topic Re: while loop exits after call to ssh in Operating System - Linux

while loop exits after call to ssh

Kevin Nikiforuk — Fri, 02 Sep 2005 14:11:02 GMT

The DBA team I work with has a shell script for starting and stopping their databases that uses sudo (1.6.6) to change to another account, then ssh (A.03.81.002) to a remote server to work with the Oracle Application Stack. Here is a code snippet:

==============================================
ORATAB=/etc/oratab

trap 'exit' 1 2 3
case ${ORACLE_TRACE} in
T) set -x ;;
esac

# Set path if path not set (if called from /etc/rc)
case ${PATH} in
"") PATH=/bin:/usr/bin:/etc
export PATH ;;
esac

cat ${ORATAB} | while read LINE
do
case ${LINE} in
\#*) #comment-line in oratab
;;
*)
# Proceed only if third field is 'Y'.
if [ "`echo $LINE | awk -F: '{print $3}' -`" = "Y" ] ; then
ORACLE_SID=`echo $LINE | awk -F: '{print $1}' -`
if [ "${ORACLE_SID}" != '*' ] ; then
APPSUSER=`grep $ORACLE_SID /home/oraoper/bin/apps.pwd | awk '{print $5} '`
echo $ORACLE_SID " " $APPSUSER
if [[ -n $APPSUSER ]]
then
typeset -u APPSNODE=`grep $ORACLE_SID /home/oraoper/bin/apps.pwd | awk '{print $6} '`
typeset -u NODE=`uname -n`
/opt/sudo/bin/sudo -u $APPSUSER ssh $APPSUSER@$APPSNODE ls -l
fi
fi
fi
;;
esac
done

==============================================

The first time it hits an SID that requires the call to sudo and ssh, it completes the sudo and ssh, but when it returns to the top of the while loop, it exits, even though there are still lines to process.

Any suggestions?

Re: while loop exits after call to ssh

John Dvorchak — Fri, 02 Sep 2005 14:20:49 GMT

ssh exits with the exit status of the command that is run. Is it possible that if all files are not listed with the ls -l that the exit status of ls is >0 and even though ssh exits, it is passing the non-zero exit status to the script.

Make sure of the permissions of the directory and files you are listing.

man ssh

Re: while loop exits after call to ssh

Bharat Katkar — Fri, 02 Sep 2005 14:22:31 GMT

Not sure about this but still can you check if this works for you:
Instead of "cat ${ORATAB} | while read LINE"
use
"cat `echo $ORATAB` | while read LINE"

i have used back quotes for echo oratab.

Regards,

Re: while loop exits after call to ssh

Kevin Nikiforuk — Fri, 02 Sep 2005 15:18:47 GMT

I've checked the return code of the sudo and it is zero.

I also tried the cat `echo ${ORATAB}` and that didn't make a difference.

Re: while loop exits after call to ssh

Alex Lavrov. — Fri, 02 Sep 2005 16:09:58 GMT

IT happens because you have a pipe there and ssh (and there some more commands) that break this pipe and the loop ends. It's a known issue.

You must use "-f" or "-n" option of ssh:

-f Requests ssh to go to background just before command execution.
This is useful if ssh is going to ask for passwords or
passphrases, but the user wants it in the background. This
implies -n. The recommended way to start X11 programs at a
remote site is with something like ssh -f host xterm.

-n Redirects stdin from /dev/null (actually, prevents reading from
stdin). This must be used when ssh is run in the background. A
common trick is to use this to run X11 programs on a remote
machine. For example, ssh -n shadows.cs.hut.fi emacs & will
start an emacs on shadows.cs.hut.fi, and the X11 connection will
be automatically forwarded over an encrypted channel. The ssh
program will be put in the background. (This does not work if
ssh needs to ask for a password or passphrase; see also the -f
option.)

Alex.

Re: while loop exits after call to ssh

Victor Fridyev — Fri, 02 Sep 2005 16:22:52 GMT

Hi,

I agree with Alex, -n resolves the problem

HTH

Re: while loop exits after call to ssh

Kevin Nikiforuk — Fri, 02 Sep 2005 16:50:24 GMT

I've done a quick test and it looks good. I'll foward it on to the DBAs and see if it works. I had noticed those flags in the man page, but didn't know they'd apply to me.

Re: while loop exits after call to ssh

Steven E. Protter — Sat, 03 Sep 2005 14:30:17 GMT

Clearly there are some very good answers in this thread. So much so, that I bookmarked it.

Please take the time to assign points to all answers and high points to the answers that magically solved the problem.

From: the peanut gallery.

SEP