execute su -c over ssh

Question

I am trying to check the BIOS version of a server over SSH, a command that requires root privileges:

ssh remote-server su -c dmidecode

but this of course fails with the error:

standard in must be a tty

How do I make this work? I cannot use sudo, and when I try to log in as root@remote-server, it won't accept the password I use for the 'su' command. I am using RedHat Enterprise Linux 4.

I would also suggest looking into using sudo instead of "su -c" — wfaulk, Oct 08 '09 at 21:32
I'd love for there to have been more information as to why "I cannot use sudo" was the case. — dannysauer, Mar 07 '16 at 18:53
@dannysauer Not all OS's have it. I am here trying to solve the same problem, except that I'm not on RedHat like OP. I'm on a unix variant with no sudo. I'm curious as to why OP cannot use it on RedHat, but I'm grateful anyway that the question has been asked. — Loduwijk, Oct 22 '19 at 18:11
sudo builds on all of the UNIX variants I'm familiar with, but I'll agree that it's not installed (or configured) on all of them. I was really more curious why it wasn't configured there (I think - it's been a few years). :D — dannysauer, Oct 24 '19 at 19:51

score 14 · Accepted Answer · answered Oct 08 '09 at 21:27

14

Use -t to force ssh to allocate a tty:

ssh -t -t remote-user su -c dmidecode

You might also consider allowing root to ssh directly. If you're using public key authentication, this may be more secure as you won't be passing a password around. If you decide to do this, consider blocking root logins from anywhere except your trusted IP addresses by putting the following in /etc/security/access.conf:

+ : root : 10.20.30.40
- : root : ALL EXCEPT LOCAL

and make sure UsePAM isn't disabled in sshd_config

answered Oct 08 '09 at 21:27

geocar

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Any reason you included two `-t`s in your example? – wfaulk Oct 08 '09 at 21:31
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According to the man page, multiple -t options "force tty allocation, even if ssh has no local tty" – Heath Oct 08 '09 at 21:46
This doesn't work for me on Fedora. It allows the script to prompt me for my password, but my password displays as plaintext, and when I press enter, it just hangs. – Cerin Jan 20 '11 at 17:20
@Chris that's a different problem. Try asking a new question. – geocar Mar 13 '11 at 01:14
@Heath thanks for the comment about the double -t, that works for me on Centos – Paul Sheldrake Sep 25 '15 at 03:20

score 0 · Answer 2 · answered Oct 08 '09 at 21:30

0

Can't you just log in to the remote server as a standard user and then use sudo?

You could also try quoting the command to be executed by ssh, as in

ssh remote-server 'su -c dmidecode'

or

ssh remote-server "su -c dmidecode"

answered Oct 08 '09 at 21:30

Massimo

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-1 because quoting the command isn't going to resolve his lack of a terminal. +1 for suggesting sudo. It's a wash. – wfaulk Oct 08 '09 at 21:34
as I specified "I cannot use sudo" – aaron Oct 08 '09 at 21:37

execute su -c over ssh

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