3. Dual Boot

This chapter discusses the necessary steps to dual boot.

3.1. Creating Free Space

To dual-boot TrueOS® with an existing operating system, first make sure there is either a free partition or an area of free space to use. For example, a system running the Windows operating system usually occupies the entire hard drive. The partition with the current operating system needs to shrink to make room to install TrueOS®. Shrinking is an operation which retains the current operating system while reducing the size of its partition. This section demonstrates how to create free space within Windows 10.


Before shrinking a partition, be sure to back up any valuable data to an external media such as a removable USB drive!

To shrink the drive, right-click the Start menu and click Disk Management. In the example shown in Figure 3.1.1, the Windows system has three partitions: a 450 MB recovery partition, a 237.93 GB data partition, and a 100 MB system partition.


Fig. 3.1.1 Disk Layout in Disk Management

This image shows all three Windows partitions filling the entire disk. The data partition must be shrunk to create space to install TrueOS®. Right-click the data partition (in this example, the (C:) partition), and select Shrink Volume, as shown in Figure 3.1.2.


Fig. 3.1.2 Shrink Volume Menu Selection

Wait as the volume is queried for available shrink space. The results are shown in Figure 3.1.3.


Fig. 3.1.3 Available Shrink Space

Here, 119307 MB of space is available. This is the maximum amount Windows can shrink this particular partition. Accept that number, or choose a smaller number for a smaller TrueOS® partition. Click Shrink to begin the shrinking process. This procedure can take several minutes to complete. When finished, the newly created free space is displayed as seen in Figure 3.1.4.


The minimum requirement for a TrueOS® install is 20 GB. It is recommended to have 50 GB.


Fig. 3.1.4 Disk with Free Space


It is important to not choose to install TrueOS® into any of the three Windows partitions at the Disk Selection screen of the installer. It is a good idea to write down the sizes of all of the partitions so the free space is recognizable when the TrueOS® installer displays the current partitions.

3.2. Requirements for Dual Booting

Dual booting with TrueOS® has several requirements:

  • An EFI or UEFI partitioning scheme. TrueOS® does not support the older MBR partition scheme, opting instead to use rEFInd for managing or booting into operating systems. TrueOS still uses the BSD boot loader, as it provides native support for ZFS boot environments. Be sure to select Install rEFInd when installing TrueOS® (see Disk or Partition Selection).
  • A partition for each operating system. Many operating systems, including TrueOS®, can only be installed into a primary or GPT partition. See Creating Free Space for an example of shrinking a disk in Windows to allow for dual booting with TrueOS®.
  • Back up any existing data! It is recommended to store this backup on a different computer, removable media such as a USB drive or DVD media.

3.3. Dual Booting

A TrueOS® installation assumes there is an existing GPT or primary partition for installation. If the computer has only one disk and TrueOS® is the only operating system, it is fine to accept the default partitioning scheme. However, if TrueOS® is to share space with other operating systems, ensure TrueOS® is installed into the correct partition, or an existing operating system may be overwritten.


As adjusting the partitions/spacing on active disks can be a complicated and difficult process, it is recommended to partition your disk for dual booting before installing any operating systems.

When installing TrueOS® onto a computer meant to contain multiple operating systems, carefully select the correct partition in the Disk Selection screen. On a system containing multiple partitions, each partition is listed.


Avoid selecting a partition containing an operating system or essential data.

Highlight the desired partition and click Customize. Clicking Next without customizing the disk layout results in the installer overwriting the contents of the primary disk.

Once installed, the system boots into the rEFInd menu seen in Figure 3.3.1.


Fig. 3.3.1 rEFInd Boot Manager

rEFInd displays any installed operating systems and boots into the default choice after a few seconds. Press any key other than Enter to pause automatic booting, then use the arrow keys to select the desired operating system. Press Enter to continue booting.