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ShadowSnap Agent Backups Fail With [Errno 4] Interrupted function call



When you try to start a backup for a system protected by the ShadowSnap agent, you receive the error message "[Errno 4] Interrupted function call."


  • Datto ALTO
  • Datto SIRIS


"[Errno 4] Interrupted function call" is a ShadowSnap error typically signifying an old or corrupted installation of ShadowSnap.

Figure 1: [Errno 4] error message


  1. Make sure the ShadowSnap agent meets all setup and compatibility requirements.
  2. Reinstall the ShadowSnap software using this article.
  3. In the device UI, force a differential merge.
  4. Take a new backup.

If the issue continues, contact Datto Technical Support.

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