Informasjonsdeling innenfor en liten gruppe er brukes ganske typisk. For
eksempel, hvis barna dine er i en skole eller barnehage, må du gå inn i en
klassegruppe for å dele forskjellig informasjon, meldinger osv. Ofte
proprietære sentraliserte plattformer som Facebook eller Whatsapp (Å, begge er
i bunn og grunn det samme uetiske selskapet, Meta!) eller noen ganger Telegram.
Mange ikke-IT-folk bruker bare det de pleide å bruke i dagliglivet. De som er
mer bekymret for personvern og sikkerhet til dem og barna deres, vil ikke
bruke noen av Meta eller andre store teknologiske apper. Men det er andre og
det er en behov til å kommunisere. Valget er enkelt: Enten blir du med i
foreldregruppen på Facebook eller så blir du ekskludert. Hvis ekskludert,
vil du ikke få oppdateringer om arrangementer, bursdager og så videre. De andre
foreldrene vil kanskje se på deg med en viss mistanke: er du en spion eller en
narkohandler som prøver å gjemme deg i en skygge av darknet? Dette er hva Cory
Doctorow kaller "the nettwork effect." Og det utnyttes og promoteres av de
gigantiske plattformene. De gjør sitt beste for å manipulere deg til å se på
plattformen og reklame deres så mye tid som mulig, ideelt sett 24 timer i
døgnet, og de lokker deg til å gi ut så mye privat data som mulig. Ingen vet
hvordan disse dataene vil bli brukt i fremtiden. Det er skjult i usikkerhet.
Den eneste sikkerheten er at brukerne utnyttes for andres fortjeneste.
Mens Facebook og andre prøver å pålegge enorme byttekostnader for å holde deg
på plattformen, er det en enkel løsning som er tilgjengelig for alle. Det er
den gamle gode e-posten. Alle har det nå. Men noen bruker det kun til å
registrere seg på nettsider, få lenker til tilbakestilling av passord og
lignende. Nei, e-post er fortsatt i live og er faktisk bedre enn mange pleide å
tro.
Epostlister
Maillister er velkjente. Vanligvis brukes de bare å spam deg med unødvendig
informasjon, reklame kampanjer og så videre. Men epostlister kan brukes til
bedre. Det er noe åpen kildekode-programvare for e-postlistebehandling som du
(jeg antar at du er administrator for gruppen) kan bruke på din egen server.
Deretter kan du abonnere alle i gruppen på listen (eller nyhetsbrevet ditt).
Okay– nå får alle i gruppen oppdateringer. Enkelt. Folk kan ha muligheten til å
abonnere seg på listen, eller avslutte abonnementet seg selv (uten din,
administratorens, manuelle handling). Det er nyttig.
E-post diskusjonsgrupper
E-postdiskusjonsgrupper eller listserv er egentlig en eldgammel (et
bedre ord: moden) teknologi som har blitt brukt for flere tiår siden. Den
brukes fortsatt mye av programvareutviklerfellesskapet med åpen kildekode. For
eksempel det berømte Linux kernel prosjektet. Ideen er bare triviell:
-
Du abonnerer på e-postlisten
-
Du får gruppens e-post ("listserv") e-postadresse, f.eks. foreldre@din.fqdn
-
Alle meldinger sendte en melding til denne gruppeadressen (ja,
foreldre@your.fqdn) spres til hver abonnents postkasse.
Deretter, hvis du abonnerer, svarer det å svare på gruppeadressen til å dele
e-postmeldingen med alle medlemmer.
Den gode gamle e-posten konkurrerer ikke om oppmerksomheten din med irrelevante
og irriterende varsler, manipulerer deg ikke til å blikk og dumscrolling. Alt
kommer bare til postkassen din. Du kan svare når som helst fra hvilken som
helst enhet, ingen spesielle apper er nødvendig.
Men slutt, for å bruke listserv trenger du din egen (eller kontrollerte)
e-postserver, domenenavn, kompetanse og tid for konfigurering og vedlikehold.
Hvis du er modig nok, kan du konfigurere din egen GNU Mailman:
Men hvis du liker å unngå bryet, er det flere åpne servere som tillater
registrering og gratis hosting for små ideelle grupper.
Det er også en Listserv on steroids som er gratis for små ikke-rpfit-grupper
(opptil 1000 abonnenter, som vanligvis er nok):
Her kan du:
-
Registrer din (admin) konto
-
Legg til gruppe-e-poster
-
Del, svarer, videresend gruppe-e-poster, med arkiver og mye annen funksjonalitet.
Doctorow, C. 2023. The internet con: how to seize the means of computation.
Verso.
