484 lines
9.3 KiB
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484 lines
9.3 KiB
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<HTML
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><HEAD
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>Sharing a Disk With DEC Unix</TITLE
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CLASS="SECT1"
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><H1
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CLASS="SECT1"
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><A
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NAME="AEN661"
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>6. Sharing a Disk With DEC Unix</A
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></H1
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><P
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>Unfortunately, DEC Unix doesn't know anything about Linux, so sharing
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a single disk between the two OSes is not entirely trivial. However,
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it is not a difficult task if you heed the tips in this section. The
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section assumes you are using <TT
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CLASS="LITERAL"
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>aboot</TT
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> version 0.5 or newer.</P
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><DIV
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CLASS="SECT2"
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><H2
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CLASS="SECT2"
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><A
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NAME="AEN665"
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>6.1. Partitioning the disk</A
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></H2
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><P
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>First and foremost: <I
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CLASS="EMPHASIS"
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>never</I
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> use any of the Linux partitioning
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programs (<TT
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CLASS="LITERAL"
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>minlabel</TT
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> or <TT
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CLASS="LITERAL"
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>fdisk</TT
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>) on a disk that is also
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used by DEC Unix. The Linux <TT
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CLASS="LITERAL"
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>minlabel</TT
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> program uses the same
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partition table format as DEC Unix <TT
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CLASS="LITERAL"
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>disklabel</TT
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>, but there are
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some incompatibilities in the data that <TT
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CLASS="LITERAL"
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>minlabel</TT
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> fills in, so
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DEC Unix will simply refuse to accept a partition table generated by
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<TT
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CLASS="LITERAL"
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>minlabel</TT
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>. To setup a Linux <TT
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CLASS="LITERAL"
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>ext2</TT
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> partition under DEC
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Unix, you'll have to change the disktab entry for your disk. For the
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purpose of this discussion, let's assume that you have an rz26 disk (a
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common 1GB drive) on which you want to install Linux. The disktab
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entry under DEC Unix v3.2 looks like this (see file
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<TT
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CLASS="LITERAL"
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>/etc/disktab</TT
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>):
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<TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><PRE
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CLASS="SCREEN"
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>rz26|RZ26|DEC RZ26 Winchester:\
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:ty=winchester:dt=SCSI:ns#57:nt#14:nc#2570:\
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:oa#0:pa#131072:ba#8192:fa#1024:\
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:ob#131072:pb#262144:bb#8192:fb#1024:\
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:oc#0:pc#2050860:bc#8192:fc#1024:\
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:od#393216:pd#552548:bd#8192:fd#1024:\
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:oe#945764:pe#552548:be#8192:fe#1024:\
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:of#1498312:pf#552548:bf#8192:ff#1024:\
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:og#393216:pg#819200:bg#8192:fg#1024:\
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:oh#1212416:ph#838444:bh#8192:fh#1024:</PRE
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></TD
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></TR
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></TABLE
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> </P
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><P
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>The interesting fields here are <TT
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CLASS="LITERAL"
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>o</TT
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><I
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CLASS="EMPHASIS"
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>?</I
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>, and
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<TT
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CLASS="LITERAL"
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>p</TT
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><I
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CLASS="EMPHASIS"
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>?</I
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>, where <I
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CLASS="EMPHASIS"
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>?</I
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> is a letter in the range
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<TT
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CLASS="LITERAL"
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>a</TT
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>-<TT
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CLASS="LITERAL"
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>h</TT
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> (first through 8-th partition). The <TT
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CLASS="LITERAL"
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>o</TT
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>
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value gives the starting offset of the partition (in sectors) and the
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<TT
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CLASS="LITERAL"
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>p</TT
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> value gives the size of the partition (also in sectors).
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See <TT
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CLASS="LITERAL"
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>disktab(4)</TT
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> for more info. Note that DEC Unix likes to
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define overlapping partitions. For the entry above, the partition
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layout looks like this (you can verify this by adding up the various
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<TT
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CLASS="LITERAL"
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>o</TT
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> and <TT
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CLASS="LITERAL"
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>p</TT
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> values):
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<TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><PRE
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CLASS="SCREEN"
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> a b d e f
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|---|-------|-----------|-----------|-----------|
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c
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|-----------------------------------------------|
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g h
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|-----------------|-----------------|</PRE
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></TD
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></TR
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></TABLE
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> </P
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><P
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>DEC Unix insists that partition <TT
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CLASS="LITERAL"
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>a</TT
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> starts at offset 0 and that
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partition <TT
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CLASS="LITERAL"
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>c</TT
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> spans the entire disk. Other than that, you can
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setup the partition table any way you like.</P
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><P
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>Let's suppose you have DEC Unix using partition <TT
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CLASS="LITERAL"
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>g</TT
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> and want to
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install Linux on partition <TT
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CLASS="LITERAL"
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>h</TT
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> with partition <TT
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CLASS="LITERAL"
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>b</TT
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> being a
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(largish) swap partition. To get this layout without destroying the
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existing DEC Unix partition, you need to set the partition types
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explicitly. You can do this by adding a <TT
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CLASS="LITERAL"
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>t</TT
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> field for each
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partition. In our case, we add the following line to the above
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disktab entry.
