49 lines
2.3 KiB
Text
49 lines
2.3 KiB
Text
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Removing Zombies,
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Nico Schottelius 2005-06-15 (Last Modified: 2005-06-15)
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First of all, the definition of a zombie:
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''Defunct ("zombie") process, terminated but not reaped by its parent.''
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[Excerpt from ps(1)]
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''In the case of a terminated child, performing a wait allows the system to
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release the resources associated with the child; if a wait is not performed,
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then terminated the child remains in a "zombie" state (see NOTES below).
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[...]
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NOTES
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A child that terminates, but has not been waited for becomes a "zom-
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bie". The kernel maintains a minimal set of information about the
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zombie process (PID, termination status, resource usage information)
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in order to allow the parent to later perform a wait to obtain
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information about the child. As long as a zombie is not removed
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from the system via a wait, it will consume a slot in the kernel
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process table, and if this table fills, it will not be possible to
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create further processes. If a parent process terminates, then its
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"zombie" children (if any) are adopted by init(8), which automati-
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cally performs a wait to remove the zombies.''
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[Excerpt from waitpid(2)]
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So you can see, that if some process misbehaves and forgets about
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its children, we, cinit, will adopt it. In the first versions of
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cinit (cinit-0.0.1 <-> cinit-0.0.7) we ignored SIGCHLD. This way
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the zombies stayed in the system. Since cinit-0.0.8 we have
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sig_chld(), which removes the zombies.
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So far so good. Now let's remove this feature. Yes, you heard right.
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If cinit does not catch the zombies they will stay in the system.
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Yes, that's ugly. And that's how it should be. You should see, which
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software is broken and should contact the authors to fix it.
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To restore the 'old' behaviour of cinit, change
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generic/set_signals.c (ignore SIGCHLD)
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Makefile: remove serv/sig_child.c from modules list
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cinit in general will keep the behaviour of reaping the vestiges,
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which broken software left behind (as it is cleaner for the system to
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deallocate unused ressources).
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