overlay-fs.MD

Create test lab

$ mkdir testlab && cd $_

$ mkdir upper lower merged work

$ echo "from lower" > lower/in_lower.txt
$ echo "from upper" > upper/in_upper.txt
$ echo "from lower" > lower/in_both.txt
$ echo "from upper" > upper/in_both.txt

Check it

root@k8s-master:~/testlab# tree .
.
├── lower
│   ├── in_both.txt
│   └── in_lower.txt
├── merged
├── upper
│   ├── in_both.txt
│   └── in_upper.txt
└── work

4 directories, 4 files

Combine

$ sudo mount -t overlay overlay -o lowerdir=`pwd`/lower,upperdir=`pwd`/upper,workdir=`pwd`/work `pwd`/merged

Check the merged file

$ cat merged/in_both.txt

$ cat merged/in_lower.txt

$ cat merged/in_upper.txt

$ df -h | grep testlab

overlay                             29G  9.7G   18G  36% /root/testlab/merged

Delete merged file

$ delete merged/in_both.txt
$ delete merged/in_lower.txt
$ delete merged/in_upper.txt