Since Linux don't have 'coreadm', we use the procedure used on Linux instead.
+ This means using the /proc filesystem and ulimit.
* In setup_snap_env(), support 'newfs' on Linux (really mke2fs) which behave a little different
* In cleanup_env(), look for any mounted zvols - !!!NEEDS BSD VERIFICATION!!!
The Linux equivalence of 'mount -F zfs' is 'mount -t zfs'.
+ The 'dev' ('devices') option never show up in a mount list
  Test this by trying to create a 'zero' device.
unshare doesn't exist on Linux, instead exportfs is used. But it have
quite different usage. And can't run as normal user...