Install Loki and start as service.

Download Loki:

cd /usr/local/bin   
curl -O -L "https://github.com/grafana/loki/releases/download/v2.4.1/loki-linux-amd64.zip"   
unzip "loki-linux-amd64.zip"

Allow exec permissions:

chmod a+x "loki-linux-amd64"

Create Loki config file:

sudo nano config-loki.yml

Put code in the file:

auth_enabled: false
server:
  http_listen_port: 3100
  grpc_listen_port: 9096
common:
  path_prefix: /tmp/loki
storage:
  filesystem:
    chunks_directory: /tmp/loki/chunks
    rules_directory: /tmp/loki/rules
replication_factor: 1
ring:
  kvstore:
    store: inmemory
schema_config:
  configs:
    - from: 2020-10-24
      store: boltdb-shipper
object_store: filesystem
schema: v11
index:
  prefix: index_
  period: 24h
ruler:
  alertmanager_url: http://localhost:9093

Config from here: https://raw.githubusercontent.com/grafana/loki/master/cmd/loki/loki-local-config.yaml

Configure Loki as a service:

Create user for Loki service:

sudo useradd --system loki

Create Loki service:

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

[Unit]
Description=Loki service
After=network.target

[Service]
Type=simple
User=loki
ExecStart=/usr/local/bin/loki-linux-amd64 -config.file /usr/local/bin/config-loki.yml

[Install]
WantedBy=multi-user.target

sudo service loki start 
sudo service loki status