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tsshbatch / tsshbatch.rst
@tundra tundra on 5 Jan 2012 10 KB Formatting and typo cleanup.

NAME

tsshbatch - Run Commands On Batches Of Machines

SYNOPSIS

tsshbatch.py [-ehvk] [-n name] [-p pw] [-H 'h1 h2 ...' | hostlistfile] command arg ...

DESCRIPTION

tsshbatch is a tool to enable you to issue a command to many hosts without having to log into each one separately. When writing scripts, this overcomes the ssh limitation of not being able to specify the password on the command line.

tsshbatch also understands basic sudo syntax and can be used to access a host, sudo a command, and then exit.

tsshbatch thus allows you to write complex, hands-off scripts that issue commands to many hosts without the tedium of manual login and sudo promotion. System administrators, especially, will find this helpful when working in large host farms.

OPTIONS

-H 'hostlist' Single quoted list of hosts on which to run the command

-e Don't report remote host stderr output
-h Print help information
-k Use ssh keys instead of name/password credentials
-n name Login name to use
-p pw Password to use when logging in and/or doing sudo
-v Print detailed program version information and exit

ENVIRONMENT

tsshbatch respects the TSSHBATCH environment variable. You may set this variable with any options above you commonly use to avoid having to key them in each time you run the program. For example:

export TSSHBATCH="-n jluser -p l00n3y"

This would cause all subsequent invocations of tsshbatch to attempt to use the login name/password credentials of jluser and l00n3y respectively.

USE CASES

  1. Different Ways To Specify Targeted Hostnames

    There are two ways to specify the list of hosts on which you want to run the specified command:

    • On the command line via the -H option:

      tsshbatch.py -H 'hostA hostB' uname -a

      This would run the command uname -a on the hosts hostA and hostB respectively.

      Notice that the list of hosts must be separated by spaces but passed as a single argument. Hence we enclose them in single quotes.

    • Via a host list file:

      tsshbatch.py myhosts df -Ph

      Here, tsshbatch expects the file myhosts to contain a list of hosts, one per line, on which to run the command df -Ph. As an example, if you want to target the hosts larry, curly and moe in foo.com, myhosts would look like this:

      larry.foo.com
      curly.foo.com
      moe.foo.com

      This method is handy when there are standard "sets" of hosts on which you regularly work. For instance, you may wish to keep a host file lis for each of your production hosts, each of your test hosts, each of your AIX hosts, and so on.

  2. Authentication Using Name And Password

    The simplest way to use tsshbatch is to just name the hosts can command you want to run:

    tsshbatch.py linux-prod-hosts uptime

    You will be promted for your username and password one time which tsshbatch will then use to log into each of the machines named in linux-prod-hosts. (Notice that his assumes your name and password are the same on each host!)

    Typing in your login credentials all the time can get tedious after awhile so tsshbatch provides a means of providing them on the command line:

    tsshbatch.py -n joe.luser -p my_weak_pw linux-prod-hosts uptime

    This allows you to use tsshbatch inside scripts for hands-free operation.

    If your login name is the same on all hosts, you can simplify this further by defining it in the environment variable:

    export TSSHBATCH="-n joe.luser"

    Any subsequent invocation of tsshbatch will only require a password to run.

    HOWEVER, there is a huge downside to this - your plain text password is exposed in your scripts, on the command line, and possibly your command history. This is a pretty big security hole, especially if you're an administrator with extensive privileges. (This is why the ssh program does not support such an option.) For this reason, it is strongly recommended that you use the -p option sparingly, or not at all. A better way is to push ssh keys to every machine and use key exchange authentication as described below.

    However, there are times when you do have use an explicit password, such as when doing sudo invocations. It would be really nice to use -p and avoid having to constantly type in the password. There are two strategies for doing this more securely than just entering it in plain text on the command line:

    • Temporarily store it in the environment variable:

      export TSSHBATCH="-n joe.luser -p my_weak_pw"

      Do this interactively after you log in, not from a script (otherwise you'd just be storing the plain text password in a different script). The environment variable will persist as long as you're logged in and disappear when you log out.

