[Bug 1824433] [NEW] dhcpd ignores $CONFIG_FILE in /etc/default/isc-dhcp-server

[Norman Wilson]

Public bug reported:

Package isc-dhcp-server 4.3.3 on Ubuntu 16.04 LTS.

On earlier (pre-systemd) systems, one could point dhcpd at a
configuration file in any location by setting
CONFIG_FILE=/new/path/dhcpd.conf in /etc/default/isc-dhcp-server.  In
this version such setting is ignored; dhcpd always uses the default
/etc/dhcp/dhcpd.conf.

In more formulaeic terms:

Put CONFIG_FILE=/var/dhcpconf/mydhcp.conf in /etc/default/isc-dhcp-server.
I expect that when service isc-dhcp-server is next started, it will use that configuration file.
In fact it still uses /etc/dhcp/dhcpd.conf.

The problem can be worked around by making /etc/dhcp/dhcpd.conf a
symlink to the desired config file, but why have /etc/default/isc-dhcp-
server at all if it doesn't work?

The offending code is in /lib/systemd/system/isc-dhcp-server.service.
Here is a relevant extract:

[Service]
EnvironmentFile=/etc/default/isc-dhcp-server
RuntimeDirectory=dhcp-server
# The leases files need to be root:dhcpd even when dropping privileges
ExecStart=/bin/sh -ec '\
    CONFIG_FILE=/etc/dhcp/dhcpd.conf; \
    if [ -f /etc/ltsp/dhcpd.conf ]; then CONFIG_FILE=/etc/ltsp/dhcpd.conf; fi; \
    [ -e /var/lib/dhcp/dhcpd.leases ] || touch /var/lib/dhcp/dhcpd.leases; \
    chown root:dhcpd /var/lib/dhcp /var/lib/dhcp/dhcpd.leases; \
    chmod 775 /var/lib/dhcp ; chmod 664 /var/lib/dhcp/dhcpd.leases; \
    exec dhcpd -user dhcpd -group dhcpd -f -4 -pf /run/dhcp-server/dhcpd.pid -cf $CONFIG_FILE $INTERFACES'

/etc/default/isc-dhcp-server is correctly read as an EnvironmentFile,
but the ExecStart command unconditionally sets CONFIG_FILE, discarding
any value from the /etc/default file.

One fix might be to change the first few lines of the ExecStart to check
whether $CONFIG_FILE has been set, and perhaps whether it is still the
default value:

ExecStart=/bin/sh -ec '\
    case $CONFIG_FILE in \
    ""|/etc/dhcp/dhcpd.conf) \
        CONFIG_FILE=/etc/dhcp/dhcpd.conf; \
        if [ -f /etc/ltsp/dhcpd.conf ]; then CONFIG_FILE=/etc/ltsp/dhcpd.conf; fi; \
        ;; \
    esac

Or it might make more sense to let whatever package is in charge of ltsp
configuration append CONFIG_FILE=/etc/ltsp/dhcpd.conf to /etc/defaults
/isc-dhcp-server, and replace the lines above with a simple

ExecStart=/bin/sh -ec '\
    CONFIG_FILE=${CONFIG_FILE:-/etc/dhcp/dhcpd.conf}; \

Either way, a fix would be appreciated.

** Affects: isc-dhcp (Ubuntu)
     Importance: Undecided
         Status: New

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https://bugs.launchpad.net/bugs/1824433

Title:
  dhcpd ignores $CONFIG_FILE in /etc/default/isc-dhcp-server

Status in isc-dhcp package in Ubuntu:
  New

Bug description:
  Package isc-dhcp-server 4.3.3 on Ubuntu 16.04 LTS.

  On earlier (pre-systemd) systems, one could point dhcpd at a
  configuration file in any location by setting
  CONFIG_FILE=/new/path/dhcpd.conf in /etc/default/isc-dhcp-server.  In
  this version such setting is ignored; dhcpd always uses the default
  /etc/dhcp/dhcpd.conf.

  In more formulaeic terms:

  Put CONFIG_FILE=/var/dhcpconf/mydhcp.conf in /etc/default/isc-dhcp-server.
  I expect that when service isc-dhcp-server is next started, it will use that configuration file.
  In fact it still uses /etc/dhcp/dhcpd.conf.

  The problem can be worked around by making /etc/dhcp/dhcpd.conf a
  symlink to the desired config file, but why have /etc/default/isc-
  dhcp-server at all if it doesn't work?

  The offending code is in /lib/systemd/system/isc-dhcp-server.service.
  Here is a relevant extract:

  [Service]
  EnvironmentFile=/etc/default/isc-dhcp-server
  RuntimeDirectory=dhcp-server
  # The leases files need to be root:dhcpd even when dropping privileges
  ExecStart=/bin/sh -ec '\
      CONFIG_FILE=/etc/dhcp/dhcpd.conf; \
      if [ -f /etc/ltsp/dhcpd.conf ]; then CONFIG_FILE=/etc/ltsp/dhcpd.conf; fi; \
      [ -e /var/lib/dhcp/dhcpd.leases ] || touch /var/lib/dhcp/dhcpd.leases; \
      chown root:dhcpd /var/lib/dhcp /var/lib/dhcp/dhcpd.leases; \
      chmod 775 /var/lib/dhcp ; chmod 664 /var/lib/dhcp/dhcpd.leases; \
      exec dhcpd -user dhcpd -group dhcpd -f -4 -pf /run/dhcp-server/dhcpd.pid -cf $CONFIG_FILE $INTERFACES'

  /etc/default/isc-dhcp-server is correctly read as an EnvironmentFile,
  but the ExecStart command unconditionally sets CONFIG_FILE, discarding
  any value from the /etc/default file.

  One fix might be to change the first few lines of the ExecStart to
  check whether $CONFIG_FILE has been set, and perhaps whether it is
  still the default value:

  ExecStart=/bin/sh -ec '\
      case $CONFIG_FILE in \
      ""|/etc/dhcp/dhcpd.conf) \
          CONFIG_FILE=/etc/dhcp/dhcpd.conf; \
          if [ -f /etc/ltsp/dhcpd.conf ]; then CONFIG_FILE=/etc/ltsp/dhcpd.conf; fi; \
          ;; \
      esac

  Or it might make more sense to let whatever package is in charge of
  ltsp configuration append CONFIG_FILE=/etc/ltsp/dhcpd.conf to
  /etc/defaults/isc-dhcp-server, and replace the lines above with a
  simple

  ExecStart=/bin/sh -ec '\
      CONFIG_FILE=${CONFIG_FILE:-/etc/dhcp/dhcpd.conf}; \

  Either way, a fix would be appreciated.

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