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Sharing your keyboard and mouse at the login screen

Updated

Written for Synergy 3 (v3.8.4) and Synergy 1 (v1.22.3), checked 20 October 2026.

Use your shared keyboard and mouse on a computer's login screen, before anyone logs in, for example to type your password on a client computer after it restarts.

On Windows, Synergy 1 and Synergy 3 both do this by default. The settings that do it also let you answer UAC prompts: Sharing your keyboard and mouse on UAC prompts

To have the app start by itself when you log in, see: Starting automatically at login

What follows depends on your product: Synergy 3 or Synergy 1

Synergy 3

On macOS, Synergy 3 does this once you turn on a setting.

Windows

Synergy 3 works on the Windows login screen by default, after a restart too, as long as sharing wasn't paused. Its background service does this, with two settings that stay on unless someone turns them off. If the login screen doesn't respond to your shared keyboard and mouse, check them:

  1. Open Synergy 3.
  2. Under Advanced, click Miscellaneous.
  3. Turn on Run in the background service (for UAC prompts and the login screen).
  4. Turn on Run as system to allow UAC interaction.

Run on the login screen, in Local settings, is needed only on macOS.

macOS

  1. Open Synergy 3.
  2. Under Advanced, click Local settings.
  3. Under Login screen, turn on Run on the login screen.
  4. When macOS asks, enter an administrator's password to allow the change.

If you see Could not enable run on login screen., Synergy 3 didn't get the permission it needs. Turn the setting on again, and allow the change when macOS asks.

The setting applies only to the Mac you turn it on for, so turn it on on each Mac whose login screen you want to use. The other settings on that page are described in: Local settings in Synergy 3: updates, appearance, login screen and config file

Mac with FileVault turned on

After your Mac restarts, type your password on the Mac's own keyboard at the first login screen. FileVault asks for your password before macOS has fully started up, and Synergy 3 can't run until then.

If you need Synergy 3 to work on that first screen as well, you'll have to turn off FileVault. Before you do: turning off FileVault removes a layer of protection, so someone with physical access to your Mac no longer needs your password to get at your data. Weigh that trade-off before you turn it off.

  1. Choose Apple menu > System Settings.
  2. Click Privacy & Security in the sidebar.
  3. Click FileVault (you may need to scroll down).
  4. Turn off FileVault.
  5. Click Turn Off Encryption.

Once decryption has finished, restart your Mac to check that Synergy 3 works on the login screen.

Linux

On Linux, type your password on the computer's own keyboard at the login screen; Synergy 3 connects once you've logged in. Synergy 3 can't run on the Linux login screen, so Run on the login screen is greyed out there.

Synergy 1

On Linux, Synergy 1 can do this with a workaround.

Windows

Synergy 1 works on the Windows login screen through its daemon, while both of these settings are on (they are by default):

  1. Open Synergy 1.
  2. Go to Edit > Preferences.
  3. On the Advanced tab, check Use background service (daemon).
  4. Check Always run as system (work at login screen and UAC).
  5. Click Save.

The service then runs Synergy 1 on the login screen after a restart too, before anyone logs in, as long as Synergy 1 was running when the computer shut down.

macOS

On a Mac, type your password on the Mac's own keyboard at the login screen. Synergy 1 runs only once a user has logged in, so it can't control the macOS login screen; Synergy 3 can, with the steps for Synergy 3 on macOS above.

Linux

These steps run the Synergy 1 core on a Linux client computer at the login screen, so you can log in with the server's keyboard and mouse. The core reads everything it needs (the server address, this computer's name, TLS and language sync) from the settings Synergy 1 has already saved, so set Synergy 1 up and get it connecting once in the normal way before you start.

Before you start: these steps only work when the login screen runs on X11, with GDM as the display manager. They do not work on a Wayland login screen, which is the default on current Ubuntu and Fedora releases. Running Synergy 1 at the login screen on Linux is not a built-in feature, so treat these steps as a workaround that our support team can't guarantee.

The service below runs the same core command as running Synergy 1 by hand, explained for every version in: Running from the command line

These steps are for Synergy 1 (v1.21 and later), installed from its DEB, RPM or Arch package rather than the Flatpak. On Synergy 1 (v1.20 and earlier), change the lines in the last section: Synergy 1 (v1.20 and earlier)

Step 1: Copy your Synergy 1 settings where the login service can read them

On the client, after Synergy 1 has connected to the server at least once (so that it trusts the server's TLS fingerprint), copy its settings and TLS folder:

sudo mkdir -p /etc/synergy-login
sudo cp ~/.config/Synergy/Synergy.conf /etc/synergy-login/
sudo cp -r ~/.config/Synergy/tls /etc/synergy-login/

Synergy 1 reads its TLS certificate and trusted fingerprints from the tls folder beside the settings file it is given, so the copy carries the trust over. Repeat this step whenever you change the settings.

Step 2: Create the wrapper script

sudo nano /usr/local/bin/synergy-login.sh

Copy and paste the following script:

#!/bin/bash
LOGFILE="/var/log/synergy-login.log"
echo "[$(date)] Starting synergy-login.sh" >> "$LOGFILE"
export DISPLAY=:0
export XAUTHORITY="/run/user/$(id -u gdm)/gdm/Xauthority"
# Wait for X session to be ready
while [ ! -f "$XAUTHORITY" ]; do
echo "[$(date)] Waiting for XAUTHORITY..." >> "$LOGFILE"
sleep 1
done
sleep 2
echo "[$(date)] XAUTHORITY found, launching synergy-core" >> "$LOGFILE"
while true; do
/usr/bin/synergy-core client --settings /etc/synergy-login/Synergy.conf >> "$LOGFILE" 2>&1
echo "[$(date)] synergy-core exited. Retrying in 5s..." >> "$LOGFILE"
sleep 5
done

Make it executable:

sudo chmod +x /usr/local/bin/synergy-login.sh

Step 3: Create the systemd service

sudo nano /etc/systemd/system/synergy.service

Copy and paste the following:

[Unit]
Description=Synergy 1 client at login screen
After=gdm.service network-online.target
Wants=network-online.target

[Service]
ExecStart=/usr/local/bin/synergy-login.sh
User=root
Restart=always
RestartSec=5

[Install]
WantedBy=graphical.target

Enable and start the service:

sudo systemctl daemon-reload
sudo systemctl enable synergy
sudo systemctl restart synergy

Step 4: Reboot and test

Reboot to test:

sudo reboot

After reboot:

  1. Wait at the login screen.
  2. Switch to a text console (Ctrl+Alt+F3).
  3. Log in.
  4. Check the log: 
    sudo tail -n 30 /var/log/synergy-login.log

You should see lines ending like these, each after a timestamp:

INFO: started client
INFO: connected to secure socket

The second line appears only when TLS is on.

Synergy 1 (v1.20 and earlier)

On these versions, the client runs as synergy-client with its settings on the command line, so change these lines in the steps above. What each option does, and how to leave out TLS: Running from the command line

In Step 1, copy the folder where these versions keep the servers they trust:

sudo mkdir -p /etc/synergy-login
sudo cp -r ~/.synergy /etc/synergy-login/profile

In Step 2, use this line in the script in place of the synergy-core line:

/usr/bin/synergy-client -f --name [computer name] --enable-crypto --profile-dir /etc/synergy-login/profile [server IP address] >> "$LOGFILE" 2>&1

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