Chapter 3 How to Set Up File Systems On the Target

This chapter explains how to set up file systems on devices physically attached to the target system, such as Flash memory, IDE disks, RAM disks and SCSI disks. If your target is an NFS client only (all its files are physically located on another system such as the host), you can skip this chapter.

Before you can perform the procedures in this chapter, you must first configure the system image. See Chapter 2, How to Configure the System Image for details.

You must also boot the new system image on the target, and mount the root file system where many of the useful actors reside. This usually involves mounting a file system located on the host workstation where you built the system image. See "Mounting an NFS File System" for details.

Setting up file systems on the target involves:

1. Preparing the media on which you will use file systems.

   If the media used is flash memory, you must first format(1M) the flash device.

   You must label the media using the disklabel(1M) utility, which writes partition information onto the media based on entries in the disktab(4CC) file.

2. Creating file systems on the media.

   The newfs_dos(1M) utility lets you create an MS-DOS file system.

   The newfs(1M) utility lets you create a UFS file system.

3. Checking file system integrity.

   The fsck_dos(1M) utility lets you check an MS-DOS file system.

   The fsck(1M) utility lets you check a UFS file system.

3.1 How to Format a Flash Memory Device

You must format Flash memory before you can label it. If your target does not have Flash memory, you can skip this section.

The following procedure initializes the Flash memory device, erasing all existing data. Be sure to back up existing data on the device before proceeding.

Formatting a Flash Memory Device

1. Make sure that you have configured your system image with the FLASH feature set to true:

   host% cd build_dir host% configurator -list features | grep FLASH FLASH bool 'true'

2. Reboot the target system with a system image that supports Flash memory and includes the special files needed to access it.

3. Format the Flash memory using the format(1M) command:

   host% rsh target arun /bin/format /dev/rflash0a

3.2 How to Label a Disk

This section describes how to label a disk using information in /etc/disktab and the disklabel utility.

Labelling consists of writing specific information, such as disk geometry in terms of cylinders, heads, sectors per track and partition overlays, at particular locations on the disk. Disk drivers use labelling information to access different areas of the disk, called partitions.

3.2.1 How to Set Up Information About Disk Geometry

Information about disk geometry is found in /etc/disktab, which disklabel reads before writing a label to a drive. ChorusOS 4.0 provides a sample /etc/disktab that contains several useful examples. The following key to the abbreviations used in /etc/disktab is included at the top of the file:

#
# Disk geometry and partition layout tables. 
# Key:
#
#   dt      controller type
#   ty      type of disk (fixed, removeable, simulated)
#   d[0-4]  drive-type-dependent parameters
#   ns      #sectors/track
#   nt      #tracks/cylinder
#   nc      #cylinders/disk
#   sc      #sectors/cylinder, ns*nt default
#   su      #sectors/unit, sc*nc default
#   se      sector size, DEV_BSIZE default
#   rm      rpm, 3600 default
#   sf      supports bad144-style bad sector forwarding
#   sk      sector skew per track, default 0
#   cs      sector skew per cylinder, default 0
#   hs      headswitch time, default 0
#   ts      one-cylinder seek time, default 0
#   il      sector interleave (n:1), 1 default
#   bs      boot block size, default BBSIZE
#   sb      superblock size, default SBSIZE
#   o[a-h]  partition offsets in sectors
#   p[a-h]  partition sizes in sectors
#   b[a-h]  partition block sizes in bytes
#   f[a-h]  partition fragment sizes in bytes
#   t[a-h]  partition types (file system, swap, etc)
#
# All partition sizes reserve space for bad sector tables.
# 5 cylinders are needed for maintenance including
# replacement sectors.
#
...

Entries in /etc/disktab consist of fields separated by colons (":") and follow the form:

label:option[=value|#value]...

Where label is a string identifier up to eight characters long with no whitespace, option is an option from the list of abbreviations above, and value is the value assigned to an option.

For detailed examples, see the root/etc/disktab file generated using make root in the build_dir directory where you build system images. Note that build_dir/root is normally the directory exported for use as the target root directory. See "Mounting an NFS File System" for details.

If you are unable to complete the disk geometry fields, boot the ChorusOS system image on the target system, and read the output concerning the disk driver displayed on the system console at boot time.

3.2.2 How to Use disklabel

Once you have correctly specified disk information in /etc/disktab, you are ready to use disklabel.

Labelling a Disk

The following procedure initializes the local disk, erasing all existing data. Be sure to back up existing data before proceeding.

1. Boot the target system with a system image that supports the hardware you want to label and that includes the special files needed to access that hardware.

2. Update the disk label on the device, using disklabel as follows:

   host% rsh target arun /bin/disklabel -w -r device label name

   where device is an abbreviated form of the device name such as sd0, label is the label found in /etc/disktab and name is an optional string identifier up to sixteen characters long with no whitespace.

3. Check that the disk label is correctly updated, using disklabel as follows:

   host% rsh target arun /bin/disklabel -r device

   where device is an abbreviated form of the device name such as sd0.

3.3 How to Create a File System

This section explains how to create a file system on a disk. If you plan to use the disk partitions in raw mode and do not need a file system, you can skip the rest of this chapter.

Once the disk has been labelled, you can write a UFS or MS-DOS file system structure to any partition you have defined for the disk, except partition c.

Creating a UFS File System

Create the file system using the newfs command as follows:

host% rsh target arun /bin/newfs raw_device

where raw_device is a raw mode special file indicating a partition such as /dev/rsd0a.

Creating an MS-DOS File System

Create the file system using the newfs_dos command as follows:

host% rsh target arun /bin/newfs_dos raw_device

where raw_device is a raw mode special file indicating a partition such as /dev/rhd0a.

Example 3-1 Creating a File System on a RAM Disk

You can pass extra parameters to newfs or newfs_dos when creating a file system on a RAM disk in order to maximize available space. The following command could be used to maximize space available on a 1 MB RAM disk:

host% rsh target arun /bin/newfs -o space -c 128 -m 0 /dev/rrd0a

See "5.2 How to Activate a Swap Partition" for details on activating a swap partition.

3.4 How to Check File System Integrity

This section explains how to check existing file systems for errors.

Before mounting a local file system with read-write access or as the root file system, and after any system crash, it is strongly recommended that you check the file systems you plan to mount.

Checking a UFS File System

Check the file system using the fsck command as follows:

host% rsh target arun /bin/fsck raw_device

where raw_device is a raw mode special file indicating a partition such as /dev/rsd0a.

Checking an MS-DOS File System

Create the file system using the fsck_dos command as follows:

host% rsh target arun /bin/fsck_dos raw_device

where raw_device is a raw mode special file indicating a partition such as /dev/rhd0a.

If no errors are found, both fsck and fsck_dos display information on the file system in use. In case of errors, both fsck and fsck_dos attempt a recovery procedure, optionally requiring confirmation. If you want to run either command in non-interactive mode, use the -y option.