Lab 9: System time and Package managers

Exercise 1: System time

Task 1: Time zone

• Check the current time zone

  $ timedatectl
  

  You should get output similar to the following:

                 Local time: Вс 2022-11-06 12:40:33 +04
             Universal time: Вс 2022-11-06 08:40:33 UTC
                   RTC time: Вс 2022-11-06 08:40:33
                  Time zone: Europe/Samara (+04, +0400)
  System clock synchronized: yes
                NTP service: active
            RTC in local TZ: no
  

• Assume that we are in Vladivostok and we want to set the timezone to Vladivostok Standard Time (GMT +10). To do this, first get a list of all available time zones.

  $ timedatectl list-timezones
  

  You will find the full name for the time zone in Vladivostok from the long list of output:

  Asia/Vladivostok
  

• Now that we have identified the name of the time zone on our system, switch to that with the following command:

  $ sudo timedatectl set-timezone Asia/Vladivostok
  

• Run timedatectl and you should get output different from what we had initially.

  $ timedatectl
                 Local time: Вс 2022-11-06 18:55:05 +10
             Universal time: Вс 2022-11-06 08:55:05 UTC
                   RTC time: Вс 2022-11-06 08:55:05
                  Time zone: Asia/Vladivostok (+10, +1000)
  System clock synchronized: yes
                NTP service: active
            RTC in local TZ: no
  

• To see how this affects system logging, restart rsyslog to trigger some system log events.

  $ systemctl restart rsyslog
  

• View the log file /var/log/syslog.

  $ tail -n 15 /var/log/syslog
  

  You should see output similar to the following with noticeable change in the timestamp.

  Nov  6 12:55:35 sna-vm systemd[1]: systemd-timedated.service: Deactivated successfully.
  Nov  6 12:57:44 sna-vm systemd[1606]: Started VTE child process 4376 launched by gnome-terminal-server process 2335.
  Nov  6 18:57:54 sna-vm systemd[1]: Stopping System Logging Service...
  Nov  6 18:57:54 sna-vm rsyslogd: [origin software="rsyslogd" swVersion="8.2112.0" x-pid="889" x-info="https://www.rsyslog.com"] exiting on signal 15.
  Nov  6 18:57:54 sna-vm systemd[1]: rsyslog.service: Deactivated successfully.
  Nov  6 18:57:54 sna-vm systemd[1]: Stopped System Logging Service.
  Nov  6 18:57:54 sna-vm systemd[1]: Starting System Logging Service...
  

Change time zone with symlink

• You can manually change the time zone with a symlink. The symlink at /etc/localtime points to the time zone that is currently configured.

  $ ls -l /etc/localtime
  lrwxrwxrwx 1 root root 36 ноя  6 18:54 /etc/localtime -> /usr/share/zoneinfo/Asia/Vladivostok
  

• Remove the symlink

  $ sudo rm -rf /etc/localtime
  

• Let’s change time zone to Moscow time. To do this, create a new symlink to the Moscow time Europe/Moscow in /usr/share/zoneinfo/.

  $ sudo ln -s /usr/share/zoneinfo/Europe/Moscow /etc/localtime
  

• Check the time zone again.

  $ timedatectl
  

Task 2: NTP

We are going to set up an NTP server and then configure a client to use this NTP server. You need two VMs to test this. You can work in pairs to set up the client-sever infrastructure.

Installing and configuring an NTP server

• First install NTP and it’s dependencies.

  $ apt install -y ntp
  $ apt install -y ntpstat
  

• Open the NTP configuration file /etc/ntp.conf and configure the remote NTP server.

  $ vi /etc/ntp.conf
  

  Locate the following lines in the configuration file
  

  Replace those lines with the following

  
  
  
  pool time1.google.com iburst
  pool time2.google.com iburst
  pool time3.google.com iburst
  pool time4.google.com iburst
  

  Also place a comment on pool ntp.ubuntu.com.
  You should have something similar to the following after this modification:
  

• Restart and enable the NTP service to apply the change.

