Drush 9 and MYSQL : The command 'mysql' is required for preflight but cannot be found. Please install it and retry.

[zetnet]

# ~/my-global-drush/vendor/bin/drush updb -d
 [bootstrap] Bootstrap to site [0.2 sec, 3.47 MB]
 [bootstrap] Drush bootstrap phase 2 [0.2 sec, 3.48 MB]
 [bootstrap] Try to validate bootstrap phase 2 [0.2 sec, 3.48 MB]
 [bootstrap] Try to validate bootstrap phase 2 [0.2 sec, 3.48 MB]
 [bootstrap] Try to bootstrap at phase 2 [0.21 sec, 3.52 MB]
 [bootstrap] Drush bootstrap phase: bootstrapDrupalRoot() [0.21 sec, 3.52 MB]
 [bootstrap] Change working directory to /home/mygigast/sites/dev2.urbanoutletshop/web [0.21 sec, 3.52 MB]
 [bootstrap] Initialized Drupal 8.4.0 root directory at /home/mygigast/sites/dev2.urbanoutletshop/web [0.21 sec, 3.52 MB]
 [bootstrap] Try to validate bootstrap phase 2 [0.21 sec, 3.52 MB]
 [bootstrap] Try to bootstrap at phase 2 [0.22 sec, 3.66 MB]
 [bootstrap] Drush bootstrap phase: bootstrapDrupalSite() [0.22 sec, 3.66 MB]
 [bootstrap] Initialized Drupal site default at sites/default [0.22 sec, 3.66 MB]
 [bootstrap] Drush bootstrap phase 5 [0.23 sec, 3.68 MB]
 [bootstrap] Try to validate bootstrap phase 5 [0.23 sec, 3.69 MB]
 [bootstrap] Try to validate bootstrap phase 5 [0.23 sec, 3.69 MB]
 [bootstrap] Try to validate bootstrap phase 5 [0.23 sec, 3.69 MB]
 [bootstrap] Try to validate bootstrap phase 5 [0.23 sec, 3.69 MB]
 [bootstrap] Try to bootstrap at phase 5 [0.23 sec, 3.69 MB]
 [bootstrap] Drush bootstrap phase: bootstrapDrupalConfiguration() [0.23 sec, 3.69 MB]
 [debug] Create from request [0.23 sec, 3.72 MB]
 [debug] Add service modifier [0.24 sec, 3.79 MB]
 [bootstrap] Try to validate bootstrap phase 5 [0.24 sec, 3.79 MB]
 [warning] system() has been disabled for security reasons filesystem.inc:368 [0.24 sec, 3.83 MB]
 [bootstrap] The command 'mysql' is required for preflight but cannot be found. Please install it and retry. [0.24 sec, 3.82 MB]
 [bootstrap] Could not bootstrap at phase 5 [0.24 sec, 3.82 MB]
 [error]  Drush command terminated abnormally due to an unrecoverable error.
Error: Call to undefined function drupal_get_installed_schema_version() in /home/mygigast/sites/XXXXXXX/web/core/includes/install.inc, line 80 [0.25 sec, 3.83 MB]
Status: 500 Internal Server Error
X-Powered-By: PHP/5.6.31
Content-type: text/html; charset=UTF-8

# mysql --version
/usr/bin/mysql  Ver 15.1 Distrib 10.0.32-MariaDB, for Linux (x86_64) using readline 5.1

[weitzman]

Can you fix this: [warning] system() has been disabled for security reasons filesystem.inc:368 [0.24 sec, 3.83 MB]