linux script with netcat stops working after x hours

Question

I've have to scripts:

#!/bin/bash

netcat -lk -p 12345 | while read line
do
    match=$(echo $line | grep -c 'Keep-Alive')
    if [ $match -eq 1 ]; then
        [start a command]
    fi
done

and

#!/bin/bash

netcat -lk -p 12346 | while read line
do
    match=$(echo $line | grep -c 'Keep-Alive')
    if [ $match -eq 1 ]; then
        [start a command]
    fi
done

I've put the two scripts in the '/etc/init.d/'

When I restart my Linux machine (RasbPi), both the scripts work fine.

I've tried them like 20 times, and they keep working fine.

But after around 12 hours, the whole system stops working. I've put in some loggin, but it seems that the scripts are not reacting anymore. But when I;

ps aux

I can see that the scripts are still running:

root      1686  0.0  0.2   2740  1184 ?        S    Aug12   0:00 /bin/bash /etc/init.d/script1.sh start
root      1689  0.0  0.1   2268   512 ?        S    Aug12   0:00 netcat -lk 12345
root      1690  0.0  0.1   2744   784 ?        S    Aug12   0:00 /bin/bash /etc/init.d/script1.sh start
root      1691  0.0  0.2   2740  1184 ?        S    Aug12   0:00 /bin/bash /etc/init.d/script2.sh start
root      1694  0.0  0.1   2268   512 ?        S    Aug12   0:00 netcat -lk 12346
root      1695  0.0  0.1   2744   784 ?        S    Aug12   0:00 /bin/bash /etc/init.d/script2.sh start

After a reboot they start working again... But thats a sin, rebooting a Linux machine periodically...

I've inserted some loggin, here's the outcome;

Listening on [0.0.0.0] (family 0, port 12345)
[2013-08-14 11:55:00] Starting loop.
[2013-08-14 11:55:00] Starting netcat.
netcat: Address already in use
[2013-08-14 11:55:00] Netcat has stopped or crashed.
[2013-08-14 11:49:52] Starting loop.
[2013-08-14 11:49:52] Starting netcat.
Listening on [0.0.0.0] (family 0, port 12345)
Connection from [16.8.94.19] port 12345 [tcp/*] accepted (family 2, sport 6333)
Connection closed, listening again.
Connection from [16.8.94.19] port 12345 [tcp/*] accepted (family 2, sport 6334)
[2013-08-14 12:40:02] Starting loop.
[2013-08-14 12:40:02] Starting netcat.
netcat: Address already in use
[2013-08-14 12:40:02] Netcat has stopped or crashed.
[2013-08-14 12:17:16] Starting loop.
[2013-08-14 12:17:16] Starting netcat.
Listening on [0.0.0.0] (family 0, port 12345)
Connection from [16.8.94.19] port 12345 [tcp/*] accepted (family 2, sport 6387)
Connection closed, listening again.
Connection from [16.8.94.19] port 12345 [tcp/*] accepted (family 2, sport 6388)
[2013-08-14 13:10:08] Starting loop.
[2013-08-14 13:10:08] Starting netcat.
netcat: Address already in use
[2013-08-14 13:10:08] Netcat has stopped or crashed.
[2013-08-14 12:17:16] Starting loop.
[2013-08-14 12:17:16] Starting netcat.
Listening on [0.0.0.0] (family 0, port 12345)
Connection from [16.8.94.19] port 12345 [tcp/*] accepted (family 2, sport 6167)
Connection closed, listening again.
Connection from [16.8.94.19] port 12345 [tcp/*] accepted (family 2, sport 6168)

Thanks

Answer 1

If none of your commands including netcat reads input from stdin you can completely make it run independent of the terminal. Sometimes background process that are still dependent on the terminal pauses (S) when they try to read input from it on a background. Actually since you're running a daemon, you should make sure that none of your commands reads input from it (terminal).

#!/bin/bash

set +o monitor # Make sure job control is disabled.

(
    : # Make sure the shell runs a subshell.
    exec netcat -lk -p 12345 | while read line  ## Use exec to overwrite the subshell.
    do
        match=$(echo $line | grep -c 'Keep-Alive')
        if [ $match -eq 1 ]; then
            [start a command]
        fi
    done
) <&- >&- 2>&- </dev/null &>/dev/null &

TASKPID=$!
sleep 1s ## Let the task initialize a bit before we disown it.
disown "$TASKPID"

And I think we could try the logging thing again:

set +o monitor

(
    echo "[$(date "+%F %T")] Starting loop with PID $BASHPID."

    for (( ;; ))
    do
        echo "[$(date "+%F %T")] Starting netcat."

        netcat -vv -lk -p 12345 | while read line
        do
            match=$(echo "$line" | grep -c 'Keep-Alive')
            if [ "$match" -eq 1 ]; then
                [start a command]
            fi
        done

        echo "[$(date "+%F %T")] Netcat has stopped or crashed."

        sleep 4s
    done
) <&- >&- 2>&- </dev/null >> "/var/log/something.log" 2>&1 &

TASKPID=$!
sleep 1s
disown "$TASKPID"