By a bash script executed in a local computer run a command (with sudo privileges) on a remote server

Run a command on a remote system from a local computer

I need to execute a command on a remote lubuntu 22.04 system by a ssh connection, but without open a shell. This instruction will be executed inside a script. The script is executed on my local system (that has an other Ubuntu distribution installed). I have found that I can do it, with success, executing on the local system the following script:

# define a variable which stored the password
MYPASSWORD='mypassword'

sshpass -p $MYPASSWORD ssh myuser@192.168.1.1 "cp /home/myuser/file1 /path/to/dest/"

In the command I have used sshpass (which is installed on my local system) to avoid the input of the password for the user myuser needed to authenticate the ssh session.

My needs

I have also to execute a cp command as the previous but the destination for the file is a subfolder of /etc and this need sudo privileges. So the script becomes:

MYPASSWORD='mypassword'

sshpass -p $MYPASSWORD ssh myuser@192.168.1.1 "cp /home/myuser/file1 /path/to/dest/"

sshpass -p $MYPASSWORD ssh myuser@192.168.1.1 "sudo -S cp /home/myuser/file1 /etc/sub/folder/"

If I execute the script, the last command of the script outputs the following request:

[sudo] password for myuser:

So the script stops its execution and waits for the sudo password.
I don’t want this!

An attempt of mine

If I execute the command:

> echo mypassword | sudo -S -s cp /home/myuser/file1 /etc/sub/folder/

directly on a terminal of the remote system it works and copies file1 to /etc/sub/folder/ without asking the sudo password.

But if I execute the following command on my local system:

sshpass -p 'mypassword' ssh myuser@192.168.1.1 "echo mypassword | sudo -S -s cp /home/myuser/file1 /etc/sub/folder/"

it doesn’t work!

My question

Is there a way to avoid the input of the password for sudo by keyboard? Is it possible to send the password automatically?

Asked By: frankfalse

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Source

I have found a workaround/solution.

Using a file that temporarily stores the password for sudo

I have modified the script executed in the local system by adding some commands showed below:

  • creation of a text file in the folder of the remote system by the echo command; the file is called password.txt and contains only the password ("mypassword") for the user myuser.
  • the file password.txt is direct as input to the sudo command by the operator <.
  • execution of the command sudo -S < /home/myuser/password.txt cp /home/myuser/file1 /etc/sub/folder/
  • deletion of the file /home/myuser/password.txt from the remote system

This solution is used in a secure development environment so not break any security constraint.

The new script

With this instructions the script executed in the local system becomes:

MYPASSWORD='mypassword'

# creation of the file password.txt on the home folder of the remote system
sshpass -p $MYPASSWORD ssh myuser@192.168.1.1 "echo $MYPASSWORD > /home/myuser/password.txt"

# execution of the command which needs the sudo privileges (on remote system)
sshpass -p $MYPASSWORD ssh myuser@192.168.1.1 "sudo -S < /home/myuser/password.txt cp /home/myuser/file1 /etc/sub/folder/"
# The '<' directs file passowrd.txt as input to sudo   ===========================

# deletion of the file password.txt
sshpass -p $MYPASSWORD ssh myuser@192.168.1.1 rm /home/myuser/password.txt

Suppress the output of sudo -S

I have found an other improvement which allows to suppress the output ([sudo] password for myuser:) of the command sudo -S which is sent from ssh to the local system.
It is enaugh to use the operator &> and the /dev/null device as showed below:

sshpass -p $MYPASSWORD ssh myuser@192.168.1.1 "sudo -S < /home/myuser/password.txt cp /home/myuser/file1 /etc/sub/folder/" &> /dev/null

Note In my local system suppression of output [sudo] password for myuser: works by following redirections:

  • &>/dev/null
  • >&/dev/null

and this is normal because previous operators are equivalent (see this post on SuperUser).

The suppression does not work by the following redirection:

  • >/dev/null
Answered By: frankfalse