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PPC64 Handbook
About the installation
Choosing the media
Configuring the network
Preparing the disks
Installing stage3
Installing base system
Configuring the kernel
Configuring the system
Installing tools
Configuring the bootloader
Working with Gentoo
Portage introduction
USE flags
Portage features
Initscript system
Environment variables
Working with Portage
Files and directories
Mixing software branches
Additional tools
Custom package repository
Advanced features
Network configuration
Getting started
Advanced configuration
Modular networking
Adding functionality
Dynamic management

Introduction to block devices

Block devices

Let's take a good look at disk-oriented aspects of Gentoo Linux and Linux in general, including block devices, partitions, and Linux filesystems. Once the ins and outs of disks are understood, partitions and filesystems can be established for installation.

To begin, let's look at block devices. SCSI and Serial ATA drives are both labeled under device handles such as: /dev/sda, /dev/sdb, /dev/sdc, etc. On more modern machines, PCI Express based NVMe solid state disks have device handles such as /dev/nvme0n1, /dev/nvme0n2, etc.

The following table will help readers determine where to find a certain type of block device on the system:

Type of device Default device handle Editorial notes and considerations
SATA, SAS, SCSI, or USB flash /dev/sda Found on hardware from roughly 2007 until the present, this device handle is perhaps the most commonly used in Linux. These types of devices can be connected via the SATA bus, SCSI, USB bus as block storage. As example, the first partition on the first SATA device is called /dev/sda1.
NVM Express (NVMe) /dev/nvme0n1 The latest in solid state technology, NVMe drives are connected to the PCI Express bus and have the fastest transfer block speeds on the market. Systems from around 2014 and newer may have support for NVMe hardware. The first partition on the first NVMe device is called /dev/nvme0n1p1.
MMC, eMMC, and SD /dev/mmcblk0 embedded MMC devices, SD cards, and other types of memory cards can be useful for data storage. That said, many systems may not permit booting from these types of devices. It is suggested to not use these devices for active Linux installations; rather consider using them to transfer files, which is their design goal. Alternatively they could be useful for short-term backups.

The block devices above represent an abstract interface to the disk. User programs can use these block devices to interact with the disk without worrying about whether the drives are SATA, SCSI, or something else. The program can simply address the storage on the disk as a bunch of contiguous, randomly-accessible 4096-byte (4K) blocks.

Partitions and slices

Although it is theoretically possible to use a full disk to house a Linux system, this is almost never done in practice. Instead, full disk block devices are split up in smaller, more manageable block devices. On most systems, these are called partitions. Other architectures use a similar technique, called slices.

Designing a partition scheme

How many partitions and how big?

The design of disk partition layout is highly dependent on the demands of the system and the file system(s) applied to the device. If there are lots of users, then it is advised to have /home on a separate partition which will increase security and make backups and other types of maintenance easier. If Gentoo is being installed to perform as a mail server, then /var should be a separate partition as all mails are stored inside the /var directory. Game servers may have a separate /opt partition since most gaming server software is installed therein. The reason for these recommendations is similar to the /home directory: security, backups, and maintenance.

In most situations on Gentoo, /usr and /var should be kept relatively large in size. /usr hosts the majority of applications available on the system and the Linux kernel sources (under /usr/src). By default, /var hosts the Gentoo ebuild repository (located at /var/db/repos/gentoo) which, depending on the file system, generally consumes around 650 MiB of disk space. This space estimate excludes the /var/cache/distfiles and /var/cache/binpkgs directories, which will gradually fill with source files and (optionally) binary packages respectively as they are added to the system.

How many partitions and how big very much depends on considering the trade-offs and choosing the best option for the circumstance. Separate partitions or volumes have the following advantages:

  • Choose the best performing filesystem for each partition or volume.
  • The entire system cannot run out of free space if one defunct tool is continuously writing files to a partition or volume.
  • If necessary, file system checks are reduced in time, as multiple checks can be done in parallel (although this advantage is realized more with multiple disks than it is with multiple partitions).
  • Security can be enhanced by mounting some partitions or volumes read-only, nosuid (setuid bits are ignored), noexec (executable bits are ignored), etc.

