errno.h is a header file component of a POSIX compliant operating system such as UNIX or Linux. Its function is to list operating system error code numbers, English code words, and comments. A cut-down version of errno.h is also required by the C standard.
On December 19, 2003 the SCO Group issued DMCA notices to selected Fortune 1000 companies, alleging the errno.h file was copied from UNIX into Linux without authorisation. Linus Torvalds, the creator and trademark holder of Linux, has denied SCO's claim, saying he wrote the code himself.