Ubuntu

Change hostname

sudo vim /etc/hosts
sudo vim /etc/hostname
sudo hostnamectl set-hostname <NEWNAME>
systemctl restart systemd-logind.service

Package install fixes

apt-get clean
apt-get autoremove
apt-get update && sudo apt-get upgrade
dpkg --configure -a
apt-get install -f

In case of postinst/preinst issues, try also

apt-get install -o APT::Immediate-Configure=false -f apt SOMEPACKAGE

Things to check

/var/log/auth.log
/var/log/syslog
/var/log/cloud-init.log

service apparmor status
apparmor_status

Solve /boot 100%

purge-old-kernels
rm *-4.4.x-yyy... not used kernels
apt-get purge linux-image-4.4.x-yyy
apt install -f