查看錯誤代碼errno是調試程序的一個重要方法。當linuc C api函數發生異常時,一般會將errno變量(需include errno.h)賦一個整數值, 不同的值表示不同的含義,可以通過查看該值推測出錯的原因。在實際編程中用這一招解決了不少原本看來莫名其妙的問題。比較麻煩的是每次都要去linux源代碼里面查找錯誤代碼的含義，現在把它貼出來，以后需要查時就來這里看了。
以下來自linux 的內核代碼中的/usr/include/asm/errno.h
#ifndef _I386_ERRNO_H
#define _I386_ERRNO_H
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#define EPERM?? 1 /* Operation not permitted */
#define ENOENT?? 2 /* No such file or directory */
#define ESRCH?? 3 /* No such process */
#define EINTR?? 4 /* Interrupted system call */
#define EIO?????? 5 /* I/O error */
#define ENXIO?? 6 /* No such device or address */
#define E2BIG?? 7 /* Arg list too long */
#define ENOEXEC?? 8 /* Exec format error */
#define EBADF?? 9 /* Bad file number */
#define ECHILD 10 /* No child processes */
#define EAGAIN 11 /* Try again */
#define ENOMEM 12 /* Out of memory */
#define EACCES 13 /* Permission denied */
#define EFAULT 14 /* Bad address */
#define ENOTBLK 15 /* Block device required */
#define EBUSY 16 /* Device or resource busy */
#define EEXIST 17 /* File exists */
#define EXDEV 18 /* Cross-device link */
#define ENODEV 19 /* No such device */
#define ENOTDIR 20 /* Not a directory */
#define EISDIR 21 /* Is a directory */
#define EINVAL 22 /* Invalid argument */
#define ENFILE 23 /* File table overflow */
#define EMFILE 24 /* Too many open files */
#define ENOTTY 25 /* Not a typewriter */
#define ETXTBSY 26 /* Text file busy */
#define EFBIG 27 /* File too large */
#define ENOSPC 28 /* No space left on device */
#define ESPIPE 29 /* Illegal seek */
#define EROFS 30 /* Read-only file system */
#define EMLINK 31 /* Too many links */
#define EPIPE 32 /* Broken pipe */
#define EDOM 33 /* Math argument out of domain of func */
#define ERANGE 34 /* Math result not representable */
#define EDEADLK???????? 35????? /* Resource deadlock would occur */
#define ENAMETOOLONG??? 36????? /* File name too long */
#define ENOLCK????????? 37????? /* No record locks available */
#define ENOSYS????????? 38????? /* Function not implemented */
#define ENOTEMPTY?????? 39????? /* Directory not empty */
#define ELOOP?????????? 40????? /* Too many symbolic links encountered */
#define EWOULDBLOCK???? EAGAIN? /* Operation would block */
#define ENOMSG????????? 42????? /* No message of desired type */
#define EIDRM?????????? 43????? /* Identifier removed */
#define ECHRNG????????? 44????? /* Channel number out of range */
#define EL2NSYNC??????? 45????? /* Level 2 not synchronized */
#define EL3HLT????????? 46????? /* Level 3 halted */
#define EL3RST????????? 47????? /* Level 3 reset */
#define ELNRNG????????? 48????? /* Link number out of range */
#define EUNATCH???????? 49????? /* Protocol driver not attached */
#define ENOCSI????????? 50????? /* No CSI structure available */
#define EL2HLT????????? 51????? /* Level 2 halted */
#define EBADE?????????? 52????? /* Invalid exchange */
#define EBADR?????????? 53????? /* Invalid request descriptor */
#define EXFULL????????? 54????? /* Exchange full */
#define ENOANO????????? 55????? /* No anode */
#define EBADRQC???????? 56????? /* Invalid request code */
#define EBADSLT???????? 57????? /* Invalid slot */
#define EDEADLOCK?????? EDEADLK
#define EBFONT????????? 59????? /* Bad font file format */
#define ENOSTR????????? 60????? /* Device not a stream */
#define ENODATA???????? 61????? /* No data available */
#define ETIME?????????? 62????? /* Timer expired */
#define ENOSR?????????? 63????? /* Out of streams resources */
#define ENONET????????? 64????? /* Machine is not on the network */
#define ENOPKG????????? 65????? /* Package not installed */
#define EREMOTE???????? 66????? /* Object is remote */
#define ENOLINK???????? 67????? /* Link has been severed */
#define EADV??????????? 68????? /* Advertise error */
#define ESRMNT????????? 69????? /* Srmount error */
#define ECOMM?????????? 70????? /* Communication error on send */
#define EPROTO????????? 71????? /* Protocol error */
