Hello Paride.

I don't know what else may be relevant to trigger the crash.
libapache2-mod-nss is not relevant at all.. I just installed it in an attemt to fix the problem but it didn't help.

I'm willing to help debug this, but I need guidance. So please don't hesitate to ask.

I will now copy/paste here the output of strace as you suggested.

#strace apache2ctl configtest > /root/out 2> /root/err

# cat /root/out
Action 'configtest' failed.
The Apache error log may have more information.

# cat /root/err
execve("/usr/sbin/apache2ctl", ["apache2ctl", "configtest"], [/* 22 vars */]) = 0
brk(NULL)                               = 0x55fa99d60000
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=37741, ...}) = 0
mmap(NULL, 37741, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fe1fd4cd000
close(3)                                = 0
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
open("/lib/x86_64-linux-gnu/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0P\t\2\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1868984, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe1fd4cc000
mmap(NULL, 3971488, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fe1fcee8000
mprotect(0x7fe1fd0a8000, 2097152, PROT_NONE) = 0
mmap(0x7fe1fd2a8000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1c0000) = 0x7fe1fd2a8000
mmap(0x7fe1fd2ae000, 14752, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fe1fd2ae000
close(3)                                = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe1fd4cb000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fe1fd4ca000
arch_prctl(ARCH_SET_FS, 0x7fe1fd4cb700) = 0
mprotect(0x7fe1fd2a8000, 16384, PROT_READ) = 0
mprotect(0x55fa98cbc000, 8192, PROT_READ) = 0
mprotect(0x7fe1fd4d7000, 4096, PROT_READ) = 0
munmap(0x7fe1fd4cd000, 37741)           = 0
getuid()                                = 0
getgid()                                = 0
getpid()                                = 25420
rt_sigaction(SIGCHLD, {0x55fa98ab0540, ~[RTMIN RT_1], SA_RESTORER, 0x7fe1fcf1d4b0}, NULL, 8) = 0
geteuid()                               = 0
brk(NULL)                               = 0x55fa99d60000
brk(0x55fa99d81000)                     = 0x55fa99d81000
getppid()                               = 25418
stat("/etc/apache2/sites-enabled", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
stat(".", {st_mode=S_IFDIR|0755, st_size=4096, ...}) = 0
open("/usr/sbin/apache2ctl", O_RDONLY)  = 3
fcntl(3, F_DUPFD, 10)                   = 10
close(3)                                = 0
fcntl(10, F_SETFD, FD_CLOEXEC)          = 0
geteuid()                               = 0
getegid()                               = 0
rt_sigaction(SIGINT, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGINT, {0x55fa98ab0540, ~[RTMIN RT_1], SA_RESTORER, 0x7fe1fcf1d4b0}, NULL, 8) = 0
rt_sigaction(SIGQUIT, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGQUIT, {SIG_DFL, ~[RTMIN RT_1], SA_RESTORER, 0x7fe1fcf1d4b0}, NULL, 8) = 0
rt_sigaction(SIGTERM, NULL, {SIG_DFL, [], 0}, 8) = 0
rt_sigaction(SIGTERM, {SIG_DFL, ~[RTMIN RT_1], SA_RESTORER, 0x7fe1fcf1d4b0}, NULL, 8) = 0
read(10, "#!/bin/sh\n#\n# Licensed to the Ap"..., 8192) = 6402
stat("/etc/apache2/envvars", {st_mode=S_IFREG|0644, st_size=1782, ...}) = 0
open("/etc/apache2/envvars", O_RDONLY)  = 3
fcntl(3, F_DUPFD, 10)                   = 11
close(3)                                = 0
fcntl(11, F_SETFD, FD_CLOEXEC)          = 0
read(11, "# envvars - default environment "..., 8192) = 1782
read(11, "", 8192)                      = 0
close(11)                               = 0
pipe([3, 4])                            = 0
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fe1fd4cb9d0) = 25421
close(4)                                = 0
read(3, "0\n", 128)                     = 2
read(3, "", 128)                        = 0
close(3)                                = 0
wait4(-1, [{WIFEXITED(s) && WEXITSTATUS(s) == 0}], 0, NULL) = 25421
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_EXITED, si_pid=25421, si_uid=0, si_status=0, si_utime=0, si_stime=0} ---
rt_sigreturn({mask=[]})                 = 25421
getrlimit(RLIMIT_NOFILE, {rlim_cur=1024, rlim_max=1024*1024}) = 0
setrlimit(RLIMIT_NOFILE, {rlim_cur=8*1024, rlim_max=8*1024}) = 0
stat("/var/run/apache2", {st_mode=S_IFDIR|0755, st_size=60, ...}) = 0
stat("/var/lock/apache2", {st_mode=S_IFDIR|0755, st_size=40, ...}) = 0
clone(child_stack=0, flags=CLONE_CHILD_CLEARTID|CLONE_CHILD_SETTID|SIGCHLD, child_tidptr=0x7fe1fd4cb9d0) = 25422
wait4(-1, Syntax OK
[{WIFSIGNALED(s) && WTERMSIG(s) == SIGSEGV && WCOREDUMP(s)}], 0, NULL) = 25422
--- SIGCHLD {si_signo=SIGCHLD, si_code=CLD_DUMPED, si_pid=25422, si_uid=0, si_status=SIGSEGV, si_utime=447, si_stime=165} ---
rt_sigreturn({mask=[]})                 = 25422
write(2, "Segmentation fault (core dumped)"..., 33Segmentation fault (core dumped)
) = 33
write(1, "Action 'configtest' failed.\n", 28) = 28
write(1, "The Apache error log may have mo"..., 48) = 48
exit_group(139)                         = ?
+++ exited with 139 +++