cvs-fast-export [-h] [-a] [-w 'fuzz'] [-g] [-l] [-v] [-q] [-V] [-T] [-p] [-P] [-i 'date'] [-A 'authormap'] [-t threads] [-R 'revmap'] [--reposurgeon] [-e 'remote'] [-s 'stripprefix']


cvs-fast-export tries to group the per-file commits and tags in an RCS file collection or CVS project repository into per-project changeset commits with common metadata. It emits a Git fast-import stream describing these changesets to standard output.

This tool is best used in conjunction with reposurgeon(1). Plain cvs-fast-export conversions contain various sorts of fossils that reposurgeon is good for cleaning up. See the Repository Editing and Conversion With Reposurgeon to learn about the sanity-checking and polishing steps required for a really high-quality conversion, including reference lifting and various sorts of artifact cleanup.

If arguments are supplied, the program assumes all ending with the extension ",v" are master files and reads them in. If no arguments are supplied, the program reads filenames from stdin, one per line. Directories and files not ending in ",v" are skipped. (But see the description of the -P option for how to change this behavior.)

Files from either Unix CVS or CVS-NT are handled. If a collection of files has commitid fields, changesets will be constructed reliably using those.

In the default mode, which generates a git-style fast-export stream to standard output:

  • The prefix given using the -s option or, if the option is omitted, the longest common prefix of the paths is discarded from each path.

  • Files in CVS Attic and RCS directories are treated as though the "Attic/" or "RCS/" portion of the path were absent. This usually restores the history of files that were deleted.

  • Permissions on all fileops related to a particular file will be controlled by the permissions on the corresponding master. If the executable bit on the master is on, all its fileops will have 100755 permissions; otherwise 100644. This tracks what GNU RCS does; the "permissions" field in CVS-NT masters is not interpreted.

  • A set of file operations is coalesced into a changeset if either (a) they all share the same commitid, or (b) all have no commitid but identical change comments, authors, and modification dates within the window defined by the time-fuzz parameter. Unlike some other exporters, no attempt is made to derive changesets from shared tags.

  • Commits are issued in time order unless the cvs-fast-export detects that some parent is younger than its child (this is unlikely but possible in cases of severe clock skew). In that case you will see a warning on standard error and the emission order is guaranteed topologically correct, but otherwise not specified (and is subject to change in future versions of this program).

  • CVS tags become git lightweight tags when they can be unambiguously associated with a changeset. If the same tag is attached to file deltas that resolve to multiple changesets, it is reported as if attached to the last of them.

  • The HEAD branch is renamed to 'master'.

  • Other tag and branch names are sanitized to be legal for git; the characters ~^\*? are removed.

  • Since .cvsignore files have a syntax (mostly) upward-compatible with that of .gitignore files, they’re renamed. In order to simulate the default ignore behavior of CVS, those defaults are prepended to root .cvsignore blobs renamed to .gitignore, and a root .gitignore containing the defaults is generated if no such blobs exist. Leading # characters on .cvsignore lines are escaped so git won’t misunderstand them as comment leaders, and spaces in these lines are mapped to line feeds because CVS treats spaces as pattern separators.

  • The CVS-NT extension keywords "owner", "group", "deltatype", "kopt", "permissions", "mergepoint", "filename", "hardlinks", and "username" are all ignored. So is the "access" keyword.

See the later section on RCS/CVS LIMITATIONS for more information on edge cases and conversion problems.

This program does not depend on any of the CVS metadata held outside the individual content files (e.g. under CVSROOT).

The variable TMPDIR is honored and used when generating a temporary directory in which to store file content during processing.

This program treats the file contents of the source CVS or RCS repository, and their filenames. as uninterpreted byte sequences to be passed through to the git conversion without re-encoding. In particular, it makes no attempt to fix up line endings (Unix \n vs, Windows \r\n vs. Macintosh \r), nor does it know about what repository filenames might collide with special filenames on any given platform.

