If you cannot open a data set, amrc may help

I had a C program which opened a dataset and read from it. I enhanced it, by adding comments and other stuff, and after lunch it failed to open

I undid all my changes, and it still it failed to open! Weird.

I got message

  • EDC5061I
    • An error occurred when attempting to define a file to the system. (errno2=0xC00B0403)
    • Programmer response : Check the __amrc structure for more information. See z/OS XL C/C++ Programming Guide for more information on the __amrc structure.
  • C00B0403:
    • The filename argument passed to fopen() or freopen() specified dsname syntax. Allocation of a ddname for the dsname was attempted, but failed.
    • Programmer response: Failure information returned from SVC 99 was recorded in the AMRC structure. Use the information there to determine the cause of the failure.

This feels like the unhelpful messages Ive seen. “An error has occurred – we know what the error is – but we wont tell you” type messages.

To find the reason I had to add some code to my program.

 file =  fopen(fileName, mode     ); 
 __amrc_type save_amrc; 
 printf("AMRC __svc99_info %hd error %hd\n",

and it printed

AMRC __svc99_info 0 528

The DYNALLOC (dynamic allocation) which uses SVC 99 to allocate data sets, has a section Interpreting error reason codes from DYNALLOC. The meaning of 528 is Requested data set unavailable. The data set is allocated to another job and its usage attribute conflicts with this request.

And true enough, in one of the ISPF sessions in one of my TSO userid I was editing the file.

It looks like

printf(“__errno2 = %08x\n”, __errno2());

Would print the same information.


It appears that you cannot tell fopen to open it for read even if it has a write lock on it.

For DYNALLOC, if the request worked, these fields may have garbage in them – as I got undocumented values.

It would be nice if the developer of the fopen code produced messages like

EDC5061I: An error occurred when attempting to define a file to the system. (errno2=0xC00B0403) (AMRC=0x00000210)

Then it would be more obvious!

How do I assemble a program in Unix System Services using the c complier?

My preferred way of assembling some code is to use JCL. The next best way is to use the “as – Use the HLASM assembler to produce object files“. (For example “as -a -d xxxx.o xxxx.s 1>a”) Unfortunately I needed to use the”C” compiler xlc, because I wanted to compile a file for a Python External command.

The basic syntax is

xlc “-Wa,LIST” zonsole.s 1>a 2>b


  • -Wa specifies these are options for the assembler source
  • LIST says generate a listing. By default it does not generate a listing, only the error file.
  • zonsole.s is my assembler source program
  • 1>a says put the listing into file a
  • 2>b says put the error file into file b

At the top of the listing file is

No Overriding ASMAOPT Parameters
No Process Statements

** ASMA425N Option conflict in invocation parameters. LIST overrides an earlier setting.

The options in the -Wa are described here

How do I use SFTP to ftp to a z/OS data set?

You cannot do it directly, you have to do a two step process.

Sending files to z/OS using SFTP

SFTP can send files to Unix Services Subsystem. It cannot send to data sets.

sftp colin@

You can use commands like

  • cd to change directory on the remote system
  • lcd change directory on the local system
  • put
  • get
  • chmod
  • chown
  • exit

There is no command “bin” nor “quote…”.

Getting from a Unix Services file to a dataset.

You can use the cp command.

To copy a binary file to a dataset

For example as if you were using FTP with BIN; quote site cyl pri=1 sec=1 recfm=fb blksize=3200 lrecl=80; put mp1b.load.xmit ‘COLIN.MP1B.LOAD.XMIT’)

cp -W “seqparms=’RECFM=FB,SPACE=(500,100),LRECL=80,BLKSIZE=3200′” mp1b.load.xmit “//’COLIN.MP1B.LOAD.XMIT'”

Where the seqparms are in upper case. If they are in mixed case you get

FSUM6258 cannot open file “… “: EDC5121I Invalid argument.


