# Using apt-get Commands in Ubuntu

> A summary for Ubuntu beginners
>
> References: [It's FOSS](https://itsfoss.com/apt-get-linux-guide/), [ttend.tistory.com](https://ttend.tistory.com/316)

\ <br>

## What is `apt-get` ?

<br>

* Ubuntu is an operating system derived from `Debian Linux`
  * Ubuntu's core utilities come from Debian!
* Debian uses the `dpkg packaging system`
  * What is a **packaging system**?
    * One of the methods for installing and maintaining software on a system
    * Using a packaging system means you don't need to receive the source code and build the program yourself!
    * Linux has the **Debian family** which uses `deb` packages and the **RedHat family (.rpm)** which uses `rpm` packages
      * Debian family

        : Debian, Ubuntu, Linspire, Xandros
      * RedHat family

        : Fedora, CentOS, RHEL, openSUSE, Mandirva

<br>

### APT (Advanced Package Tool)

* A command line tool for interacting with the packaging system
  * You can also use the `dpkg` command, but `apt` is more user-friendly for handling packages!
* You can install, upgrade, and clean packages with `apt`
* It is a high level tool

\ <br>

### High Level & Low Level Tool

<br>

#### Low level package tool

* Manages the tasks of installing and removing package files
  * ex) `dpkg` for Debian family, `rpm` for RedHat family

<br>

#### High level package tool

* Manages metadata search and dependency resolution tasks

\ <br>

### Main Tools of APT

: The main tools of apt are `apt-get` and `apt-cache`

<br>

#### apt-get

* Used to install, upgrade, and clean packages

<br>

#### apt-cache

* Used to find new packages

\ <br>

## Using apt-get commands

<br>

### Updating packages with apt-get

<br>

#### Command

```bash
sudo apt-get update
```

<br>

#### Result

* `Hit`
  * Means there is no change in the package version
* `Ign`
  * Means the package was ignored
    * There can be various reasons
      * ex)
        * When it is so up-to-date that there is no need to check for a newer version
        * When an error occurred while searching for the package but it was a minor error so it was ignored
          * In conclusion, it is not an error so no need to worry!
* `Get`
  * When there is a new version of the package, **apt-get** downloads that information
    * The new version information, not the package itself!

\ <br>

### Upgrading packages with apt-get

* Once you have an updated package database through `$ sudo apt-get update`, you can now upgrade the packages

<br>

#### Command

> Upgrade all packages

```bash
sudo apt-get upgrade
```

* Adding `-y` at the end means you don't need to separately type `y` when asked whether to upgrade

> Upgrade a specific package

```bash
sudo apt-get upgrade [package name]
```

<br>

#### Result

\ <br>

## Using apt-cache commands

<br>

### Searching for packages with apt-cache

* Useful for finding specific libraries

<br>

#### Command

> When you know the exact package name

```bash
apt-cache search [package name]
```

> When searching for packages starting with a specific name

```bash
apt-cache pkgnames [package name]
```

<br>

#### Result

\ <br>


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