By default, CVS $-keywords in the masters are not interpreted or expanded; this prevents corruption of binary content. However, this will be overridden if a master has an explicit "expand" metadata field specifying a CVS expansion type ("kv", "kvl", "k", "v", "o" or "b").

This program treats change comments as uninterpreted byte sequences to be passed through to the git conversion without change or re-encoding. If you need to re-encode (e.g, from Latin-1 to UTF-8) or remap CVS version IDs to something useful, use cvs-fast-export in conjunction with reposurgeon(1).



Display usage summary.

-w 'fuzz'

Set the timestamp fuzz factor for identifying patch sets in seconds. The default is 300 seconds. This option is irrelevant for changesets with commitids.


Don’t trust commit-IDs; match by ordinary metadata. Will be useful if you have something like a CVS-NT repository in which per-file commits were made in such a way that the cliques don’t have matching IDs.


Generate a picture of the commit graph in the DOT markup language used by the graphviz tools, rather than fast-exporting. With two -g options, tag each report on a CVS component commit with a prefix character; + for an added file, | for a changed one, - for a deleted one. With the -r option, don’t collate - graph the CVS forest instead (-T) forces more verbosity.


Warnings normally go to standard error. This option, which takes a filename, allows you to redirect them to a file. Convenient with the -p option.


Dump a list of author IDs found in the repository, rather than fast-exporting.

-A 'authormap'

Apply an author-map file to the attribution lines. Each line must be of the form

ferd = Ferd J. Foonly <> America/Chicago

and will be applied to map the Unix username 'ferd' to the DVCS-style user identity specified after the equals sign. The timezone field (after > and whitespace) is optional and (if present) is used to set the timezone offset to be attached to the date; acceptable formats for the timezone field are anything that can be in the TZ environment variable, including a [+-]hhmm offset. Whitespace around the equals sign is stripped. Lines beginning with a # or not containing an equals sign are silently ignored.

-R 'revmap'

Write a revision map to the specified argument filename. Each line of the revision map consists of three whitespace-separated fields: a filename, an RCS revision number, and the mark of the commit to which that filename-revision pair was assigned. Doesn’t work with -g.


Show verbose progress messages mainly of interest to developers.


Run quietly, suppressing warning messages about absence of commitids and other minor problems for which the program can usually compensate but which may indicate conversion problems. Meant to be used with cvsconvert(1), which does its own correctness checking.


Force deterministic dates for regression testing. Each patchset will have a monotonic-increasing attributed date computed from its mark in the output stream - the mark value times the commit time window times two.


Ship a header comment for reposurgeon to use, declaring "cvs" if a .cvsignore master or CVSROOT file has been seen and "rcs" otherwise. Emit for each commit a list of the CVS file:revision pairs composing it as a bzr-style commit property named "cvs-revisions". From version 2.12 onward, reposurgeon(1) can interpret these and use them as hints for reference-lifting.


Append to each commit comment identification of the CVS commits that contributed to it.


Emit the program version and exit.

-e 'remote'

Exported branch names are prefixed with refs/remotes/'remote' instead of refs/heads, making the import appear to come from the named remote.

-s 'stripprefix'

Strip the given prefix instead of longest common prefix

-t 'threadcount'

Running multithreaded increases the program’s memory footprint proportionally to the number of threads, but means the conversion may run in less total time because an I/O operation involving one master file will not block compute-intensive processing of others. By default, the program conservatively assumes it can use two threads per processor available. You can use this option to set the number of threads; the value 0 forces sequential processing with no threading.


Enable progress reporting. This also dumps statistics (elapsed time and size of maximum resident set) for several points in the conversion run.


Normally cvs-fast-export will skip any filename presented as an argument or on stdin that does not end with the RCS/CVS extension ",v", and will also ignore a pathname containing the string CVSROOT (this avoids annoyances when running from or above a top-level CVS directory). A strict reading of RCS allows masters without the ,v extension. This option sets promiscuous mode, disabling both checks.

