Software Management

Using package management systems.

Need for a Package Manager

Tools for installing, updating, removing, managing software.
Install new / updated software across network.
Package - File look up, both ways.
Database of packages on the system including versions.
Dependency checking.
Signature verification tools.
Tools for building packages.

Package Types

Package
- RPM Used to manage packages of:
  - Red Hat Enterprise
    Derivatives:
    - CentOS
    - Fedora
    - Oracle Linux
  - SUSE Enterprise Linux
    Derivatives:
    - openSUSE
- DEB
  Used to manage packages of:
  - Debian
    Derivatives:
    - Ubuntu
      Derivatives:
      -Mint
    - Knoppix
      Run from live CD.

Since, we are using Ubuntu OS, we should get familiar with Debian package type.

`lsb_release` command

To check the operating system, use the command below.

Codename is helpful while searching version specific packages.

 ~$ lsb_release -a
 No LSB modules are available.
 Distributor ID:	Ubuntu
 Description:	Ubuntu 22.04.1 LTS
 Release:	22.04
 Codename:	jammy

Architectures

Linux OS is available for a wide variety of architectures, and hence the packages.
Package
- amd64 | x86_64
- i386 | x86
- arm : mobile devices.
- ppc64el | OpenPower : RISC-IV (Shakti Processor)
- all | noarch | src : source codes/ pieces of softwares.
It is important to install system compatible package to avoid any risk.
But, thankfully package manager takes care of this.
Use uname -a to check system architecture.

Package Management Tools

Package Type
- RPM : Yellowdog Updater Modifier (yum)
  - Red Hat Package Manager (rpm) : yum internally calls this package to update software.
  - Dandified YUM (dnf) : modified version of yum
- DEB
  - synaptic : GUI based
  - aptitude : command line based
    - Advanced Package Tool (apt) is used by both synaptic and aptitude at the backend.
      - dpkg : used by apt at the backend.
        
        dpkg-deb : used by dpkg at the backend.

Package Management in Ubuntu Using `apt`

Inquiring Package DB

apt-cache search keyword
- Search packages for a keyword
- Run the commands below in terminal to see the output.
```
 apt-cache search fortune
```
  In the output we are interested in line that starts with fortunes Click to see sample output More on the command fortune.
```
 apt-cache search nmap		
```
  In the output we are interested in nmap - The Network Mapper line.
```
 apt-cache search wget		
```
  In the output we are interested in wget - retrieves files from the web line.
apt-cache pkgnames
- List of all packages installed
- pkgnames is a keyword to list all packages in the system.
```
 apt-cache pkgnames | less
```
- get sorted output using sort command.
```
 apt-cache pkgnames | sort | less
```
- passing search key (nm) to pkgnames to search only for packages which start with nm.
```
 apt-cache pkgnames nm
```
- Try commands above in terminal.
apt-cache show [-a] package
- Display package records of a package
- To see the details of package nmap
```
 apt-cache show nmap
```
  - Sample Output
  - Filename: pool/universe/n/nmap/nmap_7.91+dfsg1+really7.80+dfsg1-2build1_amd64.deb
  - The text in italic has foramt that signifies special information, that can be seen here
  - package name: nmap
  - varsion: 7.91+dfsg1+really7.80+dfsg1
  - revision: 2build1
  - architecture: amd64
  - The priority of nmap is extra. See Priorities
  - Section: universe/net means that the package comes uder network utility. See Sections
- Try commands below in terminal
```
 apt-cache show wget
```
```
 apt-cache show fortunes
```

Package Names

The filenames follow specific format, it includes package name, version, release/revision and architecture separated by some special characters.

Package
- RPM
  - Format : package-version-release.architecture.rpm
- DEB
  - Format : package_version-revision_architecture.deb

Package Priorities

The apt-cache show pkgname command also lists the priority of the package. A user can decide about installing a package based on priority.

required
- essential to proper functioning of the system.
important
- provides functionality that enables the system to run well.
standard
- inluded in the standard system installation.
optional
- can omit if you do not have enough storage.
extra
- could conflict with packages with higher priority, has specialized requirements, install only if needed.
e.g. for wget, the priority is standard, for fortunes the priority is optional

Package Sections

focal : https://packages.ubuntu.com/focal
jammy : https://packages.ubuntu.com/jammy
Package section signifies the use case of the package.
There are a large number of package sections.
e.g.
- The package fortunes belongs to section universe/games.
- package wget belongs to section web.