  $ systemctl restart ntp
  $ systemctl enable ntp
  

• Allow NTP port on the firewall.

  $ sudo ufw allow ntp
  

• It will take some time for your NTP server to synchronize with the google NTP servers. Wait for about a minute and run the following command to check the sync status:

  $ ntpstat
  

  You should get output similar to the following:

  synchronised to NTP server (185.125.190.56) at stratum 3 
     time correct to within 977 ms
     polling server every 64 s
  

  The local NTP server is ready.

• View all NTP peers.

  $ ntpq -p
       remote           refid      st t when poll reach   delay   offset  jitter
  ==============================================================================
   time1.google.co .POOL.          16 p    -   64    0    0.000   +0.000   0.004
   time2.google.co .POOL.          16 p    -   64    0    0.000   +0.000   0.004
   time3.google.co .POOL.          16 p    -   64    0    0.000   +0.000   0.004
   time4.google.co .POOL.          16 p    -   64    0    0.000   +0.000   0.004
  +time1.google.co .GOOG.           1 u   15   64    1   70.098   +3.123   8.037
  *time2.google.co .GOOG.           1 u   17   64    1   38.087   +6.703   6.897
  +time3.google.co .GOOG.           1 u   15   64    1   39.216   +4.192   7.641
  +time4.google.co .GOOG.           1 u   18   64    1   62.781   +8.027  13.030
  

Configuring the client

We show two approaches for configuring the client. You can use either the systemd service systemd-timesyncd that comes with systemd-based systems by default, or use chronyd.

1. Using systemd-timesyncd

• Edit the service configuration file:

  $ vi /etc/systemd/timesyncd.conf
  

  Add the following line to the file

  NTP=<ntp-server-address>
  

  You should have something like this:
  
  Save and exit the file.
• Restart the time sync service

  $ systemctl restart systemd-timesyncd
  

• Check the status of the time synchronisation:

  $ timedatectl timesync-status
         Server: 192.168.132.136 (192.168.132.136)
  Poll interval: 1min 4s (min: 32s; max 34min 8s)
           Leap: normal
        Version: 4
        Stratum: 2
      Reference: D8EF2308
      Precision: 4us (-18)
  Root distance: 33.583ms (max: 5s)
         Offset: -9.704ms
          Delay: 675us
         Jitter: 0
   Packet count: 1
      Frequency: -81,109ppm
  

2. Using chrony

• Install chrony

  $ apt -y install chrony
  

• Edit the chrony configuration file:

  $ vi /etc/chrony/chrony.conf
  

  Locate the following lines and remove them
  
  Then add the address of the local NTP server we have configured in the form:

  server <ntp-server-address> iburst prefer
  

  
  Save the configuration and exit.
• Restart and enable the chronyd service.

  $ systemctl restart chrony
  $ systemctl enable chrony
  

• View all sources

  $ chronyc sources -v
  

  Remember that chrony is a client/server utility. Therefore, other devices can be configured to use this “client” as their NTP “server”.

Test the setup

• First check the current time on the client system.

  $ timedatectl
                 Local time: Вс 2022-11-06 18:35:16 MSK
             Universal time: Вс 2022-11-06 15:35:16 UTC
                   RTC time: Пн 2022-11-07 11:49:46
                  Time zone: Europe/Moscow (MSK, +0300)
  System clock synchronized: yes
                NTP service: active
            RTC in local TZ: no
  

• Go to the NTP server and change the date to something completely wrong.

  $ timedatectl set-time 2030-06-10
  

• Go to the client system and restart the timesync service to force an immediate sync with the local NTP server.

  $ systemctl restart systemd-timesyncd
  OR
  $ systemctl restart chrony
  

• Check the time on the client machine, and you should see that the client has been configured with the new date we added to the server.

