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Editorial Team
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Asked: 2026-05-16T23:00:33+00:00

I have problems with understanding the –blocking-io option in rsync. Here’s the descripton from

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I have problems with understanding the –blocking-io option in rsync. Here’s the descripton from the man page:

“This tells rsync to use blocking I/O when launching a remote shell transport. If the remote shell is either rsh or remsh, rsync defaults to using blocking I/O, otherwise it defaults to using non-blocking I/O. (Note that ssh prefers non-blocking I/O.)”

  • When using rsync as the transport,
    i.e. you don’t use -e, does this have
    an effect at all?

  • I guess the result of running rsync
    with or without that option is the
    same and the difference is in ‘how’
    rsync does the transfer?

  • What’s the main reason I would wanted
    to use this option? Performance?
    Looks like rsync provides sensible
    defaults for me, so why would I want
    to use it at all?

  • And the last one: What does “Note
    that ssh prefers non-blocking I/O”
    mean?

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1 Answer

  1. Editorial Team

    Sorry part of my research got mixed up. That is my fault. (Corrected or added stuff is in italics)

    Q1: Yes. Rsync uses asynchronous I/O (non-blocking). By using that option, you are forcing it to use blocking I/O mode. This would be used when the remote shell (rsh) cannot handle non-blocking mode.

    Q2: Yes. The end result will be the same.

    Q3: You would want to use this option if the remote shell is not capable of handling non-blocking i/o

    Q4: “Non-blocking mode makes sure when your connection dies, your screen session won’t block (‘hang’).” (http://webcache.googleusercontent.com/search?q=cache:xmCnC0y5QU0J:www.warp13.co.uk/irssissh+ssh+blocking+mode&cd=13&hl=en&ct=clnk&gl=us&client=firefox-a) SSH just prefers that

    I hope that helps!

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