Most linux admins work from shell and there is not much requirement to connect to the X window. But, in some cases, we need to access graphic console (X window Manager). For example, if a user needs to install oracle and he/she might need access to linux remote GUI; then I personally recommend to disable X manager, once the requirement is finished as part of security measures.
Usually in /etc/inittab file, sysadmin would be setting it to level 3. So we have to change the level to 5. This makes it effective on the next restart.
# Default runlevel. The runlevels used by RHS are:
# 0 - halt (Do NOT set initdefault to this)
# 1 - Single user mode
# 2 - Multiuser, without NFS (The same as 3, if you do not have networking)
# 3 - Full multiuser mode
# 4 - unused
# 5 - X11
# 6 - reboot (Do NOT set initdefault to this)
Enable X Window Manager (GDM or XDM or KDM). If its already running, you can find which X window by running the below ps command. XDM and KDM are supported on older versions of Linux. From RHEL 5 onwards XDM X window manager is supported.
# ps ax | grep [gkx]dm
To enable XDM manager, you have to edit /etc/gdm/custom.conf file as below:
Step 3 :
Restart X Window Services using init command:
[root@Server1 ~]# init 3
[root@Server1 ~]# init 5
Step 3 :
Next step would be to configure the access rules. Run gdsetup command.
a ) Click the Remote tab on GDM setup utility. Change the Style pull-down menu selection from 'Remote login disabled' to 'Same
b) Under the Security tab enable "Allow local system administrator login" and "Allow remote system administrator login"
Step 4 :
Restart GDM utility service as below:
[root@Server1 ~]# /usr/sbin/gdm-restart
Step 5 :
You can now test X window using the below X command.
[root@Server1 ~]# X -query localhost :1
step 6 :
XDMCP are using the below ports and make sure these ports are open in firewall.
XDMCP 177 UDP
X11 protocol 6000-6005 TCP
xfs: X font server 7100 TCP