  $ timedatectl
                 Local time: Пн 2030-06-10 00:01:19 MSK
             Universal time: Вс 2030-06-09 21:01:19 UTC
                   RTC time: Вс 2030-06-09 21:01:19
                  Time zone: Europe/Moscow (MSK, +0300)
  System clock synchronized: yes
                NTP service: active
            RTC in local TZ: no
  

• The local NTP server will later sync with the Google NTP servers we configured earlier and correct its time. The client machine will then sync with the local NTP server and correct its time too.
• Wait for about a minute or two and check the time on the NTP server to see the change.

  $ timedatectl
                 Local time: Вс 2022-11-06 18:42:19 MSK
             Universal time: Вс 2022-11-06 15:42:19 UTC
                   RTC time: Вс 2022-11-06 15:42:19
                  Time zone: Europe/Moscow (MSK, +0300)
  System clock synchronized: yes
                NTP service: n/a
            RTC in local TZ: no
  

  The time on the client machine will also be corrected after a while.

Exercise 2: Package managers

A package manager automates the process of installing, configuring, upgrading, and removing packages.
There are several package managers depending on the OS. This lab focuses on Ubuntu package managers.
Note that Ubuntu is based on the Debian distro and it uses the same APT packaging system as Debian and shares a huge number of packages and libraries from Debian repositories.

Task 3: dpkg

dpkg is a tool that allows the installation and analysis of .deb packages. It can also be used to package software.

• View a list of all installed packages

  $ dpkg -l
  

  You should get an output similar to the following:
  

• Install a local .deb file using the command dpkg -i <deb-package>.
  Let’s download and install Google Chrome browser

  $ wget https://dl.google.com/linux/direct/google-chrome-stable_current_amd64.deb
  $ dpkg -i google-chrome-stable_current_amd64.deb
  

• Verify the package installation using dpkg -s <deb-package>

  $ dpkg -s google-chrome-stable
  

  You get an output similar to the following

  Package: google-chrome-stable
  Status: install ok installed
  Priority: optional
  Section: web
  Installed-Size: 299404
  Maintainer: Chrome Linux Team <chromium-dev@chromium.org>
  Architecture: amd64
  Version: 107.0.5304.87-1
  Provides: www-browser
  Depends: ca-certificates, fonts-liberation, libasound2 (>= 1.0.17), libatk-bridge2.0-0 (>= 2.5.3), libatk1.0-0 (>= 2.2.0), libatspi2.0-0 (>= 2.9.90), libc6 (>= 2.17), libcairo2 (>= 1.6.0), libcups2 (>= 1.6.0), libcurl3-gnutls | libcurl3-nss | libcurl4 | libcurl3, libdbus-1-3 (>= 1.5.12), libdrm2 (>= 2.4.60), libexpat1 (>= 2.0.1), libgbm1 (>= 8.1~0), libglib2.0-0 (>= 2.39.4), libgtk-3-0 (>= 3.9.10) | libgtk-4-1, libnspr4 (>= 2:4.9-2~), libnss3 (>= 2:3.26), libpango-1.0-0 (>= 1.14.0), libwayland-client0 (>= 1.0.2), libx11-6 (>= 2:1.4.99.1), libxcb1 (>= 1.9.2), libxcomposite1 (>= 1:0.4.4-1), libxdamage1 (>= 1:1.1), libxext6, libxfixes3, libxkbcommon0 (>= 0.4.1), libxrandr2, wget, xdg-utils (>= 1.0.2)
  Pre-Depends: dpkg (>= 1.14.0)
  Recommends: libu2f-udev, libvulkan1
  Description: The web browser from Google
   Google Chrome is a browser that combines a minimal design with sophisticated technology to make the web faster, safer, and easier.
  

• List all files installed by a package with the command dpkg -L <package-name>

  $ dpkg -L google-chrome-stable
  

• Remove a package using dpkg -r <package-name>

  $ dpkg -r google-chrome-stable
  

• Check the status of the package again and you should see that it is in the deinstall state, but the configuration files are still present.

