Linux Errno Decoder
Turn an errno number such as 13 into its symbol and message, or look up a symbol such as EACCES.
All 131 assigned errno values
On Linux, a failing system call or C library function returns -1 and stores a positive error number in the thread-local errno; a system call wrapper often returns the negated number directly, so -13 is the same error as 13. Symbols and numbers follow the kernel's asm-generic/errno.h, which x86-64, arm64 and other modern architectures share: values run from 1 to 133 with 41 and 58 unassigned. The message text is what glibc's strerror prints, which is why the kernel's own description sometimes differs by a word. EWOULDBLOCK is the same value as EAGAIN (11) on Linux, EDEADLOCK is EDEADLK (35) and ENOTSUP is EOPNOTSUPP (95); unlike some Unix systems, EWOULDBLOCK and EAGAIN can never be told apart here. Successful calls never clear errno, so only read it after a call reports failure, and use strerror_r in threaded C code. Some very old architectures number a few values differently. Decoding is a lookup in this page: nothing is executed, stored or sent anywhere.