However, multiple partitions have certain disadvantages as well:

  • If not configured properly, the system might have lots of free space on one partition and little free space on another.
  • A separate partition for /usr/ may require the administrator to boot with an initramfs to mount the partition before other boot scripts start. Since the generation and maintenance of an initramfs is beyond the scope of this handbook, we recommend that newcomers do not use a separate partition for /usr/.
  • There is also a 15-partition limit for SCSI and SATA unless the disk uses GPT labels.
If you intend to uses Systemd, /usr/ must be available on boot, either as part of the root filesystem or mounted via an initramfs.

What about swap space?

There is no perfect value for the swap partition. The purpose of swap space is to provide disk storage to the kernel when internal memory (RAM) is under pressure. A swap space allows for the kernel to move memory pages that are not likely to be accessed soon to disk (swap or page-out), freeing memory. Of course, if that memory is suddenly needed, these pages need to be put back in memory (page-in) which will take a while (as disks are very slow compared to internal memory).

When the system is not going to run memory intensive applications or has lots of memory available, then it probably does not need much swap space. However, swap space is used to store the entire contents of memory in case of hibernation. If the system requires support for hibernation, then swap space larger than or equal to the amount of memory is necessary.

As a general rule of thumb, the swap space size is recommended to be twice the internal memory (RAM). For systems with multiple hard disks, it is wise to create one swap partition on each disk so that they can be utilized for parallel read/write operations. The faster a disk can swap, the faster the system will run when data in swap space must be accessed. When choosing between rotational and solid state disks, it is better for performance to put swap on the SSD. Also, swap files can be used as an alternative to swap partitions; this is mostly interesting for systems with very limited disk space.

Default: Using mac-fdisk

These instructions are for the Apple G5 system.

Start mac-fdisk:

root #mac-fdisk /dev/sda

First delete the partitions that have been cleared previously to make room for Linux partitions. Use the d key in mac-fdisk to delete those partition(s). It will ask for the partition number to delete.

Second, create an Apple_Bootstrap partition by pressing the b key. It will ask for a block from which to start. Enter the number of the first free partition, followed by entering a p. For instance this is 2p.

This partition is not a "boot" partition. It is not used by Linux at all; there is no need to place any filesystem on it and it should never be mounted. PPC users do not need an extra partition for /boot.

Now create a swap partition by pressing the c key. Again mac-fdisk will ask what block to start from. As we used 2 before to create the Apple_Bootstrap partition, enter 3p. When asked for the size, enter 512M (or whatever size needed). When asked for a name, enter swap (mandatory).

To create the root partition, enter c, followed by 4p to select from what block the root partition should start. When asked for the size, enter 4p again. mac-fdisk will interpret this as "Use all available space". When asked for the name, enter root (mandatory).

To finish up, write the partition to the disk using w and q to quit mac-fdisk.

To make sure everything is okay, run mac-fdisk once more to verify all the partitions are present. If a partition is absent, or it is missing some of the changes that were made, then reinitialize the partitions by pressing i in mac-fdisk. Note that this will recreate the partition map and thus remove all the partitions.

Alternative: Using fdisk

The following instructions are for IBM pSeries, iSeries, and OpenPower systems.
When planning to use a RAID disk array for the Gentoo installation on POWER5-based hardware, first run iprconfig to format the disks to Advanced Function format and create the disk array. Emerge sys-fs/iprutils after the installation is complete.

If the system has an ipr-based SCSI adapter, start the ipr utilities now.

root #/etc/init.d/iprinit start

The following parts explain how to create the example partition layout described previously, namely:

Partition Description
/dev/sda1 PPC PReP Boot partition
/dev/sda2 Swap partition
/dev/sda3 Root partition

Change or modify the partition layout according to personal preference.

Viewing current partition layout

fdisk is a popular and powerful tool to split a disk into partitions. Fire up fdisk on the current disk (in our example, we use /dev/sda):

root #fdisk /dev/sda
Command (m for help)

If there is still an AIX partition layout on the system, then the following error message will be displayed:

root #fdisk /dev/sda
  There is a valid AIX label on this disk.
  Unfortunately Linux cannot handle these
  disks at the moment.  Nevertheless some
  1. fdisk will destroy its contents on write.
  2. Be sure that this disk is NOT a still vital
     part of a volume group. (Otherwise you may
     erase the other disks as well, if unmirrored.)
  3. Before deleting this physical volume be sure
     to remove the disk logically from your AIX
     machine.  (Otherwise you become an AIXpert).

