Setup a PiHole and add them to the blocklist. Then make the PiHole password stupid long and write it down. Then take the paper, put it in a safe, and put it in the highest shelf in the back of your closet. Recurse safes and passwords as much as needed.

You’re gonna have better luck changing your habits than you will making a block that you yourself can’t overcome.

Therapy of some sorts is probably going to be more effective than making self-blocks, especially if you're technically competent. I wish you luck with stopping whatever addiction it is.

/etc/hosts and set the websites to go to 0.0.0.0 or 127.0.0.1

Any of the adblockers can do this. Pihole, adguard home, technitium. Ublock origin to. You can probably do it pretty painstakingly through the hosts file as well.

Maybe block on your router and save your router password such that you need to jump through several hoops to unlock it, eg password saved in one password manager DB whose master password is in another DB whose password is in another DB, etc. If you have to unlock like 10 password databases to get into your router, you'll probably give up on whatever bad habit you were trying to do as it's too much effort.

https://greasyfork.org/en/scripts/1682-google-hit-hider-by-domain-search-filter-block-sites

DNS... set your system up to use an external DNS provider like OpenDNS where you can select categories to block.

I used this to block adult, gambling, malware, etc at the grandparent's house when the kids were growing up and starting to search the internet for school homework, etc.

If it's done in the router you'll cover all devices and you give someone else the password, so you can't change it.

Only thing I can think of is to remove your default account from the sudoers file and have an account with a frustratingly long password written on physical paper hold the keys to the kingdom. That will make a whole lot of other things a hurdle too though.

Therapy is probably a better option.

LeechBlock NG isn't exactly what your'e looking for but it still may help. Of course, it'll have no effect if UBO and the DNS already shut everything off.

If redirecting with /etc/hosts isn't enough, you could set up a cron job (I guess as root?) to re-copy a hosts file back to /etc/hosts every half hour or something. That way even if you do manually change /etc/hosts for an quick peak of an illicit website, it'll go back to being blocked in a short amount of time. This'll add a bit of the "pain in the ass" factor.

I use NextDNS and it has feature to block domains. Unfortunately i often unblock it back.

use the redirector addon to auto redirect somewhere else

Private DNS service.

Don't look for a solution that is technical where the problem is mental.

thanks for the great technical suggestions everyone

You can use iptables to block connections, by example, using ufw the uncomplicated firewall:

# apt install ufw bind9-dnsutils  #  Install ufw and nslookup
# uIPs=$((nslookup reddit.com && \
  nslookup www.reddit.com && \
  nslookup redd.it && \
  nslookup redditstatic.com && \
  nslookup www.redditstatic.com) \
  | awk '/^Address: / { print $2 }' | sort -u); \
for uip in ${uIPs}; do \
  echo -n "${uip} " &&  \
  ufw deny from "${uip}" comment 'deny reddit.com'; \
  ufw deny out to "${uip}" from any comment 'deny reddit.com'; \
done;
# ufw enable
# ufw status numbered

i'm curious what websites are you doing. what's the threat model??

NextDNS is a good option for your use case. It allows you to block entire categories of websites and even has an option to setup a schedule on when you are allowed to access them. It also has blocklists you can pick from and the ability to blacklist and whitelist individual domains. And the free plan is very generous. You can just try it and see how it works for you.

See a psychiatrist. You already have root on these systems... if you are truly a split personality then fences aren't going to prevent your other self from doing whatever they want.