Have you ever wonder a simple way to copy files and run commands on multiple machines from one command? Well there are several tools available that will allow us to do just that. I will discuss just pssh (Parallel SSH).

pssh (Parallel SSH)

pssh (Parallel SSH) is a command line tool that includes pscp and allows you to send commands and copy files to multiple server via a list or individually. Makes it very easy to distribute commands and files to a few or hundreds of servers.

Installation is pretty simple with Fedora and RHEL.

$ sudo yum install pssh

Say I wanted to copy two files to multiple hosts to the /tmp directory and limit the command to execute to 5 systems at a time and execute as root I would run the following command on RHEL 5.x and higher.

$ pscp.pssh -vA -h ~/myhosts.txt -l id -p 5 -e /tmp upgrade_prog upgrade_prog.tar.gz /tmp/

-vA switch tells pscp to run in verbose mode and ask for a password.
-h switch tells pscp the list of hosts are located in this file and this location.
-p switch says execute on 5 systems at a time
-e switch tells pscp to output the error log to /tmp on my system
Then finally the files to send and the destination on the systems.

NAME
pscp — parallel process kill program
SYNOPSIS
pscp  [-vAr]  [-h  hosts_file]  [-H  [user@]host[:port]] [-l user] [-p par] [-o outdir] [-e errdir] [-t timeout] [-O options] [-x
args] [-X arg] local remote
DESCRIPTION
pscp is a program for copying files in parallel to a number of hosts.  It provides features such as passing a  password  to  scp,
saving output to files, and timing out.
OPTIONS
-h host_file
–hosts host_file
Read  hosts  from  the  given  host_file.  Lines in the host file are of the form [user@]host[:port] and can include blank
lines and comments (lines beginning with “#”).  If multiple host files are given (the -h option is used more  than  once),
then pscp behaves as though these files were concatenated together.  If a host is specified multiple times, then pscp will
connect the given number of times.
-H     [user@]host[:port]
–host [user@]host[:port]
-H     “[user@]host[:port] [ [user@]host[:port ] … ]”
–host “[user@]host[:port] [ [user@]host[:port ] … ]”
Add the given host strings to the list of hosts.  This option may be given multiple times, and may be used in  conjunction
with the -h option.
-l user
–user user
Use the given username as the default for any host entries that don’t specifically specify a user.
-p parallelism
–par parallelism
Use the given number as the maximum number of concurrent connections.
-t timeout
–timeout timeout
Make connections time out after the given number of seconds.  With a value of 0, pscp will not timeout any connections.
-o outdir
–outdir outdir
Save  standard  output to files in the given directory.  Filenames are of the form [user@]host[:port][.num] where the user
and port are only included for hosts that explicitly specify them.  The number is a counter that is incremented each  time
for hosts that are specified more than once.
-e errdir
–errdir errdir
Save standard error to files in the given directory.  Filenames are of the same form as with the -o option.
-x args
–extra-args args
Passes  extra  SSH command-line arguments (see the ssh(1) man page for more information about SSH arguments).  This option
may be specified multiple times.  The arguments are processed to split on whitespace,  protect  text  within  quotes,  and
escape with backslashes.  To pass arguments without such processing, use the -X option instead.
-X arg
–extra-arg arg
Passes  a single SSH command-line argument (see the ssh(1) man page for more information about SSH arguments).  Unlike the
-x option, no processing is performed on the argument, including word splitting.  To pass multiple command-line arguments,
-O options
–options options
SSH  options in the format used in the SSH configuration file (see the ssh_config(5) man page for more information).  This
option may be specified multiple times.
-A
–askpass
Prompt for a password and pass it to ssh.  The password may be used for either to unlock a key or for password authentica-
tion.   The  password is transferred in a fairly secure manner (e.g., it will not show up in argument lists).  However, be
aware that a root user on your system could potentially intercept the password.
-v
–verbose
Include error messages from ssh with the -i and \ options.
-r
–recursive
Recursively copy directories.

TIPS
The ssh_config file can include an arbitrary number of Host sections.  Each host entry specifies ssh options which apply only  to
the given host.  Host definitions can even behave like aliases if the HostName option is included.  This ssh feature, in combina-
tion with pssh host files, provides a tremendous amount of flexibility.

EXIT STATUS
The exit status codes from pscp are as follows:
0      Success
1      Miscellaneous error
2      Syntax or usage error
3      At least one process was killed by a signal or timed out.
4      All processes completed, but at least one scp process reported an error (exit status other than 0).

As with PSCP you can use PSSH to run Command multiple hosts. The syntax is similar to PSCP.

pssh -vA -h ~/myhosts.txt -l id -p 5 -t 5 -e /tmp -o /tmp hostname

This example is running the hostname command on the list of servers and writes the output to the /tmp directory.

Using the two commands you can accomplish many tasks on multiple servers with a short amount of time and effort.

Update: When pssh or pssh.pscp to a system for the first time you will receive a failure, this is due to the ssh key not existing in your known_hosts file. If you use the -X arg option you can pass -oStrictHostKeyChecking=no ssh parameter and it will add the key to your known_hosts file. Using -x args you can string multiple ssh options.

Example:

pssh -vA -h ~/myhosts.txt -l id -p 5 -t 5 -e /tmp -o /tmp -X "-oStrictHostChecking=no" hostname