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Object PRE-POST scripts

End Users use JOD Distribution Commands to manage their JOD Distribution installation. They can start/stop, install/uninstall (as a service) and get his state.

JOD Distribution Commands, during their execution, are configured to check for special scripts in the script folder; if those scripts exist, then they are executed.

Those special scripts act as hooks and allow Makers to inject distribution's specific commands to be executed before or after start/stop, install/uninstall the distribution.

Here the full list of JOD Distribution Commands, and the hook they try to call:

JOD Dist CmdPRE-ScriptPOST_Script
startscripts/pre-startupscripts/post-startup
start FOREGROUNDscripts/pre-startupscripts/post-shutdown
stopscripts/pre-shutdownscripts/post-shutdown
installscripts/pre-installscripts/post-install
uninstallscripts/pre-uninstallscripts/post-uninstall
Depending on which version of the JOD Distribution Commands is executed (Bash or Powershell), corresponding PRE-POST script (sh or ps1) will be used as hook.

So the PRE script executed by bash start.sh will be the scripts/pre-startup.sh scripts, meanwhile for the powershell uninstall.ps1 command, the POST hook is the scripts/post-uninstall.ps1.

The start JOD Dist Cmd always call the scripts/pre-startup hook before the JOD agent execution. But, when the distribution startup as a FOREGROUND process, it does NOT call the scripts/post-startup hook as usual, instead it execute the scripts/post-shutdown hook. That assures Maker a place where put their startup/shutdown code independently to the start JOD Dist Cmd working mode (background or foreground).

Common PRE-POST operations​

PRE and POST script are useful in many case to customize

Check working Operating System​

Many JOD Distribution are implemented to work only on a specific OS(s).
If that's you case, we suggest adding an OS check to each PRE-hook.

pre-XYZ.sh:wrong OS check
# Check supported OS
supportedOS=("Unix" "BSD" "Solaris")
failOnUnsupportedOS "${supportedOS[@]}"

In the previous example we added a check that fails if executing OS is not in the supportedOS list. With 'executing OS' we are referring to OS where your JOD Distribution were installed by End User.

Available OS names are:

  • Unix
  • MacOS
  • BSD
  • Solaris
  • Win32

Requirements checks​

If your distribution require special hardware configuration, 3rd party software or specific files installed on execution OS, you can add custom checks to the pre-startup and/or pre-install hooks. So if checks fail, End user can't startup/install the JOSP object and receive detailed message on what was wrong.

Check command availability:

dists/resources/scripts/pre-startup.sh:check 'top' command availability
# Check top
if command -v top &>/dev/null; then
  echo "'top' command installed"
else
  echo "Missing Java, please install it"
  logFat "'top' command not installed, exit"
fi

A common tip, is to implement all requirements checks in the pre-startup script, then call it from the pre-install script. That allow you to write them only once. See Hook script call another Hook script.

Check Hardware configuration:

ToDo: Write Check Hardware configuration

Check Files exist:

ToDo: Write Check Hardware configuration

Execution environment setup​

Often occurs that a distribution must perform some setup to the environment where it will be executed by the End User.

Here an example that set executable all script contained in the scripts/sendors directory.

dists/resources/scripts/pre-startup.sh:setup execution environment
# Set sensors scripts executables
chmod +x $SCRIPT_DIR/sensors/*

Remember that the PRE-POST hooks are called every time the End User execute a JOD Dist Cmd, so if you would do some operations only once, please add some check before it to avoid repeating same operations each hook execution.

PreStartup initialization and PostShutdown cleanup​

Sometimes a JOD Distribution must perform some operations before his startup (init) and after his shutdown (clean). For example to enable and then disable some service required during the JOD agent execution.

You can add initialization commands to the pre-startup hooks and the cleanup comands to post-shutdown. Those commands will always be called during JOD Agent startup and shutdown even if it executed as foreground process or installed as a service.

Dynamic configurations (object info and struct)​

Another reason to use the PRE hooks is to generate a dynamic configurations for your distribution like the object's structure. That's made possible by adding generation commands to the pre-startup hook.

Following example use the JOD_MWO_LOCATION value from distribution specific configs and replace it with corresponding placeholder in the struct_TMPL.jod file, then save result to the configs/struct.jod file.

dists/resources/scripts/pre-startup.sh:generate struct.jod file dynamically
JOD_STRUCT_TMPL=$JOD_DIR/struct_TMPL.jod
JOD_STRUCT=$JOD_DIR/configs/struct.jod
logInf "Update JOD instance's structure to Location = $JOD_MWO_LOCATION"
sed -e "s/\${JOD_MWO_LOCATION}/$JOD_MWO_LOCATION/" $JOD_STRUCT_TMPL >$JOD_STRUCT

More complex object's structure can be generated using the APIs from scripts/jod/struct/builder.sh script provided by the JOD Distribution TEMPLATE. *NB!: This is an experimental feature, and it's available only for bash version.

You can generate dynamically not just the object's structure, but also any other script/configs/resource required by your distribution.

Hook script call another hook script​

When two or more Hook scripts must perform same operations, you can write all commands once in a single Hook script. Then call it from all other Hook scripts.

Here the pre-install script example that call the pre-startup hook:

pre-install.sh:call pre-startup.sh hook
logInf "Execute pre-startup.sh..."
if [ -f "$JOD_DIR/scripts/pre-startup.sh" ]; then
execScriptCommand $JOD_DIR/scripts/pre-startup.sh || ( [ "$?" -gt "0" ] \
&& logWar "Error executing PRE startup script, exit $?" && exit $? \
|| logWar "Error executing PRE startup script, continue $?" )
else
logDeb "PRE startup script not found, skipped (missing $JOD_DIR/scripts/pre-startup.sh)"
fi

Distribution specific configs​

The PRE-POST scripts in conjunction with the JOD Configs file are a powerful tool to create JOD Distribution that can adapt their self to the execution environment and end user needs.

Just declaring your variables in the dists/configs/jod_configs.sh|ps1 file from your distribution project dir, they will be available also to the PRE-POST scripts. Then, End user can easily configure distribution behaviour simply editing the JOD Config file.

Define distribution config​

Define JOD_MWO_LOCATION variable to the dists/configs/jod_configs.sh|ps1 file with a default value.

dists/configs/jod_configs.sh:define distribution specific configs
# ############### #
# MyDist's config #
# ############### #

# My Dist XY config
# Config desription and values examples
# set a value as default value or keep it as empty string ""
export JOD_MWO_LOCATION="Rome"

Use distribution config from a PRE-POST script​

Read JOD_MWO_LOCATION variable value from the dists/resources/scripts/pre-startup.sh|ps1 script.

dists/resources/scripts/pre-startup.sh:read distribution specific configs
logInf "Update JOD instance's structure to Location = $JOD_MWO_LOCATION"