Here the simpeline

REALMNT="/mnt/media_rw/extSdCard" mount -t ext4 -o rw,noatime /dev/block/mmcblk1p1 "$REALMNT" sdcard "$REALMNT" /storage/extSdCard 1023 1023 &

And here writable ext4 on external sd

chown media_rw:media_rw /mnt/media_rw/extSdCard chmod g+w /mnt/media_rw/extSdCard

You can change "extSdCard" like "sdcard1" where your external sdcard mounted

Iam used stockrom with Kingroot, but I try Supersu its trouble with mounting filesystem

Here the simpeline

#!/system/bin/sh
REALMNT="/mnt/media_rw/extSdCard"
mount -t ext4 -o rw,noatime /dev/block/mmcblk1p1     "$REALMNT"
sdcard "$REALMNT" /storage/extSdCard 1023 1023 &

And here writable ext4 on external sd

#!/system/bin/sh
chown media_rw:media_rw /mnt/media_rw/extSdCard
chmod g+w /mnt/media_rw/extSdCard

You can change "extSdCard" like "sdcard1" where your external sdcard mounted

Iam used stockrom with Kingroot, but I try Supersu its trouble with mounting filesystem

Here the simpeline

REALMNT="/mnt/media_rw/extSdCard" mount -t ext4 -o rw,noatime /dev/block/mmcblk1p1 "$REALMNT" sdcard "$REALMNT" /storage/extSdCard 1023 1023 &

You can change "extSdCard" like "sdcard1" where your external sdcard mounted

Iam used stockrom with Kingroot, but I try Supersu its trouble with mounting filesystem

Here the simpeline

REALMNT="/mnt/media_rw/extSdCard" mount -t ext4 -o rw,noatime /dev/block/mmcblk1p1 "$REALMNT" sdcard "$REALMNT" /storage/extSdCard 1023 1023 &

And here writable ext4 on external sd

chown media_rw:media_rw /mnt/media_rw/extSdCard chmod g+w /mnt/media_rw/extSdCard

You can change "extSdCard" like "sdcard1" where your external sdcard mounted

Iam used stockrom with Kingroot, but I try Supersu its trouble with mounting filesystem