In Debian installation process, the preseed.cfg file allows for automated installations by pre-configuring various installation parameters. In this article I will focus on the d-i preseed/late_command string parameter, which is used to run custom commands at the end of the installation process.
Here is an example that I recently used in my packer-vbox-debian-latest project:
d-i preseed/late_command string \
mkdir --mode=700 /target/home/testuser/.ssh; \
wget -q http://10.0.2.2:8081/key.pub -O /target/home/testuser/.ssh/authorized_keys; \
in-target chown testuser:testuser /home/testuser/.ssh; \
in-target chown testuser:testuser /home/testuser/.ssh/authorized_keys; \
in-target chmod 0600 /home/testuser/.ssh/authorized_keys
As you can see, sometimes /target is used, other times in-target, I must admit I struggled a bit to understand the difference and when to use one instead of the other.
The /target directory
When you are installing Debian, the installer needs a place to set up the new system, and this place is called /target. During the installation process, /target acts as a temporary workspace where the new system’s root filesystem is prepared. Essentially, the installer mounts the new system’s root partition to /target, allowing it to configure and manipulate the filesystem and its contents as if it were the actual running system.
The in-target command
The in-target command is used within the preseed file to execute commands in the context of the newly installed system, rather than within the installer’s environment. When you use in-target, it effectively chroots into /target and runs the specified command as if you were executing it on the new system.
Conclusion
- Use
/targetwhen you need to create or manipulate files and directories directly on the new system’s filesystem during the installation process. - Use
in-targetwhen you need to execute commands within the context of the new system, as it effectively chroots into/targetand runs commands as if you were operating within the new system itself.