Once upon a time, Tony Mountifield tony@softins.co.uk said:
That shouldn't matter. The running programs will have mapped the original glibc into memory, which will create a reference to the original inode, even though the directory entries pointing to it are gone. See the output of "lsof" for one of those processes, and you will see the libraries tagged as (deleted).
There can be problems when a running process tries to dlopen() a shared library file and gets a new version. For example, if a running process tries to do a host or user lookup (and hadn't used the method before), it could crash.
Also, just because a process is still running OK with the old library doesn't mean you want it to; there could be a security change in the update that means old processes are vulnerable.
You can use the "needs-restarting" program from the yum-utils package to see a list of processes that appear to need a restart due to library (or binary) changes. It isn't 100% accurate, but it is pretty close. There are some things that can't be restarted (like PID 1); then you should probably reboot.