How to run Slicer as a Daemon

The term "daemon" is a well established phrase from UNIX meaning a process that runs in the background. Daemons are usually managed by an init system which can monitor and restart them.

Do you need to run Slicer as a systemd service right off the bat? It depends.

You may not need a systemd service if you're still in the development and testing phase. It's easier and more convenient to start running Slicer in a tmux. You can attach and detach as you like, and it'll stay running in the background. A permanent service comes in useful when you need to run Slicer on boot-up and to ensure it gets restarted if it crashes for any reason. Learn how Alex uses tmux to run processes in the background.

Not only can we monitor Slicer's logs via journalctl, but we can manage it with standard systemctl commands.

You can run one or many Slicer daemons in this way, just make sure the host group CIDRs do not overlap, and that the API binds to a different UNIX socket or a different TCP port.

Let's say you wanted to create a service for a hostgroup named "vm":

mkdir -p ~/vm/
cd ~/vm/
slicer new vm > ./slicer.yaml

To listen on a UNIX port instead, use slicer new vm --api-auth=false --api-bind ./slicer.sock > ./slicer.yaml.

Create a service named i.e. vm.service:

[Unit]
Description=Slicer for vm

[Service]
User=alex
Type=simple
WorkingDirectory=/home/alex/vm
ExecStart=sudo /usr/local/bin/slicer up ./slicer.yaml
Environment=SUDO_USER=alex
Restart=always
RestartSec=30s
KillMode=mixed
TimeoutStopSec=30

[Install]
WantedBy=multi-user.target

Next, make sure the target user i.e. alex has password-less sudo permissions to run slicer:

Run visudo, then add this line to the end of the file, replacing alex with your username:

alex ALL=(ALL) NOPASSWD: ALL

Or you could be more specific and only allow slicer to elevate to sudo for your user:

export USER=alex

echo "$USER ALL=(ALL) NOPASSWD: /usr/local/bin/slicer" | sudo tee /etc/sudoers.d/$USER-slicer

Install the service, and set it to start up on reboots:

sudo cp ./vm.service /etc/systemd/system/
sudo systemctl daemon-reload
sudo systemctl enable --now vm.service

Assuming you went for the UNIX socket option, you could run i.e.

sudo slicer --url ~/vm/slicer.sock vm list
HOSTNAME                  IP              RAM          CPUS     STATUS     CREATED              TAGS                
--------                  --              ---          ----     ------     -------              -----               
vm-1                      192.168.137.2   4GiB         2        Running    2026-02-27 16:30:53      

For the TCP option (with the default port of 8080), you'd run:

sudo slicer vm list
HOSTNAME                  IP              RAM          CPUS     STATUS     CREATED              TAGS                
--------                  --              ---          ----     ------     -------              -----               
vm-1                      192.168.137.2   4GiB         2        Running    2026-02-27 16:30:53      

To view the logs for the service run:

# Page through all logs
sudo journalctl -f --output=cat -u vm

# Page through all logs
sudo journalctl --output=cat -u vm

# View all logs since today/yesterday
sudo journalctl --output=cat --since today -u vm
sudo journalctl --output=cat --since yesterday -u vm

To stop the service run sudo systemctl stop vm, and to prevent it loading on start-up run: sudo systemctl disable vm.

You can create multiple Slicer services to run different sets of VMs or configurations on the same host.