gracefully closing node.js applications via signal handling

To make your node.js application gracefully respond to shutdown signals, use process.on(SIGNAL,HANDLER).

For example, to respond to SIGINT (typically Ctrl-c), you can use:

process.on( "SIGINT", function() {
  console.log('CLOSING [SIGINT]');
  process.exit();
} );

Note that without the process.exit(), the program will not be shutdown. (This is you chance to override or "trap" the signal.)

Some common examples (in CoffeeScript):

process.on 'SIGHUP',  ()->console.log('CLOSING [SIGHUP]');  process.exit()
process.on 'SIGINT',  ()->console.log('CLOSING [SIGINT]');  process.exit()
process.on 'SIGQUIT', ()->console.log('CLOSING [SIGQUIT]'); process.exit()
process.on 'SIGABRT', ()->console.log('CLOSING [SIGABRT]'); process.exit()
process.on 'SIGTERM', ()->console.log('CLOSING [SIGTERM]'); process.exit()

PS: On Linux (and similar) you can enter kill -l on the command line to see a list of possible signals, and kill -N PID to send signal N to the process with process ID PID.

Shell script for service-like CoffeeScript/Node.js apps using forever

This is an example of a (bash) shell script that uses the forever module to start and stop a CoffeeScript application as if it were a service.

(Also at rodw/coffee-as-a-service-via-forever.sh.)

Cheat Sheet for Linux Run Levels

"Standard" Linux uses the following run levels:

• Run Level 0 is halt (shutdown).
• Run Level 1 is single-user mode.
• Run Level 2 is multi-user mode (without networking)
• Run Level 3 is multi-user mode (with networking). This is the normal "terminal" mode. (I.e., before the display manager is run).
• Run Level 4 is undefined.
• Run Level 5 is multi-usermode with a GUI display manager (X11).
• Run Level 6 is reboot.

In Debian and its derivatives run levels 2 thru 5 are the same: multi-user mode with networking, and with a display manager if available.

• Run Level 0 is halt (shutdown).
• Run Level 1 is single-user mode.
• Run Level 2-5 is multi-user mode with networking and a GUI display manager when available.
• Run Level 6 is reboot.

Debian also adds Run Level S, which is executed when the system first boots.

Also see Wikipedia's article on run levels.

How to disable services in Debian/Linux

The easy way is to install sysv-rc-conf:

aptitude install sysv-rc-conf
sysv-rc-conf

Manually, use update-rc.d and specify the run levels, like so:

update-rc.d SERVICE_NAME stop 0 1 6 3 . start 2 4 5 .