System Configuration

Time Synchronization (NTP)

The Network Time Protocol (NTP) keeps the system clock accurate by synchronizing it with time servers on the internet. Accurate system time is critical for:

• Log correlation across servers (debugging, security audits)
• TLS certificate validation (certificates have time-based validity)
• Scheduled jobs (cron, systemd timers)
• Distributed system consistency (databases, clusters)

How NTP Works

NTP uses a hierarchical structure called strata:

Stratum	Source	Example
0	Reference clock (atomic, GPS)	Cesium clock, GPS receiver
1	Directly connected to Stratum 0	National time servers (NIST, USNO)
2	Synchronized from Stratum 1	pool.ntp.org servers
3+	Synchronized from higher strata	Your local machine, internal NTP servers

Your machine typically synchronizes from Stratum 2/3 servers with millisecond-level accuracy.

timedatectl - systemd Time Management

Modern distributions use systemd-timesyncd (basic SNTP client) or chrony/ntpd for full NTP.

# View current time, timezone, and NTP synchronization status
timedatectl

# List available timezones
timedatectl list-timezones | grep America

# Set timezone
sudo timedatectl set-timezone America/New_York

# Enable/disable NTP synchronization
sudo timedatectl set-ntp true
sudo timedatectl set-ntp false

# Set time manually (only when NTP is disabled)
sudo timedatectl set-time "2025-03-15 14:30:00"

# Check NTP sync status
timedatectl show-timesync

chrony - NTP Daemon (Recommended)

chrony handles time synchronization more aggressively than the older ntpd and is the default on RHEL 8+:

# Check synchronization status
chronyc tracking
chronyc sources -v           # show all configured sources and their state

# View the configured NTP servers/pools
cat /etc/chrony.conf

# Force an immediate time step (useful after long downtime)
sudo chronyc makestep

Tip

For a deeper dive into NTP stratum theory, chrony/ntpd configuration as a client or server, and timedatectl, see Network Tools & Services.

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Network Manager

NetworkManager is the standard network configuration daemon on most modern Linux desktop and server distributions. It:

• Detects and manages wired, wireless, and mobile broadband interfaces
• Handles connection profiles (static IP, DHCP, VPN, etc.)
• Exposes a D-Bus API used by desktop applets and CLI tools

Architecture

nmcli / nmtui / nm-applet (GUI)
            |
    NetworkManager daemon
            |
    +-------+-------+
    |               |
  Wired           Wi-Fi (wpa_supplicant)
  (kernel)        (kernel)

Configuration Concepts

Concept	Description
Connection profile	Named set of settings (IP, DNS, gateway); stored in /etc/NetworkManager/system-connections/
Device	Physical or virtual NIC (e.g., enp3s0, wlan0)
Active connection	A profile applied to a device
DHCP	Automatic IP assignment; used for most connections by default

How NetworkManager handles wired connections:

• Detects link state automatically (cable plugged/unplugged)
• Requests DHCP lease on link-up
• For static configs: edits the connection profile via nmcli

nmcli Quick Reference

# Show all connections (profiles)
nmcli connection show

# Show active connections
nmcli connection show --active

# Show device status
nmcli device status

# Connect/disconnect a profile
nmcli connection up "Profile Name"
nmcli connection down "Profile Name"

# Set static IP on a connection
nmcli connection modify eth0-static \
  ipv4.addresses "192.168.1.100/24" \
  ipv4.gateway "192.168.1.1" \
  ipv4.dns "8.8.8.8" \
  ipv4.method manual

# Reload all connections
sudo nmcli connection reload

nmtui - Text UI

For an interactive, menu-driven interface (useful over SSH):

sudo nmtui          # opens a terminal UI for editing connections

VPN Support

NetworkManager supports many VPN types via plugins:

VPN Technology	NetworkManager Plugin
OpenVPN	NetworkManager-openvpn
WireGuard	NetworkManager-wireguard
Cisco AnyConnect / OpenConnect	NetworkManager-openconnect
Microsoft PPTP	NetworkManager-pptp
IPSec / L2TP	NetworkManager-l2tp

# Install OpenVPN plugin (RHEL/Fedora)
sudo dnf install NetworkManager-openvpn

# Import an OpenVPN .ovpn file
nmcli connection import type openvpn file client.ovpn
nmcli connection up client

Tip

For deeper network interface configuration (bonding, teaming, bridge setups, nmcli advanced usage) see Network Devices & Configuration.

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Locale and Language

System locale controls date/number format, language, and character encoding:

localectl                            # show current locale settings
localectl list-locales | grep en_US  # find available locales
sudo localectl set-locale LANG=en_US.UTF-8

# Per-session override
export LANG=en_US.UTF-8
export LC_ALL=en_US.UTF-8

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Screen Resolution (X11)

xdpyinfo | grep dim                  # current screen dimensions
xrandr                               # list outputs and supported resolutions
xrandr --output HDMI-1 --mode 1920x1080  # set resolution

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System Hostname

hostnamectl                          # show hostname, OS info, kernel version
sudo hostnamectl set-hostname myserver   # set a new hostname (persistent)

# Types of hostnames:
# Static: persisted in /etc/hostname; used by default
# Transient: may be set by DHCP/mDNS at runtime
# Pretty: human-readable string (can contain spaces)
sudo hostnamectl set-hostname "My Dev Server" --pretty