A subsystem is an operating environment in as400 systems that manages resource allocation, usage, and job handling. Multiple subsystems that function independently of one another may be present in the system. A subsystem description is an object that defines a subsystem’s run-time properties. Jobs operate within the subsystem. The subsystem description explains the amount, location, and resource allocation of each work that enters the subsystem.

The following sections will review subsystems used for server jobs, IBM-supplied subsystems, create subsystems, start subsystems, end subsystems, work with subsystems, and commands, and check if subsystems are active.

Subsystem for server jobs
The server jobs are configured to operate in separate subsystems based on their function. The server jobs use the following subsystems.

• QSYSWRK
• QUSRWRK
• QSERVER

QSYSWRK subsystem
This subsystem is responsible for running all daemon jobs.

QUSRWRK subsystem
Server jobs for the servers Network Print, Remote Command, Program Call, Central, Data Queue, Signon, and Database are executed in the QUSRWRK subsystem.

QSERVER subsystem
The file server and database server daemon jobs are executed in the QSERVER subsystem.

IBM subsystem
IBM provides the following subsystems, which are listed:

• QBASE
• QSERVER
• QSPL
• QSYSWRK
• QUSRWRK
• QCTL
• QUINTER
• QBATCH
• QCMN
• QBASE

One such controlling subsystem is the QBASE subsystem. Communication, Batch, and Interactive Jobs are supported. An autostart job starts the subsystems QSERVER, QSPL, and QUSRWRK.

QSERVER subsystem
A file server subsystem is called Qserver.

QSPL subsystem
Reader and writer jobs are supported by the QSPL subsystem, which is a spool subsystem.

QSYSWRK subsystem
A system work subsystem is called a QSYSWRK subsystem. It initiates automatically when the system boots up.

QUSRWRK subsystem
A user work subsystem is called QUSRWRK. It includes jobs that servers launch to carry out tasks for users.

QCTL subsystem
This subsystem is a control subsystem. It includes an autostart job that launches the QINTER, QBATCH, QCMN, QUSRWRK, QSERVER, and QSPL subsystems.

QUINTER subsystem
This subsystem facilitates interactive tasks.

QBATCH subsystem
This subsystem supports batch jobs.

QCMN subsystem
This subsystem supports the communication jobs to be executed within it, such as Client access and server jobs.

Create subsystem in as400
We must create the essential elements before creating a subsystem to carry out interactive and batch activities. After that, we can start or stop the subsystem. The following is a list of what has to be done first:

• Subsystem Description
• Job Queue
• Class Object
• Routing Entries

A few more actions after the subsystem is created:

• Start subsystem
• End subsystem

Create Subsystem Description
A system object, including general and storage pool definitions, is called a subsystem description. How the subsystem uses memory for work, where work can enter the subsystem, how much work it can manage, how much memory will be utilized for primary storage, and how storage pool properties determine the jobs run inside the subsystem.

The Subsystem Description can be created using the command CRTSBSD.
CRTSBSD SBSD(libraryName/SubsystemName)
POOLS((1 *BASE))
MAXJOBS(10)
TEXT('Test subsystem')
10 jobs can be active at a time in the subsystem and operate in pool 1 with primary storage memory as *BASE.

Create job Queue
Use the CRTJOBQ command to create a job queue.
CRTJOBQ JOBQ(LibraryName/JobQueueName) TEXT('Test Job Queue')

Add Job Queue Entry
After creating the JOBQ, use the command ADDJOBQE to attach it to the subsystem.
ADDJOBQE SBSD(LibraryName/SubsystemName) JOBQ(LibraryName/JobQueueName) MAXACT(5)
The MAXACT option indicates the most jobs that this JOBQ can process concurrently.

Create Class
Use the CRTCLS command to create a class.
CRTCLS CLS(LibraryName/ClassName) RUNPTY(40)

The class defines run time attributes like Run priority, Time slice, Default wait time, Maximum temporary storage, etc.

Add Routing Entry
The ADDRTGE command can add a routing entry to the subsystem description. To utilize routing entry 50, the character string TEST must begin at position 1 in the routing data. Through this item, any number of routing stages can be enabled at once. The programs will operate in storage pool 1 by utilizing the library class.
ADDRTGE SBSD(LibraryName/SubsystemName) SEQNBR(50) CMPVAL(TEST)
PGM(LibraryName/ProgramName) CLS(LibraryName/ClassName)

Once the subsystem is created successfully, please follow the steps below.

Start subsystem
Start the subsystem by using the command STRSBS. The subsystem can be used to submit jobs once they have been started.
STRSBS SBSD(LibraryName/SubsystemName)

End subsystem
The ENDSBS command terminates the subsystem.
ENDSBS SBSD(SubsystemName)
Work with subsystem
Use the command WRKSBS on the command line to work with the subsystem.
Some important subsystem commands

• Start subsystem command: Use the STRSBS command to initiate a subsystem.
• End subsystem command: Use the ENDSBS command to terminate a subsystem.
• Delete subsystem description command: Use the DLTSBSD command to eliminate a subsystem description. The subsystem must not be in an active state to use the DLTSBSD command.
• Change subsystem description command: Use the CHGSBSD command to change the subsystem description.
• Display subsystem description command: Use the DSPSBSD command to view the subsystem description.
• Start subsystem using BRMS: Use the STRSBSBRM command to start a subsystem with BRMS.
• Work with subsystem: Use the WRKSBS command to interact with subsystems.
• Work with subsystem description: Use the WRKSBSD command to interact with subsystem descriptions.
• Work with subsystem jobs: Use the WRKSBSJOB command to work with subsystem jobs.