Linux commands cheat sheet

SWAP management

Disable Swap memory

swapoff -a

Networking

Get the ip

ip addr show

Get Dhcp lease for interface ethx

dhclient -v ethx

Configure a network interface Use netplan:

 cat /etc/netplan/01-netcfg.yaml

Output:

network:
  version: 2
  renderer: networkd
  ethernets:
    enp0s8:
      dhcp4: no
      addresses: [192.168.56.103/24]

Commands to generate and apply the updates to the network config

netplan generate
netplan apply

Firewall

List all rules in IP tables

iptables -L

iptables commands

iptables -P INPUT ACCEPT iptables -P OUTPUT ACCEPT iptables -P FORWARD ACCEPT iptables -F

Uncomplicated firewall status / enable https://help.ubuntu.com/community/UFW

ufw status

Example commands to allow / deny all traffic

ufw default allow incoming
ufw default deny incoming

Add port 6443 tcp

ufw allow 6443/tcp

Allow port ranges:

ufw allow 1000:2000/tcp

Hostname

Get the current data for the current host:

hostnamectl status

get the hostname

hostname

set hostname:

hostnamectl set-hostname <yourhostname here>

System logging

Kernel log:

dmesg | tail

log file locations

Authorization log

/var/log/auth.log

Daemon Log

/var/log/daemon.log

Debug log

/var/log/debug

Kernel log

/var/log/kern.log

System log

/var/log/syslog

systemctl status appname

Application logs

Apache

/var/log/apache2/

X11

/var/log/Xorg.0.log

Last logins log

/var/log/lastlog read with lastlog command

Containers

Containerd

https://iximiuz.com/en/posts/containerd-command-line-clients/

list all namespaces

sudo ctr namespaces list

list all containers running in kubernetes

sudo ctr -n k8s.io containers list

list all tasks running

sudo ctr -n k8s.io task list

Check the content of an interface

 sudo tcpdump -i tunl0

Restart all daemons

sudo systemctl daemon-reload

check what a command does

strace command

strace kubectl get endpoints

Crictl

config file in crictl /etc/crictl.yaml config options: https://github.com/kubernetes-sigs/cri-tools/blob/master/docs/crictl.md