Frequently Asked Questions - PKZIP/SecureZIP UNIX

This section lists some commonly asked questions about PKZIP and related subjects. We hope you will find this information helpful.

Why do I get the message "SYS1041: The name specified is not recognized as an internal or external command, operable program or batch file." or " Bad command or file name" or "XXXX: not found"?

These messages tell you that your operating system cannot find the program to which you are referring. This occurs because you are either not spelling the name of the program correctly, or you did not put a space between the program name and its options, or the program has not been properly installed. If you are trying to run PKZIP and you get this error, it may be because pkzipc is not in your search path.

Why didn't the files I zipped get any smaller?

On occasion, you may find that the files you add to a .ZIP file do not compress. These files are "stored." This occurs when a file is either already compressed or encrypted. You will often find that files distributed with commercial applications are already compressed.

I zipped up a bunch of files but now I have LESS disk space?

When PKZIP compresses files, it makes a copy of the original file. The original file(s) still exist. If you wish to recover space that was taken up by the original file(s), you must either delete them yourself, or instruct PKZIP to delete the file(s) with the move option.

What is the difference between add=freshen and add=update?

The freshen and update sub-options are very similar. This may be confusing at first, but the difference between them is easy to understand.

Freshen tells PKZIP to archive any files which match those already in the .ZIP file. These files are re-compressed only if they are newer than the files already in the .ZIP file. Each file is evaluated individually.

Update archives all files, with one distinction. If the update option is not used, all files specified are compressed and added to the .ZIP file, even if they already exist in the .ZIP file. By using the update sub-option, you instruct PKZIP to compare what is already in the .ZIP file against what it was asked to compress. If a file is already present in the .ZIP file as well as the source directory, PKZIP compresses a file only if it is newer than the copy of the file within the .ZIP file. If a file in the source directory is not already present in the target .ZIP file, PKZIP adds it to the .ZIP file.

Is PKZIP compression "lossy" or "lossless"?

PKZIP uses a "lossless" compression scheme. This means that 100% of the original data is preserved and re-created. There is no difference between the data that you put in and the data that you get back out.

There are other compression methods that are known as "lossy." The idea behind these compression methods is that if you throw away some of the data, it becomes less complex and therefore can be compressed more. This type of compression is only useful for data that need not be precise. This applies to some applications that use pictures and sound.

How do I include subdirectory information in my .ZIP file?

Use the directories option to include subdirectory information in your .ZIP file. This option recurses subdirectories and preserves path names. For example:

pkzipc -add -directories test.zip *

In this example, the current directory as well as all subdirectories and files contained therein are archived in a file called test.zip.

When a .ZIP file is created with paths stored, these paths are visible in a view of the file (view).

To re-create these subdirectories, or to place files into their original subdirectories, the directories option must be used with the extract command.

I zipped up some subdirectories, but I cannot get them to come back.

Did you remember to use the directories option when you originally created the .ZIP file? Did you use the directories option when you extracted the contents of your .ZIP file? To verify that there are paths in the .ZIP file, do a view of the file:

pkzipc -view test.zip

If you do not see paths as part of the file names within the .ZIP file, then paths are not stored and therefore cannot be recovered. If you do see paths make sure that you are using the directories option when you extract the files. For example:

pkzipc -extract -directories test.zip

How do I unzip a single file that is in a subdirectory in the .ZIP file?

Type pkzipc -extract with the name of the .ZIP file and the name of the particular file you want. With a .ZIP file that contains paths, the procedure is the same.

Assume you are working with a file called test.zip that contains the following files:

file1.txt
temp/file2.txt
temp/tut/file3.txt

To extract only file3.txt from this .ZIP file, you must specify the complete name and path.

pkzipc -extract test.zip temp/tut/file3.txt

If you wanted to extract it with its subdirectory, simply include the directories option on the command line.

How do I unzip a directory without also extracting its subdirectories?

Using the test.zip file we discussed in the previous question, we could extract the entire contents of the temp subdirectory easily:

pkzipc -extract -directories test.zip "temp/*"

If we did it as shown above we would not only extract all the files in the temp subdirectory, but also the tut subdirectory below it and any files it contains.

To extract only the temp subdirectory but not its subdirectories, we must exclude the subdirectories we do not wish to extract:

pkzipc -extract -directories test.zip "temp/*" - exclude="temp/tut/*"

If the temp subdirectory had multiple subdirectories nested in it, you would need to exclude each one individually on the command line.

I forgot my passphrase; what do I do?

Try to remember the passphrase.
Try passphrases that are "close" to what you think it was.
Try mixed upper and lower case versions of your passphrase.

Note

Do not forget or lose your passphrases! PKWARE has no special means for "getting around" the encryption and may not be able to assist in the recovery of an encrypted file. To help avoid the loss of data, you may wish to use a password manager, or keep a written copy of your passphrase(s) in a secure place.

What does "Unknown Compression Method" mean?

There are many different methods of compression. In the history of PKZIP alone, there have been seven different methods to date. The .ZIP file format was designed so that additional methods of compression can be added as they are developed. Therefore, the .ZIP file format will never need to be abandoned. This means that the .ZIP file in question was created or updated by a newer version of PKZIP than is being used to extract the data. You must use a newer version of PKZIP to extract these files.

How can I make PKZIP run faster?

PKZIP defaults to a compression method that is average in both compression amount and speed. If you want to get the most speed out of PKZIP, try specifying a faster compression method with a level sub-option (for example, -level=0). See "Setting the Compression Level." Compression speeds are highly dependent on the location of files being added, as well as the temporary file PKZIP creates when performing certain compression operations. If these files are located on a network drive, you may want to move them to a local drive before running PKZIP. Be aware of the effects file location can have on PKZIP's speed.

How many files can be in a .ZIP file?

There is no limit to the number of files you can add to a .ZIP file. However, if you use the 204 option for PKZIP 204g compatibility, your .ZIP file may contain no more than 16,383 file entries.

Can I send a .ZIP file to a different type of computer?

As of the publication of this manual, PKWARE supports PKZIP on almost every platform in use today, from mainframe to mobile. You can send a .ZIP file to anyone with confidence, no matter what type of computer they have.