Tag: ubuntu

Install and configure SSH on Debian or Ubuntu

SSH is a protocol that enables secure connections over unsecured networks. It supports the use of asymmetric encryption for user authentication. Private keys are kept locally, while public keys are stored on the remote machine.

The following configuration disables root logins on the remote machine. Only users belonging to the group ssh-users may establish a connection. Access to the remote machine is tied to the local user’s private key.

In this example, the name of the remote machine is debian-server, which has the address 192.168.1.10 on the network. sid is a user on debian-server, whereas bookworm is a user on the local machine. Choose an encryption passphrase to secure the private key that you will generate in Step 5.

On the remote machine

Step 1

Install the secure shell server with the following command:

$ sudo apt install --yes openssh-server

Step 2

If you are using ufw as a host-based firewall

Configure ufw to allow connections to the secure shell server.

$ sudo ufw limit ssh

If you are using firewalld as a host-based firewall

Configure firewalld to allow connections to the secure shell server.

$ sudo -- bash -c 'firewall-cmd --zone=public --add-service=ssh --permanent && firewall-cmd --reload && firewall-cmd --info-zone=public'

Step 3

Restrict access to the remote machine to members of a specific group. Start by creating the group ssh-users.

$ sudo addgroup --system ssh-users

Add the user sid to the group ssh-users.

$ sudo adduser sid ssh-users

On the local machine

Step 4

Install the secure shell client with the following command.

$ sudo apt install openssh-client

Step 5

Generate a new key pair for the local user bookworm:

$ ssh-keygen -t ed25519 -o -a 100

Save the key pair to the directory /home/bookworm/.ssh/. Choose a name that facilitates easy identification.

Enter file in which to save the key (/home/bookworm/.ssh/id_ed25519): ~/.ssh/id_ed25519-debian-server

The use of an appropriate passphrase to secure the private key is mandatory.

Step 6

Create the file ~/.ssh/config to configure the secure shell client.

$ nano ~/.ssh/config

Add the follwing minimal entry for the host debian-server.

Host debian-server
   Hostname 192.168.1.10
   IdentitiesOnly yes

Step 7

Deploy the public key with the following command.

$ ssh-copy-id -i ~/.ssh/id_ed25519-debian-server.pub sid@debian-server

Step 8

Log into the remote machine.

$ ssh -i ~/.ssh/id_ed25519-debian-server sid@debian-server

When prompted to confirm the authenticity of the host debian-server, type yes and press [Enter].

The authenticity of host 'debian-server (192.168.1.10)' can't be established.
ED25519 key fingerprint is SHA256:C9RxLLVbvFwVJc0L4JHzcuHQSaPHJZe/GrRDvqy6rAG.
This key is not known by any other names.
Are you sure you want to continue connecting (yes/no/[fingerprint])?

In the next step, enter the passphrase for your private key.

Enter passphrase for key '/home/bookworm/.ssh/id_ed25519-debian-server':

Step 9

On the remote machine, download a file to harden the ssh server. You are encouraged to inspect its contents.

$ sudo -- bash -c 'wget -P /etc/ssh/sshd_config.d/ --show-progress https://edafe.de/debian/sshd_config.conf'

Activate the modifications on the remote machine.

$ sudo systemctl restart ssh.service

Step 9

On the local machine, open a new terminal window and run the following command.

$ $ ssh -i ~/.ssh/id_ed25519-debian-server sid@debian-server

In the next step, enter the passphrase for your private key.

Enter passphrase for key '/home/bookworm/.ssh/id_ed25519-debian-server':

Display the active configuration for the remote ssh server and verify its settings, paying particular attention to options for maxauthtries, permitrootlogin and passwordauthentication.

$ sudo sshd -T

All done!

For more in-depth information, please see stribika’s post-Snowden advice on hardening OpenSSH server installations.

The book SSH The Secure Shell by Daniel Barrett, Richard Silverman and Robert Byrnes is still useful today and has information on other clever stuff you can do with SSH.

