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I have a USB stick which contained a single FAT32 partition and was working fine. Then I ran the Ubuntu Server 18.04 installer, shrinking the partition and adding a logical Ext4 partition to install Ubuntu. Now macOS won't recognize the disk, it says I have to initialize it. I want to figure out what I need to change to make macOS mount the FAT32 partition.

diskutil list

/dev/disk2 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:     FDisk_partition_scheme                        *31.0 GB    disk2
   1:             Windows_FAT_32                         8.0 GB     disk2s1
   2:                      Linux                         6.0 GB     disk2s5

# diskutil mount /dev/disk2s1
Volume on disk2s1 failed to mount
# diskutil repairVolume disk2s1
Error starting file system repair for disk2s1: Unrecognized file system (-69846)

gpt -r show disk2

   start      size  index  contents
       0         1         MBR
       1      2047         
    2048  15625000      1  MBR part 12
15627048      1238         
15628286  11716610      2  MBR part 5
27344896  33210368      

fdisk /dev/disk2

Disk: /dev/disk2    geometry: 3769/255/63 [60555264 sectors]
Signature: 0xAA55
         Starting       Ending
 #: id  cyl  hd sec -  cyl  hd sec [     start -       size]
------------------------------------------------------------------------
*1: 0C    1   0   1 - 1023  63  32 [      2048 -   15625000] Win95 FAT32L
 2: 05 1023  63  32 - 1023  63  32 [  15628286 -   11716610] Extended DOS
 3: 00    0   0   0 -    0   0   0 [         0 -          0] unused      
 4: 00    0   0   0 -    0   0   0 [         0 -          0] unused      
Signature: 0xAA55
         Starting       Ending
 #: id  cyl  hd sec -  cyl  hd sec [     start -       size]
------------------------------------------------------------------------
 1: 83 1023  63  32 - 1023  63  32 [  15628288 -   11716608] Linux files*
 2: 00    0   0   0 -    0   0   0 [         0 -          0] unused      
 3: 00    0   0   0 -    0   0   0 [         0 -          0] unused      
 4: 00    0   0   0 -    0   0   0 [         0 -          0] unused 

On a Linux machine it mounts just fine, and fdisk -l looks different:

Disk /dev/sdb: 28.9 GiB, 31004295168 bytes, 60555264 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0xb5327c62

Device     Boot    Start      End  Sectors  Size Id Type
/dev/sdb1  *        2048 15627047 15625000  7.5G  c W95 FAT32 (LBA)
/dev/sdb2       15628286 27344895 11716610  5.6G  5 Extended
/dev/sdb5       15628288 27344895 11716608  5.6G 83 Linux
  • Did you resize the filesystem? If you don't need the files that were on the original partition, you could just initialize the volume on macOS. – user3052786 Feb 3 at 22:16

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