Accidentally removed /bin. How do I restore it?

Is it possible?

Well, most trivial and important utilities are installed in /bin, and now you lost access to all of them. In fact, if you reboot, your system will not be able to boot-up anymore.

Anyway, we are going to fix the issue and make /bin's contents as close as is possible to where it was. The only difference would be some symbolic links which we will fix too.

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How?

First, we should chroot into your broken system, but with a minor difference! After that we will get a list of installed packages on your system which have any installed file in /bin directory, then we are going to only download the needed packages and extract the necessary files into /bin. Then we'll be done.

For example, after chroot, we can get a list of packages which have installed files in /bin using:

dpkg --search /bin | cut -f1 -d: | tr ',' '\n'

And we can also use:

dpkg --listfiles PACKAGE-NAME | grep "^/bin/" # or awk '$0 ~ "^/bin/

to list installed files by these packages in /bin.

Then we simply create a list of all packages that are necessary to us, then download them and extract them to /bin with something like:

xargs apt download < list-packages
dpkg-deb -x PACKAGE .
mv ./bin/* /bin

However we must use a script to check all installed packages on our system, because doing it manually is just madness.

So I wrote a script which does everything we need. It finds all necessary packages for us to restore /bin, shows us the name of each package and their related files that belongs to /bin. Here is a screenshot:

At the end we choose to reinstall all packages or only download and extract the necessary files to /bin (which is the recommended option):

You can grab a copy of this script or download it directly.

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Lets start

chroot

Boot your system with a live disk which has same architecture as your installed Ubuntu, open a terminal and get root access:

sudo -i

Mount your root file system (for me it's /dev/sda1):

mount /dev/sda1 /mnt

We will need connectivity to the Internet, so copy resolv.conf from live Ubuntu to your mounted root partition:

cp /etc/resolv.conf /mnt/etc/resolv.conf

Now copy the script to somewhere on the mounted partition, e.g:

cp /media/ubuntu/usb/restore-bin.sh /mnt/restore-bin.sh

or you can download it using wget, etc. like:

wget https://git.io/v9fRm -O /mnt/restore-bin.sh

Mount other necessary paths:

mount --bind /dev /mnt/dev
mount --bind /sys /mnt/sys
mount -t proc /proc /mnt/proc

And here is the minor difference: how can we chroot to a broken system when there is no /bin directory in there? Which shell should we run?

So create a temporary bin directory. e.g: named bintmp within your broken system root:

mkdir /mnt/bintmp

Then bind the live /bin into that:

mount --bind /bin /mnt/bintmp

Chroot into the system while setting the /bintmp/bash as your login shell:

chroot /mnt /bintmp/bash

Export the /bintmp as your PATH environment variable:

export PATH=/bintmp:$PATH

Give the script the executable bit:

chmod +x restore-bin.sh

Run the script:

./restore-bin.sh

Wait for the search to be completed then answer the question we saw in the screenshot. It will start to restore the /bin and we are almost done.

After it's done, use CTRL+D to get out of chroot environment and unmount the mounted paths:

umount -R /mnt

Reboot the system.

Restoring the links within /bin

Now almost all of files within /bin directory are back, except around 5 symbolic links which are managed by update-alternatives.

In your running system, run:

sudo update-alternatives --all

It asks you some questions; you can simply press ENTER to accept them all.

And now we are done.

If your current system still has a running shell and internet access, this can be done using tools existing elsewhere on the system. I'm assuming you only deleted /bin. /bin of course has the most convenient utility that you could use in such a situation (busybox), but without that, we'll have to get a little creative.

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Since you already have a running shell, and since sudo is in /usr/bin, let's get ourselves a running root shell before we do further damage. But /bin/bash and most other shells are gone! Luckily, Linux still has an in-memory copy of the shell you're using. So:

sudo /proc/$$/exe

Strictly speaking we don't need a root shell for much of what follows. But anyway.

Now, dpkg still works, at least for finding which packages have files in /bin:

dpkg -S /bin

We can use awk to process it and get the package names, and xargs and apt-get to download the packages (all in /usr/bin). If you have a temporary directory that you can use, cd there, because your current directory is going to get a bit messy:

dpkg -S /bin | awk -F '[, :]' '{NF--}1' | xargs apt-get download

Now, the biggest problem we have is that /bin/tar is missing, and without it, dpkg can't extract the archives. We can get two-thirds of the way there, because:

1. .deb files are actually ar archives (again in /usr/bin):

   ar x tar_*.deb
   

2. Consisting of two .tar.* archives, data and control:

   $ echo *.tar.*
   control.tar.gz data.tar.xz
   

3. While the gzip utilities are in /bin, unxz is in /usr/bin:

   unxz data.tar.xz
   

Now we have a data.tar file without tar to extract tar from it.

Python to the rescue! This is where sudo is really needed:

$ sudo python -c 'import tarfile; tarfile.open("data.tar").extractall("/")'
$ echo /bin/*
/bin/tar

Now we can use dpkg to extract the remaining deb files to get a reasonably complete /bin:

for i in *.deb; do dpkg-deb -x "$i" /; done

However, we should still do a proper installation of the deb files, so that symlinks etc. that would be created by packages are re-created:

sudo apt install --reinstall ./*.deb

Or:

sudo dpkg -i *.deb
sudo apt-get install -f

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Notes:

1. We can't use Python 2 to directly extract the data.tar.xz file, since Python 2 only supports gzip and bzip2 compression. Python 3, however, does support it, so you can use Python 3 directly without unxz:

   sudo python3 -c 'import tarfile; tarfile.open("data.tar.xz").extractall("/")'
   

2. After getting back /bin/tar, you still need to extract some of the deb files before you can use apt-get: the shells, coreutils, etc. Easier to just extract all of them and re-install later.

You could temporarily put files from a live CD or another system into your /bin to make your system usable, then replace them with files from your Ubuntu installation by running apt-get install --reinstall for packages which have stuff in /bin.