7.3. Create virtual filesystem link targets

This step prepares mount targets for runtime virtual filesystems in the custom tree layout before entering chroot.

All commands in this section should be run as root.

Create the target directories

mkdir -p "$LBI_ROOT/system/devices"
mkdir -p "$LBI_ROOT/system/processes"
mkdir -p "$LBI_ROOT/system/system"
mkdir -p "$LBI_ROOT/system/run"

mkdir -p "$LBI_ROOT/system/devices/pts"
mkdir -p "$LBI_ROOT/system/devices/shm"

Create top-level compatibility links

rm -f "$LBI_ROOT/dev"
rm -f "$LBI_ROOT/proc"
rm -f "$LBI_ROOT/sys"
rm -f "$LBI_ROOT/run"

ln -sf system/devices "$LBI_ROOT/dev"
ln -sf system/processes "$LBI_ROOT/proc"
ln -sf system/system "$LBI_ROOT/sys"
ln -sf system/run "$LBI_ROOT/run"

Mount virtual filesystems

mount -o bind /dev "$LBI_ROOT/dev"
mount -t devpts devpts "$LBI_ROOT/dev/pts" -o gid=5,mode=0620
mount -t proc proc "$LBI_ROOT/proc"
mount -t sysfs sysfs "$LBI_ROOT/sys"
mount -t tmpfs tmpfs "$LBI_ROOT/run"

if [ -h "$LBI_ROOT/dev/shm" ]; then
    install -d -m 1777 "$LBI_ROOT/system/run/shm"
else
    mount -t tmpfs -o nosuid,nodev tmpfs "$LBI_ROOT/dev/shm"
fi

POSIX sh helper script

A ready-to-run helper script is provided here:

• scripts/mount-virtual-fs.sh

Run it as root with LBI_ROOT exported in your environment.

Quick verification

ls -ld "$LBI_ROOT/dev" "$LBI_ROOT/proc" "$LBI_ROOT/sys" "$LBI_ROOT/run"

Command Explanations

• mkdir -p "$LBI_ROOT/system/...": Creates the target-side mount points used for device, process, sysfs, runtime, pts, and shared-memory filesystems.
• rm -f "$LBI_ROOT/dev" and the matching commands: Remove stale top-level placeholders before recreating the compatibility links.
• ln -sf system/devices "$LBI_ROOT/dev": Maps the conventional /dev path to the book's /system/devices layout.
• ln -sf system/processes, system/system, and system/run: Provide /proc, /sys, and /run compatibility paths for tools that expect standard Linux locations.
• mount -o bind /dev "$LBI_ROOT/dev": Makes the host device tree visible inside the target tree for chroot work.
• mount -t devpts, mount -t proc, mount -t sysfs, and mount -t tmpfs: Mount the virtual filesystems needed by shells, process tools, kernel interfaces, and runtime state.
• install -d -m 1777 "$LBI_ROOT/system/run/shm": Creates a world-writable sticky shared-memory directory when /dev/shm is a symlink.
• ls -ld ...: Verifies that the top-level compatibility paths resolve to the intended targets.