Old deprectated system(id) call returns: uid=10079(hbob) gid=506(psacln) groups=506(psacln)
Current UID exec'ing this script: 10079
UID's username: hbob
Current GID exec'ing this script: 506
[Excerpt from Wordpress permissions docs, here]
The above may not apply to shared hosting systems that use the "suexec" approach for running PHP binaries. This is a popular approach used by many web hosts. For these systems, the php process runs as the owner of the php files themselves, allowing for a simpler configuration and a more secure environment for the specific case of shared hosting.
Note: suexec methods should NEVER be used on a single-site server configuration, they are more secure only for the specific case of shared hosting.
In such an suexec configuration, the correct permissions scheme is simple to understand.
In this specific type setup, WordPress will detect that it can directly create files with the proper ownership, and so it will not ask for FTP credentials when upgrading or installing plugins.