Don't worry, new empty DOS partition table can be created by pressing o.

This will destroy any installed AIX version!

Type p to display the disk current partition configuration:

Command (m for help):p
Disk /dev/sda: 30.7 GB, 30750031872 bytes
141 heads, 63 sectors/track, 6761 cylinders
Units = cylinders of 8883 * 512 = 4548096 bytes
   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1          12       53266+  83  Linux
/dev/sda2              13         233      981571+  82  Linux swap
/dev/sda3             234         674     1958701+  83  Linux
/dev/sda4             675        6761    27035410+   5  Extended
/dev/sda5             675        2874     9771268+  83  Linux
/dev/sda6            2875        2919      199836   83  Linux
/dev/sda7            2920        3008      395262   83  Linux
/dev/sda8            3009        6761    16668918   83  Linux

This particular disk is configured to house six Linux filesystems (each with a corresponding partition listed as "Linux") as well as a swap partition (listed as "Linux swap").

Removing all partitions

First remove all existing partitions from the disk. Type d to delete a partition. For instance, to delete an existing /dev/sda1:

Command (m for help):d
Partition number (1-4): 1

The partition has been scheduled for deletion. It will no longer show up when typing p, but it will not be erased until the changes have been saved. If a mistake was made and the session needs to be aborted, then type q immediately and hit Enter and none of the partitions will be deleted or modified.

Now, assuming that indeed all partitions need to be wiped out, repeatedly type p to print out a partition listing and then type d and the number of the partition to delete it. Eventually, the partition table will show no more partitions:

Command (m for help):p
Disk /dev/sda: 30.7 GB, 30750031872 bytes
141 heads, 63 sectors/track, 6761 cylinders
Units = cylinders of 8883 * 512 = 4548096 bytes
Device Boot    Start       End    Blocks   Id  System

Now that the in-memory partition table is empty, let's create the partitions. We will use a default partitioning scheme as discussed previously. Of course, don't follow these instructions to the letter but adjust to personal preference.

Creating the PPC PReP boot partition

First create a small PReP boot partition. Type n to create a new partition, then p to select a primary partition, followed by 1 to select the first primary partition. When prompted for the first cylinder, hit Enter. When prompted for the last cylinder, type +7M to create a partition 7 MB in size. After this, type t to set the partition type, 1 to select the partition just created and then type in 41 to set the partition type to "PPC PReP Boot". Finally, mark the PReP partition as bootable.

The PReP partition has to be smaller than 8 MB!
Command (m for help):p
Disk /dev/sda: 30.7 GB, 30750031872 bytes
141 heads, 63 sectors/track, 6761 cylinders
Units = cylinders of 8883 * 512 = 4548096 bytes
   Device Boot      Start         End      Blocks   Id  System
Command (m for help):n
Command action
      e   extended
      p   primary partition (1-4)
Partition number (1-4): 1
First cylinder (1-6761, default 1): 
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-6761, default
6761): +8M
Command (m for help):t
Selected partition 1
Hex code (type L to list codes): 41
Changed system type of partition 1 to 41 (PPC PReP Boot)
Command (m for help):a
Partition number (1-4): 1
Command (m for help):

Now, when looking at the partition table again (through p), the following partition information should be shown:

Command (m for help):p
Disk /dev/sda: 30.7 GB, 30750031872 bytes
141 heads, 63 sectors/track, 6761 cylinders
Units = cylinders of 8883 * 512 = 4548096 bytes
   Device Boot      Start         End      Blocks   Id  System
/dev/sda1  *            1           3       13293   41  PPC PReP Boot

Creating the swap partition

Now create the swap partition. To do this, type n to create a new partition, then p to tell fdisk to create a primary partition. Then type 2 to create the second primary partition, /dev/sda2 in our case. When prompted for the first cylinder, hit Enter. When prompted for the last cylinder, type +512M to create a partition 512MB in size. After this, type t to set the partition type, 2 to select the partition just created and then type in 82 to set the partition type to "Linux Swap". After completing these steps, typing p should display a partition table that looks similar to this:

