Bug #2712: Wait for grandchild to be ready when daemonizing - Lighttpd - lighty labs

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Bug #2712

closed

Wait for grandchild to be ready when daemonizing

Added by pasdVn almost 9 years ago. Updated over 8 years ago.

Status:

Fixed

Priority:

Normal

Category:

core

Target version:

1.4.40

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Description

When lighttpd does the sys-v-init daemonizing (without the -D switch) the parent process will immeadeatly terminate after the first fork (see function daemonize in server.c).
This can cause problems, when right after the start of lighttpd the presence/correctness of the pid is checked or the pid of the daemon process is tried to grabbed by `pidof lighttpd` or similar. The second problem becomes a problem because of the double forking. If the timing "fits" you get only the pid of the child but not the grandchild (or both).

Following this guide (http://www.freedesktop.org/software/systemd/man/daemon.html) it is a more clean way to terminated the parent process only if the child is fully up and running (after every initialization is ok and the pid file is written).

I wrote a patch that fixes this behaviour. As suggested in the reference above it uses a pipe as communication channel between parent and grandchild.

Files

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daemonize_startup_behaviour.diff (1.99 KB) daemonize_startup_behaviour.diff		pasdVn, 2016-01-31 19:27
daemonize_startup_behaviour_v2.diff (1.9 KB) daemonize_startup_behaviour_v2.diff		pasdVn, 2016-02-10 17:56

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Updated by gstrauss almost 9 years ago

The child should

    close(pipefd[0]);

before returning from daemonize(), or else that fd leaks in the child.

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Updated by gstrauss almost 9 years ago

Additionally, when there are multiple workers, the first worker (greatgrandchild) calls write(), and then the grandparent calls read() and close(). Once you fix the pipefd[0] leak in the grandchild (which I mentioned in the comment above), then subsequent workers might fail to write() with EPIPE after the grandparent calls close() on the read-end of the pipe (pipefd[0]).

Please consider moving the write() to a location prior to spawning of workers, but after the daemonized grandchild is up and running, and after the grandchild has written its pid to the pidfile. Such a location would be a reasonable place for the grandparent to exit while still ensuring that pidof would return the proper pid of the running grandchild.

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Updated by pasdVn almost 9 years ago

File daemonize_startup_behaviour_v2.diff daemonize_startup_behaviour_v2.diff added

Thanks for your feedback. I moved the grandchild's write() directly before the fork-loop where the workers are created. I think this is the best place under this circumstances.

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