Install OneDrive Client for Linux on Debian or Ubuntu

In the absence of an official client from Microsoft, the OneDrive Client for Linux connects your Debian or Ubuntu system to OneDrive Personal, OneDrive for Business, OneDrive for Office365, Sharepoint and other such deployments.

Step 1

Install the OneDrive Client from the Debian or Ubuntu repository.

$ sudo -- bash -c 'apt update && apt install --yes onedrive'

Step 2

Begin to connect the client to your OneDrive account.

$ onedrive --synchronize

You will be presented with a message similar to the following:

Configuring Global Azure AD endpoints
Authorize this app visiting:

https://login.microsoftonline.com/common/oauth2/v2.0/authorize?client_id&scope=Files.ReadWrite%20Files.ReadWrite.all%20Sites.Read.All%Sites.ReadWrite.All%20offline_accessresponse_type=code&redirect_uri=https://login.microsoftonline.com/common/oauth2/nativeclient

Enter the response uri:

Copy or [Ctrl + Click] the URI beginning with https://login.microsoftonline.com/.

In a web browser

Use the URI from the previous step to sign into your Microsoft account. You will be redirected to a response URI displaying a blank page. Copy the response URI from the address field of your browser.

In the terminal

Paste the response URI into the terminal. On successful authentication, the OneDrive Client will connect to your Microsoft account and begin to download your data.

Initializing the Synchronization Engine …
Syncing changes from OneDrive …
Creating local directory:
Downloading file … done.
Uploading differences of ~/OneDrive
Uploading new items of ~/OneDrive

Step 3

After downloading your data to ~/OneDrive, validate the configuration of the client.

$ onedrive --display-config

If required, you may change the default configuration.

Step 4

Enable OneDrive Client for the local user bookworm.

$ sudo -- bash -c 'systemctl enable onedrive@bookworm.service && systemctl start onedrive@bookworm.service && systemctl status onedrive@bookworm.service'

All done!

Install and configure nullmailer using Fastmail as a smarthost

If you want to receive status updates from your Debian or Ubuntu system in your inbox, you need to employ the help of a mail tansfer agent (MTA). nullmailer is a relay-only forwarding MTA that can be used as an alternative to more complex MTAs such as Exim, Sendmail or Postfix. Instructions for setting up Exim are available for comparison.

nullmailer can be configured to use Fastmail as a smarthost and hence ensure the deliverability of your messages. In principle, these instructions should also be applicable to service providers other than Fastmail.

In the following example configuration, debian is the hostname, bookworm the local username and linus.torvalds@fastmail.com the Fastmail username.

Step 1

Log into your Fastmail account and set up a new app password for SMTP authentication.

Step 2

Create the new directory /etc/nullmailer and the file /etc/nullmailer/adminaddr.

$ sudo mkdir /etc/nullmailer && sudo nano /etc/nullmailer/adminaddr

Your Fastmail username is the only entry in /etc/nullmailer/adminaddr.

linus.torvalds@fastmail.com

Step 3

Install the required packages.

$ sudo apt-get install --yes nullmailer mailutils

Step 4

Perform the initial configuration using debconf. Reconfigure nullmailer at any time after the initial installation using the following comand.

$ sudo dpkg-reconfigure nullmailer

Setting the mail name

Set the system mail name. If you are setting up on a home network, you should use home.arpa as the domain name.

Configuring nullmailer

Mailname of your system:

debian.home.arpa

Ok

Configuring the smarthost

Set the Fastmail server as the smarthost. Use the app password you set in Step 1.

Configuring nullmailer

Smarthosts:

smtp.fastmail.com smtp --port=587 --auth-login --starttls --user=linus.torvalds@fastmail.com --pass=password

Ok

Step 5

Test your configuration with the following command.

echo "Test mail from nullmailer on debian.home.arpa to the local root user and forwarded on to Fastmail" | mail -s "Test nullmailer" root

Check your Inbox, Linus!

Install Syncthing for continuous file synchronisation on Debian or Ubuntu

Syncthing is an open source tool that synchronises data across multiple devices. It transfers your files peer-to-peer, without the requirement to upload your information to the cloud. Packages are available for Android, Windows, macOS and Linux (including Synology DSM).

