329

I would like to run a script from the main ubuntu shell as a different user that has no password.

I have full sudo privileges, so I tried this:

sudo su -c "Your command right here" -s /bin/sh otheruser

Then I have to enter my password, but I am not sure if that script is now really running under that user.

How can I confirm that the script is really running under that user now?

464

You can do that with su or sudo, no need for both.

sudo -H -u otheruser bash -c 'echo "I am $USER, with uid $UID"' 

The relevant parts of man sudo:

-H   The -H (HOME) option requests that the security policy set
     the HOME environment variable to the home directory of the
     target user (root by default) as specified by the password
     database.  Depending on the policy, this may be the default
     behavior.
-u user     The -u (user) option causes sudo to run the specified
      command as a user other than root.  To specify a uid
      instead of a user name, use #uid.  When running commands as
      a uid, many shells require that the '#' be escaped with a
      backslash ('\').  Security policies may restrict uids to
      those listed in the password database.  The sudoers policy
      allows uids that are not in the password database as long
      as the targetpw option is not set.  Other security policies
      may not support this.

su can only switch user without providing a password if you are root. See Caleb's answer

You can modify the /etc/pam.d/su file to allow su without password. See this answer.

If you modified your auth file to the following, any user that was part of group somegroup could su to otheruser without a password.

auth       sufficient pam_rootok.so
auth       [success=ignore default=1] pam_succeed_if.so user = otheruser
auth       sufficient   pam_succeed_if.so use_uid user ingroup somegroup

Then test from terminal

rubo77@local$ su otheruser -c 'echo "hello from $USER"'
hello from otheruser
13
  • 4
    Can you please add how to do it with just su too?
    – rubo77
    Oct 6 '14 at 12:33
  • 2
    This asks me for a password :-(
    – IanVaughan
    Jul 20 '15 at 12:39
  • 1
    @IanVaughan, With default configuration (of sudo), you will get asked for a password unless you run it as root. You can configure sudo to "allow user A to run cmd C as user B without requiring a password". See help.ubuntu.com/community/Sudoers
    – geirha
    Jul 21 '15 at 12:54
  • 1
    I'm prompted for a password when running this as root. Any suggestions?
    – Nate
    Nov 28 '15 at 0:26
  • 1
    @NamGVU keep in mind that order matters. If your sudoers has a rule further down that sets other permissions for your user, or a group you're a member of, that will override your NOPASSWD rule.
    – geirha
    Mar 28 '19 at 7:12
141

If you want to use su instead of sudo, I believe you can use something like this:

su - <username> -c "<commands>"
  • - will simulate a login of the specified user
  • -c tells it that you want to run a command

ps. Unfortunately I'm not able to install ruby using rvm with this method, but that's probably not related.

5
  • 7
    I needed to add sudo to the beginning otherwise it asked me for my password.
    – IanVaughan
    Jul 20 '15 at 12:42
  • 2
    This definitely doesn't work without sudo. with sudo it works, for example: sudo su - www-data -c "touch /tmp/test"successfully created a file as www-data
    – rubo77
    Sep 24 '16 at 8:41
  • 1
    To use "su" you need the root password, the point of "sudo" is to avoid that. If you have the root password using "su" as above should work fine. Jun 30 '17 at 7:51
  • "unfortunately I'm not able to install ruby using rvm with this method": when I used this command, the resulting path was bare (e.g., /bin:/usr/bin), so my command (similar to your rvm) wasn't found.
    – PLG
    Nov 11 '20 at 18:25
  • and what about switching to a specific group?
    – woodz
    Jan 17 at 12:27
11

The answers above are really useful to me but to answer the actual question...

How can I affirm that the script is really running under that user now?-

Use:

ps -ef | grep <command-name>

The output should include your script and the actual user executing it. People on BSD-like systems, e.g. MAC can find similar information with:

ps aux | grep <command-name>
2
  • Linux users can use ps aux. Sep 20 '18 at 20:08
  • 1
    @DeanHowell; True, but MAC users can not use "ps -ef" and the "ps aux" is BSD options, only available as a compatibility feature while the "ps -ef" is standardized Unix/POSIX options. Sep 22 '18 at 10:26
5

Make sure you switch to root user with command sudo su and then use the command

su user -s <command>

For example: su www-data -s bin/magento cache:clean

3

I had the same problem. Just type in the command screen -dmS testscreen this will create a detached screen on your non-sudo user account and then you can log it and check if this screen is there by screen -ls.

1

You can use sudo to do this. First, you need to modify the /etc/sudoers file to add a rule that allows the hudson user to become the other user for the script in question. Let's assume you have a user1 account that needs to run /usr/local/bin/my_script.sh.

Run visudo to modify the sudoers file. Then, use the following sudo command to run the script from hudson.

It's very important that you use visudo to modify the sudoers file in order to check the file for errors before putting it in place. Also, I'd suggest a quick read through man sudoers in order to clearly understand what the above does before adding it to your configuration.

1
  • You should show the actual line(s) that would be inserted into sudoers file. Nov 11 '20 at 18:51

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