Ubuntu – How to debug why Ubuntu boots to BusyBox?

boot

When I turn my PC on, it asks me if I want to boot Ubuntu 16.04 or Windows 10.
When I choose Ubuntu 16.04, it look like it is booting, but then it just show me this screen:

BusyBox v1.22.1 (Ubuntu 1:1.22.0-15ubuntu1) built-in shell (ash)
Enter 'help' for a list of built-in commands

(initramfs)

I was installing Ubuntu by CD. First time, when was installation complete, the system was running without any problems, but when I turned my PC off (there wasn't any problems or messages during the shutdown) and then turned it on and choosed Ubuntu this happend.

Best Answer

Boot from a live USB stick or DVD and run:

sudo fsck -a /dev/sda1

Important! --> replace `/dev/sda1` with your Ubuntu partition.

Youo can locate the correct partition with the command lsblk which will provide you with output similar to what you see below your Ubuntu partition is the one shown at mountpoint /:

NAME   MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT
sda      8:0    0 119.2G  0 disk 
├─sda1   8:1    0  12.4G  0 part 
└─sda2   8:2    0 106.9G  0 part /
sdb      8:16   0   1.8T  0 disk 
└─sdb1   8:17   0   1.8T  0 part /home
sdc      8:32   0   2.7T  0 disk 
├─sdc1   8:33   0   2.7T  0 part /srv
└─sdc2   8:34   0     1G  0 part [SWAP]
sr0     11:0    1  1024M  0 rom

Related Solutions

Ubuntu – the root filesystem requires a manual fsck

You need space between command and argument. The command is fsck, and the argument is the device /dev/sda1. Try fsck /dev/sda1. Note that there is a space between fsck and /dev/sda1.

Additionally you may want to use fsck -y /dev/sda1 to answer yes automatically to any questions fsck asks.

Ubuntu – Ubuntu 18.04 on kernel 4.15.0-34-generic boots to BusyBox

The problem is that /sbin/cryptsetup is not in initramfs file /boot/initrd.img-4.15.0-36-generic.

You need to add CRYPTSETUP=y in /etc/cryptsetup-initramfs/conf-hook. You also need to add the initramfs option in /etc/crypttab. Then, you have to run update-initramfs, which solves this problem.

Detailed solution:

In an other Ubuntu machine, use "Startup Disk Creator" to create a bootable Ubuntu 18.04 USB drive
Plug in this USB drive in a USB port of the computer that boots to BusyBox
When the live USB Ubuntu is ready, connect to Internet (WiFi or wired)
Open a terminal
```
ubuntu@ubuntu:~$ sudo su
```

Find the encrypted block device.

root@ubuntu:~# blkid|grep LUKS
/dev/nvme0n1p3: UUID="4b206e76-1531-48ae-95be-ae0ed7a244c1" TYPE="crypto_LUKS" PARTUUID="21db499d-b87b-41c6-864f-04d1531cb083"

Decrypt the device

root@ubuntu:~# cryptsetup open UUID="4b206e76-1531-48ae-95be-ae0ed7a244c1" nvme0n1p3_crypt
Enter passphrase for /dev/disk/by-uuid/4b206e76-1531-48ae-95be-ae0ed7a244c1:

List mapped devices. control is a file used to send command to the device mapper. nvme0n1p3_crypt is the decrypted device. ubuntu--vg-root is a LVM logical volume in the LVM ubuntu-vg volume group.
```
root@ubuntu:~# ls /dev/mapper/*
/dev/mapper/control  /dev/mapper/ubuntu--vg-root  /dev/mapper/nvme0n1p3_crypt
```
Create mount point. This is where we will mount the / of our system that won't boot.
```
root@ubuntu:~# mkdir -p /mnt/ubuntu-root
```

Mount root logical volume

root@ubuntu:~# mount /dev/mapper/ubuntu--vg-root /mnt/ubuntu-root/

Mount pseudo file systems

root@ubuntu:~# mount -o bind /sys /mnt/ubuntu-root/sys
root@ubuntu:~# mount -o bind /proc /mnt/ubuntu-root/proc
root@ubuntu:~# mount -o bind /dev /mnt/ubuntu-root/dev

Copy DNS information

root@ubuntu:~# cp /etc/resolv.conf /mnt/ubuntu-root/etc/

Change root

root@ubuntu:~# chroot /mnt/ubuntu-root/

Mount /boot, which contains the initramfs file. This partition is unencrypted.
```
root@ubuntu:/# mount /boot/
```
Install binwalk (to see the content of the init ram file system)
```
root@ubuntu:~# apt update
root@ubuntu:~# apt install binwalk
```

Find offset of gzipped initramfs content

root@ubuntu:~# binwalk /boot/initrd.img-4.15.0-36-generic | grep gzip
1605632       0x188000        gzip compressed data, from Unix, last modified: 2018-10-18 13:00:32

The problem is that the initramfs file system does not contain cryptsetup. So, that is why there is no LUKS password prompt.

root@ubuntu:/# cd /root/
root@ubuntu:~# mkdir initramfs-4.15.0-36-generic
root@ubuntu:~# cd initramfs-4.15.0-36-generic
root@ubuntu:~/initramfs-4.15.0-36-generic# dd if=/boot/initrd.img-4.15.0-36-generic bs=1605632 skip=1 | gunzip | cpio -i
root@ubuntu:~/initramfs-4.15.0-36-generic# ls sbin/cryptsetup
ls: cannot access 'sbin/cryptsetup': No such file or directory

To decrypt root at boot, the initramfs needs to contain:

sbin/cryptsetup
lib/modules/4.15.0-36-generic/kernel/drivers/md/dm-crypt.ko

Add the initramfs option in /etc/crypttab

root@ubuntu:/# cat /etc/crypttab 
nvme0n1p3_crypt UUID=4b206e76-1531-48ae-95be-ae0ed7a244c1 none luks,discard,initramfs

Add CRYPTSETUP=y in /etc/cryptsetup-initramfs/conf-hook

Run update-initramfs:

root@ubuntu:~# update-initramfs -k 4.15.0-36-generic -c -v &> update-initramfs-4.15.0-36-generic.cryptsetup.log

Now, we have cryptsetup in initramfs and the Linux kernel module dm-crypt.ko too:

root@ubuntu:~# grep /sbin/cryptsetup update-initramfs-4.15.0-36-generic.cryptsetup.log
Adding binary /sbin/cryptsetup

root@ubuntu:~# grep dm-crypt.ko update-initramfs-4.15.0-36-generic.cryptsetup.log
Adding module /lib/modules/4.15.0-36-generic/kernel/drivers/md/dm-crypt.ko

Now, run update-initramfs, without -c (new) and without -v (verbose):
```
root@ubuntu:~# update-initramfs -k 4.15.0-36-generic -u
```

Verify that the initramfs is actually correct

root@ubuntu:~# binwalk /boot/initrd.img-4.15.0-36-generic | grep gzip
1605632       0x188000        gzip compressed data, from Unix, last modified: 2018-10-18 14:26:29

root@ubuntu:~# dd if=/boot/initrd.img-4.15.0-36-generic bs=1605632 skip=1 2> /dev/null | gunzip | cpio -t 2> /dev/null |grep sbin/crypt 
sbin/cryptsetup

root@ubuntu:~# dd if=/boot/initrd.img-4.15.0-36-generic bs=1605632 skip=1 2> /dev/null | gunzip | cpio -t 2> /dev/null |grep dm-crypt.ko
lib/modules/4.15.0-36-generic/kernel/drivers/md/dm-crypt.ko

Now, reboot.