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I can run the shell command:

unionfs-fuse /changedata=RW:/immutedata=RO -o cow /data

This mounts the filesystem exactly how I want to. Now I need to incorporate it into the automounter so that it's remounted upon demand.

What I tried in /etc/auto.misc:

/data -fstype=fuse,cow /changedata=RW:/immutedata=RO

What automount --debug -f /etc/auto.master says when I do ls /data:

handle_packet: type = 5
handle_packet_missing_direct: token 19, name /data, request pid 6063
attempting to mount entry /data
lookup_mount: lookup(file): looking up /data
lookup_mount: lookup(file): /data -> -fstype=fuse,cow /changedata=RW:/immutedata=RO
parse_mount: parse(sun): expanded entry: -fstype=fuse,cow /changedata=RW:/immutedata=RO
parse_mount: parse(sun): gathered options: fstype=fuse,cow
parse_mount: parse(sun): dequote("/changedata=RW:/immutedata=RO") -> /changedata=RW:/immutedata=RO
parse_mapent: parse(sun): gathered options: fstype=fuse,cow
parse(sun): invalid location 
dev_ioctl_send_fail: token = 19
failed to mount /data

Google reveals little. Man pages are rather empty on the incorporation of this filesystem.

Maybe I should just put it in /etc/fstab and ask users to remount?

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