Troubleshooting Flashcards
Where would you go to start looking at config data with regards to performance issues with CPU, memory and other hardware?
/proc
Holds data on kernel, configs and processes
What information can you get with dmidecode
Just about every system spec like bios, sys, baseboard, chassis, processor, memory, cache etc
Use -t to specify a section
Where would you find kernal modules?
/lib/modules some distros also use /usr/lib/modules and hard link it.
Where might you find module config files?
/etc/modules.conf on older machines
Otherwise try:
/etc/modprobe.d
/etc/modules-load.d
/usr/lib/modprobe.d
/run/modprobe.d
Where would you look for potential kernal module errors
dmesg or /var/log/dmesg
Why use modprobe over insmod
Modprobe only needs the module name (not the absolute path) and it references the ‘modules.dep’ file for dependencies
What does depmod do?
Scans the system and determines and required modules and dependencies then updates them.
Tools to find issues with network adapters
ethtool -S ADAPTER
ip -s link show ADAPT
netstat -i ADAPT
Commands to check for latency and saturation issues
iperf, iperf3
mtr
nc
ss -s
tracepath
How would you use tshark to analyse an interface for 10 packets
sudo tshark -i INTERFACE -c 10
How to setup an iperf server to listen for 120 seconds
Allow port 5001 on firewall
Then
iperf -s -t 120
Setup iperf as a client for a throughput test
iperf -c IP -b kb -d -P 5 -e -i 10
How to check your routing table?
ip route show
How to view ARP and NDisc tables
ip neigh
What does iostat do?
Gives performance statistics showing CPU > disk wait times.
