filesys/overlayfs_example.sh

This is filesys/overlayfs_example.sh, an example to accompany the book, The Linux Programming Interface.

This file is not printed in the book; it is a supplementary file for Chapter 14.

In the listing below, the names of Linux system calls and C library functions are hyperlinked to manual pages from the Linux man-pages project, and the names of functions implemented in the book are hyperlinked to the implementations of those functions.

Download filesys/overlayfs_example.sh

Cover of The Linux Programming Interface

Distribution version

#!/bin/sh
#
# OverlayFS example

if test $# -ne 1; then
    echo "Usage: $0 <directory-name>"
    exit 1
fi

set -e

mkdir $1
cd $1

mkdir upper lower1 lower2 work merged

echo 'From lower 1' > lower1/all_low
echo 'From lower 2' > lower2/all_low

echo 'From lower 1' > lower1/all
echo 'From lower 2' > lower2/all

echo 'From lower 2' > lower2/lower_2

echo 'From lower 1' > lower1/hidden

mkdir lower1/dir_1
touch lower1/dir_1/file

sudo mount -t overlay \
	 -o lowerdir=./lower1:./lower2,upperdir=./upper,workdir=./work \
	 overlay ./merged

echo 'Upper' >> merged/all
rm merged/hidden

# ls merged

Download filesys/overlayfs_example.sh

Note that, in most cases, the programs rendered in these web pages are not free standing: you'll typically also need a few other source files (mostly in the lib/ subdirectory) as well. Generally, it's easier to just download the entire source tarball and build the programs with make(1). By hovering your mouse over the various hyperlinked include files and function calls above, you can see which other source files this file depends on.