Linux provides tools to manage disk partitions and file systems. A system administrator should be able to:

• Understand the PC architecture concerning hard disks
• Manage partitions (i.e. display information, create, delete, modify, etc.)
• Create a file system on a new partition (e.g. ext3, swap)

A file system can only be used when mounted. It is important to know how to:

• Create a mount point
• Mount (and unmount) a file system
• Mount using labels and UUIDs
• Manage fstab
• Manage swap

Of course, as soon as data exists on a file system, it is important to monitor the system regularly:

• Check an existing file system
• Monitor free space using df
• Monitor usage using du
• Monitor SMART status using smartctl

In a file system where users are allowed to create files, it is sometimes important to be able to impose user quotas. A Linux system administrator should be able to:

• Set up quota for an existing file system
• Use quotaon and quotaoff
• Set limits with edquota (and understanding soft and hard limits)
• Check quotas using quota
• Produce reports using repquota
• Warn users using warnquota

Even though Linux has a lot of commands, sometimes it is necessary to write simple (and some not so simple) scripts when we have to automate jobs.

The Bash shell is capable of running scripts and it also possible to write scripts in the various programming languages that exist in Linux (such as AWK, Python and Ruby).

The following scripts need to be written and tested:

• booklist
  Manage a book database: print, insert, select, delete, update
• compareperm
  Check whether two files have the same permissions
  Usage: compareperm file1 file2
• findhardlinks
  Find links (not symbolic) to a given file
  Usage: findhardlinks file [directory]
• largestfile
  prints the largest file in a directory
  Usage: largestfile directory
• summarise
  prints number of normal files, directories and symbolic links
  summarise directory. Two versions of the script can be written: one that does three passes through the files and can be slow and a second version which only does one pass through the files and, consequently, is quicker.
• anagrams
  finds and prints all the anagrams in /usr/share/dict/words. The technique used was described by Jon Bentley in his magnificent book, Programming Pearls.

The Red Hat Package Manager (RPM) is an open packaging system, which runs on Red Hat Enterprise Linux as well as other Linux and UNIX systems like SuSE, Mandriva, Fedora and CentOS.

RPM is used to:

• Install new packages
• Uninstall existing packages
• Upgrade existing packages to the latest version
• Verify the integrity of existing packages

RPM also has powerful querying facilities. Those can be used, for example, for listing all installed packages, getting information on an installed package, identifying from which package a specific file is from, etc.

As RPM installs files obtained from the Internet, it also supports the use of cryptographic keys to authenticate packages.

Package Management Tool

RPM is a command line program and can be somewhat complex to use. For those who prefer graphical applications, there exists the a graphical package management tool.

YUM (Yellowdog Updater Modified)

YUM is now the standard tool for package management in Red Hat Enterprise Linux and derivatives. For most usual tasks, YUM should be used in preference to RPM as it supports new features that are now considered to be essential by most system administrators.

For example, YUM can install packages from various sources, called repositories. Those repositories can be on the Internet (e.g. an official Red Hat repository), on a LAN as well as local. Creating a local repository is a relatively straightforward task. This opens a lot of possibilities like downloading packages from a mirror, creating a repository of them on the LAN and configuring all computers in an organisation to use that rapidly-accessible repository.

Furthermore, YUM is better than RPM as it tracks (and resolves) dependencies among packages automatically. This makes installing complex packages trivial.

Package Management with APT

The Advanced Packaging Tool (APT) as used in Debian, Ubuntu and Linux Mint is the equivalent of RPM/YUM.

In general, system administrators prefer using the aptitude tool instead of the apt-get and apt-cache commands which are lower level tools with fewer capabilities.

aptitude can either be used as a command line tool or as a text application (see picture above). In both cases, aptitude can then:

• install a package with its dependencies
• remove a package while leaving its configuration files
• purge a package with its configuration files
• remove auto-installed packages which are no longer required
• display detailed information about packages
• search for packages which match a regular expression

aptitude is more advanced than YUM as it knows how to track dependencies both on installation and removals. YUM only resolves dependencies when installing packages.

