RHEL/CentOS quick reference

Networking

Get the IP address (RHEL 7+)

ip addr show

Open a port (RHEL 7+)

sudo firewall-cmd --get-active-zones
sudo firewall-cmd --zone=public --add-port=8000/tcp --permanent
sudo firewall-cmd --reload

Close a port (RHEL 7+)

sudo firewall-cmd --get-active-zones
sudo firewall-cmd --zone=public --remove-port=8000/tcp --permanent
sudo firewall-cmd --reload

SSH X11 Forwarding

Enable SSH X11 forwarding

  1. Install prerequisite packages:

     sudo yum -y xorg-x11-xauth

  2. Edit /etc/ssh/sshd_config and add this line:

     X11UseLocalhost no

Test SSH X11 forwarding

  1. SSH to the server with the -X flag:

     ssh -X myserver

  2. Install xclock

     sudo yum -y install xorg-x11-apps

  3. Run xclock

     xclock

Use SSH X11 forwarding as another user

  1. SSH to the server with the -X flag

     ssh -X myserver

  2. Configure xauth

    • RHEL 7:

        xauth extract - $DISPLAY > /tmp/.Xauthority
  chmod 666 /tmp/.Xauthority
  sudo -iu someuser
  xauth merge /tmp/.Xauthority

    • RHEL 6:

        xauth extract -  :`echo $DISPLAY | cut -d : -f 2` > /tmp/.Xauthority
  chmod 666 /tmp/.Xauthority
  sudo -iu someuser
  xauth merge /tmp/.Xauthority

    • Alternatively (not recommended):

      1. Copy your .Xauthority file to that user’s home folder

         sudo cp ~/.Xauthority ~someuser

      2. Change the ownership of the file to that user

         sudo chown someuser: ~someuser/.Xauthority

      3. Become that user

         sudo -iu someuser

  3. Test X forwarding

     xclock

  4. Cleanup (optional, recommended)

    • RHEL 7:

        xauth remove $DISPLAY
  rm /tmp/.Xauthority

    • RHEL 6:

        xauth remove  :`echo $DISPLAY | cut -d : -f 2`
  rm /tmp/.Xauthority

    • Alternatively (not recommended):

      1. Remove the .Xauthority file

         rm ~someuser/.Xauthority