[Bug 1448657] Re: isc-dhcp-server: Can't create PID file /run/dhcp-server/dhcpd.pid: Permission denied

[Nicorac]

Ubuntu 18.04 here, no apparmor.

Directory /run is on tempfs, so it is empty at start.
I suppose PID file /run/dhcp-server/dhcpd.pid can't be created because directory /run/dhcp-server is missing at startup and I haven't found where it will be created.

I've fixed systemd unit "/lib/systemd/system/isc-dhcp-server.service" by creating the needed "/run/dhcp-server" folder before starting dhcpd:
-----------------
[Unit]
Description=ISC DHCP IPv4 server
Documentation=man:dhcpd(8)
Wants=network-online.target
After=network-online.target
After=time-sync.target
ConditionPathExists=/etc/default/isc-dhcp-server
ConditionPathExists=|/etc/ltsp/dhcpd.conf
ConditionPathExists=|/etc/dhcp/dhcpd.conf

[Service]
EnvironmentFile=/etc/default/isc-dhcp-server
RuntimeDirectory=dhcp-server
# The leases files need to be root:dhcpd even when dropping privileges
ExecStartPre=/bin/mkdir -p /run/dhcp-server
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; \
    if [ ! -d /run/dhcp-server ]; then mkdir -p /run/dhcp-server ; chown dhcpd /run/dhcp-server ; chmod 775 /run/dhcp-server; fi; \
    exec dhcpd -user dhcpd -group dhcpd -f -4 -pf /run/dhcp-server/dhcpd.pid -cf $CONFIG_FILE $INTERFACES'

[Install]
WantedBy=multi-user.target
-----------------

Still need to fix hardcoded PID filename instead of /etc/default/isc-
dhcp-server value...

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https://bugs.launchpad.net/bugs/1448657

Title:
  isc-dhcp-server: Can't create PID file /run/dhcp-server/dhcpd.pid:
  Permission denied

Status in isc-dhcp package in Ubuntu:
  Confirmed

Bug description:
  Just upgraded from 14-10 to 15-04, and now see the following in
  syslog:

  Apr 26 10:50:08 server kernel: [70470.960718] audit: type=1400 audit(1430045408.725:8): apparmor="DENIED" operation="capable" profile="/usr/sbin/dhcpd" pid=8619 comm="dhcpd" capability=1  capname="dac_ove
  rride"
  Apr 26 10:50:08 server sh[8619]: Can't create PID file /run/dhcp-server/dhcpd.pid: Permission denied.

  Description:    Ubuntu 15.04
  Release:        15.04

  isc-dhcp-server:
    Installed: 4.3.1-5ubuntu2

  ----------- 8x -----------------

  # cat /etc/default/isc-dhcp-server

  # Defaults for isc-dhcp-server initscript
  # sourced by /etc/init.d/isc-dhcp-server
  # installed at /etc/default/isc-dhcp-server by the maintainer scripts

  #
  # This is a POSIX shell fragment
  #

  # Path to dhcpd's config file (default: /etc/dhcp/dhcpd.conf).
  #DHCPD_CONF=/etc/dhcp/dhcpd.conf

  # Path to dhcpd's PID file (default: /var/run/dhcpd.pid).
  #DHCPD_PID=/var/run/dhcpd.pid

  # Additional options to start dhcpd with.
  #       Don't use options -cf or -pf here; use DHCPD_CONF/ DHCPD_PID instead
  #OPTIONS=""

  # On what interfaces should the DHCP server (dhcpd) serve DHCP requests?
  #       Separate multiple interfaces with spaces, e.g. "eth0 eth1".
  INTERFACES=""

  ----------- 8x -----------------

  # ls -la /var/run
  lrwxrwxrwx 1 root root 4 Oct 24  2013 /var/run -> /run

  # ls -la /run/dhcp-server/
  total 0
  drwxr-xr-x  2 dhcpd dhcpd   40 Apr 26 10:59 .
  drwxr-xr-x 34 root  root  1060 Apr 26 11:33 ..

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