[Bug 1235298] [NEW] dhclient appears to hang for a long time when no DHCP server available

[TJ]

Public bug reported:

isc-dhcp 4.2.4-7ubuntu7 on 13.10 saucy amd64 server with multi-homed
interfaces.

During "service networking start" or a manual "ifup -a", or a regular
"ifup ethX", an interface configured to use DHCP to acquire its (IPv4)
address will give the appearance of causing dhclient (or the calling
process/script) to hang.

This was discovered on a multi-homed server having five Ethernet
interfaces, only one of which is currently connected to anything.  All
interfaces are defined as:

auto ethX
iface ethX inet dhcp

Due to two separate Ubuntu-specific patches:

1) Fail to obey the "-1" command-line switch : "debian/patches/onetry_retry_after_initial_success"
2) increase time-out from 1 to 5 minutes: "debian/patches/dhclient-safer-timeout"

dhclient will hang for 5 minutes for each interface using DHCP. On a
multi-homed system with 5 interfaces that is 25 minutes!

The patch for (1) is not doing what it claims. There is no initial
success, and it over-rides the user's specific command-line parameter
"-1", which causes dhclient to hang around (in the foreground) for the
entire 5 minutes time-out, blocking the calling process. The code should
not be arbitrarily altering a specific command-line option. If "-1 is
undesirable the calling process (e.g. ifupdown) should have its calling
arguments changed.

The patch for (2) is wrong. Imposing a new default ought to have been
done via the 'dhclient.conf' "timeout" option.

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

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https://bugs.launchpad.net/bugs/1235298

Title:
  dhclient appears to hang for a long time when no DHCP server available

Status in “isc-dhcp” package in Ubuntu:
  New

Bug description:
  isc-dhcp 4.2.4-7ubuntu7 on 13.10 saucy amd64 server with multi-homed
  interfaces.

  During "service networking start" or a manual "ifup -a", or a regular
  "ifup ethX", an interface configured to use DHCP to acquire its (IPv4)
  address will give the appearance of causing dhclient (or the calling
  process/script) to hang.

  This was discovered on a multi-homed server having five Ethernet
  interfaces, only one of which is currently connected to anything.  All
  interfaces are defined as:

  auto ethX
  iface ethX inet dhcp

  Due to two separate Ubuntu-specific patches:

  1) Fail to obey the "-1" command-line switch : "debian/patches/onetry_retry_after_initial_success"
  2) increase time-out from 1 to 5 minutes: "debian/patches/dhclient-safer-timeout"

  dhclient will hang for 5 minutes for each interface using DHCP. On a
  multi-homed system with 5 interfaces that is 25 minutes!

  The patch for (1) is not doing what it claims. There is no initial
  success, and it over-rides the user's specific command-line parameter
  "-1", which causes dhclient to hang around (in the foreground) for the
  entire 5 minutes time-out, blocking the calling process. The code
  should not be arbitrarily altering a specific command-line option. If
  "-1 is undesirable the calling process (e.g. ifupdown) should have its
  calling arguments changed.

  The patch for (2) is wrong. Imposing a new default ought to have been
  done via the 'dhclient.conf' "timeout" option.

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