Managing Compressed Tar Archives
tar command _File archiving and compression is useful when backing up and transferring data over a network. One of the oldest and most common commands for creatng and working with backup archives is the tar command.
The tar command can list the contents
of archives or extract their files to the current system.
Listing Options of the tar Command
The tar command expects one of the three following options:
Use the -c or --create option to create an archive.
Use the -t or --list option to list the contents of an archive.
Use the -x or --extract option to extract an archive.
Other commonly used options are:
Use the -f or --file= option with a file name as an argument of the archive to operate.
Use the -v or --verbose option for verbosity; useful to see which files get added to or extracted from the archive
Archiving Files and Directories
The following command creates an archive named archive.tar with the contents of file1, file2, and file3 in the user's home directory.
[user@host ~]$ tar -cf archive.tar file1 file2 file3
[user@host ~]$ ls archive.tar
archive.tar
The above tar command can also be executed using the long version options.
[user@host ~]$ tar --file=archive.tar --create file1 file2 file3
To create the tar archive named, /root/etc.tar, with the /etc directory as content as user root:
[root@host ~]# tar -cf /root/etc.tar /etc
tar: Removing leading `/' from member names
[root@host ~]#
Listing Contents of an Archive
The t option directs tar to list the contents (table of contents, hence t) of the archive. Use the f option with the name of the archive to be queried. For example:
[root@host ~]# tar -tf /root/etc.tar
etc/
etc/fstab
etc/crypttab
etc/mtab
...output omitted.
Extracting Files from an Archive
To restore files from the /root/etc.tar archive to the /root/etcbackup directory, run:
[root@host ~]# mkdir /root/etcbackup
[root@host ~]# cd /root/etcbackup
[root@host etcbackup]# tar -tf /root/etc.tar
etc/
etc/fstab
etc/crypttab
etc/mtab
...output omitted...
[root@host etcbackup]# tar -xf /root/etc.tar
In this example, an archive named, /root/myscripts.tar, is extracted in the /root/scripts directory while preserving the permissions of the extracted files:
[root@host ~]# mkdir /root/scripts
[root@host ~]# cd /root/scripts
[root@host scripts]# tar -xpf /root/myscripts.tar
Creating a Compressed Archive
Use one of the following options to create a compressed tar archive:
-z or --gzip for gzip compression (filename.tar.gz or filename.tgz)
-j or --bzip2 for bzip2 compression (filename.tar.bz2)
-J or -xz for xz compression (filename.tar.xz)
To create a gzip compressed archive named /root/etcbackup.tar.gz, with the contents from the /etc directory on host:
[root@host ~]# tar -czf /root/etcbackup.tar.gz /etc
tar: Removing leading `/' from member names
To create a bzip2 compressed archive named /root/logbackup.tar.bz2, with the contents from the /var/log directory on host:
[root@host ~]$ tar -cjf /root/logbackup.tar.bz2 /var/log
tar: Removing leading `/' from member names
To create a xz compressed archive named, /root/sshconfig.tar.xz, with the contents from the /etc/ssh directory on host:
[root@host ~]$ tar -cJf /root/sshconfig.tar.xz /etc/ssh
tar: Removing leading `/' from member names
After creating an archive, verify the content of an archive using the tf options. It is not mandatory to use the option for compression agent when listing the content of a compressed archive file. For example, to list the content archived in the /root/etcbackup.tar.gz file, which uses the gzip compression, use the following command:
[root@host ~]# tar -tf /root/etcbackup.tar.gz /etc
etc/
etc/fstab
etc/crypttab
etc/mtab
...output omitted...
Extracting a Compressed Archive
To extract the contents of a gzip compressed archive named /root/etcbackup.tar.gz in the /tmp/etcbackup directory:
[root@host ~]# mkdir /tmp/etcbackup
[root@host ~]# cd /tmp/etcbackup
[root@host etcbackup]# tar -tf /root/etcbackup.tar.gz
etc/
etc/fstab
etc/crypttab
etc/mtab
...output omitted...
[root@host etcbackup]# tar -xzf /root/etcbackup.tar.gz
To extract the contents of a bzip2 compressed archive named /root/logbackup.tar.bz2 in the /tmp/logbackup directory:
[root@host ~]# mkdir /tmp/logbackup
[root@host ~]# cd /tmp/logbackup
[root@host logbackup]# tar -tf /root/logbackup.tar.bz2
var/log/
var/log/lastlog
var/log/README
var/log/private/
var/log/wtmp
var/log/btmp
...output omitted...
[root@host logbackup]# tar -xjf /root/logbackup.tar.bz2
To extract the contents of a xz compressed archive named /root/sshbackup.tar.xz in the /tmp/sshbackup directory:
[root@host ~]$ mkdir /tmp/sshbackup
[root@host ~]# cd /tmp/sshbackup
[root@host logbackup]# tar -tf /root/sshbackup.tar.xz
etc/ssh/
etc/ssh/moduli
etc/ssh/ssh_config
etc/ssh/ssh_config.d/
etc/ssh/ssh_config.d/05-redhat.conf
etc/ssh/sshd_config
...output omitted...
[root@host sshbackup]# tar -xJf /root/sshbackup.tar.xz
Listing a compressed tar archive works in the same way as listing an uncompressed tar archive.
Transferring Files Between Systems Securely
Transferring Files Using Secure Copy
The following example demonstrates how to copy the local /etc/yum.conf and /etc/hosts files on host, to the remoteuser's home directory on the remotehost remote system:
[user@host ~]$ scp /etc/yum.conf /etc/hosts remoteuser@remotehost:/home/remoteuser remoteuser@remotehost's password: password yum.conf 100% 813 0.8KB/s 00:00 hosts 100% 227 0.2KB/s 00:00
You can also copy a file in the other direction, from a remote system to the local file system. In this example, the file /etc/hostname on remotehost is copyed to the local directory /home/user. The scp command authenticates to remotehost as the user remoteuser.
[user@host ~]$ scp remoteuser@remotehost:/etc/hostname /home/user remoteuser@remotehost's password: password hostname 100% 22 0.0KB/s 00:00
To copy a whole directory tree recursively, use the -r option. In the following example, the remote directory /var/log on remotehost is copied recursively to the local directory /tmp/ on host. You must connect to the remote system as root to make sure you can read all files in the remote /var/log directory.
[user@host ~]$ scp -r root@remoteuser:/var/log /tmp root@remotehost's password: password...output omitted...
Transferring Files Using the Secure File Transfer Program
Just like the scp command, the sftp command uses [user@]host to identify the target system and user name. If you do not specify a user, the command will attempt to log in using your local user name as the remote user name. You will then be presented with an sftp> prompt.
[user@host ~]$ sftp remoteuser@remotehost remoteuser@remotehost's password: password Connected to remotehost. sftp>
To upload the /etc/hosts file on the local system to the newly created directory /home/remoteuser/hostbackup on remotehost. The sftp session always assumes that the put command is followed by a file on the local file system and starts in the connecting user's home directory; in this case, /home/remoteuser:
sftp> mkdir hostbackup sftp> cd hostbackup sftp> put /etc/hosts Uploading /etc/hosts to /home/remoteuser/hostbackup/hosts /etc/hosts 100% 227 0.2KB/s 00:00 sftp>
To download /etc/yum.conf from the remote host to the current directory on the local system, execute the command get /etc/yum.conf and exit the sftp session with the exit command.
sftp> get /etc/yum.conf Fetching /etc/yum.conf to yum.conf /etc/yum.conf 100% 813 0.8KB/s 00:00 sftp> exit [user@host ~]$
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