  $ dpkg -s google-chrome-stable
  Package: google-chrome-stable
  Status: deinstall ok config-files
  

  The -r option simply removes the package but all the configuration files are preserved.

• To remove a package along with its configuration files, specify the --purge option.

  $ dpkg --purge google-chrome-stable
  

• Check the status of the package to verify that the package and all its configuration files have been removed.

  $ dpkg -s google-chrome-stable
  dpkg-query: package 'google-chrome-stable' is not installed and no information is available
  Use dpkg --info (= dpkg-deb --info) to examine archive files.
  

Task 4: APT

The Advanced Packaging Tools (APT) is a package manager on Ubuntu systems. apt acts as a user friendly tool that interacts with dpkg. Unlike dpkg, apt allows download and installation of packages from online repositories.

• View all available packages in your repository

  $ apt list
  

• List only installed packages

  $ apt list --installed
  

• Search for a package using apt search <package-name>. Let’s search for “chromium”.

  $ apt search chromium
  

  
• After knowing the correct package name, you can find out more details about the package using apt show <package-name>

  $ apt show chromium-browser
  

• Proceed to install the package using apt install <package-name>

  $ apt install chromium-browser
  

• Remove a package using apt remove <package-name>

  $ apt remove chromium-browser
  

You can install or remove multiple packages in one command by separating them by spaces. e.g apt install package1 package2 package3.
To remove multiple packages is similar e.g apt remove package1 package2 package3.

• Specify the remove option in combination with the --purge option to remove a package along with its configuration.

  $ apt remove --purge chromium-browser
  

• Specify autoremove to remove the package and its dependencies, if not used by any other application. The format is shown below:

  $ apt autoremove <package-name>
  

• You can update the APT package index to get a list of the available packages. This list can indicate installed packages that need upgrading, as well as new packages that have been added to the repositories.
  The reposiroties are defined in the /etc/apt/sources.list file and in the /etc/apt/sources.list.d directory.
• View the sources.list file to see all the defined repositories.

  $ cat /etc/apt/sources.list
  

• To update the local package index with latest updates to repositories, use the following command:

  $ apt update
  

• APT maintains a list of packages (package index) in /var/lib/apt/lists/.

  $ ls -lah /var/lib/apt/lists/
  

• To upgrade a single package that has been previously installed, run the apt install <package-name> command.
• To upgrade all installed packages, run the following command:

  $ apt upgrade
  

  This command will upgrade all packages that can be upgraded without installing additional packages or removing conflicting installed packages.
• Run apt full-upgrade to upgrade the packages, the kernel, and remove conflicting packages or install new ones. The full-upgrade option is “smart” and can remove unnecessary dependency packages, or install new ones (if required).

Task 5: sources.list

• View the sources.list file without the comments

  $ grep -o '^[^#]*' /etc/apt/sources.list
  deb http://ru.archive.ubuntu.com/ubuntu/ jammy main restricted
  deb http://ru.archive.ubuntu.com/ubuntu/ jammy-updates main restricted
  deb http://ru.archive.ubuntu.com/ubuntu/ jammy universe
  deb http://ru.archive.ubuntu.com/ubuntu/ jammy-updates universe
  deb http://ru.archive.ubuntu.com/ubuntu/ jammy multiverse
  deb http://ru.archive.ubuntu.com/ubuntu/ jammy-updates multiverse
  deb http://ru.archive.ubuntu.com/ubuntu/ jammy-backports main restricted universe multiverse
  deb http://security.ubuntu.com/ubuntu jammy-security main restricted
  deb http://security.ubuntu.com/ubuntu jammy-security universe
  deb http://security.ubuntu.com/ubuntu jammy-security multiverse
  

