FreeBSD Handbook
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# A.5 Using CTM

CTM is a method for keeping a remote directory tree in sync with a central one. It has been developed for usage with FreeBSD's source trees, though other people may find it useful for other purposes as time goes by. Little, if any, documentation currently exists at this time on the process of creating deltas, so contact the ctm-users mailing list for more information and if you wish to use CTM for other things.

## A.5.1 Why Should I Use CTM?

CTM will give you a local copy of the FreeBSD source trees. There are a number of “flavors” of the tree available. Whether you wish to track the entire CVS tree or just one of the branches, CTM can provide you the information. If you are an active developer on FreeBSD, but have lousy or non-existent TCP/IP connectivity, or simply wish to have the changes automatically sent to you, CTM was made for you. You will need to obtain up to three deltas per day for the most active branches. However, you should consider having them sent by automatic email. The sizes of the updates are always kept as small as possible. This is typically less than 5K, with an occasional (one in ten) being 10-50K and every now and then a large 100K+ or more coming around.

You will also need to make yourself aware of the various caveats related to working directly from the development sources rather than a pre-packaged release. This is particularly true if you choose the “current” sources. It is recommended that you read Staying current with FreeBSD.

## A.5.2 What Do I Need to Use CTM?

You will need two things: The CTM program, and the initial deltas to feed it (to get up to “current” levels).

The CTM program has been part of FreeBSD ever since version 2.0 was released, and lives in `/usr/src/usr.sbin/ctm` if you have a copy of the source available.

The “deltas” you feed CTM can be had two ways, FTP or email. If you have general FTP access to the Internet then the following FTP sites support access to CTM:

ftp://ftp.FreeBSD.org/pub/FreeBSD/CTM/

or see section mirrors.

FTP the relevant directory and fetch the `README` file, starting from there.

If you wish to get your deltas via email:

Subscribe to one of the CTM distribution lists. ctm-cvs-cur supports the entire CVS tree. ctm-src-cur supports the head of the development branch. ctm-src-9 supports the 9.X release branch, etc.. (If you do not know how to subscribe yourself to a list, click on the list name above or go to http://lists.FreeBSD.org/mailman/listinfo and click on the list that you wish to subscribe to. The list page should contain all of the necessary subscription instructions.)

When you begin receiving your CTM updates in the mail, you may use the `ctm_rmail` program to unpack and apply them. You can actually use the `ctm_rmail` program directly from a entry in `/etc/aliases` if you want to have the process run in a fully automated fashion. Check the `ctm_rmail` manual page for more details.

> Note: No matter what method you use to get the CTM deltas, you should subscribe to the ctm-announce mailing list. In the future, this will be the only place where announcements concerning the operations of the CTM system will be posted. Click on the list name above and follow the instructions to subscribe to the list.

## A.5.3 Using CTM for the First Time

Before you can start using CTM deltas, you will need to get to a starting point for the deltas produced subsequently to it.

First you should determine what you already have. Everyone can start from an “empty” directory. You must use an initial “Empty” delta to start off your CTM supported tree. At some point it is intended that one of these “started” deltas be distributed on the CD for your convenience, however, this does not currently happen.

Since the trees are many tens of megabytes, you should prefer to start from something already at hand. If you have a -RELEASE CD, you can copy or extract an initial source from it. This will save a significant transfer of data.

You can recognize these “starter” deltas by the `X` appended to the number (`src-cur.3210XEmpty.gz` for instance). The designation following the `X` corresponds to the origin of your initial “seed”. `Empty` is an empty directory. As a rule a base transition from `Empty` is produced every 100 deltas. By the way, they are large! 70 to 80 Megabytes of `gzip`'d data is common for the `XEmpty` deltas.

Once you have picked a base delta to start from, you will also need all deltas with higher numbers following it.

## A.5.4 Using CTM in Your Daily Life

To apply the deltas, simply say:

    # cd /where/ever/you/want/the/stuff
    # ctm -v -v /where/you/store/your/deltas/src-xxx.*

CTM understands deltas which have been put through `gzip`, so you do not need to `gunzip` them first, this saves disk space.

Unless it feels very secure about the entire process, CTM will not touch your tree. To verify a delta you can also use the `-c` flag and CTM will not actually touch your tree; it will merely verify the integrity of the delta and see if it would apply cleanly to your current tree.

There are other options to CTM as well, see the manual pages or look in the sources for more information.

That is really all there is to it. Every time you get a new delta, just run it through CTM to keep your sources up to date.

Do not remove the deltas if they are hard to download again. You just might want to keep them around in case something bad happens. Even if you only have floppy disks, consider using `fdwrite` to make a copy.

## A.5.5 Keeping Your Local Changes

As a developer one would like to experiment with and change files in the source tree. CTM supports local modifications in a limited way: before checking for the presence of a file `foo`, it first looks for `foo.ctm`. If this file exists, CTM will operate on it instead of `foo`.

This behavior gives us a simple way to maintain local changes: simply copy the files you plan to modify to the corresponding file names with a `.ctm` suffix. Then you can freely hack the code, while CTM keeps the `.ctm` file up-to-date.

## A.5.6 Other Interesting CTM Options

### A.5.6.1 Finding Out Exactly What Would Be Touched by an Update

You can determine the list of changes that CTM will make on your source repository using the `-l` option to CTM.

This is useful if you would like to keep logs of the changes, pre- or post- process the modified files in any manner, or just are feeling a tad paranoid.

### A.5.6.2 Making Backups Before Updating

Sometimes you may want to backup all the files that would be changed by a CTM update.

Specifying the `-B backup-file` option causes CTM to backup all files that would be touched by a given CTM delta to `backup-file`.

### A.5.6.3 Restricting the Files Touched by an Update

Sometimes you would be interested in restricting the scope of a given CTM update, or may be interested in extracting just a few files from a sequence of deltas.

You can control the list of files that CTM would operate on by specifying filtering regular expressions using the `-e` and `-x` options.

For example, to extract an up-to-date copy of `lib/libc/Makefile` from your collection of saved CTM deltas, run the commands:

    # cd /where/ever/you/want/to/extract/it/
    # ctm -e '^lib/libc/Makefile' ~ctm/src-xxx.*

For every file specified in a CTM delta, the `-e` and `-x` options are applied in the order given on the command line. The file is processed by CTM only if it is marked as eligible after all the `-e` and `-x` options are applied to it.

## A.5.7 Future Plans for CTM

Tons of them:

- Use some kind of authentication into the CTM system, so as to allow detection of spoofed CTM updates.

- Clean up the options to CTM, they became confusing and counter intuitive.

## A.5.8 Miscellaneous Stuff

There is a sequence of deltas for the `ports` collection too, but interest has not been all that high yet.

## A.5.9 CTM Mirrors

CTM/FreeBSD is available via anonymous FTP from the following mirror sites. If you choose to obtain CTM via anonymous FTP, please try to use a site near you.

In case of problems, please contact the ctm-users mailing list.

California, Bay Area, official source

  - ftp://ftp.FreeBSD.org/pub/FreeBSD/development/CTM/

South Africa, backup server for old deltas

  - ftp://ftp.za.FreeBSD.org/pub/FreeBSD/CTM/

Taiwan/R.O.C.

  - ftp://ctm.tw.FreeBSD.org/pub/FreeBSD/development/CTM/

  - ftp://ctm2.tw.FreeBSD.org/pub/FreeBSD/development/CTM/

  - ftp://ctm3.tw.FreeBSD.org/pub/FreeBSD/development/CTM/

If you did not find a mirror near to you or the mirror is incomplete, try to use a search engine such as alltheweb.

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