I have installed multiple php on the server running DirectAdmin(Version 1.6.40). But php5.6 is not working.
The php-fpm56 is showing STOPPED on Service Monitor,
I go to cutombuild to update the php-5.6
But I got the error messagses as below:

Executing /usr/local/directadmin/plugins/custombuild/admin/build php_expert 5.6 php-fpm...

Found /usr/local/directadmin/custombuild/php-5.6.40.tar.gz

Extracting ...

Done.

Configuring php-5.6.40...

patching file sapi/fpm/fpm/fpm_children.c

patching file sapi/fpm/fpm/fpm_request.c

patching file sapi/fpm/fpm/fpm_scoreboard.c

patching file sapi/fpm/fpm/fpm_scoreboard.h

patching file sapi/fpm/fpm/fpm_status.c

patching file sapi/fpm/fpm/fpm_worker_pool.c

Patching PHP to fix OpenSSL >=1.1 compatibility.

patch: **** Only garbage was found in the patch input.

Patching php-fpm for per-user process grouping

patching file sapi/fpm/fpm/fpm_children.c

Hunk #1 succeeded at 415 with fuzz 2 (offset -16 lines).

Patching php-fpm to not fail on startup if User quota maxed out on socket chown

patching file sapi/fpm/fpm/fpm_unix.c

Hunk #1 succeeded at 236 (offset 1 line).

checking for grep that handles long lines and -e... /bin/grep

checking for egrep... /bin/grep -E

checking for a sed that does not truncate output... /bin/sed

checking build system type... x86_64-unknown-linux-gnu

checking host system type... x86_64-unknown-linux-gnu

checking target system type... x86_64-unknown-linux-gnu

shtool:echo:Warning: unable to determine terminal sequence for bold mode

shtool:echo:Warning: unable to determine terminal sequence for bold mode

checking for cc... cc

checking whether the C compiler works... yes

checking for C compiler default output file name... a.out

checking for suffix of executables...

checking whether we are cross compiling... no

checking for suffix of object files... o

checking whether we are using the GNU C compiler... yes

checking whether cc accepts -g... yes

checking for cc option to accept ISO C89... none needed

checking how to run the C preprocessor... mv: cannot stat 'conftest.er1': No such file or directory

mv: cannot stat 'conftest.er1': No such file or directory

cc -E

checking for icc... no

checking for suncc... yes

checking whether cc understands -c and -o together... cat: confdefs.h: No such file or directory

checking how to run the C preprocessor... cc -E

cat: confdefs.h: No such file or directory

cat: confdefs.h: No such file or directory

checking for ANSI C header files... cat: confdefs.h: No such file or directory

checking for sys/types.h... cat: confdefs.h: No such file or directory

checking for sys/stat.h... cat: confdefs.h: No such file or directory

checking for stdlib.h... cat: confdefs.h: No such file or directory

checking for string.h... cat: confdefs.h: No such file or directory

checking for memory.h... cat: confdefs.h: No such file or directory

checking for strings.h... cat: confdefs.h: No such file or directory

checking for inttypes.h... cat: confdefs.h: No such file or directory

checking for stdint.h... cat: confdefs.h: No such file or directory

checking for unistd.h... cat: confdefs.h: No such file or directory

checking minix/config.h usability... cat: confdefs.h: No such file or directory

checking minix/config.h presence... cat: confdefs.h: No such file or directory

checking for minix/config.h... no

checking whether it is safe to define __EXTENSIONS__... cat: confdefs.h: No such file or directory

checking whether ln -s works... yes

checking for system library directory... lib

checking whether to enable runpaths... yes

checking if compiler supports -R... no

checking if compiler supports -Wl,-rpath,... no

checking for gawk... gawk

checking for bison... bison -y

checking for bison version... invalid

configure: WARNING: This bison version is not supported for regeneration of the Zend/PHP parsers (found: 3.0, min: 204, excluded: 3.0).

checking for re2c... no

configure: WARNING: You will need re2c 0.13.4 or later if you want to regenerate PHP parsers.

checking whether to enable computed goto gcc extension with re2c... no

checking whether to force non-PIC code in shared modules... no

checking whether /dev/urandom exists... yes

checking for pthreads_cflags...

checking for pthreads_lib...

