dhcpclient and dhcpd do not stop on sigterm

Hello Prashantkumar:

I suspect you may be running a packaged version of the software, rather than our officially released software. Unless you build from our source and define ENABLE_GENTLE_SHUTDOWN (undefined by default), neither dhcpd nor dhclient install signal handlers and will, if sent a SIGTERM promptly stop.

As you can see from the following strace of dhcpd built without ENABLE_GENTLE_SHUTDOWN (the default), the process terminates forthwith:

dhcpd without ENABLE_GENTLE_SHUTDOWN:
-------------------------------------------------------------------------------
tmark@cserver ~ $ sudo /usr/bin/strace -ttT -s 100 -ff -p `pgrep dhcpd`
/usr/bin/strace: Process 15129 attached
06:55:40.028953 select(22, [4 5 7 8 9], [], NULL, NULL) = ? ERESTARTNOHAND (To be restarted if no handler) <10.294941>
06:55:50.324192 --- SIGTERM {si_signo=SIGTERM, si_code=SI_USER, si_pid=15191, si_uid=0} ---
06:55:50.340149 +++ killed by SIGTERM +++
--------------------------------------------------------------------------------

Defining ENABLE_GENTLE_SHUTDOWN adds signal handlers that for dhclient will cause it to release it's address(es) and for dhcpd, IF it's part of a failover pair, to go through partner down.   Here's dhcpd strace after rebuilding with ENABLE_GENTLE_SHUTDOWN but not running as part of a failover pair:

-----------------------------------------------------------------------------
tmark@cserver ~ $ sudo /usr/bin/strace -ttT -s 100 -ff -p `pgrep dhcpd`
/usr/bin/strace: Process 14926 attached
06:53:30.163410 select(22, [4 5 7 8 9], [], NULL, NULL) = ? ERESTARTNOHAND (To be restarted if no handler) <18.171104>
06:53:48.334888 --- SIGTERM {si_signo=SIGTERM, si_code=SI_USER, si_pid=15020, si_uid=0} ---
06:53:48.334957 rt_sigreturn({mask=[]}) = -1 EINTR (Interrupted system call) <0.000014>
06:53:48.335074 sendto(3, "<182>Mar 27 06:53:48 dhcpd: Received signal 15, initiating shutdown.", 68, MSG_NOSIGNAL, NULL, 0) = 68 <0.000108>
06:53:48.335258 write(2, "Received signal 15, initiating shutdown.", 40) = 40 <0.000147>
06:53:48.335447 write(2, "\n", 1)       = 1 <0.000103>
06:53:48.335597 select(22, [4 5 7 8 9], [], NULL, {0, 0}) = 0 (Timeout) <0.000019>
06:53:48.335714 close(9)                = 0 <0.000023>
06:53:48.335789 sendto(3, "<182>Mar 27 06:53:48 dhcpd: Disabling output on LPF/enp0s10/08:00:27:c7:c6:20/178.16.1.0/24", 91, MSG_NOSIGNAL, NULL, 0) = 91 <0.000030>
06:53:48.335856 write(2, "Disabling output on LPF/enp0s10/08:00:27:c7:c6:20/178.16.1.0/24", 63) = 63 <0.000103>
06:53:48.335991 write(2, "\n", 1)       = 1 <0.000127>
06:53:48.336165 close(5)                = 0 <0.006051>
06:53:48.342269 sendto(3, "<182>Mar 27 06:53:48 dhcpd: Disabling input on LPF/enp0s10/08:00:27:c7:c6:20/178.16.1.0/24", 90, MSG_NOSIGNAL, NULL, 0) = 90 <0.000035>
06:53:48.342347 write(2, "Disabling input on LPF/enp0s10/08:00:27:c7:c6:20/178.16.1.0/24", 62) = 62 <0.000114>
06:53:48.342497 write(2, "\n", 1)       = 1 <0.000123>
06:53:48.342664 sendto(3, "<182>Mar 27 06:53:48 dhcpd: Disabling output on LPF/enp0s9/08:00:27:30:e5:6c/175.16.1.0/24", 90, MSG_NOSIGNAL, NULL, 0) = 90 <0.000064>
06:53:48.342764 write(2, "Disabling output on LPF/enp0s9/08:00:27:30:e5:6c/175.16.1.0/24", 62) = 62 <0.000110>
06:53:48.342943 write(2, "\n", 1)       = 1 <0.000091>
06:53:48.343063 close(7)                = 0 <0.016188>
06:53:48.359464 sendto(3, "<182>Mar 27 06:53:48 dhcpd: Disabling input on LPF/enp0s9/08:00:27:30:e5:6c/175.16.1.0/24", 89, MSG_NOSIGNAL, NULL, 0) = 89 <0.000124>
06:53:48.359753 write(2, "Disabling input on LPF/enp0s9/08:00:27:30:e5:6c/175.16.1.0/24", 61) = 61 <0.001290>
06:53:48.361294 write(2, "\n", 1)       = 1 <0.000565>
06:53:48.362482 unlink("output/v4.pid") = 0 <0.001224>
06:53:48.364292 exit_group(0)           = ?
06:53:48.366991 +++ exited with 0 +++
-------------------------------------------------------------------------------

Please note the log message being emitted, reflecting that the signal has been received;

   06:53:48.335258 write(2, "Received signal 15, initiating shutdown.", 40) = 40 <0.000147>

And you can see from the above that does a bit more tidying up before stopping.

If you are not building from our released source, you may wish to try that:

    https://www.isc.org/downloads/dhcp/

otherwise, you will need to reach out to the packager.

Regards,

Thomas Markwalder
ISC Software Engineering

dhcpclient and dhcpd do not stop on sigterm

dhcpclient and dhcpd do not stop on sigterm

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