Linux nm* Command Set: Comprehensive Overview

Author: System Administration Reference
Date: October 2025
Topic: Network Management and Symbol Table Commands

Introduction

The nm* command family in Linux/UNIX encompasses several distinct utilities, primarily divided into two categories:

1. Network Management Tools - Commands like nmcli, nmtui, and nm-connection-editor that interface with NetworkManager
2. Symbol Table Tools - The nm command itself, used for examining binary object files

1. NetworkManager Command Suite

1.1 nmcli - NetworkManager Command Line Interface

Basic Syntax

nmcli [OPTIONS] OBJECT { COMMAND | help }

Common Objects

Essential nmcli Commands

Viewing Network Status

# Show all connections
nmcli connection show

# Show all devices and their status
nmcli device status

# Show detailed device information
nmcli device show eth0

# Show NetworkManager status
nmcli general status

Managing Connections

# Activate a connection
nmcli connection up "connection-name"

# Deactivate a connection
nmcli connection down "connection-name"

# Delete a connection
nmcli connection delete "connection-name"

# Reload connection files from disk
nmcli connection reload

Creating Connections

# Create a new Ethernet connection with DHCP
nmcli connection add type ethernet con-name "MyEthernet" ifname eth0

# Create a static IP connection
nmcli connection add type ethernet con-name "StaticIP" ifname eth0 \
  ip4 192.168.1.100/24 gw4 192.168.1.1

# Create a WiFi connection
nmcli device wifi connect "SSID" password "password"

# Create WiFi connection with specific settings
nmcli connection add type wifi con-name "MyWiFi" ifname wlan0 ssid "SSID" \
  wifi-sec.key-mgmt wpa-psk wifi-sec.psk "password"

Modifying Connections

# Modify IP address
nmcli connection modify "MyConnection" ipv4.addresses 192.168.1.150/24

# Modify DNS servers
nmcli connection modify "MyConnection" ipv4.dns "8.8.8.8 8.8.4.4"

# Change to DHCP
nmcli connection modify "MyConnection" ipv4.method auto

# Add additional IP address
nmcli connection modify "MyConnection" +ipv4.addresses 192.168.1.151/24

nmcli connection down "MyConnection" && nmcli connection up "MyConnection"

nmcli Output Formatting

# Terse output (script-friendly)
nmcli -t device status

# Custom fields
nmcli -f NAME,TYPE,DEVICE connection show

# Pretty output (default)
nmcli -p device status

# Colored output
nmcli -c yes device status

1.2 nmtui - NetworkManager Text User Interface

A menu-driven interface for users who prefer a visual approach without requiring a full GUI.

Usage

# Launch main menu
nmtui

# Directly edit connections
nmtui edit

# Directly activate connections
nmtui connect

# Set system hostname
nmtui hostname

1.3 nm-connection-editor - GUI Connection Editor

Full-featured GUI application for desktop environments. Provides comprehensive access to all connection settings including VPN, bonding, bridging, and advanced options.

# Launch connection editor
nm-connection-editor

# Edit specific connection
nm-connection-editor -c "connection-name"

1.4 Other NetworkManager Tools

nm-online

Utility to determine if NetworkManager is online (has network connectivity)

# Wait for network connectivity (useful in scripts)
nm-online -t 30  # Wait up to 30 seconds

# Check connectivity status
nm-online -q && echo "Online" || echo "Offline"

nmcli monitor

Monitor NetworkManager changes in real-time

# Monitor all NetworkManager activity
nmcli monitor

# Monitor specific connection
nmcli connection monitor "MyConnection"

2. nm - Symbol Table Examination Tool

2.1 Overview

The nm command is part of the GNU binutils package and is essential for examining compiled binaries, debugging, and understanding program structure.

2.2 Basic Syntax

nm [OPTIONS] [FILE...]

2.3 Common Options

2.4 Symbol Types

nm displays a letter code for each symbol indicating its type:

2.5 Practical Examples

Basic Usage

# List all symbols in a binary
nm /bin/ls

# List symbols in a library
nm /usr/lib/libc.so.6

# List symbols in object file
nm myprogram.o

Filtering and Analysis

# Show only undefined symbols (dependencies)
nm -u /bin/ls

# Show only global (external) symbols
nm -g myprogram.o

# Show dynamic symbols only
nm -D /usr/lib/libssl.so

# Demangle C++ symbols
nm -C mycppprogram

# Sort by symbol size (find largest symbols)
nm --size-sort -S mybinary

# Find specific symbol
nm mybinary | grep "main"

# Show line numbers (if debug info available)
nm -l mybinary

Library Analysis

# List all functions exported by a shared library
nm -D --defined-only /usr/lib/libpthread.so.0

# Find what symbols a program needs
nm -u myprogram

# Check if a library provides a specific symbol
nm -D /usr/lib/libm.so.6 | grep "sin"

Debugging Scenarios

# Find duplicate symbols across multiple object files
nm *.o | grep " T " | sort

# Identify missing symbols causing link errors
nm -u myprogram | grep " U "

# Compare symbols between two versions of a library
nm libfoo.so.1 > v1_symbols.txt
nm libfoo.so.2 > v2_symbols.txt
diff v1_symbols.txt v2_symbols.txt

