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6.2. aptitude, apt-get, and apt Commands

APT is a vast project, whose original plans included a graphical interface. It is based on a library which contains the core application, and apt-get is the first front end — command-line based — which was developed within the project. apt is a second command-line based front end provided by APT which overcomes some design mistakes of apt-get.
Numerous other graphical interfaces then appeared as external projects: synaptic, aptitude (which includes both a text mode interface and a graphical one — even if not complete yet), wajig, etc. The most recommended interface, apt, is the one that we will use in the examples given in this section. Note however that apt-get and aptitude have a very similar command line syntax. When there are major differences between apt, apt-get and aptitude, these differences will be detailed.

6.2.1. Inisialisasi

For any work with APT, the list of available packages needs to be updated; this can be done simply through apt update. Depending on the speed of your connection, the operation can take a while since it involves downloading a certain number of Packages/Sources/Translation-language-code files, which have gradually become bigger and bigger as Debian has developed (at least 10 MB of data for the main section). Of course, installing from a CD-ROM set does not require any downloading — in this case, the operation is very fast.

6.2.2. Instalasi dan Penghapusan

With APT, packages can be added or removed from the system, respectively with apt install package and apt remove package. In both cases, APT will automatically install the necessary dependencies or delete the packages which depend on the package that is being removed. The apt purge package command involves a complete uninstallation — the configuration files are also deleted.
If the file sources.list mentions several distributions, it is possible to give the version of the package to install. A specific version number can be requested with apt install package=version, but indicating its distribution of origin (Stable, Testing or Unstable) — with apt install package/distribution — is usually preferred. With this command, it is possible to go back to an older version of a package (if for instance you know that it works well), provided that it is still available in one of the sources referenced by the sources.list file. Otherwise the snapshot.debian.org archive can come to the rescue (see sidebar LEBIH JAUH Paket versi lama: snapshot.debian.org).

Contoh 6.3. Instalasi versi unstable dari spamassassin

# apt install spamassassin/unstable

6.2.3. Pembaharuan Sistem

Regular upgrades are recommended, because they include the latest security updates. To upgrade, use apt upgrade, apt-get upgrade or aptitude safe-upgrade (of course after apt update). This command looks for installed packages which can be upgraded without removing any packages. In other words, the goal is to ensure the least intrusive upgrade possible. apt-get is slightly more demanding than aptitude or apt because it will refuse to install packages which were not installed beforehand.
apt will generally select the most recent version number (except for packages from Experimental and stable-backports, which are ignored by default whatever their version number). If you specified Testing or Unstable in your sources.list, apt upgrade will switch most of your Stable system to Testing or Unstable, which might not be what you intended.
To tell apt to use a specific distribution when searching for upgraded packages, you need to use the -t or --target-release option, followed by the name of the distribution you want (for example: apt -t stable upgrade). To avoid specifying this option every time you use apt, you can add APT::Default-Release "stable"; in the file /etc/apt/apt.conf.d/local.
For more important upgrades, such as the change from one major Debian version to the next, you need to use apt full-upgrade. With this instruction, apt will complete the upgrade even if it has to remove some obsolete packages or install new dependencies. This is also the command used by users who work daily with the Debian Unstable release and follow its evolution day by day. It is so simple that it hardly needs explanation: APT's reputation is based on this great functionality.
Unlike apt and aptitude, apt-get doesn't know the full-upgrade command. Instead, you should use apt-get dist-upgrade (”distribution upgrade”), the historical and well-known command that apt and aptitude also accept for the convenience of users who got used to it.

6.2.4. Pilihan Konfigurasi

Besides the configuration elements already mentioned, it is possible to configure certain aspects of APT by adding directives in a file of the /etc/apt/apt.conf.d/ directory. Remember for instance that it is possible for APT to tell dpkg to ignore file conflict errors by specifying DPkg::options { "--force-overwrite"; }.
Jika Web hanya dapat diakses melalui proxy, tambahkan baris seperti Acquire::http::proxy "http://proxy-anda:3128". Untuk sebuah proxy FTP, tulis Acquire::ftp::proxy "ftp://proxy-anda". Untuk menemukan lebih banyak pilihan konfigurasi, baca laman manual apt.conf(5) dengan perintah man apt.conf (untuk rincian pada laman manual, lihat Bagian 7.1.1, “Halaman Manual”).

