AIX
# cd /
# umount <directory>
eg.
# umount /cdrom
If managed by cdromd daemon
# cdeject cd0
HP-UX
# pfs_umount <directory>
eg
# pfs_umount /cdrom
or umount
# cd /
# umount /cdrom
Solaris
# cd /
# umount /cdrom
If using vold
# eject cdrom
# cd /
# umount