In this post a sample of how to perform a code page conversion of z/OS Unix files in a batch job. The different iconv utility lines show invocation for different code pages.
//* //STEP1 EXEC PGM=BPXBATCH //STDERR DD SYSOUT=* //STDPARM DD * SH iconv -f UTF-8 -t IBM-1140 < inutf8 > outebc /* // SH iconv -f IBM-1140 -t IBM-1252 < inebc > out1252 // SH iconv -f IBM-1252 -t IBM-1140 < in1252 > out1140 // SH iconv -f IBM-1140 -t UTF-8 < inebc > oututf8 //
As mentioned in the previous post, another sample. This one copies a z/OS unix file to an MVS dataset. Also using OCOPY.
//STEP5 EXEC PGM=IKJEFT01 //INUNIX DD PATH='/mydir/infile.txt',PATHOPTS=(ORDONLY) //OUTMVS DD DSN='TEST.MVS.OUTDS',DISP=SHR //* //SYSTSPRT DD SYSOUT=* //SYSTSIN DD * //SYSTSIN DD * OCOPY IND(INUNIX) OUTDD(OUTMVS) TEXT CONVERT(YES) PATHOPTS(USE) /*
Recently I had to get some people started with a few utilities. I thought to share this here. They will be in the next few posts for searchability reasons.
There are more ways to Rome, as we say here, so please feel free share you variants in a comment. (I unfortunately need manually curate comments to filter out the spam which is even with this small site overwhelming.)
//STEP1 EXEC PGM=IKJEFT01 //INMVS DD DSN=TEST.TRADMVS.DATA, // DISP=SHR //OUTFILE DD FILEDATA=TEXT, // PATHOPTS=(OWRONLY,OCREAT,OTRUNC), // PATHMODE=SIRWXU, // PATH='/mydir/myunixfile.txt’ //SYSTSPRT DD SYSOUT=* //SYSPRINT DD SYSOUT=*//SYSTSIN DD * OCOPY IND(INMVS) OUTDD(OUTFILE) //*
Here’s a link to the IBM documentation on OCOPY.
You probably know that you can use Rexx programs in z/OS Unix.
What you may not know is that you can also run a TSO or MVS Rexx program from the z/OS Unix environment.
There is a unix command called tso for this. It works as simple as this:
tso –t “exec ‘YOUR.MVS.REXXPDS(TESTREXX)’ EXEC”
will execute your TESTREXX program.
You may want or need to allocate TSO datasets or other datasets in order to execute the Rexx.
You can simply allocate these through the export command.
export ddname=YOUR.MVS.DATASET
You can add these exports to you shell script, or add them to your .profile.
In the previous DBAOTM post I have introduced you to the z/OS operating system, the flagship operating system for the mainframe. In this post I will introduce you into the Unix side that z/OS has been equipped with over the past two decades.
Since the 1990s IBM has added Unix functionality to z/OS. The first extension was z/OS Unix System Services – z/OS Unix in short – and recently we IBM have added z/OS Container Extensions.
The Unix part of z/OS is a runtime environment that is an integral part of the z/OS operating system. z/OS Unix is fully Unix (Posix) compliant. z/OS Unix provides an interactive command interface that is called a shell in Unix terminology.
IBM has developed this part in the 1990s to make it easier to port applications from other platforms to z/OS. Many off-the-self and open source middleware and application packages that are available on z/OS make use of z/OS Unix. Examples are IBM’s own WebSphere Application Server and IBM Integration Bus, the banking product BASE24-eps from ACI, and open source tools like PHP and Git.
z/OS Unix has regular files the same as other Unix systems. In the z/OS Unix shell you can use normal Unix commands like ls, cd, more and many more of the standard Unix commands. You can set up a telnet or SSH session with z/OS Unix and do many more things you can also do with other Unix environments.
A very recent development on z/OS (it came with z/OS 2.4, end 2019) is the possibility to run Linux Docker Containers on z/OS.
Docker containers are a hardware independent and lightweight manner to run many applications in a virtualized configuration. The Docker technology has been available on x86 platforms for a long time. With Docker containers you get a virtualization solution that does not need a complete virtual machine with an operating system running in it for every application. Instead your application is running in a small container that provides only a limited set of virtualization facilities. Just the things that the application needs. You can run many Docker containers – so applications – on a single real operating system image.
