diff --git a/scripts/_common.sh b/scripts/_common.sh
index f07a1be..1e3195f 100644
--- a/scripts/_common.sh
+++ b/scripts/_common.sh
@@ -1,2 +1,88 @@
 #!/bin/bash
-# unused at the moment
+# Source: https://github.com/YunoHost-Apps/coin_ynh/
+
+# Open a connection as a user
+#
+# example: ynh_psql_connect_as 'user' 'pass' <<< "UPDATE ...;"
+# example: ynh_psql_connect_as 'user' 'pass' < /path/to/file.sql
+#
+# usage: ynh_psql_connect_as user pwd [db]
+# | arg: user - the user name to connect as
+# | arg: pwd - the user password
+# | arg: db - the database to connect to
+ynh_psql_connect_as() {
+    ynh_die "ynh_psql_connect_as is not yet implemented"
+}
+
+# # Execute a command as root user
+#
+# usage: ynh_psql_execute_as_root sql [db]
+# | arg: sql - the SQL command to execute
+# | arg: db - the database to connect to
+ynh_psql_execute_as_root () {
+        su -c "psql" - postgres <<< ${1}
+}
+
+# Execute a command from a file as root user
+#
+# usage: ynh_psql_execute_file_as_root file [db]
+# | arg: file - the file containing SQL commands
+# | arg: db - the database to connect to
+ynh_psql_execute_file_as_root() {
+     ynh_die "ynh_psql_execute_file_as_root is not yet implemented"
+}
+
+# Create a database and grant optionnaly privilegies to a user
+#
+# usage: ynh_psql_create_db db [user [pwd]]
+# | arg: db - the database name to create
+# | arg: user - the user to grant privilegies
+# | arg: pwd - the password to identify user by
+ynh_psql_create_db() {
+    db=$1
+    # grant all privilegies to user
+    if [[ $# -gt 1 ]]; then
+        ynh_psql_create_user ${2} "${3}"
+        su -c "createdb -O ${2} $db" -  postgres
+    else
+        su -c "createdb $db" -  postgres
+    fi
+}
+
+# Drop a database
+#
+# usage: ynh_psql_drop_db db
+# | arg: db - the database name to drop
+ynh_psql_drop_db() {
+    su -c "dropdb ${1}" -  postgres
+}
+
+# Dump a database
+#
+# example: ynh_psql_dump_db 'roundcube' > ./dump.sql
+#
+# usage: ynh_psql_dump_db db
+# | arg: db - the database name to dump
+# | ret: the psqldump output
+ynh_psql_dump_db() {
+    ynh_die "ynh_psql_dump_db is not yet implemented"
+}
+
+
+# Create a user
+#
+# usage: ynh_psql_create_user user pwd [host]
+# | arg: user - the user name to create
+# | arg: pwd - the password to identify user by
+ynh_psql_create_user() {
+        ynh_psql_execute_as_root \
+        "CREATE USER ${1} WITH PASSWORD '${2}';"
+}
+
+# Drop a user
+#
+# usage: ynh_psql_drop_user user
+# | arg: user - the user name to drop
+ynh_psql_drop_user() {
+    su -c "dropuser ${1}" - postgres
+}