Exec Format Error

You tried to execute a file that is not in a valid executable format. The most common format for binary programs under linux is called ELF. Note that your shell will run ascii files that have the executable bit set as a shell script (ie run it as shell commands).

You can reproduce this by doing
$ dd if=/dev/random of=myfile bs=1k count=1 $ chmod +x myfile $ ./myfile zsh: exec format error: ./myfile

Note that there is a very slight possibility that you could create a valid program that does something bad to your system!!

Note, you can have user defined ways of running programs using Linux's binfmt_misc. See