Java Programming

Here I have a question about log4j on unix.

In my application, I create a log file daily accrding to log4j RollingFileAppender.
sometimes this log file's user and group is same with user and group which executing this application.
However occasionally this log file's user and group is different from login user, this will cause the following exception.
I dont know why sometime its user and group are different.


log4j:ERROR setFile(null,true) call failed.
java.io.FileNotFoundException: /opt/nortel/logs/mjm/traces/20080822.log (Permission denied)
at java.io.FileOutputStream.openAppend(Native Method)
at java.io.FileOutputStream.<init>(FileOutputStream.java:177)
at java.io.FileOutputStream.<init>(FileOutputStream.java:102)
at org.apache.log4j.FileAppender.setFile(FileAppender.java:272)
at org.apache.log4j.RollingFileAppender.setFile(RollingFileAppender.java:156)
at org.apache.log4j.FileAppender.activateOptions(FileAppender.java:151)
at com.nortel.oam.mjm.logging.DatestampedRollingFileAppender.activateOptions(DatestampedRollingFileAppender.java:76)
at org.apache.log4j.config.PropertySetter.activate(PropertySetter.java:247)
at org.apache.log4j.xml.DOMConfigurator.parseAppender(DOMConfigurator.java:210)
at org.apache.log4j.xml.DOMConfigurator.findAppenderByName(DOMConfigurator.java:140)
at org.apache.log4j.xml.DOMConfigurator.findAppenderByReference(DOMConfigurator.java:153)
at org.apache.log4j.xml.DOMConfigurator.parseChildrenOfLoggerElement(DOMConfigurator.java:415)
at org.apache.log4j.xml.DOMConfigurator.parseRoot(DOMConfigurator.java:384)
at org.apache.log4j.xml.DOMConfigurator.parse(DOMConfigurator.java:783)
at org.apache.log4j.xml.DOMConfigurator.doConfigure(DOMConfigurator.java:666)
at org.apache.log4j.xml.DOMConfigurator.doConfigure(DOMConfigurator.java:616)
at org.apache.log4j.xml.DOMConfigurator.doConfigure(DOMConfigurator.java:584)
at com.nortel.oam.mjm.logging.osgi.impl.Log4jXMLWatchdog.doOnChange(Log4jDOMConfigurator.java:33)
at org.apache.log4j.helpers.FileWatchdog.checkAndConfigure(FileWatchdog.java:80)
at org.apache.log4j.helpers.FileWatchdog.<init>(FileWatchdog.java:49)
at com.nortel.oam.mjm.logging.osgi.impl.Log4jXMLWatchdog.<init>(Log4jDOMConfigurator.java:27)
at com.nortel.oam.mjm.logging.osgi.impl.Log4jDOMConfigurator.configureAndWatch(Log4jDOMConfigurator.java:17)
at com.nortel.oam.mjm.logging.osgi.impl.Log4jDOMConfigurator.configureAndWatch(Log4jDOMConfigurator.java:12)
at com.nortel.oam.mjm.logging.osgi.impl.Activator.start(Activator.java:34)
at org.knopflerfish.framework.BundleImpl.start0(BundleImpl.java:373)
at org.knopflerfish.framework.PermissionOps.callStart0(PermissionOps.java:198)
at org.knopflerfish.framework.BundleImpl.start(BundleImpl.java:320)
at org.knopflerfish.framework.Framework.startBundle(Framework.java:503)
at org.knopflerfish.framework.Main.handleArgs(Main.java:312)
at org.knopflerfish.framework.Main.main(Main.java:193)