Scribbles for my memory

I run a lid-closed laptop with two external monitors as a remote-access host. Remote desktop into it works perfectly, but the physical monitors sitting on my desk were pitch black. Cables fine, monitors powered, nothing in the logs.

The screens weren't broken — they were just DPMS-blanked, and nothing I did remotely could wake them:

$ sudo XAUTHORITY=/var/run/lightdm/root/:0 DISPLAY=:0 xset q
DPMS (Display Power Management Signaling):
  Standby: 600    Suspend: 0    Off: 900
  DPMS is Enabled
  Monitor is Off

One command brings them back:

sudo XAUTHORITY=/var/run/lightdm/root/:0 DISPLAY=:0 xset dpms force on

The reason it happened at all is the part worth remembering: xrdp gives you a second X server. The console session is Xorg :0; your RDP session is Xorg :10. They're separate processes with separate idle timers. Every keystroke and mouse move you make remotely resets the idle timer on :10 — and :0 never hears about any of it. So :0 sits there accumulating idle time forever and blanks on schedule, no matter how busy you look on the other display.

If the host is supposed to stay lit, disable blanking in the console user's session, not yours. On XFCE:

xfconf-query -c xfce4-power-manager -p /xfce4-power-manager/dpms-enabled -s false
for k in blank-on-ac blank-on-battery dpms-on-ac-sleep dpms-on-ac-off \
         dpms-on-battery-sleep dpms-on-battery-off; do
  xfconf-query -c xfce4-power-manager -p /xfce4-power-manager/$k -s 0
done

Those only take effect when xfce4-power-manager restarts, so log the console user out and back in. Note the settings persist to ~/.config/xfce4/xfconf/xfce-perchannel-xml/, not ~/.config/xfconf/ — I looked in the wrong place first.

One trap after all that: I logged back in, confirmed DPMS is Disabled, and declared victory too early. xset q still read timeout: 600. That's X's own built-in screensaver, a completely separate mechanism that the power manager's blank-on-ac=0 never touched. DPMS controls whether the monitor gets powered down; the X screensaver just paints over the screen while it stays on. From a chair three feet away the two are indistinguishable, and remote input can't dismiss either one. Kill both, from the console user's autostart:

xset s off s noblank -dpms

Check for timeout: 0 and DPMS is Disabled before you believe it.

On a Toshiba CB35-3340 (Bay Trail Chromebook running MX Linux / Debian 13 on MrChromebox firmware), the internal Intel Wireless 7260 disappears every few hours. The SSID list goes empty, every scan fails with -EIO, and toggling wifi does nothing. Only a reboot brought it back.

The giveaway is in the kernel log:

iwlwifi 0000:01:00.0: iwlwifi device memory mapped registers:
iwlwifi 0000:01:00.0: 00000000: ffffffff ffffffff ffffffff ffffffff
WARNING: ... __iwl_trans_pcie_grab_nic_access+0x14c/0x150 [iwlwifi]
iwlwifi 0000:01:00.0: Error sending STATISTICS_CMD: enqueue_hcmd failed: -5

MMIO reads returning all-ones means the device is off the bus, not merely confused. That is why modprobe -r iwlwifi && modprobe iwlwifi fails with Could not load the [0] uCode section — there is nothing there to load firmware into.

Two things fix the recovery path. First, let the driver admit the device is gone:

I wanted a second local account to read /home/davidw. The user was already in group davidw, and ls looked like it should just work:

$ ls -ld /home/davidw
drwxrwx---+ 272 davidw davidw 16384 Aug 19 16:56 /home/davidw

Group davidw has rwx, right there in the middle. Except every access failed:

$ sudo -u desk ls /home/davidw
ls: cannot open directory '/home/davidw': Permission denied

The + at the end of the mode string is the tell. Once a file has a POSIX ACL, the middle triad printed by ls stops being the group permission and becomes the ACL mask — a ceiling on what every named user, named group, and the owning group may get. The real group entry is only visible via getfacl:

$ getfacl -p /home/davidw
user::rwx
user:libvirt-qemu:--x
group::---          <-- the actual group permission: nothing
mask::rwx           <-- this is what ls printed as "rwx"
other::---

So the directory was 700 all along. Someone (libvirt, in my case) added user:libvirt-qemu:--x at some point, and adding any named entry forces a mask into existence — set wide enough to cover that entry. ls dutifully displayed the mask, and it looked exactly like group access.

The mask cuts both ways: it can also revoke access that getfacl seems to grant. An entry of user:desk:rwx under mask::r-x yields read-only — getfacl marks it for you:

user:desk:rwx                   #effective:r-x

Two consequences worth internalizing. First, on any path with a +, getfacl is the only source of truth; don't reason from ls. Second, chmod g+rx on an ACL'd file doesn't set the group permission — it sets the mask, which is almost never what you meant. Grant access with a named entry instead, which is narrower and trivially reversible:

sudo setfacl -m u:desk:rwx /home/davidw   # grant
sudo setfacl -x u:desk     /home/davidw   # revert

One unrelated snag if you're doing this to share a checkout: git will refuse the now-reachable repos with detected dubious ownership in repository, because they're owned by a different uid. Fix it per-user, not with sudo:

sudo -u desk git config --global --add safe.directory '*'

Git Bash and MSYS2 can load different Git executables while sharing the same ~/.gitconfig. http.sslbackend=schannel works with Git for Windows, but an MSYS2-native Git may support only OpenSSL and fail with Unsupported SSL backend.

Remove the MSYS2 Git package and put Git for Windows first in MSYS2's PATH:

pacman -R --noconfirm git
printf '%s\n' 'export PATH="/c/Program Files/Git/cmd:$PATH"' >> ~/.bashrc
source ~/.bashrc
hash -r

Use one shared configuration:

git config --global http.sslbackend schannel
git config --global credential.helper manager

Verify both shells resolve the same executable:

type -a git
git --version
git ls-remote origin HEAD

This keeps certificate verification in the Windows certificate store and avoids shell-specific OpenSSL CA or stale credential-store differences. Do not disable TLS verification with http.sslVerify=false.

Log in at the physical console, then RDP in as the same user, and you get a black screen. Worse, unlike Windows, the remote connection can't kick the console session — so any machine you walked away from while logged in is a machine you can't reach.

Neither is really an RDP problem, and one trick fixes both: create a second Unix account that owns the console.

sudo adduser desk

desk logs in at the display manager and holds the physical machine. Your real user never logs in locally at all — its desktop exists only as an xrdp session. When you're sitting at the machine, desk connects to it over loopback:

xfreerdp3 /v:127.0.0.1 /u:youruser +clipboard /multimon

Now every client is equal. Connect from a laptop on the other side of the world and it takes over the same session your local xfreerdp was showing; the local one just exits and desk's desktop is still sitting there underneath. Don't wrap that command in an auto-reconnect loop, or the machine at home will keep stealing the session back and you'll never get in from outside.

The black screen was never about RDP — it was one user running two concurrent desktop sessions, colliding on all the per-user singletons: the session D-Bus, xfce4-session, ibus, gvfs. The second session's window manager never comes up. Two different uids have none of that.

The takeover failure is a separate mechanism. "Taking over" is really xrdp-sesman reconnecting you to a session in its own table. A console session started by lightdm was never in that table, so nothing can ever reattach to it — which is also why a second RDP client can kick the first: those two are the same session.