Getting error 'docker not found' while running the pipleline.

Getting error 'docker not found' while running the pipleline. Have run the simple code 'docker info'. Running and registering Gitlab Runner using official docker images. Executor I set as 'docker' in one runner and as 'shell' in the other runner. shell scripting code like 'echo' command working using both the runners. But docker commands are not working and giving error. It's not giving error and giving problem every time