doc/pages/02.contribute/04.packaging_apps/12.hooks/packaging_apps_hooks.md

The use of YunoHost hooks

Hooks allow you to trigger a script when an action is performed by the system.
The most obvious case is adding a user. If the app has a post_user_create hook, this hook will be triggered as soon as a user is added.
Therefore, this allows an application to execute actions based on events occurring on the system.

List of available hooks

• post_domain_add
  After adding a domain.
• post_domain_remove
  After deleting a domain.
• post_user_create
  After adding a user.
• post_user_delete
  After deleting a user.
• post_iptable_rules
  After reloading the firewall.
• pre_backup_delete
  Before deleting a backup.
• post_backup_delete
  After deleting a backup.
• post_app_addaccess
  After adding an authorized user to an application.
• post_app_removeaccess
  After the removal of a user's authorization on an application.
• post_app_clearaccess
  After erasing all the access rules on an application.
• post_app_install After installing an application.
• post_app_upgrade After upgrading an application.
• post_app_remove After removing an application.
• post_app_change_url After modifying the path and/or the domain name of an application.
• post_cert_update After updating a certificate
• conf_regen
  Before and after the regeneration of a service configuration.
  Services supported by regen-conf:
• avahi-daemon
• dnsmasq
• dovecot
• fail2ban
• glances
• metronome
• mysql
• nginx
• nslcd
• nsswitch
• postfix
• rspamd
• slapd
• ssh
• ssl

Hooks setup

With the exception of the conf_regen hook, all hooks are used in the same way.
First of all, you have to understand that a hook is a simple bash script that will be executed by YunoHost when the indicated event occurs.
To add a hook to YunoHost, you must use a "hooks" folder at the root of the application package. Then, put your script in this folder under the name of the corresponding hook.

For example:
For the hook post_user_create, the script which will have to be executed for this hook should be placed in hooks/post_user_create in the app package.

During the installation and the upgrade of the application, the scripts in the hooks folder will be duplicated in the folder /etc/yunohost/hooks.d/ in the folder corresponding to the hook, then under the name 50-$app.
All hooks belonging to an application will be removed when the apllication is deleted.

Building a hook script

As a bash script, a hook script must start with the bash shebang.

#!/bin/bash

Then you have to take the arguments given by YunoHost when calling the script.
Each hook offers different arguments.

post_domain_add and post_domain_remove

domain=$1

post_user_create

username=$1
mail=$2
password=$3 # Clear password
firstname=$4
lastname=$5

post_user_delete

username=$1
purge=$2  # True/False Indicates whether the user folder has been deleted or not.

post_iptable_rules

upnp=$1  # True/False Indicates if UPnP is activated or not.
ipv6=$2  # True/False Indicates whether IPV6 is enabled or not.

pre_backup_delete and post_backup_delete

backup_name=$1

post_app_install, post_app_upgrade, post_app_remove and post_app_change_url

Usable variables in these scripts are the same as those available in associated actions scripts.

Example: for post_app_install the variables are the same as for the script install

post_app_addaccess and post_app_removeaccess

app_id=$1
users=$2  # All authorized users on the app. Separated by commas.

post_app_clearaccess

app_id=$1

post_cert_update

domain=$1

The rest of the script depends on what you want to do in it.

conf_regen special case

The conf_regen hook is a more delicate hook, either for its implementation or for its content.

conf_regen hook setup

A conf_regen hook should not be placed in the application's hooks folder. It must be set up manually.
The hook should be copied, indicating to which service it is linked.

cp hook_regen_conf /usr/share/yunohost/hooks/conf_regen/50-SERVICE_$app

When removing the application, this hook must be removed manually.

Building conf_regen hook script

conf_regen hook is called two times, a first time after analysis of the configuration and before any modification of the files, then a second time after applying the modifications, if there has been modifications.

conf_regen hook script should look like this:

#!/bin/bash

force=${2:-0}  # 0/1 --force argument
dryrun=${3:-0}  # 0/1 --dry-run argument
pending_conf=$4 # Path of the pending conf file

do_pre_regen() {
  # Put your code here for pre regen conf.
}

do_post_regen() {
  # Put your code here for post regen conf.
  # Be careful, this part will be executed only if the configuration has been modified.
}

case "$1" in
  pre)
    do_pre_regen
    ;;
  post)
    do_post_regen
    ;;
  *)
    echo "Hook called with unknown argument \`$1'" >&2
    exit 1
    ;;
esac

exit 0