Running # su - oliver --command bash gives a shell but also prints the warning bash: no job control in this shell, and indeed Ctrl+Z and fg/bg don't work in that shell.

Running # su - oliver --session-command bash gives a shell without printing the warning, and job control indeed works.

The suggestion to use --session-command comes from Starting a shell from scripts using su results in "no job control in this shell" which states "[a security fix for su] changed the behavior of the -c option and disables job control inside the called shell".

But I still don't quite understand this. When should one use --command and when should one use --session-command? Is --command (aka -c) more secure? Or should one always use --session-command, and --command is just left in for backwards compatibility?

FWIW, I'm using RHEL 6.4.