In CentOS/RHEL 7, the systemctl utility replaces some older power management commands used in previous versions. The table below compares the older and new equivalent systemctl commands. The old commands listed in the table still exist for compatibility reasons.
| Older Command | systemctl equivalent | Description |
|---|---|---|
| halt | systemctl halt | Halts the system |
| poweroff | systemctl poweroff | Powers off the system |
| reboot | systemctl reboot | Restarts the system |
| pm-suspend | systemctl suspend | Suspends the system |
| pm-hibernate | systemctl hibernate | Hibernates the system |
| pm-suspend-hybrid | systemctl hybrid-sleep | Hibernates and suspends the system |
Suspend
– Suspending the system saves the system state in RAM and with the exception of the RAM module, powers off most of the devices in the machine.
– When you turn the machine back on, the system then restores its state from RAM without having to boot again.
– Because the system state is saved in RAM and not on the hard disk, restoring the system from suspend mode is significantly faster than restoring it from hibernation, but as a consequence, a suspended system state is also vulnerable to power outages.
Hibernate
– Hibernating the system saves the system state on the hard disk drive and powers off the machine.
– When you turn the machine back on, the system then restores its state from the saved data without having to boot again.
– Because the system state is saved on the hard disk and not in RAM, the machine does not have to maintain electrical power to the RAM module, but as a consequence, restoring the system from hibernation is significantly slower than restoring it from suspend mode.