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# The Repository

The CVS repository stores a complete copy of all the files and directories which are under version control.

Normally, you never access any of the files in the repository directly. Instead, you use CVS commands to get your own copy of the files into a working directory, and then work on that copy. When you've finished a set of changes, you check (or commit) them back into the repository. The repository then contains the changes which you have made, as well as recording exactly what you changed, when you changed it, and other such information. Note that the repository is not a subdirectory of the working directory, or vice versa; they should be in separate locations.

CVS can access a repository by a variety of means. It might be on the local computer, or it might be on a computer across the room or across the world. To distinguish various ways to access a repository, the repository name can start with an access method. For example, the access method `:local:` means to access a repository directory, so the repository `:local:/usr/local/cvsroot` means that the repository is in ``/usr/local/cvsroot'` on the computer running CVS. For information on other access methods, see section Remote repositories.

If the access method is omitted, then if the repository does not contain ``:'`, then `:local:` is assumed. If it does contain ``:'` then either `:ext:` or `:server:` is assumed. For example, if you have a local repository in ``/usr/local/cvsroot'`, you can use `/usr/local/cvsroot` instead of `:local:/usr/local/cvsroot`. But if (under Windows NT, for example) your local repository is ``c:\src\cvsroot'`, then you must specify the access method, as in `:local:c:\src\cvsroot`.

The repository is split in two parts. ``$CVSROOT/CVSROOT'` contains administrative files for CVS. The other directories contain the actual user-defined modules.

- Specifying a repository: Telling CVS where your repository is
- Repository storage: The structure of the repository
- Working directory storage: The structure of working directories
- Intro administrative files: Defining modules
- Multiple repositories: Multiple repositories
- Creating a repository: Creating a repository
- Backing up: Backing up a repository
- Moving a repository: Moving a repository
- Remote repositories: Accessing repositories on remote machines
- Read-only access: Granting read-only access to the repository
- Server temporary directory: The server creates temporary directories

## Telling CVS where your repository is

There are several ways to tell CVS where to find the repository. You can name the repository on the command line explicitly, with the `-d` (for "directory") option:

    cvs -d /usr/local/cvsroot checkout yoyodyne/tc

Or you can set the `$CVSROOT` environment variable to an absolute path to the root of the repository, ``/usr/local/cvsroot'` in this example. To set `$CVSROOT`, `csh` and `tcsh` users should have this line in their ``.cshrc'` or ``.tcshrc'` files:

    setenv CVSROOT /usr/local/cvsroot

`sh` and `bash` users should instead have these lines in their ``.profile'` or ``.bashrc'`:

    CVSROOT=/usr/local/cvsroot
    export CVSROOT

A repository specified with `-d` will override the `$CVSROOT` environment variable. Once you've checked a working copy out from the repository, it will remember where its repository is (the information is recorded in the ``CVS/Root'` file in the working copy).

The `-d` option and the ``CVS/Root'` file both override the `$CVSROOT` environment variable. If `-d` option differs from ``CVS/Root'`, the former is used (and specifying `-d` will cause ``CVS/Root'` to be updated). Of course, for proper operation they should be two ways of referring to the same repository.

## How data is stored in the repository

For most purposes it isn't important how CVS stores information in the repository. In fact, the format has changed in the past, and is likely to change in the future. Since in almost all cases one accesses the repository via CVS commands, such changes need not be disruptive.

However, in some cases it may be necessary to understand how CVS stores data in the repository, for example you might need to track down CVS locks (see section Several developers simultaneously attempting to run CVS) or you might need to deal with the file permissions appropriate for the repository.

- Repository files: What files are stored in the repository
- File permissions: File permissions
- Windows permissions: Issues specific to Windows
- Attic: Some files are stored in the Attic
- CVS in repository: Additional information in CVS directory
- Locks: CVS locks control concurrent accesses
- CVSROOT storage: A few things about CVSROOT are different

### Where files are stored within the repository

The overall structure of the repository is a directory tree corresponding to the directories in the working directory. For example, supposing the repository is in

    /usr/local/cvsroot

here is a possible directory tree (showing only the directories):

    /usr
     |
     +--local
     |   |
     |   +--cvsroot
     |   |    |
     |   |    +--CVSROOT
              |      (administrative files)
              |
              +--gnu
              |   |
              |   +--diff
              |   |   (source code to GNU diff)
              |   |
              |   +--rcs
              |   |   (source code to RCS)
              |   |
              |   +--cvs
              |       (source code to CVS)
              |
              +--yoyodyne
                  |
                  +--tc
                  |    |
                  |    +--man
                  |    |
                  |    +--testing
                  |
                  +--(other Yoyodyne software)

With the directories are history files for each file under version control. The name of the history file is the name of the corresponding file with ``,v'` appended to the end. Here is what the repository for the ``yoyodyne/tc'` directory might look like:

      $CVSROOT
        |
        +--yoyodyne
        |   |
        |   +--tc
        |   |   |
                +--Makefile,v
                +--backend.c,v
                +--driver.c,v
                +--frontend.c,v
                +--parser.c,v
                +--man
                |    |
                |    +--tc.1,v
                |
                +--testing
                     |
                     +--testpgm.t,v
                     +--test2.t,v

The history files contain, among other things, enough information to recreate any revision of the file, a log of all commit messages and the user-name of the person who committed the revision. The history files are known as RCS files, because the first program to store files in that format was a version control system known as RCS. For a full description of the file format, see the `man` page rcsfile(5), distributed with RCS, or the file ``doc/RCSFILES'` in the CVS source distribution. This file format has become very common--many systems other than CVS or RCS can at least import history files in this format.

