Network interface settings

This example checks the correct setup of the default gateway interface on a Linux server.

• The interface name is taken from the default route (/proc/net/route)
• ethtool is used to get information about the interface settings. Since ethtool needs root permissions sudo will be the door openener. Please adjust the sudo settings → visudo.

check_multi -f interface.cmd

• no Parameters
  Note: this command file autodetects the default gateway for a host. If you want to monitor multiple devices of a host, you can either build a loop over all interfaces or add a parameter -s IF=<interface>.

• Link: is the link up?
• Speed: interface speed (10,100,1000,10000)
• Duplex: Full duplex or half duplex
• Autoneg: on or off

• UNKNOWN: empty result or ethtool error
• WARNING: Speed < 100 or duplex not full
• CRITICAL: Link not up

#
# network_interface.cmd (adopted for Linux hosts)
#
# Copyright (c) 2008-2009 Matthias Flacke (matthias.flacke at gmx.de)
#
# Matthias Flacke, 20.01.2008
 
# determine def_gw interface from /proc/net/route
command [ def_gw  ] = awk '$2 == "00000000" {print $1}' /proc/net/route
 
# get ethtool output and store it in temporary file
command [ ethtool ] = sudo /sbin/ethtool $def_gw$ > /tmp/if_$def_gw$.txt \
                      && echo OK
 
# get interface settings using ethtool
command [ link    ] = awk '/Link detected:/    {print $3}' /tmp/if_$def_gw$.txt 
command [ speed   ] = awk '/Speed:/            {print $2}' /tmp/if_$def_gw$.txt 
command [ duplex  ] = awk '/Duplex:/           {print $2}' /tmp/if_$def_gw$.txt 
command [ autoneg ] = awk '/Auto-negotiation:/ {print $2}' /tmp/if_$def_gw$.txt 
 
# evaluate results
state   [ UNKNOWN ] =  "$def_gw$"  eq "" || ethtool != OK
state   [ WARNING ] = ("$speed$"   && "$speed$"   !~ /100/)   || \
                      ("$duplex$"  && "$duplex$"  !~ /FULL/i)
state   [ CRITICAL] =  "$link$"    && "$link$"    eq "no"