很简单，两个目录间隔，增加一个反斜杠 \  ，用 \: 代替：。

范例：我的设置

[root@sh disk]# cat /etc/auto.master |grep -v '#'
/misc   /etc/auto.misc
/disk   /etc/auto.disk
/net    -hosts
+dir:/etc/auto.master.d
+auto.master

新增加的/etc/auto.disk，映射目录是 /disk

#
# This is an automounter map and it has the following format
# key [ -mount-options-separated-by-comma ] location
# Details may be found in the autofs(5) manpage

#cd             -fstype=iso9660,ro,nosuid,nodev :/dev/cdrom

# the following entries are samples to pique your imagination
Photos_1        -fstype=ext4           :/dev/disk/by-uuid/1d09e797-f127-40d5-940c-81a3dab1cf33
Works_1         -fstype=ext4           :/dev/disk/by-uuid/9aa81cbe-f543-4efd-9617-3edd3978a9b3
EntVideos_1     -fstype=ext4           :/dev/disk/by-uuid/67f5416b-d62e-4a7a-9fd2-1e8fb31435e8
vdisk           -fstype=fuse.mergerfs  :/disk/Photos_1\:/disk/EntVideos_1

注意最后一行，两个间隔是 \: 

/disk/vdisk 的虚拟目录，由/disk/Photos_1  （3T硬盘1）+ /disk/EntVideos_1（3T硬盘 2） 叠加而来。然后 /disk/vdisk 开放给samba使用。

参考文献：https://wzyboy.im/post/1148.html