Understanding SVN Architecture

Centralized Repository Model

SVN maintains a central repository accessible via HTTP(S), SVN protocol, or file-based access. All version control operations revolve around this central source of truth.

Working Copy and Metadata

Each user’s working copy contains administrative metadata in .svn/ folders. Problems often arise when these become desynchronized or corrupted.

Common SVN Issues

1. Working Copy Locked or Corrupted

Occurs when a previous operation (e.g., commit, update) was interrupted, leaving the working copy in a locked state.

svn: E155004: Working copy at 'path' is locked

2. Repository Inaccessible or Corrupted

Happens when the repository database (FSFS or BDB) is damaged, or network issues prevent access via HTTP(S) or SVN.

3. Authentication and Authorization Failures

Triggered by misconfigured svnserve.conf, authz files, or expired credentials in the user's authentication cache.

4. Merge Conflicts or Update Failures

Developers may see unexpected conflicts during updates, often due to out-of-date working copies or custom local edits.

5. Hook Script Failures on Server

Pre-commit or post-commit hooks can fail silently if improperly configured or if they lack execution permissions.

Diagnostics and Debugging Techniques

Recover Working Copy Locks

Use:

svn cleanup path/to/working_copy

to remove stale locks and retry pending operations.

Check Repository Health

On the server, run:

svnadmin verify /path/to/repository

to detect repository corruption.

Enable Verbose Logging

Modify svnserve.conf to increase log level or capture output in Apache error logs when using mod_dav_svn.

Test Hooks Manually

Run scripts directly under the repository’s hooks/ directory:

./pre-commit test-repo txn-0001

Inspect Authentication Cache

Client-side credentials are stored in:

~/.subversion/auth/svn.simple/

Delete invalid or expired entries and re-authenticate.

Step-by-Step Resolution Guide

1. Unlock a Working Copy

Execute cleanup first:

svn cleanup

If issues persist, delete the working copy and re-checkout:

svn checkout https://svn.example.com/project/trunk

2. Repair a Corrupted Repository

Ensure backups exist. Run:

svnadmin recover /repo/path

Then verify integrity:

svnadmin verify /repo/path

3. Fix Authentication Issues

Check server-side access rules:

[groups]
devs = alice,bob
[project:/]
@devs = rw

Ensure client credentials are refreshed using:

svn --username alice --password secret update

4. Resolve Merge Conflicts

Use:

svn status

to identify conflicted files. Then resolve:

svn resolve --accept=working path/to/conflicted_file

5. Debug Hook Scripts

Ensure executable permissions:

chmod +x hooks/pre-commit

Capture logs with tee or write errors to a file inside the script.

Best Practices for SVN Stability

  • Always perform svn update before commits to avoid conflicts.
  • Use descriptive commit messages and enable pre-commit message enforcement.
  • Backup repositories using svnadmin hotcopy regularly.
  • Document hook logic and use version control to track hook script changes.
  • Encourage shallow working copies with sparse checkouts for large repos.

Conclusion

Apache Subversion remains a viable choice for centralized version control, particularly in regulated or legacy environments. By proactively managing working copies, monitoring repository health, and maintaining secure authentication and hook workflows, teams can ensure reliable versioning and minimize downtime or developer frustration.

FAQs

1. How do I fix a locked working copy?

Run svn cleanup. If that fails, consider re-checking out the repository or deleting corrupted metadata.

2. What causes SVN commit failures?

Common causes include merge conflicts, failed hook scripts, or lack of write permissions in the repository config.

3. Can I recover a corrupted repository?

Yes, using svnadmin recover and svnadmin verify. Always restore from backup if corruption is severe.

4. Where are my client credentials stored?

On Unix systems, in ~/.subversion/auth/. On Windows, it's under %APPDATA%\Subversion\auth.

5. Why won’t my hook script execute?

It may lack execute permissions or be missing required environment variables. Use logging inside the script to debug.