• Each line in the sources.list has a structure in the following order: Type, URL, Distribution, and Component. Let’s analyse the first line in the sources.list above.
  • The Type is deb. The term deb indicates that it is a repository of binaries.
  • The repository URL is http://ru.archive.ubuntu.com/ubuntu/. This is the location of the repository where the packages will be downloaded.
  • The Distribution is jammy. This is the short code name of the release. Run $ cat /etc/os-release to view the VERSION_CODENAME of your system.
  • The Components are main and restricted. These are information about the licensing of the packages in the repository.
    • main contains Canonical supported free and open source software.
    • restricted contains proprietary drivers for devices.
    • universe contains community supported free and open source software.
    • multiverse contains software restricted by copyright or legal issues.

Adding repositories

• Let’s try to install a package that is not in Ubuntu repository by default. Install MongoDB

  $ apt install mongo-db
  

  You should get an output similar to the following

  Reading package lists... Done
  Building dependency tree... Done
  Reading state information... Done
  E: Unable to locate package mongodb-org
  

  We need to add the MongoDB repository to our repository sources.
• The basic syntax of the add-apt-repository command is as follows:

  $ add-apt-repository [options] repository
  

  The repository can be a regular repository entry that can be added to sources.list in the format deb http://ru.archive.ubuntu.com/ubuntu/ distro component or a PPA repository in the ppa:<user>/<ppa-name> format.
• First import MongoDB PGP key. The key is used to verify the integrity of packages that are downloaded from this repository.

  $ curl -fsSL https://www.mongodb.org/static/pgp/server-6.0.asc | sudo gpg --dearmor -o /etc/apt/trusted.gpg.d/mongodb-6.gpg
  

• Create a list for MongoDB

  $ add-apt-repository 'deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu focal/mongodb-org/6.0 multiverse'
  

  Alternatively, you can manually create the list file and add the repository to it.

  echo "echo "deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu focal/mongodb-org/6.0 multiverse" | sudo tee /etc/apt/sources.list.d/mongodb-org-6.0.list
  

• View the new list file that has been created

  $ cat /etc/apt/sources.list.d/*mongodb*.list
  

• The add-apt-repository command automatically updates the local package database for you. If you added the repository via an alternative means, you need to run $ apt update to update the local package database.
• View the package index directory to see the MongoDB related files created.

  $ ls -lah /var/lib/apt/lists/ | grep mongodb
  

  MongoDB requires libssl1.1 (>= 1.1.1). So let’s download and install this package before proceeding

  $ wget http://archive.ubuntu.com/ubuntu/pool/main/o/openssl/libssl1.1_1.1.1f-1ubuntu2.16_amd64.deb
  $ dpkg -i ./libssl1.1_1.1.1f-1ubuntu2.16_amd64.deb
  

• You can now proced to install MongoDB from the newly enabled repository.

  $ apt install mongodb-org
  

  You can answer the prompt that asks you to type Y to verify your choice by adding the option -y to your install command in the format apt install mongodb-org -y. This is very useful when writing scripts that install packages.

• Verify that MongoDB has been installed

  $ mongod --version
  

• You can remove a previously enabled repository using the format add-apt-repository --remove repository. Let’s remove the MongoDB repository

  $ add-apt-repository --remove 'deb [ arch=amd64,arm64 ] https://repo.mongodb.org/apt/ubuntu focal/mongodb-org/6.0 multiverse'
  

• Run the following commands to verify that the repository has been removed.

  $ ls -lah /var/lib/apt/lists/ | grep mongodb
  $ cat /etc/apt/sources.list.d/*mongodb*.list
  

Task 6: Creating a custom Ubuntu package

• Create a directory for the package. We will name the package snalab.

  $ mkdir snalab
  

• Create the internal structure by placing your program files where they should be installed to on the target system. In this case, we want to place the program file in /usr/local/bin on the target system, therefore we create the directory snalab11/usr/local/bin.