To copy a text file to a data set

If you use SFTP to copy a text file to Unix Services, it gets sent in bin, and, on z/OS, looks like


You can tag a file so Unix Services knows it is an ASCII file, using

chtag -tc ISO8859-1 aaa

This makes the file editable from Unix Services, but you cannot just use cp to copy and create a dataset, as above.

You can convert it from ASCII to EBCDIC using

iconv -f ISO8859-1 -t IBM-037 ascii_file  > ebcdic-file

Then use

cp -W “seqparms=’RECFM=VB,SPACE=(CYL,(1,1)),LRECL=800,BLKSIZE=8000′” ebcdic-file “//’COLIN.EBCDFILE'”

Oh p*x, I’ve lost my changes

I have been using pax to backup the files in my Unix Services directory and needed to restore a file so I could compare it with the last version ( and work out why my updates didnt work). Unfortunately I managed to overwrite my latest version instead of creating a copy.
I backed up my directory using

pax -W “seqparms=’space=(cyl,(10,10))'” -wzvf “//’COLIN.PAX.PYMQI2′” -x os390 /u/tmp/pymqi2/

This created a data set COLIN.PAX.PYMQI2 with the give space parameters, and os390 format.

To list the contents of this file use

pax -f “//’COLIN.PAX.PYMQI2′”

To display a subset of the files use

pax -f “//’COLIN.PAX.PYMQI2′” /u/tmp/pymqi2/code

which gave


And provide more information using the -v option

drwxrwxrwx 1 COLIN    1000      0 Jan 22 17:04 /u/tmp/pymqi2/code/
drwxr-xr-x 1 COLIN    1000      0 Feb 11 13:10 /u/tmp/pymqi2/code/pymqi/
-rw-r--r-- 1 OMVSKERN 1000 133011 Feb 22 13:15 /u/tmp/pymqi2/code/pymqi/init.py
-rw-r----- 1 COLIN    1000 119592 Feb  3 12:59 /u/tmp/pymqi2/code/pymqi/old__init__.old
-rwx------ 1 OMVSKERN 1000 119565 Jan 22 16:43 /u/tmp/pymqi2/code/pymqi/aa

The whoops

To restore an individual file and overwrite the original I used the -r option.

pax -rf “//’COLIN.PAX.PYMQI2′” /u/tmp/pymqi2/pymqi/__init__.py

I was expecting the file to be restored relative to the directory I was in; No – because I had backed up the files using an absolute path it restored the file to the same place, and so it overwrote my changes to the file. I had changed to a temporary directory, but I had not realised how the command worked.

There are several ways of doing it properly.

Restore with rename

pax -rf “//’COLIN.PAX.PYMQI2′” -i /u/tmp/pymqi2/pymqi/__init__.py

The -i option means rename.

I ran the command and it prompted me to rename it

Rename “/u/tmp/pymqi2/pymqi/__init__.py” as…


Set “do not overwrite”

I could also have used the -k option which prevents the overwriting of existing files.

Rename on restore

I could also have used the rename

pax -rf “//’COLIN.PAX.PYMQI2′” -s#/u/tmp/pymqi2/pymqi#/tmp/# /u/tmp/pymqi2/pymqi/__init__.py

Where the -s#/u/tmp/pymqi2/pymqi#/tmp/# / says use the regular expression to change /u/tmp/pymqi2/pymqi to /tmp and so restore it to a different place. Note: The more obvious -s/abc/xyz/, where / is used as the delimiter, would not work, as there is a ‘/’ in the file path.

All of the above

I could have use all of the options -i -k -s…. .

A better way to backup.

I had specified an absolute directory /u/tmp/pymi2/. If I was in this directory when I did the backup I could have used

pax … -x os390 .

Where the . at the end means from this directory, and so backup a relative directory.

If I list the files I get

pax -f “//’COLIN.PAX.PYMQI2A'” ./aa

And now if I restore the file…

pax -rf “//’COLIN.PAX.PYMQI2A'” ./aa

It restored the file into my working directory /tmp/aa .

So out of all the good ways of backing up and restoring – I chose the worst one. It only took me about 2 hours to remake all the changes I had lost.