Både voksne og barn blir stadig mer avhengige av smarttelefonene sine. Et
morsomt begrep for slike rusavhengige er smarttelefonzombie. Men dette er
ikke morsomt. Faktisk, smarttelefoner dreper. For eksempel har det
vært en økning i antall dødsfall hos barn fordi barna sitter klistret
til telefonene sine
Stadig flere barn nå eier smarttelefoner. Nesten alle ungdommer
eier en smarttelefon i Norge, Storbritannia, USA og mange andre
land. Smarttelefonavhengighet er en verdensomspennende plage (Olson et al.,
2022).
Imidlertid, forskning viser at smarttelefonavhengighet fører til en rekke
alvorlige psykologiske, helse- og velværeproblemer, inkludert nevrologiske
lidelser (e.g. Ratan et al., 2022;
Achangwa et al., 2023). Mange
undersøkelser viser at bruk av smarttelefoner påvirker
studentenes akademiske prestasjoner negativt (e.g. Amez &
Boert, 2020; Sapci
etal. 2021).
Smarttelefonen din er en dedikert spionenhet, men enda mer bekymringsfull
er det faktum at apper målrettet mot barn sporer, samler inn personlige
data og laster dem opp til ukjente tredjeparter (e.g.
Reyes et al., 2018).
Men det handler ikke bare om data og reklame. Smarttelefoner kan
direkte påvirke fysisk sikkerhet av barn. En russisk studie indikerte
at nesten 50% av barna får nye bekjentskaper i sosiale medier og 36%
av dem møter disse nye menneskene i virkeligheten etterpå (Kaspersky Lab,
2022).
Vi må løse en avveining mellom behovet for å kommunisere med barna våre,
men unngå avhengighet. Så hva er løsningen? Jeg tror det er en kombinasjon
av gammel stil (men ikke foreldet!) knapptelefon og et stort nettbrett.
Knappetelefoner er klassiske, men ikke udaterte!
Fordeler med knappetelefon, i tillegg til at det neppe forårsaker avhengighet,
inkludere
-
BATTERI fungerer lange eller veldig lange, ingen grunn til å tenke på
lading, det er liten risiko for å sitte igjen med en død, utladet telefon
i det mest uleilige øyeblikket. Batteriet dør ikke i kulden. Batteriet
er avtakbart og kan enkelt skiftes ut. Det er ingen risiko for at barnet
vil lade ut batteriet på grunn av intens spilling på telefonen. Det
vil ikke skje i verste øyeblikk, for eksempel når han eller hun trenger
hjelp fra foreldrene
-
SIKKERHET: det er ingen konstant tilkobling til Internett, viktige data,
passord, personlige dokumenter, kredittkortdata lagres ikke på telefonen:
det er ingen risiko for lekkasje eller hacking, selv om telefonen er mistet
eller stjålet. Plasseringen kan ikke spores og lekkes. Mange hackere og
sikkerhetseksperter bær ikke smarttelefoner. Men knappetelefonen tjener
sin hovedfunksjon, kommunikasjon, helt perfekt.
-
PRIS telefonen er billig, ikke bry deg om det, den er lett å erstatte hvis
den er ødelagt, mistet eller druknet. Men dette er spesielt viktig siden du
alltid har telefonen med deg. Barn er ofte uforsiktige og kan bryte ned ting.
-
FYSISK STYRKE: En liten skjerm, sterk telefon, går ikke i stykker med
det minste fall, mindre utsatt for vann. Jeg har erfaring med at en telefon
ble vasket i vaskemaskin og fortsatte å virke etterpå.
-
FYSISK KNAPPER er fortsatt et av de beste
brukergrensesnittene,
praktisk å bruke. Du kan konfigurere ett-tasts hurtigvalg. Knapper er
også lettere å bruke med hansker i kaldt vær.
-
STØRRELSE en liten telefon passer lett i lommen. Det er bare praktisk.
-
IKKE FORELDET en trykkknapptelefon kan betraktes som en "fysisk
app" som ikke blir foreldet og rett og slett alltid fungerer uten
å kreve konstante "oppdateringer."
Knappetelefon blir ofte sett på som noe enkelt og kjedelig, selv om det ikke
er helt utdatert. Men det finnes noen få moderne, elegante, designertelefoner,
for eksempel Punkt (overpriset!).
Nettbrett gir mye bedre brukeropplevelse
Men vi kan ikke frata barna våre internett, spillkommunikasjon med venner
og alt annet som en smarttelefon gir! Riktig nok, men det finnes et bedre
enhet enn smarttelefon: nettbrett
-
STOR SKJERM: nettbrettet har en stor skjerm som gir mye bedre
brukeropplevelse for alle bruksområder: Internett, video, spill, tegning,
skriving og til og med lydsamtaler. En stor skjerm kan bare ikke sammenlignes
med den lille skjermstubb på typisk smarttelefon. Det er mye bedre for
alle slags kreative aktiviteter.
