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I am struggling for a few days to configure dnsmasq to automatically reload or take into knowledge the new hosts added to /etc/hosts or to another configured file /etc/hosts.dnsmasq.

Is this even possible?

  • Nope. Interestingly, it can poll /etc/resolv.conf for changes, but not /etc/hosts. You could use an inotify to trigger SIGHUP or service reload. – Aaron Copley Sep 18 '15 at 12:43
  • The thing is that in my project, the hosts will be changed like a few times per minute. This will make dnsmasq restart a few times per minute. Is this a very bad problem? – roshkattu Sep 18 '15 at 12:44
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    Consider a "proper" DNS server with a database backend that takes live changes. – Aaron Copley Sep 18 '15 at 16:10
  • @AaronCopley which one, for example? – Groosha Nov 8 '17 at 15:37
  • If you really want changes that frequent, wouldn't you be better of using dhcp? dnsmasq will happily (and automatically) serve hostnames received that way – Kees-Jan Dec 9 '17 at 9:39
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There are two ways to cause dnsmasq to reload a hosts file:

  1. As Aaron Copley noted in his comment, send SIGHUP to dnsmasq. From the man page:

    When it receives a SIGHUP, dnsmasq clears its cache and then re-loads /etc/hosts and /etc/ethers and any file given by --dhcp-hostsfile, --dhcp-hostsdir, --dhcp-optsfile, --dhcp-optsdir, --addn-hosts or --hostsdir. The dhcp lease change script is called for all existing DHCP leases. If --no-poll is set SIGHUP also re-reads /etc/resolv.conf. SIGHUP does NOT re-read the configuration file.

    Note that dnsmasq doesn't restart in this case, but it does re-read a number of other files (and calls the dhcp lease change script for all existing DHCP leases). If triggering reloads too quickly is a concern, you can debounce the signal.

  2. Use the --hostsdir option. Again from the man page:

    --hostsdir=<path>
            Read all the hosts files contained in the directory. New or changed files are read automatically. See --dhcp-hostsdir for details.

    For reference, here is the documentation for --dhcp-hostsdir:

    --dhcp-hostsdir=<path>
            This is equivalent to dhcp-hostsfile, except for the following. The path MUST be a directory, and not an individual file. Changed or new files within the directory are read automatically, without the need to send SIGHUP. If a file is deleted or changed after it has been read by dnsmasq, then the host record it contained will remain until dnsmasq receives a SIGHUP, or is restarted; ie host records are only added dynamically.

    This has a few advantages compared to the first option: dnsmasq will re-read the host file(s) automatically, no SIGHUP required, and; only the host files are reloaded, no other actions are taken.

    One potential disadvantage is that, as the documentation for --dhcp-hostsdir points out, new host entries are dynamically added but deleted or changed entries are not updated. Simon Kelley, the author of dnsmasq, has confirmed that this is by design.

  • To respond to the latter comment... it is by lack of design - he was too lazy to implement just a diff... let's see who gets around to it first... if it turns out to be necessary. – Dagelf Dec 28 '18 at 2:32

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