The usefulness of this project cannot be overstated.

Running the Syncthing stable channel

Syncthing is included in the Debian and Ubuntu repositories, respectively. These instructions are targeting the latest release of the Syncthing stable channel. It is therefore necessary to add the Syncthing repository to your list of APT sources.

In the following example, bookworm is the local username.

Step 1

Add the Syncthing release key for validation of packages downloaded from the Syncthing repository.

$ sudo curl -o /usr/share/keyrings/syncthing-archive-keyring.gpg https://syncthing.net/release-key.gpg

Step 2

Add the Syncthing repository.

$ echo "deb [signed-by=/usr/share/keyrings/syncthing-archive-keyring.gpg] https://apt.syncthing.net/ syncthing stable" | sudo tee /etc/apt/sources.list.d/syncthing.list

Step 3

Install Syncthing on your system.

$ sudo -- bash -c 'apt update && apt install --yes syncthing apt-transport-https'

Step 4

Enable Syncthing for the local user bookworm.

$ sudo -- bash -c 'systemctl enable syncthing@bookworm.service && systemctl start syncthing@bookworm.service && systemctl status syncthing@bookworm.service'

Step 5

You may need to edit your firewall settings to open ports for incoming and outgoing traffic.

If you are using ufw as a host-based firewall

Configure ufw to allow connections to Syncthing.

$ sudo ufw limit syncthing

If you are using firewalld as a host-based firewall

Configure firewalld to allow connections to Syncthing.

$ sudo -- bash -c 'firewall-cmd --zone=public --add-service=syncthing --permanent && firewall-cmd --reload && firewall-cmd --info-zone=public'

Step 6

Access the Syncthing configuration page by using your browser to navigate to the following address:

http://localhost:8384

Step 7

Complete your setup by referring to the Syncthing documentation.

What’s your favourite desktop and why?

In response to Voice of the Masses

My favourite Desktop is Unity because it is not MATE. This has been bugging me for quite some time.
Like almost everyone else on the planet, I was unhappy when in 2011 Canonical declared Unity Ubuntu’s new default desktop. After years of using GNOME 2, I just thought that Unity felt a bit awkward. But I stuck with it, mainly for a perceived lack of alternatives and my wish to avoid PPAs if at all possible.
Fast-forward a few years and, thanks to the excellent Martin Wimpress, I hear of MATE Desktop Environment almost every other podcast I listen to. With the release of Ubuntu 15.10, MATE is finally elevated to official flavour status and I was sure to be making the switch away from Unity.
I ended up using MATE for about one day before going back to Unity. It was quite an uncomfortable thing to have to admit, but there was a problem: After years of using Unity, I just thought that MATE felt a bit awkward…
ubuntu-mate.org

Executing Linux commands in the background using screen

The screen command allows you to detach a running process from a session and then reattach it at a later time. Its use is simple:

user@debian:~$ screen yourlinuxcommand

Now that yourlinuxcommand is executing, press Ctrl+A followed by D to detach the screen.
Obtain a list of all the running screen processes:

user@debian:~$ screen -ls
There is a screen on:
       18470.pts-0.server(02/03/14 10:03:43)     (Detached)
1 Socket in /var/run/screen/S-user.

Note the screen id in the above output. Use the screen id to reattach the session at anytime:

user@debian:~$ $ screen -r 18470.pts-0.server

www.thegeekstuff.com, www.linuxjournal.com

Redirecting mail for the local root user

postfix is Ubuntu’s default mail transfer agent (MTA) and can be configured to deliver mail using a relay host that requires SMTP authentication. Get the necessary packages with the following command:

user@ubuntu:~$ sudo apt-get install postfix bsd-mailx

Begin to configure your postfix installation by choosing satellite system as the general type of configuration. Enter the local machine name as the mail name (eg mycomputer.edafe.de) and the SMTP server address of your email service provider as the SMTP relay host (eg smtp.relayhost.com). Edit the file /etc/postfix/main.cf and add the following:

smtp_sasl_auth_enable = yes
smtp_sasl_password_maps = hash:/etc/postfix/sasl_passwd
smtp_sasl_security_options = noanonymous

