Author Archives: mike

JMX and firewalls… or how to hate RMI slightly less

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So at least with Java 1.6 the JVM can use SOCKS for proxying RMI requests, so to get the wonderful jvisualvm (think 1.5 visualGC) working use the following incantations.

This requires the initial RMI registry port is open to the client.

First the initial SSH to server enabling the SOCKS tunnel

$ ssh -D localhost:9696 servername

And now for jvisualvm
jvisualvm -J-Dnetbeans.system_socks_proxy=localhost:9696 -J-Djava.net.useSystemProxies=true

props to http://stackoverflow.com/questions/1609961/visualvm-over-ssh for the hints

java log files

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So debugging java can be a mighty pain, a little few lines of ways to make it simpler.


# grep -m 1 -n '^2010-06-30 14:20:' catalina.out
11746233:2010-06-30 14:20:01,011 DEBUG com.beginning.of.line
# grep -m 1 -n '^2010-06-30 14:21:' catalina.out
11747788:2010-06-30 14:21:00,161 WARN org.apache.commons.httpclient.HttpMethodBase - Going to buffer response body of large or unknown size. Using getResponseBodyAsStream instead is recommended
# sed -n '11746233,11747788p' < catalina.out

This gives start line and end line between any two greps and then the body of the log file from those two lines.

disabling atime updates on macos X

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Create the following plist file somewhere useful, e.g. /Library/LaunchDaemons/com.local.noatime.plist

<?xml version=”1.0″ encoding=”UTF-8″?>
<!DOCTYPE plist PUBLIC “-//Apple//DTD PLIST 1.0//EN” “http://www.apple.com/DTDs/PropertyList-1.0.dtd”>
<plist version=”1.0″>
<dict>
<key>Label</key>
<string>com.my.noatime</string>

<key>ProgramArguments</key>
<array>
<string>mount</string>
<string>-vuwo</string>
<string>noatime</string>
<string>/</string>
</array>
<key>RunAtLoad</key>
<true/>
</dict>
</plist>

Then run the following to pick up the change, or indeed, reboot:


% sudo launchctl load /Library/LaunchDaemons/com.local.noatime.plist

And you should now see the root file system mounted with noatime option, which should improve longevity of SSD boot drives

# mount
/dev/disk0s2 on / (hfs, local, journaled, noatime)

Snow Leopard and the jvm

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So in a startling case of “Apple knows best” they have gone and removed the 1.5 JVM – I know it’s pretty old and people were complaining about not having a 1.6 JVM for a long time – but really!

So the following post steps you through re-enabling the 1.5 VM and now semi-happy days

SNMP over SSH tunnels

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Sometimes you just need to tunnel UDP based protocols – such as SNMP – and the easiest ways is to use socat


socat tcp4-listen:6667,reuseaddr,fork UDP:DESTINATION:161
socat udp4-listen:161,reuseaddr,fork tcp:localhost:6667

And in combination with your normal SSH tunnel


ssh -L6667:localhost:6667 BASTION_HOST