Hello developers, Hendrik supposed me to build the nagios source without the option '-O2'. I have done this, but nothing changed. The SIGSEGV also happens in Version 3.0a2 without the '-O2' option. Output from gdb: #0 0xb7e43e84 in mallopt () from /lib/tls/libc.so.6 #1 0xb7e42dcb in free () from /lib/tls/libc.so.6 #2 0x080774ac in my_free () #3 0x08073d4f in clear_volatile_macros () #4 0x0806c92c in log_host_event () #5 0x080706a8 in handle_host_state () #6 0x0805bfa8 in process_host_check_result_3x () #7 0x0805bc42 in handle_async_host_check_result_3x () #8 0x08057533 in reap_check_results () #9 0x0806ac7d in handle_timed_event () #10 0x0806aaea in event_execution_loop () #11 0x080554f1 in main () Output from strace: [pid 21706] gettimeofday({1175066605, 112492}, NULL) = 0 [pid 21706] nanosleep({0, 250000000}, <unfinished ...> [pid 21707] <... select resumed> ) = 0 (Timeout) [pid 21707] read(4, "", 4096) = 0 [pid 21707] select(0, NULL, NULL, NULL, {0, 500000} <unfinished ...> [pid 21706] <... nanosleep resumed> NULL) = 0 [pid 21706] time([1175066605]) = 1175066605 [pid 21706] time(NULL) = 1175066605 [pid 21706] gettimeofday({1175066605, 368499}, NULL) = 0 [pid 21706] nanosleep({0, 250000000}, NULL) = 0 [pid 21706] time([1175066605]) = 1175066605 [pid 21706] time(NULL) = 1175066605 [pid 21706] gettimeofday({1175066605, 624476}, NULL) = 0 [pid 21706] nanosleep({0, 250000000}, <unfinished ...> [pid 21707] <... select resumed> ) = 0 (Timeout) [pid 21707] read(4, "", 4096) = 0 [pid 21707] select(0, NULL, NULL, NULL, {0, 500000} <unfinished ...> [pid 21706] <... nanosleep resumed> NULL) = 0 [pid 21706] time([1175066605]) = 1175066605 [pid 21706] time(NULL) = 1175066605 [pid 21706] gettimeofday({1175066605, 880492}, NULL) = 0 [pid 21706] nanosleep({0, 250000000}, NULL) = 0 [pid 21706] time([1175066606]) = 1175066606 [pid 21706] gettimeofday({1175066606, 136283}, NULL) = 0 [pid 21706] time([1175066606]) = 1175066606 [pid 21706] open("/tmp/nagios2r2UEC", O_RDONLY) = 7 [pid 21706] fstat64(7, {st_mode=S_IFREG|0600, st_size=0, ...}) = 0 [pid 21706] close(7) = 0 [pid 21706] unlink("/tmp/nagios2r2UEC") = 0 [pid 21706] time([1175066606]) = 1175066606 [pid 21706] rt_sigaction(SIGPIPE, {0xb7f3fa70, [], 0}, {SIG_IGN}, 8) = 0 [pid 21706] send(3, "<14>Mar 28 09:23:26 nagios: Warn"..., 163, 0) = 163 [pid 21706] rt_sigaction(SIGPIPE, {SIG_IGN}, NULL, 8) = 0 [pid 21706] open("/usr/local/nagios/var/nagios.log", O_RDWR|O_APPEND|O_CREAT, 0666) = 7 [pid 21706] time([1175066606]) = 1175066606 [pid 21706] fstat64(7, {st_mode=S_IFREG|0644, st_size=538, ...}) = 0 [pid 21706] mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0xb7fd8000 [pid 21706] write(7, "[1175066606] Warning: Return cod"..., 149) = 149 [pid 21706] close(7) = 0 [pid 21706] munmap(0xb7fd8000, 4096) = 0 [pid 21706] gettimeofday({1175066606, 140312}, NULL) = 0 [pid 21706] write(1, "Warning: Return code of 127 for "..., 135Warning: Return code of 127 for check of host 'localhost' was out of bounds. Make sure the plugin you're trying to run actually exists.) = 135 [pid 21706] write(1, "\n", 1 ) = 1 [pid 21706] time([1175066606]) = 1175066606 [pid 21706] time([1175066606]) = 1175066606 [pid 21706] munmap(0xd5db370d, 842745699) = -1 EINVAL (Invalid argument) [pid 21706] munmap(0xd7024313, 1664839277) = -1 EINVAL (Invalid argument) [pid 21706] --- SIGSEGV (Segmentation fault) @ 0 (0) --- [pid 21706] mmap2(NULL, 2097152, PROT_NONE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_NORESERVE, -1, 0) = 0xb6c36000 [pid 21706] munmap(0xb6c36000, 827392) = 0 [pid 21706] munmap(0xb6e00000, 221184) = 0 [pid 21706] mprotect(0xb6d00000, 135168, PROT_READ|PROT_WRITE) = 0 [pid 21706] --- SIGSEGV (Segmentation fault) @ 0 (0) --- [pid 21707] <... select resumed> ) = ? ERESTARTNOHAND (To be restarted) [pid 21707] +++ killed by SIGSEGV +++ [pid 21708] <... read resumed> 0xb76358c0, 511) = ? ERESTARTSYS (To be restarted) [pid 21708] +++ killed by SIGSEGV +++ +++ killed by SIGSEGV +++ Thanks in advance, FliTTi aka Matthias