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Лекция 4:

Shared OS installation

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Аннотация: Separate disks; Sharing adisk; Sharing with Linux or another BSD; Repartitioning with FIPS.

In many cases, you won't want to install FreeBSD on the system by itself: you may need to use other operating systems as well. In this chapter, we’ll look at what you need to do to prepare for such an installation. If you're only running FreeBSD on the machine, you don't need to read this chapter, and you can move onto "Installing FreeBSD" , Installing FreeBSD.

Before you start the installation, read this chapter carefully. It's easy to make a mistake, and one of the most frequent results of mistakes is the total loss of all data on the hard disk.

Currently, only the ia32 (Intel) port of FreeBSD is capable of sharing with other operating systems. We'll concentrate on how to share your system with Microsoft, because that's both the most difficult and the most common, but most of this chapter applies to other operating systems as well. You may want to refer to the discussion of Microsoft and FreeBSD disk layouts on page 34.

Separate disks

The first question is: do you need to share a disk between FreeBSD and the other operating system? It's much easier if you don't have to. In this section, we'll look at what you need to do.

Many operating systems will only boot from the first disk identified by the BIOS, usually called the C: disk in deference to Microsoft. FreeBSD doesn't have this problem, so the easiest thing is to install FreeBSD on the entire second disk. BIOS restrictions usually make it difficult to boot from any but the first two disks.

In this case, you don't really need to do anything special, although it's always a good idea to back up your data first. Install FreeBSD on the second disk, and choose the Boot Manager option in the partition editor (page 64). This will then give you the choice of booting from the first or second disk. Note that you should not change the order of disks after such an installation; if you do, the system will not be able to find its file systems after boot.

Sharing a disk

If you intend to share a disk between FreeBSD and another operating system, the first question is: is there enough space on the disk for FreeBSD? How much you need depends on what you want to do with FreeBSD, of course, but for the sake of example we'll take 120 MB as an absolute minimum. In the following section, we'll consider what to do if you need to change your partitions. If you already have enough space for a FreeBSD partition (for example, if you have just installed Microsoft specifically for sharing with FreeBSD, and thus have not filled up the disk), continue reading on page 66.

Sharing with Linux or another BSD

Sharing with other free operating systems is relatively simple. You still need to have space for FreeBSD, of course, and unlike Microsoft, there are no tools for shrinking Linux or BSD file systems: you'll have to remove them or recreate them. You can find some information about sharing with Linux in the mini-Howto at http://www linux.org/docs/ldp/howto/mini/Linux+FreeBSD.html.

NetBSD and Open BSD file systems and slices are very similar to their FreeBSD counterparts. They're not identical, however, and you may find that one of the systems recognizes the partition of another system and complains about it because it's not quite right. For example, NetBSD has a d partition that can go outside the boundary of the slice. FreeBSD does not allow this, so you get a harmless error message.

Repartitioning with FIPS

Typically, if you've been running Microsoft on your machine, it will occupy the entire disk. If you need all this space, of course, there's no way to install another operating system as well. Frequently, though, you'll find that you have enough free space in the partition. Unfortunately, that’s not where you want it: you want the space in a new partition. There are a number of ways to do so:

  • You can reinstall the software. This approach is common in the Microsoft world, but FreeBSD users try to avoid it.
  • You can use FIPS to shrink a Microsoft partition, leaving space for FreeBSD. FIPS is a public domain utility, and it is included on the FreeBSD CD-ROM.
  • If you can't use FIPS, use a commercial utility like PartitionMagic.This is not included on the CD-ROMs, and we won't discuss it further.

In the rest of the section, we'll look at how to shrink a partition with FIPS. If you do it with PartitionMagic, the details are different, but the principles are the same. In particular:

Before repartitioning your disk, make a backup. You can shoot yourself in the foot with this method, and the result will almost invariably be loss of data.

If you've been running Microsoft on your system for any length of time, the data in the partition will be spread all around the partition. If you just truncate the partition, you'll lose a lot of data, so you first need to move all the data to the beginning of the partition. Do this with the Microsoft defragmentation utility. Before proceeding, consider a few gotchas:

  • The new Microsoft partition needs to be big enough to hold not only the current data, but also anything you will want to put in it in the future. If you make it exactly the current size of the data, it will effectively be full, and you won't beable to write anything to it.
  • The second partition is also a Microsoft partition. To install FreeBSD on it, you need to convert it into a FreeBSD partition.
  • FIPS may result in configuration problems with your Microsoft machine. Since it adds a partition, any automatically assigned partitions that followwill have a different drive letter. In particular, this could mean that your CD-ROM drive will ''move.'' After you delete the second Microsoft partition and change it into a FreeBSD partition, it will ''move'' back again.

For further information, read the FIPS documentation in /cdrom/tools/fips.doc. In particular, note these limitations:

  • FIPS works only with Hard Disk BIOSes that use interrupt 0x13 for low-level hard disk access. This is generally not a problem.
  • FIPS does not split partitions with 12 bit FATs, which were used by older versions of Microsoft. These are less than 10 MB in size and thus too small to be worth splitting.
  • FIPS splits only Microsoft partitions. The partition table and boot sector must conform to the MS-DOS 3.0+ or Windows 95 conventions. This is marked by the system indicator byte in the partition table, which must have the value 4 (16 bit sector number) or 6 (32 bit sector number). In particular, it will not split Linux or Windows 2000 and later partitions.
  • FIPS does not yet work on extended Microsoft partitions.
  • FIPS needs a free partition entry. It will not work if you already have four partitions.
  • FIPS will not reduce the original partition to a size of less than 4085 clusters, because this would involve rewriting the 16 bit FAT to a 12 bit FAT.
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