Category Archives: Linux

dotnet says the runtime and sdk exists on Linux but Rider and Visual Code thinks they don’t

As part of my Macbook Air using Linux Mint, I’ve been getting my development environments set up.

I got .NET 8 and .NET 9 installed so that running both of the following listed them

dotnet --list-sdks
dotnet --line-runtimes

But Visual Studio Code and Rider complain that .NET 8 and .NET 9 need to be installed.

It was this Stackoverflow post that had the answer.

I deleted the /etc/dotnet folder as per the previous link suggests and things started working.

Installing Linux on my old Macbook Air

I’ve an old Intel based Macbook Air which, unfortunately Apple no longer support updates for, it’s a great little machine which I want to keep running. So, I do what I always do when the OS outgrows the hardware, I install Linux on it.

I would usually install Ubuntu but thought I’d try something lighter weight, by installing Linux Mint.

  • The first thing we need to do is download the ISO from the Linux Mint site (I went with the Cinnamon Edition).
  • New we need to write the ISO to a USB drive to create a bootable USB, I used Ubuntu and already had the tools for this but Etcher seems to be the go to application for this nowadays, so you could download/install this and create your bootable USB from the ISO.

Once you have the bootable USB, it’s over to your Mac.

  • Boot your Mac up whilst holding the Option key to go to the startup manager
  • Select the EFI drive (coloured orange)
  • Select “Start Cinnamon” option

The above will take you into a LIVE mode, i.e. you’ve not installed Linux but are running from the USB. Let’s check everything works for you before you commit to installing Linux Mint. From the Linux Mint, Cinnamon desktop…

  • Open Drive Manager look for your network adapter
  • Apply/install any required drivers
  • From network icon in desktop select your WiFi network

Play around with the OS and check it’s what you want to install and all works, then if you’re going to commit and overwrite MacOS

  • Double click the Install Linux Mint icon

I had an issue when I installed Mint, in that it no longer installed the drivers for the WiFi when I went to Driver Manager to select them. Instead it wanted to go online to get them – difficult as the WiFi drivers are what I’m trying to install and I had no ethernet attachment and to be honest, I know the drivers are on the USB as it worked in LIVE mode.

To get things working, I found that if I mounted the USB drive and searched for the Broadcom packages (and these are what was installed via testing in LIVE) and now double clicking on the two files/packages within the USB installation directories, then I could install the drivers and everything worked.

Disclaimer: I’ve only just installed Linux Mint on the Macbook Air, so I haven’t down any extensive testing.

Postgresql in Docker

Let’s run up the Docker image with an instance of PostgreSQL

docker run --name mypostgres -d postgres

Now, connect to the instance so we can create a database etc.

docker exec -it mypostgres bash

createdb -U postgres MyDatabase

Note: if you find this error message psql: FATAL: role “root” does not exist, you’ll need to switch to the postgres user, see below.

Switch to the postgres user (su substitute user).

su postgres
psql

At which point, we’re now in the psql application and can create databases etc.

Setting up Ubuntu Server firewall

UFW is used as the firewall on Linux and in my case on Ubuntu server. UFW comes with a UI, but we’re going to use this on a headless server (hence no UI being used).

Status and enabling/disabling the firewall

Simply run the following to check whether your firewall is active or not

sudo ufw status

To enable the firewall simply use the following

sudo ufw enable

Use disable to disable the firewall (as you probably guessed).

Once enabled run the status command again and you should see a list showing which ports we have defined rules for and these will show whether to ALLOW or REJECT connections to port. For example 

To                         Action      From
--                         ------      ----
22/tcp                     ALLOW       Anywhere
80/tcp                     ALLOW       Anywhere
443/tcp                    ALLOW       Anywhere
80                         ALLOW       Anywhere

Allow and reject access

We can allow access to a port, reject access to ports and reject outgoing traffic on ports. When we allow, reject incoming or reject outgoing access we’re creating firewall rules.

To allow access to SSH, for example we do the following

sudo ufw allow 22

This will allow tcp and udp access, but we can be more precise and just allow tcp by using

sudo ufw allow 22/tcp

As you can see from the previous output from the status option, we’ve enabled 22/tcp already.

To reject access to a port we use reject.

