Why Your SSH Loop Stops After One Host—and How to Fix It

Scenario

You want a script that reads a list of server IPs from ip.txt (one IP per line) and, using a pre‑configured SSH key, fetches each server's uptime without prompting for a password.

Initial script (while loop)

#!/bin/bash
while read ips; do
  echo $ips;
  upt=`ssh root@$ips "uptime"`;
  echo $upt;
done < ip.txt

This script reads the IPs correctly, but it only processes the first IP and then exits.

Problem Analysis

The while loop reads ip.txt via input redirection. When the ssh command runs inside the loop, it also reads from standard input, consuming the remaining lines of ip.txt. As a result, the loop thinks there is no more input and terminates after the first iteration.

Solution Strategies

1. Use a for loop

A for loop iterates over the list without pre‑loading the entire file, avoiding the stdin conflict.

#!/bin/bash
for ips in `cat ip.txt`; do
  echo ${ips};
  upt=`ssh root@${ips} uptime`;
  echo $upt;
done

2. Keep the while loop but add -n to ssh

The -n option redirects ssh 's standard input from /dev/null, preventing it from consuming the remaining IPs.

#!/bin/bash
while read ips; do
  echo $ips;
  upt=`ssh -n root@$ips "uptime"`;
  echo $upt;
done < ip.txt

Both approaches ensure that the script processes every IP address in the list.