This is the official patch for the SEGV issue with incorrect pthread usage.

https://gitlab.alpinelinux.org/alpine/aports/issues/10156
https://github.com/alpinelinux/aports/pull/6951

Patch downloaded from:
https://github.com/bareos/bareos/commit/649ae58a65f6cdbcf7ee770a0d5b5cf51b5e412b
(patch had to be modified slightly to apply)

As soon as this patch is included in in upstream release, this patch may be removed.
As far as I can see, this should be the case with bareos 18.2.7 or later.

--- old/core/cmake/BareosFindAllLibraries.cmake
+++ new/core/cmake/BareosFindAllLibraries.cmake
@@ -84,3 +84,4 @@
 endif()
 
 find_package(Readline)
+INCLUDE(thread)
--- /dev/null
+++ new/core/cmake/thread.cmake
@@ -0,0 +1,21 @@
+INCLUDE(CheckIncludeFiles)
+INCLUDE(CheckCSourceCompiles)
+
+# check for extra non-portable header-file
+CHECK_INCLUDE_FILES("pthread.h;pthread_np.h" HAVE_PTHREAD_NP_H)
+
+# pthread_attr_get_np - e.g. on FreeBSD
+SET(CMAKE_REQUIRED_LIBRARIES ${PTHREAD_LIBRARIES})
+IF(HAVE_PTHREAD_NP_H)
+  CHECK_C_SOURCE_COMPILES("
+    #include <pthread.h>
+    #include <pthread_np.h>
+    int main() { pthread_attr_t a; pthread_attr_get_np(pthread_self(), &a); }
+    " HAVE_PTHREAD_ATTR_GET_NP)
+ELSE()
+  CHECK_C_SOURCE_COMPILES("
+    #include <pthread.h>
+    int main() { pthread_attr_t a; pthread_attr_get_np(pthread_self(), &a); }
+    " HAVE_PTHREAD_ATTR_GET_NP)
+ENDIF()
+SET(CMAKE_REQUIRED_LIBRARIES)
--- old/core/src/dird/CMakeLists.txt
+++ new/core/src/dird/CMakeLists.txt
@@ -37,7 +37,7 @@
    ua_cmds.cc ua_configure.cc ua_db.cc ua_dotcmds.cc ua_input.cc ua_impexp.cc
    ua_label.cc ua_output.cc ua_prune.cc ua_purge.cc ua_query.cc ua_restore.cc
    ua_run.cc ua_select.cc ua_server.cc ua_status.cc ua_tree.cc ua_update.cc
-   vbackup.cc verify.cc)
+   vbackup.cc verify.cc pthread_detach_if_not_detached.cc)
 IF(HAVE_WIN32)
    LIST(APPEND DIRD_OBJECTS_SRCS ../win32/dird/dirdres.rc)
 ENDIF()
--- old/core/src/dird/dird.cc
+++ new/core/src/dird/dird.cc
@@ -661,6 +661,7 @@
    is_reloading = false;
    return reloaded;
 }
+
 } /* namespace directordaemon */
 
 /*
--- /dev/null
+++ b/core/src/dird/pthread_detach_if_not_detached.cc
@@ -0,0 +1,48 @@
+/*
+   BAREOS® - Backup Archiving REcovery Open Sourced
+
+   Copyright (C) 2019-2019 Bareos GmbH & Co. KG
+
+   This program is Free Software; you can redistribute it and/or
+   modify it under the terms of version three of the GNU Affero General Public
+   License as published by the Free Software Foundation and included
+   in the file LICENSE.
+
+   This program is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+   Affero General Public License for more details.
+
+   You should have received a copy of the GNU Affero General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+   02110-1301, USA.
+*/
+#include "include/hostconfig.h"
+#include <pthread.h>
+#if defined(HAVE_PTHREAD_NP_H)
+#include <pthread_np.h>
+#endif
+#include "pthread_detach_if_not_detached.h"
+
+namespace directordaemon {
+void DetachIfNotDetached(pthread_t thr)
+{
+#if defined(HAVE_WIN32)
+  pthread_detach(thr);
+#else
+  /* only detach if not yet detached */
+  int _detachstate;
+  pthread_attr_t _gattr;
+#if defined(HAVE_PTHREAD_ATTR_GET_NP)
+  pthread_attr_init(&_gattr);
+  pthread_attr_get_np(thr, &_gattr);
+#else
+  pthread_getattr_np(thr, &_gattr);
+#endif
+  pthread_attr_getdetachstate(&_gattr, &_detachstate);
+  pthread_attr_destroy(&_gattr);
+  if (_detachstate != PTHREAD_CREATE_DETACHED) { pthread_detach(thr); }
+#endif
+}
+}  // namespace directordaemon
--- /dev/null
+++ b/core/src/dird/pthread_detach_if_not_detached.h
@@ -0,0 +1,29 @@
+/*
+   BAREOS® - Backup Archiving REcovery Open Sourced
+
+   Copyright (C) 2019-2019 Bareos GmbH & Co. KG
+
+   This program is Free Software; you can redistribute it and/or
+   modify it under the terms of version three of the GNU Affero General Public
+   License as published by the Free Software Foundation and included
+   in the file LICENSE.
+
+   This program is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+   Affero General Public License for more details.
+
+   You should have received a copy of the GNU Affero General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+   02110-1301, USA.
+*/
+
+#ifndef BAREOS_DIRD_THREAD_H_
+#define BAREOS_DIRD_THREAD_H_
+#include <pthread.h>
+
+namespace directordaemon {
+void DetachIfNotDetached(pthread_t thr);
+}  // namespace directordaemon
+#endif // BAREOS_DIRD_THREAD_H_
--- old/core/src/dird/job.cc
+++ new/core/src/dird/job.cc
@@ -39,6 +39,7 @@
 #include "dird/fd_cmds.h"
 #include "dird/job.h"
 #include "dird/migration.h"
+#include "dird/pthread_detach_if_not_detached.h"
 #include "dird/restore.h"
 #include "dird/sd_cmds.h"
 #include "dird/stats.h"
@@ -455,7 +456,7 @@
 {
    JobControlRecord *jcr = (JobControlRecord *)arg;
 
