Running a Program on a Remote Server Using SSH
by: C.S. Deam
How do you run a program on a remote server using ssh?
For this example weกll have two servers, one named Johnny and another named Cash. Both are running openssh. Our goal is to have a program on Johnny login to Cash and run a program on Cash. To make the task a little more complex weกll be using different users on each machine.
The first thing weกll need to do is generate public and private keys on Johnny. So, logged into Johnny as user กboyก we create public and private keys by creating them in the .ssh directory as follows:
Johnny$> pwd
/home/boy/.ssh
Johnny$> sshkeygen t rsa f sue
Generating public/private rsa key pair.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in sue.
Your public key has been saved in sue.pub.
The key fingerprint is:
8d:e9:c0:g1:c7:1f:e3:b3:2f:38:12:aa:b5:3b:2e:b3 boy@Johnny
Johnny$>
In the example above we picked an arbitrary name, sue, to identify the files that hold the generated keys. When prompted to enter a passphrase (twice) we simply hit enter twice.
As the output of sshkeygen indicates, the public key has been saved in a file named sue.pub.
The output of sshkeygen implies, but doesn’t indicate directly, that the private key is in a file named sue (Yes, a user named boy created a file named sue.)
Johnny$>ls l
rwx 1 sue suegrp 887 Oct 17 14:27 sue
rwx 1 sue suegrp 223 Oct 17 14:27 sue.pub
The private key file, sue, will remain on Johnny for the reaminder of this exercise, but the public key must be moved to the remote server, Cash. Note that the .ssh directory itself, as well as the sue and sue.pub files should have permissions of 700.
Now youกll need to ftp the sue.pub file from Johnny to Cash. The user on Cash that weกll login as is user กnamedก.
Johnny$> ftp Cash
Connected to Cash
220 Cash Propery of Xyz. Authorized users only
Name (Cash:boy): named
331 Password required for named.
Password:
230Last unsuccessful login: Fri Oct 17 13:12:55 2003 on ftp from Johnny 230Last login: Fri Oct 17 16:02:11 2003 on /dev/pts/1 from Johnny
230 User named logged in.
ftp> cd .ssh
ftp> mput sue.pub
mput sue.pub? y
200 PORT command successful.
150 Opening data connection for sue.pub.
226 Transfer complete.
224 bytes sent in 0.000781 seconds (280.1 Kbytes/s)
local: sue.pub remote: sue.pub
ftp>bye
221 Goodbye.
Johnny$>
Now weกll telnet into Cash and concatenate the sue.pub file into /home/named/.ssh/authorized_keys file.
Cash$> pwd
/home/named/.ssh
Cash$> cat sue.pub >> authorized_keys
Cash$> exit
Connection closed.
Johnny$>
Letกs recap what weกve done so far.
1) Weกve created public and private keys on Johnny.
2) Weกve ftpกd the public key file, sue.pub, from Johnny to Cash.
3) Weกve telnetted to Cash, and concatenated the contents of sue.pub into authorized_keys
We’re now ready to manually login from Johnny to Cash using ssh.
Johnny$> ssh i /home/boy/.ssh/sue named@Cash
The authenticity of host กCash (xxx.yyy.zzz.aaa)ก can’t be established.
RSA key fingerprint is 65:11:7d:ef:ed:a3:cc:34:d1:b5:ba:c9:16:22:31:23.
Are you sure you want to continue connecting (yes/no)? yes
================================================================
*** NOTICE TO ALL USERS ***
================================================================
Cash$>exit
Connection to Cash closed.
Johnny$>
Now on Johnny, create a shell script called กboynamedsue.shก with the following one line of contents and chmod the script to 777.
ssh i /home/boy/.ssh/sue named@Cash /usr/bin/ls l
Next, execute the script on Johnny.
Johnny$> boynamedsue.sh
================================================================
*** NOTICE TO ALL USERS ***
================================================================
rwxrwxrx 1 named namedgrp 10020 Oct 17 14:35 namedfile1.txt
rwrr 1 named namedgrp 680 Aug 14 16:18 namedfile.html
rw 1 named namedgrp 1148 Aug 18 09:51 mbox
drwxrxrx 2 named namedgrp 512 Jun 17 13:38 old
Johnny$>
You just executed a program on Johnny, that logged into Cash and ran a program (unix กls lก).
The next step youกll want to take is to replace the ก/usr/bin/ls lก command in the boynamedsue.sh program with the path and name of the program that you want to run.
About The Author
C.S. Deam is a small business owner. His eBook Computer Nuggets: NonTechie Internet Tips For InLaws, OutLaws, and the Rest of Society is a great gift for nontechie family members and is available at www.LinkertonPublishing.com where you can sign up for FREE ECourses & Newsletters to help you on your path to selfemployment.
This article was posted on December 27, 2003
by C.S. Deam