Securing Remote Access and Copy with SSH and SCP

A Brief Pep talk: Continuing the preparation

In part 9, we covered several topics such as Swap Space, Memory, Semaphores, File handles and Hangcheck-timer. A good thing about being familiar with all the components that make Oracle RAC work is that you, as a DBA, become more interested in the technologies involved in it, and that makes learning a fun thing.

Let’s get on to installing the rest of it. We will pick up from where we left in the last article.

  • Remote access checks (both rsh,rcp – not recommended and ssh,scp – recommended)

Remote Access : Secure (SSH &SCP) and Non-Secure (RSH & RCP)

There are two ways of doing things–the secure way and the non-secure way. Since version 10g R1, Oracle has included support for SSH and thus instead of using rsh and rcp, you can use ssh and scp; “s” as you guessed stands for secure. The rsh and rcp commands are not required for RAC but for installation and patchset installation to copy files across nodes.

Installation of SSH must be done before you begin Oracle installation.

SSH and SCP way

Ok let’s see how we can install the SSH suite. If you saw my article about the NXMachine then you can guess about the public and private key mechanism. Now SSH (secure shell) must be configured for oracle user on all cluster nodes. OUI uses ssh and scp commands during installation to run (secure) remote commands and (securely) copy files to the other cluster nodes.

Is SSH running on my server? (These are generally disabled by default). Oracle uses OpenSSH version 3 (There is already version 4.3 as of this writing). Now if ssh and scp are not available, it defaults to rsh and rcp. Do configure SSH in such a way that these commands do not prompt for a password.

Do I have my SSH installed?

Do this when logged on as “oracle” userm

$ pgrep sshd
[[email protected] ~]# pgrep sshd

In addition, for the manual do “man sshd” to get enough on that information on SSHD.

Having checked that, we go ahead using ssh-keygen creating both RSA and DSA keys. What does the ssh-keygen do? According to the manual:

ssh-keygen generates, manages and converts authentication keys for ssh(1). ssh-keygen can create RSA keys for use by SSH protocol version 1 and RSA or DSA keys for use by SSH protocol version 2. The type of key to be generated is specified with the -t option. If invoked without any arguments, ssh-keygen will generate an RSA key for use in SSH protocol 2 connections. ssh-keygen is also used to generate groups for use in Diffie-Hellman group exchange (DH-GEX).

Creating RSA and DSA keys on each node:

1.  You should be logged as the “oracle user.

2.  Create an .ssh directory in the oracle user’s home (directory) with appropriate permissions:

$ mkdir ~/.ssh
$ chmod 700 ~/.ssh

3.  Enter the following commands to generate an RSA key for version 2 of the SSH protocol:

/usr/bin/ssh-keygen -t rsa

Accept the default locations for key file, enter passphrase twice and you are done. This command writes the public key to the ~/.ssh/ file and the private key to the ~/.ssh/id_rsa file.

4.  To generate a DSA key for version 2 of the SSH protocol, do the following:

5. Carry out similar activities, like accepting defaults
and your unique password.

Never distribute the private key to anyone! (If you deal with security, you know this is the best way to get all wet and naked for a hacker!)

~Edit the authorized_keys on every node. For instance, if you have 4 nodes your authorized_keys file (located in /.ssh/ ) will have eight entries. If you do not have “authorized_keys”, doing this will create it:

$ touch ~/.ssh/authorized_keys
$ cd ~/.ssh
$ ls
[[email protected] .ssh]# ls
authorized_keys id_dsa id_rsa

~Do a cat for local and remote keys :

ssh nick01rh4  cat /home/oracle/.ssh/ >> authorized_keys
ssh nick01rh4 cat /home/oracle/.ssh/ >> authorized_keys
ssh nick02rh4 cat /home/oracle/.ssh/ >> authorized_keys
ssh nick02rh4 cat /home/oracle/.ssh/ >> authorized_keys
ssh brian03rh4 cat /home/oracle/.ssh/ >> authorized_keys
ssh brian03rh4 cat /home/oracle/.ssh/ >> authorized_keys
ssh brian04rh4 cat /home/oracle/.ssh/ >> authorized_keys
ssh brian04rh4 cat /home/oracle/.ssh/ >> authorized_keys

~Do a word count per node, they all must have 8 lines:

wc –l authorized_keys
8 authorized_keys

~Copy the keys across nodes using scp protocol:

scp authorized_keys nick02rh4:/home/oracle/.ssh/
scp authorized_keys brian01rh4:/home/oracle/.ssh/
scp authorized_keys brian02rh4:/home/oracle/.ssh/

This should go seamlessly, without issuing passwords. You will be prompted to edit your oracle user password if you didn’t do the cat.  If you did the cat for local and remote keys, you get to enter the passphrase once. The moment the nodes establish the SSH protocol, they know of each other’s private keys that unlock the public keys (so to speak):

~Setting up Oracle user equivalence: (I forgot the dsa passphrase for a while).

