I had issue on last flectra 1.7 install on ubuntu 20.04 command in snippets sudo npm install -g less less-plugin-clean-css rtlcss -y have installed v4.0.0 of less package which makes flectra crash. I needed to revert to less@3.13.0 to make the application works properly.

Small edit to help this script run without error on Ubuntu 20.4 at clean installation

#!/bin/bash
sudo adduser --system --quiet --shell=/bin/bash --home=/opt/flectra --gecos 'flectra' --group flectra
sudo mkdir /etc/flectra && mkdir /var/log/flectra/
sudo apt-get update && apt-get upgrade -y && apt-get install postgresql postgresql-server-dev-12 build-essential python3-pillow python3-lxml python3-dev python3-pip python3-setuptools npm nodejs git gdebi libldap2-dev libsasl2-dev  libxml2-dev libxslt1-dev libjpeg-dev -y
sudo service postgresql restart
git clone --depth=1 --branch=1.0 https://gitlab.com/flectra-hq/flectra.git /opt/flectra/flectra
sudo chown flectra:flectra /opt/flectra/ -R && sudo chown flectra:flectra /var/log/flectra/ -R && cd /opt/flectra/flectra && sudo pip3 install -r requirements.txt
sudo apt-get install software-properties-common
sudo apt install nodejs npm
sudo npm install -g less@3.13.0 postcss@^8.2.1 less-plugin-clean-css rtlcss -y
cd /tmp && wget https://github.com/wkhtmltopdf/wkhtmltopdf/releases/download/0.12.5/wkhtmltox_0.12.5-1.bionic_amd64.deb && sudo gdebi -n wkhtmltox_0.12.5-1.bionic_amd64.deb && rm wkhtmltox_0.12.5-1.bionic_amd64.deb
sudo ln -s /usr/local/bin/wkhtmltopdf /usr/bin/ && sudo ln -s /usr/local/bin/wkhtmltoimage /usr/bin/
sudo su - postgres -c "createuser -s flectra"
sudo su - flectra -c "/opt/flectra/flectra/flectra-bin --addons-path=/opt/flectra/flectra/addons -s --stop-after-init"
sudo mv /opt/flectra/.flectrarc /etc/flectra/flectra.conf
sudo sed -i "s,^\(logfile = \).*,\1"/var/log/flectra/flectra-server.log"," /etc/flectra/flectra.conf
sudo sed -i "s,^\(logrotate = \).*,\1"True"," /etc/flectra/flectra.conf
sudo sed -i "s,^\(proxy_mode = \).*,\1"True"," /etc/flectra/flectra.conf
sudo cp /opt/flectra/flectra/debian/init /etc/init.d/flectra && chmod +x /etc/init.d/flectra
sudo ln -s /opt/flectra/flectra/flectra-bin /usr/bin/flectra
sudo update-rc.d -f flectra start 20 2 3 4 5 .
sudo service flectra restart

some extra note:

• change worker on flectra.conf >0
• install nginx with detail config as below:
• install certbot with detail:

sudo apt install certbot python3-certbot-nginx

vi /etc/nginx/conf.d/domain.conf

upstream flectra {
    server 0.0.0.0:7073 weight=1 fail_timeout=300s;
}
upstream flectra-im {
    server 0.0.0.0:7072 weight=1 fail_timeout=300s;
}
server {
    # server port and name
    listen 80;
    server_name    domain.com;

    # Specifies the maximum accepted body size of a client request, 
    # as indicated by the request header Content-Length. 
    client_max_body_size 200m;
    #log files
    access_log    /var/log/nginx/flectra-access.log;
    error_log    /var/log/nginx/flectra-error.log;
    
    proxy_connect_timeout       600;
    proxy_send_timeout          600;
    proxy_read_timeout          600;
    send_timeout                600;
    keepalive_timeout    600;
    
    gzip on;
    gzip_disable "msie6";
    gzip_vary on;
    gzip_proxied any;
    gzip_comp_level 6;
    gzip_buffers 16 8k;
    gzip_http_version 1.1;
    gzip_types text/plain text/css application/json application/javascript application/x-javascript text/xml application/xml application/xml+rss application/rss+xml text/javascript image/svg+xml application/vnd.ms-fontobject application/x-font-ttf font/opentype image/bmp image/png image/gif image/jpeg image/jpg;
	
    # increase proxy buffer to handle some OpenERP web requests
    proxy_buffers 16 64k;
    proxy_buffer_size 128k;
    location / {
        proxy_pass    http://flectra;
        # force timeouts if the backend dies
        proxy_next_upstream error timeout invalid_header http_500 http_502 http_503;
	# Add Headers for odoo proxy mode
	# set headers
 	proxy_set_header X-Forwarded-Host $host;
 	proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
 	proxy_set_header X-Forwarded-Proto $scheme;
 	proxy_set_header X-Real-IP $remote_addr;
        # by default, do not forward anything
        # proxy_redirect off;
    }
    location /longpolling {
    	 proxy_pass    http://flectra-im;
    }
    # cache some static data in memory for 60mins.
    # under heavy load this should relieve stress on the web interface a bit.
    location ~* /web/static/ {
        proxy_cache_valid 200 60m;
        proxy_buffering    on;
        expires 864000;
        proxy_pass http://flectra;
    }
} 

certbot --nginx -d domain.com

systemctl restart nginx

systemctl restart flectra

Just updated another version of this Snippet with detail process for beginer to install new Flectra or Convert from Odoo 11 to flectra:

https://gitlab.com/gimitec/flectra/-/snippets/2057602