Gzip and Gunzip in Linux: Compress, Extract, and Keep Files

What you need	Command or tool	Expected result
Compress one file	gzip file.log	Only file.log.gz
Compress and keep the original	gzip -k file.log	Both files remain
Decompress a .gz file	gunzip file.log.gz	Only file.log
Decompress and keep the archive	gzip -dk file.log.gz	Both files remain
Package an entire directory	tar with gzip compression	One .tar.gz archive
Produce a ZIP file	ZIP tool	A .zip archive

Which should you use: gzip, gunzip, tar.gz, or ZIP?

GNU gzip compresses file contents or a data stream. A plain .gz file holds one compressed input. tar collects multiple files and directories into an archive. Combine the two and you get a .tar.gz or .tgz file.

Take three filenames. server.log.gz is a compressed log you can decompress or inspect with gzip tools. backup.tar.gz is a compressed tar archive of file entries, and GNU tar extracts it. submission.zip is a ZIP archive.

If a downloaded file named download.gz refuses to decompress, check its real format with the file utility:

file download.gz

This helps when a server sends a wrongly named download or someone renamed a file without changing its format.

Compress a file and keep the original

For a file named sample.log, run:

gzip sample.log

gzip deletes sample.log once it has written sample.log.gz.

To keep the original, add -k. gzip then leaves sample.log next to sample.log.gz:

gzip -k sample.log

Practice on a disposable file

mkdir gzip-practice && cd gzip-practice && printf 'INFO started\nERROR example\n' > sample.log

Compress with -k and list the directory:

gzip -k sample.log
ls -1

The listing shows both files:

sample.log
sample.log.gz

Decompress a .gz file without discarding the archive

gunzip reverses gzip compression. gzip -d does the same, and -k keeps the compressed input. For sample.log.gz, use one of these:

gunzip sample.log.gz

gzip -d sample.log.gz

gzip -dk sample.log.gz

Starting state	Command	Files after successful decompression
Only sample.log.gz exists	gunzip sample.log.gz	sample.log
Only sample.log.gz exists	gzip -d sample.log.gz	sample.log
Only sample.log.gz exists	gzip -dk sample.log.gz	sample.log and sample.log.gz

The practice directory above already contains sample.log, so try gzip -dk in a separate folder that holds only the .gz file.

Compress multiple files or a directory: gzip -r vs tar

A student working in Lubuntu described the problem in r/linuxquestions: “I then opened the terminal and used gzip -r to compress the directory but instead it compressed every file inside the directory, no the directory itself.”

gzip -r does exactly that. It goes through a directory tree and compresses each eligible file on its own. Take this directory:

reports/
  jan.log
  feb.log

Run:

gzip -r reports/

The result is two separately compressed files:

reports/
  jan.log.gz
  feb.log.gz

Create one compressed archive with tar

Starting from a separate original copy of reports/ with the two uncompressed logs, use GNU tar:

tar -czf reports.tar.gz reports/

-c creates the archive, -z applies gzip compression, and -f sets the output filename.

tar packs a directory into one transferable file and leaves the original directory in place. A submission that requires ZIP needs a real ZIP archive, because .tar.gz is a different format.

View and search compressed text without extracting it

zgrep 'ERROR' app.log.gz prints matching lines from a compressed log, and no restored copy lands on disk. zless app.log.gz opens the contents for browsing. zcat app.log.gz sends the full decompressed text to standard output. Don't send a very large or binary file through zcat to the terminal, because the output becomes unwieldy or unreadable.

Choose a compression level or write to standard output

gzip has compression levels that trade effort against output size.

• -1: Faster compression.
• -6: The documented default.
• -9: More effort for a smaller result.

Data that is already compressed gains little.

To compare levels, run two of them on a representative, noncritical file and write to separate output names:

gzip -1 -c sample.log > speed.gz
gzip -9 -c sample.log > size.gz

sample.log stays in place. Compare the two output sizes.

Send compressed data to a new output filename

-c writes the output to standard output (stdout), and shell redirection puts it in a file:

gzip -c sample.log > stream-copy.gz

This creates stream-copy.gz and keeps sample.log.

Decompress to stdout like this:

gzip -dc sample.log.gz > restored.log

-d selects decompression, -c sends the result to stdout, and the shell writes it to restored.log.

Test a .gz file and check the restored data

gzip -t tests the internal consistency of a compressed stream and writes no output file.

gzip -t sample.log.gz

A damaged stream triggers an error and a nonzero exit status.

What the gzip integrity check means

The gzip format stores a CRC32 value calculated from the uncompressed data and an ISIZE field with the uncompressed length modulo 2³². RFC 1952 defines both.

CRC32 detects errors. A valid gzip stream doesn't prove who produced it.

Compare recovered bytes with a trusted original

If you still have the original sample.log from the disposable exercise, compare it with the decompressed stream:

gzip -dc sample.log.gz | cmp - sample.log

cmp reads its first input from standard input when you pass -. A matching result means the bytes it received are identical to those in sample.log. A pipeline reports only the final command's status, so it can hide a gzip error unless pipefail is enabled. Run gzip -t sample.log.gz first, and count the data as verified only when both the test and the comparison succeed.

gzip -l lists information about compressed files. Its uncompressed size is unreliable for very large inputs and concatenated gzip members, so don't treat it as a byte-accurate measurement.

Troubleshoot gzip errors without making the problem worse

Symptom	Possible cause	First safe diagnostic
not in gzip format	Wrong file type, misleading extension, or a stream already decompressed	Run file on the input, and in a pipeline check which earlier step already decompressed it
Destination already exists	The output name matches an existing file	Keep the existing file and check what it contains
Corrupt or truncated gzip data	The compressed stream failed its integrity check	Run gzip -t on the file
Permission or storage error	The output location isn't writable or is out of space	Check write permission and free space on the output folder
Failure after a decompression pipeline	An earlier step already removed the gzip layer	Find which program in the pipeline did the decompression
Empty redirected output	The command didn't send the intended data to stdout	Check the -c and -d options

When a pipeline decompresses gzip twice

“How is the gzipped archive not in gzip format?” a reader asked in r/linuxquestions while troubleshooting a decompression pipeline.

In that pipeline, gunzip -c had already removed the gzip layer before tar tried to decompress the stream again. Once the first step produces a tar stream, a second gzip step fails on it.

If you have a real gzip-compressed tar archive as a regular file, GNU tar handles the compression itself. Extract into a new directory so existing reports/ files stay untouched:

mkdir restored-test && tar -xf reports.tar.gz -C restored-test

tar detects the compression, decompresses it, and puts the reports/ tree inside restored-test/.

When the restored filename already exists

Say sample.log.gz should decompress to sample.log, but a file with that name already exists. Keep the existing file until you know whether it holds data you still need.

Don't use -f to force past an unexplained collision, because it changes overwrite behavior. A truncated download needs another copy. Don't change permissions or delete unrelated files at random to get past a permission or space error.