Another handy tool i've grown to like is Monit, which makes keeping tabs on memory-hungry processes much easier.
Basically once configured it helps keep an eye on particular process (e.g PostFix, PostGreSQL, Apache or your disk space). If one is starting to use too much memory, your running low on disk space or it's just no longer responding it can automatically restart it for you and alert you in the process; making system administration that little bit easier.
Installing
Install with Aptitude using,
sudo aptitude install Monit
After which it will tell you it's won't start until it's been configured,
Starting daemon monitor: -e monit won't be started/stopped
unless it it's configured
-e please configure monit and then edit /etc/default/monit
-e and set the "startup" variable to 1 in order to allow
-e monit to start
Configuring
First make a backup copy of it's initial config, in case you need to rollback:
sudo cp /etc/monit/monitrc /etc/monit/monitrc.orig
Now edit it with:
sudo nano /etc/monit/monitrc
- uncomment set daemon 120, so monit will run every two minutes.
- uncomment set alert and enter the email address you want to use for email alerts.
- uncomment include /etc/monit.d/* so it will read in all config files within that directory.
save and create the monit.d directory,
sudo mkdir /etc/monit.d
By using a wildcard for that last config change you can build up separate .monitrc files for each service you want to monitor, making future modifications easier.
For example, monitor disk usage using:
sudo nano /etc/monit.d/system.monitrc
check system mysite.com
if loadavg (1min) > 4 then alert
if loadavg (5min) > 2 then alert
if memory usage > 85% then alert
check device rootfs with path /dev/sda1
if space usage > 85% then alert
Starting
After making your changes, check the syntax you used is correct with,
sudo monit -t
...if you uncommented the last line include /etc/monit.d/* and you've got no config files in there you'll get an error stating it can't find any config files there. don't worry too much about that, no need running it if you haven't got anything for it to do.
Now edit,
sudo nano /etc/default/monit
And change startup=0 to 1 to enable it, save the file and run,
sudo /etc/init.d/monit start
To start the service, stop it with,
sudo /etc/init.d/monit stop
...based partly on an example from Monit for Peace of Mind & Monitoring Ubuntu Services with Monit. More info at the official Monit site.
Plus a good example pastie here,
