I'm having the same problem with Nagios 3.1.0 after upgrading from 8.10 to 9.04. The nohup trick didn't work for me. If I run nagios straight from the command-line, without the daemon (-d) switch, I get this. Could it be related? I don't know what "stack smashing" is.

Nagios 3.1.0
Copyright (c) 1999-2009 Ethan Galstad (http://www.nagios.org)
Last Modified: 01-25-2009
License: GPL

Nagios 3.1.0 starting... (PID=3078)
Local time is Fri May 08 21:03:36 EDT 2009
*** stack smashing detected ***: ./nagios terminated
======= Backtrace: =========
/lib/tls/i686/cmov/libc.so.6(__fortify_fail+0x48)[0xb7e98da8]
/lib/tls/i686/cmov/libc.so.6(__fortify_fail+0x0)[0xb7e98d60]
./nagios[0x8083ba2]
./nagios(check_for_nagios_updates+0x6a)[0x8083c1a]
./nagios(main+0x552)[0x8058cc2]
/lib/tls/i686/cmov/libc.so.6(__libc_start_main+0xe5)[0xb7db1775]
./nagios[0x80586d1]
======= Memory map: ========
08048000-080d7000 r-xp 00000000 08:01 8308982    /usr/local/nagios/bin/nagios
080d7000-080d8000 r--p 0008e000 08:01 8308982    /usr/local/nagios/bin/nagios
080d8000-080d9000 rw-p 0008f000 08:01 8308982    /usr/local/nagios/bin/nagios
080d9000-080da000 rw-p 080d9000 00:00 0
09dd4000-09df5000 rw-p 09dd4000 00:00 0          [heap]
b752d000-b753a000 r-xp 00000000 08:01 4620341    /lib/libgcc_s.so.1
b753a000-b753b000 r--p 0000c000 08:01 4620341    /lib/libgcc_s.so.1
b753b000-b753c000 rw-p 0000d000 08:01 4620341    /lib/libgcc_s.so.1
b753c000-b754e000 r-xp 00000000 08:01 4621550    /lib/tls/i686/cmov/libresolv-2.9.so
b754e000-b754f000 r--p 00011000 08:01 4621550    /lib/tls/i686/cmov/libresolv-2.9.so
b754f000-b7550000 rw-p 00012000 08:01 4621550    /lib/tls/i686/cmov/libresolv-2.9.so
b7550000-b7552000 rw-p b7550000 00:00 0
b7552000-b7553000 ---p b7552000 00:00 0
b7553000-b7d53000 rw-p b7553000 00:00 0
b7d53000-b7d5d000 r-xp 00000000 08:01 4620537    /lib/tls/i686/cmov/libnss_files-2.9.so
b7d5d000-b7d5e000 r--p 00009000 08:01 4620537    /lib/tls/i686/cmov/libnss_files-2.9.so
b7d5e000-b7d5f000 rw-p 0000a000 08:01 4620537    /lib/tls/i686/cmov/libnss_files-2.9.so
b7d5f000-b7d68000 r-xp 00000000 08:01 4621542    /lib/tls/i686/cmov/libnss_nis-2.9.so
b7d68000-b7d69000 r--p 00008000 08:01 4621542    /lib/tls/i686/cmov/libnss_nis-2.9.so
b7d69000-b7d6a000 rw-p 00009000 08:01 4621542    /lib/tls/i686/cmov/libnss_nis-2.9.so
b7d6a000-b7d7f000 r-xp 00000000 08:01 4620480    /lib/tls/i686/cmov/libnsl-2.9.so
b7d7f000-b7d80000 r--p 00014000 08:01 4620480    /lib/tls/i686/cmov/libnsl-2.9.so
b7d80000-b7d81000 rw-p 00015000 08:01 4620480    /lib/tls/i686/cmov/libnsl-2.9.so
b7d81000-b7d83000 rw-p b7d81000 00:00 0
b7d83000-b7d8a000 r-xp 00000000 08:01 4620513    /lib/tls/i686/cmov/libnss_compat-2.9.so
b7d8a000-b7d8b000 r--p 00006000 08:01 4620513    /lib/tls/i686/cmov/libnss_compat-2.9.so
b7d8b000-b7d8c000 rw-p 00007000 08:01 4620513    /lib/tls/i686/cmov/libnss_compat-2.9.so
b7d96000-b7d97000 rw-p b7d96000 00:00 0
b7d97000-b7d99000 r-xp 00000000 08:01 4620461    /lib/tls/i686/cmov/libdl-2.9.so
b7d99000-b7d9a000 r--p 00001000 08:01 4620461    /lib/tls/i686/cmov/libdl-2.9.so
b7d9a000-b7d9b000 rw-p 00002000 08:01 4620461    /lib/tls/i686/cmov/libdl-2.9.so
b7d9b000-b7ef7000 r-xp 00000000 08:01 4620450    /lib/tls/i686/cmov/libc-2.9.so
b7ef7000-b7ef8000 ---p 0015c000 08:01 4620450    /lib/tls/i686/cmov/libc-2.9.so
b7ef8000-b7efa000 r--p 0015c000 08:01 4620450    /lib/tls/i686/cmov/libc-2.9.so
b7efa000-b7efb000 rw-p 0015e000 08:01 4620450    /lib/tls/i686/cmov/libc-2.9.so
b7efb000-b7efe000 rw-p b7efb000 00:00 0
b7efe000-b7f05000 r-xp 00000000 08:01 7962657    /usr/lib/libltdl.so.7.2.0
b7f05000-b7f06000 r--p 00006000 08:01 7962657    /usr/lib/libltdl.so.7.2.0
b7f06000-b7f07000 rw-p 00007000 08:01 7962657    /usr/lib/libltdl.so.7.2.0
b7f07000-b7f08000 rw-p b7f07000 00:00 0
b7f08000-b7f1d000 r-xp 00000000 08:01 4621548    /lib/tls/i686/cmov/libpthread-2.9.so
b7f1d000-b7f1e000 r--p 00014000 08:01 4621548    /lib/tls/i686/cmov/libpthread-2.9.so
b7f1e000-b7f1f000 rw-p 00015000 08:01 4621548    /lib/tls/i686/cmov/libpthread-2.9.so
b7f1f000-b7f21000 rw-p b7f1f000 00:00 0
b7f21000-b7f45000 r-xp 00000000 08:01 4620467    /lib/tls/i686/cmov/libm-2.9.so
b7f45000-b7f46000 r--p 00023000 08:01 4620467    /lib/tls/i686/cmov/libm-2.9.so
b7f46000-b7f47000 rw-p 00024000 08:01 4620467    /lib/tls/i686/cmov/libm-2.9.so
b7f49000-b7f4e000 r-xp 00000000 08:01 4620529    /lib/tls/i686/cmov/libnss_dns-2.9.so
b7f4e000-b7f4f000 r--p 00004000 08:01 4620529    /lib/tls/i686/cmov/libnss_dns-2.9.so
b7f4f000-b7f50000 rw-p 00005000 08:01 4620529    /lib/tls/i686/cmov/libnss_dns-2.9.so
b7f50000-b7f53000 rw-p b7f50000 00:00 0
b7f53000-b7f54000 r-xp b7f53000 00:00 0          [vdso]
b7f54000-b7f70000 r-xp 00000000 08:01 4620368    /lib/ld-2.9.so
b7f70000-b7f71000 r--p 0001b000 08:01 4620368    /lib/ld-2.9.so
b7f71000-b7f72000 rw-p 0001c000 08:01 4620368    /lib/ld-2.9.so
bfa5c000-bfa71000 rw-p bffeb000 00:00 0          [stack]
Aborted