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Commitbb24439

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Detach postmaster process from pg_ctl's session at server startup.
pg_ctl is supposed to daemonize the postmaster process, so that it's notaffected by signals to the launching process group. Before this patch, ifyou had a shell script that used "pg_ctl start", and you interrupted theshell script after postmaster had been launched, postmaster was alsokilled. To fix, call setsid() after forking the postmaster process.Long time ago, we had a 'silent_mode' option, which daemonized thepostmaster process by calling setsid(), but that was removed back in 2011(commitf7ea6be). We discussed bringing that back in some form, butpg_ctl is the documented way of launching postmaster to the background, soputting the setsid() call in pg_ctl itself seems appropriate.Just putting postmaster in a separate session would change the behaviorwhen you interrupt "pg_ctl -w start", e.g. with CTRL-C, while it's waitingfor postmaster to start. The historical behavior has been thatinterrupting pg_ctl aborts the server launch, which is handy if the serveris stuck in recovery, for example, and won't fully start up. To keep thatbehavior, install a signal handler in pg_ctl, to explicitly killpostmaster, if pg_ctl is interrupted while it's waiting for the server tostart up. This isn't 100% watertight, there is a small window afterforking the postmaster process, where the signal handler doesn't know thepostmaster's PID yet, but seems good enough.Arguably this is a long-standing bug, but I refrained from back-batching,out of fear of breaking someone's scripts that depended on the oldbehavior.Reviewed by Tom Lane. Report and original patch by Paul Guo, withfeedback from Michael Paquier.Discussion:https://www.postgresql.org/message-id/CAEET0ZH5Bf7dhZB3mYy8zZQttJrdZg_0Wwaj0o1PuuBny1JkEw%40mail.gmail.com
1 parentd9cdb1b commitbb24439

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‎src/bin/pg_ctl/pg_ctl.c

Lines changed: 51 additions & 1 deletion
Original file line numberDiff line numberDiff line change
@@ -103,12 +103,13 @@ static char backup_file[MAXPGPATH];
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staticcharpromote_file[MAXPGPATH];
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staticcharlogrotate_file[MAXPGPATH];
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106+
staticvolatilepgpid_tpostmasterPID=-1;
107+
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#ifdefWIN32
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staticDWORDpgctl_start_type=SERVICE_AUTO_START;
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staticSERVICE_STATUSstatus;
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staticSERVICE_STATUS_HANDLEhStatus= (SERVICE_STATUS_HANDLE)0;
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staticHANDLEshutdownHandles[2];
111-
staticpid_tpostmasterPID=-1;
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#defineshutdownEvent shutdownHandles[0]
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#definepostmasterProcess shutdownHandles[1]
@@ -471,6 +472,20 @@ start_postmaster(void)
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/* fork succeeded, in child */
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475+
/*
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* If possible, detach the postmaster process from the launching process
477+
* group and make it a group leader, so that it doesn't get signaled along
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* with the current group that launched it.
479+
*/
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#ifdefHAVE_SETSID
481+
if (setsid()<0)
482+
{
483+
write_stderr(_("%s: could not start server due to setsid() failure: %s\n"),
484+
progname,strerror(errno));
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exit(1);
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}
487+
#endif
488+
474489
/*
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* Since there might be quotes to handle here, it is easier simply to pass
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* everything to a shell to process them. Use exec so that the postmaster
@@ -719,6 +734,30 @@ read_post_opts(void)
719734
}
720735
}
721736

737+
/*
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* SIGINT signal handler used while waiting for postmaster to start up.
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* Forwards the SIGINT to the postmaster process, asking it to shut down,
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* before terminating pg_ctl itself. This way, if the user hits CTRL-C while
741+
* waiting for the server to start up, the server launch is aborted.
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*/
743+
staticvoid
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trap_sigint_during_startup(intsig)
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{
746+
if (postmasterPID!=-1)
747+
{
748+
if (kill(postmasterPID,SIGINT)!=0)
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write_stderr(_("%s: could not send stop signal (PID: %ld): %s\n"),
750+
progname, (pgpid_t)postmasterPID,strerror(errno));
751+
}
752+
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/*
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* Clear the signal handler, and send the signal again, to terminate the
755+
* process as normal.
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*/
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pqsignal(SIGINT,SIG_DFL);
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raise(SIGINT);
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}
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staticchar*
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find_other_exec_or_die(constchar*argv0,constchar*target,constchar*versionstr)
724763
{
@@ -827,6 +866,17 @@ do_start(void)
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828867
if (do_wait)
829868
{
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/*
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* If the user interrupts the startup (e.g. with CTRL-C), we'd like to
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* abort the server launch. Install a signal handler that will
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* forward SIGINT to the postmaster process, while we wait.
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*
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* (We don't bother to reset the signal handler after the launch, as
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* we're about to exit, anyway.)
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*/
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postmasterPID=pm_pid;
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pqsignal(SIGINT,trap_sigint_during_startup);
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830880
print_msg(_("waiting for server to start..."));
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832882
switch (wait_for_postmaster(pm_pid, false))

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