AS/400 Library List

Most systems have a way to find objects when a specific path is not specified. The same is true of the AS/400 and it uses an object called the library list (*LIBL). This object doesn't exist on its own and is always associated with another object like a job or a job description (*JOBD). As of OS/400 V5R1 the user portion of the Library List can contain up to 250 library names. Prior to that it could only have 25 libraries. (This is something to keep in mind when selling software because on OS/400 V4R5 and below a job description with more than 25 libraries in its library list cannot be restored.)

A job's library list consists of four sections:

System portion: Always at the top and contains AS/400 system libraries like QSYS, QHLPSYS, QUSRSYS, etc. The system portion can hold up to 15 library names. The default contents of the system portion are specified in the QSYSLIBL system value. The contents of the system portion can be changed for the current job to differ from QSYSLIBL by using the CHGSYSLIBL command.
Product portion: When a CL command is executed that specifies a production library, that library will be added to the product portion of the library list for the duration of the command. It follows the system portion and the O/S will maintain up to two libraries in it.
Current library: Is a special library associated with a user profile and there can only be one in the list at a time. This library is useful for programmers to have their personal library at the top of the list regardless of what the user portion is changed to. It can be changed locally using the CHGCURLIB command. To change it for the user on all future jobs use the CHGUSRPRF command.
User portion: The last part of the library list that contains all of the application libraries. The list is normally assigned to the job from the job description but for batch jobs this can be overridden using the SBMJOB command's INLLIBL parameter. A job's library list can be changed locally with the EDTLIBL, CHGLIBL, ADDLIBLE, and RMVLIBLE command.

As was mentioned above the user portion of the library list for any job can be stored in a job description so that when a job starts up it will use the list specified there. Some job descriptions specify the special value *SYSVAL which means that the library list can be found in the system value QUSRLIBL. The AS/400 Operating System will allow the programmer to delete a library that is in a job description or either of the library list system values provided there are no jobs locking the library. However, all future jobs that use these now tainted lists will fail to start.

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