-
LAVERE ER BEDRE: Det er ikke så lett å ta en tablett med deg hele
tiden. Med andre ord er tilgjengeligheten lavere og det er noen små
kostnader forbundet med bruken. Faktisk må du gå til laderen eller et
bord, ta nettbrettet og først deretter bruke det. Det er ganske stor
forskjell fra smarttelefonen som ofte alltid ligger i lommen. Dette gjør
det mindre sannsynlig at du blir avhengig av et nettbrett.
-
STOR OG MERKBAR: Bruk av nettbrett er lettere å legge merke til. Dette
gjør det også lettere for foreldrene å overvåke og kontrollere barnas
nettbrettbruk.
Konklusjon
Konklusjonen er denne: i stedet for en smarttelefon, er det tilrådelig
å gi en grunnleggende knappetelefon til barnet ditt å bære med seg. Men
de bør også eie et nettbrett hjemme for å bruke til internett, videoer,
spill, studier og alt smarttelefonen som normalt brukes til.
Anbefalt lesing
- Gabrielsen, Bjørn (2020) Skjermslaver: hva skjermene har gjort med oss,
og hva vi kan gjøre med dem. Kagge (ISBN: 9788248925231).
Oppdatering: lenker
Messaging continues to be of rise. The new generation is more willing to
send texts than to call. Communicating with an instant messenger has an
unique advantage over the old good email: you can easily send replies
over replies quickly, resulting in a dialogue. But there is a serious problem:
many of the instant messengers are commercial products that work such that
their "users" are in fact the exploitable resource having no control or
choice.
Most corporations are fair providers of various products and services we
can buy. But not these "Big Tech" that offer "free applications," including
instant messengers. There is, obviously, nothing free on the Earth. Then,
if you do not pay, then you are the product not the customer. The Big
Tech corporations exploit the "end-users" to suck out private data,
often for further resale. Nearly all of these messengers have centralised
architecture and the user's account is linked to the telephone number,
completely destroying privacy. The link to the telephone number is also
very inconvenient because you cannot get several accounts easily, this
requires obtaining several mobile subscriptions. It's just illogical,
expensive and silly. Centralized architecture dictates that the
communication is kept on the corporate servers
so theoretically many employees can read
messages by abuse.
Some of the products are advertised as end-to-end encrypted. But nearly
all of them are closed source so there is no way to check how this is
implemented and if and when the service owner can have access to private
messages content. Moreover, we have evidence for the opposite. Many
so called "end-to-end encrypted" messages are actually read by AI and human
contractors.
Even if communication is technically end-to-end encrypted, the company owns
and fully controls the server, the client application and network traffic, so
a man-in-the-middle attack by silently changing certificates is possible
(e.g. in the context of lawful intercept, or unlawful abuse). Metadata
(technical information information about all aspects of communication,
including the addressees, their locations, IP addresses, telephone number
etc.) is always accessible to the service. But metadata is often even
more informative than the message content. How such metadata is used is
typically unclear. The user has no authority here at all.
Nearly all of these messengering systems have closed proprietary protocol. This
means that how you use the product is completely controlled by the owner
company. The only way to use the product is with the official application.
You cannot just choose for yourself which application program to use. This
is cardinally different from the email, for example, where you can use the
provider's web interface, its mobile app or any of the many available email
applications such as Thunderbird or
K-9 Mail. With such a third-party application you
can easily consolidate several email accounts in one place and easily make
use of the functionality the provider does not offer, such as end-to-end
encryption. Another
major problem is monopoly and lack of interoperability. The "users" (in
reality, the exploited resource) are completely restricted to the owner's
platform and are unable to communicate with the other (especially competing)
platforms (e.g. Facebook to Snapchat) as a way to keep users within the silo.
This is as if you were unable to call/send sms across different mobile
operators. And this is silly. To break down monopoly, ensure fairer
competition and interoperability across the services, the EU has developed
the Digital Markets Act (DMA) regulation.
This is a big step, but it does not solve many of the problems with
centralization, privacy and regular security flaws.
Take back your freedom, privacy and security
So, why use the restricted, inconvenient, monopolistic, insecure and non-private platforms for
the trivial task of sending instant messages? There are several ways
to configure one's own privately controlled instant messaging system:
XMPP and Matrix. XMPP is
lightweight and more private, yet covers all the typical instant communication
purposes: text, file share and voice. Moreover, XMPP servers are by default
federated:
it is easy to send messages across the different servers like in the
email. There are many different applications for all operating systems and
platforms the user can choose.
It is very easy to set up one's own XMPP server for a small group,
company,
the family or just an individual. You will need
two things:
-
Server that will be the central hub for the communication network running
24x7. This can be anything, from a Rasberry PI in a cupboard to a Virtual
Private Server
(VPS) somewhere in a data centre or just an old PC running in your
basement. A small scale VPS useful for an XMPP server can be very cheap,
up to a three Euro per month. There exist even cheaper options, such as
EUR 6 per year. There are also dedicated search engines
to help locate cheap VPS, e.g. LowendBox
and ServerHunter.
