Magento 2 Installation – Errors Installing Sample Data: Class Not Found

I've also been struggling to install the sample data. It appears that somthing is currently broken here (Oct 2015) and the instructions in the devdocs didn't work for me either. I was experiencing the same composer issues and the magento sampledata:install isn't even there.

Instead I've been following the "From GitHub Repository" instructions on the sample data's readme file:

Just clone the repo somewhere (can be outside your project folder, since the tool is taking care of symlinking the individual modules):

git clone https://github.com/magento/magento2-sample-data.git ~/sample-data

Then run the "installer" script:

php -f ~/sample-data/dev/tools/build-sample-data.php -- --ce-source="$PATH_TO_YOUR_MAGENTO2_PROJECTROOT"

After that run the update script:

cd $PATH_TO_YOUR_MAGENTO2_PROJECTROOT
bin/magento setup:upgrade

And you should see the sample data being installed (takes a while...):

[...]
Module 'Magento_DownloadableSampleData':
Installing data..
Module 'Magento_ThemeSampleData':
Installing data..
Module 'Magento_OfflineShippingSampleData':
Installing data..
Module 'Magento_ConfigurableSampleData':
Installing data..
Module 'Magento_BundleSampleData':
Installing data..
Module 'Magento_ProductLinksSampleData':
Installing data..
Module 'Magento_ReviewSampleData':
Installing data..
[...]

Don't forget to clear caches and fix permissions and you should see all the sample data in the backend and the frontend now...

Install sample data before installing Magento, I have waste lot of time in this. Read official documentation to install sample data.

To import database via terminal use this command

mysql -u <db_user> -p <database> < sample.sql

mysql -u root -p  test < sample.sql