Loading ...Execute Commands on Multiple Linux or UNIX Servers
This is Part I in a series on Execut Commands on Multiple Linux or UNIX Servers Simultaneously. The full series is Part I, Part II, and Part III. Some time it is necessary to execute commands on Multiple Linux or UNIX Servers, for example you would like to find out who is logged on and what they are doing on three Linux or UNIX boxes or better find out system utilization, disk space and much more. With the help of ssh you can easily setup such nice system.
SSH Setup
Admin Linux workstation -> Server # 1 with ssh adm.my.com -> server1.my.com
SSH client is a program for logging into a remote machine and for executing commands on a remote machine. If command is specified, command is executed on the remote host instead of a login shell.
$ ssh user@server1.my.com w
Above command will gather up all logged in users information. However if you put this command in script to gather information from three server as follows it will prompt for a password:
ssh user@server1.my.com w
ssh user@server2.my.com w
ssh user@server3.my.com w
To get rid of password you can setup ssh key based login. Once ssh keys are in place you can simply create a script as follows:
#!/bin/bash # Linux/UNIX box with ssh key based login SERVERS="192.168.1.1 192.168.1.2 192.168.1.3" # SSH User name USR="jadmin" # Email SUBJECT="Server user login report" EMAIL="admin@somewhere.com" EMAILMESSAGE="/tmp/emailmessage.txt" # create new file >$EMAILMESSAGE # connect each host and pull up user listing for host in $SERVERS do echo "--------------------------------" >>$EMAILMESSAGE echo "* HOST: $host " >>$EMAILMESSAGE echo "--------------------------------" >>$EMAILMESSAGE ssh $USR@$host w >> $EMAILMESSAGE done # send an email using /bin/mail /bin/mail -s "$SUBJECT" "$EMAIL" < $EMAILMESSAGE
You need to setup your hostname and email id and then execute shell script. This is very simple yet powerful method to execute commands simultaneously on multiple Linux/UNIX servers. If you are really interested to see application output then visit here, it was produced by this script (see our forum for more). This is just small script but you are only limited by your own imagination. Few more advanced tools do exist I will cover them some time later.
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You may also be interested in other helpful articles:
- Howto Use SSH To Run Command On A Remote Machine
- Execute commands on multiple hosts using expect tool
- How do I find the exit status of a remote command executed via ssh?
- Get more juice out of multiprocessor system with xjobs
- Tentakel to execute commands on multiple Linux or UNIX Servers
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Why not use dsh:
http://www.netfort.gr.jp/~dancer/software/dsh.html
If you want to fully parallelize the script you can wrap the ssh command in parentheses in order to execute in a subshell, I believe. That way the script doesn’t wait for the program to finish. I use this to dynamically test all the workstations in my lab (~150) to see which ones are up and running, so I can generate a machine list for a distributed MPICH program.
Very nice script. I use(d?) to manually write a “for” loop every time I need to run the same command on multiple hosts.
I’ve just modified your sample script, declaring another variable (COMMAND=$@) to use instead of “w”, so I can run
./dsh cat /etc/hosts to get the content of all servers’ /etc/hosts in my mailbox.
Excellent article! Thank you.