1. M/Monit 是什么？
简单而言，Monit 是一款轻量级，好用的监控工具，它能够监控unix系统，网络，云服务等任务，它还能够自动重启服务。
下面是一段官方的描述：
Easy, proactive monitoring of Unix systems, network and cloud services. Conduct automatic maintenance and recovery and execute meaningful causal actions in error situations
2. 如何安装 M/Monit ?
apt 类系统上安装：
sudo apt-get install monit
yum 类系统上安装:
sudo yum install monit
3. M/Monit 主要目录
以ubuntu系统为例，monit的配置目录主要在 /etc/monit, 主要包含：
drwxr-xr-x 2 root root 4096 Nov 5 05:33 conf.d
-rw------- 1 root root 10962 Nov 5 04:30 monitrc
drwxr-xr-x 2 root root 4096 Nov 4 10:24 monitrc.d
drwxr-xr-x 2 root root 4096 Nov 4 10:24 templates
其中 monitrc 是主配置文件，config.d 是各种具体任务监控的配置目录，monitrc 会包含 conf.d 所有文件。 monitrc.d 里面有很多配置模版，你可以直接使用，只需要做个软链到 conf.d 即可。
4. 一些常用任务监控脚本
nginx 监控
check process nginx with pidfile /var/run/nginx.pid
group www
group nginx
start program = "/etc/init.d/nginx start"
stop program = "/etc/init.d/nginx stop"
# if failed port 80 protocol http request "/" then restart
if 5 restarts with 5 cycles then timeout
depend nginx_bin
depend nginx_rc
check file nginx_bin with path /usr/sbin/nginx
group nginx
include /etc/monit/templates/rootbin
check file nginx_rc with path /etc/init.d/nginx
group nginx
include /etc/monit/templates/rootbin
redis 监控
if failed port 6379 then alert
系统资源监控
check system matter.build
if loadavg (1min) > 4 then alert
if loadavg (5min) > 2 then alert
if memory usage > 75% then alert
if swap usage > 25% then alert
if cpu usage (user) > 70% then alert
if cpu usage (system) > 30% then alert
if cpu usage (wait) > 30% then alert
check device var with path /
if SPACE usage > 80% then alert
sidekiq 监控
check process rails_app-sidekiq
with pidfile /var/www/rails_app/shared/pids/sidekiq.pid
stop program = "/usr/bin/env HOME=/home/deploy /bin/bash -c '[ ! -f /var/www/rails_app/current/tmp/pids/sidekiq.pid ] || kill `cat /var/www/rails_app/current/tmp/pids/sidekiq.pid` || true'"
if changed pid then alert
unicorn 监控
if failed unixsocket /tmp/unicorn.rails_app_production.sock then alert