mksysb Command

Commands Reference, Volume 3

mksysb Command

Purpose

Creates an installable image of the root volume group either in a file or onto a bootable tape.

Syntax

mksysb [ -b Number ] [ -e ] [ -p ] [ -v ] [ -X ] [ -i | -m ] Device | File

Description

The mksysb command creates a backup of the operating system (that is, the root volume group). You can use this backup to reinstall a system to its original state after it has been corrupted. If you create the backup on tape, the tape is bootable and includes the installation programs needed to install from the backup.

The file-system image is in backup-file format. The tape format includes a boot image, a bosinstall image, and an empty table of contents followed by the system backup (root volume group) image. The root volume group image is in backup-file format, starting with the data files and then any optional map files.

One of the data files mksysb uses is the /bosinst.data file. If a /bosinst.data file doesn't exist, /var/adm/ras/bosinst.data is copied to / (root). In AIX Version 4.3.3 and later versions, mksysb always updates the target_disk_data stanzas in bosinst.data to match the disks currently in the root volume group of the system where the mksysb command is running.

If you are using a customized /bosinst.data file and do not want the target_disk_data stanzas updated, you must create the file /save_bosinst.data_file. The mksysb command does not update /bosinst.data if the /save_bosinst.data_file exists.

Notes:
The image the mksysb command creates does not include data on raw devices or in user-defined paging spaces.

If you are using a system with a remote-mounted /usr file system, you cannot reinstall your system from a backup image.

The mksysb command may not restore all device configurations for special features, such as /dev/netbios and some device drivers not shipped with the product.

Some rspc systems do not support booting from tape. When you make a bootable mksysb image on an rspc system that does not support booting from tape, the mksysb command issues a warning indicating that the tape will not be bootable. You can install a mksysb image from a system that does not support booting from tape by booting from a CD and entering maintenance mode. In maintenance mode you will be able to install the system backup from tape.

To create a backup of the operating system to CD, please refer to the mkcd command.

Flags

-b Number	Specifies the number of 512-byte blocks to write in a single output operation. When the backup command writes to tape devices, the default is 100 for backups by name. The write size is the number of blocks multiplied by the block size. The default write size for the backup command writing to tape devices is 51200 (100 * 512) for backups by name. The write size must be an even multiple of the tape's physical block size.
-e	Excludes files listed in the /etc/exclude.rootvg file from being backed up. The rules for exclusion follow the pattern matching rules of the grep command. Note: If you want to exclude certain files from the backup, create the /etc/exclude.rootvg file, with an ASCII editor, and enter the patterns of file names that you do not want included in your system backup image. The patterns in this file are input to the pattern matching conventions of the grep command to determine which files will be excluded from the backup. If you want to exclude files listed in the /etc/exclude.rootvg file, select the Exclude Files field and press the Tab key once to change the default value to yes. For example, to exclude all the contents of the directory called scratch, edit the exclude file to read as follows: /scratch/ For example, to exclude the contents of the directory called /tmp, and avoid excluding any other directories that have /tmp in the pathname, edit the exclude file to read as follows: ^./tmp/ All files are backed up relative to . (current working directory). To exclude any file or directory for which it is important to have the search match the string at the beginning of the line, use ^ (caret character) as the first character in the search string, followed by . (dot character), followed by the filename or directory to be excluded. If the filename or directory being excluded is a substring of another filename or directory, use ^. (caret character followed by dot character) to indicate that the search should begin at the beginning of the line and/or use $ (dollar sign character) to indicate that the search should end at the end of the line.
-i	Calls the mkszfile command, which generates the /image.data file. The /image.data file contains information on volume groups, logical volumes, file systems, paging space, and physical volumes. This information is included in the backup for future use by the installation process. Note: Before running the mkszfile command, ensure that enough space is available in the /tmp file to store a boot image. This space is needed during both backup and installation. To determine the amount of space needed in the /tmp file, issue the following command: bosboot -q -a -d device If you use the -X flag with the mksysb command, you do not need to run the bosboot command to determine the amount of space needed in the /tmp file.
-m	Calls the mkszfile command, with the -m flag to generate map files.
-p	Disables software packing of the files as they are backed up. Some tape drives use their own packing or compression algorithms. This flag only applies to AIX Version 4.2 or later.
-v	Verbose mode. Lists files as they are backed up. This flag only applies to AIX Version 4.2 or later.
-X	Specifies to automatically expand the /tmp file system if necessary. The /tmp file system may need to be extended to make room for the boot image when creating a bootable backup to tape. This flag only applies to AIX Version 4.2 or later.

Parameters

Device | File

Specifies the name of the device or file.

Examples

To generate a system backup and create an /image.data file (generated by the mkszfile command) to a tape device named /dev/rmt0, enter:
```
mksysb -i /dev/rmt0
```
To generate a system backup and create an /image.data file with map files (generated by the mkszfile command) to a tape device named /dev/rmt1, enter:
```
mksysb -m /dev/rmt1
```
To generate a system backup with a new /image.data file, but exclude the files in directory /home/user1/tmp, create the file /etc/exclude.rootvg containing the line /home/user1/tmp/, and enter:
```
mksysb -i -e /dev/rmt1
```
This command will backup the /home/user1/tmp directory but not the files it contains.
To generate a system backup file named /mksysb_images/node1 and a new /image.data file for that image, enter:
```
mksysb -i /userimage/node1
```
Note: This file will not be bootable and can only be installed using Network Installation Management (NIM).

Files

/usr/bin/mksysb

Contains the mksysb command.

Related Information

The backup command, bosboot command, mkcd command, mkszfile command.

The /image.data file.

A procedure to verify the mksysb backup can be found in the article "To Verify a Backup Tape" in the AIX Installation Guide.

A procedure to install from a system backup can be found in the article "Installing BOS from a System Backup" in the AIX Installation Guide.