Solaris ZFS Administration Guide

Booting From a ZFS Root File System

Both SPARC based and x86 based systems use the new style of booting with a boot archive, which is a file system image that contains the files required for booting. When booting from a ZFS root file system, the path names of both the boot archive and the kernel file are resolved in the root file system that is selected for booting.

When the system is booted for installation, a RAM disk is used for the root file system during the entire installation process.

Booting from a ZFS file system differs from booting from a UFS file system because with ZFS, a device specifier identifies a storage pool, not a single root file system. A storage pool can contain multiple bootable datasets or ZFS root file systems. When booting from ZFS, you must specify a boot device and a root file system within the pool that was identified by the boot device.

By default, the dataset selected for booting is the one identified by the pool's bootfs property. This default selection can be overridden by specifying an alternate bootable dataset that is included in the boot -Z command.

Booting From an Alternate Disk in a Mirrored ZFS Root Pool

You can create a mirrored ZFS root pool when the system is installed, or you can attach a disk to create a mirrored ZFS root pool after installation. Review the following known issues regarding mirrored ZFS root pools:

Booting From a ZFS Root File System on a SPARC Based System

On a SPARC based system with multiple ZFS BEs, you can boot from any BE by using the luactivate command.

During the installation and Solaris Live Upgrade process, the ZFS root file system is automatically designated with the bootfs property.

Multiple bootable datasets can exist within a pool. By default, the bootable dataset entry in the /pool-name/boot/menu.lst file is identified by the pool's bootfs property. However, a menu.lst entry can contain a bootfs command, which specifies an alternate dataset in the pool. In this way, the menu.lst file can contain entries for multiple root file systems within the pool.

When a system is installed with a ZFS root file system or migrated to a ZFS root file system, an entry similar to the following is added to the menu.lst file:

title zfsnv109BE
bootfs mpool/ROOT/zfsnv109BE

When a new BE is created, the menu.lst file is updated. Until CR 6696226 is fixed, you must update the menu.lst file manually after you activate the BE with the luactivate command.

When a new BE is created, the menu.lst file is updated automatically.

On a SPARC based system, two new boot options are available:

Example 5–5 Booting From a Specific ZFS Boot Environment

If you have multiple ZFS BEs in a ZFS storage pool on your system's boot device, you can use the luactivate command to specify a default BE.

For example, the following ZFS BEs are available as described by the lustatus output:

# lustatus
Boot Environment           Is       Active Active    Can    Copy      
Name                       Complete Now    On Reboot Delete Status    
-------------------------- -------- ------ --------- ------ ----------
zfsnv109BE                   yes      yes    yes       no     -         
zfsnv1092BE                  yes      no     no        yes    -      

If you have multiple ZFS BEs on your SPARC based system, you can use the boot -L command. For example:

ok boot -L
Rebooting with command: boot -L                                       
Boot device: /pci@1f,0/pci@1/scsi@4,1/disk@2,0:a  File and args: -L
1 zfsnv109BE
2 zfsnv1092BE
Select environment to boot: [ 1 - 2 ]: 2

To boot the selected entry, invoke:
boot [<root-device>] -Z mpool/ROOT/zfsnv1092BE

Program terminated
ok boot -Z rpool/ROOT/zfsnv1092BE

Example 5–6 SPARC: Booting a ZFS File System in Failsafe Mode

On a SPARC based system, you can boot from the failsafe archive located in /platform/`uname -i`/failsafe as follows. For example:

ok boot -F failsafe

If you want to boot a failsafe archive from a particular ZFS bootable dataset, use syntax similar to the following:

ok boot -Z rpool/ROOT/zfsnv109BE -F failsafe

Booting From a ZFS Root File System on an x86 Based System

The following entries are added to the /pool-name/boot/grub/menu.lst file during the installation process or Solaris Live Upgrade operation to boot ZFS automatically:

title Solaris Express Community Edition zfsnv109BE X86
bootfs rpool/ROOT/zfsnv109BE
findroot (pool_rpool,0,a)
kernel$ /platform/i86pc/kernel/$ISADIR/unix -B $ZFS-BOOTFS
module$ /platform/i86pc/$ISADIR/boot_archive

If the device identified by GRUB as the boot device contains a ZFS storage pool, the menu.lst file is used to create the GRUB menu.

