A couple things could be going wrong here.
1) you need to properly set permissions on your launchdaemon files.
Apple's TN2083 (Technote) states:
When you install your daemon, make sure that you set the file system permissions correctly. Apple recommends that daemons be owned by root, have an owning group of wheel, and use permissions 755 (rwxr-xr-x) for executables and directories, and 644 (rw-r--r--) for files.
2) have you tried loading your daemon via "launchctl
" yet?
try this:
launchctl load /Library/LaunchDaemons/com.user.purge.plist
launchctl start /Library/LaunchDaemons/com.user.purge.plist
launchctl list
and see if it appears there