45

I know that I can use apt-get remove <package> to remove a program.

But apt is a program itself. Could I use apt-get remove apt to remove it, or would it get confused part way through?

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  • 2
    Is that an actual or just a hypothetical question? In case 1: Try it out. Else: I think it should be able to purge itself if it doesn't try to launch any of its components after having removed them. Files that are already opened can be removed without problems. – Byte Commander♦ Jan 17 '16 at 14:12
  • @ByteCommander It's both, but I can't really try it right now. – Tim Jan 17 '16 at 14:15
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    You can but you probably shouldn't. Linux rarely asks why its user wants to shoot themselves in the foot, it just assumes you have a good reason and lets you pull the trigger... – Shadur Jan 18 '16 at 10:41
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    For completeness, Fedoras' dnf won't let you do it. # dnf remove dnf Dependencies resolved. Error: The operation would result in removing the following protected packages: dnf. – Davidmh Jan 18 '16 at 16:28
  • What an interestingly evil question that is! A logical follow-up is: can you recover from that, or does it require a complete re-installation? – KlaymenDK Jan 19 '16 at 9:01
79

APT lets you simulate your commands using the option -s. You can try this yourself, issuing the command apt-get -s remove apt (no sudo needed).

This yields the following output:

Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages were automatically installed and are no longer required:
  apturl-common xul-ext-ubufox
Use 'apt-get autoremove' to remove them.
The following packages will be REMOVED:
  apt apt-utils apturl nautilus-share python3-software-properties
  software-properties-common software-properties-gtk ubuntu-desktop
  unattended-upgrades
WARNING: The following essential packages will be removed.
This should NOT be done unless you know exactly what you are doing!
  apt
0 upgraded, 0 newly installed, 9 to remove and 0 not upgraded.
Remv ubuntu-desktop [1.341]
Remv nautilus-share [0.7.3-1ubuntu5]
Remv apturl [0.5.2ubuntu9]
Remv software-properties-gtk [0.96.13.1]
Remv software-properties-common [0.96.13.1]
Remv python3-software-properties [0.96.13.1]
Remv unattended-upgrades [0.86.2ubuntu1]
Remv apt-utils [1.0.10.2ubuntu1]
Remv apt [1.0.10.2ubuntu1]

So the answer should be: yes, you can.

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  • 8
    I'm not sure that apt's simulate mode covers the full fallout for something like this. Surely this would be an edge case that the code may or may not address. – Sparhawk Jan 17 '16 at 23:20
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    This doesn't require sudo (-s mode doesn't make any changes), so it's probably better to run it without sudo as a precaution. – Fake Name Jan 18 '16 at 0:17
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    Apt might well be able to determine how to remove apt. But can it actually do it? It's easy to imagine that it might delete a file that it later depends on, leaving the installation in an inconsistent state. – user253751 Jan 18 '16 at 4:19
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    @immibis I'd be more concerned about that for removing dpkg. Apt itself just tells dpkg what to do, dpkg is what actually performs the (un)installations. – Random832 Jan 18 '16 at 18:46
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    So if apt tells dpkg what to do, what happens when you remove dpkg... lol – SuperSluether Jan 18 '16 at 19:20
30

You can...

sudo apt-get remove apt
Reading package lists... Done
Building dependency tree      
Reading state information... Done
The following packages will be REMOVED:
  apt apt-utils apturl nautilus-share python3-software-properties
  software-center software-properties-common software-properties-gtk
  ubuntu-desktop ubuntu-extras-keyring ubuntu-minimal unattended-upgrades
WARNING: The following essential packages will be removed.
This should NOT be done unless you know exactly what you are doing!
  apt
0 upgraded, 0 newly installed, 12 to remove and 0 not upgraded.
After this operation, 9,031 kB disk space will be freed.
You are about to do something potentially harmful.
To continue type in the phrase 'Yes, do as I say!'
?] Yes, do as I say!
(Reading database ... 179817 files and directories currently installed.)
Removing ubuntu-desktop (1.327) ...
Removing nautilus-share (0.7.3-1ubuntu5) ...
Removing apturl (0.5.2ubuntu4) ...
dpkg: warning: while removing apturl, directory '/usr/lib/python3/dist-packages/AptUrl/gtk/backend' not empty so not removed
Removing software-properties-gtk (0.94) ...
dpkg: warning: while removing software-properties-gtk, directory '/usr/lib/python3/dist-packages/softwareproperties/gtk' not empty so not removed
Removing software-properties-common (0.94) ...
Removing python3-software-properties (0.94) ...
Removing unattended-upgrades (0.82.8) ...
Removing ubuntu-minimal (1.327) ...
Removing apt-utils (1.0.9.2ubuntu2) ...
Removing software-center (13.10-0ubuntu4.1) ...
Removing ubuntu-extras-keyring (2010.09.27) ...
OK
Removing apt (1.0.9.2ubuntu2) ...
Processing triggers for man-db (2.7.0.2-2) ...
Processing triggers for gconf2 (3.2.6-2ubuntu1) ...
Processing triggers for hicolor-icon-theme (0.13-1) ...
Processing triggers for shared-mime-info (1.2-0ubuntu3) ...
Processing triggers for gnome-menus (3.10.1-0ubuntu2) ...
Processing triggers for desktop-file-utils (0.22-1ubuntu2) ...
Processing triggers for bamfdaemon (0.5.1+14.10.20140925-0ubuntu1) ...
Rebuilding /usr/share/applications/bamf-2.index...
Processing triggers for mime-support (3.55ubuntu1) ...
Processing triggers for dbus (1.8.8-1ubuntu2) ...
Processing triggers for libc-bin (2.19-10ubuntu2) ...

and will be warned you are about to do something very destructive. I must say ... the list of packages looks horrific for a space saving of less then 6000kb :D

It does finish but there is no way back using "apt-get". Ubuntu Software Center will no longer work and you would need to use "dpkg" to re-install a package manager (and manually also need to install all the dependencies).

