Instructions for Setting Up a CentOS 7 System with Bridged Networking for Virtual Machines

CentOS 7 bridging network card for virtual machines

My goal is to set up virtualization where the guests can access the entire LAN as well as the host over the network. The host should also be able to reach all the guests via the network.

This task was so simple, but somehow it eluded me for over a year. I use this document to establish a new kvm host in my network pool.

Install virtualization tools

sudo yum -y install libvirt qemu-kvm virt-install
sudo systemctl enable libvirtd.service ; sudo systemctl start libvirtd.service
sudo setsebool -P virt_use_nfs 1

Adjust the ethernet configuration

sudo su -
{
this_nic="$( nmcli device show | awk '/^GENERAL.DEVICE:/ && $2 ~ /e.*/ {print $2}' )"
indir=/etc/sysconfig/network-scripts
this_bridge=br0
this_nic_count="$( printf "%s\n" "${this_nic}" | sed '/^\s*$/d' | wc -l )"
if test ${this_nic_count} -ne 1 ;
then
   echo "Other than 1 nic detected. Please deal with manually. Aborted."
else
   # prepare values for bridge definition
   this_mac="$( ip -o link | grep "${this_nic}" | grep -oE 'ether [a-fA-F0-9:]{17}' | awk '{print $2}' | tr '[[:lower:]]' '[[:upper:]]' )"
   this_ipaddr="$( ip -o address show "${this_nic}" | grep -oE 'inet [0-9\.]{7,15}' | awk '{print $2}' )"
   # define bridge interface
   {
      echo "DEVICE=${this_bridge}"
      echo "TYPE=Bridge"
      echo "ONBOOT=yes"
      echo "DELAY=0"
      grep -h -E 'DNS1|DNS2|DOMAIN|IPADDR|PREFIX|BOOTPROTO|GATEWAY|DEFROUTE' "${indir}/ifcfg-${this_nic}"
   } > "${indir}/ifcfg-${this_bridge}"
   # define ethernet card
   old_nic_file="${indir}/ifcfg-${this_nic}"
   temp_nic_file="${indir}/ifcfg-${this_nic}-new"
   {
      echo "DEVICE=${this_nic}"
      echo "HWADDR=${this_mac}"
      echo "ONBOOT=yes"
      echo "BRIDGE=${this_bridge}"
      grep -h -E 'UUID' "${old_nic_file}"
   } > "${temp_nic_file}"
   chmod --reference "${old_nic_file}" "${temp_nic_file}"
   /bin/mv -f "${temp_nic_file}" "${old_nic_file}"
fi
}

systemctl restart network.service NetworkManager.service

Using the virtual host

With the setup complete, the environment is ready to serve virtual machines!

Install a virtual machine

vm=c7-03a ; time sudo virt-install -n "${vm}" --memory 2048 --vcpus=1 --os-variant=centos7.0 --accelerate -v --disk path=/var/lib/libvirt/images/"${vm}".qcow2,size=20 -l /mnt/public/Support/SetupsBig/Linux/CentOS-7-x86_64-Minimal-1804.iso --initrd-inject=/mnt/public/Support/Platforms/CentOS7/centos7-ks.cfg --extra-args "ks=file:/centos7-ks.cfg SERVERNAME=${vm} NOTIFYEMAIL=bgstack15@ipa.example.com" --debug --network type=bridge,source=br0 --noautoconsole

Delete a virtual machine

vm=c7-03a; sudo virsh destroy "${vm}"; sudo virsh undefine --remove-all-storage "${vm}";

References

Weblinks

  1. https://wiki.libvirt.org/page/Networking

Internal files

  1. file:///mnt/public/Support/Platforms/CentOS7/centos7-ks.cfg
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List current xvnc sessions in xrdp so you can reconnect to your old one

tl;dr

{ echo "user pid Xdisplay port"; { ps -ef | awk '/Xvnc :[[:digit:]]+/ {print $1,$2,$9}' | while read tu tpid tvnc; do sudo netstat -tlpn | awk -v "tpid=${tpid}" '$0 ~ tpid {print $4;}' | sed -r -e 's/^.*://;' -e "s/^/${tu} ${tpid} ${tvnc} /;" ; done ; } | sort -k3 ; } | column -c4 -t

The story

I connected to a gnome session on a terminal server, and disconnected. I wanted to reconnect to my current session, but apparently I got a new X session. After some research, I learned you can configure xrdp to prompt for the port number so you can get back to the previous session. However, then you have to know what to type in. After doing a manual ps and netstat, I found some useful numbers. What I needed to enter was the tcp port number, so 5919.

The explanation

You can have an entry in the /etc/xrdp/xrdp.ini file like the following block.

[xrdp8]
name=Reconnect
lib=libvnc.so
username=ask
password=ask
ip=127.0.0.1
port=ask

When you connect over RDP, select the “Reconnect” module and type in a port number, which you can find from the output of the oneliner.

{ echo "user pid Xdisplay port"; { ps -ef | awk '/Xvnc :[[:digit:]]+/ {print $1,$2,$9}' | while read tu tpid tvnc; do sudo netstat -tlpn | awk -v "tpid=${tpid}" '$0 ~ tpid {print $4;}' | sed -r -e 's/^.*://;' -e "s/^/${tu} ${tpid} ${tvnc} /;" ; done ; } | sort -k3 ; } | column -c4 -t
user       pid    Xdisplay  port
mjohnso    11448  :17       5917
mjohnso    12939  :18       5918
bgstack15  1219   :19       5919

References

Weblinks

  1. https://askubuntu.com/questions/133343/how-do-i-set-up-xrdp-session-that-reuses-an-existing-session#360835

Check if network port is open

On the local system, check if something is listening to the port:

netstat -tlpn

On a remote system, you can use telnet or ncat to check to see if you can actually get to the port:

echo '' | telnet myserver 1054

If successful, telnet returns ‘Connected to myserver’ before closing out.

echo '' | nc -v myserver 1054
$ echo '' | nc -v myserver 1054
Ncat: Version 6.40 ( http://nmap.org/ncat )
Ncat: Connected to 192.168.50.35:1054.
$ echo '' | nc -v myserver 1055
Ncat: Version 6.40 ( http://nmap.org/ncat )
Ncat: No route to host.