Red Hat Enterprise Linux Server が /var/log/messages に "signal 15" メッセージを表示して再起動する理由

Issue

• サーバーは "signal 15" で再起動されます。
• サーバーは自動的に再起動されます。
• サーバーが予期せず再起動します。

• /var/log/messages の exiting on signal 15 はどういう意味ですか?

  shutdown: shutting down for system reboot
  init: Switching to runlevel: 6
  [...]
  exiting on signal 15
  syslogd 1.4.1: restart.
  syslog: syslogd startup succeeded
  

• サーバーが予期せず再起動し、/var/log/messages にシャットダウンメッセージが記録されます。

  <hostname> shutdown[7180]: shutting down for system reboot <--- This log shows manual REBOOT triggered by someone
  <hostname> snmpd[4058]: cmaX: subMIB 18 handler has disconnected 
  <hostname> sshd[7113]: Transferred: sent 5192, received 3424 bytes
  <hostname> snmpd[4058]: cmaX: subMIB 1 handler has disconnected 
  <hostname> .
  <hostname> .
  <hostname> .
  <hostname> snmpd[4058]: cmaX: subMIB 21 handler has disconnected 
  <hostname> snmpd[4058]: cmaX: subMIB 22 handler has disconnected 
  <hostname> snmpd[4058]: cmaX: subMIB 23 handler has disconnected 
  <hostname> hpasmxld[4551]: Process has been instructed to stop from the user interface. Stopping hpasmxld process. . . 
  <hostname> xinetd[4114]: Exiting...
  <hostname> vasd[25173]: vasd IPC handler (PID 25173) exiting
  <hostname> vasd[11150]: vasd parent process (PID 11150) exiting
  <hostname> kernel: ACPI: PCI interrupt for device 0000:01:04.6 disabled
  <hostname> ntpd[4129]: ntpd exiting on signal 15
  <hostname> vasproxyd[11280]: 11280: Got SIGTERM/SIGINT. Shutting down...
  <hostname> rpc.statd[3730]: Caught signal 15, un-registering and exiting.
  <hostname> portmap[9171]: connect from 127.0.0.1 to unset(status): request from unprivileged port
  <hostname> kernel: Kernel logging (proc) stopped.
  <hostname> kernel: Kernel log daemon terminating.
  <hostname> exiting on signal 15
  <hostname> syslogd 1.4.1: restart.