Compile Busybox
3. Compile Busybox:¶
BusyBox combines tiny versions of many common UNIX utilities into a single small executable.
cd ${WORKDIR}/source
git clone --depth=1 https://git.busybox.net/busybox
cd busybox
make menuconfig
# Now, enter the first sub-menu (Settings). Go down until you reach the section Build options. Select the Build static binary (no shared libs)
# Optional: Go back to main menu. Scroll down until you find the Shells section. Two first options should be Choose which shell is aliased to 'sh' name and Choose which shell is aliased to 'bash' name. Choose each and tell BusyBox to alias sh to Ash and bash to Hush. You might also want to tweak some options but they are not required
# Exit then save
make -j $(nproc)
make CONFIG_PREFIX=${WORKDIR}/build/amd64/initramfs install
The built Busybox binaries are installed into the build/amd64/initramfs directory.
Now create a init script within initramfs to launch Busybox upon boot:
3.1. Advance (advanced init and login)¶
cd ${WORKDIR}/build/amd64/initramfs
# create some directories to give it a minimal Linux-like look
mkdir -p {etc,dev,mnt,root,sys,proc,dev,run,tmp,var,home,etc/init.d}
# /etc : We need to fill in a couple of files here
cat <<EOF > etc/inittab
# https://github.com/brgl/busybox/blob/master/examples/inittab
::sysinit:/etc/init.d/rcS
tty1::respawn:/sbin/getty 0 tty1
tty2::respawn:/sbin/getty 0 tty2
tty3::respawn:/sbin/getty 0 tty3
tty4::respawn:/sbin/getty 0 tty4
tty5::respawn:/sbin/getty 0 tty5
tty6::respawn:/sbin/getty 0 tty6
# Enable these ttyS if you want to use serial (qemu -serial stdio)
#ttyS0::respawn:/sbin/getty -L ttyS0 9600 vt100
::restart:/sbin/init
::ctrlaltdel:/sbin/reboot
::shutdown:/bin/umount -a -r
::shutdown:/sbin/swapoff -a
EOF
cat <<\EOF > etc/init.d/rcS
#!/bin/sh
mount -t sysfs sysfs -o nosuid,noexec,nodev /sys
mount -t proc proc -o nosuid,noexec,nodev /proc
mount -t devtmpfs devtmpfs -o nosuid,mode=0755 /dev
mount -t tmpfs tmpfs -o nosuid,nodev,mode=755 /run
mkdir -p /dev/pts
mount -t devpts devpts -o nosuid,gid=5,mode=620 /dev/pts
mount -a
mdev -s
hostname tinilinux
ip link set lo up
echo 5 > /proc/sys/kernel/printk
syslogd
cat <<!
Boot took $(cut -d' ' -f1 /proc/uptime) seconds
_____ _ _ _ _
|_ _(_)_ __ (_) | (_)_ __ _ ___ __
| | | | '_ \| | | | | '_ \| | | \ \/ /
| | | | | | | | |___| | | | | |_| |> <
|_| |_|_| |_|_|_____|_|_| |_|\__,_/_/\_\\
Welcome to TiniLinux
!
