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Difference between writing file from /dev/zero and truncate

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}

0

$ timeout 1 cat /dev/zero > file1



$ wc -c file1

270422016 file1



$ du file1

264084 file1

Questions :

(1) How do 270422016 null characters come out to be 264084 bytes (i.e 258M).

$ truncate -s 270422016 file2



$ wc -c file2

270422016 file2



$ du file2

0 file2

Questions :

(2) file2 has been created with same number of null characters as file1 has, but the size of file2 is zero, why?

(3) What did /dev/zero do that truncate didn't or vice versa?

disk-usage devices truncate

share|improve this question

asked 19 mins ago

GypsyCosmonautGypsyCosmonaut

90211435

add a comment | 

0

$ timeout 1 cat /dev/zero > file1



$ wc -c file1

270422016 file1



$ du file1

264084 file1

Questions :

(1) How do 270422016 null characters come out to be 264084 bytes (i.e 258M).

$ truncate -s 270422016 file2



$ wc -c file2

270422016 file2



$ du file2

0 file2

Questions :

(2) file2 has been created with same number of null characters as file1 has, but the size of file2 is zero, why?

(3) What did /dev/zero do that truncate didn't or vice versa?

disk-usage devices truncate

share|improve this question

asked 19 mins ago

GypsyCosmonautGypsyCosmonaut

90211435

add a comment | 

$ timeout 1 cat /dev/zero > file1



$ wc -c file1

270422016 file1



$ du file1

264084 file1

Questions :

(1) How do 270422016 null characters come out to be 264084 bytes (i.e 258M).

$ truncate -s 270422016 file2



$ wc -c file2

270422016 file2



$ du file2

0 file2

Questions :

(2) file2 has been created with same number of null characters as file1 has, but the size of file2 is zero, why?

(3) What did /dev/zero do that truncate didn't or vice versa?

disk-usage devices truncate

share|improve this question

asked 19 mins ago

GypsyCosmonautGypsyCosmonaut

90211435

$ timeout 1 cat /dev/zero > file1



$ wc -c file1

270422016 file1



$ du file1

264084 file1

$ truncate -s 270422016 file2



$ wc -c file2

270422016 file2



$ du file2

0 file2

share|improve this question

asked 19 mins ago

GypsyCosmonautGypsyCosmonaut

90211435

share|improve this question

asked 19 mins ago

GypsyCosmonautGypsyCosmonaut

90211435

asked 19 mins ago

GypsyCosmonautGypsyCosmonaut

90211435

asked 19 mins ago

GypsyCosmonautGypsyCosmonaut

90211435

1 Answer
1

active

oldest

votes

1

1. du does not show size in bytes, but 1024-byte-blocks. So the numbers are actually identical ( 264084 * 1024 = 270422016 )




2. truncate creates a sparse file provided the filesystem supports such things




3. /dev/zero actually produces infinite bytes which are then written to file, and writing zeroes consumes space like writing any other content. Another way of producing a similar file without writing zeroes would be using fallocate.

share|improve this answer

answered 10 mins ago

frostschutzfrostschutz

28.1k25892

add a comment | 

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1

1. du does not show size in bytes, but 1024-byte-blocks. So the numbers are actually identical ( 264084 * 1024 = 270422016 )




2. truncate creates a sparse file provided the filesystem supports such things




3. /dev/zero actually produces infinite bytes which are then written to file, and writing zeroes consumes space like writing any other content. Another way of producing a similar file without writing zeroes would be using fallocate.

share|improve this answer

answered 10 mins ago

frostschutzfrostschutz

28.1k25892

add a comment | 

1

1. du does not show size in bytes, but 1024-byte-blocks. So the numbers are actually identical ( 264084 * 1024 = 270422016 )




2. truncate creates a sparse file provided the filesystem supports such things




3. /dev/zero actually produces infinite bytes which are then written to file, and writing zeroes consumes space like writing any other content. Another way of producing a similar file without writing zeroes would be using fallocate.

share|improve this answer

answered 10 mins ago

frostschutzfrostschutz

28.1k25892

add a comment | 

1. du does not show size in bytes, but 1024-byte-blocks. So the numbers are actually identical ( 264084 * 1024 = 270422016 )




2. truncate creates a sparse file provided the filesystem supports such things




3. /dev/zero actually produces infinite bytes which are then written to file, and writing zeroes consumes space like writing any other content. Another way of producing a similar file without writing zeroes would be using fallocate.

share|improve this answer

answered 10 mins ago

frostschutzfrostschutz

28.1k25892

share|improve this answer

answered 10 mins ago

frostschutzfrostschutz

28.1k25892

answered 10 mins ago

frostschutzfrostschutz

28.1k25892

answered 10 mins ago

frostschutzfrostschutz

28.1k25892