Set the system to provide a command line upon choosing system request (option 3).
As a programmer, I'm often trying to track the course of another interactive program to see what files are used, which other programs are called, etc...Setting the attention program, (ie. system value QATNPGM), to QSYS/QUSCMDLN is an option but this is not always practical as some ERP system's override the attention program preventing the command line from appearing.
Now, by default, when OS/400 is installed (and any subsequent upgrades), there is no extended command line when choosing option 3 from the system request menu.
To allow for an extended command line when choosing  from the system request menu, all you need to do is to edit a message description.
1. WRKMSGD MSGID(CPX2313) MSGF(QCPFMSG)
You'll notice the description text 'ENDRQS DSPJOB DSPMSG SNDMSG
SIGNOFF DSPMSG DSCJOB DSPWSUSR ENDRDBRQS '
2. Change the DSPJOB to WRKJOB
The change takes immediate effect and is system-wide (we only have this activated on our development box). It works well for getting access to a command line whilst still in the WRKQRY program.
Incidentally, by changing the ENDRQS portion of the message description to blanks, you will disable the option 2 (ie. End previous request) for those of you who may have a need for that.