Basics

This section is dedicated to the basic tasks we can perform in ubuntu Linux

How to add user in Ubuntu Lniux

Ubuntu-logo.png

At some point in your Ubuntu Linux server or desktop administration journey, you will need to create a user.
Usually, we create users in the servers for administration on more than one person or a service account that
needs to be created in order for the service to only run as that user. This creates a security barrier in the services you run.
Here we have steps on how to complete this function. Follow the instructions and if you encounter an error, please email support.

This tutorial assumes that:
You know the IP address of the machine intended for changes, and
can Login the machine with Telnet, Serial or, SSH

Note:
Only "sudo" can create a user, So, the first thing we have to do is check if the user you login with is a "sudo". 
Check with the command sudo -l 

 

1. Check "sudo" privileges by running sudo -l


code:

mslsadmin@remote01:~$ sudo -l
[sudo] password for mslsadmin:
Matching Defaults entries for mslsadmin on remote01:
    env_reset, mail_badpass, secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin, use_pty

User mslsadmin may run the following commands on remote01:
    (ALL : ALL) ALL
mslsadmin@remote01:~$

2. Use the sudo adduser  command to add the new user and follow the prompt:

code:

mslsadmin@remote01:~$ sudo adduser test
Adding user `test' ...
Adding new group `test' (1001) ...
Adding new user `test' (1001) with group `test' ...
Creating home directory `/home/test' ...
Copying files from `/etc/skel' ...



3. Continue the prompt and create a password for the new user :

code:

New password: ****
Retype new password:*******
passwd: password updated successfully
Changing the user information for test

note:
While entering the password you might not see that keys are actually being entered. This is completely normal and may differ from other Linux distributions or console applications.


4. Next the adduser prompt will ask you for more information about the user,  Enter relevant information or, if you want to skip the prompt, leave the options blank and press ENTER. 

code:

Changing the user information for test
Enter the new value, or press ENTER for the default
        Full Name []: Test User
        Room Number []:
        Work Phone []:
        Home Phone []: d
        Other []:

5. Confirm your changes and choose "Y" 

code:

Is the information correct? [Y/n] Y

Congratulations! You successfully created an user in Ubuntu Linux

Install Docker Engine on Ubuntu

To get started with Docker Engine on Ubuntu, make sure you meet the prerequisites, and then follow the installation steps.

Prerequisites 

Note

If you use ufw or firewalld to manage firewall settings, be aware that when you expose container ports using Docker, these ports bypass your firewall rules. For more information, refer to Docker and ufw.

OS requirements 

To install Docker Engine, you need the 64-bit version of one of these Ubuntu versions:

Docker Engine for Ubuntu is compatible with x86_64 (or amd64), armhf, arm64, s390x, and ppc64le (ppc64el) architectures.

Uninstall old versions 

Before you can install Docker Engine, you must first make sure that any conflicting packages are uninstalled.

Distro maintainers provide an unofficial distributions of Docker packages in APT. You must uninstall these packages before you can install the official version of Docker Engine.

The unofficial packages to uninstall are:

Moreover, Docker Engine depends on containerd and runc. Docker Engine bundles these dependencies as one bundle: containerd.io. If you have installed the containerd or runc previously, uninstall them to avoid conflicts with the versions bundled with Docker Engine.

Run the following command to uninstall all conflicting packages:

$ for pkg in docker.io docker-doc docker-compose podman-docker containerd runc; do sudo apt-get remove $pkg; done

apt-get might report that you have none of these packages installed.

Images, containers, volumes, and networks stored in /var/lib/docker/ aren't automatically removed when you uninstall Docker. If you want to start with a clean installation, and prefer to clean up any existing data, read the uninstall Docker Engine section.

Installation methods 

You can install Docker Engine in different ways, depending on your needs:

Install using the apt repository 

Before you install Docker Engine for the first time on a new host machine, you need to set up the Docker repository. Afterward, you can install and update Docker from the repository.