A typical operating system running on the server is Linux (very secure,
highly configurable, free and open source).
-
Domain name that needs to be used to connect to the XMPP server. Domain
can be registered to the user (e.g. myname.no), which costs about
30 Euro yearly. But a sub-domain can be obtained for free using the
https://freedns.afraid.org or similar
"free DNS" services. In the later case you might have something like
myownchat.mooo.com or myownchat.ptchat.net. It is possible to run the
XMPP server purely on IP address even without domain name, but it is much
less convenient (e.g. then federation with other servers is lost).
Given you have got a server (VPS or dedicated machine) and the domain,
configuring an XMPP server can be done on 1-2-3. There exist several Linux
variants (distributives) with different management commands (usually for
installing software). I assume Debian Linux
is used below (the same commands also work for Ubuntu and other Debian-based
Linux systems).
1. Install XMPP server software
Login. When you have got a server of any kind, you need tologin
to it, typically with ssh:
here the user name on the server is debian and the server ip
is 1.2.3.4. Typically, you may need to create the ssh key and
upload it to the server to authenticate (refer the server documentation, e.g.
this).
I assume logging-in is not a problem.
Prepare server. First of all, update the software on the new server
sudo apt update -y && sudo apt-get upgrade -y
Install some useful monitoring and security-enhancing utilities
sudo apt install -y mc htop atop nload nmon tree zip pwgen fail2ban dnsutils iptables-persistent locate unattended-upgrades
Install certbot, a system that manages the
TLS certificates
for secure connection
sudo apt -y install certbot
Install the ejabberd server, which is is very
reliable and light on resources
sudo apt install ejabberd
Firewall. To allow incoming network access to this server by the XMPP
clients and also third-party servers, the server needs to configure
the firewall rules. This can be done differently in different
installations. For example, some VPS may do this using a friendly web
interface. The standard Linux firewall is done via iptables.
The XMPP system requires incoming acces via ports 5222, 5223, 5269, 5443,
5280, 3478. To determine the ports refer to the listen section of the XMPP
configuration file below.
sudo iptables -A INPUT -p tcp --dport 5222 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 5223 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 5269 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 5443 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 5280 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
# STUN is over udp
sudo iptables -A INPUT -p udp --dport 3478 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
The port 7777 is used for a proxy for peer-to-peer (bytestream) file
transfer. If peer-to-peer file sharing is intended for use, an additional
rule should be set allowing incoming connections:
sudo iptables -A INPUT -p tcp --dport 7777 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
To see what firewall rules are in effect issue this:
iptables -L --line-numbers
It makes sense to save the iptables rules so they are automatically get in
effect after reboot
iptables-save > /etc/iptables/rules.v4
2. Configure your XMPP server
Secure connection certificate. Get a free
Let's Encrypt
TLS certificate.
I assume you have got a free domain myownchat.ptchat.net from
https://freedns.afraid.org.
Note that ejabberd can manage (issue and update) TLS certificates on its
own, but this needs some configuration as described in the
acme configuration option:
https://docs.ejabberd.im/admin/configuration/basic/#acme.
An advantage of the standalone certificate management system (as here) is
that it is slightly less tricky and can easily be used with a
web server on the same machine.
Why not also configure a web server for a small static web site here?
Ejabberd is very lightweight and will happily coexist with many other
servers running on the same machine.
sudo certbot --standalone certonly -d myownchat.ptchat.net
This command will ask a few questions and issue a TLS certificate. This process
is done over http so http port 80 must allow incoming connections. If this is
not so, use the following command:
sudo iptables -A INPUT -p tcp --dport 80 -m conntrack --ctstate NEW,ESTABLISHED -j ACCEPT
Do not forget to save iptables rules with the iptables-save as above.
The certificate files are located in
/etc/letsencrypt/live/myownchat.ptchat.net/fullchain.pem directory.
For the sake of security, the certificate directories have by default no
access to anyone except the admin (root) user. But this precludes the XMPP
server ejabberd to access the certificate. This can be easily fixed with the
following commands
First, add ejabberd to the root group
sudo adduser ejabberd root
Second, allow access to the certificate directories to the group
sudo chmod g+rx /etc/letsencrypt/live/myownchat.ptchat.net
sudo chmod g+rx /etc/letsencrypt/live
sudo chmod g+rx /etc/letsencrypt/
Configure ejabberd. Once the preparations are done, it is time to
configure the ejabberd messaging server. Edit the configuration file
(assuming the mcedit text editor is used)
sudo mcedit /etc/ejabberd/ejabberd.yml
This is a long configuration file that may look scary. But in fact only a few
changes are required to make the server running with the default options. But
note that the indents are important, try to keep them as in the original file.
