Category: OMVS

Should I use tar or pax to backup my Unix files?

I am running this on z/OS and want to copy Unix files from one z/OS image to another.

The tar command is very popular, and works for most people.

The pax command is similar to tar, but It can also save and restore file attributes that cannot be handled by any other format such as: files greater than 8 GB, large UID, and GID values , large time values and z/OS -specific attributes like user audit and auditor audit flags and file format.

You create a file using

pax -o saveext -wf pax_file_name files_to_add

and

pax -ppx -rf pax_file_name

to extract the files.

Thanks to Gwydion Tudur for the pointers about extended attributes.

Using a data set

You can use a data set as an output file for example you specify “//’COLIN.PAX.HTTP2′”

pax -E -f “//’COLIN.PAX.HTTP2′”

This will display the contents of the file, for example if gives

drwxrwxrwx        1 OMVSKERN SYS1           0 Aug  4 10:03 ./                                  
drwxrwxrwx        1 OMVSKERN SYS1           0 Nov 15  2021 ./images/                           
drwxrwxrwx        1 OMVSKERN SYS1           0 Nov 15  2021 ./images/ihs/                       
-rwxrwxrwx  --s-  1 OMVSKERN SYS1         223 Nov 15  2021 ./images/ihs/administration.gif     
                 
-rwxrwxrwx  --s-  1 COLIN    SYS1         373 Jun 17  2023 ./colin.html

Using a data set makes it more portable, for example it is a data set, not a file in a Unix file system.

File owners

Within the .pax file the file owner is a name. When the file is unpacked, you can use the -p o option to preserves the user ID and group information. On my system userid OMVSKERN has uid 0, and group SYS1 has gid 0. On my newer z/OS system the file got the uid of COLIN on the new system – not from the old system.

Without the -po option, the files get the uid from the userid executing the pax command.

Where are my omvs address spaces?

I was running a Java program in batch, and it started an OMVS address space to run the Java. When Java stopped, I could not find the OMVS output – because I was looking in the wrong place!

The program I was trying to run was RSEAPI. When this starts it creates other jobs with jobnames like RSEAPI6.

Display the jobs

In SDSF it had

JOBNAME  StepName ProcStep JobID    Owner  
RSEAPI6  STEP1             STC06719 STCRSE 
RSEAPI1  STEP1             STC06722 STCRSE 
RSEAPI   RSEAPI   RSEAPI   STC06728 STCRSE

The jobid of the RSEAPIn jobs are lower than the value for RSEAPI, this is because the address spaces were reused.

Shutdown or cancel

I cancelled RSEAPI6 and the other jobs stopped as well.

If you look in the spool for RSEAPI* it only showed job RSEAPI

Where are the other jobs?

There are system address spaces BPXAS. If your program issues a spawn or fork, it runs the work one of these address spaces. When the work request finishes, the address space stays running and becomes available for other work.

If you were hoping to find End of Step SMF statistics displayed (such as CPU and IO counts), these will be displayed when the BPXAS address space shuts down, and the figures are for all work which ran in that address space.

Purging the BPXAS job output

If you display the BPXAS jobs, it shows it is PROTected. This stops the casual end user from purging it. You have to add PROT to the command, for example $PS6723,PROT

Interacting with these address spaces

I tried to set CEE run time options to display the run time storage options, and to set heap size etc. I could not find how to do this.