Set up the repository 

  1. Update the apt package index and install packages to allow apt to use a repository over HTTPS:

    $ sudo apt-get update
$ sudo apt-get install ca-certificates curl gnupg

  2. Add Docker's official GPG key:

    $ sudo install -m 0755 -d /etc/apt/keyrings
$ curl -fsSL https://download.docker.com/linux/ubuntu/gpg | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg
$ sudo chmod a+r /etc/apt/keyrings/docker.gpg

  3. Use the following command to set up the repository:

    $ echo \
  "deb [arch="$(dpkg --print-architecture)" signed-by=/etc/apt/keyrings/docker.gpg] https://download.docker.com/linux/ubuntu \
  "$(. /etc/os-release && echo "$VERSION_CODENAME")" stable" | \
  sudo tee /etc/apt/sources.list.d/docker.list > /dev/null

    Note

    If you use an Ubuntu derivative distro, such as Linux Mint, you may need to use UBUNTU_CODENAME instead of VERSION_CODENAME.

  4. Update the apt package index:

    $ sudo apt-get update

Install Docker Engine 

  1. Install Docker Engine, containerd, and Docker Compose.
 

To install the latest version, run:

$ sudo apt-get install docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin

  1. Verify that the Docker Engine installation is successful by running the hello-world image.

    $ sudo docker run hello-world

    This command downloads a test image and runs it in a container. When the container runs, it prints a confirmation message and exits.

You have now successfully installed and started Docker Engine.

Tip

Receiving errors when trying to run without root?

The docker user group exists but contains no users, which is why you’re required to use sudo to run Docker commands. Continue to Linux postinstall to allow non-privileged users to run Docker commands and for other optional configuration steps.

Upgrade Docker Engine 

To upgrade Docker Engine, follow the installation instructions, choosing the new version you want to install.

Install from a package 

If you can't use Docker's apt repository to install Docker Engine, you can download the deb file for your release and install it manually. You need to download a new file each time you want to upgrade Docker Engine.

  1. Go to https://download.docker.com/linux/ubuntu/dists/open_in_new.

  2. Select your Ubuntu version in the list.

  3. Go to pool/stable/ and select the applicable architecture (amd64, armhf, arm64, or s390x).

  4. Download the following deb files for the Docker Engine, CLI, containerd, and Docker Compose packages:

    • containerd.io_<version>_<arch>.deb
    • docker-ce_<version>_<arch>.deb
    • docker-ce-cli_<version>_<arch>.deb
    • docker-buildx-plugin_<version>_<arch>.deb
    • docker-compose-plugin_<version>_<arch>.deb

  5. Install the .deb packages. Update the paths in the following example to where you downloaded the Docker packages.

    $ sudo dpkg -i ./containerd.io_<version>_<arch>.deb \
  ./docker-ce_<version>_<arch>.deb \
  ./docker-ce-cli_<version>_<arch>.deb \
  ./docker-buildx-plugin_<version>_<arch>.deb \
  ./docker-compose-plugin_<version>_<arch>.deb

    The Docker daemon starts automatically.

  6. Verify that the Docker Engine installation is successful by running the hello-world image.

    $ sudo service docker start
$ sudo docker run hello-world

    This command downloads a test image and runs it in a container. When the container runs, it prints a confirmation message and exits.

You have now successfully installed and started Docker Engine.

Tip

Receiving errors when trying to run without root?

The docker user group exists but contains no users, which is why you’re required to use sudo to run Docker commands. Continue to Linux postinstall to allow non-privileged users to run Docker commands and for other optional configuration steps.

Upgrade Docker Engine 

To upgrade Docker Engine, download the newer package files and repeat the installation procedure, pointing to the new files.

