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Distributed Systems Administration Utilities User's Guide > Chapter 4 Command Fanout

Security Configuration


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The command fanout tools support both remote shell (rsh or rcmd) and ssh transports. Each requires specific security setup steps in order to authorize the user initiating the command fanout operation to execute a command on the remote target systems. The command fanout tools require that the remote system not prompt for a password. Both rsh and ssh transports must be preconfigured on each remote system to allow non-interactive access. The following sections describe the required setup steps to enable command fanout operations for each transport.

Remote Shell Security Setup

When using the remote shell command transport, the local user must have a $HOME/.rhosts file configured on each remote target system. Refer to the rhosts(4) reference manpage for details on configuring the $HOME/.rhosts file.

ssh Security Setup

ssh uses public host keys to authenticate remote hosts and supports public key authentication to authenticate users. When users’ public keys are properly configured on a set of remote systems, they can access those systems without being prompted for a password. Manually configuring ssh for non-interactive access is a multistep process where ssh configuration files are edited on each system. The csshsetup tool greatly simplifies configuring ssh trust relationships. For example, when using the command fanout tools in a Serviceguard cluster, you typically want to be able to issue commands from any member and target any other member. This requires an n^2 distribution of ssh public keys. Start by creating a text file listing the members the cluster, one per line. Invoke csshsetup using this file. Note that this command needs to be issued only once since it configures each member of the cluster:

# csshsetup -r -f members_list.txt

The -r option instructs csshsetup to distribute the keys in a round-robin or n^2 fashion. The user will be prompted for his password on each remote host. csshsetup then automates the entire public key distribution process.

Note that csshsetup is not specific to Serviceguard clusters; it can be used for arbitrary groups of systems. Also, the trust relationship does not have to be bidirectional. Omit the -r option when setting up a one-way trust relationship between the current host and a set of remote target hosts. For additional details, refer to the csshsetup(1) reference manpage.

Security Notes

The remote shell protocol is an inherently insecure protocol. It is the protocol used by the Berkeley “r commands,rlogin, rcp, remsh, and so on. Many system administrators disable the use of the “r” commands as a matter of policy. For example, the Bastille security hardening tool offers a default option to disable these insecure services. If disabled, the pdsh -R rsh option to use the remote shell transport will not work.

If the “r” services are not disabled, use of the pdsh -R rsh option by unprivileged users is still disabled by default because of the inherent security risk. By default, only users with root privileges can use the pdsh -R rsh option. This is because the remote shell rcmd library call requires the use of a privileged port. Even though privileged users can use -R rsh, the ssh transport is still preferred.

If the hosts and users are trusted in your environment, you can enable the use of the pdsh -R rsh option for unprivileged users with the following commands:

# cd /opt/dsau/bin/pdsh

# chown root:bin pdsh

# chmod u+s pdsh

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