Configuring SAPI modules

checking for AOLserver support... no

checking for Apache 1.x module support via DSO through APXS... no

checking for Apache 1.x module support... no

checking whether to enable Apache charset compatibility option... no

checking for Apache 2.0 filter-module support via DSO through APXS... no

checking for Apache 2.0 handler-module support via DSO through APXS... no

checking for Apache 1.x (hooks) module support via DSO through APXS... no

checking for Apache 1.x (hooks) module support... no

checking whether to enable Apache charset compatibility option... no

checking for Caudium support... no

checking for setproctitle... no

checking sys/pstat.h usability... no

checking sys/pstat.h presence... no

checking for sys/pstat.h... no

checking for PS_STRINGS... no

checking for CLI build... yes

checking for Continuity support... no

checking for embedded SAPI library support... shared

checking for FPM build... yes

checking for setenv... no

checking for clearenv... no

checking for setproctitle... (cached) no

checking for library containing socket... no

checking for library containing inet_addr... no

checking errno.h usability... no

checking errno.h presence... yes

configure: WARNING: errno.h: present but cannot be compiled

configure: WARNING: errno.h: check for missing prerequisite headers?

configure: WARNING: errno.h: see the Autoconf documentation

configure: WARNING: errno.h: section "Present But Cannot Be Compiled"

configure: WARNING: errno.h: proceeding with the compiler's result

checking for errno.h... no

checking fcntl.h usability... no

checking fcntl.h presence... yes

configure: WARNING: fcntl.h: present but cannot be compiled

configure: WARNING: fcntl.h: check for missing prerequisite headers?

configure: WARNING: fcntl.h: see the Autoconf documentation

configure: WARNING: fcntl.h: section "Present But Cannot Be Compiled"

configure: WARNING: fcntl.h: proceeding with the compiler's result

checking for fcntl.h... no

checking stdio.h usability... no

checking stdio.h presence... yes

configure: WARNING: stdio.h: present but cannot be compiled

configure: WARNING: stdio.h: check for missing prerequisite headers?

configure: WARNING: stdio.h: see the Autoconf documentation

configure: WARNING: stdio.h: section "Present But Cannot Be Compiled"

configure: WARNING: stdio.h: proceeding with the compiler's result

checking for stdio.h... no

checking for stdlib.h... (cached) no

checking for unistd.h... (cached) no

checking sys/uio.h usability... no

checking sys/uio.h presence... yes

configure: WARNING: sys/uio.h: present but cannot be compiled

configure: WARNING: sys/uio.h: check for missing prerequisite headers?

configure: WARNING: sys/uio.h: see the Autoconf documentation

configure: WARNING: sys/uio.h: section "Present But Cannot Be Compiled"

configure: WARNING: sys/uio.h: proceeding with the compiler's result

checking for sys/uio.h... no

checking sys/select.h usability... no

checking sys/select.h presence... yes

configure: WARNING: sys/select.h: present but cannot be compiled

configure: WARNING: sys/select.h: check for missing prerequisite headers?

configure: WARNING: sys/select.h: see the Autoconf documentation

configure: WARNING: sys/select.h: section "Present But Cannot Be Compiled"

configure: WARNING: sys/select.h: proceeding with the compiler's result

checking for sys/select.h... no

checking sys/socket.h usability... no

checking sys/socket.h presence... yes

configure: WARNING: sys/socket.h: present but cannot be compiled

configure: WARNING: sys/socket.h: check for missing prerequisite headers?

