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6_maintain_systems.md

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objectives: 6_maintain_systems

####Configure networking, update connections / devices

  • Devices and connections are two distinct things
    • devices are actual interfaces on the system
    • connections can be bound & be turned on/off
    • only 1 connection can be up at a time
  • nmcli con show or nmcli dev status - display network connections or devices
  • nmcli con del <name|UUID> - remove a connection / interface
  • nmcli con add con-name <name> ifname <interface> type ethernet ip4 1.1.1.1/24 gw4 1.1.1.1
    • create a connection (provide ip / gateway)
  • nmcli con reload - reload configs into network manager
  • ip address show or ip a - check configuration
    • nmcli con show <name> - all information about a connection
  • nmcli con down <name> - stop a connection
  • nmcli con up <name> - start a connection
  • To modify a connection:
    • nmcli con mod <name> ipv4.address 1.1.1.1/24 - ip address
    • nmcli con mod <name> ipv4.gateway 1.1.1.1 - gateway
    • nmcli con reload - reload configs into network manager
    • nmcli con up <name> - ensure connection is up
    • nmcli con delete <name> - delete the connection when through

#####Hostname updates: statically or dynamically

  • hostnamectl <--static|--transient|--pretty> - view all current hostnames (static, transient, pretty)
  • hostnamectl set-hostname <name> - set the hostname
    • use --static, --transient, --pretty for individual hostnames
  • hostname resolution relies on /etc/nsswitch.conf
    • hosts: files dns - entry resloves first through files (static) then dns (dynamic)
      • static comes from /etc/hosts file
      • dynamic comes from /etc/resolve.conf file
  • nmcli con mod <interface> +ipv4.dns 1.1.1.1 - add DNS server
    • +ipv4.dns - adds a server
    • ipv4.dns - replaces it
    • -ipv4.dns - removes a server
  • nmcli con up <interface> - restart connection

####Schedule tasks using at and cron

Minute Hour Day Of Month Month Day Of Week CMD
0-59 0-23 1-31 1-12 1-7 /root/script.sh
  • crontab -u <username> -e - edit users crontab
  • wildcards * can be used to match every value
  • cron jobs that neet to run routinely can be placed in /etc/cron.{daily,weekly,monthly}
    • these must be executable

#####Configure time services using NTP

  • timedatectl - get current config
  • timedatectl list-timezones - list available time zones
  • timedatectl set-timezone <timezone> - set the timezone eg: America/Chicago
  • yum install -y ntp - install ntp
  • systemctl enable ntpd.service - enable ntpd at boot
  • systemctl start ntpd.service - start ntpd
    • config file is at /etc/ntp.conf

#####Configure time services using Chrony

  • yum install -y chrony - install chrony
  • systemctl enable cronyd.service - enable chronyd at boot
  • systemctl start cronyd.service - start chronyd
  • ntpdate <timeserver> - synchronize server
    • config file is located at /etc/chrony.conf

####Install and update packages from Redhat network, remote repo or local file system

  • yum-config-manager --add-repo=http://myrepo.com - leverage this tool to generate repo file
  • vi /etc/yum.repos.d/<remote>.repo - modify the repository to
[base]
[myrepo.com]
name=added from http://myrepo.com
baseurl=http://myrepo.com
enabled=1
gpgcheck=0                        # <----- add this line!