EOF
chmod +x etc/init.d/rcS
cat <<EOF > etc/hostname
tinilinux
EOF
cat <<EOF > etc/passwd
root::0:0:root:/root:/bin/bash
EOF
cat <<EOF > etc/group
root:x:0:root
EOF
cat <<EOF > etc/fstab
# https://www.linuxfromscratch.org/lfs/view/10.0/chapter10/fstab.html
# file system mount-point type options dump fsck order
# sysfs /sys sysfs nosuid,noexec,nodev 0 0
# proc /proc proc nosuid,noexec,nodev 0 0
# devtmpfs /dev devtmpfs nosuid,mode=0755 0 0
# tmpfs /run tmpfs nosuid,nodev,mode=755 0 0
# devpts /dev/pts devpts nosuid,gid=5,mode=620 0 0
# /dev/sda2 / ext4 defaults 0 1
# /dev/sda1 /boot/efi vfat umask=0077 0 1
EOF
cat <<EOF > init
#!/bin/sh
exec /linuxrc
EOF
chmod +x init
3.2. Advance (network)¶
mkdir -p etc/network/if-up.d
mkdir -p etc/network/if-pre-up.d
mkdir -p etc/network/if-down.d
mkdir -p etc/network/if-post-down.d
mkdir -p var/run
mkdir -p usr/share/udhcpc
cat <<EOF > etc/hosts
127.0.0.1 localhost
127.0.1.1 tinilinux
EOF
cat <<EOF > etc/network/interfaces
# enable dhcp for eth0 interface: https://wiki.alpinelinux.org/wiki/Udhcpc
auto eth0
iface eth0 inet dhcp
hostname tinilinux
EOF
cat <<\EOF > usr/share/udhcpc/default.script
#!/bin/ash
# https://github.com/mschlenker/TinyCrossLinux/blob/master/patches/usr-share-udhcpc-default.script
PATH=/bin:/sbin:/usr/bin:/usr/sbin
export PATH
[ -z "$1" ] && echo "Error: should be called from udhcpc" && exit 1
RESOLV_CONF="/etc/resolv.conf"
[ -n "$broadcast" ] && BROADCAST="broadcast $broadcast"
[ -n "$subnet" ] && NETMASK="netmask $subnet"
case "$1" in
deconfig)
ifconfig $interface 0.0.0.0
;;
renew|bound)
ifconfig $interface $ip $BROADCAST $NETMASK
if [ -n "$router" ] ; then
echo "deleting routers"
while route del default gw 0.0.0.0 dev $interface ; do
:
done
for i in $router ; do
route add default gw $i dev $interface
done
fi
echo -n > $RESOLV_CONF
[ -n "$domain" ] && echo search $domain >> $RESOLV_CONF
for i in $dns ; do
echo adding dns $i
echo nameserver $i >> $RESOLV_CONF
done
;;
esac
exit 0
EOF
chmod +x usr/share/udhcpc/default.script
# add line "ifup eth0" after "ip link set lo up":
sed -i 's/ip link set lo up/ip link set lo up\nifup eth0/g' etc/init.d/rcS
3.3. SSH (dropbear)¶
Build dropbear binary from source
cd ${WORKDIR}/source
git clone --depth=1 https://github.com/mkj/dropbear.git
cd dropbear
./configure --enable-static
cp src/default_options.h localoptions.h # update options if you want
make PROGRAMS="dropbear dbclient dropbearkey dropbearconvert scp" MULTI=1 STATIC=1 strip
Copy dropbear binary to initramfs
cp ${WORKDIR}/source/dropbear/dropbearmulti ${WORKDIR}/build/amd64/initramfs/usr/bin/
cd ${WORKDIR}/build/amd64/initramfs/usr/bin/
ln -s dropbearmulti scp
ln -s dropbearmulti dropbearkey
ln -s dropbearmulti dropbearconvert
ln -s dropbearmulti dropbear
ln -s dropbearmulti ssh
ln -s dropbearmulti dbclien
cd ${WORKDIR}/build/amd64/initramfs/
mkdir -p {var/log,etc/default,etc/dropbear}
touch var/log/lastlog
cat <<EOF > etc/shells
/bin/bash
/bin/sh
EOF
After boot, start dropbear with
or add to rcS
3.4. curl¶
I prefer curl over wget, so if you want to use curl
# check version and arch here: https://github.com/stunnel/static-curl/releases
curl -LO https://github.com/stunnel/static-curl/releases/download/8.6.0-1/curl-linux-x86_64-8.6.0.tar.xz
tar -xvf curl-linux-x86_64-8.6.0.tar.xz
rm curl-linux-x86_64-8.6.0.tar.xz
# you may want to compress the binary: $ upx --brute curl
mv curl usr/bin