I've read about what charachers should usernames use, in linux, here: https://serverfault.com/a/578264/330936 but I would like to know if is there any problem if I will use the at sign "@" in my usernames. I will use it especially for my ftp accounts (I have a simple webserver with CentOS 7).
I don't want to be portable to other older versions of linux, nor other distros (maybe debian).
Is there any problem in using
@ in usernames?