Run a task in background and know the time of its termination

Question

I need to run a unix shell script (my_script) in background and monitor it from web interface.

I start the actual script from php like so:

$command = 'my_script';
$pid= exec("nohup {$command} > {$logFile} & echo $!");

Then $pid contains the pid of my process and I can find out if the process is still running by checking file_exists("/proc/{$pid}").

However, here's the problem: how do I find out when the process has terminated and how long it ran when it is terminated?

Also, is there a good way to find out when the process has started? I can record the timestamp in PHP before or after I make the exec call, but that will be somewhat inaccurate.

EDIT:

To clarify, PHP script can't wait for shell script to finish. The shell script needs to be run in the background. I can probably wrap three commands (record time started, run my_script, record time finished) into one shell with sh -c pass it to nohup, but I would prefer the whole sequence to be atomic, so that I do not end up with only start time recorded if something goes wrong.

Answer 1

You'll need to get rid of the intermediary shell and start it as your direct child, probably with something like proc_open (I'm no PHP expert). Then you'll get a SIGCHLD when the child terminates. You can install a signal handler for it (pcntl_signal most likely) and in it nonblockingly (WNOHANG) wait (pcntl_waitpid ) on your child's PID and if the wait succeeds, record the time and remove the signal handler.

file_exists("/proc/{$pid}") is unreliable if you don't control the wait calls (if pid isn't your child) because PIDs get recycled.

Answer 2

This seems to call for at/batch since you are using a web front end. The results can either be emailed to the user or a que which gets poled by the user (using client side javascript or just plain user based checking).

Answer 3

The easiest way to record a script's exit conditions is to make it record them.

#!/bin/sh
trap 'date +"
    My name is $0. My PID is $$.
    My start time was '"$(date)."'
    The time is now %X on %x.
    My exit code is $?. Goodbye.
"   >/tell/somebody' EXIT
: now do some stuff

An EXIT trap should work in every exit scenario but one which is initiated by a SIGKILL.

If you cannot edit the script in question just wrap the script in a shell whose instructions you can control - such as with sh -c as you mentioned:

trap=': the trap' sh -c '
trap "$trap" 0;. "$0"'   \
    ./script/i/cant/edit \
    positional params    &

A similar thing might done w/ sh -s, but the value of $0 may not be as simply as controlled. With some shells you need to exec a new infile/replacement shell in order to alter it (I sometimes use symlinks and PATH=. w/ exec to change/drop all path components in a process name).

echo 'trap "$trap" EXIT'   |
cat - ./script/i/cant/edit | 
trap=': the trap' sh -s -- \
    positional params go here &