To be able to install Gentoo, you must create the necessary partitions. This chapter describes how to partition a disk for future usage. 6 2011-08-23
Introduction to Block Devices Partitions

Although it is theoretically possible to use a full disk to house your Linux system, this is almost never done in practice. Instead, full disk block devices are split up in smaller, more manageable block devices. These are called partitions.

Designing a Partitioning Scheme How Many and How Big?

The number of partitions is highly dependent on your environment. For instance, if you have lots of users, you will most likely want to have your /home separate as it increases security and makes backups easier. If you are installing Gentoo to perform as a mailserver, your /var should be separate as all mails are stored inside /var. A good choice of filesystem will then maximise your performance. Gameservers will have a separate /opt as most gaming servers are installed there. The reason is similar for /home: security and backups. You will definitely want to keep /usr big: not only will it contain the majority of applications, the Portage tree alone takes around 500 Mbyte excluding the various sources that are stored in it.

As you can see, it very much depends on what you want to achieve. Separate partitions or volumes have the following advantages:

  • You can choose the best performing filesystem for each partition or volume
  • Your 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 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 one big disadvantage: if not configured properly, you might result in having a system with lots of free space on one partition and none on another. There is also a 15-partition limit for SCSI and SATA.

Using fdisk on MIPS to Partition your Disk SGI Machines: Creating an SGI Disk Label

All disks in an SGI System require an SGI Disk Label, which serves a similar function as Sun & MS-DOS disklabels -- It stores information about the disk partitions. Creating a new SGI Disk Label will create two special partitions on the disk:

  • SGI Volume Header (9th partition): This partition is important. It is where the bootloader will reside, and in some cases, it will also contain the kernel images.
  • SGI Volume (11th partition): This partition is similar in purpose to the Sun Disklabel's third partition of "Whole Disk". This partition spans the entire disk, and should be left untouched. It serves no special purpose other than to assist the PROM in some undocumented fashion (or it is used by IRIX in some way).
The SGI Volume Header must begin at cylinder 0. Failure to do so means you won't be able to boot from the disk.

The following is an example excerpt from an fdisk session. Read and tailor it to your needs... 

# fdisk /dev/sda

Command (m for help): x

Expert command (m for help): m
Command action
   b   move beginning of data in a partition
   c   change number of cylinders
   d   print the raw data in the partition table
   e   list extended partitions
   f   fix partition order
   g   create an IRIX (SGI) partition table
   h   change number of heads
   m   print this menu
   p   print the partition table
   q   quit without saving changes
   r   return to main menu
   s   change number of sectors/track
   v   verify the partition table
   w   write table to disk and exit

Expert command (m for help): g
Building a new SGI disklabel. Changes will remain in memory only,
until you decide to write them. After that, of course, the previous
content will be irrecoverably lost.

Expert command (m for help): r

Command (m for help): p

Disk /dev/sda (SGI disk label): 64 heads, 32 sectors, 17482 cylinders
Units = cylinders of 2048 * 512 bytes

----- partitions -----
Pt#     Device  Info     Start       End   Sectors  Id  System
 9:  /dev/sda1               0         4     10240   0  SGI volhdr
11:  /dev/sda2               0     17481  35803136   6  SGI volume
----- Bootinfo -----
Bootfile: /unix
----- Directory Entries -----

Command (m for help):
If your disk already has an existing SGI Disklabel, then fdisk will not allow the creation of a new label. There are two ways around this. One is to create a Sun or MS-DOS disklabel, write the changes to disk, and restart fdisk. The second is to overwrite the partition table with null data via the following command: dd if=/dev/zero of=/dev/sda bs=512 count=1. Getting the SGI Volume Header to just the right size This step is often needed, due to a bug in fdisk. For some reason, the volume header isn't created correctly, the end result being it starts and ends on cylinder 0. This prevents multiple partitions from being created. To get around this issue... read on.

Now that an SGI Disklabel is created, partitions may now be defined. In the above example, there are already two partitions defined for you. These are the special partitions mentioned above and should not normally be altered. However, for installing Gentoo, we'll need to load a bootloader, and possibly multiple kernel images (depending on system type) directly into the volume header. The volume header itself can hold up to eight images of any size, with each image allowed eight-character names.

The process of making the volume header larger isn't exactly straight-forward; there's a bit of a trick to it. One cannot simply delete and re-add the volume header due to odd fdisk behavior. In the example provided below, we'll create a 50MB Volume header in conjunction with a 50MB /boot partition. The actual layout of your disk may vary, but this is for illustrative purposes only. 

