Upgrade

mergerfs can be upgraded live by mounting on top of the previous instance. Simply install the new version of mergerfs and follow the instructions below.

Run mergerfs again or if using /etc/fstab (or systemd mount file) call for it to mount again. Existing open files and directories will continue to work fine though they won't see any differences that the new version would provide since it is still using the previous instance. If you plan on changing settings with the new mount you should / could apply those before mounting the new version.

$ sudo mount /mnt/mergerfs
$ mount | grep mergerfs
media on /mnt/mergerfs type mergerfs (rw,relatime,user_id=0,group_id=0,default_permissions,allow_other)
media on /mnt/mergerfs type mergerfs (rw,relatime,user_id=0,group_id=0,default_permissions,allow_other)

A problem with this approach is that the underlying instance will continue to run even if the software using it stop or are restarted. To work around this you can use a "lazy umount". Before mounting over top the mount point with the new instance of mergerfs issue: umount -l <mergerfs_mountpoint>. Or you can let mergerfs do it by setting the option lazy-umount-mountpoint=true.

If the intent is to change settings at runtime then the runtime interface should be used.