4.1.6. SDK File System Optimization/Customization¶
The purpose of this article is to explain the file system that is delivered as part of the Processor SDK Linux J721e and how this file system can be modified to customize it for your use case. The tools discussed in this article are installed by default in the Processor SDK Linux J721e file system for your convenience.
Pre-built File Systems
The Processor SDK Linux J721e ships with a default file system:
- tisdk-default-image-<machine>.tar.gz - This file system is created by taking a base file system and adding all the additional SDK components such as 3D graphics, matrix, profiling tools, etc. It is somewhat larger than a base file system, but is meant to have most of the tools developers would need when working with TI processors.
This file system contains the opkg package manager and can be used as a starting point for system optimization as discussed in the next sections.
The Basics of OPKG
opkg - list commands
opkg is the package manager used in the SDK file system to install and remove packages. You can get a list of the full commands supported by opkg by running the following command on the target device:
opkg - list installed packages
To the list of packages are part of the file system and the version of each package you can run the following command on the target device:
target# opkg list-installed
This list only contains information about packages that were installed using the package manager. Applications that were built and copied to the file system and not installed as a .ipk package are not tracked by opkg
opkg - list package contents
Sometimes it is useful to know what files a package has installed. To do this you can use the following command:
target# opkg files <pkgname>
Where <pkgname> is the name of the package as given in the opkg list-installed output. This command will produce a list of all the files on the file system that belong to the given package.
opkg - find a file owner
Sometimes you may find a file on the target file system that you want to remove, or just know where it came from. In this case you can use the following command:
target# opkg search <file>
This command will find which package installed the given file. This may be useful later when you want to remove an particular file because this command can help you find the package to remove.
opkg - finding dependencies
Sometimes when you want to remove a package it is useful to find out what other packages depend on the package you are removing. While the opkg remove command will tell you the immediate dependencies you can find the longer list of dependencies using:
target# opkg whatdepends <pkgname>
This command will print the list of packages the depend on the package you entered, as well as the packages that depend on those packages, and so forth.
One of the simplest ways to modify the contents of the file system is to use the opkg utility to remove packages (or install if you have pre-built packages). Removing a package is often as simple as:
target# opkg remove <pkgname>
However, sometimes a package is a DEPENDENCY of another package. In this case you have the following options:
- Use the –force-depends option
- This option will force the removal of the package but will leave any packages that depend on this package installed. This can be useful in the case that you want to remove a particular package, but that package is depended on by some other package that you do not want removed.
- Use the –force-removal-of-dependent-packages option
- This option will go up the dependency list and remove all packages in the dependency chain. You should check all the packages being removed to make sure they are indeed packages you want to remove and do not contain other files you want.
- Remove the individual packages that depend on this package first
- This way you can control exactly which dependent packages are removed and which are left in place.
target# opkg remove --force-removal-of-dependent-packages <pkgname>
opkg will print the packages that depend on the package being removed. It is usually a good idea to use the opkg files command for the packages that depend on the one being removed so that you can make sure that no files you really want to keep are going to be removed.
You can also use the whatdepends option discussed above to see the dependency list for a package
By using the opkg remove command in conjunction with the commands for listing packages, finding file owners, and listing package contents, you can quickly strip down a full file system into something smaller and more optimized for your use case. However, once a package is removed it cannot currently be re-installed without generating the .ipk file to install it.
In most cases installing additional applications can be as simple as copying the the binary executable to the file system. However, if you have built your own .ipk packages you can use opkg to install those ipks into the target file system. One major advantage of using the package manager is the ability to track the package and it’s content with the opkg package manager. More details will be coming about how to build your own packages, but for now please refer to Building the SDK and this link to learn more about building custom file systems with Arago.