Networking

Linux Networking

Start, Stop and Check the Status of Network Services

nmtui
nmcli
systemctl list-units | grep network
system restart network.service .service is assumed when not added
We want to seperate services across multiple servers
systemctl is-enabled nginx check if a service is enabled
enable and disable
6 different commands to restart network in RHEL/CentOS 7/8 | GoLinuxCloud

VLSM

128 64 32 16 8 4 2 1 128 192 224 240 248 252 254 255 /25 /26 /27 /28 /29 /30 /31 /32 126 62 30 14 6 2

api/images/CpF95Xo6Qe0f/00a45b0621c58fcbe4cbb4142ee2b334.png

Software

Nebula
wireguard

Linux Networking

There exists a cli tool for configuring networking
The tool is called ````nmtui````
sudo networkmanager

Chapter 6, Configure Networking and Hostname Resolution Statically or Dynamically

Troubleshooting

ip addr
ip addr show {device name}}
ip -s link show {divice name}}# Show statistic information
ping -c5 {ip address}} # Only does it 5 times
tracepath {ip address}}
traceroute {ip address}}
netstat ## works but is old

ss -a ## show all listening and established connections
# -t for TCP
# -u for UDP
# -n

# Network Manager
ls /sys/class/net
nmclie dev status
nm-connection-editor # GUI app
nmtui
nmcli con show # --active
nmcli con add help
nmcli con add con-name "mycon" autoconnect yes type ethernet ifname {device, can press tab}} ip4 {Ip address}} gw3 {gateway}}
nmclie {up or down}} {device name}}
nmclie con mod "{Device name}}" # Tab way to victory
nmclie con delete {Divice name}}

# /etc/resolv.conf

# /etc/nsswitch.conf
# Modify "hosts:" To change order of DNS

# Changing hostname
hostnamectl
hostnamectl set-hostname dentropyserver.com
hostnamectl status
# ssh will try and connect to all hostnames in /etc/resolv.conf search

cat /etc/sysconfig/network-scripts/ifcfg-{WHATEVER}}

getent hosts {hostname}}

Schedule Tasks Using at and cron

yum install at
systemctl enable atd
systemctl start atd

at now +t minutes
at 12:00am
# Type command you want at that time

atq # Queued jobs
atrm {job number}}

at now +1 minute
# > logger "The systems current uptime is $(uptime)"
# Press ctrl+d twice to confirm the job

# Search "at" in /etc
# at.deny and cron.deny block users
# There is also at.allow and cron.allow but you need to add those

# crontab and system cron are different
# systemcon is in /etc
# do not use crontab file anymore

# There are many cron directories in /etc some labled daily, hourly, monthly, and weekly
# Put commands in those folders for obious reasons
# in /etc/cron.d

rpm -qc {application}}

# anacrontab
# anacron checks if jobs have been run and if the machine was off runs the job
# anacron jobs have to be in cron.d

cd /var/spool/anacron # Shows when things were last executed

Start and Stop Services and Configure Services to Start Automatically at boot

How do I attach different services to different targets?

yum install httpd
systemctl status httpd
systemctl start httpd
systemctl is-enabled httpd
systemctl list-unit-files --type=service | grep httpd
systemctl get-default # Current target
systemctl list-dependencies | grep httpd
systemctl enable httpd

# Determine if started by target
cd /etc/systemd/system/multi-user.target.wants/
systemctl list-dependencies multi-user.target | grep httpd
systemctl list-dependencies graphical.target  | grep httpd

## Reboot into seperate targets

systemctl get-default
systemctl set-default {target}}

Install Red Hat Enterprise Linux Automatically Usinh Kickstart

# TODO too lazy

Configure a Physical Machine to Host Virtual Guests

sudo su -
# qemu does the actual virtualization
# In advanced PDF
yum install virt-manager qemu-kvm qemu-img
yum install libvirt libvert-python python-virtinst libvirt-client
systemctl enable libvirtd
systemctl start libvirtd
virsh

Install Red Hat Enterprise Linux Systems as Virtual Guests

Use virt-manager to setup a VM Networking does not work

ls /sys/class/net
nmclie con show
cd /etc/sysconfig/network-scripts
cat ifcfg-ens3
nmclie con up en3
# Networking should work now
ip addr
nmclie con mod "en3" connection.autoconnect yes
# VM Networking should start at boot now

Configure Systems to Lauch Virtual Machines at Boot

sudo su -
systemctl status libvirtd
virsh
## The following commands are in a virsh terminal
list --all
autostart {name of VM}}

Configure Network Services to Start Automatically at Boot

systemctl list-units | grep network.target
systemctl list-dependencies multi-user.target | grep network
cd /etc/sysconfig/network-scripts
nmcli con show
cat ifcfs-{Device name}}
nmcli con mod "{Device name}}" connection.autoconnect yes
cat ifcfs-{Device name}}

Configure a System to Use Time Services

timedatectl # Shows system time
man timedatectl
timedatectl set-ntp {true/false}}
timedatectl list-timezones
tzselect # Helps find your time zone
timedatectl set-timezone {time zone}}
timedatectl set-time 12:12:12

# NTP uses cronyd
systemctl status chronyd
chronyc sources -v # Check if NTP out of sync
systemctl restart chronyd
# Stratum is number of hops
chronyc tracking
# NPT slowly changes time to not break applications

# Change Time Servers
vim /etc/chrony.conf
# One can edit servers here
# Mentioned puppet and importance of time
# iburst is default option

# How to apply changes to chrony.conf
systemctl restart chronyd

chronyc sources -v
# Question marks are bad

timedatectl