Package Management

Getting additional software can be done many ways, from compiling source code to downloading individual package files. But it's much easier to let your OS Package Manager handle things for you.

Yum

Basics

Yum (Yellowdog Update Manager) is the default package manager for the downstream operating systems in the RHEL family, namely Centos. It handles package repositories, dependency resolution, software groups, and keeps a transactional record of changes.

Multiple repositories (sources) can be added to a system. For example, the base repository for Centos is hosted at http://mirror.centos.org/centos/. To view the current known repos, you have a few options:

ls -l /etc/yum.repos.d/ - repo files are stored here

└── yum.repos.d/
    ├── CentOS-Base.repo
    ├── CentOS-CR.repo
    ├── CentOS-Debuginfo.repo
    ├── CentOS-Vault.repo
    ├── epel.repo
    └── epel-testing.repo

using the builtin commands
yum repolist
yum repoinfo

Process Overview

Client contacts known repositories for changes
Updates local list of packages
Select package to install
Yum checks for dependencies
Yum dloads required packages and installs
Yum updates local RPM database

Maintainance

sudo yum check-update
sudo yum update

Getting Info

sudo yum info - shows installed pkgs
sudo yum list installed
sudo yum list updates
sudo yum list available 'package*'
sudo yum deplist pkg - shows dependencies
yum group list - show available groups
yum group info "Development Tools" - show group details

Searching

yum search pkg
yum search all pkg
yum list all | grep pkg
yum provides

Installing

sudo yum install -y pkg
sudo yum reinstall
sudo yum upgrade

Uninstalling

sudo yum remove - removes package only
sudo yum autoremove - removes package and deps

History

yum history

ID     | Login user               | Date and time    | Action(s)      | Altered
-------------------------------------------------------------------------------
    18 | admin <admin>            | 2019-08-07 00:24 | Install        |    1
    17 | admin <admin>            | 2019-08-07 00:23 | Erase          |    1 EE
    16 | admin <admin>            | 2019-08-07 00:08 | Erase          |    1 EE
    15 | admin <admin>            | 2019-08-06 23:52 | Install        |    5
    14 | admin <admin>            | 2019-06-25 12:46 | Install        |    2
    13 | admin <admin>            | 2019-06-25 12:45 | Install        |   10

ID — an integer value that identifies a particular transaction
Login user — the name of the user to initiate a transaction
Date and time — the date and time when a transaction was issued
Action(s) — a list of actions that were performed
Altered — the number of packages that were affected by transaction

- yum history undo/redo <ID#> - use ID number to uninstall or reinstall

Package Groups

yum grouplist - list available groups
yum group install group-name - install group
yum install @group-name - install group