GNet Solutions » FreeBSD Administration

I have a FreeBSD VM with some jails that use a bridged network interface that changes networks fairly often. Rather than manually changing all the IP addresses manually, I wrote a script that changes the IP address of the jail config based on the network the VM is attached to.

• Create a new shell script:
  

  vi /usr/local/bin/chjailip.sh
  

  • And add the following:
    

    #!/bin/sh
    # Script to change ezjail config IP address
    
    # Get the current primary interface IP and change it to .99
    nextcloudip=`ifconfig | grep 255.255.255.255 | grep -Eo '(\b[0-9]{1,3}\.){3}[0-9]{1,3}\b' | grep -v 255 | sed 's/\.[0-9]*$/\.99/'`
    
    # Replace the newjail ezjail configs IP address with the newly updated IP
    sed -i '' -e "s/newjail_ip=\"*.*\"/newjail_ip=\"$newjailip\"/" /usr/local/etc/ezjail/newjail
    

• Make the script executable:
  

  chmod +x /usr/local/bin/chjailip.sh
  

• Edit the crontab:
  

  crontab -e
  

  • And add the script to run every reboot:
    

    @reboot /usr/local/bin/chjailip.sh
    

Resources¶

• https://stackoverflow.com/questions/5277156/using-sed-to-search-and-replace-an-ip-address-in-a-file
• https://unix.stackexchange.com/questions/397107/how-to-change-last-value-ip-address-with-sed/397109