Macで、Debianインストール用のCDイメージをUSBメモリに書き込みました。そのときの作業ログです。

iMac:~ $ diskutil list
/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *500.1 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:                  Apple_HFS Macintosh HD            499.2 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
/dev/disk3
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     FDisk_partition_scheme                        *4.0 GB     disk3
   1:                 DOS_FAT_32                         4.0 GB     disk3s1
iMac:~ ishidate$ mount
/dev/disk0s2 on / (hfs, local, journaled)
devfs on /dev (devfs, local, nobrowse)
map -hosts on /net (autofs, nosuid, automounted, nobrowse)
map auto_home on /home (autofs, automounted, nobrowse)
/dev/disk3s1 on /Volumes/Untitled (msdos, local, nodev, nosuid, noowners)
iMac:~ ishidate$ sudo dd if=debian-8.0.0-i386-netinst.iso of=/dev/disk3
Password:
dd: /dev/disk3: Resource busy
iMac:~ ishidate$ sudo umount /Volumes/Untitled
umount(/Volumes/Untitled): Resource busy -- try 'diskutil unmount'
iMac:~ ishidate$ diskutil umount /Volumes/Untitled
Volume (null) on disk3s1 unmounted
iMac:~ ishidate$ sudo dd if=debian-8.0.0-i386-netinst.iso of=/dev/disk3
645120+0 records in
645120+0 records out
330301440 bytes transferred in 1325.887596 secs (249117 bytes/sec)
iMac:~ ishidate$