The RCS files used in CVS differ in a few ways from the standard format. The biggest difference is magic branches; for more information see section Magic branch numbers. Also in CVS the valid tag names are a subset of what RCS accepts; for CVS's rules see section Tags--Symbolic revisions.

### File permissions

All ``,v'` files are created read-only, and you should not change the permission of those files. The directories inside the repository should be writable by the persons that have permission to modify the files in each directory. This normally means that you must create a UNIX group (see group(5)) consisting of the persons that are to edit the files in a project, and set up the repository so that it is that group that owns the directory.

This means that you can only control access to files on a per-directory basis.

Note that users must also have write access to check out files, because CVS needs to create lock files (see section Several developers simultaneously attempting to run CVS).

Also note that users must have write access to the ``CVSROOT/val-tags'` file. CVS uses it to keep track of what tags are valid tag names (it is sometimes updated when tags are used, as well as when they are created).

Each RCS file will be owned by the user who last checked it in. This has little significance; what really matters is who owns the directories.

CVS tries to set up reasonable file permissions for new directories that are added inside the tree, but you must fix the permissions manually when a new directory should have different permissions than its parent directory. If you set the `CVSUMASK` environment variable that will control the file permissions which CVS uses in creating directories and/or files in the repository. `CVSUMASK` does not affect the file permissions in the working directory; such files have the permissions which are typical for newly created files, except that sometimes CVS creates them read-only (see the sections on watches, section Telling CVS to watch certain files; -r, section Global options; or CVSREAD, section All environment variables which affect CVS).

Note that using the client/server CVS (see section Remote repositories), there is no good way to set `CVSUMASK`; the setting on the client machine has no effect. If you are connecting with `rsh`, you can set `CVSUMASK` in ``.bashrc'` or ``.cshrc'`, as described in the documentation for your operating system. This behavior might change in future versions of CVS; do not rely on the setting of `CVSUMASK` on the client having no effect.

Using pserver, you will generally need stricter permissions on the CVSROOT directory and directories above it in the tree; see section Security considerations with password authentication.

Some operating systems have features which allow a particular program to run with the ability to perform operations which the caller of the program could not. For example, the set user ID (setuid) or set group ID (setgid) features of unix or the installed image feature of VMS. CVS was not written to use such features and therefore attempting to install CVS in this fashion will provide protection against only accidental lapses; anyone who is trying to circumvent the measure will be able to do so, and depending on how you have set it up may gain access to more than just CVS. You may wish to instead consider pserver. It shares some of the same attributes, in terms of possibly providing a false sense of security or opening security holes wider than the ones you are trying to fix, so read the documentation on pserver security carefully if you are considering this option (section Security considerations with password authentication).

### File Permission issues specific to Windows

Some file permission issues are specific to Windows operating systems (Windows 95, Windows NT, and presumably future operating systems in this family. Some of the following might apply to OS/2 but I'm not sure).

If you are using local CVS and the repository is on a networked file system which is served by the Samba SMB server, some people have reported problems with permissions. Enabling WRITE=YES in the samba configuration is said to fix/workaround it. Disclaimer: I haven't investigated enough to know the implications of enabling that option, nor do I know whether there is something which CVS could be doing differently in order to avoid the problem. If you find something out, please let us know as described in section Dealing with bugs in CVS or this manual.

### The attic

You will notice that sometimes CVS stores an RCS file in the `Attic`. For example, if the CVSROOT is ``/usr/local/cvsroot'` and we are talking about the file ``backend.c'` in the directory ``yoyodyne/tc'`, then the file normally would be in

    /usr/local/cvsroot/yoyodyne/tc/backend.c,v

but if it goes in the attic, it would be in

    /usr/local/cvsroot/yoyodyne/tc/Attic/backend.c,v

instead. It should not matter from a user point of view whether a file is in the attic; CVS keeps track of this and looks in the attic when it needs to. But in case you want to know, the rule is that the RCS file is stored in the attic if and only if the head revision on the trunk has state `dead`. A `dead` state means that file has been removed, or never added, for that revision. For example, if you add a file on a branch, it will have a trunk revision in `dead` state, and a branch revision in a non-`dead` state.

### The CVS directory in the repository

The ``CVS'` directory in each repository directory contains information such as file attributes (in a file called ``CVS/fileattr'`; see fileattr.h in the CVS source distribution for more documentation). In the future additional files may be added to this directory, so implementations should silently ignore additional files.

This behavior is implemented only by CVS 1.7 and later; for details see section Using watches with old versions of CVS.

### CVS locks in the repository

For an introduction to CVS locks focusing on user-visible behavior, see section Several developers simultaneously attempting to run CVS. The following section is aimed at people who are writing tools which want to access a CVS repository without interfering with other tools acessing the same repository. If you find yourself confused by concepts described here, like read lock, write lock, and deadlock, you might consult the literature on operating systems or databases.

Any file in the repository with a name starting with ``#cvs.rfl'` is a read lock. Any file in the repository with a name starting with ``#cvs.wfl'` is a write lock. Old versions of CVS (before CVS 1.5) also created files with names starting with ``#cvs.tfl'`, but they are not discussed here. The directory ``#cvs.lock'` serves as a master lock. That is, one must obtain this lock first before creating any of the other locks.

