在svn版本库中hooks目录下面：
sudo cp pre-commit.tmpl pre-commit
将pre-commit中的内容注释掉、添加如下内容：
REPOS="$1"
TXN="$2"
SVNLOOK=/usr/bin/svnlook
LOGMSG=`$SVNLOOK log -t "$TXN" "$REPOS" | grep "[a-zA-Z0-9]" | wc -c`
if [ "$LOGMSG" -lt 5 ];
then
echo "Log message cann't be empty! you must input more than 5 chars as comment!." 1>&2
exit 1
fi
exit 0
保存退出后，并添加执行的权限：
suod chmod a+x pre-commit