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README.md

svn-git-mirror

License: PolyForm Noncommercial 1.0.0 Copyright (c) 2026 Uberwald. All rights reserved. Commercial use requires a separate license from Uberwald. Send email to contact@uberwald.me

Py sidecar SVN↔Git bidirectional mirror. Uses own mapping DB (not git svn) so Git commit hashes never change.

Validated against huge SVN/GIT repos with 70K commits and more than 120 branches

Works with any Git server that exposes bare repos on disk (Gitea, Forgejo, GitLab, bare git init --bare, etc.). The Gitea-specific integration code (svn_mirror/gitea.py, svn_mirror/webhook.py) serves as a working example and can be adapted to other Git servers — see Adapting to other Git servers.

Architecture

┌──────────────┐   SVN poll    ┌───────────────────┐
│   SVN remote │ ◄───────────  │  svn-mirror       │
│  (http/svn+) │ ────────────► │  daemon / sync    │
└──────────────┘               │                   │
                               │  ┌──────────────┐ │
┌──────────────┐   git push    │  │ canonical    │ │
│   Git server │ ◄───────────  │  │ bare repo    │ │
│  (webhook)   │ ────────────► │  └──────────────┘ │
└──────────────┘   git fetch   │                   │
                               │  SQLite mapping   │
                               └───────────────────┘
  • Canonical bare repo: the single source of truth on the Git side
  • Mapping DB: SQLite table (svn_revision, svn_branch) ↔ git_commit_hash
  • SVN WC: per-branch working copy checked out for applying Git→SVN diffs
  • Daemon: polls SVN on interval, pushes Git→SVN on webhook or interval

Requirements

  • Python 3.11+
  • git + git-svn (for one-time git svn clone --no-metadata during init)
  • svn CLI (Subversion client)
  • A Git server with bare repos accessible on disk (Gitea, Forgejo, GitLab, or plain git init --bare)
  • UTF-8 system locale (SVN needs it for non-ASCII filenames)

Install system deps

# Debian / Ubuntu
apt install python3 python3-pip git git-svn subversion

# RHEL / Rocky / Alma
yum install python3 python3-pip git git-svn subversion

# OpenSUSE
zypper install python311 python311-pip git git-svn subversion glibc-locale

UTF-8 locale

SVN requires a UTF-8 locale to handle filenames with accents/spaces:

sudo localedef -i en_US -f UTF-8 en_US.UTF-8
export LC_ALL=en_US.UTF-8

Add to ~/.bashrc or ~/.profile to make it permanent.

Installation

# Clone
git clone https://github.com/your-org/svn-git-server /opt/svn-git-server
cd /opt/svn-git-server

# Install Python deps
pip install -r requirements.txt

Only dependency: PyYAML. The rest is stdlib + CLI tools.

Configuration

Create /etc/svn-mirror/config.yml:

data_dir: /var/svn-mirror

mirrors:
  - id: my-project
    enabled: true

    svn:
      url: https://svn.example.com/svn/myproject
      layout: std              # "std" for standard /trunk /branches /tags
      # For non-standard layout:
      # layout: custom
      # trunk: trunk
      # branches: branches
      # tags: tags
      username:                # SVN login (omit if anonymous access)
      password:                # SVN password

    # ── Git server integration ──────────────────────────────────
    # The config below uses "gitea" as the section name for historical
    # reasons. In practice this works with any Git server that exposes
    # bare repos on disk. See "Adapting to other Git servers" below.
    gitea:
      owner: myorg
      repo: myproject
      repos_path: /var/lib/gitea/data/repositories  # path to bare repos on disk
      webhook_secret: "choose-a-random-secret"      # shared HMAC secret
      webhook_host: "0.0.0.0"
      webhook_port: 8080

    authors:
      "john": "John Doe <john@example.com>"
      "jane": "Jane Doe <jane@example.com>"

    sync_interval: 120   # SVN→Git poll interval (seconds)

repos_path — finding your Git server's repos on disk

The sidecar accesses your Git server's repos on disk, not via HTTP API. Find the path:

Setup Typical path
Gitea binary /var/lib/gitea/data/repositories
Gitea Docker /data/git/repositories
Forgejo /var/lib/forgejo/data/repositories
GitLab /var/opt/gitlab/git-data/repositories
git user home /home/git/repositories
Plain bare repos wherever you ran git init --bare

If unset the tool tries common defaults. Set it explicitly to be safe.

Note: repo should be the repo name without .git suffix — the tool appends it. For example: repo: myproject, not repo: myproject.git.

Quick start

1. Validate config

python -m svn_mirror check --config /etc/svn-mirror/config.yml

2. Create mirror directories

python -m svn_mirror create --mirror my-project --config /etc/svn-mirror/config.yml

Creates {data_dir}/mirrors/{id}/ with:

  • canonical-repo.git — bare Git repo
  • mapping.db — SQLite mapping DB
  • state.json — mirror state
  • sync.lock — flock-based concurrency lock

3. Initial SVN import

python -m svn_mirror init --mirror my-project --config /etc/svn-mirror/config.yml

Runs git svn clone --no-metadata (one-time bootstrap), then tears down git-svn metadata. All ongoing sync is handled by the tool's own engine.