Install using the convenience script 

Docker provides a convenience script at https://get.docker.com/open_in_new to install Docker into development environments non-interactively. The convenience script isn't recommended for production environments, but it's useful for creating a provisioning script tailored to your needs. Also refer to the install using the repository steps to learn about installation steps to install using the package repository. The source code for the script is open source, and you can find it in the docker-install repository on GitHubopen_in_new.

Always examine scripts downloaded from the internet before running them locally. Before installing, make yourself familiar with potential risks and limitations of the convenience script:

Tip: preview script steps before running

You can run the script with the --dry-run option to learn what steps the script will run when invoked:

$ curl -fsSL https://get.docker.com -o get-docker.sh
$ sudo sh ./get-docker.sh --dry-run

This example downloads the script from https://get.docker.com/open_in_new and runs it to install the latest stable release of Docker on Linux:

$ curl -fsSL https://get.docker.com -o get-docker.sh
$ sudo sh get-docker.sh
Executing docker install script, commit: 7cae5f8b0decc17d6571f9f52eb840fbc13b2737
<...>

You have now successfully installed and started Docker Engine. The docker service starts automatically on Debian based distributions. On RPM based distributions, such as CentOS, Fedora, RHEL or SLES, you need to start it manually using the appropriate systemctl or service command. As the message indicates, non-root users can't run Docker commands by default.

Use Docker as a non-privileged user, or install in rootless mode?

The installation script requires root or sudo privileges to install and use Docker. If you want to grant non-root users access to Docker, refer to the post-installation steps for Linux. You can also install Docker without root privileges, or configured to run in rootless mode. For instructions on running Docker in rootless mode, refer to run the Docker daemon as a non-root user (rootless mode).

Install pre-releases 

Docker also provides a convenience script at https://test.docker.com/open_in_new to install pre-releases of Docker on Linux. This script is equal to the script at get.docker.com, but configures your package manager to use the test channel of the Docker package repository. The test channel includes both stable and pre-releases (beta versions, release-candidates) of Docker. Use this script to get early access to new releases, and to evaluate them in a testing environment before they're released as stable.

To install the latest version of Docker on Linux from the test channel, run:

$ curl -fsSL https://test.docker.com -o test-docker.sh
$ sudo sh test-docker.sh

Upgrade Docker after using the convenience script 

If you installed Docker using the convenience script, you should upgrade Docker using your package manager directly. There's no advantage to re-running the convenience script. Re-running it can cause issues if it attempts to re-install repositories which already exist on the host machine.

Uninstall Docker Engine 

  1. Uninstall the Docker Engine, CLI, containerd, and Docker Compose packages:

    $ sudo apt-get purge docker-ce docker-ce-cli containerd.io docker-buildx-plugin docker-compose-plugin docker-ce-rootless-extras

  2. Images, containers, volumes, or custom configuration files on your host aren't automatically removed. To delete all images, containers, and volumes:

    $ sudo rm -rf /var/lib/docker
$ sudo rm -rf /var/lib/containerd

You have to delete any edited configuration files manually.

Configuring networks

Ubuntu ships with a number of graphical utilities to configure your network devices. This document is geared toward server administrators and will focus on managing your network on the command line.

Ethernet interfaces

Ethernet interfaces are identified by the system using predictable network interface names. These names can appear as eno1 or enp0s25. However, in some cases an interface may still use the kernel eth# style of naming.

Identify Ethernet interfaces

To quickly identify all available Ethernet interfaces, you can use the ip command as shown below.

ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever
2: enp0s25: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 00:16:3e:e2:52:42 brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet 10.102.66.200/24 brd 10.102.66.255 scope global dynamic eth0
       valid_lft 3257sec preferred_lft 3257sec
    inet6 fe80::216:3eff:fee2:5242/64 scope link
       valid_lft forever preferred_lft forever

Another application that can help identify all network interfaces available to your system is the lshw command. This command provides greater details around the hardware capabilities of specific adapters. In the example below, lshw shows a single Ethernet interface with the logical name of eth4 along with bus information, driver details and all supported capabilities.

sudo lshw -class network
  *-network
       description: Ethernet interface
       product: MT26448 [ConnectX EN 10GigE, PCIe 2.0 5GT/s]
       vendor: Mellanox Technologies
       physical id: 0
       bus info: pci@0004:01:00.0
       logical name: eth4
       version: b0
       serial: e4:1d:2d:67:83:56
       slot: U78CB.001.WZS09KB-P1-C6-T1
       size: 10Gbit/s
       capacity: 10Gbit/s
       width: 64 bits
       clock: 33MHz
       capabilities: pm vpd msix pciexpress bus_master cap_list ethernet physical fibre 10000bt-fd
       configuration: autonegotiation=off broadcast=yes driver=mlx4_en driverversion=4.0-0 duplex=full firmware=2.9.1326 ip=192.168.1.1 latency=0 link=yes multicast=yes port=fibre speed=10Gbit/s
       resources: iomemory:24000-23fff irq:481 memory:3fe200000000-3fe2000fffff memory:240000000000-240007ffffff

Ethernet Interface logical names

Interface logical names can also be configured via a Netplan configuration. If you would like control which interface receives a particular logical name use the match and set-name keys. The match key is used to find an adapter based on some criteria like MAC address, driver, etc. The set-name key can be used to change the device to the desired logical name.

network:
  version: 2
  renderer: networkd
  ethernets:
    eth_lan0:
      dhcp4: true
      match:
        macaddress: 00:11:22:33:44:55
      set-name: eth_lan0

Ethernet Interface settings

ethtool is a program that displays and changes Ethernet card settings such as auto-negotiation, port speed, duplex mode, and Wake-on-LAN. The following is an example of how to view the supported features and configured settings of an Ethernet interface.

sudo ethtool eth4
Settings for eth4:
    Supported ports: [ FIBRE ]
    Supported link modes:   10000baseT/Full
    Supported pause frame use: No
    Supports auto-negotiation: No
    Supported FEC modes: Not reported
    Advertised link modes:  10000baseT/Full
    Advertised pause frame use: No
    Advertised auto-negotiation: No
    Advertised FEC modes: Not reported
    Speed: 10000Mb/s
    Duplex: Full
    Port: FIBRE
    PHYAD: 0
    Transceiver: internal
    Auto-negotiation: off
    Supports Wake-on: d
    Wake-on: d
    Current message level: 0x00000014 (20)
                   link ifdown
    Link detected: yes

IP addressing

The following section describes the process of configuring your system’s IP address and default gateway needed for communicating on a local area network and the Internet.

Temporary IP address assignment

For temporary network configurations, you can use the ip command which is also found on most other GNU/Linux operating systems. The ip command allows you to configure settings which take effect immediately – however they are not persistent and will be lost after a reboot.

To temporarily configure an IP address, you can use the ip command in the following manner. Modify the IP address and subnet mask to match your network requirements.

sudo ip addr add 10.102.66.200/24 dev enp0s25

The ip can then be used to set the link up or down.

To verify the IP address configuration of enp0s25, you can use the ip command in the following manner:

ip address show dev enp0s25
10: enp0s25: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default qlen 1000
    link/ether 00:16:3e:e2:52:42 brd ff:ff:ff:ff:ff:ff link-netnsid 0
    inet 10.102.66.200/24 brd 10.102.66.255 scope global dynamic eth0
       valid_lft 2857sec preferred_lft 2857sec
    inet6 fe80::216:3eff:fee2:5242/64 scope link
       valid_lft forever preferred_lft forever6

To configure a default gateway, you can use the ip command in the following manner. Modify the default gateway address to match your network requirements.

sudo ip route add default via 10.102.66.1

You can also use the ip command to verify your default gateway configuration, as follows:

ip route show
default via 10.102.66.1 dev eth0 proto dhcp src 10.102.66.200 metric 100
10.102.66.0/24 dev eth0 proto kernel scope link src 10.102.66.200
10.102.66.1 dev eth0 proto dhcp scope link src 10.102.66.200 metric 100

