QEMU: /bin/sh: can't access tty; job control turned off

Question

As a development environment for linux kernel, I'm using qemu with setting up initramfs as similar to what is shown here , with few additional executable. Basically, it uses busybox for creating minimal environment and package it up using cpio. Content of init is shown below.

$ cat init
mount -t proc none /proc
mount -t sysfs none /sys

echo -e "\nBoot took $(cut -d' ' -f1 /proc/uptime) seconds\n"
exec /bin/sh

Using following command to start VM:

qemu-system-x86_64 -kernel bzImage -initrd initramfs -append "console=ttyS0" -nographic

It throws following error:

/bin/sh: can't access tty; job control turned off

Although, system functions normal in most cases. But, I'm not able to create background process:

$ prog &
/bin/sh: can't open '/dev/null'
$ fg
/bin/sh: fg: job (null) not created under job control

Root of all problems seem to be not having access to tty . How can I fix this?

EDIT: Apart from Accepted answer, as a get around cttyhack of busybox can be used.

$cat init
#!/bin/sh

mount -t proc none /proc
mount -t sysfs none /sys
mknod -m 666 /dev/ttyS0 c 4 64

echo -e "\nBoot took $(cut -d' ' -f1 /proc/uptime) seconds\n"
setsid  cttyhack sh
exec /bin/sh

Answer 1

From Linux From Scratch Chapter 6.8. Populating /dev

6.8.1. Creating Initial Device Nodes

When the kernel boots the system, it requires the presence of a few device nodes, in particular the console and null devices. Create these by running the following commands:

 mknod -m 600 /dev/console c 5 1 mknod -m 666 /dev/null c 1 3 

You should then continue with the steps in "6.8.2. Mounting tmpfs and Populating /dev". Note the <-- below, and I suggest you read the entire free LFS .

mount -n -t tmpfs none /dev
mknod -m 622 /dev/console c 5 1
mknod -m 666 /dev/null c 1 3
mknod -m 666 /dev/zero c 1 5
mknod -m 666 /dev/ptmx c 5 2
mknod -m 666 /dev/tty c 5 0 # <--
mknod -m 444 /dev/random c 1 8
mknod -m 444 /dev/urandom c 1 9
chown root:tty /dev/{console,ptmx,tty}