Create a bootable USB in OSX permalink

I often find myself having to (re-)lookup the steps to create a bootable USB drive containing some variant of Linux to help me recover or update my system. Below are those steps.

  1. Convert the .iso file to .img using the convert option of hdiutil:

    ~ ❯❯❯ hdiutil convert -format UDRW -o output.img linuxmint-17.2-cinnamon-64bit.iso
Reading Driver Descriptor Map (DDM : 0)…
Reading Linux Mint 17.2 Cinnamon 64-bit  (Apple_ISO : 1)…
Reading Apple (Apple_partition_map : 2)…
Reading Linux Mint 17.2 Cinnamon 64-bit  (Apple_ISO : 3)…
..................................................................................
Reading EFI (Apple_HFS : 4)…
..................................................................................
Reading Linux Mint 17.2 Cinnamon 64-bit  (Apple_ISO : 5)…
..................................................................................
Elapsed Time:  6.512s
Speed: 238.9Mbytes/sec
Savings: 0.0%
created: output.img.dmg

    In this case, I’m converting a Linux Mint 17.2 Rafaela live CD .iso.

    Note: OSX puts the .dmg ending on the output file automatically.

  2. Get the list of current USB devices:

    ~ ❯❯❯ diskutil list
/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *251.0 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:          Apple_CoreStorage                         250.1 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
/dev/disk1
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Macintosh HD           *249.8 GB   disk1
                                 Logical Volume on disk0s2
                                 E3DC7498-72BB-4E26-9652-AAF99F84DC1F
                                 Unencrypted
/dev/disk2
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *16.0 GB    disk2
   1:                        EFI EFI                     209.7 MB   disk2s1
   2:                  Apple_HFS Backups                 15.7 GB    disk2s2

  3. Insert your USB drive.

  4. Determine the device node assigned to your flash media by diff-ing the list of USB devices:

    ~ ❯❯❯ diskutil list
/dev/disk0
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *251.0 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:          Apple_CoreStorage                         250.1 GB   disk0s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk0s3
/dev/disk1
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Macintosh HD           *249.8 GB   disk1
                                 Logical Volume on disk0s2
                                 A0A0A0A0-B1B1-C2C2-D3D3-E4E4E4E4E4E4
                                 Unencrypted
/dev/disk2
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *16.0 GB    disk2
   1:                        EFI EFI                     209.7 MB   disk2s1
   2:                  Apple_HFS Backups                 15.7 GB    disk2s2
/dev/disk3
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     Apple_partition_scheme                        *4.0 GB     disk3
   1:        Apple_partition_map                         4.1 KB     disk3s1
   2:                  Apple_HFS                         2.3 MB     disk3s2

    In my case, I’m targeting /dev/disk3. Obviously, from this point out, replace the disk number as needed.

  5. Unmount the USB device:

    ~ ❯❯❯ diskutil unmountDisk /dev/disk3
Unmount of all volumes on disk3 was successful

    (replace N with the disk number from the last command; in the previous example, N would be 2).

  6. Use the dd command to write the contents of the newly generated .img file to the USB device:

    ~ ❯❯❯ sudo dd if=output.img.dmg of=/dev/rdisk3 bs=1m
1555+1 records in
1555+1 records out
1631322112 bytes transferred in 328.764960 secs (4961971 bytes/sec)

    Helpful tips about the dd command:

    • Using /dev/rdisk instead of /dev/disk may be faster
    • If you see the error dd: Invalid number '1m', you are using GNU dd. Use the same command but replace bs=1m with bs=1M
    • If you see the error dd: /dev/diskN: Resource busy, make sure the disk is not in use. Start the ‘Disk Utility.app’ and unmount (don’t eject) the drive

  7. Eject and remove the USB device from the computer:

    ~ ❯❯❯ diskutil unmountDisk /dev/disk3
Unmount of all volumes on disk3 was successful
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