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.
Begin by creating the directories on which these virtual file systems will be mounted:
mkdir -pv /{proc,sys,run}
The kernel has already mounted devtmpfs. Mount the remaining virtual kernel
file systems:
mkdir -pv /dev/{pts,shm}
mount -vt devpts devpts -o gid=5,mode=0620 /dev/pts
mount -vt proc proc /proc
mount -vt sysfs sysfs /sys
mount -vt tmpfs tmpfs /run
mount -vt tmpfs tmpfs /dev/shm -o nosuid,nodev
The meaning of the mount options for devpts:
gid=5
This 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=0620
This 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.
Now with the proc filesystem
mounted, we can replace the device nodes for standard I/O streams
with symlinks to pseudo files in /proc/self/fd (which are symlinks to the files
connected to the standard I/O streams for the current process).
And, create another symlink recommended by the kernel
documentation. These are necessary for I/O redirection in the
building system of some packages to function properly:
ln -sfv /proc/self/fd/0 /dev/stdin ln -sfv /proc/self/fd/1 /dev/stdout ln -sfv /proc/self/fd/2 /dev/stderr ln -sv /proc/self/fd /dev