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If you are using kmod-zfs you should expect that some of the kernels will not boot (because the zfs.ko module is not included in the corresponding initramfs images):

When updating your CentOS system with kmod-zfs, please update also your zfs.repo by typing the correct version. And you should check that your kernel have the zfs.ko module installed. Do not reboot until you are sure you have a working kernel. And make backups of your kernels and initramfs images. Just a user not understanding what is happening when they fire off a few commands and reboot. ZFS on Centos for years here. The kernel and ZFS are not always in lock step and you need to be mindful about which kernel you boot too. topslakr In my case I was using 7.3 repository when I installed the system and I need to change it to 7.4 (there are multiple lines with the version string): [root@localhost ~]# mcedit /etc/yum.repos.d/zfs.repo [root@localhost ~]# cat /etc/yum.repos.d/zfs.repo [zfs] name=ZFS on Linux for EL7 - dkms baseurl=http://download.zfsonlinux.org/epel/7.4/$basearch/ enabled=0 metadata_expire=7d gpgcheck=1 gpgkey=file:///etc/pki/rpm-gpg/RPM-GPG-KEY-zfsonlinux...

If you are using additional kernel modules like ZFS, I recommend to make a backup of your working kernels (and initramfs images) before to run 'yum update', because otherwise you can end up with non-working kernels (initramfs images). I have bad experience with kmod-zfs. The original working (before) kernel (the initramfs) was rebuilt (overwritten) without the zfs kernel module. You can make backups of your kernels (and their initramfs images) like this: [root@localhost ~]# ls /boot/ config-3.10.0-514.10.2.el7.x86_64 config-3.10.0-514.el7.x86_64 grub grub2 initramfs-0-rescue-263ede4315d14b8ba4b3a93abc833aea.img initramfs-3.10.0-514.10.2.el7.x86_64.img initramfs-3.10.0-514.el7.x86_64.img initrd-plymouth.img symvers-3.10.0-514.10.2.el7.x86_64.gz symvers-3.10.0-514.el7.x86_64.gz System.map-3.10.0-514.10.2.el7.x86_64 System.map-3.10.0-514.el7.x86_64 vmlinuz-0-rescue-263ede4315d14b8ba4b3a93abc833aea vmlinuz-3.10.0-514.10.2.el7.x86_64 vmlinuz-3.10.0-514.el7.x86_64 [root@localhos...

Don't panic if you are using zfs-dkms, it looks like the bug affects only kmod-zfs. Update: I was wrong - did not changed the version of the repo from 7.3 to 7.4. When updating your CentOS system with kmod-zfs, please update also your zfs.repo.