Applications running in user space utilize various file systems exported by the kernel to communicate with the kernel itself. These file systems are virtual: no disk space is used for them. The content of the file systems resides in memory. These file systems must be mounted in the $LFS directory tree so the applications can find them in the chroot environment.
Begin by creating directories on which the file systems will be mounted:
mkdir -pv $LFS/{dev,proc,sys,run}
During a normal boot of the LFS system, the kernel automatically
mounts the devtmpfs filesystem on
the /dev directory; the kernel
creates device nodes on that virtual filesystem during the boot
process or when a device is first detected or accessed. The udev
daemon may change the owner or permission of the device nodes
created by the kernel, or create new device nodes or symlinks to
ease the work of distro maintainers or system administrators. (See
Section 9.3.2.2,
“Device Node Creation” for details.) If the host
kernel supports devtmpfs, we can
simply mount a devtmpfs at
$LFS/dev and rely on the kernel to
populate it (the LFS building process does not need the additional
work onto devtmpfs by udev daemon).
But, some host kernels may lack devtmpfs support and these host distros
maintain the content of /dev with
different methods. So the only host-agnostic way for populating
$LFS/dev is bind mounting the host
system's /dev directory. A bind mount
is a special type of mount that allows you to create a mirror of a
directory or mount point at some other location. Use the following
command to do this:
mount -v --bind /dev $LFS/dev
Now mount the remaining virtual kernel filesystems:
mount -v --bind /dev/pts $LFS/dev/pts mount -vt proc proc $LFS/proc mount -vt sysfs sysfs $LFS/sys mount -vt tmpfs tmpfs $LFS/run
In some host systems, /dev/shm is a
symbolic link to /run/shm. The /run
tmpfs was mounted above so in this case only a directory needs to
be created.
In other host systems /dev/shm is a
mount point for a tmpfs. In that case the mount of /dev above will
only create /dev/shm as a directory in the chroot environment. In
this situation we must explicitly mount a tmpfs:
if [ -h $LFS/dev/shm ]; then mkdir -pv $LFS/$(readlink $LFS/dev/shm) else mount -t tmpfs -o nosuid,nodev tmpfs $LFS/dev/shm fi