Auto detect network interface card, network init.d

Question

I have build my LFS linux that based in this book, it's working fine and network interface card is working. Even it's configuring IP automatically with using dhcpcd service.

According chapter 9 in that books, there's file called

/etc/sysconfig/ifconfig.eth0 The problem is, what if I'm using wlan0, do I need to modify config file or rename eth0 to wlan0 every change network interface card MANUALLY, I expect it's detected automatically

Here init network script that generated by LFS book in /etc/init.d/network that related with /etc/sysconfig/ifconfig.*

### BEGIN INIT INFO
# Provides:            $network
# Required-Start:      $local_fs localnet swap
# Should-Start:        $syslog firewalld iptables nftables
# Required-Stop:       $local_fs localnet swap
# Should-Stop:         $syslog firewalld iptables nftables
# Default-Start:       3 4 5
# Default-Stop:        0 1 2 6
# Short-Description:   Starts and configures network interfaces.
# Description:         Starts and configures network interfaces.
# X-LFS-Provided-By:   LFS
### END INIT INFO

case "${1}" in
   start)
      # Start all network interfaces
      for file in /etc/sysconfig/ifconfig.*
      do
         interface=${file##*/ifconfig.}

         # Skip if $file is * (because nothing was found)
         if [ "${interface}" = "*" ]; then continue; fi

         /sbin/ifup ${interface}
      done
      ;;

   stop)
      # Unmount any network mounted file systems
       umount --all --force --types nfs,cifs,nfs4

      # Reverse list
      net_files=""
      for file in  /etc/sysconfig/ifconfig.*
      do
         net_files="${file} ${net_files}"
      done

      # Stop all network interfaces
      for file in ${net_files}
      do
         interface=${file##*/ifconfig.}

         # Skip if $file is * (because nothing was found)
         if [ "${interface}" = "*" ]; then continue; fi

         # See if interface exists
         if [ ! -e /sys/class/net/$interface ]; then continue; fi

         # Is interface UP?
         ip link show $interface 2>/dev/null | grep -q "state UP"
         if [ $? -ne 0 ];  then continue; fi

         /sbin/ifdown ${interface}
      done
      ;;

   restart)
      ${0} stop
      sleep 1
      ${0} start
      ;;

   *)
      echo "Usage: ${0} {start|stop|restart}"
      exit 1
      ;;
esac

exit 0

# End network

Answer 1

By reading the script, it is obvious that it will process all /etc/sysconfig/ifconfig.* files:

   start)
      # Start all network interfaces
      for file in /etc/sysconfig/ifconfig.*
      do
         interface=${file##*/ifconfig.}

The script will pick the name of the interface to configure from the filename, so you should simply write the settings you want for eth0 to /etc/sysconfig/ifconfig.eth0, and the settings you want for wlan0 to /etc/sysconfig/ifconfig.wlan0 respectively.

Also, note that for wireless network interfaces (like wlan0), you'll most likely also need to install and configure the wpa_supplicant, to handle the modern forms of wireless network security.

Being able to read shell scripts written by other people is a valuable skill for a Linux system administrator. Sometimes you may need to read a script to verify that it actually does what it claims to do; sometimes you may need to figure out what a script actually does in order to troubleshoot some problem, or because the available documentation is insufficiently detailed.