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    would need to use "dpkg" to re-install a package manager (and manually also need to install all the dependencies), so in other words, sudo apt-get remember-what-2002-was-like – user1717828 Jan 17 '16 at 15:18
  • Couldn't you boot into a Live CD, then chroot and apt-get, much like Arch does? – Sparhawk Jan 17 '16 at 23:17
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    @Sparhawk Not sure what you're aiming for; after you chroot, you are in your normal system's root, and would be looking for apt-get there, which you removed. I think apt-get (or maybe it is dpkg) allows specifying an alternate root directory, but I can't seem to find quickly how you would do that. – user Jan 18 '16 at 15:12
  • None of the packages it removes are particularly "scary" IMO except for, of course, apt itself. – Random832 Jan 18 '16 at 18:48
  • @MichaelKjörling I was thinking that you could run the manual path to apt-get, installing in the new "root", but I forgot that you'd need all the config/cache files too. Your possible suggestion would certainly be cleaner though (if there is that option). – Sparhawk Jan 18 '16 at 22:13
12

Once, back when I ran CoreUbuntu, I installed a buggy package from source which apt decided obsoleted apt. Next time I ran apt autoremove, I didn't actually look at the list of software to be removed and apt was in the list.

Imagine my surprise next time I typed apt install <package-name> and got The program 'apt' is currently not installed. You can install it by typing: sudo apt-get install apt.

Luckily, for some reason, autoremove didn't remove any of apt's dependencies so all I had to do was wget apt's .deb archive and reinstall using dpkg -i.

As shown in the other answers, if you remove apt with apt, you'll be in more trouble because of the dependencies it tries to resolve.

I find it interesting but it is indeed the case that (certainly for Debian, and perhaps Fedora/openSUSE to an extent?) many modern distros are defined and built largely upon the infrastructure provided by their package manager of choice.

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    I bet the reason apt didn't remove the dependencies is that the buggy package you have installed listed them as required. Makes sense if that package was meant as a replacement. – Dmitry Grigoryev Jan 18 '16 at 16:35
5

Technically, apt can't remove apt... because apt doesn't know how to remove, install or upgrade packages. The tasks of installing, removing, upgrading, configuring packages are left to dpkg. Although you can tell apt to remove the package called "apt", what it does is checks the reverse dependencies of the apt package, take note of those packages and orders dpkg to remove them. Which is what can be seen in the other answers.

Even without apt you can use dpkg to install, remove or upgrade packages, just that it will be more painful to track dependencies and upgrades needed, which is the raison d'être of apt.

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  • Yeah, apt is really just a simpler frontend for dpkg, and if you remove dpkg then is it really Ubuntu anymore? – cat Jan 19 '16 at 14:36
  • @cat I think it will still be... as long as you don't purge the package or remove the /var/lib/dpkg/status file. You can recover dpkg if you like too. – Braiam Jan 19 '16 at 14:47
1

Of course you can. Apt and dpkg are themselves packages, and they are meant to be able to be updated via themselves, so there are provisions for removal; otherwise /var/lib/dpkg/info/dpkg.prerm and /var/lib/dpkg/info/dpkg.postrm would not have reason to exist :)

If you accidentally removed them in a way that left you without dpkg, you could still manually unpack the .deb archive for dpkg unless you also got rid of binutils, tar, gzip/bzip2.

--purge on any packages involved with the apt toolchain could give you nasty problems, though; hard to tell what owns certain files in /var/lib/dpkg. If /var/lib/dpkg/status got deleted and there was no current backup, then yes, the package manager would be beyond repair on that system.

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-1

I swear I saw the apt binaries under /usr/local/bin on an Ubuntu-based system not long ago, but they're not there on my current Ubuntu MATE 15.04 system (they're in /usr/bin with most of the other binaries). If it was in /usr/local/bin then it probably wouldn't be possible to uninstall it with apt because the files in /usr/local/bin are supposed to be ignored by the package manager. I must admit that putting apt (and dpkg as well) under /usr/local/bin would be a good idea.

A more interesting question is - what happens if you uninstall dpkg? Sure enough, dpkg is listed as a package by apt, but I'm not going to try uninstalling it now (haven't got a virtual machine set up at the moment). Theoretically one could also uninstall it with dpkg itself. I'm going to take an educated guess that the only way to re-install it would be to do so manually, then hope that it picks up the existing configuration files (so you don't have to manually tell the system all over again what packages are installed) and then tell it that the package dpkg is now installed again.

(A joke:) A Debian user's equivalent of # rm -rf / is # apt-get purge ".*".

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  • If anything coming from an official distribution package ends up in /usr/local/bin, file a bug against that package. – rackandboneman Jan 20 '16 at 10:42
  • The thing is that it wasn't coming from a package; it was installed separately from the package manager with the express purpose of avoiding the "apt-get remove apt" and "apt-get remove dpkg" problems. I think it was Linux Mint actually, which I used to use as my main system. – Micheal Johnson Jan 20 '16 at 14:34

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