core_pattern is used to specify a core dumpfile pattern name:

• max length is 64 characters
• the default value is "core"
• core_pattern is used as a pattern template for the output filename
• certain string patterns (beginning with "%") are substituted with their actual values.
• backward compatibility with core_uses_pid: if core_pattern does not include "%p" (default does not) and core_uses_pid is set, then .PID will be appended to the filename.
• corename format specifiers:
  • %p - pid
  • %u - uid
  • %g - gid
  • %s - signal number
  • %t - UNIX time of dump
  • %h - hostname
  • %e - executable filename
  • %% - output one "%"
  • %<NUL> - "%" is dropped
  • %<OTHER> - both are dropped