[求助] MongoDB 无法自启动

系统：Mac os x 10.9.2 / MongoDB 2.4.10
症状：MongoDB 无法自启动
****补充****
问题很怪异：
终端运行 mongod --config /opt/local/etc/mongodb/mongodb.conf 可正常启动
launchctl load /Library/LaunchDaemons/org.mongodb.mongod.plist 也没问题
launchctl list 也能看到 org.mongodb.mongod
而 launchctl start org.mongodb.mongod 却提示 launchctl start error: Bad file descriptor
重启电脑 mongodb 也不能自动启动。

下面是 plist 文件：
<?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>org.mongodb.mongod</string>
<key>ProgramArguments</key>
<array>
<string>/opt/local/bin/mongod</string>
<string>run</string>
<string>--config</string>
<string>/opt/local/etc/mongodb/mongodb.conf</string>
</array>
<key>RunAtLoad</key>
<true/>
<key>KeepAlive</key>
<true/>
<key>WorkingDirectory</key>
<string>/usr/local/mongodb</string>
<key>StandardErrorPath</key>
<string>/var/log/mongodb/output.log</string>
<key>StandardOutPath</key>
<string>/var/log/mongodb/output.log</string>
</dict>
</plist>