To obtain a readlock, first create the ``#cvs.lock'` directory. This operation must be atomic (which should be true for creating a directory under most operating systems). If it fails because the directory already existed, wait for a while and try again. After obtaining the ``#cvs.lock'` lock, create a file whose name is ``#cvs.rfl'` followed by information of your choice (for example, hostname and process identification number). Then remove the ``#cvs.lock'` directory to release the master lock. Then proceed with reading the repository. When you are done, remove the ``#cvs.rfl'` file to release the read lock.

To obtain a writelock, first create the ``#cvs.lock'` directory, as with a readlock. Then check that there are no files whose names start with ``#cvs.rfl'`. If there are, remove ``#cvs.lock'`, wait for a while, and try again. If there are no readers, then create a file whose name is ``#cvs.wfl'` followed by information of your choice (for example, hostname and process identification number). Hang on to the ``#cvs.lock'` lock. Proceed with writing the repository. When you are done, first remove the ``#cvs.wfl'` file and then the ``#cvs.lock'` directory. Note that unlike the ``#cvs.rfl'` file, the ``#cvs.wfl'` file is just informational; it has no effect on the locking operation beyond what is provided by holding on to the ``#cvs.lock'` lock itself.

Note that each lock (writelock or readlock) only locks a single directory in the repository, including ``Attic'` and ``CVS'` but not including subdirectories which represent other directories under version control. To lock an entire tree, you need to lock each directory (note that if you fail to obtain any lock you need, you must release the whole tree before waiting and trying again, to avoid deadlocks).

Note also that CVS expects writelocks to control access to individual ``foo,v'` files. RCS has a scheme where the ``,foo,'` file serves as a lock, but CVS does not implement it and so taking out a CVS writelock is recommended. See the comments at rcs_internal_lockfile in the CVS source code for further discussion/rationale.

### How files are stored in the CVSROOT directory

The ``$CVSROOT/CVSROOT'` directory contains the various administrative files. In some ways this directory is just like any other directory in the repository; it contains RCS files whose names end in ``,v'`, and many of the CVS commands operate on it the same way. However, there are a few differences.

For each administrative file, in addition to the RCS file, there is also a checked out copy of the file. For example, there is an RCS file ``loginfo,v'` and a file ``loginfo'` which contains the latest revision contained in ``loginfo,v'`. When you check in an administrative file, CVS should print

    cvs commit: Rebuilding administrative file database

and update the checked out copy in ``$CVSROOT/CVSROOT'`. If it does not, there is something wrong (see section Dealing with bugs in CVS or this manual). To add your own files to the files to be updated in this fashion, you can add them to the ``checkoutlist'` administrative file.

By default, the ``modules'` file behaves as described above. If the modules file is very large, storing it as a flat text file may make looking up modules slow (I'm not sure whether this is as much of a concern now as when CVS first evolved this feature; I haven't seen benchmarks). Therefore, by making appropriate edits to the CVS source code one can store the modules file in a database which implements the `ndbm` interface, such as Berkeley db or GDBM. If this option is in use, then the modules database will be stored in the files ``modules.db'`, ``modules.pag'`, and/or ``modules.dir'`.

For information on the meaning of the various administrative files, see section Reference manual for Administrative files.

## How data is stored in the working directory

While we are discussing CVS internals which may become visible from time to time, we might as well talk about what CVS puts in the ``CVS'` directories in the working directories. As with the repository, CVS handles this information and one can usually access it via CVS commands. But in some cases it may be useful to look at it, and other programs, such as the `jCVS` graphical user interface or the `VC` package for emacs, may need to look at it. Such programs should follow the recommendations in this section if they hope to be able to work with other programs which use those files, including future versions of the programs just mentioned and the command-line CVS client.

The ``CVS'` directory contains several files. Programs which are reading this directory should silently ignore files which are in the directory but which are not documented here, to allow for future expansion.

``Root'`
  This file contains the current CVS root, as described in section Telling CVS where your repository is.
``Repository'`
  This file contains the directory within the repository which the current directory corresponds with. It can be either an absolute pathname or a relative pathname; CVS has had the ability to read either format since at least version 1.3 or so. The relative pathname is relative to the root, and is the more sensible approach, but the absolute pathname is quite common and implementations should accept either. For example, after the command

      cvs -d :local:/usr/local/cvsroot checkout yoyodyne/tc

  ``Root'` will contain

      :local:/usr/local/cvsroot

  and ``Repository'` will contain either

      /usr/local/cvsroot/yoyodyne/tc

  or

      yoyodyne/tc

``Entries'`
  This file lists the files and directories in the working directory. It is a text file according to the conventions appropriate for the operating system in question. The first character of each line indicates what sort of line it is. If the character is unrecognized, programs reading the file should silently skip that line, to allow for future expansion. If the first character is ``/'`, then the format is:

      /name/revision/timestamp[+conflict]/options/tagdate

  where ``['` and ``]'` are not part of the entry, but instead indicate that the ``+'` and conflict marker are optional. name is the name of the file within the directory. revision is the revision that the file in the working derives from, or ``0'` for an added file, or ``-'` followed by a revision for a removed file. timestamp is the timestamp of the file at the time that CVS created it; if the timestamp differs with the actual modification time of the file it means the file has been modified. It is in Universal Time (UT), stored in the format used by the ISO C asctime() function (for example, ``Sun Apr 7 01:29:26 1996'`). One may write a string which is not in that format, for example, ``Result of merge'`, to indicate that the file should always be considered to be modified. This is not a special case; to see whether a file is modified a program should take the timestamp of the file and simply do a string compare with timestamp. conflict indicates that there was a conflict; if it is the same as the actual modification time of the file it means that the user has obviously not resolved the conflict. options contains sticky options (for example ``-kb'` for a binary file). tagdate contains ``T'` followed by a tag name, or ``D'` for a date, followed by a sticky tag or date. Note that if timestamp contains a pair of timestamps separated by a space, rather than a single timestamp, you are dealing with a version of CVS earlier than CVS 1.5 (not documented here). If the first character of a line in ``Entries'` is ``D'`, then it indicates a subdirectory. ``D'` on a line all by itself indicates that the program which wrote the ``Entries'` file does record subdirectories (therefore, if there is such a line and no other lines beginning with ``D'`, one knows there are no subdirectories). Otherwise, the line looks like:

      D/name/filler1/filler2/filler3/filler4

  where name is the name of the subdirectory, and all the filler fields should be silently ignored, for future expansion. Programs which modify `Entries` files should preserve these fields.
``Entries.Log'`
  This file does not record any information beyond that in ``Entries'`, but it does provide a way to update the information without having to rewrite the entire ``Entries'` file, including the ability to preserve the information even if the program writing ``Entries'` and ``Entries.Log'` abruptly aborts. Programs which are reading the ``Entries'` file should also check for ``Entries.Log'`. If the latter exists, they should read ``Entries'` and then apply the changes mentioned in ``Entries.Log'`. After applying the changes, the recommended practice is to rewrite ``Entries'` and then delete ``Entries.Log'`. The format of a line in ``Entries.Log'` is a single character command followed by a space followed by a line in the format specified for a line in ``Entries'`. The single character command is ``A'` to indicate that the entry is being added, ``R'` to indicate that the entry is being removed, or any other character to indicate that the entire line in ``Entries.Log'` should be silently ignored (for future expansion). If the second character of the line in ``Entries.Log'` is not a space, then it was written by an older version of CVS (not documented here).
``Entries.Backup'`
  This is a temporary file. Recommended usage is to write a new entries file to ``Entries.Backup'`, and then to rename it (atomically, where possible) to ``Entries'`.
``Entries.Static'`
  The only relevant thing about this file is whether it exists or not. If it exists, then it means that only part of a directory was gotten and CVS will not create additional files in that directory. To clear it, use the `update` command with the ``-d'` option, which will get the additional files and remove ``Entries.Static'`.
``Tag'`
  This file contains per-directory sticky tags or dates. The first character is ``T'` for a branch tag, ``N'` for a non-branch tag, or ``D'` for a date, or another character to mean the file should be silently ignored, for future expansion. This character is followed by the tag or date. Note that per-directory sticky tags or dates are used for things like applying to files which are newly added; they might not be the same as the sticky tags or dates on individual files. For general information on sticky tags and dates, see section Sticky tags.
``Checkin.prog'`
``Update.prog'`
  These files store the programs specified by the ``-i'` and ``-u'` options in the modules file, respectively.
``Notify'`
  This file stores notifications (for example, for `edit` or `unedit`) which have not yet been sent to the server. Its format is not yet documented here.
``Notify.tmp'`
  This file is to ``Notify'` as ``Entries.Backup'` is to ``Entries'`. That is, to write ``Notify'`, first write the new contents to ``Notify.tmp'` and then (atomically where possible), rename it to ``Notify'`.
``Base'`
  If watches are in use, then an `edit` command stores the original copy of the file in the ``Base'` directory. This allows the `unedit` command to operate even if it is unable to communicate with the server.
``Baserev'`
  The file lists the revision for each of the files in the ``Base'` directory. The format is:

      Bname/rev/expansion

  where expansion should be ignored, to allow for future expansion.
``Baserev.tmp'`
  This file is to ``Baserev'` as ``Entries.Backup'` is to ``Entries'`. That is, to write ``Baserev'`, first write the new contents to ``Baserev.tmp'` and then (atomically where possible), rename it to ``Baserev'`.
``Template'`
  This file contains the template specified by the ``rcsinfo'` file (see section Rcsinfo). It is only used by the client; the non-client/server CVS consults ``rcsinfo'` directly.

## The administrative files

The directory ``$CVSROOT/CVSROOT'` contains some administrative files. See section Reference manual for Administrative files, for a complete description. You can use CVS without any of these files, but some commands work better when at least the ``modules'` file is properly set up.

The most important of these files is the ``modules'` file. It defines all modules in the repository. This is a sample ``modules'` file.

    CVSROOT         CVSROOT
    modules         CVSROOT modules
    cvs             gnu/cvs
    rcs             gnu/rcs
    diff            gnu/diff
    tc              yoyodyne/tc

The ``modules'` file is line oriented. In its simplest form each line contains the name of the module, whitespace, and the directory where the module resides. The directory is a path relative to `$CVSROOT`. The last four lines in the example above are examples of such lines.

The line that defines the module called ``modules'` uses features that are not explained here. See section The modules file, for a full explanation of all the available features.

### Editing administrative files

You edit the administrative files in the same way that you would edit any other module. Use ``cvs checkout CVSROOT'` to get a working copy, edit it, and commit your changes in the normal way.