On an x86 based system with multiple ZFS BEs, you can select a BE from the GRUB menu. If the root file system corresponding to this menu entry is a ZFS dataset, the following option is added.


Example 5–7 x86: Booting a ZFS File System

When booting from a ZFS file system, the root device is specified by the boot -B $ZFS-BOOTFS parameter on either the kernel or module line in the GRUB menu entry. This value, similar to all parameters specified by the -B option, is passed by GRUB to the kernel. For example:

title Solaris Express Community Edition zfsnv1095BE X86
findroot (pool_rpool,0,a)
bootfs rpool/ROOT/zfsnv109BE
kernel$ /platform/i86pc/kernel/$ISADIR/unix -B $ZFS-BOOTFS
module$ /platform/i86pc/$ISADIR/boot_archive

Example 5–8 x86: Booting a ZFS File System in Failsafe Mode

The x86 failsafe archive is /boot/x86.miniroot-safe and can be booted by selecting the Solaris failsafe entry from the GRUB menu. For example:

title zfsnv109BE failsafe
findroot (pool_rpool,0,a)
bootfs rpool/ROOT/zfsnv109BE
kernel /boot/platform/i86pc/kernel/unix -s -B console=ttyb
module /boot/x86.miniroot-safe

Example 5–9 x86: Fast Rebooting a ZFS Root File System

In the Solaris Express Community Edition, build 100, the fast reboot feature provides the ability to reboot within seconds on x86 based systems. With the fast reboot feature, you can reboot to a new kernel without experiencing the long delays that can be imposed by the BIOS and boot loader. The ability to fast reboot a system drastically reduces down time and improves efficiency.

You must still use the init 6 command when transitioning between BEs with the luactivate command. For other system operations where the reboot command is appropriate, you can use the reboot f command. For example:

# reboot -f

Booting For Recovery Purposes in a ZFS Root Environment

Use the following procedure if you need to boot the system so that you can recover from a lost root password or similar problem.

You will need to boot failsafe mode or boot from alternate media, depending on the severity of the error. In general, you can boot failsafe mode to recover a lost or unknown root password. The OpenSolaris release does not support failsafe mode.

If you need to recover a root pool or root pool snapshot, see Recovering the ZFS Root Pool or Root Pool Snapshots.

ProcedureHow to Boot ZFS Failsafe Mode

  1. Boot failsafe mode.

    On a SPARC system:

    ok boot -F failsafe

    On an x86 system, select failsafe mode from the GRUB prompt.

  2. Mount the ZFS BE on /a when prompted:

    ROOT/zfsBE was found on rpool.
    Do you wish to have it mounted read-write on /a? [y,n,?] y
    mounting rpool on /a
    Starting shell.
  3. Change to the /a/etc directory.

    # cd /a/etc
  4. If necessary, set the TERM type.

    # TERM=vt100
    # export TERM
  5. Correct the passwd or shadow file.

    # vi shadow
  6. Reboot the system.

    # init 6

ProcedureHow to Boot ZFS From Alternate Media

If a problem prevents the system from booting successfully or some other severe problem occurs, you will need to boot from a network install server or from a Solaris installation CD, import the root pool, mount the ZFS BE, and attempt to resolve the issue.

You can use this procedure on a system that is running the Open Solaris release to recover a lost root password or similar problem.

  1. Boot from an installation CD or from the network.

    On a SPARC system:

    ok boot cdrom -s 
    ok boot net -s 

    If you don't use the -s option, you will need to exit the installation program.

    On an x86 system, select the network boot or boot from local CD option.

  2. Import the root pool and specify an alternate mount point. For example:

    # zpool import -R /a rpool
  3. Mount the ZFS BE. For example:

    # zfs mount rpool/ROOT/zfsBE
  4. Access the ZFS BE contents from the /a directory.

    # cd /a
  5. Reboot the system.

    # init 6