php - When I run composer install inside CakePHP3 I get extension missing errrors -

when run composer install inside cakephp3 project next errors:

  problem 1     - installation request cakephp/cakephp 3.2.12 -> satisfiable cakephp/cakephp[3.2.12].     - cakephp/cakephp 3.2.12 requires ext-mbstring * -> requested php extension mbstring missing system.   problem 2     - cakephp/cakephp 3.2.12 requires ext-mbstring * -> requested php extension mbstring missing system.     - cakephp/debug_kit 3.2.9 requires cakephp/cakephp >=3.1.0 <4.0 -> satisfiable cakephp/cakephp[3.2.12].     - installation request cakephp/debug_kit 3.2.9 -> satisfiable cakephp/debug_kit[3.2.9]. 

i using ubuntu 16.04 (note disabled packages php5)

how fix issue?

as error message states environment missing mbstring extension install it: sudo apt install php-mbstring