Bash script not executing command properly when run from script

Question

I have a shell script as follows

#!/bin/bash
USER=someuser
HOSTNAMEORIP=somehostname
SCRIPT="/etc/rc.d/netif restart && /etc/rc.d/routing restart"
su -c "ssh -l ${USER} ${HOSTNAMEORIP} ${SCRIPT}" -s /bin/sh someotheruser

If I login to the machine and just run the "/etc/rc.d/netif restart && /etc/rc.d/routing restart" it works. But if i run the entire script above, i get sh: 1: /etc/rc.d/routing: not found as if it's not handling the script part the same. I can even use the above script without a user like this

#!/bin/bash
USER=someuser
HOSTNAMEORIP=somehostname
SCRIPT="/etc/rc.d/netif restart && /etc/rc.d/routing restart"
ssh -l ${USER} ${HOSTNAMEORIP} ${SCRIPT}

And it works but I need to use su -c <command> -s /bin/sh user because another application is calling the script and the user associated is the only one with ssh-key login/no password to the other machine.

How can i make su -c "ssh -l ${USER} ${HOSTNAMEORIP} ${SCRIPT}" -s /bin/sh someotheruser run the script properly in this use case?

I think it's running /etc/rc.d/routing restart on the calling machine rather than the machine you are sshing to. Try separating SCRIPT into two commands rather than together. — madebydavid
– madebydavid, Commented Jul 15, 2017 at 16:12
I mean two separate ssh commands: su -c "ssh -l ${USER} ${HOSTNAMEORIP} ${SCRIPT1}" -s /bin/sh someotheruser su -c "ssh -l ${USER} ${HOSTNAMEORIP} ${SCRIPT2}" -s /bin/sh someotheruser — madebydavid
– madebydavid, Commented Jul 15, 2017 at 16:39

that other guy · Accepted Answer · 2017-07-15 16:42:08Z

5

Let's just work through it. This command:

su -c "ssh -l ${USER} ${HOSTNAMEORIP} ${SCRIPT}" -s /bin/sh someotheruser

Will execute this string as a shell command:

ssh -l someuser somehostname /etc/rc.d/netif restart && /etc/rc.d/routing restart

This is clearly wrong, and will fail with the same error.

To fix it, let's fix the command and work backwards. You should be executing

ssh -l someuser somehostname '/etc/rc.d/netif restart && /etc/rc.d/routing restart'

Therefore, you can update your script like this:

#!/bin/bash
USER=someuser
HOSTNAMEORIP=somehostname
SCRIPT="/etc/rc.d/netif restart && /etc/rc.d/routing restart"
su -c "ssh -l ${USER} ${HOSTNAMEORIP} '${SCRIPT}'" -s /bin/sh someotheruser
#                                     ^---      ^---

Note that this hinges on the fact that $SCRIPT does not contain embedded single quotes. If does or if you don't know, you can use $(printf "%q" "$SCRIPT") instead of '$SCRIPT' in the embedded string to have bash auto-escape it.

Or you can switch to sudo. Since it uses safe and robust execve(2) semantics instead of system(3) semantics, you wouldn't have to nest escaping:

sudo -u someotheruser ssh -l "$USER" "$HOSTNAMEORIP" "$SCRIPT"

edited Jul 15, 2017 at 16:42

answered Jul 15, 2017 at 16:36

that other guy

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3 Comments

Technophobe01 Over a year ago

@jtlindsey My sense was that the ssh -t -t would fix the issue by allowing the ssh to allocate a tty. I'll noodle on the problem further.

Gordon Davisson Over a year ago

@Technophobe01 That won't help, since the quoting problem means && /etc/rc.d/routing restart is being parsed and executed on the local computer, not passed to ssh.

Technophobe01 Over a year ago

Gordon Davisson - Agreed. 'That other guy' provided a nice clean answer and explanation. :-)

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