Опубликован: 06.08.2012 | Доступ: свободный | Студентов: 1189 / 25 | Оценка: 5.00 / 5.00 | Длительность: 53:41:00
Лекция 8:

Тaking control

< Лекция 7 || Лекция 8: 123456 || Лекция 9 >

Removing PC Card devices

The next thing we'd like to do is to unmount the file system when you remove the flash card. Unfortunately, that isn't possible. Unmounting can involve data transfer, so you have to do it before you remove the card. If you forget, and remove the card without unmounting, the system may panic next time you try to access the card.

After unmounting, you can remove the card. On the console you'll see something like:

ad4: removed from configuration
ad4: no status, reselecting device
ad4: timeout sending command=e7 s=ff e=04
ad4: flushing cache on detach failed
ata2: detached

Alternate PC Card code

The PC Card implementation described here, called NEWCARD, is new in FreeBSD Release 5. At the time of writing, the older implementation, called OZDCARD, is still included in the system. It's possible that you might have an older card that is supported by OLDCARD but not by NEWCARD. In that case, you will need to build a kernel with OLDCARD support. Check the NOTES files in /usr/src/sys/conf and /usr/src/sys/arch/conf, where arch is the architecture of your system, and the man pages pccard and pccard.conf.

Configuring PC Card devices at startup

A number of entries in /etc/rc.conf relate to the use of PC Card devices, but nearly all of them are for OLDCARD. You only need one for NEWCARD:

devd_enable="YES"

This starts devd at system startup.

Emulating other systems

A large number of operating systems run on Intel hardware, and there is a lot of software that is available for these other operating systems, but not for FreeBSD.

Emulators and simulators

There are a number of ways to execute software written for a different platform. The most popular are:

Simulation is a process where a program executes the functions that are normally performed by the native instruction set of another machine. They simulate the low-level instructions of the target machine, so simulators don't have to run on the same kind of machine as the code that they execute. A good example is the port emulators/p11, which simulates a PDP-11 minicomputer, the machine for which most early versions of UNIX were written.

  • Simulators run much more slowly than the native instruction set: for each simulated instruction, the simulator may execute hundreds of machine instructions. Amusingly, on most modern machines, the p11 emulator still runs faster than the original PDP-11: modern machines are over 1,000 times faster than the PDP-11.
  • In general, emulators execute the program instructions directly and only simulate the operating system environment. As are sult, they have to run on the same kind of hardware, but they're not noticeably slower than the original. If there is any difference in performance, it's because of differences between the host operating system and the emulated operating system.
  • Another use for the term emulator is where the hardware understands a different instruction set than the native one. Obviously this is not the kind of emulator we're talking about here.

FreeBSD can emulate many other systems to a point where applications written for these systems will run under FreeBSD. Most of the emulators are in the Ports Collection in the directory /usr/ports/emulators.

In a number of cases, the emulation support is in an experimental stage. Here's an overview:

  • FreeBSD will run most BSD/OS programs with no problems. You don't need an emulator.
  • FreeBSD will also run most NetBSD and OpenBSD executables, though not many people do this: it's safer to recompile them under FreeBSD.
  • FreeBSD runs Linux executables with the aid of the linux kld (loadable kernel module). We'll look at how to use it in the next section.
  • FreeBSD can run SCO COFF executables with the aid of the ibcs2 kld. This support is a little patchy: although the executables will run, you may run into problems caused by differences in the directory structure between SCO and FreeBSD. We'll look at it on page 164.
  • A Microsoft Windows emulator is available. We'll look at it on page 165.

Emulating Linux

Linux is a UNIX-like operating system that in many ways is very similar to FreeBSD. We discussed it on page 10. Although it looks very UNIX-like, many of the internal kernel interfaces are different from those of FreeBSD or other UNIX-based systems. The Linux compatibility package handles these differences, and most Linux software will run on FreeBSD. Most of the exceptions use specific drivers that don't run on FreeBSD, though there is a considerable effort to minimize even this category.

To install the Linux emulator, you must:

  • Install the compatibility libraries. These are in the port /usr/ports/emulators/lin-uxbase.
  • Run the Linux emulator kld, linux.