Logging

EL6 Linux can be configured to log the various events occurring in files residing in /var/log. It is also possible to log to the console as well as to log to a remote log server.

Logging is done by the syslog demon which defines the following seven priorities: debug (less critical), info, notice, warning, err, crit, alert and emerg (the most critical). syslog is configured using the syslog.conf file.

The work to be done is to enable remote logging and make other computers log to it.

One important consequence of (heavy) logging is the need for log rotation. This makes sure that the log files remain at a manageable size and also takes care of archiving old log files. Log rotation can also be used to delete old log files which are not relevant anymore.

What is the relationship between cron and log rotation? How is log rotation configured?

Of course, the whole purpose of logging is to monitor the log files on a regular basis in order to detect unexpected events. Look at the various log files in /var/log and think about the different unexpected events that might appear in them and how those events might be detected.

At what frequency should log files be monitored? How?

In EL7 onwards, logging is managed by system and logs can be examined using journalctl.

Backup

A Linux system administrator should be able to:

• Plan a backup strategy
• Dump a raw device to a file or restore a raw device from a file (using dd for example)
• Perform partial and manual backups and restore the files (using tar for example)
• Synchronise two directories (using rsync for example)

There are various tools that are available for doing backups. Some are dated (e.g. dump/restore) and are being deprecated. It is important that the proper tools be used when needed.

System time

Finally, it is important that the time and date be properly set (EL6 and EL7) as essential services like cron and anacron depend on time being correct.

The work to be done is to ensure that the Linux server gets its time and date from a NTP (Network Time Protocol) server found on the Internet (i.e. become an NTP client). Setting up an NTP server is not required.

Geolocation and Google Maps are two important features of most Android devices.

Geolocation is a feature which Android applications can use to obtain the position of the device. Geolocation uses either the GPS, the GSM network or Wifi to determine (with different levels of accuracy) the latitude and longitude of the device. It can also determine the altitude, bearing as well as speed of the device if possible.

The application to develop should display all relevant geolocation information when the user clicks on Where am I?!? The location should be automatically updated when the device moves.

Essential Android classes for geolocation include LocationManager, LocationListener and Location.

Google Maps

The application will have to be enhanced to display a Google Map of the position of the device instead of just textual information. This Google Map will be updated whenever the device moves.

To display a map from Google Maps in Android 3.0 and up, it is important to use the Google Play Services.

• Ensure that you have installed the Google Play services application on your physical device.
• Make sure that the Google Play services is setup properly for the project in Android Studio. Google Play Services includes the Google Maps capability.
• Google Maps requires an API Key to work. Obtain the key corresponding to the debug certificate.
• Finally, the AndroidManifest of the project as well as the layout need to be modified accordingly.

Once this is done, the idea is to use classes provided by Google to control with the map shown.

In Android, an Intent is a message which allows you to request functionality from other Android components, whether those components are from the same application or from a different one. An intent can be used for instance to open an activity from the same app or to open an activity from another app.

SongExplorerForAll v7

In SongExplorerForAll v6, we created an about menu in the action bar. Here, clicking on the about menu displays a dialog which gives information about the app.

When creating an intent, we have to specify the type of action to perform. Here, we use ACTION_VIEW which is basically used when we need to display data to the user.

SongExplorerForAll v8

Another type of action is ACTION_SEND. This is used when we want the user to be able to share some data through another app. In SongExplorerForAll v8, when the user clicks on the share icon in the action bar, the latter will be able to share information about the Song Explorer For All app. The user is presented with a list of apps which can perform the sharing action (e.g. Gmail), from which he/she can choose.

There are two types of intents namely explicit intents and implicit intents. When using explicit intents, we have to explicitly specify the component to start by name. On the other side, when using implicit intents, we simply declare the action to perform. The Android system then finds appropriate component(s) to handle the intent. If there are several apps which can handle the intent, we can show a chooser dialog.