6.2.5. Mengelola Prioritas Paket

Salah satu aspek yang paling penting dalam konfigurasi APT adalah mengelola prioritas asosiasi dengan setiap sumber paket. Misalnya, Anda mungkin ingin meluaskan satu distribusi dengan satunya atau dua paket terbaru dari Testing, Unstable atau Experimental. Ini memungkinkan untuk menetapkan prioritas setiap paket yang tersedia (paket yang sama dapat memiliki beberapa prioritas tergantung versinya atau distribusi yang menyediakannya). Prioritas ini akan memengaruhi perangai APT: untuk setiap paket, ini akan selalu memilih versi dengan prioritas tertinggi (kecuali jika versinya lebih tua dari yang terinstall dan jika prioritasnya kurang dari 1000).
APT mendefinisikan beberapa prioritas bawaan. Setiap versi paket terinstall memiliki prioritas 100. Versi tak-terinstall memiliki prioritas 500 secara bawaan, namun ini dapat melompat ke 990 jika ini merupakan rilis target (ditentukan dengan pilihan baris-perintah -t atau arahan konfigurasi APT::Default-Release.
Anda dapat memodifikasi prioritas dengan menambahkan entri pada berkas /etc/apt/preferences dengan nama paket terdampak, versi mereka, asal mereka dan prioritasnya.
APT tidak akan pernah menginstall versi lebih lama sebuah paket (itulah, sebuah paket yang nomor versinya lebih rendah dari salah satu paket yang telah terinstall) kecuali jika prioritasnya lebih besar dari 1000. APT akan selalu menginstall paket dengan prioritas tertinggi yang mengikuti batasan ini. Jika dua paket memiliki dua prioritas yang sama, APT akan menginstall yang terbaru (yang nomor versinya tertinggi). Jika dua paket versinya sama namun berbeda dalam konten mereka, APT akan menginstall versi yang tidak terinstall (aturan ini telah dibuat untuk mencakupi kasus sebuah pembaharuan paket tanpa peningkatan nomor revisinya, yang biasanya diperlukan).
Dalam istilah yang lebih konkrit, sebuah paket yang prioritasnya kurang dari 0 tidak akan pernah diinstall. Sebuah paket dengan prioritas snata 0 dan 100 hanya akan diinstall jika tidak ada versi lain dari paket yang telah terinstall. Dengan prioritas antara 100 dan 500, paket hanya akan diinstall jika tidak ada versi lebih baru terinstall atau tersedia dalam distribusi lainnya. Prioritas paket antara 501 dan 990 hanya akan diinstall jika tidak ada versi yang lebih baru terinstall atau tersedia di distribusi target. Dengan sebuah prioritas antara 990 dan 1000, paket akan diinstall kecuali jika versi terinstall lebih baru. Prioritas yang lebih besar dari 1000 akan selalu mengutamakan instalasi paket bahkan jika memaksa APT untuk menurunkan versi ke versi yang lebih tua.
When APT checks /etc/apt/preferences, it first takes into account the most specific entries (often those specifying the concerned package), then the more generic ones (including for example all the packages of a distribution). If several generic entries exist, the first match is used. The available selection criteria include the package's name and the source providing it. Every package source is identified by the information contained in a Release file that APT downloads together with the Packages files. It specifies the origin (usually “Debian” for the packages of official mirrors, but it can also be a person's or an organization's name for third-party repositories). It also gives the name of the distribution (usually Stable, Testing, Unstable or Experimental for the standard distributions provided by Debian) together with its version (for example 8 for Debian Jessie). Let's have a look at its syntax through some realistic case studies of this mechanism.
Mari anggap bahwa Anda hanya ingin menggunakan paket dari versi stable Debian. Yang disediakan dalam versi lain tidak boleh diinstall kecuali jika diminta secara eksplisit. Anda dapat menulis entri berikut dalam berkas /etc/apt/preferences:
Package: *
Pin: release a=stable
Pin-Priority: 900

Package: *
Pin: release o=Debian
Pin-Priority: -10
a=stable menentukan nama distribusi yang dipilih. o=Debian membatasi jangkauan ke paket yang berasal dari “Debian”.
Let's now assume that you have a server with several local programs depending on the version 5.14 of Perl and that you want to ensure that upgrades will not install another version of it. You could use this entry:
Package: perl
Pin: version 5.14*
Pin-Priority: 1001
Rujukan dokumentasi untuk berkas konfigurasi ini tersedia pada laman manual apt_preferences(5), yang dapat Anda tampilkan dengan man apt_preferences.

