dnsmasq Command in Linux
The Linux dnsmasq is a lightweight DNS, DHCP, PXE, router advertisement, and TFTP server. It is a versatile server that provides all options without installing a full DNS server. It is designed to provide DHCP and DNS services to a LAN.
The Linux dnsmasq accepts queries and attempts to answer them using a local cache or forwards them to an upstream DNS server (e.g., Googles public DNS server). It also reads the systems host file to resolve the local hosts to answer the DHCP-configured hosts.
Table of Contents
This tutorial will cover the following topics −
- Prerequisites for Using dnsmasq Command
- Syntax of dnsmasq Command
- dnsmasq Command Options
- Examples of dnsmasq Command in Linux
Prerequisites for Using dnsmasq Command
Before using dnsmasq, ensure it is installed using the command given below −
dnsmasq --version
If the version is displayed, the dnsmasq is installed. Otherwise, install it using the instructions below.
To install dnsmasq on Ubuntu, Debian, and Debian-based distributions, use −
sudo apt install dnsmasq
To get it on Fedora, use −
sudo dnf install dnsmasq
Syntax of dnsmasq Command
The general syntax of using the Linux dnsmasq command is as follows −
dnsmasq [options]
The [options] field specifies various configuration options, such as the custom configuration file, DHCP allocation range, DNS cache size, and other settings.
dnsmasq Command Options
The options used with the dnsmasq command are listed in the table below −
| Flags | Options | Description |
|---|---|---|
| -a ip | --listen-address= ip | To specify the local IP address or addresses to listen on |
| -c size | --cache-size= size | To specify the cache size in entries (default is 150) |
| -C file | --conf-file= file | To specify the configuration file |
| -d | --no-daemon | To run in the debug mode instead of the daemon |
| -E | --expand-hosts | To expand hosts in the /etc/host file with domain suffix |
| --filter-A | To avoid including the IPv4 record in the DNS answer | |
| --filter-AAAA | To avoid including the IPv6 record in the DNS answer | |
| -F ip | --dhcp-range= ip | To enable DHCP in the given range of addresses with lease duration |
| --dhcp-hostsfile= path | To read DHCP host specs from the file | |
| --dhcp-optsfile= path | To read DHCP option specs from the file | |
| --dhcp-hostsdir= path | To read DHCP host specs from a directory | |
| --dhcp-optsdir= path | To read DHCP options from a directory | |
| -h | --no-hosts | To avoid loading the /etc/hosts file |
| -H | --addn-hosts= path | To specify the host file in addition to default /etc/hosts |
| --hostsdir= path | To specify the host to read the hosts | |
| -i | --interface= interface | To specify the interface name to listen |
| -I | --except-interface | To specify the interface name not to listen |
| -k | --keep-in-foreground | To keep the dnsmasq running in the foreground instead of running as a daemon |
| -K | --dhcp-authoritative | To specify the current server a DHCP server in the local network |
| -M opts | --dhcp-boot= opts | To specify the BOOTP options for the DHCP server |
| -N | --no-negcache | To avoid caching the failed results |
| -o | --strict-order | To use nameserver strictly in the order given in /etc/resolve.conf |
| -p port | --port= port | To specify the port to listen for DNS requests (default is 53) |
| -q | --log-queries | To log DNS queries |
| --quite-dhcp | To not log DHCP | |
| -R | --no-resolve | To avoid reading the resolve.conf file |
| -r file | --resolve-file=file | To specify the resolve file (default is /etc/resolve.conf) |
| -s domain | --domain=domain | To specify the domain to be assigned in DHCP leases |
| --test | To test the configuration file syntax | |
| -v | --version | To display the version of the dnsmasq command |
| --help | To display brief help related to the command | |
| -8 file | --log-facility= file | To specify the file to store the log entries instead of Syslog |
Examples of dnsmasq Command in Linux
This section demonstrates the usage of the Linux dnsmasq command with examples −
- Starting dnsmasq Server with Default Settings
- Starting dnsmasq Server and Enabling Log
- Starting dnsmasq Server with DHCP Range and Lease Time
- Starting dnsmasq Server with Specific Interface
- Starting dnsmasq Server with Multiple Options
- Starting dnsmasq Server with Custom Settings
Starting dnsmasq Server with Default Settings
To start the dnsmasq server with the default options, execute the dnsmasq command −
dnsmasq
To run the above command, the dnsmasq server must be properly configured.
Starting dnsmasq Server and Enabling Log
Log queries help in troubleshooting the errors. To enable the log before starting the dnsmasq, use the -q or --log-queries option.
dnsmasq -q
To store the log queries in a different file, use the -8 or --log-facility option.
dnsmasq -q --log-facility=/home/user/dnsmasq.log
Starting dnsmasq Server with DHCP Range and Lease Time
The dnsmasq can be used as a DHCP server for local networks. To start the dnsmasq server with DHCP address ranges and lease time, use the -F or --dhcp-range options −
dnsmasq -F 192.168.10.80,192.168.10.160,6h
Here the IP address range starts from 192.168.1.80 and ends on 192.168.10.160. While the 6h (6 hours) is the lease time.
Starting dnsmasq Server with Specific Interface
To listen to a specific interface, you can specify it with the dnsmasq command. Use the -i or --interface option followed by the interface name.
dnsmasq -i enp0s0
Starting dnsmasq Server with Multiple Options
In the above examples, only one option is specified; however, multiple options can also be mentioned according to requirement. For example, in the following command, the interface name is mentioned, along with the DHCP IP range and lease time. The -h option prevents the server from reading the default host file, while the -q option enables the logging of DNS queries.
dnsmasq -i enp0s0 -F 192.168.10.80,192.168.10.160,6h -h -q
Or −
dnsmasq --interface=enp0s0 --dhcp-range=192.168.10.80,192.168.10.160,6h --no-hosts --log-queries
Starting dnsmasq Server with Custom Settings
In the above examples, the options and settings are mentioned with the dnsmasq command. Mentioning many options in the terminal can make it a bit complex. All the options and settings can also be specified in a separate file. This file can be mentioned using the -C or --conf-file options.
To create a custom dnsmasq configuration file, use any text editor.
sudo nano /etc/custom.conf
The above command creates a file named custom.conf in the /etc directory. However, it can be created in any directory with any name. Now, add the setting as mentioned in the following image −
To verify the dnsmasq configuration file syntax, use the --test option −
dnsmasq -C /etc/custom.conf --test
Now, execute the following command to start the server with the custom configuration file.
dnsmasq -C /etc/custom.conf
Conclusion
The dnsmasq is a lightweight DNS, DHCP, PXE, and TFTP server primarily designed for small local area networks. This tool can be used for DNS caching, DNS forwarding, and DNS filtering. It is also used as a DHCP server for the local network and supports network booting through PXE.
This tutorial explained the dnsmasq command, its installation, syntax, options, and usage through different examples.