How to set $HOME before startup script in Google Compute Engine

Question

In my use case, I am trying to use the $HOME variable to identify my app server path in the instance startup.

I am using Google compute engine with a startup script which uses $HOME variable. But it looks $HOME is not set or the user is not created while startup script executes in google cloud.

It throws $HOME not set error. Is there any workaround for this? Now I have to restart the instance after creating for the first time. So that the $HOME variable will be set when I restart. But this is an ugly hack for production.

Could someone help me with this?

Answer 1

The startup script is executed as root when the user have been not created yet and no user is logged in (you can check it running at startup $ users and comparing the output of $ cat /etc/shadow after a reboot).

Honestly I don't understand how just a reboot can make your $HOME be populated at startup time since on Linux, the HOME environment variable is set by the login program:

• by login on console, telnet and rlogin sessions
• by sshd for SSH
• connections by gdm, kdm or xdm for graphical sessions.

However if you need to reboot and you don't want to do it manually you can reboot just once after the creation of a machine:

if [ -f flagreboot ]; then
 ...
 your script
 ...
else
 touch flagreboot
 reboot
fi

On the other hand if you know which is going to be the $HOME path of your application you can think to simply export this variable at startup to populate it manually.

 $ export HOME=/home/username

Answer 2

printenv
cd $HOME
touch test.txt
echo $HOME >> test.txt
echo $PWD >> test.txt
printenv > env.txt

I included the above code in my startup script. Strangely, the $HOME, $PWD and many other environment variables are not set while the startup script is runninng. Here are the contents of of the files I created during the startup.

test.txt:

/

env.txt:

PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin
PWD=/
LANG=en_US.UTF-8
SHLVL=2
_=/usr/bin/printenv

Here's the output(some values removed) of printenv command, immediately after the VM creation.

XDG_SESSION_ID=
HOSTNAME=server1
SELINUX_ROLE_REQUESTED=
TERM=xterm-256color
SHELL=/bin/bash
HISTSIZE=1000
SSH_CLIENT=
SELINUX_USE_CURRENT_RANGE=
SSH_TTY=/dev/pts/0
USER=
LS_COLORS=
MAIL=/var/spool/mail/xyz
PATH=/usr/local/bin:/usr/bin:/usr/local/sbin:/usr/sbin:/home/*<username>*/.local/bin:/home/*<username>*/bin
PWD=/home/*<username>*
LANG=en_US.UTF-8
SELINUX_LEVEL_REQUESTED=
HISTCONTROL=ignoredups
SHLVL=1
HOME=/home/*<username>*
LOGNAME=*<username>*
SSH_CONNECTION=
LESSOPEN=||/usr/bin/lesspipe.sh %s
XDG_RUNTIME_DIR=/run/user/1000
_=/usr/bin/printenv

To summarize, not all the environment variables are set at the time the startup script executes. They are populated some time after. I find that wierd, but that's how it's works.