Ubuntu: Suspend and reboot at specific times using Cron

If you have a server at home and you want it to be on only during specific times and not 24/7, this script is for you.

Cron not only is the best tool for this, it also handles scheduled tasks.

Cron is a system daemon used to execute desired tasks (in the background) at designated times.

Method

Install Cron on Ubuntu if it is not already installed.

Create a new file, suspend_until, in your ~/Documents/ and place the following contents in it. This script is written by Romke van der Meulen.

#!/bin/bash
    
    # Auto suspend and wake-up script
    #
    # Puts the computer on standby and automatically wakes it up at specified time
    #
    # Written by Romke van der Meulen <redge.online@gmail.com>
    # Minor mods fossfreedom for AskUbuntu
    #
    # Takes a 24hour time HH:MM as its argument
    # Example:
    # suspend_until 9:30
    # suspend_until 18:45
    
    # ------------------------------------------------------
    # Argument check
    if [ $# -lt 1 ]; then
    echo "Usage: suspend_until HH:MM"
    exit
    fi
    
    # Check whether specified time today or tomorrow
    DESIRED=$((`date +%s -d "$1"`))
    NOW=$((`date +%s`))
    if [ $DESIRED -lt $NOW ]; then
    DESIRED=$((`date +%s -d "$1"` + 24*60*60))
    fi
    
    # Kill rtcwake if already running
    sudo killall rtcwake
    
    # Set RTC wakeup time
    # N.B. change "mem" for the suspend option
    # find this by "man rtcwake"
    sudo rtcwake -a -m disk -t $DESIRED &
    
    # feedback
    echo "Suspending..."
    
    # give rtcwake some time to make its stuff
    sleep 2
    
    # then suspend
    # N.B. dont usually require this bit
    #sudo pm-suspend
    
    # Any commands you want to launch after wakeup can be placed here
    # Remember: sudo may have expired by now
    
    # Wake up with monitor enabled N.B. change "on" for "off" if
    # you want the monitor to be disabled on wake
    xset dpms force on
    
    # and a fresh console
    clear
    echo "Good morning!"

Change the permission of the file so that it is executable.
```
    $ sudo chmod +x ~/Documents/suspend_until
```
Run crontab.
```
    $ sudo crontab -e
```
Place the following line at the end of the file.
```
      00 02 * * * /home/user/Documents/suspend_until 09:00
```
This basically tells the server to execute the suspend_until script at 2:00 AM. The 09:00 appended at the end of the line tells the server to wake up at 9:00 AM. The details are all explained in the script.
Save the crontab file and reboot.