1.Environment:RedHat Linux Enterprise 6+Vmware Workstation 12 Pro

2.Linux shutdown and restart command summary

shutdown command : shutdown -h now (immediate poweroff)

 halt (immediate poweroff)

poweroff (immediate poweroff)

reboot command : shutdown -r now (reboot immediate)

reboot (reboot immediate)

3.Different 

a.shutdown -h now  and shutdown -r now belong to root user or root privileges.

b.halt and reboot is belong to any other user.

c.halt is the same as poweroff .