Command (m for help):p
Disk /dev/sda: 30.7 GB, 30750031872 bytes
141 heads, 63 sectors/track, 6761 cylinders
Units = cylinders of 8883 * 512 = 4548096 bytes
   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1           3       13293   41  PPC PReP Boot
/dev/sda2               4         117      506331   82  Linux swap

Creating the root partition

Finally, create the root partition. To do this, type n to create a new partition, then p to tell fdisk to create a primary partition. Then type 3 to create the third primary partition, /dev/sda3 in our case. When prompted for the first cylinder, hit Enter. When prompted for the last cylinder, hit enter to create a partition that takes up the rest of the remaining space on the disk. After completing these steps, typing p should display a partition table that looks similar to this:

Command (m for help):p
Disk /dev/sda: 30.7 GB, 30750031872 bytes
141 heads, 63 sectors/track, 6761 cylinders
Units = cylinders of 8883 * 512 = 4548096 bytes
   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1           3       13293   41  PPC PReP Boot
/dev/sda2               4         117      506331   82  Linux swap
/dev/sda3             118        6761    29509326   83  Linux

Saving the partition layout

To save the partition layout and exit fdisk, type w.

Command (m for help):w

Creating file systems


Now that the partitions have been created, it is time to place a filesystem on them. In the next section the various file systems that Linux supports are described. Readers that already know which filesystem to use can continue with Applying a filesystem to a partition. The others should read on to learn about the available filesystems...


Linux supports several dozen filesystems, although many of them are only wise to deploy for specific purposes. Only certain filesystems may be found found stable on the ppc64 architecture - it is advised to read up on the filesystems and their support state before selecting a more experimental one for important partitions. ext4 is the recommended all-purpose all-platform filesystem.

A next generation filesystem that provides many advanced features such as snapshotting, self-healing through checksums, transparent compression, subvolumes, and integrated RAID. Kernels prior to 5.4.y are not guaranteed to be safe to use with btrfs in production because fixes for serious issues are only present in the more recent releases of the LTS kernel branches. Filesystem corruption issues are common on older kernel branches, with anything older than 4.4.y being especially unsafe and prone to corruption. Corruption is more likely on older kernels (than 5.4.y) when compression is enabled. RAID 5/6 and quota groups unsafe on all versions of btrfs. Furthermore, btrfs can counter-intuitively fail filesystem operations with ENOSPC when df reports free space due to internal fragmentation (free space pinned by DATA + SYSTEM chunks, but needed in METADATA chunks). Additionally, a single 4K reference to a 128M extent inside btrfs can cause free space to be present, but unavailable for allocations. This can also cause btrfs to return ENOSPC when free space is reported by df. Installing sys-fs/btrfsmaintenance and configuring the scripts to run periodically can help to reduce the possibility of ENOSPC issues by rebalancing btrfs, but it will not eliminate the risk of ENOSPC when free space is present. Some workloads will never hit ENOSPC while others will. If the risk of ENOSPC in production is unacceptable, you should use something else. If using btrfs, be certain to avoid configurations known to have issues. With the exception of ENOSPC, information on the issues present in btrfs in the latest kernel branches is available at the btrfs wiki status page.
This is the tried and true Linux filesystem but doesn't have metadata journaling, which means that routine ext2 filesystem checks at startup time can be quite time-consuming. There is now quite a selection of newer-generation journaled filesystems that can be checked for consistency very quickly and are thus generally preferred over their non-journaled counterparts. Journaled filesystems prevent long delays when the system is booted and the filesystem happens to be in an inconsistent state.
The journaled version of the ext2 filesystem, providing metadata journaling for fast recovery in addition to other enhanced journaling modes like full data and ordered data journaling. It uses an HTree index that enables high performance in almost all situations. In short, ext3 is a very good and reliable filesystem.
Initially created as a fork of ext3, ext4 brings new features, performance improvements, and removal of size limits with moderate changes to the on-disk format. It can span volumes up to 1 EB and with maximum file size of 16TB. Instead of the classic ext2/3 bitmap block allocation ext4 uses extents, which improve large file performance and reduce fragmentation. Ext4 also provides more sophisticated block allocation algorithms (delayed allocation and multiblock allocation) giving the filesystem driver more ways to optimize the layout of data on the disk. Ext4 is the recommended all-purpose all-platform filesystem.
The Flash-Friendly File System was originally created by Samsung for the use with NAND flash memory. As of Q2, 2016, this filesystem is still considered immature, but it is a decent choice when installing Gentoo to microSD cards, USB drives, or other flash-based storage devices.
IBM's high-performance journaling filesystem. JFS is a light, fast, and reliable B+tree-based filesystem with good performance in various conditions.
A B+tree-based journaled filesystem that has good overall performance, especially when dealing with many tiny files at the cost of more CPU cycles. ReiserFS version 3 is included in the mainline Linux kernel, but is not recommended to be used when initially installing a Gentoo system. Newer versions of the ReiserFS filesystem exist, however they require additional patching of the mainline kernel to be utilized.
A filesystem with metadata journaling which comes with a robust feature-set and is optimized for scalability. XFS seems to be less forgiving to various hardware problems, but has been continuously upgraded to include modern features.
Also known as FAT32, is supported by Linux but does not support standard UNIX permission settings. It is mostly used for interoperability with other operating systems (Microsoft Windows or Apple's OSX) but is also a necessity for some system bootloader firmware (like UEFI).
This "New Technology" filesystem is the flagship filesystem of Microsoft Windows since Windows NT 3.1. Similar to vfat above it does not store UNIX permission settings or extended attributes necessary for BSD or Linux to function properly, therefore it should not be used as a root filesystem. It should only be used for interoperability with Microsoft Windows systems (note the emphasis on only).

