CHAPTER 4 The UNIX File System

4.3 Compatibility

SunOS 5.X and SunOS 4.1.X formatted disks are compatible. There are a few tags that can be added to the 5.X disks during formatting or labeling that are ignored if the disk is used on a 4.1.X system. Likewise, if a 4.1.X disk is used on a 5.X system these missing tags will be assigned the default values.

The expanded disk label includes:

volume name to identify the disk device, up to 8 characters
partition tags to identify partition usage; valid tags are:

unassigned
boot
root
swap
usr
backup
stand
var
home

partition flags that specify read/write access and whether the partition is mountable; valid flags are:

w read/write
r read only
m mountable
u unmountable

The default partition tag and flag values for a disk are:

0 root wm
1 swap wu
2 backup wm
3 unassigned wm
4 unassigned wm
5 unassigned wm
6 usr wm
7 unassigned wm

The format utility can be used to set volume names and retag the partitions. The prtvtoc command can be used to examine the disk label. You can also examine the disk labels with the verify subroutine of the format command:

# format> verify

format> verify

Primary label contents:

ascii name = <SUN0424 cyl 1151 alt 2 hd 9 sec 80>

pcyl = 2500

ncyl = 1151

acyl = 2

nhead = 9

nsect = 80

Part Tag Flag Cylinders Size Blocks

0 root wm 0 - 51 18.28MB (52/0/0)

1 swap wu 52 - 143 32.34MB (92/0/0)

2 backup wm 0 - 1150 404.65MB (1151/0/0)

3 unassigned wm 0 0 (0/0/0)

4 unassigned wm 0 0 (0/0/0)

5 - wm 144 - 627 170.16MB (484/0/0)

6 usr wm 628 - 1026 140.27MB (399/0/0)

7 home wm 1027 - 1150 43.59MB (124/0/0)

The fmthard command can be used to update the VTOC (Volume Table of Contents) of a hard disk. The disk needs to be first labeled by format.

Unix System Administration - 8 AUG 1996

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