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NSD is a complete implementation of an authoritative DNS nameserver. This page covers starting and stopping the daemon, command-line options, and signal handling.

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Starting NSD

The recommended way to start NSD is using nsd-control:
  1. Start the daemon: 
    nsd-control start
  2. Verify it’s running: 
    nsd-control status
    Output: 
    version: 4.x.x
verbosity: 0
Alternatively, you can start NSD directly: 
nsd -c /etc/nsd/nsd.conf

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Command-Line Options

NSD supports the following command-line options:

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Network Options

  • -4 - Only listen to IPv4 connections
  • -6 - Only listen to IPv6 connections
  • -a ip-address[@port] - Listen to specified IP address (can be specified multiple times)
  • -p port - Answer queries on specified port (default: 53)

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Configuration Options

  • -c configfile - Read specified config file instead of default /etc/nsd/nsd.conf
  • -d - Do not fork, stay in the foreground (debug mode)
  • -l logfile - Log messages to specified file
  • -P pidfile - Use specified PID file instead of default

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Server Options

  • -N server-count - Start specified number of server processes (default: 1)
    • Useful on machines with multiple CPUs
  • -n noncurrent-tcp-count - Maximum concurrent TCP connections per server (default: 100)

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Identity and NSID

  • -i identity - Return specified identity when queried for CH TXT ID.SERVER
    • Default: hostname from gethostname(3)
  • -I nsid - Add specified NSID to EDNS section
    • Can be hex characters or ascii_ prefix with ASCII string

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Security Options

  • -t chrootdir - Chroot to specified directory upon startup
  • -u username - Drop privileges to specified user after binding socket
    • Format: username, id, or id.gid (e.g., nsd, 80, or 80.80)

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Verbosity and Statistics

  • -V level - Set verbosity level for logging (default: 0)
  • -s seconds - Produce statistics dump every N seconds (equivalent to periodic SIGUSR1)
  • -v - Print version number and exit
  • -h - Print help information and exit

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Daemon Mode

By default, NSD runs as a daemon:
  • Reads configuration file
  • Forks into background
  • Binds to port 53 (or specified port)
  • Answers DNS queries
To run in foreground mode (for debugging or systemd): 
nsd -d

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Stopping NSD

Use nsd-control to stop the daemon gracefully: 
nsd-control stop
This sends SIGTERM to the daemon, which:
  • Stops answering queries
  • Saves state if necessary
  • Exits cleanly

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Signal Handling

NSD reacts to the following signals:

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SIGTERM

Graceful shutdown:
  • Stop answering queries
  • Shutdown all processes
  • Exit normally
kill -TERM $(cat /var/run/nsd.pid)

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SIGHUP

Reload log file and optionally update zones:
  • Reopen log file (assists log rotation)
  • Update TSIG keys
  • Reload modified zone files
kill -HUP $(cat /var/run/nsd.pid)
Or use: 
nsd-control reload

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SIGUSR1

Dump BIND8-style statistics:
  • Writes statistics to log file
  • Only works if compiled with --enable-bind8-stats
kill -USR1 $(cat /var/run/nsd.pid)
Or use: 
nsd-control stats

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Process Management

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Multiple Server Processes

Run multiple server processes for better performance: 
nsd -N 4
Or in nsd.conf: 
server:
    server-count: 4
Multiple server processes are only useful on machines with multiple CPUs and/or network adapters.

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TCP Connections

Limit concurrent TCP connections per server: 
nsd -n 200
Or in nsd.conf: 
server:
    tcp-count: 200

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Example Startup Commands

Basic startup: 
nsd
Custom config file: 
nsd -c /usr/local/etc/nsd.conf
IPv4 only with custom port: 
nsd -4 -p 5353
Foreground mode with verbose logging: 
nsd -d -V 3
Multiple servers with specific interfaces: 
nsd -N 4 -a 192.0.2.1 -a 192.0.2.2
Chroot and drop privileges: 
nsd -t /var/nsd -u nsd

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Checking Server Status

Check if NSD is running: 
nsd-control status
Exit codes:
  • 0 - Server is running
  • 1 - Error occurred
  • 3 - Server is not running (connection refused)

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Files

Default locations:
  • PID file: /var/run/nsd.pid
  • Config file: /etc/nsd/nsd.conf
  • Log output: syslog daemon facility (unless -d or -l specified)

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See Also

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