Using “tar” on RHEL 8

Using “tar” on RHEL 8 shows how to use the “tar” command to perform backups and archives, with or without compression, and provides a lot of examples of usage. All the practical examples are shown using Red Hat Enterprise Linux; however, they work on any Linux flavor.

First and foremost: What is “tar”?

The command “tar” stands for “tape archive”.
Originally used to back up data to tapes, but now commonly used for:

• Bundling many files/directories into a single archive file.
• Often combined with compression (gzip, bzip2, xz) to reduce size.

A “.tar” file is just an archive, with no compression by default.
A “.tar.gz” or “tgz” is a tar archive compressed with gzip.
A “.tar.bz2”, “tbz”, or “tbz2” is a tar archive compressed with bzip2.

Basic Command Structure and Common Options

The “tar” basic command structure is:

tar [options] [archive-file] [files...]

Where:
[options] tell tar what to do (create, extract, list, etc.).
[archive-file] is the .tar or .tar.gz file – is the name of the tar file.
[files...] are the files or directories you want to archive/extract.

The “tar” common options are:

Option	Meaning
c	Create an archive
x	Extract from an archive
t	List archive contents
f	File name is given next
v	Verbose — show files being processed
z	Use gzip compression/decompression
j	Use bzip2 compression/decompression
J	Use xz compression/decompression
C dir	Change to directory before processing
r	Append directories or files to an existing archive

Creating Archives

To create archives without compression. For example:

tar -cf /tmp/backup-etc.tar -C /etc .

Where:
– c = Create a new tar file
– f /tmp/backup = Output file name
-C /etc = Change to directory /etc before processing
. = Considering all contents inside the current directory

To create archives with GZIP compression:

tar -czf /tmp/backup-etc.tar.gz -C /etc .

Where:
-z = GZIP compression
.tar.gz = is the common extension when using GZIP compression

To create archives with BZIP2 compression:

tar -cjf /tmp/backup-etc.tar.bz2 -C /etc .

Where:
-j = BZIP2 compression
.tar.bz2 = is the common extension when using BZIP2 compression

Note: Just a curiosity, based on our simple test, the BZIP compression is more space-saving than GZIP compression:

Tar file + GZIP to the entire /etc = 8.4 MB:

Tar file + BZIP2 to the entire /etc = 6.6 MB:

Listing Contents on Archive Files

The “tar” option to list contents into a file “.tar” is “-t”:
If you have a “tar” archive file and want to list its content:

# Listing content of the ".tar" file:
tar -tf backup-etc.tar

# Listing content of the "tar.gz" file:
tar -tzf backup-etc.tar.gz

# Listing content of the "tar.bz2" file:
tar -tjf backup-etc.tar.bz2

If you need to see additional details such as permissions, user owner, group owner, etc, you can use the verbose option (-v). For example:

tar -tvf backup-etc.tar

tar -tvzf backup-etc.tar.gz

tar -tvjf backup-etc.tar.bz2

Extracting Archives

The “tar” option to extract the content of a “.tar” file is “-x”:

tar -xf /tmp/backup-etc.tar

To extract a “.tar” file to a specific directory:

tar -xf /tmp/backup-etc.tar -C /tmp/extracted

To extract a “tar.gz” file (compressed with GZIP):

tar -xzf /tmp/backup-etc.tar.gz -C /tmp/extracted

To extract a “tar.bz2” file (compressed with BZIP2):

tar -xjf /tmp/backup-etc.tar.bz2 -C /tmp/extracted

Quick Reference Table

Action	gzip (.tar.gz)	bzip2 (.tar.bz2)
Create	tar -czf file.tar.gz files...	tar -cjf file.tar.bz2 files...
List	tar -tzf file.tar.gz	tar -tjf file.tar.bz2
Extract	tar -xzf file.tar.gz	tar -xjf file.tar.bz2

Practical Examples

1- Back up the /etc directory into a compressed archive. Do it twice using GZIP and BZIP2. Save the archive file in the /tmp directory:

# Compressing using GZIP:
tar -czvf /tmp/backup-etc.tar.gz -C /etc .

# Compressing using BZIP2:
tar -cjvf /tmp/backup-etc.tar.bz2 -C /etc .

2- Extract a single file:

Extract the file “passwd” from the GZIP file /tmp/backup-etc.tar.gz:

tar -tzf backup-etc.tar.gz | grep -i passwd
tar -xzf backup-etc.tar.gz ./passwd

Extract the file “hosts” from the BZIP2 file /tmp/backup-etc.tar.bz2:

tar -tjf backup-etc.tar.bz2 | grep -i hosts
tar -xjf backup-etc.tar.bz2 ./hosts

3- Add files (append) into existing “tar” files:

• We can append files to uncompressed “.tar” files directly.
• We cannot append directly to compressed archives (.tar.gz or .tar.bz2) – we must decompress them first, append, and then recompress.

Note: tar archives store files sequentially, but once they’re compressed, the data is in a single continuous compressed stream.
Appending directly would corrupt that stream, so you must decompress, modify, and recompress.

3.1- Append to an uncompressed “.tar”.
Add/append the file “added-tar.txt” to the archive “backup-etc.tar”:

tar -rf backup-etc.tar added-tar.txt

# to confirm if the file was added:
tar -tf backup-etc.tar | grep -i added-tar.txt

3.2- Append the file “added-gzip.txt” to the archive “backup-etc.tar.gz”:

# Decompress:
gunzip backup-etc.tar.gz

# Append the file:
tar -rf backup-etc.tar added-gzip.txt

# Recompress:
gzip backup-etc.tar

# To confirm if the file was added/appended:
tar -tzf backup-etc.tar.gz | grep -i added-gzip.txt

3.3- Append the file “added-bzip2.txt” to the archive “backup-etc.tar.bz2”:

# Decompress:
bunzip2 backup-etc.tar.bz2

# Append:
tar -rf backup-etc.tar added-bzip2.txt

# Recompress:
bzip2 backup-etc.tar

# Confirm:
tar -tf backup-etc.tar.bz2 | grep -i added-bzip2.txt

That’s it for now 🙂