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The buildroot build system has hooks that allow you to insert scripts at various points of the build.  This allows you to modify the artifacts after various points of the build.  In the repo that you clones cloned into the "site-top" directory, there is a "script" directory.  This directory contains these scripts.  We have a "post-build.sh" script that performs various tasks.  You can read about the post-build scripts here and here.

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I will use br-2019.08-2 since my changes represent the second SLAC release of the 2019.08 version of buildroot.

Archiving your buildroot

Don't forget to copy your entire buildroot-<year>.<month>-<version>-<architecture> to /afs/slac/g/lcls/tftpboot/linuxRT/boot.