Specify a commit that is a "detached head"

You can sync a commit that is not at the head of any named branch.

1. Find an older tag:

p4 graph ref-hist -n //hth/mary

//hth/mary a0ace6d80a34d257e13da1a47d1fab1c1 tag refs/tags/tag77 create helen 2019/01/08 16:35:18

2. Sync to this tag:

p4 sync a0ace6d80a34d257e13da1a47d1fab1c1

3. Run p4 have

p4 have

//depot/projectA/submit_trigger.pl#1 - /opt/perforce/servers/17100/graph_ws/depot/projectA/submit_trigger.pl

//hth/mary graph_ws f9baf26 DETACHED HEAD

For details about the Git concept of "DETACHED HEAD", see https://git-scm.com/docs/git-checkout.