How can I get information about an network interface uptime?

Question

I have an Ubuntu machine and a Debian machine.

On both I want to be able to see for how long an network interface has been connected. (That is, connected to a network getting an IP etc. Not the physical state of a cabel). Uptime in seconds or date + time since last change or anything similar.

As of now I have written a little script to do the task but it seems there should be a more general way to check this. A program or something in /proc or such.

My script:

#!/bin/bash

if [ -f /etc/os-release ]; then

    if TMP=$(grep -i 'ubuntu' /etc/os-release); then

        # we are on ubuntu
        for i in $(/bin/ls -1 /var/log/syslog* | sort -r); do
                TMP=$(zgrep '(eth0): device state change: ip-config -> activated' "$i" | tail -1 | sed "s/ "$(hostname)"/*/")
        done

        WHEN=$(echo "$TMP" | cut -f1 -d '*')
        SEC=$(echo "$(date +%s) - $(date -d "$WHEN" +%s)" | bc)
        echo "Last link up: $WHEN ($SEC seconds ago)."

    elif TMP=$(grep -i 'debian' /etc/os-release); then

        # we are on debian
        TMP=$(grep 'eth0: link up' /var/log/syslog* | tail -1 | cut -f2- -d':' | sed "s/ "$(uname -n)" kernel:/*/")
        WHEN=$(echo "$TMP" | cut -f1 -d '*')
        SEC=$(echo "$(date +%s) - $(date -d "$WHEN" +%s)" | bc)
        echo "Last link up: $WHEN ($SEC seconds ago)."

    fi

else
    echo "File /etc/os-release not found."
fi

Answer 1

On my machine dhclient is restarted by NetworkManager when re-connecting to the network. So maybe you can use the start time of the dhclient process?

ps -o start,cmd $(pgrep dhclient)

Answer 2

The Linux kernel does not track the time an interface is started.

Within struct net_device there is no field which holds a jiffies value for when an interface is started.

The best you can manage is some inferred method from userspace scripts and logs.

Answer 3

Here is my variant (very similar to your):

~ # expr $(echo $(date +%s) - $(date -d "`grep 'eth0: leased' /var/log/messages | tail -1 | awk '{print $1, $2, $3}'`" +%s))
1116
~ #

1116 - seconds after IP leased.

Answer 4

This should do what you want, in seconds:

#!/bin/bash
STARTTIME=`date +%s`
GATEWAY=`ip r s | grep default | cut -d' ' -f3`
INTERVAL=1
while ping -c 1 -W 1 ${GATEWAY} >/dev/null 2>&1; 
do
  awk -v STIME="$STARTTIME" 'BEGIN {
   DTIME=systime()-STIME;
   printf "Seconds of uptime since %s: %d\n",
     strftime("%a %b %e %H:%M:%S %Z %Y",STIME),
     DTIME; }';
  sleep $INTERVAL;
done

echo "HOST DROPPED!"

Which outputs:

user@host $ sh test-script.sh
Seconds of uptime since Sat Nov 15 01:14:26 EST 2014: 0
Seconds of uptime since Sat Nov 15 01:14:26 EST 2014: 1
Seconds of uptime since Sat Nov 15 01:14:26 EST 2014: 2
Seconds of uptime since Sat Nov 15 01:14:26 EST 2014: 3
Seconds of uptime since Sat Nov 15 01:14:26 EST 2014: 4
HOST DROPPED!

Theory: Get a timestamp STARTTIME, then test every INTERVAL whether the gateway (via ip route show) is still up, if so, substract the current timestamp from the original and print. If not, exit and indicate that the host has dropped its connection. See the manpages for explanation of each of the command options. If you don't want output every second, increase INTERVAL.