configure: WARNING: sys/socket.h: see the Autoconf documentation

configure: WARNING: sys/socket.h: section "Present But Cannot Be Compiled"

configure: WARNING: sys/socket.h: proceeding with the compiler's result

checking for sys/socket.h... no

checking sys/time.h usability... no

checking sys/time.h presence... yes

configure: WARNING: sys/time.h: present but cannot be compiled

configure: WARNING: sys/time.h: check for missing prerequisite headers?

configure: WARNING: sys/time.h: see the Autoconf documentation

configure: WARNING: sys/time.h: section "Present But Cannot Be Compiled"

configure: WARNING: sys/time.h: proceeding with the compiler's result

checking for sys/time.h... no

checking arpa/inet.h usability... no

checking arpa/inet.h presence... yes

configure: WARNING: arpa/inet.h: present but cannot be compiled

configure: WARNING: arpa/inet.h: check for missing prerequisite headers?

configure: WARNING: arpa/inet.h: see the Autoconf documentation

configure: WARNING: arpa/inet.h: section "Present But Cannot Be Compiled"

configure: WARNING: arpa/inet.h: proceeding with the compiler's result

checking for arpa/inet.h... no

checking netinet/in.h usability... no

checking netinet/in.h presence... yes

configure: WARNING: netinet/in.h: present but cannot be compiled

configure: WARNING: netinet/in.h: check for missing prerequisite headers?

configure: WARNING: netinet/in.h: see the Autoconf documentation

configure: WARNING: netinet/in.h: section "Present But Cannot Be Compiled"

configure: WARNING: netinet/in.h: proceeding with the compiler's result

checking for netinet/in.h... no

checking sysexits.h usability... no

checking sysexits.h presence... yes

configure: WARNING: sysexits.h: present but cannot be compiled

configure: WARNING: sysexits.h: check for missing prerequisite headers?

configure: WARNING: sysexits.h: see the Autoconf documentation

configure: WARNING: sysexits.h: section "Present But Cannot Be Compiled"

configure: WARNING: sysexits.h: proceeding with the compiler's result

checking for sysexits.h... no

checking for prctl... no

checking for clock_gettime... no

checking for clock_gettime in -lrt... no

checking for clock_get_time... no

checking for ptrace... no

checking for proc mem file... no

configure: WARNING: FPM Trace - ptrace, pread, or mach: could not be found

checking if gcc supports __sync_bool_compare_and_swap... no

checking for TCP_INFO... no

checking for SO_LISTENQLEN... no

checking for sysconf... no

checking for times... no

checking for kqueue... no

checking for port framework... no

checking for /dev/poll... no

checking for epoll... no

checking for poll... no

checking for select... no

checking for apparmor... no

checking for pkg-config... /bin/pkg-config

checking for libsystemd... version 239

checking systemd/sd-daemon.h usability... no

checking systemd/sd-daemon.h presence... yes

configure: WARNING: systemd/sd-daemon.h: present but cannot be compiled

configure: WARNING: systemd/sd-daemon.h: check for missing prerequisite headers?

configure: WARNING: systemd/sd-daemon.h: see the Autoconf documentation

configure: WARNING: systemd/sd-daemon.h: section "Present But Cannot Be Compiled"

configure: WARNING: systemd/sd-daemon.h: proceeding with the compiler's result

checking for systemd/sd-daemon.h... no

configure: error: Your system does not support systemd.

*** There was an error while trying to configure php. Check the configure file

Anyone can assist to fix the problem? Your problem is that the build config file for php 5.6 assumed you used an older autoconf (2.56 or lower). The newer autoconf versions up to 2.64 require slight modifications to allow it to generate the proper headers and makefiles. At least up to version 2.64 it does state that in version 2.70 the behavior changed again so it might work. If you have the ability to update autoconf to 2.70 or higher you may want to try that. Probably not. At this moment there are a couple of thousend servers running DA 1.643 because they want to run old stuff on Centos 6 still (if I heard correctly).
Others because they don't want to new licensing system for obvious reasons (internal licenses, my thoughts).