3. Related Commands and Tools

3.1 Network-Related

• ip - Show/manipulate routing, devices, policy routing
• ifconfig - Configure network interfaces (deprecated, use ip)
• systemctl - Control NetworkManager service
• journalctl - View NetworkManager logs

# Control NetworkManager service
systemctl status NetworkManager
systemctl restart NetworkManager
systemctl enable NetworkManager

# View NetworkManager logs
journalctl -u NetworkManager -f

3.2 Binary Analysis Tools

• objdump - Display information from object files
• readelf - Display information about ELF files
• ldd - Print shared library dependencies
• strings - Find printable strings in files
• file - Determine file type

4. Configuration Files

4.1 NetworkManager Configuration

Main Configuration

[main]
plugins=ifupdown,keyfile
dns=default

[ifupdown]
managed=false

[device]
wifi.scan-rand-mac-address=yes

Connection Profiles

Each connection is stored as a separate file with restrictive permissions (600).

4.2 Example Connection File

[connection]
id=MyEthernet
uuid=12345678-1234-1234-1234-123456789abc
type=ethernet
autoconnect=true
interface-name=eth0

[ethernet]

[ipv4]
method=manual
address1=192.168.1.100/24,192.168.1.1
dns=8.8.8.8;8.8.4.4;

[ipv6]
method=auto

5. Common Use Cases and Workflows

5.1 Setting Up Static IP Address

# Method 1: Using nmcli
nmcli connection modify "Wired connection 1" \
  ipv4.method manual \
  ipv4.addresses "192.168.1.100/24" \
  ipv4.gateway "192.168.1.1" \
  ipv4.dns "8.8.8.8,8.8.4.4"

nmcli connection up "Wired connection 1"

# Method 2: Using nmtui
nmtui edit

5.2 Troubleshooting Network Issues

# Check device status
nmcli device status

# Check connection status
nmcli connection show --active

# Restart NetworkManager
systemctl restart NetworkManager

# Check logs
journalctl -u NetworkManager -n 50

# Test connectivity
nmcli general status
ping -c 4 8.8.8.8

5.3 Finding Symbol Dependencies

# Find what libraries a program needs
ldd /bin/ls

# Find undefined symbols in object file
nm -u myprogram.o

# Verify library provides required symbol
nm -D /usr/lib/libfoo.so | grep "symbol_name"

# Check for symbol conflicts
nm *.o | grep " T symbol_name"

6. Best Practices and Tips

6.1 NetworkManager Best Practices

• Always use connection names with quotes if they contain spaces
• Use nmcli -t for scripting to get consistent, parseable output
• Test configuration changes before committing them permanently
• Keep backups of custom connection files from /etc/NetworkManager/system-connections/
• Use nmcli connection reload after manually editing connection files

6.2 Symbol Analysis Best Practices

• Use -C option for C++ programs to demangle names
• Combine with grep, awk, and sort for powerful analysis
• Use --size-sort to identify bloated symbols
• Check for undefined symbols before linking
• Use nm -D for dynamic libraries to see exported symbols

7. Scripting Examples

7.1 Network Configuration Script

#!/bin/bash
# Check if connection exists, create if not

CONNECTION="MyStaticIP"
INTERFACE="eth0"
IP="192.168.1.100/24"
GATEWAY="192.168.1.1"
DNS="8.8.8.8,8.8.4.4"

if nmcli connection show "$CONNECTION" &>/dev/null; then
    echo "Connection exists, modifying..."
    nmcli connection modify "$CONNECTION" \
        ipv4.addresses "$IP" \
        ipv4.gateway "$GATEWAY" \
        ipv4.dns "$DNS"
else
    echo "Creating new connection..."
    nmcli connection add \
        type ethernet \
        con-name "$CONNECTION" \
        ifname "$INTERFACE" \
        ipv4.method manual \
        ipv4.addresses "$IP" \
        ipv4.gateway "$GATEWAY" \
        ipv4.dns "$DNS"
fi

nmcli connection up "$CONNECTION"

7.2 Symbol Analysis Script

#!/bin/bash
# Find all undefined symbols across multiple object files

echo "Undefined symbols across all object files:"
for obj in *.o; do
    echo "=== $obj ==="
    nm -u "$obj" | grep " U " | awk '{print $2}' | sort -u
done

8. Troubleshooting Guide

8.1 NetworkManager Issues

8.2 nm Symbol Issues

9. Additional Resources

Man Pages

man nmcli
man nmcli-examples
man nm-settings
man nm-online
man NetworkManager.conf
man nm

Online Documentation

• NetworkManager Developer Documentation
• GNU Binutils Manual (for nm)
• Linux Network Administrators Guide