You have the option of adding commands to run on the system once the installation is complete, but before the system is rebooted for the first time. This section must start with %post and end with %end.

The %post section is useful for functions such as installing additional software or configuring an additional name server. The post-install script is run in a chroot environment, therefore, performing tasks such as copying scripts or RPM packages from the installation media does not work by default. You can change this behavior by using the --nochroot option as described in the following section. Then the %post script will run in the installation environment, not in chroot on the installed target system.

Because the post-install script runs in a chroot environment, most systemctl commands will refuse to perform any action.

During execution of the %post section, the installation media must be still inserted.

%post script section options

The following options can be used to change the behavior of post-installation scripts. To use an option, append it to the %post line at the beginning of the script. For example:

%post --interpreter=/usr/libexec/platform-python
-- Python script omitted --
%end

--interpreter=

Allows you to specify a different scripting language, such as Python. For example:

%post --interpreter=/usr/libexec/platform-python

Any scripting language available on the system can be used; in most cases, these are /usr/bin/sh, /usr/bin/bash, and /usr/libexec/platform-python.

The platform-python interpreter uses Python version 3.6. You must change your Python scripts from previous RHEL versions for the new path and version. Additionally, platform-python is meant for system tools: Use the python36 package outside the installation environment. For more details about Python in Red Hat Enterprise Linux, see Introduction to Python.

--nochroot

Allows you to specify commands that you would like to run outside of the chroot environment.

The following example copies the file /etc/resolv.conf to the file system that was just installed.

%post --nochroot
cp /etc/resolv.conf /mnt/sysroot/etc/resolv.conf
%end

--erroronfail

Displays an error and halts the installation if the script fails. The error message will direct you to where the cause of the failure is logged. The installed system might get into an unstable and unbootable state. You can use the inst.nokill option to debug the script.

--log=

Logs the script’s output into the specified log file. The path of the log file must take into account whether or not you use the --nochroot option. For example, without --nochroot:

%post --log=/root/ks-post.log

and with --nochroot:

%post --nochroot --log=/mnt/sysroot/root/ks-post.log