Checksums

It is important to know the packages we are installing are authentic.
Checksums help in knowing if the package is authentic or not.
This is important because while downloading the package (either from official/unofficial source) may get tampered.
Even with small change in code, the checksum strings changes drastically.
The following commands used to check for diffrent checksums.

`md5sum`

md5sum [filename]

It gives 128 bit checksum string irrespective of size of file.

 ~$ md5sum nmap_show.txt
 2717ed2e8f6dd4a63a20c0317d695161  nmap_show.txt

When no input file is given, it reads the standard input (- is the default filename for stdin).

Write text and hit <ctrl+D>.

 ~$ md5sum
 Overflow on /dev/null, please empty the bit bucket.
 e67ef45f18ba7f8a6c339c08af30f72b  -
 ~$ md5sum
 Overglow on /dev/null, please empty the bit bucket.
 ea16952d936440cdddcb1a68cdbb7295  -

`sha1sum`

sha1sum [filename]

It gives 160 bit SHA1 checksum string.

We will read the standard input, on same string given in md5sum.

 ~$ sha1sum
 Overflow on /dev/null, please empty the bit bucket.
 61d7ab21e9961d11640172e3183b86296c01874d  -
 ~$ sha1sum
 Overglow on /dev/null, please empty the bit bucket.
 b52111e02999a26af3ebb2cdef7f0893dbbb92b1  -

Try this command with filename on any file you wish.

`sha256sum`

sha256sum [filename]

It gives 256 bit SHA256 checksum string.

We will read the standard input, on same string given in md5sum.

 ~$ sha256sum
 Overflow on /dev/null, please empty the bit bucket.
 27983a23a8319160adc6b4e2cadfac29f4e445e50998e0a5b4888c0becf51ffe  -
 ~$ sha256sum
 Overglow on /dev/null, please empty the bit bucket.
 e2919763cc71cd324d29f96483c7f46eb3d6b64ab17ce3448aaca4da9b2e5b39  -

Try this command with filename on any file you wish.

Who can install packages?

Only administrators called sudoers can install / upgrade / remove packages.

/etc/sudoers
- su : super user
- do : can execute
- This file constains list of sudoers.
- Only sudoers can read this file.
```
 ~$ whoami
 guest
 ~$ sudo cat /etc/sudoers
 [sudo] password for guest:
 Sorry, try again.
 [sudo] password for guest:
 guest is not in the sudoers file. This incident will be reported.
```
  - When we run the command sudo cat /etc/sudoers it asks for password.
  - For wrong password, the password is asked again.
  - If the passwrod is correct, but the user is not listed in the file, it will notify in and report the login attempt to administrator.
  - If $USER is listed in /etc/sudoers, the file content will be dumped on screen for right password.
- The failure if any is recorded in /var/log/auth.log file.
- To open this file you should have super user privilege.
- The file lists timestamps and corresponding session details.

Which website is used to download packages?

The details of websites are given in the following hierarchy.

/etc/apt : directory
- sources.list : regular file
```
 /etc/apt$ cat sources.list
```
  - The output is urls for repositories used for installing updates, upgrades and source code.
  - It also has comments starting with # symbol.
  - The comments describe the url, and it gives information about for what purpose the url is being used.
- sources.list.d : directory / folder
  - This folder contains files which has information about the repositories of third-party softwares.

`apt-get` and `apt`

Updating and Installing Packages

This command is used to fetch updates and upgrades from repositories listed in sources.list and files in sources.list.d.
This command should be run as sudo.
update : This option is used to fetch the update details.
- The details fetched is saved as cache.
```
 sudo apt-get update
```
  or
```
 sudo apt update
```
upgrade : This option is used to upgrade all installed packages.
- This option reads the details fetched by apt-get update command.
```
 sudo apt-get upgrade
```
  or
```
 sudo apt upgrade
```
- This lists how many updates are available and how much data needs to be downloaded.
- This command asks for comformation to proceed the download.
install : It is used to install a package.
- To install fortunes package. See fortune command.
```
 sudo apt-get install fortunes 
```
reinstall : It is used to download and install the new version of the package.
- To reinstall fortunes package.
```
 sudo apt-get reinstall fortunes 
```

Removing or Cleaning up Packages

autoremove : Remove packages that were automatically installed to satisfy a dependency and not needed.
```
 sudo apt autoremove
```
- By removing these packages you can free some space.
clean : Clean local repository of retrieved packages.
- apt-get clean
- Usually, we may want to revert back to a particular version of a package, it may be ok to keep the retrieved package files.
remove : This option is used to remove a particular package
```
 sudo apt-get remove fortunes fortune-mod
```
- This command removes the fortunes package.
- fortune-mod contains fortune cookies, hence it also needs to be removed.
purge : Purge package files from the system.
- apt-get purge pkgname
- Removes package files and configuration files.
- Be careful while using this command.

dpkg suite

`dpkg`

Package management in Ubuntu using dpkg. The following filesystem contains text information about packages.

