if /var/log/mail.log is empty or not work try:

#if /var/log/mail.log is empty or not work try:
service syslog restart 
#or 
sudo service rsyslog restart

if system datatime incorrect

# if system datatime incorrect
sudo apt-get install ntp
tzselect # set time zone
sudo dpkg-reconfigure tzdata
sudo timedatectl set-ntp on
sudo timedatectl set-timezone Asia/Hong_Kong
sudo ntpq -p

apache start / stop

# /etc/init.d/apache2 restart
OR
$ sudo /etc/init.d/apache2 restart

OR
$ sudo service apache2 restart

change to root user

sudo -s

firewall-cmd

firewall-cmd --reload

restart apache

systemctl restart apache2

kill process by PID

It’s a single line, but you’d need to put it into a shell alias or shell script in order to make it easy to use:

 kill $(lsof -i tcp:8080 | tail -n +2 | awk '{ print $2 }')

If you want to see and kill processes that don’t belong to you, then sudo needs to get involved:

 sudo kill $(sudo lsof -i tcp:8080 | tail -n +2 | awk '{ print $2 }')

ubuntu javascript default path

/usr/share/javascript 

merge copy to targe folder

rsync -av /source/ /destination/
(after checking)
rm -rf /source/