SAP servers record events and problems in system logs. If your SAP system runs on UNIX hosts, then there are two types of system logging:Each SAP application server has a local log that contains messages generated by this server.You can also enable central logging. With central logging, each application server also copies its local log entries to a central log.
On Windows NT and AS/400 hosts, only local logs (one per application server) are kept.These logs are not collected into a central log.
Each SAP application server maintains a single local log. System messages are logged in a single ring buffer on the server. When this log file reaches the maximum allowable size, the system starts overwriting the file from the beginning.
If you like, you can configure your server so that messages are issued to a central log file as well as to a local log.(Central logging is not available on AS/400 and Windows NT host systems.) A central log file is maintained on a selected application server.Individual SAP application servers (or instances) send their local messages to this single system. This system collects the messages from each instance and writes them to the central log.
A central log consists of two files: an active file and an old file. The active file contains the current log. The active file contains the current log. When the active file reaches the maximum length specified in the system profile, the system performs a log switch.The system deletes the old log file, uses the active file as old file, and creates a new active log file.
The system does not notify you when it replaces an old log.
A local log is always up to date. This is not always true for a central log. There can be brief delays between when the system records a message in a local log and when the same message is written in the central log. Delays can occur because the send processes on local systems sleep between periods of activity. The period of inactivity varies with the message volume on a particular system.
Central log files can take longer to build when a message is sent from a system that normally has little log activity. Longer delays and lost messages on local hosts can result from major network disruptions or failure of the collection process on the machine containing the central log.