ssh + multiple ssh connection failed

Question

I have 47 Linux client machines and one Solaris server machine (all Linux client machines are red-hat 5.1)

all clients perform ssh connection to the server in order to verify if /tmp/generic_error.txt exist in the server

clients do the ssh exactly on 12:00 PM

I see something strange

Some of clients not recognized that /tmp/generic_error.txt exist in the server in spite this file was exist

So my first conclusion is that I can't perform multiple ssh from 47 machine to one server ?

But I don’t sure if I right ?

Please advice what the best process to perform ssh from 47 Linux clients to one server exactly on the same time?

remark - I can’t touch and configure the "ssh key-based authentication" because the Lenox’s machines must have password (part of our security policy)

example of the expect script in the linux's clients - this expect verify if /tmp/generic_error.txt exists in the server (this action should be performed exactly on 12:00 PM on all 47 linux clients)

10.10.18.61 - server machine

 expect=`cat << EOF

 set timeout -1
 spawn  ssh  10.10.18.61
       expect {
                 ")?"   { send "yes\r"  ; exp_continue  }

                 word:  {send freenelsonmandela\r}
              }
 expect >  {send "ls /tmp/generic_error.txt\r"}
 expect >    {send exit\r}
 expect eof
 EOF`

exe expect:

expect -c  "$expect"  | grep "generic_error.txt"  | grep -v ls

I would advise against using expect paired with ssh in such a way. You should probably set up (passwordless) public key authentication instead: http://www.debian-administration.org/articles/152. It's simpler in the long run, and more secure. — Eduardo Ivanec, Feb 12 '12 at 15:57
Yes, expect is probably not a good idea. I don't see in the script that you ever check for the answer for the `ls`. Idea: You could also copy the file with scp to the local machine. If it's there after the scp, you know it exists on the server. — AndreasM, Feb 13 '12 at 12:17
About scp I also must use the expect script in order to automate the password , Any way what’s the alternative for expect? this is only the single way to remote to other machine when need to enter the password — Eytan, Feb 13 '12 at 15:12
@Eytan, look at Eduardo's first comment. You can set up SSH key-based authentication, where you don't need to supply a password. It will be MUCH better to do that than trying to manage everything in expect. It probably wouldn't hurt to introduce some slightly randomness on the start time for the job. Yeah, handling 50 simultaneous ssh connection requests at the same time may be OK, but why do it unless you have to? — cjc, Feb 13 '12 at 15:26
hi CJC – look about "SSH key-based authentication" the problem is I can’t touch and configure ssh key-based authentication because the Lenox’s machines must have password (internal security policy in our company) this is the fact and I can’t change it , so I must to find other solution ........ — Eytan, Feb 13 '12 at 15:32
@eytan: This policy is self defeating because the script you are using right now has the password unencrypted in it. You should ask your superiors who put that policy in place if this is ok. The "exe expect" part is also bad: if there is an error with the `ls` it could output "generic_error.txt not found" and your exe will think everything is ok. Please take a moment to rethink your approach. — AndreasM, Feb 13 '12 at 16:24
@Eytan, the security policy is flawed then, since key-based authentication is more secure than password-based. You can have both password and key-based authentication at the same time; the key-based method is more secure than the password-based one, so you're not really losing anything security-wise, and, as AndreasM points out, you have the plain-text password in the expect script anyway. — cjc, Feb 13 '12 at 17:13
hi all - logical you are right , but I can’t change or configure the SSH key-based authentication , because I not the right person who take responsible on this issue - I only work in company and for now we can’t change the rules sorry if I return on my original question – only what I want is suggestion how to enable multiple ssh from many machines on the same time about the ls command , we can replace the ls with file command so if file command output will be ASCII then it’s also good results for me — Eytan, Feb 13 '12 at 20:53
Alternatively maybe you can run http server and serve this file over http — Alan, Feb 23 '12 at 07:03

score 0 · Accepted Answer · answered Feb 25 '12 at 01:07

If i understand correctly, you have 47 clients that need to know if some file exists on serverhost. And this needs to be run all at the same time.

Lets start with the smallest component, your file test. You can expand this some

This should work with most shells

ls /tmp/file 2>&1 >/dev/null && echo Found || echo Not Found

Or BASH

[ -f /tmp/file ] && echo Found || echo Not Found

You may want to check around more for the shell you are using, likely ksh, and double check its builtins for checking to see if a file is present.

Now slightly outwards, at the end of your expect, you are not doing anything with the results. this is likely the cause of most of your issue. you can access $expect_out(buffer) which will contain what ever was between the last matches.

typically this is used as:

puts "$expect_out(buffer)"

ssh + multiple ssh connection failed

1 Answers1