How to discover downtime cause in Linux server?

[postcd]

Hello,

server was down some minutes and ping was like 10 failed, 1 OK
SSH unconnectable

I want to ask how to discover cause or any way to setup some script whiich can monitor server and log the cause of downtime?

These are only logs updated during downtime:
cron
maillog
lastlog
wtmp
secure

cat maillog....
Aug 1 15:3**** stat=Deferred: Connection refused by my.fqdn.hostname.
Aug 1 15:38:49 SC-D7150 sendmail[380549]: t71FcnXw380549: localhost [127.0.0.1] did not issue MAIL/EXPN/VRFY/ETRN during connection to MTA

The Linux dist. is CentOS.. thank You

 

[Paul Lopez]

Follow the below steps to resolve the issue...

- First check the logs /var/log/syslog /var/log/messages /var/log/dmesg

- Try to grep reboot , shutdown e.t.c

- Monitor your server for some time using top , free -m e.t.c in different terminals and see if any PIDS are taking excessive memory resources

- A command like this will give you some clue

- grep -E 'error|panic|warning' /var/log/messages