CODEWITHSUNDEEP
linuxbashshellunix
acmoune
acmoune

Reputation: 3433

How to check if a daemon successfully started as part of a script?

Let's say I have this script:

start daemon1 &
start daemon2 &
echo "Running..."

daemon2 can only be started if daemon1 was started successfully. if daemon1 did not start successfully, then the script most be aborted

"Running..." should be displayed only if daemon2 started successfully. if daemon2 did not start successfully, then the script most be aborted

How can I make this with a shell script ?

Upvotes: 0

Views: 1297

Answers (2)

Mark
Mark

Reputation: 4453

I propose you capture the daemon's pid (process id) and then determine if the pid exists (after some delay in case daemon1 takes a while to process to start and crash). So here is a way of achieving that (in Linux, I'm ignoring the 'start' in your commands since I'm not familiar with the windows cmdline environment ):

start daemon1 &
pid1=$!
sleep 3 # give daemon1 some time to get going 
if  
  kill -0 $pid1 2>/dev/null
then
  start daemon2 &
  pid2=$!
  sleep 3 # give daemon2 some time to get going 
  if
     kill -0 $pid2 2>/dev/null
  then
     echo "Running..."
  fi
fi

The necessary ingredients for this recipe are:

  1. $! returns the child's pid (of the last background process run)

  2. kill -0 <pid> is a way of determining if a pid is valid (in the process table)

Upvotes: 1

doca
doca

Reputation: 1558

You can check the PID of the started process to see if it is running

start daemon1 &
P=$!
if kill -0 $P > /dev/null 2>&1 ; then 
    start daemon2 &
    P=$!
    if kill -0 $P > /dev/null 2>&1 ; then
        echo "Running..."
    fi
fi

Untested code. Comment if something is not right

Upvotes: 2

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