Errno.h

0 Error 0.  Not used.

1 EPERM Operation not permitted.  An attempt was made to perform an oper-
ation limited to processes with appropriate privileges or to the
owner of a file or other resources.

2 ENOENT No such file or directory.  A component of a specified pathname
did not exist, or the pathname was an empty string.

3 ESRCH No such process.  No process could be found corresponding to that
specified by the given process ID.

4 EINTR Interrupted function call.  An asynchronous signal (such as
SIGINT or SIGQUIT) was caught by the process during the execution
of an interruptible function.  If the signal handler performs a
normal return, the interrupted function call will seem to have
returned the error condition.

5 EIO Input/output error.  Some physical input or output error occurred.
This error will not be reported until a subsequent operation on
the same file descriptor and may be lost (over written) by any
subsequent errors.