Dealing with ZFS Boot Problems

As a Sys Admin who gives his user’s plenty of power to sometimes things get messed up in the boot process so that the system cannot boot properly.  No prob0lem you say, boot from CDROM into single-user mode and mount partition, find and fix the problem……. ummmm, wait.  How do I do that?  This article covers how to mount ZFS in single-user mode.  Fixing the problem is up to you.


  1. First get an OK prompt.   With a Fujitsu-based system this is accomplished by logging into the contol interface and issuing a sendbreak -d 0.  Refer to your manual, or drop me a comment if you need a hand with this.
  2. Insert the CDROM and issue a “boot cdrom -s”
  3. “zfs list” is going to show you all of the available zpools.
    NAME                        USED  AVAIL  REFER  MOUNTPOINT
    rpool                      12.5G  54.4G    97K  /rpool
    rpool/ROOT                 6.97G  54.4G    21K  legacy
    rpool/ROOT/s10s_u8wos_08a  6.97G  54.4G  6.97G  /
    rpool/dump                 1.00G  54.4G  1.00G  -
    rpool/export               2.53G  54.4G  23.5K  /export
    rpool/export/home          2.53G  54.4G  2.53G  /export/home
    rpool/swap                    2G  56.4G    16K  -
  4. zfs get mountpoint rpool/ROOT/s10s_u8wos_08a is going to show you that the mountpoint is / and we know that is already in use.
    NAME                       PROPERTY    VALUE       SOURCE
    rpool/ROOT/s10s_u8wos_08a  mountpoint  /           local
  5. Change that mount point temporarily with the command “zfs set mountpoint=/mnt rpool/ROOT/s10s_u8wos_08a”
  6. “zfs mount rpool/ROOT/s10s_u8wos_08a”

At this point simply cd on over to the problem file and fix it.  In my case the user had modified the /etc/vsftab file so that it could no longer boot so I had to edit /mnt/etc/vfstab.

About Jay Farschman - Jay currently works as a Senior Systems Administrator for an asset management company in Colorado where he works with companies that produce hardware, telecommunications software and financial services.  Jay previously owned a consulting company and provided training and consulting services for three Fortune 500 companies and numerous small businesses where he leveraged Linux to provided exceptional value

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