Run this script before cloning a template

preclone-deb.sh optimized for ubuntu 18.04

#!/bin/bash

# apt   
apt --yes --purge autoremove
apt clean

# cleanup /var/log
/usr/sbin/logrotate –f /etc/logrotate.conf
find /var/log/ -name "*.gz" -exec rm {} \;
find /var/log/ -name "*.1" -exec rm {} \;
/bin/cat /dev/null > /var/log/wtmp
journalctl --vacuum-size=10M

# clean tmp
/bin/rm –rf /tmp/*
/bin/rm –rf /var/tmp/*

# clean root history
/bin/rm -f ~root/.bash_history
unset HISTFILE

# remote SSH keys
systemctl stop ssh.service
rm -f /etc/ssh/*key*

# clean up personal stuff
rm -rf /root/.ssh
rm -f /root/.bash_history

# clean out udev persistance
rm -f /etc/udev/rules.d/70-persistent-*.rules

# backup rc.local before modification
#mv -f /etc/rc.local{,.preclone}

cat > /etc/rc.local << EOF
#!/bin/bash
#
# post-clone script (cleans up, re-initializes and such after clone)
#

# the sshd keys have been remove by the pre-clone script - generate new ones
/usr/sbin/dpkg-reconfigure openssh-server
systemctl restart ssh.service

# restore original rc.local (keep at the bottom)
#/bin/mv -f /etc/rc.local{.preclone,}
/bin/rm -f /etc/rc.local

exit 0
EOF

# make the new script executable
chmod 755 /etc/rc.local

# Discard unused space
fstrim -a

# power off the system
shutdown -h now