Applying a filesystem to a partition

To create a filesystem on a partition or volume, there are user space utilities available for each possible filesystem. Click the filesystem's name in the table below for additional information on each filesystem:

Filesystem Creation command On minimal CD? Package
btrfs mkfs.btrfs Yes sys-fs/btrfs-progs
ext2 mkfs.ext2 Yes sys-fs/e2fsprogs
ext3 mkfs.ext3 Yes sys-fs/e2fsprogs
ext4 mkfs.ext4 Yes sys-fs/e2fsprogs
f2fs mkfs.f2fs Yes sys-fs/f2fs-tools
jfs mkfs.jfs Yes sys-fs/jfsutils
reiserfs mkfs.reiserfs Yes sys-fs/reiserfsprogs
xfs mkfs.xfs Yes sys-fs/xfsprogs
vfat mkfs.vfat Yes sys-fs/dosfstools
NTFS mkfs.ntfs Yes sys-fs/ntfs3g

For instance, to have the EFI system partition partition (/dev/sda1) as FAT32 and the root partition (/dev/sda3) as ext4 as used in the example partition structure, the following commands would be used:

root #mkfs.vfat -F 32 /dev/sda1
root #mkfs.ext4 /dev/sda3

When using ext2, ext3, or ext4 on a small partition (less than 8 GiB), then the file system must be created with the proper options to reserve enough inodes. This can be done using one of the following commands, respectively:

root #mkfs.ext2 -T small /dev/<device>
root #mkfs.ext3 -T small /dev/<device>
root #mkfs.ext4 -T small /dev/<device>

This will generally quadruple the number of inodes for a given file system as its "bytes-per-inode" reduces from one every 16kB to one every 4kB.

Now create the filesystems on the newly created partitions (or logical volumes).

Activating the swap partition

mkswap is the command that is used to initialize swap partitions:

root #mkswap /dev/sda2

To activate the swap partition, use swapon:

root #swapon /dev/sda2

Create and activate the swap with the commands mentioned above.

Mounting the root partition

Now that the partitions are initialized and are housing a filesystem, it is time to mount those partitions. Use the mount command, but don't forget to create the necessary mount directories for every partition created. As an example we mount the root partition:

root #mount /dev/sda3 /mnt/gentoo
If /tmp/ needs to reside on a separate partition, be sure to change its permissions after mounting:
root #chmod 1777 /mnt/gentoo/tmp
This also holds for /var/tmp.

Later in the instructions the proc filesystem (a virtual interface with the kernel) as well as other kernel pseudo-filesystems will be mounted. But first we install the Gentoo installation files.