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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:


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)"/*/")

        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)."


    echo "File /etc/os-release not found."
share|improve this question
There's no such thing as "being connected to a network" other than having a physical cable connection. Having an IP address assigned to a NIC is not an indicator of a network state. If you want to determine network connectivity for a NIC, you will have to monitor it actively (for example, by sending periodic pings to another target or having a persistent TCP connection). –  Oliver Salzburg Jul 8 '13 at 20:09
Hum, well then when my router reboots (takes about 1 minute), my NIC has it's IP removed and then reassigned again (byt NetworkManager). my iMac does something similar. What I really want to know is when the router rebooted. In the logs in my iMac and in linux I can see when it was reassigned again, but I guess without something like NetworkManager it would still have it's IP assigned? Maybe I should take a closer look at NetworkManager instead. Thank you. –  Stefan Lithén Jul 8 '13 at 20:54
I'm assuming that NetworkManager (or another component) performs monitoring on active connections. If a connection breaks, it determines availability of your gateway (router), once it detects that it is down, it might release the IP address assigned through DHCP. Or maybe it waits for the gateway to be available again and then asks for the IP address to be reassigned. Either way, this question proposes using ip monitor (among other things), it might be worth a look. –  Oliver Salzburg Jul 8 '13 at 21:14
Maybe placing a script in /etc/dhcp3/dhclient-enter-hooks.d/ could also be an option. But I'm not finding enough information to say how exactly it works. –  Oliver Salzburg Jul 8 '13 at 21:21

2 Answers 2

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 - seconds after IP leased.

share|improve this answer

On my machine dhclient is restarted my 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)
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