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Full Discussion: HP-UX 10.20 devices
Operating Systems HP-UX HP-UX 10.20 devices Post 14652 by Kelam_Magnus on Monday 4th of February 2002 02:08:06 PM
Old 02-04-2002
/dev/zero vs /dev/null

Since yall brought this up, I have a question.

What is the difference between. These two commands

1) cat /dev/null > somefile

2) cat /dev/zero > somefile

3) > somefile



Zeroing out a file.

I know that "dd can be used to create a file of X bytes for testing and to "hold" space in a filesytem and for doing "disk dumps" an d for destroying data on a disk ( not the prescribed method).

I think I know another reason for /dev/zero. That would be to zero out a disk for reuse.

Any insight would be informative.

Smilie Smilie
 

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WREN(3) 						     Library Functions Manual							   WREN(3)

NAME
wren, ata - hard disk interface SYNOPSIS
bind #H[drive] /dev bind #w[target[.lun]] /dev /dev/hd0disk /dev/hd0partition /dev/sd0disk /dev/sd0partition ... DESCRIPTION
The hard disk interfaces (wren, #w, is a SCSI disk; ata, #H, is an IDE or ATA disk) serve a one-level directory giving access to the hard disk partitions. The parameter to attach defines the numerical SCSI target and logical unit number or the IDE drive number to access. Both default to zero. Each partition name is prefixed by hd and the numeric drive identifier. The partition always exists and covers the entire disk. The size of each partition as reported by stat(2) is the number of bytes in the partition, so the size of is the size of the entire disk. The partition also always exists; it is the last block on the disk for SCSI, second to last for IDE. If it contains valid partition data, those partitions will be visible as well. Every time the device is bound, the partitions are updated to reflect any changes in the parti- tion file. The format of the partition file is the string plan9 partitions on a line, followed by partition specifications, one per line, consisting of a name and textual strings for the block start and limit for each partition on the disk. The program prep(8) writes the partition table for the disk; its use is preferred to writing it by hand. SEE ALSO
prep(8), scsi(3) SOURCE
/sys/src/9/port/devwren.c /sys/src/9/pc/devata.c WREN(3)
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