If you require DNS for your temporary network configuration, you can add DNS server IP addresses in the file /etc/resolv.conf. In general, editing /etc/resolv.conf directly is not recommended, but this is a temporary and non-persistent configuration. The example below shows how to enter two DNS servers to /etc/resolv.conf, which should be changed to servers appropriate for your network. A more lengthy description of the proper (persistent) way to do DNS client configuration is in a following section.

nameserver 8.8.8.8
nameserver 8.8.4.4

If you no longer need this configuration and wish to purge all IP configuration from an interface, you can use the ip command with the flush option:

ip addr flush eth0

Note
Flushing the IP configuration using the ip command does not clear the contents of /etc/resolv.conf. You must remove or modify those entries manually (or re-boot), which should also cause /etc/resolv.conf, which is a symlink to /run/systemd/resolve/stub-resolv.conf, to be re-written.

Dynamic IP address assignment (DHCP client)

To configure your server to use DHCP for dynamic address assignment, create a Netplan configuration in the file /etc/netplan/99_config.yaml. The following example assumes you are configuring your first Ethernet interface identified as enp3s0.

network:
  version: 2
  renderer: networkd
  ethernets:
    enp3s0:
      dhcp4: true

The configuration can then be applied using the netplan command:

sudo netplan apply

Static IP address assignment

To configure your system to use static address assignment, create a netplan configuration in the file /etc/netplan/99_config.yaml. The example below assumes you are configuring your first Ethernet interface identified as eth0. Change the addresses, routes, and nameservers values to meet the requirements of your network.

network:
  version: 2
  renderer: networkd
  ethernets:
    eth0:
      addresses:
        - 10.10.10.2/24
      routes:
        - to: default
          via: 10.10.10.1
      nameservers:
          search: [mydomain, otherdomain]
          addresses: [10.10.10.1, 1.1.1.1]

The configuration can then be applied using the netplan command.

sudo netplan apply

NOTE
netplan in Ubuntu Bionic 18.04 LTS doesn’t understand the “to: default” syntax to specify a default route, and should use the older gateway4: 10.10.10.1 key instead of the whole routes: block.

The loopback interface is identified by the system as lo and has a default IP address of 127.0.0.1. It can be viewed using the ip command.

ip address show lo
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host
       valid_lft forever preferred_lft forever

Name resolution

Name resolution (as it relates to IP networking) is the process of mapping hostnames to IP addresses, and vice-versa, making it easier to identify resources on a network. The following section will explain how to properly configure your system for name resolution using DNS and static hostname records.

DNS client configuration

Traditionally, the file /etc/resolv.conf was a static configuration file that rarely needed to be changed, or it automatically changed via DCHP client hooks. systemd-resolved handles nameserver configuration, and it should be interacted with through the systemd-resolve command. Netplan configures systemd-resolved to generate a list of nameservers and domains to put in /etc/resolv.conf, which is a symlink:

/etc/resolv.conf -> ../run/systemd/resolve/stub-resolv.conf

To configure the resolver, add the IP addresses of the appropriate nameservers for your network to the netplan configuration file. You can also add optional DNS suffix search-lists to match your network domain names. The resulting file might look like the following:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp0s25:
      addresses:
        - 192.168.0.100/24
      routes:
        - to: default
          via: 192.168.0.1
      nameservers:
          search: [mydomain, otherdomain]
          addresses: [1.1.1.1, 8.8.8.8, 4.4.4.4]

The search option can also be used with multiple domain names so that DNS queries will be appended in the order in which they are entered. For example, your network may have multiple sub-domains to search; a parent domain of example.com, and two sub-domains, sales.example.com and dev.example.com.

