If you see this error on Ubuntu terminal when install Laravel by Composer show file permissions error like below:

Cannot create cache directory /home/webadmin/.composer/cache/repo/https—packagist.org/, or directory is not writable. Proceeding without cacheCannot create cache directory /home/webadmin/.composer/cache/files/, or directory is not writable. > Cannot create cache directory /home/webadmin/.composer/cache/files/, or directory is not writable. Proceeding without cache

Then do like below:

Change the group permission for the folder

sudo chown -R yourusername /home/yourusername/.composer/cache/repo/https—packagist.org

and the Files folder too

sudo chown -R yourusername /home/yourusername/.composer/cache/files/

I’m assuming “yourusername” is your username.

If the problem still persists try

sudo chown -R yourusername /home/yourusername/.composer

Now, there is a chance that you won’t be able to create your app directory, if that happens do the same for your html folder or the folder you are trying to create your laravel project in.

Resource link:http://stackoverflow.com/questions/35874482/cannot-create-cache-directory-or-directory-is-not-writable-proceeding-withou