Would it be difficult to increase the limit or would it just be a one-place change?I have a system that could really elegantly make use of the Unix multiuser model for process isolation but I'd need much longer usernames than just 32 characters.Is the name length standardized (POSIX)?
Linux/Unix username length limit
users;useradd;multiuser
Don't try making the login name longer, you'll probably find loads of places it breaks.Note that you don't have a problem with the number of possible login names (you only get UID_MAX-UID_MIN uids anyway, which is  59,000 on my system).The problem is just with how descriptive they are, but fortunately there's another field intended to be descriptive: the GECOS/comment field. Just put the URL in there, and make the username either a 32-character hash of that, or simply the UID in base 10.Then, best case you can always hash the URL to get UID, and worst case you need a reverse lookup from URL to UID, which is pretty trivial for 59,000 items - even a grep of /etc/passwd would be sufficient.