/var/lib/dpkg
- arch : regular file
  - Architectures for which packages are installed on the system.
- available : regular file
  - Contains all packages and it's full information.
  - apt-cache show nmap
- status : regular file
  - Information about the packages whether they are installed or not.
- info : directory / folder
  - Set of files for each package.
  - files for wget package.
```
 ~$ ls wget*
 wget.conffiles  wget.list  wget.md5sums
```
  - wget.conffiles : contains path of configuration file, which is /etc/wgetrc
  - wget.list : contains list of files that are copied on the system during installation.
  - wget.md5sums : contains md5sum of files used by wget package.
  - This md5sum data can be used to check if the file is authentic or not.
dpkg -l pattern
- List all packages whose names match the pattern.
```
 dpkg -l nmap
```
- prints name, version, architecture and description of package nmap.
dpkg -L package
- List installed files that came from package.
```
 dpkg -L nmap
```
- Prints list of directories and files added to the system and used by nmap package.
dpkg -s package
- Report the status of package.
```
 dpkg -s nmap
```
- Prints the status of whether the package nmap is installed or not and other info.
- The output is similar to apt-cache show command.
dpkg -S pattern
- Search installed packages for a file using pattern.
- Prints the name of the package that made the particular executable available.
```
 dpkg -S /usr/bin/perl
```
- Prints the name of the package that the executable /usr/bin/perl belongs to.
- Perl is scripting language used specifically for text processing using regex.
dpkg -i package_version-revision_architecture.deb
- You can directly install deb package using the command.
By default use package management pointing to a reliable repository.
This will take care of compatibility and dependency if any for the package.
Uninstalling packages using dpkg is not recommended!
Other package management tools: apt, dpkg, snap, docker

`dpkg-query`

It is a tool to query the dpkg database. Prints package names and section name to which the package belongs.

dpkg-query -W [package-name-pattern...]
- Show the list of packages
dpkg-query -f=format
- Specify format for the output.
- Some formats : Section, binary:Package
- Introduce escapes using \.
  
  ' \n ' : newline, ' \r ' : carriage return, ' \t ' : tab.
Examples
- Prints name of the section and package of each package.
```
 dpkg-query -W -f="${Section} ${binary:Package}\n" | less
```
- Prints name of the section and package of each package in alphabetically sorted order.
```
 dpkg-query -W -f="${Section} ${binary:Package}\n" | sort | less
```
- Using grep utility we are printing only those lines which contain the word shells.
- More on grep in next week (Week-4).
```
 dpkg-query -W -f="${Section} ${binary:Package}\n" | grep shells
```

Games

`fortune`

fortune: print funny quotes, thoughts (Some quotes may be harsh, but it's just for fun.).
package fortunes has data files containing fortune cookies.

~$ fortune
Any circuit design must contain at least one part which is obsolete, two parts
which are unobtainable, and three parts which are still under development.

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Lecture3-4.md

Lecture3-4.md

Software Management

Need for a Package Manager

Package Types

`lsb_release` command

Architectures

Package Management Tools

Package Management in Ubuntu Using `apt`

Inquiring Package DB

Package Names

Package Priorities

Package Sections

Checksums

`md5sum`

`sha1sum`

`sha256sum`

Who can install packages?

Which website is used to download packages?

`apt-get` and `apt`

Updating and Installing Packages

Removing or Cleaning up Packages

dpkg suite

`dpkg`

`dpkg-query`

Games

`fortune`

Files

Lecture3-4.md

Latest commit

History

Lecture3-4.md

File metadata and controls

Software Management

Need for a Package Manager

Package Types

lsb_release command

Architectures

Package Management Tools

Package Management in Ubuntu Using apt

Inquiring Package DB

Package Names

Package Priorities

Package Sections

Checksums

md5sum

sha1sum

sha256sum

Who can install packages?

Which website is used to download packages?

apt-get and apt

Updating and Installing Packages

Removing or Cleaning up Packages

dpkg suite

dpkg

dpkg-query

Games

fortune

`lsb_release` command

Package Management in Ubuntu Using `apt`

`md5sum`

`sha1sum`

`sha256sum`

`apt-get` and `apt`

`dpkg`

`dpkg-query`

`fortune`