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I have a user user1 which is part of wheel group and has all the root privileges .

user1 is able to change password for user2 using the below command (My understanding is that here passwd is run as root):

[user1@rhel-85 ~]$ sudo passwd user2

However, when user1 tries to run passwd as user2, I am getting an error:

[user1@rhel-85 ~]$ su -u user2 passwd
Try 'su --help' for more information.
[user1@rhel-85 ~]$ 
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    You seem to confuse sudo and su. These two programs have different command line syntax and slightly different purpose. Do you mean sudo -u user2 passwd?
    – Bodo
    Commented Jan 27, 2022 at 18:09
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    You are right. This is working fine sudo -u user2 passwd. By the way, can you please help understand difference between sudo and su?
    – meallhour
    Commented Jan 27, 2022 at 18:18

1 Answer 1

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su is used to launch a root shell that allows all further commands to use root access. su has no -u option...

https://man7.org/linux/man-pages/man1/su.1.html

This is why it is saying/complains;

Try 'su --help' for more information.

You would need to add user1 to the wheel group, then as Bodo points out, execute;

sudo -u user2 passwd

It's clear to me that sudo is your intended use here, as you are trying to execute a single command with temporary privilege elevation. (which is what sudo is for).

However, for completeness and as user Bib points out, you could execute;

su - _user_ foo

...which would allow you to run as root for another user.

This is the 'login shell' option for su (-, -l or --login). This is also handy for granting root privileges in the scenario, where the user doesn't have sudo privileges (and where the admin don't want them to, either.).

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    Well, you sure as heck can use su - _user_ to run a command as another user. It's not limited to root.
    – Bib
    Commented Jan 27, 2022 at 18:26
  • yes, Bib. you can do that. that's the login shell option. I never said that wasn't a possibility or that su was limited to root... i was stating why they got the error and what the difference between su and sudo are.
    – jrdnjhntsn
    Commented Jan 27, 2022 at 18:35

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