SSH allows secure (encrypted and authenticated) connections between two hosts. These connections include terminal sessions, file transfers, TCP port forwarding, as well as X window forwarding which I will be covering here. X forwarding is a form of tunneling that allows you to run a GUI application on a remote machine but let you view and interact with it on your local machine.

To try this out you will need both X and SSH installed on your local and remote machines. Make sure that you are able to log into the the remote machine over SSH before you continue.

Simple SSH command, ensure that this works before continuing. You may have to enter a password for the user before it will allow you access.

$ ssh user@remotehost

The next step is to add the ‘-X‘ option. This will turn on X forwarding and allow you to remotely run X programs. In this case we will run xclock.

$ ssh -X user@remotehost xclock

You should see the xclock window appear on your screen. You can interact with it like any other local application window. Close it when you are done.

If you have a slower connection you can turn on compression by adding the ‘-C‘ option to the command above. This will compress all data communications with the gzip algorithm.

$ ssh -C -X user@remotehost xclock

If you are experiencing any problems turn on verbose output with the ‘-v‘ option. This will give you a lot more output and tell you what is going on underneath.

$ ssh -v -X user@remotehost xclock

If you are still having issues look in the ssh configuration file here/etc/ssh/ssh_config, and make sure that you don’t have X forwarding settings disabled.

Related posts

1. Securely copy remote files with scp
2. Share a remote filesystem over SSH
3. How to SSH into Ubuntu LiveCD

TAR is the GNU Tape ARchive utility. It is used to pack the contents of multiple files or directories in an archive file called a tarball. Tar can preserve directory organization including file ownership, permissions, links, as well as directory structure. To save space you can optionally enable compression with gzip, bzip2, or another external program.

For these examples I’m going to be using this sample directory which contains a few files.

/mydir
/mydir/script.sh
/mydir/picture.jpg
/mydir/document.txt

Lets create a tarball from this directory. Run the following command.

$ tar -cvf mydir.tar mydir

Lets go over these options.

-c create tarball
-v verbose
-f output file

To extract this tarball.

$ tar -xvf mydir.tar

The new option ‘-x‘ instructs tar to extract the archive.

Add compression with gzip when creating the archive by including the -z option.

$ tar -cvzf mydir.tgz mydir

Extracting the archive is similar. Make sure to include the gzip option as well.

$ tar -xvzf mydir.tgz

You can also use the bzip2 utility to compress the archive, use the -j option.

$ tar -cvjf mydir.tbz mydir

And extract it.

$ tar -xvjf mydir.tbz

To preserve permissions use ‘-p‘ when creating as well as extracting.

$ tar -cvzpf mydir.tgz mydir

$ tar -xvzpf mydir.tgz

You may have noticed the file extensions used on the archives are different. Here is a quick rundown on the naming conventions. Understanding the extensions allows you to quickly figure out how to extract it.

*.tar (uncompressed tar archive)
*.tgz or *.tar.gz (gzip compressed tar archive)
*.tbz or *.tar.bz2 (bzip2 compressed tar archive)

You want to avoid including files in the current working directory when creating a tarball. When extracted these files will be dumped into the user’s current working directory instead of its own subdirectory, potentially overwriting files and creating a big mess.

Another helpful option to use is ‘-C ‘. This will extract a tarball in a specific directory.

$ tar -xvzf mydir.tgz -C /tmp/testdir

A good way to check for any problems with extraction or to see exactly a tarball contains is to execute tar with the -t option. This will list the contents of a tarball and show the location they will be extracted.

$ tar -tf mydir.tgz

mydir/
mydir/script.sh
mydir/picture.jpg
mydir/document.txt

This will also help you avoid situations where a tarball might use an absolute path (path starting at root ‘/’) when extracting instead of a relative path (path that is relative to your current directory) like the previous examples. This is not necessarily a bad thing, but it can be dangerous if you don’t realize this before extracting, since an absolute path can install to anywhere on your system.

Related posts

1. Determine file type with the file command
2. Securely copy remote files with scp
3. Extract the contents of an RPM package