-i 'date'

Enable incremental-dump mode. Only commits with a date after that specified by the argument are emitted. Disables inclusion of default ignores. Each branch root in the incremental dump is decorated with git-stream magic which, when interpreted in context of a live repository, will connect that branch to any branch of the same name. The date is expected to be RFC3339 conformant (e.g. yy-mm-ddThh:mm:ssZ) or else an integer Unix time in seconds.


A very typical invocation would look like this:

find . | cvs-fast-export >

Your cvs-fast-export distribution should also supply cvssync(1), a tool for fetching CVS masters from a remote repository. Using them together will look something like this:

cvssync groff
find groff | cvs-fast-export >

Progress reporting can be reassuring if you expect a conversion to run for some time. It will animate completion percentages as the conversion proceeds and display timings when done.

The cvs-fast-export suite contains a wrapper script called 'cvsconvert' that is useful for running a conversion and automatically checking its content against the CVS original.


Translating RCS/CVS repositories to the generic DVCS model expressed by import streams is not merely difficult and messy, there are weird RCS/CVS cases that cannot be correctly translated at all. cvs-fast-export will try to warn you about these cases rather than silently producing broken or incomplete translations, but there be dragons. We recommend some precautions under SANITY CHECKING.

CVS-NT and versions of GNU CVS after 1.12 (2004) added a changeset commit-id to file metadata. Older sections of CVS history without these are vulnerable to various problems caused by clock skew between clients; this used to be relatively common for multiple reasons, including less pervasive use of NTP clock synchronization. cvs-fast-export will warn you ("commits before this date lack commitids") when it sees such a section in your history. When it does, these caveats apply:

  • If timestamps of commits in the CVS repository were not stable enough to be used for ordering commits, changes may be reported in the wrong order.

  • If the timestamp order of different files crosses the revision order within the commit-matching time window, the order of commits reported may be wrong.

One more property affected by commitids is the stability of old changesets under incremental dumping. Under a CVS implementation issuing commitids, new CVS commits are guaranteed not to change cvs-fast-export’s changeset derivation from a previous history; thus, updating a target DVCS repository with incremental dumps from a live CVS installation will work. Even if older portions of the history do not have commitids, conversions will be stable. This stability guarantee is lost if you are using a version of CVS that does not issue commitids.

Also note that a CVS repository has to be completely reanalyzed even for incremental dumps; thus, processing time and memory requirements will rise with the total repository size even when the requested reporting interval of the incremental dump is small.

These problems cannot be fixed in cvs-fast-export; they are inherent to CVS.


The program’s transient RAM requirement is proportional to the total volume of all attributions and comments in the repository (excluding the file content). While it was originally written near the end of the 32-bit era, running it on a 32-bit machine against today’s repositories would be asking for trouble; you might well overflow counters or bust the 4GB addressing limit. On the other hand, any 64-bit machine with 64GB or above of RAM should have ample headroom.

The program requires temporary disk space equivalent to the sum of the sizes of all revisions in all files. Time performance is primarily I/O bound and can be improved by running on an SSD rather than spinning rust.

On stock PC hardware in 2020, cvs-fast-export achieves processing speeds upwards of 64K CVS commits per minute on real repositories.


Branches occurring in only a subset of the analyzed masters are not correctly resolved; instead, an entirely disjoint history will be created containing the branch revisions and all parents back to the root.

The program does try to do something useful cases in which a tag occurs in a set of revisions that does not correspond to any gitspace commit. In this case a tagged branch containing only one commit is created, guaranteeing that you can check out a set of files containing the CVS content for the tag. The commit comment is "Synthetic commit for incomplete tag XXX", where XXX is the relevant tag. The root of the branchlet is the gitspace commit where the latest CVS revision in in the tagged set first occurs; this is the commit the tag would point at if its incompleteness were ignored. The change in the branchlet commit is also applied forward in the nearby mainline.