If you have multiple domains you wish to search, your configuration might look like the following:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp0s25:
      addresses:
        - 192.168.0.100/24
      routes:
        - to: default
          via: 192.168.0.1
      nameservers:
          search: [example.com, sales.example.com, dev.example.com]
          addresses: [1.1.1.1, 8.8.8.8, 4.4.4.4]

If you try to ping a host with the name server1, your system will automatically query DNS for its Fully Qualified Domain Name (FQDN) in the following order:

  1. server1.example.com

  2. server1.sales.example.com

  3. server1.dev.example.com

If no matches are found, the DNS server will provide a result of notfound and the DNS query will fail.

Static hostnames

Static hostnames are locally defined hostname-to-IP mappings located in the file /etc/hosts. Entries in the hosts file will have precedence over DNS by default. This means that if your system tries to resolve a hostname and it matches an entry in /etc/hosts, it will not attempt to look up the record in DNS. In some configurations, especially when Internet access is not required, servers that communicate with a limited number of resources can be conveniently set to use static hostnames instead of DNS.

The following is an example of a hosts file where a number of local servers have been identified by simple hostnames, aliases and their equivalent Fully Qualified Domain Names (FQDN’s):

127.0.0.1   localhost
127.0.1.1   ubuntu-server
10.0.0.11   server1 server1.example.com vpn
10.0.0.12   server2 server2.example.com mail
10.0.0.13   server3 server3.example.com www
10.0.0.14   server4 server4.example.com file

Note
In this example, notice that each of the servers were given aliases in addition to their proper names and FQDN’s. Server1 has been mapped to the name vpn, server2 is referred to as mail, server3 as www, and server4 as file.

Name Service Switch (NSS) configuration

The order in which your system selects a method of resolving hostnames to IP addresses is controlled by the Name Service Switch (NSS) configuration file /etc/nsswitch.conf. As mentioned in the previous section, typically static hostnames defined in the systems /etc/hosts file have precedence over names resolved from DNS. The following is an example of the line responsible for this order of hostname lookups in the file /etc/nsswitch.conf.

hosts:          files mdns4_minimal [NOTFOUND=return] dns mdns4

To modify the order of these name resolution methods, you can simply change the hosts: string to the value of your choosing. For example, if you prefer to use legacy unicast DNS versus multicast DNS, you can change the string in /etc/nsswitch.conf as shown below:

hosts:          files dns [NOTFOUND=return] mdns4_minimal mdns4

Bridging multiple interfaces

Bridging is a more advanced configuration, but is very useful in multiple scenarios. One scenario is setting up a bridge with multiple network interfaces, then using a firewall to filter traffic between two network segments. Another scenario is using bridge on a system with one interface to allow virtual machines direct access to the outside network. The following example covers the latter scenario:

Configure the bridge by editing your netplan configuration found in /etc/netplan/, entering the appropriate values for your physical interface and network:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp3s0:
      dhcp4: no
  bridges:
    br0:
      dhcp4: yes
      interfaces:
        - enp3s0

Now apply the configuration to enable the bridge:

sudo netplan apply

The new bridge interface should now be up and running. The brctl provides useful information about the state of the bridge, controls which interfaces are part of the bridge, etc. See man brctl for more information.

networkd-dispatcher for hook scripts

Users of the former ifupdown may be familiar with using hook scripts (e.g., pre-up, post-up) in their interfaces file. Netplan configuration does not currently support hook scripts in its configuration definition.

Instead, to achieve this functionality with the networkd renderer, users can use networkd-dispatcher. The package provides both users and packages with hook points when specific network states are reached, to aid in reacting to network state.

Note:
If you are on Desktop (not Ubuntu Server) the network is driven by Network Manager - in that case you need NM Dispatcher scripts instead.

The Netplan FAQ has a great table that compares event timings between ifupdown/systemd-networkd/network-manager.

It is important to be aware that these hooks run asynchronously; i.e. they will not block transition into another state.

The Netplan FAQ also has an example on converting an old ifupdown hook to networkd-dispatcher.

Resources