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NOTE: CentOS Enterprise Linux 5 is built from the Red Hat Enterprise Linux source code. Other than logo and name changes CentOS Enterprise Linux 5 is compatible with the equivalent Red Hat version. This document applies equally to both Red Hat and CentOS Enterprise Linux 5.

17.6. Configuring an OpenSSH Client

To connect to an OpenSSH server from a client machine, you must have the openssh-clients and openssh packages installed on the client machine.

17.6.1. Using the ssh Command

The ssh command is a secure replacement for the rlogin, rsh, and telnet commands. It allows you to log in to a remote machine as well as execute commands on a remote machine.

Logging in to a remote machine with ssh is similar to using telnet. To log in to a remote machine named penguin.example.net, type the following command at a shell prompt:

ssh penguin.example.net

The first time you ssh to a remote machine, you will see a message similar to the following:

The authenticity of host 'penguin.example.net' can't be established.
DSA key fingerprint is 94:68:3a:3a:bc:f3:9a:9b:01:5d:b3:07:38:e2:11:0c.
Are you sure you want to continue connecting (yes/no)?

Type yes to continue. This will add the server to your list of known hosts (~/.ssh/known_hosts) as seen in the following message:

Warning: Permanently added 'penguin.example.net' (RSA) to the list of known hosts.

Next, you will see a prompt asking for your password for the remote machine. After entering your password, you will be at a shell prompt for the remote machine. If you do not specify a username the username that you are logged in as on the local client machine is passed to the remote machine. If you want to specify a different username, use the following command:

ssh username@penguin.example.net

You can also use the syntax ssh -l username penguin.example.net.

The ssh command can be used to execute a command on the remote machine without logging in to a shell prompt. The syntax is ssh hostname command. For example, if you want to execute the command ls /usr/share/doc on the remote machine penguin.example.net, type the following command at a shell prompt:

ssh penguin.example.net ls /usr/share/doc

After you enter the correct password, the contents of the remote directory /usr/share/doc will be displayed, and you will return to your local shell prompt.

17.6.2. Using the scp Command

The scp command can be used to transfer files between machines over a secure, encrypted connection. It is similar to rcp.

The general syntax to transfer a local file to a remote system is as follows:

scp <localfile> [email protected]:<remotefile>

The <localfile> specifies the source including path to the file, such as /var/log/maillog. The <remotefile> specifies the destination, which can be a new filename such as /tmp/hostname-maillog. For the remote system, if you do not have a preceding /, the path will be relative to the home directory of username, typically /home/username/.

To transfer the local file shadowman to the home directory of your account on penguin.example.net, type the following at a shell prompt (replace username with your username):

scp shadowman username@penguin.example.net:shadowman

This will transfer the local file shadowman to /home/username/shadowman on penguin.example.net. Alternately, you can leave off the final shadowman in the scp command.

The general syntax to transfer a remote file to the local system is as follows:

scp [email protected]:<remotefile> <newlocalfile>

The <remotefile> specifies the source including path, and <newlocalfile> specifies the destination including path.

Multiple files can be specified as the source files. For example, to transfer the contents of the directory downloads/ to an existing directory called uploads/ on the remote machine penguin.example.net, type the following at a shell prompt:

scp downloads/* username@penguin.example.net:uploads/

17.6.3. Using the sftp Command

The sftp utility can be used to open a secure, interactive FTP session. It is similar to ftp except that it uses a secure, encrypted connection. The general syntax is sftp [email protected]. Once authenticated, you can use a set of commands similar to those used by FTP. Refer to the sftp man page for a list of these commands. To read the man page, execute the command man sftp at a shell prompt. The sftp utility is only available in OpenSSH version 2.5.0p1 and higher.


 
 
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