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infix/doc/override-package.md
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Package override
================
This guide demonstrates how the `local.mk` file is utilized to override
a Linux Buildroot package. The example of `tcpdump` serves to illustrate
this process.
In an instance such as `Infix` using tcpdump, the `local.mk` file is modified
as shown below:
```
TCPDUMP_OVERRIDE_SRCDIR = /path/to/tcpdump/repo
```
and stored in the `output/` folder, alongside the `.config` file:
```
user@PC:~/infix$ll output/ | grep -e 'local.mk' -e '.config'
-rw-r--r-- 1 group user 119936 Nov 10 18:04 .config
-rw-r--r-- 1 group user 43 Nov 10 18:25 local.mk
```
The execution of `make tcpdump-rebuild all` triggers a process where
Buildroot synchronizes the tcpdump source code from the specified override directory
to `output/build/tcpdump-custom`, followed by the rebuilding of the entire project.
```
user@PC:~/infix$ make tcpdump-rebuild all
```
```
user@PC:~/infix$ ll /output/build/ | grep tcpdump
drwxr-xr-x 7 group user 20480 Nov 10 18:26 tcpdump-4.99.4/
drwxr-xr-x 7 group user 12288 Nov 10 18:28 tcpdump-custom/
```
Buildroot follows a process of downloading and processing tarballs
(extraction, configuration, compilation, and installation).
The source code is stored in a temporary directory:
`output/build/<package>-<version>` (i.e. `tcpdump-4.99.4/`),
which is removed and recreated with each `make` command. That is why
the direct modifications in the `output/build` directory are generally
**not recommended**.
To manage the development changes more effectively, where the package source code
remains untouched, Buildroot incorporates the `<pkg>_OVERRIDE_SRCDIR` feature.
For a comprehensive understanding of utilizing Buildroot during development,
including detailed elaboration on the `<pkg>_OVERRIDE_SRCDIR` feature,
refer to section 8.13.6 in [Using Buildroot during development](https://nightly.buildroot.org/).