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In-depth manual

Available interfaces

Pi-hole stats can be accessed via a standard Unix socket (var/run/pihole/FTL.sock), a telnet-like connection (TCP socket on port 4711) as well as indirectly via the Web API (admin/api.php), and the command line (pihole -c -j). You can out find more details below.

Command-line arguments

  • debug - Don't go into daemon mode (stay in foreground) + more verbose logging
  • test - Start FTL and process everything, but shut down immediately afterward
  • version - Don't start FTL, only show the version
  • tag - Don't start FTL, show only git tag
  • branch - Don't start FTL, show only git branch FTL was compiled from
  • no-daemon or -f - Don't go into background (daemon mode)
  • help or -h - Don't start FTL, show help
  • dnsmasq-test - Test resolver config file syntax
  • -- everything behind -- will be passed as options to the internal resolver

Command-line arguments can be arbitrarily combined, e.g. pihole-FTL debug test

File locations

  • /var/log/pihole-FTL.log log file
  • /var/run/pihole-FTL.pid PID file
  • /var/run/pihole-FTL.port file containing port on which FTL is listening
  • /var/run/pihole/FTL.sock Unix socket

Domain lists format

Since Pi-hole v4.0, we use a simpler domain list format for the two important blocklist files gravity.list and black.list. In contrast to the traditional HOSTS format (which caused a lot of overhead), the domain list format is the minimal possible solution for saving memory while still using plain text lists for your convenience. When FTLDNS imports these two files, they are walked by our improved list parser speeding up the loading of blocklists significantly. Regardless of which blocking mode (IP or NXDOMAIN) is selected, FTLDNS will always load the lists into its internal hashed cache to be able to determine the blocking status within a few milliseconds, even when you're using huge blocking lists on low-end devices. With everything we do, we design FTLDNS for maximum efficiency also on low-performance devices.

Linux capabilities

Capabilities (POSIX 1003.1e, capabilities(7)) provide fine-grained control over superuser permissions, allowing the use of the root user to be avoided. To perform permission checks, traditional UNIX implementations distinguish two categories of processes: privileged processes (superuser or root), and unprivileged processes. Privileged processes bypass all kernel permission checks, while unprivileged processes are subject to full permission checking based on the process's credentials (user and group permissions and supplementary process capabilities). Capabilities are implemented on Linux using extended attributes (xattr(7)) in the security namespace. Extended attributes are supported by all major Linux file systems, including Ext2, Ext3, Ext4, Btrfs, JFS, XFS, and ReiserFS.

For your safety and comfort, pihole-FTL is run by the entirely unprivileged user pihole. Whereas dnsmasq is running as root process, we designed pihole-FTL to be run by the entirely unprivileged user pihole. As a consequence, pihole-FTL will not be able to access the files of any other user on this system or mess around with your system's configuration.

However, this also implies that FTLDNS cannot bind to ports 53 (DNS) among some other necessary capabilities related to DHCP services. To establish a strong security model, we explicitly grant the pihole-FTL process additional capabilities so that pihole-FTL (but no other processes which may be started by pihole) can bind to port 53, etc., without giving any additional permissions to the pihole user.

We specifically add the following capabilities to pihole-FTL:

  • CAP_NET_BIND_SERVICE: Allows FTLDNS binding to TCP/UDP sockets below 1024 (specifically DNS service on port 53)
  • CAP_NET_RAW: use raw and packet sockets (we need a RAW socket for handling DHCPv6 requests)
  • CAP_NET_ADMIN: modify routing tables and other network-related operations (to allow for handling DHCP requests)

Users that cannot use Linux capabilities for various reasons (lacking kernel or file system support) can modify the startup scripts of pihole-FTL to ensure the daemon is started as root. However, be aware that you do so on your own risk (although we don't expect problems to arise).

Last update: February 5, 2020