When installing certain software on server sometimes it will shut down the server?

what are the reasons for this?

This shouldn't happen at all - reboots are not required for changes to any software apart from the kernel, and Linux systems should not shutdown unless an administrator requires it. You'll have to give a bit more information to make it possible to work out what is going on here.

Specifically - the distribution and version (if you fill in the field in your profile it appears under your name with each post), the command that you run to install the software, and what happens.

here I'm trying to install snort

gcc -DHAVE_CONFIG_H -I. -I. -I../../.. -I../include -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c sid637.c -o sid637.o >/dev/null 2>&1
/bin/sh ../../../libtool --tag=CC --mode=link gcc -g -O2 -Wall -DDYNAMIC_PLUGIN -L/usr/lib -lpcre -L/usr/lib/mysql -o lib_sfdynamic_example_rule.la -module sfsnort_dynamic_detection_lib.lo rules.lo sid109.lo sid637.lo -ldl -lmysqlclient -lz -lpcre -lpcap -lm -lnsl -ldl
ar cru .libs/lib_sfdynamic_example_rule.a .libs/sfsnort_dynamic_detection_lib.o .libs/rules.o .libs/sid109.o .libs/sid637.o
ranlib .libs/lib_sfdynamic_example_rule.a
creating lib_sfdynamic_example_rule.la
(cd .libs && rm -f lib_sfdynamic_example_rule.la && ln -s ../lib_sfdynamic_example_rule.la lib_sfdynamic_example_rule.la)
make[6]: Leaving directory `/root/snortinstall/snort-2.6.1.5/src/dynamic-examples/dynamic-rule'
make[5]: Leaving directory `/root/snortinstall/snort-2.6.1.5/src/dynamic-examples/dynamic-rule'
make[5]: Entering directory `/root/snortinstall/snort-2.6.1.5/src/dynamic-examples'
make[5]: Nothing to be done for `all-am'.
make[5]: Leaving directory `/root/snortinstall/snort-2.6.1.5/src/dynamic-examples'
make[4]: Leaving directory `/root/snortinstall/snort-2.6.1.5/src/dynamic-examples'
make[3]: Leaving directory `/root/snortinstall/snort-2.6.1.5/src/dynamic-examples'
make[3]: Entering directory `/root/snortinstall/snort-2.6.1.5/src'
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c codes.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c debug.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c decode.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c log.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c mstring.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c parser.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c profiler.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c plugbase.c

Broadcast message from root (Tue Jun 5 12:37:57 2007):

The system is going down for system halt NOW!
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c snort.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c snprintf.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c strlcatu.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c strlcpyu.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c tag.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c ubi_BinTree.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c ubi_SplayTree.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c util.c
util.c: In function `DropStats':
util.c:1400: warning: implicit declaration of function `HttpInspectDropStats'
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c detect.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c signature.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c mempool.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c sf_sdlist.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c fpcreate.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c fpdetect.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c pcrm.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c byte_extract.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c sfthreshold.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c packet_time.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c event_wrapper.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c event_queue.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c inline.c
gcc -DHAVE_CONFIG_H -I. -I. -I.. -I.. -I../src -I../src/sfutil -I/usr/include/pcap -I../src/output-plugins -I../src/detection-plugins -I../src/dynamic-plugins -I../src/preprocessors -I../src/preprocessors/flow -I../src/preprocessors/portscan -I../src/preprocessors/flow/int-snort -I../src/preprocessors/HttpInspect/include -I../src/preprocessors/Stream5 -I/usr/include/pcre -I/usr/include/mysql -DENABLE_MYSQL -g -O2 -Wall -DDYNAMIC_PLUGIN -c ipv6.c
/bin/sh ../libtool --tag=CC --mode=link gcc -g -O2 -Wall -DDYNAMIC_PLUGIN -L/usr/lib -lpcre -L/usr/lib/mysql -o snort codes.o debug.o decode.o log.o mstring.o parser.o profiler.o plugbase.o snort.o snprintf.o strlcatu.o strlcpyu.o tag.o ubi_BinTree.o ubi_SplayTree.o util.o detect.o signature.o mempool.o sf_sdlist.o fpcreate.o fpdetect.o pcrm.o byte_extract.o sfthreshold.o packet_time.o event_wrapper.o event_queue.o inline.o ipv6.o output-plugins/libspo.a detection-plugins/libspd.a dynamic-plugins/libdynamic.a preprocessors/libspp.a preprocessors/flow/portscan/libportscan.a preprocessors/flow/libflow.a parser/libparser.a preprocessors/HttpInspect/libhttp_inspect.a preprocessors/Stream5/libstream5.a sfutil/libsfutil.a -ldl -lmysqlclient -lz -lpcre -lpcap -lm -lnsl -ldl

The "broadcast message" means that someone with root access ran the "shutdown" command or equivalent - the fact that it happened during a software compile is likely to be a coincidence. Shutdowns can be set with a time delay, so it may have been done slightly earlier in the day.

Thats impossible. I only have root access

This only happens when installing large programs