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