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I've been doing more research into system administration recently, and I have created a checklist of things to do when you need to secure an Ubuntu machine. This guide is not strictly for Ubuntu but commands were ran on an Ubuntu machine. Most of the things in this checklist more advanced Linux users will already know, but I figured this would be a good starting point for newer Linux users. Here is the checklist for people that would not like to read the entire thread, but more detailed explanation's how to do everything in this list is inside this thread. Update your system Setup automatic updates Create a low privileged user Create SSH private public key pair Secure SSH config Setup firewall Disable ping requests When securing a machine, the very first thing you will need to do is ensure that all your packages are up to date. Believe it or not, a most vulnerabilities lay inside of packages that are not updated to the most recent stable version. Ensue your machine is updated by doing the following. sudo apt update && sudo apt upgrade Now that your machine is updated. Lets install a package to have updates be installed automatically. For this run sudo apt install unattended-upgrades -y Now we need to ensure that auto updates are active. Run the following command sudo nano /etc/apt/apt.conf.d/50unattended-upgrades After the file loads you will see towards a top a line that reads "${distro_id}:${distro_codename}-updates"; Ensure this line IS NOT COMMENTED OUT (Remove the // at the beginning of the line) After this, I like to setup my new user. To do this run the following command. adduser {User Name} Now that the user has been created, I will give this user sudo permissions. Run the following command sudo usermod -aG sudo {User Name} Now we can switch to this user to start setting up our SSH keys run su {User Name} Now that we have our user setup, we need to ensure that our SSH connection is secure. Lets start by creating our users ssh directory to store the public key file. sudo mkdir /.ssh && sudo chmod 700 /.ssh Now on your local machine, open whatever terminal your using. (CMD, Bash Terminal, etc.) and lets create our private public key pair ssh-keygen -t rsa -b 4096 This will create two files as an output, an ID_RSA and ID_RSA.pub The file that has the .pub extension is our public key that we need to get on the server into the users .ssh folder we just created. The ID_RSA file is your private key to login to the machine, never send this to anyone. Before we edit the config, disable your firewall on the machine, (We will change SSH Port, and do not want to be locked out. We will also re enable this after.) Run sudo ufw disable Now that our keys have been created and we moved the public key to the server, we will need to edit the config of the SSH server. Run the following sudo nano /etc/ssh/sshd_config Now that we are in the file, we will want to do a few things. Change port Set "AddressFamily" to "inet" (This will disable IPV6 Authentication) Set "PermitRootLogin" to "no" (This will disable root login over ssh) Set "PasswordAuthentication" to "no" (This will disable password authentication to ensure that we only can use keys) Create a new line that reads "AllowUsers {Username}" (This will ensure that only users added in this file on this line, will be able to login via SSH) After you do this you will need to restart your ssh server. (Ensure you did not mess anything up at this point, because if you do there is a change you can be locked out of your machine.) To restart SSH ru sudo systemctl restart sshd Now we will configure our firewall to work with our needs. The first command I like to run is sudo ss -tupln This will give me an idea of what ports are being used for the machine, you should also look through this for things to disable. Now that we know what ports we are utilizing, lets add those ports to the firewall rules (DONT FORGET YOUR SSH PORT THAT WE CHANGED). To add a port to the firewall rule run sudo ufw allow {port} At this point we can start our firewall again. Run Code sudo ufw enable Another thing I like to do is disable ping requests to the server. To do this run Code sudo nano /etc/ufw/before.rules Under the line that reads "#ok icmp codes for INPUT" add the following Code -A ufw-before-input -p icmp --icmp-type echo-request -j DROP Now that we have saved this file, in order for this to take affect you must reboot your machine, run Code sudo reboot

Note that this is not officially stated by Youtube, but reported by users and proven on youtube site itself. Youtube probably somewhere around apple keynote event updated their URL system, now working in JSON. This broke all apps from youtube-dl through 3rd party youtube clients to youtube video and music download/ripping sites (those that actually just passed the webm link to video file on google) and now uses some authentication methods (based on my IP, timeout and other things being in the URL) The most notable mentions are as said youtube-dl, whose hotfix has as of writing this already been published, but no tested version - bugs expected - NewPipe (3rd party youtube client I am personally using! and onlinevideoconverter.com/ytmp3.cc and others. It is predicted that this update was intentional on breaking the download sites, instead of just better security for direct video files. From: https://github.com/TeamNewPipe/NewPipe/issues/2615

Hello again I have run into a problem with this satement: SELECT result.project_id, result.seconds_elapsed_issue FROM ( SELECT iss.project_id, inter.issue_id, SUM(seconds_elapsed) AS seconds_elapsed_issue FROM intervals inter LEFT JOIN issues iss ON iss.issue_id = inter.issue_id WHERE dt_start BETWEEN "2018-01-01T00:00:00Z" AND "2018-10-05T23:59:59Z" GROUP BY inter.issue_id ) AS result GROUP BY project_id; I get the error: [42000][1055] Expression #2 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'result.seconds_elapsed_issue' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by. can anyone explain what's going wrong here?

I am planning to make an app for the metro system in my city. I am stumped as to how to implement the backend if I know the source and destination. I basically want to make a clean user-friendly app that gives the info shown in the photo(From Official website) http://www.delhimetrorail.com/metro-fares.aspx Any Sort of help is appreciated. I am completely stumped

Hello! I have a question regarding some tables I want to join to retrieve information about some time spent on different projects. I have three tables: projects p COLS: | id(PK) | project_id | project_name | deleted | hourly_rate | issues i COLS: | id(PK) | issue_id | issue_name | is_open | project_id | internal_note | intervals iv COLS: | id(PK) | manuscript_person_id | issue_id | interval_id | seconds_elapsed | Now - I need to join these three together so I get total elapsed seconds in a project based on the issues in the given projects. The the `p.project_name` must not start with the prefix "K - ". The `i.internal_note` must not contain the letters in the following order "SKIF" I have written a query that fetches all projects that doesn't contain the prefix "K - ": SELECT p.project_id, p.hourly_rate FROM projects p WHERE p.project_name NOT LIKE "K - %" And I have also written a query that finds all issues in those projects that does not have the "K - " prefix and internal_note does not contain "SKIF" SELECT i.issue_id, i.internal_note FROM issues i JOIN projects p ON i.project_id = p.project_id WHERE project_name NOT LIKE "K - %" AND i.internal_note NOT LIKE "%SKIF%" My problem now lies in tying these together with the summed up elapsed seconds from intervals grouped first by i.issue_id and then by p.project_id in the end so I will end up with a result that looks like so: | p.project_id | p.hourly_rate | some_join.elapsed_seconds | ----|--------------|---------------|---------------------------| 1 | 836 | 900 | 367929 | ----|--------------|---------------|---------------------------| 2 | 928 | 950 | 367929 | ----|--------------|---------------|---------------------------| 3 | 1125 | 942 | 367929 | ----|--------------|---------------|---------------------------| 4 | 1337 | 827 | 367929 | ---------------------------------------------------------------- etc..... How would one suggest to attack this problem?