Command (m for help): n
Partition number (1-16): 1
First cylinder (5-8682, default 5): 51
 Last cylinder (51-8682, default 8682): 101

(Notice how fdisk only allows Partition #1 to be re-created starting at a     )
(minimum of cylinder 5?  Had you attempted to delete & re-create the SGI      )
(Volume Header this way, this is the same issue you would have encountered.   )
(In our example, we want /boot to be 50MB, so we start it at cylinder 51 (the )
(Volume Header needs to start at cylinder 0, remember?), and set its ending   )
(cylinder to 101, which will roughly be 50MB (+/- 1-5MB).                     )

Command (m for help): d
Partition number (1-16): 9

(Delete Partition #9 (SGI Volume Header))

Command (m for help): n
Partition number (1-16): 9
First cylinder (0-50, default 0): 0
 Last cylinder (0-50, default 50): 50

(Re-Create Partition #9, ending just before Partition #1)

If you're unsure how to use fdisk have a look down further at the instructions for partitioning on Cobalts. The concepts are exactly the same -- just remember to leave the volume header and whole disk partitions alone.

Once this is done, you are safe to create the rest of your partitions as you see fit. After all your partitions are laid out, make sure you set the partition ID of your swap partition to 82, which is Linux Swap. By default, it will be 83, Linux Native.

Now that your partitions are created, you can continue with Creating Filesystems.

Cobalt Machines: Partitioning your drive

On Cobalt machines, the BOOTROM expects to see a MS-DOS MBR, so partitioning the drive is relatively straightforward -- in fact, it's done the same way as you'd do for an Intel x86 machine. However there are some things you need to bear in mind.

  • Cobalt firmware will expect /dev/sda1 to be a Linux partition formatted EXT2 Revision 0. EXT2 Revision 1 partitions will NOT WORK! (The Cobalt BOOTROM only understands EXT2r0)
  • The above said partition must contain a gzipped ELF image, vmlinux.gz in the root of that partition, which it loads as the kernel

For that reason, I recommend creating a ~20MB /boot partition formatted EXT2r0 upon which you can install CoLo & your kernels. This allows you to run a modern filesystem (EXT3 or ReiserFS) for your root filesystem.

I will assume you have created /dev/sda1 to mount later as a /boot partition. If you wish to make this /, you'll need to keep the PROM's expectations in mind.

So, continuing on... To create the partitions you type fdisk /dev/sda at the prompt. The main commands you need to know are these:

  • o: Wipe out old partition table, starting with an empty MS-DOS partition table
  • n: New Partition
  • t: Change Partition Type
    • Use type 82 for Linux Swap, 83 for Linux FS
  • d: Delete a partition
  • p: Display (print) Partition Table
  • q: Quit -- leaving old partition table as is.
  • w: Quit -- writing partition table in the process. 
# fdisk /dev/sda

The number of cylinders for this disk is set to 19870.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
   (e.g., DOS FDISK, OS/2 FDISK)

(Start by clearing out any existing partitions)
Command (m for help): o
Building a new DOS disklabel. Changes will remain in memory only,
until you decide to write them. After that, of course, the previous
content won't be recoverable.


The number of cylinders for this disk is set to 19870.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
   (e.g., DOS FDISK, OS/2 FDISK)
Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

(You can now verify the partition table is empty using the 'p' command)

Command (m for help): p

Disk /dev/sda: 10.2 GB, 10254827520 bytes
16 heads, 63 sectors/track, 19870 cylinders
Units = cylinders of 1008 * 512 = 516096 bytes

   Device Boot      Start         End      Blocks   Id  System

(Create the /boot partition)

Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
p
Partition number (1-4): 1

(Just press ENTER here to accept the default)

First cylinder (1-19870, default 1):
Last cylinder or +size or +sizeM or +sizeK (1-19870, default 19870): +20M

(and now if we type 'p' again, we should see the new partition)
Command (m for help): p

Disk /dev/sda: 10.2 GB, 10254827520 bytes
16 heads, 63 sectors/track, 19870 cylinders
Units = cylinders of 1008 * 512 = 516096 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1          40       20128+  83  Linux

(The rest, I prefer to put in an extended partition, so I'll create that)

Command (m for help): n
Command action
   e   extended
   p   primary partition (1-4)
e
Partition number (1-4): 2

(Again, the default is fine, just press ENTER.)

First cylinder (41-19870, default 41):
Using default value 41

(We want to use the whole disk here, so just press ENTER again)
Last cylinder or +size or +sizeM or +sizeK (41-19870, default 19870):
Using default value 19870

(Now, the / partition -- I use separate partitions for /usr, /var,
etc... so / can be small. Adjust as per your preference.)

