unix command

[Tony Willis_1]

how to create a file for certain size, example 100mb file from unix prompt

[harry d brown jr]

how about a file full of zeroes?

dd if=/dev/zero of=/somefilepath bs=1k count=100000

live free or die
harry

[harry d brown jr]

/dev/zero, if it doesn't exist on your system looks like this:

# ls -l /dev/zero
crw-rw-rw- 1 bin sys 3 0x000004 Aug 13 2001 /dev/zero
#


mknod /dev/zero c 3 4


live free or die
harry

[H.Merijn Brand (procura]

d3:/tmp 115 > rm xx
d3:/tmp 116 > ls -l xx
ls: xx: No such file or directory
d3:/tmp 117 > perl -e 'open XX,">xx";truncate XX,100*1024*1024'
d3:/tmp 118 > ls -l xx
-rw-rw-rw- 1 merijn softwr 104857600 Aug 21 21:16 xx
d3:/tmp 119 >

[keith persons · Accepted solution]

you can also use the prealloc(1) command to preallocate space on a disk. One caveat tho is the file will revert to actual disk space used if it isn't fully populated on the first open. i.e. prealloc filename 1000 then edit file and place only 50 bytes in file - on close it will no longer be size 1000 but 50.

hope this is clear, let me know if you're confused at all.

[Tom Danzig]

prealloc filename 100000

[Tony Willis_1]

thanks for all the answers. prealloc command is the easiest solution in our situation