Create the file /etc/postfix/sasl_passwd and make the following entries:

smtp.relayhost.com user:password

Substitute smtp.relayhost.com with the address of the SMTP relay host and user:password with your login details. Continue by executing the following three commands:

user@ubuntu:~$ sudo chown root.root /etc/postfix/sasl_passwd
user@ubuntu:~$ sudo chmod 600 /etc/postfix/sasl_passwd
user@ubuntu:~$ sudo postmap hash:/etc/postfix/sasl_passwd

Instruct postfix to reload its settings with the following command:

user@ubuntu:~$ sudo /etc/init.d/postfix reload

Making changes to the alias table

The aliases table provides a system-wide mechanism to redirect mail for local recipients. Edit the file /etc/aliases to contain the following entries:

postmaster: root
root: localuser
localuser: user@yourdomain.com

The localuser is the system administrator. Substitute user@yourdomain.com with the email address that you would like mail for the root user to be redirected to. Finally, update /etc/aliases.db using the following command:

user@ubuntu:~$ sudo newaliases

Mail for the local root user from now on will automatically be forwarded to user@yourdomain.com , using smtp.relayhost.com as the relay host.
www.postfix.org, help.ubuntu.com

Monitoring hard disks with smartmontools

SMART stands for Self-Monitoring, Analysis and Reporting Technology and is built into most modern hard disks. The smartd daemon is part of smartmontools and monitors a disk’s SMART data for any signs of hardware problems. SMART is available with Parallel and Serial ATA disks, drives appearing as either /dev/hd* or /dev/sd*, respectively. Use the following command to obtain relevant information for your system:

user@ubuntu:~$ df -hl

If required, start by configuring postfix to redirect mail for the local root user. Get the necessary packages with the following command:

user@ubuntu:~$ sudo apt-get install smartmontools bsd-mailx

Configuring smartd

Edit the file /etc/smartd.conf and comment out any lines beginning with DEVICESCAN. If you are using a netbook or a laptop, add the following line for the smartd daemon to monitor the device /dev/sda:

/dev/sda -a -d ata -n standby -o on -S on -m root -M daily -M test

If you are using a desktop or a server, add the following line for the smartd daemon to monitor the device /dev/hda:

/dev/hda -a -d ata -n never -o on -S on -s (L/../../7/04|S/../.././02) -m root -M daily -M test

See man smartd.conf for more information on how to tailor the operation of smartd to your needs.

Starting smartd

Edit the file /etc/default/smartmontools and uncomment the line containing start_smartd=yes. Restart the smartd daemon with the following command:

user@ubuntu:~$ sudo /etc/init.d/smartmontools restart

Verify that the local root user has received a test message from the smartd daemon. From now on, the smartd daemon will monitor the disk and, in the event of impending disk failure, alert the local root user by email.

Desktop Linux for the Windows power user

“As a lifelong Windows user, system builder, ex-gamer, and performance freak, I’m not drinking anyone’s Kool-Aid. I just want the most amount of control over my system as possible, and at this point in time, Ubuntu is the best follow-up to Windows XP.” Adam Overa walks the Windows user through the Ubuntu installation process from downloading the CD image to finding help online.
www.tomshardware.com

Ubuntu Linux is for everyone

Ubuntu is a relatively new flavour of Linux. Since the release of ‘Warty Warthog’ in October 2004, it has become the most popular Linux distribution worldwide. Similar to its parent, Debian GNU/Linux, Ubuntu is based entirely on free software. It inherits outstanding package management and provides one-click access to thousands of downloadable applications. Ubuntu 8.10 (Intrepid Ibex) is the latest version and available for download from today.
www.ubuntu.com

Editing configuration files with nano

There are many different tools that you can use to edit configuration files. Because of its simplicity, I personally like to use Nano:

user@ubuntu:~$ sudo nano /path/to/the/file

You can change the default settings for nano by editing its configuration file. For example, to stop nano from wrapping text simply make the following changes to /etc/nanorc:

## Don't wrap text at all.

set nowrap

www.nano-editor.org