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System logs

  • System logs
Generic system:
/var/log/messages
/var/log/dmesg

Syslog

Authentication:
secure
auth*

Programs and daemons:
cron 
/var/log/program

Packages:
yum.log

History:
history

Local resources

Tools
  • top
See processes section.
  • iotop
  • lsof
  • systat package ( vmstat, iostat, sar ...)
vmstat -s 
vmstat -t

Free – Amount of free/idle memory spaces.
si – Swaped in every second from disk in Kilo Bytes.
so – Swaped out every second to disk in Kilo Bytes.
  • iostat (sysstat package on RH)
iostat -d # Disk statistics
iostat -p sda # Stats for /dev/sda
Practical Cases
  • Application consuming CPU
  • Application writing to disk

Networking

Tools
  • ping
Used to send ICMP packets
ping google.com
To use in scripting:
ping localhost -n 1
  • tcpdump
A packet sniffer. Will allow you to monitor and record the dump of traffic via the interface.
Better analyze further using Wireshark tool.
  • netstat
Undestanding what is actually listening

netstat -anpl | grep nginx
netstat -l
netstat -st

  • traceroute / tracepath

  • nslookup

Performs dns
  • NIC configuration check
Check parameters like MTU
ifconfig
ip a
ip route
route
  • netcat
  • curl
Practical Cases
  • Checking ports blocked by firewall and debugging connections
  • Checking what is application listening