How to Fix an Error Installing Azure CLI on Linux Mint?

When I first tried to install the Azure CLI on my Linux Mint 19 machine, I thought it would be simple just follow the manual instructions from Microsoft, But the process quickly threw me into error land. Let me walk you through what happened, what I learned, and how I fixed it.

The Error That Stopped Me

The official instructions started with this line:

sudo apt-get install ca-certificates curl apt-transport-https lsb-release gnupg

But instead of installing smoothly, I hit this error:

openssh-server
E: Sub-process /usr/bin/dpkg returned an error code (1)

Naturally, I tried the usual:

sudo dpkg --configure -a
sudo apt-get install -f

but no luck. Both commands failed with a service error:

● ssh.service - OpenBSD Secure Shell server
   Loaded: loaded (/lib/systemd/system/ssh.service; enabled; vendor preset: enabled)
   Active: activating (auto-restart) (Result: exit-code)
  Process: 22323 ExecStartPre=/usr/sbin/sshd -t (code=exited, status=255)

At this point, Azure CLI wasn’t even the real problem the openssh server package was broken, and because dpkg aborted, apt couldn’t proceed.

What Was Really Happening

That cryptic message:

E: Sub-process /usr/bin/dpkg returned an error code (1)

basically means: “a package failed during post-install configuration.”

In my case, openssh-server was the culprit. Its post-install script runs:

/usr/sbin/sshd -t

That command checks the SSH configuration for errors. Since it failed with status 255, dpkg refused to continue. Until I fixed SSH, I couldn’t install anything.

Common Causes of sshd -t = 255

Through trial and error (and a bit of digging), I discovered these are the usual suspects:

• A broken /etc/ssh/sshd_config file (typos, invalid directives, duplicates).
• Missing or unreadable SSH host keys (/etc/ssh/ssh_host_*).
• Port conflicts (something else already listening on port 22).
• Wrong permissions or ownership on config or key files.

My Quick Fix

Here’s how I fixed it, in order. You can follow these too:

# 1) Test sshd config
sudo /usr/sbin/sshd -t -f /etc/ssh/sshd_config || echo "sshd_config has an error"

# 2) Regenerate host keys if missing
sudo ssh-keygen -A

# 3) Correct permissions
sudo chown root:root /etc/ssh/sshd_config
sudo chmod 644 /etc/ssh/sshd_config
sudo chmod 600 /etc/ssh/ssh_host_*_key 2>/dev/null || true
sudo chmod 644 /etc/ssh/ssh_host_*_key.pub 2>/dev/null || true

# 4) Check if port 22 is in use
sudo ss -ltnp | grep ':22' || true

# 5) Reset sshd_config to default (backup first!)
sudo cp /etc/ssh/sshd_config /etc/ssh/sshd_config.bak.$(date +%s)
sudo apt-get -y --reinstall install openssh-server
sudo cp /usr/share/openssh/sshd_config /etc/ssh/sshd_config 2>/dev/null || true

# 6) Retest and restart SSH
sudo /usr/sbin/sshd -t -f /etc/ssh/sshd_config
sudo systemctl enable --now ssh

# 7) Finally unstick apt/dpkg
sudo dpkg --configure -a
sudo apt-get -f install

After this, apt worked again. That felt like a win!

Installing Azure CLI Properly

Once SSH was fixed, I could finally continue with the Azure CLI installation.

# 1) Install dependencies
sudo apt-get update
sudo apt-get install -y ca-certificates curl apt-transport-https lsb-release gnupg

# 2) Add Microsoft repo for Ubuntu 18.04 (Mint 19 base = bionic)
curl -sL https://packages.microsoft.com/keys/microsoft.asc | sudo apt-key add -
echo "deb [arch=amd64] https://packages.microsoft.com/repos/azure-cli/ bionic main" | \
  sudo tee /etc/apt/sources.list.d/azure-cli.list

# 3) Update and install CLI
sudo apt-get update
sudo apt-get install -y azure-cli

# 4) Verify install
az version

If you’re on Mint 20/21, just swap bionic with focal or jammy.

Practice Utilities I Use

To make sure everything was solid, I tested a few things:

Check SSH service health

systemctl status ssh --no-pager
journalctl -u ssh -b --no-pager | tail -200

Confirm Azure CLI works

az login
az account show --output table
az group list --output table

Cleanup if needed

sudo apt-get remove -y azure-cli
sudo rm -f /etc/apt/sources.list.d/azure-cli.list
sudo apt-get update

Final Thought

When I first tried to install the Azure CLI on my Linux Mint 19 machine, I thought it would be simple—just follow the manual instructions from Microsoft, right? But the process quickly threw me into error land. Let me walk you through what happened, what I learned, and how I fixed it.