Created attachment 191499 [details]
svn diff for changed kernel files
We use longer usernames for FTP/SSH logins within our webhosting cluster and have manually been patching this to the kernel source tree for several years now. It has not caused any instability even under heavy concurrent connections.
The attached diffs double the size of ut_user (include/utmpx.h) and MAXLOGNAME (sys/sys/param.h)
The layout of struct utmpx is part of the libc ABI and the format of files stored on disk so this can't just be changed. The effort required to make this change properly would be substantial. At a minimum, libc compatibility shims would be required with new symbol versions and a mechanism to handle there change in the format of /var/run/utx.active, /var/log/utx.lastlogin, and /var/log/utx.log. See getutxent(3) for one set of effected interfaces. A number of syscalls use MAXLOGNAME and might need to be altered as well.