I'm new to the whole Raspberry Pi and Bash scripting thing, so bear with me.

I run raspberry autopilot on a remotely controlled vehicle thru a 3G/4G connection. Raspberry Pi is installed onboard the vehicle. It connects to an OpenVPN server, and sends UDP telemetry to a machine on the VPN network.

The 3G/4G coverage is not stable so I need to keep an eye on it. I have crontab script which runs every minute:


wget -q --tries=10 --timeout=20 --spider http://google.com
if [[ $? -eq 0 ]]; then
        dt=$(date '+%d/%m/%Y %H:%M:%S');
        echo "Online $dt" >> /home/pi/navio-drone/keepalive.log
        dt=$(date '+%d/%m/%Y %H:%M:%S');
        # Timestamped message to log file
        echo "Offline $dt" >> /home/pi/navio-drone/keepalive.log
        # Disconnect  from OpenVPN
        echo $(date -u) "Stopping OpenVPN connection" >> /home/pi/navio-drone/keepalive.log
        systemctl stop [email protected]
        # Trigger power to USB ports to reset Huawei modem, 1 sec delay
        echo $(date -u) "Resetting USB modem connection" >> /home/pi/navio-drone/keepalive.log
        ./uhubctl -a 2 -l 1-1 -d 1
        # Sleep 45 sec (let modem to find network) and connect to OpenVPN server
        echo $(date -u) "Sleeping 45 seconds" >> /home/pi/navio-drone/keepalive.log
        sleep 45
        echo $(date -u) "Starting OpenVPN connection" >> /home/pi/navio-drone/keepalive.log
        systemctl start [email protected]

How would you tidy up this script and specifically get rid of

`sleep 45`

in it? Sometimes it takes 30 sec, sometimes 50 for the modem to reconnect to network.


My ip addr output(4G interface connected):

pi@navio:~ $ ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
3: wlan0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
    link/ether b8:27:eb:b3:46:ba brd ff:ff:ff:ff:ff:ff
6: enxb827ebe613ef: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc pfifo_fast state DOWN group default qlen 1000
    link/ether b8:27:eb:e6:13:ef brd ff:ff:ff:ff:ff:ff
11: enx00a0c60429a0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN group default qlen 1000
    link/ether 00:a0:c6:04:29:a0 brd ff:ff:ff:ff:ff:ff
    inet brd scope global enx00a0c60429a0
       valid_lft forever preferred_lft forever
    inet6 fe80::240e:3007:3e42:4e64/64 scope link
       valid_lft forever preferred_lft forever
12: tun0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN group default qlen 100
    inet peer scope global tun0
       valid_lft forever preferred_lft forever
    inet6 fe80::8604:8c6b:e6f1:e9d7/64 scope link flags 800
       valid_lft forever preferred_lft forever

My ip route output(4G interface connected):

pi@navio:~ $ ip route via dev tun0
default via dev enx00a0c60429a0 src metric 211 via dev enx00a0c60429a0 via dev tun0 dev enx00a0c60429a0 proto kernel scope link src metric 211 dev tun0 proto kernel scope link src

I would appreciate any suggestions.

2 Answers 2


It is difficult to give some specific hints because there is no information about the network setup. But usually you can check if an interface is online. There is a tool from systemd that can check it:

rpi ~$ /lib/systemd/systemd-networkd-wait-online --help
systemd-networkd-wait-online [OPTIONS...]

Block until network is configured.

  -h --help                 Show this help
     --version              Print version string
  -q --quiet                Do not show status information
  -i --interface=INTERFACE  Block until at least these interfaces have appeared
     --ignore=INTERFACE     Don't take these interfaces into account
     --timeout=SECS         Maximum time to wait for network connectivity

You can look with ip addr what interfaces available and what interface has to be online after resetting the USB modem connection. I don't know if the tool detects the interface for the 4G connection but it is worth a try. Just replace the sleep 45 statement for example with:

sudo /lib/systemd/systemd-networkd-wait-online --interface=wlan0 --timeout=120 --quiet

That returns immediately when the interface wlan0 gets online or with an error after 120 seconds. It does not stress the CPU when waiting like a busy loop.

Here are yet another two possibilities. In /sys/class/net/$NETINTERFACE/carrier the kernel shows if the interface has got a carrier. With a bash function you can test it:


function has-carrier {
    until [ $(cat /sys/class/net/wlan0/carrier) -eq 1 ] || [ $attempt_num -eq $MAX_ATTEMPTS ]; do
        echo attempt $attempt_num: no carrier
        sleep 3

    if [ $attempt_num -eq $MAX_ATTEMPTS ]; then
        echo attempt $attempt_num: timeout
        exit 1
        echo attempt $attempt_num: carrier
        exit 0


This function will check the carrier every 3 seconds for 30 attempts. After 90 seconds (3 sec * 30 attempts) it will timeout.

Then there is a daemon ifplugd that may be usable. It mainly checks wired ethernet ports but it also has a feature:

  • Configure WLAN devices (on detecting a successful association to an AP)

Check with apt show ifplugd.

  • /lib/systemd/systemd-networkd-wait-online --interface=enx00a0c60429a0 --timeout=120 --quiet times out with error while interface is up. Is that a correct behavior?
    – Vladimir P
    Jan 1, 2019 at 19:09
  • btw, this interface state is unknown when checked with ip addr
    – Vladimir P
    Jan 1, 2019 at 19:16
  • @user95138 Please edit your question and add the output from ip addr and from ip route when a 4G connection is established. When testing you can also omit option --quiet to see messages.
    – Ingo
    Jan 1, 2019 at 19:28
  • Fixed the question. The output without quiet is just “ignoring: lo” which probably means it ignores loopback interface.
    – Vladimir P
    Jan 1, 2019 at 19:41
  • @user95138 Try to prefix the command with sudo. I have updated my answer with it. I've just looked at the tool and it seems it only checks for gained carrier. You can find this status in journalctl -b (or even not). I'm looking at it, just a moment ...
    – Ingo
    Jan 1, 2019 at 20:23

Replaced it with:

sleep 10 # Not going to be faster than 10sec anyway
echo $(date) "Waiting for network to recover" 
itest=$(ping -c 1 -W 2 | grep "1 packets transmitted, 1 received")
while [ "$itest" == "" ]
   sleep 2
   itest=$(ping -c 1 -W 2 | grep "1 packets transmitted, 1 received")
echo $(date) "Connected to cellular network"

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