It is possible to commit an erroneous administrative file. You can often fix the error and check in a new revision, but sometimes a particularly bad error in the administrative file makes it impossible to commit new revisions.

## Multiple repositories

In some situations it is a good idea to have more than one repository, for instance if you have two development groups that work on separate projects without sharing any code. All you have to do to have several repositories is to specify the appropriate repository, using the `CVSROOT` environment variable, the ``-d'` option to CVS, or (once you have checked out a working directory) by simply allowing CVS to use the repository that was used to check out the working directory (see section Telling CVS where your repository is).

The big advantage of having multiple repositories is that they can reside on different servers. The big disadvantage is that you cannot have a single CVS command recurse into directories which comes from different repositories. Generally speaking, if you are thinking of setting up several repositories on the same machine, you might want to consider using several directories within the same repository.

None of the examples in this manual show multiple repositories.

## Creating a repository

To set up a CVS repository, first choose the machine and disk on which you want to store the revision history of the source files. CPU and memory requirements are modest, so most machines should be adequate. For details see section Server requirements.

To estimate disk space requirements, if you are importing RCS files from another system, the size of those files is the approximate initial size of your repository, or if you are starting without any version history, a rule of thumb is to allow for the server approximately three times the size of the code to be under CVS for the repository (you will eventually outgrow this, but not for a while). On the machines on which the developers will be working, you'll want disk space for approximately one working directory for each developer (either the entire tree or a portion of it, depending on what each developer uses).

The repository should be accessable (directly or via a networked file system) from all machines which want to use CVS in server or local mode; the client machines need not have any access to it other than via the CVS protocol. It is not possible to use CVS to read from a repository which one only has read access to; CVS needs to be able to create lock files (see section Several developers simultaneously attempting to run CVS).

To create a repository, run the `cvs init` command. It will set up an empty repository in the CVS root specified in the usual way (see section The Repository). For example,

    cvs -d /usr/local/cvsroot init

`cvs init` is careful to never overwrite any existing files in the repository, so no harm is done if you run `cvs init` on an already set-up repository.

`cvs init` will enable history logging; if you don't want that, remove the history file after running `cvs init`. See section The history file.

## Backing up a repository

There is nothing particularly magical about the files in the repository; for the most part it is possible to back them up just like any other files. However, there are a few issues to consider.

The first is that to be paranoid, one should either not use CVS during the backup, or have the backup program lock CVS while doing the backup. To not use CVS, you might forbid logins to machines which can access the repository, turn off your CVS server, or similar mechanisms. The details would depend on your operating system and how you have CVS set up. To lock CVS, you would create ``#cvs.rfl'` locks in each repository directory. See section Several developers simultaneously attempting to run CVS, for more on CVS locks. Having said all this, if you just back up without any of these precautions, the results are unlikely to be particularly dire. Restoring from backup, the repository might be in an inconsistent state, but this would not be particularly hard to fix manually.

When you restore a repository from backup, assuming that changes in the repository were made after the time of the backup, working directories which were not affected by the failure may refer to revisions which no longer exist in the repository. Trying to run CVS in such directories will typically produce an error message. One way to get those changes back into the repository is as follows:

- Get a new working directory.
- Copy the files from the working directory from before the failure over to the new working directory (do not copy the contents of the ``CVS'` directories, of course).
- Working in the new working directory, use commands such as `cvs update` and `cvs diff` to figure out what has changed, and then when you are ready, commit the changes into the repository.

## Moving a repository

Just as backing up the files in the repository is pretty much like backing up any other files, if you need to move a repository from one place to another it is also pretty much like just moving any other collection of files.

The main thing to consider is that working directories point to the repository. The simplest way to deal with a moved repository is to just get a fresh working directory after the move. Of course, you'll want to make sure that the old working directory had been checked in before the move, or you figured out some other way to make sure that you don't lose any changes. If you really do want to reuse the existing working directory, it should be possible with manual surgery on the ``CVS/Repository'` files. You can see section How data is stored in the working directory, for information on the ``CVS/Repository'` and ``CVS/Root'` files, but unless you are sure you want to bother, it probably isn't worth it.

## Remote repositories

Your working copy of the sources can be on a different machine than the repository. Using CVS in this manner is known as client/server operation. You run CVS on a machine which can mount your working directory, known as the client, and tell it to communicate to a machine which can mount the repository, known as the server. Generally, using a remote repository is just like using a local one, except that the format of the repository name is:

    :method:user@hostname:/path/to/repository

The details of exactly what needs to be set up depend on how you are connecting to the server.

If method is not specified, and the repository name contains ``:'`, then the default is `ext` or `server`, depending on your platform; both are described in section Connecting with rsh.

- Server requirements: Memory and other resources for servers
- Connecting via rsh: Using the `rsh` program to connect
- Password authenticated: Direct connections using passwords
- GSSAPI authenticated: Direct connections using GSSAPI
- Kerberos authenticated: Direct connections with kerberos

### Server requirements

The quick answer to what sort of machine is suitable as a server is that requirements are modest--a server with 32M of memory or even less can handle a fairly large source tree with a fair amount of activity.

The real answer, of course, is more complicated. Estimating the known areas of large memory consumption should be sufficient to estimate memory requirements. There are two such areas documented here; other memory consumption should be small by comparison (if you find that is not the case, let us know, as described in section Dealing with bugs in CVS or this manual, so we can update this documentation).