The interesting thing is that in a conceptual way Docker is a quite like z/OS as we have seen it in section Address Spaces are processes. On a z/OS operating system you can run many applications in “Address Spaces”. With Docker you run many container processes on a single real operating system image.
I will talk a bit more about Docker in section Linux in z/OS Container Extensions.
A small elaboration, as you may already get confused with the Unix on the mainframe. I mentioned Linux for the mainframe, now I talk about z/OS Unix and Linux in Containers.
It is important to understand the difference between z/OS Unix, z/OS Container Extensions and Linux for Z.
z/OS Unix and z/OS Container Extensions are an integral part of z/OS. You get these options with z/OS.
z/OS Unix applications use the Unix flavour that z/OS provides, which is not Linux.
In z/OS Container Extensions you get the option to run applications with the Linux flavour of Unix, and run these in a containerized setup.
Linux for Z is an operating system that is in no way related to z/OS. Applications running on Linux for Z use the Linux flavour, and in an LPAR or Virtual Machine of its own.
I have tried to put all the Unix variants on z/OS in the picture below. You see z/OS Unix, as part of a z/OS operating systems, you see a z/OS container process running a Linux Docker container, and separate from z/OS there is an LPAR running Linux for Z.
Now we have seen the basics of z/OS, we can turn to the more specialized and specific parts. In the next post I will discuss the unique clustering feature of z/OS, called parallel sysplex.
On 2 December, in a session organized by the Dutch GSE, the IBM User Group, specialists from the IBM Garage in Montpellier performed a presentation and live demonstration of running Linux containers in a z/OS Container Extension (zCX). After the session there was a short discussion about use cases for z/OS Container Extensions, introduced by a view on this topic by Rabobank.
You can find the presentation in the GSE Google Drive: Link to the presentation
And we’ve also recorded the whole event, so you can watch it on the GSE NL YouTube channel:
In the previous DBAOTM post I have described the operating systems available for the IBM mainframe and seen z/OS is the flagship in this category. In this post I will introduce you into the z/OS operating system concepts and terminology. The goal of this piece is to give you a good idea what is special about z/OS are and how the peculiarities relate to more commonly known concepts in Unix and Windows operating systems.
I will describe the z/OS operating system into two parts, and discuss these separately. The traditional part is MVS and this part deviates most from what we know from Windows and Unix. The second part is z/OS Unix, an extension that can run Unix applications, very much similar to other Unix flavours.
Next in my discussion, in upcoming posts about z/OS, I will talk about the unique clustering facility that z/OS brings, called parallel sysplex. Finally I will cover the green screens that the mainframe is often associated with, and discuss where this is still used. I will discuss modern tools and IDE’s for z/OS that come with modern user interfaces, replacing the old green-screen based tools.
The MVS side of z/OS is the traditional mainframe side. This is the part that has its roots in the 1960s. MVS and its predecessors were built in the era in which batch processing with punch cards was the basic way of interacting with the mainframe. In MVS we find the features that today look a bit awkward.
First let’s have a look at he basic operation of a batch process in z/OS. The batch process is core to the MVS part of z/OS. In essence, today it still works in the same way as it was when designed in the 1960.
To run a program on z/OS you need to have a means to tell it what to do. You do this by creating a script, which is usually quite small. The language for this script is called JCL – Job Control Language.
With the JCL script you tell the computer which program to run, and for that, what the input is for that program and where the output must be written to. This looks like a piece of code like this:
//RUNPROG EXEC PGM=PROGRAM1 //INPUT DD DISP=SHR,DSN=MY.INPUT.DATA //OUTPUT DD DISP=NEW,MY.OUTPUT.DATA
This code looks awful of course, despite its simplicity. This is because the language was designed for punch cards. Punch cards can carry 80 characters per line, and every line also needed some special positions to control the operation of the punch card reader. Also, to make things as simple as possible for the punch card reader, everything is in uppercase. All in all, JCL is probably easily readable for a punchcard reader device, but from an aesthetical and ergonomic perspective it is horrendous.
