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Description of problem: initscripts may have a possibility to kill different process while stop the process, in case using pid file. Version-Release number of selected component (if applicable): initscripts-9.20.2-1.fc14.1.i686 How reproducible: Always Steps to Reproduce: This example try to show the developer that startup script always trust the contents of PID file without checking it. In real life scenario, see "Additional info" section. (1) Start up sshd (2) Run top(1) (3) Find out pid of the top(1). In this case, pid 3728. (4) Edit /var/run/sshd.pid, replace the PID to top's pid. (5) See the status of sshd. # /etc/init.d/sshd status openssh-daemon (pid 3728) is running (6) Stop the sshd # /etc/init.d/sshd stop Stopping sshd: Actual results: (5)The script reports process PID 3728 is running, although it is not a sshd. (6)The script kills top(1), because the process have pid 3728. Expected results: The startup script should check if pid within pid file is really related to the script. Additional info: Following is an example scenario of how this problem happen in real life. 1. A daemon process (in this case sshd) segfault. The pid file was not erased, because stop script was not run. 2. OS is still running, and some process reuse the same PID that the sshd used to use. The process keep running like a daemon. 3. Admin stop the sshd. The /etc/init.d/functions sees /var/run/sshd.pid file then find out a pid, and kill the process. This symptom may happen on Red Hat Enterprise Linux, as well. This symptom may happen all scripts which make use of pid file while "stop","status" and "restart".
Hello again, I had a troubleshooting case with 3rd party (I mean not Fedora nor RHEL) startup script related to "wrong pid in pid file". In short, the 3rd party script was not carefully coded, in my case. (Detail) The 3rd party startup script uses pidof immediately after the target daemon started. The daemon takes a few moment to finish initializing. And during the initialization, the daemon fork some child processes. And the child processes will exit before fully initialized the daemon. If pidof command executed during the process initialization, it may find multiple processes with different PIDs. Then pidof may pick one of them from /proc without knowing which one is parent or child. In bad scenario, the pidof picked child process's PID, which is not exist after the daemon initialization. The time when script stop the script uses the pid file, but the pid within the pid file may used by another process. Then the script kills the other process. This case is "Blame the 3rd party script" scenario. But I believe this type of accident can be avoided if the stop script verify the contents of PID file is really the target process for kill or not.
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