Monit

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Monit, not to be confused to M/Monit, is an AGPL3.0 licensed system and process monitoring tool. Monit can automatically restart crashed services, display temperatures from standard hardware (through lm_sensors and hard drives from smartmontools for example). Service alerts can be sent based on a wide criteria including a single occurrence or occurrences over a period of time. It can be accessed directly through the command line or ran as a web app using its integrated HTTP(S) server. This allows quick and streamlined snapshot of a given systems status.

Installation

Install the monit package and any software for optional testing such as lm_sensors or smartmontools. Once you have completed the configuration, be sure to enable and start monit.service.

Configuration

Monit keeps a main configuration file as /etc/monitrc. You can choose to edit this file but if you wish to run scripts (such as to get hard drive temperatures or health status) you should uncomment the last directive of include /etc/monit.d/*, save /etc/monitrc and create /etc/monit.d/.

Note: Monit requires the /etc/monitrc file (and potentially files stored in /etc/monit.d) to have 0700 permissions. Failure to comply will result in Monit failing to start.

Configuration syntax

Monit utilizes a configuration syntax that makes it very easy to read; essentially check WHAT followed by if THING condition THEN action format. Any occurrence of if, and, with(in), has, us(ing|e), on(ly), then, for, of in the configuration file is for human readability only and are completely ignored by Monit.

Configuration examples

Mailserver declaration

set mailserver smtp.myserver.com port 587
        username "MyUser" password "MyPassW0rd"
using tlsv12

Email notification format

set mail-format {
      from: Monit@MyServer
   subject: $SERVICE $EVENT at $DATE
   message: Monit $ACTION $SERVICE at $DATE on $HOST: $DESCRIPTION.
}
Note: The above variables such as $SERVICE are not generic examples but are specific variable names which Monit replaces with what the alert is, on what system, etc.

CPU, memory and swap utilization 

check system $HOST
    if loadavg (15min) > 15 for 5 times within 15 cycles then alert
    if memory usage > 80% for 4 cycles then alert
    if swap usage > 20% for 4 cycles then alert

Filesystem(s) usage 

check filesystem rootfs with path /
    if space usage > 90% then alert

check filesystem NFS with path /mnt/nfs_share
    if space usage > 90% then alert

Process monitoring

check process sshd with pidfile /var/run/sshd.pid
   start program  "systemctl start sshd"
   stop program  "systemctl stop sshd"
   if failed port 22 protocol ssh then restart
check process smbd with pidfile /run/samba/smbd.pid
   group samba
   start program = "/etc/init.d/samba start"
   stop  program = "/etc/init.d/samba stop"
   if failed host 192.168.1.250 port 139 type TCP  then restart
   depends on smbd_bin

check file smbd_bin with path /usr/bin/smbd
   group samba
   if failed permission 755 then unmonitor
   if failed uid root then unmonitor
   if failed gid root then unmonitor
Note: For the above samba example, the first block has depends on smbd_bin, this makes the testing of Samba require the actual smbd process

Hard drive health and temperature using scripts

Temperature

Create the file /etc/monit.d/scripts/hdtemp.sh as well as the /etc/monit.d/scripts folder if necessary. 

/etc/monit.d/scripts/hdtemp.sh
 #!/usr/bin/sh
 HDDTP=`/usr/bin/smartctl -a /dev/sd${1} | grep Temp | awk -F " " '{printf "%d",$10}'`
 #echo $HDDTP # for debug only
 exit $HDDTP
monitrc or /etc/monit.d/*.monit file
check program SSD-A-Temp with path "/etc/monit.d/scripts/hdtemp.sh a"
    every 5 cycles
    if status > 40 then alert
    group health

check program HDD-B-Temp with path "/etc/monit.d/scripts/hdtemp.sh b"
    every 5 cycles
    if status > 40 then alert
    group health

In this example, the /etc/monit.d/scripts/hdtemp.sh script assumes your drive path is /dev/sdX where X is filled in by the letter at the end of the check declaration. A similar method is used for the SMART health status in the next example.

SMART health status

/etc/monit.d/scripts/hdhealth.sh
 #!/usr/bin/sh
 STATUS=`/usr/bin/smartctl -H /dev/sd${1} | grep overall-health | awk 'match($0,"result:"){print substr($0,RSTART+8,6)}'`
 if [ "$STATUS" = "PASSED" ] 
 then
     # 1 implies PASSED
     TP=1
 else 
     # 2 implies FAILED
     TP=2
 fi
 #echo $TP # for debug only
 exit $TP
monitrc or /etc/monit.d/*.monit file
check program SSD-A-Health with path "/etc/monit.d/scripts/hdhealth.sh a"
    every 120 cycles
    if status != 1 then alert
    group health

check program HDD-B-Health with path "/etc/monit.d/scripts/hdhealth.sh b"
    every 120 cycles
    if status != 1 then alert
    group health
Tip: The group declaration will cause Monit to display all assigned checks with the same group name (in this case samba) together.

Alert recipients: global or subsystem based

Alerts can be set globally, where a given user / email address is alerted for any alert condition; or you can set an alert recipient for each type of check (eg network alerts go to recipient A; process alerts go to recipient B). You can set as many global or subsystem recipients as you like, just make multiple declarations.

Global alerts

Global alerts are set outside of any subsystem checks; for ease of reading they should be set in the same location as the mailserver declaration. 

SET ALERT email@domain

Subsystem alerts

Subsystem alerts are set very similarly to global alerts except they lack the SET flag. 

ALERT email@domain

See also