Re: Getting boot not to hang if ethernet not plugged into modem

[Adam Aube <aaube01@baker.edu>]

Cheryl Homiak wrote:

> Is there something one can put in /etc/network/interfaces or somewhere so
> that ethernet card coming up will be conditional. right now, if I boot on
> either my laptop or desktop with "auto" set for eth0 and the cable modem
> isn't connected to the ethernet card, the whole boot hangs for quite a
> while.

Which means eth0 is set to use DHCP, and you are waiting for the DHCP to
timeout. What you need is a script to run in a "pre-up" line to detect if
there is a connection on the NIC.

Several scripts have been posted to this list. I have a variant adapted from
one of them. It works for both wired and wireless NICs. For wired NICs, it
uses mii-tool to see if there is a connection on the cable. For wireless
NICs, it uses iwconfig to make sure the NIC supports wireless (meaning it's
plugged in - my wireless NIC is PCMCIA).

Just setup /etc/network/interfaces like this:

iface eth0 inet dhcp
        pre-up /usr/local/bin/checknic.sh wired

For wireless NICs, replace "wired" with wireless. The script is posted at
the end of this message.

Adam

#!/bin/bash
# checknic.sh - Checks status of network connection
# Called by ifupdown in the pre-up section
# Usage: $0 (wired|wireless)

# Status statements
MIIACK="link ok"
WIFINACK="no wireless extensions"

# System programs
GREP="/bin/grep"
IFCONFIG="/sbin/ifconfig"
IWCONFIG="/sbin/iwconfig"
MIITOOL="/sbin/mii-tool"

# Test connection for link
$IFCONFIG $IFACE 0.0.0.0 > /dev/null 2>&1 || exit 1
case $1 in
  wired)
    (( `$MIITOOL $IFACE | $GREP -c "$MIIACK"` > 0 )) && exit 0
  ;;
  wireless)
    (( `$IWCONFIG $IFACE | $GREP -c "$WIFINACK"` < 1 )) && exit 0
  ;;
  *)
    exit 2
  ;;
esac

exit 1