The first area of big memory consumption is large checkouts, when using the CVS server. The server consists of two processes for each client that it is serving. Memory consumption on the child process should remain fairly small. Memory consumption on the parent process, particularly if the network connection to the client is slow, can be expected to grow to slightly more than the size of the sources in a single directory, or two megabytes, whichever is larger.

Multiplying the size of each CVS server by the number of servers which you expect to have active at one time should give an idea of memory requirements for the server. For the most part, the memory consumed by the parent process probably can be swap space rather than physical memory.

The second area of large memory consumption is `diff`, when checking in large files. This is required even for binary files. The rule of thumb is to allow about ten times the size of the largest file you will want to check in, although five times may be adequate. For example, if you want to check in a file which is 10 megabytes, you should have 100 megabytes of memory on the machine doing the checkin (the server machine for client/server, or the machine running CVS for non-client/server). This can be swap space rather than physical memory. Because the memory is only required briefly, there is no particular need to allow memory for more than one such checkin at a time.

Resource consumption for the client is even more modest--any machine with enough capacity to run the operating system in question should have little trouble.

For information on disk space requirements, see section Creating a repository.

### Connecting with rsh

CVS uses the ``rsh'` protocol to perform these operations, so the remote user host needs to have a ``.rhosts'` file which grants access to the local user.

For example, suppose you are the user ``mozart'` on the local machine ``toe.grunge.com'`, and the server machine is ``chainsaw.yard.com'`. On chainsaw, put the following line into the file ``.rhosts'` in ``bach'`'s home directory:

    toe.grunge.com  mozart

Then test that `rsh` is working with

    rsh -l bach chainsaw.yard.com 'echo $PATH'

Next you have to make sure that `rsh` will be able to find the server. Make sure that the path which `rsh` printed in the above example includes the directory containing a program named `cvs` which is the server. You need to set the path in ``.bashrc'`, ``.cshrc'`, etc., not ``.login'` or ``.profile'`. Alternately, you can set the environment variable `CVS_SERVER` on the client machine to the filename of the server you want to use, for example ``/usr/local/bin/cvs-1.6'`.

There is no need to edit `inetd.conf` or start a CVS server daemon.

There are two access methods that you use in CVSROOT for rsh. `:server:` specifies an internal rsh client, which is supported only by some CVS ports. `:ext:` specifies an external rsh program. By default this is `rsh` but you may set the `CVS_RSH` environment variable to invoke another program which can access the remote server (for example, `remsh` on HP-UX 9 because `rsh` is something different). It must be a program which can transmit data to and from the server without modifying it; for example the Windows NT `rsh` is not suitable since it by default translates between CRLF and LF. The OS/2 CVS port has a hack to pass ``-b'` to `rsh` to get around this, but since this could potentially cause problems for programs other than the standard `rsh`, it may change in the future. If you set `CVS_RSH` to `SSH` or some other rsh replacement, the instructions in the rest of this section concerning ``.rhosts'` and so on are likely to be inapplicable; consult the documentation for your rsh replacement.

Continuing our example, supposing you want to access the module ``foo'` in the repository ``/usr/local/cvsroot/'`, on machine ``chainsaw.yard.com'`, you are ready to go:

    cvs -d :ext:bach@chainsaw.yard.com:/usr/local/cvsroot checkout foo

(The ``bach@'` can be omitted if the username is the same on both the local and remote hosts.)

### Direct connection with password authentication

The CVS client can also connect to the server using a password protocol. This is particularly useful if using `rsh` is not feasible (for example, the server is behind a firewall), and Kerberos also is not available.

To use this method, it is necessary to make some adjustments on both the server and client sides.

- Password authentication server: Setting up the server
- Password authentication client: Using the client
- Password authentication security: What this method does and does not do

#### Setting up the server for password authentication

First of all, you probably want to tighten the permissions on the ``$CVSROOT'` and ``$CVSROOT/CVSROOT'` directories. See section Security considerations with password authentication, for more details.

On the server side, the file ``/etc/inetd.conf'` needs to be edited so `inetd` knows to run the command `cvs pserver` when it receives a connection on the right port. By default, the port number is 2401; it would be different if your client were compiled with `CVS_AUTH_PORT` defined to something else, though.

If your `inetd` allows raw port numbers in ``/etc/inetd.conf'`, then the following (all on a single line in ``inetd.conf'`) should be sufficient:

    2401  stream  tcp  nowait  root  /usr/local/bin/cvs
    cvs --allow-root=/usr/cvsroot pserver

You could also use the ``-T'` option to specify a temporary directory.

The ``--allow-root'` option specifies the allowable CVSROOT directory. Clients which attempt to use a different CVSROOT directory will not be allowed to connect. If there is more than one CVSROOT directory which you want to allow, repeat the option.

If your `inetd` wants a symbolic service name instead of a raw port number, then put this in ``/etc/services'`:

    cvspserver      2401/tcp

and put `cvspserver` instead of `2401` in ``inetd.conf'`.

Once the above is taken care of, restart your `inetd`, or do whatever is necessary to force it to reread its initialization files.

Because the client stores and transmits passwords in cleartext (almost--see section Security considerations with password authentication, for details), a separate CVS password file may be used, so people don't compromise their regular passwords when they access the repository. This file is ``$CVSROOT/CVSROOT/passwd'` (see section The administrative files). Its format is similar to ``/etc/passwd'`, except that it only has two or three fields, username, password, and optional username for the server to use. For example:

    bach:ULtgRLXo7NRxs
    cwang:1sOp854gDF3DY

The password is encrypted according to the standard Unix `crypt()` function, so it is possible to paste in passwords directly from regular Unix ``passwd'` files.