Any line starting with # is considered a comment, this can be easily used
to disable specific options by "commenting them out."
First, set up the host name that is used for the server, it is the same as
the domain:
hosts:
- myownchat.ptchat.net
Second, configure the location of the TLS certificates that are used by the
server:
certfiles:
- "/etc/letsencrypt/live/myownchat.ptchat.net/fullchain.pem"
- "/etc/letsencrypt/live/myownchat.ptchat.net/privkey.pem"
Configure the admin users who can manage the XMPP server:
acl:
admin:
user:
- ""
- "myname": "myownchat.ptchat.net"
Then, add configuration for http-file-upload module that will allow file
sharing (sending files):
mod_http_upload:
put_url: https://@HOST@:5443/upload
custom_headers:
"Access-Control-Allow-Origin": "https://@HOST@"
"Access-Control-Allow-Methods": "GET,HEAD,PUT,OPTIONS"
"Access-Control-Allow-Headers": "Content-Type"
It is convenient to keep the latest messages on the server, it is done with
the "mam" module:
mod_mam:
assume_mam_usage: true
default: always
Ejabberd supports several other communication protocols in addition to
XMPP. For example, it also works with MQTT that is
typically used for IoT devices. If this functionality is not used,
just comment out the MQTT module to disable it.
The STUN and TURN protocol is mainly used for voice calls and needs the
actual IP address of the server (replace with your server IP addfress)
-
port: 3478
ip: "::"
transport: udp
module: ejabberd_stun
use_turn: true
## The server's public IPv4 address:
turn_ipv4_address: "1.2.3.4"
An important issue is wether to allow anonymous registrations of new users.
I strongly recommend not allowing this for security reasons. For a small
private server, you will normally add users manually and set them initial
passwords. Every user can then change password within the client program. So,
you need to disable the mod_register by commenting it out:
# mod_register:
# ## Only accept registration requests from the "trusted"
# ## network (see access_rules section above).
# ## Think twice before enabling registration from any
# ## address. See the Jabber SPAM Manifesto for details:
# ## https://github.com/ge0rg/jabber-spam-fighting-manifesto
# ip_access: trusted_network
Start server! And that's all minimal configuration. Now it's time to
start the server:
sudo systemctl start ejabberd
If there are any errors and the server fails to start, Linux logs can be
inspected with this command:
or logs for only ejabberd:
sudo journalctl -xe --unit ejabberd
Additional stuff. The above is enough to make the XMPP server running for
text. If voice is required, you need to configure the DNS as described here:
https://www.process-one.net/blog/how-to-set-up-ejabberd-video-voice-calling/.
DNS is normally configured using the control panel of the domain registrar.
The TLS certificate that is managed by certbot
is updated each 90 days. This is an automatic process, but the ejabberd
server must know when certificate is changed. This can be done using the
deploy hook. Just create the hook file reloadxmpp.sh (the file name can be
anything):
sudo mcedit /etc/letsencrypt/renewal-hooks/deploy/reloadxmpp.sh
and add the following commands:
#!/bin/sh
ejabberdctl reload_config
This file must be executable, so issue this command:
sudo chmod ugo+x /etc/letsencrypt/renewal-hooks/deploy/reloadxmpp.sh
The last note on the server is that it should be regularly updated for
bug fixes and security updates. This is done automatically by installing
unattended-upgrades above. Yet, it is a good practice to log in regularly
over the ssh, check logs and update the system:
sudo apt update -y && sudo apt-get upgrade -y
3. Configure the XMPP users and client application
Register new users. First, you need to register the XMPP users. The
quickest method is to use the command line on the server, the command
ejabberdctl has advanced functions.
A secure random password can be generated withy pwgen, e.g. the following
generates passwords with 18 symbols:
It normally generates an array of possible passwords to choose from.
Now, to register the user myname, It is the admin user configured in the main
configuration file /etc/ejabberd/ejabberd.yml above.
# user domain password
sudo ejabberdctl register myname myownchat.ptchat.net pee8chogh9Heel6hei
Other users can be configured similarly. Note that the full user name for XMPP
has the same format se email: myname@myownchat.ptchat.net. This is due to
the federated nature of both systems: you need to know both the user and
the server with whom to communicate.
For this example let's register two additional users:
sudo ejabberdctl register john.dow myownchat.ptchat.net ohyeeLeefo9yief4gu
sudo ejabberdctl register anna.karenina myownchat.ptchat.net hejo7phiy2iFeW9She
Use! The final step is configure the client program on the
user's device. The biggest difficulty at this step is the plenty
of choice. For any major platform, one can choose any of the many
available XMPP client programs. Some email
programs, e.g. Thunderbird also support
XMPP (although only a limited subset of features). Check out the
https://xmpp.org. The configuration for the client
is simple:
-
Server: your server, in the example above it is myownchat.ptchat.net
-
User name: your user name. In the example we used above, it can be
myname
Note that the option to create new account must NOT be enabled as
long as the account has already been created on the sever and the in-band
registration (mod_register, see above) is disabled for
security.
