Logging events that occur on the router is an important tool available to router and network administrators. Logging provides real-time and historical information about router operations, which you can use to help trace and analyze the sequences of events leading to a problem on the router or network, or both. The JUNOS software provides two mechanisms for logging events:
system logging (sometimes called
syslog) and tracing. With system logging, the JUNOS software generates system log messages (also called syslog messages) that record events that occur systemwide on the router, such as a user logging in to the router or an interface starting up; failure and error conditions, such as a login failure or the unexpected closure of a peer process; and emergency or critical conditions, such as a router shutting down due to excessive heat. JUNOS system logging is very similar to the Unix
syslog function. Tracing (sometimes also called trace logging) is specific to routing protocols and records information about protocol operation, such as the exchange of protocol packets when a protocol is starting or sending regularly scheduled updates.
Both system logging and tracing save log messages to files. These files are stored in the /var/log directory on the router’s hard disk for M-series and T-series routers and in the /cf/var/log directory on J-series routers. You can redirect system log messages to a remote server that is running a standard syslogd utility, ...