Updating glabel.8 man page

[freebsd_ny-central.org]

Summary

PR 276724 indicates that the current glabel man page does not describe the corner case of attempting to set a label on an already mounted partition.

• Added a paragraph indicating that glabel requires an exclusive lock on the partition
• Added that any file system first needs to be unmounted for the label to persist across reboot
• Added that if the affected device node is root, that single user mode with r/o mount will be required

[jrm]

lib/geom/label/glabel.8

178

179

There's trailing whitespace at the end of the line after file system.

180

[freebsd_ny-central.org]

Thanks for the reminder and for the feedback. I've fixed the trailing whitespace now.

[freebsd_ny-central.org]

Aaand I missed the other two changes. Now added those as well.