Some programs accept the full user name without specifying user and domain
separately. Then the user is just myname@myownchat.ptchat.net. If you
plan to use the peer-to-peer (bytestream) file transfer (but
this is not mandatory), you should also find where the file transfer proxy is
configured and set it with the proxy subdomain, for our example it should be
proxy.myownchat.ptchat.net. And that is all for basic client configuration.
I recommend the Blabber XMPP application for
devices running Android. Yaxim is the best option for
minimalists, it is notoriously miniature (only a few megabytes) and works great
even on the oldest and weakest devices. Miranda NG
is a powerful XMPP client program for Windows. There are also a few
web-based clients: https://conversejs.org/ and
https://web.xabber.com/ that you can try right
away without installing anything.
The final step is to fill the contact list (called roster) with the addresses
of the people (or maybe devices, because XMPP can be easily configured for
bots accepting commands). Just remember that the address is full name as in
email: user@server.domain. One useful option is so called Shared roster
groups: then you can configure
a group of contacts without the need to add them manually.
Happy chatting!
Further
There are many advanced options and possibilities in ejabberd. Just check
the documentation at the official web site: https://www.ejabberd.im/
and documentation https://docs.ejabberd.im/.
There are also a few useful tutorials, e.g.
https://www.process-one.net/blog/how-to-move-the-office-to-real-time-im-on-ejabberd/
Because Subversion works best (and can track) plain text files,
it is not well adapted for versioning normal Microsoft Office or
LibreOffice/OpenOffice documents. However, both are actually zipped XML
files. Therefore, it is possible both directly (binary) and using flat XML
text (full version control/merge support).
Microsoft Office
For Microsoft Office, there are extensions for Subversion:
Msofficesvnf,
OfficeSVN and
MagnetSVN.
Also, TortoiseSVN can use native Microsoft Word
"compare versions" tool to check for differences between versions. Check out
the Diff-Scripts in the TortoiseSVN installation directory. Note that these
scripts are js and can be blocked by corporate or university security policy:
ask the IT!
Subversion keywords
Subversion keywords (properties) can be managed in Microsoft Word files using
SvnProperties4MSOffice.
For more information see
https://gotomation.info/2019/01/svn-version-control-office-documents/.
If special software for adapting Office files is not used, it is
recommended to use Microsoft uncompressed XML formats for all
outputs. While they take more disk space (because it is unzipped), these
are plain text XML, so Subversion treats them very efficiently. Also, svn keywords/tags
can be used within the text without any additional tools.
LibreOffice or OpenOffice
For LibreOffice, the easiest way is to use .fodt format for saving
the document (instead of .odt or .docx), FODT is a flat XML format. A drawback
is that it is unzipped and takes much more disk space. But Subversion does not
store all versions of the whole file, it saves effectively differences between
the versions. Therefore, there is little or no overhead within the version control system
of working with fodt files.
Quite importantly, it is then trivial to add keywords to the fodt
file on the svn system. Then, it is easy to include normal svn
keywords/tags] such as $Revision 1234$ into whenever needed into
the fodt file and it will autoupdate on every commit without any
additional tools. But note that the whole tag $Revision 1234$
must have the same formatting (i.e. no bold/italic/other font within
and including the $ $ delimiters).
For more information see
https://wiki.documentfoundation.org/Libreoffice_and_subversion
and https://wiki.documentfoundation.org/Svn:keywords.
Conflicts
To avoid conflicts when several people are working concurrently with
svn-tracked files, use svn locks. This is because the files are like
binary and cannot be easily merged, unlike normal plain text code. In fact,
they could be merged, but do not always expect merge to work as expected
because the text file includes complex tags and these may be broken at merge.
It is also difficult to resolve conflicts visually. A useful trick is
to set this property on the file: svn propset svn:needs-lock "true"
file_name.fodt. Then, any svn update will result this file becoming
read-only. To allow editing, file lock must be enabled. This ensures that
only one user can edit the file at a time.
How differences between versions can be checked?
Because the Libreoffice files are not just text, checking differences
is not trivial. Normal diff tool will result in lots of messy XML
differences.
But there is a Linux bash script that helps comparing
the files through converting FODT to PDF and then running diffpdf
utility:
There is also a Windows/DOS batch script that does this trick:
The script requires diffpdf program that is found in most Linux
distributions. A Windows version is open source but id not normally distributed
in the binary ".exe" form
How to use diffodt script
-
Compare working copy with the latest revision from svn: diffodt paper.fodt
-
Compare the working document with r9925: diffodt 9925 paper.fodt
-
Compare two specific versions of the document: diffodt 9925 9987 paper.fodt
Integrating Subversion into LibreOffice User Interface
Lo_SVN is a LibreOffice extension that adds a basic Subversion functionality
into the LibreOffice interface. Then, basic svn commands are available from
the LibreOffice menu.
