How to install and use Signal messenger without a smartphone

(Last Updates: PC Operating system on 26.01.2022; Using Groups v2 on 27.03.2021; Using signal-cli as a user systemd daemon on 18.05.2020.)

Signal is an encrypted end-to-end messenger for Android, iOS and Desktop OS (Windows, MacOS and Debian). In this tutorial we discuss how to install and use it without a smartphone.

Please note that we tested this manual on a Linux PC using the Linux shell. The described process may work when using the shell on Mac or the PowerShell on Windows, but we are not sure since we have never tried it.

Signal-cli + Signal-Desktop

Signal-cli is a command line interface for Signal. It’s used to register a new signal account and then link a Signal-Desktop app to this account. If you really use Signal without a smartphone, signal-cli functions as the single-point-of-truth.

Go to the following link and download the latest signal-cli release: https://github.com/AsamK/signal-cli/releases/latest

In our case this is v0.6.2

  $ wget https://github.com/AsamK/signal-cli/releases/download/v0.6.2/signal-cli-0.6.2.tar.gz
  $ tar xfv signal-cli-0.6.2.tar.gz
  $ cd signal-cli-0.6.2

To be able to use Signal you have to register yourself with a phone number (doesn’t has to be a mobile number).

  $ bin/signal-cli -u YOUR_NUMBER register

You will then get a SMS with a verfication number if it’s a mobile number or else a call. You use this number then to verify your account:

  $ bin/signal-cli -u YOUR_NUMBER verify VERIFICATIONCODE

Install the latest version of Signal-Desktop from here: https://signal.org/download/

Now you have to start Signal-Desktop and extract the actual QR-Code. For this, start Signal-Desktop. It should display a barcode to link your Signal-Desktop app to a Signal device. You can either decode the barcode on your local machine or use a smartphone to scan the barcode.

Android:

1. Install Barcode Scanner on your device
2. Scan barcode and tsdevice-Link should appear

Linux:

1. Toggle Developer Tools, go to Network Tab
2. search for data:image/png entry, click on it and the actual barcode should be displayed
3. Right click on the bar code to save it for instance as /tmp/qr.png
4. use zbarimg (zbar-tools) to decode it:

   $ zbarimg /tmp/qr.png
   QR-Code:tsdevice:/?uuid...

5. Copy tsdevice-Link

Now you can link your Signal-Desktop to your Signal account through signal-cli:

  $ bin/signal-cli -u YOUR_NUMBER addDevice --uri "tsdevice:/?uuid..."

Add contacts

We use signal-cli daemon to synchronise contacts (with names^^) with our Signal-Desktop instance.

On Ubuntu, you have to install libunixsocket-java package (otherwise the signal-cli daemon can’t start)

Fill in contacts in the signal-cli config: .local/share/signal-cli/data/YOUR_NUMBER in the dict

   "contactStore" : {
     "contacts" : [ {
       "name" : "name",
       "number" : "+49xxxx"
     }, {
       "name" : "name2",
       "number" : "+49yyyyy",
     }]}

Start signal-cli daemon:

  $ bin/signal-cli -u YOUR_NUMBER daemon

And then synchronise contacts in the Signal Desktop App (File->Preferences->Contacts->Import Now)

Using groups v2

In October 2020 Signal introduced groups v2 . These offer some (security) features such as more granular permissions and actual admins and further stuff like @mentioning specific people.

In order to be able to use the new groups with your stand-alone signal-cli + signal-Desktop setup, you have to update your signal profile, since up to this point no “proper” user profile existed for your account if you didn’t have the mobile app.

Update profile (for example adding a name and an avatar):

  $ bin/signal-cli -u YOUR_NUMBER updateProfile --name my_name --avatar ./my_avatar.jpg

Troubleshooting

• If signal-cli daemon reports following error

Envelope from: <yournumer> (device: 2)
Timestamp: xxxxx
Exception: org.whispersystems.libsignal.InvalidMessageException: No valid sessions. (ProtocolInvalidMessageException)
Failed to decrypt message.

then:

  $ bin/signal-cli -u YOUR_NUMBER send -e -m "foo" YOUR_NUMBER

• In the same config, set the Active parameter for all groups to true, in order to be able to send messages in groups.

Signal-cli as a daemon

You may want to run signal-cli as a user systemd service to prevent that the key material gets out of sync for signal-cli.

Symlink the signal-cli executable to ~/.bin/signal-cli:

  $ ln -s <ABSOLUTE-PATH-TO>/signal-cli-0.X.X/bin ~/.bin/signal-cli

(This way you only have to update the symlink and not all the configs, if you get a newer signal-cli version.)

Add following line to your ~/.bashrc or ~/.bash_profile:

export PATH=$PATH:$HOME/.bin

And place following systemd service config in ~/.config/systemd/user/signal-cli@.service:

[Unit]
Description=Signal cli for %I
Requires=dbus.socket
After=dbus.socket
Wants=network-online.target
After=network-online.target

[Service]
Type=dbus
Environment="SIGNAL_CLI_OPTS=-Xms2m"
ExecStart=%h/.bin/signal-cli -u %I daemon --ignore-attachments
BusName=org.asamk.Signal

[Install]
WantedBy=multi-user.target

Start the service with:

  $ systemctl --user start signal-cli@<YOUR NUMBER>

And verify it is running with:

  $ systemctl --user status signal-cli@<YOUR NUMBER>

If you change something in the config, stop the service:

  $ systemctl --user stop signal-cli@<YOUR NUMBER>

reload the daemon:

  $ systemctl --user daemon-reload

And start it again.

That’s it! Happy messaging.