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Full Discussion: How to output 1s endlessly like /dev/zero?
Top Forums UNIX for Advanced & Expert Users How to output 1s endlessly like /dev/zero? Post 302398916 by LessNux on Friday 26th of February 2010 12:05:21 AM
Old 02-26-2010
Question How to output 1s endlessly like /dev/zero?
/dev/zero can output 0's (null characters) endlessly. I am looking for a technique to output 1's (0xFF or 0b11111111) endlessly in a similar manner as /dev/zero.

The following dd statement writes 4 terabytes of 0's to the drive /dev/sdb. This dd statement does not cause any memory shortage.

Code:
dd bs=4K count=1G if=/dev/zero of=/dev/sdb

On the other hand, I would like to write 1's almost endlessly. The following perl statement attempts to write 4 terabytes of 1's. However, its huge buffer at the redirection causes the "Out of memory" error, and hence the perl statement fails.

Code:
perl -e 'print "\xFF\xFF\xFF\xFF"x1024x1024x1024x1024' > /dev/sdb

Is there any technique to output 1's (0xFF or 0b11111111) endlessly in a similar manner as /dev/zero? I wonder if this goal can be achieved by using /dev/loop or something.

Thanks a lot in advance.


----------

Mac OS X note: The dd command on Mac OS X has slightly different syntax from that on Linux. The dd command on Mac OS X may expect lowercase letters for k, m and g. If the above dd statement does not work on Mac OS X, try the following.

dd bs=4k count=1g if=/dev/zero of=/dev/disk1
Last edited by zxmaus; 02-27-2010 at 02:36 AM.. Reason: added code tags
 

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LEARN ABOUT LINUX

mkdevmaps

mkdevmaps(1M)                                             System Administration Commands                                             mkdevmaps(1M)

NAME

       mkdevmaps - make device_maps entries

SYNOPSIS

       /usr/sbin/mkdevmaps

DESCRIPTION

       The  mkdevmaps  command  writes  to standard out a set of device_maps(4) entries describing the system's frame buffer, audio, and removable
       media devices.

       The mkdevmaps command is used by the init.d(4) scripts to create or update the /etc/security/device_maps file.

       Entries are generated based on the device special files found in /dev. For the different  categories  of  devices,  the  mkdevmaps  command
       checks for the following files under /dev:

       audio           /dev/audio, /dev/audioctl, /dev/sound/...
       tape            /dev/rst*, /dev/nrst*, /dev/rmt/...
       floppy          /dev/diskette, /dev/fd*, /dev/rdiskette, /dev/rfd*
       removable disk  /dev/dsk/c0t?d0s?, /dev/rdsk/c0t?d0s?
       frame buffer    /dev/fb

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE         |      ATTRIBUTE VALUE        |
       +-----------------------------+-----------------------------+
       |Availability                 |SUNWcsu                      |
       +-----------------------------+-----------------------------+
       |Interface Stability          |Obsolete                     |
       +-----------------------------+-----------------------------+

SEE ALSO

       allocate(1), bsmconv(1M), attributes(5)

NOTES

       mkdevmaps might not be supported in a future release of the Solaris operating system.

SunOS 5.10                                                          8 Oct 2003                                                       mkdevmaps(1M)
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