-   pthread_detach(pthread_self());
+   DetachIfNotDetached(pthread_self());
    Dsm_check(100);
 
    Dmsg0(200, "=====Start Job=========\n");
--- old/core/src/dird/ua_server.cc
+++ new/core/src/dird/ua_server.cc
@@ -34,6 +34,7 @@
 #include "dird/authenticate.h"
 #include "dird/authenticate_console.h"
 #include "dird/job.h"
+#include "dird/pthread_detach_if_not_detached.h"
 #include "dird/ua_cmds.h"
 #include "dird/ua_db.h"
 #include "dird/ua_input.h"
@@ -41,6 +42,7 @@
 #include "dird/ua_server.h"
 #include "lib/bnet.h"
 
+
 namespace directordaemon {
 
 /**
@@ -77,7 +79,7 @@
  */
 void *HandleUserAgentClientRequest(BareosSocket *user_agent_socket)
 {
-   pthread_detach(pthread_self());
+   DetachIfNotDetached(pthread_self());
 
    JobControlRecord *jcr = new_control_jcr("-Console-", JT_CONSOLE);
 
--- old/core/src/include/config.h.in
+++ new/core/src/include/config.h.in
@@ -34,6 +34,12 @@
 /* Define to 1 if you have 4.4BSD and OSF1 statfs to get filesystem type */
 #cmakedefine FSTYPE_STATFS @FSTYPE_STATFS@
 
+// Define to 1 for pthread_attr_get_np() instead of pthread_getattr_np()
+#cmakedefine HAVE_PTHREAD_ATTR_GET_NP @HAVE_PTHREAD_ATTR_GET_NP@
+
+// Define to 1 if pthread_*_np() are in a seperate header
+#cmakedefine HAVE_PTHREAD_NP_H @HAVE_PTHREAD_NP_H@
+
 /* Define to 1 if you have SVR4 statvfs to get filesystem type */
 #cmakedefine FSTYPE_STATVFS @FSTYPE_STATVFS@
 
--- old/core/src/lib/jcr.cc
+++ new/core/src/lib/jcr.cc
@@ -79,6 +79,7 @@
 static pthread_mutex_t job_start_mutex = PTHREAD_MUTEX_INITIALIZER;
 static pthread_mutex_t last_jobs_mutex = PTHREAD_MUTEX_INITIALIZER;
 
+static bool jcr_initialized = false;
 #ifdef HAVE_WIN32
 static bool tsd_initialized = false;
 static pthread_key_t jcr_key; /* Pointer to jcr for each thread */
@@ -324,6 +325,8 @@
   if (status != 0) {
     BErrNo be;
     Jmsg1(nullptr, M_ABORT, 0, _("pthread key create failed: ERR=%s\n"), be.bstrerror(status));
+  } else {
+    jcr_initialized = true;
   }
 }
 
@@ -681,7 +684,10 @@
  */
 JobControlRecord *get_jcr_from_tsd()
 {
-  JobControlRecord *jcr = (JobControlRecord *)pthread_getspecific(jcr_key);
+  JobControlRecord* jcr = (JobControlRecord*)INVALID_JCR;
+  if (jcr_initialized){
+    jcr = (JobControlRecord*)pthread_getspecific(jcr_key);
+  }
 
   /*
    * Set any INVALID_JCR to nullptr which the rest of BAREOS understands
@@ -696,7 +702,7 @@
  */
 uint32_t GetJobidFromTsd()
 {
-  JobControlRecord *jcr = (JobControlRecord *)pthread_getspecific(jcr_key);
+  JobControlRecord* jcr = get_jcr_from_tsd();
   uint32_t JobId        = 0;
 
   if (jcr && jcr != INVALID_JCR) { JobId = (uint32_t)jcr->JobId; }