7.4.3. BusyBox shell init environment
On top of the Linux kernel, the BusyBox /bin/sh shell will also define other variables.
We can explore the shenanigans that the shell adds on top of the Linux kernel with:
./run --kernel-cli 'init=/bin/sh'
From there we observe that:
env
gives:
SHLVL=1 HOME=/ TERM=linux PWD=/
therefore adding SHLVL and PWD to the default kernel exported variables.
Furthermore, to increase confusion, if you list all non-exported shell variables https://askubuntu.com/questions/275965/how-to-list-all-variables-names-and-their-current-values with:
set
then it shows more variables, notably:
PATH='/sbin:/usr/sbin:/bin:/usr/bin'