You don't have to reboot the system to just eject CD / DVD from drive. Sometime Linux locks down your CD / DVD if a process reading / accessing file / directory on that DVD / CD.
Getting Your CD/DVD Out Of Drive
Simply right click on CD / DVD icon and select Eject / Unmount option. Press eject button to get the cd/dvd out. If this failed, try following method to eject the cd:
Find Out CD/DVD drive mount location
Run df or mount command to find out location, enter the following at terminal / shell prompt:
Filesystem Size Used Avail Use% Mounted on /dev/sda2 92G 22G 66G 25% / varrun 1013M 140K 1013M 1% /var/run varlock 1013M 0 1013M 0% /var/lock udev 1013M 88K 1013M 1% /dev devshm 1013M 0 1013M 0% /dev/shm lrm 1013M 34M 979M 4% /lib/modules/2.6.22-14-generic/volatile /dev/sda1 98G 19G 79G 20% /media/sda1 /dev/sda5 274G 185G 89G 68% /share /dev/scd0 3.5G 3.5G 0 100% /media/cdrom0
In this example, my CD / DVD device name is /dev/scd0 and mounted under /media/cdrom0. Now issue the following command as root user:
Warning: Following command may result into data loss. Sometime fuser command will kill all process on the system. You have been warned.
$ sudo fuser -km /media/cdrom0
# fuser -km /media/cdrom0
Now you may able to eject CD or DVD from the drive.
Related: See How to forcefully remove unmount a Linux disk partition / device using lsof and fuser command.