sub-process /usr/bin/dpkg returned an error code (1) ubuntu apache2 (OpsWorks)

When do
apt-get install apache2

got error:

sub-process /usr/bin/dpkg returned an error code (1) ubuntu apache2

Solution:  do these first:

apt-get remove --purge apache2
apt-get install -f
apt-get autoremove

may need if you remove apache2 got same issue:
umount /var/log/apache2

umount /var/www

Then:
apt-get install apache2