Command (m for help): n
Command action
   l   logical (5 or over)
   p   primary partition (1-4)
l
First cylinder (41-19870, default 41):<Press ENTER>
Using default value 41
Last cylinder or +size or +sizeM or +sizeK (41-19870, default 19870): +500M

(... and similar for any other partitions ...)

(Last but not least, the swap space. I recommend at least 250MB swap,
preferrably 1GB)

Command (m for help): n
Command action
   l   logical (5 or over)
   p   primary partition (1-4)
l
First cylinder (17294-19870, default 17294): <Press ENTER>
Using default value 17294
Last cylinder or +size or +sizeM or +sizeK (1011-19870, default 19870): <Press ENTER>
Using default value 19870

(Now, if we check our partition table, everything should mostly be ship
shape except for one thing...)

Command (m for help): p

Disk /dev/sda: 10.2 GB, 10254827520 bytes
16 heads, 63 sectors/track, 19870 cylinders
Units = cylinders of 1008 * 512 = 516096 bytes

Device Boot      Start         End      Blocks      ID  System
/dev/sda1               1          21       10552+  83  Linux
/dev/sda2              22       19870    10003896    5  Extended
/dev/sda5              22        1037      512032+  83  Linux
/dev/sda6            1038        5101     2048224+  83  Linux
/dev/sda7            5102        9165     2048224+  83  Linux
/dev/sda8            9166       13229     2048224+  83  Linux
/dev/sda9           13230       17293     2048224+  83  Linux
/dev/sda10          17294       19870     1298776+  83  Linux

(Notice how #10, our swap partition is still type 83?)

Command (m for help): t
Partition number (1-10): 10
Hex code (type L to list codes): 82
Changed system type of partition 10 to 82 (Linux swap)

(That should fix it... just to verify...)

Command (m for help): p

Disk /dev/sda: 10.2 GB, 10254827520 bytes
16 heads, 63 sectors/track, 19870 cylinders
Units = cylinders of 1008 * 512 = 516096 bytes

Device Boot      Start         End      Blocks      ID  System
/dev/sda1               1          21       10552+  83  Linux
/dev/sda2              22       19870    10003896    5  Extended
/dev/sda5              22        1037      512032+  83  Linux
/dev/sda6            1038        5101     2048224+  83  Linux
/dev/sda7            5102        9165     2048224+  83  Linux
/dev/sda8            9166       13229     2048224+  83  Linux
/dev/sda9           13230       17293     2048224+  83  Linux
/dev/sda10          17294       19870     1298776+  82  Linux Swap

(Now, we write out the new partition table.)

Command (m for help): w
The partition table has been altered!

Calling ioctl() to re-read partition table.
Syncing disks.

#

And that's all there is to it. You should now be right to proceed onto the next stage: Creating Filesystems.

Creating Filesystems Introduction

Now that your partitions are created, it is time to place a filesystem on them. If you don't care about what filesystem to choose and are happy with what we use as default in this handbook, continue with Applying a Filesystem to a Partition. Otherwise read on to learn about the available filesystems...

Applying a Filesystem to a Partition

To create a filesystem on a partition or volume, there are tools available for each possible filesystem:

ext2mkfs.ext2ext3mkfs.ext3ext4mkfs.ext4reiserfsmkfs.reiserfsxfsmkfs.xfsjfsmkfs.jfs
Filesystem Creation Command

For instance, to have the boot partition (/dev/sda1 in our example) in ext2 and the root partition (/dev/sda3 in our example) in ext3, you would use: 

# mkfs.ext2 /dev/sda1
# mkfs.ext3 /dev/sda3

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

If you're installing on a Cobalt server, remember /dev/sda1 MUST be of type EXT2 revision 0; Anything else (e.g. EXT2 revision 1, EXT3, ReiserFS, XFS, JFS and others) WILL NOT WORK! You can format the partition using the command: mkfs.ext2 -r 0 /dev/sda1. Activating the Swap Partition

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

# mkswap /dev/sda2

To activate the swap partition, use swapon: 

# swapon /dev/sda2

Create and activate the swap with the commands mentioned above.

Mounting

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

# mount /dev/sda3 /mnt/gentoo
# mkdir /mnt/gentoo/boot
# mount /dev/sda1 /mnt/gentoo/boot
If you want your /tmp to reside on a separate partition, be sure to change its permissions after mounting: chmod 1777 /mnt/gentoo/tmp. This also holds for /var/tmp.

We will also have to mount the proc filesystem (a virtual interface with the kernel) on /proc. But first we will need to place our files on the partitions.

Continue with Installing the Gentoo Installation Files.