How is wget able to download an iso file when only iso.gz is listed under the FTP library

I hit a behavior of wget from FTP server (URL: ftp://foo.com/bar/...) that was unfamiliar to me. Can you direct me to some documentation or explain how is the following possible?

If I wget the folder's URL I get an index.html (shown at the bottom of the post) with the following listing which shows that only the zipped file is available: os_image_123_0-incr-repo.iso.gz

I can wget this file's URL and I will get a gzip file with specific MD5 checksum.

c4fd702b3ad296561b2ec7e4b888e624  os_image_123_0-incr-repo.iso.gz
os_image_123_0-incr-repo.iso.gz:        gzip compressed data - deflate method , original file name

However I can also wget the same file URL omitting the .gz extension, leaving only the filename os_image_123_0-incr-repo.iso and I will now get an iso file, which is not listed in the index.html.

08daf88aca95325c3aa9ae6406e02198  os_image_123_0-incr-repo.iso
os_image_123_0-incr-repo.iso:   ISO 9660 filesystem image

It's as if wget "knows" to extract the iso from the iso.gz file.

Is this what happens? How does it work?

This is the content listed in the index.html for the folder:

2016 Apr 13 14:45  Directory   <a href="ftp://foo.com/bar/05/.RE/">.RE/</a> 
2016 Apr 13 14:36  File        <a href="ftp://foo.com/bar/05/README.11.3.7">README.11.3.7</a>  (3097 bytes)
2016 Apr 13 14:36  File        <a href="ftp://foo.com/bar/05/md5sum-repo-iso-123_0.txt">md5sum-repo-iso-123_0.txt</a>  (63 bytes)
2016 Apr 13 13:02  File        <a href="ftp://foo.com/bar/05/md5sums.txt">md5sums.txt</a>  (321 bytes)
2016 Apr 13 09:52  File        <a href="ftp://foo.com/bar/05/os_image_123_0-ai-sparc.iso">os_image_123_0-ai-sparc.iso</a>  (570142720 bytes)
2016 Apr 13 09:53  File        <a href="ftp://foo.com/bar/05/os_image_123_0-ai-x86.iso">os_image_123_0-ai-x86.iso</a>  (496521216 bytes)
2016 Apr 13 13:02  File        <a href="ftp://foo.com/bar/05/os_image_123_0-fallback_boot-sparc.pkg">os_image_123_0-fallback_boot-sparc.pkg</a>  (103859114 bytes)
2016 Apr 13 14:37  File        <a href="ftp://foo.com/bar/05/os_image_123_0-incr-repo.iso.gz">os_image_123_0-incr-repo.iso.gz</a>  (3613854717 bytes)
2016 Apr 13 09:52  File        <a href="ftp://foo.com/bar/05/os_image_123_0-text-sparc.iso">os_image_123_0-text-sparc.iso</a>  (885370880 bytes)
2016 Apr 13 09:53  File        <a href="ftp://foo.com/bar/05/os_image_123_0-text-x86.iso">os_image_123_0-text-x86.iso</a>  (795648000 bytes)
2016 Apr 13 14:38  Directory   <a href="ftp://foo.com/bar/05/zipped-repo/">zipped-repo/</a>

Adding wget output.

[my_user 503 0 /tmp]$ wget ftp://foo.bar.com/products/Solaris_11/s11.3/support/sru07/05/sol-11_3_7_5_0-incr-repo.iso.gz
--2016-05-10 06:39:19--  ftp://foo.bar.com/products/Solaris_11/s11.3/support/sru07/05/sol-11_3_7_5_0-incr-repo.iso.gz
           => ‘sol-11_3_7_5_0-incr-repo.iso.gz’
           Resolving foo.bar.com (foo.bar.com)... 10.10.11.11
           Connecting to foo.bar.com (foo.bar.com)|10.10.11.11|:21... connected.
           Logging in as anonymous ... Logged in!
           ==> SYST ... done.    ==> PWD ... done.
           ==> TYPE I ... done.  ==> CWD (1) /products/Solaris_11/s11.3/support/sru07/05 ... done.
           ==> SIZE sol-11_3_7_5_0-incr-repo.iso.gz ... 3613854717
           ==> PASV ... done.    ==> RETR sol-11_3_7_5_0-incr-repo.iso.gz ... done.
           Length: 3613854717 (3.4G) (unauthoritative)

           sol-11_3_7_5_0-incr-repo.iso.gz        100%[===========================================================================>]   3.37G  99.5MB/

           2016-05-10 06:39:56 (94.4 MB/s) - ‘sol-11_3_7_5_0-incr-repo.iso.gz’ saved [3613854717]

[my_user 505 0 /tmp]$ wget ftp://foo.bar.com/products/Solaris_11/s11.3/support/sru07/05/sol-11_3_7_5_0-incr-repo.iso
--2016-05-10 06:43:25--  ftp://foo.bar.com/products/Solaris_11/s11.3/support/sru07/05/sol-11_3_7_5_0-incr-repo.iso
           => ‘sol-11_3_7_5_0-incr-repo.iso’
           Resolving foo.bar.com (foo.bar.com)... 10.10.11.11
           Connecting to foo.bar.com (foo.bar.com)|10.10.11.11|:21... connected.
           Logging in as anonymous ... Logged in!
           ==> SYST ... done.    ==> PWD ... done.
           ==> TYPE I ... done.  ==> CWD (1) /products/Solaris_11/s11.3/support/sru07/05 ... done.
           ==> SIZE sol-11_3_7_5_0-incr-repo.iso ... done.

           ==> PASV ... done.    ==> RETR sol-11_3_7_5_0-incr-repo.iso ... done.

           sol-11_3_7_5_0-incr-repo.iso               [                                                            <=>             ]   4.04G  32.3MB/

           2016-05-10 06:45:39 (30.9 MB/s) - ‘sol-11_3_7_5_0-incr-repo.iso’ saved [4337887232]

RaamEE

Posted 2016-05-09T08:48:03.590

Reputation: 422

You wrote "shows that only the zipped file is available", yes the listing just below shows 08daf88aca95325c3aa9ae6406e02198 os_image_123_0-incr-repo.iso. Also I do not understand your two separate listings, both labeled index.html – Martin Prikryl – 2016-05-09T09:10:46.157

Also what's the URL? Is it ftp:// or http://? What the server is? – Martin Prikryl – 2016-05-09T09:15:14.290

Thanks @MartinPrikryl - I edited the post to make it more readable. It is a FTP:// server. It's an internal server at my workplace, so can't share it for anyone to try it themselves. – RaamEE – 2016-05-10T05:47:07.607

But what FTP server software that is? – Martin Prikryl – 2016-05-10T05:50:18.377

I dont have this information. – RaamEE – 2016-05-10T06:27:55.327

A log file from any FTP client may show that. Actually a log file and a complete output of the wget may be useful. – Martin Prikryl – 2016-05-10T06:28:58.507

Added the output of wget. log file doesn't contain additional information beyond that in the output I added. – RaamEE – 2016-05-10T06:55:22.043

OK, so try another FTP client. E.g. some GUI one, FileZilla or WinSCP. – Martin Prikryl – 2016-05-10T07:13:35.360

How is wget able to download an iso file when only iso.gz is listed under the FTP library

Answers