When authenticating a password, the server first checks for the user in the CVS ``passwd'` file. If it finds the user, it compares against that password. If it does not find the user, or if the CVS ``passwd'` file does not exist, then the server tries to match the password using the system's user-lookup routine (using the system's user-lookup routine can be disabled by setting `SystemAuth=no` in the config file, see section The CVSROOT/config configuration file). When using the CVS ``passwd'` file, the server runs as the username specified in the third argument in the entry, or as the first argument if there is no third argument (in this way CVS allows imaginary usernames provided the CVS ``passwd'` file indicates corresponding valid system usernames). In any case, CVS will have no privileges which the (valid) user would not have.

It is possible to "map" cvs-specific usernames onto system usernames (i.e., onto system login names) in the ``$CVSROOT/CVSROOT/passwd'` file by appending a colon and the system username after the password. For example:

    cvs:ULtgRLXo7NRxs:kfogel
    generic:1sOp854gDF3DY:spwang
    anyone:1sOp854gDF3DY:spwang

Thus, someone remotely accessing the repository on ``chainsaw.yard.com'` with the following command:

    cvs -d :pserver:cvs@chainsaw.yard.com:/usr/local/cvsroot checkout foo

would end up running the server under the system identity kfogel, assuming successful authentication. However, the remote user would not necessarily need to know kfogel's system password, as the ``$CVSROOT/CVSROOT/passwd'` file might contain a different password, used only for CVS. And as the example above indicates, it is permissible to map multiple cvs usernames onto a single system username.

This feature is designed to allow people repository access without full system access (in particular, see section Read-only repository access); however, also see section Security considerations with password authentication. Any sort of repository access very likely implies a degree of general system access as well.

Right now, the only way to put a password in the CVS ``passwd'` file is to paste it there from somewhere else. Someday, there may be a `cvs passwd` command.

#### Using the client with password authentication

Before connecting to the server, the client must log in with the command `cvs login`. Logging in verifies a password with the server, and also records the password for later transactions with the server. The `cvs login` command needs to know the username, server hostname, and full repository path, and it gets this information from the repository argument or the `CVSROOT` environment variable.

`cvs login` is interactive -- it prompts for a password:

    cvs -d :pserver:bach@chainsaw.yard.com:/usr/local/cvsroot login
    CVS password:

The password is checked with the server; if it is correct, the `login` succeeds, else it fails, complaining that the password was incorrect.

Once you have logged in, you can force CVS to connect directly to the server and authenticate with the stored password:

    cvs -d :pserver:bach@chainsaw.yard.com:/usr/local/cvsroot checkout foo

The ``:pserver:'` is necessary because without it, CVS will assume it should use `rsh` to connect with the server (see section Connecting with rsh). (Once you have a working copy checked out and are running CVS commands from within it, there is no longer any need to specify the repository explicitly, because CVS records it in the working copy's ``CVS'` subdirectory.)

Passwords are stored by default in the file ``$HOME/.cvspass'`. Its format is human-readable, but don't edit it unless you know what you are doing. The passwords are not stored in cleartext, but are trivially encoded to protect them from "innocent" compromise (i.e., inadvertently being seen by a system administrator who happens to look at that file).

The password for the currently choosen remote repository can be removed from the CVS_PASSFILE by using the `cvs logout` command.

The `CVS_PASSFILE` environment variable overrides this default. If you use this variable, make sure you set it before `cvs login` is run. If you were to set it after running `cvs login`, then later CVS commands would be unable to look up the password for transmission to the server.

#### Security considerations with password authentication

The passwords are stored on the client side in a trivial encoding of the cleartext, and transmitted in the same encoding. The encoding is done only to prevent inadvertent password compromises (i.e., a system administrator accidentally looking at the file), and will not prevent even a naive attacker from gaining the password.

The separate CVS password file (see section Setting up the server for password authentication) allows people to use a different password for repository access than for login access. On the other hand, once a user has non-read-only access to the repository, she can execute programs on the server system through a variety of means. Thus, repository access implies fairly broad system access as well. It might be possible to modify CVS to prevent that, but no one has done so as of this writing. Furthermore, there may be other ways in which having access to CVS allows people to gain more general access to the system; no one has done a careful audit.

Note that because the ``$CVSROOT/CVSROOT'` directory contains ``passwd'` and other files which are used to check security, you must control the permissions on this directory as tightly as the permissions on ``/etc'`. The same applies to the ``$CVSROOT'` directory itself and any directory above it in the tree. Anyone who has write access to such a directory will have the ability to become any user on the system. Note that these permissions are typically tighter than you would use if you are not using pserver.

In summary, anyone who gets the password gets repository access, and some measure of general system access as well. The password is available to anyone who can sniff network packets or read a protected (i.e., user read-only) file. If you want real security, get Kerberos.

### Direct connection with GSSAPI

GSSAPI is a generic interface to network security systems such as Kerberos 5. If you have a working GSSAPI library, you can have CVS connect via a direct TCP connection, authenticating with GSSAPI.

To do this, CVS needs to be compiled with GSSAPI support; when configuring CVS it tries to detect whether GSSAPI libraries using kerberos version 5 are present. You can also use the ``--with-gssapi'` flag to configure.

