Postmaster terminated without any error message

We have Postgresql 7.2 under Redhat 7.2. Postmaster can be started and we can use it without problem. However postmaster will terminate abnormally after 1 or 2 hours and leave no error messages. Next time we brought it up and it will stay for some time time and then shutdown by itself. The following are the log that we put into a file. Please advice what problem may cause this.

postmaster: PostmasterMain: initial environ dump:
-----------------------------------------
PWD=/home/postgres
HOSTNAME=tmspac.propagation.net
LESSOPEN=|/usr/bin/lesspipe.sh %s
SSH_CONNECTION=69.196.96.92 1202 66.221.32.226 22
USER=postgres
LS_COLORS=no=00:fi=00:di=01;34:ln=01;36:pi=40;33:so=01;35:bd=40;33;01:cd=40;33;01:
or=01;05;37;41:mi=01;05;37;41:ex=01;32:*.cmd=01;32:*.exe=01;32:*.com=01;32:*.btm=01;32:*.b
at=01;32:*.sh=01;32:*.csh=01;32:*.tar=01;31:*.tgz=01;31:*.arj=01;31:*.taz=01;31:*.lzh=01;3
1:*.zip=01;31:*.z=01;31:*.Z=01;31:*.gz=01;31:*.bz2=01;31:*.bz=01;31:*.tz=01;31:*.rpm=01;31
:*.cpio=01;31:*.jpg=01;35:*.gif=01;35:*.bmp=01;35:*.xbm=01;35:*.xpm=01;35:*.png=01;35:*.ti
f=01;35:
MACHTYPE=i386-redhat-linux-gnu
MAIL=/var/spool/mail/tmspac
INPUTRC=/etc/inputrc
BASH_ENV=/home/tmspac/.bashrc
LANG=en_US
LOGNAME=postgres
SHLVL=3
SHELL=/bin/bash
HOSTTYPE=i386
OSTYPE=linux-gnu
HISTSIZE=1000
HOME=/home/postgres
TERM=vt100
PATH=/bin:/usr/bin:/usr/local/bin:/usr/local/mysql/bin:/usr/local/java/bin:/home/t
mspac/bin
SSH_TTY=/dev/pts/0
OLDPWD=/var/lib/pgsql/data
_=/usr/bin/postmaster
-----------------------------------------
FindExec: searching PATH ...
ValidateBinary: can't stat "/bin/postgres"
FindExec: found "/usr/bin/postgres" using PATH
invoking IpcMemoryCreate(size=1417216)
FindExec: searching PATH ...
ValidateBinary: can't stat "/bin/postmaster"
FindExec: found "/usr/bin/postmaster" using PATH
2004-10-07 17:13:11 DEBUG: database system was interrupted at 2004-10-07 15:45:42 CDT
2004-10-07 17:13:11 DEBUG: checkpoint record is at 0/1B5F88
2004-10-07 17:13:11 DEBUG: redo record is at 0/1B5F88; undo record is at 0/0; shutdown TR
UE
2004-10-07 17:13:11 DEBUG: next transaction id: 257; next oid: 32940
2004-10-07 17:13:11 DEBUG: database system was not properly shut down; automatic recovery
in progress
2004-10-07 17:13:11 DEBUG: ReadRecord: record with zero length at 0/1B5FC8
2004-10-07 17:13:11 DEBUG: redo is not required
2004-10-07 17:13:13 DEBUG: database system is ready
2004-10-07 17:13:13 DEBUG: proc_exit(0)
2004-10-07 17:13:13 DEBUG: shmem_exit(0)
2004-10-07 17:13:13 DEBUG: exit(0)
2004-10-07 17:13:13 DEBUG: reaping dead processes
2004-10-07 17:18:15 DEBUG: proc_exit(0)
2004-10-07 17:18:15 DEBUG: shmem_exit(0)
2004-10-07 17:18:15 DEBUG: exit(0)