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From CVS to Subversion

Joachim “Joe” Feise UC Irvine, Information & Computer Sciences http://www.feise.com/~jfeise/. From CVS to Subversion. Why Version Control?. Avoiding accidental overwrites History of changes Who changed what when? Who is to blame (or praise)? What was the state x days/months/… ago?

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From CVS to Subversion

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  1. Joachim “Joe” Feise UC Irvine, Information & Computer Sciences http://www.feise.com/~jfeise/ From CVS to Subversion

  2. Why Version Control? • Avoiding accidental overwrites • History of changes • Who changed what when? Who is to blame (or praise)? • What was the state x days/months/… ago? • Management tool 2

  3. Traditional Version Control • Lock-modify-unlock • Example systems • RCS, SCCS, Perforce, VSS, … • Results in serialization of access • Lock file, edit file, unlock file • Restrictive: lock prevent others from modifying file • May cause administrative problems • Long locks cause delays • Makes collaboration harder • Manual unlocking may be necessary • Scenario: forgetting to unlock before going on vacation 3

  4. CVS Advantages • Copy-modify-merge • Files are copied to a local area, and modified there • No locking • Changes are only visible after merge • Merge is the hard part • Automatic merge • Only works with small changes • Manual merge • Markers in files • Binary files are not merged 4

  5. Basic CVS Configuration • Creating the archive • addgroup cvs; adduser cvs • cvs –d /path/to/repository init • Adjust owner/group, set sticky group bit • Add users to cvs group • Importing files • Recreates existing file structure in CVS • cvs -m “initial checkin” top-directory vendor-tag release-tag 5

  6. CVS Network Access • rsh • Don't use it! • pserver • Listening on port 2401 by default • Add entry to /etc/inetd.conf • Beware: password transmitted in CLEARTEXT • Separate CVS password is possible (CVSROOOT/passwd) 6

  7. Secure Network CVS • SSH • CVS_RSH=ssh; export CVS_RSH • cvs -d :ext:user@server.name:/path/to/repository command • User has to have shell account • gserver, kserver • For Kerberos, Windows (SSPI) 7

  8. Secure CVS Sandbox • Using sendmail's smrsh • cvs wrapper does the chroot • Needs a static version of cvs • LDFLAGS=-static ./configure –disable-client; make • Allows multiple chrooted repositories • Details: http://freshmeat.net/projects/idx-chrooted-ssh-cvs/ 8

  9. Secure CVS Sandbox, continued • cvs users home directories mkdir -p home chown 0:0 home • chrooted environment for each project mkdir -p <project>/{bin,chrooted-cvs,smrsh.bin} mkdir -p <project>/chrooted-cvs/{bin,cvs,cvs-locks,dev,etc,tmp} chown 0:0 <project>/chrooted-cvs/{bin,dev,etc,tmp} chmod 1777 <project>/chrooted-cvs/tmp • setting access rights chown cvsowner.cvs <project>/chrooted-cvs/cvs chmod 770 <project>/chrooted-cvs/cvs chown 0:0 <project>/chrooted-cvs/cvs-locks chmod 666 <project>/chrooted-cvs/cvs-locks • create /dev/null (major/minor specific to Linux) mknod <project>/chrooted-cvs/dev/null c 1 3 • Create /etc/passwd and /etc/group in the chrooted environment 9

  10. Eclipse CVS Demo • CVS support included in base install • SSH2 support included since Eclipse 3.0 10

  11. CVS Drawbacks • Cleartext password • Complex chroot, ssh setup for security • Checkin not atomic • No cross-directory locks • Rename/Move loses history • No directory versioning • Deleted files end up in special Attic directory • Special flags for binary files needed 11

  12. Subversion • Copy-modify-merge model • Like CVS • Successor to CVS • Some of the same people • Clean, modular code • Metadata (properties) • Name, value pairs • Values can be files • Versioned, too • Easy migration path 12

  13. Subversion Advantages • Versioned directories • Allows to recreate the exact state • Atomic checkins • Everything is a transaction • Rename/move maintains history • Unified binary/text file handling • Uses database for the archive • Hot backup possible • Minimizes network traffic • Pristine copy is stored locally 13

  14. Subversion Configuration • Creating the archive • Archive can not be on a network share • svnadmin create /path/to/repos • svn import <project> file:///path/to/repos/some/project • Access through URIs • file://localhost/path/to/repos • svn://domain.com:port/path/to/repos • http://domain.com:port/path/to/repos • https://domain.com:port/path/to/repos 14

  15. Subversion Network Access • svnserve • Lightweight server • Listening on port 3690 by default • Runs as daemon or through entry to /etc/inetd.conf • Runs as specific user • -r option restricts operations to specific path • CRAM-MD5 (RFC 2195) authentication challenge protocol • Can be tunneled through SSH • Apache 2 • Port 80 is usually open • Takes advantage of Apache's authentication modules • Repository has to be writeable by Apache 15

  16. Secure Subversion • svnserve • Tunneling through SSH • Variant of the svn: scheme • svn+ssh://domain.com:port/path/to/repos • Apache 2 • mod_svn module • Authentication through Apache • basic, digest, ldap, ... • no shell access • SSL (https) for encryption 16

  17. Subversion Hooks • Triggered by repository event • Different commit stages • Post-commit hook usually used to send emails, modify log files or make backups • Hooks for changing special properties • Sample hook scripts provided 17

  18. Subversion Cautions • Permissions • Ownership and permission of the repositories • Access through multiple methods • Umask settings • Different process owners • e.g., nobody for Apache, users for direct access, ... • For svn+ssh:, sticky group bit necessary • Some clients not yet polished enough 18

  19. CVS to Subversion • Conversion tool: cvs2svn • http://cvs2svn.tigris.org/ • Can convert branches • Handles tags 19

  20. Eclipse Subversion Demo • Subclipse plugin • Install via Help/Software Updates/New Updates • http://subclipse.tigris.org/update • Requires svn command line tool • Quirk with SSL (https) • no dialog box to accept certificate • certificate has to be accepted with command line 20

  21. Books • CVS • “Cederquist” (http://www.cvshome.org/docs/manual) • Open Source Development with CVS (http://cvsbook.red-bean.com/) • CVS Pocket Reference • Essential CVS • … • Subversion • Version Control with Subversion (http://svnbook.red-bean.com/) 21

  22. Links • CVS • http://www.cvshome.org/ • GUI clients • http://www.kde.org/apps/cervisia/ • http://www.wincvs.org/ • http://www.tortoisecvs.org/ • chroot+SSH • http://freshmeat.net/projects/idx-chrooted-ssh-cvs/ • Subversion • http://subversion.tigris.org/ • GUI clients • http://rapidsvn.tigris.org/ • http://tortoisesvn.tigris.org/ • http://svnup.tigris.org/ • Eclipse plugin • http://subclipse.tigris.org 22

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