Unless there an explicit expand directive in the CVS master, this program does the equivalent of cvs -kb when checking out masters, not performing any $-keyword expansion at all. This differs drom CVS’s default behavior om checkoutbut has the advantage that binary files will never be clobbered. It has the disadvantage that the data in $-headers is not reliable; at best you’ll get the unexpanded version of the $-cookie, at worst you might get the committer/timestamp information for when the master was originally checked in, rather than when it was last checked out. It’s good practice to remove all dollar cookies as part of post-conversion cleanup.

CVS vendor branches are a source of trouble, and this program will ship a warning when it sees them. Sufficiently strange combinations of imports and local modifications will translate badly, producing incorrect content on master and elsewhere. Some of these problems can be prevented by ensuring that the last (latest) commit in your repository is on trunk, rather than a branch.

Some other CVS exporters try, or have tried, to deduce changesets from shared tags even when comment metadata doesn’t match perfectly. This one does not; the designers judge that to trip over too many pathological CVS tagging cases.

When running multithreaded, there is an edge case in which the program’s behavior is nondeterministic. If the same tag looks like it should be assigned to two different gitspace commits with the same timestamp, which tag it actually lands on will be random.

CVSNT is supported, but CVSNT extension fields includig "permissions" "hardlinks", "mregepoint" and "username" are ignored.

Non-ASCII characters in user IDs are not supported.


After conversion, it is good practice to do the following verification steps:

  1. If you ran the conversion directly with cvs-fast-export rather than using cvsconvert, use diff(1) with the -r option to compare a CVS head checkout with a checkout of the converted repository. The only differences you should see are those due to RCS keyword expansion, .cvsignore lifting, and manifest mismatches due to CVS not tracking file deaths quite correctly. If this is not true, you may have found a bug in cvs-fast-export; please report it with a copy of the CVS repo.

  2. Examine the translated repository with gitk(1) looking (in particular) for misplaced tags or branch joins. Often these can be manually repaired with little effort using reposurgeon(1). These flaws do 'not' necessarily imply bugs in cvs-fast-export; they may simply indicate previously undetected malformations in the CVS history. However, reporting them may help improve cvs-fast-export.

A more comprehensive sanity check is described in Repository Editing and Conversion With Reposurgeon; browse it for more.


0 if all files were found and successfully converted, 1 otherwise.


Most of the messages cvs-fast-export emits are self-explanatory. Here are a few that aren’t. Where it says "check head", be sure to sanity-check against the head revision.

vendor branch detected

Source tree contains vendored commits. Check head carefully, branch content might have landed on trunk. If this happens, you may be able to prefent it ny adding a dummy commit to trunk.

null branch name, probably from a damaged Attic file

The code was unable to deduce a name for a branch and tried to export a null pointer as a name. The branch is given the name "null". It is likely this history will need repair.

fatal: internal error - duplicate key in red black tree

Multiple tags with identical names exist in one of your master files. This is a sign of a corrupted revision history; you will need to manually inspect the master and remove one of the duplicates.

tag could not be assigned to a commit

RCS/CVS tags are per-file, not per revision. If developers are not careful in their use of tagging, it can be impossible to associate a tag with any of the changesets that cvs-fast-export resolves. When this happens, cvs-fast-export will issue this warning and the tag named will be discarded.

discarding dead untagged branch

Analysis found a CVS branch with no tag consisting entirely of dead revisions. These cannot have been visible in the archival state of the CVS at conversion time; it is possible they may have been visible as branch content at some point in the repository’s past, but without an identifying tag that state is impossible to reconstruct.

warning - unnamed branch

A CVS branch with a live revision lacks a head label. A label with "-UNNAMED-BRANCH" suffixed to the name of the parent branch will be generated.

