# Kopia — Cross-Platform Backup Tool with Encryption, Compression, and a Polished UI

> Kopia is a modern backup tool that gives you Borg-style deduplication + encryption + compression, with native support for S3/GCS/Azure/B2/WebDAV/SFTP — and a polished web UI for managing snapshots on macOS, Linux, and Windows.

## Install

Save in your project root:

# Kopia — Modern Backup with Deduplication + Cloud Backends

## Quick Use
```bash
# Install
brew install kopia                        # macOS
sudo apt install kopia                    # Debian/Ubuntu (via kopia's apt repo)
winget install KopiaUI.KopiaUI            # Windows GUI

# Connect/create a repository (S3 example)
kopia repository create s3 \
  --bucket=my-backups \
  --access-key=... --secret-access-key=... \
  --region=us-east-1

# Snapshot a directory
kopia snapshot create /home/alice

# List snapshots
kopia snapshot list --all

# Restore
kopia snapshot restore /path/to/snapshot/id /restore/target
```

## Introduction
Kopia is a newer, polished sibling to Borg and Restic. It focuses on friendly UX — including a desktop GUI (KopiaUI) and a web UI — while keeping the fundamentals: content-addressable storage, client-side encryption, compression, and snapshot-level policies. Native backends for S3/GCS/Azure/B2/WebDAV/SFTP avoid the rclone indirection other tools need.

With over 13,000 GitHub stars, Kopia is popular with users who want "Borg's reliability but with a UI my less-technical colleague can operate". It's cross-platform and runs identically on macOS, Linux, and Windows.

## What Kopia Does
Kopia splits files into variable-size blocks (content-addressable), deduplicates across all snapshots in a repository, encrypts everything with ChaCha20+Poly1305 or AES-GCM, and optionally compresses. Policies (per path) control retention (keep N hourly/daily/weekly/monthly/annual). A repository server lets many client machines share a single dedup pool without giving them direct storage credentials.

## Architecture Overview
```
[Client machine(s)]
      |
[Kopia binary — CLI + web UI]
   snapshot, policy, restore
      |
[Content-addressable storage layer]
   split into chunks, dedup, encrypt (AEAD)
   compress (zstd / s2 / pgzip / lz4)
      |
+----+----+----+----+----+----+----+
|    |    |    |    |    |    |    |
S3  GCS Azure B2 WebDAV SFTP FS RClone
      |
[Kopia Repository Server (optional)]
   client machines connect to the server,
   the server talks to storage
   per-user policies, bandwidth limits
```

## Self-Hosting & Configuration
```bash
# Set a global policy
kopia policy set --global \
  --keep-latest 10 \
  --keep-hourly 24 --keep-daily 7 --keep-weekly 4 --keep-monthly 24 \
  --compression=zstd-better-compression \
  --add-ignore '*.log' --add-ignore 'node_modules'

# Per-directory override
kopia policy set /home/alice/projects \
  --add-ignore '.git' --add-ignore '.venv' --max-file-size 100M

# Repository server (multi-machine access without sharing storage creds)
kopia server start --tls-generate-cert --address 0.0.0.0:51515 \
  --server-username admin --server-password admin-pass

# Client machine
kopia repository connect server --url https://backup-server:51515 \
  --server-cert-fingerprint abcdef... --username alice --password ...

# Schedule (cron example)
0 * * * * kopia snapshot create /home/alice --quiet

# Web UI at http://localhost:51515 (or wherever server runs)
# KopiaUI desktop app bundles server + UI for solo users
```

## Key Features
- **Native cloud backends** — S3, GCS, Azure, B2, WebDAV, SFTP, local, rclone
- **Strong encryption** — AEAD (ChaCha20-Poly1305 or AES-GCM-SIV)
- **Compression** — zstd, s2, pgzip, lz4; per-policy selection
- **Content-addressable + dedup** — same block stored once across snapshots/machines
- **KopiaUI** — polished desktop app for macOS/Linux/Windows
- **Web UI** — browser interface for repository servers
- **Policy-based retention** — hourly/daily/weekly/monthly/annual per path
- **Cross-platform** — binary for every major OS and arch

## Comparison with Similar Tools
| Feature | Kopia | Borg | Restic | Duplicati | Synology Active Backup |
|---|---|---|---|---|---|
| Cloud backends | Native (many) | SSH-only | Native (many) | Native (many) | Synology-centric |
| GUI | Yes (Kopia UI) | No | No (3rd party) | Yes | Yes |
| Compression | Yes (many algos) | Yes | Yes (Zstd in v0.15) | Yes | Yes |
| Repository server | Yes (multi-user) | Via SSH | Via rest-server | No | Synology server |
| License | Apache-2.0 | BSD | BSD | LGPL | Proprietary |
| Best For | Modern UX + cloud | Linux servers + SSH target | Cloud-target backups | Novice users + GUI | Synology ecosystems |

## FAQ
**Q: Kopia vs Borg vs Restic?**
A: All three are excellent. Borg is the veteran (fastest on some Linux workloads). Restic has cloud backends + simpler CLI. Kopia has cloud backends + GUI + multi-user repository server. For teams: Kopia. For servers with SSH-only targets: Borg. For script-centric cloud backups: Restic.

**Q: How does Kopia compare on dedup efficiency?**
A: Very similar to Borg/Restic — content-defined chunking with a ~4MB average chunk. Dedup ratios of 5-10x are typical for full-system backups.

**Q: Can I share one repository across many machines?**
A: Yes — that's one of Kopia's strengths. Use the Kopia Repository Server; each client authenticates with its own credentials; dedup spans everyone's data.

**Q: Is KopiaUI as capable as the CLI?**
A: 90%+ for everyday use. For advanced policies or scripting, drop to the CLI. KopiaUI is a friendly wrapper — the same binary powers both.

## Sources
- GitHub: https://github.com/kopia/kopia
- Website: https://kopia.io
- License: Apache-2.0

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Source: https://tokrepo.com/en/workflows/0754326f-3859-11f1-9bc6-00163e2b0d79
Author: AI Open Source