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Full Discussion: cat /dev/null
Top Forums UNIX for Dummies Questions & Answers cat /dev/null Post 302177152 by freakydancer on Thursday 20th of March 2008 07:41:08 AM
Old 03-20-2008
cat /dev/null

Hi,

Excuse my ignorance here - I'm a networks man and my knowledge of all things unix is somewhat limited.

We have a very large file (/var/tmp/mond.log) that we need to zero - does the "cat /dev/null > /var/tmp/mond.log" command achieve this?
 

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

NAME
xfs_estimate - estimate the space that an XFS filesystem will take SYNOPSIS
xfs_estimate [ -h ] [ -b blocksize ] [ -i logsize ] [ -e logsize ] [ -v ] directory ... xfs_estimate -V DESCRIPTION
For each directory argument, xfs_estimate estimates the space that directory would take if it were copied to an XFS filesystem. xfs_esti- mate does not cross mount points. The following definitions are used: KB = *1024 MB = *1024*1024 GB = *1024*1024*1024 The xfs_estimate options are: -b blocksize Use blocksize instead of the default blocksize of 4096 bytes. The modifier k can be used after the number to indicate multiplica- tion by 1024. For example, xfs_estimate -b 64k / requests an estimate of the space required by the directory / on an XFS filesystem using a blocksize of 64K (65536) bytes. -v Display more information, formatted. -h Display usage message. -i, -e logsize Use logsize instead of the default log size of 1000 blocks. -i refers to an internal log, while -e refers to an external log. The modifiers k or m can be used after the number to indicate multiplication by 1024 or 1048576, respectively. For example, xfs_estimate -i 1m / requests an estimate of the space required by the directory / on an XFS filesystem using an internal log of 1 megabyte. -V Print the version number and exits. EXAMPLES
% xfs_estimate -e 10m /var/tmp /var/tmp will take about 4.2 megabytes with the external log using 2560 blocks or about 10.0 megabytes % xfs_estimate -v -e 10m /var/tmp directory bsize blocks megabytes logsize /var/tmp 4096 792 4.0MB 10485760 % xfs_estimate -v /var/tmp directory bsize blocks megabytes logsize /var/tmp 4096 3352 14.0MB 10485760 % xfs_estimate /var/tmp /var/tmp will take about 14.0 megabytes xfs_estimate(8)
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