shell script to ssh remote machines and print the output of the top command

Question

I want to write a shell script to do the following four things:

1. ssh a remote machine (say hosti)
2. print the machine name to a file (top_out)
3. print the first few lines of the output of the 'top' command to the same file as in step2
4. repeat 1-3 for an other machine

I tried this:

#! /bin/bash

for i in 1 2 3 4 5 6 7 8

do
    echo "host$i" >> ~/mysh/top_out
    ssh host$i "top -n1 -b | head -n 15>> ~/mysh/top_out"
    echo "done"
done

The output file that I got had saved the top output for some machines (say like host5-8), but it was blank for the early machinessay like host1-4. If I tried without the line "echo "host$i" >> ~/mysh/top_out", I can get the top output for all the host1-8.

Answer 1

When you do

ssh host$i "top -n1 -b | head -n 15>> ~/mysh/top_out"

you’re writing the output to ~/mysh/top_out on the remote host, not the local machine. The remote host might not be using the same physical home directory as your local machine. If you have NFS or something sharing your home directory on some machines but not all, then you’d see the symptoms you described.

Try doing

ssh host$i "top -n1 -b | head -n 15" >> ~/mysh/top_out

instead, or to make things slightly cleaner, maybe even

#!/bin/bash

for i in $(seq 1 8); do
    (echo "host$i"
     ssh host$i "top -n1 -b | head -n 15") >> ~/mysh/top_out
    echo "done host$i"
done

Answer 2

you can try an expect script to save the output of each hosts after it connects to it, you can also add more commands to it, p.s. : this assumes you have the same username and password for all hosts :

#/usr/bin/expect -f

#write your hosts on a new line inside a file and save it in your workging directory as:

#host 1
#host 2
#host 3

#user '' for password if it contains special chars
#pass arguments to the script as ./script $username '$password' $hosttxt
set user [lindex $argv 0]
set pass [lindex $argv 1]
#pass path to txt file with line separated hosts
set fhost [lindex $argv 2]
#set this to the  path where you need to save the output e.g /home/user/output.txt
set wd "/home/$user/log.txt"
#open hosts file for parsing
set fhosts [open $fhost r]
exec clear
#set loguser 1

proc get_top {filename line user pass} {
     spawn ssh -l $user $line
      expect {
          "$ " {}
      "(yes/no)? " {
            send "yes\r"
            expect -re "assword:|assword: "
            send "$pass\r"
      }
     -re "assword:|assword: " {
            send "$pass\r"
      }
     default {
        send_user "Login failed\n"
     exit 1
    }
  }
  expect "$ " {}
  send "top -n1 -b | head -n 15\r"
  expect -re "\r\n(.*)\r(.*)(\\\$ |# )"  {
       set outcome "$expect_out(1,string)\r"
       send "\r"
  }

  puts $filename "$outcome\n\n-------\n"
}


 while {[gets $fhosts line] !=-1} {
       set filename [open $wd "a+"]
       get_top $filename $line $user $pass
       close $filename
 }