How do you make an array and initialize it with a sequence of values? For
example, I want a list from 0.25 to 1.5 that is separated with 0.25. In
other words I want something similar to seq(0.25,5,0.5) in R.
Equally spaced real array with fixed increment in Fortran
Producing an equally spaced array from V1 to VN with
increments ΔV
1. Each of the values in the above vector can be calculated as:
)
2. The total number of values N in the array ending with a fixed known
VN is equal to
3. It is not possible to use a simple piece of code like this to produce real type
array in Fortran:
4. Such a construction cannot be used in modern Fortran, even though old
versions could accept a similar construction based on implied loop with real
type index counter:
real :: r ! Index must be integer in loops!
print *, (r, r=V1,VN,Incr)
5. In modern Fortran standard do loops can only have integer indexing
variable. Real indexing in do loops is one of the very few features that
had been deleted from the language because it can create lots of problems
in float point computations due to finite precision in computer hardware.
The old code might work with modern compilers but it may require special
legacy compiler options. The printing-only code as above may still work but
would issue a compiler warning.
6. Initialising such equally spaced real type arrays in Fortran implied
loops must use the formulas defined in 1. and 2.
# Produce exactly N_VALS values starting from INIT with increments INCR
Array = [( INIT + INCR * (i-1), i=1,N_VALS )]
Where the number of array elements N_VALS is calculated as:
N_VALS = floor( (END - INIT) / INCR + 1 )
N_VALS = ceiling( (END - INIT) / INCR + 1 )
The floor and ceiling functions convert real value to integer as the lower
or upper nearest integer; they can give different values when division cannot
be done without the remainder
# All values starting from INIT with increments INCR and up to the limit END
Array = [( INIT + INCR * (i-1), i=1,floor((END-INIT)/INCR+1) )]
7. This code does not seem to be a very simple and elegant solution.
Ideally, the code should be packaged into a function returning the desired
grid array. But such function could not be used in declarations of array
parameters. In the later case the one-liner code should be used as above.
Integer arrays
By the way, it is quite easy to produce an integer array, e.g. here is an
initialisation for array from 1 to 100 (|1,2,3,...,100|). This can be
useful for indexing arrays.
integer, parameter, dimension(*) :: IDX_ARRAY = (/(i,i=1,100)/)
Examples:
A. Produce an array of 10 values starting from 1.0 with increments 0.1
Array = [( 1.0 + (i-1) * 0.1, i=1,10 )]
Result:
1.00000000 1.10000002 1.20000005 1.29999995 1.39999998
1.50000000 1.60000002 1.70000005 1.79999995 1.90000010
Declaration of a parameter array:
real, parameter, dimension(*) :: Array = [( 1.0 + (i-1) * 0.1, i=1,10 )]
However, note that not all compilers may support assumed array size
dimension(*) in such array declaration statement, this requires newer Fortran
standard (fortunately, recent versions of Intel and GNU Fortran do support
assumed size arrays). In such a case declaration must explicitly set the
number of array elements:
real, parameter, dimension(10) :: Array = [( 1.0 + (i-1) * 0.1, i=1,10 )]
B. Produce an array of starting from 1.0 to 2.0 with increments 0.145;
note that lower value (floor) for the array size is used:
Array = [( 1.0 + 0.145 * (i-1), i=1, floor((2.0-1.0)/0.145 + 1) )]
Result:
1.00000000 1.14499998 1.28999996 1.43499994 1.57999992
1.72499990 1.87000000
C. The same as (B) but the upper value (ceiling) for the array size is used:
Array = [( 1.0 + 0.145 * (i-1), i=1, ceiling((2.0-1.0)/0.145 + 1) )]
Result:
1.00000000 1.14499998 1.28999996 1.43499994 1.57999992
1.72499990 1.87000000 2.01499987
D. In the case B., declarations of parameter arrays can be done like this:
real, parameter, dimension(*) :: Array = &
[( 1.0 + 0.145 * (i-1), i=1, floor((2.0-1.0)/0.145 + 1) )]
or, if the compiler does not support assumed size arrays (*), with explicitly
calculated array size:
real, parameter, dimension(floor((2.0-1.0)/0.145 + 1)) :: Array = &
[( 1.0 + 0.145 * (i-1), i=1, floor((2.0-1.0)/0.145 + 1) )]
Test program
! This program illustrates how to produce equally spaced real vectors with
! fixed increment in Fortran.
!
! 1. Produce exactly N_VALS values starting from INIT with increments INCR
! Array = [( INIT + INCR * (i-1), i=1,N_VALS )]
!
