Difference between /dev/urandom and /dev/./urandom (Was: swingbench connection issue)
- From: Yong Huang <yong321@xxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Wed, 14 Nov 2012 09:19:22 -0800 (PST)
> This seems to have solved it
> https://kr.forums.oracle.com/forums/thread.jspa?threadID=941911
>
> *rm /dev/random*
> *ln -s /dev/urandom /dev/random
>
>
> *strange that the problem arises with one database on the box but not
> another on the same box
I have another puzzle related to /dev/(u)random. I posted somewhere else
without an answer.
On RHEL 6, a very simple JDBC java program returns instantly if I pass
/dev/./urandom to -Djava.security.egd (entropy gathering device). But if I pass
/dev/urandom to it, or omit this option altogether (I assume it uses
/dev/random), it takes a long time (unless entropy happens to have accumulated
enough in the past, which doesn't happen often on this headless server).
$ time java -Djava.security.egd=file:/dev/./urandom -cp
.:/u01/app/oracle/product/11.2.0/db/jdbc/lib/ojdbc6.jar:/u01/app/oracle/product/11.2.0/db/jdk/jre/lib
TestClient <-- ojdbc5.jar behaves the same as ojdbc6
Got it. <-- this is just the output of TestClient
real 0m0.848s <-- always subsecond
user 0m1.064s
sys 0m0.083s
$ time java -Djava.security.egd=file:/dev/urandom -cp
.:/u01/app/oracle/product/11.2.0/db/jdbc/lib/ojdbc6.jar:/u01/app/oracle/product/11.2.0/db/jdk/jre/lib
TestClient
Got it.
real 0m7.999s <-- anywhere from a few to tens of seconds
user 0m1.041s
sys 0m0.100s
This is very reproducible. I can't think of any difference whether there's one
more "directory" layer "." between /dev/ and urandom. Literally, it just tells
the process to go to *the current* directory which is already /dev/, before it
goes on to read urandom. Any thought?
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