Running the Linux emulator

Normally you load the Linux emulator when you boot the system. Put the following line in your /etc/rc.conf:

linux_enable="YES"

If you don't want to do this for some reason, you can start it from the command line:

# kldload linux

You don't interact directly with the emulator module: it's just there to supply kernel functionality, so you get a new prompt immediately when you start it.

linux is a kld, so it doesn't show up in a ps listing. To check whether it is loaded, use

kldstat :

$ kldstat
Id  Refs     Address  Size    Name
 1     5  0xc0100000  1d08b0  kernel
 2     2  0xc120d000  a000    ibcs2.ko
 3     1  0xc121b000  3000    ibcs2_coff.ko
 5     1  0xc1771000  e000    linux.ko

This listing shows that the SCO UNIX emulation (ibcs2) has also been loaded.

The Linux emulator and many Linux programs are located in the directory hierarchy /usr/compat/linux. You won't normally need to access them directly, but if you get a Linux program that includes libraries destined for /lib, you will need to manually place them in /usr/compat/linux/lib. Be very careful not to replace any files in the /usr/lib hierarchy with Linux libraries; this would make it impossible to run FreeBSD programs that depend on them, and it's frequently very difficult to recover from such problems. Note that FreeBSD does not have a directory /lib, so the danger is relatively minor.

Linux procfs

Linux systems have a file system called procfs, or Process File System, which contains information used by many programs. FreeBSD also has a procfs, but it is completely different. To be able to run Linux programs which refer to procfs, place the following entry in your /etc/fstab file:

Linproc  /compat/linux/proc  linprocfs  rw  0  0

Problems executing Linux binaries

One of the problems with the ELF format used by older Linux binaries is that they may contain no information to identify them as Linux binaries. They might equally well be BSD/OS or UnixWare binaries. That's normally not a problem, unless there are library conflicts: the system can't decide which shared library to use. If you have this kind of binary, you must brand the executable using the program brandelf. For example, to brand the Star Office program swriter3, you would enter:

# brandelf -t Linux /usr/local/StarOffice-3.1/linux-x86/bin/swriter3

This example deliberately shows a very old version of Star Office: it's not clear that there are any modern binaries that cause such problems.

Emulating SCO UNIX

SCO UNIX, also known as SCO OpenDesktop and SCO Open Server, is based on UNIX System V3.2. This particular version of UNIX was current in the late 1980s. It uses an obsolete binary format called COFF (Common Object File Format).

Like Linux support, SCO support for FreeBSD is supplied as a loadable kernel module. It's not called sco, though: a number of older System V.3.2 systems, including Interactive UNIX, also support the ibcs2 1ibcs2 stands for Intel Binary Compatibility System 2standard. As a result, the kld is called ibcs2.

Run ibcs2 support like Linux support: start it manually, or modify /etc/rc. conf to start it automatically at boot up:

ibcs2_enable="YES"  # Ibcs2  (SCO) emulation loaded at startup (or NO).

Alternatively, load the kld:

# kldload ibcs2

One problem with SCO emulation is the SCO shared libraries. These are required to execute many SCO executables, and they're not supplied with the emulator. They are supplied with SCO's operating systems. Check the SCO license to determine whether you are allowed to use them on FreeBSD. You may also be eligible for a free SCO license—see the SCO web site for further details.

Emulating Microsoft Windows

The wine project has been working for some time to provide an emulation of Microsoft's Windows range of execution environments. It's changing continually, so there's little point describing it here. You can find up-to-date information at http://www.winehq.com/about/, and you can install it from the port emulators/wine . Be prepared for a fair amount of work.

Accessing Microsoft files

Often you're not as interested in running Microsoft applications as decoding their proprietary formats. For example, you might get a mail message with an attachment described only as

[-- Attachment #2: FreeBSD.doc
[-- Type: application/octet-stream, Encoding: x-unknown, Size: 15K
[-- application/octet-stream is unsupported (use 'v' to view this part)

This attachment has an unspecific MIME type2 See Chapter 26, Electronic mail: clients,page 489, for more information about MIME, but you might guess that it is Microsoft Word format because the file name ends in .doc. That doesn’t make it any more legible. To read it, you need something that understands the format. A good choice is OpenOffice.org, a clone of Microsoft’s ‘‘Office’’ product. Install from the Ports Collection (/usr/ports/editors/openoffice).

OpenOffice.org is not a good example of the UNIX way. It breaks a number of conventions, and in general it's a lot more difficult to use than normal FreeBSD tools. Its only real advantage is that you can process Microsoft document formats.

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