install script you see I am doing a systemd version check to correct the ExecStartPre=+... and ExecStop=+... lines
  • You should always use Table 2. Automatic directory creation and environment variables
  • With the note that only RuntimeDirectory is used in systemd < 231
  • /bin/bash -c "$(which ...) ... is a great way to make your single service file work on all platforms since rhel and debian based systems have standard executables in differing locations and complain about executable path is not absolute
  • eg /bin/bash -c '$(which mkdir) -p /var/log/your-service'