6.2.6. Bekerja dengan Beberapa Distribusi

apt being such a marvelous tool, it is tempting to pick packages coming from other distributions. For example, after having installed a Stable system, you might want to try out a software package available in Testing or Unstable without diverging too much from the system's initial state.
Even if you will occasionally encounter problems while mixing packages from different distributions, apt manages such coexistence very well and limits risks very effectively. The best way to proceed is to list all distributions used in /etc/apt/sources.list (some people always put the three distributions, but remember that Unstable is reserved for experienced users) and to define your reference distribution with the APT::Default-Release parameter (see Bagian 6.2.3, “Pembaharuan Sistem”).
Let's suppose that Stable is your reference distribution but that Testing and Unstable are also listed in your sources.list file. In this case, you can use apt install package/testing to install a package from Testing. If the installation fails due to some unsatisfiable dependencies, let it solve those dependencies within Testing by adding the -t testing parameter. The same obviously applies to Unstable.
In this situation, upgrades (upgrade and full-upgrade) are done within Stable except for packages already upgraded to another distribution: those will follow updates available in the other distributions. We will explain this behavior with the help of the default priorities set by APT below. Do not hesitate to use apt-cache policy (see sidebar TIP apt-cache policy) to verify the given priorities.
Semuanya berpusat pada fakta bahwa APT hanya memedulikan paket yang versinya lebih tinggi atau sama dengan yang terinstall (asumsikan bahwa /etc/apt/preferences tidak digunakan untuk memaksa prioritas yang lebih tinggi dari 1000 untuk beberapa paket).
Mari asumsikan bahwa Anda telah menginstall versi 1 dari sebuah paket dari Stable dan versi 2 dan 3 tersedia masing-masing dalam Testing dan Unstable. Versi terinstall memiliki prioritas 100 tetapi versi tersedia dalam Stable (sangat mirip) memiliki prioritas 990 (karena merupakan bagian dari rilis target). Paket dalam Testing dan Unstable memiliki prioritas 500 (prioritas bawaan untuk versi tak-terinstall). Pemenangnya ialah versi 1 tersebut dengan prioritas 990. Paket “tetap di Stable”.
Mari ambil contoh paket lain yang versi 2 telah terinstall dari Testing. Versi 1 tersedia di Stable dan versi 3 di Unstable. Versi 1 (prioritas 990 - kurang dari 1000) diabaikan karena kurang dari versi yang terinstall. Ini hanya meninggalkan versi 2 dan 3, keduanya prioritas 500. Berhadapan dengan alternatif ini, APT memilih versi terbaru, salah satu dari Unstable. Jika Anda tidak ingin sebuah paket terinstall dari Testing untuk migrasi ke Unstable, Anda harus menerapkan sebuah prioritas kurang dari 500 (490 misalnya) ke paket yang datang dari Unstable. Anda dapat memodifikasi /etc/apt/preferences untuk efek ini:
Package: *
Pin: release a=unstable
Pin-Priority: 490

6.2.7. Pelacakan Otomatis Paket Terinstall

One of the essential functionalities of apt is the tracking of packages installed only through dependencies. These packages are called “automatic”, and often include libraries for instance.
With this information, when packages are removed, the package managers can compute a list of automatic packages that are no longer needed (because there is no “manually installed” packages depending on them). apt-get autoremove will get rid of those packages. aptitude and apt do not have this command: the former because it removes them automatically as soon as they are identified, and the latter probably because the user should not have to manually run such a command. In all cases, the tools display a clear message listing the affected packages.
Ini merupakan kebiasaan yang baik untuk menandai sebagai otomatis beberapa paket yang tidak Anda perlukan secara langsung jari mereka secara otomatis terhapus ketika mereka tak lagi diperlukan. apt-mark auto paket akan menandai paket yang diberikan secara otomatis di mana apt-mark manual paket melakukan sebaliknya. aptitude markauto dan aptitude unmarkauto bekerja dengan cara yang sama walaupun mereka menawarkan fitur yang lebih untuk mendandai beberapa paket pada saat yang sama (lihat Bagian 6.4.1, “aptitude). Antarmuka interaktif berbasis-konsol dari aptitude juga membuatnya mudah untuk meninjau “automatic flag” pada banyak paket.
People might want to know why an automatically installed package is present on the system. To get this information from the command line, you can use aptitude why package (apt and apt-get have no similar feature):
$ aptitude why python-debian
i   aptitude         Recommends apt-xapian-index         
i A apt-xapian-index Depends    python-debian (>= 0.1.15)