Auth: If the SVN server requires login, set username and password in the config. The password is piped to git svn's stdin prompt (git svn does not accept --password on the command line).

The tool also caches credentials via svn info --username X --password Y before git svn clone so the SVN auth cache is populated.

External definitions: If the SVN repo uses svn:externals pointing to different repositories, the tool passes --ignore-externals to all svn checkout / svn update calls. The externals are not followed.

4. Sync SVN → Git

python -m svn_mirror sync --mirror my-project --config /etc/svn-mirror/config.yml

5. Push Git → SVN

python -m svn_mirror push --mirror my-project --config /etc/svn-mirror/config.yml

6. Check status

python -m svn_mirror status --mirror my-project --config /etc/svn-mirror/config.yml

Deployment modes

Mode A: Polling daemon (simple)

python -m svn_mirror daemon --config /etc/svn-mirror/config.yml

Note: daemon does not accept --mirror — it processes all enabled mirrors. Use screen (or tmux) to run in background:

screen -dmS svn-mirror bash -c 'python3.11 -m svn_mirror daemon --config /etc/svn-mirror/config.yml 2>&1 | tee /tmp/daemon.log'

Polls SVN every sync_interval seconds. Pushes new Git commits to SVN on the same interval.

systemd unit

# /etc/systemd/system/svn-mirror.service
[Unit]
Description=svn-git-mirror daemon
After=network-online.target

[Service]
Type=simple
ExecStart=/usr/bin/python3 -m svn_mirror daemon --config /etc/svn-mirror/config.yml
Restart=always
User=root
WorkingDirectory=/opt/svn-git-server

[Install]
WantedBy=multi-user.target

systemctl daemon-reload
systemctl enable --now svn-mirror

Mode B: Webhook-only (event-driven)

python -m svn_mirror webhook --config /etc/svn-mirror/config.yml

Listens for push webhooks on POST /webhook. When a push arrives it fetches the new commits from the Git server and runs sync_git_to_svn.

Example — Gitea webhook config: Go to repo → Settings → Webhooks → Add:

  • Target URL: http://your-server:8080/webhook
  • Secret: same as webhook_secret in config
  • Events: "Push"

Example — GitLab webhook config: Go to repo → Settings → Webhooks:

  • URL: http://your-server:8080/webhook
  • Secret token: same as webhook_secret in config
  • Trigger: "Push events"

Note: The webhook receiver currently parses the Gitea payload format (X-Gitea-Signature header, repository.owner.login field). To use another Git server, adapt the header name and payload parsing in svn_mirror/webhook.py. See Adapting to other Git servers.

Mode C: systemd service (recommended)

The daemon handles bidirectional sync: SVN→Git polling AND Git→SVN push on each cycle. One service is all you need.

Quick install via script

Use the provided install script to generate and enable the systemd service running as a given user (e.g. git):

sudo ./deploy/install.sh --install-dir /opt/svn-git-server --user git

This will:

  • Create a Python virtualenv at <install-dir>/.venv and install deps
  • Generate svn-mirror.service
  • Enable the service (auto-start on boot)

Options:

Option Default Description
--install-dir DIR (required) Where the code is installed
--user USER gitea System user to run the service as
--config FILE <install-dir>/config.yml Config file path
--venv DIR <install-dir>/.venv Virtualenv path
--uninstall — Remove service instead of installing

Note: The default --user is gitea for historical reasons. Use whatever user owns your Git server's repos (e.g. git, forgejo, gitlab).

After install, start the service:

sudo systemctl start svn-mirror

Check logs:

journalctl -u svn-mirror -f

To uninstall:

sudo ./deploy/install.sh --uninstall

Manual setup (screen/tmux)

screen -dmS svn-mirror python3.11 -m svn_mirror daemon --config /etc/svn-mirror/config.yml

Mode D: Post-receive hook (filesystem)

For setups without network access to a webhook receiver, install a post-receive hook in your Git server's repo that calls sync directly. Example — Gitea/Forgejo:

# Create hook (one-time setup)
tee /home/gitea/repo/myorg/myproject.git/hooks/post-receive.d/sync-to-svn << 'HOOK'
#!/bin/bash
cd /opt/svn-git-server
. .venv/bin/activate
python3.11 -m svn_mirror sync --mirror my-project --config /etc/svn-mirror/config.yml
HOOK
chmod +x /home/gitea/repo/myorg/myproject.git/hooks/post-receive.d/sync-to-svn

Each git push to the Git server then triggers an immediate SVN sync.

