Linux 2.4.21 added core_pattern (which was already in 2.6).

Noted a few more reasons why a core dump file might not be produced.

man5/core.5

@@ -51,6 +51,14 @@ is not writable
 or is not a regular file 
 (e.g., it is a directory or a symbolic link).
 .IP *
+A (writable, regular) file with the same name as would be used for the 
+core dump already exists, but there is more than one hard link to that 
+file.
+.IP *
+The file system where the core dump file would be created is full; 
+or has run out of i-nodes; or is mounted read only; 
+or the user has reached their quota for the file system.
+.IP *
 The directory in which the core dump file is to be created does 
 not exist.
 .IP *
@@ -79,7 +87,7 @@ By default, a core dump file is named
 but the 
 .I /proc/sys/kernel/core_pattern
 file
-(new in Linux 2.5) 
+(since Linux 2.6 and 2.4.21)
 can be set to define a template that is used to name core dump files.
 The template can contain % specifiers which are substituted
 by the following values when a core file is created:
@@ -111,9 +119,8 @@ does not include "%p" and
 (see below)
 is non-zero, then .PID will be appended to the core filename.
 
-Linux 2.4 does not provide
-.IR /proc/sys/kernel/core_pattern ,
-but does provide a more primitive method of controlling
+Since version 2.4, Linux has also provided
+a more primitive method of controlling
 the name of the core dump file.
 If the
 .I /proc/sys/kernel/core_uses_pid
@@ -141,7 +148,7 @@ filename via a %p specification in
 .\" it might be worth incorporating it into the text:
 .\" Always including the PID in the name of the core file made
 .\" sense for LinuxThreads, where each thread had a unique PID,
-.\" but doesn't seem to server any purposewith NPTL, where all the 
+.\" but doesn't seem to server any purpose with NPTL, where all the 
 .\" threads in a process share the same PID (as POSIX.1 requires).  
 .\" Probably the behaviour is maintained so that applications using 
 .\" LinuxThreads continue appending the PID (the kernel has no easy