Anyway, with the above snippet of JCL you tell the computer to run PROGRAM1, use MY.INPUT.DATA as input file, and MY.OUTPUT.DATA as output file. If you feed this into the mainframe running z/OS it will try do execute this as such.
Figure – JCL to describe work to be done
In the old days the JCL was punched by the programmer on paper punch cards, one card for every line of JCL. The stack of cards were then inserted into a punch card reader attached to the mainframe.
Nowadays card reader devices do not exist anymore. They are replaced by a piece of software that is part of z/OS and called the internal reader.
The user starts his program by typing a “Submit” command with the JCL as a parameter or selecting the Submit option in the user interface of a modern IDE, as illustrated in Figure 7.
Figure – Submit JCL from a modern IDE
Now z/OS, the reader software, will read the JCL, find the program and the files needed, and start the execution of the program.
The execution of the program is peformed by a dedicated process for the task at hand. In Unix and Windows you call these execution concepts simply: processes. But in the MVS part of z/OS this process concept is called an Address Space. You can imagine many tasks are running at the same time for many users. All these tasks are run in Address Spaces on z/OS.
Although the name Address Space seems to indicate this just has something to do with memory, it is actually the same concept as a process in Windows and Unix.
The Address Space gives the program the memory that is needs to execute. This is called virtual storage on z/OS.
The odd thing is that Mainframers often refer to memory as storage. They could do this without getting confused with disk storage because that was called DASD – an abbreviation of Direct Access Storage Device.
Take care when a mainframer talks about storage, he might mean memory, but also disk storage.
On the MVS side data is stored in datasets. Datasets are files, but with some quirks I will discuss in a minute.
Datasets are administered in catalogs. Catalogs are designed to keep a record of dataset names and the place where these datasets are stored.
Datasets are so-called record-oriented. This means a dataset is defined with details that prescribe a structure for how the data is organized.
When you define a data in z/OS you must define how big the records are, how z/OS must and how z/OS must organize the data in the dataset.
The organization of a dataset can be a linear layout. We then call these sequential datasets. A dataset can also have a more complex hierarchical layout. We call these VSAM datasets (I will spare you the meaning of the abbreviation).
In sequential files the data is order from first records to last record. To read or write a sequential dataset you start at the beginning and proceed with the next record until you are done.
VSAM datasets have a sort of database structure. The records you store in a VSAM files have a key value. You do not usually browse through the VSAM dataset, but you read a specific record based of its key value. z/OS finds the record in the file with that key value. To do this, VSAM keeps indexes of key values and records. The benefit of VSAM files is that they can provide very fast access to the records is has stored.
When you create and MVS dataset you also have to specify a number of physical characteristics. These are characteristics like record size, format of the records, the size of blocks on disk that will hold the records, and more. These things were mostly aimed to optimize access speed and storage on disk. But with modern storage hardware these things have become obsolete. Many of these details can be removed for the user of z/OS, but unfortunately oftentimes this often is not yet done.
The applications you build on z/OS nowadays would only use sequential files only. The things that VSAM solved for applications in the past can now be much easier done in a database management system like Db2. The main use of VSAM that remains is for special operating system and middleware datasets, when very fast access to data is required. Under the hood of z/OS and the middleware.
Figure – Sequential and VSAM file structures
When you compare a Unix or Windows file to a dataset, you observe that a file in Unix and Windows does not have this prescribed structure that an MVS dataset has. From the user program perspective a file is just a big string of bytes. The data in the files can be organized internally. Often this is done with control characters, like Carriage Return (CR) and Linefeed (LF). The applications themselves have to provide that structure to the files.
Figure – File structure in Unix
In the traditional part of z/OS, data in the datasets is encoded in the Extended Binary Coded Decimal Interchange (EBCDIC) character set. This is a character set that was developed before ASCII (American Standard Code for Information Interchange) became commonly used.
Most systems that you are familiar with use ASCII. By the way, we will see z/OS UNIX files are encoded in ASCII.
Normally you will not notice anything different when you read files on z/OS and you will be unaware of the EBCDIC representation of data. However, if you want to transfer files between Windows or Unix and z/OS datasets, you will need to convert the characters from their ASCII representation to their EBCDIC representation, and vice versa. Typically file transfer programs will do this operation for you, called code page transformation, as part of the transfer action.