The connection is authenticated using GSSAPI, but the message stream is not authenticated by default. You must use the `-a` global option to request stream authentication.

The data transmitted is not encrypted by default. Encryption support must be compiled into both the client and the server; use the ``--enable-encrypt'` configure option to turn it on. You must then use the `-x` global option to request encryption.

GSSAPI connections are handled on the server side by the same server which handles the password authentication server; see section Setting up the server for password authentication. If you are using a GSSAPI mechanism such as Kerberos which provides for strong authentication, you will probably want to disable the ability to authenticate via cleartext passwords. To do so, create an empty ``CVSROOT/passwd'` password file, and set `SystemAuth=no` in the config file (see section The CVSROOT/config configuration file).

The GSSAPI server uses a principal name of cvs/hostname, where hostname is the canonical name of the server host. You will have to set this up as required by your GSSAPI mechanism.

To connect using GSSAPI, use ``:gserver:'`. For example,

    cvs -d :gserver:chainsaw.yard.com:/usr/local/cvsroot checkout foo

### Direct connection with kerberos

The easiest way to use kerberos is to use the kerberos `rsh`, as described in section Connecting with rsh. The main disadvantage of using rsh is that all the data needs to pass through additional programs, so it may be slower. So if you have kerberos installed you can connect via a direct TCP connection, authenticating with kerberos.

This section concerns the kerberos network security system, version 4. Kerberos version 5 is supported via the GSSAPI generic network security interface, as described in the previous section.

To do this, CVS needs to be compiled with kerberos support; when configuring CVS it tries to detect whether kerberos is present or you can use the ``--with-krb4'` flag to configure.

The data transmitted is not encrypted by default. Encryption support must be compiled into both the client and server; use the ``--enable-encryption'` configure option to turn it on. You must then use the `-x` global option to request encryption.

You need to edit `inetd.conf` on the server machine to run `cvs kserver`. The client uses port 1999 by default; if you want to use another port specify it in the `CVS_CLIENT_PORT` environment variable on the client.

When you want to use CVS, get a ticket in the usual way (generally `kinit`); it must be a ticket which allows you to log into the server machine. Then you are ready to go:

    cvs -d :kserver:chainsaw.yard.com:/usr/local/cvsroot checkout foo

Previous versions of CVS would fall back to a connection via rsh; this version will not do so.

## Read-only repository access

It is possible to grant read-only repository access to people using the password-authenticated server (see section Direct connection with password authentication). (The other access methods do not have explicit support for read-only users because those methods all assume login access to the repository machine anyway, and therefore the user can do whatever local file permissions allow her to do.)

A user who has read-only access can do only those CVS operations which do not modify the repository, except for certain "administrative" files (such as lock files and the history file). It may be desirable to use this feature in conjunction with user-aliasing (see section Setting up the server for password authentication).

Unlike with previous versions of CVS, read-only users should be able merely to read the repository, and not to execute programs on the server or otherwise gain unexpected levels of access. Or to be more accurate, the known holes have been plugged. Because this feature is new and has not received a comprehensive security audit, you should use whatever level of caution seems warranted given your attitude concerning security.

There are two ways to specify read-only access for a user: by inclusion, and by exclusion.

"Inclusion" means listing that user specifically in the ``$CVSROOT/CVSROOT/readers'` file, which is simply a newline-separated list of users. Here is a sample ``readers'` file:

    melissa
    splotnik
    jrandom

(Don't forget the newline after the last user.)

"Exclusion" means explicitly listing everyone who has write access--if the file

    $CVSROOT/CVSROOT/writers

exists, then only those users listed in it have write access, and everyone else has read-only access (of course, even the read-only users still need to be listed in the CVS ``passwd'` file). The ``writers'` file has the same format as the ``readers'` file.

Note: if your CVS ``passwd'` file maps cvs users onto system users (see section Setting up the server for password authentication), make sure you deny or grant read-only access using the cvs usernames, not the system usernames. That is, the ``readers'` and ``writers'` files contain cvs usernames, which may or may not be the same as system usernames.

Here is a complete description of the server's behavior in deciding whether to grant read-only or read-write access:

If ``readers'` exists, and this user is listed in it, then she gets read-only access. Or if ``writers'` exists, and this user is NOT listed in it, then she also gets read-only access (this is true even if ``readers'` exists but she is not listed there). Otherwise, she gets full read-write access.

Of course there is a conflict if the user is listed in both files. This is resolved in the more conservative way, it being better to protect the repository too much than too little: such a user gets read-only access.

## Temporary directories for the server

While running, the CVS server creates temporary directories. They are named

    cvs-servpid

where pid is the process identification number of the server. They are located in the directory specified by the ``TMPDIR'` environment variable (see section All environment variables which affect CVS), the ``-T'` global option (see section Global options), or failing that ``/tmp'`.

In most cases the server will remove the temporary directory when it is done, whether it finishes normally or abnormally. However, there are a few cases in which the server does not or cannot remove the temporary directory, for example:

- If the server aborts due to an internal server error, it may preserve the directory to aid in debugging
- If the server is killed in a way that it has no way of cleaning up (most notably, ``kill -KILL'` on unix).
- If the system shuts down without an orderly shutdown, which tells the server to clean up.

In cases such as this, you will need to manually remove the ``cvs-servpid'` directories. As long as there is no server running with process identification number pid, it is safe to do so.

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