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Brad Thompson
Asked: 2019-07-06 10:07:34 +0800 CST

Ping failure monitor

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the network frequently fails and I would like to monitor the output. I tried to makeshift a command like:

ping www.google.fr | while read pong; do echo "$(date): $pong"; done 1>/dev/null && 2> ~/ping_err.log

but the STDERR is still redirected to STDOUT instead ping_err.log

note: I want only STDERR in the file (not 2>&1)

Thanks!

networking

3 Answers

  1. Rather than answer your stderr redirection question, I'll suggest a better (IMHO) way:

    In https://github.com/waltinator/net-o-matic.git - Watch for (WiFi) network going down, then do a user-specified thing to fix it.

    There's a way to monitor your connection: 

      ip monitor address | \
    egrep --line-buffered \
    '^Deleted [[:digit:]]+: [[:alnum:]]+[[:space:]]+inet[[:space:]].* scope global ' | \
    while read line ; do
       ...

    My net-o-matic script also contains a way to ask once:

    function netstate () {
    # Return network state as "UP" or "DOWN"
    #Adjust how you decide net is UP/DOWN
    ip link show | egrep -q 'UP,LOWER_UP.* state UP'
    if [[ $? -eq 0 ]] ; then
        echo "UP"
    else
        echo "DOWN"
    fi
}
    • 2

  2. Using your code, this seems to work:

    $ ping www.google.fr 2>&1 > /dev/null | while read pong; do echo "$(date): $pong" ; done 2>&1 > ping_err.log
[no output]
$ cat ping_err.log

vie jul  5 15:56:09 -03 2019: ping: sendmsg: La red es inaccesible
vie jul  5 15:56:10 -03 2019: ping: sendmsg: La red es inaccesible
vie jul  5 15:56:11 -...
    • 2

  3. I expanded @schrodigerscatcuriosity's answer a bit with:

    ping -i 10 -O -q 192.168.88.2 2>&1 | while read pong; do echo "$(date): $pong" ; done 2>&1 | tee ping_err.log
    • -i 10 wait 10 seconds before sending each packet
    • -O for logging outstanding ICMP ECHO reply before sending next packet
    • -q for quiet output (except for timeouts)
    • | tee to simultaneously print the output to console and file
    • 2