Linux – How to terminate Linux tee command without killing application it is receiving from

killlinuxpipescriptingtee

I have a bash script that runs as long as the Linux machine is powered on. I start it as shown below:

( /mnt/apps/start.sh 2>&1 | tee /tmp/nginx/debug_log.log ) &

After it lauches, I can see the tee command in my ps output as shown below:

$ ps | grep tee
  418 root       0:02 tee /tmp/nginx/debug_log.log
3557 root       0:00 grep tee

I have a function that monitors the size of the log that tee produces and kills the tee command when the log reaches a certain size:

monitor_debug_log_size() {
                ## Monitor the file size of the debug log to make sure it does not get too big
                while true; do
                                cecho r "CHECKING DEBUG LOG SIZE... "
                                debugLogSizeBytes=$(stat -c%s "/tmp/nginx/debug_log.log")
                                cecho r "DEBUG LOG SIZE: $debugLogSizeBytes"
                                if [ $((debugLogSizeBytes)) -gt 100000 ]; then
                                                cecho r "DEBUG LOG HAS GROWN TO LARGE... "
                                                sleep 3
                                                #rm -rf /tmp/nginx/debug_log.log 1>/dev/null 2>/dev/null
                                                kill -9 `pgrep -f tee`
                                fi
                                sleep 30
                done
}

To my surprise, killing the tee command also kills by start.sh instance. Why is this? How can I end the tee command but have my start.sh continue to run? Thanks.

Best Answer

When tee terminates, the command feeding it will continue to run, until it attempts to write more output. Then it will get a SIGPIPE (13 on most systems) for trying to write to a pipe with no readers.

If you modify your script to trap SIGPIPE and take some appropriate action (like, stop writing output), then you should be able to have it continue after tee is terminated.

Better yet, rather than killing tee at all, use logrotate with the copytruncate option for simplicity.

To quote logrotate(8):

copytruncate

Truncate the original log file in place after creating a copy, instead of moving the old log file and optionally creating a new one. It can be used when some program cannot be told to close its logfile and thus might continue writing (appending) to the previous log file forever. Note that there is a very small time slice between copying the file and truncating it, so some logging data might be lost. When this option is used, the create option will have no effect, as the old log file stays in place.

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