OpenExtensions for z/VM "Q"s and "A"s
Question:
Is there anything special I need to know about
archiving files with OpenExtensions for z/VM?
Answer:
You can bundle files together in single "archive" files with utilities
like pax, tar, and cpio. Usually, the filename of
such an archive file will indicate the type of utility used to create the
file; for example, the filename foobar.tar indicates a file
created by the tar utility. The three utilities provide basically the
same function: reading and writing archive files.
The important thing to know is that tar and cpio can only read and write
files of their respective formats, but pax can read or write in any CPIO
ASCII format, CPIO binary format, TAR format, or USTAR format. So given a
pax, tar, or cpio file, you can use pax to "explode" or "unwind" the
archive into its individual files. Later, I'll give examples in pax since
it's easier that way and there's really no need to learn to use the
others if you're only reading on OpenExtensions for z/VM.
ASCII to EBCDIC conversion
Where is your archive file coming from? If it was created on a
traditional *IX type system, text files are probably encoded in ASCII and
you will want to convert the data to EBCDIC on OpenExtensions for z/VM.
pax can do this conversion automatically. Many archives have been
processed with this method, and there hasn't been a hint of a conversion
problem (that is, translating to the wrong character). The option to
perform ASCII to EBCDIC conversion is:
-o from=ISO8859-1,to=IBM-1047
If you don't know whether you need the conversion or not, try it without
first, maybe with just a single file in the archive.
This conversion feature is rather unique to OpenExtensions for z/VM because we're
an EBCDIC system. If you're creating an archive that may be ported to an
ASCII system, it might be a good idea to do the conversion in reverse so
that data is stored in ASCII form.
Compressed archives
Is your archive compressed? Typically, archives are compressed to
save disk space and transmission time. The convention for any
compressed file is to end the filename with .Z (for example,
the filename
foobar.pax.Z).
All three utilities can read and write compressed archives when they are
run with the -z option.
Binary file transfer
Usually it's a good idea with archive files (especially when they are
compressed) to use BINARY transfer options whenever possible. This
applies when you are using FTP get and put subcommands as well as the
"OPENVM GETBFS ... (BFSLINE 1" and "OPENVM PUT ... (BFSLINE NONE"
commands.
A typical scenario in obtaining an archive might be:
- Obtain an archive from anonymous FTP server. Use BINARY mode when
you perform the get!
- Move the file into the filesystem. Use the "BFSLINE NONE" option
on the OPENVM PUTBFS
If you don't use BINARY mode everywhere you have the ability to,
your archive will most likely be corrupted and unusable.
Examples of the pax command
To unwind all ASCII files from a compressed tar file:
pax -o from=ISO8859-1,to=IBM-1047 -rzf foobar.tar.Z
To obtain a listing of all files contained in a tar file (it doesn't
matter whether the files contain ASCII or EBCDIC data since the file
names must always be stored in ASCII form):
pax -vf foobar.tar
To unwind an individual ASCII file called README from an
uncompressed pax file:
pax -o from=ISO8859-1,to=IBM-1047 -rf foobar.pax README
To back up files in your current working directory and all
subdirectories:
pax -wzf ../backup.pax.Z .
Note that I deliberately wrote the archive file to a different
directory than the directory I am archiving. If you accidentally
include the archive file, when someone is unwinding the archive, that
person could overwrite his/her copy of the archive before everything
in the archive is unwound. The moral is to write your archive to a
directory not in the tree of your current working directory.
For further information, refer to the
IBM OpenExtensions for z/VM: User's Guide , SC24-5727
and the
IBM OpenExtensions for z/VM: Command Reference , SC24-5728.
For more questions and answers, go to our
archive of questions and answers.
|
