How to use ssh command to count distributed cluster information in Linux Shell

1. Ideas for statistics of distributed cluster information

Use password-free remote login commands to enable one machine to access machines in other clusters. Therefore, there are several important steps to achieve:

• Learn how to use shh

• Achieve password-free login

• Writing shell program

2. SSH encryption principle

Asymmetric encryption technology is an encryption method that uses different keys for encryption and decryption. Among them, RSA and DSA are asymmetric encryption methods. Of course, the asymmetric encryption algorithm has a premise, that is, there is a pair of keys that can encrypt and decrypt each other. Usually this pair of keys will become the public key and private key of the holder. The public key is a key that others can know, while the private key can only be known by the holder. Of course, if the private key is leaked to outsiders, there may be information security issues.

Suppose: A wants to send encrypted data to B. The first method is: A uses his own private key to encrypt, and B uses A's public key to decrypt after obtaining the data. The second method is: A uses B's public key to encrypt the data, and B uses his own private key to decrypt the data after obtaining it.

SSH remote login uses the first method.

3. SSH command

The commonly used method is

ssh -i [private key file name] -p [port number] user@hostname [executed Command]

The private key file name defaults to $HOME/.ssh/id_rsa or $HOME/.ssh/id_dsa, and the port number defaults to 22.

For example:

ssh   myname@128.180.146.89  #输入目标主机的密码后进行远程操作，exit命令退出

4. Use ssh-keygen and ssh-copy-id to achieve password-free login

ssh-keygen     #直接全部回车，先都默认

Then a key pair file will be generated in the $HOME/.ssh/ directory, among which *.pub Unified into a public key file, and the other is a private key file.

Next, copy the contents of the public key file to $HOME/.ssh/authorized_keys of the target host user. The copy method can be operated manually by yourself. You can also use the following command to achieve

ssh-copy-id -i [public key file name] user$hostname

For example:

ssh-copy-id -i  $HOME/.ssh/id_rsa.pub  myname@128.180.146.89

And then Execute the remote login command to achieve password-free login. If a password is still required for the second login, it may be due to file and file directory permission issues. It may also be because the connected private key and public key are not a pair.

5. Linux Shell Script Implementation

sshtest.sh file:

#!/bin/bash
func___setenv(){
   RTS_ECT_DIR="$HOME"
   #.....
}
######################################
#
#   程序主体
######################################
 
#调用环境变量
func___setenv
 
#读取机器连接信息
while read line
do
ssh_cmd=
ssh_linkhost=`echo ${line}`
    while  read  cmdline
    do
    #空命令行跳过
    if [ -z "$cmdline" ]; then
        continue 
    fi
    
    #读取的命令行拼接;
    if [ ! -n "$ssh_cmd" ]; then
        ssh_cmd=`echo ${$cmdline}` ;
    else
        ssh_cmd="${ssh_cmd};"`echo ${$cmdline}` ;
    fi
    done <${RTS_ECT_DIR}/sshcmd.cfg
#执行远程命令
ssh $ssh_linkhost $ssh_cmd </dev/null
done <${RTS_ECT_DIR}/sshlink.cfg

sshlink.cfg file: The key must be configured first before you can log in without a password

myname@128.180.146.89
myName@128.180.146.90
Myname@128.180.146.91

sshcmd.cfg file: fill in

ps -ef|grep java 
df -h

according to your own needs. Sixth, ssh only loops once.

If the penultimate line of the above code is changed to

ssh $ssh_linkhost $ssh_cmd

Then the while loop will only loop once. Because while read line will put the loop information into the standard input, and the ssh command will read all the input buffer, so while is not in the loop. So the ssh command needs to be redirected

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