Note: If you’re access your server using SSH you probably don’t want to reject access to port 22, for obvious reasons, i.e. port 22 is used by SSH and this will block your access via SSH.

sudo ufw reject 80

Application profiles

UFW includes application profiles which allow us to enable predefined lists of permissions

sudo ufw app list

The applications listed from this command can also be seen by listing /etc/ufw/applications.d, so for example on my system I have a file name openssh-server, if you open this with nano (or your preferred editor), you’ll see an INI file format, for example 

[OpenSSH]
title=Secure shell server, an rshd replacement
description=OpenSSH is a free implementation of the Secure Shell protocol.
ports=22/tcp

We can also use 

sudo ufw app info OpenSSH

Replacing OpenSSH with the name of the application profile you want to view

As you can see, if our application profiles are just INI files, then you can create your own file and place it into the aforementioned folder and make it available to UFW. Once you’ve created your file you’ll need to tell UFW to load the application definitions using

sudo ufw app update MyApp

Replace MyApp with your application name in the above.

Ofcourse once we have these profiles we can allow, reject etc. using the application name, i.e.

sudo ufw allow OpenSSH

Logging

By default logging is disabled, we can turn it on using

sudo ufw logging on

Setting up swift on Ubuntu 20.04

This is an update to Setting up swift on Ubuntu 18.04 – installing Swift on Ubuntu 20.04.

Check out Downloads for the current info. from swift.org.

  • We need to install dependencies, so start with 
    apt-get install binutils git gnupg2 libc6-dev libcurl4 libedit2 libgcc-9-dev libpython2.7 libsqlite3-0 libstdc++-9-dev libxml2 libz3-dev pkg-config tzdata uuid-dev zlib1g-dev
  • Next we need to download the tar for the version of Swift you’re targeting, mine’s Swift 5.5.2 
    wget https://download.swift.org/swift-5.5.2-release/ubuntu2004/swift-5.5.2-RELEASE/swift-5.5.2-RELEASE-ubuntu20.04.tar.gz

Next up we should verify this download

  • First download the signature using 
    wget https://swift.org/builds/swift-5.5.2-release/ubuntu2004/swift-5.5.2-RELEASE/swift-5.5.2-RELEASE-ubuntu20.04.tar.gz.sig
  • Now import the key 
    wget -q -O - https://swift.org/keys/all-keys.asc | gpg --import -
  • Now run the following 
    gpg --keyserver hkp://keyserver.ubuntu.com --refresh-keys Swift
gpg --verify swift-5.5.2-RELEASE-ubuntu20.04.tar.gz.sig

Assuming everything’s verified we now want to extract the download into our preferred location – in my case I am just creating a folder name ~/Swift and extracting the tar to this location, running the following from this location

tar xzf swift-5.5.2-RELEASE-ubuntu20.04.tar.gz

Finally let’s update the path – I’ve added this to the last line of my .bashrc

export PATH=~/Swift/swift-5.5.2-RELEASE-ubuntu20.04/usr/bin:"${PATH}"

Checking who last logged in and when on Ubuntu Server

You might want to see a list of who logged into your Ubuntu server last or over a time period. Or maybe you want to take a look at more than just that and see more of an audit trail…

last

We can use the command last to display a “listing of last logged in users”. For example let’s just get the tail of the list using

last | tail

or ofcourse we might simple look through all entries using

last | less

What about if we know the user we’re interested in, then we can simply use

last -x Bob

Replacing Bob with the username you wish to look for.

There’s options to specify listing data after a specific time or before a time and more see

last --help

What if we want even more information.

/var/log/auth.log

Last works well if you’re interested in users logging into the server, but what about if we just want to check who’s access a shared drive or the likes, then we can check the /var/log/auth.log like this

sudo cat /var/log/auth.log
// or 
sudo less /var/log/auth.log
// or
sudo tail /var/log/auth.log

As per standard piping of commands, I’ve included an example of using less and tail, but basically we want to list the contents of the auth.log file. Ofcourse as it’s a file we can grep it (or whatever) as required.

This auth.log file lists sessions being opened and closed, cron jobs and lots more besides.

Ubuntu server auto upgrade

I have an Ubuntu server happily living it’s life as a NAS (and more) server which every now and then (if I forget to keep track of updates) it runs out of space on /boot causing issues removing old releases or partial updates to be a bit of a problem. So how do we either turn on or off automatic upgrades?

