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# 1  
Old 09-03-2014
Shell sIs there something special I need to do when using sudo in a script?
I have a script in which I used "sudo -s" I notice some extremely strange behavior when executing this script. To investigate this I decided to recreate the problem in the following script. I notice that "sudo -s" is only being executed one time. Soon after completely falls apart. Is there something special I need to do to get this to work?

Code:
     1  #! /bin/sh
     2  
     3  echo "test"
     4  echo "the script is working"
     5  
     6  sudo -s 
     7  
     8  echo "reading script after first sudo"
     9  sudo -s
    10  echo " reading script after second sudo"
    11  
    12  echo "the script is still working" 
    13  echo " still working"

Produces the following results...

Code:
./btest
test
the script is working
#
!!!note script stops here. first sudo worked!!!!

# 2  
Old 09-03-2014
'sudo -s' does not mean "run the lines after this in a new shell". It means "run a completely new, independent shell with root permissions".

It works in terminal because the shell runs text from standard-input, so ends up reading the same thing even after the new shell is launched. Scripts are not fed into standard input, so the new subshell doesn't share the same input lines.

Try this:

Code:
/bin/bash < myscript.sh

That feeds it into stdin, causing the sharing you expected.

Generally though, if you want to run a script as sudo, it's sudo script, not a script containing sudo.
Last edited by Corona688; 09-03-2014 at 04:02 PM..
# 3  
Old 09-03-2014
Quote:
Originally Posted by Corona688
'sudo -s' does not mean "run the lines after this in a new shell". It means "run a completely new, independent shell with root permissions".

It works in terminal because the shell runs text from standard-input, so ends up reading the same thing even after the new shell is launched. Scripts are not fed into standard input, so the new subshell doesn't share the same input lines.

Try this:

Code:
/bin/bash < myscript.sh

That feeds it into stdin, causing the sharing you expected.



Generally though, if you want to run a script as sudo, it's sudo script, not a script containing sudo.




Hi, thanks for the response. I think I am barking up the wrong tree here. sudo does not seem to be the way to go. Maybe I would be better off changing the permissions of my script so that it runs as root.
# 4  
Old 09-03-2014
Quote:
Originally Posted by busi386
Hi, thanks for the response. I think I am barking up the wrong tree here. sudo does not seem to be the way to go. Maybe I would be better off changing the permissions of my script so that it runs as root.
Scripts don't work that way either. setuid doesn't work on scripts on many systems, or works in unexpected ways.

Maybe if you explained what you were actually trying to do, instead of showing us broken programs that don't do what you want to do, we'd understand what you wanted to do.
# 5  
Old 09-03-2014
How about this? A script that attempts to run itself with sudo unless it's root already. $0 is a special variable meaning "the file this script was run on", "$@" is a special variable meaning "all arguments". UID is a special variable which is set to the current user ID, which would be 0 if the script was running as root.

So if the UID isn't 0, it runs "sudo ./myscript.sh "given" "arguments". The exec causes it to replace itself so the 'exit 1' after it is redundant, just there in case the 'exec' fails for some reason.

Code:
#!/bin/sh

if [ "$UID" -ne 0 ]
then
        if [ ! -f "$0" ]
        then
                echo "Can't find '$0', can't elevate privileges" >&2
                exit 1
        fi

        echo "Attempting to run '$0' with sudo" >&2

        exec sudo "$0" "$@"
        exit 1
fi

echo "This part should run as root"
echo "UID is $UID"

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