I am writing a shell script where I want to automate service Restart process on multiple Unix servers. I as a normal user do not have rights to run services restart commands. Only s_user has rights to run them.

Procedure to restart services:

  1. Login to server with my username and password.
  2. To Run the Restart service I need to switch user to s_user using below command: ( I need this command without password prompt)

    sudo su - s_user 

The above command prompts for password where I will provide my password to restart services. This procedure I have to do in all the servers.I want to skip the password prompt by supplying the password to su through stdin.

The following commands I have tried so far:

1.   echo 'password'|sudo -S su -c " .../bin/services stop" 
[sudo]password for abc.xyz: Sorry, user abc.xyz is not allowed to execute '/bin/su - s_user' -c /bin/services stop' as root on [Servername]                        

In the above command I gave my password. I have also tried giving the s_user password but it gives below output:

[sudo]password for abc.xyz: Sorry,try again.
[sudo]password for abc.xyz:
sudo:pam_authenticate:Conversation error

I replaced ‘su’ with ‘u’ in the below command, but still I am getting the same output error as 1st command.

2.  echo 'password'|sudo -S u -c " .../bin/services stop" 

I have provided s_user in the below command, but still I am getting the same output error as 1st command.

3.  echo 'password'|sudo -S su - s_user -c ".../bin/service stop" 

Next I have tried the below command.

4.  echo 'my password'|su -c ".../bin/services stop" -s /bin/sh abc.xyz
Standard in must be a tty

I have also tried the below command.

5.  su -c "command_to_restart_the_services" -s /bin/sh abc.xyz 

I am able to run the command successfully.

6.  echo password|sudo -S su - user-to-switch
    sudo -S su - user-to-switch

The above command still ask for the password.


• I cannot use “expect”, it’s not installed in my machines.

• I cannot edit the "sudoer" file. I do not have rights.

  • I would convince the sysadmin to configure sudo to allow me to restart the services directly, with or without a password prompt as desired.
    – user
    Aug 20, 2016 at 19:51
  • single sign-on feature Mar 28, 2018 at 0:17
  • You don't need to use su with sudo. sudo has an option to specify a sure -u. And your admin gave you full root access, using sudo. Add the sudo configuration yourself. Jul 3, 2018 at 23:22

3 Answers 3


I see you are using sudo to become root, and then su to become s_user. To do this you will use your password (for sudo). You do not need the password for s_user.

You could do it by instead adding your ssh key to the s_user account, but I think this solution in this case is sub-optimal.

First I will point out that you don't need su, and it is best not to use it. So instead of sudo su - s_user -c command, do sudo -u s_user command. You will still be asked for your password. However you can now configure /etc/sudoers

Add a file /etc/sudoers.d/s_commands, containing something like (but checked, with /usr/bin/visudo):

Cmnd_Alias S_COMMAND=/usr/bin/command, /usr/bin/anotherCommand
%s_group ALL = (s_user) NOPASSWD : S_COMMAND

This will allow password less use of those commands, as s_user, but only for users in group s_group (you will have to add the group).

Then set up a shell alias, something like: alias s_command="sudo -u s_user command".


  • su takes the password of the user that you are switching to.
  • sudo, by default, takes the password of the user you are (you are switching from).
  • sudo does not read password from stdin, it reads from tty.

A way to do this is to use ssh.

Using ssh-copy-id you can store the authentification:

ssh-copy-id s_user@

(if no key have been set, use ssh-keygen to generate one)

Next you can use ssh instead of sudo to execute command without password prompt:

ssh s_user@ " .../bin/services stop"
  • Thanks for your reply, I am new to this unix environment. Can you please provide some more details on when to run this command i mean after doing sudo login? Also, I am not sure what would be the impact post implementing these. These servers are currently in use and I am afraid if something goes wrong.Can you please provide me step by step guide to perform this authenfication task. Please help!!! Aug 21, 2016 at 20:35
  • Somehow the ssh s_user@ command makes something equivalent to sudo -u s_user, after running ssh-copy-id s_user@ that prompt for password the ssh command doesnot prompt for password.
    – mpromonet
    Aug 21, 2016 at 21:26

This is not exactly the answer to your question, but could be a solution for your task.

I suppose you know the password for s_user on every server, and there is sshd installed on those servers (and works as expected; depends on what OS runs on the servers).

As mpromonet stated, you may use ssh, but without logging into the servers with your own credentials.

On your computer:

First, generate your own key pair with ssh-keygen. This will be stored in ~/.ssh directory by default.

Next, for every server involved call ssh-copy s_user@<server>; you will be asked for the password of s_user on the server.

Now to check if all went well just try ssh s_user@<server>. If this works without being asked for a password your done.

In your script (on your local computer) you now can call

ssh s_user@<server> "whatever-command-you-need-to-run"

without beeing asked for passwords.

Rem.: I supposed here your local computer runs a UN*X like OS as well. If you are running Windows, you may instead use the programs coming with the putty packet for Windows.

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