Taming the tar command: Tips for managing backups in Linux

Ever try something, it didn’t work, and you didn’t make a backup first?

One of the key rules for working as a system administrator is always to make a backup. You never know when you might need it. In my personal experience, it has saved me more times than I can count. It’s a common practice to complete and sometimes makes a difference in your finished work.

The tar utility has a ton of options and available usage. Tar stands for tape archive and allows you to create backups using: tar, gzip, and bzip. It compresses files and directories into an archive file, known as a tarball. This command is one of the most widely-used commands for this purpose. Also, the tarball is easily movable from one server to the next.

How to create a tar backup

In this example, we create a backup called backup.tar of the directory /home/user.

# tar -cvf backup.tar /home/user

Let’s break down these options:

-c - Create the archive
-v - Show the process verbosely
-f - Name the archive

How to create a tar.gz backup

In this example, we create a gzip archive backup called backup.tar.gz of the directory /home/user.

# tar -cvzf backup.tar.gz /home/user

Let’s break down these options:

-c - Create the archive
-v - Show the process verbosely
-f - Name the archive
-z - Compressed gzip archive file

How to exclude files when creating a tar backup

In this example, we create a gzip backup called backup.tar.gz, but exclude the files named file.txt and file.sh by using the --exclude [filename] option.

# tar --exclude file.txt --exclude file.sh -cvzf backup.tar.gz

How to extract content from a tar (.gz) backup

In this example, we extract content from a gzip backup backup.tar.gz, specifically a file called file.txt from the directory /backup/directory in the gzip file.

# tar -xvzf backup.tar.gz /backup/directory/file.txt

Let’s break down these options:

-x - Extract the content
-v - Show the process verbosely
-f - Name the archive
-z - compressed gzip archive file

How to list contents of a tar(.gz) backup

In this example, we list the contents from a gzip backup backup.tar.gz without extracting it.

# tar -ztvf backup.tar.gz

Let’s break down these options:

-t - List the contents
-v - Show the process verbosely
-f - Name the archive
-z - compressed gzip archive file

How to use the wildcard option

In this example, we use the wildcard option on a backup backup.tar. Wildcards allow you to select files without having a specific search for keywords. This is helpful in situations where you are trying to locate something but do not want to specify the name or want to add in all options matching that particular search.

# tar -cf backup.tar “*.xml”

Let’s break down these options:

-c - Create the backup
-f - Name the archive

How to append or add files to a backup

In this example, we add onto a backup backup.tar. This allows you to add additional files to the pre-existing backup backup.tar.

# tar -rvf backup.tar /path/to/file.xml

Let’s break down these options:

-r - Append to archive
-v - Verbose output
-f - Name the file

How to split a backup into smaller backups

In this example, we split the existing backup into smaller archived files. You can pipe the tar command into the split command.

# tar cvf - /dir | split --bytes=200MB - backup.tar

Let’s break down these options:

-c - Create the archive
-v - Verbose output
-f - Name the file

In this example, the dir/ is the directory that you want to split the backup content from. We are making 200MB backups from the /dir folder.

How to check the integrity of a tar.gz backup

In this example, we check the integrity of an existing tar archive.

To test the gzip file is not corrupt:

#gunzip -t backup.tar.gz

To test the tar file content's integrity:

#gunzip -c backup.tar.gz | tar t > /dev/null

OR

#tar -tvWF backup.tar

Let’s break down these options:

-W - Verify an archive file
-t - List files of archived file
-v - Verbose output

Use pipes and greps to locate content

In this example, we use pipes and greps to locate content. The best option is already made for you. Zgrep can be utilized for gzip archives.

#zgrep <keyword> backup.tar.gz

You can also use the zcat command. This shows the content of the archive, then pipes that output to a grep.

#zcat backup.tar.gz | grep <keyword>

Egrep is a great one to use just for regular file types.

Wrap up

Tar has a lot of things you can do with it. It allows you to create the archive and manage it easily with the available tools in your terminal. If tar is not installed, you can do so depending on your operating system. Tar is useful in several different cases. As a system administrator, I created plenty of backups and recovered from some of them, too. It’s always safer to make a backup of a file or directory before making changes, in case you need to revert to the original setup. Having that security is something we all need.

[ Good backups are an important part of any security and disaster recovery plan. Want to learn more? Check out the IT security and compliance checklist. ]

Edited 3/24/23 to correct a code typo.