Note: Direct filesystem git push to a Git server's on-disk bare repo may be blocked by the server's pre-receive hook (Gitea and GitLab both do this). The daemon/sync uses its own push_to_gitea() to work around this by using git fetch instead of git push. To force-push (e.g. initial import), temporarily disable the hook:

mv /path/to/repo.git/hooks/pre-receive{,.disabled}
# push...
mv /path/to/repo.git/hooks/pre-receive{.disabled,}

Reconciliation (fixing divergence)

If the sync was interrupted (daemon down for days) and commits landed on both SVN and Git independently, the tool can re-sync them.

# 1. Assess divergence (dry-run, no changes)
python -m svn_mirror reconcile --assess --mirror my-project --config /etc/svn-mirror/config.yml

# 2. Reconcile (creates SVN commit merging Git changes into SVN)
python -m svn_mirror reconcile --mirror my-project --config /etc/svn-mirror/config.yml

# 3. Normal sync to bring Git in line
python -m svn_mirror sync --mirror my-project --config /etc/svn-mirror/config.yml

The reconciliation:

  • Backs up the mapping DB
  • Applies each Git developer commit (not yet in DB) onto the SVN trunk WC
  • Commits to SVN as a single [reconcile] revision
  • Records the mapping so sync_git_to_svn doesn't re-push those commits
  • Leaves last_svn_revision unchanged — sync processes pending SVN revisions naturally

SVN author fix: After svn commit / svn copy, the tool sets the correct author via svn propset --revprop -r REV svn:author "Real Author". This requires the pre-revprop-change hook on the SVN server:

# On the SVN server — create this script, make it executable
# /srv/svn/pixkit/hooks/pre-revprop-change
#!/bin/bash
REPOS="$1"; REV="$2"; USER="$3"; PROPNAME="$4"; ACTION="$5"
[ "$PROPNAME" = "svn:author" ] || [ "$PROPNAME" = "svn:log" ] || exit 1
exit 0

Dry-run mode:

python -m svn_mirror reconcile --dry-run --mirror my-project --config /etc/svn-mirror/config.yml

Shows the assessment report and what would be done, without making any changes.

All commands

Command Description
check Validate config and prerequisites
create Create mirror directory structure
init Run git svn clone initial import
destroy Delete all mirror data
status Show mirror status
sync Bidirectional sync (SVN→Git + Git→SVN)
push Git→SVN direction only
daemon Continuous polling loop
webhook Webhook receiver (Gitea format; adaptable)
reconcile Fix divergence (see above)

File layout

{data_dir}/mirrors/{id}/
├── canonical-repo.git/      # bare Git repo (canonical Git copy)
├── mapping.db               # SQLite mapping DB
├── state.json               # mirror metadata
├── authors.txt              # git svn authors file
├── sync.lock                # flock-based concurrency lock
└── svn-wc/                  # SVN working copies (per branch)

Caveats

  • Auth: SVN username/password in config is sent to git svn clone pipe and CLI args. Password is stored in plaintext in config file.
  • Binary files: supported (fix in sync.py uses raw bytes for hash-object)
  • Empty directories: SVN tracks them, Git does not — skipped during sync
  • Large repos: initial git svn clone time depends on SVN history size; 6+ GiB repos can take several hours over HTTPS
  • One trunk only: reconciliation only handles refs/heads/master ↔ SVN trunk. Other branches are not yet supported by the reconcile tool.
  • git svn username: --username is supported but --password is not (the tool pipes password to stdin instead).
  • All SVN branches become Git branches: If the SVN repo uses branches for release tags, the Git canonical repo will contain hundreds of branches. Consider filtering via refs/tags/ in the push refspec.
  • Git server filesystem push: Direct git push to a Git server's on-disk bare repo may be blocked by the server's pre-receive hook (Gitea, GitLab). The daemon/sync uses its own push_to_gitea() to work around this by using git fetch instead.

Adapting to other Git servers

The core SVN↔Git sync engine is server-agnostic. The Gitea-specific code is limited to two files and can be adapted to other Git servers (Forgejo, GitLab, Gitea, plain bare repos, etc.):

What Where What to change
Push to Git server svn_mirror/gitea.py — push_to_gitea() Uses git fetch into the bare repo (generic). The _trigger_gitea_post_receive() function calls the gitea binary — replace with your server's hook trigger or remove it.
Webhook receiver svn_mirror/webhook.py Parses X-Gitea-Signature header and Gitea JSON payload. Adapt the header name (X-Gitlab-Token, etc.) and payload fields (repository.owner.login → your server's equivalent).
Config section svn_mirror/config.py — GiteaConfig The gitea: config block. The fields (owner, repo, repos_path, webhook_*) are generic; only the section name is Gitea-specific.
Default repo paths svn_mirror/config.py — repo_dir Hardcoded Gitea defaults. Add your server's path or set repos_path explicitly.

For plain bare repos (no Git server), no adaptation is needed — just set repos_path to the directory containing your bare repos and skip the webhook/post-receive integration (use the daemon or manual sync).

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