diskutil

Mounts and unmounts volumes and disks, checks disks for consistency, erases optical disks, wipes disks with a security wipe, partitions disks, manipulates RAID sets, and so on.

This utility is the command-line counterpart to the Disk Utility application.

fsck, fsck_msdos, fsck_hfs

Checks a file system for consistency.

hdiutil

Creates and manipulates disk images, including attaching disk images for mounting.

mount and umount

(Also mount_afp, mount_autofs, mount_cd9660, mount_cddafs, mount_fdesc, mount_ftp, mount_hfs, mount_msdos, mount_nfs, mount_ntfs, mount_smbfs, mount_udf, mount_union, mount_url, mount_volfs, and mount_webdav)

Mounts and unmounts volumes.

If you unmount automounted volumes behind the back of the disk arbitrartion system, you can cause strange behavior in the GUI. Use these commands with care, and if you are trying to unmount an automounted volume, use hdiutil or diskutil instead.