docs: terminals: mention subreaper requirement
I realised that the terminal documentation which covers detached terminals fails to mention that callers need to make themselves a subreaper. Probably a good idea to mention this. I've also included a minor comparison to LXC. Signed-off-by: Aleksa Sarai <asarai@suse.de>
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@ -228,6 +228,19 @@ Unfortunately using detached mode is a bit more complicated and requires more
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care than the foreground mode -- mainly because it is now up to the caller to
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care than the foreground mode -- mainly because it is now up to the caller to
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handle the `stdio` of the container.
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handle the `stdio` of the container.
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Another complication is that the parent process is responsible for acting as
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the subreaper for the container. In short, you need to call
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`prctl(PR_SET_CHILD_SUBREAPER, 1, ...)` in the parent process and correctly
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handle the implications of being a subreaper. Failing to do so may result in
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zombie processes being accumulated on your host.
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These tasks are usually performed by a dedicated (and minimal) monitor process
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per-container. For the sake of comparison, other runtimes such as LXC do not
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have an equivalent detached mode and instead integrate this monitor process
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into the container runtime itself -- this has several tradeoffs, and runc has
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opted to support delegating the monitoring responsibility to the parent process
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through this detached mode.
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#### Detached Pass-Through ####
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#### Detached Pass-Through ####
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In detached mode, pass-through actually does what it says on the tin -- the
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In detached mode, pass-through actually does what it says on the tin -- the
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