The SNTP daemon (SNTPD) is a TCP/IP daemon that is used to synchronize time between a client and a server. Simple Network Time Protocol (SNTP) is a protocol for synchronizing clocks across a WAN or LAN through a specific formatted message. An External Time Reference (ETR), named stratum 0, is chosen as the highest timer reference used for synchronization. A stratum 1 server is attached to and receives the time from the stratum 0 timer. For example, the z/OS® sysplex timer could be a stratum 0 timer, and z/OS Communications Server would be a stratum 1 server. A client attached to the stratum 1 server can also be a stratum 2 server, receiving the time from the stratum 1 server, and so on. SNTP uses UDP packets for data transfer with the well-known port number 123. RFC 2030 (Mills 1996) describes SNTP. You can start SNTPD from the z/OS shell or as a started procedure. TCP/IP must be started prior to starting SNTPD.
SNTPD is an SNTP server. If the server is configured for unicast mode only (that is, neither the multicast mode or the broadcast mode start parameters are specified), then the server just waits for requests from clients and then responds. If the server is also configured for multicast or broadcast mode, it sends unsolicited messages at the intervals that are specified on the multicast mode or the broadcast mode start parameters.
The /etc/sntpd.pid is a temporary
SNTP daemon pid file that the SNTP daemon creates. This file contains
the process ID of the current invocation of the SNTP daemon.
- If /etc/sntpd.pid is a symbolic link, it must have an owning UID or GID that matches the EUID or EGID that is assigned to the SNTP daemon.
- If /etc/sntpd.pid is a hard link or the target of a hard link, users that are outside the owner or group of the directory in which /etc/sntpd.pid is stored cannot have write access to the directory. Additionally, write access to /etc/sntpd.pid must be limited to the owning UID or group, for example, --w--w----permissions.