bash problem

unihiekka · 11-09-2005, 10:45 AM

Hi ya!

I am writing a bash script in which I have to use commands that are only available for the superuser. The problem is that I need the su command in bash, so I have to enter the password, but after that it does not run the rest of the script. How can I come around that problem? Or can I "integrate" the password in the script somehow?!

Code:

#!/bin/bash
# ATOMIC CLOCK SYNC
echo "Atomic Clock Synchroniser"
su
ntpdate ntp.nasa.gov
hwclock --systohc
echo "Clocks synchronised"
exit
exit
#EOF

The programme should synchronise my clock (and hardware clock) to some atomic clock. I will make a button of it on my desktop, so I can - whenever I want - synchronise, since my clock should not be synchronised necessarily all the time. I just want to click it and done, not entering my password if that is possible...

Thanks!

druuna · 11-09-2005, 10:57 AM

Hi,

When your script executes the su command it starts a new shell (and patiently waits). After it is closed (by you, manually) it will return control to the script and execute the commands below it (as your regular user). That is the reason why this approach does not work.

Try using something like:

Code:

#!/bin/bash
# ATOMIC CLOCK SYNC
echo "Atomic Clock Synchroniser"
su - -c "ntpdate ntp.nasa.gov ; hwclock --systohc"
echo 'Clocks synchronised'"
# EOF

man su for details.

MensaWater · 11-09-2005, 11:01 AM

Rather than having a non-root user become root you might want to do it via root's cron. See the thread at: http://www.linuxquestions.org/questi...hreadid=381120

To add entries to crontab you type "crontab -e" after becoming root. Once its in cron it will run periodically as root to set your time.

Having said that - the answer to your question as phrased is you need to do the
"su -c <command>" syntax.

You could either have it do the su -c for each of the commands (ntpdate and hwclock) OR just put both commands in a separate script and have your first one do su -c calling that separate script name.

homey · 11-09-2005, 11:54 AM

Might be a good idea to put some checking in there...

Code:

#!/bin/bash
# ATOMIC CLOCK SYNC needs ntp package
echo Atomic Clock Synchroniser
   su - -c "which ntpdate > /dev/null 2>&1"
if [ $? = 1 ]; then
   echo "The ntp package isn't installed"
   exit 1
else
   su - -c "ntpdate ntp.nasa.gov ; hwclock --systohc"
   echo "Clocks synchronised"
fi

schneidz · 11-09-2005, 02:51 PM

hmm. i dont use it, but isnt that what sudo is for?

MensaWater · 11-09-2005, 02:59 PM

Quote:

Originally posted by schneidz
hmm. i dont use it, but isnt that what sudo is for?

Yes but sudo requries you to input your own password on invocation so wouldn't be a work around. Sudo will cache the password for your session for some finite period of time but if you wait to long between sudo commands it will ask for your password again. This is so someone doesn't leave their terminal open and walk away allowing some other user to get access to things they shouldn't have.

As I mentioned in my prior post the best way is to just run this via cron. Presumably he doesn't want password because he wants to automate it and that's exactly what cron is designed for.

puffinman · 11-09-2005, 03:21 PM

Why not just run the ntp daemon? It will maintain the clock accuracy better with fewer large jumps in the time, as periodically running ntpdate might tend to do.

MensaWater · 11-10-2005, 06:40 AM

I was initially going to say run ntp daemon myself but found it doesn't come with Debian even though ntpdate does. Presumably there's an ntpd package one could download but for me it was just as fast to set it up in cron.

On my RedHat systems I do run ntpd. On my HP-UX I run xntpd.