  $ mkdir -p snalab/usr/local/bin
  

• Create the program file (script) snalab/usr/local/bin/snalab and add the following to it.

  #!/bin/bash
  echo "Hello World. This is SNA Lab"
  

• Give the program file execute permission

  chmod +x snalab/usr/local/bin/snalab
  

• Create a directory DEBIAN in snalab

  $ mkdir snalab/DEBIAN
  

• Create the control file in the DEBIAN directory. The control file contains package description and information about the maintainer. Create the file snalab/DEBIAN/control and add the following content.

  
  
  
  
  Package: snalab
  Version: 1.0
  Maintainer: Awwal
  Architecture: all
  Description: Hello SNA
  

  These are mandatory fields in the control file. There are several other fields that can be defined.

• Build the package with dpkg

  $ dpkg-deb --build --root-owner-group snalab
  

  The --root-owner-group flag makes all deb package content owned by the root user. Without this flag, all files and folders would be owned by your user, which might not exist in the target system the deb package would be installed to.

• You should have a debian package in your CWD named snalab.deb. Proceed to install this package.

  $ dpkg -i snalab.deb
  

  You should get an output similar to the following

  Selecting previously unselected package snalab11.
  (Reading database ... 195723 files and directories currently installed.)
  Preparing to unpack snalab11.deb ...
  Unpacking snalab11 (1.0) ...
  Setting up snalab11 (1.0) ...
  

• Run the newly installed package.

  $ snalab
  Hello World. This is SNA Lab
  

You can have a compiled application in place of the script we have used.

Questions to answer

Instruction: Show all steps taken including screenshots of commands executed, files created, and configuration added.

1. What alternative do you have for configuring your NTP server pool if you don’t want to be dependent on NTP servers on the internet. The time must be accurate and appear to be in sync with other devices globally. Describe how you will perform this setup.

   The accuracy of the time should be strongly considered.

2. You have two Linux servers whose time won’t stay in sync for various reasons. They tend to drift so much that they have a 30 second difference after 7 days of operation. What can you do to ensure that they stay in sync with each other without relying on external devices or servers?

   Hint: Inaccurate time is not a problem in this case. The goal is to ensure that both servers are in sync.

3. What are the differences between apt and apt-get?
4. Why should System Administrators prefer apt upgrade over apt full-upgrade?
5. Show how you will install Atom text editor from the apt repository. Provide explanation for every step you take.
   • After adding the repository, show the output when you run $ apt search atom

   You are not allowed to manually download the debian package and install it.

6. Create an Ubuntu package that meets the following requirements:
   • The package creates the directory /var/helloworld/ on the target system.
   • The package contains the python script /var/helloworld/helloworld.py. The python script is simple:

     #!/usr/bin/env python3
     print("Hello, World!")
     

   • The package should deploy a bash script helloworld that executes /var/helloworld/hello.py on the target system.

Take the following steps after building the package

• List the content of the package with the command $ dpkg -c <package-name>.deb.
• Install the package and show all artifacts added to your system by the package.

After a user installs your package, he should be able to run $ helloworld from the terminal without additinonal steps.
The expected flow of execution is helloworld (bash script) -> helloworld.py -> Output (Hello, World!)

Bonus

The bonus tasks encourage you to failiarize yourself with CentOS and RPM packages. Linux distributions such as Red Hat and CentOS are very common and they utilize RPM packages.

7. Find and add new source repository to be used for yum.
   • Install a package from it (for example MongoDB).
   • Check with the RPM package manager to verify that the package was installed, and provide details such as dependencies needed.
   • Find logs related to all actions from the previous steps.
8. Sometimes you might have access to an open-source application source code but might not have the RPM file to install it on your system. In that situation, you can either compile the source code and install the application from source code or build an RPM file from source code by yourself and use the RPM file to install the application. There might also be a situation where you want to build a custom RPM package for the application that you developed.
   Create an RPM package to deploy any application of your choice.