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I gzip directories very often at work. What I normally do is

tar -zcvf file.tar.gz /path/to/directory

Is there a way to specify the compression level here? I want to use the best compression possible even if it takes more time to compress.

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4 Answers

GZIP=-9 tar cvzf file.tar.gz /path/to/directory

assuming you're using bash. Generally, set GZIP environment variable to "-9", and run tar normally.

Also - if you really want best compression, don't use gzip. Use lzma or 7z.

And when using gzip (which is good idea for various of reasons anyway) consider using pigz program and not the gzip.

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What's the logic of using pigz over gzip? But yeah, the remark on compression ratio is, at least according to the initial Google search, quite well founded. –  new123456 Jul 2 '11 at 4:03
    
pigz is faster. That's all. I don't see much point in having compression take longer, while end result is virtually the same. –  user7385 Jul 2 '11 at 10:10
    
Is -9 on purpose or a typo? –  Pineapple Under the Sea Feb 21 '13 at 2:29
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On purpose. This is specifically the answer to OP question. –  user7385 Feb 22 '13 at 18:13
    
pigz is "parallel gzip" which uses all your cores for gzip compression. You can watch top and see it using anywhere between 200%-400$ CPU. –  Felipe Alvarez Dec 9 '13 at 2:01
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Instead of using the gzip flag for tar, gzip the files manually after the tar process, then you can specify the compression level for the gzip program:

tar -cvf files.tar /path/to/file0 /path/to/file1 ; gzip -9 files.tar

Or you could use:

tar cvf - /path/to/file0 /path/to/file1 | gzip -9 - > files.tar.gz

The -9 in the gzip command line tells gzip to use the maximum possible compression level (default is -6).

Edit: Fixed pipe command line based on @depesz comment.

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Using pipes should be done with: tar cvf - /path/to/directory | gzip -9 - > file.tar.gz –  user7385 Jul 1 '11 at 18:40
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1st example should end with file.tar, since gzip adds the ".gz" extension. –  bonsaiviking Feb 4 '13 at 18:20
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why don't you skip f -? if there is no file, then it is stdin/out –  akostadinov Sep 19 '13 at 18:52
    
addition to the previos comment. From "man tar" section Environtment: TAPE Device or file to use for the archive if --file is not specified. If this environment variable is unset, use stdin or stdout instead. –  Mikl Sep 24 '13 at 17:08
    
and we can reduce "gzip -9 -" -> "gzip -9". From "man gzip" section Description: If no files are specified, or if a file name is "-", the standard input is compressed to the standard output. –  Mikl Sep 24 '13 at 17:18
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Modern versions of tar support the xz archive format (GNU tar, since 1.22 in 2009, Busybox since 1.17.0 in 2010).

It's based on lzma2, kind of like a 7-Zip version of gz. This gives better compression if you are ok with the requirement of needing xz support.

tar -Jcvf file.tar.xz /path/to/directory

I just found out here (basically a dupe of this question, but in the Unix stackexchange) that there is also a XZ_OPT=-9 environment variable to control the XZ compression level similar to the GZIP one in the other post.

XZ_OPT=-9 tar -Jcvf file.tar.xz /path/to/directory
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+1 xz is far better than both bzip2 and gzip. Here's a comparison: tukaani.org/lzma/benchmarks.html –  User1 Dec 25 '12 at 15:44
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tar cv /path/to/directory | gzip -9 > file.tar.gz

This is Matrix Mole's second solution, but slightly shortened:

When calling tar, option f states that the output is a file. Setting it to - (stdout) makes tar write its output to stdout which is the default behavior without both f and -.

And as stated by the gzip man page, if no files are specified gzip will compress from standard input. There is no need for - in the gzip call.

Option -9 sets the highest compression level.

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This works beautifully. Also if you run as root, permissions & owners are preserved too. Otherwise you must specify. Also if it wasn't obvious "-9" is best compression and "-1" is fastest compression. "-1" still takes a looong time if you have lots of files ;-) –  PJ Brunet Dec 12 '13 at 4:04
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