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Frequently Asked Questions
- How secure is PalMA?
- Once in a while, the PalMA device will not start or suddenly stop responding. Why?
- Why is PalMA only showing a single Window with a URL?
- How can I adapt the positions of the QR code according to the palma*png files in screensaver.php?
- How can I automatically turn on/turn off a PalMA station?
- Is PalMA a VNC application?
- Can PalMA be deployed on ARM-based mini computers?
- What about AirPlay and Miracast?
PalMA has been developed for use in an intranet, not for networks with direct connection to the Internet.
The intended deployment scenario is within the campus network of a University that grants access to users only after authentication by WiFi. Using log files, timestamps and IP addresses, all illegitimate usage in such networks can be traced to a single person or a single workstation. These limitations notwithstanding, we are striving for making PalMA as secure as possible.
For example, access to the database and uploaded files is denied
if the Apache web server has been configured to comply with the access control
restrictions defined in the .htaccess.
When employing fast hardware, such as the Intel NUC line of small form factor PCs, the Linux NetworkManager sometimes fails to establish a connection on system start.
A workaround is to remove the network-manager package (sudo apt-get remove network-manager) and set up connections manually by adding the following configuration
to /etc/network/interfaces:
# cat /etc/network/interfaces
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).
# The loopback network interface
auto lo
iface lo inet loopback
# The primary network interface
allow-hotplug eth0
iface eth0 inet dhcp
We also strongly recommend uninstalling the avahi-daemon package (sudo apt-get remove avahi-daemon). The Avahi-Daemon is a zero-configuration
networking
implementation which can lead to PalMA stations suddenly and unexpectedly
assigning themselves a new IP address (and therefore losing connection of
course). Once per week, one of the 30 PalMA stations used to mysteriously fail
until we discovered avahi-daemon as the culprit and removed it.
This means that the installed version of the WWW browser dwb is out of date.
An bug fixed in the newest version
prevented dwb from opening a second window for a new URL.
There is a workaround to make every window use its own instance: Edit the
configuration file
settings/dwb/settings
and add the following line to the end of the file:
single-instance=false
The script theme/ub-mannheim/lc/screensaver.php is loading two images in the
<body> of the HTML. Only one of them is visible though.
Every image has an ID, in our case: Variant1 and Variant2.
The QR code has the ID QR-Code. Using this ID, the position can be set using CSS:
#Variant2 #QR-Code {
top: 22%;
}
This defines the vertical position of the QR code for image 2 (=Variant2) to
be offset from the top by 22 percent.
I you examine the code more closely, you will find that we have already provided the CSS for up to five images.
The display of the URI is similarly handled in CSS.
Alternatively, one could construct the screensaver image using HTML code by combining HTML blocks and images -- this can significantly simplify the correct positioning of QR code and URL.
The Linux command to shutdown is poweroff. This command can be scheduled
using the cron system.
Mannheim University Library is using the vastly more powerful
CFEngine that can also handle
complex scenarios such as holidays or multi-day library closures.
To automatically turn on a PalMA station, either schedule a fixed time in the
machine's BIOS or send a
Wake-on-LAN package via Ethernet.
At Mannheim University Library, we again use CFEngine for this purpose: Every morning, a continually running Linux server iterates through a list of all PalMA stations and wakes them up using Wake-on-LAN according to specific rules.
When uploading larger videos is a change in the PHP configuration and the
Increase of the value max_filesize necessary. At the same time it is necessary
change the maximum of the Dropzone configuration value to the same value.
Otherwise, interactions between the two components may occur
and the file can not be processed successfully by PalMA.
PalMA is a web application that uses a variety of Linux applications in the background, such as LibreOffice, Zathura or VLC.
VNC is used to display the screens of users' devices (esp. notebooks running Windows, Mac OS X and Linux).
In comparison with Intel's small form factor PCs, ARM-based mini computers consume far less energy, typically between 2 and 5 watts, compared to 10 watts for Intel NUCs.
With some limitations, PalMA can be deployed on a Raspberry Pi 1: Office documents cannot be loaded in a sensible amount of time, because LibreOffice requires too much memory and processor power. Screen sharing without zoom is possible though.
With the Raspberry Pi 2, it's quite another story: With a full gigabyte of RAM and a 900 MHz quad core CPU, these machines can not only run LibreOffice but serve as a full-fledged PalMA station. The latest models Raspberry Pi 3 and Raspberry Pi 4 are even better.
All older models of the Raspberry Pi family are limited to Full HD (which is quite sufficient for most use cases). The latest Raspberry Pi 4 supports up to two 4K displays and is therefore a good choice for PalMA.
The MINIX NEO X8-H Plus Android TV box is capable of 4K resolutions and with 2GB of RAM and 2GHz of CPU faster than the older Raspberry Pi models. We did not succeed using the NEO X8 as a PalMA station.
ODROID C2 is similar to Raspberry Pi 3 (same case), but a bit faster. In addition it supports 4K resolution and CEC. ODROID C2 runs Ubuntu and is a good inexpensive platform for PalMA.
AirPlay is protocol for sharing (among other data) screens with other Airplay clients using WiFi. Miracast offers the same functionality for Google's Android operating system.
Both protocols are proprietary (there are no free implementations) and vendor-specific (targeting only a limited range of operating systems). They are well-suited for small-scale between predetermined, homogenous clients, such as a smart home network or a conference room. For a large-scale network with a very diverse userbase like a University network, no proprietary solution fits the bill.
In principle, PalMA can be extended to support Airplay in the future. The license fees per Palma station would be between 10 and 20 Euros and would require extensive development efforts.