23.5. Synchronizing Source

There are various methods for staying up-to-date with the FreeBSD sources. This section compares the primary services, Subversion and CTM.


While it is possible to update only parts of the source tree, the only supported update procedure is to update the entire tree and recompile all the programs that run in user space, such as those in /bin and /sbin, and kernel sources. Updating only part of the source tree, only the kernel, or only the userland programs will often result in problems ranging from compile errors to kernel panics or data corruption.

Subversion uses the pull model of updating sources. The user, or a cron script, invokes the svn program which updates the local version of the source. Subversion is the preferred method for updating local source trees as updates are up-to-the-minute and the user controls when updates are downloaded. It is easy to restrict updates to specific files or directories and the requested updates are generated on the fly by the server. How to synchronize source using Subversion is described in Section A.4, “Using Subversion.

CTM does not interactively compare the local sources with those on the master archive or otherwise pull them across. Instead, a script which identifies changes in files since its previous run is executed several times a day on the master CTM machine. Any detected changes are compressed, stamped with a sequence-number, and encoded for transmission over email in printable ASCII only. Once downloaded, these deltas can be run through ctm.rmail which will automatically decode, verify, and apply the changes to the user's copy of the sources. This process is more efficient than Subversion and places less strain on server resources since it is a push, rather than a pull, model. Instructions for using CTM to synchronize source can be found at Section A.3, “Using CTM”.

If a user inadvertently wipes out portions of the local archive, Subversion will detect and rebuild the damaged portions. CTM will not, and if a user deletes some portion of the source tree and does not have a backup, they will have to start from scratch from the most recent base delta and rebuild it all with CTM.

All FreeBSD documents are available for download at http://ftp.FreeBSD.org/pub/FreeBSD/doc/

Questions that are not answered by the documentation may be sent to <freebsd-questions@FreeBSD.org>.
Send questions about this document to <freebsd-doc@FreeBSD.org>.