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<TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><PRE
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CLASS="SCREEN"
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> :ta=unused:tb=swap:tg=4.2BSD:th=resrvd8:</PRE
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></TD
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></TR
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></TABLE
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> </P
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><P
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>Now why do we mark partition <TT
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CLASS="LITERAL"
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>h</TT
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> as "reservd8" instead of "ext2"?
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Well, DEC Unix doesn't know about Linux. It so happens that partition
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type "ext2" corresponds to a numeric value of 8, and DEC Unix uses the
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string "reservd8" for that value. Thus, in DEC Unix speak, "reservd8"
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means "ext2". OK, this was the hard part. Now we just need to
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install the updated disktab entry on the disk. Let's assume the disk
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has SCSI id 5. In this case, we'd do:
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<TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><PRE
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CLASS="SCREEN"
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># disklabel -rw /dev/rrz5c rz26</PRE
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></TD
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></TR
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></TABLE
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> </P
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><P
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>You can verify that everything is all right by reading back the
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disklabel with <TT
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CLASS="LITERAL"
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>disklabel -r /dev/rrz5c</TT
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>. At this point, you
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may want to reboot DEC Unix and make sure the existing DEC Unix
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partition is still alive and well. If that is the case, you can shut
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down the machine and start with the Linux installation. Be sure to
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skip the disk partitioning step during the install. Since we already
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installed a good partition table, you should be able to proceed and
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select the 8th partition as the Linux root partition and the 2nd
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partition as the swap partition. If the disk is, say, the second SCSI
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disk in the machine, then the device name for these partitions would
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be <TT
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CLASS="LITERAL"
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>/dev/sdb8</TT
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> and <TT
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CLASS="LITERAL"
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>/dev/sdb2</TT
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>, respectively (note that
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Linux uses letters to name the drives and numbers to name the
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partitions, which is exactly reversed from what DEC Unix does; the
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Linux scheme makes more sense, of course ;-).</P
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></DIV
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><DIV
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CLASS="SECT2"
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><H2
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CLASS="SECT2"
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><A
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NAME="AEN708"
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>6.2. Installing <TT
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CLASS="LITERAL"
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>aboot</TT
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></A
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></H2
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><P
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><I
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CLASS="EMPHASIS"
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>First big caveat</I
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>: with the SRM firmware, you can boot one and
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only one operating system per disk. For this reason, it is generally
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best to have at least two SCSI disks in a machine that you want to
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dual-boot between Linux and DEC Unix. Of course, you could also boot
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Linux from a floppy if speed doesn't matter or over the network, if
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you have a <TT
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CLASS="LITERAL"
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>bootp</TT
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>-capable server. But in this section we assume
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you want to boot Linux from a disk that contains one or more DEC Unix
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partitions.</P
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><P
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><I
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CLASS="EMPHASIS"
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>Second big caveat</I
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>: installing <TT
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CLASS="LITERAL"
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>aboot</TT
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> on a disk shared with
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DEC Unix renders the first and third partition unusable (since those
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<I
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CLASS="EMPHASIS"
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>must</I
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> have a starting offset of 0). For this reason, we recommend
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that you change the size of partition <TT
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CLASS="LITERAL"
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>a</TT
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> to something that is just
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big enough to hold <TT
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CLASS="LITERAL"
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>aboot</TT
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> (1MB should be plenty).</P
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><P
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>Once these two caveats are taken care of, installing <TT
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CLASS="LITERAL"
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>aboot</TT
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> is
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almost as easy as usual: since partition <TT
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CLASS="LITERAL"
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>a</TT
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> and <TT
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CLASS="LITERAL"
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>c</TT
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> will
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overlap with <TT
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CLASS="LITERAL"
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>aboot</TT
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>, we need to tell <TT
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CLASS="LITERAL"
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>swriteboot</TT
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> that this is
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indeed OK. We can do this under Linux with a command line of the
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following form (again, assuming we're trying to install <TT
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CLASS="LITERAL"
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>aboot</TT
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> on
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the second SCSI disk):
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<TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><PRE
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CLASS="SCREEN"
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># swriteboot -f1 -f3 /dev/sdb bootlx</PRE
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></TD
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></TR
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></TABLE
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> </P
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><P
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>The <TT
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CLASS="LITERAL"
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>-f1</TT
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> means that we want to force writing <TT
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CLASS="LITERAL"
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>bootlx</TT
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> even
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though it overlaps with partition 1. The corresponding applies for
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partition 3.</P
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><P
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>This is it. You should now be able to shutdown the system and boot
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Linux from the harddisk. In our example, the SRM command line to do
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this would be:
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<TABLE
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BORDER="0"
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BGCOLOR="#E0E0E0"
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WIDTH="100%"
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><TR
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><TD
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><PRE
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CLASS="SCREEN"
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>>>> boot dka5 -fi 8/vmlinux.gz -fl root=/dev/sdb8</PRE
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></TD
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></TR
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></TABLE
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> </P
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