#define EMULTIHOP?????? 72????? /* Multihop attempted */
#define EDOTDOT???????? 73????? /* RFS specific error */
#define EBADMSG???????? 74????? /* Not a data message */
#define EOVERFLOW?????? 75????? /* Value too large for defined data type */
#define ENOTUNIQ??????? 76????? /* Name not unique on network */
#define EBADFD????????? 77????? /* File descriptor in bad state */
#define EREMCHG???????? 78????? /* Remote address changed */
#define ELIBACC???????? 79????? /* Can not access a needed shared library */
#define ELIBBAD???????? 80????? /* Accessing a corrupted shared library */
#define ELIBSCN???????? 81????? /* .lib section in a.out corrupted */
#define ELIBMAX???????? 82????? /* Attempting to link in too many shared libraries */
#define ELIBEXEC??????? 83????? /* Cannot exec a shared library directly */
#define EILSEQ????????? 84????? /* Illegal byte sequence */
#define ERESTART??????? 85????? /* Interrupted system call should be restarted */
#define ESTRPIPE??????? 86????? /* Streams pipe error */
#define EUSERS????????? 87????? /* Too many users */
#define ENOTSOCK??????? 88????? /* Socket operation on non-socket */
#define EDESTADDRREQ??? 89????? /* Destination address required */
#define EMSGSIZE??????? 90????? /* Message too long */
#define EPROTOTYPE????? 91????? /* Protocol wrong type for socket */
#define ENOPROTOOPT???? 92????? /* Protocol not available */
#define EPROTONOSUPPORT 93????? /* Protocol not supported */
#define ESOCKTNOSUPPORT 94????? /* Socket type not supported */
#define EOPNOTSUPP????? 95????? /* Operation not supported on transport endpoint */
#define EPFNOSUPPORT??? 96????? /* Protocol family not supported */
#define EAFNOSUPPORT??? 97????? /* Address family not supported by protocol */
#define EADDRINUSE????? 98????? /* Address already in use */
#define EADDRNOTAVAIL?? 99????? /* Cannot assign requested address */
#define ENETDOWN??????? 100???? /* Network is down */
#define ENETUNREACH???? 101???? /* Network is unreachable */
#define ENETRESET?????? 102???? /* Network dropped connection because of reset */
#define ECONNABORTED??? 103???? /* Software caused connection abort */
#define ECONNRESET????? 104???? /* Connection reset by peer */
#define ENOBUFS???????? 105???? /* No buffer space available */
#define EISCONN???????? 106???? /* Transport endpoint is already connected */
#define ENOTCONN??????? 107???? /* Transport endpoint is not connected */
#define ESHUTDOWN?????? 108???? /* Cannot send after transport endpoint shutdown */
#define ETOOMANYREFS??? 109???? /* Too many references: cannot splice */
#define ETIMEDOUT?????? 110???? /* Connection timed out */
#define ECONNREFUSED??? 111???? /* Connection refused */
#define EHOSTDOWN?????? 112???? /* Host is down */
#define EHOSTUNREACH??? 113???? /* No route to host */
#define EALREADY??????? 114???? /* Operation already in progress */
#define EINPROGRESS???? 115???? /* Operation now in progress */
#define ESTALE????????? 116???? /* Stale NFS file handle */
#define EUCLEAN???????? 117???? /* Structure needs cleaning */
#define ENOTNAM???????? 118???? /* Not a XENIX named type file */
#define ENAVAIL???????? 119???? /* No XENIX semaphores available */
#define EISNAM????????? 120???? /* Is a named type file */
#define EREMOTEIO?????? 121???? /* Remote I/O error */
#define EDQUOT????????? 122???? /* Quota exceeded */
#define ENOMEDIUM?????? 123???? /* No medium found */
#define EMEDIUMTYPE???? 124???? /* Wrong medium type */
#define ECANCELED?????? 125???? /* Operation Canceled */
#define ENOKEY????????? 126???? /* Required key not available */
#define EKEYEXPIRED???? 127???? /* Key has expired */
#define EKEYREVOKED???? 128???? /* Key has been revoked */
#define EKEYREJECTED??? 129???? /* Key was rejected by service */
/* for robust mutexes */
#define EOWNERDEAD????? 130???? /* Owner died */
#define ENOTRECOVERABLE 131???? /* State not recoverable */
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#endif