What is /dev/null /dev/zero

crahuldba@gmail.com · 10-22-2010, 02:53 AM

Hello Friends
Can any one explain thi use of /dev/null and /dev/zero and what is the deference in them.
please answer
i face this question in interview
Thanks & Regards
Rahul

druuna · 10-22-2010, 02:58 AM

Hi,

A quick internet search would have given you the answer:

- /dev/zero
- /dev/null

In short: /dev/null is a "black hole" all put in is gone. /dev/zero generates zero's.

Hope this helps.

aries_baluyot · 10-22-2010, 03:33 AM

Quote:

Originally Posted by crahuldba@gmail.com

Hello Friends
Can any one explain thi use of /dev/null and /dev/zero and what is the deference in them.
please answer
i face this question in interview
Thanks & Regards
Rahul

http://digg.com/news/technology/dev_...The_Difference

aus9 · 10-22-2010, 04:09 AM

hi

can I suggest you ask the mods if you can change your username from x at gmail dot com to something else so you get less spam

Yes I know gmail as a spam filter.

regards

ionrivera · 10-22-2010, 04:13 AM

Real world example:

/dev/null:

If I want to discard all data written to largelogfile.log to free-up some space:

Code:

cat /dev/null > /var/log/largelogfile.log

If my script produces error, and wants to hide error message from stderr.

Code:

./myscript 2> /dev/null

If I want to redirect output to multiple files and want to hide stdout to screen:

Code:

echo YES|tee file1 file2 file3> /dev/null

/dev/zero:

If I want to add 100MB more swap memory:

Code:

dd if=/dev/zero of=/extra-swap bs=10000 count=10000 
#this will create 100MB storage file

mkswap /extra-swap 
#generate swap signature

swapon /extra-swap 
#this will enable /swap-extra file as a new extra swap memory

If I want to completely destroy my MBR:

Code:

dd if=/dev/zero of=/dev/sda bs=512 count=1