errno(3) Library Functions Manual errno(3) errno - (libc -lc) #include errno . errno errno ( -1 -1 NULL ) errno. errno . ( getpriority(2)) -1 . errno errno . ISO C errno int errno . errno . . errno. POSIX.1 EAGAIN EWOULDBLOCK . Linux . UNIX Linux. . perror(3) strerror(3) . Linux errno(1) ( moreutils): $ errno -l; EPERM 1 (Operation not permitted) ENOENT 2 (No such file or directory) ESRCH 3 (No such process) EINTR 4 (Interrupted system call) EIO 5 / (Input/output error) ... errno(1) : $ errno 2; ENOENT 2 (No such file or directory) $ errno ESRCH; ESRCH 3 (No such process) $ errno -s permission; EACCES 13 (Permission denied) : POSIX.1-2001 POSIX.1-2001 POSIX.1 . POSIX.1-2008 POSIX.1-2008 POSIX.1 . C99 C99. : E2BIG (POSIX.1-2001). EACCES (POSIX.1-2001). EADDRINUSE (POSIX.1-2001). EADDRNOTAVAIL (POSIX.1-2001). EAFNOSUPPORT (POSIX.1-2001). EAGAIN ( EWOULDBLOCK) (POSIX.1-2001). EALREADY (POSIX.1-2001). EBADE . EBADF (POSIX.1-2001). EBADFD . EBADMSG (POSIX.1-2001). EBADR . EBADRQC . EBADSLT . EBUSY (POSIX.1-2001). ECANCELED (POSIX.1-2001). ECHILD (POSIX.1-2001). ECHRNG . ECOMM . ECONNABORTED (POSIX.1-2001). ECONNREFUSED (POSIX.1-2001). ECONNRESET (POSIX.1-2001). EDEADLK (POSIX.1-2001). EDEADLOCK EDEADLK. ( Linux MIPS PowerPC SPARC) " ". EDESTADDRREQ (POSIX.1-2001). EDOM (POSIX.1 C99). EDQUOT (POSIX.1-2001). EEXIST (POSIX.1-2001). EFAULT (POSIX.1-2001). EFBIG (POSIX.1-2001). EHOSTDOWN . EHOSTUNREACH (POSIX.1-2001). EHWPOISON . EIDRM (POSIX.1-2001). EILSEQ (POSIX.1, C99). glibc POSIX.1 " ". EINPROGRESS (POSIX.1-2001). EINTR (POSIX.1-2001); signal(7). EINVAL (POSIX.1-2001). EIO / (POSIX.1-2001). EISCONN (POSIX.1-2001). EISDIR (POSIX.1-2001). EISNAM . EKEYEXPIRED . EKEYREJECTED . EKEYREVOKED . EL2HLT 2 . EL2NSYNC 2 . EL3HLT 3 . EL3RST 3 . ELIBACC . ELIBBAD . ELIBMAX . ELIBSCN .lib a.out ELIBEXEC . ELNRNG . ELOOP (POSIX.1-2001). EMEDIUMTYPE . EMFILE (POSIX.1-2001). RLIMIT_NOFILE getrlimit(2). /proc/sys/fs/nr_open. EMLINK (POSIX.1-2001). EMSGSIZE (POSIX.1-2001). EMULTIHOP (POSIX.1-2001). ENAMETOOLONG (POSIX.1-2001). ENETDOWN (POSIX.1-2001). ENETRESET (POSIX.1-2001). ENETUNREACH (POSIX.1-2001). ENFILE (POSIX.1-2001). /proc/sys/fs/file-max ( proc(5)). ENOANO . ENOBUFS (POSIX.1 ( XSI STREAMS)). ENODATA xattr(7). POSIX.1-2001 ( XSI STREAMS) " STREAM". ENODEV (POSIX.1-2001). ENOENT (POSIX.1-2001). . ENOEXEC (POSIX.1-2001). ENOKEY . ENOLCK (POSIX.1-2001). ENOLINK (POSIX.1-2001). ENOMEDIUM . ENOMEM / (POSIX.1-2001). ENOMSG (POSIX.1-2001). ENONET . ENOPKG . ENOPROTOOPT (POSIX.1-2001). ENOSPC (POSIX.1-2001). ENOSR STREAM (POSIX.1 ( XSI STREAMS)). ENOSTR STREAM (POSIX.1 ( XSI STREAMS)). ENOSYS (POSIX.1-2001). ENOTBLK . ENOTCONN (POSIX.1-2001). ENOTDIR (POSIX.1-2001). ENOTEMPTY (POSIX.1-2001). ENOTRECOVERABLE (POSIX.1-2008). ENOTSOCK (POSIX.1-2001). ENOTSUP (POSIX.1-2001). ENOTTY / (POSIX.1-2001). ENOTUNIQ . ENXIO (POSIX.1-2001). EOPNOTSUPP (POSIX.1-2001). (ENOTSUP EOPNOTSUPP POSIX.1 .) EOVERFLOW (POSIX.1-2001). EOWNERDEAD (POSIX.1-2008). EPERM (POSIX.1-2001). EPFNOSUPPORT . EPIPE (POSIX.1-2001). EPROTO (POSIX.1-2001). EPROTONOSUPPORT (POSIX.1-2001). EPROTOTYPE (POSIX.1-2001). ERANGE (POSIX.1, C99). EREMCHG . EREMOTE . EREMOTEIO / . ERESTART . ERFKILL . EROFS (POSIX.1-2001). ESHUTDOWN . ESPIPE (POSIX.1-2001). ESOCKTNOSUPPORT . ESRCH (POSIX.1-2001). ESTALE (POSIX.1-2001). NFS . ESTRPIPE . ETIME (POSIX.1 ( XSI STREAMS)). ( POSIX.1 " STREAM ioctl(2) ".) ETIMEDOUT (POSIX.1-2001). ETOOMANYREFS : . ETXTBSY (POSIX.1-2001). EUCLEAN . EUNATCH . EUSERS . EWOULDBLOCK ( EAGAIN) (POSIX.1-2001). EXDEV (POSIX.1-2001). EXFULL . if (somecall() == -1) { printf("somecall() failed\n"); if (errno == ...) { ...; } } errno somecall() ( printf(3)). errno : if (somecall() == -1) { int errsv = errno; printf("somecall() failed\n"); if (errsv == ...) { ...; } } POSIX errno . . errno . errno errno ( extern int errno). . C. errno(1), err(3), error(3), perror(3), strerror(3) 3 . . : . 6.18 8 2026 errno(3)