Xdmcp port 6000 is not listening

Fedora 33 beta

We use it for GUI installations like Oracle.

/etc/gdm/custom.conf

[security]
DisallowTCP=false

[xdmcp]
enable=true

Rebooted the machine.

# netstat -an|grep 6000

No listening port

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# Fix wrong case
sudo sed -i -e "/^enable=/s/^e/E/" /etc/gdm/custom.conf
sudo systemctl restart gdm.service

# Check ports
> sudo ss -l -n -p -A inet | grep -e gdm
udp   UNCONN 0      0            0.0.0.0:177       0.0.0.0:*    users:(("gdm",pid=5168,fd=12)) 

# Show SELinux port mappings
> sudo semanage port -l | grep -e xdmcp
xdmcp_port_t                   tcp      177
xdmcp_port_t                   udp      177

Wrong case is now fixed.

Rebooted

# more /etc/gdm/custom.conf
# GDM configuration storage

[daemon]
# Uncomment the line below to force the login screen to use Xorg
#WaylandEnable=false

[security]
DisallowTCP=false

[xdmcp]
Enable=true

[chooser]

[debug]
# Uncomment the line below to turn on debugging
#Enable=true


# ss -l -n -p -A inet | grep -e gdm
udp   UNCONN 0      0            0.0.0.0:177        0.0.0.0:*    users:(("gdm",pid=877,fd=12))            
# semanage port -l | grep -e xdmcp
xdmcp_port_t                   tcp      177
xdmcp_port_t                   udp      177



# netstat -an|grep 6000
# 

Still the same issue. In Fedora 32, it is working fine. In Fedora 33 Beta, it’s not.

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If possible, use the default port that is 177/udp.
Firewall configuration by default:

sudo firewall-cmd --permanent --add-service=xdmcp
sudo firewall-cmd --reload

Otherwise, specify a custom port and make sure this is allowed by both SELinux and firewall.

Above didn’t work. I also disabled firewall and SELinux, rebooted the machine and it didn’t work either.

I issued ps -ef | grep -i xorg and I got the following:

Fedora 32:
/usr/libexec/Xorg vt2 -displayfd 3 -auth /run/user/1000/gdm/Xauthority -listen tcp -background none -noreset -keeptty -verbose 3

Fedora 33 Beta (ran from Boxes of Fedora 32):
/usr/libexec/Xorg vt2 -displayfd 3 -auth /run/user/1000/gdm/Xauthority -background none -noreset -keeptty -novtswitch -verbose 3

‘-listen tcp’ parameter is missing in Fedora 33 Beta while a new one ‘-novtswitch’ is being added.

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I tried this myself and have no problems on F33.

[root@localhost ~]# cat /etc/gdm/custom.conf 
# GDM configuration storage

[daemon]
# Uncomment the line below to force the login screen to use Xorg
#WaylandEnable=false

[security]
DisallowTCP=false

[xdmcp]
Enable=true

[chooser]

[debug]
# Uncomment the line below to turn on debugging
#Enable=true

And I also do not see ‘listen tcp’.

/usr/libexec/Xorg vt2 -displayfd 3 -auth /run/user/1000/gdm/Xauthority -background none -noreset -keeptty -novtswitch -verbose 3

 # netstat -tulpen  | grep dm
 udp        0      0 0.0.0.0:177             0.0.0.0:*                           0          29328      811/gdm
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We need Fedora 33 Beta (as a client) to be listening on port 6000 in order to remotely run X commands like ‘runInstaller’, ‘netmgr’, ‘dbca’, etc… commands of Oracle server running On Oracle SPARC Solaris.

In Fedora 32, the output of ‘netstat -an’ is showing:

$ netstat -an | grep 6000
tcp 0 0 0.0.0.0:6000 0.0.0.0:* LISTEN
tcp6 0 0 :::6000 :::* LISTEN

In Fedora 33 Beta, there is no port 6000 listening after modification of /etc/gdm/custom.conf file and reboot.

Looks like you do not need xdmcp. Are you running wayland or X on Fedora 33 beta? In case of wayland I can imagine nothing is listening in the 6000 port range.
How do you connect to solaris? With ssh, telnet or xdmcp chooser?