chpt(8)

Name

chpt − change a disk partition table

Syntax

/etc/chpt [ −a ] [ −d ] [ −q ] [ −v ] [ [ −px offset size ] ... ] device

Description

The chpt command lets you alter the partition sizes of a disk pack. Using chpt, you can tailor your system disks and their partitions to suit your system’s individual needs.

If you want to create a file system on a partition that has been modified, you must use newfs(.).

The standard procedure to change a partition table is:

1.Look at the current partition table using the −q option.

2.If a file system does not exist on the a partition, create one using the newfs() command.

If a file system exists on the a partition but does not contain a partition table in its superblock, copy the partition table from the driver to the superblock using the chpt command with the −a option.

3.Change the partition offsets and sizes using the −px option. You can change all the partitions for one pack on one command line.

The device must be either the a or c partition of the raw device, depending upon where the file system resides. For example, if the file system resides in the a partition of an RM05 in drive 0, device is rhp0a.

A file system must exist on the a or c partition of the pack. If you do not have a file system there, create one using newfs(.).

Options

−aCopies the partition table in the device driver to the disk pack.

−dCopies the default partition table to the disk pack and to the current partition table in the driver. The default partition table is the table that was built with the disk driver.

−qRuns chpt without modifying the partition tables. This prints the partition table of the specified disk pack. It prints the default partition table in the driver if there is no partition table on the disk pack.

−vPrints verbose messages showing the progress of chpt.

−pxChanges the parameters of partition x on the disk pack to the specified offset and size. x is the partition you are modifying (a, b, c, d, e, f, g, or h). Offset is the new beginning sector, and size is the new total number of sectors of the partition being modified.

Examples

This example shows how to change the partition table on an RM05 disk pack in drive 1. The commands in this example change the the size of the h partition to include the g partition. Comments are in parenthesis to the right of commands.

% chpt -q /dev/rhp1a(view partition table)
/dev/rhp1a
No partition table found in superblock...
using default table from device driver.
Current partition table:
partition       bottom       top      size    overlap
    a                0     15883     15884    c
    b            16416     49855     33440    c
    c                0    500383    500384    a,b,d,e,f,g,h
    d           341696    357579     15884    c,g
    e           358112    414047     55936    c,g
    f           414048    500287     86240    c,g
    g           341696    500287    158592    c,d,e,f
    h            49856    341201    291346    c
%

Note

In all of the tables generated by chpt, bottom is the offset (starting sector), top is the ending sector, and size is the number of sectors in the partition. The overlap is the other sectors that are partially or entirely included in the partition.

% bc(basic calculator)
500287-49856(top of g minus bottom of h)
450431
450431+1(add 1 because it is zero−based)
450432(size of new h partition)
%

From the query, you can see that there is no partition table in the superblock of the a partition. If this is because there is no file system in the a partition, run the newfs command to create one.

For this example, assume that there is a file system in the a partition of the disk, but the file system does not contain a partition table in its superblock. Therefore, run chpt with the −a option to copy the partition table in the driver to the superblock of the a partition.

% chpt -a /dev/rhp1a(add table to a partition)
%

Now you have a partition table to change.

% chpt -v -ph 49856 450432 /dev/rhp1a(change h)
/dev/rhp1a
New partition table:
partition       bottom top     size    overlap
    a                0   15883   15884 c
    b            16416   49855   33440 c
    c                0 500383 500384 a,b,d,e,f,g,h
    d           341696 357579   15884 c,g,h
    e           358112 414047   55936 c,g,h
    f           414048 500287   86240 c,g,h
    g           341696 500287 158592 c,d,e,f,h
    h            49856 500287 450432 c,d,e,f,g
%

Caution

Changing partition tables indiscriminately can result in losing large amounts of data.

Check for file systems on all the partitions of the disk before using the −p option. If a file system exists whose partition may be destroyed, copy it to a backup medium. After you have changed the partitions, restore the backed up file system.

Restrictions

You must have superuser privileges to use chpt.

You can not shrink or change the offset of a partition with a file system mounted on it or with an open file descriptor on the entire partition.

You can not change the offset of the a partition.

Museum

Related Articles