The configuration for this is stored in the file 20auto-upgrades. So we can edit the file using

sudo nano /etc/apt/apt.conf.d/20auto-upgrades

Within the file you’ll see something like this

APT::Periodic::Update-Package-Lists "1";
APT::Periodic::Unattended-Upgrade "1";

Note: The “1” in the above are not True/False but the minimum number of days. So we could change from “1” to run weekly by changing this value to “7”. A value of “0” will disable the feature.

You can create the file yourself or run the following command to create the file (it can be used to turn on/off by running it on an existing file but that’s all)

sudo dpkg-reconfigure -plow unattended-upgrades

If you want to change the frequency of checks for updates you’ll need to edit the 20auto-upgrades manually (as already discussed).

References

AutomaticSecurityUpdates.
UnattendedUpgrades

Mounting a USB HDD on Ubuntu server

I’m running up my latest Raspberry Pi with a connected USB SSD and forgot how to mount the thing. So this post is a little reminder. Ofcourse the instruction are not exclusive to Raspberry Pi’s or Ubuntu, but hey I just wanted a back story to this post.

So you’ve connected your USB drive and you’ve got a SSH terminal (i.e. via PuTTY) session connected to you Ubuntu server, what’s next?

Where’s my drive

The first thing you need to figure out is where your drive is, i.e. what /dev/ location it’s assigned to.

  • Try running df, which reports disk space and usage, from this you might be able to spot your drive, in my case it’s /dev/sda1 and its obvious by the size of the drive
  • If this is not conclusive then run sudo fdisk -l this may help locate the disk

Mounting the drive

Assuming we’ve located the device, and for this example it is on /dev/sda1, how do we mount this drive?

  • Create a folder that will get mapped to our mounted drive, for example mkdir /media/external or whatever you want to name it
  • To mount the drive we now use 
    sudo mount -t ntfs-3g /dev/sda1 /media/external

    Obviously this drive I’m mounting is an NTFS formatted drive, you might be using vfat or something else instead, so check. Then we simply have the source (/dev/sda1) mapping to the destination (/media/external) that we created.

    Note: without the mount taking place, ls the destination and you’ll see no files (if they exist on your drive). After you mount the drive. ls the destination to see the files on the USB drive.

As it currently stands, when you reboot you’ll have to mount the drive again.

Auto-mounting the drive

In scenarios where we’re not removing the drive and simply want the OS to automount our drive, we need to do a couple of things.

  • Find the UUID for the drive by running sudo blkid, next to the device, i.e. /dev/sda1 should be a UUID, copy or note down the string.
  • Run sudo nano fstab
  • Add a new line to the bottom of the file along these lines 
    UUID=ABCDEFGHIJK /media/external auto nosiud,nodev,nofail 0 0

    and save the file

  • Run sudo mount -a to check for errors

Now when you reboot the machine the USB drive should be mounted automatically.

Using the Windows Subsystem for Linux

Whilst I have Linux machines available to me, they’re not always powered up or the remoting

See Windows Subsystem for Linux Installation Guide for Windows 10 for details on installing the WSL.

For completeness here’s the steps I took.

  • Run PowerShell as Admin and then execute the following

    Enable-WindowsOptionalFeature -Online -FeatureName Microsoft-Windows-Subsystem-Linux
  • Go to the Microsoft Store and type Run Linux on Windows into the search text box. In the store currently, there’s the options of Ubuntu, openSUSE Leap 42, SUSE Linux Enterprise Server 12, Debian and Kali Linux.

    Install your preferred distro – I went for Ubuntu simply because that’s what I have on most of my Linux boxes.

  • Once installed you’ll need to go to the command prompt | Properties and select the Options tab. From here ensure that Use legacy console (requires relaunch) is unchecked.

Once everything is initialized you’ll be in the user’s (whatever user name you created) home folder – on Windows this folder is stored in C:\Users\{username}\AppData\Local\Packages\CanonicalGroupLimited.UbuntuonWindows_79rhkp1fndgsc\LocalState\rootfs\home

We can access the C drive using

cd /mnt/c

Running the Linux from Windows

When you want to run the Windows Subsystem for Linux going forward, simply execute

wsl