Difference between /dev/urandom and /dev/./urandom?
Yong Huang <[email protected]>
| Newsgroups | gmane.linux.redhat.general |
|---|---|
| Message-ID | <[email protected]> |
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, it takes a long time (unless entropy has accumulated enough in the past, which doesn't happen often on this headless server; if that happened, try a few more times). $ 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. 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 I have one more "directory" layer ".". 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? (Those that need to refresh your memory on /dev/random and urandom, can read http://www.usn-it.de/index.php/2009/02/20/oracle-11g-jdbc-driver-hangs-blocked-by-devrandom-entropy-pool-empty/ ) -- redhat-list mailing list unsubscribe mailto:[email protected]?subject=unsubscribe https://www.redhat.com/mailman/listinfo/redhat-list