OpenBSD doesn't have -ef flags for ps. Both linux and OpenBSD have -x flags which works just as greate here
Merge pull request #1529 from aquaplanet/fix-sshagent-openbsd

Fix ssh-agent plugin for OpenBSD, making it more portable
Fix bad ps syntax in ssh-agent plugin
Merge pull request #2220 from nishigori/fix-bad-ps-syntax

When using ssh-agent plugin, It output a warning message