In Unix and Windows files are organized in a directory structure, and a hierarchy of file systems to manage the various disks on which the files may be stored. Files systems are defined on hard disks and hold the physical files, and the directory structure provides an organizing hierarchical mechanism for the files in the file systems. The root file system holds the operating system’s core files, other files systems can be mounted to extend the file storage over multiple storage devices.
The operating systems can find a file if you give it the name of the file and the directory in which it is defined.
Figure – File system and directory structures
In the MVS part of z/OS, the datasets are organized in catalogs. A catalog is in essence an index of dataset names in the z/OS system and the disk names on which the datasets are stored. With the catalog mechanism, if the user knows the name of the dataset, the catalog can tell on which disk it can be found.
To make the mechanism of catalogs a bit easier for the system administrator, catalogs are divided in a master catalog and user catalogs. There is one master catalog and there can be many user catalogs. The master catalog contain the system datasets. The user catalogs contain the user and application datatsets. The system administrator can define which datasets are administered in which catalog. When the system administrator decides to administer datasets for application APP2 in a certain user catalog, he put a little information in the master catalog to inform z/OS about that. This information is called an ALIAS.
To find a dataset with a certain name, z/OS first looks in the master catalog. z/OS finds it there, or it finds an ALIAS reference. The ALIAS reference tells z/OS to look in the associated user catalog for a dataset with that name. When z/OS has found the antry for a dataset, it uses the disk name in the index entry to access the file on disk.
Again, comparing this to Unix, you can say that the master catalog has a similar function as the root filesystem: it is meant for the operating system and middleware datasets. The user catalogs are like mounted file systems: for application and user datasets.
A catalog is however a registration that is separate from the physical storage. In Unix, the registration of files is done on the filesystems themselves. With a catalog this is not the case. In fact, a catalog is just a dataset itself. A VSAM dataset to be precise. It can be stored on any disk.
Figure – The structure of master and user catalogs
This concludes an introduction to the MVS side of the z/OS operating system. In a next post I will turn to the Unix side of z/OS.
In the previous posts I have given an overview of the most important mainframe hardware components. In this article I will summarize what operating systems you can run on this hardware. But first…
This post appears as part of a number of articles in the category “Don’t Be Afraid Of The Mainframe”.
A little late to answer this question, but I thought it was good to address this here.
A mainframe is a large computer that is designed to run many different computing tasks at the same time. A mainframe stems from the time where hardware was expensive, and a single central solution for computing was the only way to economically run computing tasks.
A lot of characteristics of that design point are still prevalent today. Hence it is good to understand this background.
A number of operating systems can run on the mainframe. I will give a short description here of the operating systems you can run on a mainframe.
For the rest of the series of articles I will focus on the two most important ones today. z/OS is the most important mainframe operating system, but also the most different from today’s mainstream operating systems. I will discuss z/OS most extensively. Linux for the mainframe is the second most important operating system and has gained popularity over the past decade. I will discuss Linux for the mainframe in a separate chapter Linux for the mainframe.
IBM often calls z/OS their flagship mainframe operating system. The roots of z/OS date back to 1964, when the operating system OS/360 was designed for the System/360 computer, the predecessor of IBM’s modern mainframe computers. In the early 70s the successor of the OS/360 operating system was developed, and named MVS (it stands for Multiple Virtual Storage, but you can forget that immediately). MVS has evolved further into OS/390 and now it is called z/OS. The name changes may suggest fundamental different systems, but these are in fact only marketing-driven name changes for MVS and the technology base is still the same, although it has very significantly evolved.
z/VM, or VM (VM stands for Virtual Machine) as it was originally named, used to be a full-fledged operating system that was design to run business applications. The operating system included a unique technology that allowed users to virtualize the mainframe hardware and split it up into small virtual machines. Nowadays we have VMWare, KVM, Xen, Hyper-V and others that do the same for x86 and other platforms. But the technology in VM was developed in the 1960s. It was far ahead of it’s time. z/VM can be considered the mother of all hypervisors.
z/VM is nowadays it is only still used as a hypervisor for the mainframe, and is no longer as an operating system for business applications.