      If you use this just make sure to observe three security precautions:

      1. Clear your screen immediately after doing this so no one walking by can see the password you just entered.
      2. Configure your shell history system to ignore commands beginning with export TSSHBATCH. That way your plain text password will never appear in the shell command history.
      3. Make sure you don't leave a logged in session unlocked so that other users could walk up and see your password by displaying the environment.

      This approach is best when you want your login credentials available for the duration of an entire login session.

    • Store your password in an encrypted file and decrypt it inline.

      First, you have to store your password in an encrypted format. There are several ways to do this, but gpg is commonly used:

      echo "my_weak_pw" | gpg -c >mysecretpw

      Provide a decrypt passphrase, and you're done.

      Now, you can use this by decrypting it inline as needed:

      #!/bin/sh
      # A demo scripted use of tsshbatch with CLI password passing
      
      MYPW=`cat mysecretpw | gpg`   # User will be prompted for unlock passphrase
      
      sshbatch.py -n joe.luser -p $MYPW hostlist1 command1 arg
      sshbatch.py -n joe.luser -p $MYPW hostlist2 command2 arg
      sshbatch.py -n joe.luser -p $MYPW hostlist3 command3 arg

      This approach is best when you want your login credentials available for the duration of the execution of a script. It does require the user to type in a passphrase to unlock the encrypted password file, but your plain text password never appears in the wild.

  3. Authentication Using Key Exchange

    For most applications of tsshbatch, it is much simpler to use key-based authentication. For this to work, you must first have pushed ssh keys to all your hosts. You then instruct tsshbatch to use key-based authentication rather than name and password. Not only does this elimintate the need to constantly provide name and passowrd, it also eliminates passing a plain text password on the command line and is thus far more secure. This also overcomes the problem of having different name/password credentials on different hosts.

    By default, tsshbatch will prompt for name and password if they are not provided on the command line. To force key-based authentication, use the -k option:

    tsshbatch.py -k AIX-prod-hosts ls -al
  4. Executing A sudo Command

    tsshbatch is smart enough to handle commands that begin with sudo. It knows that such commands require a password even if you used key exchange to intially log in. That's because, once you are logged in - whether via name/password or via key exchange - sudo requires your password again to promote your privileges.

    When using name/password authentication, with tsshbatch you need do nothing special to run sudo commands on your targeted hosts (assuming you have the privilege of doing so there).

    However, when using key exchange-based authentication, if you want to run sudo commands, you will also have to provide a password by one of the means described previously. That's because, once you are logged into a host, your password is required again to do sudo privilege promotion.

OTHER

You must have a reasonably current version of Python installed. If your Python installation does not install paramiko you'll have to install it manually, since tsshbatch requires these libraries.

BUGS AND MISFEATURES

When sudo is presented a bad password, it ordinarily prints a string indicating something is wrong. tsshbatch looks for this to let you know that you've got a problem and then terminates further operation. This is so that you do not attempt to log in with a bad password across all the servers you have targeted. (Many enterprises have policies to lock out a user ID after some small number of failed login/access attempts.)

However, some older versions of sudo (noted on a RHEL 4 server running sudo 1.6.7p5) do not return any feedback when presented with a bad password. This means that tsshbatch cannot tell the difference between a successful sudo and a system waiting for you to reenter a proper password. In this situation, if you enter a bad password, the the program will hang. Why? tsshbatch thinks nothing is wrong and waits for the sudo command to complete. At the same time, sudo itself is waiting for an updated password. In this case, you have to kill tsshbatch and start over. This typically requires you to put the program in background (`Ctrl-Z in most shells) and then killing that job from the command line.

There is no known workaround for this problem.

COPYRIGHT AND LICENSING

tsshbatch is Copyright (c) 2011 TundraWare Inc.

For terms of use, see the tsshbatch-license.txt file in the program distribution. If you install tsshbatch on a FreeBSD system using the 'ports' mechanism, you will also find this file in /usr/local/share/doc/tsshbatch.

AUTHOR

Tim Daneliuk
tsshbatch@tundraware.com

DOCUMENT REVISION INFORMATION

$Id: tsshbatch.rst,v 1.107 2012/01/05 19:07:23 tundra Exp $

You can find the latest version of this program at:

http://www.tundraware.com/Software/tsshbatch