Applications running in userspace utilize various file systems created by the kernel to communicate with the kernel itself. These file systems are virtual: no disk space is used for them. The content of these 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 the directories on which these virtual file systems will be mounted:
mkdir -pv $LFS/{dev,proc,sys,run}During a normal boot of an LFS system, the kernel automatically
mounts the devtmpfs
file system on the
/dev directory; the kernel
creates device nodes on that virtual file system during the boot process,
or when a device is first detected or accessed. The udev daemon may
change the ownership or permissions of the device nodes created by the
kernel, and create new device nodes or symlinks, to ease the work of
distro maintainers and system administrators. (See 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.
But some host kernels lack devtmpfs support; these
host distros use different methods to create the content of
/dev.
So the only host-agnostic way to populate the
$LFS/dev directory is
by bind mounting the host system's
/dev directory. A bind mount is
a special type of mount that makes a directory subtree or a file
visible at some other location. Use the following
command to do this.
mount -v --bind /dev $LFS/dev
Now mount the remaining virtual kernel file systems:
mount -vt devpts devpts -o gid=5,mode=0620 $LFS/dev/pts mount -vt proc proc $LFS/proc mount -vt sysfs sysfs $LFS/sys mount -vt tmpfs tmpfs $LFS/run
The meaning of the mount options for devpts:
gid=5This ensures that all devpts-created device nodes are owned by
group ID 5. This is the ID we will use later on for the tty group. We use the group ID instead
of a name, since the host system might use a different ID for its
tty group.
mode=0620This ensures that all devpts-created device nodes have mode 0620 (user readable and writable, group writable). Together with the option above, this ensures that devpts will create device nodes that meet the requirements of grantpt(), meaning the Glibc pt_chown helper binary (which is not installed by default) is not necessary.
In some host systems, /dev/shm is a
symbolic link to a directory, typically
/run/shm.
The /run tmpfs was mounted above so in this case only a
directory needs to be created with the correct permissions.
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 install -v -d -m 1777 $LFS$(realpath /dev/shm) else mount -vt tmpfs -o nosuid,nodev tmpfs $LFS/dev/shm fi