Accessing Atari ST disk images on Linux

This post leverages support for Atari Hard Disk Interface Partition (AHDI) partition tables in the Linux kernel, activated by default in Debian, and in the parted partition editor.

Accessing the content of a partition using a user mounted loop device

This is the easiest procedure and should be tried to first. Depending if your Linux kernel has support for AHDI partition tables, and the size of the FAT system on the partition, this procedure might not work. In that case, try the procedure using mtools further below.

Attach a disk image called hd80mb.image to a loop device:

$ udisksctl loop-setup --file hd80mb.image
Mapped file hd80mb.image as /dev/loop0

Notice how the kernel detected the partition table:

$ dmesg | grep loop0
[160892.151941] loop0: detected capacity change from 0 to 164138
[160892.171061]  loop0: AHDI p1 p2 p3 p4

Inspect the block devices created for each partition:

$ lsblk | grep loop0

If the partitions are not already mounted by udisks2 under /media/, mount them manually:

$ sudo mount /dev/loop0p1 /mnt/
$ ls /mnt/
SHDRIVER.SYS

When you are finished copying data, unmount the partition, and detach the loop device.

$ sudo umount /mnt
$ udisksctl loop-delete --block-device /dev/loop0

Accessing the content of a partition using mtools and parted

This procedure uses the mtools package and the support for the AHDI partition scheme in the parted partition editor.

Display the partition table, with partitions offsets in bytes:

$ parted st_mint-1.5.img -- unit B print
...
Partition Table: atari
Disk Flags: 

Number  Start       End         Size        Type     File system  Flags
 1      1024B       133170175B  133169152B  primary               boot
 2      133170176B  266339327B  133169152B  primary
 3      266339328B  399508479B  133169152B  primary
 4      399508480B  532676607B  133168128B  primary

Set some Atari-friendly mtools options:

$ export MTOOLS_SKIP_CHECK=1
$ export MTOOLS_NO_VFAT=1

List the content of the partition, passing as parameter the offset in bytes of the partition: For instance here we are interested in the second partition, and the parted output above indicates that this partition starts at byte offset 133170176 in the disk image.

$ mdir -s -i st_mint-1.5.img@@133170176
 Volume in drive : has no label
Directory for ::/

demodata          2024-08-27  11:43 
        1 file                    0 bytes

Directory for ::/demodata

We can also use the command mcopy with a similar syntax to copy data from and to the disk image. For instance we copy a file named file.zip to the root directory of the second partition:

$ mcopy -s -i st_mint-1.5.img@@133170176 file.zip ::

Recompiling mtools to access large partitions

With disk images having large AHDI partitions (well considered large in 1992 …), you might encounter the error

mdir -s -i cecile-falcon-singlepart-1GB.img@@1024
init: sector size too big
Cannot initialize '::'

This error is caused by the non-standard large logical sectors that the TOS uses for large FAT partitions (see the Atari Hard Disk Filesystem reference on page 41, TOS partitions size)

We can inspect the logical sector size using fsck tools:

$ udiskctl loop-setup --file cecile-falcon-singlepart-1GB.img
$ sudo fsck.fat -Anv /dev/loop0p1
fsck.fat 4.2 (2021-01-31)
...
Media byte 0xf8 (hard disk)
16384 bytes per logical sector

To access the partition, you need to patch mtools, so that it supports a logical sector size of 16384 bytes. For this you need to change the MAX_SECTOR macro from 8192 to 16384 in msdos.h in the mtools distribution and recompile. A rebuilt mtools is then able to access the partition:

$ /usr/local/bin/mdir -s -i cecile-falcon-singlepart-1GB.img@@1024
 Volume in drive : has no label
Directory for ::/

CECILE   SYS      8462 1998-03-27  22:42 
NEWDESK  INF       804 2024-09-09   9:23 
        2 files               9 266 bytes
                      1 072 463 872 bytes free