Loner T,
Thank you so much for the information and being so patient with a newbie. Unfortunately I think even changing the partition type is proving to be an issue, and I am moving backwards! Here is the output of diskutil list, modified just slightly so that my actual name is redacted, but all else is intact:
Redacteds-MacBook-Pro:~ redacted$ diskutil list
/dev/disk0
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *500.1 GB disk0
1: Apple_HFS 209.7 MB disk0s1
2: Apple_HFS Macintosh HD 250.0 GB disk0s2
3: Apple_Boot Recovery HD 650.0 MB disk0s3
4: Microsoft Basic Data BOOTCAMP 249.2 GB disk0s4
Shouldn't partition 1, highlighted in red be EFI? To effect such a change, I ran GPT fdisk; here is the dialogue from the command line.
redacteds-MacBook-Pro:~ redacted$ sudo gdisk /dev/disk0
Password:
GPT fdisk (gdisk) version 0.8.10
Warning: Devices opened with shared lock will not have their
partition table automatically reloaded!
Partition table scan:
MBR: protective
BSD: not present
APM: not present
GPT: present
Found valid GPT with protective MBR; using GPT.
Command (? for help): t
Partition number (1-4): 1
Current type is 'Apple HFS/HFS+'
Hex code or GUID (L to show codes, Enter = AF00): L
0700 Microsoft basic data 0c01 Microsoft reserved 2700 Windows RE
3000 ONIE boot 3001 ONIE config 4100 PowerPC PReP boot
4200 Windows LDM data 4201 Windows LDM metadata 7501 IBM GPFS
7f00 ChromeOS kernel 7f01 ChromeOS root 7f02 ChromeOS reserved
8200 Linux swap 8300 Linux filesystem 8301 Linux reserved
8302 Linux /home 8400 Intel Rapid Start 8e00 Linux LVM
a500 FreeBSD disklabel a501 FreeBSD boot a502 FreeBSD swap
a503 FreeBSD UFS a504 FreeBSD ZFS a505 FreeBSD Vinum/RAID
a580 Midnight BSD data a581 Midnight BSD boot a582 Midnight BSD swap
a583 Midnight BSD UFS a584 Midnight BSD ZFS a585 Midnight BSD Vinum
a800 Apple UFS a901 NetBSD swap a902 NetBSD FFS
a903 NetBSD LFS a904 NetBSD concatenated a905 NetBSD encrypted
a906 NetBSD RAID ab00 Apple boot af00 Apple HFS/HFS+
af01 Apple RAID af02 Apple RAID offline af03 Apple label
af04 AppleTV recovery af05 Apple Core Storage be00 Solaris boot
bf00 Solaris root bf01 Solaris /usr & Mac Z bf02 Solaris swap
bf03 Solaris backup bf04 Solaris /var bf05 Solaris /home
bf06 Solaris alternate se bf07 Solaris Reserved 1 bf08 Solaris Reserved 2
bf09 Solaris Reserved 3 bf0a Solaris Reserved 4 bf0b Solaris Reserved 5
c001 HP-UX data c002 HP-UX service ea00 Freedesktop $BOOT
eb00 Haiku BFS ed00 Sony system partitio ed01 Lenovo system partit
Press the <Enter> key to see more codes: L
ef00 EFI System ef01 MBR partition scheme ef02 BIOS boot partition
fb00 VMWare VMFS fb01 VMWare reserved fc00 VMWare kcore crash p
fd00 Linux RAID
Hex code or GUID (L to show codes, Enter = af00): ef00
Changed type of partition to 'EFI System'
Command (? for help): q
Redacteds-MacBook-Pro:~ redacted$
By the above dialog, one would assume that the partition type would have changed. Then I promptly rebooted the machine. Am I missing something stupid simple here that's not causing the writes to be committed to disk? Do I have to use single user mode, or log in as root?
Thanks again for your help and patience