SSH traversal IPs for connection

Today production to batch connect the server and execute the command: Write all the IP to a iplist file, then use while read and for to traverse the stitching SSH command found two problems: SSH connection parameter-N and while read and for read the difference

Script

IPList

192.168.4.12

192.168.4.13

192.168.4.14

tongjidf.sh

#!/bin/bash

cmd= "Df-m | grep app "

While Read line

Do

SSH [email protected]${line} $cmd

Done <./iplist

The results of the execution found that only one address was connected 192.168.4.12, the following address was not executed

and changed it into a for.

#!/bin/bash

Cmd= "Df-m|grep App"

For IPs in ' Cat IPList '

Do

SSH [email protected]${line} $cmd

Done

This script can be implemented by connecting all of the above addresses and then executing commands.

Finally found a saying that is for is a row of reads, while the while read line is a read into the memory

The second is that SSH reads the local content by default, and the-n parameter blocks it, but reads it from/dev/null/, so that SSH is connected in the form of a while-read line

- n redirects stdin from/dev/null (actually, prevents reading from stdin).  This must was used when SSH was run in the background. A
Common trick is the use of this to run X11 programs in a remote machine. For example, Ssh-n shadows.cs.hut.fi Emacs & would start
An emacs on shadows.cs.hut.fi, and the X11 connection'll be automatically forwarded over an encrypted C  Hannel. The SSH pro-
Gram'll is put in the background. (This does isn't work if SSH needs to ask for a password or passphrase; see also The-f

SSH traversal IPs for connection