Shell script to check if process is running

Question

There is some weird behavior going on that leads me to think there may be something going on...

So I have a shell script executed by cron. Basically it is meant to check if Node.js is running. If so, log the date... if not then log nothing! At the time I built it I tested it and saw it logged when a node script was running and did not log when it stopped running...

Recently I knew Node went down and thought it was the perfect opportunity to check if the script did what its supposed to do. It didnt! And it does not... :(

Here is the script:

#!/bin/bash

if ps -Al | grep -v grep | grep -q node 
then
        date > /etc/nodeCheck.log 
else
        date > /dev/null 
fi

Permissions on this .sh are correct, paths used exist, running

$ps -A | grep -v grep | grep -q node

returns nothing and

$echo $?
1

So shouldn't it be going to the else block? node is a process started after bootup. The shell script does not work correctly both when run by cron or by me when I am SSH'd in.

Am I missing something fundamental here?

TIA

Niko

Answer 1

Another way to check process by name:

if killall -s 0 node &>/dev/null; then
    ...

Or if shell doesn't support &>:

if killall -s 0 node >/dev/null 2>&1; then

Answer 2

This isn't exactly an answer to your question, but perhaps it's a solution to your problem.

One of the issues I've had with Node is that the server process doesn't store its pid anywhere. So rather than having a thing that cron runs to "check" whether it's running, I wrapped the node executable in a script that simply relaunches it if it crashes.

#!/bin/sh

cd /path/to/my/software

while sleep 1; do
  date '+%Y-%m-%d %T - nodejs restarted' 
  logger "nodejs restarted"; date '+%Y-%m-%d %T - nodejs restarted' | Mail -v -s "nodejs restarted on `hostname -s`" [e-mail]
  node main.js
done

This script gets run once, when the system starts up. It launches Node, and if Node never crashes, all is well and good, but if it does, I get a notification, a log entry, and a restart.

I run this in FreeBSD, but it should run equally well in Linux or other operating systems.

Answer 3

Unless you're running BSD ps, you should be able to use a -C flag or pgrep

-C cmdlist      Select by command name. This selects the processes whose executable 
                name is given in cmdlist.

For example,

if ps -C node > /dev/null
then
        date > /etc/nodeCheck.log 
else
        date > /dev/null 
fi

or

if pgrep node > /dev/null
then
        date > /etc/nodeCheck.log 
else
        date > /dev/null 
fi