~ Testing your Oracle user equivalence by doing this on all nodes:

nick01rh4 date
ssh nick02rh4 date
ssh brian03rh4 date
ssh brian04rh4 date

This should now go seamlessly.

In order to ensure that X11 forwarding will not hinder the installation process , create a user-level SSH client configuration file for the Oracle software owner user, as follows: Using gedit for instance, edit or create the ~oracle/.ssh/config file. Make sure that the ForwardX11 attribute is set to no. For instance:

a. Host *
b. ForwardX11 no

Remember that OUI must run from this same session or remember to repeat the steps when running OUI from another terminal.

$ exec /usr/bin/ssh-agent $SHELL
$ /usr/bin/ssh-add

RSH and RCP method

To learn more about RSH and RCP see this. It is important to note is that both SSH and RSH build trust among nodes using host equivalency.

~Check for the binaries:

[[email protected] ~]# rpm -q rsh rsh-server

~If not ,install them (or yum it):

su –
#rpm –ivh rsh*

~Edit the “disable” attribute in the /etc/xinetd.d/rsh file to set it to “no” and xinetd must be reloaded. Do this on ALL NODES:

#chkconfig rsh on
#chkconfig rlogin on
#service xinted reload

~Create hosts equiv files on all nodes for host equivalency (in order to establish trust among the nodes) as /etc/hosts.equiv file on all cluster nodes by doing:

#su –
#touch /etc/hosts.equiv
#chmod 600 /etc/hosts.equiv
#chown root:root /etc/hosts.equiv

Edit the file:

# cat /etc/hosts.equiv
+nick01rh4 oracle
+nick02rh4 oracle
+brian01rh4 oracle
+brian02rh4 oracle
+nick01rh4-priv oracle
+nick02rh4-priv oracle
+brian01rh4-priv oracle
+brian02rh4-priv oracle

Do I have the correct version of RSH?

We do not want Kerberos rsh so we do the following:

~Run the following command from the node from where you will be doing the installation:

su – oracle
$ rsh nick01rh4 ls -l /etc/hosts.equiv
$ rsh nick01rh4-priv ls -l /etc/hosts.equiv
$ rsh nick02rh4 ls -l /etc/hosts.equiv
$ rsh nick02rh4-priv ls -l /etc/hosts.equiv
$ rsh brian01rh4 ls -l /etc/hosts.equiv
$ rsh brian01rh4-priv ls -l /etc/hosts.equiv
$ rsh brian02rh4 ls -l /etc/hosts.equiv
$ rsh brian02rh4-priv ls -l /etc/hosts.equiv


Well you can never say enough about security and get away with it. Securing your Oracle database is like securing your house. You would not want anything to go wrong with it. The private and public keys infrastructure helps us secure our traffic. OpenSSH is a major player and almost every big application has it running. Amazingly enough, it is open source (meaning free)! In our next article, we will continue with our preparations. I will write more on OpenSSH and Oracle on my Oracle Blog.

» See All Articles by Columnist Tarry Singh

Tarry Singh
Tarry Singh
I have been active in several industries since 1991. While working in the maritime industry I have worked for several Fortune 500 firms such as NYK, A.P. Møller-Mærsk Group. I made a career switch, emigrated, learned a new language and moved into the IT industry starting 2000. Since then I have been a Sr. DBA, (Technical) Project Manager, Sr. Consultant, Infrastructure Specialist (Clustering, Load Balancing, Networks, Databases) and (currently) Virtualization/Cloud Computing Expert and Global Sourcing in the IT industry. My deep understanding of multi-cultural issues (having worked across the globe) and international exposure has not only helped me successfully relaunch my career in a new industry but also helped me stay successful in what I do. I believe in "worknets" and "collective or swarm intelligence". As a trainer (technical as well as non-technical) I have trained staff both on national and international level. I am very devoted, perspicacious and hard working.

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