I used diskutil to see that the CD is /dev/disk4. The CD currently in the drive has twelve tracks, so the number of mount points looks correct.
/dev/disk4 (external, physical): #: TYPE NAME SIZE IDENTIFIER 0: CD_partition_scheme *391.4 MB disk4 1: CD_DA 32.0 MB disk4s1 2: CD_DA 39.4 MB disk4s2 3: CD_DA 29.7 MB disk4s3 4: CD_DA 24.9 MB disk4s4 5: CD_DA 40.0 MB disk4s5 6: CD_DA 39.4 MB disk4s6 7: CD_DA 36.8 MB disk4s7 8: CD_DA 25.7 MB disk4s8 9: CD_DA 31.2 MB disk4s9 10: CD_DA 32.6 MB disk4s10 11: CD_DA 35.1 MB disk4s11 12: CD_DA 24.5 MB disk4s12
When I try
diskutil eject /dev/disk4 or
diskutil eject /dev/disk4s1 I get Volume timed out while waiting to eject.
If I reboot, the CD in the drive is mounted fine.
I'm using a Newer Technology miniStack connected to a late 2015 iMac running OS X 10.11.6.
Is there a way to force the CD to eject to save myself from having to reboot my computer every couple days?