ssh hang in shell script

aggrishabh · 05-20-2016, 05:21 PM

Hi All,

i have a script which is doing ssh to many servers in for loop and execute sed command.

sometime sed hangs and so the whole script.

sed -i s:^password.*:"password --md5 NEW_PASS": /boot/grub/grub.conf

above sed command is working fine for most of the hosts but hangs for some specially RHEL5. please suggest if something is wrong with the command.
Also is there any way we can move to next serer in list if command fail to execute in 5 or 10 sec without user intervention.

keefaz · 05-20-2016, 08:18 PM

you could use 'screen' (if available) to detach from current terminal so the commands are executed in background somewhat.

Code:

for server in server1 server2 server3; do
  ssh $server screen -d -m sed -i 's/^password.*/password --md5 NEW_PASS/' /boot/grub/grub.conf
done

Turbocapitalist · 05-20-2016, 11:52 PM

Quote:

Originally Posted by aggrishabh

Also is there any way we can move to next serer in list if command fail to execute in 5 or 10 sec without user intervention.

ssh will pass on the exit code of the remote program, but running screen remotely will eat that though it might allow time for the program to complete, if time is what it needs.

Keefaz' loop could be modified to use 'timeout'

Code:

for server in server1 server2 server3; do
  ssh $server timeout -k 10 5 sed -i 's/^password.*/password --md5 NEW_PASS/' /boot/grub/grub.conf
  echo Status was $?
done

That would send a TERM signal after 5 seconds to 'sed' if it is still running. Then if that didn't work it would send a KILL signal after 10 seconds. But if 'sed' ran to a natural completion its return code would be passed to the original shell, the one running the loop. If 'timeout' stops 'sed' then the exit code will be 124 or 137

jpollard · 05-21-2016, 08:51 AM

Quote:

Originally Posted by aggrishabh

Hi All,

i have a script which is doing ssh to many servers in for loop and execute sed command.

sometime sed hangs and so the whole script.

sed -i s:^password.*:"password --md5 NEW_PASS": /boot/grub/grub.conf

above sed command is working fine for most of the hosts but hangs for some specially RHEL5. please suggest if something is wrong with the command.
Also is there any way we can move to next serer in list if command fail to execute in 5 or 10 sec without user intervention.

I'm not certain of this, but in some cases a system may need a terminal attached for it work properly. You might
try using

Code:

ssh -t $server <rest of your command>

Next, I would suggest updating those RH5 systems to something newer.