warning - no master branch generated

cvs-fast-export could not identify the default (HEAD) branch and therefore there is no "master" in the conversion; this will seriously confuse git and probably other VCSes when they try to import the output stream. You may be able to identify and rename a master branch using reposurgeon(1).

warning - xxx newer than yyy

Early in analysis of a CVS master file, time sort order of its deltas doesn’t match the topological order defined by the revision numbers. The most likely cause of this is clock skew between clients in very old CVS versions. The program will attempt to correct for this by tweaking the revision date of the out-of-order commit to be that of its parent, but this may not prevent other time-skew errors later in analysis.

warning - skew_vulnerable in file xxx rev yyy set to zzz

This warning is emitted when verbose is on and only on commits with no commit ID. It calls out commits that cause the date before which coalescence is unreliable to be pushed forward.

tip commit older than imputed branch join

A similar problem to "newer than" being reported at a later stage, when file branches are being knit into changeset branches. One CVS branch in a collection about to be collated into a gitspace branch has a tip commit older than the earliest commit that is a a parent on some (other) tip in the collection. The adventitious branch is snipped off.

some parent commits are younger than children

May indicate that cvs-fast-export aggregated some changesets in the wrong order; probably a harmless result of clock skew, but check head.

warning - branch point later than branch

Late in the analysis, when connecting branches to their parents in the changeset DAG, the commit date of the root commit of a branch is earlier than the date of the parent it gets connected to. Could be yet another clock-skew symptom, or might point to an error in the program’s topological analysis. Examine commits near the join with reposurgeon(1); the branch may need to be reparented by hand.

more than one delta with number X.Y.Z

The CVS history contained duplicate file delta numbers. Should never happen, and may indicate a corrupted CVS archive if it does; check head.

{revision|patch} with odd depth

Should never happen; only branch numbers are supposed to have odd depth, not file delta or patch numbers. May indicate a corrupted CVS archive; check head.

duplicate tag in CVS master, ignoring

A CVS master has multiple instances of the same tag pointing at different file deltas. Probably a CVS operator error and relatively harmless, but check that the tag’s referent in the conversion makes sense.

tag or branch name was empty after sanitization

Fatal error: tag name was empty after all characters illegal for git were removed. Probably indicates a corrupted RCS file.

revision number too long, increase CVS_MAX_DEPTH

Fatal error: internal buffers are too short to handle a CVS revision in a repo. Increase this constant in cvs.h and rebuild. Warning: this will increase memory usage and slow down the tests a lot.

snapshot sequence number too large, widen serial_t

Fatal error: the number of file snapshots in the CVS repo overruns an internal counter. Rebuild cvs-fast-export from source with a wider serial_t patched into cvs.h. Warning: this will significantly increase the working-set size

too many branches, widen branchcount_t

Fatal error: the number of branches descended from some single commit overruns an internal counter. Rebuild cvs-fast-export from source with a wider branchcount_t patched into cvs.h. Warning: this will significantly increase the working-set size

corrupt delta in

The text of a delta is expected to be led with d (delete) and a (append) lines describing line-oriented changes at that delta. When you see this message, these are garbled.

edit script tried to delete beyond eof

Indicates a corrupted RCS file. An edit line count was wrong, possibly due to an integer overflow in an old 32-bit version of RCS.

internal error - branch cycle

cvs-fast-export found a cycle while topologically sorting commits by parent link. This should never happen and indicates either damaged metadata or a serious internal error in cvs-fast-export: please file a bug report.

internal error - lost tag

Late in analysis (after changeset coalescence) a tag lost its commit reference. This should never happen and probably indicates an internal error in cvs-fast-export: please file a bug report.

internal error - child commit emitted before parent exists

This should never happen; please file a bug report.


Report bugs to Eric S. Raymond <>. Please read "Reporting bugs in cvs-fast-export" before shipping a report. The project page itself is at


rcs(1), cvs(1), cvssync(1), cvsconvert(1), reposurgeon(1), cvs2git(1).