What does “w” do with urandom

randomw

> strace w 2>&1 | grep urandom
read(4, "/usr/bin/grep\0urandom\0", 2047) = 22
>

Why does "w" need urandom? How to avoid this?

UPDATE: 

> strace w 2>&1 | awk '/urandom/'
read(4, "awk\0/urandom/\0", 2047)       = 14
>

so it is the filtering that has something to do with urandom? 

> strace who 2>&1 | grep urandom
>

Then why isn't "who" affected?

Best Answer

As explained in other answers and comments the reason for what you observe is the way Bash handles pipes. In order to filter what you really want in similar situations you can try to enclose the first letter of the grep argument in [] like this:

$ strace w 2>&1 | grep random
read(4, "grep\0random\0", 2047)         = 12
$ strace w 2>&1 | grep '[r]andom'
$ strace w 2>&1 | grep '[c]lose'
close(3)                                = 0
close(3)                                = 0
close(3)                                = 0
close(3)                                = 0
close(3)                                = 0
close(3)                                = 0
(...)

EDIT:

As correctly noted by R. in the comment below in fact strace does not see the other side of the pipe. Similarly to ps aux | grep grep which also shows grep grep in its output w is is walking through /proc directory and finds grep process there.

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