! 2. All values starting from INIT with increments INCR and up to the limit END
! Array = [( INIT + INCR * (i-1), i=1,floor((END-INIT)/INCR+1) )]
!-------------------------------------------------------------------------------
program spaced_array
! Integer counter for implied loops defining vectors.
integer :: i
! Example A. Produce an array of 10 values
! starting from 1.0 with increments 0.1
real, parameter, dimension(*) :: Array1 = [( 1.0 + (i-1) * 0.1, i=1,10 )]
! Example B. Produce an array of starting from 1.0 to 2.0
! with increments 0.145.
! Note that lower value (floor) for the array size is used.
real, parameter, dimension(*) :: Array2 = &
[( 1.0 + 0.145 * (i-1), i=1, floor((2.0-1.0)/0.145 + 1) )]
! Example C. The same as (B) but the upper value (ceiling) for the
! array size is used.
real, parameter, dimension(*) :: Array3 = &
[( 1.0 + 0.145 * (i-1), i=1, ceiling((2.0-1.0)/0.145 + 1) )]
! Print the sizes of the arrays that were declared above.
print *, "Array sizes (Array1, Array2, Array3)", &
size(Array1), size(Array2), size(Array3)
! Print the parameter arrays that were declared above.
print *, "Array1", Array1
print *, "Array2", Array2
print *, "Array3", Array3
end program spaced_array
PDF Card
A PDF version of this document is available here: https://budaev.info/images/spaced-array.pdf.
The HEDTOOLS
tools library has a module for working with random numbers
BASE_RANDOM. There is, in
particular, a set of procedures for generating
Gaussian random values: RNORM
and RNORM_ARRAY.
These are based on the Kinderman & Monahan, augmented with quadratic
bounding curves method (Leva, 1992: algorithm 712, Trans. Math. Software,
18, 4, 434-435).
I have made a quick comparison of the quality of the Gaussian random numbers
generated by the simple Box-Muller method (Box & Muller, 1958)
Classical (ancient) Fortran code:
normrand_number = dsqrt(-2.*dlog(drand(0)))*dcos(2.*pi*drand(0))
that has been used in TEG codes so far...
and the algorithm 712 as implemented in HEDTOOLS using this test program
(see attachment).
Fortran code for the test program:
program test_bm
use csv_io
use base_random, rand_x => rand ! Alias rand() as rand_x() for ifort.
!use IFPORT, only : rand_x => rand ! This is the Intel Fortran tweak.
integer, parameter :: prec = 8, arrsize=100000
character(len=255), parameter :: filename1="file_01.csv", filename2="file_02.csv"
real(kind=prec), dimension(arrsize) :: norand1, norand2
real :: timer_start, timer_end
!-------------------------------------------------------------------------------
! Generating Box-Muller random numbers
call cpu_time(timer_start) ! START
do i=1, arrsize
norand1(i) = sqrt(-2.*log(rand_x(0)))*cos(2.*pi*rand_x(0))
end do
call cpu_time(timer_end) ! END
print *, "Box-Muller took: ", timer_end - timer_start
! Write random normal data to CSV
call CSV_MATRIX_WRITE(norand1, filename1)
!-------------------------------------------------------------------------------
!-------------------------------------------------------------------------------
! Generating based on algorithm 712
call cpu_time(timer_start) ! START
call RNORM_ARRAY(norand2)
call cpu_time(timer_end) ! END
print *, "Alg. 712 took: ", timer_end - timer_start
! Write random normal data to CSV
call CSV_MATRIX_WRITE(norand2, filename2)
!-------------------------------------------------------------------------------
end program test_bm
Comparison of Box-Muller and A712
The alg. 712 looks slightly faster than the simple Box-Muller transform.
alg. 712 is much better, as the Box-Muller significantly deviates from the
normal distribution, alg. 712 does not (using the Anderson-Darling test from
the nortest R package).
# Gaussian random numbers by Box-Muller deviate from the Normal distribution:
> ad.test(data_bm$X1)
Anderson-Darling normality test
data: data_bm$X1
A = 581.7, p-value < 2.2e-16
# Gaussian random numbers by Kinderman & Monahan's A712 do not deviate from the Normal distribution:
> ad.test(data_a712$X1)
Anderson-Darling normality test
data: data_a712$X1
A = 0.46975, p-value = 0.2474
So, the alg. 712 procedure implemented in HEDTOOLS should be used instead
of the Box-Muller method.
References
-
Box, G. E. P., & Muller, M. E. (1958). A note on the generation of
random normal deviates. The Annals of Mathematical Statistics, 29(2),
610–611. http://doi.org/10.1214/aoms/1177706645
-
Leva, J. L. (1992). Algorithm 712; a normal random number
generator. ACM Transactions on Mathematical Software, 18(4),
454–455. http://doi.org/10.1145/138351.138367