The z/VSE operating system is the small brother of z/OS. It was developed in parallel to MVS, and targeted smaller customers. Nowadays it is not used very much anymore, but it is still developed and supported by IBM.
The operating system z/TPF (Transaction Processing Facility) was developed especially for real-time computing. Organizations that needed to process large volumes of small transactions very fast, such as credit card companies, airline and hotel reservation systems, and banks have deployed this specialized mainframe operating system.
IBM has ported Linux to the IBM mainframe architecture and the first release was formally announced in the year 2000. Since that time many other software products, commercial as well as open source software, have been made available on Linux for Z, as it is now called.
Configuration for Linux for the mainframe are most often virtualized with z/VM, the hypervisor for the mainframe we saw above. With z/VM you can create and manage many virtual machines on the mainframe in which you can then run a Linux instance. I will discuss Linux for the mainframe separately in a number of special posts.
A mainframe has a large number of CPUs. The CPUs can be configured in different modes, called specialty engines.
In this post I will discuss what these specialty engines are, and how they are used.
This post appears as part of a number of articles in the category “Don’t Be Afraid Of The Mainframe”.
The normal setup to use a CPU is as a general purpose CPU, and alternatively CPUs can be configured as so called specialty engines. This is a special sort of setup that only an IBM engineer can do because the CPU configuration is agreed when you acquire mainframe hardware. We will see why this is.
A general-purpose CPU can be used for, well, everything. But to make it easy, in reality a general-purpose CPU is used only for traditional workload types, like your COBOL and PL/I programs.
When a CPU is configured as a specialty engine, the CPU can only be used for a special function. So a specialty engine is not special in the sense that it is designed for a particular function. Rather, it is a regular CPU that is configured so that it can be used only for a particular function.
The purpose of specialty engines is to make it cheaper for organizations to run particular functions on the mainframe. For traditional workloads the run on the general-purpose CPUs you pay your normal software bill based on MSUs, as we have seen in section Understanding the cost of software on z/OS, MLC and OTC. Functions that run on a specialty engine, however, are not accounted for in the MSU numbers. Therefore, it is up to your software vendor therefore decides whether to enable software to run on a specialty engine. IBM has enabled certain functions for speciality engines, and other vendors have done so similarly for selected mainframe software components.
What is also important to realize, is that even though the general purpose and the specialty engines are using exactly the same hardware, the acquisition cost of a specialty engine is significantly lower than the price for a general-purpose CPU.
The most important types of specialty engines are called zIIP and IFL. I will spare you what the abbreviates mean – they are never used.
A zIIP is a specialty engine that is only usable in a z/OS environment. The special functions you can run on a zIIP are: all Java programs, certain Db2 functions, and z/OS Containers (more on that in separate posts). There are a number of other mainframe software vendors that also enable their software for zIIPs, and they have special conditions for these software products.
An IFL is a specialty engine used to Linux on the mainframe. IFLs have nothing to do with z/OS. The CPUs configured as IFLs can only be used for Linux applications in LPARs running Linux. I will discuss Linux on the mainframe in a separate section Linux for the mainframe.
The other types of specialty engines enable the use of the pool of processors in a mainframe for computing needed to support “real” business workloads. These run “technical processing” tasks. The CPU usage is therefore also not accounted for in the software bill. These processor types are the following:
The Integrated Coupling Facility (ICF) processor is used with a Coupling Facility. A coupling facility is a special LPAR that provides special operating system functions in a sysplex. We will discuss the Coupling Facility concepts briefly in section Special sysplex components: the Coupling Facility.
The System Assistance Processor (SAP) specialty engine is used to run I/O operations independently from your central CPUs, in a mainframe component called the IO Subsystem. This type of processors is used when moving data from memory to storage. This not only makes sure that this processing does not add to your software bill, but the IO Subsystem construct also gives the mainframe its extremely fast, high-volume IO processing capability.
Bil Pereira’s channel is a great and very informative Youtube channel. He is adopting new tech for the mainframe and tries it all out, while explaining his experiments on his Youtube channel.
