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Top Forums Programming how to delete a file permanently from computer Post 302347332 by imagtek on Tuesday 25th of August 2009 11:45:23 AM
Old 08-25-2009
'deleting' a file

A file is not deleted until it has been overwritten on the disk (at least 3 times) with other data. Otherwise, the information still exists on the system, its space on the disk is simply flagged as available by the OS. Over time, the contents of the file are overwritten by other applications, but the time interval is unpredictable.

To ensure that information is destroyed and cannot be accessed via forensic methods, you simply rewind the file and fill it with garbage and close it. Then open, write garbage, close. It is necessary to ensure that the actual disk sectors that map to the file are written to, not simply the disk cache in memory.

Unless you are working for a security agency, financial institution or some such, simply deleting the file should be enough.

There are software packages out there that will wipe a disk clean, but if you are discarding a computer and you have sensitive information on a disk, removing the drive(s) and taking a sledgehammer to it also works.
 

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voldiskadd(8)						      System Manager's Manual						     voldiskadd(8)

NAME
voldiskadd - Adds one or more disks for use with the Logical Storage Manager SYNOPSIS
/usr/sbin/voldiskadd disk-address-list DESCRIPTION
The voldiskadd utility sets up new disks that are added to the system after the initial system installation and configures the disks for use by the Logical Storage Manager. A valid disk label must exist on the disk before using the voldiskadd utility. One or more disks may be specified using a disk-address-list. Disk addresses in the list have the form dskn (for the entire disk) or dsknp (for a specific partition). When specifying multiple disks, use a space between entries. Disk address names relate directly to device names in the /dev/disk directory. For example, here are some valid voldiskadd disk-address-list specifications: # voldiskadd dsk1 # voldiskadd dsk2 dsk3a The file, /etc/vol/disks.exclude, may be used to exclude disks from use by voldiskadd. Each line of the file specifies the name of a disk to exclude (for example, dsk5). The voldiskadd utility prompts the user for a disk group name and disk media name for the disks. If a new disk group name is specified, that disk group is created for the new disks. If no disk group name is specified, the disks are left as unassigned replacement disks for future use. If an existing disk group name is specified, the user is prompted for whether the disks should be designated as spares for the disk group. If a disk is found to already contain non-Logical Storage Manager partitioning, the user is asked whether the disk should be encapsulated. Encapsulation turns each partition of the disk into a volume. A disk should be encapsulated if it contains file systems or data that should not be overwritten. If encapsulation is not desired for a disk, the disk can be initialized as a new disk for use by the Logical Storage Manager. For new disks, all space on the disk becomes free space in the disk's disk group. Context-sensitive help is available at every prompt by typing ?. Also, a list option can be used to get information on available target disks for an operation. The voldiskadd utility supports the following general classes of actions: Initializing a disk with reserved regions and partitions. Disk initialization is performed by calling voldisksetup command. Adding a disk to an existing disk group. This operation can be performed independently of the initialization of the disk drive to add a disk's storage space to a disk group's free space pool. The volassist command may subsequently allocate from that free space. The disk can also be added as a hot spare device. Creating new disk groups in which to import new disks. If no disk group exists for importing disks, the option of creating the disk group is offered. Encapsulating disks that have exist- ing contents. This is the default action for disks that do not have a valid, existing Logical Storage Manager private region, but that do have a disk label. Encapsulation is performed by calling volencap. Reconnecting a drive that was temporarily inaccessible. This situation is detected automatically, by noting that the specified drive has a disk ID that matches a disk media record with no currently associated physical disk. After reconnection, any stale plexes referring the disk are reattached, and any stopped volumes referring the disk are restarted. This reattach action is performed by calling the volrecover script. ERRORS
You may receive the following messages when using the voldiskadd command: Initialization of disk device special-device failed. Error: special-device or an overlapping partition is open. This message indicates that the partition you specified or an overlapping partition on the disk is actively in use. The partition could be a mounted UFS or AdvFS filesystem, initialized as an LSM disk or used as a swap device. special-device is marked in use for fstype in the disklabel. If you continue with the operation you can possibly destroy existing data. Would you like to continue?? [y,n,q,?] (default: n) This message indicates that the fstype of a partition or an overlapping partition is set in the disk label. The voldiskadd command prints this message to warn that a disk partition may have valid data which could be destroyed. If you are sure that the disk partition does not have valid data and that the partition can be added to LSM, you can ignore the warning message by entering y at the prompt. The voldiskadd command will proceed to initialize the disk partition and add it to LSM. FILES
A list of disks to exclude from use by voldiskadd. SEE ALSO
disklabel(8), volassist(8), voldisk(8), voldiskadm(8), voldisksetup(8), voldg(8), volintro(8) voldiskadd(8)
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