Permissions¶

KasmVNC's data-loss-prevention knobs are wired to environment variables. Defaults are restrictive — clipboard sharing is disabled in both directions until you explicitly enable it.

Boolean values accept 1, yes, true, on, or enabled; anything else counts as off.

Variables¶

Variable	Default	Xkasmvnc flag	Effect
`KASM_ALLOW_CLIPBOARD_IN`	`0`	`-AcceptCutText`	Allow pasting from local machine into the container.
`KASM_ALLOW_CLIPBOARD_OUT`	`0`	`-SendCutText`	Allow copying from the container out to the local machine.
`KASM_ALLOW_PRIMARY_SELECTION`	`0`	`-SendPrimary`	Share X primary selection (middle-click paste).
`KASM_CLIPBOARD_IN_MAX`	`0`	`-DLP_ClipAcceptMax`	Max bytes accepted per paste; `0` = unlimited.
`KASM_CLIPBOARD_OUT_MAX`	`0`	`-DLP_ClipSendMax`	Max bytes sent per copy; `0` = unlimited.
`KASM_CLIPBOARD_DELAY_MS`	`0`	`-DLP_ClipDelay`	Minimum ms between clipboard operations (anti-spam).
`KASM_CLIPBOARD_MIME_TYPES`	(kasm default)	`-DLP_ClipTypes`	Comma-separated MIME allowlist, e.g. `text/plain,text/html`.
`KASM_WATERMARK_TEXT`	(none)	`-DLP_WatermarkText`	Overlay text on the desktop as a screenshot deterrent.
`KASM_DLP_LOG`	`off`	`-DLP_Log`	`off`, `info`, or `verbose`.
`QGIS_DESKTOP_ALLOW_TERMINAL`	`1`	(not a Kasm flag)	`0` removes the terminal emulators from the container. See Terminal access.

verbose DLP log captures keystrokes

KASM_DLP_LOG=verbose writes KEYSTROKES AND CLIPBOARD CONTENT to the server log. That means typed passwords and any pasted content end up on disk. Only use it with legal review in place.

Watermark expansion¶

KASM_WATERMARK_TEXT supports two kinds of substitution:

${USER} and $USER are expanded by start-desktop.sh before Xkasmvnc sees them, using the first QGIS_DESKTOP_USERS entry, else VNC_USER, else the OS $USER. So RESTRICTED - ${USER} becomes RESTRICTED - bob when QGIS_DESKTOP_USERS=bob:... is set.
strftime tokens (%H:%M, %Y-%m-%d, etc.) are expanded by KasmVNC at render time.

ASCII only

The default watermark font ships without glyphs like em dash (U+2014). Stick to ASCII in the watermark text or you will see fallback rectangles.

Examples¶

Block copy/paste both directions, watermark the desktop:

docker run --rm -p 8443:8443 --cap-add=NET_ADMIN \
  -e KASM_WATERMARK_TEXT='${USER} %H:%M' \
  ghcr.io/kartoza/qgis-desktop-docker:ltr

Allow paste in but block copy out, with a 4 KB cap and plain-text only:

docker run --rm -p 8443:8443 --cap-add=NET_ADMIN \
  -e KASM_ALLOW_CLIPBOARD_IN=1 \
  -e KASM_CLIPBOARD_IN_MAX=4096 \
  -e KASM_CLIPBOARD_MIME_TYPES=text/plain \
  ghcr.io/kartoza/qgis-desktop-docker:ltr

Fully permissive (matches the KasmVNC upstream default posture):

docker run --rm -p 8443:8443 --cap-add=NET_ADMIN \
  -e KASM_ALLOW_CLIPBOARD_IN=1 \
  -e KASM_ALLOW_CLIPBOARD_OUT=1 \
  -e KASM_ALLOW_PRIMARY_SELECTION=1 \
  ghcr.io/kartoza/qgis-desktop-docker:ltr

Terminal access¶

By default the desktop ships XFCE's terminal emulator, and a user can reach a shell from the panel launcher, the applications menu, Ctrl-Alt-T, or Thunar's right-click Open Terminal Here. For a deployment where people are meant to use a mapping application and nothing else:

docker run --rm -p 8443:8443 --cap-add=NET_ADMIN \
  -e QGIS_DESKTOP_ALLOW_TERMINAL=0 \
  ghcr.io/kartoza/qgis-desktop-docker:ltr

At boot, while it is still root, the entrypoint:

Deletes the terminal emulators — the /bin symlink and the binary it points at, inside this container's own filesystem layer. This is the control that holds: every route above ends in exec()ing one of those names, and none of them can succeed once the executable is gone.
Deletes the command-runner dialogs (xfce4-appfinder, xfrun4, exo-open), which would otherwise let a user type an arbitrary command into a "choose an application" prompt.
Hides the menu entries and removes the panel launcher, so the desktop does not offer an affordance that is only going to fail.

Step 3 is cosmetic; steps 1 and 2 are the control. Nothing is written to the image — a fresh container starts from the image again, so the setting is per container and reversible by restarting without it.

This is not a sandbox

QGIS ships a Python console, and anything that can run Python can start a subprocess. Removing the terminal raises the bar for a casual user and removes the obvious affordance; it does not contain a determined one. The boundaries that do that are the unprivileged UID the desktop runs as, the egress lockdown, and the container itself. If you need to stop code execution outright, do not hand out a desktop with a scripting console in it.

Combine it

QGIS_DESKTOP_ALLOW_TERMINAL=0 composes with everything else — it is what the analyst locked-down scenario uses on top of clipboard blocking, the watermark and the egress allowlist.

File transfer¶

KasmVNC 1.4.0 standalone does not expose a runtime toggle for the file upload/download feature — that lives in the commercial Kasm Workspaces platform. If you need to block file transfer, put the container behind a reverse proxy and drop the upload/download endpoints there, or drop the container's outbound network with --network none.