When reading about openslug and unslung the name busybox turns up repeatedly. It's important to know what busybox is (and isn't) if you are going to do anything more sophisticated than install a few packages and leave it at that.
In plain English:
Multi-call binary means its a single program combining the functions of a large number of utilities. When you first install openslug it will have links for each function so you can use the functions as you would normally but it is important to realise that you are getting a cut-down or "light" version of the function.
For example lets consider the gzip compression tool:
As you can see, the full version of gzip supports far more options than the busybox gzip, however the busybox version will be sufficient for most simple tasks. You are most likely to see problems when trying to run scripts intended for a full Linux install, in which case you have three options:
Although I've done it on occasions I don't recommend option 3. Don't try 4 unless you're certain the two programs launch and reload the same way. Usually 1 is the quickest safe option. Finding alternative scripts is tricky as many scripts available on the net are intended for PC-based servers and they can be huge and very complex.An example of a command with missing options is "start-stop-daemon". Scripts often use the -o/--oknodo option when stopping a process to instruct it not to return an error if the process is already ended or the -R/--retry option to indicate that it should keep on trying to end processes for a time. The busybox version does not support these options.