Golang : Execute terminal command to remote machine example

Problem:

You need to query a remote machine with ssh to extract information such as memory usage or CPU information. Instead of opening a terminal and ssh to each individual remote machine, you want to write a Golang program that will execute a command and parse the output to your terminal or save to text files for processing.

How to do that?

Solution:

This is similar to Python's paramiko module that allow developers to create a remote session to a Unix/Linux machine. For Golang, we will use golang.org/x/crypto/ssh and golang.org/x/crypto/ssh/terminal packages to achieve similar result. In the code example below, we will connect to a remote Linux machine and execute the command cat /proc/cpuinfo to extract the CPU information. It can return static response from commands such as ps -ef or whoami, but not top command.

NOTE: If you're planning to query specific command only. Feel free to modify and hard code the command into the program instead of asking username/password input from the user. Make sure that the program has proper ownership and use proper mechanism to hide the plain password hard coded into the program.

Here you go!

---

 package main

 import (
 "bufio"
 "bytes"
 "fmt"
 "golang.org/x/crypto/ssh"
 "golang.org/x/crypto/ssh/terminal"
 "net"
 "os"
 "strings"
 )

 func GetCredential() (string, string) {
 reader := bufio.NewReader(os.Stdin)

 fmt.Print("Enter Username: ")
 username, _ := reader.ReadString('\n')

 fmt.Print("Enter Password: ")
 bytePassword, err := terminal.ReadPassword(0)
 if err != nil {
 panic(err)
 }
 password := string(bytePassword)

 return strings.TrimSpace(username), strings.TrimSpace(password)
 }

 func main() {
 if len(os.Args) != 3 {
 fmt.Printf("Usage : %s <hostname> <port> \n", os.Args[0])
 os.Exit(0)
 }

 hostname := os.Args[1]
 port := os.Args[2]

 username, password := GetCredential()
 config := &ssh.ClientConfig{
 User: username,
 Auth: []ssh.AuthMethod{ssh.Password(password)},
 HostKeyCallback: func(hostname string, remote net.Addr, key ssh.PublicKey) error {
 return nil
 },
 }
 fmt.Println("\nConnecting to ", hostname, port)

 hostaddress := strings.Join([]string{hostname, port}, ":")
 client, err := ssh.Dial("tcp", hostaddress, config)
 if err != nil {
 panic(err.Error())
 }

 for {
 session, err := client.NewSession()
 if err != nil {
 panic(err.Error())
 }
 defer session.Close()

 fmt.Println("To exit this program, hit Control-C")
 fmt.Printf("Enter command to execute on %s : ", hostname)

 // fmt.Scanf is unable to accept command with parameters
 // see solution at
 // https://www.socketloop.com/tutorials/golang-accept-input-from-user-with-fmt-scanf-skipped-white-spaces-and-how-to-fix-it
 //fmt.Scanf("%s", &cmd)

 commandReader := bufio.NewReader(os.Stdin)
 cmd, _ := commandReader.ReadString('\n')
 //log.Printf(cmd)
 fmt.Println("Executing command ", cmd)

 // capture standard output
 // will NOT be able to handle refreshing output such as TOP command
 // executing top command will result in panic
 var buff bytes.Buffer
 session.Stdout = &buff
 if err := session.Run(cmd); err != nil {
 panic(err.Error())
 }

 fmt.Println(buff.String())

 }
 }

---

Sample output after cat /proc/cpuinfo on a remote Linux machine:

 ./remoteQuery 1xx.xxx.xx.xx xxxx
 Enter Username: xxxxxxx
 Enter Password:
 Connecting to  1xx.xxx.xx.xx xxxx
 To exit this program, hit Control-C
 Enter command to execute on 1xx.xxx.xx.xx : cat /proc/cpuinfo
 Executing command  cat /proc/cpuinfo

 processor : 0
 vendor_id : GenuineIntel
 cpu family : 6
 model  : 62
 model name : Intel(R) Xeon(R) CPU E5-2630L v2 @ 2.40GHz
 stepping : 4
 microcode : 0x1
 cpu MHz  : 2399.998
 cache size : 15360 KB
 physical id : 0
 siblings : 1
 core id  : 0
 cpu cores : 1
 apicid  : 0
 initial apicid : 0
 fpu  : yes
 fpu_exception : yes
 cpuid level : 13
 wp  : yes
 flags  : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 ss syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon rep_good nopl pni pclmulqdq vmx ssse3 cx16 pcid sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx f16c rdrand hypervisor lahf_lm vnmi ept fsgsbase tsc_adjust smep erms xsaveopt arat
 bugs  :
 bogomips : 4799.99
 clflush size : 64
 cache_alignment : 64
 address sizes : 40 bits physical, 48 bits virtual
 power management:

Happy coding!

References:

https://www.socketloop.com/tutorials/golang-accept-input-from-user-with-fmt-scanf-skipped-white-spaces-and-how-to-fix-it

https://github.com/Juniper/go-netconf/issues/27

https://stackoverflow.com/questions/23019890/golang-write-input-and-get-output-from-terminal-process