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4
user/security-in-qubes/firewall.md
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@ -40,8 +40,8 @@ If the qube is running, you can open Settings from the Qube Popup Menu.
ICMP and DNS are not accessible in the GUI, but can be changed via `qvm-firewall` described below.
Connections to Updates Proxy are not made over a network so can not be allowed or blocked with firewall rules, but are controlled using the relevant policy file (see [R4.x Updates proxy](/doc/software-update-vm/) for more detail).
Note that if you specify a rule by DNS name it will be resolved to IP(s) *at the moment of applying the rules*, and not on the fly for each new connection.
This means it will not work for servers using load balancing, and traffic to complex web sites which draw from many servers will be difficult to control.
Note that if you specify a rule by DNS name it will be resolved to IP(s) *at the moment the rules take effect* (including each time the qube or netvm starts), and not on the fly for each new connection.
This means it will not work reliably for servers that have different IPs at different times as a result of DNS-based load balancing.
Instead of using the firewall GUI, you can use the `qvm-firewall` command in Dom0 to edit the firewall rules by hand.
This gives you greater control than by using the GUI.

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user/troubleshooting/gui-troubleshooting.md
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@ -6,16 +6,22 @@ ref: 233
title: GUI troubleshooting
---
## Can't click on anything after connecting 4k external display
## Can't click on parts of the screen after connecting high-resolution external display
When you connect a 4K external display, you may be unable to click on anything but a small area in the upper-right corner.
When you connect a high-resolution external display, you may be unable to click on parts of the screen.
When a qube starts, a fixed amount of RAM is allocated to the graphics buffer called video RAM.
This buffer needs to be at least as big as the whole desktop, accounting for all displays that are or will be connected to the machine.
By default, it is as much as needed for the current display and an additional full HD (FHD) display (1920×1080 8 bit/channel RGBA).
This logic fails when the machine has primary display in FHD resolution and, after starting some qubes, a 4K display is connected.
This logic fails when the machine has primary display in FHD resolution and, after starting some qubes, a high-resolution display is connected.
If the buffer is too small, and internal desktop resize fails.
To determine if this is the problem affecting you, look at the Xorg log inside the Qube at `/home/user/.local/share/xorg/Xorg.0.log` for lines like the following:
~~~
[ 1623.988] (EE) DUMMYQBS(0): Unable to set up a virtual screen size of 3440x1440 with 17101 Kb of video memory available. Please increase the video memory size.
~~~
The solution to this problem is to increase the minimum size of the video RAM buffer, as explained in [GUI Configuration](/doc/gui-configuration/#video-ram-adjustment-for-high-resolution-displays).
## Screen blanks / Weird computer glitches like turning partially black or black boxes