 
Subject
Monit is a small, easy to configure monitoring system for *nix systems that will attempt to restart services that have failed. Grab the tarball, extract, configure, make, and make install:
[usr-1@srv-1 ~]$ tar -xzf mon*4.7*.gz
[usr-1@srv-1 ~]$ cd mon*7
[usr-1@srv-1 monit-4.7]$ ./configure
checking for gcc... gcc
checking for C compiler default output file name... a.out
checking whether the C compiler works... yes
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monit has been configured with the following options:
Architecture: LINUX
SSL support: enabled
SSL include directory: /usr/include
SSL library directory: /usr/lib
resource monitoring: enabled
resource code: sysdep_LINUX.c
Compiler flags: -g -O2 -Wall -D _REENTRANT -I/usr/include
Linker flags: -lpthread -lcrypt -lresolv -lnsl
-L/usr/lib -lssl -lcrypto
pid file location: /var/run
[usr-1@srv-1 monit-4.7]$
[usr-1@srv-1 monit-4.7]$ make
bison -y -dt p.y
/bin/mv -f y.tab.h tokens.h
flex -i l.l
gcc -c -DLINUX -I. -I./device -I./http -I./process -I./protocols
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protocols/rdate.o protocols/rsync.o protocols/smtp.o protocols/ssh.o
protocols/tns.o device/sysdep_LINUX.o process/sysdep_LINUX.o
y.tab.o lex.yy.o -lfl -lpthread -lcrypt -lresolv -lnsl -L/usr/lib
-lssl -lcrypto -o monit
[usr-1@srv-1 monit-4.7]$
[usr-1@srv-1 monit-4.7]$ su
Password:
[root@srv-1 monit-4.7]# make install
/usr/bin/install -c -m 755 -d /usr/local/bin || exit 1
/usr/bin/install -c -m 755 -d /usr/local/man/man1 || exit 1
/usr/bin/install -c -m 555 -s monit /usr/local/bin || exit 1
/usr/bin/install -c -m 444 monit.1 /usr/local/man/man1/monit.1 || exit 1
[root@srv-1 monit-4.7]#
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The configuration file is stored in /etc/monitrc. The top part of the configuration file sets the polling intervals, logging options, and web interface options. After that, just add on sections for the services to check and recover. Here is a sample config file that checks sshd:
[root@srv-1 usr-1]# cat /etc/monitrc
set daemon 120 # Poll at 2-minute intervals
set logfile syslog facility log_daemon
set alert root@localhost
set httpd port 2812 and use address localhost
allow localhost # Allow localhost to connect
allow admin:monit # Allow Basic Auth
check process sshd with pidfile /var/run/sshd.pid
start program "/etc/init.d/sshd start"
stop program "/etc/init.d/sshd stop"
if failed port 22 protocol ssh then restart
if 5 restarts within 5 cycles then timeout
[root@srv-1 usr-1]#
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Let's start the monit daemon:
[root@srv-1 usr-1]# monit
Starting monit daemon with http interface at [localhost:2812]
[root@srv-1 usr-1]#
[root@srv-1 usr-1]# tail /var/log/messages
Apr 27 08:36:20 srv-1 monit[3258]: Starting monit daemon with http interface
at [localhost:2812]
Apr 27 08:36:20 srv-1 monit[3260]: Starting monit HTTP server
at [localhost:2812]
Apr 27 08:36:20 srv-1 monit[3260]: monit HTTP server started
Apr 27 08:36:20 srv-1 monit[3260]: Monit started
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The logon, as we set in the monitrc, is admin with a password of monit:
Here is what the administration web console looks like:
For a test, let's stop sshd and try and connect from another host:
[root@srv-1 usr-1]# /etc/init.d/sshd stop
Stopping sshd: [ OK ]
[root@srv-1 usr-1]#
srv-5:~ usr4$ ssh usr-1@10.50.100.1
ssh: connect to host 10.50.100.1 port 22: Connection refused
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Just wait a bit and try and reconnect:
srv-5:~ usr4$ ssh usr-1@10.50.100.1
Last login: Thu Apr 27 08:37:52 2006 from 10.50.100.200
[usr-1@srv-1 ~]$
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We are back in! The logs show that monit did what it was supposed to do:
Apr 27 08:52:25 srv-1 monit[3260]: 'sshd' process is not running
Apr 27 08:52:25 srv-1 monit[3260]: 'sshd' trying to restart
Apr 27 08:52:25 srv-1 monit[3260]: 'sshd' start: /etc/init.d/sshd
Apr 27 08:52:25 srv-1 sshd: succeeded
Apr 27 08:54:25 srv-1 monit[3260]: 'sshd' process is running with pid 4113
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