ERRNO(9) BSD Kernel Developer's Manual ERRNO(9)
errno -- kernel internal error numbers
This section provides an overview of the error numbers used internally by the kernel and indicate neither success nor failure. These error
numbers are not returned to userland code.
Kernel functions that indicate success or failure by means of either 0 or an errno(2) value sometimes have a need to indicate that
``special'' handling is required at an upper layer or, in the case of ioctl(2) processing, that ``nothing was wrong but the request was not
handled''. To handle these cases, some negative errno(2) values are defined which are handled by the kernel before returning a different
errno(2) value to userland or simply zero.
The following is a list of the defined names and their meanings as given in <errno.h>. It is important to note that the value -1 is not
used, since it is commonly used to indicate generic failure and leaves it up to the caller to determine the action to take.
-2 EJUSTRETURN Modify regs, just return. No more work is required and the function should just return.
-3 ERESTART Restart syscall. The system call should be restarted. This typically means that the machine dependent system call trap code
will reposition the process's instruction pointer or program counter to re-execute the current system call with no other work
-4 EPASSTHROUGH Operation not handled by this layer. The operation was not handled and should be passed through to another layer. This
often occurs when processing ioctl(2) requests since lower layer processing may not handle something that subsequent code at a higher
-5 EDUPFD Duplicate file descriptor. This error is returned from the device open routine indicating that the l_dupfd field contains the file
descriptor information to be returned to the caller, instead of the file descriptor that has been opened already. This error is used
by cloning device multiplexors. Cloning device multiplexors open a new file descriptor and associate that file descriptor with the
appropriate cloned device. They set l_dupfd to that new file descriptor and return EDUPFD. vn_open(9) takes the file descriptor
pointed to by l_dupfd and copies it to the file descriptor that the open call will return.
-6 EMOVEFD Move file descriptor. This error is similar to EDUPFD except that the file descriptor in l_dupfd is closed after it has been
An errno manual page appeared in Version 6 AT&T UNIX. This errno manual page appeared in NetBSD 3.0.
December 3, 2004 BSD